Method of attaching a sensor to a pickup head and pickup head

A soft adhesive agent whose force occurring at the time of curing is small is applied between a rib and a PD, and after the curing of the soft adhesive agent, a hard adhesive agent whose force occurring at the time of curing is large is applied between the rib and a plate. Thus since a sensor portion is fixed to a main-body base with two kinds of adhesive agents including the soft adhesive agent and the hard adhesive agent, it is possible to suppress the positional offset of the sensor portion at the time of its attachment, and it is possible to sufficiently ensure reliability with respect to the temperature change as well.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of attaching a sensor to a pickup head for reading data recorded on an optical disk such as a CD or a DVD, as well as a pickup head with the sensor attached thereto by that method.

2. Description of the Related Art

Conventionally, a pickup head is known as a device for reading data recorded on an optical disk such as a CD or a DVD. As is known, the pickup head is so arranged that data recorded on the optical disk is read by applying light emitted from a light source (laser diode (LD)) to a data recorded surface of the optical disk and detecting the reflected light by a light receiving element (photodiode (PD)).

The light receiving element is attached such that the center of its light receiving surface and the focal point of a focusing lens for focusing the reflected light from the optical disk are aligned with each other. A general pickup head is not provided with an adjusting mechanism for adjusting the position of the light receiving element attached to a main body. The reason is that the provision of the adjusting mechanism causes the problems of the main body of the pickup head becoming large in size and the higher cost.

Accordingly, in the general pickup head, when the light receiving element is attached to the main body of the pickup head, the light receiving element is fixed to the main body with an adhesive agent in a state in which the center of the light receiving surface and the focal position are aligned with each other.

Techniques for fixing an optical part to a main body with an adhesive agent are disclosed in, for example, JP-A-62-61033, JP-A-60-69611, and JP-A-63-223702.

However, the following problems have been encountered in a case where the light receiving element is fixed to the main body with an adhesive agent whose tensile force occurring at the time of curing is small (hereafter, this adhesive agent will be referred to as a soft adhesive agent).

The soft adhesive agent after curing undergoes large expansion and contraction in accordance with the change in the ambient temperature, so that the position where the light receiving element is attached is likely to change. For this reason, there has been a problem in that the pickup head with the light receiving element attached to the main body with the soft adhesive agent does not excel in the reliability with respect to the change in the ambient temperature.

On the other hand, in a case where the light receiving element is fixed to the main body with an adhesive agent whose tensile force occurring at the time of curing is greater than that of the aforementioned soft adhesive agent (hereafter, this adhesive agent will be referred to as a hard adhesive agent), the hard adhesive agent after curing undergoes small expansion and contraction in accordance with the change in the ambient temperature, so that it is possible to sufficiently ensure the reliability with respect to the temperature change. However, since the tensile force occurring at the time of curing is large, there has been a problem in that the position of the light receiving element changes at the time of curing.

Thus the soft adhesive agent has an advantage in that the positional offset of the light receiving element is small at the time of curing (attachment), but its reliability with respect to the change in the ambient temperature is low, whereas the hard adhesive agent has an advantage in that high reliability can be obtained with respect to the change in the ambient temperature, but the positional offset of the light receiving element is large at the time of curing (attachment).

SUMMARY OF THE INVENTION

The object of the invention is to provide a method of attaching a sensor to a pickup head which makes it possible to suppress the positional offset of the sensor at the time of the curing of the adhesive agent, and affords high reliability with respect to the temperature change.

The method of attaching a sensor to a pickup head in accordance with the invention has the following arrangements to overcome the above-described problems.

(1) In a method of attaching a sensor to a pickup head for fixing the sensor to a main body of the pickup head with an adhesive agent, the sensor is positioned to an attaching position of the main body of the pickup head, a first adhesive agent whose force occurring at the time of curing is small is applied so as to temporarily fix the sensor to the main body of the pickup head, and after the curing of the first adhesive agent, a second adhesive agent whose force occurring at the time of curing is greater than that of the first adhesive agent is applied so as to finally fix the sensor to the main body of the pickup head.

In this method, since the sensor (light receiving element) is temporarily fixed to the main body of the pickup head with the first adhesive agent whose tensile force occurring at the time of curing is small, it is possible to sufficiently suppress the positional offset of the sensor at the time of the curing (attachment) of the first adhesive agent. In addition, after the curing of the first adhesive agent, the second adhesive agent whose tensile force occurring at the time of curing is greater than that of the first adhesive agent is applied to fix the pickup head. Although the tensile force of the second adhesive agent occurring at the time of curing is large, since the sensor has already been temporarily fixed by the first adhesive agent, the positional offset of the sensor due to the tensile force occurring at the time of the curing of the second adhesive agent is suppressed, so that the sensor can be attached with high accuracy.

In addition, since the sensor is fixed to the main body by applying the second adhesive agent, it is possible to suppress the positional change of the sensor accompanying the expansion or contraction of the first adhesive agent with respect to the temperature change. Accordingly, it is possible to sufficiently ensure reliability with respect to the change in the ambient temperature.

The first adhesive agent referred to herein is an adhesive agent whose content of glass filler as its component is small or which contains no glass filler, and the second adhesive agent referred to herein is an adhesive agent whose content of glass filler as its component is large (larger than that of the first adhesive agent).

(2) A light receiving element of the sensor is disposed between two opposing ribs provided at a sensor attaching position of the main body of the pickup head, the first adhesive agent is applied between an inner side of each of the ribs and the light receiving element, and the second adhesive agent is applied between an outer side of each of the ribs and a plate to which the light receiving element is attached.

In this method, the light receiving element of the sensor is disposed between the opposing ribs provided on the main body, and the first adhesive agent is applied between the inner side of each of the ribs and the light receiving element. Since the light receiving element is fixed to the main body by the first adhesive agent, it is possible to suppress the positional offset of the light receiving element at the time of the curing of the first adhesive agent.

In addition, the second adhesive agent is applied on the outer sides of the ribs between the outer side of each of the ribs and the plate to which the light receiving element is attached, thereby fixing the plate to the main body. Since the plate is fixed to the main body by the second adhesive agent, it is possible to suppress the positional change of the plate accompanying the change in the ambient temperature, with the result that it is possible to suppress the positional change of the light receiving element attached to the plate. Consequently, it is possible to sufficiently ensure reliability with respect to the change in the ambient temperature.

In addition, as for the aforementioned sensor, one which is difficult to be deformed in the process of attaching the sensor is suitable, and one whose material is, for example, stainless steel is suitable.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1is a side view of a pickup head in accordance with an embodiment of the invention, andFIG. 2is a bottom view of the pickup head.

In a pickup head1in this embodiment, a laser diode3(hereafter referred to as the LD3), which is a light emitting element, is disposed on a side surface of a main-body base2. In addition, a sensor portion5having a photodiode12(hereafter referred to as the PD12), which is a light receiving element, is attached to a bottom surface of the main-body base2.

FIGS. 3A and 3Bare schematic diagrams illustrating the sensor portion. The sensor portion5is arranged such that a PD12is attached to a plate11made of stainless steel. The plate11has an opening11ain its central portion, as shown in FIG.3B. The PD12is fixed to the plate11so as to be positioned at the center of the opening11aby soldering PD's pins (leads)12ato the plate11, for example. Two positioning holes11bare formed in the plate11.

Further, two opposing ribs15are formed on the bottom surface of the main-body base2. The interval between inner sides of these two opposing ribs15is slightly longer than the length of the PD12. In addition, the interval between outer sides of the two opposing ribs15is slightly shorter than the length of the opening11aformed in the plate11.

When the two ribs15formed on the bottom surface of the main-body base2are inserted in the opening11aof the plate11, the PD12is located between the opposing ribs15. The positioning of the PD12is effected in this state, and the sensor portion5is fixed to the main-body base2with an adhesive agent. The positioning of the PD12is effected by using an jig7shown in FIG.1.

It should be noted that disposed inside the main-body base2are a beam splitter21for bending the light emitted from the LD3upwardly inFIGS. 1 and 4, a first focusing lens22for focusing the light bent by the beam splitter21onto a recorded surface of an optical disk25, and a second focusing lens23for focusing the light reflected by the recorded surface of the optical disk25and transmitted through the first focusing lens22and the beam splitter21(see FIG.4).

The positioning of the PD12using the aforementioned jig7is the operation of positioning the sensor portion5with respect to three perpendicular directions of X, Y, and Z such that the focal position of the second focusing lens23and the center of the light receiving surface of the PD12are aligned.

Hereafter, a detailed description will be given of the attaching method for fixing the sensor portion5to them a in-body base2with an adhesive agent.FIGS. 5Ato5C are diagrams illustrating this method.

Firstly, jig7is inserted into the positioning hole11bof the plate11and the position where the sensor portion5is attached to the main-body base2is adjusted. Specifically, the attaching position of the sensor portion5is adjusted such that the focal position of the second focusing lens23and the center of the light receiving surface of the PD12are aligned. This adjustment is effected by using the jig7. At this time, as shown inFIG. 5A, the PD12is located between the two opposing ribs15formed on the bottom surface of the main-body base2, and the two opposing ribs15are inserted in the opening11aof the plate11.

As described above, the interval between the inner sides of the two ribs15is slightly longer than the length of the PD12, and the interval between the outer sides of the two ribs15is slightly shorter than the length of the opening11aformed in the plate11. As for the sensor portion5, the position of the PD12with respect to the main-body base2can be changed concerning the three perpendicular directions of X, Y, and Z, and the focal position of the second focusing lens23and the center of the light receiving surface of the PD12are aligned.

In addition, since stainless steel is used as the material of the plate11making up a part of the sensor portion5, the plate11does not become deformed by the force acting at the time of adjustment, and the positioning of the attaching position can be effected with high accuracy.

As shown inFIG. 5D, there is a case in which the PD12is not positioned at the center between the ribs15when the focal position of the second focusing lens23and the center of the light receiving surface of the PD12are aligned. Even in this case, the positional offset of the PD12at the time of the curing of the adhesive agent is suppressed by the following procedures.

Upon completion of the positioning of the sensor portion5, an adhesive agent31whose tensile force (expanding or contracting force) occurring at the time of curing is small (hereafter, this adhesive agent will be referred to as the soft adhesive agent31) is applied between the inner side surface of each rib15and the PD12, and the soft adhesive agent31is allowed to cure (see FIG.5B). The soft adhesive agent31is an adhesive agent whose content of glass filler as its component is small or which contains no glass filler. At this time, the sensor portion5is held at the position adjusted by the jig7. In addition, since the tensile force of the soft adhesive agent31occurring at the time of curing is small, the position of the sensor portion5practically does not offset from the adjusted position at the time of the curing of the soft adhesive agent31applied between the inner side surface of each rib15and the PD12.

Accordingly, since the position of the sensor portion5after the curing of the soft adhesive agent31practically does not change from the aforementioned adjusted position, the accuracy with which the sensor portion5is attached is excellent. As the jig7, it is unnecessary to use an expensive one. Preferably, hardness of the soft adhesive agent31is not more than shore hardness D75. As the soft adhesive agent31, LCR0639 (produced by TOAGOUSEI CO., LTD.; shore hardness D61) can be used, for example. The soft adhesive agent31takes, for example, 5 to 20 seconds to be cured by irradiating ultraviolet light.

When the soft adhesive agent31is cured, the jig7is removed. At this time, the sensor portion5is temporarily fixed to the main-body base2by the soft adhesive agent31. It should be noted that the temporary fixation referred to herein is not such fixation that the position changes when a small force is applied. By the temporary fixation, the position of the sensor portion5does not change insofar as a relatively large force is applied.

Next, an adhesive agent32whose tensile force occurring at the time of curing is stronger than that of the soft adhesive agent31(hereafter referred to as the hard adhesive agent32) is applied between the outer side surface of each rib15and the plate11, and the hard adhesive agent32is allowed to cure (see FIG.5C). The hard adhesive agent32is an adhesive agent whose content of glass filler as its component is large (i.e., an adhesive agent which contains a greater amount of glass filler than the soft adhesive agent31). As this hard adhesive agent32cures, the sensor portion5is finally fixed to the main-body base2, and the attaching operation is thereby completed. Preferably, hardness of the hard adhesive agent32is not less than shore hardness D80. As the hard adhesive agent32, X-8803SS (produced by kyoriz CO., LTD.; shore hardness D84) can be used, for example. The hard adhesive agent32takes, for example, 20 to 60 seconds to be cured by irradiating ultraviolet light.

Although a larger tensile force than that of the soft adhesive agent31occurs at the time of the curing of the hard adhesive agent32, since the sensor portion5has already been fixed to the main-body base2by the soft adhesive agent31, the sensor portion's position does not offset from the adjusted position by the tensile force occurring when the hard adhesive agent32cures.

As for the sensor portion5which is finally fixed to the main-body base2by the above-described method, even if the soft adhesive agent31expands or contracts with respect to the change in the ambient temperature, since the hard adhesive agent32fixes the sensor portion5to the main-body base2, the position of the sensor portion5does not change.

Accordingly, the pickup head1with the sensor portion5fixed to the main-body base2by the above-described method is capable of sufficiently ensuring reliability with respect to the change in the ambient temperature.

FIG. 6shows a bottom portion of a pickup head in accordance with another embodiment of the invention. A PD12is attached to a plate11made of stainless steel. The PD12is fixed to the plate11so as to be positioned at the center of an opening11aby soldering PD's pins (leads)12ato the plate11, for example.

Two opposing ribs15are formed on the bottom surface of the main-body base. The interval between inner sides of these two opposing ribs15is slightly longer than the length of the PD12. In addition, the interval between outer sides of the two opposing ribs15is slightly shorter than the length of the opening11aformed in the plate11.

Firstly, jig7shown inFIG. 1is inserted into the positioning hole11bof the plate11and the position where the sensor portion5is attached to the main-body base is adjusted.

When the two ribs15formed on the bottom surface of the main-body base are inserted in the opening11aof the plate11, the PD12is located between the opposing ribs15.

Upon completion of the positioning of the sensor portion5, a soft adhesive agent31is applied between the inner side surface of each rib15and the PD12. The soft adhesive agent31is applied at a center point of each rib15. At this time, the sensor portion5is held at the position adjusted by the jig7.

When the soft adhesive agent31is cured, the jig7is removed. At this time, the sensor portion5is temporarily fixed to the main-body base by the soft adhesive agent31.

Next, a hard adhesive agent32is applied between the inner side surface of each rib15and PD12. The hard adhesive agent32is applied to both sides of the soft adhesive agent31.

In the above-described embodiments, the jig7is removed when the soft adhesive agent31is cured. The jig7may be removed after the hard adhesive agent32is applied or after the hard adhesive agent32is cured.

As described above, since the sensor is fixed to the main body of the pickup head with two kinds of adhesive agents including the first adhesive agent whose tensile force occurring at the time of curing is small and the second adhesive agent whose tensile force occurring at the time of curing is greater than that of the first adhesive agent, it is possible to suppress the positional offset of the sensor at the time of its attachment, and it is possible to sufficiently ensure reliability with respect to the temperature change as well.