KR100306448B1 - Linear actuator and optical equipment with the same - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a linear actuator, and provides a linear actuator having a simple structure having a small influence of leakage magnetic flux of a driving magnetic circuit applied to a magnetic sensor and having an excellent signal-to-noise ratio (S / N) and an optical device using the same. As a solution means, a pair of magnetic circuits 8a and 8b are combined with one movable coil 9, and the magnetic circuit 8a is composed of yokes 6a and 7a. The magnetic circuit 8b has the same configuration, and the magnetic sensor 10 is positioned on the stator side and the magnetic scale 11 on the mover side. ) Are provided so as to face each other.

Description

LINEAR ACTUATOR AND OPTICAL EQUIPMENT WITH THE SAME}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a linear actuator, and is very suitable for application when driving a moving lens group of an optical device such as a still camera or a video camera.

Nowadays, so-called linear actuators, which are driven linearly by magnetic circuits composed of magnets and yokes, are used in industrial devices such as robots, printing devices such as plotters and printers, and recording / reproducing devices such as hard disks and magneto-optical disks. In addition, it is generally used in a wide range of fields such as optical devices such as still cameras and video cameras.

In this linear actuator, for example, when the moving lens group for adjusting the focus of the camera is moved to a predetermined position, and an object image is formed on an imaging surface such as an imaging device, the recording / reproducing head of the hard disk is further defined. In the case of accessing the track of the track, position detection means for detecting the position of the movable portion is formed in order to accurately position the movable portion such as the moving lens group or the recording / reproducing head.

This position detecting means is roughly divided into two types, optical and magnetic. As an optical detection means, a combination of an optical sensor composed of a light emitting element such as an LED and a light receiving element such as a phototransistor, and an optical scale in which the light transmitting portion and the light blocking portion are alternately formed at a fine pitch are known. As a magnetic detection means, it is common to combine magnetic sensors, such as a magnetoresistive element (MR element) and a hall element, and the magnetic scale which magnetized to the magnetic substance at the fine pitch.

In the conventional optical position detecting means, since the output light amount of the optical sensor changes with temperature, there is a need for a control system capable of allowing adjustment circuits and temperature differences to cope with temperature changes. In addition, an adjustment mechanism for precisely adjusting the three geometric positional relations between the light emitting element, the optical scale and the light receiving element so that the light emitted from the light emitting element passes through the light-transmitting portion of the fine pattern in the optical scale to reach the light receiving element is provided. need. As a result, there is a problem that the sensor becomes large in size and cost up.

On the other hand, in the conventional magnetic position detection device, since the temperature characteristic of the magnetic sensor such as the MR element is better than that of the optical sensor, an adjustment circuit for coping with the temperature change is unnecessary. As for the adjustment of the positional relationship, only the amount of gap between the magnetic sensor and the magnetic scale is adjusted so that the magnetic sensor can detect the sine wave magnetic field intensity pattern magnetized on the magnetic scale. The adjusting mechanism is simple. Therefore, the magnetic detection means has the advantage that the sensor can be made compact and inexpensive. For this reason, magnetic position detection means are frequently used in linear actuators for position control of a moving lens group for focus adjustment of an optical device such as a camera.

However, in the conventional magnetic position detecting means or in the linear actuator, since the magnetic sensor is located near the magnetic circuit for driving, the leakage magnetic flux from the magnetic circuit for driving causes the signal-to-noise ratio (S / The adverse effect that N) worsens occurs. In order to prevent this, it is conceivable to magnetically shield the driving magnetic circuit and the magnetic sensor. However, it is difficult to completely shield the leakage magnetic flux, and the structure becomes complicated.

Therefore, in order to solve the adverse effect on the magnetic sensor of the leakage magnetic flux, a disk drive device having the following structure is proposed in Japanese Patent Laid-Open No. 5-62383. That is, a pair of linear motors in which magnets and coils are arranged symmetrically and inverted only in polarity of the magnets in the left and right directions is used as a moving means of the head base. As a position detecting means, a magnetic sensor is mounted on the movable head base, and a magnetic scale is mounted on a fixed member on the moving trajectory of the magnetic sensor, and the magnetic sensor is positioned at the center position of a pair of left and right linear motors. To place. Or on the contrary, a magnetic scale is provided in the head base of a movable side, and the magnetic sensor is provided in the fixed member.

According to this, the leakage magnetic flux generated from the bilaterally arranged symmetrical motors cancels each other in at least three directions in one direction because the polarities of the magnets in the left and right linear motors are inverted at the center positions of the two linear motors. . Therefore, the adverse effect to the magnetic sensor by a magnet is alleviated. Moreover, the leakage magnetic flux in the driving direction (X direction) and the vertical direction (Z direction) at the magnetic sensor position acts to cancel each other.

However, in the conventional disk drive apparatus, since the polarities of the left and right magnets are reversed, it is necessary to reverse the direction of the current flowing through the coil by the pair of left and right linear motors. For this reason, two coils are necessarily required, resulting in the enlargement of a linear actuator, cost up, and increase of power consumption. In addition, the magnetic flux generated by the current flowing through the two coils does not cancel at the magnetic sensor position but increases doubling, adversely affecting the magnetic sensor. In addition, in the horizontal direction (Y direction), the leakage magnetic flux remains without cancelation, and thus the magnetoresistance change rate of the MR element changes, resulting in deterioration of sensitivity.

An object of the present invention is to provide a linear actuator having a small influence of leakage magnetic flux of a driving magnetic circuit applied to a magnetic sensor and excellent in signal-to-noise ratio (S / N) and an optical device using the same.

1 is an internal perspective view of a lens driving apparatus using a linear actuator according to a first embodiment of the present invention.

2 and 3 are cross-sectional and longitudinal sectional views, respectively, of the lens driving apparatus shown in FIG.

4 is a diagram showing magnetoresistance change rate characteristics of a magnetoresistive element (MR element) used in the lens driving apparatus shown in FIG.

Fig. 5 is a schematic perspective view of the position detecting means used for the lens driving device shown in Fig. 1.

6 and 7 show the flow of magnetic flux in the cross section and the longitudinal section of the linear actuator shown in FIG. 1.

Fig. 8 is a cross sectional view of the lens driving apparatus using the linear actuator according to the second embodiment of the present invention.

FIG. 9 is a diagram showing the flow of magnetic flux in a cross section of the linear actuator shown in FIG. 8. FIG.

Fig. 10 is a perspective view of the inside of the lens driving apparatus using the linear actuator in the third embodiment of the present invention.

11 and 12 are cross-sectional and longitudinal sectional views of the lens driving device shown in FIG. 10.

13 and 14 show the flow of magnetic flux in the cross section and the longitudinal section of the linear actuator shown in FIG. 10. FIG.

<Description of the symbols for the main parts of the drawings>

1: lens holder, 2: lens,

3: lens barrel, 4a 4b: guide shaft,

5a, 5b: magnet, 6a, 6b: main yoke,

7a, 7b: side yoke, 8a, 8b: magnetic circuit,

9: coil, 10: magnetic sensor,

11: magnetic scale, 12a, 12b: magnetoresistive element (MR element)

13a, 13b: magnetic circuit, 21: lens holder,

22: lens, 23: lens barrel,

25: magnet, 26: main yoke,

27: side yoke, 28: magnetic circuit.

The linear actuator of the present invention has a stator composed of at least one magnetic circuit having a magnet magnetized perpendicularly to the yoke and the driving direction, and has a predetermined gap with respect to the magnet, so that the current is orthogonal to the magnetic flux generated by the magnet. And a magnetic sensor provided at one of the movable element and the stator, and a magnetic sensor provided at a position opposite to the magnetic scale at the other side, by energizing the coil. Position detecting means is provided. Since the linear actuator of this invention is comprised by one movable coil, the influence which the leakage magnetic flux of a coil has on a magnetic sensor becomes small.

One preferred aspect of the linear actuator of the present invention is that in the linear actuator, two magnetic circuits of the first and second are formed, and the quantum circuit is arranged so that the magnetization directions of the magnets face each other. . As a result, the leakage magnetic flux in the magnetization direction of the magnet in the symmetrical center position cancels each other, and the leakage magnetic flux in the vertical direction is further reduced in the driving direction jumping into the magnetic sensor.

In addition, it is preferable to use an MR element for the magnetic sensor, and arrange the MR element so that the direction of the current flowing through the MR element is substantially parallel to the magnetization direction of the magnets of the first and second magnetic circuits. Thereby, the effect of preventing the deterioration of the sensitivity of the magnetic sensor due to the magnetic disturbance can be obtained.

Moreover, it is preferable to arrange | position a magnetic substance in the side surface of the magnet in a 1st and 2nd magnetic circuit, respectively. As a result, the leakage magnetic flux is attracted to the magnetic body, and the leakage magnetic flux in two directions perpendicular to the driving direction at the magnetic sensor position can be further reduced. In addition, by integrating the magnetic body with the yoke, the structure can be made simpler.

One of the other preferable aspects of this invention is to use one magnetic circuit which has a structure of substantially left-right symmetry from a driving direction to a stator. Also in this configuration, the leakage magnetic flux in the driving direction that jumps into the magnetic sensor can be further reduced. Also in this one aspect, it is preferable to use an MR element for the magnetic sensor.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

First, the linear actuator in the first embodiment of the present invention will be described with reference to the drawings. 1 to 3, the lens holder 1 holding the lens 2 is provided with guide shafts 4a and 4b whose both ends are fixed to the lens barrel 3 and arranged in parallel with the optical axis. Therefore, it slides in an optical axis direction (X direction).

As the stator of the linear actuator for driving the lens holder 1 in the optical axis direction, the magnetic circuits 8a and 8b are fixed to the lens barrel. The magnetic circuit 8a includes a magnet 5a magnetized in a direction perpendicular to the driving direction (X direction), a U-shaped main yoke 6a, and a plate-shaped side yoke 7a. X direction) has a substantially symmetrical structure. The magnetic circuit 8b is composed of the magnet 5b, the main yoke 6b and the side yoke 7b, and is disposed to face the magnetic circuit 8a. On the other hand, as a movable member, a coil 9 fixed to the lens holder 1 is formed so as to have a predetermined gap with respect to the magnets 5a and 5b, and the magnetic flux generated by the magnets 5a and 5b. The current flows through the coil 9 so as to be orthogonal to the lens 9, so that the lens holder 1 moves in the optical axis direction.

In order to perform position control of the lens holder 1, as the position detecting means, the magnetic sensor 10 is attached to the lens barrel 3, and the magnetic scale 11 is attached to the lens holder 1, respectively. The magnetic sensor 10 is a symmetric center in the driving direction (X direction) of the magnetic circuits 8a and 8b, and is provided at a symmetric center position between the pair of magnetic circuits 8a and 8b. The magnetic scale 11 is provided so as to face the detection surface of the magnetic sensor 10 at a predetermined distance. The magnetic scale 11 is applied to the ferromagnetic material such as ferrite in the driving direction alternately with the S pole and the N pole at a predetermined pitch. The provision of this magnetic pole is performed by the magnetizing method of moving the ferromagnetic material at a constant speed with respect to the magnetic head as the magnetizing jig.

The magnetic sensor 10 includes a two-phase magneto-resistive sensor composed of MR elements 12a and 12b made of a ferromagnetic thin film such as NiFe or NiCo, which has a property of changing resistance by a magnetic field. Is being used. The MR elements 12a and 12b are arranged in the driving direction at quarter intervals of the magnetization pitch between the S pole and the N pole of the magnetic scale 11. Then, the magnetic sensor 10 and the magnetic scale 11 are arranged so as to be parallel to the magnetization directions of the magnets 5a and 5b in the direction of the current flowing through the MR elements 12a and 12b.

4 shows the magnetoresistance change rate characteristics of the MR elements 12a and 12b that the resistance value decreases as a magnetic field is applied. In this MR element, the resistance value is almost unchanged for the magnetic field perpendicular to the current direction of the MR elements 12a and 12b and perpendicular to the detection surface (Y direction), but the MR elements 12a and 12b The resistance value changes substantially with respect to the magnetic field perpendicular to the current direction in the direction and parallel to the detection plane (X direction). The resistance value slightly changes in the magnetic field in the parallel direction (Z direction) with respect to the current direction of the MR elements 12a and 12b.

From this characteristic, the MR element 12a corresponds to the magnetic field intensity change pattern of the sinusoidal wave shape generated in the X direction by changing the position of the magnetic scale 11 having the magnetization pattern shown in Fig. 5 with respect to the magnetic sensor 10. , The resistance value of (12b) changes. Here, the sine wave shape change pattern of the sine wave which is 180 degrees out of phase with the X direction occurs, but the resistance values of the MR elements 12a and 12b hardly change due to the above characteristics. Therefore, when the voltages applied to the MR elements 12a and 12b are used as output signals, the output signals are waveforms of two sinusoidal waveforms having 90 degrees out of phase. By modulating interpolation of these two signal waveforms by a signal processing circuit (not shown), the position and driving direction of the lens holder 1 are detected. And based on this detection data, the position of the lens 2 can be controlled with high precision by a control circuit (not shown).

Next, the effect of the leakage magnetic flux from the magnetic circuits 8a and 8b for driving on the magnetic sensor 10 will be described. As described above, the MR elements 12a and 12b have a characteristic that the magnetoresistance changes in the X direction and the Z direction. In particular, the X direction has a high sensitivity of the magnetoresistance change, and the signal waveform is offset by the magnetic disturbance superimposed on the signal of the sine wave shape change pattern generated from the magnetic scale. This causes a problem such as waveform distortion of the output signal of the MR element and increases the error of position detection. In addition, although the sensitivity of the magnetoresistance change is small in the Z direction, the magnetoresistance change rate decreases due to the magnetic disturbance in the Z direction, thereby causing a problem that the sensitivity of the MR element is deteriorated.

As described above, magnetic disturbances in the X and Z directions are problematic for the MR elements 12a and 12b. However, in the case of the first embodiment, the pair of magnetic circuits 8a and 8b is driven in the driving direction (X). Direction), the leakage magnetic flux in the X direction of the magnetic sensor 10 located at the center of symmetry becomes a small value, as shown in FIG.

Here, in the abnormal state where the magnetic circuits 8a and 8b are symmetric in the driving direction (X direction) and the magnetic sensor 10 is located at the symmetric center position thereof, the value of the leakage magnetic flux in the X direction is 0, Even when the magnetic circuits 8a and 8b are approximately symmetric in the driving direction (X direction) or the magnetic sensor 10 is in the substantially symmetric center position as in the present embodiment, the leakage magnetic flux in the X direction is minute. Positive, and does not lose its effect.

In addition, in the first embodiment, an example of two magnetic circuits is shown, but the magnet 25 and the main yoke (like the linear actuator in the third embodiment shown in Figs. One magnetic circuit 28 composed of 26 and side yokes 27 may be provided. In this case, the lens barrel 10 is arranged so that the magnetic sensor 10 faces the magnetic scale 11 in the driving direction (X direction) of the magnetic circuit 28 and faces the magnetic scale 11 on the movable side with a predetermined distance. 23) is installed. Thereby, as shown in FIG. 13, the leakage magnetic flux in the X direction of the magnetic sensor 10 turns into a minute value, and the effect similar to the above can be acquired.

In the first embodiment, the pair of magnetic circuits 8a and 8b are symmetrically arranged so that the magnetization directions of the magnets 5a and 5b are opposite, i.e., symmetrically with respect to the Z direction. Therefore, as shown in Fig. 6, the leakage magnetic flux in the Z direction cancels each other in the magnetic sensor 10 positioned at the center of symmetry, and the value of the leakage magnetic flux in the Z direction is zero. In addition, even when a pair of magnetic circuits 8a and 8b are in a substantially symmetrical position in the Z direction or when the magnetic sensor 10 is in a substantially symmetrical center position, the leakage magnetic flux in the Z direction is a small amount. It does not lose the effect. In the first embodiment, the magnetic sensor 10 is arranged so that the direction of the current flowing through the MR elements 12a and 12b is parallel to the magnetization direction (Z direction) of the magnets 5a and 5b. The sensitivity deterioration of the MR elements 12a and 12b can be prevented. However, even if the direction of the current flowing through the MR elements 12a and 12b is substantially parallel to the magnetization direction (Z direction) of the magnets 5a and 5b, the effect is not lost.

In the first embodiment, the magnetic sensor 10 is provided in the lens barrel 3 on the fixed side, and the magnetic scale 11 is provided in the lens holder 1 on the movable side. The magnetic flux 11 in the lens barrel 3 and the magnetic sensor 10 in the movable lens holder 1 can also reduce the leakage magnetic flux in the Z direction as described above.

In the linear actuator according to the third embodiment shown in Figs. 10, 11 and 12, the magnet 25, the main yoke 26 and the side yoke 27 are arranged so as to be symmetrical from the driving direction. One magnetic circuit 28 is provided in the lens barrel 23 on the fixed side, and a coil 29 is provided in the lens holder 21 on the movable side. As the position detecting means, the magnetic sensor 10 is placed on the lens barrel 23 so as to face the symmetric center position of the magnetic circuit 28 in the driving direction and to face the magnetic scale 11 on the movable side with a predetermined distance. It is installed. Thereby, as shown in FIG. 14, the leakage magnetic flux in the Z direction of the magnetic sensor 10 becomes 0, and the effect similar to the above can be acquired. However, even if the magnetic circuit 28 is substantially symmetrical and the magnetic sensor 10 is near its symmetrical center position, the leakage magnetic flux in the Z direction becomes a small amount and does not lose its effect.

In this third embodiment, since the magnetic sensor 10 is disposed so that the direction of the current flowing through the MR elements 12a and 12b is perpendicular to the magnetization direction (Y direction) of the magnet 5, The sensitivity decrease of the MR elements 12a and 12b can be prevented. However, even if the direction of the current flowing through the MR elements 12a and 12b is substantially perpendicular to the magnetization direction (Y direction) of the magnet 5, the effect is not lost.

In the third embodiment, the magnetic sensor 10 is provided in the lens barrel 23 on the fixed side, and the magnetic scale 11 is provided in the lens holder 21 on the movable side. Even if the magnetic scale 11 is provided at 23 and the magnetic sensor 10 is provided at the lens holder 21 on the movable side, the leakage magnetic flux in the Z direction can be made a small value as described above.

Next, the linear actuator in the second embodiment of the present invention will be described with reference to FIGS. 8 and 9. The second embodiment is a modification of the first embodiment. As shown in Fig. 8, the magnet 5a is folded by bending a part of the magnetic sensor 10 side in the main yokes 14a and 14b. The magnetic circuits 13a and 13b in which the magnetic bodies 15a and 15b are formed on the side of the magnetic sensor 10 side of 5b are respectively used.

With this configuration, as shown in Fig. 9, the flow of the magnetic flux in which the leaked magnetic fluxes from the magnets 5a, 5b and the main yokes 14a, 14b are directed to the magnetic bodies 15a, 15b. This occurs, and the leakage magnetic flux in the Y direction and the Z direction at the position of the magnetic sensor 10 decreases. Therefore, for example, when the magnetic circuits 13a and 13b slightly shift from the symmetrical position, or when the magnetic sensor 10 slightly shifts from the symmetrical positions of the pair of magnetic circuits 13a and 13b. Therefore, there is an effect that the influence of the magnetic disturbance on the magnetic sensor 10 is further reduced. In addition, in the present embodiment, the magnetic bodies 14a and 14b are constituted by a part of the main yoke 14a and 14b, but these may be constituted by other members.

This invention is not limited to the said 1st, 2nd, 3rd embodiment, Needless to say that various modifications are possible. In these embodiments, a magnetic sensor using an MR element is used. However, if the magnetic sensor outputs an output signal corresponding to the strength of the magnetic force, the sensor is mounted so that the sensor is matched with the direction of the magnetic disturbance in the X or Z direction. The present invention can be applied to all kinds of magnetic sensors. In addition, the present invention is not limited to linear actuators for driving mobile lens groups of optical devices such as cameras, and recording and playback devices such as hard disks and magneto-optical disks, printing devices such as plotters and printers, and industrial equipment such as robots. It can also be applied to linear actuators used in various fields such as the above, and the same effect can be raised.

Claims (8)

A stator having a magnet and a yoke magnetized in a direction perpendicular to the driving direction, the stator including at least one magnetic circuit configured substantially in the left and right symmetry in the driving direction, A movable member having a predetermined gap with respect to the magnet and having one coil moving in the driving direction by energizing a current so as to be orthogonal to the magnetic flux generated by the magnet; Magnetic scales provided at either of the mover and the stator, at positions substantially opposite to the magnetic scales at the other side, and at orthogonal to the driving direction and at a substantially symmetrical center position of the magnetic circuit. A linear actuator comprising a position detecting means made of a sensor. The magnetization apparatus of claim 1, wherein the stator includes a first magnetic circuit having a first magnet and a second magnetic circuit having a second magnet, and the magnetization direction of the first magnet is opposite to the magnetization direction of the second magnet. And the first magnetic circuit and the second magnetic circuit are arranged, and the position detecting means is arranged such that the magnetic scale and the magnetic sensor are located at substantially symmetric centers of the first and second magnetic circuits. Linear actuator 3. A linear element according to claim 2, wherein the magnetic sensor is made of an MR element, and the MR element is arranged such that the current direction of the MR element is substantially parallel to the magnetization directions of the first and second magnets. Actuator. The linear actuator according to claim 2 or 3, wherein a magnetic substance is disposed on side surfaces of the first and second magnets parallel to the magnetization directions of the first and second magnets. The linear actuator according to claim 4, wherein each of the magnetic bodies is integrated with each yoke of the first and second magnetic circuits. The magnetic stator according to claim 1, wherein the stator is formed of one magnetic circuit composed of substantially left and right symmetry in the driving direction, and the magnetic scale and the magnetic sensor are located in a substantially symmetric center of the magnetic circuit in the driving direction. And the position detecting means is arranged. 7. The linear actuator according to claim 6, wherein the magnetic sensor is made of an MR element, and the MR element is disposed so that the current direction of the MR element is substantially perpendicular to the magnetization direction of the magnet. An optical apparatus for forming an object image on an imaging surface by an optical system including a moving lens group, comprising: at least one of the linear actuators of claims 1 to 7 as driving means for driving the moving lens group. Optical instruments.