JPS6226650A - Position correction device - Google Patents

Abstract

PURPOSE:To obtain correct error signal in which a DC components is excluded and to execute stably fast forward reproduction and the reproduction using track jumping by providing a circuit to cancel the change of DC part of a tracking error signal. CONSTITUTION:The output of a four-divided photo diode 1 is respectively inputted to adding amplifiers 2 and 3, the output signals V1 and V2 are inputted to a subtracting amplifier 22 and the output signal V3 is inputted to the non- inverting input terminal of the subtracting amplifier 22. To the inverting input terminal, an output signal V5 of an actuator equivalent circuit 20 is inputted. The actuator equivalent circuit 20 generates the signal V5 corresponding to the displacement of the lens, inputs the signal to the subtracting amplifier 22 and the subtracting amplifier 22 removes the DC component by subtracting the signal V5 from an error signal V3. Thus, since a correcting error signal V6 having the alternating current component only is generated and the servo control is executed so that the correcting error signal V6 goes to zero, the highly accurate tracking control can be executed.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to improvements in tracking servo mechanisms in information reading devices such as video disc players, CDs, and optical disc devices.

[Prior art]

Conventionally, in order to extract a tracking error signal using an optical pickup in this type of device, there are two methods: one is to provide an auxiliary beam as in the 3-beam method, and the other is to use the irradiation light without using an auxiliary beam as in the push-pull and hetero gain methods. There is a method that utilizes the interference of light that occurs between the light and the light reflected from areas other than the pits. Although the method using an auxiliary beam can accurately extract the error signal, it has the disadvantage that the optical system becomes complex. In addition, with the method that uses optical interference, the optical system does not become complicated, but in the case of the push-pull method, a direct current component (hereinafter referred to as DC component) appears in the tracking error signal depending on the amount of displacement of the tracking actuator. However, there is a drawback that a stable servo mechanism cannot be obtained in operations where the displacement of the actuator becomes large, such as fast forwarding during playback or track jumping. In the hetero gain method, DC
Although the components do not appear, the disadvantage is that the circuit becomes complicated.

[Problems to be solved by the invention]

FIG. 8 is a block diagram showing the configuration of a conventional push-pull type tracking control device. Reflected light from the disk on which information is stored is irradiated onto a four-part photodiode 1 via a polarizing beam splitter and a total reflection prism. Element 1 of 4-split photodiode 1
The outputs of a and lb are input to a summing amplifier 2 and summed. Then, the first signal ■1 which is the output signal of the summing amplifier 2
is input to the subtraction amplifier 4. Similarly, elements 1c, ld
The outputs of are input to the summing amplifier 3 and added, and the added second signal 2 is input to the subtracting amplifier 4. The first and second signals Vl and V2 are differentially amplified by a subtracting amplifier 4, and then the phase of the tracking error signal 3, which is the output thereof, is compensated in a compensation amplifier circuit 6. Next, the output signal is input to the driver 7 and amplified, and the tracking actuator 8 is driven by the output signal 4 of the driver 7. The tracking actuator 8 bends the optical axis of the laser by displacing the lens by a minute amount perpendicular to the optical axis of the laser. That is, feedback control is performed so that the position of the laser beam spot is displaced on the disk so that the tracking error signal (3) approaches zero, and the laser beam spot accurately follows the track. When the central axis of the lens of the tracking actuator coincides with the optical axis of the laser beam, that is, when the displacement of the lens is zero, the optical axis of the laser beam and the disk surface are perpendicular. Therefore, the intensity of the laser beam spot on the disk surface becomes uniform. Therefore, the tracking error signal ■3 when the tracking servo is OFF is as shown in Fig. 6 (a
), it oscillates around zero volts, and no DC component appears. This vibration occurs because the laser beam spot deviates from the center of the track due to eccentricity of the disk or the like. Therefore, accurate tracking can be achieved by performing servo control so that this error signal (3) always approaches zero. However, if the central axis of the lens and the optical axis are misaligned, the optical axis of the laser beam and the disk surface will not be perpendicular. Therefore, the intensity of the laser beam spot on the disk surface is biased. Therefore, even if the laser beam spot accurately follows the track, the intensity distribution of the reflected light from the disk surface that is irradiated onto the 4-split photodiode 1 will be different from the photodiode groups (la, lb) and (lc, ld). In contrast, it is non-objective. For this reason, Figure 6 (
As shown in b) and (C), the tracking error signal varies by DCm, e.g. Dl, D2, depending on the displacement of the tracking actuator, that is, the direction and magnitude of the displacement between the central axis of the lens and the optical axis. etc. The displacement l of the tracking actuator and the DCC component (V) of the tracking error signal have a substantially proportional relationship as shown in FIG. However, the servo system
Regardless of the presence or absence of the DC component, the tracking error signal simply moves toward zero, so the laser beam spot cannot be accurately controlled to the center of the track. The present invention attempts to solve these problems of conventional devices.

[Purpose of the invention]

The present invention is characterized in that, in extracting a tracking error signal using a push-pull method, a circuit is provided for canceling a change in the DC component of the tracking error signal depending on the displacement of a tracking actuator, thereby eliminating the DCm component. accurate error signal is obtained.
The purpose is to enable stable fast-forward playback, playback using track jumps, etc.

[Means to solve the problem]

The present invention extracts an error signal corresponding to a deviation in the irradiation position of light onto an optical recording medium by a push-pull method based on detection of reflected light from the recording medium, and extracts an error signal corresponding to a shift in the irradiation position of light onto an optical recording medium, and extracts an error signal corresponding to a shift in the irradiation position of light onto an optical recording medium, and In a position correction device that corrects the irradiation position by bending an optical axis, a drive mechanism that changes the irradiation position and a drive signal to the drive mechanism are input,
a conversion circuit that outputs a signal equivalent to a DC component appearing in the error signal due to a change in the irradiation position caused by the drive signal; and a correction circuit that outputs a correction signal that cancels the output signal of the conversion circuit from the error signal. and a drive circuit that outputs the drive signal to the drive mechanism based on the correction signal. The point is to newly provide a conversion circuit, that is, a circuit that has a transfer characteristic equal to the transfer characteristic showing the relationship between the input signal (4) to the tracking error signal (3) to the drive mechanism when servo control is not performed, and to By correcting the tracking error signal according to the amount of drive of the drive mechanism and removing the DC component from the error signal, it is possible to accurately track the center of the track even if the beam is eccentric. It is something to do.

[Effect]

The conversion circuit is a driver TJh that displaces the optical axis of the laser beam.
It has a transfer characteristic that is equivalent to the transfer characteristic of a control system that shows the relationship between the tracking error signal and the input signal to the mechanism. The drive signal that is input to the drive mechanism is input to this conversion circuit, and its output is input to a correction circuit to be subtracted from a conventional tracking error signal. The correction circuit subtracts the output of the conversion circuit from the error signal,
A true error signal from which the DC component has been removed, that is, a tracking error signal that is at zero level when the laser beam spot is located at the center of the track, is generated. The drive circuit drives the drive mechanism based on the corrected error signal. After all, servo control is performed so that the true tracking error signal from which the DC component has been removed becomes zero, so that the laser beam can accurately follow the center of the track.

【Example】

The present invention will be explained below based on specific examples. FIG. 1 is a block diagram showing the configuration of a position correction device according to a specific embodiment of the present invention. Also,
FIG. 2 is a diagram showing the configuration of an optical system for irradiating a laser beam and detecting the irradiation position. A linearly polarized laser beam 31 emitted from a semiconductor laser 30 passes through a collimator lens 32, is reflected by a polarizing beam splitter 33 in the direction of the disk (the path shown in the figure), is converted into a circularly polarized beam by a 174-wave plate 34, and is sent to a focus and tracking actuator. 8 and is irradiated onto the disk. The reflected light 35 from the disk passes through the actuator 8 and is sent to the collimator lens 32 by the 174 wavelength plate 34.
The transmitted light is converted into a linearly polarized beam having a phase difference of 90 degrees, and as a result, it is transmitted through the polarizing beam splitter 33 toward the total reflection prism 36.
The light is incident on the four-divided photodiode 1. The four-division photodiode 1 is used for focus control by a combination of (la, lc) and (lb, 1d), and for tracking control by a combination of (1a, lb) and (lc, ld). The outputs of the four-part photodiodes 1 are respectively input to the summing amplifiers 2.3 as described above. These output signals Vl and V2 are input to the subtracting amplifier 22, and the output signal (3) is input to the non-inverting input terminal of the subtracting amplifier 22, which is the above-mentioned correction circuit. Further, the output signal 5 of the actuator equivalent circuit 20 constituting the above conversion circuit is input to the inverting input terminal. The output signal (6) of the subtraction amplifier 22 is input to the compensation (PI) amplifier circuit 6, and the output signal (2) is input to the driver 7. The drive signal (4), which is the output of the driver, drives the tracking actuator 8 and is input to the actuator equivalent circuit 20. The actuator equivalent circuit 20 is a kind of low-pass filter, and its transfer characteristics are shown in FIGS. 3(a) and 3(b).
) has the gain and phase characteristics shown below. This characteristic is based on the drive signal V42 that drives the tracking actuator 8.
It is obtained by measuring the transfer function between the amount of displacement of the actuator and the amount of displacement of the actuator. The tracking actuator 8 is constructed as shown in FIGS. 4 and 5. The laser beam 35 is incident on the lens 82 through a communication hole 810 provided in the base 81 . The bobbin 83 is arranged so as to be able to swing around the bin 84, and fixes the lens 82 thereon.
Tracking coil 8 that swings 2 around the bin 84
5 and a focusing coil 86 that adjusts the distance between the lens 82 and the disk to shift the focal point of the beam. Furthermore, an inner yoke 87 is provided inside the bobbin 83 perpendicularly to the base 81, and an outer yoke 87 is provided outside the bobbin 83.
8 are arranged facing each other, and a magnet 89 is provided thereon. These constitute a magnetic circuit for electrically displacing the position of the lens 82. The actuator equivalent circuit 20 generates a signal 5 corresponding to the displacement of the lens 82 and inputs it to the subtraction amplifier 22. Further, the subtracting amplifier 22 removes the DC component by subtracting the signal 5 from the error signal 3. Therefore, as shown in FIG. 6(a), a correction error signal 6 having only an alternating current component is always generated. This device uses this correction error signal ■6
Nervo control is performed so that the value is zero. Therefore, highly accurate tracking control is possible.

【Effect of the invention】

The present invention provides a laser beam position correction device for push-pull type tracking control, in which a drive signal is input to a drive mechanism that changes the laser beam irradiation position, and the laser beam irradiation position is caused by the drive signal. a conversion circuit that outputs a signal equivalent to the DC component appearing in the error signal due to a change in the error signal, and a correction circuit that outputs a correction signal that cancels the output signal of the conversion circuit from the error signal, This is a position correction device characterized in that the drive mechanism is driven by the position correction device. Therefore, due to the asymmetry of the light intensity distribution of the laser beam spot on the disk surface due to the optical axis displacement of the laser beam during tracking control, the tracking error signal contains a DC component that is harmful to servo control. , the beam can be controlled to accurately follow the center of the track. Therefore, an accurate error signal from which DC components are removed can be obtained, and fast-forward playback, playback using track jumps, etc. can be stably performed.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of a position correction device according to a specific embodiment of the present invention, and FIG.
Figure 3 is a principle diagram showing the configuration of the optical system for irradiating the laser beam used in the device of the same example, and Figure 3 is a characteristic diagram showing the transfer function of the actuator equivalent circuit used in the device of the example. Figures 4 and 5 are a perspective view and a sectional view showing the configuration of the tracking actuator used in the same embodiment device, respectively. Figure 6 is a waveform diagram of the tracking error signal when the tracking servo is OFF, and Figure 7 is the actuator. DC included in the displacement amount and tracking error signal
FIG. 8, which is a characteristic diagram showing the relationship with the a minute, is a block diagram showing the configuration of a conventional device. 1-4-divided photodiode 30-semiconductor laser 32-collimator lens 33-
Polarizing beam splitter 34-1/4 wavelength plate 36-total reflection prism 81-base 82-lens 83-bobbin 84-bin 85-tracking coil

Claims (1)

[Scope of Claims] An error signal corresponding to a shift in the position of light irradiation onto an optical recording medium is extracted by a push-pull method based on detection of reflected light from the recording medium, and irradiation is performed based on the error signal. A position correction device that corrects the irradiation position by bending the optical axis of light includes a drive mechanism that changes the irradiation position; a drive signal is input to the drive mechanism; and a change in the irradiation position caused by the drive signal causes the irradiation position to change. a conversion circuit that outputs a signal equivalent to a DC component appearing in the error signal; a correction circuit that outputs a correction signal that cancels the output signal of the conversion circuit from the error signal; and a correction circuit that outputs a correction signal that cancels the output signal of the conversion circuit from the error signal; A position correction device comprising: a drive circuit that outputs output to the drive mechanism.