Patent Application
20160003646
Disclosed embodiments relate to encoders, motors with encoder, and servo systems.
An optical entire-circumference encoder that irradiates substantially all of a plurality of slits formed in an entire circumference of a disk with light and receives the reflected light or transmitted light is known.
According to one aspect of the disclosure, there is provided an encoder including a disk, one or more first slits, a light source, and a plurality of first light receiving elements. The disk is fixed to a rotating body. The one or more first slits are arranged on the disk in a part in a circumferential direction around a rotation center of the disk and each is configured to reflect or transmit light. The light source is arranged approximately on a rotational axis of the rotating body and is configured to emit light to a region that encompasses at least a rotational locus of the first slit by rotation of the disk. The plurality of first light receiving elements is arranged extending along a circumferential direction around the rotational axis and is configured to receive light that is reflected by or transmits through the first slit.
Hereinafter, an embodiment will be described with reference to the accompanying drawings.
<1. Servo System>
First, the configuration of a servo system according to the embodiment is described with reference to
The motor M is an example of a power generation source without the encoder 100. The motor M is a rotary motor, in which a rotor (not illustrated) rotates with respect to a stator (not illustrated), and outputs a rotational force by rotating, around a rotational axis AX, a shaft SH fixed to the rotor.
Note that the motor M itself may be referred to as a servo motor, but in the embodiment, a configuration including the encoder 100 is referred to as a servo motor SM. That is, the servo motor SM corresponds to an example of the motor with encoder. Hereinafter, for convenience of description, a case is described, where a motor with encoder is a servo motor that is controlled to follow target values, such as a position and a speed. However, the present disclosure is not necessarily limited to the servo motor. A motor with encoder shall include even the motors used for other than a servo system, as long as an encoder is attached to the motor, e.g., in a case where the output of an encoder is used only for display.
The motor M is not particularly limited as long as the encoder 100 is capable of detecting positional data and the like, for example. Moreover, the motor M is not limited to an electric motor that uses electricity as the power source, but may be a motor using another power source, for example such as a hydraulic motor, a pneumatic motor, or a steam motor. However, for convenience of description, hereinafter, a case is described, where the motor M is an electric motor.
The encoder 100 is coupled to the opposite side of a rotational force output side of the shaft SH of the motor M, but not necessarily limited to the opposite side, and the encoder 100 may be coupled to the rotational force output side of the shaft SH. Moreover, the encoder 100 may not be directly coupled to the motor M, but may be coupled via another mechanism, for example such as a reduction device or a rotation direction conversion device. The encoder 100 detects the position (referred to also as the rotation angle) of the motor M by detecting the position of the shaft SH (rotating body), and outputs positional data indicative of the position.
The encoder 100 may detect, in place of or in addition to the position of the motor M, at least one of the speed (referred to also as the rotation speed, angular velocity, or the like) of the motor M and the acceleration (referred to also as the rotational acceleration, angular acceleration, or the like) of the motor M. In this case, the speed and acceleration of the motor M can be detected, for example, by firstly-differentiating or secondarily-differentiating the position by time or by counting detection signals (e.g., incremental signals described later) for a predetermined time period. For convenience of description, hereinafter, the description is made assuming that the physical quantity detected by the encoder 100 is a position.
The controller CT acquires the positional data output from the encoder 100, and controls the rotation of the motor M based on the positional data. Accordingly, in the embodiment in which an electric motor is used as the motor M, the controller CT controls the rotation of the motor M by controlling the electric current or voltage that is applied to the motor M based on the positional data. Furthermore, the controller CT may acquire a host control signal from a host controller (not illustrated), and control the motor M in the manner that a rotational force capable of realizing a position or the like indicated by the host control signal is output from the shaft SH of the motor M. Note that, when the motor M uses another power source, such as a hydraulic, pneumatic, or steam power source, the controller CT can control the rotation of the motor M by controlling the supply of such power source.
<2. Encoder>
Next, the encoder 100 according to the embodiment is described. As illustrated in
Here, for convenience of description of the structure of the encoder 100, the directions, such as an up-direction and down-direction, are defined as follows and used as needed. In
(2-1. Disk)
The disk 110 is formed in the shape of a disk as illustrated in
As illustrated in
(2-2. Optical Detection Mechanism)
An optical detection mechanism includes the first slit Sa and slit track SI and the optical module 120. The first slit Sa (grid-shaped hatching portion in
(2-2-1. Disk)
The disk 110 is formed from a material, for example such as metal, which reflects light. Then, a material having a lower reflectivity (e.g., chrome oxide or the like) is arranged, by coating or the like, in a part on the surface of the disk 110, where light is not allowed be reflected, in the manner that a reflective slit is formed in a portion where the material is not arranged. Note that the reflective slit may be formed by forming a portion that does not reflect light, as a rough surface by sputtering or the like and reducing the reflectivity of the portion.
Note that, the material of the disk 110, a method for manufacturing the disk 110, and the like are not limited in particular. For example, the disk 110 may be formed from a material, such as glass or a transparent resin, which transmits light. In this case, the reflective slit may be formed by arranging a light reflective material (e.g., aluminum or the like) on the surface of the disk 110 by vapor deposition or the like.
The first slit Sa is arranged closer to the rotation center O than the slit track SI, i.e., arranged on an inner side of the slit track SI in the radial direction (the direction of an arrow R illustrated in
The slit track SI is arranged concentrically with the slit track SA on the opposite side (outer side in the radial direction R) of the rotation center O from the first slit Sa, on the upper face of the disk 110. The slit track SI includes a plurality of second slits Si that is arranged so as to have an incremental pattern extending along the circumferential direction C around the rotation center O.
The “incremental pattern” is a pattern that is regularly repeated at a predetermined pitch P as illustrated in
Note that, in the embodiment, as described above, an angle θ corresponding to the circumferential length of the first slit Sa coincides with an angle θ corresponding to the pitch P of the second slit Si of the slit track SI. As a result, the resolution of an absolute signal based on the first slit Sa coincides with the number of second slits Si of the slit track SI. However, the number of second slits Si of the slit track SI is not limited to this example, but is preferably set to the same as the resolution of the absolute signal or more.
(2-2-2. Optical Module)
The optical module 120 is formed as one substrate BA parallel to the disk 110, as illustrated in
The optical module 120 includes the light source 121 and a plurality of light receiving arrays PA, PI on a surface facing the disk 110 of the substrate BA, as illustrated in
As illustrated in
The light source 121 is not limited in particular as long as it can emit light to an irradiation region, but an LED (Light Emitting Diode) can be used, for example. The light source 121 is configured as a point light source in which an optical lens or the like is not particularly arranged, and emits diffusion light from a light emitting part. Note that, the “point light source” does not necessary need to be a strict point. Light may be emitted from a finite light emitting surface of a light source if the light source is regarded to be able to emit diffusion light from a approximately punctate position, in design or in principle of operation. Moreover, the “diffusion light” is not limited to the light that is emitted in all directions from a point light source, but includes light that is emitted while being diffused in a finite and definite direction. That is, the “diffusion light” referred to herein includes any light having diffusibility rather than parallel light. The use of such point light source allows the light source 121 to approximately uniformly irradiate the first slit Sa and slit track SI that rotate at the facing positions, with light. Moreover, because condensing and diffusion of light by an optical element are not performed, an error or the like due to the optical element is less likely to be generated and the rectilinearity of light toward the slit track can be improved.
The light receiving arrays PA, PI are arranged concentrically about the light source 121 (rotational axis AX), and the light receiving array PA is arranged spaced apart by a predetermined distance PG from the light receiving array PI in the radial direction R, closer to the rotational axis AX (inner side in the radial direction R) than the light receiving array PI. The light receiving array PA includes a plurality of first light receiving elements Pa (corresponds to a thin dot-hatching portion of
With the configuration, the light reflected by the first slit Sa that is located at a predetermined rotation angle by rotation of the disk 110 is received by a corresponding first light receiving element Pa among the plurality of first light receiving elements Pa, and a position, where the first light receiving element Pa that output the light receiving signal is arranged, is detected as a position (absolute position) within one rotation of the shaft SH. This light receiving signal is referred to as the “absolute signal.” As a result, the absolute position of the shaft SH is detected with a resolution corresponding to the number (32 in this example) of first light receiving elements Pa.
On the other hand, the light receiving array PI is arranged on the opposite side (outer side in the radial direction R) of the rotational axis AX from the light receiving array PA. The light receiving array PI includes a plurality of second light receiving elements Pi (correspond to a thick dot-hatching portion of
Four second light receiving elements Pi are arranged in the range of the angle θ corresponding to one pitch of the first light receiving element Pa. That is, the light receiving array PI includes a plurality of sets (indicated by “SET” in
Because the incremental pattern represents a position in one pitch, the signal of each phase in one set and the signal of each phase in another set corresponding thereto will have similarly varying values. Accordingly, the signals of the same phase are added across a plurality of sets. Accordingly, from a large number of second light receiving elements Pi of the light receiving array PI illustrated in
By using signals whose phases differ from each other by 90°, e.g., by using the B phase signal in addition to the A phase signal, the rotation direction of the disk 110 can be detected depending on whether the phase of a signal firstly detected is the A phase or B phase. Moreover, by using the signals whose phases differ from each other by 180°, i.e., by using the signal of the A-bar phase or B-bar phase in addition to the A phase or B phase, the reliability of the signal can be secured. Furthermore, by arranging a plurality of sets extending along the circumferential direction C, the place where the signal of each phase is detected is distributed in a wide range and the signals of the same phase are added and averaged across a plurality of sets as described above, in the manner that an influence of a variation in the amount of received light can be reduced.
Note that, in the embodiment, a case is described, where four light receiving elements are included in one set corresponding to one pitch of the incremental pattern, as an example, but the number of light receiving elements in one set is not limited in particular, and for example two light receiving elements (for the A phase and for the B phase) may be included in one set.
As the first light receiving element Pa and second light receiving element Pi, a photodiode can be used, for example. However, they are not limited to the photodiode, and are not limited in particular as long as the element can receive the light emitted from the light source 121 and convert it to an electric signal.
Note that the light emitted from the light source 121 is diffusion light. Accordingly, the image of a slit track projected on the optical module 120 is enlarged by a predetermined magnification ε corresponding to an optical path length. That is, as illustrated in
Similarly, the length in the circumferential direction C in the optical module 120 results in the length of a shape of the circumferential direction C in the disk 110 projected on the optical module 120, i.e., the shape influenced by the magnification ε. That is, as illustrated in
As illustrated in
ε=(2G−Δd)/(G−Δd) (Formula 1)
(2-3. Positional Data Generator)
The positional data generator 130 acquires, at a timing when the absolute position of the motor M is measured, the absolute signal representing an absolute position and the incremental signal including four signals whose phases shift from each other by 90°, from the optical module 120. Then, the positional data generator 130 calculates, based on the acquired signals, the absolute position of the motor M represented by these signals and outputs the positional data representing the absolute position to the controller CT.
Note that, the method for generating positional data by the positional data generator 130 is not limited in particular, but various methods can be used. Here, an example is described, in which the absolute position is calculated from the incremental signal and the absolute signal to generate positional data.
The positional data generator 130 first identifies the position (absolute position) within one rotation of the shaft SH based on a light receiving signal of the first light receiving element Pa. That is, the light reflected by the first slit Sa located at a predetermined rotation angle by rotation of the disk 110 is received by a corresponding first light receiving element Pa among a plurality of first light receiving elements Pa in the light receiving array PA, and the corresponding first light receiving element Pa outputs a light receiving signal to the positional data generator 130. Then, for example, the positional data generator 130 is connected in parallel to a plurality of first light receiving elements Pa, respectively, in the manner that the position, where the first light receiving element Pa that output the light receiving signal is arranged, can be identified as the absolute position of the shaft SH.
Note that, when the first slit Sa is located facing an intermediate position between two adjacent first light receiving elements Pa (located facing in the travelling direction of light), in other words, when each of the adjacent first light receiving elements Pa is located facing a vicinity of an edge of the first slit Sa, the detection accuracy of the absolute position might decrease because the amplitudes of the light receiving signals of both the adjacent first light receiving elements Pa become a transitional point between “H” (a state where the amplitude of the signal exceeds a threshold) and “L” (a state where the amplitude of the signal is equal to or less than the threshold) and unstable. Then, the positional data generator 130 can determine which first light receiving element Pa the first slit Sa is located facing, using the incremental signal including four signals whose phases shift from each other by 90°. Accordingly, the encoder 100 according to the embodiment can more accurately identify the absolute position from the absolute signal.
On the other hand, the positional data generator 130 mutually subtracts the incremental signals each having a 180° phase difference from each other among the respective incremental signals of four phases from the light receiving array PI. As describe above, by subtracting the signals each having a 180° phase difference from each other, a manufacturing error, a measurement error, and the like of the reflective slits within one pitch can be canceled. The signals as a result of subtraction described above are referred to as a “first incremental signal” and a “second incremental signal”, herein. These first incremental signal and second incremental signal (simply referred to as an “A phase signal” and a “B phase signal”, or the like) each have a 90° phase difference from each other in electric angle. Then, from these two signals, the positional data generator 130 identifies a position within one pitch. This method for identifying a position within one pitch is not limited in particular. For example, when the incremental signal that is a periodic signal is a sinusoidal signal, the examples of the method for identifying a position within one pitch include a method for calculating an electric angle φ by calculating the arctangent of a dividing result of two sinusoidal signals of the A phase and B phase. Alternatively, there is also a method for converting two sinusoidal signals to an electric angle φ using a tracking circuit. Alternatively, there is also a method for identifying an electric angle φ associated with the values of the signals of the A phase and B phase in a table produced in advance. Note that, in this case, the positional data generator 130 preferably analog-to-digital converts two sinusoidal signals of the A phase and B phase for each detection signal and multiplies (interpolates and divides) the resulting two digital signals to improve the resolution and then generates the positional data.
Then, the positional data generator 130 generates the positional data representing an accurate absolute position by combining an absolute position of a relatively coarse accuracy based on the absolute signal with an accurate position within one pitch based on the incremental signal.
<3. Example of Effects Obtained By Embodiment>
In the embodiment described above, the first slit Sa is arranged in a part in the circumferential direction C around the rotation center O of the disk 110. Moreover, the light source 121 is arranged on the rotational axis AX of the shaft SH, and the light source 121 emits light to a region that encompasses at least the rotation locus of the first slit Sa by rotation of the disk 110. The light reflected by the first slit Sa located at a predetermined rotation angle by rotation of the disk 110 is received by a corresponding first light receiving element Pa among a plurality of first light receiving elements Pa arranged extending along the circumferential direction C around the rotational axis AX. As a result, with the resolution corresponding to the number of first light receiving elements Pa, a position (absolute position) within one rotation of the shaft SH is detected.
The encoder 100 configured in this manner does not need a fixed slit and a light guide member or the like for guiding the emitted light of the light source 121 to the first slit Sa and guiding the reflection light thereof to the first light receiving element Pa. Accordingly, the device configuration can be simplified, and a reduction in size of the encoder 100 can be achieved. Moreover, the examples of the encoder that detects the absolute position include a Gray code encoder and a multiplex incremental signaling type encoder, which however need a slit and a light receiving element, each having a plurality of tracks. In contrast, the encoder 100 of the embodiment is suitable for a reduction in size because it can detect the absolute position using one track.
In the encoder 100, due to a mechanical fluctuation, a temperature change, and the like, the gap between the light source 121 or first light receiving element Pa and the disk 110 (the first slit Sa) may vary. Then, for example, in the case of an encoder that emits light to a partial region in the circumferential direction C of the disk 110 and uses the reflection light thereof or the like, when the gap varies, the projection image of the first slit Sa by the reflection light or the like will fluctuate in angle, thus resulting in a reduction in detection accuracy. In the embodiment, the reflection light and the like obtained from the entire circumference is used, and therefore even if the gap varies, the projection image of the first slit Sa will not fluctuate in angle. Accordingly, even if the gap varies, the absolute position can be accurately detected and thus the detection accuracy is superior.
For example, when the rotation center O of the disk 110 and the rotational axis AX of the shaft SH are eccentric, an error is generated in the positional relationship between the first slit Sa and the first light receiving element Pa. In the embodiment, the light source 121 emits light to a region that encompasses at least the rotation locus of the first slit Sa, i.e., the entire circumference of the disk 110, and receives the reflection light thereof, and therefore even if an error is generated in the positional relationship between the first slit Sa and the first light receiving element Pa, the error can be cancelled, for example, by summing the receiving light signals of the first light receiving elements Pa that are arranged at the positions different by 180° in the circumferential direction. Accordingly, the robustness against eccentricity can be improved.
Moreover, in the embodiment, the absolute position is detected based on the light receiving signal (one-bit signal) of each first light receiving element Pa. Accordingly, the absolute position can be identified using one-bit signal, not using a signal including a plurality of bits as with a random system, in which for example a random signal pattern (serial bit sequence) of one track is arranged in the disk 110 and the absolute position is detected based on the light receiving signals from a plurality of light receiving elements. Therefore, the amount of signal processing can be reduced. As a result, the processing speed will increase and thus the generation of a deviation in measurement timing can be suppressed. Moreover, because the number of bits of the light receiving signal is small, the absolute position can be easily corrected.
Moreover, in the embodiment, in particular, the first slit Sa is configured to reflect the light emitted from the light source 121, and the first light receiving element Pa is configured to receive the light reflected by the first slit Sa. By configuring the encoder 100 as a reflective encoder in this manner, a plurality of first light receiving elements Pa can be arranged close to the light source 121. Therefore, a further reduction in size of the device can be achieved.
Moreover, in the embodiment, in particular, the encoder 100 includes the slit track SI having the incremental pattern included in the disk 110 and the light receiving array PI configured to receive the light reflected by the slit track SI. Therefore, by interpolating and dividing the incremental signal, an accurate absolute position can be detected. Accordingly, a compact and high-resolution absolute-value encoder can be obtained.
Moreover, in the embodiment, in particular, four second light receiving elements Pi are arranged in an angle range corresponding to one pitch of the first light receiving element Pa. If only one second light receiving element Pi is arranged in the one-pitch range of the first light receiving element Pa, then there is a possibility below. That is, when the first light receiving element Pa is located facing a vicinity of the edge of the first slit Sa, the second light receiving element Pi is also located facing the vicinity of the edge of the second slit Si and the amplitude of the light receiving signal is in the transitional region of a bit (between “H” and “L” of the light receiving signal). Therefore, the detection accuracy of the absolute position might decrease. In order to avoid this, two first slits Sa are offset in the radial direction R so as to form two tracks, and furthermore the two slits Sa (possibly first light receiving elements Pa) are offset from each other by a predetermined pitch (e.g., a half pitch) in the circumferential direction C, in the manner that when the amplitude of the light receiving signal of one of the first light receiving elements Pa becomes in the transitional region of a bit, the absolute position can be identified using the light receiving signal from the other first light receiving element Pa, or vice versa. As a result, the detection accuracy of the absolute position can be improved. However, in this case, the first slit Sa and the first light receiving element Pa need to be arranged on two tracks, thus possibly resulting in an increase in size of the encoder 100.
Then, in the embodiment, four second light receiving elements Pi are arranged in the angle range corresponding to one pitch of the first light receiving element Pa, in the manner that even when the amplitude of the light receiving signal of one of the first light receiving elements Pa becomes in the transitional region of a bit, the absolute position can be identified depending on whether the light receiving signal of the second light receiving element Pi is within a range from 270° to 360° or a range from 0° (360° to 90° in electric angle, for example. Accordingly, there is no need to form the first slit Sa and the first light receiving element Pa on two tracks, unlike the above, and the first slit Sa and the first light receiving element Pa just need to be arranged on one track. Therefore, the encoder 100 can be further miniaturized.
Moreover, in the embodiment, in particular, a plurality of first light receiving elements Pa is arranged closer to the rotational axis AX, i.e., closer to the inner peripheral, than the light receiving array PI. As described above, the resolution of the absolute signal based on the first slit Sa and first light receiving element Pa coincides with the number of second slits Si of the slit track SI. Accordingly, as illustrated in
In the embodiment, a plurality of first light receiving elements Pa is arranged closer to the inner peripheral than the light receiving array PI, and therefore on the disk 110 side, the slit track SI will be arranged closer to the outer peripheral than the first slit Sa. As a result, a larger circumferential length of the second slit Si can be secured. As a result, due to the relationship with the light source width of the light source 121, a reduction of the detection accuracy (accuracy of the incremental signal) of the second slit Si can be prevented.
Moreover, in the embodiment, in particular, a plurality of first light receiving elements Pa is arranged spaced by the predetermined distance PG from the light receiving array PI in the radial direction R about the rotational axis AX. Due to this gap, for example even when the rotation center O of the disk 110 and the rotational axis AX of the shaft SH are eccentric and an error is generated in positional relationships between the first slit Sa and the first light receiving element Pa and between the slit track SI and the light receiving array PI, this error can be absorbed and a crosstalk generated between the first light receiving element Pa and the light receiving array PI can be reduced. Accordingly, the robustness against eccentricity can be further increased.
<4. Variations>
Hereinabove, an embodiment has been described with reference to the accompanying drawings. However, the scope of the technical idea set forth in the claims is not limited to the embodiment described here. It is obvious that those skilled in the art which the embodiment belongs to would conceive to perform various changes, modifications, combinations, and the like within the scope of the technical idea. Accordingly, the techniques after these changes, modifications, combinations, and the like are performed shall also naturally belong to the scope of the technical idea set forth in the claims. Hereinafter, these variations are described one by one.
(4-1. Case Where Light Receiving Array PA is Arranged on Outer Peripheral Side of Light Receiving Array PI)
In the embodiment, a case has been described, where the light receiving array PA is arranged closer to the inner peripheral than the light receiving array PI, but on the contrary the light receiving array PA may be arranged on the outer peripheral side. The variation is described using
As illustrated in
As illustrated in
When the amount of received light of the first light receiving element Pa is increased and the detection accuracy of the absolute signal is increased by increasing the circumferential length of the first slit Sa and the area of each first light receiving element Pa, a configuration may be employed, in which the light receiving array PA is arranged closer to the outer peripheral than the light receiving array PI and the first slit Sa is arranged closer to the outer peripheral than the slit track SI in the disk 110, as with the variation.
(4-2. Case Where Parts of Light Receiving Array PA and Light Receiving Array PI are Not Arranged)
In the embodiment, a case has been described, where the light receiving array PA and light receiving array PI are configured in the manner that each light receiving element is arranged over the entire circumference in the circumferential direction C, but for example, a configuration may be employed, in which the light receiving element is not arranged in a part in the circumferential direction C. The variation is described using
Even in this case, when the first slit Sa is located facing the split track t1 on which the first light receiving element Pa is arranged, the light receiving signal (“H” signal) is output from any one of the first light receiving elements Pa, while when the first slit Sa is located facing the split track t1 on which the first light receiving element Pa is not arranged, the light receiving signal (“H” signal) is output from none of the first light receiving elements Pa. Therefore, if there is one split track t1 on which the first light receiving element Pa is not arranged, a position within one rotation of the shaft SH can be identified. That is, the positional data generator 130 identifies, when the light emitted from the light source 121 is reflected by the split track t1 on which the first light receiving element Pa is not arranged, a position within one rotation without using the light receiving signal from the first light receiving element Pa.
The light receiving array PI is configured in the manner that each of the second light receiving elements Pi is arranged on the rest of the split tracks t2, the split tracks t2 are obtained by equally dividing the second track T2 in the circumferential direction C by a number (128 in this example) set based on the resolution of the encoder 100, the rest of the split tracks t2 are obtained by excluding any one or more of the split tracks t2 from the split tracks t2. In the variation, as illustrated in
Note that the arrangement configuration of the second light receiving element Pi is not limited to the example illustrated in
Even if some of the second light receiving elements Pi are not arranged in this manner, an influence on the detection accuracy is small and thus can be neglected because the incremental signal from the light receiving array PI is added by the signals of the same phase across a plurality of second light receiving elements Pi as described above.
Note that, in the examples illustrated in
When the wire routing on the substrate BA is attempted to be simplified, a configuration may be employed, in which a region where the first light receiving element Pa is not arranged is disposed on the first track T1, as with the variation. As a result, the wirings for elements (the light source 121 in the example of
When the wire-routing on the substrate BA is attempted to be further simplified, a configuration may be employed, in which a region, where the second light receiving element Pi is not arranged, is disposed on the second track T2, as with the variation. As a result, the wirings for elements (the light source 121 and each first light receiving element Pa in the example of
Furthermore, when a reduction in the robustness against eccentricity is attempted to be prevented, a configuration may be employed, in which the split track t2, on which the second light receiving element Pi is not arranged, is arranged at every 90° (or may be arranged at every) 60° in the circumferential direction in the second track T2, as with the variation. As a result, the symmetry of the light receiving array PI can be secured.
Note that, in
(4-3. Case Where Gap is Not Disposed Between Light Receiving Array PA and Light Receiving Array PI)
In the embodiment, a case has been described, where the light receiving array PA is arranged spaced by the predetermined distance PG from the light receiving array PI in the radial direction R, but a configuration may be employed, in which a gap is not disposed between the light receiving arrays PA, PI. The variation is described using
Even a gap is not disposed between the light receiving array PA and the light receiving array PI in this manner, an influence of the crosstalk generated between the light receiving array PA and the light receiving array PI is considered to be small due to the following reasons. That is, the light receiving signal (incremental signal) of the light receiving array PI is added by the signals of the same phase across a plurality of second light receiving elements Pi and averaged, and therefore a crosstalk from the light receiving array PA to the light receiving array PI has a small influence on the light receiving signal of the light receiving array PI. On the other hand, a threshold at which the light receiving signal of the second light receiving element Pi becomes “H” is significantly lower than a threshold at which the light receiving signal of the first light receiving element Pa becomes “H”, i.e., the amount of received light in the second light receiving element Pi is significantly smaller than the amount of received light in the first light receiving element Pa, and therefore a crosstalk from the light receiving array PI to the light receiving array PA has a small influence on the light receiving signal of the first light receiving element even if a part of the light to be received by the second light receiving element Pi is received by the first light receiving element Pa. Accordingly, even if a gap is not disposed between the light receiving arrays PA, PI, an accurate absolute position can be detected.
When attempting to achieve a further reduction in size of the encoder 100, a configuration may be employed, in which the light receiving array PA and the light receiving array PI are arranged in contact with each other, as with the variation. As a result, as compared with the case where a gap is disposed between the light receiving array PA and the light receiving array PI, the diameter of the light receiving array on the outer peripheral side can be reduced by the amount of this gap. Moreover, a light-receiving area of each light receiving array may be increased by the amount of the gap without reducing the diameter of the light receiving array on the outer peripheral side.
Note that, in the examples illustrated in
Note that, in the example illustrated in
(4-4. Case Where Light Receiving Array PA and Light Receiving Array PI are Overlappingly Arranged)
In the embodiment, a case has been described, where the light receiving array PA and the light receiving array PI are offset in the radial direction R and concentrically arranged. However, the arrangement configuration of the light receiving arrays PA, PI is not limited thereto, and for example, the light receiving arrays PA, PI may be overlappingly arranged on one track. The variation is described using
As illustrated in
Moreover, as illustrated in
In the variation, when the light source 121 emits light to a region that encompasses at least the slit track SI, the light reflected by the two second slits Si located at a predetermined rotation angle by rotation of the disk 110 is received by a corresponding exposed portion of first light receiving elements Pa among the plurality of first light receiving elements Pa that is arranged extending along the circumferential direction C around the light source 121 (rotational axis AX). Then, in the positional data generator 130 and each first light receiving element Pa, the threshold is set in the manner that with the amount of reflection light by one second slit Si the light receiving signal is “L” while with the amount of reflection light by two second slits Si, the light receiving signal becomes “H.” As a result, with the resolution corresponding to the number of first light receiving elements Pa, a position (absolute position) within one rotation of the shaft SH is detected.
When attempting to achieve a further reduction in size of the encoder 100, a configuration may be employed, in which the light receiving array PA and the light receiving array PI are overlappingly arranged, as with the variation. As a result, both the slit side and the light receiving element side can be configured as one track, respectively.
(4-5. Others)
In the embodiment, a case has been described, in which the encoder 100 includes the slit track SI having the incremental pattern and the light receiving array PI configured to receive the light reflected by the slit track SI, but the encoder 100 does not necessarily include these slit track SI and light receiving array PI. That is, the encoder 100 includes the first slit Sa arranged in a part in the circumferential direction C around the rotation center O of the disk 110, and a plurality of first light receiving elements Pa that is arranged extending along the circumferential direction C arranged around the rotational axis AX and configured to receive the light reflected by the first slit Sa, in the manner that the position (absolute position) within one rotation of the shaft SH can be detected with a resolution corresponding to the number of corresponding first light receiving elements Pa.
Moreover, in the embodiment, the so-called reflection type encoder, in which the light source 121 and the light receiving arrays PA, PI are arranged on the same side with respect to the disk 110, has been taken as an example and described, but the type of the encoder is not limited thereto. That is, the encoder may be the so-called transmission type encoder, in which the light source 121 and the light receiving arrays PA, PI are arranged on the opposite sides across the disk 110. In this case, in the disk 110, the first slit Sa and the second slit Si may be formed as a light-transmissive slit, respectively, or alternatively the first slit Sa and the second slit Si may be formed by forming the disk 110 from a light-transmissive material, such as glass and a transparent resin, and turning the portion except the slit into a rough surface by sputtering or the like or applying a material having a low transmissivity. In the variation, the light source 121 and the light receiving arrays PA, PI are arranged on the opposite sides across the disk 110, but the optical module 120 in the variation includes the light source 121 and light receiving arrays PA, PI that are formed as separate bodies in this manner. Also when such a transmission type encoder is used, the similar effect as the effect of the embodiment is obtained.
This is a continuation application PCT/JP2013/056696, filed Mar. 11, 2013, which was published under PCT article 21(2) in English.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/JP2013/056696 | Mar 2013 | US |
| Child | 14850899 | US |
