JPH06149378A - Servo controller - Google Patents

Abstract

PURPOSE:To obtain a servo characteristic excellent in stability by a servo controller whose circuit configuration is simple. CONSTITUTION:An error signal Xe obtained by subtracting a position signal Xf of a control object from a target position signal X0 by an analog subtracter 1 is converted into a digital signal by an A/D converter 20, and stored in a register 22. Driving currents Id running through an actuator 5 which drives the control object are detected by a current detector 6, converted into a signal Vi, and the value is converted into the digital signal by an A/D converter 21, and stored in a register 23. In a computing element 3, the data Xe from the register 22 are inputted, phase-corrected by a phase correcting filter 31, and the data Vi from the register 23 are subtracted from the obtained data by a subtracter 32, and a PWM signal modulated according to the subtracted result is outputted from a PW modulator 33. The PWM signal is power- amplified by a PWM amplifier 4, and used for driving the actuator 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a servo control device, and more particularly to a closed loop control servo control device for controlling drive means including an inductance component used in an optical disk device or the like.

[0002]

2. Description of the Related Art A read-only optical disk device using an optical disk such as a CD (compact disk) or LD (laser disk) on which information has already been recorded, or an optical disk or a magneto-optical disk capable of recording and reproducing information. The information recording / reproducing optical disk device used is widely used because of its storage capacity and recording density, high-speed data transfer, random access, low cost and small size of the device. .

However, in order to perform random access, it is necessary for an optical pickup for recording / reproducing information to move at high speed in the radial direction of the optical disc to find a target (recording) track. Further, a servo control device having a fast response characteristic is used in various places such as a tracking system for tracking the swing of a track due to the eccentricity of an optical disc that rotates at a high speed, and a focusing system for correcting vertical movement of a surface due to the warp of an optical disc.

For example, in the case of a focusing system, as shown in FIG. 8, a conventional servo controller for controlling a moving coil type actuator 50 for driving an objective lens in accordance with the vertical movement of a surface is an analog subtractor 41. , A conversion storage unit 42, a computing unit 43 for performing digital computation, and a PW
It is composed of an M amplifier 44.

The subtracter 41 inputs the target position signal X0
The error signal Xe is output by taking the difference between the position signal Xf of the objective lens fed back and the error signal Xe. The error signal Xe is converted into a digital value by the A / D converter 45 constituting the conversion storage unit 42, and stored in the register 46. After being stored, it is output to the arithmetic unit 43.

The calculator 43 performs a digital calculation on the input digital value in accordance with the characteristics of the phase correction filter 47, and outputs a PWM (pulse width modulation) signal according to a preset condition of the PW modulator 48 according to the calculation result. Output. That PW
The M signal is power-amplified by the PWM amplifier 44, and drives the actuator 50 in the direction in which the error signal Xe becomes zero.

As described above, by passing through the digital phase correction filter 47 for correcting the phase of the entire closed loop system due to the inertia due to the weight of the objective lens and the delay of the position sensor that detects the position and outputs the position signal Xf. , Stable servo control was performed without delay in response or oscillation.

However, since the coil of the actuator 50 has some resistance R and inductance L, if a linear amplifier 49 as shown in FIG. 9A is used in the power amplification stage, for example, FIG. As shown in, the crossover frequency fc (= R / 2πL) determined from R and L
In the above high frequency range, the gain decreases with a slope of -20 dB / dec (decibel / decimal).

At the same time, as shown in FIG. 10B, a phase delay of 45 ° already occurs at the crossover frequency fc. Due to the gain reduction and the phase delay shown in FIG. 10, there are problems such as instability before and after the crossover frequency fc and oscillation in the high frequency range.
Current feedback type linear amplifier 49a as shown in FIG.
Was used.

[0010]

However, when a linear amplifier is used for driving the actuator 8, the power efficiency is low and heat is generated greatly, and a heat sink is required, which makes it difficult to reduce the size. PW with high power efficiency to suppress heat generation
When the M amplifier is used, the current feedback PWM amplifier has a problem that the number of parts increases and the circuit becomes complicated.

Even if a radiator plate is provided to allow for an increase in size and weight, a large amount of heat will raise the ambient temperature, which will adversely affect other parts constituting the optical pickup. Therefore, recently, as in the conventional example shown in FIG.
The number of servo control devices that use PWM amplifiers and do not apply current feedback is increasing, and as a result, they often suffer from unstable operation and high-frequency transmission.

The present invention has been made in view of the above points, and an object thereof is to obtain a servo characteristic having a simple circuit configuration of a servo control device and excellent stability.

[0013]

In order to achieve the above object, the present invention controls the drive means of the controlled object according to the error signal from the target position of the controlled object to bring the controlled object to the target position. A servo control device for closed loop control to approach, in a servo control device equipped with a digital arithmetic unit for performing a calculation of a phase correction filter for correcting the phase of the entire closed loop system, a current detection unit for detecting a drive current flowing in the drive unit, A subtraction means for subtracting the drive current value detected by the current detection means from the operation result of the phase correction filter using the digital operation unit, and the drive current is supplied to the drive means according to the output result of the subtraction means. It is a thing.

Therefore, a first A / D conversion means for converting the error signal into a digital signal, a first register for storing output data of the first A / D conversion means and outputting it to a digital arithmetic unit, and a current Provided are second A / D conversion means for converting the drive current value detected by the detection means into a digital value, and a second register for storing output data of the second A / D conversion means and outputting it to a digital arithmetic unit. It is a thing.

Alternatively, selection means for inputting the error signal and the drive current value detected by the current detection means and selectively outputting any one of them, and A / D conversion for digitally converting the analog data output by the selection means. Of the digital data output by the A / D converter, the first register for storing the digital data of the error signal and outputting the digital data to the digital calculator, and the driving current of the digital data output by the A / D converter. A second register for storing the digital data of the value and outputting it to the digital arithmetic unit, and a timing control means for outputting a timing signal to the selection means and the first and second registers to control the respective selection timings. It is provided.

The timing control means may be means for controlling the selection means so as to alternately select the error signal and the drive current value.

In each of the above servo control devices,
The smoothing means for performing the operation of smoothing the digital data of the drive current value using the digital arithmetic unit is provided on the drive current value input side of the subtraction means.

Alternatively, a smoothing means for smoothing the output result of the subtracting means using a digital arithmetic unit is provided, and a drive current is supplied to the driving means according to the output result of the smoothing means.

[0019]

In the servo controller constructed as described above, the current detecting means detects the drive current flowing through the drive means, and the subtracting means determines the drive current value detected by the digital arithmetic unit used for the phase correction filter calculation. Subtract from the phase-corrected filtered error signal. A drive current corresponding to the result of the subtraction is supplied to the drive means for driving.

Therefore, stable servo characteristics can be obtained without causing unstable operation or high-frequency oscillation due to the inductance of the driving means. Moreover, since only the current detection means is provided as hardware, the number of parts does not increase so much, the cost is low, and the circuit is simple.

Therefore, the first A / Ds provided respectively
The first register stores digital data obtained by converting the error signal into a digital signal by the conversion unit, and the second register stores digital data obtained by converting the drive current value by the second A / D conversion into the latest data. Since the data is held, the digital arithmetic unit can read out necessary data at any time to perform arithmetic operation.

Alternatively, when the selecting means selects and outputs the error signal according to the timing signal output by the timing control means, the first register stores the digital data converted by the A / D converter and selects it. When the means selects and outputs the drive current value, the second register stores the digital data converted by the A / D converter, so that one A / D converter is used instead of the two A / D converter means. The same effect can be obtained with the converter, and the cost can be reduced.

If the timing control means alternately selects and outputs the error signal and the drive current value, the first and second
Since the data stored in each of the registers has the smallest time difference with each other, the accuracy of servo control is improved.

A smoothing means for performing a smoothing operation using a digital arithmetic unit is provided on the drive current value input side of the subtracting means to smooth the drive current value, and thereby a PWM amplifier or a DC amplifier is provided.
Even when a noisy driving means such as a motor is used, an erroneous operation or an unstable operation such as oscillation can be prevented.

Even if such a smoothing means is provided in the subsequent stage of the subtracting means, the output result of the subtracting means is smoothed and a driving current is supplied to the driving means in accordance with the smoothed data.
Similar effects are obtained.

[0026]

1 is a block diagram showing the configuration of a first embodiment of a servo control device according to the present invention. As with the conventional example shown in FIG. 8, an actuator 5 for driving an objective lens of a focusing system is shown. It is a servo control device for controlling.

In the first embodiment shown in FIG. 1, an analog subtractor 1, a conversion storage unit 2, an arithmetic unit 3 which is a digital arithmetic unit such as a CPU or a DSP (digital signal processor), and a control unit A PWM amplifier 4 that drives a moving coil type actuator 5 that is a drive unit that drives an objective lens (not shown), which is an object, in the optical axis direction according to the vertical movement of the optical disc surface, and a current detector 6 that is a current detection unit. It is composed by.

The conversion storage unit 2 includes an A / D converter 20 which is a first A / D conversion means, an A / D converter 21 which is a second A / D conversion means, an A / D converter 20,
21 for storing the digital data output by each
The register 22 and the second register 23 of FIG. The calculator 3 is a calculator that performs digital calculation according to each characteristic of the phase correction filter 31, the subtracter 32 that is a subtraction unit, and the PW (pulse width) modulator 33 that outputs a PWM signal according to the output result. is there.

FIG. 2 is a circuit diagram showing an example of the configuration of each of the actuator 5, the PWM amplifier 4, and the current detector 6 shown by an equivalent circuit composed of an inductance L and a resistance R. The PWM amplifier 4 is a switching transistor. The current detector 6 includes Q1 and Q2 and diodes D1 and D2 for preventing reverse voltage. The current detector 6 includes a resistor R0 for current detection, an operational amplifier 16, a capacitor C1 for smoothing a signal, and a resistor R.
1 and R2.

The PWM amplifier 4 includes transistors Q1 and Q1 according to the polarity of the PWM signal input from the PW modulator 33.
When 2 is alternately turned on, the power-amplified drive current Id is output to drive the actuator 5 and drive the objective lens (not shown) in the direction in which the error signal Xe becomes zero.

The drive current Id is converted into a voltage signal V0 (= Id × R0) by the resistor R0 of the current detector 6 connected in series with the actuator 5, and the voltage signal V0 is amplified by R2 / R1 times by the operational amplifier 16. After that, the voltage signal Vi corresponding to the driving current value
It is fed back to the / D converter 21.

In FIG. 1, an analog subtractor 1 including, for example, an operational amplifier having a linear characteristic takes an error signal by calculating a difference between an input target position signal X0 and a fed back position signal Xf of an objective lens (not shown). Xe (=
The analog value of (Xf−X0) is output to the A / D converter 20.

The A / D converter 20 of the conversion storage unit 2 converts the error signal Xe into digital data, and the register 22
Stores the converted digital error data Xe. Further, the A / D converter 21 converts the fed back drive current value Vi into digital data, and the register 23 stores the converted digital current data Vi.

The calculator 3 first inputs the error data Xe from the register 22 and performs digital calculation (filtering) according to the characteristics of the phase correction filter 31. next,
The current data Vi is input from the register 23, and the subtractor 32
Error data Xe filtered according to the characteristics of
Subtract from. Further, the PWM signal, which is pulse-width modulated according to the subtraction result, is output to the PWM amplifier 4 at a cycle preset by the characteristics of the PW modulator 33. The operation after the PWM amplifier 4 is as already described with reference to FIG.

As described above, in the first embodiment, the feedback processing of the drive current is performed by the arithmetic unit 3,
Compared with the conventional example, the current detector 6 and the second A / D
Only by adding the converter 21 and the register 23, stable servo control can be performed without unstable operation, malfunction, or oscillation due to the inductance L of the actuator 5. Further, the structure is much simpler than that of a general current feedback type PWM amplifier, so that the size and cost are small.

In order to explain general servo control by taking focusing system servo control as an example, the subtracter 1
The error signal Xe was calculated from the target position signal X0 and the position signal Xf by the following. However, in the actual focusing / servo control system of the optical pickup, the error signal Xe itself from the regular interval between the recording surface of the optical disk and the objective lens is , The obtained error signal Xe is directly input to the A / D converter 20 because it is obtained by combining a plurality of outputs of the optical pickup.

FIG. 3 is a block diagram showing the configuration of the second embodiment of the present invention, in which the number of A / D converters, which are relatively costly, is the same as that of the conventional example at a lower cost than the conventional example. To obtain the effect of. That is, the second embodiment is different only in the conversion storage unit 2a, and the other parts are the same as those in the first embodiment shown in FIG.

The conversion storage unit 2a of the second embodiment shown in FIG.
Is a selection means, which is an analog two-channel multiplexer 24 in which the error signal Xe and the voltage signal Vi corresponding to the drive current are input to the first and second channels, respectively,
It is composed of an A / D converter 25 which is an A / D converter, a first register 26 and a second register 27, and a timing signal generator 28 which is a timing control means for outputting a timing signal to each. .

FIG. 4 shows timing signals Tm, Tr1 and Tr2 output from the timing signal generator 28, and a multiplexer 2 which operates according to the timing signals.
4, A / D converter 25, first and second registers 2
It is a time chart which shows an example of the processing contents of 6 and 27. The numbers in parentheses attached to the respective signals indicate the order relation with a certain time point set to zero.

Timing signal Tm shown in FIG.
Depending on the level of
When the level is high, the gate of the first channel (ch1) is opened to output the signal Xe, and when the level is low, the gate of the second channel (ch2) is opened to output the signal Vi.

The A / D converter 25 is cleared by the rising and falling edges of the timing signal Tm, and as shown in (C) of FIG.
The analog signal output from is converted into 8-bit digital data, for example. The timing signal generator 28 is
When the conversion of the / D converter 25 is completed, as shown in (D) and (F) of FIG.
1 and Tr2 are alternated to the first and second registers 2 respectively
Output to 6 and 27.

The first and second registers 26 and 27 output from the A / D converter 25 when the timing signal Tr1 or Tr2 is input, as shown in (E) and (G) of FIG. Digital data Xe or Vi
Is stored and held until the next timing signal is input. Therefore, the registers 26 and 27 always hold the latest data, and output the latest data held when the arithmetic unit 3 needs it.

As described above, in the second embodiment, by providing the multiplexer 24 and the timing signal generator 28, one A / D converter 25 can provide two signals X.
Since e and Vi can be processed, the same effect can be obtained at a lower cost than the first embodiment. Further, since the multiplexer 24 alternately selects and outputs the two signals Xe and Vi under the control of the timing signal generator 28,
The registers 26 and 27 hold the latest data with the smallest time difference, and the accuracy of servo control is improved.

FIG. 5 is a waveform diagram showing an example of the drive voltage Vd output from the PWM amplifier 4 shown in FIG. 2 and the drive current Id flowing through the actuator 5. The drive voltage Vd of the PWM amplifier 4 is repeatedly inverted between + 5V and -5V according to the polarity of the PWM signal input from the PW modulator 33,
The average drive voltage Va is determined by the duty ratio.

The drive current Id has a sawtooth ripple waveform as shown in FIG. 5, and its average drive current Ia is PW.
If the angular velocity of the M signal is ω (2π times the PWM frequency), it can be obtained by the equation 1.

[0046]

## EQU1 ## Ia = Va / (R + jωL)

The ripple of the drive current Id generated by the PWM method is generally high in the PWM frequency.
The signal C is removed by the capacitor C1 of the DC amplifier of the current detector 6 shown in FIG. 4 and hardly appears in the fed back signal Vi, but external noise or driving means (for example, a DC motor or a linear motor) is included in the signal Vi. In some cases, fluctuations that cannot be removed by the capacitor C1 are included, which causes unstable operation.

FIGS. 6 and 7 show the third and fourth aspects of the present invention.
FIG. 3 is a block diagram showing the configuration of the embodiment, in which the operation is stabilized by providing smoothing means for performing an operation for smoothing digital data using a digital calculator. The same parts as those of the first embodiment shown in FIG.

The third embodiment shown in FIG. 6 is different from the first embodiment in that a smoothing means LPF (low-pass filter) 34 is provided in the arithmetic unit 3a, and the second storage unit 2 of the conversion storage unit 2 is provided. This is because the digital data Vi corresponding to the drive current value input from the register 23 is smoothed and then output to the subtractor 32 and subtracted from the error data Xe that has passed through the phase correction filter 31.

As described above, since the data Vi to be subtracted is smoothed to remove noise and fluctuations, even if the drive current Id is supplied to the actuator 5 according to the output result of the subtractor 32. The operation does not become unstable, and stable servo control is performed.

In the fourth embodiment shown in FIG. 7, the output result of the subtractor 32 is smoothed by the LPF 35 provided in the arithmetic unit 3b, and then converted into the PWM signal by the PW modulator 33. Is. In this way, the data Vi to be subtracted contains noise and fluctuations, and the subtractor 3
Even if the output result of No. 2 contains noise or variation whose polarity is inverted, since the PWM signal does not include noise or variation, stable servo control is performed as in the third embodiment.

In the fourth embodiment, if the crossover frequency of the LPF 35 is near the upper limit of the frequency band of the phase correction filter or is within the frequency band, the phase correction filter 31
The characteristic of a is determined by the phase correction filter 3 of the first to third embodiments.
It is better to modify the characteristics of No. 1 in advance by the characteristics of the LPF 35, but if the crossover frequency is sufficiently high, the phase correction filter 31a may have the same characteristics as the phase correction filter 31. .

Further, in the third and fourth embodiments, the smoothing means is not limited to the LPFs 34 and 35, but may be a digital integrator. Furthermore, the conversion storage unit 2 may be replaced by the conversion storage unit 2a of the second embodiment shown in FIG.

Although the control object and its driving means have been described above by taking the actuator for driving the objective lens of the optical pickup of the optical disk device as an example, the control of the optical pickup having a mass much larger than that of the objective lens. Since a linear motor or the like, which is a driving means, requires much larger power than an actuator, heat generation becomes a serious problem unless a PWM amplifier with high power efficiency is used.
Further, since the electric current is larger than that of the actuator and noise is easily generated, the servo control device according to the present invention becomes more effective.

[0055]

As described above, the servo control device according to the present invention has a simple circuit configuration and provides stable servo characteristics.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a first embodiment of a servo control device according to the present invention.

FIG. 2 is a circuit diagram showing an example of each configuration of a PWM amplifier, an actuator and a current detector shown in FIG.

FIG. 3 is a block diagram showing the configuration of a second embodiment of the servo control device.

4 is a time chart showing an example of the operation of each element of the conversion storage unit shown in FIG.

5 is a waveform diagram showing an example of a drive voltage Vd and a drive current Id output from the PWM amplifier shown in FIG.

FIG. 6 is a block diagram showing the configuration of a third embodiment of the servo control device.

FIG. 7 is a block diagram showing the configuration of a fourth example of the servo control device.

FIG. 8 is a block diagram showing a configuration of a conventional example of a servo control device.

FIG. 9 is a circuit diagram showing an example of a linear amplifier that drives an actuator.

FIG. 10 is a diagram showing an example of gain characteristics and phase characteristics of an actuator.

[Explanation of symbols]

3, 3a, 3b arithmetic unit (digital arithmetic unit) 5 actuator (driving means) 6 current detector (current detection means) 20 A / D converter (first A / D conversion means) 21 A / D converter (second) A / D conversion means) 22, 26 First register 23, 27
Second register 24 Multiplexer (selection means) 25 A / D converter (A / D converter) 28 Timing signal generator (timing control means) 31, 31a Phase correction filter 32 Subtractor (subtraction means) 34, 35 LPF ( Low-pass filter: smoothing means)

Claims (6)

[Claims] 1. A servo control device for closed loop control, which controls the drive means of the controlled object according to an error signal from the target position of the controlled object to bring the controlled object closer to the target position, the closed loop system In a servo control device including a digital arithmetic unit that performs an operation of a phase correction filter that corrects the entire phase, a current detection unit that detects a drive current flowing in the drive unit, and the phase correction filter using the digital arithmetic unit. And a subtracting means for subtracting the drive current value detected by the current detecting means from the calculation result of the above, and the drive current is supplied to the drive means according to the output result of the subtracting means. apparatus. 2. The servo control device according to claim 1, wherein a first A / D conversion means for converting the error signal into a digital signal, and output data of the first A / D conversion means for storing the digital signal A first register for outputting to a computing unit, a second A / D conversion unit for converting the drive current value detected by the current detection unit into a digital value, and output data of the second A / D conversion unit are stored. And a second register for outputting to the digital arithmetic unit. 3. The servo control device according to claim 1, further comprising a selection unit that inputs the error signal and the drive current value detected by the current detection unit and selectively outputs one of them. An A / D converter for converting the analog data output by the means into a digital signal, and a first data storing means for storing the digital data of the error signal among the digital data output by the A / D converter for output to the digital arithmetic unit. A register, a second register for storing the digital data of the drive current value out of the digital data output by the A / D converter and outputting the digital data to the digital arithmetic unit, the selecting means, and the first and second And a timing control means for outputting a timing signal to each of the registers to control each selection timing. 4. The servo control device according to claim 3, wherein the timing control means is means for controlling the selection means to alternately select the error signal and the drive current value. 5. The servo control device according to claim 1, wherein the smoothing means that performs an operation for smoothing the digital data of the drive current value using the digital arithmetic unit is the subtracting means. The servo control device is provided on the drive current value input side of the. 6. The servo control device according to claim 1, further comprising a smoothing unit that performs a calculation for smoothing an output result of the subtracting unit by using the digital computing unit. A servo control device is characterized in that a drive current is caused to flow to the drive means in accordance with the output result of the above.