Patent Grant
10481391
This application is a U.S. National Phase of International Application No. PCT/JP2016/066791, filed on Jun. 6, 2016, which claims the benefit of Japanese Patent Application No. 2015-116270, filed Jun. 9, 2015, including the specification, claims, and drawings, the entire disclosures of which is incorporated by reference herein.
The present disclosure relates to a movable reflective element and a two-dimensional scanner.
A movable reflective element capable of tilting a reflective surface is used as an element for controlling the direction of light beams or directional radio waves. Particularly, the movable reflective element capable of tilting the reflective surface with two axes of freedom is used as an installed component of a two-dimensional scanner for two-dimensional scanning of light beams or the like. The two-dimensional scanner for scanning light beams two-dimensionally using the movable reflective element is installed in, for example, a projector for projecting an image. The two-dimensional scanner for scanning directional radio waves two-dimensionally using the movable reflective element is installed in, for example, an onboard radar.
Recently, use of a micro-electro-mechanical system (MEMS) element that can be fabricated using semiconductor fabrication processes has been proposed for the movable reflective element. For example, Patent Literature 1 discloses a movable reflective element including outer actuators extending from inner sides of a fixed frame to a rotation axis of a movable frame, and inner actuators extending from the movable frame to a rotation axis (perpendicular to the rotation axis of the movable frame) of a mirror. The movable frame is oscillated by the outer actuators about one rotation axis at a low frequency (horizontal scanning frequency), while the mirror is oscillated by the inner actuators about the other rotation axis at a high frequency (vertical scanning frequency). Use of such a movable reflective element enables light reflected by the mirror to be scanned two-dimensionally in the horizontal and vertical directions.
Patent Literature 1: Japanese Patent No. 4092283
For the movable reflective element for two-dimensional scanning, a ratio of the vertical scanning frequency to the horizontal scanning frequency may be on the order of one tenth, depending on the device in which the movable reflective element is installed. A desired approach for low-voltage driving of the outer and inner actuators with such a ratio is to set a ratio of a frequency of the inner actuator to a frequency of the outer actuator to be on the order of one tenth. Setting of the frequency ratio to be on the order of one tenth requires the outer actuator to have a length significantly greater than the length of the inner actuator.
In the movable reflective element disclosed in Patent Literature 1, however, the length of the outer actuator is limited to a distance between an inner side of the fixed frame and a middle point of an outer side of the movable frame in which a rotation shaft is provided. This limitation poses difficulties in lowering the frequency ratio between the outer and inner actuators to the desired value.
The present disclosure has been made to overcome the above difficulties, and an objective of the present disclosure is to provide a movable reflective element and a two-dimensional scanner that are capable of achieving miniaturization and the optimal frequency ratio.
To achieve the foregoing objective, a movable reflective element according a first aspect of the present disclosure includes:
a plate-like fixed frame;
a plate-like movable frame disposed within the fixed frame to define a gap between the movable frame and the fixed frame;
a plate-like mirror including a reflective surface and disposed within the movable frame to define a gap between the mirror and the movable frame;
first actuators that are a pair of linear flexible members, each first actuator connecting the fixed frame to the movable frame and including piezoelectric elements formed in an extension extending in a first direction from an inner side of the fixed frame, the piezoelectric elements stretching and contracting in the first direction, the first actuators being disposed one on either side of the movable frame in a second direction that intersects the first direction, wherein deformation of the first actuators caused by stretching and contracting of the piezoelectric elements oscillates the movable frame about a first rotation axis in relation to the fixed frame; and
second actuators that are a pair of linear flexible members, each second actuator connecting the movable frame to the mirror and including piezoelectric elements formed in an extension extending in the second direction from an inner side of the movable frame, the piezoelectric elements stretching and contracting in the second direction, the second actuators are disposed one on either side of the mirror in the first direction, wherein deformation of the second actuators caused by stretching and contracting of the piezoelectric elements oscillates the mirror about a second rotation axis in relation to the movable frame, the second rotation axis intersecting the first rotation axis,
wherein the extension of each first actuator in the first direction has a length that is longer than a distance between the inner side of the fixed frame to which the first actuator is connected and a middle point of an outer side of the movable frame in the first direction.
Each first actuator may include:
a first arm including the piezoelectric elements and having one end connected to the inner side of the fixed frame, the first arm linearly extending in the first direction in the gap between the fixed frame and the movable frame from the one end beyond the middle point of the outer side of the movable frame;
a second arm having one end connected to another end of the first arm, the second arm extending in the second direction; and
a third arm having one end connected to another end of the second arm and another end connected to the middle point of the outer side of the movable frame, the third arm extending along the first arm from the other end of the second arm in a direction opposite to a direction extending from the one end to the other end of the first arm.
Each second actuator may include:
a fourth arm including the piezoelectric elements and having one end connected to the inner side of the movable frame, the fourth arm linearly extending in the second direction in the gap between the movable frame and the mirror from the one end beyond a middle point of an outer side of the mirror;
a fifth arm having one end connected to another end of the fourth arm, the fifth arm extending in the first direction; and
a sixth arm having one end connected to another end of the fifth arm and another end connected to the middle point of the outer side of the mirror in the second direction, the sixth arm extending along the fourth arm from the other end of the fifth arm in a direction opposite to a direction extending from the one end to the other end of the fourth arm.
The first actuators that are the pair of members may be disposed with two-fold rotational symmetry around the mirror,
the second actuators that are the pair of members may be disposed with two-fold rotational symmetry around the mirror, and
an orientation of the first arm from the one end to the other end and an orientation of the fourth arm from the one end to the other end may be the same with respect to a rotational direction about the mirror.
The first actuators that are the pair of members may be disposed with two-fold rotational symmetry around the mirror,
the second actuators that are the pair of members may be disposed with two-fold rotational symmetry around the mirror, and
an orientation of the first arm from the one end to the other end and an orientation of the fourth arm from the one end to the other end may be opposite with respect to a rotational direction about the mirror.
Each second actuator may include a seventh arm including the piezoelectric elements and having one end connected to the inner side of the movable frame and another end connected to a corner portion of the mirror, the seventh arm extending linearly in the second direction in the gap between the movable frame and the mirror from the one end beyond a middle point of an outer side of the mirror.
Each first actuator may include an eighth arm including the piezoelectric elements and having one end connected to the inner side of the fixed frame and extending linearly in the first direction in the gap between the fixed frame and the movable frame from the one end beyond the middle point of the outer side of the movable frame, and
each first actuator may be connected to the movable frame at a portion other than the middle point of the outer side of the movable frame without turning back at another end of the eighth arm.
Each first actuator may include a ninth arm extending in the second direction in the gap between the fixed frame and the movable frame from the other end of the eighth arm beyond the middle point of the outer side of the movable frame in the second direction and connected to a corner portion of the movable frame.
Each second actuator may include a tenth arm including the piezoelectric elements and having one end connected to the inner side of the movable frame and extending linearly in the second direction in the gap between the movable frame and the mirror from the one end beyond the middle point of the outer side of the mirror, and
each second actuator may be connected to the mirror at a portion other than the middle point of the outer side of the mirror along the second direction without turning back at another end of the tenth arm.
Each second actuator may include an eleventh arm extending in the first direction from the other end of the tenth arm beyond a middle point of the outer side of the mirror in the first direction and connected to a corner portion of the mirror.
The movable frame may include recessed portions provided on two outer sides in the second direction, and
each first actuator may include:
Each second actuator may include:
a fifteenth arm including the piezoelectric elements and having one end connected to the movable frame, the fifteenth arm extending linearly in the second direction in the gap between the movable frame and the mirror from the one end beyond the middle point of the outer side of the mirror;
a sixteenth arm extending in the first direction in the gap between the movable frame and the mirror from an other end of the fifteenth arm to the middle point of the outer side of the movable frame; and
a seventeenth arm having one end connected to another end of the sixteenth arm and another end connected to the middle point of the outer side of the mirror.
The movable reflective element may further include at least one of:
a first wide portion provided in a portion connecting each first actuator to the fixed frame, the first wide portion having a width larger than a width of the first actuator; or
a second wide portion provided in a portion connecting each second actuator to the movable frame, the second wide portion having a width larger than a width of the second actuator.
Independently driven sets of the piezoelectric elements may be included in at least one of the first actuator or the second actuator.
The movable reflective element may include at least one of:
first detection electrodes each having a width smaller than a width of the first actuator, the first detection electrodes detecting displacement of the respective first actuators; or
second detection electrodes each having a width smaller than a width of the second actuator, the second detection electrodes detecting displacement of the respective second actuators
Each first detection electrode may be provided in a portion connecting the corresponding first actuator to the fixed frame, and
each second detection electrode may be provided in a portion connecting the corresponding second actuator to the movable frame.
The movable frame may be formed thicker than the mirror.
At least one of the first actuator or the second actuator may have a width that varies from the fixed frame toward the movable frame or from the movable frame toward the mirror.
The movable frame may further include a weight attached thereto.
The movable reflective element may include at least one of:
a first restriction extending from the inner side of the movable frame and disposed in the gap between the movable frame and the mirror, the first restriction restricting movement of the mirror to the movable frame; or
a second restriction extending from the inner side of the fixed frame and disposed in the gap between the fixed frame and the movable frame, the second restriction restricting movement of the movable frame to the fixed frame.
The mirror may have an outer periphery formed to avoid the first restriction and to have the center of gravity of the mirror in a stationary state to be the center of the mirror, and
the movable frame may have an outer periphery formed to avoid the second restriction and to have the center of gravity of the movable frame in a stationary state to be the center of the movable frame.
A two-dimensional scanner according to a second aspect of the present disclosure includes:
the movable reflective element according to the present disclosure; and
a controller for causing the movable reflective element to be driven two-dimensionally to perform two-dimensional scanning.
According to the present disclosure, the length of the first actuator that extends in the first direction is longer than the distance between the inner side of the fixed frame to which the first actuator is connected and the middle point of the outer side of the movable frame in the first direction. In this way, the length of the first actuator can be significantly greater than the length of the second actuator. This enables the movable frame and the mirror to have a desired ratio of drive frequencies thereof while allowing for a compact size of the entire movable reflective element, which achieves miniaturization and the optimal frequency ratio.
Embodiments of the present disclosure are described in detail below with reference to the drawings.
First, Embodiment 1 of the present disclosure is described. In Embodiment 1, a basic structure of a movable reflective element 100 and the operation thereof are described. Movable reflective elements 100 of Embodiment 1 and below-described Embodiments 2-4 are designed based on similar ideas, and belong to the same group.
Configuration of a Movable Reflective Element Excluding a Layer D Featuring a Reflective Surface and an Electrode Layer
As illustrated in
The fixed frame 110 is a plate-like frame disposed at the outermost periphery. The movable frame 120 is a rectangular plate-like frame disposed inside the fixed frame 110. The mirror 130 is a rectangular plate-like member disposed inside the movable frame 120. The actuators 140 are a pair of members each connecting the fixed frame 110 to the movable frame 120. The actuators 150 are a pair of members each connecting the movable frame 120 to the mirror 130.
Here, an XYZ three-dimensional orthogonal coordinate system is defined with the origin O at the center of gravity of the mirror 130. In this XYZ coordinate system, in the drawing sheet of
The fixed frame 110 is fixed to an external object. The movable frame 120 and the mirror 130 are used without being fixed directly to the external object. The actuators 140 are disposed at both sides of the movable frame 120 in the X-axis direction between the fixed frame 110 and the movable frame 120 to connect the fixed frame 110 to the movable frame 120. The actuators 150 are disposed at both sides of the mirror 130 in the Y-axis direction between the movable frame 120 and the mirror 130 to connect the movable frame 120 to the mirror 130.
As illustrated in
Inclusion of the A layers 130A, 140A, and 150A described above in the movable reflective element 100 is not essential. Specifically, the mirror 130 and the actuators 140 and 150 may have a two-layer structure of the B layers 130B, 140B, and 150B and the C layers 130C, 140C, and 150C, respectively.
As illustrated in
The fixed frame 110 is depicted with a dot hatch pattern in
In
The actuators 140 are depicted with a basket-weave hatch pattern in
The mirror 130 is depicted with a hatch pattern of equally spaced oblique lines in
The actuators 150 are depicted with a basket-weave hatch pattern in
Next, the overall configuration of the movable reflective element 100 is described.
As described above, the three layers of the A layer 100A, the B layer 100B, and the C layer 100C have the same planar view shapes (shapes indicated in the top view of
The D layer 100D includes upper electrode layers 140D formed on the actuators 140, upper electrode layers 150D formed on the actuators 150, a reflective layer 130D formed on the mirror 130, and detection electrodes 160D and 170D. The D layer, other than wiring, is not formed in the fixed frame 110 or the movable frame 120. The wiring, however, is not depicted for the fixed frame 110 or the movable frame 120 illustrated in
As described above, the D layer serving as wiring is formed on the fixed frame 110. However, since the upper electrode layers 140D and 150D need to be electrically isolated to form discrete piezoelectric elements, forming the D layer having the same planar view shape over the entire upper surface of the C layer is not desirable.
Next, materials of the A layer 100A, the B layer 100B, the C layer 100C, and the D layer 100D included in the movable reflective element 100 are described. First, the A layer 100A is a substrate layer that is a support substrate for other layers, and is made of a material that allows for support of the B layer 100B, the C layer 100C, and the D layer 100D, which are formed on the upper surface of the A layer 100A. However, the actuators 140 and 150 need to have flexibility at least in the up/down direction (Z-axis direction). Specifically, the A layer 100A serving as the substrate layer is made of a material having some degree of flexibility so as to cause each of the actuators 140 and 150 to flex within a necessary range (the range necessary for tilting the mirror 130 at a required angle). In the present embodiment, a silicon substrate forms the A layer 100A. Specifically, as illustrated in
The BOX layer 100A2 in the A layer 100A is not necessarily included, and the A layer 100A may have a two-layer structure of the support layer 100A1 and the active layer 100A3. That is, the A layer 100A may be a single silicon substrate.
The B layer 100B forms a lower electrode of the piezoelectric element. The D layer 100D forms an upper electrode of the piezoelectric element. Thus both of the layers are made of electrically conductive materials.
The C layer 100C forms a piezoelectric element, and is made of a piezoelectric material that exhibits a piezoelectric effect. For example, the C layer 100C is formed of a thin film of lead zirconate titanate (PZT) or potassium sodium niobate (KNN). In the present embodiment, the piezoelectric element has a sandwich structure including the piezoelectric material layer (C layer 100C) sandwiched between the electrically conductive material layers (B layer 100B and D layer 100D).
In the D layer 100D, the portions 140D formed in the actuators 140 and the portions 150D formed in the actuators 150 form the upper electrode layers for the respective piezoelectric elements, as described above. The D layer 130D formed in the mirror 130 serves as a reflective surface of the mirror 130. Thus, it suffices that the upper electrode layers 140D and 150D of the actuators 140 and 150 are electrically conductive, which means thus the surfaces of the upper electrode layers 140D and 150D do not need to be reflective. In contrast, it suffices that the surface of the D layer 130D formed in the mirror 130 is reflective, which means that the D layer 130D does not need to be electrically conductive.
However, in mass production of the movable reflective element 100, the upper electrode layers 140D and 150D and the reflective layer 130D are formed as the D layer 100D made of the same material. In this case, the material having functions of both the electrode layer and the reflective layer is used as the material of the D layer 100D.
Specifically, since the D layer 100D is required to have an upper surface serving as a reflective surface (mirror), the upper portion of the D layer 100D is desirably formed by a thin-film layer of material having high reflectivity and excellent resistance to corrosion, for example, gold (Au). The thin-film layer of gold (Au), which has a good resistivity to light and electromagnetic waves as well as an excellent resistance to corrosion, is able to retain stable reflective performance over a long period of time. The B layer 100B may be made of any metal layer since it suffices that the B layer 100B serves as the lower electrode (electrically conductive layer).
The movable reflective element 100 illustrated in
After formation of a four-layer laminated structure, the D layer 100D is patterned to leave only hatch areas illustrated in
Next, example dimensions of components of the movable reflective element 100 are described. The A layer 100A is a 5 mm×5 mm square×0.3 mm thick silicon substrate. The B layer 100B is an approximately 300 nm thick thin-film layer of platinum. The C layer 100C is an approximately 2 μm thick PZT layer. The D layer 100D is an approximately 300 nm thick thin-film layer of platinum/gold. Here, the thickness of the actuators 140 and 150 and the mirror 130 is 0.10 mm by etching of the silicon substrate 100A (A layer) at the lower surface thereof. This etching results in formation of a 0.20 mm gap between the lower surfaces of the actuators 140 and 150 and the mirror 130 and the upper surface of the base plate 200. In the top view of
The dimension of each component can be optionally changed. The thickness, the width, and the length of each of the actuators 140 and 150 may be changed to any dimension that allows the mirror 130 to be flexible enough to tilt in a predetermined angular range (range satisfying performance necessary for a movable mirror). The thickness of the fixed frame 110 may be set to any dimension that allows the movable reflective element 100 to be firmly fixed on the base plate 200.
Movement of Actuators
Next, the movement of the actuators 140 and 150 is described. As illustrated in
Similarly, the actuator 150 includes the A layer (substrate layer) 150A, the B layer (lower electrode layer) 150B, the C layer (piezoelectric material layer) 150C, and the D layer (upper electrode layer) 150D, as illustrated in
When the voltage is applied across the electrode layers so that the D layer (upper electrode layer) 140D is positive and the B layer (lower electrode layer) 140B is negative, the C layer (piezoelectric material layer) 140C stretches in the longitudinal direction (direction perpendicular to the thickness direction). Conversely, the C layer (piezoelectric material layer) 140C has a property of contracting in the longitudinal direction when a voltage is applied across the electrode layers so that the D layer (upper electrode layer) 140D is negative and the B layer (lower electrode layer) 140B is positive. The degree of stretching and contracting depends on the applied voltage.
Thus, as illustrated in
In contrast, as illustrated in
It is of course possible that the C layer (piezoelectric material layer) 140C has a property of contracting in the longitudinal direction when the voltage is applied across the electrode layers so that the D layer (upper electrode layer) 140D is positive and the B layer (lower electrode layer) 140B is negative, while the C layer 140C has a property of stretching in the longitudinal direction when the voltage is applied across the electrode layers so that the D layer (upper electrode layer) 140D is negative and the B layer (lower electrode layer) 140B is positive. In this case, the actuator 140 bows to become downwardly convex upon application of the voltage with the positive polarity, and bows to become upwardly convex upon application of the voltage with the negative polarity.
In either case, application of the voltage having the predetermined polarity across the D layer (upper electrode layer) 140D and the B layer (lower electrode layer) 140B causes deformation illustrated in
The above-described movements also apply to the actuator 150.
Returning to
The detection electrode 160D is provided at a portion connecting the actuator 140 to the fixed frame 110, and the detection electrode 170D is provided at a portion connecting the actuator 150 to the movable frame 120. These portions are places where the actuators 140 and 150 deform greatly. Thus arrangement of the detection electrode 160D and 170D in such places enables stable detection of the displacement of the actuators 140 and 150.
As illustrated in
As described above, when the voltage of such polarity that the D layer (upper electrode layer) 140D side is positive is applied across the B layer (lower electrode layer) 140B and the D layer (upper electrode layer) 140D of the piezoelectric elements of the actuator 140, the +Y side of the movable frame 120 is enabled to move downwardly to tilt relative to the Y-axis direction, as illustrated in
In contrast,
As described above, when the voltage of such polarity that the D layer (upper electrode layer) 150D side is positive is applied across the B layer (lower electrode layer) 150B and the D layer (upper electrode layer) 150D of the piezoelectric elements of the actuator 150, the +X end of the mirror 130 is enabled to move downwardly to tilt, as illustrated in
Arrangement of the piezoelectric elements can be reversed. For example, the actuator 140 may have piezoelectric elements on the upper side thereof, while the actuator 150 may have piezoelectric elements on the lower side thereof. Alternatively, each of the actuators 140 and 150 may have piezoelectric elements on both the upper and lower sides of each actuator body 140A and 150A. In practice, however, forming the piezoelectric elements on the upper side of each actuator body 140A and 150A is preferable for simplification of the fabrication process.
In the movable reflective element 100 according to Embodiment 1, the mirror 130 having the reflective surface is connected via the flexible actuator 150 to the movable frame 120, which in turn is connected via the actuator 140 to the fixed frame 110. Compared with a traditional supporting technique with a gimbal structure, this simple configuration provides a sufficient range of displacement angle. Implementation of the gimbal structure in mechanical rotating mechanism may increase the number of parts and the complexity of the structure. Implementation of the gimbal structure with a torsion bar simplifies the structure, but may limit the range of the maximum displacement angle to the range of the maximum torsion angle of the torsion bar, which results in difficulties in ensuring a sufficient displacement angle. The present embodiment provides the mirror 130 supported by the actuators 140 and 150, and thus ensures a sufficient displacement angle with a simple configuration.
The movable reflective element 100 having a configuration illustrated in
The movable reflective element 100 has actuators 140 extending in the Y axis and actuators 150 extending in the X axis. The actuators 140 and 150 each have the piezoelectric elements fixed on the upper or lower side, and the piezoelectric elements stretch or contract in the longitudinal direction upon application of the voltage with the respective polarities. Thus, when the voltage is applied to the piezoelectric elements of the actuator 140 to cause the piezoelectric elements to contract, the mirror 130 tilts relative to the Y-axis direction (rotates about the X axis) as illustrated in
The present embodiment provides a structure in which the actuator 140, the movable frame 120, the actuator 150, and the mirror 130 are disposed on the fixed frame 110. However, the fixed frame 110 is not necessarily a frame body, but may be, for example, any other non-frame structure to which one end of the actuator 140 can be fixed.
However, since the actuators 140 and 150 and the mirror 130 are movable components for which displacement occurs, contact with an external object is to be avoided. In this regard, the frame shape like the fixed frame 110 enables surrounding of the movable components inside the frame, which protects the movable components against contact with the external object.
The shapes of the fixed frame 110, the movable frame 120, and the mirror 130 are not limited to the rectangle-like shape, but may be oval or polygonal.
The present embodiment provides the base plate 200 that supports the fixed frame 110. Providing the base plate 200 and fixing the lower surface of the fixed frame 110 to the upper surface of the base plate 200 leave the actuator 140, the movable frame 120, the actuator 150 and the mirror 130 suspended above the base plate 200, and enable tilting of the mirror 130 within a range of freedom defined by the size of the gap formed above the base plate 200. In addition, excess displacement in the mirror 130 can be prevented, which prevents the actuators 140 and 150 from overly flexing and being damaged. In the present embodiment, the small thicknesses of the actuators 140 and 150 and the mirror 130 compared with the fixed frame 110 allows the suspended structure, but the same thicknesses of such components can also allow a suspended structure by providing a so-called spacer 300 on the lower surface of the fixed frame 110.
According to the movable reflective element 100 of Embodiment 1 as described above, the length of the actuator 140 in the Y-axis direction is longer than a distance between the inner side of the fixed frame 110 and the middle point of the outer side of the movable frame 120 in the Y-axis direction. This further increases a ratio of the length of the actuator 140 to the length of the actuator 150. This enables the movable frame 120 and the mirror 130 to have a desired ratio of drive frequencies. In addition, the mirror 130 can be oscillated within a range that is sufficient in practice, for example without multiple folding of the actuators 140 and 150. Thus the movable reflective element 100 of Embodiment 1 can achieve optimization of the drive frequencies and miniaturization.
Provided that the base plate 200 is a device enclosure for the movable reflective element 100, the base plate 200 can be regarded as a component incorporated into the product itself of the movable reflective element 100. However, the product itself of the movable reflective element 100 can take a form not to include the base plate 200. In this case, a mount surface of some device, on which the movable reflective element is mounted as a component, functions as the base plate 200.
Next, Embodiment 2 of the present disclosure is described.
The actuators 140 in the above-described Embodiment 1 are linear, while the actuators 140 in Embodiment 2 are substantially L-shaped. This L-shaped configuration allows increased lengths of the actuators 140 in the Y-axis direction.
As illustrated in
One end of the arm 340A is connected to the inner side of the fixed frame 110. The arm 340A extends linearly in the Y-axis direction in a gap between the fixed frame 110 and the movable frame 120 from the one end of the arm 340A beyond the middle point of the outer side of the movable frame 120, that is, beyond the X axis. The arm 340B of the actuator 140 extends from the other end of the arm 340A in the X axis without turning back, and is connected to a corner portion of the movable frame 120, which is a portion other than the middle point (on the Y axis) of the outer side of the movable frame 120.
One end of each actuator 150 is connected to the inner side of the movable frame 120. The actuator 150 includes an arm (the tenth arm) extending linearly in the X-axis direction in a gap between the movable frame 120 and the mirror 130 from the one end of the arm beyond the middle point of the outer side of the mirror 130, that is, beyond the Y axis. The actuator 150 extends from the other end of the arm in the X-axis direction without turning back, and is connected to a corner portion of the mirror 130, which is a portion other than the middle point of the outer side of the mirror 130.
The arm 340A of the actuator 140 as illustrated in
The actuators 150 each also include piezoelectric elements (150B, 150C, and 150D), as illustrated in
According to the movable reflective element 100 of Embodiment 2 as described above, the length of the actuator 140 in the Y-axis direction is longer than a distance between the inner side of the fixed frame 110 and the middle point of the outer side of the movable frame 120 in the Y-axis direction. This further increases a ratio of the length of the actuator 140 to the length of the actuator 150. This enables the movable frame 120 and the mirror 130 to have a desired ratio of drive frequencies. In addition, the mirror 130 can be oscillated within a range that is sufficient in practice, for example without multiple folding of the actuators 140 and 150. Thus the movable reflective element 100 of Embodiment 2 achieves optimization of the drive frequencies and miniaturization.
Next, Embodiment 3 of the present disclosure is described. Embodiment 3 differs from Embodiment 1 in that the actuators 150 in Embodiment 3 are substantially L-shaped.
As illustrated in
The arm 350B extends in the Y-axis direction in a gap between the movable frame 120 and the mirror 130 from the other end of the arm 350A, and is connected to a corner portion of the mirror 130 beyond the middle point of the outer side of the movable frame 120 in the Y-axis direction.
As illustrated in
As described above, according to the present embodiment, the length of the actuator 150 is not limited to a distance between the inner side of the movable frame 120 and the middle point of the outer side of the mirror 130. This enables the movable frame 120 and the mirror 130 to have a desired ratio of drive frequencies thereof. In addition, the mirror 130 can be oscillated within a range that is sufficient in practice, for example without multiple folding of the actuators 140 and 150. Thus the movable reflective element 100 of Embodiment 3 achieves optimization of the drive frequencies and miniaturization.
Next, Embodiment 4 of the present disclosure is described. The actuators 140 and 150 of the movable reflective element 100 of Embodiment 4 are both substantially L-shaped.
As illustrated in
The actuator 150 has arms 350A and 350B. One end of the arm 350A is connected to the inner side of the movable frame 120, and extends linearly in the X-axis direction in a gap between the movable frame 120 and the mirror 130 from the one end of the arm 350A beyond the middle point of the outer side of the mirror 130. The arm 350B extends in the Y-axis direction from the other end of the arm 350A, and is connected to a corner portion of the mirror 130 beyond the middle point of the outer side of the mirror 130.
The arm 340A illustrated in
The arm 350A illustrated in
According to the movable reflective element 100 of Embodiment 4 as described above, the length of the actuator 140 is not limited to a distance between the inner side of the fixed frame 110 and the middle point of the outer side of the movable frame 120, and the length of the actuator 150 is not limited to a distance between the inner side of the movable frame 120 and the middle point of the outer side of the mirror 130. This enables the movable frame 120 and the mirror 130 to have a desired ratio of drive frequencies thereof. In addition, the mirror 130 can be oscillated within a range that is sufficient in practice, for example without multiple folding of the actuators 140 and 150. Thus the movable reflective element 100 of Embodiment 4 achieves optimization of the drive frequencies and miniaturization.
Next, Embodiment 5 of the present disclosure is described. Movable reflective elements 100 of Embodiment 5 and Embodiments 6 and 7, which are described below, are designed based on similar ideas and belong to the same group.
As illustrated in
The actuators 140 are disposed on both sides of the movable frame 120 in the X-axis direction between the fixed frame 110 and the movable frame 120. The actuators 150 are disposed on both sides of the mirror 130 in the Y-axis direction between the movable frame 120 and the mirror 130.
As illustrated in
As illustrated in
The actuator 140 includes three parts, each being specified as an arm 240A (the first arm), an arm 240B (the second arm), and an arm 240C (the third arm). That is, the actuator 140 includes the arms 240A, 240B, and 240C.
First, the configuration of the +X-side actuator 140 (240A, 240B, and 240C) is described.
The −Y-side end of the arm 240A is connected to the inner side (portion around the +X-side corner of the inner side facing toward the +Y side) of the fixed frame 110. The arm 240A extends in the Y-axis direction in a gap between the fixed frame 110 and the movable frame 120 from the −Y-side end toward the +Y side. The arm 240A has a width that allows the arm 240A to extend along the arm 240C in a gap between the fixed frame 110 and the movable frame 120. The arm 240A extends linearly beyond the middle point N (see
The +X-side end of the arm 240B is connected to the +Y-side end of the arm 240A. The width and thickness of the arms 240B are substantially the same as those of the arm 240A. The arm 240B extends in the X-axis direction from the +X-side end toward the movable frame 120.
The +Y-side end of the arm 240C is connected to the −X-side end of the arm 240B. The arm 240C turns around at the −X end of the arm 240B and extends along the arm 240A. The width and thickness of the arm 240C are substantially the same as those of the arm 240A. The arm 240C is connected at the −Y end thereof to the middle point (on the X axis) N of the outer side of the movable frame 120.
As illustrated in
The −X-side actuator 140 also includes the arms 240A, 240B, and 240C. In the −X-side actuator 140, the arm 240A extends in the −Y direction from the +Y-side inner side of the fixed frame 110 beyond the middle point N of the outer side of the movable frame 120, the arm 240B extends in the +X direction from the −Y-side end of the arm 240A, and the arm 240C extends in the +Y direction from the +X-side end of the arm 240B and is connected to the middle point N of the outer side of the movable frame 120. That is, the actuators 140, the pair of members, are disposed with two-fold rotational symmetry around the center of gravity of the mirror 130. Similarly, the actuators 150, the pair of members, are disposed with two-fold rotational symmetry around the mirror 130.
As illustrated in
The voltage of such polarity that the D layer (upper electrode layer) 140D side is positive is applied across the B layer (lower electrode layer) 140B and the D layer (upper electrode layer) 140D. In this case, as illustrated in
Application of the voltage with the reverse polarity across the B layer (lower electrode layer) 140B and the D layer (upper electrode layer) 140D causes the piezoelectric elements (140B, 140C, and 140D) having the three-layer structure of the B layer 100B, the C layer 100C, and the D layer 100D to contract in the longitudinal direction, which causes the A layer 100A of the flexible arm 240A to be stressed on the upper surface side in a direction of contracting in the plane. As a result, the arm 240A bows to become downwardly convex. The downwardly convex bow of the arm 240A causes, via the arm 240B, the +Y end of the arm 240C to move upwardly to tilt, and the entire actuator 140 tilts with the +Y end moving upwardly. This enables the movable frame 120 and the mirror 130 to tilt with the +Y ends thereof moving upwardly, as illustrated in
For the pair of actuators 140, the polarity of the voltage applied to the +X-side piezoelectric element is opposite to the polarity of the voltage applied to the −X-side piezoelectric element. This enables the movable frame 120 to oscillate about the X axis to the fixed frame 110.
The degree of tilt depends on the applied voltage. Thus adjusting the polarity and value of the applied voltage enables freely-selected adjustment of tilt angles of the mirror 130 relative to the X-axis direction.
Referring back to
For the pair of actuators 150, the polarity of the voltage applied to the +Y-side piezoelectric element is opposite to the polarity of the voltage applied to the −Y-side piezoelectric element. This enables the mirror 130 to oscillate about the Y axis relative to the movable frame 120.
According to the movable reflective element 100 of Embodiment 5 as described above, the length of the actuator 140 in the Y-axis direction is longer than a distance between the inner side of the fixed frame 110 and the middle point of the outer side of the movable frame 120 in the Y-axis direction. This further increases a ratio of the length of the actuator 140 to the length of the actuator 150. This enables the movable frame 120 and the mirror 130 to have a desired ratio of drive frequencies. In addition, the mirror 130 can be oscillated within a range that is sufficient in practice, for example without multiple folding of the actuators 140 and 150. Thus the movable reflective element 100 of Embodiment 5 achieves optimization of the drive frequencies and miniaturization.
The movable reflective element 100 according to Embodiment 5 enables the increased length of the actuator 140, thereby having a length in the Y-axis direction shorter than the length in the X-axis direction. As described below, when the direction of oscillation about the X axis is set to correspond to a vertical scanning direction of beams, the Y-axis direction of the movable reflective element 100 that is incorporated into a device such as a projector or the like is enabled to correspond to the direction of the thickness of the device. Thus use of the movable reflective element 100 according to Embodiment 5 achieves a compact and thinner device, into which the movable reflective element 100 is incorporated, since the Y-axis length of the movable reflective element 100 is reduced.
Since the actuator 140 is connected to the middle point N of the outer side of the movable frame 120, a moment other than moments in the X and Y directions has little effect on the movable frame 120, which prevents the vibration of the movable frame 120 from being unbalanced in either of the directions or twisted. The actuator 150 with a simple configuration achieves a compact movable frame 120.
Next, Embodiment 6 of the present disclosure is described.
As illustrated in
The actuator 150 includes an arm 250A (the fourth arm), an arm 250B (the fifth arm), and an arm 250C (the sixth arm). First, the configuration of the +Y-side actuator 150 (250A, 250B, and 250C) is described.
The +X-side end of the arm 250A is connected to the inner side (portion around the +Y-side corner of the inner side facing toward the −X side) of the movable frame 120. The arm 250A extends in the X-axis direction in a gap between the movable frame 120 and the mirror 130 from the +X side end toward the −X side. The arm 250A has a width that allows the arm 250A to extend in the −X direction with the arms 250A and 250C spaced apart in a gap between the movable frame 120 and the mirror 130. The arm 250A extends beyond the middle point K (on the Y axis) of the outer side of the mirror 130 in the X-axis direction, that is, beyond the Y axis. The arm 250A extends to the vicinity of the inner side facing the +X side of the movable frame 120.
The +Y-side end of the arm 250B is connected to the −X-side end of the arm 250A. The width and thickness of the arm 250B are substantially the same as those of the arm 250A. The arm 250B extends in the Y-axis direction from the +Y-side end toward the mirror 130.
The −X-side end of the arm 250C is connected to the −Y-side end of the arm 250B. The arm 250C extends along the arm 250A so as to turn back from the −Y end of the arm 250B toward the +X side. The width and thickness of the arm 250C are substantially the same as those of the arm 250A. The arm 250C is connected at the +X end thereof to the middle point (on the Y axis) K of the outer side of the mirror 130.
The arm 250A includes piezoelectric elements (150B, 150C, and 150D) formed therein. The piezoelectric elements are formed of the B layer (lower electrode layer) 150B, the C layer (piezoelectric material layer) 150C, and the D layer (upper electrode layer) 150D.
The −Y-side actuator 150 also includes the arms 250A, 250B, and 250C. In the −Y-side actuator 150, the arm 250A extends in the +X direction from the −X-side inner side of the movable frame 120 beyond the middle point of the outer side of the mirror 130, the arm 250B extends in the +Y direction from the +X-side end of the arm 250A, the arm 250C extends in the −X direction from the +Y-side end of the arm 250A and is connected to the middle point K of the outer side of the mirror 130.
When the voltage is not applied across the B layer (lower electrode layer) 150B and the D layer (upper electrode layer) 150D of the piezoelectric elements (150B, 150C, and 150D) of the actuator 150, the mirror 130 is supported by the movable frame 120 and kept horizontally, as illustrated in
When the voltage of such polarity that the D layer (upper electrode layer) 150D side is positive is applied across the B layer (lower electrode layer) 150B and the D layer (upper electrode layer) 150D, the piezoelectric elements having a three-layer structure of the B layer 150B, the C layer 150C, and the D layer 150D of the arm 250A stretch in the longitudinal direction (direction perpendicular to the thickness direction) to cause the flexible A layer 150A to be stressed on the upper surface side in a direction of stretching in the plane direction (direction along the X axis). As a result, the arm 250A bows to become upwardly convex. The upwardly convex bow of the arm 250A causes, via the arm 250B, the +X end of the arm 250C to move downwardly to tilt, and thus the entire actuator 150 tilts with the +X end moving downwardly. As illustrated in
Application of the voltage with the reverse polarity across the B layer (lower electrode layer) 150B and the D layer (upper electrode layer) 150D causes the piezoelectric elements (150B, 150C, and 150D) having the three-layer structure of the B layer 100B, the C layer 100C, and the D layer 100D to contract in the longitudinal direction, which causes the A layer 100A of the flexible arm 250A to be stressed on the upper surface side in a direction of contracting in the plane. As a result, the arm 250 bows to become downwardly convex. The downwardly convex bow of the arm 250A causes, via the arm 250B, the +X end of the arm 250C to move upwardly to tilt, and the entire actuator 250 tilts with the +X end moving upwardly. The mirror 130 thereby rotates about the Y axis, and rotation −Ry about the Y axis occurs, as illustrated in
For the pair of actuators 150, the polarity of the voltage applied to the +Y-side piezoelectric element is opposite to the polarity of the voltage applied to the −Y-side piezoelectric element. This enables the mirror 130 to oscillate about the Y axis relative to the movable frame 120.
The degree of tilt depends on the applied voltage. Thus adjusting the polarity and value of the applied voltage enables any adjustment of tilt angles of the mirror 130 relative to the X-axis direction.
According to the movable reflective element 100 of Embodiment 6 as described above, the length of the actuator 140 in the Y-axis direction is longer than a distance between the inner side of the fixed frame 110 and the middle point of the outer side of the movable frame 120 in the Y-axis direction. This further increases a ratio of the length of the actuator 140 to the length of the actuator 150. This enables the movable frame 120 and the mirror 130 to have a desired ratio of drive frequencies. In addition, the mirror 130 can be oscillated within a range that is sufficient in practice, for example without multiple folding of the actuators 140 and 150. Thus the movable reflective element 100 of Embodiment 6 achieves optimization of the drive frequencies and miniaturization.
In Embodiment 6, the actuators 140, the pair of members, are disposed with two-fold rotational symmetry around the origin O of the mirror 130. The actuators 150 that are the pair of members are also disposed with two-fold rotational symmetry around the mirror 130. In addition, an orientation of the arm 240A from one end connected to the fixed frame 110 toward the other end and an orientation of the arm 250A from one end connected to the movable frame 120 toward the other end are the same with respect to a rotational direction about the center of gravity of the mirror 130.
The actuators 140 and the actuators 150 are both substantially S-shaped. This enables optimization of a ratio of drive frequencies and miniaturization of the movable frame 120. This also enables the mirror 130 to be held without bias and oscillated in balanced manner.
Next, Embodiment 7 of the present disclosure is described.
The movable reflective element 100 according to Embodiment 7 is the same as the movable reflective element 100 according to Embodiment 6 except for the orientations of the actuators 150.
As illustrated in
For example, when two-dimensional scanning of beams with the movable reflective element 100 according to Embodiment 6 causes an projected image to be distorted, use of the movable reflective element 100 according to Embodiment 7 instead may result in correction of distortion of the image. In such cases, the movable reflective element 100 according to Embodiment 7 may be used.
According to the movable reflective element 100 of Embodiment 7 as described above, the length of the actuator 140 in the Y-axis direction is longer than a distance between the inner side of the fixed frame 110 and the middle point of the outer side of the movable frame 120 in the Y-axis direction. This further increases a ratio of the length of the actuator 140 to the length of the actuator 150. This enables the movable frame 120 and the mirror 130 to have a desired ratio of drive frequencies. In addition, the mirror 130 can be oscillated within a range that is sufficient in practice, for example without multiple folding of the actuators 140 and 150. Thus the movable reflective element 100 of Embodiment 7 achieves optimization of the drive frequencies and miniaturization.
There are various other method for correcting distortion of images caused by the above-described two-dimensional scanning. For example, as illustrated in
Places where such weights 400 are attached are not limited to the movable frame 120. The weights 400 may be attached, for example, to the mirror 130. Alternatively, the weights 400 may be attached to the actuators 140 and/or 150.
Next, Embodiment 8 of the present disclosure is described. Movable reflective elements 100 of Embodiment 8 and Embodiment 9, which is described below, are designed based on similar ideas and belong to the same group.
As illustrated in
The movable frame 120 includes recessed portions 220 provided on the middle point of the outer sides of the movable frame 120 on both sides in the Y-axis direction. The recessed portions 220 are provided for piezoelectric elements described below to be disposed in arms 340C. The recessed portions 220 are desirably provided on the middle points of the outer sides of the movable frame 120 on both sides in the Y-axis direction, but the places where the recessed portions are provided are not limited thereto, and any portion on the above-described outer sides is acceptable.
The actuators 140 each includes an arm 340A (the twelfth arm), an arm 340B (the thirteenth arm), and an arm 340C (the fourteenth arm). The actuators 150 each includes an arm 350A (the fifteenth arm), an arm 350B (the sixteenth arm), and an arm 350C (the seventeenth arm).
The arm 340A extends in the Y-axis direction from the inner side of the fixed frame 110, which is located on the middle point of the fixed frame 110 in the Y-axis direction, and extends beyond the outer side of the movable frame 120 in the Y-axis direction. One end of the arm 340B is connected to the other end of the arm 340A. The arm 340B extends in the −X-axis direction from the one end. One end of the arm 340C is connected to the other end of the arm 340B. The arm 340C extends along the arm 340A, and the other end of the arm 340C is connected to the recessed portion 220 of the movable frame 120.
The length of the arm 340A in the Y-axis direction is longer than a distance between the inner side located on the middle point of the fixed frame 110 in the Y-axis direction and the outer side of the movable frame 120 in the Y-axis direction. The distance between the inner side of the fixed frame 110 located on the middle point thereof in the Y-axis direction and the outer side of the movable frame 120 in the Y-axis direction is the same in design as the distance between the inner side of the corner of the fixed frame 110 between the −Y and +X sides (or the inner side of the corner of the fixed frame 110 between the +Y and −X sides) and the middle point of the outer side of the movable frame 120 in the Y-axis direction.
The arm 350A extends in the −X-axis direction from the inner side of the movable frame 120 beyond the middle point of the outer side of the mirror 130 in the X-axis direction, that is, beyond the Y axis. One end of the arm 350B is connected to the other end of the arm 350A. The arm 350B extends in the Y-axis direction from the one end. One end of the arm 350C is connected to the other end of the arm 350B. The other end of the arm 350C extends in the X-axis direction and is connected to the middle point of the outer side of the mirror 130.
As illustrated in
The arm 350A includes the upper electrode layer 150D formed therein. This results in the piezoelectric elements formed in the arm 350A. Application of the voltage with the positive polarity or the negative polarity to the piezoelectric elements of the arm 350A causes the arm 350A to bow upwardly or downwardly. As a result, the mirror 130 oscillates about the Y axis.
According to the movable reflective element 100 of Embodiment 8 as described above, the individually movable sets of piezoelectric elements are formed in the actuator 140. Combined movement of these sets of piezoelectric elements enables the actuator 140 to finely control the oscillation state of the movable frame 120.
According to the movable reflective element 100 of Embodiment 8, the length of the actuator 140 in the Y-axis direction is longer than a distance between the inner side located on the middle point of the fixed frame 110 in the Y-axis direction and the outer side of the movable frame 120 in the Y-axis direction. This further increases a ratio of the length of the actuator 140 to the length of the actuator 150. This enables the movable frame 120 and the mirror 130 to have a desired ratio of drive frequencies. In addition, the mirror 130 can be oscillated within a range that is sufficient in practice, for example without multiple folding of the actuators 140 and 150. Thus the movable reflective element 100 of Embodiment 8 achieves optimization of the drive frequencies and miniaturization.
The movable reflective element 100 of Embodiment 8 is provided with wide portions 111. The wide portions 111 are provided in portions connecting the actuators 140 to the fixed frame 110 and have a width larger than the width of the actuators 140. The wide portions 111 help reinforce the portions, which fluctuate greatly, connecting the actuators 140 to the fixed frame 110.
Additionally, the portions connecting the actuators 150 to the movable frame 120 may also be provided with wide portions that are wider than the width of the actuators 150. Alternatively, the wide portions may be provided only in the portions connecting the actuators 150 to the movable frame 120, rather than the wide portions 111. Since either connecting portion fluctuates greatly, the wide portions help provide the reinforcement.
Next, Embodiment 9 of the present disclosure is described.
Embodiment 9 differs from Embodiment 8 in the configuration of the upper electrode layers formed in the actuators 140. As illustrated in
The arm 340B is provided with upper electrode layers 140D21 and 140D22. The upper electrode layer 140D21 is a pair of electrodes extending from the portion connecting to the arm 340A to the vicinity of the middle point of the arm 340B. The upper electrode layer 140D22 is a pair of electrodes extending from the middle point of the arm 340B to the portion connecting to the arm 340C.
The arm 340C is provided with a pair of upper electrode layers 140D3. The pair of upper electrode layers 140D3 is a pair of electrodes extending from the portion connecting to the arm 340B to the recessed portion 220 of the movable frame 120.
As described above, the actuator 140 can include the upper electrode layers formed in the length and width directions of the respective arms 340A, 340B, and 340C. This means that each of the arms 340A, 340B, and 340C includes the individually driven set of piezoelectric elements formed therein. Forming such a set of piezoelectric elements for each of the arms 340A, 340B, and 340C to be individually driven enables movement of each of the arms 340A, 340B, and 340C to be finely controlled, thereby providing more precise two-dimensional scanning of the movable reflective element 100.
The piezoelectric elements may be at least one of the paired actuators 140 or at least one of the paired actuators 150.
The actuator 140 of Embodiment 9 needs a space for forming a circuit pattern for supply of power to the downstream piezoelectric elements, and thus the widths of the sets of upper electrode layers are decreased along the path from the movable frame 120 toward the fixed frame 110.
In Embodiment 9, as illustrated in
In Embodiment 9, the actuator 150 may be configured to have a width increasing in the path from the mirror 130 toward the movable frame 120.
As described above, the uniform width is not required for the actuators 140 and 150. That is, the width may be increased from the movable frame 120 side toward the fixed frame 110 side, or may be increased from the mirror 130 side toward the movable frame 120 side. Alternatively, the widths of the actuators 140 and 150 may be partially varied.
According to the movable reflective element 100 of Embodiment 9 as described above, the length of the actuator 140 in the Y-axis direction is longer than a distance between the inner side located on the middle point of the fixed frame 110 in the Y-axis direction and the outer side of the movable frame 120 in the Y-axis direction. This further increases a ratio of the length of the actuator 140 to the length of the actuator 150. This enables the movable frame 120 and the mirror 130 to have a desired ratio of drive frequencies. In addition, the mirror 130 can be oscillated within a range that is sufficient in practice, for example without multiple folding of the actuators 140 and 150. Thus the movable reflective element 100 of Embodiment 9 achieves optimization of the drive frequencies and miniaturization.
Next, Embodiments 10 to 12 of the present disclosure are described.
The movable reflective element 100 of Embodiment 10 differs from that of Embodiment 4, as illustrated in
The restrictions 500 extend from the inner sides of the movable frame 120 and are disposed in the gaps between the movable frame 120 and the mirror 130 in order to restrict movement of the mirror 130 relative to the movable frame 120.
The restrictions 501 extend from the inner sides of the fixed frame 110 and are disposed in gaps between the fixed frame 110 and the movable frame 120 in order to restrict movement of the movable frame 120 relative to the fixed frame 110.
The movable reflective element 100 illustrated in
Inclusion of such restrictions 500 and 501 prevents the movable frame 120, the mirror 130, and the like from being damaged due to applied external force.
Specifically, the outer periphery of each of the mirrors 130 of Embodiments 10 and 12 is formed so as to avoid the restrictions 500. Such forming of the outer periphery of each mirror 130 causes the restrictions 500 to abut against the outer periphery of the mirror 130 when external force is applied to the movable reflective element 100. Such configuration thus can prevent damage caused by great movement of the mirror 130 in the X-axis and Y-axis directions when the external force is applied.
Similarly, the outer periphery of each of the movable frames 120 of Embodiments 10 and 12 is formed so as to avoid the restrictions 501. Such forming of the outer periphery of the movable frame 120 causes the restrictions 501 to abut against the outer periphery of the movable frame 120 when external force is applied to the movable reflective element 100. Such configuration thus can prevent damage caused by great movement of the movable frame 120 in the X-axis and Y-axis directions when the external force is applied.
The outer periphery of each of the mirrors 130 of Embodiments 10 and 12 is formed so that the outer periphery avoids the restrictions 500 and the center of gravity of the mirror 130 in the stationary state is the center of the mirror 130. Specifically, the outer periphery of opposing sides of the above-described mirror 130 has a point-symmetrical shape with respect to the center of the mirror 130. This provides dummy cutouts at portions where the mirror has no need to avoid the restrictions 500. Such a shape of the outer periphery causes the center of gravity of the mirror 130 in the stationary state to be the center of the mirror 130, and prevents occurrence of tilt in the stationary state.
Similarly, the outer periphery of each of the movable frames 120 of Embodiments 10 and 12 is formed so that the outer periphery avoids the restrictions 501 and the center of gravity of the movable frame 120 in the stationary state is the center of the movable frame 120. Specifically, the outer periphery of opposing sides of the above-described movable frame 120 has a point-symmetrical shape relative to the center of the movable frame 120. This provides dummy cutouts at portions where the mirror has no need to avoid the restrictions 501. Such a shape of the outer periphery causes the center of gravity of the movable frame 120 in the stationary state to be the center of the movable frame 120, and prevents occurrence of tilt in the stationary state.
Although the shapes of the restrictions 500 and 501 illustrated in
The movable reflective elements 100 of Embodiments 1 to 12 as described above can each combine as appropriate the following features of: providing sets of piezoelectric elements in the actuators 140 and 150; having the widths of the detection electrodes smaller than the widths of the actuators; providing detection electrodes in portions connecting the fixed frame 110 to the actuators 140 and in portions connecting the mirror 130 to the actuators 150; forming the movable frame 120 thicker than the mirror 130; varying the widths of the actuators 140 and 150; attaching a weight 400 to the movable frame 120; and providing the restrictions 500 and 501.
Next, Embodiment 13 of the present disclosure is described. In the description regarding Embodiment 13, a two-dimensional scanner including the movable reflective element 100 is described.
The movable reflective elements 100 according to Embodiments 1 to 12 are each capable of tilting, with two axes of freedom, the reflective surface formed on the surface of the mirror 130. Thus two-dimensional scanning can be achieved by the two-dimensional scanner, in which the movable reflective element 100 is incorporated, for scanning light beams or directional radio waves two-dimensionally. Scanning of light beams by this two-dimensional scanner achieves a projector for projecting an image on a screen, while scanning of directional radio waves achieves an onboard radar.
Since the movable reflective elements 100 according to Embodiments 1 to 12 are suitable for miniaturization and low current consumption as MEMS elements, the movable reflective elements 100 can be optimally used by incorporation into small devices, such as portable phones, smartphones, tablet electronic terminals, and are suitable for enabling the small devices to have projector capabilities. Radar has recently become an indispensable technique for use in automobiles, and there is a need to radiate a wide range of directional radio waves. Use of the movable reflective elements 100 according to Embodiments 1 to 12 provides a compact in-vehicle device capable of providing a wide range of radar illumination.
The following description is made for a case in which a two-dimensional scanner is configured to drive the movable reflective element 100 according to Embodiments 1 to 12 with alternating-current signals and the two-dimensional scanner is incorporated into a projector. This two-dimensional scanner is also applicable for the above-described in-vehicle radar device.
The two-dimensional scanner 20 includes a movable reflective element 100 and a controller 22. The movable reflective element 100 is the movable reflective element 100 according to Embodiments 1 to 12. Application of alternating voltage to piezoelectric elements included in the movable reflective element 100 enables a mirror 130 having a reflective surface M parallel to the XY-plane to tilt relative to the Y-axis direction (about X axis) and relative to the X-axis direction (about Y axis). The controller 22 provides drive signals (alternating voltage) to the piezoelectric elements of the movable reflective element 100.
The movable reflective element 100 includes actuators 140 and 150, as described above. The controller 22 provides a first drive signal having a first period H1 to the piezoelectric elements of the actuators 150 and provides a second drive signal having a second period H2 to the piezoelectric elements of the actuators 140.
The laser light source 30 generates a laser beam, and irradiates with the laser beam a reflective surface M of the movable reflective element 100 in the two-dimensional scanner 20. The laser beam reflected at the reflective surface M forms a spot S in place on the screen 10. Two-dimensional tilting of the reflective surface M of the movable reflective element 100 enables two-dimensional scanning of a position of the spot S formed on the screen 10.
The display control device 40 performs, on the basis of externally provided image data, a display control for displaying an image on the screen 10. Specifically, the display control device 40 provides to the laser light source 30 a modulation signal based on the image data for an image to be displayed, and provides a control signal to the controller 22 of the two-dimensional scanner 20.
The laser light source 30 generates, on the basis of the modulation signal provided by the display control device 40, a laser beam having intensity and/or wavelength modulated, and irradiates with the laser beam the reflective surface M of the mirror 130 of the movable reflective element 100 in the two-dimensional scanner 20. When the image to be displayed is a monochrome image, the intensity of a monochromatic laser beam, which is generated by the laser light source 30, may be modulated. When the image to be displayed is a color image, a complex light source for generating three-primary color (RGB) laser beams may be used as an example of the laser light source 30, and the intensities of the laser beams may be modulated individually for each primary color.
The two-dimensional scanner 20 oscillates the mirror 130 of the movable reflective element 100 on the basis of the control signal received from the display control device 40 so that the spot S formed on the screen 10 by the laser beam reflected on the reflective surface M moves on the screen 10 two-dimensionally.
The control signal provided by the display control device 40 to the two-dimensional scanner 20 is a signal that indicates switching on/off of an oscillation motion of the mirror 130 of the movable reflective element 100 and timing of the oscillation motion. The display control device 40 provides to the two-dimensional scanner 20 a control signal synchronized to the timing of the modulation signal provided to the laser light source 30. As a result, the position of the spot S on the screen 10 is synchronized with modulation content of the laser beam forming the spot S, which results in the image displayed on the screen 10 in accordance with the image data.
The following is a description of the specific operation of the beam scan by the two-dimensional scanner 20. Here, the description for the movable reflective element 100 embedded in the two-dimensional scanner 20 is made, as an example, using the movable reflective element 100 according to Embodiment 5.
The upper graph of
As illustrated in
The voltage value of the second drive signal Dy rises from −Vy to +Vy in steps, each having a unit time corresponding to the period H1, in the period of time from t0 to t6 along the time axis t, and this cycle repeats with the period H2. When such a second drive signal Dy is applied to the piezoelectric elements of the actuators 140 of the movable reflective element 100 illustrated in
In practice, the first drive signal Dx may be supplied to the D layer (upper electrode layer) 150D of the actuator 150 with the B layer (lower electrode layer) 100B of the movable reflective element 100 fixed to a ground potential, and the second drive signal Dy may be supplied to the D layer (upper electrode layer) 140D of the actuator 140, thereby achieving drive operation of the two-dimensional scan.
As illustrated in
Subsequently, the spot S jumps from the scan point Q12 to the scan point Q1, and the zigzag scan from the scan point Q1 to the scan point Q12 is performed again. This means that the next frame of the image is displayed. Here, the horizontal scan period illustrated in solid lines corresponds to the period H1 illustrated in
On the waveform of the drive signal, the scan points Q1, Q3, Q5, Q7, Q9, and Q11 of
When the first drive signal Dx, which is a sine wave having the voltage value ranging from −Vx to +Vx and the period H1, is provided to the piezoelectric elements of the actuator 150 of the movable reflective element 100 illustrated in
In practice, the first drive signal Dx may be supplied to the D layer (upper electrode layer) 100D with the B layer (lower electrode layer) 100B of the movable reflective element 100 fixed to a ground potential, and the second drive signal Dy may be supplied to the D layer (upper electrode layer) 100D, thereby achieving the drive operation.
As illustrated in
In practice, as described above, mechanical delay may arise until tilt of the mirror 130 after stretching and contracting of the piezoelectric elements of the movable reflective element 100, even though the drive signals Dx and Dy illustrated in
In the “figure-eight-shaped scanning scheme”, the movement path of the spot S, which differs from that of the commonly used raster scanning, is not a path along the pixel arrangement (two-dimensional matrix of rows and columns) of a typical image. When the “figure-eight-shaped scanning scheme” is used in the projector 80 illustrated in
However, when the two-dimensional scanner is used as, for example, backlight illumination for liquid crystal display elements instead of the projector, the image data is not need, thus dispensing with the modulation process associated with the laser light source 30. Thus in the application to such backlight illumination, use of the “figure-eight-shaped scanning scheme” capable of providing the smooth scan path is preferable compared with the use of the raster scan.
Adjustment of Resonance Frequency
When the two-dimensional scanner 20 according to Embodiment 13 is applied to the projector 80 or the like, the reflective surface M of the movable reflective element 100 has preferably the widest possible range of tilt angle. An increase in the tilt angle of the reflective surface M needs an increase in an amplitude of the oscillatory motion of the mirror 130. The increase in the amplitude needs an increase in the voltage to be supplied to the piezoelectric elements. However, even when the alternating signals with the same voltage are supplied, the amplitude of the oscillatory motion of the mirror 130 varies depending on the frequency. This is because the energy efficiency in the oscillating system is typically highest when the mirror 130 is vibrated at a resonance frequency inherent to the oscillating system.
For example, the resonance frequency f of the mirror 130 of the movable reflective element 100 having a structure as illustrated in
When the mirror 130 is vibrated at the resonance frequency f, supply of the alternating drive signal with a voltage on the order of 5 V to the piezoelectric elements is sufficient, although when the mirror 130 is vibrated at a particular non-resonance frequency, the alternating drive signal with a voltage of 500 to 1000 V may be needed in some cases. When the movable reflective element 100 is formed as a fine semiconductor element such as a MEMS element, drive of the movable reflective element 100 at such a high voltage may cause dielectric breakdown.
In light of the above, the vibration of the mirror 130 of the movable reflective element 100 at the resonance frequency f is preferable for practical operation. In other words, when the movable reflective element 100 has a predetermined application, the mechanical structure of the movable reflective element 100 is preferably designed so that the oscillation frequency suitable for the application coincides with the resonance frequency f.
For example, consider that the two-dimensional scanner 20 according to Embodiment 13 is used for the projector 80 as illustrated in
Here, it is assumed in the projector 80 that, for example, the frequency fx of the drive signal Dx in the direction along the X axis direction is set to fx=10 kHz (period H1= 1/10000 sec), and the frequency fy of the drive signal Dy in the direction along the Y axis is set to fy=100 Hz (period H1= 1/100 sec). Such settings of the drive signals correspond to the settings in which the horizontal scan time between the scan points Q1 and Q2 in
Thus, when the movable reflective element 100 is previously determined to be used in the application in which the vibration in the direction along the X axis is set at the frequency fx=10 kHz and the vibration in the direction along the Y axis is set at the frequency fy=100 Hz, care may be preferably taken at the design phase of the movable reflective element 100 such that these frequencies fx and fy are the resonance frequencies. The projector 80 into which such designed movable reflective element 100 is incorporated operates highly efficiently because the mirror 130 is vibrated at the natural resonance frequencies.
As described above, when the two-dimensional scanner 20 is used by incorporation into the projector 80, a large difference typically occurs between the horizontal scan time and the vertical scan time. Thus a large difference also occurs between the resonance frequency fx for the direction along the X axis and the resonance frequency fy for the direction along the Y axis, both of which frequencies are required for the movable reflective element 100. In fact, in the example above, fx=10 kHz while fy=100 Hz, in which a significant 100-fold difference occurs between both the frequencies. Thus the movable reflective element 100 for such a projector 80 is required to have different resonance frequencies fx and fy in the respective directions along the X axis and the Y axis of the mirror 130.
In general, there are multiple resonance frequencies f for an oscillating system, and the resonance frequencies are referred to as a first-order resonance frequency, a second-order resonance frequency, and so on, in order of increasing frequency. Thus, when the movable reflective element is designed such that the resonance frequency for the direction along the X axis is fx and the resonance frequency for the direction along the Y axis is fy, the designing may be performed such that a certain-order resonance frequency for the direction along the X axis is fx and a certain-order resonance frequency for the direction along the Y axis is fy.
However, if any of the resonance frequencies for the direction along the X axis coincides with any of the resonance frequency for the direction along the Y axis, some disadvantageous interference may occur between the vibration in the direction along the X axis and the vibration in the direction along the Y axis. Thus, in practice, the designing is preferably performed such that none of the resonance frequencies for the direction along the X axis coincides with any of the resonance frequencies for the direction along the Y axis.
Although various forms of designs to produce different resonance frequencies fx and fy can be contemplated, the form that the inventors consider as being the most practical adjusts the resonance frequencies fx and fy in accordance with the length, width or thickness of each of the actuators 140 and 150. The following description is made for a specific method of design to produce different resonance frequencies fx and fy on the basis of the structure of the movable reflective element 100 illustrated in
In general, designing the width W1 of the actuator 140 to be narrower than the width W2 of the actuator 150 achieves the effect of making the resonance frequency of the direction in the X axis of the mirror 130 higher than the resonance frequency of the direction in the Y axis of the mirror 130. Conversely, of course, when the resonance frequency of the direction along the Y axis is set higher than the resonance frequency of the direction along the X axis, the width W1 of the actuator 140 may be designed to be greater than the width W2 of the actuator 150.
As illustrated in
When the thickness of the actuator 140 is defined as T1 and the thickness of the actuator 150 is defined as T2 in the movable reflective element 100 illustrated in
For convenience, in
For the thickness T1 and T2, when T1 is set less than T2, the relationship between the k-order resonance frequency fx(k) for the direction along the X axis of the mirror 130 and the k-order resonance frequency fy(k) for the direction along the Y axis of the mirror 130 can be expressed as fx(k)>fy(k). Thus, implementation is easier of the structure in which, as in the example above, the resonance frequency for the direction along the X axis is 10 kHz and the resonance frequency for the direction along the Y axis is 100 Hz. In fact, it suffices that assuming k=1, the relationship between the first-order resonance frequency fx(1) for the direction along the X axis of the mirror 130 and the first-order resonance frequency fy(1) for the direction along the Y axis of the mirror 130 is set to fx(1)>fy(1).
The same applies to the movable reflective elements 100 according to the other embodiments. In general, designing the thickness T1 of the actuator 140 to be smaller than the thickness T2 of the actuator 150 achieves the effect of making the resonance frequency of the direction along the X axis of the mirror 130 higher than the resonance frequency of the direction in the Y axis of the mirror 130. Conversely, of course, setting of T2 less than T1 may be performed in the case of setting the resonance frequency in the direction along the Y axis to be higher than the resonance frequency along the X axis.
Although the method for adjusting the width of each of the actuators 140 and 150 and the method for adjusting the thickness of each of the actuators 140 and 150 (
Feedback Control
As described above, the controller 22 included in the projector 80 illustrated in
The two-dimensional scanner 20 includes the movable reflective element 100 and the controller 22. The movable reflective element 100 has, for example, a structure similar to the movable reflective element 100 illustrated in
The movable reflective element 100 illustrated in
That is, the actuator 140 and the actuator 150 have a total of four piezoelectric elements. A part of the four piezoelectric elements functions as a drive piezoelectric element, and another part functions as a detection piezoelectric element. Specifically, the piezoelectric elements formed in regions of the D layers (upper electrode layer) 140D and 150D function as drive piezoelectric elements, and the piezoelectric elements formed in regions in the D layer (upper electrode layer) 160D and 170D function as detection piezoelectric elements.
The four piezoelectric elements have the same basic layer structure, and thus have no difference in the physical configuration or the basic functions. Here, the distinction made by referring to the piezoelectric elements as the “drive piezoelectric elements” and the “detection piezoelectric elements” is made for distinction of the functions as viewed from the controller 22 side. The B layer (lower electrode layer) 100B of each piezoelectric element is fixed to the ground potential, and each of the D layers (upper electrode layer) 140D, 150D, 160D, and 170D are connected to an X-axis-direction vibration controller 221 or a Y-axis-direction vibration controller 222 included in the controller 22 illustrated in
Here, the X-axis-direction vibration controller 221 provides an X-axis-direction drive signal Dx to the D layer (upper electrode layer) 150D, while the Y-axis-direction vibration controller 222 provides a Y-axis-direction drive signal Dy to the D layer (upper electrode layer) 140D. These drive signals Dx and Dy are, for example, drive signals illustrated in
The X-axis-direction vibration controller 221 performs feedback control by generating the X-axis-direction drive signal Dx by referencing this X-axis-direction detection signal Sx as a feedback signal, and the Y-axis-direction vibration controller 222 performs feedback control by generating the Y-axis-direction drive signal Dy by referencing the Y-axis-direction detection signal Sy as a feedback signal.
Here, the C layer (piezoelectric material layer) 100C included in the piezoelectric elements formed in the actuators 140 and 150 has the property of stretching and contracting elastically in the longitudinal direction as illustrated in
Specifically, the piezoelectric elements illustrated in
Upon supply of the drive signals as the X-axis-direction drive signals Dx and the Y-axis-direction drive signals Dy, the drive piezoelectric element formed on each of the actuators 140 and 150 repeats an stretching and contracting motion at a given cycle, which also causes an stretching and contracting motion at a given cycle on the detection piezoelectric element formed on each of the actuators 140 and 150. The X-axis-direction detection signal Sx and the Y-axis-direction detection signal Sy that are returned to the controller 22 as the feedback signals are signals indicating such a cyclic stretching and contracting motion of each of the actuators 140 and 150, and thus are signals indicating the vibration in the X-axis direction and the Y-axis direction of the mirror 130.
As mentioned above, the laser beam irradiated by the laser light source 30 reflects at the reflective surface M of the mirror 130 to form the spot S at a predetermined position on the screen 10. Thus the X-axis-direction detection signal Sx corresponds to the signal indicating the position of the spot S in the X-axis direction, while the Y-axis-direction detection signal Sy corresponds to the signal indicating the position of the spot S in the Y-axis direction. The X-axis-direction vibration controller 221 can perform feedback control to generate the X-axis-direction drive signal Dx for scan of the spot S on the screen 10 in the direction along the X axis on the basis of the signal Sx indicating the position of the spot S on the screen 10 in the X-axis direction. Similarly, the Y-axis-direction vibration controller 222 can perform feedback control to generate the Y-axis-direction drive signal Dy for scan of the spot S on the screen 10 in the direction along the Y axis on the basis of the signal Sy indicating the position of the spot S on the screen 10 in the direction along the Y axis.
Although the feedback controls provided for the movable reflective element 100 illustrated in
Specifically, the controller 22 is provided with the X-axis-direction vibration controller 221 and the Y-axis-direction vibration controller 222. Here, the X-axis-direction vibration controller 221 may generate the X-axis-direction drive signal Dx supplied to the drive piezoelectric element provided in the actuator 150 on the basis of the X-axis-direction detection signal Sx that is fed back from the detection piezoelectric element provided in the actuator 150 extending along the X axis. The Y-axis-direction vibration controller 222 may generate the Y-axis-direction drive signal Dy supplied to the drive piezoelectric element provided in the actuator 140 on the basis of the Y-axis-direction detection signal Sy that is fed back from the detection piezoelectric element provided in the actuator 140 extending along the Y axis.
In this way, with the controller 22 having the feedback control functions, the controller 22 can monitor whether the mirror 130 oscillates properly, and if not, performs control automatic correction of the improper oscillating motion.
The display control device 40 illustrated in
In this example case, the X-axis-direction scan control signal Cx contains information indicating a predetermined amplitude Gx and a predetermined frequency φx for the direction along the X axis, and the Y-axis-direction scan control signal Cy contains information indicating a predetermined amplitude Gy and a predetermined frequency φy for the direction along the Y axis. The display control device 40 can set the amplitude and the frequency of the oscillatory motion of the mirror 130 to a desired value using these scan control signals Cx and Cy. The larger image is displayed on the screen 10 with the amplitudes Gx and Gy set to greater values, and the image is displayed on the screen 10 at a higher frame rate with the frequencies φx and φy set to higher values.
In practice, as mentioned above, it is preferable to enable efficient vibration that the predetermined frequency φx for the direction along the X axis is set to the X-axis-direction resonance frequency fx unique to the movable reflective element 100, while the predetermined frequency φy for the direction along the Y axis is set to the Y-axis-direction resonance frequency fy unique to the movable reflective element 100.
The X-axis-direction vibration controller 221 provides a feedback control to increase and decrease the amplitude and the frequency of the X-axis-direction drive signal Dx so that the amplitude and the frequency of the fed-back X-axis-direction detection signal Sx is a value that is in accordance with the predetermined amplitude Gx and the predetermined frequency φx indicated by the X-axis-direction scan control signal Cx. Similarly, the Y-axis-direction vibration controller 222 provides a feedback control to increase and decrease the amplitude and the frequency of the Y-axis-direction drive signal Dy so that the amplitude and the frequency of the fed-back Y-axis-direction detection signal Sy is a value that is in accordance with the predetermined amplitude Gy and the predetermined frequency φy indicated by the Y-axis-direction scan control signal Cy.
The X-axis-direction vibration controller 221 provides an X-axis-direction scan position signal Ux to the display control device 40, while the Y-axis-direction vibration controller 222 provides a Y-axis-direction scan position signal Uy to the display control device 40. Here, the X-axis-direction scan position signal Ux is a signal indicating the current position (phase) of the spot S on the screen 10 for the direction along the X axis, while the Y-axis-direction scan position signal Uy is a signal indicating the current position (phase) of the spot S on the screen 10 for the direction along the Y axis. These scan position signals Ux and Uy can be generated on the basis of the respective phases of the X-axis-direction detection signal Sx and the Y-axis-direction detection signal Sy.
Since the display control device 40 can recognize the current position of the spot S on the screen 10 on the basis of these scan position signals Ux and Uy, the display control device 40 provides, as a modulation signal to the laser light source 30, the data indicating pixel value of pixel in accordance with the position, based on the image data. The laser light source 30 can modulate the intensity of the generated laser beam on the basis of the provided modulation signal. Thus, the pixel that is proper in accordance with the position can be displayed at the position of the spot S on the screen 10 even when the “figure-eight-shaped scanning scheme” as illustrated in
Self-Excited Vibration Control
In the above description, the mirror 130 oscillating at the resonance frequencies inherent to the individual axial directions when the mirror 130 is caused to oscillate is described as obtaining good energy efficiency, and designing the natural resonance frequencies to be frequencies of the intended drive signals is described as preferable if the movable reflective element 100 has a predetermined application. In addition, commanding of the vibration at the unique resonance frequencies fx and fy by the control signals Cx and Cy provided from the display control device 40 to the controller 22 is described above as preferable.
In fact, however, there may be some difficulties in indicating the accurate resonance frequencies fx and fy of the movable reflective element 100 by the display control device 40. This may occur because mass-produced products based on the same design drawing do not have all the same natural resonance frequency of the movable reflective element 100. A first factor is the occurrence of the dimensional variations among the individual products due to variations in the mass production line. Even industrial products produced in accordance with the same specification inevitably have slight dimensional variations among the individual products.
A second factor is the occurrence of stress distortion unique to the movable reflective element 100 due to the manner of mounting when the movable reflective element 100 is mounted in the projector. For the projector 80 illustrated in
A third factor is variations of the external environment, such as temperature, in use. For example, the resonance frequencies vary greatly because the temperatures in the environment of use are greatly different in summer versus winter. In addition, in use with the movable reflective element 100 embedded in the projector, the temperature in the environment of use varies minute by minute because the temperature of the light source gradually increases after start-up.
Since the variations in the resonance frequencies are in fact inevitable due to such various factors, the projector 80 with the feedback control functions illustrated in
An example variation is described below that enables the mirror 130 to vibrate at the accurate resonance frequencies fx and fy even if the resonance frequencies vary due to the above-described various factors. The basic principle is to provide the X-axis-direction vibration controller 221 and the Y-axis-direction vibration controller 222 with self-excited vibration control functions. That is, the X-axis-direction vibration controller 221 performs X-axis-direction self-excited vibration control causing the mirror 130 to vibrate at a predetermined amplitude Gx and the resonance frequency fx for the direction along the X axis, while the Y-axis-direction vibration controller 222 performs Y-axis-direction self-excited vibration control causing the mirror 130 to vibrate at a predetermined amplitude Gy and the resonance frequency fy for the direction along the Y axis.
The X-axis-direction scan control signal Cx provided by the display control device 40 to the two-dimensional scanner 20 is a signal for scan instruction indicating that the scan is to be made at the predetermined amplitude Gx for the direction along the X axis, and does not contain information for specifying the frequency. Similarly, the Y-axis-direction scan control signal Cy provided by the display control device 40 to the two-dimensional scanner 20 is a signal for scan instruction indicating that the scan is to be made at the predetermined amplitude Gy for the direction along the Y axis, and does not contain information for specifying the frequency.
The two-dimensional scanner 20 drives the mirror 130 in an oscillatory motion on the basis of the scan instructions to cause the spot S, which is formed on the screen 10 by the laser beams reflected on the mirror 130, to move on the screen 10 in two dimensions. During this oscillatory motion, the amplitudes are controlled to be in accordance with the predetermined amplitudes Gx and Gy as instructed by the display control device 40, but the frequencies are self-determined by the two-dimensional scanner 20 without being externally specified.
Specifically, when the display control device 40 provides the X-axis-direction scan control signal Cx, which indicates the vibration at the predetermined amplitude Gx, to the X-axis-direction vibration controller 221 in the two-dimensional scanner 20, the X-axis-direction vibration controller 221 performs self-excited vibration control in the direction along the X axis on the basis of this X-axis-direction scan control signal Cx. Similarly, when the display control device 40 provides the Y-axis-direction scan control signal Cy, which indicates the vibration at the predetermined amplitude Gy, to the Y-axis-direction vibration controller 222 in the two-dimensional scanner 20, the Y-axis-direction vibration controller 222 performs self-excited vibration control in the direction along the Y axis on the basis of this Y-axis-direction scan control signal Cy.
Such self-excited vibration control can be provided by detection of phases of the X-axis-direction detection signal Sx and the Y-axis-direction detection signal Sy provided as the feedback signals. The can be achieved with the use of the basic principle that, in general, in a state in which a predetermined drive signal D is provided to an oscillating system to cause an oscillator to oscillate, when the actual movement of the oscillator is detected as a detection signal S, the phase difference between the drive signal D and the detection signal S is π/2 if the oscillator oscillates at the natural resonance frequency of the oscillator.
As illustrated in
Similarly, the Y-axis-direction drive signals Dy are provided from the Y-axis-direction vibration controller 222 to the movable reflective element 100, and the Y-axis-direction detection signals Sy are fed back to the Y-axis-direction vibration controller 222 as the feedback signals. Here again, if the oscillation frequency in the direction along the Y axis is the resonance frequency fy, the phase difference between the drive signal Dy and the detection signal Sy is π/2. Thus the Y-axis-direction vibration controller 222 may perform feedback control to adjust the phase of the drive signal Dy so as to maintain a π/2 phase difference.
The X-axis-direction vibration controller 221 may incorporate a self-excited vibration circuit for performing feedback control that increases or decreases the amplitude of the X-axis-direction drive signal Dx on the basis of the amplitude of the fed-back X-axis-direction detection signal Sx so that the amplitude for the direction along the X axis of the mirror 130 is maintained at the predetermined amplitude Gx, and that maintains the π/2 phase difference between the X-axis-direction drive signal Dx and the X-axis-direction detection signal Sx so that the oscillation frequency for the direction along the X axis of the mirror 130 is maintained at the resonance frequency fx.
Similarly, the Y-axis-direction vibration controller 222 may incorporate a self-excited vibration circuit for performing feedback control that increases or decreases the amplitude of the Y-axis-direction drive signal Dy on the basis of the amplitude of the fed-back Y-axis-direction detection signal Sy so that the amplitude for the direction along the Y axis of the mirror 130 is maintained at the predetermined amplitude Gy, and that maintains the π/2 phase difference between the Y-axis-direction drive signal Dy and the Y-axis-direction detection signal Sy so that the oscillation frequency for the direction along the Y axis of the mirror 130 is maintained at the resonance frequency fy.
With the controller 22 having such self-excited vibration control functions, the two-dimensional scanner 20 can oscillate the mirror 130 autonomously at the accurate resonance frequencies without frequencies externally specified. That is, even when the resonance frequencies are different for individual products or vary in time depending on the temperature environment or the like, the mirror 130 can be vibrated at the correct resonance frequency and can maintain movement that has good energy efficiency.
The beam scanning scheme that the typical self-excited vibration circuit uses is the “figure-eight-shaped scanning scheme” as illustrated in
That is, the X-axis-direction vibration controller 221 provides to the display control device 40 the X-axis-direction scan position signal Ux indicating that the phase of the X-axis-direction detection signal Sx reaches a predetermined value, while the Y-axis-direction vibration controller 222 provides to the display control device 40 the Y-axis-direction scan position signal Uy indicating that the phase of the Y-axis-direction detection signal Sy reaches a predetermined value. The display control device 40 refers to the timing indicated by the X-axis-direction scan position signal Ux and the Y-axis-direction scan position signal Uy, and provides to the laser light source 30 the modulation signal corresponding to the individual pixel included in the image data at the proper timing (timing at which the spot S is positioned on the screen 10 in place corresponding to the pixel).
For example, if a signal indicating the points of time when the phase of the X-axis-direction detection signal Sx reaches 0, π/2, π, and 3π/2 is used as the X-axis-direction scan position signal Ux, the display control device 40 is notified of the timing of the spot S on the screen 10 reaching each of the scan points Q1, Q2, Q3, . . . , Q19 in
Of course, if a specific signal for notification of the points of time when the phase reaches 0, π/4, π/2, 3π/4, π, 5π/4, 3π/2, and 7π/4 is, for example, used as the scan position signals Ux and Uy, more accurate position information of the spot S can be provided.
In the above-described embodiments, both the X-axis-direction vibration controller 221 and the Y-axis-direction vibration controller 222 have the self-excited vibration control functions, although a configuration may be used in which only one of the controllers has the self-excited control function. For example, if only the X-axis-direction vibration controller 221 has the self-excited vibration control function, while the Y-axis-direction vibration controller 222 is provided with the Y-axis-direction scan control signal Cy having information that specifies the predetermined oscillation frequency φy, the self-excited vibration based on the resonance frequency fx occurs for the direction along the X axis, and an excited vibration based on the externally specified frequency φy occurs for the direction along the Y axis.
The foregoing describes some example embodiments for explanatory purposes. Although the foregoing discussion has presented specific embodiments, persons skilled in the art will recognize that changes may be made in form and detail without departing from the broader spirit and scope of the invention. Accordingly, the specification and drawings are to be regarded in an illustrative rather than a restrictive sense. This detailed description, therefore, is not to be taken in a limiting sense, and the scope of the invention is defined only by the included claims, along with the full range of equivalents to which such claims are entitled.
This application claims the benefit of Japanese patent Application No. 2015-116270, filed on Jun. 9, 2015, the entire disclosure of which is incorporated by reference herein.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2015-116270 | Jun 2015 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2016/066791 | 6/6/2016 | WO | 00 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2016/199730 | 12/15/2016 | WO | A |
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| Number | Date | Country | |
|---|---|---|---|
| 20180157031 A1 | Jun 2018 | US |
