JP3200905B2 - Automatic adjustment device for servo loop - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a servo loop used for recording or reproduction of an optical disk, such as a tracking servo or a focus servo, for automatically adjusting each parameter, particularly for automatically adjusting a gain. It relates to an automatic adjustment device.

[0002]

2. Description of the Related Art A feedback control system such as a focus servo and a tracking servo is used for reproducing a compact disk or an optical video disk, or recording and reproducing a magneto-optical disk or a phase change optical disk. In such a servo loop, variations in the emission characteristics of the semiconductor laser, differences in the reflectivity of the disk,
Alternatively, the stability of the servo loop changes due to a difference in characteristics of the light receiving element, an installation error, or the like. Therefore, in order to operate the servo loop stably, various constants in the servo loop have been automatically adjusted by hand in recent years and recently by using a microprocessor. As an example of such automatic adjustment, for example, Japanese Patent Laid-Open No. 2-154
For example, there is a gain adjustment of a tracking servo loop disclosed in Japanese Patent Application Publication No. 30, and a DC offset adjustment of tracking disclosed in Japanese Patent Application Laid-Open No. 1-128237.

[0003]

However, in the automatic adjustment as described above, there is a risk that a signal may be saturated somewhere in the servo loop, resulting in erroneous adjustment. This is a serious problem especially in the digitalization of servos, which has been promoted in recent years for intelligent servos and cost reduction. The digitization causes a quantization error, and the noise of the drive signal tends to increase as compared with the analog servo. In such a situation, signal saturation occurs which has not occurred in the conventional analog servo. This event, for example,
This appears remarkably when a high-pass filter for high-frequency compensation is constituted by a digital filter.

[0004]

According to the present invention, there is provided a saturation detecting means for detecting a saturation of a signal in a servo loop, and an automatic adjustment when the saturation detecting means does not detect the saturation of the signal. This is a servo loop automatic adjustment device provided with an automatic adjustment means for judging an abnormal state when detected, and interrupting the automatic adjustment.

[0005]

According to the present invention, by providing the above means,
Automatic adjustment processing is performed only when a non-linear state due to signal saturation does not occur in the servo loop, thereby preventing malfunction of automatic adjustment.

[0006]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of an automatic servo loop adjusting device according to a first embodiment of the present invention. In FIG. 1, the servo loop adjusted by the automatic adjusting means 101 has the following configuration. The error detection means 102 receives the target value 103 and the control value 104, compares them, and outputs an error signal 105. The control means 106 receives the error signal 105 and outputs a drive signal 107 corresponding to the error signal to the control object 108. The control object 108 operates according to the drive signal 107, and the control value
4 is output. Here, the output control value 104 enters the error detection means 102 and is compared with the target value 103 to detect an error. For such a servo loop, the automatic adjusting means 101 operates as follows. The automatic adjustment unit 101 detects the internal state of the servo loop and changes each constant of the control unit 106 so that the servo loop operates stably. A number of proposals have been made on the detection of the internal state of the servo loop and the change of each constant at this time, as described in the conventional example, but they are not directly related to the gist of the present invention. Is abbreviated. Now, the saturation detecting means 109 outputs each signal (error signal 105, drive signal 107, and signal 11 used in the internal processing of the control means 106) in the servo loop.
Saturation of one or more signals in 1) or a state equivalent thereto is detected. When saturation is detected, a saturation detection signal 110 is output to the automatic adjustment unit 101. When the saturation detection signal 110 is input, the automatic adjustment unit 101 interrupts the automatic adjustment and sends an instruction to the control unit 106 to keep each constant as it is. This can prevent malfunction of automatic adjustment due to saturation.

As described above, according to this embodiment, the automatic adjusting means performs the automatic adjustment of the servo loop while monitoring the saturation of the signal in the servo loop by the saturation detecting means. Can prevent malfunction of automatic adjustment due to signal saturation.
The operation of the servo loop can be stabilized.

Next, a second embodiment will be described with reference to the drawings. FIG. 2 is a block diagram of an automatic servo loop adjusting device according to a second embodiment of the present invention. The present embodiment is an example in which the present invention is applied to automatic adjustment of the gain of a tracking servo in reproducing an optical disk. Hereinafter, the operation will be described.

First, the operation of the tracking servo loop in this embodiment will be described. The spindle motor 201 rotates the optical disc 202. The tracking actuator 203 moves the position of the light spot on the optical disk 202 by moving the objective lens in the pickup 204, and the servo loop controls the tracking actuator 203 so that the position of the light spot is on the track. The pickup 204 has a built-in light receiving element and outputs a signal corresponding to the light reflected from the optical disk 202 to the error detection circuit 205. The error detection circuit 205 outputs a tracking error signal 206 indicating a deviation between the track position and the position of the light spot based on the signal from the pickup 204. Examples of the error detection method include a three-beam method, a far-field method, and a phase difference method. Since such a tracking error detection method is already known, a description thereof will be omitted. The tracking error signal 206 output from the error detection circuit 205 enters the analog-to-digital conversion circuit 207, is subjected to digital-to-analog conversion, and enters the digital filter 208. The digital filter 208 operates as a so-called loop filter. That is, the driving value 209 is output so that the input tracking error signal becomes zero. The drive value 209 output from the digital filter 208 enters a digital-to-analog conversion circuit 210 and is converted to digital-to-analog.
Output to the drive circuit 211. The drive circuit 211 performs processing such as amplification and voltage-current conversion on the input drive signal, and outputs a drive signal 219 to the tracking actuator 203. With this drive, the pickup 204
Is controlled so that the light spot irradiated on the optical disk 202 follows the track.

In such a servo loop, the loop gain is not optimal due to variations in the sensitivity of the light receiving element and the operating sensitivity of the tracking actuator 203, and the servo tends to be unstable. Therefore, the gain is automatically adjusted by the following method. Reference numeral 212 denotes an automatic adjustment unit in this embodiment, which includes a disturbance generation circuit 213 and a gain measurement setting circuit 214. First, the disturbance generating circuit 21
3 generates a test signal 215 having a predetermined frequency and amplitude, and adds this signal to an error signal via an adder 216. Next, the gain measurement setting circuit 214 receives the test signal 215 and the signal at the measurement point 217, obtains the compression ratio of the test signal 215 from the level difference between the two signals, and obtains the gain of the servo loop from the compression ratio. Then, the current gain is compared with the target gain. If the current gain is small, the gain is increased, and if the current gain is large, the constant of the digital filter 208 is changed so as to decrease the gain. Adjust the gain.

The analog saturation detection circuit 218 outputs the drive signal 2
19 and monitor the saturation of this signal. Drive signal 2
A signal 19 entering the tracking actuator 203 is a signal closest to the behavior of the light spot to be controlled in this case. Therefore, monitoring this signal is desirable for monitoring saturation of the servo loop. In FIG.
4 shows a configuration diagram and a signal waveform diagram of the analog saturation detection circuit 218. In FIG. 3, the drive signal 219 is supplied to the first comparator 30.
1 and is compared with the first reference voltage 302 (waveform 3
06). The first reference voltage 302 is the normal drive signal 21
Reference numeral 9 denotes a voltage for checking whether the level is close to the saturation level or has reached the saturation level. First comparator 3
The output waveform of 01 is shown at 307. The output signal from the first comparator 301 passes through the integration circuit 303 and passes through the second comparator 3
Enter 04. The output waveform of the integration circuit 303 is shown at 308. The second comparator 304 compares the input signal with a second reference voltage 305, and outputs the result of the comparison as a saturation detection signal 220. 309 is an output waveform of the second comparator 303. With this configuration, it is possible to obtain an output of the saturation detection signal 220 according to the frequency of saturation. When saturation is detected by the above operation, the saturation detection signal 220 enters the disturbance generating circuit 213 and the gain measurement setting circuit 214, and stops both operations. As a result, the injection of the test signal 215 is interrupted, and the gain of the digital filter 208 is held at the value at the time when the saturation detection signal 220 was output because no new constant change is performed.

As described above, according to this embodiment, the saturation of the signal in the servo loop, particularly the saturation of the drive signal for driving the tracking actuator which is close to the actual operation of the controlled object, is set as the monitored object, thereby achieving accurate saturation. , It is possible to detect the non-linearity of the servo loop, thereby preventing the erroneous adjustment of the automatic adjustment and stabilizing the servo.

In the above-described second embodiment, the saturation of the drive signal entering the tracking actuator is monitored to improve the accuracy of the saturation detection. However, this method is not suitable for realizing a servo circuit as an LSI. 2, ie, the analog-to-digital conversion circuit 207, the digital filter 208,
Digital-to-analog converter 210, disturbance generator 21
3. The gain measurement setting circuit 214 and the adder 216 can all be constituted by digital circuits or software, and these can be integrated into one digital LSI. Therefore, when it is assumed that these are formed into one LSI, the input of the LSI includes, in addition to a terminal for inputting an error signal required at least for servo operation and an output terminal to the drive circuit, a saturation detection signal. A control terminal for input is required. In the second embodiment, an analog saturation detection circuit 401 that performs saturation detection using an analog circuit
However, for example, when a circuit for detecting saturation is incorporated in an LSI, it is necessary to provide a second analog-to-digital conversion circuit for inputting a drive signal that is an analog signal. In a third embodiment described below,
Focusing on this point, an example which is more suitable for LSI will be described.

FIG. 4 is a block diagram of an automatic servo loop adjusting device according to a third embodiment of the present invention.

The control of the tracking actuator by the servo loop and the operation of automatic gain adjustment of the servo loop are the same as those described in the second embodiment. That is, tracking servo is performed using a servo loop including an error detection circuit 205, an analog / digital conversion circuit 207, a digital filter 208, a digital / analog conversion circuit 210, a drive circuit 211, a tracking actuator 203, and the like. The test signal 215 is injected into the loop, and the gain of the servo loop is adjusted based on the compression ratio of the test signal at the measurement point 217. Here, when the operation of the servo loop is considered in detail, the following can be understood. Gain measurement setting circuit 2
Numeral 14 changes the gain of the servo loop by changing the constant of the digital filter 208. The output (drive value 209) from the digital filter 208 is
After the digital-to-analog conversion is performed by the digital-to-analog conversion circuit 210, the digital signal is input to the drive circuit 211 and the drive signal 2 is output.
19, and drives the tracking actuator 203. Here, when the dynamic range of the output of the digital-to-analog conversion circuit 210 is set so as not to exceed the dynamic range of the input of the drive circuit 211 due to a change in the gain of the digital filter 208, the difference between the two circuits is determined. It can be said that the saturation of the drive signal does not occur at the time. Alternatively, the same can be said between the dynamic range of the error signal 206 output from the error detection circuit 205 and the analog-to-digital conversion circuit 207 inputting the dynamic range. Therefore, if the above condition is satisfied, there is a possibility that saturation may occur.
Can be considered only when the gain of the digital filter 209 becomes too large and the output of the digital filter 209 is saturated. That is, when the above condition is satisfied, the monitoring target of the detection is the output of the digital filter 209 (the driving value 20).
By setting 9), it can be said that signal saturation in the servo loop can be immediately detected.

Hereinafter, this embodiment will be described in detail. The digital saturation detection circuit 401 receives the drive value 209 and monitors and detects saturation by the following method. For example, assuming that the control value 209 is an 8-bit two's complement numerical value, the control value 209 is from -127 to +128.
Take the value up to. In this case, when the digital filter 208 continuously outputs +128 several times, it can be determined that this is a saturated state. In addition, even if +128 is not continuous, for example, when it becomes intermittent and frequently becomes +128, the control value 209 can be determined to be on the verge of saturation. As described above, when the control value 209 is saturated or is in a state similar to the saturation, the digital saturation detection circuit 401
02 is a gain measurement setting circuit 214 and a disturbance generation circuit 213
Send to In the gain measurement setting circuit 214, the saturation detection signal 4
When 02 is input, the adjustment of the gain based on the current gain is interrupted. When the disturbance detection circuit 213 receives the saturation detection signal 220, the disturbance generation circuit 213 stops outputting the inspection signal 215. As a result, the test signal 215 disappears during the servo loop, and the change of the constant of the digital filter 208 is interrupted. Therefore, the gain at the time when the saturation is detected is bolded.

In this embodiment, the range indicated by 403
That is, the digital-to-analog conversion circuit 207, digital filter 208, digital-to-analog conversion circuit 210, disturbance generation circuit 213, adder 216, gain measurement setting circuit 214, and digital saturation detection circuit 401 can be integrated into one digital LSI. It is. In this case, since the target of the saturation detection is the control value 209 which is the output of the digital filter 208, a control terminal for interrupting the gain adjustment at the time of saturation is not required, and the servo LS
It suffices to provide only an error signal input terminal and a drive signal control terminal which are the minimum required for I.

As described above, according to the present embodiment, the control terminal for interrupting the gain adjustment can be eliminated by using the control value 209 output from the digital filter 209 as the inspection target of the saturation detection. This makes it possible to realize a servo loop automatic adjustment device with fewer terminals and suitable for LSI.

In the first embodiment, as an operation of the automatic adjustment means 101 when the saturation detection signal 110 is received, an example has been described in which the automatic adjustment is interrupted and each constant is held as it is. For example, if the saturation is detected during the automatic gain adjustment, the automatic adjustment is interrupted and a gain slightly lower than the current gain is set in the control means 106. If so, any processing may be executed.

In the second embodiment, an example of the means for detecting the saturation of an analog signal has been described. However, any method capable of detecting the saturation of the analog signal may be used. For example, a method of converting the drive signal from digital to analog and comparing the digital data with a predetermined value, or measuring the number of saturations per unit time, and judging that the saturation is complete when the value exceeds a certain value, etc. Conceivable.

In the second embodiment, the driving circuit 211
Monitors the saturation of the drive signal 302 output by the digital-to-analog converter, the saturation of the analog signal output by the digital-to-analog conversion circuit 210 may be detected. By monitoring this, it is possible to detect the saturation of the output analog signal due to the failure of the analog-to-digital conversion circuit 202 and the like.

Further, in the second and third embodiments, as an example of the processing when the gain measurement setting circuit 214 receives the saturation detection signal, the constant change of the digital filter 208 is stopped. Saturation detection signal 220,
The constant at the time when the signal 402 enters is continuously set in the digital filter 208 thereafter, or the saturation detection signal 2
The constant setting using the gain measurement result after that point, such as setting the constant of the digital filter 208 so as to lower the gain a little from the point when 20, 402 enters, or setting it to a predetermined value. If not, any processing may be performed.

[0024]

As described above, according to the present invention,
Saturation detection means for detecting the saturation of the signal in the servo loop, and automatic adjustment when the saturation detection means does not detect the saturation of the first signal, and judges an abnormal state when the saturation is detected, and performs the automatic adjustment. With the provision of the automatic adjustment means for interrupting, the automatic adjustment is performed only in a stable state where the saturation of the signal in the servo loop does not occur, so that a malfunction of the automatic adjustment can be prevented.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an automatic servo loop adjusting device according to a first embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of an automatic servo loop adjusting device according to a second embodiment of the present invention;

3 is a block diagram and a waveform diagram showing a configuration example and a signal waveform of a saturation detection circuit 218 in FIG. 2;

FIG. 4 is a block diagram showing a configuration of an automatic servo loop adjusting device according to a third embodiment of the present invention.

DESCRIPTION OF SYMBOLS 101, 212 Automatic adjustment means 109 Saturation detection means 208 Digital filter 218 Analog saturation detection circuit 401 Digital saturation detection circuit

Continuation of the front page (56) References JP-A-61-134803 (JP, A) JP-A-2-56601 (JP, A) JP-A-2-273236 (JP, A) JP-A-61-86805 (JP) JP-A-55-4657 (JP, A) JP-A-61-32103 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G05D 3/00 G05B 13/02 G05D 3/12 305 G11B 21/10

Claims (1)

(57) [Claims] 1. A comparison between the target value and the control value, performs an error detecting means for outputting an error signal, and a control means for outputting a driving signal corresponding to the error signal, the operation according to the drive signal, Output the control value
Disk having a servo loop composed of an object to be controlled
In the apparatus, an automatic adjustment means for detecting an internal state of the servo loop and automatically adjusting a constant of the control means; and a saturation detection means for detecting saturation of a signal in the servo loop, wherein the automatic adjustment means Stops the operation after the saturation detecting means detects the saturation of the signal in the servo loop,
An automatic adjustment device for a servo loop, wherein a constant of the means is fixed .