JPH0156453B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to an optical information reproducing device for reproducing recorded information by focusing a light beam onto an information recording carrier, and particularly relates to a light beam focusing position control means. Regarding.

[Technical background of the invention and its problems] An information recording carrier that records information such as audio, video, and various data in an optically readable form, such as the presence or absence of bits, is called an optical disk, and has already been used for audio. It has been put into practical use as compact discs, video discs, document files, etc. In an optical information reproducing device that reads and reproduces recorded information by irradiating such an information recording carrier with a light beam at a minute spot, one operation to accurately read the information on the information recording carrier is , a focusing position control (controlling the focusing position, that is, the relative distance between the focusing optical system of the light beam and the information surface of the information recording carrier so that the diameter of the irradiation spot of the focused light on the information surface of the information recording carrier is always kept small); (focusing servo) is required. This focusing position control is mainly performed using a focusing error signal generated from a detection signal of reflected light from the information recording carrier as a focusing position control signal.

By the way, in such a device, at least in the initial stage of its operation, it is necessary to pull the servo to the operating point (control target point) x0 of focusing position control. In this case, if the control loop is simply closed, the range of change (pull-in range) ±x1 of the focusing error signal If is very narrow (about several tens of microns), as shown in Figure 1.
It is difficult to pull in, and generally this alone will not bring it into the pull-in range. In particular, for example, a magnetic levitation type drive mechanism is used, in which the initial position of the servo's driven object (objective lens, etc.), that is, the position when there is no driving force, is far away from the servo's operating point. In that case, there is no retraction.

Therefore, in the initial stage of operation, the control loop is kept open and the driven body is forcibly scanned to the operating point using a scanning signal such as a triangular wave or sawtooth wave, and when the driven body reaches the vicinity of the operating point. The control loop is closed and the operating point is reached. Whether the driven object has reached the vicinity of the operating point is determined by
The level of the amount of reflected light and the level of the high frequency signal (information signal component) I0 due to the recorded bits are detected, and the determination is made based on whether the detected level exceeds a predetermined level. That is, a switch is inserted in front of a drive circuit for driving the drive mechanism, and under the control of the switch, a focusing error signal is cut off at the initial stage of operation, and a scanning signal is applied to the drive circuit as a focusing position control signal.
Then, a comparison circuit determines whether the level of the high-frequency signal exceeds a predetermined level, and when the level exceeds a predetermined level, control is performed in which the focusing error signal is used as a focusing position control signal and the scanning signal is cut off.

When such control is performed using an electromagnetic drive mechanism, the transient response of the servo until convergence to the operating point is shown in FIG. In the figure, a is the focused position control signal α(t) applied to the drive mechanism via the drive circuit, b is the speed v(t) of the driven body, and c is the position x(t) of the driven body. Each is shown below. There is a relationship between these: v(t)=K/m×∫α(t)dt...(1) x(t)=∫v(t)dt...(2). However, K is a conversion coefficient from the focused position control signal to driving force, and m is the mass of the driven body. Further, the broken line in FIG. 2c shows the pull-in range ±x1 of the focusing error signal shown in FIG. 1, and the one-dot chain line shows the range ±x2 of the determination level of the comparison circuit for determining the level of the high-frequency signal.

Assume that the drive mechanism is driven by a focusing position control signal α(t)=At as shown in FIG. 2a, and that the focusing position control signal switches from a scanning signal to a focusing error signal at time t1. The velocity v1 at is v1=K/mx∫ ^t1/0 Atdt=K′At1 ² /2 (K′=K/m). Thereafter, the driven body is accelerated until x=0 (servo operating point=focused point), and after that, it is decelerated and finally converges to x=0. This situation is shown in characteristic A. However, if v1 is too large, x will exceed the determination level x2 as shown in characteristic B, and the scanning signal will be generated again, so it will take a considerable amount of time to pull in.

When the initial position of the driven body is x0, v1 is v1=K′A(6|×0|/K′A) ^2/3 …(4), and |x0| ^2/3 and A ^1/3 is proportional to. Therefore, if |x0| is too large or A is too large, that is, if the frequency of the scanning signal is high, v1 will become large. Therefore, in order to reduce v1 when |x0| is large, it is necessary to make A extremely small. This means that t1 is very long because t1=(6x0/KA) ^1/3 ...(5), and after this time t1, x becomes
The time t2 required to converge to x0 also becomes longer. Also |
Even if x0| is small, if you want to shorten t1, it is necessary to increase A, but as can be seen from equation (5), there is a limit to this.

As described above, conventional focusing position control has a problem in that there is a limit to shortening the retraction time at the initial stage of operation, and it takes several seconds depending on |x0|. This is considerably longer than the rise time of other information reproducing devices that do not require focus position control, and an improvement has been desired.

[Object of the Invention] An object of the present invention is to provide an optical information reproducing device that can effectively shorten the pull-in time for focusing position control at the initial stage of operation.

[Summary of the Invention] The present invention provides a method for controlling the focusing position of focused light irradiated onto an information recording carrier, as a means for bringing the control based on a focusing error signal from an impossible state to a possible state at the initial stage of operation, etc. Means for adding a scanning signal to the focusing position control signal for forcing the focusing position to scan near the control target point while opening a control loop for focusing position control based on the error signal, and integrating the driving signal for the objective lens. an integrator, a means for determining whether the output of the integrator is positive or negative and generating a deceleration signal consisting of a rectangular pulse signal for decelerating the scanning speed at the focusing position; The present invention is characterized in that it has means for adding a deceleration signal for decelerating the scanning speed of the focus position control signal to the focusing position control signal, and for closing the control loop at the same time as or after the application of the deceleration signal.

That is, at the end of the scanning signal, a driving force in the opposite direction is applied to cancel the driving force that had been applied to the objective lens up to that point, and the scanning of the objective lens is forcibly and rapidly decelerated, and the servo operating point is immediately set. In other words, it is designed to converge to the control target point.

[Effects of the Invention] According to the present invention, the scanning speed of the objective lens by the scanning signal is not limited as in the conventional case, and the time required for pulling in the focusing position control is reduced regardless of the position of the objective lens at the initial stage of operation. Can be shortened. In particular, since this invention uses a rectangular pulse signal obtained by determining whether the integral value of the driving signal of the objective lens is positive or negative as the deceleration signal, the level of the signal can be made sufficiently large regardless of the focusing error signal to produce a large deceleration effect. is obtained. Therefore, compared to, for example, a case where the focusing error signal is directly used as a deceleration signal, the scanning speed of the focusing position by the scanning signal can be made faster, and the pull-in time for controlling the focusing position can be further shortened.

This effect is particularly noticeable when the initial position of the objective lens is far away from the servo operating point, such as when a magnetically levitated drive mechanism is used. The ratio of the rising time of the focusing servo to the time can be reduced. Further, even if the focusing servo is disturbed due to some disturbance during operation, it is possible to quickly return to a steady state and continue stable operation.

Furthermore, among optical information reproducing devices, in devices that require high-speed access, such as those used as memory in computer systems, it is necessary to converge the focusing position to the operating point at high speed not only at the initial stage of operation but also every time the access is made. Although this is necessary, it is fully possible to satisfy such requirements according to the present invention.

[Embodiment of the Invention] FIG. 3 shows the configuration of an optical information reproducing apparatus according to an embodiment of the invention. In the figure, an information recording carrier 1 is an optical disk such as a compact disk or a video disk, on which information is recorded in an optically readable form such as a row of pits 2.

Reproduction of information recorded on the information recording carrier 1 is performed as follows. That is, 3 is a light source such as a laser oscillator, and the light beam emitted from this light source 3 is made into parallel light by a collimation lens 4, and then guided to an objective lens 6 via a beam splitter 5. The light is focused by a lens 6 and irradiated as a minute spot onto the surface (information surface) of the information recording carrier 1 on which the pit rows 2 are formed. The objective lens 6 can be moved (scanned) in the optical axis direction by, for example, a magnetically levitated drive mechanism 7. The light reflected from the information surface of the information recording carrier 1 is guided to a photodetector 9 via an objective lens 6, a beam splitter 7, and an astigmatism lens 8. Photodetector 9
is a divided type detector, such as a two-divided or three-divided detector, and its output is supplied to an information signal generation circuit 10, which generates an information signal recorded on the information recording carrier 1 in a known manner.
Io is generated.

On the other hand, the output of the photodetector 9 is also supplied to a focusing error signal generation circuit 11, where the focusing error of the light beam focused by the objective lens 6, that is, the focusing position (focal point) of the focused light, is determined in a known manner. A focusing error signal If corresponding to the error in the relative position between the information surface of the information recording carrier 1 and the information surface of the information recording carrier 1 is generated. This focusing error signal If is supplied to a servo compensation circuit 12, and normally the focusing error signal taken out via this servo compensation circuit 12 is supplied to an adder 14 via a first switch 13. The output of the adder 14 is supplied as a focus position control signal 15 to a drive circuit 16 for driving the drive mechanism 7 of the objective lens 6.

At the beginning of the operation of the device, the first switch 13 is turned off and the second switch 17 is turned on. 15
added to. Note that the first and second switches 13 and 17 are connected to a comparator 19 that compares the output level of a level detector 18 that detects the level of the high-frequency signal that is the output signal lo of the information signal generation circuit 10 with a predetermined determination level. Controlled by output.

The configuration described so far is the same as the conventional one. In addition to this configuration, the present invention includes first and second integration circuits 21 and 22 that integrate the output (drive signal) 20 of the drive circuit 16, and determines whether the output of the first integration circuit 21 is positive or negative and generates a rectangular pulse signal. a positive/negative determining circuit 23 for obtaining a deceleration signal 24 consisting of a positive/negative determining circuit 23; a third switch 25 for supplying the output (decelerating signal) 24 of this positive/negative determining circuit 23 to the adder 14; An attenuation circuit 26 for attenuation and a comparator 27 for determining the output level of this attenuation circuit 26 and controlling the second switch 25 are added. Note that the switches 21a and 22a are for starting the integrating operation of the integrating circuits 21 and 22.

The operation of this embodiment is explained in the same manner as in FIG.
(t), V(t) and x(t) will be explained with reference to the time chart of FIG.

At the start of operation of the device, that is, at time t=0 when retraction of focus position control starts, switches 13 and 2 are first turned on.
2a and 25 are turned off, and switches 17 and 21a are turned on. In this case, by turning on the switch 17, a scanning signal Is consisting of, for example, a rectangular wave or a sawtooth wave is generated.
is the focus position control signal 15 via the adder 14
(α), the objective lens 6 is forcibly scanned along the optical axis direction by the drive circuit 16 and drive mechanism 7 toward the information recording carrier 1 side, that is, toward the vicinity of the control target point. At this time, the integration of the drive signal 20 is changed to the first by turning on the switch 21a.
is started by the integrating circuit 21 of .

Next, when the output of the level detector 18 reaches a predetermined level and the output of the comparator 19 is inverted at time t1, the switches 17 and 21a are turned off and the switches 13, 22a and 25 are turned on. In this case, when the switch 13 is turned on, the focusing error signal If from the focusing error signal generating circuit 11 taken out via the servo compensation circuit 12 is supplied to the adder 14, and when the switch 25 is turned on, the focusing error signal If is output from the integrating circuit 21. The deceleration signal which is the output signal (rectangular wave) 24 of the positive/negative determination circuit 23 connected to the adder 1
4. That is, at the same time that the deceleration signal 24 is added to the focus position control signal 15, the control loop is closed by turning on the switch 13. By this operation, the objective lens 6 is rapidly decelerated, and the focus position control is quickly moved to the retraction range ±x1.

In parallel with this operation, when the switch 22a is turned on, the integral value of the drive signal 20 integrated by the second integrator 22 is passed through the attenuation circuit 26 to the comparator 27.
When the output level of the attenuation circuit 26 reaches a predetermined value and the output of the comparator 27 is inverted, the switch 25 returns to the OFF state and the deceleration signal 24 is stopped. Thereby, the position of the objective lens 6 is converged on the control target point.

By performing the above control, as shown in FIG. 4a, the amplitude A of the focusing position control signal .alpha. from t=0 to t1, that is, the scanning signal Is, can be made larger than before, and t1 can be shortened accordingly. That is, if the initial positions x0 of the objective lens 6 are equal, the velocity v1 of the objective lens 6 at time t1 is 1/3 of the ratio of A.
t1 is shortened to -1/3 times the power. Thereafter, when the maximum backward driving force allowed by the drive circuit 16 and drive mechanism 7 is applied to the objective lens 6 by the deceleration signal 24, the scanning of the objective lens 6 is rapidly decelerated as shown in FIG. 4b. Therefore, its speed v
If the control loop is closed at time t3 when
It will be converged on.

Furthermore, at time t3, when x returns to near x0
Even if the control loop is closed at t3' (not shown), it can be quickly converged to x0. However, the integral value V2 (output of the second integrator 22) of the drive signal 20 (output of the second integrator 22) during this reverse direction drive is different from the integral value V1 (output of the first integrator 21) of the drive signal 20 based on the scanning signal Is up to t1. ), the velocity v3′ at t3′ becomes −v1
This results in too much acceleration in the opposite direction. Therefore, the integral value of the drive signal 20 during this reverse direction drive is limited to the value before and after the integral value of the drive signal 20 applied up to t1. This allowable range is determined by the ratio of t1 when deceleration control according to the present invention is performed to t1 in the conventional case where deceleration control is not performed, and the larger the ratio, the narrower it becomes.

Now, if t1 is 1/2 of t1', then A needs to be 8 times as large as in the conventional case, and v1 is v1 as in the conventional case.
is twice the maximum allowable value v1'. To set the velocity v3′ at t3′ at this time as |v3′|≦|v1′|, t1
The ratio V1:V2 of the integral value V1 of the drive signal up to and the integral value V2 of the drive signal during reverse direction driving is 1:0.5 to 1.5.
It may be within the range of . That is, by controlling V1:V2 to fall within this range, the scanning time t1 can be reduced to less than half of the conventional value. On the other hand, the time (t2 - t1) until the focused position control converges after time t1 is generally sufficiently short compared to t1. Therefore, the time required for focusing position control is also reduced by approximately 1/2.

Note that the present invention is not limited to the above-mentioned embodiment, and for example, the method of determining time t1 may be other than the above-mentioned method, and the conditions are not limited to the time when the focusing position control falls within the retraction range ±x1. , there is no problem even if it is outside the retraction range as long as it is in the vicinity. This is because the position x of the objective lens (driven object) asymptotically approaches x0 even after time t1, as shown in FIG.

Further, in the above embodiment, the timing to close the control loop (the time when the switch 13 is turned on) is the same as the time t1 when the application of the deceleration signal 24 starts, but it can be set after t1, for example, at the same time as the end time t3 of the deceleration signal 24. Of course, it is possible. In addition, various modifications can be made to the present invention without departing from the scope thereof.

[Brief explanation of drawings]

Fig. 1 is a diagram showing an example of the characteristics of a focusing error signal used for focusing position control in an optical information reproducing device, Fig. 2 is a time chart for explaining the conventional focusing position control operation, and Fig. 3 is a diagram of the present invention. A diagram showing the configuration of an optical information reproducing device according to an embodiment of
FIG. 4 is a time chart for explaining the focusing position control operation. 1... Information record carrier, 2... Pitt, 3... Light source, 6
...Objective lens, 7...Drive mechanism, 9...Photodetector, 1
0... Information signal generation circuit, 11... Focusing error signal generation circuit, 13... Control loop opening/closing switch, 14...
Adder, 15... Focusing position control signal, 16... Drive circuit, 17... Scanning signal application switch, 18... Level detector, 19... Comparator, 20... Drive signal, 2
1, 22... Integrator, 23... Positive/negative determination circuit, 24...
Deceleration signal, 26... Attenuation circuit, 27... Comparator.

Claims (1)

[Claims] 1. A light source, an objective lens for focusing and irradiating a light beam emitted from this light source onto an information recording carrier, and light detection by detecting reflected light from the information recording carrier due to irradiation of the focused light from this objective lens. means for obtaining a signal; means for generating a focusing error signal corresponding to an error in the focusing position of the focused light irradiated onto the information recording carrier from the photodetection signal; and controlling the focusing position in response to the focusing error signal. an optical information reproducing device comprising: a focusing position control means for generating a focusing position control signal for controlling the objective lens; and a means for generating a driving signal for driving the objective lens based on the focusing position control signal obtained by the means. In the above, the focusing position control means opens a control loop for focusing position control based on the focusing error signal and controls the focusing position as a means for bringing the control based on the focusing error signal from a state in which it is impossible to a state in which it is possible. means for adding a scanning signal for forcibly scanning the position to the control target point to the focusing position control signal; an integrator for integrating the drive signal; and determining whether the output of the integrator is positive or negative to detect the focusing position. means for generating a deceleration signal consisting of a rectangular pulse signal for decelerating the scanning speed; and means for adding the deceleration signal to the convergence position control signal when the convergence position moves to the vicinity of the control target point; and means for closing the control loop at the same time as or after the application of .