JPH0231388A - Digital servo device - Google Patents

Abstract

PURPOSE:To prevent an abnormal tracking control state by controlling a driving means or a digital filter with the speed signal detected from a position error signal. CONSTITUTION:The position error signal (tracking error signal) from a pit string on a disk 1 is generated by an optical device 2 and subjected to A/D conversion in an A/D converter 3 by a sampling clock 9. A pulse width modulation (PWM) signal is outputted by a PWM circuit 5 based on the result of the filter processing of a digital filter 4 and passes an optical driving device 6 to drive the optical device 2. When the counted value of edges of the tracking error signal in the sampling period is equal to or larger than 2, a control signal is set to the high level for a prescribed time to disconnect the PWM circuit 5 and a driving part 62. Thus, the abnormal tracking control state is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a digital servo device that controls an object to be controlled using digital signals.

BACKGROUND OF THE INVENTION In recent years, the applications of digital servo devices have been rapidly expanding due to advances in digital signal processing technology, advances in circuit integration technology, and increased speed of circuit operation.

For example, a digital servo may be used for the optical servo of a compact disc player.

Optical servo systems include a focus servo system in a direction perpendicular to the surface of a rotating disc-shaped recording medium (hereinafter referred to as a disk), and a tracking servo system in a radial direction of the disk. In order to stabilize the optical device against fluctuations in the direction perpendicular to the disk surface, the focus servo system first generates a focus error signal in accordance with the amount of deviation of the focus from the disk surface, as shown in FIG. Next, the optical device is driven through a focus control loop filter so that the focus error signal becomes zero. If the optical device is driven so that the absolute value of the focus error signal is small when the amount of deviation is near zero (between signal peaks), the focus error signal will be zero, but otherwise the amount of deviation will not be zero, so focus pull-in At this time, the loop of the focus servo system is opened, the optical device is moved until the amount of deviation becomes near zero, and then the loop of the focus servo system is closed so that the amount of deviation becomes zero. In order to settle the optical device on the bit string arranged in a spiral pattern from the center of the rotating disk after focusing is normally completed, the tracking servo system first detects the deviation of the beam spot from the bit string as shown in Figure 8. A tracking error signal is generated according to the amount.

When the servo is first applied to a certain track (tracking pull-in), the optical device crosses the track due to the deviation of the disk rotation axis, and a track cross signal is generated as shown in FIG. Next, the optical device is driven so that the tracking error signal becomes zero through a tracking control loop filter. If the optical device is driven so that the absolute value of the tracking error signal becomes small, the tracking error signal becomes zero. Note that in the digital servo, the optical device is normally driven by PWM (pulse width modulation) driving.

The function of the optical device itself is not only to detect the servo error signal as described above, but also to read information signals from the disk.

An example of the above-mentioned conventional digital servo device will be described below with reference to the drawings.

FIG. 2 is a configuration diagram when a conventional digital servo device is used for tracking servo of a compact disc player. In FIG. 2, 1 is a disk that is an information recording medium, 2 is an optical device that reads information signals from disk 1 and detects a tracking error signal that is a positional error from the bit string of disk 1, and 3 is an optical device that detects a tracking error signal. An AD converter that performs AD conversion, 4 a digital filter that filters the AD converted tracking error signal, 5 a PWM circuit that converts the digital filter output into a PWM signal, and l1i2 a drive that drives the optical device 2 based on the PWM signal. 8 is a sampling clock, and 1G is a motor for rotating the disk 1.

Regarding the digital servo device configured as above,
The operation will be explained below.

First, the optical device 2 generates a tracking error signal, which is a positional error signal from the bit string of the disk.

Next, the tracking error signal is AD converted by the AD converter 3 using the sampling clock 9. Here, the sampling clock 9 is determined by the maximum processing time in the digital filter 4, and the cycle of the sampling clock 9 is determined so as to exceed the maximum processing time in the digital filter 4.

Next, the digital filter 4 filters the AD-converted tracking error signal. Based on the result of the filter processing, the PWM circuit 5 outputs a PWM signal, which drives the optical device 2 through the drive section 62 .

Problems to be Solved by the Invention However, with the above configuration, there are multiple cases where control is stable with respect to the sampling period as shown in Figure 6, and when the disc is normally played, the control is stable as shown in Figure 6 (A) However, if a strong impact is applied to the digital servo device from the outside, the control may become stable as shown in Figure 8 (B) or (C), and the optical device may The problem was that the track was traversed at a constant speed, and normal tracking control was not performed.

In view of the above-mentioned problems, the present invention provides that when a strong impact is applied to the digital servo device from the outside, the
The purpose of the present invention is to provide a digital servo device that solves the problem that the optical device crosses the track on the disk at a constant speed and normal tracking control is not performed because the control is stabilized as follows.

Means for Solving the Problems In order to solve the above problems, the digital servo device of the present invention includes an information recording medium, an information reading device for reading information from the information recording medium, and an information recording location of the information recording medium. a positional error detection means for detecting a positional error of the information readout position from a regular information readout position; an AD converter that converts a positional error signal detected by the positional error detection means into a digital signal; a digital filter that inputs and filters a positional error signal converted into a digital signal; a driving means that drives the information reading device based on the output of the digital filter; and a positional error signal detected by the positional error detection means. It is comprised of a speed detection means for detecting speed, and a control means for controlling the driving means or the digital filter based on the speed signal detected by the speed detection means.

Operation The present invention has the above-described configuration, and detects an abnormality by controlling the speed detecting means for detecting the speed from the position error signal detected by the position error detecting means, and the driving or digital filter using the speed signal detected by the speed detecting means. This means that accurate tracking control will not be performed.

Embodiment Hereinafter, a digital servo device according to an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows a configuration diagram of a digital servo device according to an embodiment of the present invention. In FIG. 1, 1 is a disk that is an information recording medium; 2 is an optical device that reads information signals from the disk 1 and detects a tracking error signal that is a positional error signal from a pit row of the disk 1; 3;
is an AD converter that AD converts the tracking error signal,
4 is a digital filter that filters the AD-converted tracking error signal, 6 is a PWM circuit that converts the digital filter output into a PWM signal, 6 is an optical drive device that drives the optical device 2 based on the PWM signal, and 7 is a tracking error signal. An edge detection circuit 8 detects edges of a signal and generates pulses; 8 is a control means for not driving the optical drive device for a certain period of time when two or more pulses are generated from the edge detection circuit 7 in a sampling period;
9 is a sampling clock, and 10 is a motor that rotates the disk.

Regarding the digital servo device configured as above,
The operation will be explained below with reference to FIGS. 1, 3, 4, 5, and 6.

First, the optical device 2 generates a tracking error signal, which is a positional error signal from the bit string of the disk.

In the case of a compact disc player, methods for generating a tracking error signal include a phase difference method, an astigmatism method, and a Knifezi method. Note that such a tracking error detection means is already well known, and since the present invention does not focus on this means, further explanation will be omitted. Next, the tracking error signal is AD converted by the AD converter 3 using the sampling clock 9. Here, the sampling clock 9 is determined by the maximum processing time in the digital filter 4, and the cycle of the sampling clock 9 is determined so as to exceed the maximum processing time in the digital filter 4.

The frequency of sampling clock 9 is 44.1KH
I made it z. The bit length of the AD converter 3 was set to 8 bits on the condition that the information signal could be read out accurately.

Next, the digital filter 4 filters the AD-converted tracking error signal. By the way,
The digital filter 4 was constructed using software. As shown in FIG. 3, the structure of the digital filter 4 includes a noise filter 41 that removes noise components of an AD-converted tracking error signal. After passing through the noise filter,
The signals are passed through a low-pass filter 42 for low-frequency compensation and a bypass filter 43 for high-frequency compensation, added, and output. Based on the result of the filter processing, a PWM signal is outputted by the PWM circuit 5 and drives the optical device 2 through the optical drive device 6.

As shown in FIG. 4, the optical drive device 6 consists of a switch 61 and a drive section B2.
The WM signal is passed to the drive section 62, and when it is at a high level, the connection between the PWM circuit 5 and the drive section B2 is cut off. If a strong external shock is applied to the digital servo device, two or more edges of the tracking error signal may appear in the sampling period, resulting in control failure as shown in Figures 6 (B) and (C). It may become stable. Therefore, when the tracking error signal crosses a certain level by the edge detection circuit 7, a pulse is generated and sent to the control means 8. In this embodiment, a pulse is generated at the point where the tracking error signal crosses zero. Specifically, Figure 6 (
(MuA) for A), (BB) for (B),
For (C), a pulse as shown in (CC) is generated. As shown in FIG. 5, the control means 8 is a 4-bit counter 8! which uses the sampling clock as a clear signal and counts the number of pulses within the sampling period. and,
A three-man OR circuit 82 which inputs the upper three bits of the 4-bit counter 81, and a stretching circuit 8 which outputs a high level signal for a certain period of time after the rising signal of the OR circuit 82.
3, and by using the output of the extension circuit 83 as a control signal, when the counter value is 2 or more, the control signal is kept at a high level for a certain period of time, and the connection between the PWM circuit 5 and the driving section 62 is cut off. As a result, control is performed only in the normal control state (two or more pulses are not generated from the edge detection circuit in the sampling period).

In this embodiment, the digital filter 4 is configured with software. The reasons for this are that changing the control parameters can be done by changing the program, making the control more versatile, and that complex processing can be configured using hardware. Considering that the scale of the hardware would increase and the cost would increase, the filter was constructed using software processing by a microcomputer, but it is also possible to use hardware.

As described above, according to this embodiment, the edge detection circuit 7 that generates pulses as many times as the edges of the tracking error signal is used as the speed detection means, and the 4-bit counter that counts the number of pulses within the sampling period is used as the control means. 81, an eight-man powered OR circuit 82 which inputs the upper three bits of the four-bit counter 81, a stretching circuit 83 which outputs a high level signal for a certain period of time after the rising signal of the OR circuit 82, and a switch 61 as a driving means. By providing the drive unit B2, it is possible to prevent an abnormal tracking control state.

Effects of the Invention As described above, the present invention provides an information recording medium, an information reading device for reading information from the information recording medium, and an error in the information reading position from the regular information reading position with respect to the information recording location of the information recording medium. a position error detection means for detecting the position error, an AD converter for converting the position error signal detected by the position error detection means into a digital signal, and a filter using the position error signal converted to the digital signal by the AD converter as input. Digital filter to process and 1
a driving means for driving the information reading device based on the digital filter output; a speed detecting means for detecting a speed from a position error signal detected by the position error detecting means; and a speed signal detected by the speed detecting means. By providing a control means for controlling the driving means or the digital filter,
It is possible to prevent an abnormal tracking control state.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of a digital servo device according to an embodiment of the present invention, FIG. 2 is a configuration diagram of a conventional digital servo device,
FIG. 3 is a configuration diagram of a digital filter according to an embodiment of the present invention.
FIG. 4 is a block diagram of the optical drive device of the present invention, FIG. 5 is a block diagram of the control means of the embodiment of the present invention, FIG. 6 is a conceptual diagram showing a plurality of stable points of the digital servo device, and FIG. 8 is a generation diagram of a focus error signal, and FIG. 8 is a generation diagram of a tracking error signal. 1... Disc, 2... Optical device, 3e.
・AD converter, 4 fist/skewer digital filter, 5-・
・PWM circuit, 6*・・Optical drive means, 7@・Φ edge detection circuit, 8・・Control means, 9
11...Sampling clock, 10...Motor, 4
DESCRIPTION OF SYMBOLS 1... Noise filter, 42... Φ low-pass filter, 43... No. 1 innocence filter, 61... Switch, 62... Drive unit, 81... 4-bit counter,
82・φ・OR circuit, 83... Extension circuit. Name of agent: Patent attorney Shigetaka Awano

Claims (2)

[Claims] (1) An information recording medium, an information reading device for reading information from the information recording medium, and a position error detection means for detecting a positional error of the information reading device from a regular information reading position with respect to an information recording location of the information recording medium. an AD converter that converts the position error signal detected by the position error detection means into a digital signal; a digital filter that inputs and processes the position error signal converted into a digital signal by the AD converter; a driving means for driving the information reading device based on the output of the digital filter; a speed detecting means for detecting the speed based on the position error signal detected by the position error detecting means;
A digital servo device comprising: a control means for controlling the driving means or the digital filter according to a speed signal detected by the speed detecting means. (2) The digital servo device according to claim 1, wherein the speed detection means detects an edge of the position error signal detected by the position error detection means.