JPS62162241A - Lens actuator - Google Patents

Abstract

PURPOSE:To obtain a small-sized lens actuator with simple structure without using laser beams for an optical head part by arranging two reflection type proximity sensors on a condenser lens holding movable part with a fine interval so that the quantity of light detected by light receiving parts of respective sensors is changed mutually with reverse polarity. CONSTITUTION:Since area of a reflection surface corresponding to one of the reflection type proximity sensors 61, 62 is increased and a reflection surface corresponding to the other is reduced when the movable part 2 is shifted from a reference position in the tracking direction, a lens position error signal 71 corresponds to the shifted distance of the movable part from the reference position. Since the quantity of reflected light is not almost changed in spite of the movement of the movable part 2 in the focusing direction, the output of a sensor is not almost influenced. Although the intervals between the sensors 61, 62 and the movable part 2 are slightly changed by the movement in the focusing direction strictly speaking because the movable part 2 is supported by a focus supporting spring 3, the same change is applied to both the sensors 61, 62 and output components from the sensors 61, 62 are applied to a differential amplifier 7 as in-phase noise, so that the signal 71 indicates only the shifted distance of the movable part 2 in the tracking direction without being influenced by the change.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a lens actuator for an optical head that records information on a recording medium using optical means, or reproduces or erases already recorded information. In particular, the present invention relates to a lens actuator that moves a condenser lens in a focusing direction perpendicular to the surface of a recording medium and in a tracking direction parallel to the surface of a recording medium.

(Prior art) A laser beam is used as a light source, and this laser beam is modulated with a pulsed signal from an external information source to record binary information on the surface of a recording medium, or to reproduce information that has already been recorded. Alternatively, in the optical head for erasing, in order to accurately record, reproduce, or erase information, focus control is used to adjust the focusing direction, that is, the optical axis of the condenser lens, so that the surface of the recording medium is always the focal position of the back optical lens. At the same time, the laser beam is focused so that the light spot of the focused laser beam on the surface of the recording medium is accurately positioned with respect to the guide groove formed in advance on the recording medium. Tracking position control is performed by driving the lens in a tracking direction perpendicular to the guide groove. At this time, the condensing lens is driven by moving the entire optical head for large movements, and by moving the optical head housing by a tracking actuator built into the optical head for small movements. This is done by moving the condensing lens.

In order to improve the performance of this tracking position control,
The present inventors have proposed an optical head equipped with a lens actuator that detects the movement of the condenser lens in the tracking direction with respect to the optical head housing. For example, the patent application in 1983
-079386. Patent application 1986-133325゜Special application 1973
8-199504 as described in each specification.

In particular, Japanese Patent Application No. 58-199504 uses a lens actuator that performs movement in the tracking direction of a condensing lens within an optical head by circular motion with a certain point on the optical head housing as the rotation center. A detector for detecting the lens position is mounted on an arm that connects a condenser lens and moves in an arc together with the condenser lens, and separates and condenses a part of the laser beam used for recording and reproduction and makes it incident on the detector. It was shown that an optical head with good lens position detection characteristics can be obtained by adopting a structure in which this is the case.

(Problems to be Solved by the Invention) However, in these conventional optical heads having a lens position detection function, a part of the laser beam used for recording and reproduction is used for lens position detection, so the optical system part of the optical head is There was a problem in that it was not possible to separate the lens actuator portion, and the amount of light obtained from the laser light source could not be sufficiently utilized for recording and reproduction. If the optical system part and lens actuator part of the optical head can be separated, the optical system part can be fixed and only the relatively lightweight lens actuator part can be moved, making the movable part lighter than when the entire optical head is moved. This makes it possible to further speed up access. In addition, in conventional optical heads, the detector is mounted on the arm, which increases the size of the movable parts, requires a lot of wiring to the movable parts, and requires a large amount of wiring to separate and focus the laser beam. Since a splitter and a lens are used, the structure is complicated and the head becomes large.

An object of the present invention is to eliminate the above-mentioned drawbacks, and to provide a lens actuator that has a built-in lens position detection function, has a simple and compact structure, and is capable of operating independently from the optical system part of an optical head. be.

(Means for Solving the Problems) The lens actuator of the present invention moves a condenser lens that condenses light from a light source onto a recording medium surface in a focusing direction perpendicular to the recording medium surface and in a tracking direction parallel to the recording medium surface. A lens actuator for moving the condenser lens, the movable part having two reflective proximity sensors installed at a small distance from the movable part that holds the condensing lens, the movable part being an object to be reflected by the reflective proximity sensor. The reflection type proximity sensor is arranged so that the amount of light reaching the light receiving section of each reflection type proximity sensor changes in opposite polarity with respect to movement in the tracking direction.

(Function) According to the actuator having the above configuration, by taking the difference between the outputs of the two reflective proximity sensors, the movement of the movable part in the tracking direction can be detected with high sensitivity and without being affected by common mode noise. Ru. The movable part operates in the focusing direction as well as in the tracking direction,
Since the sensors are arranged so that the change in the output of the reflective proximity sensor due to the movement in the focus direction becomes a common mode for the two sensors, the adverse effects caused by the movement in the focus direction are eliminated. Needless to say, it is resistant to circuit common mode noise. Furthermore, according to the actuator having this configuration, there is no need to use the light from the laser light source used in the optical system of the optical head, and the entire amount of laser light can be used for recording and reproduction, and the optical system part and the lens actuator part can be separated. Furthermore, since there is no need to mount a detector on the movable part, the configuration can be simplified and the device can be made smaller and lighter.

(Example) FIG. 1 is a three-sided view schematically showing an example of the present invention. FIG. 1(a) is a plan view partially including an external circuit diagram added for convenience of explanation, and FIG. 1(b) is an elevational view. A movable part 2 that holds the condensing lens 1 is connected to an arm 4 so as to be movable in the focusing direction indicated by an arrow 11 in the figure via a focus support spring 3 consisting of two leaf springs arranged parallel to each other. Ru. The arm 4 is connected to the lens actuator housing 8 via the rotation support part 5 so as to be able to swing integrally with the movable part 2 in the tracking direction indicated by an arrow 12 in the figure.

On the other hand, a reflective type proximity sensor generates an output according to the distance to the object by reflecting the light emitted from the built-in light emitting diode on an external object and receiving the reflected light with the built-in photodetector. The sensors 61 and 62 have a minute interval from the reflective surface 21 including the tracking direction and the focusing direction of the movable portion 2, and the reflective surface 21 is located at a reference position near the center of the movable range of the movable portion 2. The lens actuator is installed in the lens actuator housing 8 so that the reflection position for each sensor is near both ends in the tracking direction (the optical path at this time is as indicated by arrows 63 and 64 in the schematic diagram). Here, the difference between the outputs of the reflective proximity sensors 61 and 62 is taken by an external differential amplifier 7, and a lens position error signal 71 is generated.

With the above configuration, when the movable part 2 shifts from the reference position in the tracking direction, the area of the reflective surface corresponding to one of the reflective proximity sensors 61 and 62 increases, and the area of the other decreases. Therefore, the lens position error signal 71 obtained by taking the difference between the outputs of both sensors corresponds to the amount of deviation of the movable part 2 from the reference position. Movement of the movable part 2 in the focusing direction has almost no effect on the sensor output because the amount of reflected light hardly changes. Strictly speaking, since the movable part 2 is supported by the focus support spring 3, the reflective proximity sensor 61, 62 is slightly affected by the movement in the focusing direction.
Although the distance between the sensor and the movable part 2 changes, the change is the same for both sensors, and this component acts as common-mode noise in the differential amplifier 7, so the lens position error signal 71 is not affected. Only the amount of deviation of the movable part 2 from the reference position in the tracking direction is shown.

In this embodiment, the driving part that operates the movable part 2 is omitted in the explanation, but in both the focusing direction and the tracking direction, the voice coil motor is formed by the coil attached to the movable part 2 and the magnetic circuit attached to the housing 8. By configuring this, the driving part can be easily configured.

Further, in this embodiment, the movable portion 2 and the reflective proximity sensor 61 are arranged so that the vicinity of both ends of the reflective surface 21 in the tracking direction becomes the reflective position of each of the reflective proximity sensors 61 and 62.
, 62, a part of the reflective surface 21 is painted, and the reflective proximity sensor 61.6 is placed on the boundary of this painted surface.
By setting the reflection position 2, the reflectance of the reflection surface changes greatly when the movable part 2 deviates from the reference position in the tracking direction, and the amount of deviation is detected from the change in the amount of received light due to this. You can also do that.

Figure 2 shows the movable part 2 and reflective proximity sensor 6 in Figure 1(a).
1 and 62 are front views showing another embodiment. The movable part 2 moves the reflective proximity sensor 61 and 62 in the tracking direction.
be installed on both sides of the The reflective surface of the movable part 2 is a surface including the focus direction, and the reflective proximity sensor 61, 62 and the movable part 2
The same effect as the embodiment shown in FIG. 1 can be obtained by appropriately setting the gap between the two. That is, when the movable part 2 deviates from the reference position in the tracking direction, the reflective proximity sensor 61.6
The reflective surface corresponding to one of 2 approaches the sensor, and the other moves away. Therefore, the reflective proximity sensor 61, 62 and the movable part 2
By setting the gap to a value such that the sensor output changes monotonically with changes in the gap within the operating range of the movable part 2, a lens position error signal obtained by taking the difference between the outputs of both sensors. indicates the amount of deviation of the movable portion 2 from the reference position. Further, the rotation support portion schematically shown in FIG. 1 can be easily constructed by using a pivot bearing or a leaf spring.

(Effects of the Invention) With the configuration described above, the laser beam used in the optical system part of the optical head is not used, and therefore the amount of light obtained from the laser light source can be used sufficiently for recording and reproduction, and the optical system part of the optical head and lens The lens actuator can be separated from the actuator portion, and has a built-in lens position detection function that is smaller and has a simpler structure.

[Brief explanation of drawings]

FIG. 1 is a three-sided view schematically showing one embodiment of the present invention.
Figure (a) is a plan view that partially includes an external circuit diagram added for convenience of explanation, Figure 1 (b) is an elevation view, and Figure 2 is Figure 1 (
It is a front view which shows another Example of the movable part 2 and reflective proximity sensor 61, 62 of a). In FIG. 1, 1... Condenser lens, 2... Movable part, 3... Focus support spring, 4... Arm, 5...
...Rotation support part, 61, 62... Reflective proximity sensor,
7... Differential amplifier, 8... Housing Figure 1 housing

Claims (3)

[Claims] (1) A lens actuator that moves a condensing lens that condenses light from a light source onto a recording medium surface in a focusing direction perpendicular to the recording medium surface and a tracking direction parallel to the recording medium surface, which is movable to hold the condensing lens. 1. A lens actuator comprising two reflective proximity sensors installed at a small distance from each other. (2) The two reflective proximity sensors use a part of the movable part as a reflection target, and the amount of light reaching the light receiving part of each reflective proximity sensor has opposite polarity with respect to the movement of the movable part in the tracking direction. 2. The lens actuator according to claim 1, wherein the lens actuator is arranged to cause a change in . (3) The two reflective proximity sensors are arranged so that the amount of light reaching the light receiving section is approximately constant with respect to the movement of the movable section in the focusing direction. lens actuator.