JPH0250533B2 - - Google Patents

Description

TECHNICAL FIELD The present invention relates to an optical pick-up servo device for reproducing optical discs, and more particularly to an optical pick-up servo device that can accurately detect scratches and dirt on a video disc, as well as disturbances and vibrations. .

Prior art and its problems In digital audio discs (DAD), video discs (VD), etc., it is necessary to perform track servo and focus servo on minute tracks using an optical head or the like. In general, the fluctuation factors included in the disk include eccentricity, warpage, uneven press, etc. In Figure 1, when frequency (logarithm) is plotted on the horizontal axis and gain is plotted on the vertical axis, the frequency increases as shown by curve N. The higher the value, the fewer the variables. In order to properly servo these, it is sufficient to have a servo loop gain as shown in FIG. 1A. However, when considering the entire disk playback device, it is desirable to have as large a servo loop gain as possible, as shown in FIG. 1B, in order to prevent servo misalignment when external vibrations are applied. However, if there are scratches or dust on the disk, noise due to the dust will be added to the error signal from the optical pickup. Noise components due to dust, scratches, etc. extend to a relatively higher frequency range than components such as eccentricity, as shown in S. For this reason, the larger the loop gain is set, the more the servo system responds to these noise S components, causing serious errors such as track deviation and track jump.
Also, in order to stabilize the servo system, please refer to Figure 1 A-A' or B.
−B′, such as A-A or B-B
It is necessary to further raise the high frequency range as shown in the figure, and there is a drawback that the servo system responds even more to the noise component S. In this way, it is necessary to increase the loop gain against external vibrations, and increase the loop gain against disk noise. This resulted in the contradictory results of reducing the loop gain, and it was difficult to satisfy both at the same time.

Purpose of the Invention The present invention has been made in view of the above-mentioned drawbacks. In these servo systems, the relative velocity signal between the movable part and the fixed part of the optical pickup is extracted, and the optical signal is effectively mixed with the servo error signal extracted from the disk. The object of the present invention is to provide a pick-up servo device.

According to the present invention, the above-mentioned object is to provide a disk player which extracts a servo error signal from a disk surface and performs servoing of an optical pick-up. This is achieved by providing an optical pickup servo device characterized in that the optical pickup servo device mixes the signal and performs servo mainly in the high frequency range using a loop gain based on the servo error signal.

Embodiments of the Invention The present invention will now be described in detail with reference to FIGS. 2 to 5.

FIG. 2A is a perspective view of the main parts of an optical pickup. An optical head 1 is attached to the tip of a swing arm 2, rotates around a shaft 3, emits a laser beam through an objective lens 4, and emits a laser beam onto a disk D. Read information. Of course, the lens system is made to be movable in the vertical direction to perform focus servo, and at the same time, track servo is performed by driving the entire swing arm 2 left and right by the actuator section 8. An example of a cross-sectional view of the actuator part is shown in Figure 2B, but the swing arm 2
A drive coil 6 is fixed to the drive coil 6, a magnet 7 is arranged below this, a yoke 8 is inserted into the coil 6, and the yoke is fixed, and there is a gap between the drive coil 6 and the coil 6 to prevent collision even when the swing arm rotates. A gap is provided between. By energizing the coil 6, the current in the coil cuts off the magnetic flux going from the magnet 7 to the yoke 8, driving the swing arm 2, thereby operating as a so-called linear motor. The track signal on the disk D, which performs track servo by the coil 6, is reproduced by the optical pickup 1, and the track error signal 11 can be extracted by known means such as the three-beam or push-pull system as in the prior art. On the other hand, below the fixed magnet 7, the arm 2 has a detection coil 9 and a yoke 10, similar to the drive section 5, and the detection coil 9 can extract a voltage proportional to the speed of movement of the swing arm 2.

Next, FIG. 3 shows a block diagram of an optical pickup servo according to the present invention, which will be explained below. Reference setting voltage
The error is mixed with the mixer 12 for V _E , and the amplifier A ₁
and put it into the drive coil 6. The optical pickup is driven by this coil. On the other hand, in this embodiment, in which the movement of the optical pickup relative to the fixed part is detected from the detection coil 9, a signal corresponding to the speed of the optical pickup is obtained. At the same time, a track error signal 11 is obtained from the signal reproduced from the optical pickup, as in the conventional case, and these signals are negatively fed back to the input via feedback amplifiers B ₁ and B ₂ respectively. The characteristics of a normal pickup are shown in Figure 1A-
As shown in A' and B-B', corresponding to the output from the amplifier _A1 , the higher the frequency, the lower the response amplitude is due to the drop on the 12 dB/octave line. This is due to the mass component of the pick-up. On the other hand, the fluctuation component N required for track servo, such as disk eccentricity, also falls at a rate of 12 dB/octave, as shown in the figure.
These are the characteristics where the acceleration is exactly constant, and in general, as explained earlier, in order to stabilize the servo system, the high range is raised to have a phase margin where the gain is zero. Return as shown in Figure 4 (a). For this reason, normally the gain settings shown in FIG. 1 are made as shown in A-A or as shown in B-B.

Here, in the present invention, the conventional feedback amplifier B ₂
The frequency characteristics of the loop system are made as shown in FIG.
On the other hand, the signal from the detection coil 9 corresponds to the speed and increases by 6 dB/octave with respect to the position corresponding signal which is the track error signal 11, so the gain of the feedback amplifier _B1 is set as shown in Fig. 4D. This allows the overall loop gain including the outputs of the feedback amplifiers B ₁ and B ₂ to be the same as the conventional one, such as AA or BB. Here, even if the overall gain is set like B-B, which is strong against external vibrations, for disk systems, the high-frequency gain is reduced like B-B', B-B'', so the loop Stable servo operation is possible without changing the stability. Therefore, the overall loop gain can be large, and it is resistant to external vibrations and is difficult to respond to noise caused by dust or scratches on the disk. Also, due to the feedback amplifier B ₂ Loop gain first
If you lower the feedback amplifier _B1 loop as shown in Figure A-A'' by adding an equalizer that corresponds to acceleration in the low range and speed in the high range, the total loop gain will be returned as shown in Figure 1 B-B. A more modern system can also be obtained.In the above embodiment, a swing arm type optical pickup system is shown, but an embodiment in which the lens system is moved is shown in FIGS. 5A and 5A.

The lens 4 is supported by two leaf springs 13 and 14, and the leaf springs are fixed to a focus drive coil 16. The lens system is driven up and down by a coil 16. Although not shown, a magnetic circuit covers the coil 16. There is a magnet 20 in the lens part, and a drive coil is also provided in the fixed part to drive the lens system in the track direction. The plate spring 14 has a protrusion 17, which is sandwiched between the light emitting element 18 and the light receiving element 19.The light emitting element 18 and the light receiving element 19 correspond to the movement of the lens system in the track direction (arrow). This can be used to detect the loop of amplifier _B2 . Of course, by differentiating the displacement output, the velocity output can be obtained. Alternatively, the angle of the mirror can be detected in the same way by inserting a mirror in the middle of the optical path and changing the angle of the mirror. Also in the focus servo, although not shown, it is possible for a speed detection coil to similarly detect the top and bottom of the lens system by optical detection or the like.

As described above, according to the present invention, at low frequencies,
The servo is mainly performed using the error signal obtained from the disk, and in the high range, the servo detects the movement of the moving part of the pickup, making it possible to obtain a servo system that is stable against scratches and vibrations.

[Brief explanation of the drawing]

Fig. 1 is a servo gain diagram showing the relationship between frequency and gain, Fig. 2 (a) is a perspective view of the main part of the pickup used in the present invention, Fig. 2 (b) is a side sectional view of the actuator section of Fig. 2 (a), FIG. 3 is a system diagram of the pick-up servo device of the present invention, FIG. 4 is a servo gain diagram for explaining the frequency and gain of the optical pick-up servo device of the present invention, and FIG. FIG. 2 is a perspective view and a plan view of a detection means showing an example. 1...Pickup, 2...Swing arm,
3...Shaft, 4...Objective lens, 6...Drive coil, 7...Magnet, 8...Yoke, 1
3, 14...Plate spring, 16...Focus drive coil, 17...Protrusion, 18...Light emitting element, 19...
...Photodetector, 20...Magnet.

Claims (1)

[Claims] 1. A first amplifier circuit that reproduces a disc and amplifies a track error signal obtained from the reproduced signal, and a mixer that mixes it into a reference signal as a first track servo input via the first amplifier circuit. a circuit, a means for amplifying the signal mixed by the mixing circuit to drive the optical pickup and track servo, a speed detection means for detecting the speed at which the movable part of the optical pickup moves with respect to a fixed reference; the second amplifier circuit, comprising: a second amplifier circuit for amplifying the moving speed signal detected by the detection means; and means for adding the output of the second amplifier circuit to the mixing circuit as a second track servo input; The high frequency characteristics of
An optical pick-up servo device characterized by controlling speed by increasing gain at high frequencies compared to the high frequency characteristics of an amplifier circuit. 2. The optical pickup servo device according to claim 1, further comprising speed detection means for detecting the amount of displacement of the movable part of the optical pickup with respect to a fixed reference and differentiating this to obtain a moving speed signal.