JPH05282815A - Servo system in information reader - Google Patents

Abstract

PURPOSE:To diminish a consumed power by suppressing an error signal to be supplied to an actuator in the state of a beam spot being subjected to transition as far as a disk standard is satisfied. CONSTITUTION:An error signal corresponding to the state of a beam spot on a disk 5 is generated by an error generation circuit 10 and a regulation circuit 11 monitors the level of the error signal. In a predetermined range where the absolute value of the level of the error signal satisfies a standard, the error signal to be supplied to an actuator(focus coil)6 is regulated, e.g. interrupted by the regulation circuit 11 so that the power consumption by the actuator 6 is suppressed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an information reading device capable of irradiating a recording track formed on a disk or the like with an information reading point by a laser beam or the like to read information, The present invention relates to a servo device in an information reading device for controlling states such as a tracking state.

[0002]

2. Description of the Related Art Recording media such as compact discs, optical video discs, and optical discs for optically recording and reproducing information are known. Information is recorded on or reproduced from these discs by focusing a laser beam by an objective lens to form a beam spot as an information reading point on the disc, and tracing this beam spot on a recording track formed on the disc. Done.

Therefore, a focus servo for keeping the focused state of the beam spot, a tracking servo for accurately following the beam spot to the track of the disc, and the like are indispensable, and these servos record the objective lens on the disc. This is done by supplying respective error signals to a focus actuator that drives in the direction orthogonal to the surface and a tracking actuator that drives the objective lens in the disk radial direction.

The focus servo generates a focus error signal according to the in-focus state of the beam spot irradiated on the disc by, for example, the astigmatism method, supplies the generated focus error signal to the focus actuator, and Keep the spot in focus.

The tracking servo also generates a tracking error signal according to the direction and amount of deviation between the recording track and the beam spot on the disk in the direction orthogonal to the recording track, for example, by the three-beam method or the push-pull method. The generated tracking error signal is supplied to the tracking actuator to control the position of the beam spot in the disc radial direction.

Of these servos, FIG. 8 to FIG.
This is for explaining the function of the focus servo. When the amount of deviation (defocus) from the in-focus point when the focus servo is open changes as shown in FIG. 8, the focus error signal is as shown in FIG. In addition, the signal just cancels the waveform of FIG. By supplying such a focus error signal to the focus actuator, the actual displacement of the beam spot from the in-focus point transits in the vicinity of the in-focus point as shown in FIG.

By the way, there is a standard for discs that defines a tracking range that these servos should satisfy. For example, the eccentricity of the disc, the waviness of the track, the wobbling of the recording surface and the amount of the unevenness can be set within a certain value. It is imposed on the disc manufacturer.

In other words, if each servo acts so as to satisfy the standard defined for the disk, the information reading ability is guaranteed.

[0009]

By the way, the cause of the focus error and the tracking error is considered to be mainly the eccentricity and unevenness peculiar to the disc, the drive system for rotating the disc, the precision of the mechanism system, the precision of the pickup, etc. The maximum error is defined by these interactions.

The disc is manufactured with relatively high precision, and for example, eccentricity peculiar to the disc, waviness of the track, unevenness of the recording surface, surface wobbling, etc. are sufficiently suppressed, and the mechanism system for rotationally driving the disc is stable. If so, not only the absolute value of the error signal is suppressed to a relatively small value, but the error signal becomes a sinusoidal signal synchronized with the rotation cycle of the disk.

That is, during one rotation of the disk,
Although the error signal does not completely become 0, it only transits in the vicinity thereof, and its peak may satisfy the standard. However, since the servo acts to match the state of the beam spot with a certain target value, the residual error signal is always supplied to the actuator that drives the objective lens. An actuator is generally composed of a coil wound around or attached to a bobbin that holds an objective lens, and a magnetic circuit that generates a magnetic flux that links the coil, and the objective is generated by an electromagnetic force generated by supplying an error signal to the coil. It drives the lens.

Therefore, by constantly supplying the error signal to the actuator, a considerable amount of electric power indicated by the diagonal lines in FIG. 9 is consumed.

The present invention has been made in order to overcome the problems of the conventional servo device, and a servo in an information reading device capable of reducing power consumption by suppressing an error signal supplied to an actuator. The purpose is to provide a device.

[0014]

According to a first aspect of the present invention, there is provided a servo apparatus in an information reading apparatus, wherein a beam spot as an information reading point is made to follow a recording track formed on a disk 5 as a recording medium. A servo device in a reading device for reading information, which is an actuator 6 as control means for controlling the state of the beam spot in accordance with an error signal corresponding to the displacement of the beam spot from the normal state on the disk 5, and the beam spot. When the displacement from the normal state is within the guaranteed range of the reading ability specified for the disk, the regulation circuit 11 as a regulation means for regulating the error signal supplied to the actuator 6 is provided. ..

The servo apparatus in the information reading apparatus according to the second aspect of the present invention further comprises a drive amplifier 12 as a gain adjusting means for adjusting the error signal with a predetermined gain and supplying it to the actuator 6, and the regulating circuit 11 Is characterized in that the gain of the drive amplifier 12 is changed according to the absolute value of the error signal.

[0016]

In the servo device of the information reading apparatus according to the first aspect of the present invention, the level of the error signal according to the state of the beam spot on the disk 5 is monitored by the regulating circuit 11. The regulation circuit 11 regulates, for example, cuts off the error signal to be supplied to the actuator 6 within a predetermined range in which the absolute value of the level of the error signal falls within the standard, and suppresses power consumption by the actuator 6.

In the servo apparatus in the information reading apparatus according to the second aspect of the present invention, the regulation circuit 11 controls the gain of the dray nib amplifier 12 that drives the actuator 6 according to the absolute value of the level of the error signal.

Therefore, the gain can be made small in the range where the level of the error signal is small, and the power consumption by the actuator 6 can be suppressed.

[0019]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a configuration of an embodiment of a servo device in an information reading device of the present invention. In the figure, for simplification of description, only a configuration necessary for focus servo is shown. The laser beam emitted from the semiconductor laser 1 is collimated by the collimator lens 2. The collimated laser beam further passes through a beam splitter 3 composed of, for example, a half mirror and an objective lens 4 and is focused on a recording surface of a disk 5, where a beam spot as an information reading point is formed.

The beam spot applied to the disk 5 is reflected and transmitted through the objective lens 4 again, and then is reflected by the beam splitter 3 and guided to the condenser lens 8. The condenser lens 8 condenses the reflected light and condenses it on the photodetector 9. The photodetector 9 is a four-division light receiving element, and the light received by each light receiving element is converted into an electric signal according to the amount of light.

On the other hand, the luminous flux incident on the photodetector 9 includes
Astigmatism is given by an optical element for astigmatism generation (not shown) such as a cylindrical lens, and the error generation circuit 10 calculates signals obtained from the four light receiving elements, and the focus error is calculated by the astigmatic focusing method. Generate a signal. The focus error signal generated by the error generation circuit 10 is supplied to the regulation circuit 11 as regulation means. The regulation circuit 11 monitors the level of the focus error signal, and suppresses the focus error signal in a predetermined range in which the absolute value of the level of the focus error signal falls within the standard defined by the disk 5, as described later.

The focus error signal obtained via the regulation circuit 11 is applied via a drive amplifier 12 to a focus coil 6 as an actuator wound around a bobbin holding the objective lens 4. The focus coil 6 has a coil axis oriented in a direction orthogonal to the disk recording surface, and a magnet 7 for generating a magnetic flux interlinking with the focus coil 6 is provided so as to surround the circumference.

Next, a specific structure of the regulation circuit 11 will be described with reference to FIGS. 2 and 3. In FIG. 2, the regulation circuit 11 includes a window comparator 111 for detecting the level of the supplied focus error signal and a switch 112 whose on / off is controlled by the output of the window comparator 111. The window comparator 111 sets the absolute value level of the focus error signal obtained when the absolute value of the defocus amount becomes a standard value or a predetermined value smaller than the standard value as a threshold level Vth, and the focus error signal has a threshold level ± Vth. A control signal is generated which is L when it is within the range, and H when it exceeds the threshold level ± Vth.

The switch 112 is closed when the control signal supplied from the window comparator 111 is H, and supplies the focus error signal to the drive amplifier 12 to form a focus servo loop. On the other hand, when the control signal is L, the switch 112 is closed. It is said that the focus servo loop is open.

In this way, since the focus error signal is not supplied to the actuator 6 when the focus error signal makes a transition within the standard, unnecessary power consumption can be avoided and the defocus amount falls within the standard. Therefore, the reading of the recorded signal is guaranteed.

This state will be described with reference to the waveform charts of FIGS. FIG. 4 shows how the defocus amount changes when the loop is open, and FIG. 5 shows the voltage supplied to the focus coil 6 at this time. Assuming that the standard allows a defocus amount of ± 1 μm, the defocus amount slightly smaller than this defocus amount (for example, ± 1 μm).
When the level of the focus error signal generated at the time of 0.9 μm) is ± Vth, the absolute value level of the focus error signal is less than ± Vth before time t1, so the output of the window comparator 111 becomes L and the switch 1
12 will be open. Therefore, the focus error signal is not supplied to the focus coil 6.

Next, at time t1, the focus error is +
When it exceeds Vth, the output of the window comparator 111 becomes H and the switch 112 is closed. Then, since the focus error signal is supplied to the focus coil 6, the objective lens 4 is driven in the direction in which the defocus amount decreases, and the focus error signal decreases. When the focus error signal becomes smaller than + Vth again at time t2, the switch 112 is opened and the supply of the focus error signal to the focus coil 6 is stopped.

At time t3, the focus error signal becomes −
When it becomes smaller than Vth, the output of the window comparator 111 becomes H, and the switch 112 is closed. Therefore, the focus error signal is supplied to the focus coil 6 again, and the defocus amount becomes smaller. 4 is driven. When the level of the focus error signal falls within ± Vth at time t4, the output of the window comparator 111 is L, the switch 112 is opened, and the supply of the focus error signal to the focus coil 6 is stopped. ..
That is, in this embodiment, the dead zone is within the range of + Vth.

Thus, from time t1 to t2, time t3
FIG. 6 shows the transition of the defocus amount when the focus error signal is supplied to the focus coil 6 only during the period from t4 to t4. According to this, it is understood that the defocus amount is sufficiently within the standard of the disk 5 even if the focus servo is not always operated.

FIG. 3 is a block diagram showing the configuration of another embodiment of the regulation circuit 11 in FIG. In this embodiment, the focus error signal is supplied to the level detector 113 and the drive amplifier 12. Level detector 1
As shown schematically in FIG. 7, when the level of the focus error signal is within the threshold level ± Vth, the gain of the drive amplifier 12 is set to be low, and the focus error signal is at the threshold level ± 13. When it exceeds Vth, a control bias for increasing the gain of the drive amplifier 12 is generated.

In the case of the present embodiment, when the focus error signal makes a transition within the range of ± Vth, the loop gain of the focus servo loop is lowered to suppress unnecessary power consumption of the focus coil 6. Also, set a plurality of threshold levels of the level detector 113,
It is also possible to control the gain of the drive amplifier 12 so as to gradually increase the focus servo loop gain as the absolute value level of the focus error signal increases.

It is also possible that the defocus amount suddenly increases. In this case, the servo loop is turned on / off or the gain is switched by simply comparing the predetermined threshold level ± Vth with the level of the focus error signal. Even if it is performed, it may be difficult to keep the defocus amount within the standard. In this case, the change value of the focus error is detected by, for example, a differentiating circuit, and when the focus error signal has a large slope in the vicinity of the standard, and the focus error signal is about to transition in the direction in which the error increases, A detection circuit for turning on the servo loop or increasing the gain may be added.

The regulating circuit 11 in the above embodiment
Can be configured by a CPU or the like. In this case, the focus error signal may be converted into a digital signal and the digital value thereof may be compared with a predetermined digital value.

Especially when a CPU is used, the transition state of the focus error signal can be monitored by calculating the difference between the immediately preceding sample value and the current sample value, so there is no need to provide the above-mentioned differentiating circuit.

Further, although the above-mentioned embodiment has explained the example of the focus servo, it can be applied to other servo systems such as tracking servo and sled servo.

[0036]

As described above, according to the servo device in the information reading apparatus of the first aspect of the present invention, the displacement of the beam spot as the information reading point from the normal state falls within the standard of the recording medium. In this case, since the error signal supplied to the control means for controlling the state of the beam spot is regulated, it is possible to reduce the power consumed by the control means while guaranteeing the reading ability.

According to the servo apparatus in the information reading apparatus of the second aspect of the present invention, since the regulating means sets the proper servo gain according to the displacement amount of the beam spot, the reading ability is guaranteed. At the same time, the power consumed by the control unit can be reduced as compared with the case where a gain higher than necessary is set.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an embodiment of a servo device in an information reading device of the present invention.

FIG. 2 is a block diagram showing a configuration of an embodiment of a regulation circuit 11 of FIG.

3 is a block diagram showing the configuration of another embodiment of the regulation circuit 11 of FIG.

FIG. 4 is a waveform chart showing an example of a defocus amount in an open loop.

5 is a waveform diagram of a signal supplied to the focus coil 6 in the embodiment of FIG.

FIG. 6 is a waveform diagram showing an example of a defocus amount guaranteed by the present invention.

FIG. 7 is a schematic diagram for explaining the operation of the regulation circuit 11 of FIG.

FIG. 8 is a waveform chart showing an example of a defocus amount in an open loop.

FIG. 9 is a waveform diagram showing an example of an error signal generated by a conventional servo device.

FIG. 10 is a waveform diagram showing an example of a defocus amount guaranteed by a conventional servo device.

[Explanation of symbols]

 1 semiconductor laser 2 collimator lens 3 beam splitter 4 objective lens 5 disk 6 focus coil (control means) 7 magnet 8 condenser lens 9 photodetector 10 error generation circuit 11 regulation circuit (regulation means) 12 drive amplifier (gain adjustment means)

Claims (2)

[Claims] 1. A servo device in a reading device for reading information by causing an information reading point to follow a recording track formed on a recording medium, the displacement of the information reading point from a normal state on the recording medium. In the case where the control means for controlling the state of the information reading point according to the corresponding error signal, and the displacement of the information reading point from the normal state falls within the guaranteed range of the reading ability defined in the recording medium, A servo device in an information reading device, comprising: a restricting unit that restricts the error signal supplied to the control unit. 2. The apparatus further comprises gain adjusting means for adjusting the error with a predetermined gain and supplying the error to the control means, wherein the regulating means changes the gain of the gain adjusting means according to an absolute value of the error signal. The servo device in the information reading device according to claim 1, characterized in that