JPH04219801A - Automatic loop gain controller - Google Patents

Abstract

PURPOSE:To reduce the size of the automatic loop gain controller and simplify it by generating a reference signal by arithmetic processing based upon numeric data of <=1 cycle of a reference signal stored in a memory. CONSTITUTION:A tracking error signal detected by a tracking detector is converted by an A/D converter into a digital value, which is inputted to a digital signal processor(DSP). The DSP performs phase compensation by inputting the tracking error signal to a phase compensating filter 11. The output of the phase compensating filter 11 is sent to an adder 16 and added to the reference signal from a reference signal generation part 17. Thus, the reference signal of specific frequency is added to a control signal to be controlled and control signals right before and after the addition are detected to adjust the loop gain of a servo device according to the detection results.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic loop gain control device for keeping the loop gain of an automatic control device having a closed loop constant.

0002

2. Description of the Related Art In recent years, as the capacity of information to be handled has increased, optical information recording and reproducing devices that use light beams to store or reproduce information on storage media have been attracting attention. (Hereinafter referred to as an optical disk device.) In order to accurately record and reproduce information, such an optical disk device uses a focusing servo system that adjusts the focusing state of a light beam, and a tracking servo system that adjusts the irradiation state of a light beam on a track. It is equipped with a servo control device such as a system.

In these focusing servo systems and tracking servo systems, it is necessary to suppress the tracking error of the optical beam to the target position from ±1 micron to 0.1 micron. The open-loop gain in the system is set in the low frequency range (15
Hz or 30Hz) is 60dB or more. Furthermore, due to its structure, the objective lens actuator exhibits a gain peaking phenomenon due to secondary resonance in a frequency band of several KHz or more.

[0004] Therefore, it has been difficult to obtain sufficient phase margin and gain margin in the focusing servo system and tracking servo system in such an optical disc device.

[0005] In a servo system in which sufficient phase margin and gain margin cannot be obtained, there is a problem in that fluctuations in open loop gain significantly impair the stability of the system.

[0006]For this purpose, in the past, Japanese Patent Application Laid-Open No. 60-2274
An automatic loop gain control circuit as disclosed in Publication No. 6 (see Figure 4) is provided to suppress open loop gain fluctuations as much as possible.

[0007] This automatic loop gain control circuit adjusts the loop gain based on the total amount of light from a multi-division sensor included in a servo control device of an optical disc device.

However, although the automatic loop gain control circuit described above can absorb fluctuations in the loop gain due to changes in the reflectance of the recording medium, changes in laser power, etc., changes in the force constant of the actuator, changes in the sensitivity of the error detector, etc. can be absorbed. It was not possible to deal with fluctuations in loop gain due to changes in gain due to circuit elements.

In order to solve this problem, a predetermined reference signal is added within the closed servo loop, and the signal immediately after the addition is compared with the signal immediately before the addition that has gone around the servo loop. Methods have been devised to adjust the gain.

0010

However, this automatic loop gain control circuit requires an oscillator to generate a reference signal, making it difficult to miniaturize and simplify the circuit.

[0011]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide an automatic loop control circuit that can be miniaturized and simplified.

[0012]The purpose is to add a reference signal of a predetermined frequency to the control signal of the controlled object in an automatic loop gain control device used in a servo control device with a closed loop configuration that controls the controlled object to be positioned with respect to the reference. means for detecting the control signal immediately before the addition means and the control signal immediately after the addition means and setting an appropriate loop gain of the servo control device in accordance with the detection results; and one of the reference signals of the predetermined frequency. The reference signal is achieved by generating the reference signal based on the numerical data.

[0013]

Embodiments Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. First, an optical disc device embodying the present invention will be described with reference to FIG.

In FIG. 1, 1 is an optical disk used as a recording medium, and 2 is an optical system of an optical head. The signals obtained by the optical system 2 are sent to a tracking error detector 3 and a focusing error detector 4, respectively, and each detector detects a tracking error signal and a focusing error signal based on the output of the optical system 2. The tracking error detector 3 and focusing error detector 4 each perform detection using a known detection method for optical disc devices. Reference numeral 5 denotes an A/D converter that A/D converts the error signals output from each of the error detectors 3 and 4 into a digital signal.

Reference numeral 6 denotes a digital signal processor (hereinafter abbreviated as DSP) which performs various calculations using the A/D converted tracking error signal and focusing error signal and controls each actuator to be described later. Also, D
SP6 also controls the loop gain, as will be described in detail later. Furthermore, a memory 7 is used when the DSP 6 performs calculations, and this memory stores numerical data of one period or less of a reference signal for generating a reference signal to be described later. In addition, 8 is a D/D converter that converts the control amount obtained by each DSP 6 from a digital signal to an analog signal.
It is an A converter. Reference numerals 9 and 10 denote a tracking actuator and a focus actuator that respectively drive the optical system 2 in the tracking direction and the focusing direction based on the control of the DSP 6.

FIG. 2 shows a block diagram of a device for automatically controlling the loop gain of the servo system in the embodiment shown in FIG. In this example, the loop gain is automatically controlled by software processing by the DSP 6 shown in FIG. Therefore, FIG. 2 is a functional block diagram that is equivalent in terms of hardware. In the figure, reference numeral 11 denotes a phase compensation filter that performs phase compensation of the tracking servo system. The tracking error signal detected by the tracking detector 3 in FIG.
The signal is converted into a digital value by the /D converter 5 and input to the DSP 6. The DSP 6 first performs phase compensation by inputting the tracking error signal to a phase compensation filter 11. Note that the phase compensation filter is generally given by the following equation (1).

[0017]

[Outside]

As a result, the output signal whose phase has been compensated by the phase compensation filter 11 is passed through the bandpass filter 1 as control data for the tracking actuator 9 shown in FIG.
2 and the adder 16. Bandpass filter 12
Now, a predetermined frequency, here a component of the center angular frequency wc of the band of the tracking servo loop, which will be described later, is extracted. The bandpass filter 12 can be achieved with a configuration similar to the above-mentioned equation (1). The extracted reference signal component is output to the peak value detection section 13, and the peak value is detected. The detected peak value S1 is output to the amplification factor calculation section 14.

On the other hand, the output of the phase compensation filter 11 is sent to the adder 16 as described above, and the output is sent to the reference signal generator 17.
is added with the reference signal from The reference signal generating section 17 is
It generates a reference signal of a predetermined frequency, and in this example, there are 3
Generates a KHz reference signal.

In the software processing of the present invention, this reference signal is generated by arithmetic processing in the DSP 6 based on numerical data of one period or less of the reference signal stored in the memory 7. FIG. 3 shows the frequency characteristics of the tracking servo system of this embodiment. w1 in the figure indicates each low frequency, which is 50 Hz here. That is, since the rotation frequency of the optical disc 1 shown in FIG. 1 is 50 Hz, the low frequency characteristics are set accordingly. Also, lol
c is the center angular frequency of the frequency band of the tracking servo loop, which is 3 KHz in this example. Therefore, in this embodiment, the reference signal frequency of the reference signal generating section 17 is set to 3 KHz, which is the same as the central angular frequency wc. Further, the bandpass filter 12 also has wc as described above.
It is set to extract frequency components in the same way as .

The control data thus added to the reference signal by the adder 16 is output to the band pass filter 18 and the loop gain control section 20. Bandpass filter 1
8, similarly to the bandpass filter 12 described above, the component of the center angular frequency wc of the tracking servo loop is extracted and output to the peak value detection section 19. Peak value detection section 1
At step 9, a peak value is detected in the same way as the peak value detection section 13, and it is outputted to the amplification factor calculation section 14 as S2. The amplification factor calculation section 14 calculates an amplification factor K=S2/S1 for both the peak value S1 outputted from the peak value detection section 13 and the peak value S2 outputted from the peak value detection section 19. That is, the current value of the loop gain is calculated by determining the ratio of the signal level before the servo loop is run through the servo loop and the signal level after the servo loop is run through the servo loop. The obtained amplification factor K is
The signal is sent to the loop gain control section 20, where the loop gain is controlled.

The loop gain control section 20 first multiplies the control data sent from the adder 16 by an arbitrary number A (A=Q×K
) and output. In this case, the loop gain control section 20 varies the multiple Q of the control data so that the amplification factor K sent from the amplification factor calculation section 14 becomes a predetermined value. In other words, by adjusting the multiple of the control data so that K becomes a predetermined value, fluctuations in the loop gain of the tracking servo system are corrected. Therefore, if K is smaller than the predetermined value, the multiple of the control data is increased. If K is large, control is performed to reduce the magnification of the control data. This loop gain control operation is performed every time the tracking error signal is sampled. The control data of the loop gain control section 20 obtained in this way is output to the D/A converter 8 and converted into an analog value. The tracking actuator 9 is driven by a command value output from the D/A converter 8.

In this embodiment, the loop gain is controlled so that the above-mentioned value of K becomes 1. Bandpass filter 12
, 18 and the reference signal generating section 17 are set to the center angular frequency wc of the frequency band of the tracking servo system, as shown in FIG. Therefore, since the gain of this wc is O (dB) as is clear from FIG. 3,
It was set so that K=1. Furthermore, it is desirable to set K to 1, but the frequency may be set within the reference signal frequency range shown in FIG. 3, and K may be set in accordance with the gain corresponding to that frequency.

[0024]

[Effects of the Invention] As explained above, according to the present invention, numerical data of one cycle or less of the reference signal to be added to the control signal is stored in the memory, and when adjusting the loop gain,
Based on the numerical data, a reference signal is generated through arithmetic processing using an arithmetic circuit called a DSP, thereby eliminating the need for an oscillator and making it possible to miniaturize and simplify the circuit.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of an optical disc device embodying the present invention.

FIG. 2 is a block diagram showing an embodiment of the automatic loop gain control device of the present invention.

FIG. 3 is a characteristic diagram showing the frequency characteristics of the tracking servo system of the embodiment.

FIG. 4 is a block diagram of a conventional device.

[Explanation of symbols]

1 Optical disc 2 Optical system 3 Tracking error detector 6 DSP 11 Phase compensation filter 13, 19 Peak value detection section 14 Amplification factor calculation section 17 Reference signal generation section 20 Loop gain control section

Claims (1)

[Claims] 1. An automatic loop gain control device used in a servo control device with a closed loop configuration that controls a controlled object to be positioned with respect to a reference, comprising means for adding a reference signal of a predetermined frequency to a control signal of the controlled object; means for detecting the control signal immediately before the addition means and the control signal immediately after the addition means, and setting an appropriate loop gain of the servo control device in accordance with the detection results; and one period of the reference signal of the predetermined frequency. Alternatively, an automatic loop gain control device comprising: storage means for storing numerical data within this range, and wherein the reference signal is generated based on the numerical data.