JP2730653B2 - Head position / speed detector for seek servo - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a disk driver for recording and reproducing information on and from an optical disk or a magneto-optical disk, and more particularly, to a head position / speed detecting device for seek servo in a disk driver of a sample servo system. Regarding improvement.

[0002]

2. Description of the Related Art The following control techniques are known for drivers for optical disks and magneto-optical disks. FIG.
As shown in FIG. 4, a control pit set consisting of a center pit PC located on the track center line of the disk and a pair of offset pits PL and PR located at positions shifted left and right from the track center line is formed at predetermined intervals. Keep it. When performing a seek control for moving a reproducing head or a recording / reproducing head to a predetermined track of a disk, a read signal of the control pit set is sampled from a head output, and a seek operation (during a track traversing operation) is performed from the signal. Detects the moving speed and position of the head,
Feedback control of an actuator (linear motor) for moving the head is performed.

FIG. 5 shows a conventional typical circuit configuration of a head position / speed detecting device for this purpose.

In FIG. 5, the read output of the optical head 1 is A
The digital signal is converted by the / D converter 2 and input to the clock recovery circuit 3, the center pit latch circuit 4, and the offset pit latch circuits 5 and 6. Each latch circuit 4, 5, 6
Is based on the sampling signal from the clock recovery circuit 3,
From the head output, the read signal SC of the center pit PC,
The read signal SL of the offset pit PL and the read signal SR of the offset pit PR are sampled. As shown in FIG. 4, if the read spot of the optical head 1 is on the track center line, the level of the read signal SC of the center pit PC is large, and the offset pits PL and PR
Of the read signals SL and SR are small and almost equal.
When the read spot passes directly above the offset pit PL, the read signal SL becomes the largest, and when the read spot passes directly above the offset pit PR, the read signal SR becomes the largest.

Therefore, during the traversal of the optical head 1, each of the latch circuits 4, 5, and 6, as shown in FIG.
Read signals SC, SL, S having waveforms that fluctuate in a substantially sinusoidal manner
R is output. Here, each of the read signals SC, SL, and SR includes the following information. (A) The peak point of the center pit read signal SC indicates that (the read spot of) the optical head 1 coincides with the track center. (B) The phase difference between the signals SC, SL, and SR depends on the moving direction of the optical head 1 (whether it is toward the inner circumference or the outer circumference of the disk).
Represents (C) The differential components of the signals SC, SL, and SR are the optical head 1
Represents the moving speed of

As shown in FIGS. 5 and 2, the center pit read signal SC is binarized by comparing it with a threshold value f appropriately set by a comparison circuit 7, and the binarized signal a of SC is output.
Becomes Since this signal a is turned on when the optical head 1 is positioned on the track, this signal is called a track detection signal a. Further, a subtraction circuit 8 produces a difference signal SLR between the offset pit read signal SL and SR, and a differentiation circuit 9 produces a differentiation signal DSLR of the difference signal SLR. In addition, 2
The binarizing circuit 12 produces a signal b obtained by binarizing the difference signal SLR with positive and negative, and the binarizing circuit 13 produces a signal c obtained by binarizing the differential signal DSLR with positive and negative.

The track counter 10 is capable of counting (enable) when the track detection signal a (SC binarized signal) is on, and is down-counted when the DSLR binarized signal c is on and off when it is off. In the count mode, the rising and falling points of the binary signal b of the SLR become count inputs. When the optical head 1 traverses toward the inner circumference of the disk, the track counter 10 counts up at the falling edge of the SLR binarized signal b. When the optical head 1 traverses toward the outer circumference, the track counter 10 counts up. 10 is SLR2
It is counted down at the rising edge of the value signal b.
In this way, the number of track traversals during head traversal is counted according to the traverse direction, and the count value of the track counter 10 is output as the position signal PO of the optical head 1.

A fall detection circuit 17 produces a fall detection signal g of the SLR binarized signal b, and the differential signal DSLR is latched by the latch circuit 11 at the timing of the signal g. Is output as the speed signal VA. That is, at the point where the difference signal SLR changes from positive to negative at a large change rate, the change rate (differential signal DSL)
R) is sampled as the speed signal VA. However, since the speed signal VA does not include the traverse direction information, a circuit for determining the traverse direction by looking at the polarity of the SC binary signal a at the timing of the falling detection signal g is provided (not shown).

When the head is traversed toward the outer periphery, for example, when the disk is eccentrically rotated, if the traverse speed is low, the relative movement direction of the head with respect to the track may be reversed. In this device,
It is necessary to properly detect the position and speed of the relative movement of the head with respect to the track.

[0010]

The conventional apparatus shown in FIG. 5 has the following problems. (1) Since the threshold value f for binarizing the center pit read signal SC is a fixed value, a relative threshold is set when the reflectivity of the disk changes or the read sensitivity of the optical head changes. The value f becomes inappropriate and correct binarization cannot be performed. Therefore, the reliability of the track detection signal a is low, and a signal error is likely to occur. (2) Since the differential signal DSLR is sampled only once in one cycle of the difference signal SLR in order to obtain the speed signal VA, the response of the speed signal VA to the actual speed of the head is poor, and high-precision servo control is performed. Can not do.

The present invention has the above-mentioned conventional problems (1).
The purpose of the present invention is to provide a seek servo head position / speed detection device capable of generating a highly stable and accurate track detection signal and generating a highly responsive speed signal. Is to provide.

[0012]

A seek servo head position / speed detecting device according to the present invention comprises a center pit located on a track center line and a pair of offset pits shifted left and right from the track center line. Means for sampling a read signal of the center pit and a pair of offset pits from an output signal of the head, wherein the read signal of the center pit is read by the pair of offset signals; Means for binarizing a value corresponding to the average value of the read signals of the offset pits as a threshold value, means for obtaining a difference signal between the read signals of the pair of offset pits, and means for differentiating the difference signal; Means for binarizing the difference signal; means for binarizing the differential signal; A counting operation can be performed when the binarized signal of the pit read signal has a predetermined polarity, and whether to count up or down is determined according to the polarity of the binarized signal of the differential signal; Track counting means for receiving a signal as a count input; means for detecting a zero-cross point of the difference signal; and inverting the polarity of the differential signal in accordance with the polarity of the binarized signal of the center pit read signal. Means for latching the operated differential signal at the zero-cross detection timing.

[0013]

When the reflectance of the disk changes or the sensitivity of the head changes, the average level of the head output changes. Of course, the level of the threshold value generated from the average value of both offset pit read signals also fluctuates, so that the threshold value for binarization of the center pit read signal is always kept at an appropriate level. Thus, an accurate and stable binarized signal (track detection signal) can be obtained.

Further, since the zero crossing point of the difference signal is twice in one cycle, the sampling interval of the speed signal is twice as long as the conventional one, and the response is improved. Further, the speed signal has a polarity corresponding to the traverse direction.

[0015]

FIG. 1 shows the configuration of an embodiment of the present invention. The same components as those of the conventional device of FIG. 5 are denoted by the same reference numerals. Since the conventional apparatus has already been described in detail, the embodiment of the present invention will be described focusing on parts different from the conventional apparatus.

In the conventional apparatus shown in FIG. 5, the threshold value f for binarizing the center pit read signal SC to generate the track detection signal a is a fixed value. On the other hand, in the apparatus shown in FIG.
And SR are added and divided by 2, and the output e (SL and SR
(Average value of) is input to the comparison circuit 7 as a threshold value for SC binarization. Therefore, the threshold value e also fluctuates in accordance with the fluctuation of the output level of the optical head 1, and the center pit read signal SC is always kept at an appropriate threshold level by two.
Accurate and stable track detection signal a
Can be obtained. The other configuration related to the operation of the track counter 10 is the same as the conventional one. According to the present invention, since the reliability of the track detection signal a is improved, the miss count in the track counter 10 is reduced, and the reliability of the position signal PO is improved.

The differential signal DSLR of the difference signal SLR between the offset pit read signals SL and SR is input to the latch circuit 11 via the polarity switching circuit 16. The polarity switching circuit 16 inverts the DSLR when the track detection signal a is on, and inputs the DSLR to the latch circuit 11 as it is when the signal a is off.

A zero-cross detection circuit 15 of FIG. 1 which replaces the falling detection circuit 17 of the conventional device of FIG.
As shown in FIG. 2, a small pulse zero-crossing detection signal g responding to both the rising edge and the falling edge of the SLR binarized signal b is generated. The latch circuit 11 responds to the zero-cross detection signal g,
The differential signal DSLR after 6 is latched and output as a speed signal VA. That is, since the differential signal DSLR is sampled twice in one cycle to generate the speed signal VA, and the polarity of the differential signal is inverted according to the traverse direction, the polarity according to the traverse direction is applied to the speed signal VA. Get on.

[0019]

As described above in detail, in the seek servo head position / speed detecting apparatus according to the present invention, even if the average level of the head output fluctuates due to fluctuations in the reflectivity of the disk and the sensitivity of the head. Since the threshold value for generating the track detection signal follows and changes and is always maintained at an appropriate level, an accurate and stable track detection signal can be generated, and a highly reliable head position signal can be generated based on the signal. Can be obtained. Further, since the sampling interval of the speed signal is twice as long as the conventional one, the responsiveness of the speed signal to the actual speed of the head is very high, so that highly accurate servo control can be performed.

[Brief description of the drawings]

FIG. 1 is a schematic block diagram of an apparatus according to an embodiment of the present invention.

FIG. 2 is a timing chart showing the operation of the above device and the conventional device of FIG. 5;

FIG. 3 is an explanatory diagram of a control pit set formed on a disk.

FIG. 4 is an explanatory diagram of a control pit set and its read signal.

FIG. 5 is a schematic configuration block diagram of a typical conventional apparatus.

[Explanation of symbols]

 PC center pit PL, PR offset pit SC center pit read signal SL, SR offset pit read signal a SC binarized signal (track detection signal) SLR difference signal DSLR differentiation signal PO position signal VA speed signal

Claims (1)

(57) [Claims] 1. A disk driver for handling a disk in which a control pit set including a center pit located on a track center line and a pair of offset pits shifted left and right from the track center line is formed at predetermined intervals. Means for detecting the position and speed of the head when seeking, the means for sampling the read signal of the center pit and a pair of offset pits from the output signal of the head, respectively, Means for binarizing a value corresponding to the average value of the read signals of the pair of offset pits as a threshold value, means for obtaining a difference signal between the read signals of the pair of offset pits, and means for differentiating the difference signal Means for binarizing the difference signal; means for binarizing the differential signal; The counting operation can be performed when the binarized signal of the pit read signal has a predetermined polarity, and whether to count up or down is determined according to the polarity of the binarized signal of the differential signal. Track counting means for receiving a signal as a count input; means for detecting a zero-cross point of the difference signal; and inverting the polarity of the differential signal in accordance with the polarity of the binarized signal of the center pit read signal. Means for latching the operated differential signal at the zero-cross detection timing.