JP3500094B2 - Optical pickup - Google Patents

Description

Description: BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to an optical pickup used in an optical disk drive, and more particularly to a driving device for minutely moving an objective lens in a focus direction or a tracking direction. 2. Description of the Related Art An objective lens driving device for an optical pickup is a device for causing an objective lens to follow the surface runout and eccentricity of an optical disk so that a light beam is always focused on a signal surface of the disk. 6 to 8 show an example of a conventional optical pickup, in which a movable portion (2) having an objective lens (1) at one end has a fixed portion via four plate springs (7) which are both used for electricity. Supported by (5). Yoke (51) provided on fixed part (5)
And a magnet (6), a focus coil (3b) and a tracking coil (3a) are provided in the movable part (2), and an electromagnetic force is generated by energizing the coils (3b) (3a). The movable portion (2) is slightly moved in the focus direction (hereinafter, Z direction) or the tracking direction (hereinafter, Y direction) to condense the light beam on the signal surface of the disk. In the above optical pickup, the center of gravity of the movable part (2) is located on the lower surface of the movable part (2) opposite to the lens mounting part, and the driving force of the focus coil (3b) is provided. The balance weight (4) for aligning with the center point of the action is fixed by bonding. When the position of the center of gravity of the movable portion (2) including the objective lens (1) in the direction orthogonal to the Z direction and the Y direction (hereinafter referred to as X direction) is shifted from the center point of the driving force of the focus coil (3b). 10, pitching, which is unnecessary vibration, occurs in the movable portion (2). Also, the moving parts
If the position of the center of gravity in the Y direction in (2) and the action center point of the tracking driving force by the tracking coil (3a) are shifted,
As shown in FIG. 11, rolling, which is unnecessary vibration, occurs in the movable portion (2). [0004] When the unnecessary vibration occurs, the servo characteristics are adversely affected. Generally, when the unnecessary vibration frequency is close to the gain intersection frequency of the servo system, the phase margin and the gain margin become small, and the servo system becomes unstable. However,
In the configuration of the conventional optical pickup, the actual center of gravity varies from the designed center of gravity due to the parts accuracy and the assembly accuracy. Due to the variation in the position of the center of gravity, unnecessary resonance occurs at the time of minute movement in the Z direction or the Y direction. Conventionally, in order to suppress the unnecessary resonance,
At the base end of the leaf spring (7) on the fixing part (5) side, damping rubber (10)
To attenuate the amplitude of the unwanted resonance (Japanese Unexamined Patent Publication No.
121893). However, in order to cope with the trend toward smaller and thinner recording / reproducing devices, optical pickups are also required to be reduced in size, and in particular, the size in the Z direction which affects the thickness of the device is greatly restricted. > Z direction dimension. Here, for example, if the weight changes by ΔM due to a component size error, and the distance from the center point of the focus driving action to the position where the weight changes is R, the moment ΔM × R with respect to the center point. Is generated, which causes unnecessary resonance. This means that even if there is a weight change of the same ΔM, the influence becomes larger as the distance R from the focus driving action center point becomes larger, and the X-direction in which the dimension of the movable portion (2) is longer is larger. However, the effect of component errors increases. Therefore, unnecessary resonance is likely to occur during driving in the focus direction. There is a demand for recording / reproducing equipment to have high recording density in addition to miniaturization and thinning, and an optical pickup corresponding to this is required. To perform high-density recording and playback,
The disk medium is rotated at a high speed for use. For this reason, it is necessary for the movable part (2) of the optical pickup to increase the rigidity of the leaf spring (7) to increase the primary resonance frequency FO, and to set the rotation frequency <the primary resonance frequency. Here, the primary resonance frequency is defined as an objective lens.
This is the natural frequency of the vibration system constituted by the weight M of the movable part (2) including (1) and the spring rigidity K of the leaf spring (7).
FO = 1 / 2π√K / M by using the weight M of the plate spring 7 and the spring rigidity K of the leaf spring (7). When the rigidity of the leaf spring (7) is increased, as a result, the ratio of the damping amount to the spring rigidity changes, so that the resonance amplitude increases, and it becomes impossible to obtain sufficient damping characteristics. In particular, unnecessary resonance in the Z direction, which tends to have an influence on component accuracy and assembly accuracy, has become a problem. Further, with the further miniaturization and thinning of recording / reproducing devices, pickups are also required to be further miniaturized and thinned. In particular, it is necessary to limit the dimension in the Z direction corresponding to the thinning. In addition, the degree of the dimension in the X direction >> the dimension in the Z direction was further increased, and the influence of the focus direction became more and more noticeable. The present invention clarifies a specific configuration that solves the above problem and realizes a small and thin optical pickup. [0010] The optical pickup of the present invention comprises a movable part (2) having an objective lens (1) at one end and a movable part (2) via a leaf spring (7) which is also used for conducting electricity. Has a fixed part (5) for supporting the moving part (2), and energizes the focus coil (3b) and the tracking coil (3a) on the movable part (2) to control the movement of the movable part (2) in the focusing direction and the tracking direction. In an optical pickup, a weight material (12) that has fluidity at the time of being attached to a counterpart member, but solidifies in a short time, such as solder and adhesive, is attached to the end of the movable portion (2). movable part
The position of the center of gravity in the direction orthogonal to both the tracking direction and the focus direction in (2) is made substantially coincident with the center point of the driving force acting on the movable portion (2). Since the position of the center of gravity of the movable section (2) in the X direction (longitudinal direction) substantially coincides with the center of the focus driving force, unnecessary resonance can be suppressed. Movable part (2)
Of the weight material (12) is shifted in advance in a direction opposite to the position where the weight material (12) is to be attached, with respect to the central point of action of the driving force, and the weight material (12) is attached in accordance with the amount of the displacement. The center of gravity can be easily adjusted by adjusting the amount. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The construction of the optical pickup of the present invention shown in FIGS. 1 to 3 is basically the same as that of the prior art shown in FIGS. 6 to 9, with one end having an objective lens (1) and the other end. Focus coil (3
b) and the movable part (2) having the tracking coil (3a)
It is supported by the fixed part (5) via a leaf spring (7) that also serves as a current. The leaf spring (7) is formed of beryllium copper, and one end is provided on both side surfaces of the movable portion (2) opposite to the lens mounting portion (21).
The other ends extend in parallel beyond the lens mounting part (21), and the other end extends over the conductive pattern (9a) on the relay board (9).
Soldered. The relay board (9) is bonded and fixed to a holding member (8), and the holding member (8) is bonded and fixed to one end of a fixing portion (5). The fixed part (5) is provided with a yoke (51) that penetrates the air core part of the focus coil (3b) and faces the tracking coil (3a), and magnets (6) and (6) are provided on the yoke (51). Adhesively fixed to form a magnetic circuit, focus coil (3b)
And a magnetic field is applied to the tracking coil (3a). The ends of the tracking coil (3a) and the focus coil (3b) are connected to the leaf spring (7), and power is supplied from the relay board (9) via the leaf spring (7). The holding member (8) is provided with recesses (8a) and (8a) at positions corresponding to the leaf springs (7) and is filled with damping rubber (10). The primary resonance amplitude is suppressed and unnecessary resonance is attenuated by penetrating the spring (7). The holding member (8) and the relay board (9) are provided with gaps (81) and (91) in order to secure an optical path of the laser beam, and the gaps (81) and (91) are provided. The laser beam that has passed through is turned 90 ° by the rising mirror (11) and the objective lens
It is emitted from (1). As shown in FIG. 2, a balance weight (4) for balancing the weight with the objective lens (1) is adhered and fixed to the lower surface of the coil-side base end of the movable part (2). Since the movable part (2) is supported by the fixed part (5) as described above, the movable part (2) is bent in the direction of the optical axis of the objective lens (1) by bending of the leaf spring (7). Drive direction, F drive direction in FIG. 2), and a direction perpendicular to the optical axis.
(Tracking drive direction, T drive direction in FIG. 1). The feature of the present invention is that the balance weight
(4) After attaching the movable part (2) including the objective lens (1) to the fixed part (5), solder (12) is attached to the coil side end of the movable part (2).
By attaching a), the position of the center of gravity in the X direction is made to substantially coincide with the center point of the driving force acting on the movable portion (2). A PCB substrate (13) having a solderable copper foil (13a) is fixed to the coil-side end of the movable part (2) by bonding or the like. The center of the copper foil part (13a) is the Z of the movable part (2).
It corresponds to the height of the directional center of gravity. When the solder is melted and attached to the copper foil portion (13a), it solidifies instantaneously. The position of the center of gravity of the movable portion (2) in the X direction can be adjusted depending on the amount of the attached solder. Since the center of the copper foil portion (13a) coincides with the height of the position of the center of gravity of the movable portion (2) in the Z direction, the copper foil portion (13a)
Does not change the position of the center of gravity in the Z direction. Therefore, it is possible to adjust the position of the center of gravity in the X direction without affecting the rolling during the tracking drive. Here, the variation of the center of gravity caused by the variation of the component accuracy and the assembly accuracy is random, and there is no guarantee that the adjustment can be always performed by attaching the solder, and the end of the movable portion (2) on the coil side is scraped off. In some cases, the weight must be adjusted. Since the movable part (2) is in an unstable state supported by the leaf spring (7), it is difficult to cut off a part of the movable part (2). If a PCB substrate having a copper foil portion is also provided at the end of the movable portion (2) on the side of the objective lens (1) and the weight can be adjusted by solder adhesion, the problem can be solved, but there is a problem in the working space and the like, which is impossible. It is. Therefore, the center of gravity of the movable portion (2) is shifted in advance to the objective lens (1) side, that is, the side opposite to the position where the solder is to be attached to the movable portion (2) with respect to the center point of the focus driving force. To design. If the amount of design movement of the center of gravity of the movable part (2) is made larger than the amount of deviation of the center of gravity caused by variations in component accuracy / assembly accuracy, the objective lens (1) is always moved with respect to the focus driving force action center point. It is possible to shift the center of gravity to the side. Thus, the solder is always attached to the PCB board (12) provided at the coil side end of the movable section (2).
The position of the center of gravity of the movable portion (2) in the X direction can be adjusted. The actual position of the center of gravity of the movable portion (2) is adjusted by adding the amount of solder while measuring the servo transfer function. If there is a displacement of the center of gravity in the X direction, it appears as unnecessary resonance in the servo transfer function in the focus direction. In the servo transfer function, the center of gravity of the movable part (2) is
When the lens is located closer to the objective lens (1) than the focus driving force acting center, that is, before solder is attached, unnecessary resonance appears as shown in FIG. On the other hand, if the amount of solder attached is too large in the adjustment of the center of gravity in the X direction,
When the center of gravity is located on the solder adhesion side of the focus driving force action center, as shown in FIG. 13, the peak shape of the unnecessary resonance of the gain is inverted and the phase is also reversed, so that it is clearly identified. it can. If the amount of added solder is adjusted optimally, the servo transfer function will be in a state without any unnecessary resonance as shown in FIG. As described above, by a simple soldering operation,
Since the position of the center of gravity of the movable portion (2) in the X direction can be made coincident with the center of action of the focus driving force, it is possible to prevent the occurrence of unnecessary resonance when the focus driving force is generated, and to achieve a favorable miniaturization of servo characteristics. A suitable optical pickup can be configured. Further, since the balance of the center of gravity in the tracking direction is not lost, pitching can be completely removed without rolling. FIGS. 4 and 5 show another embodiment in which a thin plate of beryllium copper (14) is provided at the end of the movable portion (2) in correspondence with the solder adhesion area, and the solder is adhered on the plate. Is shown. In the practice of the present invention, the weight material to be attached for adjusting the position of the center of gravity of the movable portion (2) is not limited to solder, but has fluidity immediately before the attachment, such as an adhesive. However, a weight material that solidifies in a short time if adhered may be used. The present invention is not limited to the configuration of the above embodiment, and various modifications can be made within the scope of the claims.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a plan view of an optical pickup. FIG. 2 is a sectional view taken along line AA of FIG. FIG. 3 is a side view of the movable portion on the side where solder is attached. FIG. 4 is a sectional view of another embodiment of a solder attachment portion. FIG. 5 is a side view of the same. FIG. 6 is a perspective view of an optical pickup in which a movable part and a fixed part are separated. FIG. 7 is a plan view of a conventional optical pickup. FIG. 8 is a cross-sectional view along the line AA of FIG. 7; FIG. 9 is a side view of the optical pickup. FIG. 10 is an explanatory view of a pitching-free resonance of a movable portion. FIG. 11 is an explanatory diagram of a rolling unnecessary resonance of a movable portion. FIG. 12 is a graph of a servo transfer function when the center of gravity of the movable part is located on the lens side. FIG. 13 is a graph of a servo transfer function when the center of gravity of the movable part is located on the coil side. FIG. 14 is a graph of a servo transfer function when the center of gravity of the movable diagram substantially coincides with the center of action of the focus driving force.

Claims (1)

(57) [Claim 1] A movable section (2) having an objective lens (1) at one end and a fixed section supporting the movable section (2) via a leaf spring (7). (5) an optical pickup for controlling the movement of the movable part (2) in the focusing direction and the tracking direction by energizing the focus coil (3b) and the tracking coil (3a) on the movable part (2). The weight material (1) which has fluidity at the time of adhering to a counterpart member but solidifies in a short time is attached to the end of the movable portion (2).
By attaching 2), the position of the center of gravity of the movable portion (2) in the direction orthogonal to both the tracking direction and the focus direction is made substantially coincident with the center point of the driving force acting on the movable portion (2). An optical pickup characterized in that a height position of the weight material (12) attached to the focus direction of the portion (2) substantially coincides with a height position of the center of gravity of the movable portion (2) in the focus direction.