JPH0473218B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an optical pickup adjustment device, and more particularly, to a device for adjusting the detection lens position of an optical pickup type video disc player.

BACKGROUND OF THE INVENTION In recent years, various players have been developed that use optical pickup devices to detect and reproduce signals recorded on video discs and the like. In this case, in order to reliably extract the signal, it is necessary to automatically control the objective lens of the optical pickup device to the optimum position (focus) according to the reproduction situation. Therefore, as shown in FIG. 5, the light from the laser light source 1 is focused on the disk 6 via the grating 2, the half prism 3, the collimator lens 4, and the objective lens 5, while the light reflected from the disk 6 is focused on the objective lens. Lens 5, collimator lens 4, half prism 3,
A focus error signal is obtained by an error detector 9 by supplying it to a detector 8 via a detection lens 7,
This signal causes the position of the objective lens 5 to be displaced so that the maximum reproduction signal level can be obtained.

As is well known, the detection lens 5 includes a cylindrical lens, and the detector 8 uses a four-part photodiode, and is configured to obtain control signals for focus servo, tracking servo, etc. . Therefore, when the light is not focused on the detector 8, it becomes a vertically or horizontally elongated elliptical spot light, as is well known.

Incidentally, the focus error detection curve, which is the output characteristic of the error detector 9, is as shown in FIG. 2B. In this case, even if the position of the detection lens 7 is adjusted, the output of the detector 8, RF (Radio
Frequency) Since the detection accuracy of the reproduced signal is relatively low as shown in Figure A, the electrical zero level of the focus error L ₀ and the maximum reproduction level L _M of the RF reproduced signal
There is a difference in the obtained in-focus point _L1 , and this difference is called a focus offset.

Therefore, conventionally, the focus offset amount is detected for each optical pickup device, and as shown in FIG. 5, an adder 10 adds the focus error from the error detector 9 and the focus offset amount. The focus offset amount is virtually zero (usually
After the phase is compensated by the phase compensation circuit 11, the driver 12
The position of the objective lens 5 was controlled using this as a drive signal.

Problems to be Solved by the Invention In the conventional device described above, the position of the detection lens 7 is adjusted based on the RF reproduction signal level, which has low detection accuracy, so the focusing accuracy of the detection lens 7 is low.
Furthermore, there is a problem in that even if control is performed using the focus offset amount, sufficient focusing accuracy cannot be obtained.

An object of the present invention is to provide an optical pickup adjustment device in which the detection lens 7 has high focusing accuracy.

Means for solving the problem In FIG. 1, the adder 13, waveform shaping circuit 14, and counter 15 are means for obtaining an RF reproduction signal from the detector 8 and detecting the magnitude of the jitter component contained in this RF reproduction signal. The microhead 17 is an embodiment of means for displacing the position of the detection lens 7 depending on the magnitude of the jitter component.

Operation: An RF reproduction signal is obtained from the detector 8, the magnitude of the jitter component contained in this RF reproduction signal is detected, and the position of the detection lens 7 is displaced depending on the magnitude of the jitter component.

Example When reading pits formed on an optical video disc or digital audio disc with an optical pickup, ideally the zero-crossing point of the reproduced signal should coincide with the zero-crossing point of the original signal on the time axis, but in reality As is well known, a signal position error (lead or lag) on the time axis called jitter occurs.

Jitter mainly occurs when the reproduction optical system already has aberrations, or when aberrations or defocus occur due to changes in the distance between the disk 6 and the objective lens 5 due to external factors. Furthermore, when the jitter increases, read errors occur in the signal reproduction system.

As described above, it is desirable that jitter should not occur, but in the device of the present invention, such jitter is actively utilized and adjusted to minimize it, thereby adjusting the position of the detection lens 7. Adjusted with high precision.

Furthermore, the patent also discloses a technical concept for further increasing the focusing accuracy of the detection lens 7 by intentionally adding disturbance to forcibly vibrate the objective lens 5 in the optical axis direction and magnifying the jitter. Hereinafter, specific examples will be described with reference to FIG. 1 and the like.

FIG. 1 shows a block system diagram of an embodiment of the apparatus of the present invention, and in the figure, the same components as those in FIG. 5 are given the same numbers and their explanations will be omitted. In the figure, the output of the detector 8 is supplied to an adder 13 where it is converted into an RF reproduction signal shown in FIG.

Generally, a phase shift occurs in the reproduced signal due to a focus shift of the objective lens 5 with respect to the recording pit of the disk 6.
The RF reproduction signal includes a jitter component as shown in FIG. For example, the counter 15 is used for RF signals (EFM signals) in compact disc players.
The minimum count is 3T (minimum unit of pit resolution).
is set, and the magnitude of the jitter component is detected by detecting how much the width of the rectangular wave signal varies from the minimum count unit 3T.

As shown by the solid line in FIG. 2C, the more the detection lens 7 is focused, the less the jitter component is, and the jitter component has a Q (rate of change) of the output RF reproduction signal of the detector 8 shown in FIG. It is generally known that detection accuracy is high because it is large as shown in the figure. In the present invention, the output of the counter 15, that is, the magnitude of the jitter component, is displayed on the meter 16, and the output of the counter 15 is displayed on the meter 16.
The detection lens 7 is displaced by , and the position of the detection lens 7 is adjusted to a position where the jitter component is minimized.

Here, FIG. 6 is a diagram showing an example of the microhead 17 together with an optical pickup, and FIG. 7 is a diagram showing the microhead 17, in which the same components as in FIG. 1 are given the same reference numerals. In both figures, the microhead 17 roughly consists of a lens holder 23 that supports the detection lens 7 and a rotating body 24 that is driven by a stepping motor 22 to displace the lens holder 23 in the left-right direction (optical axis direction) in both figures. Become.
As shown in the figure, the rotational driving force of the stepping motor 22 is transmitted to the rotating shaft 24a of the rotating body 24 via a gear 25.
transmitted to. An eccentric pin 24b that engages with a groove 23a formed in the lower part of the lens holder 23 is disposed on the upper part of the rotating body 24 and is displaced with respect to the axis of the rotating shaft 24a. As a result, the eccentric pin 24b is rotationally driven by the rotation of the stepping motor 22, and the lens holder 23 is slid and displaced in the left and right directions in both figures. According to the microhead 17 having the above configuration, the output signal of the counter 15 is used as a drive signal by the driver 20 to rotate the stepping motor 22 as shown in FIG. 1, so that adjustment is automated and suitable for mass production. . In addition, as another configuration of the micro head, there is one in which the detection lens is displaced by manually operating a micrometer configured to engage and interlock with the lens holder, thereby adjusting the position of the detection lens. It's okay. When the position of the detection lens 7 is adjusted, as shown in FIG. 2D, for example, the focus error curve, which was previously shown as a dashed line, becomes as shown as a solid line.

In this way, the present invention adjusts the position of the detection lens 7 using the jitter component, which has higher detection precision than the RF reproduction signal, so the focusing precision of the detection lens 7 is higher than that of the conventional one.

On the other hand, when a sinusoidal disturbance signal is forcibly supplied from the terminal 18 and added to the focus error in the adder 19 to control the objective lens 5, the jitter component is Detection accuracy becomes higher. In this case, as shown in FIG. 4, if the frequency of the disturbance signal is low, the servo loop gain is large, making it difficult to perform the necessary displacement of the objective lens. On the other hand, as the frequency becomes higher, as is well known, the objective lens 5
Since it becomes difficult to move due to its inertial force, it is difficult to obtain the necessary displacement of the objective lens, so the frequency near the gain intersection of the servo loop _{is 0} (usually around 1kHz).
And the amplitude is set to correspond to a defocus of the detection lens 7 equivalent to ±0.5 μm.

By the way, as is well known, when a focus shift occurs, jitter increases, and as shown in FIG. 8, jitter changes approximately parabolically as the focus offset voltage applied to the terminal 18 as a disturbance signal increases or decreases.
Here, the curve represents the change in jitter when the detection lens is displaced, and the curve represents the case where the lens is at the in-focus position, and the curve represents the case where it deviates from the in-focus position in the opposite direction. As shown in the figure, the focus offset voltage is set to V _EX
When increasing and decreasing between and _-V Therefore, when a disturbance signal (focus offset voltage) is applied to the terminal 18 in the form of a sine waveform as shown in FIG. 9A, the jitter changes as shown in FIG. 9B with respect to this disturbance signal. In other words, the curves shown in Fig. 8 change as follows: curve ', curve ', curve ', and curve ', where the detection lens is shifted from the in-focus position. The rate of change of jitter with respect to changes in the disturbance signal is greater than that of the curve ' in the state at the in-focus position.

In this way, if a disturbance signal is added to the focus error, the detection precision of the jitter component becomes higher, and therefore the focusing precision of the detection lens 7 becomes even higher than when the disturbance signal is not added.

Effects of the Invention According to the device of the present invention, a jitter component whose detection precision is higher than that of the output RF reproduction signal of the detector is used.
Since the position of the detection lens is displaced to minimize this, the adjustment accuracy is higher than that of conventional devices that adjust the position of the detection lens based on the RF reproduction signal, and therefore the focusing accuracy of the detection lens is improved. is high;
It is possible to obtain a highly accurate reproduction signal, and by adding a disturbance signal to the focus error signal, the focusing accuracy of the detection lens can be further increased. It has the advantage of not requiring any adjustment.

[Brief explanation of the drawing]

FIG. 1 is a block system diagram of an embodiment of the device of the present invention, FIGS. 2 to 4 are signal waveform diagrams for explaining the operations of the conventional device and the device of the present invention, and FIG. 5 is an example of the conventional device. 6 is a diagram showing an example of a microhead together with a pickup, FIG. 7 is a diagram showing an example of a microhead, and FIGS. 8 and 9 are signal waveforms for explaining the operation of the device of the present invention. It is a diagram. DESCRIPTION OF SYMBOLS 1... Laser light source, 3... Half prism, 5... Objective lens, 6... Disk, 7... Detection lens, 8...
Detector, 9...Error detector, 13, 19...Adder, 14...Waveform shaping circuit, 15...Counter, 1
6...Meter, 17...Micro head, 18...Disturbance signal input terminal, 23...Lens holder, 24...Rotating body, 24b...Eccentric pin.

Claims (1)

[Claims] 1. Light emitted from a laser light source is irradiated onto a recording medium through an optical element such as a half prism for dividing the optical path and an objective lens, and the light reflected from the recording medium is transmitted through the objective lens. is transmitted and reflected in a substantially right angle direction by the optical element, and then focused almost on the detector by the detection lens, and the position of the objective lens is controlled based on the obtained focus error signal, and the recording is performed. An optical pickup adjustment device for reading signals on a medium includes means for obtaining an RF reproduction signal from the detector and detecting the magnitude of a jitter component contained in the RF reproduction signal, and a means for detecting the magnitude of a jitter component contained in the RF reproduction signal, and a means for detecting a magnitude of a jitter component contained in the RF reproduction signal, and a means for detecting a magnitude of a jitter component included in the RF reproduction signal, and a means for detecting a magnitude of a jitter component included in the RF reproduction signal, and a means for detecting a magnitude of a jitter component included in the RF reproduction signal, and a means for detecting a magnitude of a jitter component included in the RF reproduction signal, and a means for detecting a magnitude of a jitter component contained in the RF reproduction signal, and a means for detecting a magnitude of a jitter component included in the RF reproduction signal, and a means for detecting a magnitude of a jitter component included in the RF reproduction signal. An optical pickup adjustment device comprising means for displacing the position in a direction in which the jitter component is minimized. 2. Light emitted from a laser light source is irradiated onto a recording medium through an optical element such as a half prism for dividing the optical path and an objective lens, and the light reflected from the recording medium is transmitted through the objective lens to form the optical system. After being reflected by the element in a substantially right angle direction, the signal on the recording medium is read by controlling the position of the objective lens based on the focus error signal obtained by focusing the signal almost on the detector with a detection lens. The optical pickup adjustment device includes means for obtaining an RF reproduction signal from the detector and detecting the magnitude of a jitter component included in the RF reproduction signal, and adjusting the position of the detection lens according to the magnitude of the jitter component. An optical pickup adjustment device comprising means for displacing the focus error signal in a direction where the focus error signal is minimized, and means for forcibly adding a disturbance signal of a constant frequency and constant amplitude to the focus error signal.