JPH0266737A - Access system for optical disk - Google Patents

Abstract

PURPOSE:To execute the stable access action even when a large adjustable speed is used by providing two speed detecting means and setting respective speed detecting gains and the cutting frequencies of LPF as prescribed. CONSTITUTION:The speed detecting gain of a second speed detecting means 7 is enlarged for a first speed detecting means 6. Cut off frequencies f1 and f2 of the LPF used for respective speed detecting means 6 and 7 are set to f1>f2. Then, even when the access action is completed and the speed of a light beam becomes small, the speed servo system with the small influence of a ripple due to the speed and frequency conversion can be realized and the stable access action can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present application relates to an optical disc access method that moves a light beam at high speed from any current information trunk of an optical disc to a target information track for recording and reproduction.

(Prior Art) Regarding access to an optical disk, a method of moving the light beam to a target trunk by speed control while detecting the moving distance and speed of the light beam with respect to the optical disk is disclosed in Japanese Patent Application Laid-Open No. 177640/1983 [Track Access in Optical Disk]. Apparatus]. Here, a method for detecting the speed of a light beam used in the conventional access method will be described below.

FIG. 2 shows an example of the configuration of a means for detecting the speed of a light beam with respect to an optical disc. In FIG. 2, when the light beam 2 is moved in the direction across the information I rank with the optical microscope 2,
The l.racking position error signal 20 optically detected by the optical system 3 is detected as a signal that periodically fluctuates every time the light beam crosses the information track 6, as shown in FIG. A push-pull method is well known as a method for detecting the racking position error signal 20.
The details are omitted here. The ranking position error signal 20 (not shown in FIG. 6) is input to the track cross pulse generating means 5, and the track cross pulse generating means 5 generates the information track 16 as shown in FIG. 6 by a simple method such as polarity determination. A track cross pulse 21 is output in which one pulse is generated each time the track crosses. In this case, the speed of the light beam 2 is the information l/rack 16 that passes within a certain time.
The speed of the light beam 2 is proportional to the frequency of the trunk cross pulse 21.

As a method of detecting the speed at which the light beam 2 changes to the optical pulse 1, a speed pulse having a constant width and size is detected at either the rising edge or the falling edge of the l-rank cross pulse, or at both timings. 33 is generated by a speed pulse generating means 30, and this speed pulse 33 is passed through a low-pass filter 31 to be smoothed, thereby performing frequency/voltage conversion of the l/rack cross pulse 21.

In detecting the speed signal 40 by frequency/voltage conversion of the track cross pulse 21, the speed signal 40 is detected as the energy of the speed pulse 33 within a certain time, so the low-pass filter 31 reduces ripples in the speed signal 40. Assuming that the cutoff family '/& number f11(z) is a first-order low-pass filter, the transfer function of the low-pass filter 31 is expressed by the following equation, and has the frequency characteristic shown in the curve 50 in FIG. 3(a).

At this time, the speed detection gain by the track cross pulse 21 is influenced by the low-pass filter 31 on the higher frequency side than fl, as shown by the curve 51 in FIG. 3(b).

On the other hand, in order to widen the speed servo band, as a method of preventing the influence of the low-pass filter 31, as shown in FIG. A method is known in which the input voltage is added to the manual power of the low-pass filter 31 via the . In FIG. 4, if the actuator 15 is an actuator using electromagnetic force such as a voice coil motor, its driving force is approximately proportional to the current flowing through the actuator 15. The current flowing through the actuator 15 is I(A), and the force constant of the actuator 15 is Kf(
N/A), the mass of the entire movable part including the optical system 3 is M (Kg
), then the speed of the light beam moving with the moving part■
is expressed by the following equation using Laplace transform.

In FIG. 4, if the gain of the amplification means 32 is Ka, then the transfer function G of the speed signal detected from the actuator current 29
i(s) is 2n・fl・Ka・I(s) Therefore, the speed detection gain due to the actuator current 29 becomes flat at frequencies equal to or higher than f1, as shown in the curve 52 in FIG. 3(C). Show characteristics. Amplifying means 3 in Fig. 4
2, and in Fig. 3(b) and (C), Gp = Gi (4
), the speed detection means 42 in FIG.
The speed signal 40 output from the
Figure 3(d) (・1-5
As shown in Figure 3, the characteristics are almost flat with respect to speed.

In conventional access, speed detection is performed using the configuration shown in FIG. 2 or 4.

(Problem to be Solved by the Invention) When the servo band of the position control system that follows the light beam 2 to the information trunk during information recording and reproduction is 2 to 3 KHz,
The speed of the light beam 2 with respect to the optical disc 1 at the end of access needs to be suppressed to about 5 to 6 mm/s.

In the speed detection described above, the speed of the light beam 2 is detected by a single speed detection means, so when the maximum speed of the light beam 2 is increased, the output of the speed signal 40 near the final speed becomes smaller, which makes it difficult to configure the servo system. This poses a problem in that the electronic circuits involved are easily affected by offsets and temperature drift, making accurate speed control difficult.

In addition, in order to move the light beam at a large acceleration/deceleration speed, it is necessary to widen the speed servo band, but in the conventional access method, the ripple in the speed signal 40 becomes large when the light beam moves at a low speed. When speed control is performed over a wide band, the actuator 15 that drives the light beam 2 in the tracking direction vibrates due to the ripple component of the speed signal 40, which causes the light beam 2 to vibrate, making it difficult to position the light beam 2 on the target track. There was an issue of becoming.

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical disk access method that eliminates the above-mentioned problems and allows stable access operations even when using large acceleration/deceleration speeds.

(Means for solving the problem) An actuator that moves a light beam from the currently located information track to a target track for recording/reproduction, and a track cross pulse that detects that the light beam crosses the information trunk on the optical disk. A track cross pulse generation means for generating a track cross pulse, and a speed detection means for converting the track cross pulse outputted from the track cross pulse generation means into a frequency voltage and adding the value of the current flowing through the actuator to detect the moving speed of the light beam with respect to the optical disk. and a means for controlling the speed so that the moving speed of the light beam outputted from the speed detecting means follows a reference speed, wherein the speed detecting means comprises two speed detecting means, a second speed detecting means, and a second speed detecting means. The speed detection gain of the speed detection means is set to be larger than the speed detection gain of the first speed detection means, and the cutoff frequency of the low-pass filter of the second speed detection means used for frequency/voltage conversion of the track cross pulse is set to be higher than the speed detection gain of the first speed detection means. An access method for an optical disc, characterized in that the cutoff frequency is set lower than the cutoff frequency of a low-pass filter of a speed detection means.

(Function) The first speed detection means 6 has the configuration shown within the broken line 42 in FIG.
Consider the case where this is realized. FIG. 5 shows a first velocity pulse waveform 43 used for frequency/voltage conversion that allows velocity detection over the entire range of light beam velocities. Assuming that the maximum speed of the light beam 2 is 1 m's and the trunk pinch is 1.6 pm, the period of the track cross pulse 21 is 1.6 ps. In order to set the speed detection range to the entire speed of the light beam 2, the first speed pulse 4 in the first speed detection means 6 is
It is necessary to make the pulse width tpl of No. 3 shorter than the period of the track cross pulse 21. At this time, when the lowest speed VL is 5 mm/s, the pulse width of the first speed pulse 43 is very small with respect to the period of the track cross pulse 21, and the amplitude Vpl of the first speed pulse 43 is VL
This is more than 200 times the speed signal level corresponding to the speed signal level. Therefore, a thick ripple appears in the first speed signal 22 due to the speed pulse 43, as shown in FIG.

Here, as shown in FIG. 5, consider a second speed detection means 7 that detects the speed of a light beam moving at a low speed using a wide second speed pulse 44.

Since the second speed detection means 7 has a wide pulse width tp2 of the second speed pulse 44, when the light beam moves at high speed,
If the period of the trunk cross pulse becomes smaller than tp2, correct speed detection cannot be performed. However, in the second speed detection means 7, since the ratio of the lowest speed VL to the amplitude Vp2 of the second speed pulse 44 is small, as shown in FIG. The ratio of ripples to the speed signal 23 can be reduced.

Here, consider the actuator current 29 during the access operation. When the light beam 2 is moved at high speed, the movable part 17
Due to the influence of viscous friction, etc., a current value that indicates a driving force larger than the driving force corresponding to acceleration/deceleration is observed. Since such disturbances appear in low frequency components, the cutoff frequency f1 of the low-pass filter is set to the first
When set low enough to sufficiently reduce the horn pull of the first speed signal 22, the influence of disturbances on the actuator current 29 in accordance with the first speed signal 22 becomes large. However, in order to stably position the light beam 2 on the target track at the end of the access operation, the speed and acceleration of the light beam 2 near the target trunk are controlled to be small.
The influence of disturbances such as friction on the actuator current 29 is small. Therefore, in the second speed detection means 7 that detects the speed when the light beam 2 moves at a low speed, the cutoff frequency f2 of the low-pass filter is set to the cutoff frequency f2 of the low-pass filter of the first speed detection means 6. By setting the cutoff frequency r1 lower than the cutoff frequency r1 of the low-pass filter, it is possible to reduce the influence of ripples.

As shown below, in the optical disc access method of the present application, when the light beam 2 moves at a low speed, the second speed detection means 7 with a large speed gain and a low cutoff frequency of the low-pass filter is used. As described above, in the optical disc access method of the present application, when the light beam 2 moves at a low speed, by using the second speed detection means 7 with a large speed gain and a low cutoff frequency of the low-pass filter, The influence of ripple on the speed signal can be reduced.

(Embodiment) FIG. 1 shows an embodiment of the optical disc access method of the present application.

While the light beam 2 moves on the optical disk 1''2 during access, the track cross pulse 21 generated by the track cross pulse generating means 5 causes the actuator current 29
At the same time, the first speed detecting means 6 and the second speed detecting means 7 are manually operated and outputted as a first speed signal 22 and a second speed signal 23. It is assumed that the configuration of the first and second speed detection means 6.7 is similar to the portion surrounded by the broken line 42 in FIG. 4. The trunk cross pulse 21 is also input to the control means 8, which outputs first and second reference speed signals 24 and 25 that instruct the acceleration and deceleration of the light beam 2 according to the amount of movement of the light beam 2. The first speed signal 22 and the first reference speed signal 24, and the second speed signal 23 and the second reference speed signal 25 are subtracted, respectively, and the first and second speed error signals 26 and 27 are output. Ru. The first and second speed error signals 26,27 are supplied to the terminal A of the switch 12 via amplifying means 10,11, respectively.

The switch 12 selects one of the input terminals A and H and outputs it as the speed control signal 28. The speed control signal 28 is applied to the actuator 1 via the power amplifying means 13.
Added to 5. The actuator 15 includes an optical system 3 such that the speed of the light beam 2 with respect to the information track 16 (FIG. 6) corresponds to a first reference speed signal 24 or a second reference speed signal 25 according to a control signal 28. The movable part 17 is driven.

The first reference speed signal 24 and the second reference speed signal 25 output from the control means 8 are transmitted to the first speed detection means 6 and the second reference speed signal 25.
It is set to output a signal proportional to the speed detection gain of the speed detection means 7. At the same time, the ratio of the gains of the amplification means 10.11 is set to the reciprocal of the ratio of the speed detection gains of the first speed detection means 6 and the second speed detection means 7. In this case, the first speed detection signal 6 and the second speed detection signal 7 have equal speed error detection gains at the input terminals A and B of the switch 12 by passing through the amplification means 10.11. For this purpose, switch 1 is
No matter which input terminal A or B is selected by the light beam 2, the speed servo band of the speed control system for moving the light beam 2 remains constant.

Here, the first speed signal 22 is manually inputted to the speed determining means 9, and when the speed of the light beam 2 with respect to the optical disk 1, that is, the speed at which the light beam 2 crosses the information track 16 is smaller than a certain value, the switch 12 is set to When the speed of the light beam is greater than a certain value, the switch 12 switches to A.
The switch 12 is controlled to select the terminal.

1. As described in detail in section 1.1, the first detection means 6
, the speed detection gain of the second speed detection means 7 is increased, and the cutoff frequency of the low-pass filter used in each speed detection means is set to fl, and f2 is set to fl.
〉f2, the configuration shown in Fig. 1 makes it possible to realize a speed servo system that is less affected by ripples due to speed/frequency conversion even if the speed of the light beam 2 decreases just before the end of the access operation, allowing stable access operations. Obtainable.

(Effects of the Invention) By using the optical disk access method of the present invention, it is possible to increase the frequency and
A speed servo system that is less affected by ripples due to voltage conversion can be realized, and even if large acceleration/deceleration speeds are used, it is possible to reduce the vibration of the light beam during access and smoothly move the light beam to the target track.

[Brief explanation of the drawing]

FIG. 1 is a block diagram for explaining the optical disc access method of the present application, FIG. 2 is a block diagram for explaining the detection of the moving speed of the light beam, and FIG. 3 is a block diagram for explaining the frequency characteristics of the speed detection means. Figure 4 is a diagram showing the frequency characteristics, Figure 4 is a block diagram for explaining the detection of the moving speed of the light beam, Figure 5 is a diagram showing each signal waveform to explain the non-pull that appears in the speed signal, Figure 6 is FIG. 3 is a diagram for explaining how a track cross pulse is generated when a light beam crosses an information track of an optical disk. In the figure, 1... Optical disk 2... Light beam 6.7... First and second speed detection means 8... Control means 12... Switch 15... Actuator

Claims (1)

[Claims] (1) An actuator that moves the light beam from the currently located information track to the target track for recording/reproduction, and a track cross pulse that detects that the light beam crosses the information track on the optical disk and generates a track cross pulse. generating means; speed detecting means for detecting the moving speed of the light beam relative to the optical disk by frequency-voltage converting the track cross pulse outputted from the track cross pulse generating means and adding the value of the current flowing through the actuator; An optical disk access method comprising: means for controlling the speed of the light beam outputted from the means so that the moving speed of the light beam follows a reference speed;
The speed detection means consists of two speed detection means, the second
The speed detection gain of the speed detection means is set to be larger than the speed detection gain of the first speed detection means, and the cutoff frequency of the low-pass filter of the second speed detection means used for frequency/voltage conversion of the track cross pulse is set to be higher than the speed detection gain of the first speed detection means. An access method for an optical disc, characterized in that the cutoff frequency is set lower than the cutoff frequency of a low-pass filter of a speed detection means.