KR19990054472A - Servo System of Optical Pickup Unit with Disturbance Predictor - Google Patents

Abstract

The present invention relates to a servo system that performs focusing and tracking servo for an optical pickup unit.

Typically, the actuator does not precisely control the position control of the objective lens because disturbed components such as eccentricity and wobble of the disk are added to the compensated actuator control signal provided from the controller of the servo system to the actuator.

Accordingly, the present invention is characterized in that it includes a predictor that predicts substantial disturbance components to be applied to the actuator and adds them to the compensated actuator control signals from the controller and provides them to the actuator to substantially cancel the disturbance components applied to the actuator.

Description

Servo System of Optical Pickup Unit with Disturbance Predictor

The present invention relates to a servo system of an optical disc player, and more particularly, to a focus / tracking servo system capable of predicting and compensating for an error occurring in an optical pickup unit.

An optical disc player is a system for non-contact reproduction of a recording bit signal engraved on a disc by a laser beam and digital signal processing thereof. In such an optical disk system, in particular, the optical pickup unit performs a function of converting light reflected from the signal surface of the disk into an electrical signal after the laser beam is incident on the signal surface of the disk.

In the optical pickup unit shown in FIG. 1, a laser beam having a predetermined oscillation wavelength generated from a light source 10 composed of a laser diode is generated as parallel light while passing through the collimator lens 12. In this way, a part of the beam in which linearity is maintained as parallel light is reflected by the beam split 14, and a part passes through the beam split 14 and is incident on the objective lens 16, and the objective lens 16 Is focused on the recording surface of the recording medium 20, which is an optical disk, to read information recorded on the disk. At this time, the light focused on the recording medium 20 is reflected from the recording surface, reflected by the beam split 14 to the field lens 18, and is incident on the photo detector 22 via the field lens 18. The photo detector 22 demodulates the incident beam and reproduces the original signal.

Typically driving the actuator coil 60 such that the signal surface of the disk 20 is located within the focal depth of the laser beam is referred to as focusing servo, and the laser beam for optical pickup accurately traces along the track of the disk. Driving the actuator coil 60 to do so is referred to as tracking servo. The focusing servo uses a focusing error signal that indicates the extent to which the signal plane of the disc 20 deviates within the depth of focus of the laser beam, and the tracking servo generates a tracking error signal that indicates the extent to which the laser beam deviates from the track of the disc 20. I use it. The operation of the servo system of the optical pickup unit for focusing and tracking described above will be described with reference to the equivalent circuit diagram shown in FIG. 2.

The disk 20 contains digital information along the track, and the laser beam focused by the objective lens 16 is radiated on the signal surface of the disk 20. At this time, an error signal component, x (t), due to the distance difference between the disk 20 and the objective lens 16 is provided to one input of the first subtractor 26 through the input terminal 24.

The actuator 60 drives the objective lens 16 in the vertical direction so that the signal surface of the disk is located within the depth of focus of the laser beam for focusing control according to the actuator control signal provided from the controller 30, or performs tracking control. For this purpose, the objective lens 16 is driven and controlled in the left and right directions so that the laser beam can accurately trace along the track of the disc. At this time, the position signal component y (t) between the objective lens and the disk signal surface is generated and output, and fed back to the type force of the first subtractor 26 along the line 62.

The first subtractor 26 subtracts the error signal component, the position signal component from y (t), and y (t) to the controller 30, and can be implemented as a lead-lag compensator. The reference numeral 30 outputs an actuator control signal whose magnitude and phase are compensated with reference to the signal subtracted by the first subtractor 26, to the actuator 60.

Actuator control signal provided to the actuator 60 is the difference between the disturbance component, d (t) generated by the external factors and the disc eccentricity, etc. through the input terminal 40 and the control signal output from the controller 30 described above. A calculation is provided to the actuator 60 to readjust the distance between the disk and the objective lens 16.

However, the above-described servo system of the related art is simple in configuration, but the actuator control signal provided to the actuator 60 is disturbance component generated by external factors, disc eccentricity, etc. through the input terminal 40, d (t). In combination with the supplied to the actuator 60, there was a problem that accurate focusing control and tracking control is impossible.

Therefore, an object of the present invention is to provide a servo device of an optical pickup system capable of eliminating disturbance components.

According to the present invention for achieving the above object, a servo system for performing focusing and tracking servo for an optical pickup unit having an objective lens that forms a beam focused on a signal surface of a disc comprises: in response to an actuator control signal; An actuator for repeatedly adjusting the distance between the objective lens and the disc by controlling the position of the objective lens; An error signal component x (t) due to the distance difference between the disc and the objective lens, and the difference between the position signal component y < (y) < / RTI > Error compensating means for generating a phase compensated actuator control signal; Means for predicting disturbance due to disc eccentricity or the like applied to the actuator control signal; And means for generating the actuator control signal by adding the disturbance component predicted by the predicting means and the output of the error compensating means.

1 is a schematic configuration diagram of a general optical pickup unit;

2 is an equivalent circuit block diagram of a focusing / tracking servo system of the prior art;

3 is an equivalent circuit block diagram of a focusing / tracking servo system having a disturbance predictor of the present invention.

<Description of the code | symbol about the principal part of drawing>

20: optical disk 30, 300: controller

60, 600: actuator 800: predictor

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

FIG. 3 shows an equivalent circuit diagram of the servo device of the optical pickup system according to the preferred embodiment of the present invention, and the present invention will be described with reference to the optical pickup unit of FIG.

While recording and reproducing information from the signal surface of the disk 20 on which the laser beam focused by the objective lens 16 is radiated, the actuator 600 focuses according to the actuator control signal provided from the controller 300. And driving control of the objective lens 16 in the vertical direction and the left and right directions for tracking control. At this time, the distance signal component between the objective lens 16 and the disk 20, which are adjusted by the actuator 600, and the error signal component x (t) by y (t) and the distance difference therebetween are generated, respectively. It is provided to the input of the first subtractor 200 via the line 620 and the input terminal 100.

The first subtractor 200 provides the distance signal, the difference signal obtained by subtracting the error signal from the y (t), and the x (t) to the controller 300 and the first adder 700.

The controller 300, which may be implemented as a lead-lag compensator, generates an actuator control signal whose magnitude and phase are compensated by the difference signal subtracted from the first subtractor 200.

Since the disturbance component d (t) such as eccentricity and wobble of the disk is added to the compensated actuator control signal provided from the controller 300 to the actuator 600, the actuator 600 is added to the objective 600. It is impossible to precisely control the lens 16. Thus, according to the present invention, the disturbance applied to the actuator 600 substantially by estimating the disturbance component d (t) to be generated and adding it to the compensated actuator control signal from the controller 300 and providing it to the actuator 600. Offset the ingredients.

Accordingly, the actuator control signal u (t) output from the controller 300 is provided to the second input of the first adder 700, summed with the difference signal output from the first subtractor 200, and the predictor 800. Is provided. The predictor 800 uses a sum signal of the difference signal component of the first subtractor 200 and the compensated actuator control signal of the controller 300, as described below, for the disturbance component to be applied to the actuator 600. To predict.

In FIG. 3, the Laplacian transform function of the signal u (t) output from the controller 300 is U (s), the Laplacian transform function of the disturbance d (t) is D (s), and the disk and the objective lens 16 are separated from each other. Assuming that the Laplacian transform function of the distance y (t) is Y (s) and the equivalent modeling of the actuator 600 is A (s), the relationship between them can be defined as in the following equation.

U (s)-D (s) = A (s) ⋅Y (s)

Equation 1 described above is summarized as Equation 2 with respect to the disturbance function, D (s).

D (s) = U (s)-A (s) ⋅Y (s)

When the partial differential is solved for the disturbance function D (s) in Equation 2, it may be expressed as a second low pass filter (LPF) transfer function of Equation 3 below.

In Equation 3 Denotes a disturbance obtained by differentially dividing the disturbance D (s). Substituting D (s) of Equation 2 into Equation 3 results in the following Equation 4.

In Equation 4 described above, s is a Laplacian operator, ζ is a damping integer, ω _n ² Is the natural undamped frequency.

Therefore, the disturbance prediction signal derived from Equation 4 described above, Is provided to the second adder 900, in which the compensated actuator control signal of the controller 300 is added and the estimated actuator control signal is added to the actuator 600.

Accordingly, the disturbance signal d (t) applied to the actuator control signal estimated by the second subtractor 500 is canceled and provided to the actuator 600. Accordingly, the actuator 600 precisely readjusts the distance between the disk and the objective lens 16 according to the output signal of the second subtractor 500.

As described above, according to the present invention, the disturbance generated in the optical pickup unit, for example, the eccentricity and shake of the disk and the offset caused by the movement in the radial direction of the objective lens and the like are predicted and used. By canceling substantially the disturbance generated, accurate distance and position adjustment between the optical disk and the objective lens can be performed.

Claims (3)

A servo system that performs focusing and tracking servo for an optical pickup unit having an objective lens that forms a beam focused on a signal surface of a disk: An actuator for repeatedly adjusting the distance between the objective lens and the disc by controlling the position of the objective lens in response to an actuator control signal; An error signal component x (t) due to the distance difference between the disc and the objective lens, and the difference between the position signal component y &lt; (y) &lt; / RTI &gt; Error compensating means for generating a phase compensated actuator control signal; Means for predicting disturbance due to disc eccentricity or the like applied to the actuator control signal; And means for generating the actuator control signal by adding the disturbance component predicted by the predicting means and the output of the error compensating means. The method of claim 1, The prediction means is: An adder for adding the difference signal between the error signal and the distance signal and the compensated actuator control signal; And a predictor for generating the predicted disturbance signal by using the signal added by the adder. The method of claim 2, The predicted disturbance signal generated by the predictor is represented by the following equation Is equal to, in the above formula, Is the predicted disturbance signal, U (s) is the Laplacian transform function of the compensated actuator control signal output from the error compensation means, D (s) is the Laplacian transform function of the disturbance signal, and Y (s) is the disk The Laplacian transform function, A (s), of the distance signal between the objective lenses is the equivalent modeling of the actuator, s is the Laplacian operator, ζ is the attenuation integer, ω _n ² Is a natural undamped frequency servo system of the optical pickup unit.