JP2002312961A - Objective lens actuator - Google Patents

Abstract

(57) Abstract: An object of the present invention is to reduce the amplitude of a resonance component caused by elastic deformation in a movable part at an installation position of an objective lens, and improve a gain margin of higher-order resonance in an actuator control operation. SOLUTION: In a frame body 12, overhang portions 12-1a, 12-1b, 12- in a tangential direction T supporting a focusing coil 7 and tracking coils 8a, 8b so as to bridge a magnetic circuit gap. 1
c, 12-1d are asymmetrical in the tangential direction T with respect to the plane formed by the focus axis F and the radial axis R, so that the rigidity distribution in the tangential direction T is asymmetric. That is, in the tangential direction T of the frame body 12, the projecting portions 12-1 a and 12-1 on the side not supported by the linear spring 9.
The overhang amounts at b, 12-1c, and 12-1d are made larger than those at the opposite side.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is applied to an optical disk driver or the like mounted on an optical information recording and / or reproducing apparatus, and is an objective lens actuator which is a drive system for performing focusing control and tracking control on an objective lens. About.

[0002]

2. Description of the Related Art Actuators used for active control of an optical disk driver are required to have characteristics that can be controlled up to a high frequency region as the speed of products increases. For this reason, characteristics that require direct improvement include:
Along with the increase in sensitivity, there is a margin for gain in a control system for elastic deformation resonance in the movable portion structure, so-called high-order resonance. The meaning of this characteristic is how much a gain difference between the gain of the actuator itself at the servo gain crossover frequency and the peak gain of the higher-order resonance of the actuator under use conditions.

The need to improve this is due to the principle reasons of servo systems. The servo stiffness is determined by the open loop characteristic: how much the loop gain or gain crossover frequency of the loop transfer function can be increased. If these are high, it becomes possible to follow a high vibration acceleration or disturbance acceleration when the optical disk as a medium rotates at high speed.

However, vibration control generally requires consideration of not only gain but also phase. Usually, the displacement response of the actuator is a second-order lag system with respect to the input signal,
In a frequency region sufficiently higher than the natural vibration frequency determined by the rigidity of the supporting structure and the movable mass, the displacement response phase becomes −18.
It will have a delay of 0 degrees or more. However, the phase is -18
Zero degrees is a so-called reverse-phase response, in which servo cannot be applied and oscillation occurs.

For this reason, the servo mechanism electrically uses the phase compensation so that the phase is advanced from -180 degrees near the gain crossover frequency. However, advancing the phase by the compensation circuit inevitably causes an increase in the gain in a frequency region higher than the gain crossover frequency, so that the gain margin indicated by the actuator alone on the open loop characteristic is reduced. become.

Further, as described above, since the gain crossover frequency itself is required to be set high,
A higher gain margin is required for the higher speed. if,
If this is insufficient, the peak gain of the higher-order resonance in the open loop characteristic will exceed 0 (dB). At this time, since the phase is delayed by -180 degrees or more in that region, the above-described oscillation occurs.

[0007]

However, there is sufficient room for improving the characteristics on the actuator side so that the oscillation does not occur as described above.
This is also very severe in practice. As with most technological developments, the degree of improvement increases to some extent with efforts or measures, but from some point the degree of improvement saturates. In recent years, this tendency has become particularly strong. With the conventional technology, it is becoming unavoidable that a trade-off such as a considerable increase in cost or deterioration in assembly workability is caused in the structure or material.

For example, in general, in order to secure a gain margin,
It is often the case that the higher resonance frequency is increased or the vibration loss of the structure is increased. By the way, in order to increase the resonance frequency, it is necessary to increase the structural rigidity or reduce the distributed mass. In order to increase the structural rigidity, it is necessary to use a material having a high elastic modulus or to increase the geometrical second moment of area. However, materials with a high modulus of elasticity generally tend to have low vibration loss or high mass density, and attempting to increase the geometrical moment of inertia of the shape increases the distribution mass due to an increase in wall thickness. Improvement is unlikely.

As a method of improving the gain margin by lowering the resonance magnification itself in principle, one method is to use a portion where the vibration amplitude of the problematic resonance is large. By attaching the weight via a spring or a structure having elasticity, a function of a dynamic damper may be provided.
However, in that case, it is necessary to prepare the weight as a separate part. Further, since it is necessary to attach the weight with a spring or an adhesive having elasticity, it is conceivable that the number of assembling steps is increased, which leads to an increase in cost or a side effect of a decrease in reliability.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned conventional problems, to reduce the amplitude of a resonance component due to elastic deformation in a movable portion at an installation position of an objective lens, and to improve a gain margin of higher-order resonance in an actuator control operation. An object of the present invention is to provide an objective lens actuator as described above.

[0011]

According to one aspect of the present invention, there is provided an optical disk recording / reproducing apparatus, comprising: a lens holder for holding an objective lens;
A fixed magnetic circuit provided on the base body, a solenoid coil for generating a focusing thrust and a tracking thrust in accordance with a current value by the fixed magnetic circuit, and a movable portion provided with the lens holder; An elastic supporting member that is displaceably supported in accordance with the amount of generation, wherein the optical axis of the objective lens is arranged at the operating center of the movable part. It is characterized in that a portion as the above asymmetric component is formed.

According to a second aspect of the present invention, in the objective lens actuator according to the first aspect, the shape of the frame structure of the lens holder is asymmetric in a tangential direction with respect to a plane formed by the focus axis and the radial axis. Thus, the rigidity distribution in the tangential direction is made asymmetric.

According to a third aspect of the present invention, in the objective lens actuator according to the first aspect, the shape of the frame structure of the lens holder is asymmetric in a radial direction with respect to a plane formed by the focus axis and the tangential axis. Thus, the rigidity distribution in the radial direction is asymmetric.

According to a fourth aspect of the present invention, in the objective lens actuator according to the second or third aspect, a part of the projecting portion in the frame structure of the lens holder is asymmetric.

According to a fifth aspect of the present invention, in the objective lens actuator according to the first aspect, the inner shape of the frame structure of the lens holder is asymmetric in a tangential direction with respect to a plane formed by the focus axis and the radial axis. By doing so, the rigidity distribution in the tangential direction is made asymmetric.

According to a sixth aspect of the present invention, in the objective lens actuator according to the first aspect, the inner shape of the frame structure of the lens holder is asymmetric in a radial direction with respect to a plane formed by the focus axis and the tangential axis. By doing so, the rigidity distribution in the radial direction is asymmetric.

According to a seventh aspect of the present invention, in the objective lens actuator according to the fifth or sixth aspect, the thickness of a corner portion inside the frame structure of the lens holder is asymmetric.

According to an eighth aspect of the present invention, in the objective lens actuator according to the first aspect, the shape of the frame structure of the lens holder is asymmetric in a focus direction with respect to a plane formed by the radial axis and the tangential axis. Thereby, the rigidity distribution in the focus direction is made asymmetric.

According to a ninth aspect of the present invention, in the objective lens actuator of the first aspect, the mass of the solenoid coil provided in the tangential direction of the lens holder is asymmetric with respect to a plane formed by a focus axis and a radial axis. By doing so, the mass distribution in the tangential direction is asymmetric.

With the above-mentioned respective structures, the rigidity distribution or the mass distribution in the frame structure of the movable portion, which is usually formed substantially symmetrically with respect to the optical axis of the lens, is asymmetrical, so that the dynamic characteristics are improved. By providing an asymmetric component, it is possible to improve the gain margin of the higher-order resonance in the control operation.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a perspective view showing the overall structure of an objective lens actuator for explaining a first embodiment of the present invention, in which the T axis direction is the tangential direction on the optical disk, and the F axis direction is the focus direction. Yes, the R-axis direction is the radial direction (tracking direction).

In FIG. 1, 1 is a stator portion, 2 is a base member as a support member, 3a and 3b are magnets,
The standing walls 2a, 2d for fixing the magnets 3a, 3b in the base body 2 and the standing walls 2b, 2c facing the standing walls 2a, 2d serve as yokes for the fixed magnetic circuit, and the yokes opposed to each other via the magnets 3a, 3b. A magnetic circuit gap G is formed between the standing wall 2a and the standing wall 2b and between the standing wall 2c and the standing wall 2d.

4 is a movable part, 5 is a lens holder, 6
Is an objective lens fixed to the upper part of the lens holder 5, 7 is a focusing coil, 8a and 8b are a pair of annular tracking coils, and 9 is a plurality of each on both sides of the holder (a total of 4 in this example). A linear spring 10 as an installed elastic support member is a printed circuit board for fixing a linear spring 9 and fixing a coil spring for fixing one end of the linear spring 9, and 11 is a fixed block.

The movable part 4 is configured such that the center of operation and the optical axis of the objective lens 6 coincide with each other, and the lens holder 5 and a focusing coil provided on a frame body 12 integrally formed on the outer periphery of the lens holder 5. 7 and a tracking coil 8a, 8b, and a printed circuit board 10 for fixing the linear spring and feeding the coil. As a support structure for the movable portion 4, the other end of the linear spring 9 is connected and fixed to a flexible printed circuit board 13 provided in the fixed block 11 through the through holes 11 a and 11 b of the fixed block 11 by soldering. ing.

In this embodiment, the wire spring 9 is a metal wire spring, and an example of soldering which also serves as a power supply connection is given as a fixing method. Can be used, and as a fixing method thereof, a method of bonding or insert molding may be used.

FIGS. 2A and 2B are perspective views showing only the movable portion in the first embodiment, and FIG. 2A shows the same side view as the state shown in FIG. b) shows the opposite side surface, and the projecting portion in the tangential direction T of the frame body 12 supporting the focusing coil 7 and the tracking coils 8a and 8b so as to straddle the magnetic circuit gap G. 12-1a, 12-1
b, 12-1c, and 12-1d are asymmetric in the tangential direction T with respect to the plane formed by the focus axis F and the radial axis R, so that the rigidity distribution in the tangential direction T is asymmetric.

In the first embodiment, in the tangential direction T of the frame body 12, the projecting portions 12-1a, 12-1 on the side not supported by the linear spring 9 shown in FIG.
The overhang amounts at b, 12-1c, and 12-1d are made larger than those at the opposite side.

With this configuration, the change in the characteristic of the position response in the tracking direction R obtained by the first embodiment is as follows.

First, when an asymmetric component of distribution rigidity in the tangential direction T in the lens holder 5 is formed,
The maximum amplitude position of the natural vibration changes. That is, the maximum amplitude position of the natural vibration deviates from the lens mounting position at the center of the lens holder 5, and as a result, the sensitivity of resonance in response at the mounting position of the objective lens 6 can be reduced.

Secondly, if there is an asymmetric component of the distribution stiffness in the tangential direction T, it splits into a plurality of modes instead of one dominant resonance, and the respective resonance sensitivities become lower than the original dominant resonance. Also in this aspect, the sensitivity of resonance can be reduced as a result.

FIG. 3 is a perspective view showing a configuration of a movable portion in an objective lens actuator for explaining a second embodiment of the present invention. FIG. 3 (a) shows the same side view as the state shown in FIG. FIG. 3B shows the opposite side surface, and the projecting portions 12-2a, 12-2b, 12-2c, 12-2d of the frame body 12 in the radial direction R.
Is asymmetric with respect to a plane formed by the focus axis F and the tangential axis T, that is, the overhang portion 12-2.
The shapes of a, 12-2b, 12-2c, and 12-2d are made different to make the rigidity distribution in the radial direction R asymmetric.

In the second embodiment, in the radial direction R of the lens holder 5, one side of the projecting portion 12-2 is provided.
a, 12-2b, the projecting part 1 on the other side facing
It is larger than the overhang amounts of 2-2c and 12-2d.

With this configuration, in the second embodiment, a characteristic change expected in the tracking direction in the first embodiment can be obtained in the focus direction.

FIG. 4 is a perspective view showing a structure of a movable portion in an objective lens actuator for explaining a third embodiment of the present invention. FIG. 4 (a) shows the same side view as the state shown in FIG. FIG. 4B shows the opposite side surface, and the tangential direction of the frame body 12 supporting the focusing coil 7 and the tracking coils 8a and 8b so as to straddle the magnetic circuit gap G. T
Overhangs 12-3a, 12-3b, 12-3c,
12-3d, inside corners 12e, 12f,
The thicknesses of 12g and 12h are asymmetrical in the tangential direction T with respect to the plane formed by the focus axis F and the radial axis R, that is, the corners 12e, 12f, 1
The shapes of 2g and 12h are made different to make the rigidity distribution in the tangential direction T asymmetric.

In the third embodiment, in the tangential direction T of the frame body 12, the amount of protrusion of the corners 12e and 12f on the side not supported by the linear spring 9 shown in FIG. The overhang amount is larger than 12 g and 12 h.

As described above, according to the third embodiment, the asymmetric component is formed by extending the protruding portions 12-3a and 12-a in the tangential direction T.
This is an example in which the inner corners 12e and 12f of 3b, 12-3c and 12-3d are formed in a mechanically reinforced shape to increase the thickness. This allows for mechanical reinforcement and
As in the first embodiment, a characteristic change that can be expected in the tracking direction can be obtained.

FIG. 5 is a perspective view showing the structure of a movable part in an objective lens actuator for explaining a fourth embodiment of the present invention. FIG. 5 (a) shows the same side view as the state shown in FIG. FIG. 5B shows the opposite side surface, and the projecting portions 12-4a, 12-4b, 12-4c, and 12-4d of the frame body 12 in the radial direction R.
At the inner corners 12i, 12j, 12k, 1
The thickness of 2 l is determined by focusing axis F and tangential axis T.
Asymmetrical in the radial direction R with respect to the plane formed by the corners 12i, 12j and 12k,
The rigidity distribution in the radial direction R is made asymmetrical by making the shape different from that of 12l.

In the fourth embodiment, in the radial direction R of the frame body 12, the inner corners 12j and 12h of one of the overhangs 12-4b and 12-4d on the side supported by the linear spring 9 are formed. The amount of the overhang is adjusted by the inner corner 12 of the opposing overhangs 12-4a and 12-4c.
i, which is larger than the overhang amount of 12 l.

With this configuration, in the fourth embodiment, a characteristic change expected in the tracking direction R in the first embodiment can be obtained in the focus direction F.

FIG. 6 is a perspective view showing a structure of a movable portion in an objective lens actuator for explaining a fifth embodiment of the present invention. FIG. 6 (a) shows the same side view as the state shown in FIG. FIG. 6B shows an opposite side surface, in which an asymmetric component is formed in the focus direction F with respect to a plane formed by the radial axis R and the tangential axis T in the frame body 12. ,
Overhangs 12-5a and 12-5 in tangential direction T
Bridge shape 1 only in focus direction F upper side with b
It is formed by connecting at 5a and 15b.

In general, according to the principle of the natural world, when one dominant peak exists, the resonance sensitivity on the weak structure side tends to increase. Therefore, according to the structure of the fifth embodiment, since the vibration amplitude itself in the tangential axis T direction is symmetrical with respect to the vibration in the tracking direction R, the position of the center objective lens 6 in the lens holder 5 is set. Although the vibration amplitude is the maximum, the sensitivity in the focus direction F can be enhanced in the focus direction F, which is the mounting position of the objective lens.
, The resonance sensitivity of the position response in the tracking direction R can be reduced.

The pair of tracking coils 8a and 8b having different masses in the frame body 12 of the movable section 4 are formed and attached to each other so that an asymmetry of the distribution mass in the tangential direction T is generated. You may. In this case, for example, it is conceivable to use different materials such as a copper wire on one side and a copper clad aluminum wire on the other side in order to change the mass by using electric wires having a common wire diameter for the tracking coils 8a and 8b. .

[0044]

As described above, according to the present invention,
The asymmetrical component in the dynamic characteristics is provided by a simple structure that asymmetrically distributes the rigidity of the frame structure in the movable part of the objective lens actuator or makes the mass distribution asymmetrical. Can be reduced at the installation position of the objective lens, and the gain margin of the higher-order resonance of the control operation can be improved.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an overall configuration of an objective lens actuator for describing a first embodiment of the present invention.

FIG. 2 is a perspective view showing only a movable portion in the first embodiment.

FIG. 3 is a perspective view showing a configuration of a movable portion in an objective lens actuator for explaining a second embodiment of the present invention.

FIG. 4 is a perspective view showing a configuration of a movable portion in an objective lens actuator for explaining a third embodiment of the present invention.

FIG. 5 is a perspective view showing a configuration of a movable part in an objective lens actuator for explaining a fourth embodiment of the present invention.

FIG. 6 is a perspective view showing a configuration of a movable part in an objective lens actuator for describing a fifth embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Stator part 2 Base body 3a, 3b Magnet 4 Movable part 5 Lens holder 6 Objective lens 7 Focusing coil 8a, 8b Tracking coil 9 Linear spring 12 Frame body

Claims (9)

[Claims] 1. An optical disk recording / reproducing apparatus, comprising:
A lens holder for holding the objective lens, a fixed magnetic circuit provided on the base body, and a solenoid coil for generating a focusing thrust and a tracking thrust according to a current value by the fixed magnetic circuit, and a movable provided with the lens holder. And an elastic support member for supporting the movable portion displaceably in accordance with the amount of thrust generated, wherein the objective lens actuator has a configuration in which an optical axis of the objective lens is disposed at an operation center of the movable portion. An objective lens actuator, wherein a portion as an asymmetric component in dynamic characteristics is formed in a frame structure of a movable portion. 2. The rigidity distribution in the tangential direction is made asymmetric by making the shape of the frame structure of the lens holder asymmetric in the tangential direction with respect to a plane formed by the focus axis and the radial axis. The objective lens actuator according to claim 1, wherein 3. The rigidity distribution in the radial direction is asymmetrical by making the frame structure of the lens holder asymmetrical in a radial direction with respect to a plane formed by a focus axis and a tangential axis. The objective lens actuator according to claim 1, wherein 4. The objective lens actuator according to claim 2, wherein a part of the projecting portion in the frame structure of the lens holder is asymmetric. 5. The rigidity distribution in the tangential direction is made asymmetrical in the tangential direction by making the inner shape of the frame structure of the lens holder asymmetric in the tangential direction with respect to a plane formed by the focus axis and the radial axis. The objective lens actuator according to claim 1, wherein: 6. The rigidity distribution in the radial direction is made asymmetric by making the inner shape of the frame structure of the lens holder asymmetric in the radial direction with respect to a plane formed by the focus axis and the tangential axis. The objective lens actuator according to claim 1, wherein 7. The objective lens actuator according to claim 5, wherein a thickness of a corner portion inside the frame structure of the lens holder is asymmetric. 8. The rigidity distribution in the focus direction is made asymmetric by making the frame structure of the lens holder asymmetric in a focus direction with respect to a plane formed by a radial axis and a tangential axis. The objective lens actuator according to claim 1, wherein 9. The mass distribution of the solenoid coil provided in the tangential direction of the lens holder is made asymmetric with respect to a plane formed by a focus axis and a radial axis, so that the mass distribution in the tangential direction is made asymmetric. The objective lens actuator according to claim 1, wherein: