JPH0370293B2 - - 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.

That is, in order to accurately track and scan the information track of an optical disk on which high-density recording is being performed, the optical axis of the optical pickup is finely adjusted and controlled using the output of a well-known optical detector that detects tracking deviations. It controls a minute drive unit and a feed motor that moves the casing itself equipped with an optical pickup in the tracking direction. Specifically, as shown in FIG.
a feed motor 7 that moves the optical pick-up in the tracking direction tr to scan the image, but also engages a rack 4 provided integrally with the pick-up housing 3 with a pinion 5 to move the relative position of the objective lens 6; On the other hand, as shown in FIG. 2, an electromagnetic drive means 13 is provided around the objective lens 6 in the pick-up housing 3 as a minute drive unit, which means that the objective lens 6 is centered around the axis 8 together with a focusing drive mechanism (not shown). A support mechanism is configured to rotatably support the support arm 9.
0, and magnets 11 and 12 are arranged near the coil 10 with opposite polarity faces facing the coil 10. By energizing the coil 10, the support arm 9 is rotated. This is for changing the relative position of the objective lens 6.

The tracking electromagnetic drive means 13 follows fast movements such as track eccentricity, while the above-mentioned feed motor is used for the resulting relative movement of the housing 3,
The objective lens 6 is controlled to be located at the center within the housing 3.

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 commonly used method is to detect an increase in voltage and drive the motor 7 so that this voltage is minimized.

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.

[Object of the Invention] It is an object of the present invention 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 that can swing or rotate freely within a housing and that is finely controlled by a tracking servo signal to minimize scanning errors in the position of the light spot of the optical pickup; and the tracking servo. A synchronization method in which a signal and a reference signal superimposed on the tracking servo signal are applied to the tracking actuator, and the differential output generated in response to the displacement of the tracking actuator is synchronously detected using the reference signal. and a position detection means having a detection means.

[Embodiments of the invention]

FIG. 3 shows an embodiment of the present invention, in which the same reference numerals refer to the conventional structure, but coils 15 and 16 are wound around the magnets 11 and 12 in opposite phases, and the elastic body 14 is On the other hand, a so-called servo signal for tracking drive is applied to the tracking coil 10, but in this embodiment, as shown in FIG. It is interposed within such a servo loop.

The reference signal is set to a constant frequency, which is higher than the upper limit of the frequency of the servo band, and both terminals of coils 15 and 16 disposed opposite to coil 10 are connected to a comparison detection circuit 20, The detection circuit 20 is also 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 20 detects changes in magnetic flux related to the tracking drive as electrical signals from the secondary coils 15 and 16 located nearby. Among these signals, only those signals having the same frequency as the reference signal described above are extracted.

The extracted signal at this frequency is an amplitude-modulated signal that is associated with the tracking drive using the reference signal as a so-called carrier wave, and due to the configuration of the embodiment, it is detected as a differential output that is symmetrical with respect to the amount of movement from the center. However, by performing synchronous detection, for example, a signal of opposite polarity corresponding to the amount of displacement can be obtained at a portion where the phase is inverted, that is, a portion driven in opposite directions from the center position of the pickup section.

As can be seen from the above, the coil 15,
16 and the comparison detection circuit 20 constitute a position detection means 21.

On the other hand, the output terminal of the comparison and detection circuit 20 is connected to the driver 19 and the motor 7, and depending on the detection output, the feed motor 7 is driven and controlled so that the pickup section is located at the center of the housing.

The present embodiment is configured as described above, and the reason why a frequency higher than the servo band is provided as a position detection signal will be described below.

In the present invention, since a reference signal for position detection is applied together with a servo signal to a coil originally provided for tracking control, the reference signal is used to detect changes in magnetic flux related to tracking drive, thereby positioning the coil. Although information can be obtained, since a new signal that is completely unrelated to the original servo signal is applied to the tracking coil that is supposed to control the drive, this causes an operation unrelated to the servo operation and causes the tracking coil that should be controlled to scan. It must not cause a situation in which it is impossible to follow the track.

However, when the servo gain is high, the servo band is strong against vibrations, etc., but it tends to malfunction due to scratches on the disk, and conversely, when the gain is low, it is strong against scratches but becomes weak against external disturbances, so it is set to a fairly limited range. In addition, the transmission characteristics of an optical pickup as an actuator generally have a low resonant frequency due to the second-order vibration (or mass) characteristics.
Since the part on the high-frequency side from f ₀ slopes downward, there is no problem if the reference signal is a frequency on the high-frequency side that is outside the servo band and corresponds to negligible actuator operation as shown in Figure 5. do not have.

The frequency is set appropriately according to the rate of gradient descent and the bandwidth, and is not particularly limited, but if it is set too high, there will be a problem with coil inductance, which will prevent accurate extraction.

For example, DAD whose servo band upper limit is around 1kHz
(Digital audio disc) player
It is sufficient to set it to around 10 kHz, and in particular, if the frame frequency (7.35 kHz) is used, there is no need for a separate oscillator for generating the reference signal, which is preferable.

Because of the above configuration, even if both the servo signal and the reference signal are applied to the tracking coil 10 via the arithmetic unit 18 as shown in FIG. Drive is controlled by servo signals.

The displacement of the coil 10 related to the drive is the coil 1
The control voltage for the motor 7 is obtained by synchronously detecting this as a reference signal in the comparison and detection circuit 20, and the pickup section is constantly located at the center of the housing. A so-called servo operation is performed so that the position is adjusted.

〔Effect of the invention〕

As described above, according to the present invention, the reference signal is superimposed on the tracking servo signal, and the resulting differential output is synchronously detected with the reference signal, so that accurate tracking drive-related Position information can be obtained, and there is no need for a structure in which elastic bodies are mechanically related as in conventional structures, so the center position to be detected does not shift due to temperature changes, and the resonant frequency and There is no hysteresis, and in addition to this, the power consumption during tracking drive is also 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
3 is a diagram showing the configuration of an electromagnetic drive means according to an embodiment of the present invention, FIG. 4 is a circuit diagram of the same embodiment, and FIG. 5 is a diagram showing transmission characteristics of the actuator. Explanation of symbols: 13... Tracking electromagnetic drive means, 6... Objective lens, 10... Tracking coil, 11, 12... Magnet, 15, 16... Coil.

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. the tracking servo signal and a reference signal superimposed on the tracking servo signal to the tracking actuator, and a differential output generated in response to the displacement of the tracking actuator. 1. An optical pickup device comprising: position detection means having synchronous detection means for synchronous detection using a reference signal.