JPH0376031A - Track polarity detector - Google Patents

Abstract

PURPOSE:To execute a stable track positioning operation at a high speed and with high accuracy by providing a speed signal generating means for generating a voltage corresponding to a moving speed of a beam spot crossing a track. CONSTITUTION:A track crossing signal 42 and a track polarity signal 40 are inputted to a direction pulse generating circuit 25, and in accordance with the track crossing direction, an FWD (forward) pulse 43 or a BWD (backward) pulse 44 is generated. In this state, by the direction in which a beam spot crosses a track, a phase of the track polarity signal 40 is varied as +90 deg. or -90 deg. against the track crossing signal 42, therefore, by detecting this phase difference, the moving direction can be detected, and whenever the beam spot crosses one track, the FWD pulse 43 or the BWD pulse 44 can be generated easily. Subsequently, the FWD pulse 43 and the BWD pulse 44 which are inputted to an F/V converting circuit 26 become track crossing speed signals 45 of + polarity and - polarity, respectively. In such a way, a stable track positioning operation can be executed at a high speed and with high accuracy.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a track polarity detector used in an optical recording/reproducing device, and particularly to a track polarity detector for detecting the polarity of lands (islands) and groups (grooves) of tracks. Regarding polarity detectors.

[Conventional technology]

Conventionally, in this type of track polarity detector, after rough positioning by a head moving mechanism, a track pull-in operation is performed to perform precise positioning. In order to perform the head seek operation at high speed, it is necessary to accurately position the head near the target track during the coarse positioning operation.For this reason, the speed of the head movement mechanism is controlled so that the head can track the target track while moving. By counting the number of crossings of the head and setting a target speed according to the amount of error from the target track, the head positioning operation with less error from the target track is performed. Furthermore, the moving speed of this head moving mechanism is determined by frequency/voltage conversion (hereinafter referred to as F/V conversion) of the track crossing signal to determine the relative moving speed between the recording medium track and the head. The signal polarity, that is, the direction of movement, was determined by the movement direction signal during movement.

[Problem to be solved by the invention]

In the above-described conventional track polarity detector, when attempting to position near the target track during rough positioning operations by the head moving mechanism, it is necessary to precisely control and reduce the speed in order to stably pull in the track. Here, the speed signal that controls head positioning calculates the moving speed by F/V converting the track crossing pulse, and the polarity of the signal is determined by the moving direction signal, so the head moving speed is sufficiently low. If the head moves in the wrong direction or in the opposite direction, a speed signal containing an accurate directional component cannot be obtained.Furthermore, if an external force is applied to the head moving mechanism due to disturbance, or if track pull-in fails, the speed The drawback is that control operations become impossible and runaway occurs, making it impossible to perform high-speed, highly accurate, and stable track positioning operations.

[Means to solve the problem]

The present invention provides a track polarity detector for an optical recording/reproducing device that irradiates a beam spot onto a track on a recording medium on which information is recorded and detects the reflected light to detect the polarity of the track. a photodetection means having a detector and converting the reflected light into an electrical signal including a track error signal; a first summing amplifier generating a track sum signal from an output signal of the photodetection means; and the photodetection means. a first waveform shaping circuit that converts an output signal obtained from the pulse train into a pulse train; a pulse/level conversion circuit that receives the pulse train and converts the presence or absence of data in the pulse train into a level signal; a switch circuit that outputs a voltage that is turned on and off depending on the presence or absence of the data; and a second summing amplifier that adds the track sum signal and the output signal of the switch circuit and outputs a corrected track sum signal. , track signal comparison means for determining the polarity of the track from the positive and negative peak values of the corrected track sum signal and outputting a track polarity signal; and a track error signal for differentially amplifying the output signal of the light detection means. and a second waveform shaping circuit that detects zero crossings of the track error signal; and a second waveform shaping circuit that receives the output signals of the track signal comparing means and the second waveform shaping circuit to generate the beam that traverses the track. The present invention is characterized by comprising speed signal generating means for generating a voltage according to the moving speed of the spot.

〔Example〕

Next, the present invention will be explained in detail with reference to the drawings.

FIG. 1 is a block diagram showing one embodiment of the track polarity detector of the present invention. In FIG. 1, a light beam irradiated from a laser diode 1 is converted into parallel light by a collimating lens 2, passes straight through a beam splitter 3, and is directed to an objective lens provided with a driving coil 4 for focusing. 5 and is irradiated onto the recording medium 6. The light beam reflected by the recording medium 6 passes through the objective lens 5 again, is reflected in the right angle direction by the beam splitter 3, is focused by the focusing lens 7, and is irradiated onto the half mirror 8. In this half mirror 8, the incident light travels straight,
The amount of light is divided into two in the perpendicular direction. half mirror 8
After a part of the light beam reflected in the right angle direction is blocked by the knife edge 9, it is irradiated onto the two-split photodetector 10. The output of the two-split photodetector lO is then subtracted by the differential amplifier 11 to become a focus error signal 46.

On the other hand, the light beam that has passed straight through the half mirror 8 is irradiated onto a four-split photodetector 12 . This 4-split photodetector 12 has four photodetecting sections arranged in a cross shape that receive reflected light from the recording medium 6.
A pair of light detection sections divided in correspondence with the radial direction of the recording medium 6 is a track error signal detection section,
The other pair divided in the circumferential direction of the recording medium 6 serves as a reproduction signal detection section. Here, the outputs of the track error signal detection section are added by the summing amplifier 14 to form the track sum signal 34, and are also input to the differential amplifier 13 and subtracted to form the track error signal 41. Further, the outputs of the reproduced signal detection section are added by a summing amplifier 15 to form a reproduced signal 30. The reproduced signal 30 is then converted into a pulse signal by the waveform shaping circuit 16 and converted into a data signal.
Further, the data pulse 31 is input to the one-shot multi-vibrator 17, and
A pulse having a constant pulse width is output by being triggered at the edge of the data pulse 31. Since this pulse width is set in advance to be longer than the longest pulse period during data recording, the data pulse train becomes the level signal 32 indicating the presence or absence of data. When the level signal 32 indicates that data is present, the analog switch 18 is turned on, and when there is no data, the analog switch 18 is turned off.

Further, when the analog switch 18 is on, the voltage VD33 for correction is applied to the summing amplifier 19 and added to the track sum signal 34. Further, an offset voltage VOFF 35 is also added to the summing amplifier 19. This voltage VOFF 35 is for canceling the DC component of the track sum signal 34, and is used to cancel the DC component of the track sum signal 34.
The output is set so that the DC component of the corrected track sum signal 36 is approximately OV. The corrected track sum signal 36 corrected by the summing amplifier 19 is input to two peak hold circuits 20 and 21. peak·
The hold circuit 20 holds the positive peak value of the corrected track sum signal 36, and the other peak hold circuit 21 holds the positive peak value of the corrected track sum signal 36.
Then, the negative peak value of the corrected track sum signal 36 is held. Furthermore, the respective output signals, a positive peak hold signal 37 and a negative peak hold signal 38, are input to the resistance divider circuit 22. This resistance divider circuit 22 has 2
The signal level of the midpoint between the positive peak hold signal 37 and the negative peak hold signal 38 is output, and this is the signal level of the comparator 23.
A comparison signal 39 is obtained. A corrected track sum signal 36 and a comparison signal 39 are input to the comparator 23 and compared. Based on the difference in brightness of the reflected light between the land portion and the group portion of the track, a track polarity signal 40 indicating the land portion and the group portion is output. Further, since the land portion has a large amount of reflected light and the group portion has a small amount of reflected light, the comparison signal 39 indicates that the + side level corresponds to the land portion and the − side level corresponds to the group portion. On the other hand, the track error signal 41 is zero-crossed by the waveform shaping circuit 24 to obtain a track crossing signal 42. The track crossing signal 42 and the track polarity signal 40 are input to the direction pulse generation circuit 25, and the FWD (forward) pulse 43 generates the BWD (f&forward) pulse 44 depending on the track crossing direction. This is due to the direction in which the beam spot traverses the track, resulting in a track polarity signal 40 relative to a track crossing signal 42.
Since the phase changes to +90° or -90', it is possible to detect the moving direction by detecting this phase difference.
It becomes easy to generate the pulse 43 or the BWD pulse 44. The FWD pulse 43 and the BWD pulse 44 are F/
When the FWD pulse 43 is inputted to the V conversion circuit H26 and performs frequency/voltage conversion, it is semi-polar, and
When the BWD pulse 44 is input, a unipolar track crossing speed signal 45 is obtained.

Next, the operation of the circuit will be explained with reference to the drawings.

FIG. 2 is an operational explanatory diagram showing the relationship between the track crossing signal and the track polarity signal. In FIG. 2, the numbers appended to each signal waveform correspond to the figure numbers in FIG. 1, respectively. The track polarity signal 40 indicating whether the beam spot is on a land or on a group is determined by the track sum signal 34, since the amount of light reflected from the recording medium 6 is different between the land portion and the group portion as described above. Lands and groups are detected from the difference in amplitude of the track sum signal 34 using the difference in light amount. In FIG. 2, a case will be described in which data is recorded on a group. Since the amount of reflected light in the track sum signal 34 decreases as data is recorded, the DC component clearly differs between the data recorded portion and the data unrecorded portion, resulting in a level difference of <VI Vl). Here, in order to be able to detect lands and groups regardless of the presence or absence of data, the presence or absence of data must be detected and the level difference (V
It can be seen that these problems can be solved by correcting 1-2). In addition, by setting the playback signal to such an extent that recording medium noise is not detected and with the slice level as low as possible, the data recording section can record data almost continuously even when the beam spot crosses the track. Since the pulses are obtained, data pulses are obtained without interruption due to track crossing. As described above, the pulse width of the level signal 32 is set in advance to be longer than the longest pulse period during data recording, and is usually set to about 1.5 to 2 nS. When this level signal 32 is at a high level, a voltage that cancels (Vl-Vl) of the track sum signal 34 is added by turning on the analog switch 18,
Furthermore, by adding an offset voltage VOFF for canceling (VI Vl) of the track sum signal 34 in the summing amplifier 19, the ACC is applied regardless of the presence or absence of data.
A corrected track sum signal 36 from which the bone components are extracted is obtained. Further, a comparison signal 39 is obtained by inputting the positive peak hold signal 37 and the negative peak hold signal 38 of the corrected track sum signal 36 to the resistance divider circuit 22, and finding the voltage at the midpoint. The track polarity signal 4θ is obtained by comparing and shaping the comparison signal 39 and the corrected track sum signal 36. There is. In the corrected track sum signal 36, the amplitude of the AC component differs by about twice between the data recorded part and the data unrecorded part, but even if the amplitude in the data recorded part is about twice as large, the D
If the C components substantially match, the track polarity signal 40 will not become undetected, and a stable track polarity signal will be obtained. In this embodiment, the slice level is set by holding the positive peak value and negative peak value of the corrected track sum signal 36. Even if the signal is passed through a filter, comparable comparison signals can be obtained.

Next, the circuit operation for obtaining the speed signal will be explained with reference to the drawings.

FIGS. 3(a) and 3(b) are explanatory diagrams of the operation of the directional pulse when crossing the track. Figures 3(a) and 3(b)
, the numbers appended to each signal waveform correspond to the figure numbers in FIG. 1, respectively. The track polarity signal 40 has a phase difference of ±90° with respect to the track crossing signal 42 depending on the track crossing direction. For example, when the track crossing signal 42 rises and the track polarity signal 40 is at a high level, it is in the inner circumferential direction. Then, in the outer circumferential direction, the track polarity signal 40 becomes low level at the rising edge of the track crossing signal 42, and the level of the track polarity signal 40 at the rising edge of the track crossing signal 42 is checked, or the track polarity signal 40 goes high. - The moving direction can be determined by detecting whether the track crossing signal 42 at level is rising or falling. It is easy to generate a direction pulse using the signal indicating the moving direction determined in this way and the track crossing signal. Figure 3(a)
3(b) shows the case where i generates a direction pulse at the rising edge of the track crossing signal 42, and FIG. 3(a)
>, the FWD pulse 43 is output, and in the case of FIG. 3(b), the BWD pulse 44 is output. Here, in the F/V conversion circuit 26, when the FWD pulse 43 is input, a secondary F/V conversion output signal is also output from the BWD.
Assuming that a unipolar F/V conversion output signal is obtained when the pulse 44 is input, a track crossing speed signal 45 corresponding to the moving direction is obtained.

〔Effect of the invention〕

As explained above, according to the track polarity detector of the present invention, it is possible to detect the cross direction of the track from the reflected light from the surface of the recording medium, thereby making it possible to generate a track cross pulse in each cross direction. A velocity component including a directional component with high quality and precision is obtained. In addition, since the land and group divisions of the track become clear, it is possible to prevent the track error signal from being pulled into the opposite polarity when pulling in the track. Even when moving, a speed signal including an accurate directional component can be obtained, and track pull-in will not fail. In addition, even if an external force is applied to the head moving mechanism due to a disturbance, etc., speed control will not become impossible and the head will not run out of control, making it possible to perform high-speed, highly accurate and stable track positioning operations. be.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the track polarity detector of the present invention, FIG. 2 is an operation explanatory diagram showing the relationship between a track crossing signal and a track polarity signal, and FIGS. b) is an explanatory diagram of the operation of the directional pulse when crossing the track. DESCRIPTION OF SYMBOLS 1... Laser diode, 2... Collimating lens, 3... Beam splitter, 4... Drive coil, 5... Objective lens, 6... Recording medium, 7...
Aperture lens, 8... Half mirror 9... Knife edge, lO... 2-split photodetector, 11.13
. . . differential amplifier, 12 . . . 4-split photodetector, 14.
15.19... Summing amplifier, 16.24... Waveform shaping circuit, 17... One-shot multi-vibrator, lto... Analog switch, 20.21... Peak hold circuit, 22.・Resistance divider circuit, 23・
... Comparator, 25 ... Direction pulse generation circuit, 2
6...F/V conversion circuit.

Claims (1)

[Claims] A track polarity detector of an optical recording/reproducing device that irradiates a beam spot onto a track on a recording medium on which information is recorded and detects the reflected light to detect the polarity of the track, which includes a four-split photodetector. a first summing amplifier that generates a track sum signal from an output signal of the light detection means; and an output obtained from the light detection means. a first waveform shaping circuit that converts a signal into a pulse train; a pulse/level conversion circuit that receives the pulse train and converts the presence or absence of data in the pulse train into a level signal; a switch circuit that outputs a voltage that turns on and off depending on the presence or absence of the signal; a second summing amplifier that adds the track sum signal and the output signal of the switch circuit to output a corrected track sum signal; track signal comparison means for determining the polarity of the track from positive and negative peak values of the track sum signal and outputting a track polarity signal; and differentially amplifying the output signal of the light detection means to obtain a track error signal; a second waveform shaping circuit that detects zero crossings of the track error signal; and a moving speed of the beam spot that traverses the track by inputting the output signals of the track signal comparison means and the second waveform shaping circuit. A track polarity detector comprising speed signal generating means for generating a voltage according to the speed signal.