JPH041928B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a track search device that automatically searches for tracks from a recorded data string formed on an optical disk.

[Technical background of the invention and its problems]

Some conventional track search devices are designed to indirectly detect the track on which an optical head is located by reading the graduations on a scale attached to a head feeding mechanism. However, this track search device has problems in terms of positional accuracy and has a complicated structure.

Therefore, recently, concentric or spiral grooves are formed on the optical disk, and a row of information recording pits is formed in these grooves, so that when the light beam emitted from the optical head crosses the grooves, A system has been proposed in which a track search is performed by detecting a pulse train occurring in a track.

However, in the above method, it is necessary to form grooves in addition to the pit rows, which complicates the structure of the optical disk itself and causes disadvantages in terms of recording density.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a track search device that can automatically search for a track from a recorded data string formed on an optical disk, has a simple configuration, and can be manufactured at low cost.

[Summary of the invention]

In order to achieve the above object, the present invention is characterized by the following configuration. That is, as the optical head moves in the radial direction of the disk, a data string cross signal indicating that the light beam crosses the recorded data string on the optical disk is obtained by a photodetector, a differential amplifier, etc. is compared with a reference level and binarized. Then, each level of the data string cross signal corresponding to the falling edge and rising edge of the binarized signal is held by a sampling hold circuit, etc., and the level difference between the two held signals is obtained, and the binary The time width from the falling edge to the rising edge of the signal is measured. Then, based on the level difference and time width of the two signals, a signal is obtained to interpolate the signal missing portion in the data string cross signal corresponding to the period from the falling edge to the rising edge, and this interpolation signal is used to interpolate the signal missing part in the data string cross signal. A track cross signal is generated by interpolating the signal missing portion of the signal. In this way, even if the recorded data string consists of only intermittent pit rows, it is possible to obtain a track cross signal that is the same as if the data were formed without continuous grooves. It is said that

[Embodiments of the invention]

FIG. 1 is a block diagram showing the configuration of one embodiment of the present invention. In the figure, reference numeral 1 denotes a disk-shaped optical disk, which is driven to rotate at a constant speed by a spindle motor 2. As shown in FIG. Reference numeral 3 denotes an optical head that is movable in the radial direction of the disk 1 by a head feeding mechanism including a voice coil motor (not shown) or the like. This optical head 3 converts a laser beam emitted from a laser diode 4 into parallel light using a collimating lens 5, and inputs the laser beam through a beam splitter 6 into a quarter-wave plate 7, converting the laser beam from direct polarization to circularly polarized light. The beam is then focused by an objective lens 8 and irradiated onto the recording surface of the disk 1 as a beam spot. Then, the reflected light reflected from the recording surface of the disk 1 is made incident on the 1/4 wavelength plate 7 through the objective lens 8 in a path opposite to that of the incident light, and is reversely converted from circularly polarized light to linearly polarized light. This inversely converted reflected light has a polarization plane different from that of the incident light.
It will be shifted by 90°. The optical path of this light is changed by a beam splitter 6 in a perpendicular direction, and the light is made to enter a photodetector 10 through a lens 9. The photodetector 10 has a light-receiving area divided into two parts, and output signals can be extracted from each light-receiving area.

The output signals of the optical head 3, that is, the respective output signals from the photodetector 10, serve as differential inputs of a differential amplifier 11. In this way, a data string cross signal is obtained from the differential amplifier 11, which indicates that the light beam has crossed the recording data string.

Now, when a data string in which recording pits P are intermittently formed on tracks T1, T2, etc. is recorded on the disk 1 as shown in FIG. 2a,
Assume that as the optical head 3 moves, the beam spot S crosses the data string as shown by the arrow. Then, from the differential amplifier 11, as shown in FIG.
As shown in FIG. 3, the signal M is generated as shown by the solid line only in the area where the recording pit P exists, and the recording pit P is
A data string cross signal in which a signal missing portion N occurs is obtained in a portion where no signal is present as shown by a broken line.

Let's return to Figure 1. The output of the differential amplifier 11, ie, the data string cross signal, is supplied to sampling and holding circuits 12 and 13 and a voltage comparator 14. The other input terminal of the voltage comparator 14 receives the positive/negative comparison reference level voltage + from the terminal 14a.
E, -E are given. Therefore, now, as shown in FIG. 3A, one input terminal of the voltage comparator 14 has V1>+E at time t1, and V1>+E at time t2.
Assume that a signal having a voltage value of 2>+E and a voltage value of 0 volts between t1 and t2 is input. Then, as shown in FIG. 3B, the voltage comparator 14 becomes "0" level at time t1, and at time t2.
A binary signal having a "1" level is output. This binary signal is supplied to a sampling pulse generator 15. The sampling pulse generator 15 generates a sampling pulse as shown in FIG. At time t2), a sampling pulse as shown in FIG. 3D is generated and applied to the sampling hold circuit 13. Therefore, the sampling and holding circuit 12 holds the input signal level V1 at time t1, and the sampling and holding circuit 13 holds the input signal level V1 at time t1.
2, the input signal level V2 is held. Each of the above sampling and hold circuits 12 and 13
The signal level held at is subtracted by V2-V1 in the subtracter 16, and a signal indicating the level difference is supplied to one input terminal of the interpolation signal generator 17. A missing signal from a missing length measuring device 18 is applied to the other input terminal of this interpolation signal generator 17. The missing length measuring device 18 receives the binary signal from the voltage comparator 14, so that
It measures t2-t1 and sends out a signal indicating the time width. Thus, the interpolation signal generator 17 outputs V2-V
A level difference signal of 1 and a missing length signal of t2-t1 are input, an interpolation signal of (V2-V1)t is generated, and this is applied to one input terminal of the adder 19. The other input terminal of the adder 19 is supplied with the output of the sampling hold circuit 12, that is, a signal at a level of V1. Therefore, the adder 19 outputs a signal corresponding to the shaded area in FIG.
It becomes one input of 0. This analog switch 2
As the other input of 0, the output signal of the differential amplifier 11, that is, the signal of the portion not shaded in FIG. 3A, is supplied with the timing adjusted by the delay circuit 21. The analog switch 20 is given the missing length signal from the missing length measuring device 18 as a switching signal, and passes the output signal from the adder 19 during the period when the missing length signal is applied, and during the other periods, the above-mentioned signal is passed. Delay circuit 21
The output signal of analog switch 20
The signal that has passed through is converted into a smooth sine wave, that is, a track cross signal, by a low pass filter 22, and then provided to a cross pulse generator 23. The cross pulse generator 23 generates a beam spot S according to the input sinusoidal track cross signal.
generates a cross pulse indicating that the vehicle has crossed tracks T1, T2, . . . and provides this to the voice coil motor speed controller 24. A voice coil motor speed controller 24 provides a speed control signal to a voice coil motor of a head feeding mechanism (not shown) to control the speed of the motor.

In this way, in this device, it is possible to obtain a track cross signal from the pit rows formed intermittently on the optical disk 1 as if a continuous groove were formed, and to control the speed of the optical head 3, etc. can be carried out accurately. Moreover, unlike conventional devices, this device does not require a scale for indicating the head position, nor is it necessary to form grooves on the optical disk 1, so the structure is simple and can be manufactured at low cost.

Note that the present invention is not limited to the above-mentioned embodiment. For example, in the above embodiment, the present invention is applied to a case where only a recording pit row is formed on an optical disk, but when data other than a recording pit row is formed on an optical disk intermittently or continuously. Of course, the present invention can also be applied to cases where

〔Effect of the invention〕

According to the present invention, a binary signal is obtained from a data string cross signal indicating that a light beam crosses recorded data, and a signal for interpolating a signal missing portion in the data string cross signal based on this binary signal. By forming a track cross signal and interpolating the signal missing portion with this interpolation signal, a track cross signal is obtained. In this case, a track cross signal similar to that obtained when continuous grooves or data are formed can be obtained. In this way, it is possible to provide a track search device which can automatically search for a track from a recorded data string formed on an optical disk, and which has a simple configuration and can be manufactured at low cost.

[Brief explanation of drawings]

1 to 3 are diagrams showing the configuration of an embodiment of the present invention. FIG. 1 is a block diagram showing the configuration, FIGS. 2a and 2b are diagrams showing the detection state of a data string cross signal, and FIG. FIG. 3 is a signal waveform diagram for explaining the interpolation signal forming means. 1... Optical disk, 2... Spindle motor,
3...Optical head, 4...Laser diode,
5...Collimating lens, 6...Beam splitter, 7...1/4 wavelength plate, 8...Objective lens, 9...
... Lens, 10 ... Photodetector, 11 ... Differential amplifier, 14 ... Voltage comparator, 19 ... Adder.

Claims (1)

[Claims] 1. A means for obtaining a data string cross signal indicating that a light beam crosses a recorded data string on an optical disk as the optical head moves in the disk radial direction, and a reference for the data string cross signal obtained by this means. means for comparing and binarizing levels, means for holding each level of the data string cross signal corresponding to the falling edge and rising edge of the signal binarized by this means; means for obtaining the level difference between the two signals; means for measuring the time width from the falling edge to the rising edge of the binary signal; and means for measuring the time width measured by the measuring means and the level difference between the two signals. interpolation means for obtaining a signal for interpolating a signal missing part in the data string cross signal corresponding to the period from the falling edge to the rising edge; and a signal of the data string cross signal using the interpolation signal obtained by the interpolation means. 1. A track search device comprising means for interpolating a missing portion to generate a track cross signal.