JPH0739057Y2 - Knife edge holder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial field of application> The present invention relates to a structure of a focus error detection unit of an optical pickup, and more particularly to a knife edge mounting mechanism used in a knife edge method.

<Prior Art> Conventionally, in an optical disc device, in order to prevent defocus of laser light emitted from an optical pickup to a disc,
Focusing servo mechanism is used. This focusing servo mechanism requires so-called focus error detection for detecting defocus, and the knife edge method is one of the detection methods.

FIG. 4A shows an example of the knife edge method in which the knife edge is provided at the focal position. The light beam emitted from the semiconductor laser 1 passes through the beam splitter 2 and the objective lens 3
It is focused by and is irradiated onto the surface of the optical disc 4. Optical disc 4
The reflected light reflected by the beam splitter 2 through the objective lens 3 and redirected by the beam splitter 2 is divided into two split photodiodes 6a and 6b.
Is received by. The converted outputs of the photodiodes 6a and 6b are input to the differential amplifier 7.

The knife edge 5 is placed at the focal position Z such that the tip of the edge is in contact with the optical axis.

In such a configuration, when the disc surface is at the in-focus position of the objective lens, the knife edge has no effect, so the output difference ab between the two-divided photodiodes 6a and 6b is zero, but it is not at the in-focus position. In this case, the output difference ab becomes a value other than zero.

Therefore, the focus error can be detected by monitoring the output of the differential amplifier 7.

The knife edge does not necessarily have to be provided at the focal position, and there is also a method of placing it at a position away from the focal position as shown in FIG. 4 (b). In this case, the two-divided photodiode is arranged in the focal plane.

<Problems to be solved by the invention> By the way, in order to ideally realize the knife-edge method, the edge part accurately divides the light flux of the condenser lens into two parts, and the edge direction is relative to the tracking error signal detection direction. Must be vertical. Otherwise, the detection sensitivity of the focus error signal is lowered, and the tracking error signal leaks into the focus error signal, causing so-called focus / tracking interference, which is inconvenient.
That is, it is important to set the attachment position of the edge,
The quality of the optical pickup greatly depends on its quality.

However, since the attachment positioning of the knife edge has traditionally been based on machining accuracy and assembly accuracy,
We were not able to show sufficient performance due to dimensional variations and assembly errors.

In view of these points, the object of the present invention is to improve the holding portion of the knife edge and adjust the position of the knife edge by using a signal detector that is actually used to bring the position to the ideal state as close as possible. The present invention intends to realize a knife edge holder capable of improving the focus error detection function of an optical pickup, reducing the need for machining accuracy, and reducing the cost.

<Means for Solving the Problem> In order to achieve such an object, according to the present invention, a knife edge holder for holding a knife edge used in a focus error detection unit of an optical pickup, wherein one end surface is A flanged cylinder with a flange formed on the other end and a knife edge attached to the other end, and an eccentric cam insertion groove formed on the outer periphery, and an optical axis direction in which the body of the flanged cylinder is loosely fitted in the center part. Bearing hole is formed, and a holding spring for holding the flange to prevent the cylinder from moving in the optical axis direction is attached. Moreover, the eccentric cam insertion hole and the optical axis when screwed to the adjacent member are attached. And a bearing member each having a screw hole formed therein so that it can be slightly moved in a direction at a right angle to, and a tip end portion of which is rotatably inserted into an eccentric cam insertion hole of the bearing member. It consists of an eccentric cam formed so as to fit in the groove for inserting the eccentric cam of the cylinder, and adjusts the rotation angle of the knife edge by the rotation of the eccentric cam, and at the same time as it is perpendicular to the optical axis by mounting the bearing member on an adjacent member. It is characterized in that the positions are adjusted in various directions and the adjustments can be performed independently.

<Operation> The eccentric cam rotates the cylinder with the knife edge attached so that the rotation angle of the knife edge can be adjusted, and the entire bearing member with the cylinder attached can be moved along the optical axis along the adjacent member of the optical pickup. The movement can be adjusted in the direction perpendicular to.

The rotation angle adjustment and the movement adjustment can be performed separately, and the knife edge can be adjusted to a state close to an ideal state by using the signal detector actually used.

<Embodiment> An embodiment of the present invention will be described in detail below with reference to the drawings.
FIG. 1 is an explanatory block diagram showing an embodiment of a knife edge holder according to the present invention (a part of which is cut away). In the figure, 2 is a cylinder with a flange, and the knife edge 1 is adhered to the other end having no flange portion. In addition,
A concave eccentric cam groove (hook groove) 8 is formed in a part of the cylinder 2.

Reference numeral 3 is a bearing member, and a bearing hole into which the cylinder 2 is loosely fitted is provided in the center portion thereof, and the cylinder 2 is rotatable around the optical axis AA '.

Reference numeral 4 denotes a presser spring, which suppresses the movement along the optical axis AA 'and gives a proper friction to alleviate the rattling caused by the shaft fitting.

Reference numeral 5 is an eccentric cam insertion hole for adjusting the rotation angle, 6 is a screw hole for fixing the cylinder 2, and 7 is a hole provided in the bearing member.
This is a hole used when fixing the bearing member 7 to the optical head main body with screws.

The end surface of the bearing member 3 serves as a guide surface during lateral adjustment.

A method of adjusting the position of the knife edge (rotation angle adjustment and left-right adjustment) in such a configuration will be described.

Rotation angle adjustment The rotation angle is adjusted by the mechanism shown in FIG. That is, the eccentric cam 5a is inserted through the eccentric cam insertion hole 5 of the bearing member 3, and the tip of the eccentric cam 5a is inserted into the eccentric cam insertion groove 8 of the cylinder 2. By rotating the eccentric cam in this state, the cylinder 2 can be rotated around the optical axis. In this way the knife edge is rotated around the optical axis. The rotation angle corresponds to the amount of eccentricity of the eccentric cam, so by preparing eccentric cams with different eccentricities and using them properly,
Rough adjustment can be appropriately performed.

Adjustment in the left-right direction Adjustment is performed using the mechanism shown in FIG. That is, an adjacent member (a member on the optical head body side) provided with a right-angled step portion
Attach the set screw through the hole 7 of the knife edge retainer. The screw hole 7 is formed to have a diameter larger than that of the set screw, and the bearing member 3 can be attached while being slightly displaced in the direction perpendicular to the optical axis by using the stepped portion of the adjacent member as a guide as shown in the drawing. As a result, the position of the knife edge can be adjusted in the direction perpendicular to the optical axis. The mounting error in the direction along the optical axis does not significantly affect the detection of the focus error.

Since this knife edge holder uses the screw hole 7 and is attached by a set screw, it can be easily removed from the optical path by removing the set screw.

<Effect of Device> As described above, the present invention has the following effects.

By rotating the eccentric cam, the knife edge can be easily rotationally adjusted around the optical axis.

Further, if eccentric cams having different eccentric amounts are prepared and used, fine / coarse adjustment can be easily performed.

By the pressing spring, it is possible to obtain appropriate friction during rotation, reduce rattling during fitting, and facilitate adjustment.

The rotation of the knife edge end face and the movement adjustment in the direction perpendicular to the optical axis can be independently performed.

Since the entire knife edge holder can be easily removed from the optical path, adjustment of the optical system before and after the knife edge holder can be performed independently.

Since the rotation angle of the knife edge and the position of the end surface can be adjusted as appropriate, the conventional machining accuracy and assembly accuracy of the knife edge are not required, and as a result, the cost can be reduced. Further, since the position of the knife edge can be set to a state close to the ideal, the focus servo characteristic of the optical pickup is improved.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of a knife edge holder according to the present invention, and FIG. 2 is a diagram showing a mechanism for adjusting a rotation angle,
FIG. 3 is a diagram showing a mechanism for adjusting in the left-right direction, and FIG. 4 is a diagram for explaining the knife edge method. 1 ... Knife edge, 2 ... Cylinder with flange, 3 ... Bearing member, 4 ... Pressing spring, 5 ... Eccentric cam insertion hole, 6
...... Screw holes, 7 ... holes, 8 ... grooves.

Claims (1)

[Scope of utility model registration request] 1. A knife edge holder for holding a knife edge used in a focus error detection part of an optical pickup, wherein a flange is formed on one end surface, the knife edge is attached to the other end, and the outer periphery is attached. A flanged cylinder with a groove for inserting an eccentric cam is formed, and a bearing hole in the optical axis direction is formed in the center part where the body of the flanged cylinder is loosely fitted, and the cylinder is pressed in the optical axis direction by pressing the flange. A presser spring for preventing movement of the eccentric cam is attached, and a hole for inserting an eccentric cam and a screw hole for slightly moving in a direction perpendicular to the optical axis when screwed to the adjacent member are formed. A bearing member, and an eccentric cam that is rotatably inserted into an eccentric cam insertion hole of the bearing member and has its tip portion formed in the cylindrical eccentric cam insertion groove. The rotation angle of the knife edge is adjusted by the rotation of the eccentric cam, and the bearing member is attached to the adjacent member to adjust the position in the direction perpendicular to the optical axis, and the adjustments can be performed independently. A knife edge holder characterized in that