JPH02310827A - Focusing controller - Google Patents

Abstract

PURPOSE:To detect a focus error without fail regardless of the sample-hold timing of a focus error signal and to speedily transfer to returning operation by providing a mean to monitor whether its own focus error signal is changed beyond a certain level range or not excepting for a loop in a focusing controller equipped with the focusing control loop. CONSTITUTION:Difference between the focus error signal being applied with sample-hold at the timing of a mirror surface and a target value, is passed through a phase compensating circuit 2 and afterwards, an actuartor 4 is driven by an actuator driver 3. Then, a servo loop is formed for focusing control. For the high frequency noise area of an output from a focus error detector 5, a high frequency component modulated by a pit is removed by an lowpass filter LFP 6. In such a case, when the focus eroor is generated, the output of the LPF 6 is inputted to an window comparator 7. Thus, the focus error is detected even in a held state and following processing can be suitably execut ed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to out-of-focus detection in focus position control of an optical information recording/reproducing device.

[Prior Art] In conventional optical information recording and reproducing devices, many methods are known for controlling the focal position. As an example of this method, a method called the Naifetsu method will be explained with reference to FIG.

In FIG. 2, 101 is an optical information recording medium, 102
is an objective lens that condenses light, 103 is a quarter wavelength plate, 1
04 is a polarizing beam splitter, 105 is a condensing lens, 1
06 is a knife, 107a and b are two-part sensors, 1
08 represents a collimator lens, and 109 represents a semiconductor laser.

The laser beam emitted from the semiconductor laser 109 is beam-shaped by the collimator lens 108. The laser beam that passes through the polarizing beam splitter 104 and is converted into linearly polarized light with a specific plane of polarization is passed through the 174 wavelength plate 1.
At step 03, the plane of polarization is rotated by 45°, and the light is focused onto the optical information recording medium 101 by the objective lens 102. The reflected light from the optical information recording medium 101 passes through the 174 wavelength plate 103.
Since the plane of polarization is rotated by 45 degrees again, the light is totally reflected by the polarizing beam splitter 104 and focused by the condenser lens 105 onto the two-split sensors 107a and 107b. At that time, the two-part sensor 10
7a, b, the knife 106 causes only approximately 1/2 of the laser beam to reach the two-split sensors 107a, b.

FIG. 3 shows the state of the beam spot on the two-split sensors l07a and b. FIG. 3(b) shows the focused state, and the amounts of light received by the two-split sensors 107a and 107b are equal. Figure 3(a) is the rear bottle, Figure 3(c)
shows the case of the front bin, and the spot positions on the two-split sensors 107a and 107b are shifted left and right depending on the amount of deviation from focus. Therefore, the difference A-B in the amount of light received by the two-split sensors 107a and 107b is determined by the objective lens position (Fig. 4(a)
)) as shown in FIG. 4(b). Therefore,
Focusing is achieved by configuring a control system using this light amount difference as a focus error signal.

The dotted line in FIG. 5 shows the movement of the focus error signal in the focused state. Here, optical information medium 1
01 has surface runout due to movement such as rotation, so it undulates like the section in Figure 5, and when it loses focus due to external impact or scratches on the media surface, it becomes a figure 8 curve like section H. After appearing, it becomes 0 level. Therefore, conventional focus error detection involves inputting the focus error signal into a certain window comparator, and detecting focus error when the focus error signal deviates from ±Δ■.

[Problems to be Solved by the Invention] However, when employing the sample servo method as one of the servo methods, the above conventional example has a problem.

The sample servo method is a method using an optical information recording medium having a format as shown in FIG. 6th
In the figure, R is the moving direction of the medium, 110 is a wobble bit for tracking, 111 is a mirror surface for focusing, and 112 is the center of the track. In such a medium, the sample servo method is a method of removing the influence of tracks or bits on the focus error signal by sample-holding the focus error signal on the mirror surface 111 and using it as the focus error signal. Therefore, the focus error signal when focusing is as shown by the solid line 30 in FIG. With the sample servo, it is fine if the focus is on as shown in section I in Figure 5, but if the focus is lost at the timing shown, character 8 will pass during the hold period of the focus error signal. Therefore, there was a problem that defocus could not be detected.

[Means for Solving the Problems] An object of the present invention is to provide a focus control device that can reliably detect out-of-focus regardless of the sample-hold timing of a focus error signal and can quickly shift to a return operation. be.

The focus control device of the present invention irradiates light onto a recording medium, focuses the light passing through the recording medium onto an optical sensor divided into at least two parts, and generates a sampling signal of a focus error signal obtained from the output of the sensor. A focus control device having a focus control loop that performs focusing from the center, characterized in that, in addition to the loop, means for monitoring whether the focus error signal itself has changed beyond a certain level range is provided. .

Such monitoring means includes a low-pass filter that removes high-frequency components of the focus error signal, and a window comparator that detects when the low-pass filter output deviates from a predetermined range.

[Operation] The present invention provides a so-called sample servo type optical information recording and reproducing device that performs focus control from a sampling signal of a focus error signal, in which a change in a focus error signal within a held period exceeds a certain level range. By providing means for monitoring whether or not the focus has changed, it is possible to immediately detect out-of-focus even in a held state, and to take appropriate subsequent measures.

[Example] Hereinafter, a focus control device according to the present invention will be described in detail based on a specific example.

An embodiment of the present invention will be described in detail using FIG.

In FIG. 1, 1 is a sample hold circuit, 2 is a phase compensation circuit, 3 is an actuator driver, 4 is an actuator that drives the objective lens, 5 is a focus error detector, 6 is a low-pass filter (LPF6), and 7 is a window comparator. It is.

The focus error detector No. 5 may have the same configuration as shown in FIG. After the difference between the focus error signal sampled and held at the timing of the mirror surface 111 and the target value is passed through the phase compensation circuit 2, the actuator 4 is driven by the actuator driver 3 to form a focus control servo loop. Further, from the output of the focus error detector 5, high frequency noise or high frequency components modulated by bits are removed by an LPF 6.

If defocus occurs as shown in FIG. 5, the output of the sample and hold circuit 1 will be as shown by the solid line 30 in FIG. 5, but the output of the LPF 6 will be as shown by the dotted line 32 in FIG. Therefore, the output of the LPF 6 is input to the window comparator 7. The reference voltage of the window comparator 7 is set to ±Δ■ shown in FIG. Then, defocus can be reliably detected regardless of the timing of sampling and holding the focus error signal and the timing of defocus.

The out-of-focus detection signal is taken into a cPU (not shown), and if it is recording, the recording operation is stopped, the laser is set to the reproduction power, and the focus pull-in operation is started.

Note that when the focus is pulled in, the sample hold timing of the focus error signal is unknown, so the LPF6
The retracting operation may be performed using the output of .

In the above embodiment, in addition to the focusing servo loop, the focus error signal is passed through the LPF and then compared with the window comparator to detect defocus, regardless of the sample hold timing of the focus error signal. This has the advantage that out-of-focus detection can be performed reliably and the return operation can be quickly carried out.

Although an embodiment including an LPF and a window comparator has been described as the above-mentioned monitoring means, it is not limited to this embodiment, and any circuit configuration that can substantially monitor changes in the focus error signal itself is included within the scope of the present invention. It is clear that

[Effects of the Invention] As described above, according to the present invention, by providing a means for monitoring whether the focus error signal itself has changed beyond a certain level range, the focus servo can be sampled and When the servo is used, even if defocus occurs during the hold period of the focus error signal, the defocus can be reliably detected and a return operation can be started.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing an embodiment of the present invention, Fig. 2 is a diagram explaining a focus error detection system, Fig. 3 is a diagram of a spot on a sensor in the focus error detection system, and Fig. 4 is a focus error signal. FIG. 5 is a diagram showing the difference in focus error signals between continuous servo and sample servo, and FIG. 6 is a diagram showing the format on the medium in the case of the sample servo method. 1... Sample and hold circuit, 2... Phase compensator,
3... Actuator driver, 4... Actuator, 5... Focus error detector, 6... Low pass filter, 7... Window comparator. Agent Patent Attorney Jo Taira Yamashita Figure 2 Figure 3 (a) Tey (b) Son (C) Xi en (A>8) (A=8)
(A<8) Figure 4 Figure 5 Figure 6

Claims (3)

[Claims] (1) Irradiating light onto a recording medium, focusing the light that passes through the recording medium onto an optical sensor divided into at least two parts, and performing focusing from a sampling signal of a focus error signal obtained from the output of the sensor. A focus control device having a focus control loop, further comprising means for monitoring whether the focus error signal itself has changed beyond a certain level range, in addition to the loop. (2) The monitoring means includes at least a low-pass filter that removes a high frequency component of the focus error signal, and a comparison means that detects that the output of the low-pass filter deviates from a predetermined range. The focus control device according to item 1. (3) The focus control device according to claim 2, wherein the comparison means is a window comparator.