JPH0414419B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an optical pickup device used in an information reading device such as a digital audio disk playback device or a video disk playback device.

[Technical background of the invention and its problems]

For example, in order to optically read a track on a recording medium such as a disk, such an optical pickup is equipped with a focusing mechanism that determines the focal point position and a tracking mechanism that determines the scanning spot position,
In particular, for tracking adjustment, in other words, to control the pick-up light spot position, see Figures 1 and 2.
The configuration shown in the figure is conventionally known as an example thereof.

In other words, in order to accurately track and scan information on optical discs on which high-density recording is performed,
Using the output of a well-known optical detection section that detects tracking deviations, a micro-drive section is used to finely control the optical axis of the optical pick-up, and a feed motor that moves the casing itself equipped with the optical pick-up in the tracking direction. Specifically, the first
As shown in the figure, when scanning the track 2 of the rotatable optical disk 1, the optical pick-up is moved in the tracking direction tr, but the rack 4, which is provided integrally with the pick-up housing 3, is engaged with the pinion 5 and the relative A feed motor 7 moves the position of the objective lens 6, and an electromagnetic drive means 13 is provided around the objective lens 6 in the pick-up housing 3 as a minute drive unit, as shown in FIG. 6 together with a focusing drive mechanism (not shown), a support mechanism is constructed to rotatably support arm 9 about shaft 8, a tracking coil 10 is wound around support arm 9, and opposite polarity surfaces are provided near coil 10. Magnets 11,1 are placed opposite to the coil 10.
2 is provided, and by exciting the coil 10, the support arm 9 is rotated and the relative position of the objective lens 6 is changed.

The tracking actuator electromagnetic drive means 1
3 follows fast movements such as track eccentricity, while the above-mentioned feed motor is used for the resulting relative movement of the housing 3, and the objective lens 6 is located at the center position within the housing 3. controlled as follows.

That is, the support arm 9 is held in the center position within the housing 3 by an elastic body 14 such as rubber or a spring, and when the arm 9 is driven against the bias of the elastic body 14, the tracking coil is A method is generally used in which an increase in voltage is detected and the motor 7 is driven so that this voltage becomes the minimum.

As is clear from such a configuration, detecting the reference position (center position) of the objective lens within the pickup housing is extremely important when moving the position of the housing itself.

However, in the past, as mentioned above, an elastic body such as rubber or a leaf spring was used to detect the center. becomes difficult to hold.

Since the elastic body is mechanically associated with the drive system, it has a resonance point due to the structure of the elastic body due to its vibration characteristics, and accurate tracking is inhibited near the resonance point.

In general, since tracking is driven against mechanical bias, power consumption is large, and if the elastic force is reduced in order to reduce power consumption, accurate position detection cannot be performed.

In particular, the use of a material such as rubber increases so-called hysteresis, in which the objective lens does not return to its original position when it is driven significantly during tracking, which is undesirable in view of the dynamic characteristics of the optical pickup.

There were other drawbacks.

[Purpose of the invention]

The object of the present invention is to eliminate such drawbacks, to provide an optical pickup device that allows accurate tracking control, is easy to assemble, and is inexpensive.

[Summary of the invention]

A tracking actuator is installed near the electromagnetic drive means to finely control the position of the light spot of the optical pickup. A differential voltage transformer is used to detect the displacement of the actuator from the reference position via electromagnetic means as a differential output. and a synchronous detection means for synchronously detecting the output of the differential transformer at a predetermined frequency, and a position control signal for driving a casing in which the actuator is mounted using the output of the synchronous detection means. That is.

[Embodiments of the invention]

FIG. 3 shows an embodiment of the present invention, and although the same reference numerals refer to the conventional structure, the coils 15 and 16 are arranged to have opposite phases to each other with respect to the magnets 11 and 12, and have approximately the same number of turns. The differential transformer means 17 is constructed by winding the transformer.

In this configuration, when the tracking coil 10 is used as a so-called primary coil (excitation coil), it is provided as a secondary coil that generates an induced electromotive force corresponding to changes in magnetic flux, and is connected with opposite polarity, so that the center position of the actuator A difference in voltage appears which is induced by the relative position of the coil 10 as it is displaced from the (reference position).

Furthermore, there is no elastic body 14 in the conventional example, and on the other hand, a so-called servo signal for tracking drive is applied to the tracking coil 10, but in this embodiment, the fourth
As shown in the figure, an arithmetic unit 20 is interposed in the servo loop in order to superimpose the reference signal passed through the LPF 19 and the servo signal.

The transmission characteristics of an optical pickup as a so-called actuator are generally secondary vibrations (or mass).
Due to the characteristics, the high frequency side slopes downward from the low resonance frequency ₀ , so the above reference signal has a high frequency side that is outside the servo band and corresponds to negligible actuator operation. It is set.

Taking a DAD (Digital Audio Disk) player specifically, when the servo gain is high, the servo band is strong against vibrations, etc., but it is more likely to malfunction due to scratches on the disk, and conversely, when the gain is low, it is resistant to scratches. As shown in Figure 7, the upper limit of the frequency band is set at around 1 kHz because the signal becomes susceptible to disturbances, while the above reference signal has a frequency of around 10 kHz, although it depends on the bandwidth and the ratio of the slope of the transmission characteristics on the high frequency side. Although it is not limited to the embodiment, it is preferable to use the frame frequency (7.35 kHz), which is used for extracting digital data, since there is no need for a separate oscillator for generating a reference signal. be.

Coil 1 disposed facing coil 10 on the other hand
Both terminals of 5 and 16 are connected to a synchronous detection circuit 21, and are provided with an input terminal for a reference signal to obtain an extraction frequency, which will be described later.In other words, the detection circuit 21 receives the differential output of coils 15 and 16 related to tracking drive. Accordingly, only signals having the same frequency as the reference signal described above are extracted.

If we focus only on this frequency, it is a signal that is amplitude-modulated using the reference signal as a so-called carrier wave in relation to the tracking drive, and the relationship between displacement and voltage is as follows.
As shown in the figure, it is detected as a differential output that is symmetrical with respect to the amount of movement from the center, but it is not only extracted from the superimposed signal by synchronous detection, but also the phase inverted part, that is, the pickup part. Outputs of opposite polarity as shown in FIG. 6 are obtained corresponding to the amount of displacement at the portions driven in opposite directions from the center position.

On the other hand, the output terminal of the synchronous detection circuit 21 is connected to a driver 22 and a motor 7, and depending on the output, the feed motor 7 is driven and controlled so that the actuator is located at the center of the housing.

This embodiment is configured as described above.

Therefore, as shown in FIG. 4, both the servo signal and the reference signal are sent to the tracking coil 1
Even if it is applied to 0, as is clear from the above characteristics, there is no substantial drive due to the reference signal frequency, and the drive is originally controlled by the servo signal for tracking control.

On the other hand, the displacement of the coil 10 related to driving causes a change in the magnetic flux to the coils 15 and 16, and by detecting this as a reference signal in the synchronous detection circuit 21, a so-called position control signal to be applied to the motor 7 is generated. obtain.

Therefore, the coils 15 and 16 and the synchronous detection circuit 21 function as a position detection means 23 for the objective lens 6.

As mentioned above, the signal is minimum (in principle “0”)
The position of the actuator should be at the center within the housing, that is, the position where the magnetic flux to both coils 15 and 16 is equal, and in this embodiment, the moving direction of the housing is such that the change in voltage associated with the tracking drive is minimized. Using this signal as a drive voltage, the motor 7 is controlled to rotate in forward and reverse directions, thereby performing a so-called servo operation to position the actuator at the center.

In the above embodiment, a reference signal for position detection is applied together with a servo signal to a coil originally provided for tracking control, but it is noteworthy that a differential transformer is used to obtain position information in connection with tracking drive. The position detecting means 23 is provided with means (in the embodiment, coils 15, 16, etc.) and means for synchronously detecting the output thereof (in the embodiment, the synchronous detection circuit 21).

That is, if a change in position is to be detected by electromagnetic induction in connection with the tracking drive, various configurations are conceivable, not limited to the present invention. In order to provide a servo loop configuration that minimizes the signal, it is desirable that the output (voltage) change corresponding to the displacement from the center has a linear characteristic as shown in Fig. 6, for example. Since the signal given from the bone actuating transformation means uses a part of the tracking mechanism, signals that do not provide position information are superimposed, and it is necessary to extract the information signal to be detected from among these signals. , it is obvious that there is no need to explain it again.

However, as described above, since synchronous detection is performed, the influence of the servo signal is minimized during information extraction, allowing accurate position detection.

(In other words, the servo signal has a period different from that of the reference signal, so it is difficult to leak into the detection output.) [Effects of the Invention] In other words, although the present invention has a simple configuration, it can cope with the displacement of the tracking actuator as described above. Since the differential output generated by the servo signal is synchronously detected with the same reference signal as the reference signal superimposed on the tracking servo signal, the drive direction is determined by extracting position information and reversing the polarity. It is possible to obtain a signal having a linear detection characteristic proportional to the amount of displacement to be provided to a system (for example, a motor, etc.) for position control.

In addition, since the differential output is synchronously detected, accurate position information related to the tracking drive can be obtained, and in particular, there is no need for a configuration in which elastic bodies are mechanically associated as in the conventional configuration, so detection is possible. The desired center position does not shift due to temperature changes, there is no resonance frequency or hysteresis, and in addition to these, the power consumption during tracking drive is small, making it practically effective.

Furthermore, since the mechanical structure can be simplified compared to the conventional structure, it is also effective in downsizing the pickup section.

[Brief explanation of drawings]

Figure 1 is a schematic diagram of the tracking control mechanism, Figure 2
The figure is a configuration diagram of an actuator of a conventional example, FIG. 3 is a configuration diagram of an actuator according to an embodiment of the present invention, FIG. 4 is a circuit diagram of the main part of the same embodiment, and FIGS. FIG. 7 shows an example of actuator transmission characteristics. Explanation of symbols, 3... Housing, 17... Differential transformation means, 21... Synchronous detection circuit, 13... Tracking actuator electromagnetic drive means.

Claims (1)

[Scope of Claims] 1. A tracking actuator that is capable of swinging or rotating within a housing and that is finely adjusted and controlled by a tracking servo signal in order to minimize the scanning error of the optical spot position of the optical pickup. applying the tracking servo signal and a reference signal superimposed on the tracking servo signal to the tracking actuator, and generating a differential output in response to changes in the tracking actuator. a position detection means having a synchronous detection means for performing synchronous detection using a reference signal; and a transport means for moving the housing in a direction to position the tracking actuator at a reference position within the housing using the output of the position detection means. An optical pickup device characterized by having: