JPH10116423A - Focus control pulling in device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a focal point from being deviated from an information surface when a focus control system is operated even when height deviation occurs due to the attaching error of a motor, a transfer base, etc., when a moving means is driven with an approaching means by operating the focus control system according to a signal of an information surface detection means and making the approaching means a hold state. SOLUTION: A microcomputer 135 makes a terminal a low level, and makes an output of a digital filter 125 zero. Further, it sets a value in a D/A converter 131, and brings a condenser lens 103 close to a disk 100. The fact that a focal position coincides with the information surface of the disk 100 is known with a zero cross detection signal high level by a comparator 132. The microcomputer 135 fixes the output value of the D/A converter 131, and switches the terminal a to a high level, and operates the digital filter 125. That is, thereafter, the microcomputer 135 operates the focus control system.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a focus control pull-in device for a focus control system for driving a focusing lens of an optical disk device so that the focus of a light beam coincides with the information surface of an optical disk.

[0002]

2. Description of the Related Art FIG. 14 is a block diagram showing a conventional focus control pull-in device.

A transfer table 115 has a laser 109, a coupling lens 108, a polarizing beam splitter 110,
A quarter-wave plate 107, a total reflection mirror 105, a photodetector 113, and an actuator 104 are mounted. The transfer table 115 is moved in the radial direction of the disk 100 by a transfer motor (not shown) such as a linear motor. It is configured to move to.

The laser 10 mounted on the transfer table 115
The light beam generated from 9 is coupled to the coupling lens 108.
After being collimated by the polarization beam splitter 110,
The light passes through the 波長 wavelength plate 107, is reflected by the total reflection mirror 105, is focused on the information surface of the disk 100 by the focusing lens 103, and is irradiated.

The light reflected by the information surface of the disk 100 passes through a converging lens 103 and a total reflection mirror 105
The light passes through a quarter-wave plate 107, a polarizing beam splitter 110, a detection lens 111, and a cylindrical lens 112 to irradiate a four-divided photodetector 113. The focusing lens 103 is attached to a movable portion of the actuator 104. The actuator 104 includes a coil and a permanent magnet. Therefore, actuator 1
When a voltage is applied to the coil 04 (not shown) using the power amplifier 128, a current flows through the coil and the coil receives a magnetic force from a permanent magnet (not shown). Therefore, the focusing lens 103 moves in a direction perpendicular to the surface of the disk 100 (vertical direction in the figure). The focusing lens 103 is the light beam 1
The focus of the optical beam 106 is controlled based on a focus error signal (hereinafter, referred to as an FE signal) indicating a deviation between the focal point 06 and the information surface of the disk 100 so that the focal point is always located on the information surface of the disk 100. You.

[0006] Disk 1 irradiated on photodetector 113
The reflected light from 00 is converted into a current by the photodetector 113 divided into four parts, and is converted into an electric current by the I / V converters 116 and 1.
17, 118 and 119 are input. I / V converter 11
6, 117, 118 and 119 convert an input current into a voltage according to the current level. Adder 120, 1
21 adds the input signals and sends them to the differential amplifier 122.
The differential amplifier 122 calculates the difference between the input voltages and outputs the calculated value. The optical system shown in FIG. 14 constitutes a focus error detection method generally called an astigmatism method.
Accordingly, the output of the differential amplifier 122 becomes an FE signal indicating a shift between the focal point of the light beam 106 and the information surface of the disk 100.

The FE signal is sent to the power amplifier 128 via the switch 801, the phase compensation circuit 800, and the adder 127. Actuator 10 by power amplifier 128
Current flows through the coil No. 4. In the switches 801 and 804, the terminal a and the terminal b are connected when the terminal d is at a high level, and the terminals a and c are connected when the terminal d is at a low level.

The phase compensation circuit 800 stabilizes the focus control system. Since the focusing lens 103 is driven according to the FE signal, the focal point of the light beam 106 is always located on the information surface.

Next, the above-described focus control pull-in will be described. First, the FE signal will be described with reference to FIG. Waveform (b) shows the FE signal. The vertical axis is FE
The horizontal axis indicates the distance between the focal position of the light beam 106 and the information surface of the disk. When the distance is u1, it indicates that the focal position of the light beam is very far from the information plane. Similarly, u2 indicates a case where the focal position coincides with the surface of the base material. In the case of u4, the focal position coincides with the information surface. Therefore, u4 = 0. u5
Case indicates that the focal position is above the information plane.
The schematic diagram (a) shows the positional relationship between the focal position of the light beam and the information surface of the disk in the case of u1, u2, u4, and u5.

When the distance is near u4, the FE signal changes like an S-shape. It is generally called an S-shaped curve. The range M shown in FIG. 15 is substantially the controllable range of the focus control. The range M is usually about 20 μm.

The focus control is performed by the FE of u4.
This is performed by detecting the timing at which the signal crosses zero and putting focus control into an operating state.

By the way, when the distance is u2, a small S
A character curve appears. This is because the base material is made of a resin such as polycarbonate, so that the light beam is reflected because the refractive index is different from that of air. Therefore, in order to prevent the zero crossing at u2 from being detected, the focusing lens 103 is moved to a position where the distance between the focal point of the light beam and the information surface of the disk 100 is u5.
Raise it until it becomes Then, the focus control system is operated at the first zero-cross timing while gradually lowering the focusing lens 103. By raising the focusing lens 103 once, the zero crossing of u4 can be accurately detected.

[0013] The comparator 132 detects the zero cross. The negative terminal of the comparator 132 is connected to the reference voltage 133 of E1. Also, FE is connected to the + terminal.
The signal is connected. Therefore, when the distance between the focal point of the light beam and the information surface of the disk becomes u3, the zero-crossing detection signal output from the comparator 132 becomes high level. At this timing, the focus control system starts operating.

If the reference voltage 133 is set to E2, the zero crossing of u4 can be detected while raising the focusing lens. However, if the response of focus control is low due to a large detection delay, the focus position may exceed the controllable range M due to overshoot. In this case, the timing at which the zero-crossing detection signal goes low indicates the timing at which the FE signal zero-crosses.

The focus control pull-in will be described with reference to the waveforms of FIG. The waveform (a) shows the output of the terminal a of the microcomputer 802. The waveform (b) shows the output of the terminal a of the signal generation circuit 803, the waveform (c) shows the focal position of the light beam, the waveform (d) shows the FE signal, and the waveform (e) shows the signal generation circuit 80.
3 is output from the terminal b, and the waveform (f) is
, And the waveform (g) shows the output of the terminal b of the microcomputer 802. The switches 801 and 804 output the signal of the terminal c to the terminal a when the terminal d is at a low level, and output the signal of the terminal b to the output terminal a when the terminal d is at a high level.

At time t0 of the waveform (a), focus control pull-in is started, and when the terminal a of the microcomputer 802 goes to a high level, the signal generation circuit 803 changes the terminal b to a low level and changes the waveform to the waveform (b) at the terminal a. The output voltage is output to the power amplifier 128 via the addition circuit 127. Therefore, the focusing lens 103 approaches the disk 100. Similarly, the focal point of the light beam 106 is
We approach the information side of 00. At time t1, the focal position coincides with the substrate surface. A small S-shaped curve appears in the FE signal. Thereafter, at time t2, the focal position coincides with the information surface.
An S-shaped curve appears in the FE signal. Thereafter, the focusing lens 103 moves further and stops at time t3.

The output of the terminal a of the signal generation circuit 803 gradually decreases after time t3. Therefore, the focal position moves toward the information surface. Further, the signal generation circuit 803 switches the terminal b to the high level at the time t3. Microcomputer 80
2 checks the zero-cross detection signal input to the terminal d when the level of the terminal b of the signal generation circuit 803 becomes high. Hereinafter, a signal that detects the zero-cross detection signal and permits the focus control to be pulled is referred to as a pull-in permission signal.

At time t4, the information surface and the focal position coincide.
The FE signal crosses zero at time t4 as shown in waveform (d). At time t5 immediately after the zero crossing, the output of the comparator 132 becomes high level. Since the terminal c is at the high level, the microcomputer 802 detects the zero cross detection signal input to the terminal d and switches the terminal b to the high level. Therefore, the terminal a and the terminal b of the switch 801 are connected, and the focus control loop is closed. That is, the focus control is activated. The microcomputer 802 takes in the envelope signal via the A / D converter 134. If the envelope signal is equal to or higher than a predetermined level, it is determined that the focus control has been normally performed. When the envelope signal is lower than the predetermined level, the focus control is performed again. The envelope signal will be described with reference to FIG. Waveform (a) shows the FE signal in the controllable range,
The waveform (b) shows the AS signal, and the waveform (c) shows the envelope signal. In FIG. 14, the signal is described as an ENV signal. A
The S signal indicates the total amount of reflected light from the disk 100 incident on the photodetector 113. The AS signal is modulated by information recorded in advance on the information surface with unevenness. The signal indicating information is a component of the amplitude L of the waveform (b). The envelope detection circuit 136 detects an information component recorded on the disc. The envelope detection signal detects this information component and becomes an amplitude L signal. Therefore, when the level of the envelope signal is equal to or higher than the predetermined level, the focus control operates normally.

[0019]

A height deviation may occur due to a mounting error of the motor 101, the transfer table 115 and the like. When a large height shift occurs in the direction in which the focusing lens 103 approaches the disk 100, the focusing lens 103 collides with the base material of the disk 100 when the focusing lens 103 approaches the disk 100. Since the disk 100 is rotating, the surface of the base material is scratched over a wide area by the collision, and the reproduction performance of the signal is largely deteriorated. Disk 100
Is stopped and the focus control is pulled in, an envelope signal is not generated. Therefore, it is necessary to rotate the motor 101 in order to determine whether or not the focus control has been correctly drawn. If the focus control cannot be normally performed, the motor 101 must be stopped again to perform the focus control pull-in, and the pull-in time of the focus control increases.

When a height shift occurs, the focus position and the information plane coincide with each other when the output value of the signal generation circuit 803 is greatly shifted from zero. That is, at the position where the focusing lens 103 is largely moved from the neutral position, the focal position and the information plane coincide. When the focus control is operated in this state, the output value of the phase compensation circuit 800 immediately after the focus control is zero, so that the focusing lens 103 attempts to move toward the neutral position. Therefore, the focal position is once shifted from the information plane. FIG.
As shown in the waveform (c), the focal position shifts immediately after time t5. Thereby, the level of the FE signal also increases as shown in the waveform (d). Thereafter, the focus position is controlled by the focus control system so as to coincide with the information surface. If the response of the focus control system is poor, the focus position may deviate from the controllable range M in some cases.

The present invention has been made in view of the above problems, and has
1. An object of the present invention is to provide a focus control pull-in device that does not damage the surface of the base material of the disk 100 even when a height shift occurs due to an error in mounting the transfer table 115 or the like. It is another object of the present invention to provide a focus control pull-in device in which the focus position does not deviate from the controllable range M when the focus control is operated.

[0022]

In order to achieve this object, a focus control pull-in device according to the first aspect of the present invention determines the amount of deviation between the focal position of a light beam for reproducing a signal from the information surface of a disk and the information surface. A focus shift detecting means for detecting, a moving means for driving the focus position in a direction perpendicular to the information surface, and the moving means so that the focus position is on the information surface based on an output of the focus shift detecting means. Focus control means for controlling; signal generating means; approach means for controlling the moving means so that the focal position approaches an information surface in accordance with an output signal of the signal generating means; and signal from the defocus detecting means. Information surface detection means for detecting that the focal point is in the vicinity of the information surface on the basis of the information surface. With operating the carcass control, it is obtained so as to the approaching means unit in hold status.

According to a second aspect of the present invention, there is provided a focus control pull-in device, wherein a focus shift detecting means for detecting a shift amount between a focus position of a light beam for reproducing a signal from an information surface of a disk and the information surface, and the focus position information as information. Moving means for driving in a direction perpendicular to the plane; and moving the moving means on the information plane based on the output of the defocus detecting means so that the focal position is on the information plane.
Focus control means for performing ID control, signal generation means,
An approaching unit that controls the moving unit so that the focal position approaches the information surface according to an output signal of the signal generating unit; and the focus is near the information surface based on a signal from the defocus detection unit. Information surface detecting means for detecting that the moving means has been driven by the approaching means, the focus control is operated in accordance with a signal from the preceding information surface detecting means, and the I signal generation system of the PID control is provided. The initial value of the integrator is set based on the value of the access means.

According to a third aspect of the present invention, there is provided a focus control pull-in device, comprising: a motor for rotating a disk; and a focus shift detecting means for detecting a shift amount between a focus position of a light beam for reproducing a signal from an information surface of the disk and the information surface. Reflected light detecting means for detecting the reflected light of the light beam from the disc, moving means for driving the focal position in a direction perpendicular to the information surface, and information on the information surface based on the output of the defocus detecting means. A focus control unit for controlling the moving unit so that the focal position is located; a signal generating unit; and controlling the moving unit such that the focal position approaches the information surface in accordance with an output signal of the signal generating unit. A first approaching means for controlling the moving means so that the focal position passes through the information surface; and a focusing means based on a signal from the defocus detecting means. An information surface detecting means for detecting the presence of the information surface and a maximum value Q of an output value of the reflected light amount detecting means when the second approaching means is operated with the motor stopped. A maximum value detecting means, when the motor is operated and the moving means is driven by the first approach means to operate the focus control means in accordance with a signal from the preceding information surface detecting means, The moving range of the focal position by the second approaching means is limited according to the maximum value Q measured by the maximum value detecting means.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The focus control pull-in apparatus of the present invention is stable because the lens position does not change DC before and after the focus control is operated even if a height shift occurs due to a mounting error of a motor, an actuator or the like. Focus control can be pulled in.

Further, even when the height is shifted due to the mounting error of the actuator or the like and the lens may collide with the disk, the movement of the lens is stopped by detecting the approach of the lens and the disk. No disk collision.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. (Embodiment 1) Hereinafter, a focus pull-in device according to Embodiment 1 of the present invention will be described with reference to FIG. The same blocks as those in the conventional example shown in FIG.

The difference from FIG. 14 is that the phase compensation circuit 80
0, switch 801, switch 804, signal generation circuit 8
03 is deleted and the analog-to-digital converter (A / D
A converter 124, a digital filter 125, and a digital / analog converter (D / A converter) 126 are added. The A / D converter 124 converts the FE signal into a digital signal. The digital filter 125 is obtained by digitally configuring the conventional phase compensation circuit 800. D / A converter 126 converts a digital signal into an analog signal. The focus control pull-in will be described with reference to FIG. The waveform (a) is a D / A converter 131
The output waveform of FIG. The waveform (b) shows the focus position, the waveform (c) shows the FE signal, and the waveform (d) shows the comparator 132.
, The waveform (e) represents the pull-in permission signal, and the waveform (f) represents the terminal a of the microcomputer 135.
Respectively are shown. The pull-in permission signal is an internal signal of the microcomputer 135.

The microcomputer 135 disables the digital filter 125 by setting the terminal a to low level. The output of the digital filter 125 becomes zero. Details will be described later. At time t10 of the waveform (a), the pull-in operation of the focus control starts. The microcomputer 135 has a terminal b
Is set to the D / A converter 131 via the. The output value of the D / A converter 131 gradually increases. D / A converter 1
A period during which the output value of the waveform 31 gradually increases is a time t of the waveform a.
This is a period from 10 to time t12. D / A converter 131
Is sent to the power amplifier 128 via the adder 127. The focusing lens 103 comes closest to the disk at time t12. The state at time t12 is a state in which the focal point position has passed the information surface of the disk and is further closer to the disk. Accordingly, the focus coincides with the information surface at time t11. After time t12, the output of the D / A converter 131 gradually decreases. Therefore, the focusing lens gradually lowers after time t12. The microcomputer 135 sets the internal pull-in permission signal to a high level, and takes in the zero-cross detection signal input to the terminal c after time t12. After time t12, the focus approaches the information surface of the disc. At time t13, the focus and the information plane match. Immediately after that, the zero-cross detection signal becomes high level. The microcomputer 135 detects at time t14 that the zero-crossing detection signal has gone high,
The output value of the A converter 131 is fixed to the value at the time t14.
Therefore, the output value of the D / A converter 131 becomes D after time t14. Then, the terminal a is switched to a high level to put the digital filter 125 into an operating state.

Therefore, after time t14, the focus control is activated. Time t of digital filter 125
The output value at 14 is zero but the D / A converter 131
Is D, the focusing lens 103 does not shift immediately after the focus control system operates. Microcomputer 13
5 takes in the envelope signal via the A / D converter 134. If the envelope signal is equal to or higher than a predetermined level, it is determined that the focus control is operating normally.

Next, the operation in which the focusing lens gradually approaches the disk during the period from time t10 to time t12 in FIG. 2 will be described using the characteristics of the actuator 104 in FIG.
FIG. 3 shows a frequency characteristic of the actuator 104. It is a diagram generally called a Bode diagram. The horizontal axis indicates frequency. The vertical axis of the characteristic diagram (a) indicates the gain. Characteristic diagram (b)
The vertical axis indicates the phase. The focusing lens 103 of the actuator 104 is attached to the transfer table 115 via a spring. In addition, a viscous substance such as rubber is attached to the spring. Assuming that the current flowing through the coil by the power amplifier 128 is i and the position of the focusing lens 103 is x, the relationship between x and y can be expressed by the differential equation of Equation 1. w is generally called a natural angular frequency, and a is called an attenuation rate.

[0032]

(Equation 1)

When the equation 1 is represented by a Bode diagram, the Bode diagram of FIG. 3 is obtained. Therefore, when the frequency is 50 Hz, the gain becomes high and the phase becomes -90 degrees. At frequencies lower than 50 Hz, the sensitivity is constant regardless of the frequency, and there is no phase delay. During the period from time t10 to t12 shown in the waveform (a) of FIG. 2, the coil current gradually increases. Time t
Since the change of the current during the period from 10 to t12 is 50 Hz or less, the position of the focusing lens 103 corresponds to the level of the current value i. The same applies to the period from time t12 to time t14.

Accordingly, D shown in the waveform (a) of FIG. 2 corresponds to the level of the drive current i of the focusing lens 103 corresponding to the height deviation.

FIG. 4 is a block diagram of the digital filter 125 shown in FIG. In FIG.
Is connected to the A / D converter 124 in FIG. 1, the terminal 201 is connected to the terminal a of the microcomputer 135, and the terminal 202 is connected to the D / A converter 126. The switch 203 switches focus control on or off. Adders 204, 205, 20
6 adds and outputs the input signal. The subtracter 207 subtracts the input signal. Multipliers 208 and 209 multiply the input signal by a coefficient and output the result. This digital filter 125
Are operating in synchronization with the rising edge of the reference clock CLK of the cycle T, and the delay circuits 210 and 211 delay the input signal by the time of the cycle T and output. Delay circuit 21
0 and 211 are random access memories (RAs) that store digital data input to the terminal a in synchronization with the rising edge of the reference clock CLK and output from the terminal b.
M). Hereinafter, the RA of the delay unit 211 will be described.
M is called RAM1 and RAM of the delay unit 210 is called RAM2. A block A indicated by a dotted line of the digital filter 125 is a phase delay compensation filter for increasing the low-frequency gain of the focus control system, and a block B is a phase lead compensation filter for securing a phase margin near the gain intersection. That is, the digital filter 125 is a phase compensation filter for implementing a PID control system. Delay circuit 210, 2
The stored value 11 is cleared when the terminal c becomes low level. That is, the operation of the delay is stopped.

FIG. 5 shows gain and phase characteristics of the digital filter 125. The characteristic (a) indicates the characteristic of the block A, the characteristic (b) indicates the characteristic of the block B, and the characteristic (c) indicates the entire characteristic obtained by adding the block A, the block B, and the P signal. Note that the vertical axis indicates gain and phase, and the horizontal axis indicates frequency in logarithm (Log). The characteristic (a) of the block A indicates integration and the slope of the gain is −20 dB /
dec. In addition, the slope of the gain near fg of the characteristic (b) of the block B is approximately 20 dB / dec. The frequency fg shown in the characteristic (c) is the gain intersection of the focus control system, and the phase advance is maximized at that frequency to secure a phase margin. The effect of the phase delay compensation filter of the block A appears below the frequency fl, and the phase is delayed accordingly. In general, fg is set to several hundred Hz to several kHz. Note that, as described above, the relationship of the displacement with respect to the drive current of the actuator 104 generally has a characteristic of a quadratic proportional element, and has a slope of −40 dB / dec near the gain intersection.

(Embodiment 2) A focus control pull-in device according to Embodiment 2 of the present invention will be described below with reference to the block diagram of FIG. The same blocks as those in the first embodiment shown in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted.

The difference from FIG. 1 is that the digital filter 1
25 is that the digital filter 250 is replaced with the microcomputer 135, and the microcomputer 135 is replaced with the microcomputer 251.

The focus pull-in will be described with reference to FIG. The waveform (a) shows the output waveform of the D / A converter 131. The waveform (b) shows the position of the focal point, and the waveform (c) shows the FE
The waveform (d) shows the zero-cross detection signal output from the comparator 132, the waveform (e) shows the pull-in permission signal, the waveform (f) shows the waveform at the terminal a of the microcomputer 251 and the waveform (g) shows the digital filter. 250 output signals are shown. The pull-in permission signal is an internal signal of the microcomputer 251.

The operation up to time t23 in FIG. 7 is the same as the operation in the first embodiment, and a description thereof will be omitted. At time t20
Corresponds to time t10. Similarly, time t21 is time t1
1, time t22 is time t12, and time t23 is time t
13 respectively.

At time t24, the microcomputer operates the D / A converter 13
Set the output of 1 to zero. Then, the digital filter 25
The initial value of the RAM of the I signal generation system inside the digital filter 125 is set so that the output of 0 becomes D. After that, the digital filter 250 is set to the operating state, thereby setting the focus control to the operating state. Therefore, time t24
Thereafter, the focus control is activated. At time t24, the output of the D / A converter 131 is zero, but the output value of the digital filter 250 is D.
Does not shift immediately after the focus control system operates. The microcomputer 251 takes in an envelope signal via the A / D converter 134. If the envelope signal is equal to or higher than a predetermined level, it is determined that the focus control has been normally performed.

Next, the digital filter 250 will be described with reference to FIG. FIG. 8 shows a digital filter 250.
FIG. Terminal 260 is A / D converter 124
It is connected to the. Terminal 262 is a D / A converter 126
The terminal 261 is connected to the terminal a of the microcomputer 251 and the terminal 27
2 is connected to the terminal f of the microcomputer 251, and the terminal 273 is connected to the terminal g of the microcomputer 251.

Digital Filter 250 of Second Embodiment
However, the difference from the digital filter 125 of the first embodiment is the function of the RAM 1. The RAM 1 is provided with a function of writing predetermined data from outside. RAM1
Is a terminal for inputting data, and a terminal e is a terminal for inputting a write pulse. When the terminal e becomes high level, the data set in the terminal d at that time is stored in the value of the RAM1.

The digital filter 2 using the waveform of FIG.
The operation of 50 will be described. The waveform (a) is the reference clock CLK of the digital filter 250. The filter operates in synchronization with the rising edge. Waveform (b) shows digital data set at terminal 272 of digital filter 250. Waveform (c) shows the waveform at terminal 273,
Waveform (d) shows the waveform at terminal 261, and waveform (e) shows the waveform at terminal 2.
62, the waveform (f) shows the output waveform of the D / A converter 131, and the waveform (g) shows the output waveform of the adder 127.

The period from time t30 to t32 indicates a period near time t24 in FIG. When the zero cross is detected at time t30, the microcomputer 251 switches the signal at the terminal a from low level to high level. Therefore switch 26
3 closes. The clear state of RAM1 and RAM2 is released. The microcomputer 251 sets digital data corresponding to D to the terminal 272 of the digital filter 250. At time t31, a write pulse is sent to digital filter 250. Therefore, the value of the RAM 1 becomes a digital value corresponding to D. At time t31, since the rising edge of the clock CLK is not input after the clear state of the digital filter 250 is released, the value of the I signal is zero. The value of the P signal is F
Since it is near the zero crossing of the E signal, it is almost zero. Therefore, the output value of the digital filter 250 is a digital value corresponding to D. The output of the digital filter 250 is sent to the D / A converter 126. Therefore, the output value of the D / A converter 126 is D. Also, at time t31, D /
The output value of the A converter 131 becomes zero. Therefore, adder 1
The output of 27 becomes D before and after time t31.

The first reference clock CL after the clear state of the digital filter 250 is released at time t32
The rising edge of K is input. The digital filter 250 starts operating.

In the second embodiment, the value of the RAM 1 changes in accordance with the height deviation even if there are different height deviations when reproducing the inner peripheral side and the outer peripheral side of the disk. On the other hand, in the first embodiment in which a constant drive current is constantly applied, if the height difference is different, the difference becomes a disturbance and deteriorates control accuracy.
Therefore, even when the amount of the height deviation is different, the control accuracy does not deteriorate.

The focus control pull-in devices according to the second and third embodiments once bring the focusing lens 103 close to the disk 100, and then gradually lower the focus lens 103 to operate the focus control at the timing when the FE signal first crosses zero. This is to prevent erroneous detection when the FE signal crosses zero on the surface of the disk substrate as described in the background art. However, if the reference voltage 133 is changed to E2 as described with reference to FIG. 15 in the related art, the focus control is performed at the timing when the zero-crossing detection signal first becomes low level while the focusing lens 103 is gradually raised. Focus control can be drawn into the camera. The focus control pull-in device described in the second and third embodiments operates the focus control at the timing when the zero-crossing detection signal first becomes low level while gradually raising the focusing lens 103 by changing the reference voltage 133 to E2. Even if it changes so that it may make it carry out, the effect aimed at by the invention is similarly exhibited. Therefore, the invention described in the second and third embodiments is not limited to the moving direction of the focusing lens 103 when operating the focus control.

Embodiment 3 Hereinafter, a focus pull-in device according to Embodiment 3 of the present invention will be described with reference to FIG. 10 which is a block diagram thereof. The same blocks as those in the first embodiment shown in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted.

The difference from FIG. 1 is that the microcomputer 135 is replaced with the microcomputer 300. Also, LPF
301 and an A / D converter 302 are added. The microcomputer 300 can take in the output of the A / D converter 302. Further, the rotation of the motor 101 can be turned on or off.

In the third embodiment, the case where the focusing lens 103 collides with the base material surface of the disk 100 when the focusing lens is raised to the upper limit of the possible range because the height deviation is large.

First, the low-pass filter 3 will be described with reference to FIG.
01 (hereinafter referred to as LPF), which is an output signal of ASL
Will be described. FIG. 3A schematically shows the relationship between the disk 100 and the focal point of the beam 106. Waveform b shows the FE signal. The schematic diagram (a) and the waveform (b) are the same as FIG. 15 used in the conventional example. Waveform (c) shows the ASL signal.

The ASL signal indicates the level of the low-frequency signal component of the total reflection light amount incident on the photodetector 113. Therefore, when the focus and the information surface of the disc 100 match, the maximum value is obtained. Although the ASL level is high even when the focal point coincides with the substrate surface of the disk 100, the reflectance of the substrate surface is very low compared to the reflectance of the information surface, so that the maximum ASL is obtained in the case of u4. .

Drawing of focus control FIG. 11
This will be described with reference to FIG. A waveform (a) in FIG. 12 shows an output waveform of the D / A converter 131. Waveform (b) shows the ASL signal,
The waveform (c) shows the FE signal, the waveform (d) shows the zero-cross detection signal, the waveform (e) shows the pull-in permission signal, and the waveform (f)
Indicates an on / off signal of the motor. The motor on / off signal indicates off at a low level and on at a high level.

The microcomputer 300 initially has the motor 101
Is stopped. The microcomputer 300 disables the digital filter 125 by setting the terminal a to low level. The output of the digital filter 125 becomes zero. The focus pull-in operation starts at time t40 of the waveform (a). The microcomputer 300 is connected to the D / A converter 13 via the terminal b.
Set the value to 1. The output value of the D / A converter 131 gradually increases. The period during which the output value of the D / A converter 131 gradually increases is the period from time t40 to time t43 of the waveform (a). The output of the D / A converter 131 is an adder 127
To the power amplifier 128. Focus is on time t4
1 and the information surface at time t42. At time t42, the ASL signal becomes maximum. Microcomputer 3
00 stores the maximum value Q of the ASL in the internal RAM q. The focus is closest to the disk at time 43. The focusing lens 103 collides with the substrate surface of the disc 100 due to the height deviation. However, since the motor 101 is off and the moving speed of the focusing lens 103 is low, the focusing lens 103 and the disk 100 are not damaged.

After time t43, the output of D / A converter 131 gradually decreases. Therefore, after time t43, the focusing lens 103 is gradually lowered. Focusing lens 1 at time t44
03 is farthest from the disk 100.

The microcomputer 300 starts the motor 10 at time t44.
Turn 1 on. Therefore, the disk 100 starts rotating. The microcomputer 300 gradually increases the output value of the D / A converter 131 at time t45. Therefore, the focal position gradually approaches the disk 100. When the value of ASL becomes Q / 2 at time t46, the microcomputer
Start. The output value of the D / A converter 131 is gradually increased until the value of the timer 303 reaches a predetermined value. The predetermined value is referred to as Tup. At time t47, the focus and the information plane match. When the measured value of the timer 303 reaches a predetermined value at time t48, the microcomputer 300 causes the D / A converter 131
Output value is gradually reduced. After time t48, the pull-in permission signal is set to the high level, and detection of the zero-cross detection signal is started.

When the zero-cross detection signal goes high at time t49, the focus control system is activated. The operation after time 49 is the same as the operation after time t14 described in Embodiment 1 with reference to FIG. Note that the microcomputer 300 takes in the envelope signal via the A / D converter 134. When the envelope signal is lower than the predetermined level, it is determined that the focus control is not operating normally, and the focus control is performed again. In this case, the motor 101 is stopped and the maximum value of ASL is not measured. The operation after time t45 in FIG. 12 is performed again.

When the Tup is large, the focusing lens 103
May approach the disk 100 and collide.

Therefore, a method of setting Tup will be described. FIG. 13 is a schematic diagram when the focal point and the information surface of the disc 100 match. The surface of the focusing lens 103 and the surface of the substrate are generally separated by about 1.5 mm. This distance is determined by the design of the optical system. If the disk 100 has no surface run-out, the lens is gradually lowered after bringing the lens close to the disk by several μm from this state. Then, the focus control may be operated according to the zero-cross detection signal. However, when the disk has a runout, the disk may move away from the focal point from the state shown in FIG. FIG.
Shows that the disk 100 moves upward in the figure.
In the worst case, the focusing lens is gradually lowering.
A case occurs where the focal point and the information plane do not match. That is, the focus control cannot be operated.

When the surface deflection is ± 300 μm, the focusing lens is raised by 600 μm from the state shown in FIG. 13 and then gradually lowered, so that the focal point always matches the information plane. Also, 600u
The distance between the lens surface and the substrate surface is at worst 6
00um. This value can be obtained by the following equation.

[0062] In this equation, the focal point and the information surface coincide with each other when the disk 100 is at the highest position due to surface deflection, and 600 μm is obtained from the position.
This shows a case where the lens is raised. The state where the disk 100 is raised most due to surface runout is 300 disks.
It is in the state that has risen.

In FIG. 12, the ASL signal is Q / 2
It is assumed that the timer 303 is operated from the point in time at which the ASL becomes Q / 2 because the focal point is 1 from the information side.
Since it is about 0 μm apart, it can be ignored compared to the above 600 μm. Further, since the timing at which the ASL reaches Q / 2 is detected, the timing of Q / 2 can be reliably detected even if there is an error in the ASL measurement. It should be noted that the value of Q / 2 must be larger than the ASL level when the focal length matches the substrate thickness. However, usually, the ASL level when the focal point coincides with the substrate thickness is sufficiently smaller than Q / 2.

The speed at which the focusing lens 103 is raised can accurately detect the FE signal and the ASL signal.
04 must be low speed unaffected by the natural vibration of 50 Hz. 2mm speed for raising the focusing lens 103
Assuming / s, the time for the lens to move 600 um is 300 ms. Therefore, the timer 303 is configured to measure 300 ms. That is, Tup
= 300 ms.

[0065]

As described above, according to the focus control pull-in apparatus according to the first aspect, the focus shift for detecting the shift amount between the focus position of the light beam for reproducing a signal from the information surface of the disk and the information surface. Detecting means, moving means for driving the focal position in a direction perpendicular to the information surface, and focus control for controlling the moving means such that the focal position is on the information surface based on the output of the defocus detecting means Means,
Signal generating means, approaching means for controlling the moving means such that the focal position approaches the information surface in accordance with an output signal of the signal generating means, and the focal point is determined based on a signal from the defocus detecting means. Information surface detecting means for detecting that the moving means is in the vicinity of a surface, wherein when the moving means is driven by the approaching means, focus control is operated in accordance with a signal from the preceding information surface detecting means, and the approaching means means Is set to the hold state, so that the focus does not deviate from the information surface when the focus control system is operated even if there is a height deviation.

According to a second aspect of the present invention, there is provided a focus control pull-in device which detects a shift amount between a focal position of a light beam for reproducing a signal from an information surface of a disc and an information surface, and the focal position. Moving means for driving the moving means in a direction perpendicular to the information plane, focus control means for performing PID control of the moving means based on the output of the defocus detecting means so that the focal position is on the information plane, and signal generating means An approaching unit that controls the moving unit so that the focal position approaches the information surface according to an output signal of the signal generating unit; and the focus is in the vicinity of the information surface based on a signal from the defocus detecting unit. Information surface detecting means for detecting the presence of the moving object. When the moving means is driven by the approach means, the focus control is operated in accordance with a signal from the preceding information surface detecting means. Since the initial value of the integrator of the I signal generation system of the PID control is set based on the value of the approach means, even if there is a difference in height between the outer circumference and the inner circumference of the disc, the focus control system is not required. The focus does not deviate from the information surface when the is operated. Further, the control accuracy is not deteriorated.

According to the focus control pull-in device of the third aspect, the motor for rotating the disk and the defocus which detects the amount of deviation between the focal position of the light beam for reproducing a signal from the information surface of the disk and the information surface. Detecting means, reflected light detecting means for detecting the reflected light of the light beam from the disc, moving means for driving the focal position in a direction perpendicular to the information surface, and information based on the output of the defocus detecting means. A focus control unit for controlling the moving unit so that the focal position is on a plane; a signal generating unit; and the moving unit such that the focal position approaches an information surface according to an output signal of the signal generating unit. A first approaching means for controlling the focus position, a second approaching means for controlling the moving means so that the focal position passes through the information surface, and a front approaching means based on a signal from the defocus detecting means. An information surface detecting means for detecting that the focal point is in the vicinity of the information surface; and a maximum value Q of an output value of the reflected light amount detecting means when the second approaching means is operated with the motor stopped. When the focus control means is operated in accordance with a signal from the preceding information surface detection means by driving the movement means by the first approach means with the motor in an operating state, comprising: ,
The moving range of the focal position by the second approach means is limited in accordance with the maximum value Q measured in advance by the maximum value detecting means. There is no collision between the lens and the disk.

[Brief description of the drawings]

FIG. 1 is a block diagram of a focus control pull-in device according to a first embodiment of the present invention;

FIG. 2 is a waveform chart showing an output signal in the first embodiment.

FIG. 3 is an actuator 10 according to the first embodiment.
Bode plot showing characteristics of 4

FIG. 4 is a block diagram of a digital filter 125 according to the first embodiment.

FIG. 5 is a Bode diagram showing characteristics of digital filter 125 according to the first embodiment.

FIG. 6 is a block diagram of a focus control pull-in device according to a second embodiment of the present invention;

FIG. 7 is a waveform chart showing an output signal in the second embodiment.

FIG. 8 is a block diagram of a digital filter 250 according to the second embodiment.

FIG. 9 is a waveform chart of an output signal in the second embodiment.

FIG. 10 is a block diagram of a focus control pull-in device according to a third embodiment of the present invention;

FIG. 11 is a diagram showing a relationship between a focal point and an information surface of a disc according to the third embodiment.

FIG. 12 is a waveform chart showing output values in the third embodiment.

FIG. 13 is a schematic diagram showing a relationship between a focal point and an information surface of a disc according to the third embodiment.

FIG. 14 is a block diagram of a conventional focus control pull-in device.

FIG. 15 is a schematic diagram showing a relationship between a focal point and an information surface of a disc in the above conventional example, and a waveform diagram showing an FE signal.

FIG. 16 is a waveform chart showing an output signal in the conventional example.

FIG. 17 shows an FE signal, an AS signal,
Waveform diagram showing ENV signal

[Explanation of symbols]

 REFERENCE SIGNS LIST 100 disk 101 motor 103 focusing lens 104 actuator 105 total reflection mirror 106 light beam 107 波長 wavelength plate 108 coupling lens 109 laser 110 polarization beam splitter 111 detection lens 112 cylindrical lens 113 photodetector 114 transfer motor 115 transfer table 116, 117, 118, 119 I / V converter 120, 121 Adder 122 Differential amplifier 123 Adder 124 A / D converter 125 Digital filter 126 D / A converter 127 Adder 128 Power amplifier 131 D / A converter 132 Comparator 133 Reference voltage 134 A / D converter 135 Microcomputer 136 Envelope detection circuit

Claims (3)

[Claims] 1. A defocus detecting means for detecting a deviation between a focal position of a light beam for reproducing a signal from an information surface of a disk and the information surface, and a moving means for driving the focal position in a direction perpendicular to the information surface. A focus control unit that controls the moving unit so that the focal position is on the information surface based on an output of the focus shift detection unit; a signal generation unit; Approaching means for controlling the moving means so that the focal position approaches the information surface;
Information surface detecting means for detecting that the focal point is in the vicinity of the information surface based on a signal from the defocus detecting means, and a signal from the preceding information surface detecting means when the moving means is driven by the approaching means. The focus control pull-in device operates the focus control in accordance with the condition (1) and sets the approach means to a hold state. 2. A defocus detecting means for detecting an amount of deviation between a focal position of a light beam for reproducing a signal from an information surface of a disk and the information surface, and a moving means for driving the focal position in a direction perpendicular to the information surface. A focus control unit for performing PID control of the moving unit so that the focus position is on the information surface based on an output of the defocus detection unit; a signal generation unit; An approach unit that controls the moving unit so that the focal position approaches the information surface; and an information surface detection unit that detects that the focus is near the information surface based on a signal from the defocus detection unit. When the moving means is driven by the approach means, the focus control is operated in accordance with a signal of the preceding information surface detecting means, and the initial value of the integrator of the I signal generation system of the PID control is set to the A focus control pull-in device which is set based on a value of an approach means. 3. A motor for rotating a disk, a defocus detecting means for detecting a deviation between a focal position of a light beam for reproducing a signal from the information surface of the disk and the information surface, and a reflection of the light beam from the disk Reflected light detecting means for detecting light; moving means for driving the focal position in a direction perpendicular to the information surface; and moving the focal position on the information surface based on the output of the defocus detecting means. Focus control means for controlling means, signal generation means, first approach means for controlling the moving means such that the focal position approaches an information surface in response to an output signal of the signal generation means, and the focus Second approach means for controlling the moving means so that the position passes through the information surface, and information surface detection means for detecting that the focus is near the information surface based on a signal from the defocus detection means A maximum value detection unit that measures the maximum value Q of the output value of the reflected light amount detection unit by driving the second approach unit with the motor stopped, and When the moving means is driven by the approaching means and the focus control means is operated in accordance with a signal from the preceding information surface detecting means, the second means is controlled in accordance with a maximum value Q previously measured by the maximum value detecting means. Wherein the range of movement of the focal position by the approaching means is limited.