JPS6346626A - Focus pulling in system for optical information recording and reproducing device - Google Patents

Abstract

PURPOSE:To attain high speed and stable focus pulling-in by using a zero cross signal of a focus error signal other than just focus position so as to switch acceleration/deceleration of a position control system of an objective lens. CONSTITUTION:A drive signal generating circuit 27 sends an acceleration signal moving forcibly the objective lens near the just focus position to an objective lens drive coil 5a at first at focusing and the objective lens 5 from the point remote from the information face of an optical disk to the nearby side. A contact of a changeover switch 23 is thrown to the position of broken lines, that is, to the focus error signal by using a zero cross signal outputted at first by a zero cross check circuit 26. As a result, the position of the objective lens 5 is moved to operate the focus servo function from this side of the just focus position in the focus pull-in path so as to reduce the focus pull-in time.

Description

[Detailed Description of the Invention] [Summary] The present invention provides an optical information recording and reproducing device that controls the position of an objective lens using a zero-crossing point of a focus error signal other than the just focus position in order to shorten the focus pull-in time. By switching the acceleration/deceleration of the system, stable focus pull-in can be performed at high speed.

[Industrial application field]

The present invention relates to an optical information recording/reproducing device, and particularly to a focus pull-in method for a focus servo function.

In recent years, the amount of information processed by computers has continued to increase, and optical information recording and reproducing devices such as optical disk devices and optical card devices with large recording capacities have attracted attention in order to record and reproduce this increased information. The improvement is remarkable.

In an optical information recording/reproducing device, the shape of the information recorded or to be recorded on the recording medium has a minute focus of 1- or less, so the laser beam is focused to a minute spot light with a diameter of about 1- A focus servo function that always maintains the focal position on the medium surface and irradiates the medium regardless of the surface runout of the recording medium is essential, and there is a desire to develop a focus servo function that performs focus pull-in at high speed and with high precision.

[Conventional technology]

FIG. 2 shows a schematic configuration diagram of a conventional optical disk device equipped with a focus servo function. In the figure, 1 is a semiconductor laser that serves as a light source, 2 is a collimating lens that converts the light beam emitted from the semiconductor laser 1 into parallel light, and 3 and 4 are optical elements for separating the light beams, and each is a polarizing beam splitter. and a λ/4 plate (λ is the wavelength of the laser beam), 5 is an objective lens equipped with a focus servo function for irradiating a spot of the light beam onto the information surface of the optical disk 6, and 5a is an objective lens 5 that This figure shows an objective lens drive coil with a focus servo function that controls the position in the optical axis direction.

7 is a reflection mirror for dividing the reflected light from the optical disk 6 into two parts, 8 and 9 are a condenser lens and a 2-split photodiode for detecting a focus error signal (focal position error signal), and 10 and 11 are the same. Tracking error signal (
A condenser lens and a two-split photodiode are used to detect the track position error signal.

When the optical disk 6 rotates, the surface of the optical disk moves up and down due to surface wobbling, and FIG. 3 shows the change in shape of the incident light on the light receiving surface of the two-split photodiode 9 at this time.

12 indicates that when the distance X between the objective lens 5 and the optical disk 6 in FIG. 2 is longer than the focal length of the objective lens 5 (far from the surface of the optical disk 6), 13 indicates that the distance , 14 is the shape of each incident light on the light receiving surface of the two-split photodiode 9 when the distance X is shorter than the focal length (closer to the surface of the optical disk 6).

A and B indicate the amount of light received by dividing the semicircular light receiving area incident on each light receiving surface of the two-split photodiode 9. The difference A-B in the divided received light amounts is determined by a differential amplifier (not shown),
When this is expressed as a focus error signal on the vertical axis as a voltage ◯, and the distance of the objective lens 5 to the optical disk surface is expressed as X on the horizontal axis, the relationship between the two is shown in the waveform diagram of the focus error signal in FIG.

In FIG. 4, far and near represent distances to the optical disk surface, respectively. Position 16 is the position where distance X and focal length match (just focus point) 2. Positions 15 and 18 are near and far positions corresponding to 14 and 12 in FIG. 3, respectively. At the just focus point 16, the value of the focus error signal (2) crosses zero on the line of distance ifX. It is sufficient if the position of the objective lens 5 can be stably controlled within the range of the linearity changing portion 19 centered on the just focus point 16. Note that, generally, zero cross points exist at 17 positions other than the just focus point 16.

That is, the focal length X of the objective lens is controlled so as to maintain the value of the focus error signal (■) at zero. This position control is called a focus servo function, and the method of moving the objective lens to the range of the linearity changing portion 19 before executing the focus servo function is called a focus pull-in method.

FIG. 5 shows a block diagram of a conventional focus servo system. In the figure, 20 is a differential amplifier which outputs the difference signal A-B explained in FIG. 3, that is, the focus error signal.
A focus error signal detection circuit 21 is configured together with the two-split photodiode 9.

22 is a just focus position detection circuit (for example, a comparator) that detects the just focus point from the focus error signal output by the differential amplifier 20, and the output of the just focus position detection circuit 22 causes the changeover switch 23 to change its connection to the solid line. It can be switched from the side to the dashed line side. 24 is a drive signal generation circuit that generates a position control signal for the objective lens 5, and 25 is a current amplifier that supplies a drive current to the lens drive coil 5a.

The position of the objective lens 5 when the focus servo function is not executed is normally maintained at a predetermined far distance from the surface of the optical disc 6 (for example, position 18 shown in FIG. 4).

In order to execute the focus servo function, first the changeover switch 23 is activated by the output signal of the drive signal generation circuit 24.
and a current amplifier 25, the lens is driven with a sufficiently large current to force the objective lens 5 to reach a predetermined short distance position (for example, position 15 shown in FIG. 4) with respect to the surface of the optical disk 6. It flows into the coil 5a.

Thereafter, it is switched to an initial drive signal (not shown) that brings the position 15 closer to the range of the linearity change portion 19, and it is detected that the just focus point 16 within the range of the linearity change portion 19 has been reached by the initial drive. Based on the output of the just focus position detection circuit 22, the contact of the changeover switch 23 is switched to the dotted line side. Since zero cross points exist at positions other than the just focus position, in order to avoid erroneous detection of the just focus position, just focus is determined at the first zero cross point detected from the time when the output signal of the drive signal generation circuit 24 is switched to the initial drive signal. The position is determined to be 16.

After switching the changeover switch 23, a focus servo function is executed to control the objective lens drive coil 5a via the current amplifier 25 so that the value of the focus error signal output by the differential amplifier 20 becomes zero.

[Problem that the invention seeks to solve]

According to the conventional method, the relative speed between the objective lens 5 and the information surface of the optical disk 6 repeatedly changes slowly, especially when performing high-speed focus servo pull-in or when there is surface wobbling of the optical disk. If the relative speed is high, the objective lens 5 deviates from the range of the linearity change portion 19 shown in FIG. 4 due to the inertial movement at the time of detecting the just focus position, making it impossible to execute the focus servo function. There is a drawback.

The present invention was created in view of the above-mentioned conventional drawbacks, and aims to provide a focus servo pull-in method that is stable and reliable regardless of the surface wobbling of an optical disk or a high-speed focus servo pull-in method.

[Means for solving problems]

As shown in FIG. 1, the focus pull-in method of the optical information recording/reproducing apparatus of the present invention is as follows: A zero cross detection circuit (26) detects zero cross points other than the just focus position included in the focus error signal.
), and when pulling the focus of the objective lens (5), a drive signal is applied to the drive coil (5a) of the objective lens to move it to the vicinity of the just focus position, and at the same time, from the time of application of the drive signal, The present invention is characterized in that the drive signal is switched to the focus error signal based on the detected output of the zero cross detection circuit (26), and the focus servo function is switched to operation.

[Effect]

At the time of focus pull-in, the first drive signal generation circuit 24
sends an acceleration signal to the objective lens drive coil 5a to forcibly move the objective lens 5 to the vicinity of the just focus position, thereby accelerating the objective lens 5 from the side far from the information surface of the optical disc 6 to the side close to it.

The contact point of the changeover switch 23 is switched to the dotted line side, that is, to the focus error signal, by the zero-cross signal output by the zero-cross detection circuit 26 from the time when the acceleration signal is output. As a result, the position of the objective lens 5 is shifted to the focus servo function from just before the just focus position 16 on the focus retraction path, without passing through the just focus position and moving to a predetermined folding position 915 close to the optical disk as in the conventional case. This makes it possible to shift to the focus position, reducing the focus pull-in time.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

Note that, in order to make the explanation of the configuration and operation easier to understand, the same parts are given the same reference numerals throughout all the figures, and repeated explanation thereof will be omitted.

FIG. 1 shows a block diagram of an embodiment of the invention. In the figure, 26 is a zero cross detection circuit that detects a zero cross point other than the just focus position included in the detected focus error signal, 27 is a drive signal generation circuit that generates a position control signal for the objective lens 5; The difference between the drive signal generation circuit 24 shown in the figure and the drive signal generation circuit 24 is that when the focus is pulled in, the drive signal generation circuit 24 first selects the changeover switch 2
3 and a current amplifier 25, a sufficiently large current is applied to the lens to force the objective lens 5 to reach a predetermined short distance position (for example, position 15 shown in FIG. 4) with respect to the surface of the optical disk 6. The current is applied to the drive coil 5a.

Thereafter, the control signal is switched to an initial drive signal (not shown) that causes the positioning machine 5 to move back and approach the range of the linearity changing portion I9, and at the same time, a control signal is sent to operate the detection function of the just focus position detection circuit 22 from the point of switching. , its control signal is emphasized by the first detected zero-crossing signal.

On the other hand, when the focus is pulled in, the drive signal generation circuit 27 sends a sufficiently large current to the lens drive coil 5a via the changeover switch 23 and the current amplifier 25 in order to make the objective lens 5 reach the vicinity of the just focus position. , a control signal is sent to operate the detection function of the zero-cross detection circuit 26 from the time when the current is applied, and the control signal is reset by the first detected zero-cross signal.

Therefore, as can be seen from the waveform diagram of the focus error signal in FIG. 17, a zero-crossing signal is output, and since there is no longer a control signal for the detection function, the zero-crossing signal at the just-focus position is not detected.

That is, since the contact point of the changeover switch 23 is switched to the broken line side at the position of the zero cross point 17, the focus servo function is activated, and the objective lens drive coil 5a, which has been applied with an acceleration signal up to the position near the zero cross point 17, is The focus error signal is switched to a deceleration signal corresponding to the focus error signal, and the relative speed between the objective lens 5 and the information surface of the optical disk 6 in the just focus positioning process 6 is set to a value that can be brought into the range of the linearity change portion 19. be able to.

As a result, the reciprocating distance between the just focus position 16 and the position 15, which was conventionally used as a retracting path, becomes unnecessary, and the retracting time is shortened by this reciprocating time.

[Effects of the Invention] As described in detail above, according to the focus pull-in method of the optical information recording/reproducing apparatus of the present invention, it is possible to shorten the focus pull-in time at the time of focus pull-in. In addition, by applying a focus error signal, that is, a deceleration signal corresponding to the position of the zero cross point 17 to the objective lens drive coil 5a, the relative speed between the objective lens 5 and the information surface of the optical disc 6 near the just focus position can be adjusted to focus. This allows for high-speed and stable focus pull-in.

[Brief explanation of drawings]

Fig. 1 is a block diagram of an embodiment of the present invention, Fig. 2 is a schematic configuration diagram of a conventional optical disk device, Fig. 3 is a light receiving pattern of a photodiode for detecting a focus error signal, and Fig. 4 is a waveform of a focus error signal. 5 shows a block diagram of a conventional focus servo system. In FIG. 1, 5a is an objective lens drive coil, 21 is a focus error signal detection circuit, 23 is a changeover switch,
Reference numeral 26 indicates a zero-cross detection circuit, and 27 indicates a drive signal generation circuit. Fig. 1 6 color table 4 nodes 1 z 7 Heboo / Figure 3) Bow r-j Fuzu T: ``7-i ε = Chi 1 to Anj 〒 η Co Figure 4

Claims (1)

[Claims] Based on the detected focus error signal, the objective lens (
5) In the optical information recording and reproducing device that operates the focus servo function, a zero cross detection circuit (26) is provided to detect a zero cross point other than the just focus position included in the focus error signal, and At the time of focus retraction, a drive signal is applied to the drive coil (5a) of the objective lens to move it near the just focus position, and the zero cross detection circuit (26) is A focus pull-in method for an optical information recording/reproducing device, characterized in that the focus servo function is switched to operate at the output.