Drive controller, imaging apparatus and drive control method

There is provided a drive controller including a determination part that compares a target stop position of a movable body, which is driven by a piezoelectric actuator driven by a piezoelectric element expanded and contracted in response to an applied voltage, with a real position of the movable body acquired on the basis of a position sensor, and determines whether or not the target stop position matches with the real position, and a drive control part that turns off energization of the piezoelectric actuator when the target stop position matches with the real position while the movable body is being driven by the piezoelectric actuator.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Japanese Priority Patent Application JP 2013-214726 filed Oct. 15, 2013, the entire contents of which are incorporated herein by reference.

BACKGROUND

The present disclosure relates to a drive controller that controls a stop of a movable body driven by a drive part, an imaging apparatus and a drive control method.

For an autofocus function, an electrically-driven zoom function and a camera shake correction mechanism, an electromagnetic conversion motor using a coil and a magnet such as a stepping motor, a voice coil motor and a DC motor is often used. In the electromagnetic conversion motor, it is difficult to keep the position when energization of the motor is turned off. In particular, when the energization is suddenly turned OFF in the middle of high-speed drive, the motor is affected by inertia of a lens movable part and is stopped at a position past the position at which the energization is turned off. Therefore, generally from a viewpoint of saving power or the like, when turning off the energization, it may be necessary to turn off the energization only after the movable body is completely stopped after a stop is instructed.

In a stepping motor for instance, as disclosed in JP2006-158019A, after the end of microstep drive, a rotor is driven to make an excitation position of the rotor coincide with an excitation position of a stator, and then energization of the motor is turned off. This prevents the motor from stopping out of an originally intended position at which the motor should actually be stopped due to detent torque that the motor has.

SUMMARY

However, in the case of tentatively stopping a motor, then moving the motor further to a stably stopped position, and turning off the energization of the motor thereafter as described in JP2006-158019A, it takes a very long time from drive to turning off of the energization. For instance, when using such a method in an autofocus (AF) mechanism, autofocusing time (that is, a shutter time lag) becomes extremely long. Not to mention, when the energization of the motor is suddenly turned off during high-speed drive, inertia causes a state called step-out in which synchronization of an energization signal and a motor rotation angle is shifted, and the motor not only passes by a stop position but also loses the motor rotation angle (that is, a focus position). Also, when the motor is disturbed by an impact or the like while the energization of the motor is off, the position is shifted to a stably stopped position different from an original stop position or slight shift from the original stop position is generated even within the stably stopped position close to the desired stop position.

Similarly in a DC motor, even when the energization is turned off after the motor is stopped, the misalignment occurs due to the influence of the detent torque, and when the energization of the motor is turned off during the high-speed drive, the motor is stopped at a position past the original stop position due to the influence of the inertia. The overshoot is not stable due to the influence of variation of loads of the motor and a gear mechanism, and it is extremely difficult to predict the overshoot and perform correction beforehand for turning off the energization of the motor before the original stop position.

In a voice coil motor, in its principle of controlling a position of a movable body using feedback control using information from a position sensor, the position of the movable body is completely unfixed when the energization of the motor is turned off to begin with. Also, even in the state of stopping by controlling the stop by servo drive, the movable body is not completely stopped due to the influence of signal noise of the position sensor that detects a real position of the movable body or the like, and maintains the positions while finely moving. Therefore, compared to the case that the energization is turned off, the motor is degraded in stop accuracy.

In such a manner, it is difficult to quickly stop the motor during the high-speed drive in a short time while maintaining high stop accuracy, and not to mention, turning off the energization of the motor during drive causes a large misalignment of the movable body. Further, the motor is easily influenced by disturbance such as signal noise, an impact or the like, the misalignment easily occurs, and position accuracy when the movable body is stopped is affected.

Accordingly, the present disclosure proposes a new and improved drive controller, imaging apparatus and drive control method capable of stopping a drive part that drives the movable body quickly with high accuracy and achieving power consumption reduction by turning off the energization of the drive part.

According to an embodiment of the present disclosure, there is provided a drive controller including a determination part that compares a target stop position of a movable body, which is driven by a piezoelectric actuator driven by a piezoelectric element expanded and contracted in response to an applied voltage, with a real position of the movable body acquired on the basis of a position sensor, and determines whether or not the target stop position matches with the real position while the movable body is being driven by the piezoelectric actuator, and a drive control part that turns off energization of the piezoelectric actuator when the target stop position matches with the real position.

According to another embodiment of the present disclosure, there is provided an imaging apparatus including an imaging unit, a lens part composed of one or more lenses that transmit light incident on the imaging unit, a plurality of drive parts that move a movable body that holds the imaging unit and the lenses respectively and moves in a predetermined direction respectively, and a plurality of drive control parts that control the individual drive parts respectively. At least one of the drive parts is a piezoelectric actuator that drives the movable body with a piezoelectric element expanded and contracted in response to an applied voltage. The drive control part of the piezoelectric actuator includes a determination part that compares a target stop position of the movable body with a real position of the movable body acquired on the basis of a position sensor, and determines whether or not the target stop position matches with the real position while the movable body is being driven by the piezoelectric actuator, and a drive control part that turns off energization of the piezoelectric actuator when the target stop position matches with the real position.

According to another embodiment of the present disclosure, there is provided a drive control method including comparing a target stop position of a movable body, which is driven by a piezoelectric actuator driven by a piezoelectric element expanded and contracted in response to an applied voltage, with a real position of the movable body acquired on the basis of a position sensor, and determining whether or not the target stop position matches with the real position while the movable body is being driven by the piezoelectric actuator, and turning off energization of the piezoelectric actuator when the target stop position matches with the real position.

According to the present disclosure, when moving the movable body moved by a piezoelectric actuator to a target stop position, the drive controller compares the target stop position of the movable body with a real position, and when determining that they match during the drive of the movable body by the piezoelectric actuator, turns off the energization to the piezoelectric actuator. Thus, the time required for moving the movable body to the target stop position can be shortened and the movable body can be stopped at the target stop position with high accuracy. By turning off the energization of the piezoelectric actuator, the power consumption reduction can be also achieved.

As described above, according to the present disclosure, the drive part that drives the movable body can be stopped quickly with high accuracy, and the power consumption reduction by turning off the energization of the drive part can be achieved. Also, the above-described effects are not necessarily definite, and together with the above-described effects, or instead of the above-described effects, one of effects indicated in this specification or other effects that can be recognized from this specification may be demonstrated.

DETAILED DESCRIPTION OF THE EMBODIMENT(S)

Descriptions will be given in the following order.

1. First embodiment (drive stop control by comparison between target stop position and real position of movable body)1.1. Configuration of imaging apparatus1.1.1. Entire configuration of imaging apparatus1.1.2. Configuration of drive part1.1.3. Movement of lens frame by piezoelectric actuator1.2. Drive control of drive part1.2.1. Outline of drive control by drive controller1.2.2. Configuration of drive controller1.2.3. Focus lens drive stop control by drive controller1.3. Summary

2. Second embodiment (timing of turning off energization of piezoelectric actuator)

3. Third embodiment (correction of target stop position)

[1.1 Configuration of Imaging Apparatus]

First, with reference toFIG. 1-FIG. 4, one configuration example of an imaging apparatus according to a first embodiment of the present disclosure will be described.FIG. 1is a schematic perspective view illustrating a front surface side appearance of the imaging apparatus according to the present embodiment.FIG. 2is a perspective view illustrating a lens drive mechanism of a focus lens121which is one of drive parts of the imaging apparatus according to the present embodiment.FIG. 3is a perspective view illustrating a lens frame300which is a movable body driven by the lens drive mechanism according to the present embodiment.FIG. 4is a planar sectional view of the lens drive mechanism of the imaging apparatus according to the present embodiment.

(1.1.1. Entire Configuration of Imaging Apparatus)

In the present embodiment, the case of application to the drive control of the focus lens121of a digital still camera100illustrated inFIG. 1will be described. The digital still camera100includes a body part110having a control part that controls the entire imaging apparatus, an imaging device, a signal processing part that processes image signals acquired by the imaging device and the like, and a lens part120having a zoom lens, a focus lens, a correction lens part and the like.

The body part110has the control part that controls the entire imaging apparatus, the imaging device, the signal processing part that processes image signals that are electric signals corresponding to image data acquired by the imaging device and the like. As the imaging device, for instance, the imaging device such as a charge coupled device (CCD) type image sensor, a complementary metal oxide semiconductor (CMOS) type image sensor and the like is usable. In the case of using the CMOS type image sensor as the imaging device, the imaging device converts an optical image formed on an imaging surface to an electric signal.

The electric signal which is an image signal is subjected to noise elimination processing and gain control processing of turning an imaging signal to a desired signal level, then converted from an analog signal to a digital signal, and outputted to the signal processing part. The signal processing part carries out, to the inputted electric signal, defect correction processing of correcting a signal of a defective pixel in the imaging device, shading correction processing of correcting a reduction in peripheral light quantity of the lens, and processing of white balance adjustment, luminance correction and the like. The electric signal processed by the signal processing part is outputted to an output part such as a display for instance as image data.

The lens part120includes the zoom lens that varies magnification, the focus lens that carries out focusing, the correction lens part that moves a position of the optical image formed on the imaging surface of the imaging device on the imaging surface and the like. The zoom lens, the focus lens and the correction lens part may be driven on the basis of lens control signals from the control part, or may be driven by user's operation. Also, the lens part120includes a mechanical shutter that mechanically adjusts an exposure amount to the imaging surface of the imaging device, and a diaphragm mechanism that adjusts a light quantity of the optical image formed on the imaging surface of the imaging device.

Lens positions of the zoom lens and the focus lens, a displacement state of the correction lens part, a setting position of the diaphragm mechanism and the like are detected by an optical system sensor, and outputted to the control part as position signals. Also, the lens part is provided with a driver that drives the zoom lens, the focus lens, the correction lens part, the diaphragm mechanism and the like on the basis of control signals from the control part.

(1.1.2. Configuration of Drive Part)

Such a digital still camera100has a drive part that moves the lens and the imaging device to a predetermined position, and the drive part is used for focusing of the lens and for shake correction of the imaging device. As one configuration example of the drive part, the drive part that drives the focus lens121will be described on the basis ofFIG. 2-FIG. 4.

The drive part that drives the focus lens121includes, as illustrated inFIG. 2, a fixing member200fixed to the digital still camera100, and the lens frame300that supports the focus lens121and is provided on the fixing member200movably in an optical axis direction. The focus lens121and the lens frame300are also called the movable body.

The fixing member200is a roughly cylindrical member and includes annular surfaces200a,200bprojected toward a center axis at both ends of an opening. At a hollow part of the fixing member200, the lens frame300is arranged. The fixing member200includes a drive shaft212and a sub shaft240of a piezoelectric actuator210provided in parallel with an optical axis respectively at positions roughly facing each other in a radial direction. By the drive shaft212and the sub shaft240, the lens frame300is supported movably in an optical axis direction. The optical axis direction is identical to a center axis direction of the fixing member200.

The piezoelectric actuator210includes a piezoelectric element214expanded and contracted in response to an applied voltage, the drive shaft212connected to one end side in an expanding/contracting direction of the piezoelectric element214, and a weight216connected to the other end side in the expanding/contracting direction of the piezoelectric element214. The piezoelectric element214and the drive shaft212, and the piezoelectric element214and the weight216are fixed with an adhesive agent for instance.

The drive shaft212is a narrow round shaft member for instance. The drive shaft212is inserted to drive shaft support holes201,203respectively formed on the annular surfaces200a,200bof the fixing member200, and is slidably supported. Also, as illustrated inFIG. 4, with the drive shaft212, a sliding contact surface302of the lens frame300is in contact between the drive shaft support holes201,203.

A drive shaft212is urged toward a sliding contact surface302by an urging member230fixed to the lens frame300with a fixing member232such as a screw, and is frictionally connected with the lens frame300. Since the drive shaft212and the sliding contact surface302of the lens frame300are frictionally connected, the lens frame300can be moved together with the drive shaft212moved in response to a piezoelectric element214. For the urging member230, a leaf spring or the like for instance is usable. The urging member230is arranged so that a direction of urging force that urges the drive shaft212turns to the direction where a sub shaft240is arranged. By the urging member230, it is possible to suppress inclination of the lens frame300and movement of the lens frame300in directions other than a driving direction.

By frictional force generated between the drive shaft212and the sliding contact surface302by the urging force of the urging member230, even in the state that the energization of the piezoelectric actuator210is turned off, positions of the drive shaft212and the sliding contact surface302can be held so as not to be shifted. Thus, the drive shaft212can be provided without play. The frictional force is set at a value sufficiently large for weight of the movable body composed of the focus lens121and the lens frame300. That is, the frictional force is set at such a value that the drive shaft212and the lens frame300can be held without a misalignment even against impact force when the camera is hit and inertia generated when the movable body is suddenly stopped during drive. In this way, the drive shaft212functions as a vibration member that drives the movable body, and also functions as a support member that supports the lens frame300in an axial direction.

The piezoelectric element214is expanded and contracted by a driving pulse voltage applied between electrodes, and generates reciprocating vibrations at different speeds. When the reciprocating vibrations of the piezoelectric element214are transmitted to the drive shaft212, the lens frame300frictionally connected to the drive shaft212is moved in a direction of the vibrations at a low speed by asymmetry of the reciprocating vibrations of the drive shaft212.

A weight216is a member having predetermined weight, and the piezoelectric actuator210is fixed to the fixing member200through the weight216. The weight216is formed into a block shape for instance.

The sub shaft240is a narrow round shaft member for instance. The sub shaft240is inserted and fixed to sub shaft support holes202and204respectively formed on the annular surfaces200a,200bof the fixing member200. Also, the sub shaft240is inserted to a guide hole332of the lens frame300between the sub shaft support holes202,204. The lens frame300is provided movably in the optical axis direction along the sub shaft240.

In the present embodiment, the drive shaft212and the sub shaft240are arranged so as to hold a centroid of the movable body including the lens121and the lens frame300therebetween. In this way, by arranging the centroid of the movable body on a straight line connecting the drive shaft212and the sub shaft240, force and moment applied to the movable body can be supported with the minimum force by the drive shaft212and the sub shaft240. The drive device according to an embodiment of the present disclosure is not limited to the example, and the drive shaft212and the sub shaft240may be arranged adjacently for instance.

Also, the fixing member200is provided with a magnetic sensor224as a position sensor that detects a position of the lens frame300holding the focus lens121. The magnetic sensor224is provided so as to face a magnet222provided on the lens frame300along the optical axis direction. When the lens frame300is moved in the optical axis direction in response to the vibrations of the piezoelectric actuator210, a position of the magnet222is also moved together with the lens frame300. The magnetic sensor224specifies the position of the lens frame300by detecting intensity of a magnetic field that changes depending on the position of the magnet222.

The lens frame300is, as illustrated inFIGS. 2 to 4, a member that is arranged at the hollow part of the fixing member200and supports the focus lens121. The lens frame300includes a lens holding part310that holds the focus lens121, a first arm part320that is extended from the lens holding part310to the side of the drive shaft212, and a second arm part330extended from the lens holding part310to the side of the sub shaft240.

On the first arm part320, the sliding contact surface302that is in contact with the drive shaft212and supports it along the axial direction is formed. At this time, the sliding contact surface302is, as illustrated inFIG. 4, arranged so as to be held between the drive shaft212and the sub shaft240in the view from a plane. The sliding contact surface302is frictionally connected with the drive shaft212urged toward a direction in which the sub shaft240is arranged by an urging member230. Also, the sliding contact surface302is in contact with an outer peripheral surface of the drive shaft212at a plurality of parts, and is formed such that a cross sectional shape in a direction orthogonal to the optical axis is an almost V shape or an almost U shape for instance.

In this way, by arranging the sliding contact surface302in a shape to be in contact with an outer peripheral surface of the drive shaft212at a plurality of parts between the drive shaft212and the sub shaft240, the lens frame300is prevented from being greatly moved in directions other than a driving direction of the drive shaft212(that is, an optical axis direction) due to an impact or the like. Note that, the position of the lens frame300is normally regulated by the urging member230and projection parts334,334to be described later. Also, generation of reaction against the urging force of the urging member230can be reduced as well. A first arm part320is provided with a magnet222so as to face a magnetic sensor224that detects the position of the lens frame300.

On a second arm part330, a guide hole332to which the sub shaft240is to be inserted is formed. The guide hole332is provided in order to prevent the lens frame300from being inclined due to the fall of the digital still camera100or the like and giving an impact to the piezoelectric element214. Also, in the drive part according to the present disclosure, the guide hole332may not be provided all the time. An inner diameter of the guide hole332is larger than an outer diameter of the sub shaft240, and the drive shaft212and the sub shaft240originally arranged in parallel are formed so as to have such a clearance that the sub shaft240and the guide hole332are not brought into contact even when considering inclination of the sub shaft240that is generated within dimensional tolerance of components.

Also, the second arm part330includes a pair of projection parts334,334in contact with an outer peripheral surface of the sub shaft240so as to hold the sub shaft240therebetween. For the projection parts334,334, as illustrated inFIG. 5, the shape viewed from the front is formed into a roughly semicircular block shape projected to the sub shaft240for instance. Thus, the sub shaft240can be surely supported with few contact parts. Note that, the shape of the projection parts334,334are not limited to the example, and the shape viewed from the front may be a V shape projected to the sub shaft240for instance.

The projection parts334,334are provided so as to hold the sub shaft240therebetween from a rotating direction of the lens frame300with the drive shaft212as the rotation center. Thus, the movement of the lens frame300rotating around the drive shaft212is regulated. Note that, while the pair of projection parts334,334are provided on a z axis negative direction side with respect to the guide hole332as illustrated inFIG. 2in the present embodiment, the present disclosure is not limited to the example, and the pair of projection parts334,334may be provided on a z axis positive direction side with respect to the guide hole332. Also, the pair of projection parts334,334may not be arranged closely in a z direction to the guide hole332as in the present embodiment, may be arranged at a predetermined distance in the z direction from the guide hole332for instance, or may be provided inside the guide hole332.

(1.1.3 Movement of Lens Frame by Piezoelectric Actuator)

The drive device according to the present embodiment moves the lens frame300that holds the focus lens121in the optical axis direction with the piezoelectric actuator210. The drive device is configured such that an optical axis C of the focus lens121held by the lens frame300, the drive shaft212and the sub shaft240are parallel to one another.

When a voltage is applied to the piezoelectric element214of the piezoelectric actuator210, the piezoelectric element214is expanded, contracted and vibrated in a reciprocating manner. When reciprocating vibrations of the piezoelectric element214are transmitted to the drive shaft212, the lens frame300frictionally connected to the drive shaft212is moved in a low-speed vibrating direction due to asymmetry of the reciprocating vibrations of the drive shaft212. In this way, the lens frame300is moved in the optical axis direction in response to the voltage applied to the piezoelectric element214.

[1.2. Drive Control of Drive Part]

(1.2.1. Outline of Drive Control by Drive Controller)

In the drive part of such a focus lens121, the drive of the piezoelectric actuator210that moves the focus lens121is controlled by the drive controller. In order to stop the focus lens121that is moved at a correct focusing position, the drive controller according to the present embodiment executes control so as to turn off a voltage applied to the piezoelectric element214when the target stop position of the focus lens121matches with a lens real position. Thus, the focus lens121can be stopped at the correct focusing position in a short time. In the present disclosure, the target stop position is a value set separately from a drive instruction value which is a target control position of the focus lens121by servo control, and is a position where the focus lens121should actually be stopped.

For instance, in the case of receiving an arithmetic result of contrast AF or phase difference AF, moving the focus lens121to the focusing position and stopping the focus lens121, a conventional drive controller executes the servo control of making the focus lens121follow so that the real position of the focus lens121matches with the drive instruction value based on the arithmetic result. In the servo control, as illustrated inFIG. 5, in terms of characteristics of the servo control, the focus lens121is decelerated immediately before the target stop position of the focus lens121, and it takes time to reach the target stop position. Even though the focus lens121is not decelerated depending on a servo parameter, an overshoot as illustrated inFIG. 6is generated, and as a result, it takes time for convergence until the focus lens121is stopped at the focusing position that is the target stop position.

After the movement of the drive part is converged and stopped, when the energization of the drive part is turned off, autofocusing time becomes long, and power consumption increases accordingly. In particular, in a device such as a camera, there is a case that the energization of the drive part of the focus lens121has to be turned off to supply power to a shutter due to a restriction of the maximum supply power. In such a case, the autofocusing time becomes extremely long.

Therefore, in the drive controller according to the present embodiment, as illustrated inFIG. 7, the energization of the piezoelectric actuator212is turned off when the real position of the focus lens121detected by the magnetic sensor224is in the target stop position at which the focus lens121is actually desired to be stopped. Thus, a decelerating action before the stop position that is generated in terms of characteristics of the servo as illustrated inFIG. 5is eliminated, the focus lens121can be brought close to the focus position while keeping the highest moving speed, and the autofocusing time can be accelerated.

(1.2.2. Configuration of Drive Controller)

On the basis ofFIG. 8, a configuration of a drive controller430of the piezoelectric actuator210that drives the focus lens121according to the present embodiment will be described.FIG. 8is a block diagram illustrating one configuration example of the drive controller430according to the present embodiment.

The drive controller430according to the present embodiment is a device that receives an arithmetic result of the contrast AF and the phase difference AF by a camera control part420, and controls the piezoelectric actuator210such that the focus lens121is moved to the focusing position which is the target stop position and stopped. The drive controller430includes, as illustrated inFIG. 8, a target stop position acquisition part432, a real position acquisition part434, a determination part436, and a drive control part438.

The target stop position acquisition part432acquires the focusing position at which the focus lens121is actually desired to be stopped as the target stop position from the camera control part420. The camera control part420carries out arithmetic processing of the contrast AF and the phase difference AF on the basis of operation input from an operation input part410of the digital still camera100by a user, and computes the focusing position at which the focus lens121is actually desired to be stopped. When the target stop position of the focus lens121is acquired from the camera control part420, the target stop position acquisition part432outputs the target stop position to the determination part436and the drive control part438.

The real position acquisition part434computes and acquires an actual position of the focus lens121driven by the piezoelectric actuator210(also called “the real position of the focus lens121”) on the basis of a detection result by the magnetic sensor224. The real position acquisition part434outputs the acquired real position of the focus lens to the determination part436and the drive control part438.

The determination part436compares the target stop position and the real position of the focus lens121, and determines whether or not the target stop position matches with the real position. A determination method by the determination part436will be described later. The determination part436outputs a determination result to the drive control part438.

The drive control part438controls the drive of the piezoelectric actuator210by controlling a voltage to be applied to the piezoelectric actuator210on the basis of the target stop position and the real position of the focus lens121. The drive control part438computes the drive instruction value on the basis of the target stop position and the real position of the focus lens121, and drives the piezoelectric actuator210on the basis of the drive instruction value. The position of the focus lens121moved by the drive of the piezoelectric actuator210is cyclically detected by the magnetic sensor224, and is outputted to the real position acquisition part434each time. The processing is repeatedly executed until it is determined by the determination part436that the target stop position matches with the real position. Then, when it is determined by the determination part436that the target stop position matches with the real position, the drive control part438turns off the energization of the piezoelectric actuator210.

(1.2.3. Focus Lens Drive Stop Control by Drive Controller)

FIG. 9illustrates processing of drive stop control of the focus lens121by the drive controller430according to the present embodiment.

The drive stop control of the focus lens121according to the present embodiment is started by receiving the operation input that may require position adjustment of the focus lens121for instance from the operation input part410of the digital still camera100by the user first, as illustrated inFIG. 9(S100). The operation input part410outputs inputted operation input information to the camera control part420.

The camera control part420which receives the operation input information carries out the arithmetic processing of the contrast AF and the phase difference AF, and computes the focusing position at which the focus lens121is actually desired to be stopped as the target stop position (S102). The camera control part420outputs the computed target stop position to the target stop position acquisition part432of the drive controller430. When the target stop position of the focus lens121is acquired from the camera control part420, the target stop position acquisition part432outputs the target stop position to the determination part436and the drive control part438.

In the meantime, the drive controller430acquires a detection value of the magnetic sensor224by the real position acquisition part432, and computes and acquires the real position of the focus lens121(S104). The real position acquisition part434outputs the acquired real position of the focus lens to the determination part436and the drive control part438.

Then, the drive controller430compares the target stop position of the focus lens121acquired in step S102and the real position of the focus lens121acquired in step S104by the determination part436(S106). Then, the determination part436determines whether or not the target stop position and the real position of the focus lens121match with each other. The determination part436may, for instance, simply compare between the target stop position and the real position of the focus lens121that are acquired, and determine whether or not these values match with each other.

Alternatively, the determination part436may take a difference between the target stop position and the real position of the focus lens121, and determine whether or not the target stop position matches with the real position on the basis of whether or not a sign of the difference value is inverted. Due to influence of detection timing of the magnetic sensor224or signal noise of the magnetic sensor224or the like, it is possible that the focus lens121passes by the focusing position without the target stop position and the real position completely matching with each other. Therefore, by computing a difference between the target stop position and the real position in real time during the drive of the focus lens121and determining a moment at which the sign of the difference value is inverted as the time when the target stop position matches with the real position, it is ensured that the focus lens121can be stopped at the focusing position.

For instance, in an example illustrated inFIG. 7, the determination part436computes the difference value by subtracting the real position from the target stop position of the focus lens121. Thus, the difference value is a positive value until the real position of the focus lens121is in the target stop position. Then, when the real position of the focus lens121exceeds the target stop position, the difference value becomes a negative value. The determination part436determines that the target stop position matches with the real position at the timing at which the sign of the difference value between the target stop position and the real position of the focus lens121is inverted from being positive to negative.

Since the example inFIG. 7illustrates the case that a focus position moves from a small value to a big value (that is, from bottom toward top), the determination part436determines the timing at which the sign of the difference value is inverted from being positive to negative. For instance, in the case that the focus position moves from a big value to a small value (that is, from top toward bottom), the difference value for which the real position is subtracted from the target stop position becomes the negative value until the real position of the focus lens121is in the target stop position. Then, when the real position of the focus lens121exceeds the target stop position, the difference value becomes the positive value. In this case, the determination part436determines the timing at which the sign of the difference value is inverted from being negative to positive.

Also, as another determination method, the case that the difference value between the target stop position and the real position of the focus lens121becomes equal to or smaller than a predetermined threshold value (coring) may be determined as the time when the target stop position matches with the real position. In this case, since it is difficult to achieve stop accuracy when exceeding the threshold (coring) of the focus lens121, it is better to use the determination method by the above-described sign inversion system when high accuracy is demanded. A determination result in step S106is outputted to the drive control part438.

Thereafter, the drive control part438controls the voltage to be applied to the piezoelectric actuator210on the basis of the determination result in step S106. When it is determined that the target stop position and the real position of the focus lens121do not match with each other in step S106, the drive control part438computes the drive instruction value on the basis of the target stop position and the real position, and drives the piezoelectric actuator210on the basis of the drive instruction value (S108). Then, the processing from step S104is repeatedly executed.

On the other hand, when it is determined that the target stop position and the real position of the focus lens121match with each other in step S106, the drive control part438turns off the energization of the piezoelectric actuator210(S110). Thus, the drive of the piezoelectric actuator210is stopped. At this time, since the drive shaft212of the piezoelectric actuator210is urged to the sliding contact surface302of the lens frame300by the urging member230, the lens frame300can keep the position when the energization of the piezoelectric actuator210is turned off.

The configuration of the drive controller430of the drive part according to the first embodiment of the present disclosure and the operation thereof are described above. According to the present embodiment, in order to stop the focus lens121that is moved at the correct focusing position, the drive controller430executes control so as to turn off the voltage applied to the piezoelectric element214when the target stop position and the real position of the focus lens121match with each other. Thus, the focus lens121can be stopped at the correct focusing position in a short time. Also, by quickly moving and stopping the focus lens121, the time during which the energization of the piezoelectric actuator210is turned off can be prolonged, and power consumption can be reduced.

Next, on the basis ofFIG. 10, the drive control method by the drive controller according to the second embodiment of the present disclosure will be described.FIG. 10is an explanatory diagram illustrating drive control by the drive controller according to the present embodiment. The configuration of the drive controller according to the present embodiment and the imaging apparatus including the drive controller is the same as the configuration in the first embodiment illustrated inFIG. 1-FIG. 4andFIG. 8, so that it is described using the same reference numerals and detailed descriptions are omitted.

In the case of adopting drive utilizing a PWM waveform as a drive method of the piezoelectric actuator210, a drive voltage applied to the piezoelectric actuator210is indicated by a cyclic rectangular wave as in each graph indicated on a lower side ofFIG. 10for instance. Here, when the energization of the piezoelectric actuator210is turned off in the middle of one cycle of the rectangular wave, as in the graph indicated at the lower left ofFIG. 10, a shape of the rectangular wave becomes a halfway shape. Such output affects an expansion and contraction operation of the piezoelectric actuator210and sound is generated when the energization is turned off.

Accordingly, in the drive controller430according to the present embodiment, as illustrated at the lower right ofFIG. 10, the energization of the piezoelectric actuator210is turned off after the rectangular wave of the drive voltage is outputted for one cycle after the sign of the difference value between the target stop position and the real position of the focus lens121is inverted. That is, after it is determined that the target stop position and the real position of the focus lens121match with each other, at the point of time at which the value of the PWM waveform of the drive voltage cyclically applied to the piezoelectric actuator210becomes zero, the energization of the piezoelectric actuator210is turned off.

In this way, when it is determined that the target stop position and the real position of the focus lens121match with each other, the drive controller430according to the present embodiment does not turn off the energization of the piezoelectric actuator210immediately in the middle of output of the rectangular wave of the drive voltage for one cycle. The drive control part438of the drive controller430shifts the switching timing of a driver, and turns off the energization of the piezoelectric actuator210consistently at the timing at which the output of the waveform for one cycle is ended. Thus, influence on the expansion and contraction operation of the piezoelectric actuator210is reduced, and the sound generated when the energization of the piezoelectric actuator210is turned off is reduced.

In the drive control according to the present embodiment, there is a case that the time of turning off the energization of the piezoelectric actuator210is slightly delayed from the time when it is actually determined that the target stop position and the real position of the focus lens121match with each other. However, since the delay is sufficiently short time to the speed of focus, position control of the focus lens121is not greatly affected.

The timing of turning off the energization of the piezoelectric actuator210by the drive controller430according to the present embodiment is effective when the imaging apparatus is performing imaging in a moving image mode in particular. By the drive control, the sound generated when the energization of the piezoelectric actuator210is turned off does not obstruct the sound acquired together with images during the moving image mode.

On the basis ofFIG. 11andFIG. 12, the drive control method by the drive controller according to the third embodiment of the present disclosure will be described.FIG. 11is a control block diagram of the drive controller according to the present embodiment.FIG. 12is an explanatory diagram illustrating correction of the target stop position by the drive controller according to the present embodiment. Note that, in the present embodiment, the configuration of the drive controller and the imaging apparatus including the drive controller is the same as the configuration in the first embodiment illustrated inFIG. 1-FIG. 4andFIG. 8, so that it is described using the same reference numerals and detailed descriptions are omitted.

A detection signal of the magnetic sensor224that is information on the real position of the focus lens121generally includes signal noise. In order to eliminate the signal noise, in the drive controller430, as illustrated inFIG. 11, a low-pass filter (also called “LPF”, hereinafter) is often applied to the detection signal of the magnetic sensor224.

In the case of utilizing real position information of the focus lens121after applying the LPF, for determination of turning off of the energization of the piezoelectric actuator210according to the first embodiment, the real position of the focus lens121is delayed timewise from the original real position due to a delay element of the LPF. That is, while the real position of the focus lens121is a position indicated by a thick dashed line inFIG. 12, when the delay element of the LPF is included in the real position of the focus lens121, time delay is generated as indicated by the dashed line. Therefore, when turning off of the energization of the piezoelectric actuator210is determined utilizing the information delayed by the LPF, the focus lens121is to be stopped past the target stop position by a distance x inFIG. 12.

In the meantime, a delay amount of the LPF is uniquely determined by a drive speed of the focus lens121. Thus, it is possible to obtain the delay amount by calculation from design information of the LPF for the drive speed. Then, the drive controller430according to the present embodiment brings forward the timing of turning off the energization of the piezoelectric actuator210depending on the moving speed of the focus lens121when moving to the target stop position, and sets the target stop position by the delay amount before in the driving direction. Thus, the focus lens121can be accurately stopped at the focusing position which is the original target stop position.

The delay mount of the LPF is changed by a setting value of the LPF as well. Normally, the setting value of the LPF is not changed when it is once set. Therefore, the delay element generated by the setting may be taken into consideration when designing the LPF, to correct the target stop position.

Note that, as another method of avoiding overshooting of the focus lens121due to the delay element of the LPF, the following method can be considered. For instance, an advance compensator is introduced after a digital LPF illustrated inFIG. 11to advance for the delay. Further, preceding information of an analog LPF illustrated inFIG. 11may be used for information to be used to determine turning off of the energization of the piezoelectric actuator210, and a value through the LPF illustrated inFIG. 11may be used for position information of the focus lens121to be used for the servo operation. Thus, only the overshoot can be improved without damaging a servo performance.

The preferred embodiments of the present disclosure are described above in detail with reference to the appended drawings, but the technical scope of the present disclosure is not limited to the examples. It is clear that a person ordinarily skilled in the art of the present disclosure can conceive various kinds of change examples or correction examples within the scope of technical ideas described in the claims, and it is understood that they of course belong to the technical scope of the present disclosure.

For instance, while the lens drive method of the AF operation is described in the above-described embodiment, the present technology is not limited to the example. For instance, the present technology is applicable to various drive modes regarding a lens movable part such as manual focus and zoom operations or the like. By applying the drive control according to the embodiment, it is possible to obtain the effects similar to the present disclosure such as shortening of operation time, reduction of power consumption, and reduction of energization off sound.

Also, in the above-described embodiment, the drive controller that turns off the energization of the piezoelectric actuator210at the timing at which the target stop position and the real position of the focus lens121match with each other in the drive stop of the piezoelectric actuator210is described. The imaging apparatus according to the present technology may further include, other than the drive controller according to the above-described embodiment, a second drive controller that controls the piezoelectric actuator210so that the focus lens121is stopped at the target stop position by feedback control based on a detection result of the position sensor.

At this time, the imaging apparatus controls the piezoelectric actuator210by either one of the drive controller according to the above-described embodiment and the second drive controller on the basis of a function state of the imaging apparatus. Since the drive controller according to the above-described embodiment turns off the energization of the piezoelectric actuator210instantaneously when the target stop position and the real position of the movable body match with each other, it is better to apply the drive controller when the movable body moves in a little amount. For instance, the piezoelectric actuator210is controlled by the drive controller according to the above-described embodiment in a still image photographing mode of photographing still images, and the piezoelectric actuator210is controlled by the second drive controller in a moving image photographing mode of photographing moving images.

When photographing the moving images with the possibility that the focus lens121is frequently driven, the energization of the piezoelectric actuator210is turned off after the movement of the movable body is converged. On the other hand, when photographing the still images, the energization of the piezoelectric actuator210is turned off when the real position of the movable body is in the target stop position, so that the power consumption can be reduced.

Also, the effects described in this specification are only explanations or examples and are not definite. That is, the technology according to the present disclosure can demonstrate other effects that are clear to those skilled in the art from descriptions of this specification, together with the above-described effects, or instead of the above-described effects.

Additionally, the present technology may also be configured as below.(1) A drive controller including:

a determination part that compares a target stop position of a movable body, which is driven by a piezoelectric actuator driven by a piezoelectric element expanded and contracted in response to an applied voltage, with a real position of the movable body acquired on the basis of a position sensor, and determines whether or not the target stop position matches with the real position; and

a drive control part that turns off energization of the piezoelectric actuator when the target stop position matches with the real position while the movable body is being driven by the piezoelectric actuator.(2) The drive controller according to (1),

wherein the determination part repeatedly calculates a difference between the target stop position and the real position, and when a sign of the difference is inverted, determines that the target stop position matches with the real position.(3) The drive controller according to (1) or (2),

wherein the target stop position is a position where the movable body is actually stopped, which is set separately from a drive instruction value which is a target control position of the movable body by servo control.(4) The drive controller according to any one of (1) to (3),

wherein, when the target stop position matches with the real position, the drive control part turns off the energization of the piezoelectric actuator at a point of time at which a value of a waveform of a drive voltage cyclically applied to the piezoelectric actuator becomes zero after a point of time of the match.(5) The drive controller according to any one of (1) to (4),

wherein the determination part corrects the target stop position in response to a delay element of the position sensor that detects the real position.(6) The drive controller according to (5),

wherein a correction amount of the target stop position is calculated on the basis of a moving speed of the movable body.(7) The drive controller according to any one of (1) to (6), including

a second drive control part that controls the piezoelectric actuator so that the movable body is stopped at the target stop position by feedback control based on a detection result of the position sensor,

wherein the piezoelectric actuator is controlled by either one of the drive control part and the second drive control part, on the basis of a function state of a device provided with the movable body.(8) An imaging apparatus including:

an imaging unit;

a lens part composed of one or more lenses that transmit light incident on the imaging unit;

a plurality of drive parts that move a movable body that holds the imaging unit and the lenses respectively and moves in a predetermined direction respectively; and

a plurality of drive control parts that control the individual drive parts respectively,

wherein at least one of the drive parts is a piezoelectric actuator that drives the movable body with a piezoelectric element expanded and contracted in response to an applied voltage, and

wherein the drive control part of the piezoelectric actuator includes

a determination part that compares a target stop position of the movable body with a real position of the movable body acquired on the basis of a position sensor, and determines whether or not the target stop position matches with the real position, and

a drive control part that turns off energization of the piezoelectric actuator when the target stop position matches with the real position while the movable body is being driven by the piezoelectric actuator.(9) The imaging apparatus according to (8),

wherein the piezoelectric actuator is composed of the piezoelectric element and a drive shaft to be driven by the piezoelectric element, and

wherein the imaging apparatus includes an urging member that urges the drive shaft to the movable body with fixed urging force.(10) A drive control method including:

comparing a target stop position of a movable body, which is driven by a piezoelectric actuator driven by a piezoelectric element expanded and contracted in response to an applied voltage, with a real position of the movable body acquired on the basis of a position sensor, and determining whether or not the target stop position matches with the real position; and

turning off energization of the piezoelectric actuator when the target stop position matches with the real position while the movable body is being driven by the piezoelectric actuator.