JP2013190705A - Aperture blade driving device - Google Patents

Abstract

Provided is a lens diaphragm driving device that can be made thinner and wider in the effective rotation range and can be mounted on an interchangeable lens.
A disk-shaped casing 2 having a fixed frame 21 and a hole seat 22, a plurality of diaphragm blades 3 provided in the casing 2, a driving wheel 4 for rotating each diaphragm blade around an optical axis, and a driving wheel 4 A rare earth sintered magnet that is magnetized in the thickness direction and is fixed to at least one of the flat yokes. And a flat air-core coil 54 supported so as to be movable relative to the drive magnets 53a and 53b in a plane orthogonal to the optical axis. It is driven to rotate by 20 ° or more along the circumferential direction.
[Selection] Figure 1

Description

The present invention relates to a diaphragm blade drive device that drives a plurality of diaphragm blades to adjust the amount of light.

  In an imaging optical device such as a digital still camera or a video camera, in order to adjust the light quantity of an imaging lens, a plurality of aperture blades are driven by a motor to change the aperture diameter. Conventionally, in this kind of light quantity adjusting device, a stepping motor is used as a drive source for the diaphragm blades, and the rotation of the motor is transmitted to a rotating member (referred to as an arrow wheel or a driving wheel) through a gear reduction mechanism. It is common. For example, in Patent Document 1 (JP-A-6-95205), a drive unit having a pinion gear attached to an output shaft of a stepping motor is fixed to, for example, a lens frame, and a drive gear that meshes with the pinion gear is attached to a side surface. The driving wheel is rotated. A plurality of light shielding members (apertures or blades) are mounted on the surface of the driving wheel, and a plate having a cam groove is provided on the back surface of the driving wheel, and each aperture is moved along the cam groove by the rotation of the driving wheel. Since all the apertures move along the same axis in the direction of the optical axis, it is disclosed that a substantially circular opening is formed on the optical axis, and the amount of light is adjusted by changing the area of the light shielding part. ing. In this aperture control device, a photo interrupter is used to detect the position of the aperture blade, and the rotation angle is adjusted according to the number of steps of the stepping motor by using the photo interrupter as a trigger for the initial rotation position. (See FIG. 4 of Patent Document 1).

By using a stepping motor as described above, the opening area can be reliably changed over a wide range, so there is an advantage that the light amount can be adjusted with high reliability, but there are the following problems. .
(1) Since only the stepping motor protrudes from the disk-shaped aperture unit, it is necessary to have a structure in which the protruding portion is allowed to escape at a portion other than the aperture unit, and the degree of freedom in design is reduced.
(2) Since the video camera (recording) mode is also adopted as the function of the digital camera, noise reduction is required. However, the operation sound of the stepping motor and the gear meshing sound are generated, and the noise reduction is achieved. Hinder.
(3) Since the rotation of the stepping motor is not transmitted directly to the driving wheel, but is transmitted via the gear, there is a gear backlash, and therefore repetitive operation may reduce the reproducibility.
(4) Since the resolution of the aperture area of the diaphragm is determined by the basic step angle and gear ratio of the stepping motor, the resolution setting range is restricted.

  In addition, it has been proposed to use a permanent magnet motor instead of a stepping motor as a driving means for the diaphragm blades. For example, in Patent Document 2 (Japanese Patent Application Laid-Open No. 54-99424), two stationary coils wound around an optical axis in a plane orthogonal to the optical axis, and rotated at positions equidistant from the optical axis, respectively. Each permanent magnet rotation consists of a plurality of permanent magnet rotors that are held at equal intervals in the center of movement, and is caused by the electromagnetic action of the magnetic flux parallel to the optical axis of the permanent magnet rotor and the current flowing in the fixed coil. An electromagnetic device for a camera is disclosed in which a shutter blade or a diaphragm blade is driven directly or indirectly by rotating a child. However, this electromagnetic device has a complicated structure and is difficult to reduce in thickness.

Therefore, in order to reduce the thickness of the diaphragm device, an electromagnetic actuator, also called a voice coil motor (VCM), is used as a driving means for the driving wheel, and the gear transmission mechanism is omitted and the driving wheel is directly driven by the electromagnetic actuator. Has been proposed. For example, in Patent Document 3 (Japanese Patent Laid-Open No. 2006-217686), an optical filter driving device for a video camera, a shutter device that opens and closes an opening for exposure with a blade, or an aperture adjustment of the opening for exposure is adjusted with a blade. It is disclosed that a movable magnet type electromagnetic actuator is used as a drive source for a diaphragm device or the like. This electromagnetic actuator has a housing, a mover having a permanent magnet and an output lever, and supported so as to be swingable around a swing shaft (output lever shaft), and a stator including a coil for excitation. The mover is divided into four magnetic domains parallel to the oscillating plane and magnetized in the thickness direction and arranged in the circumferential direction of the oscillating shaft, and the magnetization directions of the four magnetic domains are set to have opposite polarities alternately. The plate-shaped permanent magnet has a configuration in which a swing shaft is arranged at the center of the plate surface. The coil is an air-core coil that is wound in a flat shape so as to face the plate surface of the permanent magnet, and has two linear portions that are substantially parallel to each other and flow in opposite directions. While facing the surface, they are opposed to each other with the rocking shaft interposed therebetween, and are arranged in a direction crossing two adjacent magnetic domains.

  In addition to this, Patent Document 4 (Japanese Patent Application Laid-Open No. 2007-183304) discloses a light-shielding blade that adjusts the amount of light beam by changing an opening area that allows the light beam to pass through, an electromagnetic coil, and a magnetic flux that generates electromagnetic waves. An electromagnetic actuator having a permanent magnet that moves relative to the electromagnetic coil by electromagnetic force due to the interaction between the current passed through the coil and the magnetic flux and is connected to the light shielding blade to move the light shielding blade, and the strength of the magnetic field of the permanent magnet And a position sensor having an output characteristic correction unit that acquires a predetermined correction parameter and corrects the output characteristic of the magnetic element based on the correction parameter is disclosed. Has been.

JP-A-6-95205 JP 54-99424 A JP 2006-217686 A JP 2007-183304 A

In the diaphragm devices described in Patent Documents 3 and 4 described above, the diaphragm blades are directly driven by an electromagnetic actuator (movable magnet type VCM), so that there is a problem when a stepping motor is used as the diaphragm blade drive means {described above (1) to (4)} can be solved. However, the range in which the DC voltage output from the position sensor (Hall element) has good linearity is only about 5 ° in terms of the rotation angle, and the Hall output voltage is within the range with good linearity. When the diaphragm blades are driven by a control method in which the diaphragm diameter is varied by being rotated by the VCM so as to be proportional, another problem that the diaphragm opening / closing range is restricted occurs.

  Accordingly, an object of the present invention is to provide a lens diaphragm driving device that can be made thinner and wider in the effective rotation range than the conventional one and can be mounted on an interchangeable lens.

In order to achieve the above object, the lens aperture driving device of the present invention comprises:
A disk-shaped casing having a circular hole centered on the optical axis, a plurality of diaphragm blades inside the casing, a moving wheel that rotates each diaphragm blade around the optical axis, and the driving wheel is directly driven. A driving wheel driving means, and a position detection means for detecting the position of the driving wheel driving means,
The driving wheel driving means includes a pair of flat yokes facing each other at a predetermined interval, a driving magnet made of a rare earth sintered magnet magnetized in the thickness direction and fixed to at least one of the flat yokes, A flat air-core coil supported so as to be relatively movable with respect to the drive magnet in a plane orthogonal to the axis, and the driving wheel is driven to rotate by 20 ° or more along the circumferential direction,
The position detecting means includes a sensor magnet fixed to the driving wheel and a magnetic field detecting element fixed to the base member so as to face the sensor magnet.

  In the present invention, the position detecting means has a Hall element fixed to the casing, and the sensor magnet has a rectangular parallelepiped shape that is magnetized in the thickness direction and arranged so that different polarity magnetic poles are adjacent to each other. The pair of sensor magnets is preferably arranged so that a gap facing the magnetic field detection element continuously increases from one end of both magnets toward the boundary.

  In the present invention, each of the sensor magnets is preferably installed such that the detection magnetic pole surface is inclined by an angle range of 10 ° to 30 ° with respect to a straight line parallel to the magnetic sensing surface of the Hall element.

  In the present invention, it is preferable that the sensor magnet is disposed so that a ridge line in the longitudinal direction is in contact with a circle centered on the optical axis when viewed from the optical axis direction.

  In the present invention, it is preferable that one of the yokes is disposed so as to generate a magnetic attractive force along the circumferential direction between the yoke and the drive magnet.

  According to the present invention, the diaphragm unit can be made thinner and quieter, and the number of parts can be reduced, the resolution of the motor is not limited, and the diaphragm opening / closing range can be further expanded, so that it has extremely high practicality.

It is a disassembled perspective view which shows the lens aperture drive device concerning embodiment of this invention. It is a perspective view which shows the external appearance of the lens aperture drive device except the hole seat concerning embodiment of this invention. FIG. 3 is a plan view of FIG. 2. It is a perspective view which shows the external appearance of the lens aperture drive device concerning embodiment of this invention. FIG. 5 is a plan view of FIG. 4. It is sectional drawing which cut | disconnected the lens aperture drive device of FIG. 5 by the AA line. FIG. 3 is an arrow view of the position detection member of the lens aperture driving device shown in FIG. 2 as viewed from the B direction. It is a top view which shows the state which the aperture blade shown in FIG. 3 fully closed. It is a top view which shows the state which the aperture blade shown in FIG. 3 opened fully. It is a figure which shows an example of the signal processing circuit of the position detection apparatus concerning embodiment of this invention. It is a figure which shows an example of magnetic flux density distribution in the surface of the Hall element shown in FIG.

  Details of the present invention will be described below with reference to the accompanying drawings. In the following description, the same functional parts are denoted by the same reference numerals.

<Overall configuration>
As shown in FIGS. 1 and 2 to 5, the lens aperture driving device 1 is formed by combining a fixed frame 21 and a hole seat 22, and has an optical axis Z (see FIGS. 4, 5, and 6) as a center. Inside the disc-shaped casing 2 having a circular hole 220, a plurality of diaphragm blades 3, and a driving wheel 4 reciprocatingly rotated within a predetermined angular range around the optical axis in order to open and close these diaphragm blades, It has a structure in which a voice coil motor (hereinafter referred to as “VCM”) 5 that is a driving wheel driving means and a position detection member 6 that detects the rotational position of the driving wheel 4 are housed. The configuration of each part of the lens aperture driving device 1 is as follows.

[casing]
The fixed frame 21 has a ring-shaped support portion 210 on the inner diameter side, and a plurality of (for example, three) step portions 212 provided at equal angular intervals on the outer peripheral side along the circumferential direction, for example. This is a substantially disk-shaped member having a fan-shaped yoke holding hole 211 at a predetermined position. The hole seat frame 22 has a circular hole 220, an outer ring portion 221 on the outer peripheral side, and a hole (not shown) in which the support shaft 31 of the diaphragm blade is fitted on the diaphragm blade side surface. A plurality of (for example, three) protrusions provided on the concentric circles having the same number as the number of blades and centered on the optical axis Z, and provided, for example, at equiangular intervals along the circumferential direction of the hole seat end surface This is a substantially disk-shaped member having 222. After assembling each component to be described later on the fixed frame 21, the tip of the projection 222 of the hole seat frame 22 is fitted into the stepped portion of the fixed frame 21, and the casing 2 is formed by coupling with the fixed frame 21. The aperture driving device 1 is assembled.

[Aperture blade]
The diaphragm blades 3 can always obtain a diaphragm aperture close to a circle centered on the optical axis by simultaneously rotating three or more blades (for example, seven in this embodiment) in the same direction at the same time. Those having a shape are used. Each diaphragm blade 3 has a support shaft 31 and a guide pin 32. Each support shaft 31 is pivotally supported by the hole seat frame 2 so as to be rotatable in the same direction as the rotation direction of the moving wheel 4, and is circular. In order to obtain a close aperture diameter, a cam groove 40 having an arc shape is formed in the moving wheel 4, and a guide pin 32 is inserted therein. The moving wheel 4 has a circular opening 40 centered on the optical axis in order to regulate the maximum aperture diameter.

[Driving wheel]
In the driving wheel 4, an annular sliding portion 41 is attached to the support portion 210 of the fixed frame 21, and is supported rotatably along the outer peripheral surface of the support portion 210. Since the magnetic circuit member 50 (back yoke 51 and drive magnets 53a and 53b) of the VCM 5 is directly attached to the driving wheel 4, the magnetic circuit member 51 of the VCM 5 is rotated in a predetermined direction (for example, counterclockwise) in FIG. As a result, the moving wheel 4 also rotates in the same direction (counterclockwise), and each diaphragm blade 3 rotates counterclockwise with the support shaft 31 as a fulcrum.

[VCM]
(Constitution)
As shown in FIG. 6, the VCM 5 includes a magnetic circuit member 50 that drives the driving wheel 4, an air-core coil 54 that is disposed in the magnetic circuit member 50, and a position detection member 6 that detects the position of the magnetic circuit member 50. Yes. The magnetic circuit member 50 is magnetized in the thickness direction with a pair of yoke members including an arc segment-shaped fixed yoke 52 fixed to the fixed frame 21 and an arc segment-shaped back yoke 51 fixed to the driving wheel 4. A pair of flat magnets 53 a and 53 b fixed to the back yoke 51 are provided. Restricting members 42 a and 42 b are fixed to the surface of the moving wheel 4 on the side facing the fixed frame 21, and the back yoke 51 is fixed between these restricting members. The drive magnets 53a and 53b are arranged such that magnetic poles of different polarities are adjacent to each other on a plane orthogonal to the optical axis, and a magnetic flux is generated between one yoke and the other yoke. A hollow disk-shaped flexible wiring board 55 is mounted on the surface of the fixed frame 21, and a flat (substantially trapezoidal) air core around which windings are wound in a plane orthogonal to the optical axis. The coil 54 is fixed.

(Position of fixed yoke)
On the plane orthogonal to the optical axis, the fixed yoke 52 can be disposed at a position shifted from the fully closed state to the fully closed direction in the direction of rotation by the suction force in the non-energized state, or further from the fully open state. It can be disposed at a position shifted in the direction of rotation by the suction force in the fully open direction. Thus, by providing the fixed yoke at a specific position, the aperture diameter can be reliably maintained in the fully closed or fully opened state even in the non-energized state.

(Material of drive magnet)
Since the thrust of the VCM is proportional to the current supplied to the air-core coil and the gap magnetic flux density, the drive magnet needs to be formed of a rare earth sintered magnet in order to improve the response. As the rare earth sintered magnet, for example, an R-T-B based sintered magnet (where R is one or more of rare earth elements including Y, Nd is always included, and T is Fe or Fe and Co) is used. can do. In particular, it is desirable to use a RTB-based sintered magnet having a maximum energy product of 45 MGOe or more and a high residual magnetic flux density.

(Operation)
Since the air-core coil 54 is interposed in a magnetic gap formed on the surfaces of the drive magnets 53a and 53b, the drive current is supplied to the coil, so that the The magnets 53a and 53b rotate around the axis, and the driving wheel 4 is driven. The diaphragm blades can be opened and closed by rotating the driving wheel 4 about the optical axis. The rotation angle of the magnet can be adjusted by adjusting the magnitude of the drive current, and the rotation direction of the magnet can be reversed by reversing the direction of the current. For example, when the magnetic pole on the side facing the air-core coil 54 of the drive magnet 53a is N and the magnetic pole on the side facing the air-core coil 54 of the drive magnet 53b is S, an electric current (arrow i in FIG. 8) flows through the air-core coil 54. 9), the drive magnet rotates in the F direction (see FIG. 8), and a state in which the aperture blades shown in FIG. 9 are fully opened appears. Further, the VCM 5 is provided with a yoke (fixed yoke) at a position having a suction function, so that a magnetic attraction force always acts between the drive magnets 53a, 53b and the fixed yoke 52 in the circumferential direction. To do. Therefore, even when the energization to the air-core coil is interrupted, it is possible to automatically maintain the aperture fully open or fully closed.

[Position detection member]
2, 3 and 7, the position detection member 6 includes a magnetic field detection element (for example, a Hall element) 7 mounted on the surface of the wiring board 55 and an outer circumferential circle 44 (however, a part of the position detection member 6 is enlarged). Sensor yokes 61a and 61b and sensor magnets 62a and 62b having a rectangular parallelepiped shape fixed to an arc-shaped holding member 43 extending in the radial direction.

When viewed from the side (see FIG. 7), the sensor magnets 62a and 62b are made of a ferromagnetic material (for example, a steel material) that has an upward gradient from one end to the other end (side closer to the other sensor magnet). The sensor yoke 61a is fixed to the surface (wiring board side) of the sensor yoke 61b made of a ferromagnetic material (for example, a steel material) having a downward gradient from one end to the other end. When viewed from the plane (optical axis direction) (see FIG. 3), the sensor yokes 61a and 61b and the sensor magnets 62a and 62b have the same width and length, and the longitudinal ridge lines of the magnets are centered on the optical axis. It arrange | positions so that it may contact | connect the circle | round | yen (larger diameter than the outer diameter of the driving wheel 4). Since these sensor magnets 62a and 62b are magnetized in the thickness direction so that the magnetic poles of different polarities are adjacent to each other (in FIG. 7, only the magnetic poles on the Hall element side are shown), A closed magnetic circuit passing through the Hall element 7 is formed toward the sensor magnet (in this embodiment, the magnets 62a to 62b).

Further, the back surface side of each sensor magnet 62a, 62b (the magnetic pole surface on the side not facing the magnetic sensitive surface of the Hall element 7) has the same projected area (area when viewed from the optical axis direction) as each magnet. A pair of flat yokes (sensor yokes 61a and 61b) made of a ferromagnetic material are fixed. These flat yokes have a function to prevent the magnetic flux generated from the sensor magnet from leaking to the outside (magnetic shield), and the permanent magnets have high magnetic properties like R-Fe-B sintered magnets. Is valid. However, the sensor yoke can be omitted when the magnetic properties of the magnet are low and the leakage magnetic flux is small.

  As shown in FIG. 7, the sensor magnets 62a and 62b are arranged so as to exhibit an inverted V shape when viewed from a direction perpendicular to the paper surface. That is, the magnets 62a and 62b are held in the holding holes 430a and 430b of the holding member 43 so as to be inclined by the angles α1 and α2 with respect to the plane orthogonal to the optical axis. Therefore, the gap between the magnetic sensitive surface of the Hall element 7 and the magnetic pole surface of the magnet 62a monotonously decreases from the position where one end of the magnet 62a and one end of the magnet 62b approach or contact each other toward the other end of each magnet. The gap between the magnetic sensitive surface of the Hall element 7 and the magnetic pole surface of the magnet 62b is also arranged so as to monotonously decrease. Here, if the gap (minimum value) is too narrow, the magnetic flux waveform tends to be distorted, and if it is too wide, the curved portion increases and the linear region becomes shorter. Therefore, it is preferably set to 1 mm or more and less than 3 mm. The angle α1 and the angle α2 may be the same or different, but are preferably set in the range of 10 ° to 30 °.

  By arranging the pair of sensor magnets in this way, the magnetic flux density on the magnetic sensing surface of the Hall element 7 changes linearly over almost the entire length of the magnet, and the output voltage of the Hall element 7 also changes linearly. . At the initial position where the magnetic flux density is zero, the output voltage of the Hall element is also zero. As the magnet rotates from this initial position, the magnetic flux density detected by the Hall element changes linearly. As a result, the voltage output from the Hall element increases or decreases monotonously, so that the current position can be accurately grasped.

  The sensor magnet can be formed of a known permanent magnet regardless of the material, but from the viewpoint of noise resistance characteristics, in order to set the input circuit side gain low and to reduce the size of the sensor unit, It is preferable to form a rare earth magnet, for example, an R—Fe—B based sintered magnet (where R is one or more of rare earth elements including Y and necessarily includes Nd).

(Hall element)
The output voltage of the Hall element depends on the electron mobility and Hall coefficient of the material, and is usually formed of an N-type semiconductor thin film (thickness of several μm) made of a III-V group compound such as GaAs, InSb, InAs or the like. Hall elements are used. In the present invention, in order to enable highly accurate position control, it is preferable to use a Hall element made of GaAs having a small Hall coefficient temperature coefficient (about −0.06% / ° C.). In addition to compound systems, Hall elements made of Si can be used, and Hall ICs in which Hall elements and signal processing circuits such as operational amplifiers are integrated can be used. It is preferable to have a circuit configuration that reduces the offset voltage and has a temperature compensation function.

(Signal processing circuit)
The Hall element 7 is connected to a position signal processing circuit 8 including an operational amplifier, for example, as shown in FIG. 10 in order to output the position of the movable member as a voltage signal. In the present invention, a drive circuit (not shown) is connected to the input terminal of the Hall element to drive the four-terminal Hall element 7 to obtain an output voltage proportional to the magnetic flux density, and the Hall element output side A circuit configuration in which a differential amplifier circuit 82 is connected to the terminals can be employed. The Hall element is driven with a constant current or a constant voltage. However, when the GaAs Hall element is driven with a constant voltage, the temperature characteristics deteriorate (about −0.3% / ° C.). In the present invention, as shown in FIG. 10, on the input side of the Hall element 7, a constant current driving circuit 81 comprising an operational amplifier OP1 having a non-inverting input terminal connected to a power source (Vc = reference voltage) and a current limiting resistor R1 is provided. It can be connected and driven by a constant current operation where the control current Ic = Vc / R1.

In the differential amplifier circuit 82 that receives the output of the Hall element, the resistor R3 is connected to the operational amplifier OP2 connected to the negative feedback, the resistor R2 connected to the inverting input terminal of the operational amplifier OP2, and the non-inverting input terminal of the operational amplifier OP2. The output voltage of the Hall element is differentially amplified by the resistors R2 and R3. Since the gain G of this differential amplifier circuit is R3 / (R2 + Rout), the position information of the driven member can be output as an appropriate voltage signal by adjusting R2 and R3.

[Operation of position detection member]
A position signal (amount of movement of the movable member) detected by the Hall element 7 is amplified to a predetermined magnification by the signal processing circuit 8, and then compared with a target position command (drive magnet position command signal) by a control circuit (not shown). Thus, a drive signal is generated and a drive current is supplied to the drive circuit of the VCM. Here, when the sensitivity center of the Hall element 7 exists at the initial position (magnetic pole boundary position where the polarity is reversed), the output voltage of the Hall element is zero, but the Hall element 7 moves relative to the sensor magnet in the circumferential direction. Therefore, since the output voltage of the Hall element changes in proportion to the magnetic flux density (increases or decreases linearly), the position of the movable member can be accurately detected. Therefore, in FIG. 3, the driving wheel 4 moves by a predetermined angle in the clockwise (counterclockwise) direction and stops at that position, so that a predetermined aperture diameter can be obtained.

[Opening and closing operation of aperture blade]
In the diaphragm driving device having the above-described configuration, the opening / closing operation of the diaphragm blades will be described with reference to FIGS. In FIG. 8 and FIG. 9, a part (three pieces) of the diaphragm blades is omitted. When no current is supplied to the air-core coil 54 of the VCM 5, the aperture blade 3 is maintained in the state shown in FIG. 8, and the aperture opening is maintained in a fully closed state. When the air-core coil 54 is energized and the moving wheel 4 rotates clockwise around the optical axis and the magnets 53a and 53b also rotate in the same direction, the aperture blade 3 moves along the cam groove 40 with the support shaft 31 as a fulcrum. Since it rotates, the aperture diameter is opened as shown in FIG. Here, when the end portion of the sensor magnet 62a faces the Hall element 7, the output voltage of the Hall element 7 becomes zero, and the supply of the drive current is interrupted at that position. Further, when changing from the fully open state shown in FIG. 9 to the minimum aperture state shown in FIG. 8, the direction of the current supplied to the air-core coil 54 may be reversed, and before the state shown in FIG. If it stops at a desired position, the aperture diameter corresponding to each stop position can be obtained. At the end of this opening / closing operation, the drive magnet 53a and the drive magnet 53b are magnetically attracted toward the fixed yoke 52, so that even if the supply of current to the air-core coil 54 is stopped, both magnets remain in their positions. And the aperture diameter can be maintained.

[Experiment 1]
In FIG. 1, the magnetic flux density distribution in the Z direction was determined when α1 = α2 = 15 ° and the gap (minimum value) between the Hall element 7 and the sensor magnets 62a and 62b was set to 2.5 mm. Here, Nd-Fe-B sintered magnet (NMX-S45SH manufactured by Hitachi Metals, length = 8 mm, width = 2 mm, thickness = 1 mm) is used as the sensor magnet, and a GaAs Hall element is used. The magnetic flux waveform when the Hall element 7 moves from the end of the sensor magnet 62a to the end of the sensor magnet 62b was obtained by simulation. Since the magnetic flux density is substantially zero between the sensor magnet 62a and the sensor magnet 62b (initial position), the offset of the output voltage is adjusted so that the output voltage of the Hall element is zero at this position.

As shown in FIG. 11, in the case of the present invention, it is understood that the change in the magnetic flux density is linear within a very wide angle range (θ2−θ1 = about 27 °). On the other hand, when the gap between the Hall element and the end of the sensor magnet is constant along the circumferential direction, the change in the magnetic flux density is linear only in the vicinity of the magnetic pole boundary and extremely narrow. It was confirmed to be in the range (about 5 °).

The effects of the present embodiment are listed as follows.
(i) The aperture unit can be flattened, and the design freedom of the entire lens can be increased, and the structure can be simplified and downsized. Also, downsizing is possible even when a drive device is built in the camera body.

(ii) Since the VCM using the movable part rotating without contact is used, there is no running noise of the motor and no gear noise from the speed reduction mechanism. Moreover, since the output of the VCM is directly transmitted to the driving wheel, the number of parts can be reduced.
(iii) Since the thrust of the drive device is proportional to the drive current passed through the coil, the resolution of the aperture area of the diaphragm can be reduced regardless of the control method.

In particular, since the initialization position is in the middle of the movement range, the movement distance required for setting the origin, that is, the origin setting time, is halved as compared with the conventional photo interrupter, so that the sensing speed can be increased.

Since an analog voltage proportional to the moving distance is output from the Hall element, the resolution can be increased by increasing the reading accuracy. Moreover, since the length dimension in the optical axis direction may be set equal to the movement length, the rotation angle of the movable member can be increased to, for example, 20 ° or more in the plane perpendicular to the optical axis direction.

(Modification)
In the above embodiment, the VCM shows a structure (movable magnet type VCM) in which the drive magnet is fixed to the driving wheel and the air-core coil is provided on the fixed frame. However, for the purpose of improving responsiveness, the VCM In order to reduce the weight, a structure (moving coil type VCM) in which a drive magnet is provided on a fixed frame and an air core coil is provided on a driving wheel may be used.

In addition, as long as the shape of the drive magnet is a flat plate shape, the shape is not limited to an arc shape but may be a rectangular parallelepiped shape. Further, instead of providing a self-holding function during non-energization using magnetic attraction, the driving wheel can be biased by a spring in a predetermined direction.

In addition to the above, the sliding of the moving wheel and the fixed frame is not limited to an annular inner and outer diameter sliding, and a sliding portion may be provided on a surface orthogonal to the optical axis, and other members such as bearings. You may make it slide using things like.

1: Lens aperture driving device,
2: casing,
21: fixed frame, 210: support portion, 211: yoke holding hole, 212: stepped portion,
22: Hole seat frame, 220: Circular hole, 221: Outer ring part, 222: Projection part,
3: aperture blade, 31: support shaft, 32: guide pin,
4: Driving wheel, 40: Cam groove, 41: Sliding part, 42a, 42b: Restricting member, 43: Holding member, 430a, 430b: Magnet member holding hole, 44: Peripheral circle 5: Voice coil motor (VCM)
50: Magnetic circuit member, 51: Back yoke, 52: Fixed yoke, 53a, 53b: Driving magnet, 54: Air-core coil, 55: Flexible substrate,
6: position detection member, 61a, 61b: sensor yoke, 62a, 62b: sensor magnet, 7: Hall element,
8: signal processing circuit, 81: constant current circuit, 82: amplifier circuit,

Claims (5)

A disk-shaped casing having a circular hole centered on the optical axis, a plurality of diaphragm blades inside the casing, a moving wheel that rotates each diaphragm blade around the optical axis, and the driving wheel is directly driven. A driving wheel driving means, and a position detection means for detecting the position of the driving wheel driving means,
The driving wheel driving means includes a pair of flat yokes facing each other at a predetermined interval, a driving magnet made of a rare earth sintered magnet magnetized in the thickness direction and fixed to at least one of the flat yokes, A flat air-core coil supported so as to be relatively movable with respect to the drive magnet in a plane orthogonal to the axis, and the driving wheel is driven to rotate by 20 ° or more along the circumferential direction,
The position detecting means includes a sensor magnet fixed to a driving wheel and a magnetic field detecting element fixed to the casing so as to face the sensor magnet. The position detecting means has a Hall element fixed to the casing, and the sensor magnet is a pair of magnets having a rectangular parallelepiped shape magnetized in the thickness direction, and is directed from one end of both magnets toward the boundary. The lens aperture driving device according to claim 1, wherein a gap facing the hall element is increased.   3. The sensor magnet according to claim 1, wherein each of the sensor magnets is installed such that a detection magnetic pole surface is inclined by an angle range of 10 ° to 30 ° with respect to a plane parallel to the magnetic sensing surface of the Hall element. The lens aperture driving device described.   The lens diaphragm according to any one of claims 1 to 3, wherein the sensor magnet is disposed such that a ridge line in a longitudinal direction is in contact with a circle centered on the optical axis when viewed from the optical axis direction. Drive device.   The lens according to any one of claims 1 to 3, wherein the driving means is arranged such that one of the yokes generates a magnetic attractive force in a circumferential direction between the yoke and the driving magnet. Aperture driving device.

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