JPH06349083A - Optical information processor - Google Patents

Abstract

PURPOSE:To decrease focus deviation caused by damage or dust even in plural control states at the time of normal recording/reproduction and access in a focus servo circuit of an optical information processor. CONSTITUTION:This processor is provide with plural control circuits 17, 18 having an open loop characteristic of a focus servo corresponding to plural different control states at the time of normal recording/reproduction and access respectively in focus servo circuits 11, 21 which control focus of a light beam for recording medium 12 based on a focus error signal obtained from the recording medium 12. A loop characteristic is decided by either of selected plural control circuits 17, 18 by switching changeover switches 16, 22 in accordance with a switching signal based on control states.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical information processing apparatus for optically recording information on a recording medium such as a card or optically reproducing information from the recording medium.

[0002]

2. Description of the Related Art Generally, when information is optically recorded on a recording medium or information is reproduced from the recording medium, a focus servo is performed so that the light beam is focused on the recording medium, and the light beam is used as an information track. Track servo is performed so as to follow.

When designing such a servo system, it is generally designed as shown in FIG. That is, the open loop characteristic of the servo system is designed to be the open loop characteristic 31 or 32 according to the minimum necessary gain characteristic 33. However, the open loop characteristic 32 can suppress the deviation as compared with the open loop characteristic 31, but the crossover frequency f2 of the open loop characteristic 32 is reduced.
Has a higher response speed than the cross frequency f1 of the open loop characteristic 31, and therefore the servo system of the open loop characteristic 32 is vulnerable to scratches and dust. Therefore, the open loop characteristic 31 is selected in order to design a servo system that is resistant to scratches and dust.

By the way, during normal recording and reproduction,
Both the focus servo loop and the tracking servo loop are turned on and follow the track while maintaining the focus.

Further, when the light beam accesses a target information track by a track jump or the like, it is necessary to accurately obtain the tracking error signal and the on-track signal even if the tracking servo loop is in the OFF state. The focus servo loop remains ON.

The reason why the tracking error signal and the on-track signal must be accurately obtained at the time of access will be described with reference to FIG. When a light beam (not shown) crosses a track as shown in FIG.
An on-track signal as shown in FIG. 6B and a tracking error signal as shown in FIG. 6C are obtained. These signals are shown in FIGS. 6 (d) and 6 (e) at predetermined threshold levels, respectively.
Binarize like. And the counter not shown is
Tracks are counted when both the binarized on-track signal and the tracking error signal are at the high level. The amount of movement of the light beam is measured by the count value of this counter.

As described above, it is understood that the on-track signal and the tracking error signal are important information at the time of access.

As described above, since the tracking servo system takes different control states during normal recording and reproduction and during access, the minimum necessary gain characteristics of the focus servo system are different as shown in FIG. In FIG. 8, the gain characteristic 1 in FIG. 8A shows the gain characteristic during normal recording and reproduction, and the gain characteristic 2 in FIG. 8B shows the gain characteristic during access.

Therefore, when designing the open loop characteristic of the focus servo system, as shown in FIG. 9, the open loop characteristic 4 is selected in accordance with the gain characteristic 2 in order to cover both the gain characteristic 1 and the gain characteristic 2. To be done.

[0010]

Since the conventional optical information processing apparatus is constructed as described above, there are drawbacks such that the focus is easily deviated due to scratches or pride during normal recording / reproduction. Have The present invention has been made in consideration of the above points, and an object thereof is to prevent defocusing due to scratches, dust, or the like regardless of the control state.

[0011]

An optical information processing apparatus according to the present invention is a focus servo circuit 11 for controlling a focus of a light beam on a recording medium 12 based on a focus error signal obtained from the recording medium 12. An optical information processing apparatus having a plurality of control circuits 21, a plurality of control circuits 17, 18, 23 and 24 having focus servo loop characteristics corresponding to a plurality of different control states, and a plurality of these control circuits according to the control states. It is characterized by having changeover switches 16 and 22 for selectively changing over the control circuits 17, 18, 23 and 24.

[0012]

The optical information processing apparatus having the above-described configuration is the recording medium 1
The focus servo circuits 11 and 21 for controlling the focus of the light beam on the recording medium 12 on the basis of the focus error signal obtained from 2 have a plurality of focus servo loop characteristics corresponding to each of a plurality of different control states. Control circuits 17, 18, 23, 24 of the plurality of control circuits 17, 18, 23, 24, which are selected by switching the changeover switches 16, 22 according to the control state.
Since the loop characteristic is determined by any one of 3 and 24, it is possible to prevent defocus due to scratches or dust regardless of the control state.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a characteristic diagram for explaining the operating principle of the present invention. In the figure, the open loop characteristic 3 of FIG.
Is an optimum open loop characteristic based on the minimum necessary gain characteristic 1 of the focus servo system during normal recording and reproduction. The open loop characteristic 4 in FIG. 1B is an optimum open loop characteristic based on the minimum necessary gain characteristic 2 of the focus servo system at the time of access. According to the present invention, the open loop characteristics 3 and 4 of the focus servo system can be switched between normal reproduction and access.

The specific operation of the present invention will be described below with reference to the block diagram shown in FIG. 2 and the characteristic diagrams shown in FIGS.

Now, let us consider three different control states when the tracking servo loop is ON during the above-mentioned normal recording / reproduction, during access, and during access.
The control state in which the tracking servo loop is turned on at the time of access is used when accurate access is performed when the moving distance at the time of access is minute. This control state is used especially at the time of track jump and when the number of tracks to be jumped is small.

FIG. 3 shows the gain characteristics of the focus servo system in these three different control states. The gain characteristic 1 in FIG. 3A shows the gain characteristic during normal recording and reproduction, and the gain characteristic 2 in FIG. 3B shows the gain characteristic during access. Furthermore, the gain characteristic 5 of FIG. 3C shows the gain characteristic when the tracking servo loop is set to 0N during access.

Here, the open loop characteristics of the focus servo system according to these gain characteristics are set as shown in FIG. That is, the open loop characteristic 3 in FIG. 4A is an open loop characteristic based on the gain characteristic 1, and the open loop characteristic 6 in FIG. 4B is an open loop characteristic based on the gain characteristic 5.
Since the gain characteristic 2 and the gain characteristic 5 are similar characteristics, only the open loop characteristic 6 based on the gain characteristic 5 is set.

A specific configuration of the optical information processing apparatus of the present invention using the open loop characteristics set as described above will be described with reference to FIG.

In the figure, the objective lens 13 focuses the light beam on the recording medium 12. The focus error detector 15 detects and outputs a focus error signal from the light beam reflected from the recording medium 12. First control circuit 1
Reference numeral 7 denotes an electrical filter that responds to only a signal in a desired frequency band with respect to an input focus error signal, and has an open loop characteristic 3 for the focus error signal.
Is a circuit for giving. The second control circuit 18 is, for example, an electric filter similar to the first control circuit, and is a circuit for giving the open loop characteristic 6 to the focus error signal.

The changeover switch 16 is switched to select whether to input the focus error signal to the first control circuit 17 or the second control circuit 18 according to the changeover signal. The drive circuit 19 sends a drive signal to the drive coil 14 according to the input focus error signal. The focus servo loop circuit 11 is formed by these configurations.

Next, the operation will be described based on the above configuration. First, during normal recording / reproduction, the changeover signal controls the changeover switch 16 to change over to the terminal a side. Therefore, the focus error signal output from the focus error detector 15 is the first control circuit 17
Is input to the control unit and is controlled to be converted into a focus error signal having an open loop characteristic 3. Then, the conversion-controlled focus error signal is passed through the drive circuit 19 to the drive coil 14
, The objective lens 13 is focus-controlled.

Next, at the time of access, the changeover signal controls the changeover switch 16 to change over to the terminal b side. Therefore, the focus error signal output from the focus error detector 15 is input to the second control circuit 18 and converted into a focus error signal having the open loop characteristic 6. Then, the conversion-controlled focus error signal is applied to the drive coil 14 via the drive circuit 19, so that the objective lens 13 is focus-controlled.

The above embodiment has explained the switching of the open loop characteristics in two control states which are different at the time of normal recording / reproducing and at the time of access. However, as shown in FIG. Alternatively, the open loop characteristics may be switched.

In FIG. 5, the same requirements as those in FIG. 2 are designated by the same reference numerals. Focus servo circuit 2 of FIG.
1, the first control circuit 23 to the Nth control circuit 24
(N ≧ 2) has N control states and gives an open loop characteristic based on each gain characteristic to the focus error signal. Then, the focus servo state selector 22
Are configured to switch according to any of the N control states.

[0025]

As described above, the optical information processing apparatus of the present invention has a plurality of focus servo circuits for controlling the focus of the light beam on the recording medium based on the focus error signal obtained from the recording medium. A plurality of control circuits having focus servo loop characteristics corresponding to different control states are provided, and the changeover switch is switched in accordance with the control state so that a loop is generated by any one of the selected control circuits. Since the characteristics are determined, the gain is not increased more than necessary in any control state, so that the focus servo is less likely to come off due to scratches, dust, or the like.

[Brief description of drawings]

FIG. 1 is a characteristic diagram illustrating an operation principle of an optical information processing device of the present invention.

FIG. 2 is a block diagram showing a specific configuration of an embodiment of the optical information processing apparatus of the present invention.

FIG. 3 is a focus gain characteristic diagram in each operating state of the optical information processing apparatus of the present invention.

FIG. 4 is an open-loop characteristic diagram based on a focus gain characteristic in each operating state of the optical information processing apparatus of the present invention.

FIG. 5 is a block diagram showing a specific configuration of another embodiment of the optical information processing apparatus of the present invention.

FIG. 6 is a time chart for explaining an operation for performing track counting during general access.

FIG. 7 is a characteristic diagram for explaining a general servo system designing method.

FIG. 8 is a gain characteristic diagram of a focus in each operating state of the conventional optical information processing apparatus.

FIG. 9 is an open loop characteristic diagram based on a gain characteristic of focus in each operating state of the conventional optical information processing apparatus.

[Explanation of symbols]

1 Gain characteristics during normal recording / reproduction 2 Gain characteristics during access 3 Open-loop characteristics based on gain characteristics during normal recording / reproduction 4, 6 Open-loop characteristics based on gain characteristics during access 5 Track servo during access Gain characteristics when loop is ON 12 Recording medium 16 Changeover switch 17 First control circuit (control circuit) 18 Second control circuit (control circuit) 22 Focus servo state selector (changeover switch) 23 First control circuit (control circuit) 24th N control circuit (control circuit)

Claims (1)

[Claims] 1. An optical information processing apparatus having a focus servo circuit for controlling focus of a light beam on a recording medium based on a focus error signal obtained from the recording medium, the optical information processing apparatus comprising a plurality of different control states. An optical information processing apparatus comprising: a plurality of control circuits each having a focus servo loop characteristic corresponding to each of the control circuits; and a changeover switch for selectively changing the plurality of control circuits according to the control state.