JP5338146B2 - Drive device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a drive device which requires small power consumption and has small operation sounds. <P>SOLUTION: The drive device includes an electro-mechanical conversion element that expands and contracts when voltage is applied, a vibration member that is reciprocatingly displaced by the expansion and contraction of a piezoelectric element with one end of the vibration member fixed to the electro-mechanical conversion element, a friction engaged member that is friction-engaged with the vibration member, and a drive circuit that applies a periodically fluctuating drive voltage to the piezoelectric element. The drive circuit changes the frequency of the drive voltage within a range higher than a predetermined lower limit frequency and higher than an audible frequency corresponding to the speed for displacing the friction-engaged member, and when the frequency of the drive voltage is the lower limit frequency, the waveform of the drive voltage is changed according to the speed for displacing the friction-engaged member. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a drive device, and more particularly to a drive device using a vibration actuator.

  In a drive device using a vibration type actuator that slides and displaces a friction engagement member that frictionally engages with a vibration member due to periodic vibration of the vibration member, there is a case where it is desired to change the displacement speed (drive speed) of the friction engagement member. is there. For example, when the lens position is constantly adjusted, such as camera shake correction or autofocusing of the imaging apparatus, it is desirable that the drive speed can be adjusted continuously.

  Patent Document 1 describes an invention in which the frequency of the drive voltage is increased in accordance with the output speed of the drive device. Patent Document 2 describes that the actuator is driven with a rectangular wave voltage and the driving speed is adjusted by changing the duty ratio of the rectangular wave voltage. Patent Document 3 describes an invention in which the driving speed is adjusted by outputting three voltages in a predetermined order and increasing or decreasing the output time of the intermediate voltage. Patent Document 4 describes a driving device that is composed of three voltages, changes the waveform by complementarily changing the duration of the intermediate voltage before and after the high voltage (low voltage), and adjusts the driving speed. Yes.

The power consumption of such a driving device is approximately proportional to the frequency of the driving voltage. When the driving speed is adjusted by the waveform of the driving voltage, even if the driving speed is low, the power consumption is not reduced, which is inefficient. On the other hand, when the driving speed is adjusted according to the frequency of the driving voltage, if the driving frequency is lower than 20 kHz, vibration in the audible range is generated and the operation sound is increased.
Japanese Patent Laid-Open No. 11-103583 JP 2001-103772 A JP 2004-80964 A JP 2007-43843 A

  In view of the above problems, it is an object of the present invention to provide a drive device that consumes less power and has less operation sound.

In order to solve the above-mentioned problems, a driving device according to the present invention includes an electromechanical transducer that expands and contracts when a voltage is applied, and one end fixed to the electromechanical transducer, and is reciprocally displaced by the expansion and contraction of the electromechanical transducer. A vibration engagement member that frictionally engages the vibration member, and a drive circuit that applies a periodically varying drive voltage to the electromechanical conversion element, the drive circuit including the friction engagement member. When the speed at which the joint member is displaced is equal to or higher than the displacement speed of the friction engagement member when the frequency of the drive voltage is a predetermined lower limit frequency higher than the audible frequency, the speed at which the friction engagement member is displaced depending on the frequency of the drive voltage is varied within the range of above the lower limit frequency, the speed for displacing the frictional engagement member, the friction when the frequency of the drive voltage is the lower limit frequency It is lower than the displacement speed of the engagement member, while maintaining the frequency of the drive voltage to the lower limit frequency, depending on the speed for displacing the frictional engagement member, and one that changes the waveform of the driving voltage To do.

  According to this configuration, since the frequency of the drive voltage is changed in the high speed region, the maximum speed can be obtained by increasing the frequency of the drive voltage to a frequency at which the actuator can respond. In addition, since the power consumption is substantially proportional to the drive frequency, the power consumption is reduced in the low speed range, and the drive efficiency is high. In addition, the driving frequency is higher than the audible range, and when driving at a very low speed, the driving frequency is kept at the upper limit frequency that is higher than the audible frequency and the waveform is changed. In addition, power consumption can be kept to a minimum.

  In the driving device of the present invention, the driving voltage may output three predetermined voltages in a predetermined order.

  According to this structure, a drive circuit is comprised with a well-known bridge circuit, and a drive voltage can be easily adjusted by microcomputer control.

  In the driving device of the present invention, the driving circuit may change the frequency of the driving voltage by changing a time for outputting an intermediate voltage among the three predetermined voltages.

  According to this configuration, frequency control is easy.

  In the driving device of the present invention, the driving circuit may include an output time of an intermediate voltage before the highest voltage and an output time of an intermediate voltage before the lowest voltage among the three predetermined voltages. Further, the waveform of the drive voltage may be changed by changing it complementarily while maintaining the total time.

  According to this configuration, the driving speed can be adjusted easily and accurately in the low speed range.

  According to the present invention, since speed control is performed according to the frequency of the drive voltage in the high speed range, power consumption can be minimized. In the low speed range, the frequency of the drive voltage is kept above the upper limit of the audible range, so that no noise is generated.

Embodiments of the present invention will now be described with reference to the drawings.
In FIG. 1, the structure of the drive device 1 which is embodiment of this invention is shown. The drive device 1 includes a piezoelectric actuator 2, a drive circuit 3 that applies a periodic drive voltage to the piezoelectric actuator 2, and a control device 4 that controls the operation of the drive circuit 3 to determine the waveform and frequency of the drive voltage. .

  The piezoelectric actuator 2 has a piezoelectric element (electromechanical conversion element) 5 that expands and contracts according to an input drive voltage, a weight 6 fixed to one end of the piezoelectric element 5, and one end fixed to the other end of the piezoelectric element 5. The shaft-shaped vibration member 7 and the friction engagement member 8 engaged with the vibration member 7 by a frictional force are included. The vibration member 7 is reciprocated in the axial direction by the expansion and contraction of the piezoelectric element 5. The friction engagement member 8 moves together with the vibration member 7 when the vibration member 7 moves slowly. However, when the vibration member 7 moves steeply, the friction engagement member 8 slides and displaces with respect to the vibration member 7 due to inertial force.

  FIG. 2 shows details of the drive circuit 3. The drive circuit 3 is a known bridge circuit having four switching elements 9, 10, 11, and 12. By connecting the pair of electrodes of the piezoelectric element 5 to the power supply 13 of the voltage Vd (V) or the ground, respectively. A voltage of ± Vd (V) can be applied to the piezoelectric element 5. The drive circuit 3 can also apply 0 (V) to the piezoelectric element 5 by short-circuiting both electrodes of the piezoelectric element 5. That is, the drive circuit 3 can apply three types of voltages, + Vd (V), 0 (V), and −Vd (V), to the piezoelectric element 5.

  FIG. 3 shows the waveform of the drive voltage output from the drive circuit 3. In the drive device 1, the drive waveform for moving the friction engagement member 7 earliest is a rectangular wave having a wave height of 2 Vd (V), and the frequency has the largest gain with respect to the sine wave of the vibration member 7 of the piezoelectric actuator 2. The resonance frequency (for example, 500 kHz) is about 0.7 times (350 kHz = period 1/350 ms), and the duty ratio is 0.3.

In the driving device 1, when the driving speed (moving speed of the frictional engagement member 7) is decreased, + Vd (V) is changed from the state in which −Vd (V) is applied to the piezoelectric element 5 in the fastest driving voltage waveform. before applying by applying the 0 (V), to lower the frequency of the driving voltage. By reducing the frequency of the drive voltage, the number of times that the friction engagement member 8 slides relative to the vibration member 7 per time is reduced, and as a result, the displacement speed of the friction engagement member 8 decreases.

  The drive circuit 3 reduces the frequency of the drive voltage to a predetermined upper limit frequency (for example, 22 kHz) slightly higher than the upper limit of the human audible range as the drive speed decreases (medium speed in the figure). When reducing the speed, a voltage of 0 (V) is output before applying −Vd (V) after applying + Vd (V) to the piezoelectric element 5 while maintaining the driving frequency at the upper limit frequency. . At this time, the total time for outputting 0 (V) per cycle is kept constant, and the voltage output time T1 of 0 (V) before outputting + Vd (V) and -Vd (V) are output. The voltage output time T2 of 0 (V) before the change is complementarily changed. At this time, the time for outputting + Vd (V) and the time for outputting -Vd (V) also change complementarily.

  When the output time T1 of 0 (V) before outputting −Vd (V) is equal to the output time T2 of 0 (V) before outputting + Vd (V), the drive voltage becomes + Vd ( The waveform is changed so that both the output time of V) and the output time of -Vd (V) are equal. At this time, since the transition waveform from −Vd (V) to + Vd (V) and the transition waveform from + Vd (V) to −Vd (V) are symmetric, the expansion and contraction of the piezoelectric element 5 are the same. Become speed. For this reason, the amount by which the friction engagement member 8 slides relative to the vibration member 7 is the same in the extending direction and the retracting direction with respect to the piezoelectric element 5, and the driving speed of the driving device 1 becomes zero.

  Further, when the output times T1 and T2 of 0 (V) and the output time of ± Vd (V) are changed complementarily, the time T1 until the change from −Vd (V) to + Vd (V) , + Vd (V) to −Vd (V), the magnitude relationship with time T2 is changed, and the driving speed of the driving device 1 increases in the negative direction (reverse direction).

  When the driving speed in the negative direction increases and the output time T1 of 0 (V) before outputting + Vd (V) becomes zero (medium speed in the negative direction in the figure), the driving circuit 3 further increases the driving speed. Therefore, the output time T2 of 0 (V) is shortened, and the drive frequency is made higher than the upper limit frequency (22 kHz). When the output time T2 of 0 (V) becomes zero, the driving frequency reaches 350 kHz, and the driving device 1 has the same speed as the highest speed in the positive direction and the driving direction is opposite, that is, the driving speed is the highest speed that is negative. Become.

  In the driving device 1, the frequency of the driving voltage does not become lower than the upper limit frequency (22 kHz) higher than the audible range. Therefore, the mechanical movement of the piezoelectric actuator 2 by this driving voltage includes only a frequency component higher than the audible range. For this reason, the driving device 1 does not generate vibration that can be heard as driving sound by human ears, and the driving sound is low.

  Further, since the driving device 1 changes the driving frequency in accordance with the driving speed in the high speed range, the power consumption thereof increases or decreases substantially in proportion to the driving speed. That is, in a frequency range higher than the upper limit frequency, energy consumption can be suppressed according to the driving speed.

  In the above embodiment, the piezoelectric element 5 is driven by the drive circuit 3 that applies three kinds of voltages in a predetermined order. However, in the present invention, a drive circuit that can output drive voltages having different waveforms may be used. . For example, as shown in FIG. 4, the voltage of + Vd (V) and the voltage of -Vd (V) are linearly transitioned, and this transition time is the same as the output time T1 and T2 of 0 (V) described above. It may be changed to.

  In the present invention, the drive voltage waveform may be changed at a predetermined frequency above the audible range when the drive speed is low, and the drive frequency may be changed when the drive speed is high. Not limited to.

The schematic block diagram of the drive device of one Embodiment of this invention. The circuit diagram of the drive circuit of FIG. The figure which shows the drive voltage waveform of the drive device of FIG. The figure which shows the drive voltage waveform of the alternative of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Drive apparatus 2 ... Piezoelectric actuator 3 ... Drive circuit 4 ... Control apparatus 5 ... Piezoelectric element (electromechanical conversion element)
6 ... Weight 7 ... Vibration member 8 ... Friction engagement member

Claims (4)

An electromechanical transducer that expands and contracts when a voltage is applied; a vibration member that has one end fixed to the electromechanical transducer and reciprocally displaces by the expansion and contraction of the electromechanical transducer; A combination member, and a drive circuit that applies a periodically varying drive voltage to the electromechanical transducer,
The drive circuit is
When the speed at which the friction engagement member is displaced is equal to or higher than the displacement speed of the friction engagement member when the frequency of the drive voltage is a predetermined lower limit frequency higher than the audible frequency, the friction engagement member is depending on the speed of displacing, by changing the frequency of the drive voltage in a range of more than the lower limit frequency,
When the speed of displacing the friction engagement member is lower than the displacement speed of the friction engagement member when the frequency of the drive voltage is the lower limit frequency, the frequency of the drive voltage is maintained at the lower limit frequency. and while, depending on the speed for displacing the frictional engagement member, the drive apparatus characterized by varying the waveform of the driving voltage.   2. The driving apparatus according to claim 1, wherein the driving voltage outputs three predetermined voltages in a predetermined order.   The drive device according to claim 2, wherein the drive circuit changes a frequency of the drive voltage by changing a time for outputting an intermediate voltage among the three predetermined voltages.   The drive circuit complements the output time of the intermediate voltage before the highest voltage and the output time of the intermediate voltage before the lowest voltage among the three predetermined voltages while maintaining the total time. 4. The driving apparatus according to claim 2, wherein the waveform of the driving voltage is changed by changing the driving voltage.

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