JP2875260B2 - Optical disk drive - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical spot positioning device, and more particularly to a positioning device suitable for use in an optical disc device.

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

[Problems to be solved by the invention]

In the prior art, there is a problem that the circuit scale becomes large because an analog circuit is used, and the device cannot be miniaturized. In the case of analog circuits, even if LSIs are used, as the number of compatible product models increases, it is necessary to design and manufacture LSIs for each model, and this has caused difficulties in terms of time and cost. Further, in the control system of the optical disk device, since the control signal of the optical spot is detected by the reflected light from the disk through the optical system, the power fluctuation of the laser light emitted from the optical system and the components of the optical system The detection characteristics change due to fluctuations in detection sensitivity caused by assembly tolerance. Further, in an actuator controlled by a control signal, characteristics related to control greatly fluctuate due to a component tolerance and an assembly tolerance.

Conventionally, for analog circuits, the most suitable LSI for each model has been created. Further, the fluctuation of the detection characteristic has been dealt with by measuring the detection characteristic and changing the setting constant of the circuit in accordance with the measurement. Furthermore, fluctuations in the control characteristics of the actuator and the like have been measured by measuring the fluctuations and changing the circuit setting constants in the same manner as in the fluctuations in the detection characteristics.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an optical spot positioning device which can solve these problems, can reduce the circuit scale, has versatility corresponding to a product model, and can easily adjust a control system.

Still another object of the present invention is to provide an optical spot positioning apparatus of a digital signal processing system capable of stably performing a pull-in and a follow-up operation of a control system at a high signal level.

[Means for solving the problem]

The positioning device of the present invention digitizes a signal processing system, measures a change in sensitivity of a control system due to a change in sensitivity of a detection system, a change in characteristics of an actuator, and the like under the control of a CPU. The first feature is that a processing procedure and a set value of the processing system are obtained and set in the signal processing system.

Also, 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, to thereby provide a digital signal processing device. Is a second feature.

[Action]

Digitizing the signal processing system facilitates storage and setting of operation setting parameters, and facilitates operations such as multiplication, division, and integration, which are difficult with analog circuits. Measure the characteristic fluctuation by yourself,
Calculation procedures and calculation parameters can be set, and the system can be made unaffected by fluctuations in the control system.

In addition, the track shift signal is used as it is for pulling in the track, so that it can be controlled according to the transient of the optical spot, and since the change of the track shift signal is not large at the time of steady tracking, the amplitude of the signal is limited. Improve accuracy.

〔Example〕

FIG. 2 shows an embodiment of the present invention. The 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. The recording pit 3 is formed along the guide groove. Semiconductor laser 14
The light emitted from the lens is coupled to the coupling lens 15 and the polarizing mirror 13.
After passing through the optical path, the optical path is turned by the mirror 10 and is incident on the objective lens 8 to form 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 polarizing mirror 13 in a direction different from that of the semiconductor laser 14, and the track shift detection optical system 15 and The light is incident on the defocus detection optical system 16 respectively. Here, the track shift detection optical system 15 uses a diffracted light detection method. The details are described in JP-A-49-60702.

The image rotation detection method is used for the defocus detection optical system. 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, and the overall configuration of the apparatus will be described with reference to FIG. The optical head 19 is attached to the voice coil motor 20 and is supported on the rail 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 detecting section 22 includes a 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 section 26.

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

FIG. 3B illustrates the operation of the position detection unit. The light emitting section 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 section 26 composed of two photodetectors and converted into an electric signal. The fixed slit 24 and the movable slit 21 have the same pitch.
The slits on the entire surface of the two photodetectors are out of phase with each other by 90 degrees. The outputs from the respective photodetectors of the light receiving unit 26 are amplified by the amplifiers 28 and 29, respectively, and input to the arithmetic circuit 27. The addition and subtraction are performed by the arithmetic circuit 27 to obtain a Vac signal indicating the moving amount of the head and a Vdc signal indicating the light emission amount of the LED. The LED of the light emitting unit 25 is controlled using the Vdc signal, and the signal detection of the position detecting unit 22 is stabilized. This detailed operation is described in detail in JP-A-60-205216.

The galvanometer mirror 9 is provided with a mid-point lock sensor for detecting the movement of the mirror 10. This is composed of a light emitting unit 11 composed of an LED or the like and a light receiving unit 12 composed of a phototransistor or the like, and reflects the light emitted from the light emitting unit 11 to a mirror 10, and the position of the reflected light in the light receiving unit 12 is It detects that it changes depending on the contact angle. 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 the track shift detecting amplifier 17, and the sum and difference of the outputs are calculated.
Obtained as signals TE and TT. A signal from the speed sensor 36 attached to the 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, there is provided a limit sensor 34 for detecting when the optical head exceeds a predetermined movable range, and when the head exceeds the predetermined range, the INGR is provided.
D signal is generated.

The following preprocessing is performed to process each sensor output into a digital signal. The speed signal 31 from the amplifier 31 is input to the filter 54, and the band is limited so that aliasing noise due to sampling is not 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. Also
The AT signal is input to the selector 39 via the level shift circuit 48 and the filter 51. The TE signal is attenuated by the attenuating circuit 52 via the level shift circuit 55, and is filtered.
The signal passes through 53 and is input to the selector 39. The signal after passing 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 through the level shift circuit 47 and the clamp circuit 56, the TT signal is input to the selector 39 via the filter 62. The signals Vac and Vdc from the position detector 27 of the external scale are input to filters 59 and 61 via level shift circuits 46 and 58, respectively, and then enter the 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 selector 39 is ADC
(Analog-to-digital conversion circuit) 42 is input and converted into a digital value in accordance with a control signal from the timing generation circuit 38, and then the converted data is output on a data bus. A DAC (digital-to-analog conversion circuit) 43
Input to DSP and DSP (digital signal processor) 41 input and CPU
The input of a latch circuit 45 for sending data to the buffer and the output of a buffer 44 for receiving a signal from the CPU are connected to each other to exchange signals. The result of signal processing by the DSP 41 is input to the DAC 43 and converted to an analog signal.
The signals are input to the sample and hold circuits 64, 65, 66, and 67, and are connected to the respective actuator driving circuits. The control signals of the sample and hold circuits are generated from the timing generation circuit 38, respectively.

DSP 41 outputs the clock signal from timing generation circuit 38 to O
The signal is input to the SC terminal, and the operation is performed at this clock timing. The DSP 41 has a data memory used for calculation, and a terminal C for selecting the chip by a signal from the CPU.
In S, data is selected by an address A0-A15 signal from an address data latch circuit 40, and only write or read is determined by an R / W signal to perform processing. CPU to D
Data to be written to the SP is temporarily stored in a buffer 44, placed on a data bus by a control signal of an address decoder / latch circuit 40, taken in by data input terminals D0 to D7 of the DSP, and read by addresses A0 to A15. Is written to the specified address. The operation result of the DSP 41 is output on a data bus, and data necessary for the CPU is taken into a latch circuit 45 by a control signal of an address decoder / latch circuit 40 and reported to the CPU. AFOK, which indicates that the focus servo pull-in operation was performed normally,
There is a SEEKERR signal or the like indicating that the access operation is abnormal.

Outputs of the hold circuits 64, 65, 66, and 67 are input to the coarse drive circuit 30, the voice coil drive circuit 32, the galvanometer mirror drive circuit 33, and the light emitting section 25 of the external scale, respectively. To control the light spot.

The configuration of the embodiment of the present invention has been described above, and 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. For the input / output time, the analog value of the sensor output is held by the sample-and-hold circuit.
This is the time required for conversion into a digital signal by C. The operation time is the operation time from when a signal is input to the DSP, the digital signal processing is actually performed, the result is output to the DAC, and the result is converted 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 the delay time on the control system appears as a phase delay of the system.

That is, in the gain phase characteristics 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 presence of the delay time means that a phase delay occurs at this crossover frequency, which impairs stability. The phase delay amount at this frequency is represented by the following equation.

Here, fc; crossover frequency fs; sampling frequency In general, it is necessary to suppress this phase delay within the range of 10 ° to 15 °. In other words, the optimal value of the phase margin is said to be between 40 ° and 50 ° in view of the safety of the control system, and it is generally necessary to secure a phase lead amount of about 55 ° by a primary phase lead circuit. This is because However, it is conceivable that this will be exceeded only by the sample and hold time. Table 1 shows the amount of phase delay when the crossover frequency and the sample frequency were changed.

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

If a DSP is applied to an optical disk 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.

Generally, considering the 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 is 10μ
s, and the sum of the input / output and the operation time is 10 μs. Assuming that the input / output time is 3 μs, the calculation time is 7 μs.

Since the current DSP has a step time of about 100 ns to 200 ns, the number of steps is only about 70 to 35.
This allowable number of steps is limited to including two control systems in the control system of the optical disk device, and it is difficult to realize all the control systems with one DSP. Therefore, in this embodiment, the focus servo, the tracking servo, and the LED light emission control of the external scale are performed by one DSP. Other control systems use another DSP. Therefore, a sampling period of 50 kHz or more is required.

Considering the optical disk control system, the tracking control bandwidth may be improved to about 4 kHz. In this case, it is necessary to use two DSPs only in the tracking control system and set the sampling period to 100 kHz or more. There is.

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

The specific configuration of the tracking control system will be described. The tracking control system is a two-stage servo system described in Japanese Patent Application Laid-Open No. 58-91536. First, the detection method will be described. As shown in FIG. 5 (a), the light emitted from the semiconductor laser 14 is focused on one surface of the disk, reflected, and then pointed by a lens 75.
Imaged on 76. The photodetector 15 is arranged before the point 76. The photodetector 15 is a two-division sensor as shown in FIG. 5 (b), and a signal from the photodetector is operated by a difference circuit 77 to obtain a TE signal. The respective signals are added by an adding circuit 78 to obtain a TT signal. These signals are
As shown, when the optical spot 74 traverses the track, signals corresponding to the position of the optical spot are generated as shown in FIGS. 4 (b) and 4 (c), respectively. That is, TE
The signal is a signal representing the deviation of the optical spot from the track center, and the TT signal is a signal having a phase difference of 90 ° from the TE signal and representing the position of the track. Using the TE and TT signals, the timing and direction of the optical spot passing through the track can be detected.

The track pull-in operation will be described with reference to FIG.
When the level of the TT signal is compared with a certain level E1 in the DSP processing, a track position signal indicating that the optical 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 optical spot is passing through the center of the track, that is, a track passing signal 81. Using these signals, before performing the tracking operation, first, the timing of the operation to draw the optical spot to the center of the track, the servo ON
A timing signal 83 can be generated. Command to start tracking operation from CPU, tracking ON signal 82
Is input to the DSP via the buffer 44 and the data bus, the program in the track pull-in mode is started, the level of the TT signal exceeds E1, and the timing when the zero crossing point of the TE signal appears appears. At the moment of establishment, the program in the track following operation mode is started. In this way, the track following operation is started when the light spot is 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 device such as a DSP is generally in 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,
When the position of the optical spot 74 is x, the amplitude is A, and the track pitch is p, the track shift signal TE is as follows. Can be expressed as If the tracking accuracy is set to 0.1 μm, the processing accuracy usually needs to be 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 signal is as large as possible. Therefore, since the signal level of the track deviation is not large at the time of track following, a signal whose amplitude is limited by the clamp 56 to some extent is used.
Since the light spot largely moves at the time of pull-in, the track shift signal almost fluctuates to the amplitude of the track shift signal. Therefore, a signal in which the track shift signal is attenuated by the ATT 52 so as to match the dynamic range of the DSP is used.

In this way, when the optical spot deviates from the track center 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 approximately
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, with this circuit the phase can be compensated,
The gain characteristic also changes and cannot be performed excessively. FIG. 7 shows a method of compensating the gain characteristic at the crossover frequency so that the slope of the gain characteristic is about 20 dB / dec and the phase margin is about 50 °.

Two stages of a phase lead circuit that rises from 1.5 kHz to 15 kHz and a phase lead circuit that rises at 1.4 kHz and flattens at 2.8 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 focus servo as an example,
The parameter setting method will be described. After incorporating the head into the device, the DSP generates a signal of the crossover frequency set from the CPU and drives the voice coil lens 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 1,
Set the DSP calculation parameters (gain and phase lead corner frequency and lead amount) so that the phase is about 50 °.
In this way, the control system can be optimally adjusted with the head incorporated. This operation is performed not only at the time of head assembly but also at the time when the operation of the apparatus is in a halt state even when the apparatus is in operation, so that fluctuation due to aging can be further absorbed.

〔The invention's effect〕

According to the present invention, the characteristic fluctuation of the control system can be easily measured and the characteristic can be easily set to the optimum value, so that it is possible to cope with the variation of the control system due to parts and assembly, and the aging.

In addition, since the control signal of the optical 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 diagram of an optical head and a configuration diagram of a detection unit of an external scale, and FIG. FIG. 5 is a diagram showing a positional relationship between a 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, and FIG. 7 is a bode diagram of a tracking control system. .

Continuation of front page (56) References JP-A-58-91536 (JP, A) JP-A-62-102431 (JP, A) JP-A-63-44384 (JP, A)

Claims (9)

(57) [Claims] A signal processing circuit for digitally processing a plurality of sensor outputs of a plurality of control systems of the light spot; a selector provided between the signal processing circuit and the plurality of sensor outputs; An optical disc device comprising: a control unit of the plurality of control systems that controls the light spot based on a calculation result of the signal processing circuit; and an optical disc device provided between the control unit of the plurality of control systems and the signal processing circuit. An optical disc further comprising a plurality of holding means, and a clock generating means for generating a clock, wherein a signal based on the clock is input to the signal processing circuit, the selector, and the plurality of holding means. apparatus. 2. The optical disk device according to claim 1, wherein said plurality of control systems include at least a focus control system and a tracking control system. 3. The optical disk device according to claim 1, further comprising digital / analog conversion means provided between said signal processing circuit and said plurality of hold means. 4. The apparatus according to claim 1, further comprising timing generation means provided between said clock processing means and said signal processing circuit, said selector and said plurality of hold means. An optical disk device according to claim 1. 5. A circuit for detecting a focus shift of a light spot, a circuit for detecting a track shift of the light spot, a signal processing circuit for digitally processing an output of the focus shift detection circuit and an output of the track shift detection circuit, and A selector provided between the signal processing circuit and the focus shift detection circuit and the track shift detection circuit, and controlling the focus of the light spot based on the output of the signal processing circuit corresponding to the output of the focus shift detection circuit An optical disc device comprising: a first drive circuit for controlling the position of the light spot based on an output of the signal processing circuit corresponding to an output of the track shift detection circuit; First holding means provided between a circuit and the first drive circuit, and first hold means provided between the signal processing circuit and the second drive circuit And a clock generating means for generating a clock. A signal based on the clock is input to the signal processing circuit, the selector, and the first and second holding means. An optical disk device characterized in that: 6. The optical disk apparatus according to claim 5, further comprising digital / analog conversion means provided between said signal processing circuit and said first and second hold means. 7. The signal processing circuit according to claim 5, further comprising a timing generation means provided between said clock generation means and said first and second hold means and said selector. 7. The optical disc device according to any one of 6. 8. A signal processing circuit for digitally processing a plurality of sensor outputs of a plurality of control systems of the light spot, a selector provided between the signal processing circuit and the plurality of sensor outputs, Analog-to-digital conversion means provided between a selector and the signal processing circuit, control means for the plurality of control systems for controlling the light spot based on a calculation result of the signal processing circuit, The digital control provided between the control means of the plurality of control systems.
An optical disc apparatus comprising: an analog conversion means; a plurality of holding means provided between the control means of the plurality of control systems and the digital / analog conversion means; a clock generation means for generating a clock; An optical disc device further comprising a processing circuit, the selector, the analog / digital conversion means, and a timing generation means provided between the plurality of hold means and the clock generation means. 9. The optical disk apparatus according to claim 8, wherein said plurality of control systems include at least a focus control system and a tracking control system.