JPH0758555B2 - Servo device for disk playback equipment - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a servo device of a disc reproducing device using a disc such as a compact disc player as a storage medium, and particularly to a tracking error or a focus error. It relates to the digitization of the error signal represented.

[Conventional technology]

Generally, as a signal recording medium, a disc reproducing device for reproducing a signal recorded on a disc, for example, a compact disc player for reproducing a recording signal of a compact disc (CD), includes focus control and tracking of a light detecting means. A servo device for controlling and sled control is installed.

As shown in FIG. 5, the disc 2 which is an optical storage medium,
Although rotated by the motor 4, the rotation speed thereof is controlled by the rotary servo mechanism so that the linear velocities of the recording tracks become equal in accordance with the signal data read from the disk 2. TS represents the control signal from the rotary servomechanism.

Photodetection means for irradiating the disk 2 whose rotation is controlled by such a rotation servo mechanism with laser light as a recording data detection medium and detecting reflected light from the pits and the mirror surface of the recording track on the disk 2. A pickup 6 is installed as. The pickup 6 irradiates the disc with, for example, a main beam corresponding to the recording track and two sub-beams displaced slightly to the left and right of the recording track so as to receive the reflected light. Therefore, the pickup 6 adjusts, together with the optical lens system, a focus mechanism that controls the optical lens system to perform focus control for forming a spot of a laser beam on the disc and an objective lens of the optical lens system in the recording track direction. The tracking mechanism and the sled mechanism for shifting the optical lens mechanism itself between the inner circumference side track and the outer circumference side track of the disk are provided, and the motor 8 operates the sled mechanism. Then, the pickup 6 is provided with a photo-detecting element corresponding to each beam in order to detect the reflected light.

The photodetection signal obtained from the pickup 6 is applied to an error signal detection circuit 10 that performs pickup signal processing, and is subjected to focus processing by addition / subtraction processing of the detection signal on the main beam spot side and the detection signal on the sub beam spot side. The error signal FE and the tracking error signal TE are detected.

The focus error signal FE is applied to the filter 12a and converted into a direct current, and then the driver is used as a focus control signal FC.
The focus drive output from the driver 14 is applied to the focus mechanism of the pickup 6. As a result, the optical system of the pickup 6 forms a main beam spot on the surface of the disc 2.

Further, the tracking error signal TE is added to the filter 12b and converted into a direct current, and then is added to the driver 18 via the adder 16 as a tracking control signal TC. Adder 16
In the case of shifting the pickup 6 to a different track, the tracking control signal TC and the jump signal JP required for jumping to a specific track are added to form the sled control signal SC. And the driver
Pickup 6 from 18 according to tracking control signal TC
The tracking drive signal is given to the tracking mechanism of 1 and the sled drive signal is given to the motor 8 at the time of track jump. As a result, the sled control is performed together with the tracking control, and the recording signal can be detected for the same or different tracks.

[Problems to be solved by the invention]

By the way, in the servo device shown in FIG. 5, the filters 12a and 12b can be made common and the filter coefficient (time constant) can be switched for each servo system.

FIG. 6 shows a specific circuit configuration of the filters 12a and 12b, which includes transistors 20 and 22 as switching elements for changing the filter coefficient.

An input terminal 24 provided on the bases of the transistors 20 and 22,
The switching signals V ₁ and V ₂ are individually added to 26, but the switching signals
When the base becomes high potential due to V ₁ , the transistor
20 becomes conductive, capacitor 28 is added, and switching signal
When V ₂ raises the base potential, the transistor
22 becomes conductive and resistance 30 is added, and each transistor 20, 22
A specific filter constant is obtained by the selective conduction / interruption state of.

When the filters 12a and 12b are configured by such an analog circuit, the capacitor 28 and the resistor 30 are connected to a transistor.
It is necessary to switch using switching means such as 20, 22. Since the filter characteristics are realized by using multiple elements such as resistors and capacitors, the unevenness of parts accuracy makes the servo system unstable, and the element temperature The characteristics affect the characteristics, and there is a change in characteristics over time, which makes optimal control difficult, and there are many external parts such as capacitors when integrated into an IC.
There were some drawbacks, such as not being able to take advantage of the benefits of IC integration.

Therefore, the present invention prevents the inconvenience of analog control and improves the reliability of servo control.

[Means for solving problems]

The servo device of the disc reproducing apparatus according to the present invention receives and selects the tracking error signal and the focus error signal obtained from the detection signal of the photodetecting means (pickup 6), as illustrated in FIGS. 1 and 2. A multiplexer (32) for alternately selecting the tracking error signal and the focus error signal by a signal, and an analog / digital conversion means (analog / digital converter) for converting the tracking error signal or the focus error signal selected through the multiplexer into a digital signal. A digital conversion section 36), a storage means (coeff-RAM 42) for storing a coefficient corresponding to the frequency characteristic to be set in the tracking error signal and the focus error signal, and the digital signal converted by the analog / digital conversion means. Tracking error signal And an error component obtained by multiplying the tracking error signal or the focus error signal by a first gain coefficient (Go) and a low frequency component from the tracking error signal or the focus error signal. , A low-frequency component is multiplied by a second gain coefficient (G ₁ ) read from the storage means, and a wide-range component is extracted from the tracking error signal or the focus error signal, and the low-frequency component is extracted as the low-frequency component. A digital signal processing unit (digital signal processing unit 38) for obtaining a tracking control signal by adding the error component obtained by multiplying the third gain coefficient (G ₂ ) read from the storage unit, and the digital signal processing unit Servo control and sequence control for applying the selection signal to the multiplexer And a stage (sequence control unit 34).

[Action]

In the servo device of the disk reproducing apparatus of the present invention, an error signal given as an analog signal is converted into a digital signal by an analog / digital conversion means, and then a servo output signal corresponding to an optimum frequency characteristic is formed by a digital signal processing means. To do. That is, the digital signal processing means (digital signal processing unit 38) is
Coefficients necessary for obtaining the optimum frequency characteristics necessary for servo control are stored in advance in the storage means (coeff-RAM42),
A control signal having a desired frequency characteristic is obtained by adding a coefficient corresponding to the error signal.

〔Example〕

FIG. 1 shows an embodiment of a servo device of a disc reproducing apparatus according to the present invention.

This servo device corresponds to the parts of the filters 12a and 12b and the adder 16 shown in FIG. 5, and each control of tracking control, sled control and focus control using a disk as a recording medium is digitized. It will be realized.

As shown in FIG. 1, the multiplexer (MPX) 32 receives the focus error signal FE or the tracking error signal TE added from the error signal detection circuit 10 shown in FIG. 5 according to the selection signal SE from the servo sequence controller 34. After alternating selection, analog-to-digital converter (ADC) 3
Add to 6.

ADC36 is a focus signal FE given as an analog signal.
And the tracking error signal TE is converted into a binary digital signal based on a constant sampling frequency fs,
The converted signal is processed by digital signal processing (digital signal p
rocessing) to a digital signal processing unit (DSP) 38.

DSP38 is the digitized focus error signal FE
And a tracking error signal TE is a calculation unit that gives necessary and optimum frequency characteristics by digital calculation processing, and is a selection signal from the servo sequence control unit 34.
The microcomputer 40 performs arithmetic processing based on SE and the servo control signal SN. In this case, a coefficient storage unit (coeff-RAM) 42 as a storage means stores a coefficient necessary for obtaining a specific frequency characteristic in advance, and the coefficient is read out as necessary and is calculated prior to calculation. Alternatively, coefficient data in the process of calculation is stored at any time, and the coefficient is updated in order to absorb fluctuation components such as secular change and temperature characteristic.

Then, the DSP 38 calculates the tracking control signal TC from the digitized tracking error signal TE and the focus control signal FC from the focus error signal FE, respectively, and outputs the thread control signal SC by setting the jump data. To do.

The tracking control signal TC, the focus control signal FC, and the sled control signal SC are applied to the digital / analog converter (DAC) 44, converted into an analog signal, and then applied to the MPX 46, from the servo sequence controller 34. Analog tracking control signal according to the selection signal SE
TC, an analog focus control signal FC or an analog thread control signal SC are sequentially output from the output terminals 48a, 48b and 48c. These control signals TC, SC, FC are applied to the driver 14 or 18 shown in FIG. 5 to perform tracking control, focus control and sled control.

Next, FIG. 2 shows an example of a digital signal processing system in the DSP 38.

This DSP38 performs signal processing for avoiding the influence of the servo gain necessary to realize the optimum control and the inductance of the actuator (coil) such as a pickup. Therefore, as shown in FIG. The digital output is an nth-order low-pass filter (LPF) 50 and a multiplier 52.
And the (n + 1) th-order high-pass filter (HPF) 54 is added to perform necessary signal processing with a digital filter. The LPF50 determines the servo characteristics and sets the response speed of control by the gain setting. , Also HPF54
Performs phase advance processing as compensation for the delay phase by the actuator included in the control system. That is, in the LPF50, extracts a low frequency component from the digital output of ADC 36, its low-frequency component is multiplied with the gain setting constant G ₁ as a second gain coefficient in the multiplier 56, the multiplier 52, digital ADC 36 The output is multiplied by a gain setting constant G ₀ as a specific first gain coefficient, the HPF54 extracts a high frequency component from the digital output of the ADC36, and the high frequency component is multiplied by the multiplier 58 as a third gain coefficient. Multiply the gain setting constant G ₂ . Each multiplier 52, 56, 58
After the output of is added by the adder 60, the added output is added to the first multiplexer (MPX) 62 to obtain the digital tracking control signal TD, and the low frequency component is extracted through the LPF 64 to extract the second multiplexer (MPX). ) From 66, obtain the digital thread control signal SD for skipping between a plurality of tracks. Then, each digital tracking control signal TD and digital sled control signal SD are taken out as an analog tracking control signal TC and an analog sled control signal SC via the DAC 44 and MPX 46.

Note that Jp ⁺ represents a characteristic signal that represents a jump from the center of the disc to the peripheral direction, and Jp ⁻ represents a characteristic signal that represents a jump from the periphery of the disc to the center direction. TD and SD can be obtained.

Therefore, in this DSP38, the LPF50 sets the frequency (f) -gain (G) characteristic and the frequency (f) -phase (φ) characteristic as shown in FIG. a represents gain and p represents phase. Multiplier 52
Then, as shown in FIG. 3B, the frequency (f) -gain (G) characteristic and the frequency (f) -phase (φ) characteristic are obtained, and the characteristics are flat. Also, in HPF54, the third
As shown in (C) of the figure, frequency (f) -gain (G)
Characteristics and frequency (f) -phase (φ) characteristics. Therefore, in the adder 60, the characteristics obtained by the LPF 50, the multiplier 52 and the HPF 54 are combined, and as shown in FIG. Optimal phase characteristics with a phase advance (φ _LC ) can be obtained at. By adjusting the gain constants G ₀ , G ₁ , and G ₂ arbitrarily, the cutoff frequency of the gain characteristics can be changed, and the control characteristics can be adjusted and the optimum response characteristics corresponding to the actuator characteristics can be obtained. it can.

Therefore, in FIG. 4, the nth-order LPFs 50, 64 and (n +
1) A specific configuration example when the degree of the next HPF 54 is n = 1 will be shown.

The first-order low-pass filter circuit 50 'includes an LPF 50 and a multiplier 56,
The secondary high pass filter circuit 54 'corresponds to the HPF 54 and the multiplier 58, and the primary low pass filter circuit 64' corresponds to the LPF 64.

80, 82, 8 in each filter circuit 50 ', 54', 64 '
4, 86, 88, 90 are adders, 68, 69, 70, 72, 74, 76, 7
Reference numerals 8 and 79 are coefficient multipliers, reference numerals 92, 94, 96 and 98 are delay units (D), and a ₀ , a ₁ , a ₂ , b ₁ and b ₂ are coefficients read from the coeff-RAM 42.

Therefore, in the first-order low-pass filter circuits 50 'and 64', the amplitude at frequency ω = 0 is normalized to 1, and the transfer function H (z) ₁ having an attenuation pole at ω = π / T is And the frequency amplitude characteristic | H (ω) ₁ | Becomes

Further, regarding the second-order high-pass filter circuit 54 ', similarly, the amplitude at the frequency ω = 0 is normalized to 1, and the transfer function H (z) ₂ having the attenuation pole at ω = π / T is And the frequency amplitude characteristic | H (ω) ₂ | Becomes However, in equation (4), W ₁ = a ₁ cos (ω /
T) ＋ b ₁ sin （ω / T） ＋ b ₂ cos （2ω / T） ＋ b ₂ sin （2ω /
T) + 2b ₁ b ₂ cos (ω / T) cos (2ω / T) + 2b ₁ b ₂ sin (ω /
T) sin (2ω / T), W ₂ = b ₁ cos (ω / T) −b ₁ sin (ω / T)
＋ b ₂ cos (2ω / T) −b ₂ sin (2ω / T) −2b ₁ b ₂ sin (ω /
T) sin (2ω / T) −2b ₁ b ₂ cos (ω / T) cos (2ω / T).

In this way, the digital signal processing of DSP38 enables MPX32
As shown in (D) of FIG. 3, the tracking error signal TE or the focus error signal FE from the ADC 36 is given a frequency characteristic suitable for the actuator, and the digital tracking control signal TD from the MPX 62, 66 is given.
Alternatively, the digital thread control signal SD is selectively output according to the selection signal SE from the servo sequence control unit 34. In that case, at the time of track jump, the tracking error signal TE is integrated and the digital thread control signal SD having no frequency characteristic is output. Then, according to the jump signal Jp ⁺ from the center of the disc to the peripheral direction and the jump signal Jp ⁻ from the periphery of the disc to the center direction,
Appropriate focus control and sled control are performed for each track jump.

Therefore, the filter in the servo system shown in Fig.
High-precision signal processing is realized by digital signal processing by DSP38 instead of approximate processing by 12a and 12b.
Reliable control can be performed. Moreover, DSP38
Since the optimum control can be performed by the program calculation processing in the processing at, the effect on the control characteristics due to the temperature characteristics of the elements and the quality irregularity due to analog processing can be avoided as well as precise control, and it can be changed over time. Can be absorbed and stable control can be realized.

〔The invention's effect〕

According to the present invention, since the servo control signal is formed by the program calculation processing of the error signal obtained from the light detection signal, external parts such as a capacitor are not required when the IC is formed, and the servo control is optimized. It is possible to achieve precise control, avoiding the influence on the control characteristics due to the temperature characteristics of the elements and uneven quality due to analog processing, realize control that does not change over time, and realize highly reliable signal reproduction. it can.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a servo device of a disc reproducing apparatus of the present invention, FIG. 2 is a diagram showing a configuration of a digital signal processing section of the servo device shown in FIG. 1, and FIG. FIG. 4 is a diagram showing frequency characteristics given by the digital signal processing unit shown in FIG. 2, FIG. 4 is a block diagram showing a concrete configuration example of the digital signal processing unit shown in FIG. 2, and FIG. Showing a servo device of a disc playback device,
FIG. 6 is a circuit diagram showing a specific configuration of a filter in the servo device of the disk reproducing device shown in FIG. 6 ... Pickup (light detecting means) 32 ... Multiplexer 34 ... Sequence control section (sequence control means) 36 ... Analog / digital conversion section (analog / digital conversion means) 38 ... Digital signal processing section (digital signal processing) Means) 42 ... Coefficient storage unit (storage means)

Claims (1)

[Claims] 1. A multiplexer that receives a tracking error signal and a focus error signal obtained from a detection signal of a photodetecting means and alternately selects the tracking error signal and the focus error signal by a selection signal, and a multiplexer that is selected through the multiplexer. An analog / digital conversion means for converting the tracking error signal or the focus error signal into a digital signal; a storage means for storing a coefficient corresponding to a frequency characteristic to be set in the tracking error signal and the focus error signal; An error component obtained by receiving the tracking error signal and the focus error signal digitized by the digital converting means and multiplying the tracking error signal or the focus error signal by a first gain coefficient; A low-frequency component is extracted from the tracking error signal or the focus error signal, the low-frequency component is multiplied by the second gain coefficient read from the storage unit, and a high-frequency component is extracted from the tracking error signal or the focus error signal. Digital signal processing means for obtaining a tracking control signal by extracting a band component and adding an error component obtained by multiplying the high band component by the third gain coefficient read from the storage means, and the digital signal processing means. And a sequence control means for applying the selection signal to the multiplexer, and a servo device for a digital reproducing device.