JPH0755603Y2 - Servo gain measuring device for optical disk device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION A Field of Industrial Application The present invention relates to a servo gain measuring device for an optical disk device,
For example, it is suitable for application when measuring the servo gain of the player servo system of an optical laser type video disc player.

B Outline of the Invention This invention is included in the servo signal measuring device of the optical disc device for measuring the servo gain of the servo system, in the disturbance signal input to the servo system under test and the measurement signal output obtained from the detection circuit of the servo system under test. The servo gain can be easily adjusted with high accuracy by displaying the comparison result of the fundamental frequency signal components.

C Conventional Technology Conventionally, an optical laser type video disk player is designed so that the positional relationship between the pick-up and disk surfaces can be automatically adjusted by using a focus servo system and a tracking servo system.

For example, the sucus servo system automatically adjusts the vertical position of the objective lens to operate so that the laser light flux is always focused on the spot surface on the disk surface to a spot having a diameter of about 1.3 [μm]. Also, the tracking servo system
It automatically adjusts the reflection angle of the tracking mirror so that the spots on the disk surface always follow the track consisting of a row of pits.

These servo systems have the characteristic that the servo gain is attenuated as the frequency of the disturbance given from the outside becomes higher. Therefore, in the LV (laser vision) standard, the servo gain attenuation is similar to the drooping characteristic of the disk standard. Assuming that the servo gain is 0, the servo gain is guaranteed to be 0 [dB] at a frequency higher than the disk standard.

Therefore, as shown in FIGS. 3A and 3B, 2 [kHZ] in the focus servo system (FIG. 3A) and 4 [kHZ] in the tracking servo system (FIG. 3). (B)) is the reference frequency, and the servo gain at this time is 0
It is necessary to adjust to [dB].

For example, as shown in FIG. 2, a detection circuit 12 including a photo diode PD1 and a differential amplifier circuit 16, a resistor R3 and R4, a capacitor C1 and a diode D1 and D2, and a servo circuit 15 for momentary excessive input Limiter circuit 13 to limit inflow
And a servo gain adjusting circuit 14 including a variable resistor VR1 and a servo circuit 15 including a power amplifier 17, a servo motor 18, and an objective lens 19 for sending a feedback back output to a detecting circuit 12 via a servo loop 24. When adjusting the servo gain of the waste servo system 11, first, the sine wave output of the first reference frequency 2 [kHz] from the oscillator 23,
The disturbance input is input to the disturbance input terminal 21 of the focus servo system 11, and the disturbance input and the servo output obtained by the detection circuit 12 are input to the X and Y axis input terminals of the oscilloscope 22, respectively. Display the Lissajous waveform on.

In this state, the operator reads the Lissajous waveform of the oscilloscope 22 and adjusts the variable resistance VR of the servo gain adjusting circuit 14 so that the ratio of the X-axis and Y-axis values becomes a predetermined value.
Adjust 1.

D The problem to be solved by the invention is that, when the servo gain is measured using such a configuration, there is no significant difference between the level of the disturbance due to the oscillator 23 and the level of the signal from the video disk main line, and the S / N
The ratio is poor, and as a result, sufficient measurement accuracy cannot be obtained. In addition, the fluctuation of the signal level due to the rotation of the video disk is directly displayed on the screen of the oscilloscope, and the litharge waveform constantly fluctuates. is there.

In addition, measuring instruments such as oscilloscopes are expensive and heavy, which poses a problem when used for field service in a general market.

The present invention has been made in consideration of the above points, and the servo gain of an optical disk device that can measure the servo gain of a servo loop system with higher accuracy without using a precision instrument such as an oscilloscope. A gain measuring device is proposed.

E Means for Solving the Problems In order to solve the problems, in the present invention, the detection output signal obtained by the detection circuit 12 for detecting the servo state of the optical disk device is supplied to the servo circuit via the gain adjusting circuit 14. 15
The servo circuit 15 controls the servo state according to the detection output signal and supplies the disturbance signal together with the detection output signal to the servo circuit 15 and outputs the disturbance signal and the detection circuit 12. In the servo gain measuring device 1 of the optical disc device for measuring the servo gain by comparing the detected output signal with the detected output signal, the detected output signal output from the detection circuit 12 is input, and the basic of the disturbance signal among the detected output signals is input. The detection output signal processing unit 1A that converts the frequency signal component to DC and outputs the measurement voltage, the reference signal processing unit 1B that converts the fundamental frequency signal component of the disturbance signal to DC and outputs the reference voltage, and the measurement voltage and the reference voltage The subtraction circuit 5 for subtraction and the display means 6 for displaying the output signal of the subtraction circuit 5 are provided.

F action When measuring the servo gain of the servo system 11, the disturbance signal is given to the servo circuit 15 of the servo system 11, and the fundamental frequency signal component of the disturbance signal is converted into a direct current by the reference signal processing unit 1B and subtracted as a reference voltage 5 Is output to. A detection output signal obtained by the detection circuit 12 of the servo system 11 that follows the disturbance signal is input to the detection output signal processing unit 1A, in which the fundamental frequency signal component of the disturbance signal is converted into a direct current and the subtraction circuit 5 is used as a measurement voltage. Is output to. The subtraction circuit 5 converts the measured voltage input from the detection output signal processing unit 1A from the reference signal processing unit 1B.
The inputted reference voltage is subtracted, and the calculation result is displayed on the display unit 6. As a result, the gain of the servo system 11 at the reference frequency can be adjusted in a stable state, and the servo gain can be measured with high accuracy.

G Embodiment Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

In FIG. 1 in which parts corresponding to those in FIG. 2 are designated by the same reference numerals, 1 indicates a servo gain measuring device for an optical disc device as a whole, and a focus servo system 11 is a first device based on the LV standard. Input the disturbance signal of reference frequency 2 [kHz],
Used when adjusting the focus servo system so that the servo gain becomes 0 [dB].

The servo gain measuring device 1 includes a measurement signal processing unit 1A, a reference signal processing unit 1B, a subtraction circuit 5, and a voltmeter 6.

The reference signal processing unit 1B supplies the disturbance signal (2 [kHz] sine wave) generated in the oscillation circuit 7 to the test input terminal 21 of the focus servo system 11 via the output terminal 9. In addition, the disturbance signal is sent to the bandpass filter 3B via the buffer circuit 2B.
To extract the fundamental frequency signal component of the disturbance signal. This fundamental frequency signal component is a low pass filter 4B
Then, the DC voltage corresponding to the signal level of the disturbance signal is rectified and smoothed, and is applied to the subtraction circuit 5 as a reference voltage.

Further, the measurement signal processing unit 1A uses the servo output obtained from the detection circuit 12 of the focus servo system 11 as a measurement signal through the measurement input terminal 8 and the buffer circuit 2A to pass the bandpass filter.
It is input to 3B, the fundamental frequency signal component in response to the reference frequency of the disturbance signal is extracted from the measurement signal, and is given to the low-pass filter 4A as the measurement signal. The low-pass filter 4A removes low-frequency noise such as fluctuations of the measurement signal due to rotation of the disk, rectifies and smoothes the measurement signal, and supplies it to the subtraction circuit 5 as a measurement voltage.

The subtraction circuit 5 subtracts the measurement voltage and the reference voltage obtained from the measurement signal processing unit 1A and the reference signal processing unit 1B, respectively,
The subtraction result is displayed on the voltmeter 6 and sent to the measurement output terminal 10.

In the above configuration, when adjusting the servo gain of the focus servo system 11, the measurement input terminal 8 and the output terminal 9 of the servo gain measuring device 1 are respectively connected to the focus servo system 11
To the test output terminal 20 and the test input terminal 21 of the
And 31 to connect.

In this state, when the servo gain measuring device 1 and the focus servo system 11 are started, the disturbance signal obtained from the oscillation circuit 7 is supplied to the focus servo system 11 through the output terminal 9, and the buffer circuit 2B and the band circuit 2B. Pass filter
It is given to the subtraction circuit 5 via 3B and the low-pass filter 4B. At this time, the disturbance signal supplied to the subtraction circuit 5 is filtered by the band-pass filter 3B and the low-pass filter 4B to extract only the fundamental frequency signal component of the reference frequency (in this case, 2 [kHz]).

On the other hand, the disturbance signal applied to the test input terminal 21 of the focus servo system 11 via the output terminal 9 and the connection line 31 is supplied to the servo circuit 15 as disturbance. At this time, the servo circuit 15 operates the objective lens 19 by the power amplifier 17 and the servo motor 18 so as to respond to the input disturbance signal in the same manner as described above with reference to FIG.

Thus, the objective lens 19 vibrates due to disturbance, causing a focus error, which is detected by the photodiode PD1 of the detection circuit 12, and the detection output is passed through the differential amplifier circuit 16 to generate a focus error. Is output to the limiter circuit 13 as a focus error voltage for correcting the.

Here, the limiter circuit 13 and the gain adjusting circuit 14 output a servo signal for correcting the focus error to the servo circuit 15, and the servo circuit 15 thereby performs the servo operation so as to cancel the disturbance.

As a result, a focus error voltage that changes so as to follow the disturbance is obtained at the output end of the detection circuit 12, and this is output to the measurement input terminal 8 of the servo gain measuring device 1 via the test output terminal 20.

Of the focus error voltage input to the servo gain measuring device 1, the fundamental frequency signal component is extracted by the buffer circuit 2A and the band pass filter 3A, and low frequency noise and the like are removed by the low pass filter 4A. At the same time, it is rectified, smoothed, and provided as a stable measurement voltage to the subtraction circuit 5.

The subtraction circuit 5 subtracts the reference voltage obtained from the reference signal processing unit 1B from the measurement voltage representing the focus error voltage of the focus servo system 11 obtained from the measurement signal processing unit 1A, and the subtraction result is a voltmeter. 6 to display.

Since the adjustment target value of the servo gain of the video disk player is 0 [dB], the operator visually confirms the calculation result of the subtraction circuit 5 by using the voltmeter 6, and the disturbance input to the focus servo system 11 So that the level of the focus error voltage detected by the detection circuit 12 becomes the same as that of the focus servo system 11.
Can be adjusted to adjust the servo gain of the focus servo system.

According to the above configuration, the servo gain can be adjusted without using a complicated device such as an oscilloscope unlike the conventional case.

Further, both the measurement signal processing unit 1A and the reference signal processing unit 1B extract only the fundamental frequency signal band by the band pass filters 3A, 3B, and remove the low frequency components by the low pass filters 4A, 4B, and at the same time, smooth the DC and smooth. Therefore, only the detection output of the servo loop system with respect to the disturbance input to the circuit under measurement can be measured in a stable state.

Although the present invention is applied to the measurement of the servo gain of the focus servo system in the above-mentioned embodiment, it may be used instead of the measurement of the servo gain of the tracking servo system. In this case, the frequency of the disturbance caused by the oscillator 7 was changed from the first reference frequency 2 [kHz] to the second reference frequency 4 [kHz], and the filtering frequency bands of the band pass filters 3A and 3B were changed in the same manner. After that, the same adjustment operation as in the above case may be performed.

Further, in the above-mentioned embodiment, the present invention is applied to the servo gain measuring device of the player servo system of the video disc player, but instead of this, the servo gain at the reference frequency of the other servo loop system is adjusted to a predetermined signal level. You may apply when you do. In this case, the frequencies of the oscillator 7 and the band pass filters 3A and 3B are selected to be predetermined values as required.

Further, in the above-described embodiment, the determination of the measurement result is performed using the built-in voltmeter 6, but the measurement output terminal
It is also possible to make more precise measurements using other measuring instruments (for example, an oscilloscope).

H Effect of the Invention As described above, according to the present invention, the servo gain of the servo loop system can be easily measured with high accuracy.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of a servo gain measuring device according to the present invention, FIG. 2 is a block diagram showing measurement of a conventional focus servo system, and FIG. 3 is a focus. It is a frequency characteristic curve figure of a servo system and a tracking servo system. 1 ... Servo gain measuring device, 2A, 2B ... Buffer circuit,
3A, 3B ... Band pass filter, 4A, 4B ... Low pass filter, 5 ... Subtraction circuit, 6 ... Voltmeter, 7 ... Oscillation circuit, 11 ... Focus servo system.

Claims (1)

[Scope of utility model registration request] 1. A detection output signal obtained by a detection circuit for detecting a servo state of an optical disk device is supplied to a servo circuit via a gain adjusting circuit, and the servo circuit outputs the detection signal to the servo circuit according to the detection output signal. A disturbance signal is supplied to the servo circuit together with the detection output signal to a servo system for controlling the state, and the servo gain is measured by comparing the disturbance signal with the detection output signal output from the detection circuit. In the servo gain measuring device of the optical disk device, the detection output signal output from the detection circuit is input, and the detection output that converts the fundamental frequency signal component of the disturbance signal of the detection output signal to DC and outputs the measurement voltage A signal processing unit, a reference signal processing unit for converting the fundamental frequency signal component of the disturbance signal into a direct current and outputting a reference voltage, the measurement voltage and the reference voltage A subtraction circuit for calculation to the servo gain measurement device for an optical disk apparatus characterized by comprising a display means for displaying an output signal of the subtraction circuit.