JPS6273434A - Tracking system for optical disc device - Google Patents

Abstract

PURPOSE:To realize an ideal tracking by using a system eliminating a tracking offset generated with beam shift so as to eliminate simultaneously the servo deviation. CONSTITUTION:An optical disc device having a condenser lens 4 and a tracking actuator 11 driving the lens 4 is provided with a means detecting the position signal of the condenser lens 4 and the offset component of an off-track signal 11 attended with the beam shift of the reflected light from an optical disc medium 5 generated in response to the position signal is subjected to a tracking correction by a beam shift correction circuit 15 utilizing a position signal. In the system above, the beam shift correction circuit 15 is provided with a servo deviation correction circuit 20 correcting simultaneously the servo deviation as well generated by a beam tracking servo gain corresponding to the drive current of the tracking actuator 11. Thus, the off-track quantity DELTAT is nearly zero. That is, the beam shift term and the servo deviation term are eliminated at the same time.

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] This is a method that uses a method to remove tracking offsets that occur due to beam shifts, and also removes servo deviations at the same time.

[Industrial application field]

The present invention relates to an optical disk device, and particularly to a tracking method for an optical head.

[Conventional technology]

FIG. 2 shows a block diagram of a conventional example. In the figure, a parallel incident light beam l from a laser light source (not shown) travels straight through a beam splitter 2 and a λ/4 plate 3, is condensed by a condenser lens 4, and is imaged on a track of an optical disk medium 5. The reflected light 6 reflected thereupon enters the two-split optical sensor 7 via the beam splitter 2 due to the action of the λ/4 plate 3.

The intensity distribution of the light on the two-split optical sensor 7 is symmetrical when on-track (the image is located exactly at the center of the pre-group 8), and asymmetrical when off-track due to the direction of deviation as shown in the figure. becomes.

An off-track signal 10 is obtained by converting the difference in intensity of the two-split optical sensor 7 into a difference in electrical signals via a differential amplifier 9. That is, when the output of the two-split optical sensor 7 is zero, it is an on-track state, and the larger the output, the greater the degree of off-trunk.

Here, to select the required trunk, use the condenser lens 4.
It is also known to use a tracking actuator 11 to move the lens in a direction perpendicular to its optical axis (in the direction of arrow P).

In this case, since the optical axis of incidence on the condenser lens 4 and the optical axis of the condenser lens 4 are shifted (beam shifted), they do not coincide with the return optical axis reflected by the optical disk medium 5, and this beam shift amount is It is added to the trunk signal 10 as an offcent amount, giving an incorrect result to trunking control.

Therefore, in order to remove this offset ffi, means for detecting the position signal of the condenser lens 4 is provided. In this example, a filter 13 having operating characteristics dynamically equivalent to that of the tracking actuator 11 is connected to the output side of a current amplifier 12 that amplifies the drive current of the trunking actuator 11, and the output of the filter 13 is used to equivalently drive the condenser lens 4. A position signal 14 is being detected.

There is also a means for attaching a sensor to the condenser lens 4 to detect a position signal.

The off-track signal 10 corresponds to this position signal 14.
Correction amount 1 for canceling the offset) I that occurs in
A beam shift correction circuit 15 that produces a beam shift correction amount of 6 is provided, and a differential amplifier 17 calculates a correction amount of 16 from the off-track signal
The offcent amount was removed by subtracting .

[Problem that the invention seeks to solve]

FIG. 3 shows an explanatory diagram of tracking without correction.

In the figure, 8 is a pre-grouped trunk, 3
Reference numeral 8 indicates a beam spot, and reference numeral 19 indicates a locus of the beam spot 18.

The off-track amount ΔT in this case is ΔT= (ε/G)+8・Ko...■ko=2
・ (Ss/Sf)・・・・・・・・・■ However, C: Eccentricity G; 0 for servo gain: Constant indicating off trunk 1 generated by beam shift Ss: Offset 7 generated by beam shift Sensitivity Sf:
It is indicated by the sensitivity of the push-pull signal.

FIG. 4 shows a tracking explanatory diagram of the conventional beam shift 1 correction method explained in FIG.

The off-track amount ΔT when using the method of removing the tracking offset caused by beam shift is ΔT-(ε/G)+ε・KO-ε・KBI・・■0=4
．． Then, ΔT=ε/G・・・・・・・・・・・・・■ However, KI: Correction constant for the output of the filter 13 (or sensor output not shown), and the beam is completely The offset caused by the shift is removed. However, the servo deviation ε, /Q still remains as shown in FIG.

As described above, in the conventional method, even if the offset caused by the beam shift is removed, the servo deviation (following error) caused by the tracking servo gain for driving the tracking actuator 11 remains, and the The disadvantage is that it does not provide good track following performance.

The present invention was created in view of the above-mentioned conventional drawbacks, and an object of the present invention is to provide a method that can also remove remaining servo deviations at the same time.

[Means for solving problems]

The tracking method of the optical disc device according to the present invention is the first one.
As shown in the figure, an optical disc device comprising a condenser lens 4 and a tracking actuator 11 for driving the condenser lens 4 is provided with means for detecting a position signal of the condenser lens 4, and a means for detecting a position signal of the condenser lens 4 is provided. In this method, the offset component of the off-track signal 11 accompanying the beam shift of the reflected light from the optical disk medium 5 that occurs in response to the above is corrected by the beam shift correction circuit 15 that uses the position signal. The beam shift correction circuit 15 includes a servo deviation correction circuit 2 that simultaneously corrects the servo deviation generated by the tracking servo gain corresponding to the drive current of the tracking actuator 11.
It is characterized by adding 0.

[Effect]

In the present invention, 2 is added to the correction constant in the above formula By adding the output servo deviation correction circuit 20, the off-trunk amount ΔT can be made almost zero. In other words, the beam shift term and the servo deviation amount can be removed at the same time.

This is made possible by utilizing the phenomenon that the beam shift amount and the servo deviation amount are all proportional to the track eccentricity ε.

〔Example] Embodiments of the present invention will be described in detail below with reference to the drawings.

In order to make the explanation of the configuration and operation easier to understand, the same parts are denoted by the same reference numerals throughout the drawings, and repeated explanation thereof will be omitted.

FIG. 1 shows a block diagram of an embodiment of the present invention. In the figure, a servo deviation correction circuit 20 is attached to the output side of the filter 13, and an adder 21 adds 0 to the output ε of the beam shift correction circuit 15 and 2 to the output ε of the servo deviation correction circuit 20. The value is output to the off-track signal 11 by the differential amplifier 17.
The offset amount included in is removed.

That is, the sum of the beam shift offset term ε and 0 and the closed loop servo deviation ε/G is output as off-track 1 to the output terminal of the differential amplifier 9. In contrast, tracking actuator 1
1 drive current is input to the filter 13 (equivalent to the dynamic operating characteristics of the trunking actuator 11), and the filter 13 outputs a position signal of the condenser lens 4 equivalently.

As the position signal of the condenser lens 4, the output of a sensor attached to the condenser lens 4 may be used.

Based on this position signal, the beam shift correction circuit 15 outputs 0 for ε, and the servo deviation correction circuit 20 outputs 2 for ε, which are added by an adder 21, and the off-track signal 11 and the output of the adder 21 are combined. is subtracted by the differential amplifier 17, and its output becomes zero.

FIG. 5 is an explanatory diagram of tracking according to an embodiment of the present invention, and as shown, ideal track followability is achieved.

For example, when the conventional off-track tolerance is ±0.1-, if the servo gain is 60 dB, the deviation followability is ±1.
00 pm. According to the present invention, since this servo deviation ε/G can also be removed, the apparent his-servo gain is improved.

If lens vignetting, etc. are ignored, the gain is theoretically infinite, but experimentally an off-track value of 0.1- is obtained at a trackability of ±300 um, which is not what it seems. This corresponds to improving the upper servo gain by 10 dB.

〔Effect of the invention〕

As explained in detail above, according to the tracking method of the optical disc device of the present invention, ideal track followability can be realized.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is a block diagram of a conventional example, FIG. 3 is an explanatory diagram of tracking without correction, and FIG. 4 is an explanatory diagram of tracking using a conventional beam shift correction method. FIG. 5 shows an explanatory diagram of tracking according to an embodiment of the present invention. In the figure, 4 is a condenser lens, 5 is an optical disk medium, 1
1 is a trunking actuator, 15 is a beam shift correction circuit, and 20 is a servo deviation correction circuit. Receiver/Figure 1 P @Figure 2

Claims (1)

[Claims] An optical disk device comprising a condensing lens (4) and a tracking actuator (11) for driving the condensing lens (4) is provided with means for detecting a position signal of the condensing lens (4), In a method of correcting tracking by a beam shift correction circuit (15) using the position signal, an offset component of an off-track signal accompanying a beam shift of reflected light from an optical disk medium (5) generated in response to the signal. , the tracking actuator (11) is connected to the beam shift correction circuit (15).
) A tracking method for an optical disk device, characterized in that a servo deviation correction circuit (20) is added for correcting a servo deviation generated by a tracking servo gain corresponding to a drive current.