JPS6374126A - Focus servo device - Google Patents

Abstract

PURPOSE:To perform the automatic control of loop gains regardless of the characteristic variation among various elements by supplying a desired addition signal to a focus error signal and controlling the gains of the focus error signal in response to the change of the addition signal caused by the loop transmission characteristics. CONSTITUTION:The focus error signal produced via a photoelectric element 1, a differential amplifier 4, etc. is added with an addition signal of a prescribed frequency received from a generating circuit 11. Then the focus servo control is carried out via an amplifying circuit 7 and an actuator 8. The addition signal is separated from the output of the circuit 7 by a BPF 13. A multiplying circuit 14 detects the phase change value in response to the servo loop transmission characteristics to the original addition signal received from the circuit 11. Then the detection value is converted into the DC value by an LPF 15 and supplied to a control circuit 16. Thus the gains of the focus error signal are controlled and the servo loop gains are automatically controlled despite variation of characteristics such as sensitivity of a light source and a photoelectric element, the reflection factor of a disk, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a focus servo device for compact disc players, optical video disc players, etc.

[Summary of the invention]

In the present invention, an addition signal is added to the focus error signal in order to control its gain.

[Conventional technology]

FIG. 3 is a block diagram of a focus servo device in a conventional compact disc player or the like. In the figure, reference numeral 1 denotes a pair (a, b) of photoelectric elements, the outputs of which are each input to a differential amplifier 4 via a low-pass filter 2.3. The output of the differential amplifier 4 is input to an attenuator 5 as a control circuit, and the output of the attenuator 5 is supplied to an actuator 8 via an equalizer 6 and an amplifier circuit 7.

The light irradiated onto a disk (not shown) and reflected therefrom is input to the photoelectric element 1 and converted into an electrical signal. The low-frequency components of the output of the photoelectric element 1 are separated by a low-pass filter 2.3. The difference between the outputs of the low-pass filters 2.3 is calculated by the differential amplifier 4, and a focus error signal is generated. The focus error signal is controlled (manually adjusted) to a predetermined level by an attenuator 5. This signal is equalized by an equalizer 6, amplified by an amplifier circuit 7, and supplied to an actuator 8.

The actuator 8 drives, for example, a pickup (objective lens), not shown, in the optical axis direction, and focuses the light to the disk onto its recording surface.

The above system is represented by a block diagram of a transfer function as shown in FIG. 4. G here is the photoelectric element 1 to the amplifier circuit 7.
G2 is the transfer function of the actuator 8. If a disturbance A in the focus direction is now applied to the pickup (disk), this disturbance A flows into the focus servo loop via the adder circuit 9. If the disturbance in the focus servo loop is B, then the addition circuit 9
In, B = A-B G-G2 (1)
Because it holds true.

B==A/(1+G,G,)・・・・・・・・・(2)
That is, the disturbance A is compressed to 1/(1+G iG z ) within the focus servo loop.

[Problem that the invention seeks to solve]

By the way, if there are variations in the reflectance of the photoelectric element 1, the light source, or the disk, the gain of the DC loop of the servo system will change. In the conventional device, the gain was manually adjusted each time using the attenuator 5 in such a case. Therefore, not only was the adjustment time-consuming, but the operability was poor.

[Means for solving problems]

The present invention provides a focus servo device including: a differential amplifier that outputs a focus error signal from the output of a photoelectric element;
an amplifier circuit that amplifies and outputs the focus error signal;
An actuator that controls the focus position in response to the output of the amplifier circuit, a generation circuit that generates an addition signal, an addition circuit that adds the addition signal to the focus error signal, and a focus servo loop that separates the components of the addition signal. The present invention is characterized by comprising a separation circuit, a comparison circuit that compares the addition signal with the output of the separation circuit, and a control circuit that controls the gain of the focus error signal in response to the output of the comparison circuit.

[Effect]

An addition signal consisting of a signal of a predetermined frequency is added to the focus error signal. The component corresponding to this sum signal is separated from the servo loop and compared with the original sum signal. The gain of the focus error signal is controlled in accordance with the comparison result.

〔Example〕

FIG. 1 is a block diagram of a focus servo device of the present invention, and parts corresponding to those in FIG. 3 are given the same reference numerals. In FIG. 1, reference numeral 11 denotes a generating circuit that generates an addition signal of a predetermined frequency.

12 is an addition circuit that adds this addition signal to the focus error signal. Reference numeral 13 denotes a bandpass filter as a separation circuit that separates the added signal component from the output of the amplifier circuit 7. 14 is a multiplication circuit (phase detection circuit) as a comparison circuit, which multiplies (compares) the signal output by the generation circuit 11 and the signal output by the bandpass filter 13, and outputs a signal corresponding to the phase difference. . The output of the multiplication circuit 14 is smoothed by a low-pass filter 15 and output as a control signal for controlling the gain of the control circuit 16. Other plantings are the same as in FIG. 3.

A focus error signal is generated by the differential amplifier 4 from the output of the photoelectric element 1, and this signal is sent to the control circuit 16.
, an adder circuit 12, an equalizer 6,.

The signal is supplied to the actuator 8 via the amplifier circuit 7 in the same manner as described above.

In the present invention, the addition circuit 12 adds the addition signal output from the generation circuit 11 to the focus error signal output from the differential amplifier 4 and controlled to a predetermined level by the control circuit 16. As a result, the objective lens moves up and down in response to the addition signal.

The addition signal in this focus servo loop is transmitted to the amplifier circuit 7.
is separated from the output by a bandpass filter 13.

The phase of this separated addition signal changes in accordance with the transfer characteristics in the focus servo loop.The 6-multiplying circuit 14 adds the reference addition signal output from the generation circuit 11 and the phase change output from the bandpass filter 13. signal and outputs a signal corresponding to the phase difference between the two. After this output is smoothed by a low-pass filter 15, the control circuit 1
6 as a control signal. The control circuit 16 automatically controls the gain (level) of the focus error signal in accordance with the control signal.

FIG. 2 is a block diagram of the transfer function of FIG.

When the addition signal is input to the block (actuator 8) of the C1 transfer function G, and the adjustment gain in the control circuit 16 is K.

D = G engineering ((A - D G,) K + C)...
・(3) Therefore, D = AKG, / (1 + KG, G,) + CG engineering / (1 + K OL Gi) ...... (4
). The bandpass filter 13 separates the second term on the right side of equation (4). Therefore, the multiplier circuit 14 generates a signal G generated from the signal C and the signal CG, /(1+xa,a,).
, /(1+KGLG,). KG, G is the open loop characteristic of the focus servo system, and when this changes, the signal G, / (1 + K
The phase of G, G, ) also fluctuates. Therefore KG, G, and G
, /(1+KG a Z ), KGiG can be controlled to an optimal value.

〔effect〕

As described above, the present invention provides a focus servo device including a differential amplifier that outputs a focus error signal from the output of a photoelectric element, an amplification circuit that amplifies and outputs the focus error signal, and a focus servo device that performs focusing in accordance with the output of the amplification circuit. An actuator that controls position, a generation circuit that generates an addition signal,
An addition circuit that adds an addition signal to the focus error signal, a separation circuit that separates the components of the addition signal from the focus servo loop, a comparison circuit that compares the addition signal with the output of the separation circuit, and a comparison circuit that corresponds to the output of the comparison circuit. A control circuit for controlling the gain of the focus error signal is provided, thereby reducing the sensitivity of the light source and photoelectric element.

Even if there are variations in the reflectance of the disk, the loop gain is automatically adjusted, improving operability.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a focus servo device of the present invention,
FIG. 2 is a block diagram of the transfer function, and FIG. 3 is a block diagram of a conventional focus servo device. FIG. 4 is a block diagram of the transfer function. 1...Photoelectric element 2.3...Low pass filter 4...Differential amplifier 5...Attenuator 6...Equalizer 7...Amplification circuit 8...Actuator 9...Addition circuit 11. ...Generation circuit 12...Addition circuit 13...Band pass filter 14...Multiplication circuit 15...Low pass filter 16...Control circuit Above Figure 1 O Figure 2

Claims (1)

[Claims] A differential amplifier that outputs a focus error signal from the output of the photoelectric element, an amplifier circuit that amplifies and outputs the focus error signal, an actuator that controls a focus position in response to the output of the amplifier circuit, and an addition signal. A generating circuit that generates the addition signal, an addition circuit that adds the addition signal to the focus error signal, a separation circuit that separates the components of the addition signal from the focus servo loop, and an output of the addition signal and the separation circuit are compared. What is claimed is: 1. A focus servo device comprising: a comparison circuit for controlling the focus error signal; and a control circuit for controlling the gain of the focus error signal in response to the output of the comparison circuit.