Patent Application
20090059373
The present invention relates generally to an actuator for optical systems and in particular to a lens actuator for a camera.
A lens actuator is used to optimize an image captured by an image capture device of a camera by controlling the position and/or movement of a lens. For example, an auto-focussing technique can be used to bring into focus in an image the subject that the user desires to capture based on the distance between the camera and the subject This can be realised by the displacement of the lens along the optical (lens) axis, or a z-axis, to control the distance between the lens and the image capturing mechanism. Another technique is vibration compensation control, which compensates for motion of the camera body, for example, due to the shaking of the camera This technique typically requires the lens, or one or more of the multiple lenses in a lens module, to be moved relative to the image capturing device to cancel the motion of the camera.
U.S. Patent Application Publication No. 2006/0028320 published in the name of Osaka on 9 Feb. 2006 describes an example of an autofocus actuator. A lens actuator has a lens holder with a coil wound around the lens holder When an electric current is supplied to the coil, the magnetic field induced by the electric current through the coil interacts with that of a permanent magnet surrounding the lens holder, causing the lens holder to be displaced along the optical axis. This autofocus actuator using a coil and the magnet realises a one-dimensional movement of the lens holder to implement an autofocus function.
For the prior art, only autofocus function can be achieved. A need exists for a mechanism adapted to provide both autofocus and vibration compensation functions.
According to a first aspect of the present disclosure, there is provided an actuator used in an optical system. The actuator comprises a housing, a carrier disposed at least partly inside the housing, a plurality of linear motion transducers coupled to the carrier and substantially evenly spaced around the carrier within the housing. Each linear motion transducer is able to produce linear motion when energized displacing the carrier relative to the housing to produce linear motion, tilting motion, or both of the carrier.
According to a second aspect of the present disclosure, there is provided an optical system comprising the above actuator and a lens disposed within the carrier of the actuator.
According to a third aspect of the present disclosure, there is provided a camera comprising the above actuator, a lens disposed within the carrier of the actuator, an image capturing mechanism for capturing an image transmitted by the lens, a spacer disposed between the actuator and the image capturing mechanism, and a controller for the actuator r to drive the linear motion transducers.
Through this arrangement, an actuator enabling both linear motion (e.g. for autofocus control) and tilting motion (e.g. for vibration control) utilizing a same structure is realised.
Other aspects of the invention are also disclosed.
Embodiments of the invention are described hereinafter with reference to the drawings, in which:
This actuator 100 can effect both linear motion and tilting motion of the carrier 103 depending on the control of the linear motion transducers 105, 106. The actuator 100 preferably comprises at least three linear motion transducers 105, 106.
The actuator 100 is preferably a lens actuator for a camera. In such an application, the carrier 103 is a lens holder that can hold a lens inside the lens holder in alignment with an aperture of the housing 101, 107 and an image capturing mechanism of the camera (e.g. a CCD array or film). The arrow z indicates the optical axis of the lens actuator and the camera (not shown). The linear motion of the carrier (lens holder) 103 enables auto-focussing, and the tilting motion of the carrier (lens holder) 103 enables vibration compensation.
The linear motion transducers 105, 106 preferably comprise one or more voice coils 105 in the housing 101, 107 and magnet element 106 each disposed relative to the voice coils 105, so that the magnet element 106 is perpendicularly oriented relative to the longitudinal axis of the respective voice coil 105. Each magnet element 106 may have corresponding voice coils 105. When energized with an electric current, the magnet element 106 is displaced relative to the voice coils 105 to cause the linear motion. The magnet element 106 is positioned so that one end of each magnet element 106 is coupled to the carrier 103 and the other end is adjacent to the voice coils 105
The linear motion transducers 105, 106 can be selectively energized. When the transducers 105, 106 are energized selectively, the resulting linear motion of each linear motion transducer 105, 106 is independent of the other transducers. This linear motion can be employed to effect vibration compensation control by tilting the carrier 103 relative to its axis.
The linear motion transducers 105, 106 can also be energized to cause substantially equal linear motions of the transducers 105, 106. When a lens is disposed within the carrier, this can be employed to displace the carrier along the lens axis thereby performing auto-focussing of the lens
Each linear motion transducer 105, 106 may comprise a piezoelectric device which alters in length along the longitudinal axis of the carrier 103 when the piezoelectric device is energized with electrical power.
Each linear motion transducer 105, 106 may comprise an electro-active polymer device which alters in length along the longitudinal axis of the carrier 103 when the electro-active polymer device is energized with an electric voltage.
Each linear motion transducer 105, 106 may comprise an ultra sonic motor.
The actuator 100 preferably further comprises a spring 102 disposed between the carrier 103 and an internal surface of the housing 101, 107 to control the movement of the carrier against the housing 101, 107. For example, the spring 102 can be a coil spring with a diameter larger than the inner diameter of the carrier 103, and aligned with the axis of the carrier 103. Alternatively, the spring 102 can be a set of leaf springs arranged around the perimeter of the carrier. The actuator 100 may have a pail of springs 102-1, 102-2, provided on opposite ends (top and bottom) of the carrier 103, for improved control of the movement of the carrier 103.
The actuator 100 can be used for an optical system (not shown) with a lens held within the carrier 103.
The actuator 100 can also be used in a camera (not shown) with a lens held within the carrier 103. The camera comprises an image capturing mechanism for capturing an image transmitted by the lens, a spacer between the actuator and the image capturing mechanism, and a controller to drive the linear motion transducers 105, 106 of the actuator 100. The camera can take a variety of forms of optical image capturing mechanisms, such as a still camera and a video camera.
The structure of the actuator 100 is described in more detail using a lens actuator as examples shown in
In
The interaction between the magnetic field of the magnet element 106 and the magnetic field induced by the electric current flowing through the coil 105 exerts a vertical force to repel each other and the magnet element 106 is displaced vertically as a result. The vertical movement of a magnet element 106 is translated to a vertical movement of a portion of the lens holder 103 to which the magnet element 106 is coupled. The bottom end of the magnet element 106 faces the coil 105 and the top end of the magnet element 106 faces the portion of the lens holder 103 designed to receive the force exerted by the magnet element 106.
The lens holder 103 has a substantially cylindrical shape and is adapted to hold a lens in place inside the cylinder. A lens can be disposed inside the lens holder 103 of the lens actuator 100. The lens holder 103 has projected portions (arms) protruding outwardly from the cylindrical body, preferably at the top end of the body Each projected portion is designed to receive the force exerted by the magnet movement and to translate the movement of the magnet element 106 to the corresponding section of the lens holder 103.
Coils 105 are made of an electrically conductive material. Elements other then the coils 105 and the magnetic element 106, such as the housing 101, the lens holder 103, are made of non-magnetic materials such as plastics, so as not to interfere with the magnetic fields of the coils 105 and the magnetic element 106.
A spring 102, or a pair of springs 102-1 and 102-2 is preferably placed at one end or the opposite ends of the lens holder 103, between the lens holder 103 and the inside of the housing 101, 107 for better control of the movement of the lens holder 103. The springs 102 provides a restoring force to the lens holder 103 in a direction opposite to the displacement of the coils 105 when energized. The springs 102 also buffer the movement of the lens holder 103 against the housing. Each of the springs 102 can be a coil spring such as shown in
In
Whilst
For example, a piezoelectric device comprising a piezoelectric material that changes in shape upon a change in the electric power applied to the piezoelectric material can be used. An electro-active polymer material that changes in shape in accordance with an applied electric voltage can also be used. In these arrangements, one end of the transducer is fixedly coupled to the housing 101, 107, and the other end that is displaced as a result of the change of shape is coupled to the arms of the lens holder 103 to cause the displacement of the lens holder 103. An ultrasonic motor is an example of the linear motion transducer 105, 106 where a part of the device is displaced to cause the displacement of the coupled lens holder 103.
When all the linear motion transducers are energized with substantially the same amount of energy (e.g. electric current in the case of a coil-magnet combination of
If the linear motion transducers 105, 106 are each subjected to different amounts of energy, this results in different amounts of displacement or change in shape of the transducers. This causes the lens holder 103 to be tilted according to the difference in displacements or changes in shape of the linear motion transducers. For this operation, only one or some of the transducers 105, 106 can be energized. If the tilting of the lens holder 103 is performed dynamically based on the movement of the camera or the lens module which may be detected by a motion detector of the camera or the lens module (not shown), the tilting of the lens holder 103 by the lens actuator 100 can be used for dynamic vibration compensation control.
The tilting of the lens holder 103 for vibration compensation control is realised with a degree of freedom according to the number and the placement of the linear motion transducers 105, 106 around the lens holder 103. With more then three transducers placed around the lens holder 103 with substantially equal distance between the transducers, the tilting of the lens holder 103 with two degrees of freedom is realised. The configuration of the lens actuator 100 with transducers distributed evenly around the perimeter of the lens holder 103, as shown in
The inside of the housing 101, 107 and the lens holder 103 desirably have relationship in size, shape, materials, etc. to allow smooth and accurate movement of the lens holder 103 inside the housing 101, 107. The protruding sections of the lens holder 103 may have depressions or protrusions for the top ends of the linear motion transducers 105, 106 to fit against. The lens holder 103 may have different configurations without departing from the scope and spirit of the invention. The housing may be in a form other than as shown in
The linear motion transducers can be electrically connected in series depending on the kind of control that is required. For autofocus control, the coils 105 can be connected in series to allow an equal value of electricity to flow through the coils 105. For vibration compensation control, the coils 105 can be connected such that the electric current flowing through the coils 105 can be controlled independently of other coils.
The control module and the electric circuit to realise the control of the transducers 105, 106 may be a part of the lens actuator 100 or may be provided externally, for example, as a part of the main body of the camera.
By causing the linear motion transducers to be given substantially the same amount of displacement plus a differential amount of displacement, autofocus control and vibration compensation control can be realised in combination.
The lens actuator 100 can be used for a variety of optical image capturing apparatuses/systems such as a still camera, a video camera or a film camera, using a digital or analogue image capturing mechanism.
If the lens actuator 100 is used in a relatively small camera such as a camera module of a cellular phone, an arrangement that allows an overall linear motion of up to 0.5-1.0 mm in z direction and a tilting motion of up to approximately +/−2 degrees of the lens holder 103 and the lens can be practiced. This is only given for purposes of illustration and other values may in fact be practiced.
The above described arrangement of the actuator is able to provide both linear motion, for example for autofocus function, and tilting motion, for example for vibration compensation control, using the configuration of the multiple linear motion transducers placed around the carrier. This has an advantage of reducing the complexity and/or the size of an actuator. A lens actuator with a reduced size is especially desirable for small digital cameras or cellular phones with camera modules.
