JP2008079395A - Drive controller of vibration actuator, lens barrel and camera - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide the drive controller of a vibration actuator performing stabilized speed control in low speed rotation region. <P>SOLUTION: The drive controller of a vibration actuator comprises drive signal control sections 1 and 3 performing switching control of on state for delivering a drive signal of some frequency to a vibration actuator 7 and off state for stopping output, sections 1 and 9 for detecting the driving speed of the vibration actuator, and sections 1 and 2 for altering the frequency of the drive signal at the time of subsequent on state based on the detection results from the speed detecting section at the time of previous on state. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a drive control device for a vibration actuator such as an ultrasonic motor, and a lens barrel and a camera including a vibration actuator that is driven and controlled by the drive control device.

  In general, an ultrasonic motor is used in an autofocus drive mechanism of a lens barrel of a camera. This ultrasonic motor includes a stator in which a piezoelectric element is arranged and a rotor driven by the stator. By changing the frequency of a drive signal supplied to the piezoelectric element, the rotational speed of the rotor is changed, and the frequency of the drive signal is lowered. While the rotational speed increases, the rotational speed decreases when the frequency of the drive signal is increased. A characteristic representing the relationship between the frequency (f) and the rotation speed (N) is referred to as fN characteristic. In the fN characteristic of the ultrasonic motor, the rotational speed changes exponentially with respect to the change in frequency (see Patent Document 1).

  However, in the low-speed rotation region, for example, even if a drive signal having a frequency corresponding to the rotation speed is supplied, it is difficult to rotate or to rotate too much, and the speed control is difficult. there were.

A method for stabilizing speed control in this low-speed rotation region has been proposed (see Patent Document 2).
JP 2003-304691 A Japanese Patent Laid-Open No. 7-170763

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a drive control device for a vibration actuator, a lens barrel, and a camera that can perform stable speed control in a low-speed rotation region.

  The vibration actuator drive control device according to claim 1 of the present invention that achieves the above object performs control to switch between an on state in which a drive signal of a certain frequency is output to the vibration actuator and an off state in which the output is stopped. Drive signal control unit (see, for example, MCU 1 and phase circuit 3 in FIG. 1), a speed detection unit (see, for example, 1 and 9 in FIG. 1) that detects the drive speed of the vibration actuator, and the speed detection in the on state And a frequency changing unit (for example, refer to MCU1 and VCO2 in FIG. 1) that changes the frequency of the drive signal in a later ON state based on the detection result of the unit.

  An example of the vibration actuator is an ultrasonic motor. The driving speed of the vibration actuator includes a rotation speed.

  The drive control apparatus for a vibration actuator according to claim 2 is characterized in that the frequency of the drive signal is a frequency corresponding to a drive speed in a stable operation region of the vibration actuator.

  The stable operation region is a region where stable speed control can be performed, for example, a region having a rotational speed larger than that including the lower limit rotational speed shown in FIG.

  The drive control apparatus for a vibration actuator according to claim 3 is characterized in that the drive signal control unit synchronizes the timing of turning on with a predetermined period (see, for example, FIG. 3 or FIG. 4). .

  The drive control apparatus for a vibration actuator according to a fourth aspect is characterized in that the drive signal control unit synchronizes the timing of turning off with a predetermined period (see, for example, FIG. 4).

  In the vibration actuator drive control device according to claim 5, the speed detection unit includes a pulse signal output unit (see, for example, the encoder 9 in FIG. 1) that outputs a pulse signal according to the driving amount of the vibration actuator. The driving speed of the vibration actuator is detected from the number of pulse signals output from the pulse signal output unit in the ON state.

  The vibration actuator drive control device according to claim 6, further comprising a pulse signal output unit that outputs a pulse signal in accordance with a drive amount of the vibration actuator, wherein the drive signal control unit outputs the pulse signal in the on state. When the number of pulse signals output from the unit reaches a predetermined number, the state is switched to the off state (see, for example, FIG. 3).

  A lens barrel according to a seventh aspect of the invention is a lens barrel according to any one of the first to sixth aspects, a vibration actuator that is driven and controlled by the drive control apparatus, and a lens that is driven by the vibration actuator. And.

  The camera according to claim 8 is the drive control device according to any one of claims 1 to 6, a vibration actuator driven and controlled by the drive control device, a lens driven by the vibration actuator, It is provided with.

  According to the vibration actuator drive control device of the present invention, the frequency of the drive signal is changed in the subsequent ON state based on the detection result of the speed detector, so that stable speed control can be performed in the low speed rotation region. .

  Embodiments of a vibration actuator drive control apparatus according to the present invention will be described below with reference to FIGS.

  FIG. 1 is a block diagram showing an embodiment of a drive control apparatus for a vibration actuator of the present invention, and FIG. 2 is a block diagram of a camera equipped with the drive control apparatus of FIG. In FIG. 2, a lens barrel 20 is detachably attached to the camera body 30. The lens barrel 20 includes a photographing lens 21, a drive control device 10, and an ultrasonic motor 7. The ultrasonic motor 7 is driven and controlled by the drive control device 10, and the ultrasonic motor is driven, whereby the photographing lens 21. Are driven in the direction of the optical axis, and focusing is performed.

  As shown in FIG. 1, the drive control apparatus 10 includes an MCU 1, a voltage controlled oscillator (VCO) 2, a phase circuit 3, vibrating body excitation circuits 4 and 5, a high voltage power supply 6, and an encoder 9. The motor 7 is driven and controlled.

  The MCU 1 includes a DA (digital / analog) output unit, and controls the ultrasonic motor 7 and other actuators in the lens barrel 20 in accordance with an indicated rotation speed and rotation direction which are input data (not shown). It is a control part to perform. The MCU 1 determines a target rotation speed in accordance with unillustrated input data, calculates an operation amount from the current rotation speed of the ultrasonic motor 7 determined by the output from the encoder 9 and the determined target rotation speed, Based on this manipulated variable, DA output is performed on the VCO 2. The DA output value is, for example, in the range of 0V to 4V, and the rotational speed of the ultrasonic motor 7 can be changed by the DA output value. Increasing the DA output value increases the rotational speed of the ultrasonic motor, and decreasing the DA output value decreases the rotational speed of the ultrasonic motor. Further, the MCU 1 sends a direction signal for instructing the rotation direction of the ultrasonic motor 7 to the phase circuit 3 and a permission signal for permitting the driving of the ultrasonic motor 7 (motor ON signal in FIGS. 3 and 4). Output.

  The VCO 2 generates a frequency four times the driving frequency of the ultrasonic motor 7 and changes the generated frequency according to the DA output value of the MCU 1. For example, the frequency generated when the DA output value from the MCU 1 is 0 V is a high frequency, and the frequency decreases as the DA output value increases. The frequency range corresponding to the range of the DA output value is set to be a frequency range sufficient for performing speed control of the ultrasonic motor 7 based on the frequency / rotational speed characteristics of the ultrasonic motor 7.

  The phase circuit 3 generates two drive signals Sa and Sb having a frequency equal to the drive frequency of the ultrasonic motor 7 based on the frequency generated by the VCO 2. The phase of the drive signal Sb differs from the drive signal Sa by 90 ° or 270 ° according to the direction signal from the MCU 1. The two drive signals Sa and Sb are input to the vibrator excitation circuits 4 and 5, respectively. The phase circuit 3 does not output the drive signals Sa and Sb unless receiving the permission signal from the MCU 1.

  The vibrating body excitation circuits 4 and 5 amplify the drive signals Sa and Sb from the phase circuit 3 to high voltage voltages that can drive the ultrasonic motor 7 and apply them to the input electrodes 7 a and 7 b of the ultrasonic motor 7.

  The high-voltage power supply 6 is a DCDC converter (not shown), boosts the power supply voltage to a high voltage that can drive the ultrasonic motor 7, and supplies power to the vibrator excitation circuits 4 and 5.

  The ultrasonic motor 7 includes a piezoelectric body that is an electromechanical transducer, and is a vibration actuator that uses the vibration of the piezoelectric body as a driving force, and has two input electrodes 7a and 7b for applying a high-frequency voltage to the piezoelectric body. . When two high-frequency voltages having different phases are applied from the vibrating body excitation circuits 4 and 5 to the input electrodes 7a and 7b, the piezoelectric body is excited to drive a rotor (not shown).

  The encoder 9 outputs a pulse signal for each predetermined rotation amount of the ultrasonic motor 7. The MCU 1 receives and counts the pulse signal from the encoder 9 and calculates the rotational speed of the ultrasonic motor 7 from the number of input pulse signals per predetermined time. That is, in the present embodiment, the rotational speed of the ultrasonic motor 7 is detected by counting with the encoder 9 and the MCU 1.

  FIG. 5 is a diagram showing the relationship (fN characteristics) between the frequency of the drive signal and the rotation speed of the ultrasonic motor. As shown in FIG. 5, in a low-speed rotation region (region indicated by a broken line in FIG. 5 and a rotation speed smaller than the lower limit rotation speed), even if a drive signal having a frequency corresponding to the rotation speed is supplied, the desired rotation is achieved. In some cases, the control state becomes unstable.

  In the drive control device 10 of the present embodiment configured as described above, a drive signal having a frequency corresponding to the number of rotations (rotation speed) within the stable operation region in which the ultrasonic motor 7 is stably rotated is used. Then, the speed is controlled by the on / off control of the drive signal, the rotational speed of the ultrasonic motor 7 at the time of the on control of the drive signal is detected, and the frequency of the drive signal is changed at the next on control, thereby reducing the speed. Stable speed control is performed even in the rotation region. The timing for turning on the drive signal (motor ON) is set every control cycle or every predetermined number of times in the control cycle. Further, the timing for turning off the drive signal (motor OFF) includes the case shown in FIG. 3 and the case shown in FIG.

  In the case shown in FIG. 3, the encoder that receives the permission signal (motor ON signal) from the MCU 1 and supplies the drive signals Sa and Sb from the phase circuit 3 to the ultrasonic motor 7 is turned on every control cycle. When the number of encoder pulses output from 9 reaches a predetermined number, a stop signal (motor OFF signal) is output from the MCU 1 to the phase circuit 3 by interrupt processing, and the drive signals Sa and Sb to the ultrasonic motor 7 are output. Stop supplying. That is, the motor is turned on and off for each control cycle. Further, when the motor of each control cycle is ON, the rotational speed is detected from the time until the number of encoder pulses output from the encoder 9 reaches a predetermined number, and the motor is driven when the motor of the next control cycle is ON based on the detection result. The frequency of the signals Sa and Sb is changed. For example, as a result of detecting the rotation speed, if the frequency is slower than the target rotation speed, the frequency of the drive signals Sa and Sb to be supplied next time is lowered, and if it is faster, the frequency is changed so as to increase. Control to target rotation speed.

  For example, the control cycle is 3 ms, the lower limit rotation speed in the stable operation region of the ultrasonic motor 7 (the lower limit portion in the region indicated by the solid line in FIG. 5) is 5 rpm, and the encoder pulse number per rotation of the ultrasonic motor 7 is 12 With 1,000 pulses, the number of encoder pulses in a control cycle of 3 ms when rotating at 5 rpm is 3 pulses. When the ultrasonic motor 7 is driven at a low speed of 2.5 rpm, if a drive signal having a frequency corresponding to 2.5 rpm is supplied, the frequency in the unstable operation region is used, so that stable speed control is possible. Cannot be done. Therefore, the drive signals Sa and Sb having a frequency corresponding to the lower limit rotation speed of 5 rpm in the stable operation region of the ultrasonic motor 7 are used, and the drive signals Sa and Sb are intermittently supplied to rotate every control cycle. By checking the speed and changing the frequency, stable speed control can be performed and the ultrasonic motor 7 can be driven at a low-speed rotation of 2.5 rpm on average.

  Specifically, driving signals Sa and Sb having a frequency corresponding to 5 rpm are supplied every 3 ms control cycle to drive the ultrasonic motor 7 (motor ON). Then, a stop signal is output from the MCU 1 to the phase circuit 3 by interrupt processing at the timing when the encoder pulse signal of 1.5 pulses is output from the encoder 9 to the MCU 1, and the supply of the drive signals Sa and Sb is stopped and the ultrasonic wave is output. The motor 7 is stopped (motor OFF). As a result, the ultrasonic motor 7 has moved by 1.5 pulses in 3 ms, and the rotational speed of the ultrasonic motor 7 becomes a target of 2.5 rpm as shown in the following equation.

  (1.5 pulses / 3 ms) x 60 seconds x 1000 ms / 12000 pulses = 2.5 rpm

  When the time (motor ON time) in which the ultrasonic motor 7 is moved by 1.5 pulses in the control cycle No. 2 of FIG. 3 is measured, the motor ON time is longer than the target value and slower than the target rotation speed (5 rpm). Yes. Therefore, when the drive signals Sa and Sb are supplied in the next control cycle No3, the DA output value output from the MCU 1 to the VCO 2 is increased, the drive frequency of the drive signals Sa and Sb is lowered, and the rotational speed of the ultrasonic motor 7 is increased. Control.

  In the control cycle No4, since the motor ON time is as the target value, the drive frequencies of the drive signals Sa and Sb supplied in the next control cycle No5 are left unchanged. However, when the time (motor ON time) in which the ultrasonic motor 7 is moved by 1.5 pulses in the control cycle No. 5 is measured, the motor ON time is further increased and is further slower than the target rotation speed. Therefore, when the drive signals Sa and Sb are supplied in the next control cycle No6, the DA output value is further increased, the drive frequency of the drive signals Sa and Sb is further lowered, and the rotational speed of the ultrasonic motor 7 is further controlled.

  When the time (motor ON time) when the ultrasonic motor 7 is moved by 1.5 pulses in the control cycle No7 is measured, the motor ON time is short this time, which is faster than the target rotation speed. Therefore, when the drive signals Sa and Sb are supplied in the next control cycle No8, the DA output value is lowered to increase the drive frequency of the drive signals Sa and Sb, and the rotation speed of the ultrasonic motor 7 is controlled to be slow.

  In this way, by measuring the supply time (motor ON time) of the drive signals Sa and Sb to the ultrasonic motor 7 for each control cycle, it is possible to detect how many rpm the rotation frequency corresponds to the drive frequency at that time. Is possible. Then, it is determined whether or not the driving frequency is an appropriate value from the detected number of rotations, and the frequency of the driving signals Sa and Sb is changed in the next control cycle, so that even in the low speed rotation region. It becomes possible to stably control the rotational speed of the ultrasonic motor 7.

  In the case shown in FIG. 4, the motors are not turned on and off in each control cycle as in the case shown in FIG. 3, but the drive signals Sa and Sb are supplied every predetermined control cycle to turn on the motor. In other control cycles, the motor for stopping the supply of the drive signals Sa and Sb is turned off.

  For example, the motor is turned on in control cycle No1, and the motor is turned off in the following three control cycles (control cycles No2, No3, and No4). Then, the motor is turned on again in the control cycle No5, and the motor is turned off in the next three control cycles (control cycles No6, No7, No8). Similar to the case shown in FIG. 3, when the motor is ON (control cycle No. 1), the rotational speed is detected from the number of encoder pulses output from the encoder 9, and the next motor ON (control cycle No. 5) is detected based on this detection result. Sometimes the frequency of the drive signals Sa, Sb is changed. For example, when the rotation speed is slower than the target rotation speed, the frequency of the drive signals Sa and Sb to be supplied next time is lowered, and when it is faster, the frequency is changed so as to average the target rotation. To speed.

  Assuming that the control cycle is the same as that shown in FIG. 3, the lower limit number of rotations of the ultrasonic motor 7 and the number of encoder pulses per rotation of the ultrasonic motor 7, 3 pulses are obtained in 12 ms (4 × 3 ms). It becomes 1.25 rpm from the following formula.

  (3 pulses / 12 ms) × 60 seconds × 1000 ms / 12000 pulses = 1.25 rpm

  When the motor of control cycle No. 1 is ON, 4 pulses are moved although it is originally 3 pulses, which is slightly faster than the target rotational speed. Therefore, in the control cycle No5 when the next motor is ON, the frequencies of the drive signals Sa and Sb to be supplied are changed to be high. As a result, the number of pulses when the motor is ON in the control cycle No. 5 becomes 3, and the ultrasonic motor 7 can be driven at a low-speed rotation of 1.25 rpm on average with stable speed control.

  In the camera 30 (see FIG. 2) in which the ultrasonic motor 7 and the drive control device 10 of the embodiment described above are mounted on the lens barrel 20, the lens 21 is driven at a relatively high speed up to the vicinity of the target position during autofocus. In addition, the lens 21 can be driven from the vicinity of the target position with relatively low speed and stable speed control.

  Further, when the lens 21 is driven in accordance with the movement of the moving subject, the lens 21 can be driven by slow speed and stable speed control in accordance with the slow movement of the subject.

  The drive control device for the vibration actuator of the present invention is not limited to the above-described embodiment. For example, in FIG. 3, the motor is turned on and off in each control cycle, but the motor may be turned on and off in every other control cycle. That is, the motor is turned on and off in the control cycle No1, the motor is turned off in the control cycle No2, and the frequencies of the drive signals Sa and Sb are changed based on the rotation speed detected when the motor is turned on in the control cycle No1. The motor may be turned ON / OFF within the control cycle No3.

  In FIG. 4, for example, the motor may be turned on or off in every other control cycle. That is, the motor is turned on in the control cycle No1, the motor is turned off in the control cycle No2, the frequency of the drive signals Sa and Sb is changed based on the rotational speed detected when the motor is turned on in the control cycle No1, and the control cycle No3 The motor may be turned on.

  Moreover, although the case where the drive control apparatus of the vibration actuator of the present invention is applied to the lens barrel 20 and the camera 30 is shown, the present invention is not limited to this.

It is a block diagram showing one embodiment of a drive control device of a vibration actuator of the present invention. FIG. 2 is a schematic side view in which a lens barrel equipped with the drive control device shown in FIG. 1 and a camera equipped with the lens barrel are partially cut away. It is explanatory drawing explaining the control content of the drive control apparatus of FIG. It is explanatory drawing explaining another control content of the drive control apparatus of FIG. It is a graph which shows the relationship between the rotation speed (rpm) of an ultrasonic motor, and the frequency (kHz) of the drive signal supplied.

Explanation of symbols

1 MCU
2 VCO
3 Phase circuits 4 and 5 Vibrating body excitation circuit 6 High voltage power supply 7 Ultrasonic motor (vibration actuator)
9 Encoder (pulse signal output part)
DESCRIPTION OF SYMBOLS 10 Drive control apparatus 20 Lens barrel 21 Lens 30 Camera

Claims (8)

A drive signal control unit for controlling switching between an on state for outputting a drive signal of a frequency in the vibration actuator and an off state for stopping the output;
A speed detector for detecting a driving speed of the vibration actuator;
A frequency changing unit that changes the frequency of the drive signal in a later ON state based on the detection result of the speed detection unit in the ON state;
A drive control device for a vibration actuator, comprising: In the drive control apparatus of the vibration actuator according to claim 1,
The drive control device for a vibration actuator, wherein the frequency of the drive signal is a frequency corresponding to a drive speed within a stable operation region of the vibration actuator. In the drive control apparatus of the vibration actuator according to claim 1 or 2,
The drive control device for a vibration actuator, wherein the drive signal control unit synchronizes the timing of turning on with a predetermined cycle. In the drive control apparatus of the vibration actuator according to claim 3,
The drive control device for a vibration actuator, wherein the drive signal control unit synchronizes the timing of turning off with a predetermined cycle. In the drive control apparatus of the vibration actuator of any one of Claim 1 to 4,
The speed detection unit includes a pulse signal output unit that outputs a pulse signal according to the driving amount of the vibration actuator,
A drive control device for a vibration actuator, wherein the drive speed of the vibration actuator is detected from the number of pulse signals output from the pulse signal output unit in the on state. In the drive control apparatus of the vibration actuator of any one of Claim 1 to 3,
A pulse signal output unit that outputs a pulse signal according to the drive amount of the vibration actuator,
The drive control device for a vibration actuator, wherein the drive signal control unit switches to the off state when the number of pulse signals output from the pulse signal output unit in the on state reaches a predetermined number. The vibration actuator drive control device according to any one of claims 1 to 6,
A vibration actuator driven and controlled by the drive control device;
A lens driven by the vibration actuator;
A lens barrel characterized by comprising: The vibration actuator drive control device according to any one of claims 1 to 6,
A vibration actuator driven and controlled by the drive control device;
A lens driven by the vibration actuator;
A camera characterized by comprising

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