JPH05274700A - Focus controller for optical disk device - Google Patents

Abstract

PURPOSE:To stably draw a focus servo by providing a control means driving individually a focus main coil and a focus auxiliary coil respectively. CONSTITUTION:An objective lens 30, a tracking coil 27, the focus main coil 28 and the focus auxiliary coil 29 are attached to an objective lens holder 31 being a movable part. Then, by a control means, the focus main coil 28 and the focus auxiliary coil 29 are controlled so as to be driven individually respectively. Thus, even when the focus servo drawing operation of a shaft slide type actuator, etc., without holding a neutral point by an elastic member and having a nonlinear characteristic like hysterisis and friction is executed, the actuator is moved gradually and the focus servo is drawn stably.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a focus control device for an optical disk device which is connected to a computer or the like and is capable of recording / reproducing / erasing data.

[0002]

2. Description of the Related Art Optical disks can record a large amount of information,
Furthermore, it is a recording medium that can be repeatedly erased and reproduced. The optical disk device includes a motor for rotating the optical disk, an optical device for recording / reproducing a signal by condensing a light beam emitted from a light source such as a semiconductor laser on a disk surface by a condensing lens. And a transfer means for transferring the optical device to scan the disk surface in the radial direction by the light beam.

Generally, the size of the information bit and the track interval of the disc are on the order of micron, and in order to reproduce or record the signal, the light beam emitted from the objective lens is accurately focused on the signal recording surface of the disc. Need to tie. However, it is impossible to form a disk into a perfect flat plate, and generally, due to factors such as the accuracy of the mounting device, the distance between the objective lens and the disk surface fluctuates as the disk rotates, and the fluctuation On the other hand, since the depth of focus of the light spot is extremely small, the light spot cannot accurately scan the signal recording surface of the disc, and normal reproduction / recording operations cannot be performed. for that reason,
A position error between the disc signal recording surface and the focal point of the light spot is detected as a focus error signal, and focus servo control is performed by this signal to keep the distance between the objective lens and the disc recording surface constant.

A conventional focus control device for an optical disk device will be described below. As shown in FIGS. 4 and 5, in the leaf spring supporting type optical pickup, the objective lens 2, the focus coil 3 and the tracking coil 4 are attached to the objective lens holder 1 which is a movable part, and the objective lens holder 1 is for supporting the neutral point. It is supported by the leaf spring 5. The objective lens holder 1 is movable in a focus control direction (perpendicular to the disc surface) and in a tracking direction (disc radial direction), and the drive effective portions of the focus coil 3 and the tracking coil 4 are magnets 6a and 6b. And the yokes 7a and 7b are arranged in each magnetic circuit.

The light beam is irradiated onto the disc from the objective lens 2, and the reflected light returns to the inside of the optical pickup,
The optical sensor detects servo information such as a focus error signal indicating a deviation between the focal position of the laser beam and the disk recording surface and a tracking error signal indicating a deviation between the position of the laser beam spot and the track center.

In order to perform the recording / reproducing operation of the optical disc, first, the focus servo operation must be performed. Focus servo operation is generally performed using a focus error signal. The knife edge method will be described as an example of means for detecting the focus error signal. As shown in FIGS. 6 to 8, the reflected light from the disk 8 passes through the objective lens 9, the sensor lens 10 and the knife edge 11, and is divided into two focus error sensors 12.
A focus error signal 14 is generated by being incident on a and 12b and taking the difference between the respective sensors by the differential amplifier 13. The principle of generating the focus error signal will be described in detail below.

When the distance between the objective lens 9 and the disk recording surface 8 is extremely large, the reflected light reaching the focus error sensors 12a and 12b from the disk recording surface 8 is weak and the focus error signal 14 becomes almost zero. As shown in FIG. 6, when the disk recording surface 8 is farther than the focal position of the light beam, the light from the sensor lens 10 is caused by the knife edge 11 to cause the focus error sensor 12b.
A large amount of light is incident on the side of the objective lens, and the objective lens is located at a focusing position (a relative positional relationship between the objective lens 9 and the disc such that the light beam emitted from the objective lens 9 focuses on the disc recording surface 8). A focus error signal 14 indicating that the position is far away is output. Further, as shown in FIG. 7, when the disk recording surface 8 is at the focal position of the light beam, the light incident on the focus error sensors 12a and 12b is just balanced, and the focus error signal 14 becomes zero. Further, as shown in FIG. 8, when the disk recording surface 8 is too close to the focus position of the light beam, more light is incident on the focus error sensor 12a, and the objective lens 9 is closer to the focus position. Then, the focus error signal 14 indicating that there is
When the distance between the objective lens 9 and the disc recording surface 8 is extremely small, the reflected light reaching the focus error sensors 12a and 12b from the disc recording surface 8 is weak, and the focus error signal 14 becomes almost zero.

In FIG. 9 showing a conventional focus control apparatus, 15 is a focus servo pull-in signal, 16,
17 is a switch device, 18 is a triangular wave oscillator, 19 is a focus coil drive amplifier, 20 is an actuator, 21
Is a focus error sensor, 22 is an adder, 23 is a comparator, 24 is an inverter circuit, and 25 is a controller.

With respect to the focus control device composed of the above-mentioned components, the relationship and operation of the components will be described. At the start of the focus servo pull-in operation, the focus servo pull-in signal 15 is at a low level, the switch device 16 is open, the focus servo is off, the switch device 17 is closed, and the triangular wave generated by the triangular wave oscillator 18 is generated. It is input to the focus coil drive amplifier 19,
A current is passed through the actuator 20. As a result, the objective lens 9 moves in the focus control direction according to the triangular wave, and the distance between the objective lens 9 and the disk recording surface 8 continuously changes. On the other hand, when the signals from the focus error sensor 21 are added by the adder 22 and passed through the comparator 23,
As shown in 0, when the objective lens 9 is in the focus servo pull-in possible area near the in-focus position, the output of the comparator 23, that is, the focus servo pull-in signal 1
5 becomes a high level, the switch device 17 is opened, and the supply of the output of the triangular wave oscillator 18 to the actuator 20 is stopped. At the same time, the switch device 16 is closed and the focus servo is turned on, and the controller 25 performs the focus servo operation.

Further, when the focus servo pull-in fails or the servo goes out during the focus servo operation, the objective lens 9 moves to the outside of the focus servo pull-in area, so that the focus servo pull-in signal becomes low level. .. In that case, the focus servo pull-in operation described above is repeated again.

In order to perform a stable servo pull-in operation, it is necessary to move the objective lens 9 as gently as possible to a focus servo pull-in area near the in-focus position. In the case of an actuator having a neutral point supported by an elastic member as in the conventional example, the objective lens moves in proportion to the current as the driving current is gradually increased, but the sliding type without the neutral point supported by the elastic member. In the case of an actuator or the like, it is difficult to move the actuator gently because a current that exceeds a threshold value in the focus coil causes a sharp movement due to its hysteresis characteristics.

[0012]

As described above, in the case of a servo pull-in operation such as a shaft sliding type actuator having no neutral point support by the elastic member, the conventional method of changing the drive current has a threshold voltage with an applied current. There is a problem in that the objective lens suddenly starts to move when the value exceeds, and it is difficult to pull in the focus servo.

The present invention solves the above-mentioned problems of the prior art. The actuator can be moved slowly, the focus servo can be pulled in stably, and the bias current value can be varied to freely control the primary resonance frequency of the actuator. It is an object of the present invention to provide a focus control device for an optical disc device which has an actuator characteristic most suitable for the specifications of the servo system.

[0014]

In order to achieve this object, a focus control device for an optical disk device according to the present invention rotates in a magnetic circuit which is attached to an objective lens holder and which is composed of a magnet and a yoke. The focus main coil arranged to generate a force in the axial direction of the support shaft, and the size of the drive effective portion which is attached to the objective lens holder and which is linked to the magnetic flux in the magnetic circuit when the objective lens holder moves. It has a configuration including a focus auxiliary coil arranged so as to change the angle, and a control unit capable of individually driving the focus main coil and the focus auxiliary coil.

[0015]

In this structure, the position of the objective lens can be controlled by the magnitude of the current flowing through the focus coil in the shaft sliding type actuator which does not have the neutral point support of the actuator by the elastic member or the like and has the hysteresis characteristic due to friction. The objective lens is moved slowly.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

As shown in FIG. 1, an objective lens 30, a tracking coil 27, a focus main coil 28, and a focus auxiliary coil 29 are attached to an objective lens holder 31 which is a movable part. The objective lens holder 31 can be rotated around a rotation support shaft 32 provided in an optical pickup fixing portion (not shown) and can be slid in the direction of the rotation support shaft 32. The tracking coil 27, the focus main coil 28, and the focus auxiliary coil 29 are the outer magnet 3
3, the outer yoke 34, the inner yoke 35, the inner magnet 26, and the rotation support shaft 32 are arranged in a magnetic circuit. The focus main coil 28 and the focus auxiliary coil 29 are independent of each other, and currents can be individually applied. By disposing the focus auxiliary coil 29 at the end of the above-mentioned magnetic circuit, it is possible to generate a force proportional to the moving distance of the objective lens holder 31 from the focus auxiliary coil 29. That is, first, a constant current is applied to the focus auxiliary coil 29 so that a downward force is generated with respect to the objective lens holder 31,
Next, when the objective lens holder 31 is moved upward by applying a current to the focus main coil 28, the drive effective portion of the focus auxiliary coil 29 in the magnetic circuit increases as it moves and is generated downward by the focus auxiliary coil 29. The power to do will increase. 4 in the figure
Reference numerals 6a and 16b are reflection mirrors.

As can be seen from FIG. 2, which shows the relationship between the position of the objective lens 30 and the force generated by the focus auxiliary coil 29, the effective length of the magnetic flux in the magnetic circuit and the focus auxiliary coil 29 interlinks changes. In the area to be turned on, a force proportional to the position of the objective lens 30 is generated by the focus auxiliary coil 29, so that the position of the objective lens 30 can be controlled by the magnitude of the current passed through the focus coil.

In FIG. 3, which shows the control circuit of the focus control device of the optical disk device of one embodiment of the present invention, 28 is shown.
Is a main focus coil, 29 is a focus auxiliary coil,
43 is a bias current application circuit, 44 is a retractable area detection circuit, 45 is a controller, 36 is a switch device,
37 is an inverter circuit, 38 is a D / A converter, 39
Is a switch device, 40 is a focus coil drive circuit, 4
Reference numeral 1 is a focus servo pull-in signal, and 42 is a drive mode switching switch.

With respect to the control circuit including the above-mentioned constituent elements, the relation and operation of each constituent element will be described. When the power is turned on, the focus servo pull-in signal 41 is at a low level, the switch device 36 is open, and the focus servo is off. First, the drive mode switching switch 42 is set to the independent drive mode in response to the control signal from the controller 45, and the bias current is supplied from the bias current generating circuit 43 only to the focus auxiliary coil 29.
Then, after the switch device 39 is closed and the drive signal for pulling in the focus servo generated by the controller 45 is converted into an analog signal by the D / A converter 38, it is input to the focus coil drive circuit 40 and a current is supplied to the focus main coil 28. Shed. Then, the objective lens 30 starts to move toward the disc by the force generated by the focus main coil 28, but as shown in FIG. 2, the focus auxiliary coil 29 causes the objective lens 30 to move.
Since a reverse force proportional to the position of the focus main coil 2 is generated,
The objective lens holder 31 is neutralized at a position where the force generated by 8 and the force generated by 8 are balanced. That is, the position of the objective lens 30 is slowly changed by changing the current passed through the focus main coil 28. Then, when the objective lens 30 reaches the focus servo pull-in possible area, it is composed of, for example, an adder for adding signals from the focus error sensor as described in the conventional example and a comparator for binarizing the output. A control signal is generated from the retractable area detection circuit 44, a focus servo pull-in signal 41 is generated from the controller 45, the switch device 39 is turned off, and the switch device 36 is turned on to complete the focus servo pull-in operation. Then, the drive mode switching switch 42 switches to the main drive mode in which only the focus main coil 28 is driven, and the focus servo operation is performed.

As described above, according to this embodiment, the focus main coil 28 is attached to the objective lens holder 31 which is a movable part.
In the magnetic circuit, the focus auxiliary coil 29 is arranged at the end of the magnetic circuit, and the control means is provided so that the focus main coil 28 and the focus auxiliary coil 29 can be individually driven. Even when performing a focus servo pull-in operation such as a shaft sliding type actuator having no neutral point and having non-linear characteristics such as hysteresis and friction, the actuator can be moved gently and the focus servo can be pulled in stably.

It is also possible to keep the bias current flowing through the focus auxiliary coil 29 during the focus servo operation. In that case, the primary resonance frequency of the actuator can be adjusted freely by further varying the bias current value. Can be controlled to have the optimum actuator characteristics for the specifications of the servo system.

[0023]

As is apparent from the above description of the embodiments, the present invention is provided in the magnetic circuit which is attached to the objective lens holder and which is composed of the magnet and the yoke, and in the axial direction of the rotation support shaft. The focus main coil, which is arranged so as to generate force, and the size of the drive effective portion, which is attached to the objective lens holder and which interlinks with the magnetic flux in the magnetic circuit, change when the objective lens holder moves. The focus auxiliary coil disposed in the above and the control means that can drive the focus main coil and the focus auxiliary coil individually can slowly move the actuator, stably pull in the focus servo, and bias. The primary resonance frequency of the actuator can be freely controlled by changing the current value, and the actuator that is most suitable for the specifications of the servo system. Those capable of realizing a focusing control device superior optical disk device having a chromatography data characteristics.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing the concept of a main part of a focus control device for an optical disc device according to an embodiment of the present invention.

FIG. 2 is a graph showing the relationship between the position of the objective lens of the focus control device of the same optical disc device with respect to the disc and the force generated by the focus auxiliary coil.

FIG. 3 is a block diagram of a control circuit of a focus control device of the optical disc device.

FIG. 4 is a plan view of a leaf spring supporting type optical pickup of a focus control device of a conventional optical disc device.

5 is a sectional view taken along line AA of FIG.

FIG. 6 is a main part showing a state when an objective lens is located farther than a focusing position with respect to a disk recording surface in a knife edge method for detecting a focus error signal of a focus control device of a conventional optical disk device. Cross section

FIG. 7 is a sectional view of an essential part showing a state where the objective lens is at a focus position with respect to the disk in the knife edge method.

FIG. 8 is a sectional view of an essential part showing a state where the objective lens is closer to the disc than the in-focus position in the knife edge method.

FIG. 9 is a block diagram of a focus control device of a conventional optical disc device.

FIG. 10 is a graph showing a principle of generating a focus servo pull-in signal of the focus control device of the optical disc device.

[Explanation of symbols]

 26 Inner Magnet 28 Focus Main Coil 29 Focus Auxiliary Coil 31 Objective Lens Holder 32 Rotation Support Shaft 33 Outer Magnet 34 Outer Yoke 35 Inner Yoke

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshihiro Fujishima 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Inventor Shingo Sakata 1006 Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd.

Claims (2)

[Claims] 1. An objective lens holder which is rotatable around a rotation support shaft and movable in the axial direction of the rotation support shaft, a magnetic circuit including a magnet and a yoke, and the objective lens. A focus main coil attached to the holder and disposed in the magnetic circuit so as to generate a force in the axial direction of the rotation support shaft; and an objective lens holder attached to the objective main lens holder. A focus auxiliary coil is provided so that the size of the drive effective portion that links with the magnetic flux in the magnetic circuit changes by moving, and the focus main coil and the focus auxiliary coil are individually driven. A focus control device for an optical disk device, which is provided with a control unit that enables the above. 2. The control means has a switch device capable of switching between an independent drive mode in which the focus main coil and the focus auxiliary coil are independently driven, and a main drive mode in which only the focus main coil is driven. A focus control device for an optical disk device according to claim 1.