JP2586741B2 - Focus adjustment device for optical pickup - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a focus adjustment device for an optical pickup in a CD (compact disk) player and the like, and more particularly to a focus adjustment device for an optical pickup suitable for automatic adjustment during production and assembly.

[0002]

2. Description of the Related Art An optical pickup for a CD or the like is configured as schematically shown in FIG. In FIG. 1, the laser light output from the laser oscillator 10 is:
The beam enters the beam splitter 14 via the diffraction grating 12,
Here, the light is reflected to the optical disk 16 side. The laser light is collimated by the collimator lens 18 and then enters the objective lens 20, where it is converged and enters the optical disk 16.

On the other hand, the laser light reflected by the optical disk 16 is supplied to an objective lens 20, a collimator lens 18,
The light passes through the beam splitter 14 and the detection lens 22 sequentially and enters the photodetector 24. by this,
Recording or reproduction of information on the optical disk 16 is performed.

The conventional focusing adjustment in such an optical pickup is performed by, for example, displacing the detection lens 22 and adjusting the position of the detection lens 22 so that the amount of jitter of the reproduced signal at this time is minimized. Have been done.

[0005] In this case, the relationship between the focus shift and the jitter amount is as follows.
Generally, it has characteristics as shown in a graph GA of FIG. By utilizing this characteristic, the position of the detection lens 22 is adjusted to the minimum point of the jitter amount. However,
Since the amount of jitter change near the in-focus point is small, a constant focus shift is alternately applied to the + side and the-side, and adjustment is performed in balance with the jitter deterioration amount in each case. At this time, the method of giving the + and-defocus may be continuous or 1 Hz.
This is performed by applying the following AC signal to the focus servo control circuit by a manual switch.

[0006]

However, such a conventional technique has the following disadvantages. (1) Since jitter has large fluctuations, the adjustment accuracy is low and it takes time to perform good adjustment. (2) In order to measure the jitter, the adjustment of each part must be completed to the extent that all servos such as tracking can be performed. (3) Since the change in the jitter amount is small, it is necessary to integrate the jitter amount. For this reason, the adjustment cannot be performed at a higher speed than the integration time, which hinders the high-speed automatic adjustment. The present invention focuses on this point, and an object of the present invention is to perform focusing adjustment easily and accurately in a short time.

[0007]

SUMMARY OF THE INVENTION The present invention relates to a focus adjusting device for an optical pickup for adjusting a focus position of an optical pickup with respect to a light beam incident from an optical disk. An out-of-focus state generating means for alternately electrically providing the in-focus state in accordance with the rotation cycle of the optical disk, and extracting a component synchronized with the cycle from the output signal of the optical pickup in the out-of-focus state And a focus detection means for obtaining information on a focus shift.

[0008]

According to the present invention, the out-of-focus state of the optical pickup is electrically generated. For example, when a disturbance signal is applied to the focus servo control means, a focus shift in the + and-directions is given at a predetermined cycle. This cycle is
It is set corresponding to the rotation cycle of the optical disk. At this time, the output signal of the optical pickup changes in accordance with the out-of-focus direction and the amount of focus shift, and information on the focus shift can be obtained from this. This allows the spin to be synchronized with the disk rotation.
Even if there is vibration of the dollar motor or optical disk,
Adjust the focus of the optical pickup without being affected.
Can be.

[0009]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a focus adjusting device for an optical pickup according to an embodiment of the present invention; a, First Embodiment First, a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 shows a configuration of a main part of the first embodiment. In the figure, the RF signal output from the photodetector 24 is input to an envelope detection circuit 30. An output side of the envelope detection circuit 30 is connected to an input side of a band-pass filter 32 for extracting a necessary frequency band component. An output side of the band-pass filter 32 is connected to an input side of a half-cycle switching circuit 34. It is connected.

The output side of the half-cycle switching circuit 34 is connected to the input side of a series circuit of an amplitude detection circuit 36, a low-pass filter 38, a meter amplifier 40, and an indicator 42. Among these, the low-pass filter 38
, An in-focus detection output is performed. next,
The output side of the oscillation circuit 44 is connected to the phase adjustment circuit 4
6 and the input side of the series circuit of the waveform shaping circuit 48, and the output side of the series circuit is connected to the control input side of the half cycle switching circuit 34 described above.
The output side of the oscillation circuit 44 is connected to the buffer circuit 5 on the other side.
The output side of the buffer circuit 50 is connected to a focus servo control circuit (not shown). The focus servo control circuit controls the focusing of an incident beam on an optical disk. A portion shown by a broken line in the drawing will be described in a second embodiment.

Of the above-described units, the oscillation circuit 44 corresponds to FIG.
To obtain the +,-alternately out-of-focus state shown in
The signal is applied as a disturbance to the focus servo control circuit via the buffer circuit 50. As a result, an electrically out-of-focus state of + and-alternately occurs. The output of the oscillation circuit 44 is input to the half cycle switching circuit 34 as a timing signal for amplitude calculation described later.

Next, the operation of the first embodiment configured as described above will be described with reference to the time chart of FIG. In this embodiment, the detected signal is 180 °.
(C) to (E) in FIG.
Shows such an inverted signal. An AC signal of an appropriate frequency output from the oscillation circuit 44 (see FIG. 3A) is supplied to the focus servo control circuit of the optical pickup as an out-of-focus disturbance signal.

Here, first, when the optical pickup is in a focused state, that is, the photodetector 24 (see FIG. 4).
Is located at the focusing center position, the output RF signal of the photodetector has a waveform whose amplitude fluctuates as shown in FIG. This is because the relationship between the focus shift and the RF signal level has characteristics as shown in a graph GB of FIG. Such an RF signal is input to the envelope detection circuit 30, where the envelope detection is performed. Therefore, the output RF detection signal of the envelope detection circuit 30 is equal to that of FIG.
As shown in FIG.

On the other hand, for example, the photodetector 2
When the focus adjustment state of No. 4 is on the negative side, FIG.
It becomes as shown in. That is, when the out-of-focus disturbance signal is applied to the negative side, the out-of-focus state is further increased, and the RF detection signal level is greatly reduced (at time T in the figure).
B-TC). However, when the out-of-focus disturbance signal is applied to the + side, the shift is canceled and approaches the center of focus, so that the amount of decrease in the level of the RF detection signal is reduced (see FIGS. TA to TB in the same figure). .

Conversely, when the focus adjustment state of the photodetector 24 is on the + side, the state becomes as shown in FIG. In other words, when the out-of-focus disturbance signal is applied to the negative side, the shift is canceled and the focus becomes closer to the center of focus, so that the amount of decrease in the level of the RF detection signal is reduced (see TB to TC in the same figure). ). However, the out-of-focus disturbance signal is +
Side, the out-of-focus state is further increased, so that the level of the RF detection signal is greatly reduced (at time T in the figure).
A to TB).

Therefore, the out-of-focus state of the optical pickup is
The decrease amount of the RF detection signal between times TA and TB shown in FIG.
It is possible to detect the same by comparing and calculating the same amount of decrease between times TB and TC. The out-of-focus disturbance signal output from the oscillation circuit 44 is subjected to necessary phase adjustment in a phase adjustment circuit 46. This is because a phase delay occurs in the transmission path (envelope detection circuit 30, band-pass filter 32) on the RF detection signal processing side and the transmission path (buffer circuit 50, focus servo control circuit (not shown)) on the focus drive side. To do that. By the operation of the phase adjustment circuit 46, the time TA to the signal TA shown in FIGS.
The phases during TC become coincident. The out-of-focus disturbance signal after the phase adjustment is supplied to the latter half cycle switching circuit 34 of the shaping process by the waveform shaping circuit 48.

In the half-cycle switching circuit 34, switching output is performed in half cycles of the out-of-focus disturbance signal with respect to the input signal, and this is supplied to the amplitude detection circuit 36. In the amplitude detection circuit 36, the input RF
A detection calculation of the amplitude of the detection signal is performed. The detection result is supplied to an indicator 42 via a low-pass filter 38 and a meter amplifier 40, thereby instructing the amount of defocus of the optical pickup. The operation of adjusting the position of the optical pickup is performed with reference to the indication of the indicator 42.

As described above, according to the present embodiment, the out-of-focus state of the optical pickup is electrically formed, and the focus adjustment is performed based on the detection signal change synchronized with the out-of-focus state. effective. (1) The detection signal has good stability and can be detected with extremely high accuracy. (2) Since the amount of jitter of the detection signal is not used, the amount of focus shift can be detected in a very short time, and high-speed automatic adjustment can be performed. (3) Other adjustments (for example, tracking servo, etc.) if the focus servo can be applied.
The adjustment work can be performed without being governed by. The rotation speed of the disk can also be set arbitrarily and is not governed by it. (4) The direction and amount of defocus to be adjusted can be clearly grasped.

B, Second Embodiment Next, a second embodiment of the present invention will be described with reference to FIG. In the second embodiment, as shown by a broken line in FIG. 1, a rotation control signal supplied to a spindle motor (not shown) for driving the optical disk 16 to rotate is input to the oscillation circuit 44. According to this embodiment, the oscillation circuit 44 oscillates in synchronization with the input rotation control signal. Therefore, the out-of-focus disturbance signal is generated in synchronization with the rotation of the optical disc 16. On the other hand,
As described above, the amplitude detection of the RF detection signal is performed in synchronization with the out-of-focus disturbance signal. Therefore, even if there is a vibration of the spindle motor or the optical disk 16 synchronized with the rotation of the disk, the focus adjustment described above can be performed without being affected by the vibration.

C, Third Embodiment Next, a third embodiment of the present invention will be described with reference to FIG. In this embodiment, the oscillation circuit 44 of FIG.
Instead of this, a frequency dividing circuit 52 and a band pass filter 54 shown in FIG. 3A are connected. The frequency dividing circuit 52 receives an FG (FREQUENCY GENERATER) signal for controlling the rotation of the spindle motor for rotating the disk. According to this embodiment, the oscillation circuit portion is used together with the one for rotating the disk, and the above-described focusing adjustment and the rotation of the disk are performed in conjunction with each other.

D, Fourth Embodiment Next, a fourth embodiment of the present invention will be described with reference to FIG. In the figure, the focus detection signal output from the low-pass filter 38 in FIG. 1 described above is input to the control circuit 56. This control circuit 5
6 is connected to the input side of the drive circuit 58, and the output side of the drive circuit 58 is connected to the input side of the focusing adjustment mechanism 60 of the optical pickup. When the focus detection signal obtained by the first embodiment is input to the control circuit 56,
The direction and amount of focus adjustment of the optical pickup are determined, and a corresponding control signal is output to the drive circuit 58. In the drive circuit 58, the position of the optical pickup is adjusted by the focusing adjustment mechanism 60 based on the input control signal. As described above, according to the fourth embodiment, the focus adjustment is automatically performed.

E, Other Embodiments The present invention is not limited to the above embodiments. For example, in the above embodiment, focus adjustment was performed using an RF signal, but jitter may be used.
In this case, a jitter fluctuation detection circuit is used instead of the envelope detection circuit 30. As described above, the out-of-focus state with respect to the optical pickup may be given at the same as the rotation cycle of the optical disc or at a fraction thereof. Further, the circuit configuration can be variously changed in design to achieve the same operation, and these are also included in the present invention.

[0023]

As described above, according to the focus adjustment apparatus for an optical pickup according to the present invention, the out-of-focus state of the optical pickup is set in accordance with the rotation cycle of the optical disk.
It is formed electrically at the specified cycle and the signal detection is performed in synchronization with the out-of-focus state, so it is synchronized with the disk rotation.
Even if there is a vibration,
There is an effect that focusing adjustment can be performed easily and accurately in a short time.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing Embodiments 1 and 2 of a focus adjustment device for an optical pickup according to the present invention.

FIG. 2 is a time chart illustrating the operation of the first embodiment.

FIG. 3 is a configuration diagram showing Embodiment 3 and Embodiment 4 of a focus adjustment device for an optical pickup according to the present invention.

FIG. 4 is an explanatory diagram showing a schematic configuration of an optical pickup.

FIG. 5 is a graph showing a change in an amount of jitter and an RF signal level with respect to a focus shift;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 16 ... Optical disk 24 ... Photodetector 30 ... Envelope detection circuit 32, 54 ... Bandpass filter 34 ... Half cycle switching circuit 36 ... Amplitude detection circuit (focus detection means) 38 ... Low-pass filter 40 ... Meter amplifier 42 ... Indicator 44 ... Oscillation circuit (out-of-focus state generation means) 46 ... Phase adjustment circuit 48 ... Waveform shaping circuit 50 ... Buffer circuit 52 ... Division circuit (out-of-focus state generation means) 56 ... Control circuit 58 ... Drive circuit 60 ... Focus adjustment mechanism

Claims (1)

(57) [Claims] 1. A focus adjusting device for an optical pickup for adjusting a focus position of an optical pickup with respect to a light beam incident from an optical disc, wherein a non-focus state of the optical pickup in a different direction with respect to the light beam is determined by a rotation cycle of the optical disc. Out-of-focus state generating means for electrically applying the information alternately in response to the above ; a component synchronized with the cycle is extracted from the output signal of the optical pickup in the out-of-focus state to obtain information on defocus. A focus detection device; and a focus adjustment device for an optical pickup.