JPH02152018A - Track passage signal detector - Google Patents

Abstract

PURPOSE:To accurately detect a track passage signal even at the time when the frequency band is close to the band of a data signal by limiting change rates of outputs of plural light receiving means and obtaining the difference between them to detect the track passage signal. CONSTITUTION:When a data signal is applied as the noise to outputs 16A and 16B of respective light reception areas 15A and 15B of a 2-divided photodetector 15, the inclination of the signal in its noise part appears as a set value in outputs 26A and 26B of change rate limiting circuits 25A and 25B of a track passage signal detecting part 17 because the change rate of the signal in the noise part is larger than a set value. When these outputs 26A and 26B are supplied to a differential amplifier 27 to obtain the difference between them, the noise part in this difference signal 28 is kept in the level just before entrance to the noise part because noise parts of outputs 26A and 26B have the same inclination. Consequently, the difference signal 28 is supplied to a comparator 29 and is compared with a comparison reference signal 30 to accurately detect a track passage signal 18 without error.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is directed to an optical disk device or the like in which when an optical head accesses a desired track on a recording medium, the optical head reads information based on light reflected from the recording medium. The present invention relates to a truck passing signal detection device for detecting a trunk passing signal for counting the number of trucks passing through.

[Conventional technology]

As an access method for an optical head in an optical disk device, etc., for example, as disclosed in Japanese Patent Application Laid-Open No. 58-91536, the number of tracks crossed by the optical head is counted based on changes in the amount of reflected light from the optical disk, and the number of tracks traversed by the optical head is counted. There is a system in which the target track position is directly positioned from the initial position.

In the conventional track passing signal detection device in this optical head access method, the reflected light from the optical disk is received by a two-split photodetector 1 as shown in FIG. A tracking error signal 4 is obtained by supplying it to a differential amplifier 3 to determine the difference, and this tracking error signal 4 is supplied to a filter 5 to remove the noise caused by the data signal on the information trunk, and then The output 6 is supplied to a comparator 7 and binarized to detect a track passing signal 8. As the filter 5, a low-pass filter that passes low-frequency components of the signal or a rate-of-change limiting filter that limits the rate of change of the signal is used.

[Problems to be Solved by the Invention] However, in the conventional track passing signal detection device described above, when the moving speed of the optical head is increased to achieve high-speed access, the frequency band of the trunking error signal 4 is However, since the frequency band of the data signal in the track is close to that of the data signal, it becomes difficult to separate the signal by the filter 5, which is a low-pass filter or a rate-of-change limiting filter, and there is a problem in that a track passing signal is erroneously detected.

That is, as shown in FIG. 8, which is a signal waveform diagram of each part of the track passing signal detection device shown in FIG. As it passes through the change rate limiting filter 5, the amplitude becomes smaller as shown by symbols 6a and 6b.
a, and as a result, the track passing signal 8 is erroneously detected.

In this way, if the track passing signal 8 is erroneously detected, the number of passing tracks cannot be counted correctly, and therefore the target track cannot be reached in one access, and several corrective actions are required. The problem arises that the access time becomes longer.

The present invention has been made in view of these conventional problems, and it is an object of the present invention to provide a truck passing signal detection device that can always accurately detect truck passing signals and is appropriately configured to shorten access time. With the goal.

[Means to solve the problem]

In order to achieve the above object, the present invention includes at least two light receiving means for receiving reflected light from a recording medium, a change rate limiting means for respectively limiting the rate of change in the output of these light receiving means, and a change rate limiting means for limiting the rate of change in the output of these light receiving means. A difference detecting means for calculating the difference between the outputs of the limiting means is provided, and the track passing signal is detected based on the output of the difference detecting means.

[For production]

In such a configuration, the signals output from the two light receiving means include track position information as well as the data signal as noise, and the noise is generated at approximately the same time for each output of the two light receiving means. However, the amplitude is different. Further, the relative speed between the recording medium and the optical head is, for example, when the disk rotation speed is 1800 rpm in an optical disk.
On a circumference with a radius of 30 mm, the speed is approximately 5.7 m/s, ec, whereas the speed perpendicular to the track due to optical head access is usually 1 m/sec or less. Therefore, even if the frequency bands of the data signal and the track passing signal are close to each other or overlap, when comparing the rate of change in the signals, the rate of change in the output of the light receiving means due to a change in track position is A! On the other hand, the rate of change A2 of the output of the light receiving means due to the movement of the data bits on the track in the tangential direction of the track is more than five times larger. Therefore, assuming that the rate of change limit value of the signal in each rate of change limiting means is Amax, this is set so that A<Amax <A2 to limit the rate of change of each output of the two light receiving means. Then, in normal times, signals due to track position changes are output as they are, and when noise occurs due to data signals, signals that change at the rate of change of Amax are output for each output. Therefore, if the outputs of these change rate limiting means are supplied to the difference detection means and a difference signal is obtained,
Normally, a difference signal due to a change in track position is output, and when noise occurs, the level immediately before the noise occurs is maintained, and when the noise ends, a difference signal due to a change in track position is output again.

[Embodiment] FIG. 1 shows a first embodiment of the present invention. This embodiment shows an access device for an optical head 12 in an optical disk device that records or reproduces information on an optical disk 11 via an optical head 12. The optical head 12 is of a known type, and includes a semiconductor laser 13 that emits a recording or reproducing beam, an objective lens 14 that focuses the beam from the semiconductor laser 13 on the optical disk 11, and a beam that is reflected from the optical disk 11 through the objective lens 14. It includes a two-split photodetector 15 that receives light. Outputs 16A and 16B of the respective light receiving areas 15A and 15B of the two-split photodetector 15 are supplied to a track passing signal detection section 17 to obtain a track passing signal 18, which is then supplied to a counter 19. In the counter 19, the number of tracks up to the target track is preset by the initial value setting section 20, and the set value is down-counted by the track passing signal 18, and the output is the remaining count value 20.
A servo circuit section 22 that supplies the control section 21 with the following information to move the optical head 12 in a direction perpendicular to the trunk is connected to l1.
Try to sell li wholesale.

FIG. 2 shows the configuration of an example of the track passing signal detection section 17. As shown in FIG. In this embodiment, the outputs 168 and 16B of the light receiving areas 15A and 15B of the two-split photodetector 15 are respectively supplied to change rate limiting circuits 25A and 25B to limit the rate of change. The outputs 26A and 26B of 25B are supplied to a differential amplifier 27 to determine the difference, and the difference signal 28 is supplied to a comparator 29 and compared with a predetermined comparison reference signal 30 to obtain a binarized track passing signal. Try to get 18.

The rate of change limiting circuit 25A, for example, as shown in FIG.
The terminal voltage of the capacitor 35 is output 26 by selectively connecting the capacitor 35 to the positive constant current source 38 and the negative constant current source 39 via the resistor 36 and the switch 37.
8 and 1 to the differential amplifier 27.
, the voltage V at the output 26A. , JT and the voltage V+S to the output 16 of the light receiving area 15A are compared in the comparator 40, and the switch 37 is controlled based on the comparison result. That is, when VIN>VOII7, the switch 37 is set to the positive constant current source 3, and VIN>VOLI7.
In this case, the switches 37 are connected to the negative constant current sources 39, respectively.

In this way, the constant current 83s and the current value of 39 can be adjusted to ±
1. If the capacitance of the capacitor 35 is C, then the light receiving area 15
When the absolute value of the rate of change of ^ to output 16 is smaller than I/C, the terminal voltage of capacitor 35, that is, output 268 changes almost following output 16A of light receiving area 15A, and
When it is larger than /C, it changes at a rate of change of ±I10, and the rate of change of the output 16A of the light receiving area 15A is limited to the set value. Note that the rate of change limiting circuit 25B is also configured in the same manner as the rate of change limiting circuit 258.

The operation of this embodiment will be explained below with reference to the signal waveform diagram of each part shown in FIG.

When a data signal is added as noise to the outputs 16A and 16B of each light receiving area 15A and 15B of the two-split photodetector 15, the rate of change of the signal in the noise section 45 is larger than the set value, so the rate of change limiting circuit 25A, At the outputs 26A and 26B of 25B, the slope of the signal of the noise section 45 appears as a set value. When these outputs 26A and 26B are supplied to the differential amplifier 27 and the difference is calculated, the output 26A is
Since the slopes of the signals of the noise section 45 of , 26B are equal,
The level of the noise portion 45 of the difference signal 28 is maintained at the value immediately before entering the noise portion. Therefore, this difference signal 28 is supplied to a comparator 29 to provide a comparison reference signal 3.
If compared with 0, the track passing signal 18 can be detected accurately without causing false detection.

In addition, in FIG. 4, waveform 4 shown by a broken line in the difference signal 28
6 is the output 168 of the light receiving area 15A, 15B, 16
13 is obtained directly, and if this is supplied to a comparator via a change rate limiting circuit to obtain a track passing signal, false detection will occur as explained in Figs. 7 and 8. There is a fear.

In this way, according to this embodiment, the track passing signal can always be accurately detected without being affected by the data signal, and therefore the access time can be shortened.

FIG. 5 shows the main part of a second embodiment of the invention. This embodiment has a positive constant voltage source 55 in place of the positive constant current source 38 in the rate of change limiting circuit 25A shown in FIG.
The other configuration is the same as that shown in FIG. 3.

That is, noise caused by data signals is generally caused by the outputs 16A of the light receiving areas 15A and 15B of the two-split photodetector 15,
As for 16B, it is rare that it occurs randomly on the positive side and the negative side, and in most cases, the amount of reflected light from the optical disk 11 decreases in the data signal portion. Therefore,
In this embodiment, V and N<V at the comparator 40.

. In case A, switch 37 is set to negative constant current r1.39,
When VIH>Volt7, the switch 37 is connected to the positive constant voltage #55, and the time constant determined by the capacitor 35 and the resistor 36 is set in consideration of the rate of change of the output 16A of the light receiving area 15A. When the rate of change of the output 16A is negative, the rate of change is limited to the rate determined by the constant current source 39 and the capacitor 35, and when the rate of change of the output 16A is positive, the rate of change is limited to the rate of change determined by the constant current source 39 and the capacitor 35. Configure it so that it does not restrict. Of course, the other rate-of-change limiting circuit 25B is similarly configured. In this way, as shown in the signal waveform diagram of each part in FIG.
6, only the rate of change of its falling edge is limited by the rate of change limiting circuit 25A, so the difference signal 28 is affected by noise for a shorter time than in the first embodiment, and therefore the trunk passing signal 18 can be detected more accurately.

Note that this invention is not limited only to the embodiments described above, and numerous modifications and changes are possible. For example, the rate-of-change limiting circuit is not limited to the one shown in FIGS. 3 and 5, but can be effectively used with other configurations as long as it limits the rate of change of the signal. Further, the present invention is not limited to optical disk devices, but can be effectively applied to recording and/or reproducing devices using other optical recording media such as magneto-optical disks and optical cards.

〔Effect of the invention〕

As described above, according to the present invention, the rate of change in the output of at least two light receiving means is limited, and then the difference between them is determined, and the track passing signal is detected based on the difference signal. Even if the frequency band of the track passing signal is close to that of the data signal, the track passing signal can always be detected accurately, and therefore the access time can be shortened.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a first embodiment of the present invention, and FIG. 2 is a diagram showing a first embodiment of the present invention.
3 is a diagram showing the configuration of an example of the rate-of-change limiting circuit shown in FIG. 2; FIG. 4 is a diagram illustrating the operation of the first embodiment. FIG. 5 is a diagram showing the main parts of the second embodiment of the present invention, FIG. 6 is a signal waveform diagram for explaining its operation, and FIGS. 7 and 8 are conventional diagrams. FIG. 11... Optical disk 12... Optical head 15
... Two-split photodetector 15A, 15B... Light receiving area 17... Track passing signal detection section 19... Counter 20... Initial value setting section 21... Control section 22... Servo circuit Parts 25A, 25B... Rate of change limiting circuit 27... Differential amplifier 29... Comparator Fig. 1 Fig. 2 Fig. 3 Fig. 5 Fig. 6

Claims (1)

[Claims] 1. A device for detecting a track passing signal when an optical head passes an information track formed on a recording medium based on reflected light from the recording medium, the device comprising at least two light receiving means for receiving the reflected light. , change rate limiting means for limiting the rate of change in the outputs of these light receiving means, and difference detecting means for calculating the difference between the outputs of these change rate limiting means, and detecting the passing of the track based on the output of the difference detecting means. A truck passing signal detection device characterized in that it is configured to detect a signal.