JP2924879B2 - Optical disk drive - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk device,
In particular, it relates to suitable positioning of a light spot.

[0002]

2. Description of the Related Art As disclosed in Japanese Patent Application Laid-Open No. 58-91536, a conventional apparatus uses an analog circuit for a light spot control system, particularly for a control signal processing circuit. That is, the control signal is detected, an operation for determining the gain characteristic and the phase characteristic of the control system is performed, and the circuit for driving the actuator is an analog system based on the result.

Japanese Patent Application Laid-Open No. 61-190762 discloses a technique for adjusting the amplitude level of a signal prior to a noise reduction circuit by limiting a signal level to a level corresponding to a maximum allowable input level of an A / D converter. No. 58-64120 discloses that instead of directly adding the outputs of the two video logarithmic amplifiers as analog quantities, the amplitudes of these two are first quantized and then amplitude limited. The logarithmic amplifier circuit in which the drawbacks caused by the above-described amplifier saturation characteristics and the drawback of noise superimposition are improved by performing digital summation after performing the above operation is described.

Japanese Patent Application Laid-Open No. Sho 59-180813 discloses a digital data generator for controlling a slice level using the output of an amplitude limiting means.

[0005]

In the prior art, since an analog circuit is used, the circuit scale becomes large, and there is a problem that the device cannot be miniaturized. In the case of analog circuits, even if LSIs are used, as the number of compatible products increases, LSIs must be designed and manufactured for each model.
There were difficulties in terms of time and cost. Further, in the control system of the optical disk device, since the control signal of the light spot is detected by the reflected light from the disk through the optical system, power fluctuation of the laser light emitted from the optical system,
In addition, detection characteristics change due to fluctuations in detection sensitivity caused by tolerances in optical system components and assembly. Further, in an actuator controlled by a control signal, characteristics related to control greatly vary due to component tolerance and assembly tolerance.

Conventionally, for an analog circuit, an LSI optimal for the model has been created for each product. In addition, fluctuations in the detection characteristics have been dealt with by measuring the detection characteristics and changing the setting constants of the circuit accordingly.
Furthermore, regarding fluctuations in control characteristics of actuators, etc.,
This was measured, and this was also dealt with by changing the setting constant of the circuit in the same manner as the fluctuation of the detection characteristics.

[0007] The object of the present invention is to solve these problems,
An object of the present invention is to provide a light spot positioning device which can reduce the circuit scale, has versatility corresponding to a product model, and can easily adjust a control system.

Further, the present invention provides a digital signal processing type light spot positioning apparatus capable of stably performing a pull-in and follow-up operation of a control system with a good signal.

[0009]

According to the positioning apparatus of the present invention, a signal processing system is digitized, and a characteristic fluctuation of a control system due to a fluctuation of a sensitivity of a detecting system, a fluctuation of a characteristic of an actuator, and the like are obtained.
The first feature is that the measurement is performed under the management of the PU, the processing procedure and the set value of the signal processing system are determined so as to obtain the optimum control characteristics, and the obtained value is set in the signal processing system.

[0010] Further, the track deviation detection signal input to the signal processing system is divided into two, one of which is amplitude-limited, and the other amplitude is pre-processed so as to be within the dynamic range of digital processing. A second feature is that input to the processing device is performed.

The above-mentioned Japanese Patent Application Laid-Open No. 61-190762 and Japanese Utility Model Application Laid-Open No. 58-64120 describe a method of adjusting the level of a reproduced signal by limiting the amplitude, but do not describe tracking. There is no description to limit the amplitude of the tracking signal. Therefore, these two documents merely show that the technique of amplitude limitation exists,
It does not suggest a means for improving the tracking accuracy of the present invention.

The amplitude limiting means described in Japanese Patent Application Laid-Open No. Sho 59-180813 is different from the amplitude limiting means described in Japanese Patent Application Laid-Open No. 61-190762 and Japanese Utility Model Application Laid-Open No. 58-64120. Is for binarizing the signal at the slice level.
On the other hand, the amplitude limit used in the present invention is used in consideration of the dynamic range of digital processing. Therefore, the amplitude limiting means described in the above-mentioned Japanese Patent Application Laid-Open No. Sho 59-180813 has no direct relation to the amplitude limitation used in the present invention.

[0013]

[Function] Digitizing a signal processing system facilitates storage and setting of operation setting parameters, and also facilitates operations such as multiplication, division, and integration which are difficult with an analog circuit. The characteristic fluctuation of the control system can be measured by itself and the calculation procedure and the calculation parameters can be set, so that the system can be made unaffected by the fluctuation of the control system.

Further, the track shift signal is used as it is for the track pull-in, so that it can be controlled in response to the transient of the light spot, and the amplitude of the signal is limited because the change of the track shift signal is not large at the time of steady following. Improve tracking accuracy.

[0015]

FIG. 2 shows an embodiment of the present invention. Optical disk 1
Is composed of a substrate 5 such as glass or plastic, a base film 6 such as UV (ultraviolet curing resin), and a Te-based recording film 4. The base film 6 is provided with a guide groove 2 for positioning a light beam. A bit 3 is formed along the guide groove. The light emitted from the semiconductor laser 14 passes through the coupling lens 15 and the polarizing mirror 13, and the optical path is turned by the mirror 10, enters the objective lens 8, and forms a light spot on the recording film surface. The reflected light beam modulated by the data recorded on the recording film surface passes through the objective lens 8 and the mirror 10 again, travels through the deflecting mirror 13 in a direction different from that of the semiconductor laser 14, and the track shift detecting optical system 15 and The light is incident on the defocus detection optical system 16. Here, the track shift detection optical system 15 uses a diffraction light detection method. The details are described in JP-A-49-60702.

The defocus detection optical system uses an image rotation detection method. This is also described in detail in JP-A-57-108811 and will not be described. In this embodiment, the galvanomirror 9 is used as an actuator for deflecting the light spot, but a two-dimensional actuator may also be used. In this case, there is no need for a voice coil lens actuator.

The configuration of the optical head has been described above. The overall configuration of the apparatus will be described with reference to FIG. The optical head 19 is attached to a voice coil motor 20 and is supported by a seal 23 via a roller 35. On the side of the head 19, there is a position detector 22 for detecting the position of the head. The detection unit 22 includes a movable slit 21 attached to the head 19, a fixed slit 24 fixed to a base (not shown) for fixing the rail 23, and a light receiving unit 26.

The positioning is first performed by roughly moving the optical head 19 and finely by the galvanometer mirror 9 mounted on the head 19.

FIG. 3B illustrates the operation of the position detector. The light emitting unit 25 emits infrared light from one LED and makes the light enter the movable slit 21. The light that has passed through the movable slit enters the fixed slit 24 and is received by a light receiving unit 26 composed of two photodetectors and converted into an electric signal. The fixed slit 24 and the movable slit 21 have the same pitch, and the slits on the entire surface of the two photodetectors of the fixed slit 24 are out of phase with each other by 90 degrees. Outputs from the respective photodetectors of the light receiving section 26 are amplified by amplifiers 28 and 29, respectively, and input to an arithmetic circuit 27. The addition and subtraction are performed by the arithmetic circuit 27, and a Vac signal indicating the amount of movement of the head and a V
dc signal is obtained. Using the Vdc signal, the LE of the light emitting unit 25
D is controlled to stabilize the signal detection of the position detection unit 22.
This detailed operation is described in detail in JP-A-60-205216.

The galvanometer mirror 9 is provided with a midpoint lock sensor for detecting the movement of the mirror 10. This is LE
The light emitted from the light emitting unit 11 is reflected by the mirror 10, and the position of the reflected light in the light receiving unit 12 is determined by the contact angle of the mirror 10. Change is detected. The configuration of the optical head and the overall configuration of the device have been described above. Hereinafter, a configuration for performing digital signal processing using these configurations will be described.

FIG. 1 shows one embodiment of the present invention. First, the sensor output from the optical head and its calculation output will be described. Outputs from the two detectors in the defocus detection optical system 16 are input to a defocus detection amplifier 18 and the sum and difference of the outputs are calculated to obtain signals AE and AT. The outputs from the two detectors in the track shift detecting optical system 15 are input to a track shift detecting amplifier 17, and the sum and difference of the outputs are calculated as signals TE and TT.
Speed sensor 36 attached to voice coil motor 20
Is input to the speed signal amplifier 31 and amplified to an appropriate signal level. On the disk spindle (not shown) side of the rail 23, a limit sensor 34 for detecting when the optical head exceeds a predetermined movable range is provided, and when the head exceeds the predetermined range, an INGRD signal is generated. .

Pre-processing is performed as follows in order to digitally process each sensor output. The speed signal 31 from the amplifier 31 is input to the filter 54 and performs band limitation.
No aliasing noise due to sampling is generated. This output is input to a selector 39, sampled and held by a timing signal generated from a timing generation circuit 38, and selects a sensor output corresponding to an address signal from an address decode / latch circuit 40.
The AE signal is input to the level shift circuit 49, and is set so that the signal amplitude falls within a dynamic range determined from a power supply voltage or the like. This output is input to the selector 39 via the filter 50. The AT signal is input to the selector 39 via the level shift circuit 48 and the filter 51. The signal amplitude of the TE signal is attenuated by the attenuation circuit 52 via the level shift circuit 55, and the TE signal is input to the selector 39 through the filter 53. The signal that has passed through the other level shift circuit 55 is input to the selector 39 via the filter 63 after the signal amplitude is limited to a certain level by the clamp circuit 57.

After passing the TT signal through the level shift circuit 47 and the clamp circuit 56, the signal
9 is input. The signals Vac and Vdc from the position detector 27 of the external scale are supplied to the level shift circuit 46,
The signal is input to filters 59 and 61 via 58, and then enters selector 39. A signal from the light receiving unit 12 of the midpoint lock sensor of the galvanometer mirror 9 is input to the selector 39 via the filter 60. The output of the selector 39 is ADC
(Analog-to-digital conversion circuit) 42 , which converts the data into a digital value in accordance with a control signal from the timing generation circuit 38, and outputs the converted data on a data bus. Also, on this data bus, an input to a DAC (digital / analog conversion circuit) 43 and a DSP (digital signal processing device)
The input of 41, the input of a latch circuit 45 for sending data to the CPU, and the output of a buffer 44 for receiving a signal from the CPU are coupled, and mutually exchange signals. DSP4
The result of the signal processing by 1 is input to the DAC 43 , converted into an analog signal, and then input to the sample and hold circuits 64, 65, 66, 67 and connected to the respective actuator drive circuits. The control signals of the sample and hold circuits are respectively supplied to the timing generation circuit 38.
It has been generated from.

The DSP 41 inputs a clock signal from the timing generation circuit 38 to the OSC terminal, and performs an operation according to the clock timing. The DSP 41 has a data memory used for calculation. The data memory is input to a terminal CS for selecting a chip by a signal from the CPU, and data is selected by an address A0 to A15 signal from the address data latch circuit 40, and an R / W signal It is determined whether writing or reading is performed according to the processing. Write data from the CPU to the DSP is temporarily stored in the buffer 44, placed on the data bus by a control signal of the address decoder / latch circuit 40, captured by the data input terminals D0 to D7 of the DSP, and designated by the addresses A0 to A15. Is written to the address. The operation result of the DSP 41 is output onto a data bus, and data necessary for the CPU is taken into the latch circuit 45 by a control signal of the address decoder / latch circuit 40 and reported to the CPU. Such signals include AFOK indicating that the focus servo pull-in operation has been performed normally, and SEEKERR signal indicating that the access operation is abnormal.

The outputs of the hold circuits 64, 65, 66, and 67 are respectively input to the coarse drive circuit 30, the voice coil drive circuit 32, the galvanomirror drive circuit 33, and the light emitting unit 25 of the external scale. The actuator controls the light spot by driving the actuator.

The configuration of the embodiment of the present invention has been described above. The control characteristics will be described below. Generally, when an analog signal is taken in and digital signal processing is performed, a delay time of the signal processing becomes a problem. The delay time is generally the sum of the input / output time, the calculation time, and the sample hold time. The input / output time is a time from when an analog value is held by a sample-and-hold circuit by a sample-and-hold circuit, after it is selected by a selector, and is converted into a digital signal by an ADC. For the calculation time, the signal is input to the DSP,
This is the calculation time required for actually performing digital signal processing, outputting the result to the DAC, and converting the result into an analog amount. The sample hold time indicates an effective delay time caused by holding the output of the DAC by the hold circuit.
The effect of this delay time on the control system appears as a phase delay of the system.

That is, in the gain phase characteristic of the servo system, if the frequency at which the gain becomes 0 dB is called a crossover frequency, the stability of the control system can be determined by the degree of phase margin at this frequency.

The fact that there is a delay means that this cross
This means that a phase lag occurs at the over frequency,
Stability will be impaired. The phase delay amount at this frequency is represented by the following equation.

[0029]

(Equation 1)

Here, fc; crossover frequency fs; sampling frequency In general, it is necessary to suppress this phase delay within the range of 10 ° to 15 °. That is, the optimal value of the phase margin is said to be 40 ° to 50 ° in view of the safety of the control system, and a phase lead amount of about 56 ° can be generally secured by a primary phase lead circuit. That's why. However, it is conceivable that this will be exceeded only by the sample and hold time. Table 1
Shows the amount of phase lag when the crossover frequency and the sample frequency are changed.

[0031]

[Table 1]

Of the remaining delay time, the input / output time is a sample hold time, an AD conversion time, and a selector time. These can be set to about 1 μs in consideration of the conversion of about 8 bits. The calculation time is a time determined by the calculation time per step of the DSP and the number of steps. When the capability of the DSP is determined, the number of steps of the program, that is, the control capability is determined.

When a DSP is applied to an optical disc positioning device, the crossover frequency is about 2 kHz in the current servo system, and the allowable value of the phase delay time by the DSP is 20 μs.

In general, from the viewpoint of optimal distribution of delay time, it is better that the delay time is shorter than the sample period, and it is better that the delay time is equal to eliminate waste. Then, the sample hold time becomes 10 μs, and the sum of the input / output and the operation time becomes 10 μs.
μs. Assuming that the input / output time is 3 μs, the calculation time is 7 μs.

In the current DSP, the step time is 100n.
The number of steps is 70 since it is about 200 ns from s.
Only about 35 from. With such an allowable number of steps, the control system of the optical disk device is limited to include two control systems, and all the control systems are connected to one DSP.
Is difficult to achieve. Therefore, in this embodiment, the focus servo, the tracking servo, and the LED emission control of the external scale are performed by one DSP. Other control systems use another DSP. The sampling period is therefore 50 kHz
z or more is required.

Considering the control system of an optical disk in the future, the tracking control band may be improved to about 4 kHz. At this time, the tracking control system uses two DSPs and sets the sampling period to 100 kHz.
Hz or higher.

That is, the delay time of one DSP is 10 μs in total, the input / output time is 2 μs, and the operation time is 3 μs.
s, and the sample hold time is 3 μs.

A specific configuration of the tracking control system will be described. The tracking control system is a two-stage servo system described in JP-A-58-91536. First, a detection method will be described. As shown in FIG. 5A, the light emitted from the semiconductor laser 14 is focused on the surface of the disk 1, reflected, and then imaged at a point 76 by a lens 75. The light detector 15 is arranged before the point 76. The photodetector 15 is a two-divided sensor as shown in FIG. 5B, and a signal from each photodetector is differentiated by a difference circuit 77 to obtain a TE signal. The respective signals are added by an adder circuit 78 to obtain a TT signal. As shown in FIG. 4, when the light spot 74 traverses the track, these signals generate signals corresponding to the position of the light spot as shown in FIGS. 4B and 4C, respectively. That is, the TE signal is a signal representing the deviation of the light spot from the track center, and the TT signal is a signal having a phase shifted from the TE signal by 90 ° and represents the position of the track. By using the TE and TT signals, the timing and the direction of the light spot passing through the track can be detected.

The track pull-in operation will be described with reference to FIG. If the level of the TT signal is compared with a certain level E1 during the DSP processing, a track position signal indicating that the light spot is on the track when the level is high can be detected. The timing at which the zero cross point of the TE signal and the track position signal 80 become "1" is represented by a signal indicating that the light spot is passing through the center of the track, that is, a track passing signal 81. By using these signals, a servo ON timing signal 83 for generating an optical spot at the center of the track can be generated before performing the tracking operation. When a command to start a tracking operation from the CPU and a tracking ON signal 82 are input to the DSP via the buffer 44 and the data path, a program in the track pull-in mode is started, the level of the TT signal exceeds E1, and the level of the TE signal is increased. There is a timing at which a zero crossing point appears, and the program of the track following operation mode is started at the moment when this condition is satisfied. With this configuration, the track following operation is started when the light spot is located at the center of the track, so that the track following is immediately performed and no transient operation such as overshoot occurs.

The dynamic range of a signal processing apparatus such as a DSP generally falls within a certain range, and there is a trade-off between the dynamic range and the processing accuracy. That is,
If the processing accuracy is increased in order to increase the tracking accuracy of the control system, the signal amplitude that can be processed is limited by the dynamic range. For example, the track shift signal TE is the light spot 74.
Is x, the amplitude is A, and the track pitch is p,

[0041]

(Equation 2)

Can be expressed as follows. If the tracking accuracy is set to 0.1 μm, the processing accuracy usually needs to be about 0.01 μm. Then, the minimum dynamic range requires 6 bits.
Considering the AD conversion accuracy, there is an error of about ± 1 bit, which must be smaller than the tracking accuracy of the control system.

For this reason, it is desirable that the input track shift signal be as large as possible. Therefore, since the signal level of the track shift is not large when following the track, a signal whose amplitude is limited by the clamp 56 is used to some extent, and the light spot moves greatly at the time of pulling in. Therefore, the track shift signal almost reaches the maximum amplitude of the track shift signal. Since it fluctuates, the ATT5 signal is adjusted so that the signal of the track deviation matches the dynamic range of the DSP.
Use the signal attenuated by 2.

In this way, when the light spot deviates from the center of the track for some reason, an abnormal warning signal can be generated by monitoring the level of the output signal of the clamp 57.

The crossover frequency of the tracking control system is about 2 kHz. Because of the delay time, the control system may become unstable because the phase is delayed as described above. Therefore, this delay amount is compensated by a phase advance circuit.

However, when this circuit is used, the phase can be compensated, but the gain characteristic also changes, so that it cannot be performed excessively. FIG. 7 shows a compensation method in which the slope of the gain characteristic at the crossover frequency is about 20 dB / dec and the phase margin is about 50 °.

A phase lead circuit which becomes flat at a rising frequency of 15 kHz from 1.5 kHz and a rising time of 1.4 kHz and 2.8.
Two stages of phase lead circuits that become flat at kHz are used.
It is the sampling frequency that determines the first 15 kHz, and even if it is desired to increase it, it is determined by the sampling capability. Taking the focus servo as an example, a parameter setting method will be described. After assembling the head into the device,
A signal of a crossover frequency set from the PU is generated from the DSP, and the voice coil lens is driven via the ADC. The crossover frequency component returned through the photodetector and the amplifier is extracted by a digital filter, and the gain ratio and the phase shift between the input signal component and the returned signal component are measured and calculated by the DSP. Is set to about 50 °, the DSP calculation parameters (gain and phase lead corner frequency and lead amount) are set. This makes it possible to optimally adjust the control system with the head incorporated. This operation is performed not only at the time of head assembly but also during operation of the apparatus while the apparatus is in operation, so that fluctuation due to aging can be further absorbed.

[0048]

According to the present invention, part from the characteristic variation of the control system can be set to the optimum value of the easily measured can easily and characteristics, the variation of the control system by assembling, and to accommodate aging Become.

Further, since the control signal of the light spot can be input in a form suitable for digital processing, it is possible to stably and reliably perform the pull-in and follow-up operation of the control system by the DSP.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of one embodiment of the present invention.

FIG. 2 is a configuration diagram of an optical head.

FIG. 3 is an overall view of an optical head and a configuration diagram of a detection unit of an external scale.

FIG. 4 is a diagram showing a positional relationship between a track shift detection signal and a track.

FIG. 5 is an explanatory diagram of detection of a track shift signal.

FIG. 6 is a time chart of a track pull-in operation.

FIG. 7 is a Bode diagram of a tracking control system.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-144428 (JP, A) JP-A-62-293522 (JP, A) JP-A-58-112102 (JP, A) JP-A-56-112 71332 (JP, A) JP-A-56-71891 (JP, A) JP-A-61-230428 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G11B 7/085 G11B 7 / 09-7/095 G11B 21/08-21/10 H03M 1/18

Claims (2)

(57) [Claims] 1. An amplitude limiting means for limiting the amplitude of a track shift signal of a light spot, a range adapting means for adjusting the amplitude level of the track shift signal within a dynamic range of digital processing, and an analog output of both means being a digital signal. An analog-to-digital conversion circuit that converts the digital signal into an analog signal, a signal processing circuit that processes the output signal of the analog-to-digital conversion circuit, and a digital-to-analog conversion circuit that converts the digital output of the signal processing circuit into an analog signal.
However, the signal processing circuit performs the above-described amplitude limiting when tracking the track.
Processing the digital signal corresponding to the output of the means and track
At the time of retraction, the data corresponding to the output of the range
An optical disc device for processing digital signals . 2. The optical disk apparatus according to claim 1 , further comprising a warning signal generating means for monitoring a level of an output signal of said amplitude limiting means and generating a warning signal.