JP2006081290A - Self-oscillation circuit and driving device using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a driving device capable of constantly driving a movable body at high speed at driving voltage of an optimum frequency even when the resonance frequency of an electromechanical transducing element is varied due to fluctuation in ambient temperature, variation in shape in mass production, or the like. <P>SOLUTION: A self-oscillation circuit includes: multiple electromechanical transducing elements 42 and 44 connected in parallel; a current detector circuit 52 that detects as voltage the currents passed through the electromechanical transducing elements 42 and 44; an offset circuit 54 that applies offset voltage to output voltage from the current detector circuit 52; and an amplifier circuit 56 that amplifies output voltage from the offset circuit 54 and applies it to the electromechanical transducing elements. The self-oscillation circuit oscillates at the primary resonance frequency of a vibration system including at least the electromechanical transducing elements 42 and 44. The driving device is driven with this self-oscillation circuit. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a self-excited oscillation circuit and a drive device using the same. More specifically, the driving device uses an electromechanical transducer such as a piezoelectric element, and is suitable for, for example, lens driving or precision stage driving.

  Conventionally, a drive device using a piezoelectric element is known as shown in FIG. FIG. 10A is an exploded perspective view of the drive device 10, and FIG. 10B is an assembly view thereof.

  The driving device 10 includes a piezoelectric element 12 as an electromechanical conversion element. The piezoelectric element 12 is a stacked piezoelectric element configured by stacking a large number of rectangular thin piezoelectric plates. Electrodes (only one shown) 14 are respectively formed on both side surfaces of the piezoelectric element 12, and each electrode 14 is connected to a drive circuit (not shown) via conductors 16 and 16.

  For example, a cylindrical weight 18 is fixed to one end of the piezoelectric element 12 in the expansion / contraction direction (longitudinal direction). For example, a round bar-shaped drive friction member 20 is fixed to the other end of the piezoelectric element 12 in the expansion / contraction direction.

  A moving body 22 is provided around the driving friction member 20 so as to be movable along the driving friction member 20. A driving object such as a lens is attached to the moving body 22.

  The moving body 22 has a slider 24. A groove 26 having a substantially semicircular cross section is formed in the slider 24, and the drive friction member 20 is fitted in the groove 26. A rectangular plate-like friction member 28 is disposed on the driving friction member 20 fitted to the slider 24. The friction member 28 is urged against the driving friction member 20 by a leaf spring 32 fixed to the slider 24 with two screws 30. Due to the biasing force of the leaf spring 32, the moving body 22 is engaged with the drive friction member 20 with a predetermined friction force.

  Next, the operation of the driving device 10 will be described with reference to FIG. FIG. 11 (a) schematically shows each state of the driving device 10, and FIG. 11 (b) shows the displacement of the piezoelectric element 12 in relation to time.

  When a pulsed drive voltage having a gradual rise and a steep fall is applied from the drive circuit to the piezoelectric element 12, the piezoelectric element 12 is in a period a in FIG. 11 when corresponding to the rise of the drive voltage. While extending relatively slowly, the piezoelectric element 12 contracts relatively rapidly and returns to the initial state as shown in period b in FIG. 11 when it corresponds to the falling portion of the drive voltage. In this case, during the period a, the moving body 22 moves in the direction indicated by the arrow A in FIG. 10B (ie, piezoelectric) in accordance with the relatively slow displacement of the driving friction member 20 caused by the piezoelectric element 12 slowly extending. It moves in a direction away from the element 12, hereinafter referred to as a feeding direction). On the other hand, in the period b, the piezoelectric element 12 is displaced relatively quickly due to the rapid contraction of the piezoelectric element 12. At this time, the inertial force of the moving body 22 overcomes the frictional force between the moving body 22 and the driving friction member 20, so that the moving body 22 slides on the driving friction member 20 and remains in that position (or driving). It moves to the piezoelectric element 12 side by a distance smaller than the displacement amount of the friction member 20). By repeating such periods a and b alternately, the drive friction member 20 vibrates with a sawtooth displacement as shown in FIG. 11B, whereby the moving body 22 moves along the drive friction member 20. To move in the feeding direction.

  On the other hand, when the moving body 22 is moved in the direction of arrow B in FIG. 10B (that is, the direction approaching the piezoelectric element 12, this direction is hereinafter referred to as the return direction), the rising portion is abrupt and the falling portion is gentle. A pulsed drive voltage is applied to the piezoelectric element 12 from the drive circuit. The principle of movement of the moving body 22 at this time is opposite to that described above. That is, when the piezoelectric element 12 rapidly expands, the moving body 22 slides on the driving friction member 20 and stays at that position, and when the piezoelectric element 12 slowly contracts, the moving body 22 is displaced by the driving friction member 20. Move with it. By repeating this, the moving body 22 moves in the return direction along the drive friction member 20.

  Further, Patent Document 1 below discloses a drive device using a plurality of piezoelectric elements connected in series instead of the piezoelectric element 12. In this drive device, by applying varying voltages having different symmetrical waveforms to each piezoelectric element, a sawtooth-like displacement is obtained for the connecting body of the piezoelectric elements and the driving friction member 20, and the moving body 22 is driven. ing.

  However, the driving device 10 and the driving device of Patent Document 1 have a problem that the frequency of the driving voltage cannot be increased and the driving speed of the moving body 20 becomes slow. Therefore, the driving friction member 20 and the moving body 22 are always in a relatively slippery state so that they can be driven even when the frequency of the driving voltage is increased, and the movement is caused by the difference in sliding amount between the expansion and contraction of the piezoelectric element. A method of driving the body 22 has been proposed. However, there is a demand for driving at a higher speed than driving using this method.

  Here, when the piezoelectric element is driven with an AC voltage, it is most efficient to drive at the resonance frequency. In the driving method disclosed in Patent Document 1, the higher-order resonance is smaller or absent compared to the primary resonance. Therefore, even if driving is performed at the resonance frequency and the displacement waveform of the driving friction member 20 is increased, the waveform becomes close to a sine wave, and the moving body 22 cannot be driven efficiently. In addition, since the resonance frequency of the piezoelectric element changes due to environmental temperature fluctuations, shape variations, etc., it is necessary to correct optimum driving conditions using a temperature sensor, speed sensor, etc., in order to always achieve stable high-speed driving. .

Japanese Patent Laid-Open No. 11-41953

  Therefore, the present invention provides a drive device that can efficiently and rapidly drive a moving body with a drive voltage having an optimum frequency even when the resonance frequency of the electromechanical transducer changes due to environmental temperature fluctuations or shape variations due to mass production. In addition, it is an object to provide a self-excited oscillation circuit that is preferably used for that purpose.

In order to solve the above problems, a self-excited oscillation circuit of the present invention includes one or a plurality of electromechanical transducers connected in parallel,
A current detection circuit for detecting a current flowing through the electromechanical transducer as a voltage;
An offset circuit for adding an offset voltage to the output voltage from the current detection circuit;
An amplification circuit that amplifies the output voltage from the offset circuit and applies the amplified voltage to the electromechanical transducer,
It oscillates at a primary resonance frequency of a vibration system including at least the electromechanical transducer.

In the self-excited oscillation circuit of the present invention, the waveform of the output voltage from the amplifier circuit is a rectangular wave,
The duty ratio of the output voltage waveform of the amplifier circuit may change depending on the offset voltage of the offset circuit.

Further, the drive device of the present invention comprises a drive circuit comprising the self-excited oscillation circuit,
A vibration generating member comprising two electromechanical transducer elements of the drive circuit and a first weight sandwiched between the electromechanical transducer elements;
A second weight fixed to one end of the vibration generating member;
A drive friction member fixed to the other end of the vibration generating member;
A movable body engaged with a predetermined frictional force around the drive friction member,
A drive voltage is applied to the electromechanical transducer by the drive circuit so as to displace the drive friction member in a sawtooth shape and move the movable body along the drive friction member. .

  In the driving device of the present invention, even if at least one of the moving speed and the moving direction of the moving body is changed by changing the duty ratio of the output voltage waveform of the amplifier circuit by changing the offset voltage of the offset circuit. Good.

  In the driving device of the present invention, an aberration correction lens is attached to the movable body, and the aberration correction lens is driven in the optical head device so as to correct the aberration of the light spot in the recording layer of the recording medium. Good. The aberration here means an aberration generated when a light spot converged on a target recording layer passes through a cover layer or another recording layer of the recording medium.

  According to the self-excited oscillation circuit of the present invention, even when the primary resonance frequency of the electromechanical transducer changes due to environmental temperature fluctuation or shape variation, the vibration system including the electromechanical transducer always follows the change. Since oscillation occurs at the primary resonance frequency, the electromechanical transducer can be driven stably and efficiently.

  Further, according to the driving device of the present invention using the self-excited oscillation circuit, the vibration system including the electromechanical transducer can always be driven at the primary resonance frequency regardless of environmental temperature fluctuation, shape variation, and the like. High-speed driving of the moving body can be realized stably.

Embodiments of the present invention will be described below with reference to the accompanying drawings.
FIG. 1A is an exploded perspective view of a drive device 40 according to an embodiment of the present invention, and FIG. The drive device 40 has substantially the same configuration as the drive device 10 described as the background art. The difference is that, instead of the piezoelectric element 12 of the driving device 10, two piezoelectric elements 42 and 44 that are connected with another disk-shaped weight (first weight) 46 smaller than the weight 18 interposed therebetween. Is provided. The two piezoelectric elements 42 and 44 are connected in parallel to the drive circuit 50 described later via the conducting wire 16. The two piezoelectric elements 42 and 44 and the weight 46 constitute a vibration generating member 48.

  The other configuration is the same as that of the driving device 10. That is, for example, a columnar weight (second weight) 18 is fixed to one end of the vibration generating member 48 in the expansion / contraction direction (longitudinal direction). For example, a round bar-shaped drive friction member 20 is fixed to the other end of the vibration generating member 48 in the expansion / contraction direction.

  A moving body 22 is provided around the driving friction member 20 so as to be movable along the driving friction member 20. A driving object such as a lens is attached to the moving body 22.

  The moving body 22 has a slider 24. A groove 26 having a substantially semicircular cross section is formed in the slider 24, and the drive friction member 20 is fitted in the groove 26. A rectangular plate-like friction member 28 is disposed on the driving friction member 20 fitted to the slider 24. The friction member 28 is urged against the driving friction member 20 by a leaf spring 32 fixed to the slider 24 with two screws 30. Due to the biasing force of the leaf spring 32, the moving body 22 is engaged with the drive friction member 20 with a predetermined friction force.

  The urging means for urging the friction member 28 to the drive friction member 20 is not limited to a leaf spring, but may be an elastic member such as a coil spring or rubber.

  FIG. 2 shows the drive circuit 50 of the drive device 40. The drive circuit 50 is a self-excited oscillation circuit composed of three circuit blocks: a current detection circuit 52, an offset circuit 54, and an amplification circuit 56. The current detection circuit 52 includes a current detection resistor 52a that detects a current flowing through the piezoelectric elements 42 and 44 as a voltage. The current detection circuit 52 includes four operational amplifiers 52b connected in series. These operational amplifiers 52b function as a fourth-order high-pass filter with a cutoff frequency of, for example, 30 kHz and a fourth-order low-pass filter with a cutoff frequency of, for example, 300 kHz, and cut and phase adjustment of an extra voltage signal.

  The offset circuit 54 includes an offset power supply 54a and an operational amplifier 54b, and adds a DC offset voltage to the output voltage from the current detection circuit 52. The offset voltage value by the offset power supply 54a is variable.

  The amplifier circuit 56 includes an operational amplifier 56a and two Zener diodes 56b connected in parallel thereto, and amplifies the output voltage from the offset circuit 54 and applies it to the piezoelectric elements 42 and 44.

  The amplifying circuit 56 outputs a substantially rectangular wave pulsed driving voltage by applying a limiter to the output voltage from the offset circuit 54 by two Zener diodes 56b. Further, by changing the offset voltage value added by the offset circuit 54, the duty ratio of the output voltage waveform of the amplifier circuit 56 is changed.

  In the present embodiment, the drive voltage is amplified by the amplifier circuit 56. However, since the current detection circuit 52 and the offset circuit 54 also have operational amplifiers, the voltage signal is output by the current detection circuit 52 and the offset circuit 54. May be amplified.

  FIG. 3 shows the transmission characteristics of the driving voltage of the driving device 40 and the displacement of the driving friction member 20. As is apparent from FIG. 3, in the drive device 40 of the present embodiment, the displacement gain (that is, the vibration amplitude) of the drive friction member 20 becomes maximum at about 103 kHz, for example. The frequency of about 103 kHz is the primary resonance frequency of the vibration system including the piezoelectric elements 42 and 44, the weight 46, and the driving friction member 20, and is the frequency at which the moving body 22 can be driven most efficiently and at high speed.

  On the other hand, FIG. 4 shows a round-trip transfer characteristic of the drive circuit 50. The oscillation frequency is determined by the condition that the gain is 0 dB or more and the phase is 0 deg. The drive circuit 50 has a gain of 0 dB and a phase of 0 deg. Oscillates. That is, this oscillation frequency always matches the primary resonance frequency of the vibration system including the piezoelectric elements 42 and 44, the weight 46, and the drive friction member 20. Therefore, in the driving device 40, even when the resonance frequency of the piezoelectric elements 42 and 44 changes due to environmental temperature fluctuations, shape variations due to mass production, etc., the piezoelectric device always uses a driving voltage having a frequency that matches the primary resonance frequency of the vibration system. The elements 42 and 44 can be driven, and stable high-speed driving of the moving body 22 can be realized.

  The drive circuit 50 is preferably used not only when driving a plurality of piezoelectric elements connected in parallel, but also when driving one piezoelectric element.

  FIG. 5 shows an output voltage waveform of the amplifier circuit 56 when the offset voltage value by the offset circuit 54 is changed to −0.4V, 0V, and + 0.4V. In either case, the pulse voltage is a rectangular wave with a frequency of 103 kHz. The duty ratio is 0.33 when the offset voltage value is −0.4 V, the duty ratio is 0.5 when the offset voltage value is 0 V, and the offset voltage value is +0.4 V. In this case, the duty ratio is 0.66. Thus, by making the offset voltage value by the offset circuit 54 variable, the duty ratio of the output voltage waveform from the amplifier circuit 56 can be changed.

  FIG. 6 shows the displacement of the drive friction member 20 when the drive voltage (offset voltage +0.4 V, frequency 103 kHz, duty ratio 0.66) shown in FIG. 5C is applied to the piezoelectric elements 42 and 44. . This displacement waveform has a substantially saw-tooth shape that repeats a relatively fast feed direction displacement and a relatively slow return direction displacement, so that the moving body 22 can be driven in the return direction. In this case, since the amplitude becomes very large, the moving body 22 always slides with respect to the drive friction member 20, but the moving body 22 is moved in the return direction due to the difference in the amount of slipping between expansion and contraction. It becomes possible to make it.

  On the other hand, when the drive voltage (offset voltage −0.4 V, frequency 103 kHz, duty ratio 0.33) shown in FIG. 5A is applied to the piezoelectric elements 42 and 44, the drive voltage is included in the rectangular wave. Since the phase of the secondary component to be shifted is 180 degrees with respect to the case where the duty ratio is 0.66, the displacement waveform of the drive friction member 20 has a substantially saw-tooth shape having an inclination opposite to that shown in FIG. That is, the displacement waveform of the drive friction member 20 in this case has a substantially serrated shape that repeats a relatively slow displacement in the feeding direction and a relatively fast displacement in the return direction. Thereby, the moving body 22 can be driven in the feeding direction. Thus, the moving direction of the moving body 22 can be changed by changing the duty ratio of the output voltage from the amplifier circuit 56.

  FIG. 7 shows the relationship between the duty ratio of the drive voltage and the moving speed of the moving body 22. As shown in FIG. 7, the moving body 22 has the highest speed near the duty ratios of 0.33 and 0.66, and the moving body 22 does not move near the duty ratio of 0.5. Thus, by changing the duty ratio of the output voltage from the amplifier circuit 56, the moving speed of the moving body 22 can also be changed.

  FIG. 8 shows the speed of the moving body 22 when the environmental temperature is changed. Here, the normal driving means that the driving is performed with a rectangular pulse driving voltage having a frequency of 103 kHz and a duty ratio of 0.66 regardless of the environmental temperature. As shown in FIG. 8, in the case of normal driving, when the environmental temperature changes, the resonance frequency of the vibration system including the piezoelectric elements 42 and 44, the weight 46, and the driving friction member 20 also changes. The frequency deviates from the resonance frequency of the vibration system, and the speed of the moving body 22 decreases. On the other hand, in the case of driving by the self-excited oscillation circuit as in the driving device 40 of the present embodiment, the driving circuit 50 always keeps the same even if the resonance frequency of the vibration system changes with the environmental temperature fluctuation. It can be seen that since the oscillation occurs at the resonance frequency, there is almost no change in the speed of the moving body 22 and stable high-speed driving can be maintained.

  Next, an example in which the driving device 40 is applied to an optical head device will be described with reference to FIG. One end of a lens ball frame 62 holding the aberration correction lens 60 is attached to the moving body 22 of the driving device 40. The other end of the lens ball frame 62 is engaged with the guide shaft 64, thereby restricting the lens ball frame 62 from rotating around the drive friction member 20. In this optical head, the laser light L emitted from the laser device 66 is irradiated as a light spot on the front recording layer 102 or the rear recording layer 104 of the recording medium 100 through the aberration correction lens 60 and the objective lens 68. It has become.

  In the recording medium 100 having a plurality of recording layers such as a DVD, since the distance between the recording layers 102 and 104 is several tens of μm, the aberration correction lens 60 is driven substantially in parallel with the laser beam L, and each recording layer It is necessary to correct the spherical aberration so that the light spot is aimed at a position suitable for 102 and 104. Although it is preferable that the movement time of the aberration correction lens 60 for spherical aberration correction is short, for example, when the conventional driving device 10 is used to drive the aberration correction lens, the driving speed is greatly reduced due to a change in environmental temperature. Even if aberration correction is performed in a state where the drive friction member 20 and the moving body 22 are always relatively sliding, it takes time to correct the aberration. On the other hand, as described above, since the driving device 40 can drive the aberration correction lens 60 at high speed regardless of the change in the environmental temperature, the spherical aberration can be corrected in a short time. In the case of using a three-wavelength laser, the moving distance of the aberration correction lens 60 becomes long, so that the driving device 40 of this embodiment is particularly effective.

  The present invention is not limited to an element-fixing type driving device that fixes an electromechanical conversion element, but a type that fixes a moving body, a type that fixes a driving friction member, a self-propelled type, etc. The present invention can be widely applied to various types of drive devices using electromechanical transducer elements.

The exploded perspective view and assembly drawing of a drive device. The block diagram of a drive circuit. The graph which shows the transmission characteristic of a drive voltage and a drive friction member displacement. The graph which shows the circuit transfer characteristic of a drive circuit. The figure which shows the drive voltage waveform at the time of changing an offset voltage. FIG. 6 is a displacement waveform diagram of the drive friction member when driven by the drive voltage shown in FIG. The graph which shows the relationship between the duty ratio of a drive voltage, and the moving speed of a moving body. The graph which shows the speed of a moving body when environmental temperature is changed. The figure which shows the example which applied the drive device to the optical head apparatus. The exploded perspective view and assembly drawing of the drive device of a prior art example. Schematic which shows each state of the drive device of a prior art example, and the displacement waveform figure of a piezoelectric element.

Explanation of symbols

18 ... weight (second weight)
20 ... Driving friction member 22 ... Moving body 40 ... Driving device 42 ... Piezoelectric element (electromechanical transducer)
44 ... Piezoelectric element (electromechanical transducer)
46 ... weight (first weight)
48 ... Vibration generating member 50 ... Drive circuit (self-excited oscillation circuit)
52 ... Current detection circuit 54 ... Offset circuit 56 ... Amplifier circuit

Claims (5)

One or a plurality of electromechanical transducers connected in parallel;
A current detection circuit for detecting a current flowing through the electromechanical transducer as a voltage;
An offset circuit for adding an offset voltage to the output voltage from the current detection circuit;
An amplification circuit that amplifies the output voltage from the offset circuit and applies the amplified voltage to the electromechanical transducer,
A self-excited oscillation circuit that oscillates at a primary resonance frequency of a vibration system including at least the electromechanical transducer. The waveform of the output voltage from the amplifier circuit is a rectangular wave,
2. The self-excited oscillation circuit according to claim 1, wherein a duty ratio of an output voltage waveform of the amplifier circuit is changed by an offset voltage of the offset circuit. A drive circuit comprising the self-excited oscillation circuit according to claim 1 or 2,
A vibration generating member comprising two electromechanical transducer elements of the drive circuit and a first weight sandwiched between the electromechanical transducer elements;
A second weight fixed to one end of the vibration generating member;
A drive friction member fixed to the other end of the vibration generating member;
A movable body engaged with a predetermined frictional force around the drive friction member,
A drive device, wherein a drive voltage is applied to the electromechanical conversion element by the drive circuit so as to displace the drive friction member in a sawtooth shape and move the moving body along the drive friction member.   The at least one of the moving speed and the moving direction of the moving body is changed by changing the duty ratio of the output voltage waveform of the amplifier circuit by changing the offset voltage of the offset circuit. The drive device described.   5. The aberration correction lens is attached to the movable body, and the aberration correction lens is driven in an optical head device so as to correct an aberration of a light spot in a recording layer of a recording medium. The drive device described.

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