JPH03269833A - Pickup actuator - Google Patents

Abstract

PURPOSE:To accurately detect the position of an objective lens by providing a sensor to detect the deviation of the objective lens in a tracking direction by using part of a laser beam made incident on the objective lens at a part confronting with the lower edge of the objective lens. CONSTITUTION:The sensor consisting of a pair of photodiodes 14, 14 which detect the rotational direction and position of a coil bobbin 4 by obtaining part of the laser beam made incident on the objective lens 8 is provided by confronting with the lower edge of the objective lens 8. Therefore, when the coil bobbin is rotated by energizing a coil 10 for track groove follow-up driving setting the shaft of the coil bobbin 4 as a fulcrum and following up to the track groove of a recording medium, part of the laser beam made incident on the objective lens 8 can be directly obtained at the lower edge of the objective lens 8, and the rotational direction and the position of the objective lens 8 can be detected, therefore, it is possible to accurately detect the tracking direction of the objective lens 4 without receiving the influence of the clearance of the shaft of the coil bobbin 4.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a pink-up actuator used in optical disc drives, video disc drives, compact disc drives, and the like.

BACKGROUND ART FIGS. 7 and 8 show the structure of a conventional pickup actuator.

In FIGS. 7 to 8, 51 is a yoke, and 52 is a heel of the yoke 51. Reference numeral 53 denotes a shaft whose lower end is fixed to the heath 52 in the correct size. A coil bobbin 54 is pivotally supported on the upper part of the shaft 53, and is attached so as to be rotatable with respect to the shaft 53 and slidable in the vertical direction. 55
are a pair of holes formed on the upper surface of the coil bobbin 54,
The yokes 51 are loosely fitted into the holes 55, respectively. 56
is a hole formed in the base 52. Reference numeral 57 indicates a hole that corresponds to the hole 56 and is provided through the coil bobbin 54 at the top and bottom. Reference numeral 58 denotes an objective lens attached to the hole 56 via an adhesive, and is used to record and reproduce information on the surface of the optical disk by applying light to the optical disk (not shown). 59 is a focusing drive coil wound around the outer periphery of the coil bobbin 54 and fixed with adhesive. Reference numeral 60 denotes four track groove following drive coils fixed to the outer periphery of the coil bobbin 54 at approximately 90 degree intervals using an adhesive.

A pair of magnets 61 are fixed to the base 52 using adhesive, and are arranged adjacent to the outer periphery of the coil bobbin 54.

And York 51. Magnet 61. The focusing drive coil 59 and the track groove following drive coil 60 constitute a magnetic circuit. Reference numeral 62 denotes a position detection pin whose base is press-fitted onto the outer circumferential portion of the coil bobbin 54, and is provided at a position symmetrical to the objective lens 58 with the axis 53 as the center. 63 is a sensor holder, -
The example is attached to the bottom surface of the base 52 with screws 64, and the other side is fitted into the downwardly protruding portion of the shaft 53. 65 is a hole formed in the middle part of the sensor holder 63;
The tip of the position detection pin 62 is inserted inside. 66 is a light emitting diode (LED), 67 is a two-split photodiode, and the light emitting diode 66 and the two-split photodiode 67 are positioned in the hole 65 in a corresponding state with the tip of the position detection pin 62 sandwiched therebetween. There is. 68
A cover 68 is attached to the base 52, and a hole 69 is formed in the cover 68 to correspond to the objective lens 58.

Note that in FIG. 7, the cover 68 is shown removed.

Next, the operation of the conventional pink-up actuator described above will be explained. In FIGS. 7 and 8, when focusing the objective lens 58 on the optical disk surface using this pickup actuator, a current is passed through the focusing drive coil 59, and the magnetic force generated in the coil 59 is used to move the coil bobbin 58. is slid along the shaft 53. Further, when the objective lens 58 is made to follow the track groove of the optical disk, a current is applied to the track groove following drive coil 60.
The coil bobbin 54 is rotated around the shaft 53 by the magnetic force generated at zero.

This allows the objective lens 58 to focus on the optical disk surface and follow the trunk groove, allowing optical information to be recorded and reproduced.

When the coil bobbin 54 rotates to cause the objective lens 58 to follow the track groove of the optical disk, the position detection pin 62 also moves to the coil bobbin 54.
A portion of the light from the light emitting diode 66 is blocked by the position detection pin 62, and the shadow of the position detection pin 62 is cast onto the two-split photodiode 67. Thereby, the position of the position detection pin 62, that is, the rotational direction and rotational position of the coil bobbin 54 can be detected. By knowing this rotational direction and rotational position, it is possible to detect the tracking direction of the objective lens 58, that is, the amount of deviation of the optical disk in the radial direction with respect to the optical axis. Furthermore, when the amount of deviation is detected, this sensor output can be fed banked to rotate a linear motor (not shown) or coil bobbin 54 to control the objective lens 58 to follow the track groove of the optical disk.

Problems to be Solved by the Invention However, in the conventional pickup actuator described above, a light emitting diode 66 and a two-part photodiode 67 are attached to the sensor holder 63 as means for detecting the rotational direction and rotational position of the coil bobbin 54. A position detection pin 62 is arranged between the photodiode 66 and the two-part photodiode 67. For this reason, if there is a clearance between the shaft 53 and the coil bobbin 53, this clearance will cause an error, and there is a problem that the position of the objective lens 58, which is provided at a position symmetrical to the position detection pin 62 with respect to the shaft 53, cannot be detected accurately. there were.

The present invention solves these conventional problems, and makes it possible to accurately detect the position I of the objective lens, to make the coil bobbin lighter and more compact, and to improve reliability. The object of the present invention is to provide a pickup actuator that can perform the following functions.

Means for Solving the Problems In order to achieve the above object, the present invention provides a sensor that detects the rotational direction and position of the coil bobbin by obtaining a portion of the laser light incident on the objective lens, and is arranged at the lower edge of the objective lens. It was established by

Therefore, according to the present invention, when the track groove following drive coil is energized and rotated about the coil bobbin shaft to cause the objective lens to follow the track groove on the recording medium, a portion of the laser light incident on the objective lens is Since the rotational direction and position of the objective lens are detected directly at the lower edge of the objective lens, the tracking direction of the objective lens, that is, the amount of deviation in the radial direction of the recording medium with respect to the optical axis, is not affected by the clearance of the coil bobbin axis. It has the effect of allowing accurate detection.

Embodiment FIGS. 1 to 3 show the performance of one embodiment of the present invention.

In FIGS. 1 to 3, 1 is a yoke, and 2 is a base of the yoke 1. Reference numeral 3 denotes a shaft whose lower end is press-fitted into the base 2. A coil bobbin 4 is pivotally supported on the upper part of the shaft 3, and is attached so as to be rotatable with respect to the shaft 3 and slidable in the vertical direction. Reference numeral 5 denotes a pair of holes formed on the upper surface of the coil bobbin 4, into which the yokes 1 are loosely fitted. 6 is a hole formed in the base 2. Reference numeral 7 denotes a hole that is provided to correspond to the hole 6 and penetrate through the upper and lower sides of the coil bobbin 4, and is formed to be larger in diameter than the hole 6. Reference numeral 8 denotes an objective lens attached to the hole 6 via an adhesive, which shines light onto an optical disk (not shown) serving as a recording medium to record and reproduce information on the surface of the optical disk. Reference numeral 9 denotes a focusing drive coil wound around the outer periphery of the coil bobbin 4 and fixed with adhesive. 10B are four track groove following drive coils fixed to the outer periphery of the coil bobbin 4 at approximately 90 degree intervals using an adhesive. A pair of magnets 11 are fixed to the base 2 using an adhesive, and are arranged adjacent to the outer periphery of the coil bobbin 4.

And York 1. Magnet 11. Focusing drive coil 9
A magnetic circuit is constituted by the track groove following drive coil 10. Reference numeral 14 denotes a pair of photodiodes. Each photodiode 14 is arranged on the lower surface of the coil bobbin 4 adjacent to the edge of the hole 7 and displaced from each other by 1 to 80 degrees. It is installed so that each part receives an equal amount of light. 1111 is a cover attached to the base 2, and a light 19 is formed on this cover 18 in correspondence with the objective lens 8. Note that in FIG. 1, the cover 18 is shown removed.

Further, FIG. 4 shows the configuration of a signal processing circuit from the photodiode 14. In FIG. 4, 20 is a differential amplifier circuit, which amplifies the difference between the output signals from the two photodiodes 14 and outputs the amplified signal.

Next, the operation of the above embodiment will be explained. In the above embodiment, when focusing the objective lens 8 on the optical disk surface using this pickup actuator, when a current is passed through the focusing drive coil 9, the coil bobbin 4 is moved to the axis 3 by the magnetic force generated in the coil 9. This allows the objective lens 8 to be focused on the optical disk surface. In addition, when the objective lens 8 is made to follow the track groove of the optical disk, when a current is applied to the track groove following drive coil 6, the coil bobbin 4 can be rotated around the axis 3 by the magnetic force generated in the coil 10. The objective lens can be made to follow the trunk groove on the surface.

In this way, when recording and reproducing optical information while focusing the objective lens 8 on the optical disc and following the trunk groove, the light passing through the hole 6 is transmitted to the coil bobbin 4.
It hits the two photodiodes 14 fixed at the bottom of the. When the coil bobbin 4 is rotated to cause the objective lens 8 to follow the track groove of the optical disk, the two photodiodes 14 facing each other in the hole 6 are deviated from the center of the hole 6. The area of the exposed photodiode I4 becomes different.

As a result, the amount of laser light hitting the photodiode 14 also differs, resulting in a difference in output between both photodiodes 14. This output difference is extracted by the differential amplifier circuit 20, and a waveform as shown in FIG. 5 is obtained depending on the direction and amount of rotation of the coil bobbin 4. In other words, in Fig. 5, when the differential output is O, it is the optimum position I, and when the differential output is a positive waveform, it is understood that the coil bobbin 4 is rotating in the positive rotation direction, and conversely, when the differential output is a negative waveform, the coil bobbin 4 is rotating in the positive rotation direction. It can be seen that 4 is rotating in the negative rotation direction. Therefore, by knowing this differential output, the rotational direction and rotational position of the coil bobbin 4 can be detected, and thereby the tracking direction of the objective lens 8, that is, the amount of deviation in the radial direction of the optical disk with respect to the optical axis can be detected. .

When controlling the objective lens 8 to follow the groove, if the coil bobbin 4 is slightly rotated but is significantly eccentric, the whole pickup actuator is moved using a linear motor (positioner, not shown), etc., and the coil bobbin 4 is rotated slightly. If the eccentricity is small despite the large rotation of the coil bobbin 4, feedback is applied by rotating the coil bobbin 4. That is, by performing double servo using an electric signal, it is possible to improve tracking followability.

FIG. 6 shows the main part configuration of another embodiment. In FIG. 6, the same reference numerals as in FIGS. 1 to 3 indicate the same components as in FIGS. 1 to 3. In Fig. 6, two photodiodes 15 are placed on the edge of the heath 2.
The photodiode 1 is attached to the bottom of the coil bobbin 4 by reflecting a part of the laser light that has passed through the hole 6.
Two mirrors 16 are fixed adjacent to the edge of the hole 6 to allow the light to enter the hole 6.

Therefore, in this embodiment, the output signal line of the photodiode 15 can be taken out without going through the coil bobbin 4. This can eliminate deterioration of the signal line and joint portion due to the sliding of the coil bobbin 4, and the suppression and complexity of the operation of the coil bobbin 4 due to the signal line.

Effects of the Invention As is clear from the above embodiments, the present invention includes a sensor that detects the deviation of the objective lens in the tracking direction by using a part of the laser light incident on the objective lens, and is provided at the lower edge of the objective lens. This makes it possible to detect the deviation of the objective lens in the trunking direction without being affected by the clearance of the rotation axis of the coil bobbin. It also has the advantage that the coil bobbin of the sliding part can be made more compact and lighter.

[Brief explanation of drawings]

1 is a plan view of a pickup actuator according to an embodiment of the present invention with the cover removed; FIG. 2 is a sectional view taken along line A-A in FIG. 1; and FIG.
A sectional view taken along line B, FIG. 4 is a circuit diagram of the main part of the actuator that performs signal processing, FIG. 5 is a signal waveform diagram of the circuit shown in FIG. 4, and FIG. 6 is another embodiment of the present invention. 7 is a plan view of the conventional pickup actuator with the cover removed, and FIG. 8 is a sectional view taken along line CC in FIG. 7. l...Yoke, 3...Axis, 4...-
・Coil bobbin, 8...1 objective lens, 9...
...Focusing drive coil, 10...Track groove following coil, 14.15...Photodiode, 16...111 Figure jl11 3rd picture Figure/4 Figure Figure

Claims (3)

[Claims] (1) An objective lens that focuses laser light onto a recording medium;
a sensor provided so as to correspond to a lower edge of the objective lens to detect a part of the laser beam incident on the objective lens, and the sensor causes the objective lens to follow a track of a recording medium. A pickup actuator characterized by controlling. (2) Claim (1) characterized in that the sensor has a plurality of photodetecting elements fixed to a lower edge of the movable objective lens to receive a portion of the laser light incident on the objective lens. Pickup actuator listed. (3) one or more reflecting mirrors fixed to the lower edge of the objective lens to which the sensor is movable and which receives part of the laser light incident on the objective lens; and a plurality of reflecting mirrors which receive reflected light from the reflecting mirrors. The pickup actuator according to claim 1, further comprising a photodetecting element.