JP3893701B2 - Linear actuator and lens barrel using the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a linear actuator, in particular, a linear actuator that drives a photographing lens in an imaging apparatus such as a camera or a video camera, an optical device, and a lens barrel.
[0002]
[Prior art]
In recent years, video camera technology has been remarkably advanced, and many performance improvements have been made in various fields such as digital recording, reduction in size and weight, longer shooting, high speed, and high magnification zoom.
[0003]
In the lens barrel that is the imaging unit, the so-called “inner focus method”, which adjusts the focus by changing the position of the focus lens group behind the zoom lens group in the optical axis direction, is advantageous for downsizing. In general, the focus lens group moves in the optical axis direction according to the change in the position of the zoom lens group based on the movement trajectory data for each subject distance stored in the microcomputer. An object image is formed on the imaging surface of the rear image sensor.
[0004]
Here, due to the characteristics of the movement trajectory data that the amount of movement of the focus surface on the telephoto side is large, it is necessary to move the focus lens group faster than the zoom lens group to move the focus lens group following the zoom lens group. In order to realize high-speed zoom and long-time shooting among the performance improvement items described above, the drive portion of this focus lens group can follow the change in position of the zoom lens group instead of the conventional stepping motor. A voice coil type linear actuator excellent in high-speed response and low power consumption is adopted.
[0005]
A configuration of a conventional lens driving device for driving the focus lens will be described with reference to FIGS. 8 is an internal perspective view of a lens driving device in a conventional lens barrel, FIG. 9 is a transverse sectional view of the lens driving device, and FIG. 10 is a longitudinal sectional view of the lens driving device.
[0006]
The lens holder 51 holds the focus lens 52 and is arranged parallel to the optical axis, and is slidable in the optical axis direction (X direction) along guide shafts 54 a and 54 b fixed to the lens barrel 53 at both ends. It is configured.
[0007]
As a stator of a linear actuator that drives the lens holder 51 in the optical axis direction, a magnet 55a magnetized perpendicular to the driving direction (X direction), a U-shaped main yoke 56a, and a plate-shaped side yoke 57a. A magnetic circuit 58a configured to be substantially symmetrical with respect to the driving direction (X direction), a magnet 55b, a main yoke 56b, and a side yoke 57b disposed substantially symmetrically at opposite positions so as to face the magnetic circuit 58a. A stator of a magnetic circuit 58b is provided on the lens barrel 53, while a coil 59 is fixed to the lens holder 51 as a mover so as to have a predetermined gap with the magnets 55a and 55b. , 55b is caused to flow perpendicularly to the magnetic flux generated by the coil 59 so that the lens holder 51 can It has a mechanism to be driven in the direction.
[0008]
In addition, in order to control the position of the lens holder 51, the magnetic sensor 60 is provided in the lens barrel 53 on the fixed side as position detecting means, and the pair of the magnetic sensor 58 has a symmetrical center in the driving direction (X direction) of the magnetic circuits 58a and 58b. Are provided at the symmetrical center position between the magnetic circuits 58a and 58b. On the other hand, the movable lens holder 51 is magnetized with S poles and N poles alternately at a predetermined pitch along the driving direction by moving a ferromagnetic material such as ferrite at a constant speed with respect to the magnetic head. A magnetic scale 61 is attached so as to face the detection surface of the magnetic sensor 60 with a predetermined distance. The magnetic sensor 60 is a two-phase magnetoresistive sensor composed of MR elements 62a and 62b made of a ferromagnetic thin film such as NiFe or NiCo having a characteristic that the resistance value changes depending on the magnetic field. The MR element 62a, 62b is a ¼ interval of the magnetization pitch from the S pole to the N pole of the magnetic scale 61 and is provided in the driving direction. The direction of the current flowing through the MR elements 62a and 62b is the magnetization direction of the magnets 65a and 65b. The magnetic sensor 60 and the magnetic scale 61 are respectively arranged in a direction parallel to the magnetic field.
[0009]
FIG. 6 is a diagram showing the magnetoresistance change rate characteristics of the MR elements 52a and 52b, and FIG. 7 is a schematic perspective view of the position detecting means.
[0010]
As the directionality of the magnetoresistance change shown in FIG. 6, the resistance value hardly changes for a magnetic field in a direction (Y direction) perpendicular to the current direction of the MR elements 52a and 52b and perpendicular to the detection surface. The resistance value changes greatly with respect to a magnetic field perpendicular to the current direction of the MR elements 52a and 52b and parallel to the detection surface (X direction), and further parallel to the current direction of the MR elements 52a and 52b. The resistance value slightly changes with respect to the magnetic field in the direction (Z direction).
[0011]
From this characteristic, when the magnetic scale having the magnetization pattern shown in FIG. 7 changes its position with respect to the magnetic sensor 50, the MR elements 52a and 52b correspond to the sinusoidal magnetic field strength change pattern generated in the X direction. The resistance value changes. Here, a sinusoidal magnetic field strength change pattern having a phase difference of 180 ° from the X direction is also generated in the Y direction, but the resistance values of the MR elements 52a and 52b hardly change due to the above characteristics.
Therefore, when the voltage applied to the MR elements 52a and 52b is used as an output signal, the output signal has two sinusoidal waveforms that are 90 ° out of phase, and these two signal waveforms are modulated by a signal processing circuit (not shown). By performing the insertion process, the position and driving direction of the lens holder 51 are detected, and the position of the lens 52 can be controlled with high accuracy by a control circuit (not shown) based on this data.
[0012]
Here, if there is a disturbance magnetic field in the X direction and Z direction, the signal waveform is offset by superimposing the disturbance magnetic field on the signal of the sinusoidal magnetic field strength change pattern in the X direction, so that the waveform of the output signal is distorted. Position detection error increases. In the Z direction, although the magnetoresistive change sensitivity is low, there is a problem that the magnetoresistive change rate is reduced and the sensitivity of the MR element is lowered.
[0013]
In this conventional lens driving device, the influence of the leakage magnetic flux from the magnetic circuits 58a and 58b on the MR elements 62a and 62b of the magnetic sensor 60 will be described with reference to FIGS. FIG. 11 is a view showing the flow of magnetic flux in the transverse section of this linear actuator, and FIG. 12 is a view showing the flow of magnetic flux in the same longitudinal section.
[0014]
The MR elements 62a and 62b have a characteristic that the magnetoresistance changes in the X direction and the Z direction. However, the magnetic sensor 60 has a symmetrical center in the driving direction (X direction) of the pair of magnetic circuits 58a and 58b and the pair of magnetic elements. By providing at the symmetrical center position between the circuits 58a and 58b, the leakage flux in the X direction at the MR element position becomes a small value as shown in FIG. 11, while the leakage in the Z direction as shown in FIG. The magnetic flux also becomes a minute value by canceling each other.
[0015]
Therefore, the lens driving device having an excellent S / N ratio that does not give the magnetic sensor 60 the influence of the leakage magnetic flux from the driving magnetic circuits 58a and 58b is realized by the above configuration.
[0016]
[Problems to be solved by the invention]
However, in the lens barrel using the linear actuator described above, a magnetic encoder composed of a magnetic scale and an MR sensor is used as a position detecting means so as to be opposed to each other so as not to be affected by the leakage magnetic flux of a pair of magnetic circuits. Therefore, the size of the lens barrel in the width direction is increased by the thickness of the magnetic encoder, and the lens barrel cannot be reduced in size. Had drawbacks.
[0017]
In view of the above problems, an object of the present invention is to provide a lens driving device using a linear actuator having a magnetic sensor as a position detecting means, and the magnetic sensor is hardly affected by leakage magnetic flux from the driving magnetic circuit, and the lens mirror. A compact lens barrel that does not increase in size in the width direction of the tube is to be provided at a low cost with a simple configuration.
[0018]
[Means for Solving the Problems]
In order to solve this problem, the present invention is a linear actuator including a stator and a movable element movable in a predetermined driving direction,
The stator includes a magnetic circuit including a magnet and a yoke magnetized perpendicularly to the driving direction, and a magnetic sensor.
The mover, the magnet with a predetermined and movably coil in the driving direction by Rukoto current is energized so as perpendicular to the magnetic flux generated by the magnet has a gap, S poles along the driving direction And N poles are alternately magnetized, and have a magnetic scale facing the magnetic sensor with a predetermined distance ,
The one magnetic circuit is configured substantially symmetrically when viewed from the driving direction,
The magnetic sensor is disposed at a substantially symmetrical center position of the one magnetic circuit as viewed from the driving direction.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of a lens barrel using the linear actuator of the present invention will be described below with reference to the drawings. FIG. 1 is an internal perspective view of a lens driving device using a linear actuator according to an embodiment of the present invention, FIG. 2 is a cross-sectional view of the lens driving device using a linear actuator according to an embodiment of the present invention, and FIG. 4 is a longitudinal sectional view of a lens driving device using a linear actuator in an embodiment of the invention, FIG. 4 is a diagram showing a flow of magnetic flux in a transverse section of the linear actuator in the embodiment of the present invention, and FIG. 5 is an embodiment of the present invention. It is a figure which shows the flow of the magnetic flux of the longitudinal cross-section of the linear actuator in a form.
[0024]
First, a linear actuator according to an embodiment of the present invention will be described with reference to FIGS. 1 to 3, the lens holder 1 holds the lens 2 and is arranged in parallel to the optical axis, and is guided along the optical axis direction (X direction) along guide shafts 4 a and 4 b fixed to the lens barrel 3 at both ends. ) Is slidable.
[0025]
As a stator of a linear actuator that drives the lens holder 1 in the optical axis direction, a magnet 5 magnetized perpendicular to the driving direction (X direction), a U-shaped main yoke 6 and a plate-shaped side yoke 7 The magnetic lens 8 is provided with a stator of the magnetic circuit 8 which is symmetrical with respect to the driving direction and substantially symmetrical with respect to the driving direction (X direction). 9 is fixed to the lens holder 1 so as to have a predetermined gap with the magnet 5, and the lens holder 1 is driven in the optical axis direction by passing a current through the coil 9 so as to be orthogonal to the magnetic flux generated by the magnet 5. It works.
[0026]
Further, in order to control the position of the lens holder 1, the magnetic sensor 10 is seen from the driving direction and the symmetrical center of the driving direction (X direction) of the magnetic circuit 8 in the lens barrel 3 on the fixed side as position detecting means. On the other hand, the movable lens holder 1 is provided with a magnetic scale 11 in which S poles and N poles are alternately magnetized with respect to the detection surface of the magnetic sensor 10. Are attached so as to face each other.
[0027]
The magnetic circuit 8 and the drive unit for the coil 9 and the position detection unit for the magnetic sensor 10 and the magnetic scale 11 are respectively located at the four corners of the lens barrel 3 centered on the lens 2 when viewed from the optical axis (drive) direction. Is provided.
[0028]
The magnetic sensor 10 is a two-phase magnetoresistive sensor composed of MR elements 12a and 12b made of a ferromagnetic thin film, as in the prior art. The MR elements 12a and 12b are magnetic scales 11. Are provided in the driving direction at intervals of 1/4 of the magnetization pitch from the S pole to the N pole, and the direction of the current flowing through the MR elements 12a, 12b is magnetic in the direction perpendicular to the magnetization direction of the magnet 5. The sensor 10 and the magnetic scale 11 are respectively arranged.
[0029]
In the lens driving device according to the embodiment of the present invention, the influence of the leakage magnetic flux from the magnetic circuit 8 on the MR elements 12a and 12b of the magnetic sensor 10 will be described with reference to FIGS. Since the MR elements 12a and 12b have a characteristic that the magnetic resistance changes in the X direction and the Z direction, the magnetic circuit 8 is configured symmetrically as viewed from the driving direction as in the present embodiment. As shown, the value of the leakage magnetic flux in the Z direction at the magnetic sensor 10 located at the center of symmetry is zero. Here, even if the magnetic circuit 8 has a substantially symmetric shape and the magnetic sensor 10 is in the vicinity of the symmetrical center position, the leakage magnetic flux in the Z direction is very small and the effect is not lost.
[0030]
Further, since the magnetic circuit 8 is configured approximately symmetrically in the driving direction (X direction), as shown in FIG. 5, the leakage flux in the X direction of the magnetic sensor 10 located at the center of symmetry is a small value. .
[0031]
In the embodiment of the present invention, since the magnetic sensor 10 is arranged 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 MR elements 12a and 12b Although a reduction in sensitivity can be prevented, the effect is not lost 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.
[0032]
In the embodiment of the present invention, a magnetoresistive magnetic sensor using an MR element is used. However, any sensor can be used as long as it outputs an output signal corresponding to the strength of the magnetic force. The present invention can be applied to all kinds of magnetic sensors by attaching the sensor so that the direction in which the light is easily received coincides with the Z direction.
[0034]
Furthermore, in the embodiment of the present invention, the magnetic circuit 8 and the coil 9 which are driving units, and the magnetic sensor 10 and the magnetic scale 11 which are position detecting units are arranged at the four corners of the lens barrel 3, respectively. Unlike the lens driving device, it is not necessary to provide the position detection unit outside the driving coil arranged outside the lens, so the size of the lens barrel in the width direction is reduced, and the lens barrel 3 is downsized. Can do.
[0035]
The present invention is not limited to the linear actuator that drives the moving lens group of the video camera described with reference to the above-described embodiment, but a recording / playback device such as a hard disk or a magneto-optical disk, a printing device such as a plotter or a printer, or a robot The present invention can also be applied to linear actuators used in the field of industrial equipment, and the same effects can be achieved.
[0036]
【The invention's effect】
With the configuration as described above, the linear actuator of the present invention provides a position detection means in which a magnetic sensor is disposed near the center position of symmetry in a magnetic circuit configured substantially symmetrically when viewed from the driving direction. The leakage magnetic flux in the Z direction jumping into the magnetic sensor can be reduced.
[0037]
Furthermore, the magnetic sensor is a magnetoresistive sensor using an MR element, and the magnetic sensor is provided near the symmetrical center position so that the direction of the current flowing through the MR element is substantially perpendicular to the magnetization direction of the magnet. The effect of preventing the deterioration of the sensitivity of the MR element due to is obtained.
[0038]
Further, in the lens barrel using this linear actuator, the driving means and the position detecting means are provided at the four corners of the lens barrel with the moving lens group as the center, respectively, when viewed from the optical axis direction. By effectively using the empty space at the four corners of the lens barrel while minimizing the adverse effects of magnetic flux leakage from the magnetic circuit, the size of the lens barrel can be reduced, and the lens barrel can be made smaller. can do. In addition, by using a single-pole linear actuator with a single magnetic circuit as a driving means, the number of parts of the magnet and the yoke can be reduced, and as a result, a lens driving device having a simple configuration can be provided at low cost. Can do.
[Brief description of the drawings]
FIG. 1 is an internal perspective view of a lens driving device using a linear actuator according to an embodiment of the present invention. FIG. 2 is a transverse cross-sectional view of the same. FIG. 5 is a diagram showing the flow of magnetic flux in the transverse section of the linear actuator. FIG. 5 is a diagram showing the flow of magnetic flux in the longitudinal section. FIG. 6 is a diagram showing the magnetoresistance change characteristic of the MR element. FIG. 8 is an internal perspective view of a lens driving device using a linear actuator in a conventional lens barrel. FIG. 9 is a transverse sectional view of the same. FIG. 10 is a longitudinal sectional view of the lens driving apparatus. Fig. 12 shows the flow of magnetic flux in the cross section of the linear actuator. Fig. 12 shows the flow of magnetic flux in the same vertical cross section.
DESCRIPTION OF SYMBOLS 1 --- Lens holder 2 --- Lens 3-Lens barrel 4a, 4b --- Guide shaft 5 --- Magnet 6 --- Main yoke 7 --- Side yoke 8 ---- Magnetic circuit 9 --- Coil 10 --- Magnetic sensor 11 --- Magnetic scale

Claims (5)

A stator and a movable element movable in a predetermined driving direction;
The stator has one magnetic circuit including a magnet and a yoke magnetized perpendicularly to the driving direction, and a magnetic sensor,
The mover, the magnet with a predetermined and movably coil in the driving direction by Rukoto current is energized so as perpendicular to the magnetic flux generated by the magnet has a gap, S poles along the driving direction And N poles are alternately magnetized, and have a magnetic scale facing the magnetic sensor with a predetermined distance ,
The one magnetic circuit is configured substantially symmetrically when viewed from the driving direction,
The magnetic sensor is a linear actuator disposed at a substantially symmetrical center position of the one magnetic circuit as viewed from the driving direction. The magnetic circuit is configured substantially symmetrically in the driving direction,
  The linear actuator according to claim 1, wherein the magnetic sensor is disposed at a substantially symmetrical center position in a driving direction of the magnetic circuit. The magnetic sensor is a magnetoresistive sensor using MR elements,
Direction of current flowing through the MR element, a linear actuator according to claim 1 or claim 2, wherein said magnetic sensor such that the magnetization direction and the driving direction substantially perpendicular of the magnet is located . 4. The linear actuator according to claim 3, wherein the magnetic circuit is substantially symmetrical with respect to the direction of the current flowing through the MR element. In an optical apparatus for forming an object image on an image plane by an optical system including a moving lens group, the linear actuator according to claim 1, 2 or 3 is used as means for driving the moving lens group. A lens driving device characterized by that.

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