JPH031747B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a means for picking up an information signal including a synchronizing signal of a constant period, such as a video signal, from a disc-shaped recording medium (hereinafter abbreviated as disk) as a concentric or spiral recording track. The present invention relates to a signal reproducing device that reproduces the information signal.

Recently, it has become possible to record signals on disk at high density.
Many PCM audio disks have been proposed for video discs, but due to their high density, some of these devices require tracking control so that the reproducing means accurately follows the recording track during reproduction, and the frequency of the reproduced signal. There are ``grooveless capacitance methods'' and ``optical methods,'' which require time base control to make the frequency equal to the frequency of the signal when it is recorded.

An object of the present invention is to improve the accuracy of the time base control and the tracking control in a reproducing apparatus that requires both the tracking control and the time base control.

Conventionally, time base control in such devices is performed by separating the synchronization signal included in the reproduced signal and comparing the phase with a reference frequency, or by detecting fluctuations in the period of the synchronization signal.
A so-called negative feedback method obtains an error signal corresponding to the time axis fluctuation component in the reproduced signal, and uses this error signal to drive an actuator movable in the tangential direction of the disk (recording track direction) in a direction that cancels out the detected error signal. This constitutes a control loop.

Tracking control can also be carried out by, for example, separating the recorded tracking signal from the reproduced signal by switching the frequency every rotation during a recording track, obtaining a tracking error signal from the difference in amplitude between the two frequencies, and calculating the difference in amplitude. This is done by driving an actuator that is movable radially in the direction of cancellation.

Control using such negative feedback reduces the influence of nonlinearity of the detector, processing circuit, actuator, etc. to approximately 1/1 of the gain of the loop, making accurate control easy. Due to the frequency characteristics of the detector, there is a limit to the accuracy (or gain) for suppressing the error signal, and in order to improve this limit, a complex phase compensation circuit is required.

On the other hand, the imbase error in the disk,
There is a close relationship between tracking errors, and for the sake of simplicity, if only the fundamental frequency component is investigated, the following will be obtained.

In Fig. 1, focusing on a specific track on the disk E that is rotating at an angular velocity of ω, and assuming that Δr is the eccentricity and r is the true radius, the radius from the disk mounting hole D to the track at the playback position. R(t)
is expressed by the following formula.

R _(t) = r - Δr _cps (ω·t) ... (1) t: time (seconds) Also, the velocity V _(t) in the tangential direction at this time is expressed by the following equation.

V _(t) = r・ω−Δr・ω・cos(ω・t) ...(2) In equations (1) and (2), the term Δr becomes the track error and time base error due to eccentricity, respectively. , most of the actuators currently in use are
Since the relationship between the input voltage and the output displacement amount is linear, the signal input to the time base actuator that moves in the tangential direction is the integral of the term Δr in equation (2). Therefore, if the input signal of the tracking actuator is expressed as T _R(t) and the input signal of the time base actuator as T _B(t), the following equations are obtained.

T _R(t) Δr _cps (ω・t) ……(3) T _B(t) Δr _sio (ω・t) ……(4) As shown in the above equation, the two signals have a phase difference of 90°. It is a signal of the same nature.

Focusing on the above points, it is disclosed in Japanese Patent Publication No. 54-20121 that a tracking signal can be phase-shifted by 90 degrees to become a time-based control signal.
Proposed. However, the method disclosed in the above patent publication uses a complete open-loop control system to move the time base actuator, so it is sensitive to fluctuations in the entire system such as the environment such as the condition and temperature of the moving parts and the sensitivity of the actuator. It is not easy to completely shift the phase in a weak and wide frequency range, and in order to obtain two control signals with one signal,
If the signal detection is disturbed by a disturbance, both controls are disturbed, which poses a problem in terms of the stability of the device.

The present invention has been proposed focusing on the above points. Embodiments of the present invention will be described below with reference to the drawings.

In FIG. 2, the disk 1 is being rotated by a turntable motor 2 at a predetermined number of rotations. Reference numeral 3 denotes a pick-up support stand on which a pick-up means 5 is placed and driven in the radial direction of the disk 1 by a feed motor 4.

The pickup means 5 is freely driven in the radial direction by a tracking actuator 6 and in the tangential direction by a time base actuator 7. 8 is a head amplifier for amplifying the detection signal of the pickup means 5;
Its output terminal is the tracking signal detection circuit 9, 1
0 and 11, and are connected to the signal demodulation circuit 16.

The outputs of the tracking signal detection circuits 9 and 10 are switched in polarity each rotation by 12 switching circuits based on the switching signal detection output recorded every rotation of the tracking signal detection circuit 11. is supplied to This differential amplifier 13
The output of the phase compensation circuit 14 and the drive circuit 15
The tracking actuator 6 is controlled through. The above is a conventionally known tracking control circuit. The demodulated output of the signal demodulation circuit 16 is applied to the synchronization signal separation circuit 17, the synchronization signal is detected,
The phase is compared with the output of the reference oscillator 18 by a phase comparator 19, and the time base actuator 7 is controlled through a phase compensation circuit 22 and a drive circuit 23. The above is a conventionally known time base control circuit.

In addition to the above configuration, the present invention provides a phase compensation circuit 20 that shifts the phase of any one of the signals in the tracking control loop, for example, the outputs of the differential amplifier 13, the phase compensation circuit 14, and the drive circuit 15 by 90 degrees. After that, the adder 21 adds the result at an appropriate addition point in the time base control loop.
Residual errors in time base control can be extremely reduced.

In this embodiment, the phase compensation circuit 20 includes:
An integrator is used to shift the phase of the fundamental wave by 90 degrees and reduce the effects of high frequencies. Furthermore, since the DC component of the tracking signal and the DC component of the time base signal are unrelated, they are added after the DC component is removed.

Furthermore, another embodiment of the present invention is shown in FIG.
Signals in the time base control loop, e.g. phase comparator 19, phase compensation circuit 22, drive circuit 23
By passing one of the outputs through the phase compensation circuit 24 and adding it to an appropriate point in the tracking control loop at the addition point 25, the residual error in the tracking control can be extremely reduced as in the previous embodiment. . Phase compensation circuit 24 in this case
Instead of advancing the phase by 90° as, after reversing,
It is better to use an integrated signal.

Furthermore, it is possible to use the above two embodiments at the same time by devising the signal extraction points and addition points, which is a very simple and effective means for improving the accuracy of the entire control system. becomes.

In addition, from a practical point of view, the dual phase compensation circuits 20 and 24 are designed with attention paid to the fact that the fundamental wave component (rotational frequency of the disk) of both control systems is the largest, and a sufficiently large effect can be obtained.

Although not shown in the figure, in order to reduce the effect when either control system is disturbed by a disturbance, a means for detecting that both control systems are disturbed by a disturbance is provided. This problem can be solved by preparing the signals and turning on and off the signals that cross each other using an analog switch or the like, which is the gist of the present invention. The disturbance detection means includes, for example, a method of detecting a drop in the reproduced signal, a method of detecting phase lock loss of the time base phase comparator 19, a method of determining the upper and lower limits of the amplitude of the detection signals of both control systems, Possible methods include detection using a comparator.

The effects of this embodiment will be explained using a simple control theory.

Figure 4 is a block diagram of a negative feedback control system including a basic disturbance thread, where R _(S) is the target value, C _(S) is the control amount, D _(S) is the disturbance, and the gain in the loop is G _1(S) respectively,
When expressed as G _{2 (S)} , the residual error amount E _(S) is expressed by the following equation.

E _(S) = R _(S) /1+G _(S) −G _2(S) /1+G _(S)・D _(S) (5) G _(S) =G _1(S)・G _2(S) ( 6) Conventional negative feedback control reduces the residual error E _(S) in equation (5) to 0.
In order to approach this, efforts have been made to make G _(S) as large as possible, to make the disturbance D _(S) as small as possible, and to make the frequency characteristics of each component flat.

However, by finding the conditions under which the residual error E _(S) becomes 0 using equation (5), we obtain the above equation (7): D _(S) = R _(S) /G _2(S) (7).

In other words, if a signal related to the target value expressed by equation (7) is added from outside the control loop instead of the disturbance D _(S) , the residual error E _(S) can theoretically be reduced to 0.
It can be done.

To paraphrase each component in FIG. 4 according to the purpose of the present invention, E _(S) is the residual jitter amount or residual tracking error, and R _(S) is the time base reference frequency or the eccentricity of the disk itself. and
From the perspective of the time base control system, D _(S) is a signal obtained by shifting the phase of the tracking signal, and from the perspective of the tracking control system, it becomes a signal obtained by shifting the phase of the time base control signal.

Furthermore, by using this method, unlike conventional control methods, there is no need to increase the loop gain to the stability limit of the control system, which improves the stability of the control system and simplifies the circuit configuration. Can be done.

As mentioned above, the present invention has been proposed based on the fact that this type of device has exactly the ideal disturbance D _(S) as shown in equations (1) to (4) above. It is something that

It is also possible to match the phases of both signals by a method other than this example, for example, by providing speed detection means in the drive means of both control systems, or by adjusting the time base drive means to the input voltage. If the speed component of the output is linear (such as a motor), the phases of the two drive signals will match exactly, so a phase compensation circuit that does not cause a phase difference is required. Further, in the above explanation, it was explained that the phases are matched, but depending on the addition point, the addition may be performed with opposite phases.

Furthermore, the present invention is also effective when performing time base control of reproduced signals using semiconductor memory elements (CCB, BBD), which have been proposed in large numbers recently.

Although not shown in the figure, control signals are exchanged between time base control, turntable motor control, tracking control, and feed motor control as necessary.

Furthermore, in this example, "grooveless capacitance method" is used.
As explained in 2013, similar effects can be obtained in optical disc playback devices in which tracking control is performed using an independent radial position detector. Similar effects can be obtained even if a speed error detection method is used in addition to the phase comparison method.

Thus, according to the present invention, tracking,
By adding at least one of the time base control signals to the other control loop after waveform processing, the residual error can be reduced compared to that caused by a single control loop while ensuring sufficient stability of both control loops. The ideal control system, which is highly accurate and highly stable, can be obtained by simple means and has the suitable performance of both open-loop control and closed-loop control. be.

[Brief explanation of the drawing]

Fig. 1 is a diagram for explaining the relationship between tracking error and time base error in a disc playback device, Figs. 2 and 3 are block diagrams showing embodiments of the present invention, and Fig. 4 is a negative feedback control. This is a basic block diagram of the system. 1...disc, 2...turntable motor,
3...Pickup support stand, 4...Feed motor, 5
...pickup means, 6.tracking actuator, 7.time base actuator,
8... Head amplifier, 9, 10... Tracking signal detection circuit, 11... Tracking signal detection circuit, 1
2... Switching circuit, 13... Differential amplifier, 14... Phase compensation circuit, 15... Drive circuit, 16... Demodulation circuit,
17... Synchronization separation circuit, 18... Reference oscillator, 19...
Phase comparator, 20, 22, 24...phase compensation circuit,
21, 25... Adder, 23... Drive circuit.

Claims (1)

[Claims] 1. A pickup means for reproducing information from a recording track of a rotationally driven disc-shaped recording medium, a tracking control signal detection means for creating a tracking control signal according to a tracking error of the recording track of the pickup means, and the tracking control. a first driving means for driving the pickup means in a direction that reduces the tracking error according to a signal; and a time base error control for creating a time base error control signal according to a time axis fluctuation component in the reproduction information signal. a signal detecting means; and a second driving means for driving the pickup means in a direction that reduces the time axis fluctuation component according to the time base error control signal, and the tracking control signal and the time base error control signal A signal reproducing device characterized in that a signal corresponding to at least one control signal is added to the other control signal.