JP2000298963A - Piezoelectric element driving device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a highly accurate and highly reliable device being indepen dent of variation of conditions such as environment. an enezgizing time, or the like, by calculating adjustment gain for reducing deviation from an ideal value based on variation of a ration of capacitance of a piezoelectric element to capacitance of a capacitor for detecting electric charges for gain in which a control signal is an input and detected voltage is output, and compensating variation of loop gain. SOLUTION: A digital compensator 310 of a CPU 300 performs compensation operation required for positioning making a position information signal 301 as an input, and outputs a coarse control signal 401 and a control signal 311. A gain measuring section 340 obtains an adjustment gain value 341 from the measuring signal 331 and a piezoelectric element voltage signal 422, and inputs it to a gain adjustment section 420. In the gain adjustment section 420, an inputted control signal 311 is multiplied by a gain adiustment value 341, and the result is outputted as a gain adjustment signal 321. This gain adjustment signal 321 is switched by a switch 350, and inputted to an electric charge control type drivig circuit as a tremor control signal 411.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a piezoelectric element driving apparatus, and more particularly to a piezoelectric element driving apparatus suitable for use in a magnetic head positioning circuit of a magnetic disk drive.

[0002]

2. Description of the Related Art In order to increase the recording density of a magnetic disk drive, a magnetic head is precisely positioned by a coarse actuator using a voice coil motor (hereinafter referred to as VCM) and a fine actuator using a piezoelectric element. A step servo system is being studied. The piezoelectric element is a material in which the crystal expands and contracts when placed in an electric field, and ultraprecision positioning is performed by utilizing such an effect. FIG. 5 shows a voltage-controlled driving circuit for a piezoelectric element.
And resistors 902 and 903 constitute an inverting amplifier. A voltage proportional to the input signal is applied to the piezoelectric element 904, and the displacement of the piezoelectric element is controlled.

In the above configuration, the piezoelectric element is controlled by the applied voltage, and the piezoelectric element generally has a hysteresis characteristic as shown in FIG. 7 by the applied voltage. Therefore, when a feedback system for head positioning is formed, this hysteresis characteristic appears as a change in loop gain.

On the other hand, for example, Japanese Patent Application Laid-Open No. Hei 9-18246
It is known that, as described in Japanese Patent Publication No. 6, when the piezoelectric element is controlled by electric charge, the hysteresis characteristic is reduced as shown in FIG. FIG. 4 shows an example of a charge control type driving circuit. In FIG. 4, a charge detecting capacitor 102 is inserted in series with a piezoelectric
01 and the charge of the charge detection capacitor 102 are equal.

The voltage across the charge detection capacitor 102 is
The signal is fed back to the operational amplifier 120 by a differential amplifier including the operational amplifier 110 and the resistors 111 to 114, and a charge proportional to the input signal Vin of the operational amplifier 120 is supplied to the piezoelectric element 101. With this configuration, in the piezoelectric element, a characteristic with a small hysteresis as shown in FIG. 6 is obtained, so that the fluctuation of the loop gain is suppressed and the positioning accuracy of the head is prevented from deteriorating.

[0006]

The above-described conventional piezoelectric element driving device has the following problems. That is, in the above configuration, the resistor 122 / the resistor 12
The ratio of 1 is A, and the resistor 113 / resistor 111 (= resistor 1
14 / resistor 112) as B, the input signal Vi
The AC gain from n to the voltage Vp applied to the piezoelectric element 101 can be expressed as Vp / Vin = (C / Cp) × (A / B). C is the capacitance of the charge detection capacitor 102, Cp
Is the capacitance of the piezoelectric element 101.

Since the piezoelectric element 101 is located inside the HDA and the charge detection capacitor 102 is located on the substrate,
The ambient temperature around the two differs depending on the environmental conditions and the energizing time. Further, since the temperature coefficients of the piezoelectric element 101 and the charge detection capacitor 102 are also different, the ratio of C / Cp changes due to these factors, and as a result, the gain from the input voltage to the voltage generated by the piezoelectric element 101 fluctuates. . In other words, the inclination of FIG. 6 changes.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to provide a piezoelectric element driving device which is highly accurate and highly reliable even when conditions such as environmental conditions and energizing time change. I do.

[0009]

To achieve the above object, according to the first aspect of the present invention, a charge detecting capacitor is inserted in series with a piezoelectric element, and the voltage across the charge detecting capacitor is fed back. And a control signal generating means for generating a control signal for driving the piezoelectric element by supplying a charge proportional to the input signal to the piezoelectric element to drive the piezoelectric element. Voltage detecting means for detecting a voltage generated in the piezoelectric element according to a control signal from the generating means; and a capacitance of the piezoelectric element and a static capacitance of the charge detecting capacitor with respect to a gain which receives the control signal as input and outputs a detected voltage. An adjustment gain calculating means for calculating an adjustment gain for reducing a deviation from an ideal value based on a change in the capacitance and an adjustment gain; The adjustment gain by multiplying the said control signal is a structure having a loop gain correcting means for correcting the loop gain variation of the feedback control.

That is, in the present invention, a charge detection capacitor is inserted in series with the piezoelectric element, and a charge control type for supplying a charge proportional to an input signal to the piezoelectric element by feeding back a voltage between both ends of the charge detection capacitor. The piezoelectric element is driven by the drive circuit. The control signal generating means generates a control signal for driving the piezoelectric element, and the voltage detecting means detects a voltage generated in the piezoelectric element.

The adjustment gain calculating means considers a gain in which a control signal is input and a detection voltage is output, and an ideal value based on a change in the ratio of the capacitance of the piezoelectric element to the capacitance of the charge detection capacitor at this gain. Calculate the adjustment gain for reducing the deviation from the value. When the adjustment gain calculation means calculates the adjustment gain, the loop gain correction means multiplies the control gain for controlling the driving of the piezoelectric element by the adjustment gain calculated by the adjustment gain calculation means, thereby controlling the loop gain fluctuation of the feedback control. to correct.

Here, the control signal generated by the control signal generating means is for driving the piezoelectric element, and is a signal for driving the piezoelectric element during driving of the piezoelectric element. Before that, a predetermined signal capable of measuring the voltage generated by the piezoelectric element may be generated. Further, the control signal may be amplified and applied to the piezoelectric element and the charge detection capacitor connected in series, and as a result, a desired voltage is generated in the piezoelectric element.

The adjustment gain calculated by the adjustment gain calculating means can reduce a deviation from an ideal value based on a change in the ratio between the capacitance of the piezoelectric element and the capacitance of the charge detection capacitor by the gain. As a specific example of the configuration, the invention according to claim 2 is the piezoelectric element driving device according to claim 1, wherein the adjustment gain calculating means calculates a max value-min value from an input detection voltage. , And a ratio to an ideal value, and the calculated ratio is used as an adjustment gain.

That is, for example, in the above-described circuit in FIG. 4, the AC gain from the input signal Vin to the voltage Vp applied to the piezoelectric element 101 is Vp / Vin =
It can be expressed as (C / Cp) × (A / B). However, since C / Cp fluctuates depending on environmental conditions, a deviation occurs from the initial ideal value of C / Cp. Therefore, if the ratio between the actually measured value and the ideal value is used as the adjustment gain and the control signal is multiplied, the ideal C / Cp
Can be corrected for the control signal so as to approach.

In order to realize the above-described invention as an apparatus, various modes can be considered. As an example of the configuration, the invention according to claim 3 is based on claim 1 or claim 2.
Wherein the control signal generating means, the voltage detecting means, and the adjustment gain calculating means are a CPU.
There is a configuration provided inside.

That is, the CPU is a device suitable for performing various controls, and the control signal generating means, the voltage detecting means, and the adjustment gain calculating means are easily implemented by configuring them in the CPU. be able to.

As described above, by correcting the control signal for driving the piezoelectric element, the driving of the piezoelectric element can be more precisely controlled. The piezoelectric element capable of precision driving can be applied to various devices, and as a preferable application example, the invention according to claim 4 is based on the piezoelectric element drive according to any one of claims 1 to 3. A magnetic head positioning circuit for a magnetic disk drive, wherein the piezoelectric element driving device determines a magnetic head position by a two-stage servo method including a coarse movement actuator including a voice coil motor and a fine movement actuator including a piezoelectric element. In this case, the configuration is used to drive this piezoelectric element.

That is, a piezoelectric element which can be driven with higher accuracy by the piezoelectric element driving device according to the present invention is used for the fine actuator. As a result, the magnetic head is positioned with high accuracy by the two-stage servo system,
It is possible to increase the recording density of the magnetic disk device.

In a magnetic disk drive, there are generally a plurality of magnetic heads, and it is considered that the present invention is applied to all of the plurality of magnetic heads. As a specific example of such a configuration, the invention according to claim 5 is based on claim 4.
Wherein the magnetic head positioning circuit controls a plurality of magnetic heads and has an individual adjustment gain for each of the magnetic heads.

That is, the magnetic head positioning circuit is configured to control a plurality of magnetic heads, and performs positioning while giving individual adjustment gains to each of these magnetic heads. Therefore, it is possible to prevent a loop gain variation for each magnetic head.

Further, according to the present invention, it is possible to cope with a change in characteristics due to environmental conditions of the piezoelectric element and the charge detecting capacitor, but the environmental conditions gradually change. Thus, as a specific example of a configuration for responding to changes in environmental conditions, the invention according to claim 6 is based on claims 1 to
6. The piezoelectric element driving device according to claim 5, wherein the loop gain correction unit performs correction at regular intervals during operation of the piezoelectric element driving device.

That is, the loop gain correction means performs correction at regular intervals during the operation of the piezoelectric element driving device, so that the correction operation follows a change in environmental conditions and the loop gain does not change even after the lapse of the constant time. .

[0023]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a head positioning circuit of a magnetic disk drive using a piezoelectric element driving device according to the present invention. In the figure,
The head positioning circuit of the magnetic disk drive is a circuit that determines the position of the magnetic head according to a position information signal that determines the position of the magnetic head. The magnetic head positioning circuit includes a CPU 300 that performs various digital operations to control a magnetic head position by using a position information signal and a piezoelectric element voltage signal as inputs, a charge control type driving circuit 100 that drives a piezoelectric element 101, and a VCM 201. Is provided with a VCM drive circuit 200 that drives the.

The CPU 300 outputs a coarse movement control signal 401 for controlling the coarse movement of the magnetic head based on the input position information signal 301 and a fine movement control signal 411 for controlling the fine movement. The piezoelectric element voltage signal 422 is input to calculate the adjustment gain. The VCM drive circuit 200 is a circuit that drives the VCM 201 in accordance with an input signal, and the coarse movement of the magnetic head position is controlled by the output signal of the VCM drive circuit 200.

The charge control type driving circuit 100 is a circuit for driving the piezoelectric element 101 while giving a charge proportional to an input signal. The output signal of the charge control type driving circuit 100 controls the fine movement of the magnetic head position. . Further, the charge control type driving circuit 100 can output a piezoelectric element voltage signal 421 for calculating an adjustment gain by the processing of the CPU 300.

The CPU 300 is a device that performs control and processing based on digital signals, and the charge control type driving circuit 100 and the VCM driving circuit 200 are circuits that perform processing based on analog signals. Therefore, CPU
A coarse motion control signal 401 which is a digital signal output from 300 is converted into an analog signal via a D / A conversion circuit 400, and is input to the VCM drive circuit 200 as a coarse motion control signal 402.

Similarly, the fine movement control signal 411, which is a digital signal, is converted into an analog signal via the D / A conversion circuit 410, and is input to the charge control type driving circuit 100 as the fine movement control signal 412. Conversely, the piezoelectric element voltage signal 421, which is an analog signal, is converted into a digital signal via the A / D conversion circuit 420, and is input to the CPU 300 as the piezoelectric element voltage signal 422.

FIG. 2 is a block diagram showing the internal configuration of the CPU 300. In the figure, a CPU 300 includes a digital compensator 310, a gain adjustment unit 320, a measurement signal generator 330, a gain measurement unit 340, and a switch 35.
0. The digital compensator 310 receives the position information signal 301 as input, performs a compensation operation necessary for positioning, and outputs a coarse movement control signal 401 and a control signal 311.

This coarse movement control signal 401 corresponds to the above-described VCM2.
01 is a control signal for driving the control signal 311.
Is a signal that is a source of the fine movement control signal 411, and the following processing is performed. That is, the measurement signal generator 330 measures the measurement signal 3 for measuring the voltage generated in the piezoelectric element 101.
31 is generated and the charge control type driving circuit 100 is operated by the switch 350 in the same path as the fine movement control signal 411 during measurement.
Is input to

The gain measuring section 340 calculates an adjustment gain from the measurement signal 331 and the piezoelectric element voltage signal 422, and the obtained gain adjustment value 341 is input to the gain adjusting section 320. The gain adjustment unit 320 receives the gain adjustment value 341 and the control signal 311, and multiplies the control signal 311 by the gain adjustment value 341 and outputs the result as a gain adjustment signal 321. The gain adjustment signal 321 is input to the charge control type driving circuit 100 as the fine movement control signal 411 while being switched by the switch 350. Therefore, the loop gain fluctuation of the charge control type driving circuit 100 is corrected.

In this sense, the gain adjustment section 320 and the measurement signal generator 330 constitute the control signal generation means, the gain measurement section 340 constitutes the voltage detection means, and the gain measurement section 340 constitutes the adjustment gain calculation means. The gain adjustment unit 320 constitutes a loop gain correction unit.

The charge control type driving circuit 100 is constituted by the circuit shown in FIG. That is, the charge detection capacitor 102 is inserted in series with the piezoelectric element 101, and the operational amplifier 120 drives the piezoelectric element 101 and the charge detection capacitor 102 connected in series.

The voltage between both ends of the charge detection capacitor 102 is supplied to the resistors 111 to 114 and the operational amplifier 110 via the voltage followers 130 and 131.
, And is fed back to the operational amplifier 120 via the resistor 122. The input signal is the fine movement control signal 411, and the output of the voltage follower 131 is the piezoelectric element voltage signal 421. Further, resistors 103 and 104 respectively connected in parallel with the piezoelectric element 101 and the charge detection capacitor 102 are for stabilizing the direct current.

Hereinafter, the operation of the piezoelectric element driving device having the above configuration will be described. In this embodiment, the magnetic disk drive using the magnetic head positioning circuit has a two-stage actuator type servo mechanism having the VCM 201 for the coarse actuator and the piezoelectric element 101 for the fine actuator. The magnetic head is VCM
201 moves to the vicinity of the target track, from which the piezoelectric element 101 is energized to perform high-precision positioning on the target track.

These operations are performed by the CPU 300 as described above.
When a seek operation near the target track is performed, a compensation operation is performed based on the position information signal 301 and a coarse movement control signal 401 is output. Coarse motion control signal 401 is D / A
The conversion is performed by the conversion circuit 400 into an analog coarse movement control signal 402, and then converted into a current by the VCM drive circuit 200 and sent to the VCM 201, thereby driving the magnetic head as desired.

When the magnetic head comes close to the target track, fine movement control is performed on the magnetic head. At this time, the CPU 300 sends the control signal 311 to the gain adjustment unit 32
0, and the gain adjustment signal 321 output by the gain adjustment unit 320 is the switch 350, the D / A conversion circuit 4
10. Control signal 31 via charge control type driving circuit 100
By giving a charge proportional to 1 to the piezoelectric element 101, the magnetic head is minutely controlled.

Next, the adjustment of the loop gain will be described. When the piezoelectric element 101 is not energized, such as during a seek operation, the switch 350 is switched so that the measurement signal 331 is converted to the fine movement control signal 411 by the D / A conversion circuit 4.
Send to 10. Here, since the measurement signal 331 is desirably an AC signal in the vicinity of the control band, a sine wave signal of about several kHz is generated by the measurement signal generator 330.

At the gain measuring section 340, the voltage applied to the piezoelectric element 101 at this time is determined by the piezoelectric element voltage signal 422.
Receive as. Thereafter, a max value-min value is calculated from the piezoelectric element voltage signal 422, which is a digital signal, a ratio with the nominal value is obtained, and the ratio is calculated as the gain adjustment value 341.
To the gain adjustment unit 320. Gain adjuster 320
Multiplies the gain adjustment value 341 by the control signal 311 and outputs the result as a gain adjustment signal 321.

Here, assuming that C / Cp = 1, if C / Cp> 1, the gain adjustment unit 320
The control signal 311 is multiplied by a gain adjustment value 341 of "1" or less and output. Conversely, when C / Cp <1,
The gain adjustment unit 320 multiplies the control signal 311 by a gain adjustment value 341 of “1” or more and outputs the result. By this operation,
C / Cp depending on environmental conditions and temperature coefficient
Is changed, the gain of the control signal 311 is adjusted by the gain adjusting section 320 in accordance therewith, so that the loop gain is kept constant.

Further, by performing this series of correction operations at regular intervals after the power is turned on to the magnetic disk device, the correction operations can follow changes in environmental conditions, thereby preventing the occurrence of loop gain fluctuations. . Further, in the case of a magnetic disk on which a plurality of magnetic heads are mounted, the piezoelectric element 101 exists for each head, and the value of Cp differs for each head. Can also respond.

As described above, according to the above-described embodiment, C /
Although the deviation from the ideal value based on the fluctuation of the environmental condition of Cp can be offset, the hardware configuration is not necessarily limited to the above. FIG. 3 is a block diagram showing another embodiment of the present invention. This embodiment differs from FIG. 1 in that the A / D conversion circuit 420 is a comparator 425.

The other configuration is the same as that of the embodiment shown in FIG. 1. In this case, the measurement signal generator 330 gradually increases the amplitude of the measurement signal 331 when the output of the comparator 9 is switched. Is stored in the gain measuring section 340, and the adjustment gain is measured from the amplitude and the nominal value. This makes it possible to configure the apparatus at lower cost.

As described above, in the present invention, a correction operation is performed in which the voltage applied to the piezoelectric element is detected, the adjustment gain is obtained from the measurement signal and the detection signal, and the control signal is multiplied by the adjustment gain and output. Therefore, even if the C / Cp ratio changes, the control signal is corrected correspondingly, so that it is possible to prevent loop gain fluctuations caused by differences in environmental conditions and temperature coefficients. Further, when this correction operation is performed for each magnetic head and an adjustment gain is given for each magnetic head, it is possible to prevent a loop gain variation for each magnetic head.

[0044]

As described above, in the present invention,
A highly accurate and highly reliable piezoelectric element driving device can be provided even when conditions such as environmental conditions and energization time change. Further, according to the second aspect of the invention, the adjustment gain can be calculated with a simple configuration.

Further, according to the invention of claim 3,
The control according to the present invention can be performed with a simple configuration. Further, according to the invention of claim 4, the accuracy of the magnetic disk device is improved, and high recording density can be achieved.

Further, according to the invention of claim 5,
The present invention can be applied to a magnetic disk drive having a plurality of magnetic heads. Further, according to the invention of claim 6, it is possible to continuously drive the piezoelectric element with high accuracy.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a head positioning circuit of a magnetic disk drive using a piezoelectric element driving device according to the present invention.

FIG. 2 is a block diagram illustrating an internal configuration of a CPU.

FIG. 3 is a block diagram showing another embodiment of the present invention.

FIG. 4 is a circuit diagram according to an example of a charge control type driving circuit.

FIG. 5 is a circuit diagram according to an example of a voltage control type driving circuit.

FIG. 6 is a diagram showing a hysteresis characteristic of a charge control type piezoelectric element.

FIG. 7 is a diagram showing a hysteresis characteristic of a voltage control type piezoelectric element.

[Explanation of symbols]

 Reference Signs List 100 charge control type drive circuit 200 VCM drive circuit 300 CPU 301 position information signal 310 digital compensator 311 control signal 320 gain adjustment unit 321 gain adjustment signal 330 measurement signal generator 331 measurement signal 340 gain measurement unit 341 gain adjustment value 350 switch 400 D / A conversion circuit 401 Coarse movement control signal 410 D / A conversion circuit 411 Fine movement control signal 420 A / D conversion circuit 422 Piezoelectric element voltage signal

Claims (6)

[Claims] 1. A charge detection capacitor is inserted in series with a piezoelectric element, and a voltage proportional to an input signal is supplied to the piezoelectric element by feeding back a voltage between both ends of the charge detection capacitor. What is claimed is: 1. A driving device for driving a piezoelectric element, comprising: control signal generating means for generating a control signal for driving the piezoelectric element; and voltage detecting means for detecting a voltage generated in the piezoelectric element by a control signal from the control signal generating means. And an adjustment for reducing a deviation from an ideal value based on a change in a ratio between the capacitance of the piezoelectric element and the capacitance of the charge detection capacitor with respect to a gain that receives the control signal and outputs a detection voltage. Adjusting gain calculating means for calculating a gain; and multiplying the control signal by the adjusting gain calculated by the adjusting gain calculating means. The piezoelectric element driving apparatus characterized by comprising a loop gain correction means for correcting the loop gain variation control. 2. The piezoelectric element driving device according to claim 1, wherein the adjustment gain calculating unit calculates m from the input detection voltage.
A piezoelectric element driving device that calculates an ax value-min value, obtains a ratio to an ideal value, and uses the calculated ratio as an adjustment gain. 3. The piezoelectric element driving device according to claim 1, wherein the control signal generating means, the voltage detecting means, and the adjustment gain calculating means are provided in a CPU. Piezoelectric element driving device. 4. The piezoelectric element driving device according to claim 1, wherein the piezoelectric element driving device includes a coarse movement actuator including a voice coil motor and a fine movement actuator including a piezoelectric element. A piezoelectric element driving device used for driving the piezoelectric element in a magnetic head positioning circuit of a magnetic disk device that determines a magnetic head position by a two-stage servo system provided with: 5. The piezoelectric element driving device according to claim 4, wherein the magnetic head positioning circuit controls a plurality of magnetic heads, and each of the magnetic heads has an individual adjustment gain. Element driving device. 6. The piezoelectric element driving device according to claim 1, wherein the loop gain correction means performs correction at regular intervals during operation of the piezoelectric element driving device. A piezoelectric element driving device characterized by the following.