JPH01245475A - Information reproducing device - Google Patents

Abstract

PURPOSE:To constantly and effectively read information without the influence of a defect by supplying a signal indicating the position of an actuator to a sample hold means via a delay means and returning the actuator to the held position at the time of detecting the defect. CONSTITUTION:When a defect detecting signal is generated from a defect detecting means 6, a switch 5 is switched to an H side synchronously therewith, the output of the delay means 8 at that time is held by the sample hold means 10 and supplied to the other input terminal of a comparing means 9. The sample hold means 10 holds the delay part of the delay means 8 slightly more than the delay quantity of the defect detecting means 6, namely, the output of a low-pass filter 7 before the influence of the defect is indicated and returns the position of the actuator 4 to a position before the influence of the defect appears. Accordingly, even when a defect detecting signal is not present to control by the output of an error detecting means 1, the actuator 4 can be rapidly retracted to a target position. Thereby, the information can be constantly and effectively read without the influence of the defect.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to an information reproducing device that reproduces information from an information recording carrier, particularly a focus servo, a tracking servo, etc. in an optical information reproducing device that optically reproduces information. Concerning improvements to the servo system.

[Conventional technology]

In an information reproducing device that reproduces information recorded on an information recording carrier such as an optical disk or an optical card, the information reading device using an optical pickup and the target information position on the information recording carrier are initially separated from each other. Generally, in order to match these positions, servo control is performed to detect the positional deviation and drive an information reading position shifting means called an actuator to align the positions. For example, this includes a focus servo for focusing a reading groove, a trunking servo for making a reading groove follow a required track, and the like.

These servos usually detect the deviation between the target position and the current read position using an error detection means 1, as shown in Figure 4, and use the output to obtain necessary system characteristics and stabilize the system. The power is supplied to the driver 3 via the compensation circuit 2, where the power is amplified and the actuator 4 is driven. Here, as the error detection means 1, for example, a knife engine method, an eccentric beam method, etc. are known in the case of focus servo.

In such a servo system, the actuator 4 is generally driven electromagnetically, and its transfer function is almost a second-order delay element, with higher-order resonance, etc. added. is normal.

[Problem to be solved by the invention]

However, in the conventional servo system shown in FIG. 4, if there is a defect such as a scratch or a foreign object on or near the information recording surface of the information recording carrier, noise will occur in the output of the error detection means l. , this noise is amplified and the etuator 4
If you drive the servo, the servo may come off. In other words, due to the influence of the defect, the deviation between the target position and the reading position deviates from the allowable residual, and not only does the information become unreadable during that period, but in extreme cases, it exceeds the detectable range of the error detection means 1. Even after the effects of the defect have passed, it may not be possible to recover.

As a solution to this problem, 18 For example, Japanese Patent Application Laid-Open No. 59-203277 discloses that a position signal generating means for generating a signal indicating the biased position of the actuator and a read signal from a recorded information detection point are missing. means for detecting and holding the output of the position signal generating means immediately before that;
An information reproducing device has been proposed which includes means for generating a difference signal between the output of the holding means and the output of the position signal generating means, and uses this difference signal to drive an actuator when a read signal is missing. There is.

However, since there is generally a delay in detecting defects,
If the position signal of the actuator immediately before the defect detection signal is held as described above, the position signal that has already been disturbed by the defect will be held, and therefore the actuator will be servo-controlled to the disturbed position. However, there is a problem that sufficient effects cannot be obtained.

On the other hand, an information reproducing device using an optical disk has been proposed in which a defect is predicted from the state of the signal one revolution before and the servo system is switched as described above. In this case, since defects are predicted from the signal from one revolution before, the above-mentioned problem due to the delay in the detection signal does not occur when adjacent tracks are successively reproduced. However, when playing tracks randomly, especially on information recording carriers such as optical cards that do not necessarily play back adjacent tracks consecutively, the previous track and the next trunk to be read may be physically far apart from each other. Therefore, a similar configuration cannot be used.

This invention was made by focusing on such conventional problems, and even if there is a delay in detecting defects on the information recording carrier, the actuator can be controlled to almost the desired position, and therefore it is possible to control the actuator to almost the desired position. It is an object of the present invention to provide an information reproducing device appropriately configured so that information can always be read effectively without any trouble.

[Means and operations for solving the problem] In order to achieve the above object, in the present invention, a deviation between an information reading position and a target information recording position is detected by an error detection means, and the actuator is activated based on the output of this error detection means. In an information reproducing apparatus that reads information from an information recording carrier while moving an information reading position to match a target information recording position by driving a a low-pass filter coupled in parallel with the actuator and having a transfer function substantially equal to that of the actuator; a delay means for delaying the output by a large amount of delay; means for sample-holding the output of the delay means in synchronization with the defect detection signal; and means for comparing the output of the sample-hold means with the output of the low-pass filter;
switch means for selecting the output of the comparing means and the output of the error detecting means based on the output of the defect detecting means and supplying the selected output to the actuator and the low-pass filter; The actuator is configured to select the output of the comparison means to drive the actuator.

〔Example〕

FIG. 1 shows a first embodiment of the invention. In this embodiment, in addition to the configuration shown in FIG.
and the driver 3, and the switch 5 is set to the L side when no defect is detected based on the output of the defect detection means 6, and set to the H side while a defect detection signal is generated. Switch to . In addition, the defect detection means 6
For example, it is configured to detect that the output of the error detection means 1 has become abnormally large and generate a defect detection signal. The output of the driver 3 is also supplied to a low-pass filter, and the output of this low-pass filter is supplied to one input terminal of the delay means 8 and the comparison means 9. The low-pass filter 7 is configured to have approximately the same transfer function as the actuator 4, so as to obtain an output signal representative of the actual position of the actuator 4. Such a low-pass filter 7 can be constructed using a second-order low-pass filter, since the transfer function of the actuator 4 can generally be approximated by a second-order lag element.

Further, the delay means 8 is configured with, for example, a low-pass filter so as to have a delay amount slightly greater than the amount of delay in detecting the defect in the defect detection means 6.

The output of the delay means 8 is supplied to the sample bold means 10, which samples and holds the output of the delay means 8 in synchronization with the defect detection signal from the defect detection means 6, and sends it to the other input terminal of the comparison means 9. supply to. Comparison means 9 is
For example, it includes a differential amplifier, the output of which is supplied to the H-side terminal of the switch 5 via a compensation circuit 11 for obtaining system characteristics necessary for defect detection and for stabilizing the system.

The operation of this embodiment will be explained below.

When no defect is detected by the defect detection means 6, the switch 5 is on the L side. Therefore, actuator 4
is driven by the driver 3 by the output of the error detection means 1 in the same way as in the conventional example shown in FIG.
and is supplied to one input terminal of the comparison means 9. In this state, when a defect detection signal is generated from the defect detection means 6, the switch 5 is switched to the H side in synchronization with it, and the output of the delay means 8 at that time is transferred to the sample and hold means 10.
The signal is held at 1 and is supplied to the other input terminal of the comparison means 9. Here, since the defect detection signal generated from the defect detection means 6 is normally delayed for a certain period after the influence of the defect actually starts to appear, the actuator 4 is driven by noise caused by the defect. and is moving from its original position. Furthermore, since the output of the low-pass filter has a transfer function similar to that of the actuator 4, it similarly outputs a signal corresponding to the moved position. On the other hand, the sample and hold means 10 holds the output of the low-pass filter before the delay amount of the delay means 8, which is slightly larger than the delay amount of the defect detection means 6, that is, before the influence of the defect appears.

The output of the sample and hold means 10 and the current output of the low-pass filter are subtracted by the comparison means 9, and the output of the comparison means 9 passes through the compensation circuit 11, and then passes through the switch 5 and the driver 3 to the low-pass filter 7 and the actuator. Added to 4.

Through this circular operation, a negative feedback system is constructed so that the output of the sample and hold means 10 and the output of the low-pass filter match.

Here, the output of the low-pass filter is actuator 4
Therefore, if the output of the low-pass filter is kept constant, the position of the actuator 4 will also be kept constant. Therefore, if the position of the actuator 4 before the influence of the defect is held by the sample and hold means IO as described above and the output of the low-pass filter 7 is controlled to be positioned at that value, the position of the actuator 4 can be changed to the position of the actuator 4 before the defect occurs. It is possible to return to the position before the effect occurred.

That is, according to this embodiment, although the actuator 4 is driven due to the influence of the defect, after the defect is detected, it returns to the position before the influence of the defect. In addition, since the target position hardly moves significantly in a short period of time and the actuator 4 is located near the target position, the influence of the defect disappears and the defect detection signal from the defect detection means 6 disappears, which causes the switch 5 Even if the control is switched to the L side and control is performed by the output of the error detection means 1, the actuator 4 can be quickly pulled into the target position. Therefore, there is no longer a phenomenon where the servo is greatly deviated due to the influence of the defect and the information cannot be read immediately even after the influence of the defect is gone, and the information is reproduced almost normally except for the defective part that directly affects the information itself. can do.

FIG. 2 shows a second embodiment of the invention. In this embodiment, a compensation circuit 12 is provided between the switch 5 and the driver 3, so that the compensation circuit 2 during normal operation and the compensation circuit 11 during defect detection in FIG. , the other configurations are the same as in FIG. This has the advantage that the circuit configuration can be simplified.

FIG. 3 shows a third embodiment of the invention. In this embodiment, the input of the low-pass filter is taken from the input of the driver 3 when the driver 3 does not have any frequency characteristics in practice and its input/output characteristics are simply proportional. The configuration is the same as that in FIG.

〔Effect of the invention〕

As described above, according to the present invention, a signal representing the position of the actuator is supplied to the sample hold means via the delay means, and the actuator is controlled to return to the held position when a defect is detected. Even if there is a delay in detection, information can always be read effectively without being affected by the delay.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing a first embodiment of the present invention, Fig. 2 is a block diagram showing a second embodiment, Fig. 3 is a block diagram showing a third embodiment, and Fig. 4 is a block diagram showing a conventional FIG. 2 is a block diagram illustrating the technology. 1...Error detection means 2...Compensation circuit 3...
Driver 4...Actuator 5...Switch 6...Defect detection means 7...Low pass filter 8...A extension means 9...Comparison means
10...Sample holding means 11, 12...
compensation circuit

Claims (1)

[Claims] 1. Detecting a deviation between the information reading position and the target information recording position by an error detection means, and driving an actuator based on the output of the error detection means to change the information reading position to the target information recording position. In an information reproducing apparatus that reads information from an information recording carrier while moving the information recording carrier so as to match the information recording carrier, a defect detection means for detecting a defect on the information recording carrier and generating a defect detection signal is coupled in parallel with the actuator. a low-pass filter having a transfer function substantially equal to that of the actuator; a delay means for delaying the output of the low-pass filter by a delay amount slightly greater than the defect detection delay amount in the defect detection means; means for sample-holding in synchronization with a detection signal; means for comparing the output of the sample-holding means with the output of the low-pass filter; and comparing the output of the comparing means and the output of the error detecting means with the output of the defect detecting means. switch means for selecting and supplying the output to the actuator and the low-pass filter based on the defect detection signal, and selecting the output of the comparison means to drive the actuator when the defect detection signal is generated. Characteristic information reproducing device.