JPH0493907A - Lens driving device - Google Patents

Abstract

PURPOSE:To realize the device which is small in size and lightweight and has good assembly performance by forming a magnetic circuit of permanent magnetic around a lens frame guide shaft, and supplying a current to a drive coil arranged crossing its magnetic flux and driving a lens frame. CONSTITUTION:When a zoom command is supplied to a drive circuit 76, a coil 83 is fed with electricity in a direction based upon the command. The coil 83 is cross-linked to the magnetic flux of the permanent magnetic, so the thrust increases when the coil is fed with electricity to move the lens frame 74. When the lens frame 74 moves, the signal Zt of a zoom encoder 68 varies. A subject distance is measured by a range finding means 71, so a distance signal Ht is calcualted. Those signals Zt and Ht are inputted to a microcomputer 72 to calculate the position of a lens group 34 for holding an image plane at a constant position and a focus signal Mt. Further, the position signal Ft of a lens group 34 is inputted to the microcomputer 72 from a focus encoder 69. The microcomputer 72 controls a circuit 73 until the signal Ft matches the signal Mt to drive the lens group 34 to the specific position.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a lens driving device that linearly drives a lens of a photographing device, such as a zoom lens, using electromagnetic force to achieve focusing operations.

2. Description of the Related Art In recent years, in response to market needs, photographic devices such as video cameras and still cameras have been made smaller and lighter while maintaining and improving performance such as autofocus responsiveness and noise reduction.

Conventional zoom lens drive devices use dedicated DC micro motors, stepping motors, etc. as drive sources to drive the focusing lens and variable magnification lens.
A single drive source drives a plurality of lenses using transmission path switching means such as a clutch.

Problems to be Solved by the Invention However, with the above-mentioned conventional configuration, (1) when the motor is incorporated into the lens barrel, the motor portion protrudes, making it impossible to completely downsize the camera-integrated VTR.

(2) The motor itself and the speed reduction mechanism become sources of noise and vibration, causing noise and discomfort to the microphone. Furthermore, the lens cannot be driven at high speed, making it extremely difficult to improve lens performance such as improving autofocus responsiveness.

(3) When driving a plurality of lenses with one drive source, there are problems such as a complicated transmission path switching means is required and it is not possible to drive a plurality of lenses at the same time.

The present invention has been made to solve the above-mentioned conventional problems, and aims to provide a lens driving device that is smaller and lighter, and that improves performance such as lens responsiveness and noise reduction.

Means for Solving the Problems To achieve this object, the lens driving device of the present invention has the following features:
a photographic lens system that forms an optical image of a subject and has a plurality of movable lens systems that are movable in the optical axis direction; a plurality of lens frames that respectively hold the plurality of movable lens systems;
a guide shaft movably supporting the plurality of lens frames in the optical axis direction; a fixed permanent magnet whose front and back surfaces are magnetized and arranged around the guide shaft; and a fixed permanent magnet that is in close contact with the surface of the fixed permanent magnet; a back yoke made of a magnetic material arranged with a gap between the back surface and the plurality of lens frames arranged around the guide axis and arranged in the gap between the back surface of the fixed permanent magnet and the back yoke; and a plurality of windings, each of which is movable integrally in the optical axis direction.

Effect The present invention has the above-described configuration, and has a unique magnetic circuit arranged around a guide shaft that movably supports a plurality of lens frames in the optical axis direction, and a magnetic circuit arranged around the guide shaft at a position crossing the magnetic flux of this magnetic circuit. Since the drive coils are arranged, it becomes possible to drive each of the plurality of lens frames independently. In addition, by arranging this back yoke in a direction substantially perpendicular to the plane containing the guide axis and the optical axis and the guide axis to form a magnetic circuit, the distance between the guide axis and the optical axis of the lens is equal to the thickness of the magnetic circuit. It becomes possible to make the structure considerably shorter. Furthermore, since the influence of twisting moments due to frictional force during driving can be suppressed, a small and lightweight lens driving device can be realized by using a small actuator with a small driving force.

In addition, a magnetic circuit using horseshoe-shaped permanent magnets is formed around a guide shaft that supports the lens frame movably in the optical axis direction, and a drive coil is arranged around the guide shaft at a position that crosses the magnetic flux of this magnetic circuit. This allows the distance between the guide shaft and the optical axis of the lens to be shortened by the thickness of the magnetic circuit, making it possible to realize a compact and lightweight lens driving device.

Furthermore, since the magnetic circuit consists of a permanent magnet and a back yoke, and is fixed, the lens frame that moves in the optical axis direction does not basically need to be made of magnetic material. Therefore, it is possible to drive with a low load without being affected by the attraction force of the magnetic circuit.

EXAMPLE Hereinafter, an example of the present invention will be described with reference to the drawings.

1 is a side view of a lens driving device according to a first embodiment of the present invention, FIG. 2 is a plan view of the same lens driving device, and FIG. 3 is a sectional view taken along the line A-B in FIG. 1. 1 to 3, the photographing lens 30 includes, in order from the object side, a first lens group 31 having a positive refractive power, a second lens group 32 having a variable magnification effect by moving on the optical axis, A third lens group 33 that has a light-condensing effect, and a fourth lens that moves on the optical axis so as to keep the image plane, which changes due to the movement of the second lens group 32 and the movement of the object, at a constant position from the reference plane. Group 34
Consists of.

Bearing parts 75a and 75b of a second lens frame 74 that holds the second lens group 32 are inserted into a guide pole 37 that is positioned and supported by the fixed frame 35 and the crystal frame 36 so as to be movable in the optical axis direction. . Similarly, bearings 39a and 39b of the fourth lens frame 38 holding the fourth lens group 34 are inserted so as to be movable in the optical axis direction. Further, a cutout groove 74a provided in the second lens frame 74 engages with the guide pole 76, and holds the second lens frame 74 on the optical axis. In addition, the guide pole 40 has a cutout groove 38 provided in the lens frame 38.
a is engaged to hold the lens frame 38 on the optical axis.

Next, the actuator will be explained.

Permanent magnets 42.43 and 77.78 have unipolar magnetized surfaces 44.45 and 79.80 (not shown), respectively, with first yokes 46.47 made of a ferromagnetic material such as iron attracted to them. ing. The first back yoke 46,47 is attracted to the second back yoke 48,49 fixed to the fixed frame 35 by the magnetic fields of the permanent magnets 42, 43 and 77,78, respectively.

With such a configuration, the permanent magnet 42.43
, 77.78, the magnetic flux that jumps into the second bank yoke 48.49 from the unipolar magnetized surfaces 50, 51 and 81.82 (not shown) flows to the first back yoke 46.47, and the permanent magnet 42 ．． 43. A closed magnetic path returning to 77 degrees and 78 degrees will be formed. A fill 53 is fixed to the fourth lens frame 38. As shown in FIG. 3, when the coil 53 is fixed to the fourth lens frame 38, the through hole 54
By providing the second back yoke 48.49 through the through hole 54.55, the coil 53 is interlinked with the magnetic flux of the permanent magnet 42.43. When current flows through the fill 53, a thrust is generated in the optical axis direction according to Fleming's left-hand rule. Similarly, a coil 83 is fixed to the second lens frame 74, and a second coil 83 is inserted into the fixed insect repellent through hole (not shown).
By passing through the back yokes 48 and 49 of the coil 83, the coil 83 becomes interlinked with the magnetic flux of the permanent magnets 77 and 78, and when a current flows through the coil 83, light is emitted according to Fleming's left hand rule. Thrust will be generated in the axial direction.

A zoom encoder 68 and a focus encoder 69 are respectively connected to the second lens group 32. It detects the position of the fourth lens group 34, and is composed of a potentiometer or the like that utilizes the fact that a terminal slides on a resistive element and the applied voltage is divided in proportion to the terminal position.

The microcomputer 72 compares the output signal Ht containing the object distance information measured by the distance measuring means 71 with the output signal 21 of the zoom encoder 68, and adjusts the light of the fourth lens group 34 to keep the image plane in a fixed position. A position on the axis is determined, and a focus signal Mt corresponding to this position is calculated. The second drive circuit 73 supplies current to the coil 53 and drives the fourth lens frame 38 according to instructions from the microcomputer 72.
It is driven by the microcomputer 72 until the focus signal Mt of No. 2 and the output signal Ft of the focus encoder 69 match. The first drive circuit 76 supplies current to the coil 83 to drive the second lens frame 74 in a direction selected by an external switch (not shown).

The operation of the lens driving device configured in this way will be explained.

In the lens configuration described in the embodiment, when the position of the second lens group 32 or the subject distance changes, the image plane moves on the optical axis and the focus becomes blurred.
It is necessary to detect the position and subject distance, calculate the position of the fourth lens group 34 where the image plane does not move, and maintain the fourth lens group 34 at that position. The operation associated with focus adjustment will be explained below. When a zooming command is given to the first drive circuit 76 by an external switch (not shown),
The fill 83 is energized in the direction given by the zooming command. The effective coil portion (not shown) facing the permanent magnets 77 and 78 of the coil 83 is always in a state of interlinking with the magnetic flux, so when the coil 83 is energized, light is emitted according to Fleming's left hand rule. Thrust is generated in the axial direction, and the second
Zooming is performed by moving the lens frame 74 in the optical axis direction. When the second lens frame 74 moves, the signal 21 of the zoom encoder 68 changes. Further, since the distance to the object is always measured by the distance measuring means 71, when the distance to the object changes, a signal Ht corresponding to the distance is calculated. These output signals Zt and Ht are input to the microcomputer 72,
2, the position of the fourth lens group 34 that keeps the image plane in a fixed position is calculated.

Also, a focus signal Mt corresponding to this position is calculated.

Furthermore, since the output signal Ft of the focus encoder 69 is always input to the microcomputer 72, the fourth lens group 3
4's current location can be constantly monitored. The output signal Ft indicating the current position of this fourth lens group 34 is compared with the focus signal Mt, and the microcomputer 7
2 controls the second drive circuit 73 and controls the fourth lens group 34.
into position. When a current is applied to the coil 53, the effective coil portion (not shown) facing the permanent magnets 42 and 43 of the coil 53 is always interlinked with the magnetic flux, so according to Fleming's left hand rule, A thrust is generated in the optical axis direction. At this time, a resultant force of the thrust is generated on the guide pole 37. Therefore, since no twisting moment is generated due to thrust, the lens frame can be moved in the optical axis direction with less thrust.

As described above, according to this embodiment, coils are fixed around the bearings of a plurality of lens frames that move in the optical axis direction, and a common hack yoke is provided on the left and right sides of the coils, and the coils are provided over the movable range of each lens frame. By arranging a fixed magnetic circuit, it is possible to construct an actuator with simple components and a reduced number of parts. Furthermore, it is possible to shorten the distance between the guide shaft and the optical axis of the lens by an amount equivalent to the thickness of the magnetic circuit, resulting in a compact and lightweight lens driving device.

In addition, since the resultant force of the thrust is not generated on the kite axis, the twisting moment due to the thrust is theoretically generated, so it is possible to drive the lens frame with less power, resulting in high driving efficiency and a small and lightweight actuator. This lens drive device is suitable for various applications and easy to assemble.

Furthermore, since the moving member is only the coil rather than the magnetic material, it is not subject to the attraction force of the magnet. Therefore, the structure has an extremely low load during driving.

In this embodiment, the first back yoke and the second back yoke disposed on the left and right sides of the guide ball are described as separate members, but there is no problem if they are made of the same member.

4 is a side view of a lens driving device according to a second embodiment of the present invention, and FIG. 5 is a sectional view taken along line CD in FIG. 4.

4 and 5, a horseshoe-shaped permanent magnet 56.
64 are each attracted to a first back yoke 58 made of a ferromagnetic material such as iron on surfaces 57 and 65 which are magnetized to a single pole. Further, the second back yoke 59 is attached to the fixed frame 35 with screws 6.
7a.

67b. The first back yoke 58 is attracted to the second yoke 59 by the magnetic field of the horseshoe-shaped permanent magnet 56 itself. The magnetic flux that jumped into the second back yoke 59 from the unipolar magnetized surfaces 60, 67 of the horseshoe-shaped permanent magnet 56.64 flows to the first hack yoke 58, and a closed magnetic path returns to the horseshoe-shaped permanent magnet 56.84. will be formed. Second lens frame 74. Air-core coils 84 and 61 are fixed to each of the fourth lens frames 38. As shown in FIG. 5, when the air-core coil 61 and the fourth lens frame 38 are fixed together, a space 62 is created, through which the second back yoke 59 is disposed. Second lens frame 7
4 is similarly arranged. Since the other components are the same as those in the first embodiment, their explanation will be omitted.

The operation of the lens driving device configured in this way will be explained. The effective coil portion 61a of the air-core coil 61 facing the horseshoe-shaped permanent magnet 56 is always interlinked with the magnetic flux. Therefore, when current flows through the air-core coil 61, according to Fleming's left-hand rule, the effective coil portion 61a
A thrust is generated in the optical axis direction, and the fourth lens frame 38 is driven in the optical axis direction. The second lens frame 74 is similarly driven.

As described above, according to this embodiment, a cylindrical air core film is fixed around the bearing part of the lens frame that moves in the optical axis direction,
By arranging a fixed magnetic circuit around it, the effective coil portion that contributes to the thrust can be made long, so that electrical energy can be efficiently converted into mechanical energy.

In the first and second embodiments, permanent magnets corresponding to each movable lens are provided, but any number of permanent magnets may be used as long as the permanent magnet covers the movable range of a plurality of movable lenses. .

Effects of the Invention As described above, the lens driving device of the present invention includes a photographing lens system that forms an optical image of a subject and has a plurality of movable lens systems that are movable in the optical axis direction, and a photographic lens system that forms an optical image of a subject and that has a plurality of movable lens systems that are movable in the optical axis direction. A plurality of lens frames to be held respectively, a guide shaft that supports the plurality of lens frames movably in the optical axis direction, a fixed permanent magnet whose front and back surfaces are magnetized and arranged around the guide shaft, and A back yoke made of a magnetic material that is in close contact with the front surface of the fixed permanent magnet and spaced from the back surface, and a back yoke that is arranged around the guide shaft and is located in the gap between the back surface of the fixed permanent magnet and the back yoke. By providing a plurality of windings that are arranged and movable in the optical axis direction integrally with the plurality of lens frames, it is possible to realize a lens drive device that is small, lightweight, and easy to assemble.

[Brief explanation of drawings]

1 is a side view of a lens driving device according to a first embodiment of the present invention, FIG. 2 is a plan view of the same lens driving device, FIG. 3 is a sectional view taken along the line A-B in FIG. The figure is a side view of the lens driving device in the second embodiment of the present invention, and FIG.
It is a sectional view of section CD of the figure. 30...Photographing lens, 37...Guide ball,
38... fourth lens frame, 42. 43. 77,
78...Permanent magnet, 4B, 47.58...1st
York, 48. 49. 59...Second yoke, 53°83...Coil, 56.64...
- Horseshoe-shaped permanent magnet, 74...second lens frame. Name of agent: Patent attorney Shigetaka Awano Haka 1 Meijyo Daizufu 5 11! 1 Majesty 53, 113 Phil Castle

Claims (4)

[Claims] (1) A photographic lens system that forms an optical image of a subject and has a movable lens system that is movable in the optical axis direction, a lens frame that holds the movable lens system, and this lens frame that is movable in the optical axis direction. a permanent magnet whose front and back surfaces are magnetized and arranged around the guide shaft; and a back yoke made of a magnetic material that is in close contact with the front surface of the permanent magnet and is arranged with a gap between the back surface and the guide shaft. and a lens drive comprising a coil disposed around the guide axis in the gap between the back surface of the permanent magnet and the back yoke, and movable in the optical axis direction integrally with the lens frame. Device. (2) The lens driving device according to claim 1, wherein the permanent magnet is arranged over a movable range of the lens frame. (3) The lens driving device according to claim 1, wherein the permanent magnet is arranged in a direction substantially perpendicular to the guide axis and a plane including the guide axis and the optical axis, and parallel to the guide axis. (4) a horseshoe-shaped permanent magnet whose inner and outer surfaces are magnetized and arranged around the guide shaft; a back yoke made of a magnetic material that is in close contact with the outer surface of the permanent magnet and is arranged with a gap between the inner surface and the inner surface;
Claim 1, further comprising a coil arranged around the guide axis, arranged between the inner surface of the permanent magnet and the back yoke, and movable in the optical axis direction integrally with the lens frame.
The lens driving device described.