Optical pickup for use in optical disk device and method of manufacturing the same

In an optical pickup, it is configured such that a first and a second thrust bearings of a motor rotation shaft, a lens holder to be moved in a thrust direction by the motor rotation shaft, and a preload unit which exerts preload of the thrust direction on the lens holder are included, and the second thrust bearing can adjust a position in the thrust direction. In addition, the first and second thrust bearings and the motor rotation shaft are made of conductor, and the optical pickup is manufactured by including the processes of: moving the second thrust bearing in a direction approaching to the motor rotation shaft till electrical continuity between the first thrust bearing and the second thrust bearing is obtained using an electrical continuity checker; subsequently moving the second thrust bearing in a direction departing from the motor rotation shaft; and subsequently fixing the second thrust bearing to the base.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical pickup for use in an optical disk device which records information on a recording surface of an optical disk and/or reproduces information recorded thereon.

2. Description of the Related Art

As correction means of spherical aberration for an optical disk, there is known means for correcting spherical aberration by moving a lens in an optical axis direction.

For example, Japanese Patent Application Laid-Open No. 2006-155839 discloses a configuration in which motor's rotating motion is converted into linear motion in a thrust direction and both a lens holder which abuts on a nut and a lens which is supported by and fixed to a lens holder are moved in an optical axis direction, by a screw mechanism which is combined by a lead screw formed on a motor rotation shaft and a nut engaged with the lead screw. As described above, in the configuration which obtains linear motion in the thrust direction by the screw mechanism, a backlash of the motor rotation shaft in the thrust direction can make a cause of vibration. In Japanese Patent Application Laid-Open No. 2006-155839, preload is exerted by a coil spring to bring the lens holder into contact with the nut. The preload is exerted in the order corresponding to the nut, the lead screw engaged with the nut, and the motor rotation shaft which fixes the lead screw, to bring the motor rotation shaft into contact with a thrust bearing provided at one end of the motor rotation shaft. As described above, there is the configuration that suppresses the backlash in the thrust direction by the preload.

FIG. 1 in Japanese Patent Application Publication No. 60-11536 discloses a configuration in which, in a mechanism that decelerates rotational speed of a motor rotation shaft by a worm gear, an adjustment screw is assembled at a tip end position of the motor rotation shaft; thrust adjustment is made by the adjustment screw; and then, the adjustment screw is fixed by the nut. In such configuration, an amount of movement of the motor rotation shaft in a thrust direction can be adjusted without exerting preload, and therefore, a backlash which makes a cause of vibration can be reduced.

In addition, Japanese Patent Application Laid-Open No. 2001-330027 discloses a configuration which can implement thrust adjustment at any time after assembling by providing display means for displaying an amount of movement of an adjustment screw in an axial direction of a rotation shaft.

In the thus configured optical pickup, there is a case that, after the nut and the lens holder abut on a stopper provided to control the movement in the thrust direction and stop, the nut and the lens holder will not move even if driven in a reverse direction. This is caused by that, when the nut and the lens holder stop by the stopper, the motor rotation shaft moves in the thrust direction by a reaction force from the stopper and a rotor mounted to the motor rotation shaft come in contact with a side surface in a motor case due to the movement, and consequently, a large frictional force is generated.

With respect to the above problems, in a configuration disclosed in Japanese Patent Application Laid-Open No. 2006-155839, it is possible to avoid that the motor rotor comes in contact with the side surface in the motor case, by increasing the preload of the coil spring to resist the reaction force from the stopper and to suppress the movement of the motor rotation shaft in the thrust direction. However, the preload of the coil spring continues to exert on each part during usual operation when reaction force from the stopper is not generated, and therefore, there is a possibility that movement in a reverse direction against the preload becomes difficult and there arise problems such as an increase in slide load and mechanical wear in a slide member such as a thrust bearing.

Meanwhile, Japanese Patent Application Publication No. 60-11536 and Japanese Patent Application Laid-Open No. 2001-330027 disclose the configuration in which the amount of movement of the motor rotation shaft in the thrust direction is adjusted by clamping the adjustment screw and contact between the motor rotor and the side surface in the motor case can be avoided. However, when the amount of movement of the motor rotation shaft in the thrust direction is set to zero, both ends of the motor rotation shaft come in contact with the adjustment screw and a thrust bearing while exerting a force thereon, and therefore, a slide resistance is generated. When a temperature rise is generated in such contact conditions, the amount of movement in the thrust direction due to an expansion of the motor rotation shaft is narrowed, and therefore, a further large slide resistance is generated. The increase in slide resistance becomes a load to the motor and leads to a lowering in output torque. On the contrary, when the amount of movement in the thrust direction is secured in order to decrease the slide resistance, the preload means is not provided in this configuration, and therefore, vibration in the thrust direction is generated. In this configuration, the amount of movement in the thrust direction needs to be strictly controlled in order to balance the reduction in slide resistance and the reduction in vibration level, and therefore, there is a possibility of a hindrance to improving production efficiency.

SUMMARY OF THE INVENTION

The present invention has been made to avoid contact between a motor rotor and a side surface in a motor case, and an object of the present invention is to provide an optical pickup in which a function that adjusts an amount of movement of a motor rotation shaft in a thrust direction is added to an optical pickup which had been enough by the configuration disclosed in Japanese Patent Application Laid-Open No. 2006-155839, and accordingly, a nut and a lens holder which stopped due to contact with a stopper are surely driven in a reverse direction and reliability is improved.

As means for solving the above problem, the present invention is configured such that, in an optical pickup which includes: a motor having a rotation shaft; a first thrust bearing at one end of the motor rotation shaft; a second thrust bearing at the other end of the motor rotation shaft; a base which fixes a motor case of the motor; a lead screw fitted to the motor rotation shaft; a screw mechanism which converts rotation of the lead screw into linear motion; a lens holder to be moved in a thrust direction by the screw mechanism; a lens to be held by the lens holder; and preload means for exerting preload of the thrust direction on the lens holder, the second thrust bearing can adjust a position in the thrust direction.

In addition, a first thrust bearing, a second thrust bearing, and a motor rotation shaft are made of conductor; and an optical pickup is manufactured by including the processes of: moving the second thrust bearing in a direction approaching to the motor rotation shaft till electrical continuity between the first thrust bearing and the second thrust bearing is obtained using an electrical continuity checker; subsequently moving the second thrust bearing in a direction departing from the motor rotation shaft; and subsequently fixing the second thrust bearing to the base.

Further, an optical pickup is manufactured by including the processes of: inserting a spacer made of conductor between the motor rotation shaft and the first thrust bearing, or between the motor rotation shaft and the second thrust bearing; moving the second thrust bearing in a direction approaching to the motor rotation shaft till electrical continuity between the first thrust bearing and the second thrust bearing is obtained using an electrical continuity checker; subsequently removing the spacer; and fixing the second thrust bearing to the base.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

First Embodiment

FIG. 1is a view showing a configuration of the optical pickup according to the first embodiment of the present invention.

InFIG. 1, reference numeral1denotes an optical disk,2denotes an optical pickup,21denotes a laser light source,22denotes a shaping lens,23denotes a coupling lens,24denotes a beam splitter,25denotes spherical aberration correction means,26denotes a reflecting mirror,27denotes an object lens,28denotes a detector lens, and29denotes a photo-detector.

The optical pickup2mounts the laser light source21, the shaping lens22, the coupling lens23, the beam splitter24, the spherical aberration correction means25, the reflecting mirror26, the object lens27, the detector lens28, and the photo-detector29in one case; and constitutes an optical system which performs recording and reproducing of information on and from the optical disk1.FIG. 1shows the optical pickup2comprising one optical system, however, a plurality of optical systems may be mounted in one case in order to accommodate a plurality of standards on optical disk1. In this case, a configuration can be made such that a component is shared in different optical systems. The laser light source21is a laser diode which oscillates and emits laser light having a specific wavelength corresponding to CD, DVD, BD, or HD-DVD. The shaping lens22, the coupling lens23, the beam splitter24, the reflecting mirror26, the object lens27, and the detector lens28are optical lens or an optical mirror made of glass or transparent plastic. Functionality coating is applied to a lens surface and a reflection surface if required. The spherical aberration correction means25is formed by an optical lens made of glass or transparent plastic and a mechanism which moves the optical lens in an optical axis direction of the lens. The optical lens which constitutes the spherical aberration correction means25may be of a two lenses configuration by adding one fixed lens. The photo-detector29is a semiconductor device which generates a voltage corresponding to light intensity irradiating a photo detection surface.

Laser light emitted from the laser light source21is made incident on the shaping lens22first. The shaping lens22is a lens which shapes laser light having an oval cross section, emitted from the laser light source21, to substantially a circular cross section. A curved surface is formed on a laser light incident surface and a laser light emitting surface of the shaping lens22. Next, laser light emitted from the shaping lens22is made incident on the coupling lens23. The coupling lens23has a function which converts the laser light diverged and emitted from the laser light source21into parallel light. The laser light converted into the parallel light is transmissive through the beam splitter24and reaches the spherical aberration correction means25. The spherical aberration correction means25has a driving mechanism of the lens and has a function which adjusts the laser light that has passed through the lens to weak divergent or weak convergent light by moving the lens in the optical axis direction. Further, the laser light is made incident on the object lens27via the reflecting mirror26and is collected on a recording surface of the optical disk1by the object lens27to form a beam spot. The optical pickup2performs recording and reproducing of information by the beam spot. In recording, on/off operation of the laser light source21is performed on the basis of recording information, and a recording pit is formed on the optical disk1by the beam spot to perform writing of information. In reproducing, laser light impinging upon the recording pit of the optical disk1and being reflected is picked up by the object lens27, and the laser light is introduced onto the detection surface of the photo-detector29via the reflecting mirror26, the spherical aberration correction means25, the beam splitter24, and the detector lens28, in the order reverse to a forward route. The photo-detector29detects returned light from the optical disk1at an internal detection surface and performs reading of information. In addition, it is configured such that focus control and tracking control of the object lens27, and lens position control of the spherical aberration correction means25are performed by processing a detection signal.

FIGS. 2 and 3show a configuration and a manufacturing method of the spherical aberration correction means25mounted on the optical pickup2according to the first embodiment of the present invention.

InFIGS. 2 and 3, reference numeral251denotes a lens,252denotes a lens holder,253denotes a screw mechanism,254denotes preload means,255denotes a motor,255adenotes a motor case,255bdenotes a rotation shaft,255cdenotes a lead screw,255ddenotes a first thrust bearing,256denotes a second thrust bearing,257denotes a base,258denotes a stopper,259denotes an assembly jig,259adenotes a driver,259bdenotes an electrical continuity checker,259cdenotes a probe, and259ddenotes a bonding instrument. The spherical aberration correction means25is incorporated in the optical pickup2shown inFIG. 1.

The spherical aberration correction means25is of a configuration in which the base257is mounted with the lens251, the lens holder252, and the screw mechanism253that are driven units; the motor255that is a power driver; and the preload means254, the second thrust bearing256, and the stoppers258that are peripheral members. The lens251is an optical lens made of transparent resin such as polyolefin with high transmittance, or glass. Correction of the spherical aberration is implemented by diverging and converging the laser light incident on the lens251by moving the lens251in the optical axis direction. The lens holder252has an aperture to hold the lens251, and the lens251is fixed by being fitted and adhered to the aperture. The lens holder252is suspended by a guiding shaft, and is configured so as to move in the optical axis direction of the lens251together with the lens251. The screw mechanism253is a nut or a claw formed with a female screw on its inner periphery. In the case where the screw mechanism253is formed by a nut as shown inFIG. 2, the nut is rotated together with rotation of the lead screw255cto be engaged therewith, and therefore, a rotation stop (not shown in the drawing) needs to be provided. The rotation stop can be realized by forming a projection or a groove on the nut and making the same abut on the lens holder252or an external member. In the case where the screw mechanism253is configured by a claw, it may be a configuration that a claw member is made and the same is fixed to the lens holder252, or a configuration that the claw is directly formed on the lens holder252. The preload means254is a member such as a spring which exerts preload of the optical axis direction on the lens holder252. The motor255is a small size direct current motor or a stepping motor which can be mounted on the optical pickup2. The lead screw255cwith grooves formed at a constant pitch on its outer periphery is formed on the output side of the rotation shaft255b. The lead screw255cis formed by direct processing on the rotation shaft255bof the motor255, or formed as a different part and then, fixed to the rotation shaft255bby caulking or the like. In addition, the motor255has the first thrust bearing255dwhich is formed at the shaft end on the opposite side to the output side of the rotation shaft255b. The first thrust bearing255dis a plate which stops movement of the rotation shaft255bin a thrust direction. The second thrust bearing256is a screw or a pin which is engaged with the base257and mounted at the shaft end on the output side of the rotation shaft255b. The second thrust bearing256is a plate which stops movement of the rotation shaft255bin the thrust direction. The second thrust bearing256has a function which adjusts a position in the thrust direction, and accordingly, an amount of movement of the rotation shaft255bin the thrust direction is adjusted. The base257is a case of the spherical aberration correction means25, and is a member which fixes the motor case255aand the second thrust bearing256. The base257is required to reduce weight in consideration of impact resistance for the optical pickup2, and therefore, resin is used. The present first embodiment is formed especially by resin which blocks electricity. This electrically insulates the first thrust bearing255dfrom the second thrust bearing256. This insulation is a function necessary for improving productivity with a manufacturing method to be described later. The stopper258is a member which restricts an amount of movement of the lens holder252or the screw mechanism253in the thrust direction.

Next, an operation of the spherical aberration correction element25will be described. The spherical aberration correction element25is driven by a motor255. The motor255rotates the rotation shaft255bby generating a torque around the rotation shaft255bby electromagnetic action by flowing a current through coils formed inside the motor. The rotation of the rotation shaft255bmakes the lead screw255crotate, so that the screw mechanism253, which performs linear motion along the groove of the lead screw255c, moves in the thrust direction. The lens holder252conducts movement, constantly being abutted on the screw mechanism253by the preload means254, and accordingly, the lens251is moved in the optical axis direction. The amount of movement of the lens holder252and the screw mechanism253in the thrust direction is restricted by the stoppers258. When the lens holder252and the screw mechanism253abut on the stopper258, the lens holder252and the screw mechanism253stop at a position as abutting on the stopper258, however, the rotation shaft255breceives a reaction force from the stopper258and starts to move in a reverse direction. The rotation shaft255bmoves till the rotation shaft255babuts on the first thrust bearing255dor the second thrust bearing256, after that, the rotation shaft255bcannot move due to loss of synchronism of the motor255and stops.

Conventionally, the second thrust bearing256mounted at the shaft end on the output side of the rotation shaft255bhas not been provided with a position adjustment function, and an amount of movement to the output shaft end side of the rotation shaft255bhas not been controlled. Therefore, there has been a case where the motor rotor had abutted on the side surface in the motor case255aand had stopped before the rotation shaft255bhas abutted on the second thrust bearing256. As described above, when the motor rotor stops due to the contact in the motor, there arises a drawback that escapement in the reverse direction cannot be made because of a large contact resistance. Consequently, in the present first embodiment, a position adjustment function with respect to the thrust direction is provided at the second thrust bearing256which is provided at the shaft end on the output side of the rotation shaft255b, and the position in the thrust direction of the second thrust bearing256is adjusted so as to abut on the second thrust bearing256before contact is made in the motor.

Next, a method of manufacturing the spherical aberration correction means25of the optical pickup2according to the first embodiment of the present invention will be described.

First, the motor255is mounted to the base257a. Next, the screw mechanism253is engaged with the lead screw255cof the motor255. Engagement of the screw mechanism253can be implemented by rotating and pulling in the rotation shaft255b. As for the rotation of the rotation shaft255b, there are methods in which a current is flown through the motor255to drive and in which a groove fitting to the driver259ais provided at the tip end of the rotation shaft255bto rotate by the driver259a. Next, the lens holder252is loaded with so as to abut on the screw mechanism253, and the base257bis fixed to the base257awhile exerting preload by the preload means254. Since an aperture with which the second thrust bearing256is engaged is provided in the base257b, the driver259ais inserted through the aperture to rotate the rotation shaft255b, and a position of the lens holder252can be readjusted. Next, the second thrust bearing256is mounted on the aperture provided in the base257busing the assembly jig259. The second thrust bearing256is assembled while adjusting an amount of movement of the rotation shaft255bin the thrust direction. First, the second thrust bearing256is fastened in a direction of the motor case255aby rotating the driver259a. At this time, the electrical continuity checker259bis provided between the driver259aand the probe259cabutted on the first thrust bearing255d, and the fastening operation is performed till electrical continuity is confirmed by the electrical continuity checker259b. After confirming the electrical continuity, the driver259ais reversely rotated for a predetermined angle to loosen the second thrust bearing256. After that, adhesive is applied to the second thrust bearing256by the bonding instrument259d, to fix to the base257b. As described above, the spherical aberration correction means25is manufactured, and accordingly, adjustment operation of the amount of movement of the rotation shaft255bin the thrust direction can be efficiently implemented.

As described above, according to the present first embodiment, the amount of movement of the rotation shaft255bin the thrust direction can be accurately controlled by the second thrust bearing256. With this, when the lens holder252and the screw mechanism253, which are stopped by abutting on the stopper258, are driven in the reverse direction, operation can be surely performed. In addition, the adjustment operation of the second thrust bearing256can be easily implemented by the assembly jig259using the electrical continuity checker259b, and therefore, operating efficiency is good and productivity is high. With these features, an optical pickup with high reliability and high productivity can be provided.

Second Embodiment

An optical pickup according to a second embodiment of the present invention will be described with reference toFIG. 4.

FIG. 4shows a configuration and a manufacturing method of spherical aberration correction means25mounted on an optical pickup2according to the second embodiment of the present invention.

InFIG. 4, reference numeral259edenotes a spacer and other configuration is the same asFIG. 3.

In the present second embodiment of the present invention, an aperture which is for attaching and detaching a spacer is provided on a base257b. The aperture is provided in a radial direction between a rotation shaft255band a first thrust bearing255d, or between the rotation shaft255band a second thrust bearing256.FIG. 4shows a structure in which the aperture is provided on the second thrust bearing256side. The spacer259eis a metal piece having a predetermined thickness and is sandwiched between the rotation shaft255band the second thrust bearing256, and accordingly, a distance between the two is correctly controlled.

A method of manufacturing spherical aberration correction means25of an optical pickup2according to the second embodiment of the present invention will be described.

First, a motor255is mounted to a base257a. Next, a screw mechanism253is engaged with a lead screw255cof the motor255. Engagement of the screw mechanism253can be implemented by rotating and pulling in the rotation shaft255b. Next, a lens holder252is loaded with so as to abut on the screw mechanism253, and the base257bis fixed to the base257awhile exerting preload by preload means254. Next, the spacer259eis inserted through the aperture for attaching and detaching the spacer provided in the base257band is sandwiched between the rotation shaft255band the second thrust bearing256. Next, the second thrust bearing256is mounted on the aperture provided in the base257busing an assembly jig259. The second thrust bearing256is assembled while adjusting an amount of movement of the rotation shaft255bin a thrust direction. First, the second thrust bearing256is fastened in a direction of the motor case255aby rotating the driver259a. At this time, an electrical continuity checker259bis provided between the driver259aand a probe259cabutted on the first thrust bearing255d, and the fastening operation is performed till electrical continuity is confirmed by the electrical continuity checker259b. After confirming the electrical continuity, removal operation of the spacer259eis performed. After that, adhesive is applied to the second thrust bearing256by a bonding instrument259d, to fix to the base257b. As described above, the spherical aberration correction means25is manufactured, and accordingly, adjustment operation of the amount of movement of the rotation shaft255bin the thrust direction can be efficiently implemented.

As described above, according to the present second embodiment, the amount of movement of the rotation shaft255bin the thrust direction can be accurately controlled by the spacer259e. With this, the adjustment operation of the second thrust bearing256can be easily implemented, and therefore, operating efficiency is good and productivity is high. With these features, an optical pickup with high productivity can be provided.