JP2011237507A - Linear actuator, and lens unit and camera equipped the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a compact linear actuator enabling the smooth movement and accurate position detection of a lens holder.SOLUTION: A linear actuator (10) driving a lens comprises: a lens holder (14); a guide shaft (18) guiding the lens holder; two voice coil motors 22a, 22b respectively equipped with driving coils 32a, 32b, driving magnets 30a, 30b, and yokes 26a, 26b leading the magnetism of the driving magnets to the driving coils, and disposed on both sides of the guide shaft so as to make a generally right angle; and a magnetic sensor (24) disposed between those two voice coil motors and detecting a position of the lense holder. The yokes are provided with guard yoke portions 36a, 36b suppressing the magnetism leaking from the driving magnets and influencing on the magnetic sensor.

Description

  The present invention relates to a linear actuator, and more particularly, to a linear actuator that drives a lens in the optical axis direction, a lens unit including the same, and a camera.

  Japanese Patent Laid-Open No. 10-225083 (Patent Document 1) describes a linear actuator. This linear actuator is used by being arranged inside a lens barrel, and is configured to move a lens holder to which a lens is attached in the optical axis direction of the lens. In this linear actuator, the lens holder is slidably supported in the direction of the optical axis by two guide shafts arranged on both side surfaces of the lens.

  Further, a driving coil is provided around the lens holder, and magnetic circuits are arranged at two positions above and below the lens so as to surround a part of the driving coil. Each magnetic circuit includes a main yoke, a side yoke, and a magnet attached to the inside of the main yoke so as to face the driving coil. As a result, when a current is passed through the driving coil, a driving force is generated between the upper and lower magnetic circuits, and the lens holder is driven in the optical axis direction along the two guide shafts. . The movement of the lens is measured by detecting the magnetism of a magnetic scale attached to the lens holder along the guide shaft by a magnetic sensor.

Japanese Patent Laid-Open No. 10-225083

  However, in the linear actuator described in Japanese Patent Laid-Open No. 10-225083, since the magnetic circuits are arranged above and below the lens, there is a problem that the entire actuator becomes large and difficult to be accommodated in the lens barrel. . Further, in this linear actuator, since two guide shafts are provided on the left and right sides of the lens, this also increases the size of the entire actuator and makes it difficult to store it in the lens barrel.

  In addition, when the lens holder is guided by the two guide shafts, sliding resistance between the guide shaft and the lens holder increases due to errors in parallelism between the two guide shafts, and the lens can be smoothly moved. The problem of being unable to move occurs. On the other hand, when the lens holder is guided by one guide shaft, the perpendicularity of the lens holder to the guide shaft is likely to be lowered, so that so-called “galling” occurs to the guide shaft, and the sliding resistance is likely to increase. There is a problem. This problem is particularly likely to occur when the driving force for driving the lens holder is not well balanced with respect to the guide shaft.

  Furthermore, it is desirable that the sensor for measuring the position of the lens holder is disposed close to the guide shaft. When the sensor is arranged at a position away from the guide shaft, there is a problem that the position measurement accuracy is lowered due to a decrease in the perpendicularity of the lens holder to the guide shaft. As a sensor for measuring the position, a magnetic sensor is preferable from the viewpoint of measurement accuracy, cost, etc. However, if the magnetic sensor is arranged in the vicinity of the driving magnet, there is a problem that the measurement accuracy decreases due to the influence of the magnet. appear.

  The present invention has been made in view of the above problems, and can be stored compactly in a lens barrel or the like while enabling smooth movement of the lens holder and accurate position detection of the lens holder. It is an object of the present invention to provide a linear actuator that can be used, a lens unit including the same, and a camera.

  In order to solve the above-described problems, the present invention is a linear actuator that drives a lens in the optical axis direction, and a lens holder to which the lens is attached, and the lens holder is moved in the optical axis direction. And a guide coil for guiding the drive magnet, a drive magnet, and a yoke for guiding the magnetism of the drive magnet to the drive coil, respectively, and arranged on both sides of the guide shaft so as to be substantially perpendicular to each other. Two voice coil motors, and a magnetic sensor that is disposed between the two voice coil motors and detects the position of the lens holder, and the yoke has a magnetism that leaks from the drive magnet and affects the magnetic sensor. It is characterized in that a guard yoke portion for suppressing the above is provided.

  In the present invention configured as described above, the lens holder to which the lens is attached is guided by the guide shaft and moved in the optical axis direction. The lens holder is moved in the optical axis direction by the driving force of two voice coil motors including a driving coil, a driving magnet, and a yoke. The two voice coil motors are disposed on both sides of the guide shaft so as to be substantially perpendicular to each other, and a magnetic sensor is disposed between the two voice coil motors.

  According to the present invention configured as described above, since the two voice coil motors are arranged so as to be substantially perpendicular to each other on both sides of the guide shaft, the driving force acting on both sides of the guide shaft is well balanced, and the drive An increase in sliding resistance due to force imbalance can be prevented. Furthermore, since a magnetic sensor is disposed between the two voice coil motors together with the guide shaft, it is possible to avoid a decrease in position measurement accuracy due to distortion of the lens holder or the like. In addition, since the yoke is provided with a guard yoke portion, a magnet for driving the voice coil motor is generated even when the magnetic sensor is disposed between the two voice coil motors and close to the voice coil motor. A decrease in position measurement accuracy due to the influence of a magnetic field can be suppressed.

  In the present invention, preferably, the guide shaft is made of a magnetic material, and the magnet that leaks from the driving magnet and affects the magnetic sensor is further suppressed by the guide shaft.

  According to the present invention configured as described above, since the influence of the driving magnet on the magnetic sensor is also suppressed by the guide shaft, it becomes possible to dispose the driving magnet and the magnetic sensor closer to each other, The linear actuator can be further reduced in size.

  In the present invention, it is preferable that the yoke is disposed inside the winding of the driving coil so as to extend substantially parallel to the optical axis, and extends outside the winding so as to be substantially parallel to the opposing yoke. The drive magnet is attached to the base yoke so as to face the winding, and the guard yoke portion covers at least a part of the drive magnet. It is provided on the side close to the magnetic sensor.

  According to the present invention configured as described above, since the guard yoke portion is provided on the side of the base yoke close to the magnetic sensor so as to cover at least a part of the driving magnet, the yoke is relatively small. While being configured, the influence of the magnetic field of the driving magnet can be suppressed.

  In the present invention, preferably, the guard yoke portion is integrally formed with the base yoke by plastically deforming the base yoke so that a step is formed on one side of the base yoke.

  According to the present invention configured as described above, since the guard yoke portion is formed integrally with the base yoke, the guard yoke portion can be formed without increasing the number of parts. In addition, since the guard yoke part is formed by forming a step on one side of the base yoke, interference with the inner wall surface of the lens barrel of the base yoke is prevented, and the linear actuator is stored more compactly in the lens barrel. It becomes possible to do.

  In the present invention, preferably, the magnetic sensor is arranged on a straight line that bisects an angle formed by two straight lines connecting the optical axis and the two voice coil motors. A guide shaft is arranged between the voice coil motor.

  According to the present invention configured as described above, since the magnetic sensors are arranged on a straight line that bisects the angle formed by the two voice coil motors, the voice coil motors and the magnetic sensors are arranged close to each other. However, the influence on the magnetic sensor from each voice coil motor can be minimized.

  Further, the present invention is a lens unit, comprising a lens barrel, an imaging lens disposed in the lens barrel, and the linear actuator of the present invention attached to the lens barrel. It is a feature.

  Furthermore, this invention is a camera, Comprising: It has the lens unit of this invention, and the camera body to which this lens unit was attached, It is characterized by the above-mentioned.

  According to the linear actuator of the present invention, and the lens unit and camera equipped with the linear actuator, the linear actuator can be compactly placed in a lens barrel while enabling smooth movement of the lens holder and accurate position detection of the lens holder. Can be stored.

It is sectional drawing of the camera by 1st Embodiment of this invention. It is a perspective view of the linear actuator built in the camera of 1st Embodiment of this invention. It is front sectional drawing of the linear actuator incorporated in the camera of 1st Embodiment of this invention. It is side surface sectional drawing of the linear actuator incorporated in the camera of 1st Embodiment of this invention. It is a figure which shows the strength of the magnetic field produced | generated by each drive magnet of the linear actuator in 1st Embodiment of this invention. It is a fragmentary sectional view of the linear actuator in 2nd Embodiment of this invention. (A) (b) The figure which shows the process sequence of the base yoke of the linear actuator in 2nd Embodiment of this invention, (c) The figure which shows the guard yoke part formed in the base yoke by the bending process.

Next, embodiments of the present invention will be described with reference to the accompanying drawings.
First, a camera according to a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a cross-sectional view of a camera according to an embodiment of the present invention.
As shown in FIG. 1, a camera 1 according to an embodiment of the present invention includes a lens unit 2 and a camera body 4. The lens unit 2 includes a lens barrel 6, a plurality of imaging lenses 8 arranged in the lens barrel, and a linear actuator 10 that moves the focus adjustment lens 16 in the optical axis direction.

  The camera 1 according to the first embodiment of the present invention searches for a position where an image formed on the film surface F is focused while moving the focus adjustment lens 16 in the optical axis direction by the linear actuator 10. The focus adjustment lens 16 is moved to the focal position. In the present embodiment, the focus adjustment lens 16 is constituted by a single lens, but the lens for stabilizing the image may be a plurality of lens groups. In this specification, the focus adjustment lens includes one lens and a lens group for stabilizing an image.

  In this embodiment, the focus adjustment lens is moved to the in-focus position by the linear actuator to perform focus adjustment. However, the linear actuator of the present invention is used for zoom adjustment for adjusting the angle of view of the lens unit. It can also be used to move the lens.

The lens unit 2 is attached to the camera body 4 and configured to form incident light on the film surface F.
The generally cylindrical lens barrel 6 holds a plurality of imaging lenses 8 therein, and allows focus adjustment by moving the focus adjustment lens 16.

  Next, the linear actuator 10 built in the camera 1 according to the first embodiment of the present invention will be described with reference to FIGS. FIG. 2 is a perspective view of the linear actuator 10. FIG. 3 is a front sectional view of the linear actuator 10, and FIG. 4 is a side sectional view of the linear actuator 10.

  As shown in FIGS. 2 to 4, the linear actuator 10 is a lens holder 14 to which a focus adjustment lens 16 is attached, and a guide shaft that guides the lens holder 14 so as to be slidable in the direction of the optical axis A. A guide shaft 18 and a sub guide shaft 20 arranged in parallel to the main guide shaft 18 are provided. Further, the linear actuator 10 includes two voice coil motors 22a and 22b that drive the lens holder 14 in the optical axis A direction, a magnetoresistive element 24 (MR element) that is a magnetic sensor that detects the position of the lens holder 14, Have

  Further, the voice coil motor 22a includes a base yoke 26a, a counter yoke 28a attached to the base yoke 26a, a driving magnet 30a attached to the base yoke 26a, and a drive provided so as to surround the counter yoke 28a. Coil 32a. Similarly, the voice coil motor 22b includes a base yoke 26b, a counter yoke 28b, a driving magnet 30b, and a driving coil 32b.

  The lens holder 14 is a substantially flat member, and a focus adjustment lens 16 is attached to a substantially central portion. As shown in FIG. 3, a bearing portion 14 a that receives the main guide shaft 18 is formed in the upper right portion thereof. The lens holder 14 is slid parallel to the optical axis A as the bearing portion 14a (FIG. 3) slides on the main guide shaft 18. Accordingly, the focus adjustment lens 16 is slid in the direction of the optical axis A while maintaining a state orthogonal to the optical axis A.

  Further, a U-shaped groove 14 b (FIG. 3) that engages with the sub guide shaft 20 is formed in the lower left portion of the lens holder 14. The sub guide shaft 20 is disposed so as to extend in the direction of the optical axis A in parallel with the main guide shaft 18, and the sub guide shaft 20 is received in the U-shaped groove 14b. The width of the U-shaped groove 14b is substantially the same as the thickness of the sub-guide shaft 20, and when the sub-guide shaft 20 is received in the U-shaped groove 14b, the deflection of the lens holder 14 centered on the main guide shaft 18 is achieved. (Rotation) is prevented. On the other hand, in the radial direction of the focus adjustment lens 16, since there is play between the U-shaped groove 14 b and the sub guide shaft 20, there is an error in the parallelism between the main guide shaft 18 and the sub guide shaft 20. Even in this case, a significant increase in the sliding resistance of the lens holder 14 is prevented.

  In addition, an elongated position detection magnet 34 (FIG. 2) is attached to the lens holder 14 along the bearing portion 14a. The position detection magnet 34 is attached to the lens holder 14 so as to extend in the optical axis A direction. The position detection magnet 34 is magnetized so that a large number of S poles and N poles are alternately formed in the longitudinal direction, and the position of the lens holder 14 is detected by detecting the magnetism with the magnetoresistive element 24. Can be measured.

  Further, a driving coil 32a constituting a part of the voice coil motor 22a is provided on the upper portion of the lens holder 14, and a driving coil 32b constituting a part of the voice coil motor 22b is provided on the side part. Is provided. As shown in FIG. 3, a straight line M1 connecting the central portion of the voice coil motor 22a and the optical axis A and a straight line M2 connecting the central portion of the voice coil motor 22b and the optical axis A are substantially perpendicular. That is, the two voice coil motors 22a and 22b are arranged on both sides of the main guide shaft 18 so as to make a substantially right angle. In the present embodiment, the angle α formed by the straight line M1 and the straight line M2 is about 100 °.

  The main guide shaft 18 is a round bar-like shaft arranged to extend in parallel with the optical axis A in order to guide the lens holder 14. The main guide shaft 18 is fixed inside the lens barrel 6 and is received in the bearing portion 14a of the lens holder 14, so that the lens holder 14 moves smoothly in the optical axis direction in the lens barrel 6. It has come to be. In the present embodiment, the main guide shaft 18 is a SUS material that is a magnetic material. Further, as shown in FIG. 3, the main guide shaft 18 is disposed between an angle of about 90 ° formed by the straight lines M1 and M2. That is, the two voice coil motors 22 a and 22 b are disposed on both sides of the main guide shaft 18. The main guide shaft 18 is located between the drive magnet 30 a and the magnetoresistive element 24.

  The sub-guide shaft 20 is a round bar-like shaft arranged so as to extend in parallel with the optical axis A in order to guide the lens holder 14. The sub guide shaft 20 is received in the U-shaped groove 14 b of the lens holder 14. Thereby, the shake in the surface orthogonal to the optical axis in the lens barrel 6 of the lens holder 14 is prevented.

  The voice coil motors 22a and 22b are arranged on both sides of the main guide shaft 18 so as to be substantially perpendicular to each other, and are configured to drive the lens holder 14 in the direction of the optical axis A. In the present embodiment, the two voice coil motors 22a and 22b are configured substantially the same, and generate substantially the same driving force in the direction of the optical axis A.

  As shown in FIG. 4, the voice coil motor 22a is joined to the base yoke 26a so as to connect the gate-shaped base yoke 26a whose both ends are bent downward and the leg portions on both sides of the base yoke 26a. A rectangular flat plate-like counter yoke 28a is provided. The opposing yoke 28a extends inward of the winding of the driving coil 32a in parallel with the optical axis A.

  A rectangular plate-like drive magnet 30a is attached to the lower surface of the gate-shaped base yoke 26a so as to face the drive coil 32a. The base yoke 26a, the opposing yoke 28a, and the driving magnet 30a constitute a magnetic circuit, and the magnetic flux is efficiently directed to the driving coil 32a. The winding of the driving coil 32a is wound so as to surround the counter yoke 28a, and the magnetic flux of the magnetic circuit crosses the winding of the driving coil 32a. Thereby, when a current flows through the winding of the driving coil 32a, a driving force in a direction parallel to the optical axis A is generated, and the lens holder 14 is moved together with the driving coil 32a.

  Further, as shown in FIG. 3, a guard yoke portion 36a is provided on the side of the base yoke 26a that is close to the magnetoresistive element 24 so as to cover the side surface of the driving magnet 30a. The guard yoke portion 36a suppresses magnetism that leaks from the driving magnet 30a and adversely affects the magnetoresistive element 24.

  In the present embodiment, the guard yoke portion 36a is formed by bonding a rectangular columnar magnetic material extending in the optical axis A direction to the lower surface of the base yoke 26a with an adhesive. In the present embodiment, the guard yoke portion 36a is configured to cover the entire one side surface of the rectangular plate-like drive magnet 30a, but the guard yoke portion 36a is a part of the side surface of the drive magnet 30a. It can also be configured to cover. In the present embodiment, the guard yoke portion 36a is in contact with the side surface of the driving magnet 30a, but the guard yoke portion 36a and the driving magnet 30a may be separated from each other. Further, the guard yoke portion 36a may be joined to the base yoke 26a by welding or screwing.

  As shown in FIG. 3, the voice coil motor 22b is disposed so as to be substantially perpendicular to the voice coil motor 22a, and has substantially the same configuration as the voice coil motor 22a. The voice coil motor 22b includes a gate-shaped base yoke 26b whose both ends are bent downward, and a rectangular flat counter yoke 28b joined to the base yoke 26b so as to connect the leg portions on both sides of the base yoke 26b. It has. The opposing yoke 28b extends inward of the winding of the driving coil 32b in parallel with the optical axis A. Also in the voice coil motor 22b, the guard yoke portion 36b is provided so as to cover the side surface of the driving magnet 30b on the side close to the magnetoresistive element 24. The guard yoke portion 36b suppresses magnetism that leaks from the driving magnet 30b and adversely affects the magnetoresistive element 24.

  The magnetoresistive element 24 is fixed in the lens barrel 6 so as to face the position detecting magnet 34 and is configured to detect the magnetism of the position detecting magnet 34. In the present embodiment, as shown in FIG. 3, the magnetoresistive element 24 is disposed on a straight line M3 that bisects the angle α formed by the straight lines M1 and M2 connecting the optical axis A and each voice coil motor. Has been. Further, the main guide shaft 18 is disposed between the magnetoresistive element 24 and the voice coil motor 22a. With this arrangement, the influence of the magnetic field generated by the drive magnets 30a and 30b on the magnetoresistive element 24 is minimized.

  The position detection magnet 34 is moved in the optical axis A direction together with the lens holder 14, and the magnetism of the moved position detection magnet 34 is detected by the magnetoresistive element 24. As described above, since the position detecting magnet 34 has a number of S poles and N poles alternately formed in the longitudinal direction, the magnetism detected by the magnetoresistive element 24 when the position detecting magnet 34 is moved. Changes. Therefore, the position of the lens holder 14 can be measured by analyzing the detection signal of the magnetoresistive element 24.

Next, the operation of the camera 1 according to the embodiment of the present invention will be described.
First, a current flows through the driving coils 32 a and 32 b of the linear actuator 10 based on a control signal from the camera body 4. Here, the currents flowing through the driving coils 32a and 32b are substantially the same, and the voice coil motors 22a and 22b generate substantially the same driving force in the direction of the optical axis A. Here, since each voice coil motor 22a, 22b is disposed on both sides of the main guide shaft 18, the balance of the driving force of each voice coil motor 22a, 22b with respect to the main guide shaft 18 is good, and the lens holder 14 Is driven smoothly. That is, when the lens holder 14 is pushed by the driving force of each voice coil motor 22a, 22b and is not exactly perpendicular to the main guide shaft 18, the sliding resistance increases and the lens holder 14 is driven smoothly. It becomes difficult. In this embodiment, since the balance of the driving force of each voice coil motor 22a, 22b is good, the lens holder 14 can easily maintain a right angle with respect to the main guide shaft 18, and an increase in sliding resistance is suppressed. .

  When the lens holder 14 is driven in the optical axis A direction, the position detection magnet 34 attached to the lens holder 14 is moved in the longitudinal direction. The magnetoresistive element 24 disposed so as to face the position detection magnet 34 detects the magnetism of the position detection magnet 34 and generates a signal. The detection signal from the magnetoresistive element 24 is analyzed by a processor (not shown) built in the camera body 4 to determine the position of the lens holder 14. Further, since the position detection magnet 34 is disposed in the vicinity of the bearing portion 14a of the lens holder 14, even if the orthogonality of the lens holder 14 with respect to the main guide shaft 18 is reduced, the influence thereof is small. An accurate position can be measured.

  Here, since the magnetoresistive element 24 is disposed between the two voice coil motors 22a and 22b disposed so as to be substantially perpendicular to each other, the magnetoresistive element 24 is located relatively close to each of the drive magnets 30a and 30b. Susceptible to its magnetic properties. If the magnetoresistive element 24 detects the magnetism of the driving magnet in addition to the magnetism of the position detecting magnet 34, this becomes an error for position measurement.

FIG. 5 is a diagram illustrating the strength of the magnetic field generated by each of the driving magnets 30a and 30b of the linear actuator 10 according to the present embodiment.
As shown in FIG. 5, when the side where the guard yoke portions 36a and 36b are provided and the side where the guard yoke portions 36a and 36b are not provided are compared with respect to the magnetic field formed around the drive magnets 30a and 30b. It can be seen that the region where the magnetic field is provided is narrower in the region (the cross-hatched region in FIG. 5) where the magnetic field is the strongest than the side where the magnetic field is not provided. Thus, in the present embodiment, by providing the guard yoke portion, the influence of the driving magnet on the magnetoresistive element 24 is suppressed. Further, a main guide shaft 18 made of a magnetic material is disposed between the voice coil motor 22a and the magnetoresistive element 24, whereby the magnetic field generated by the driving magnet 30a is applied to the magnetoresistive element 24. The impact is further suppressed.

  According to the camera 1 of the first embodiment of the present invention, the two voice coil motors 22a and 22b are arranged on both sides of the main guide shaft 18 so as to be substantially perpendicular to each other. The working driving force is well balanced, and an increase in sliding resistance due to unbalanced driving force can be prevented. That is, it is possible to avoid a significant increase in sliding resistance due to the occurrence of “galling” between the lens holder 14 and the main guide shaft 18.

  Further, according to the camera 1 of the present embodiment, the magnetoresistive element 24 and the main guide shaft 18 are disposed between the two voice coil motors 22 a and 22 b together with the main guide shaft 18. Are close to each other, and even when the lens holder 14 is distorted by a driving force or the like, the influence on the position measurement accuracy can be kept low.

  Further, according to the camera 1 of the present embodiment, the base yokes 26a and 26b are provided with the guard yoke portions 36a and 36b, respectively, so that the magnetoresistive element 24 is close to the voice coil motors 22a and 22b, Even if it is disposed between the two voice coil motors, the influence of the magnetic field generated by the drive magnets 30a, 30b of the voice coil motors 22a, 22b can be made sufficiently small.

  Further, according to the camera 1 of the present embodiment, the main guide shaft 18 made of a magnetic material is disposed between the magnetoresistive element 24 and the driving magnet 30a. The influence of 30a is also suppressed by the main guide shaft 18. As a result, the influence of the driving magnet 30a on the magnetoresistive element 24 can be further suppressed, and the driving magnet 30a and the magnetoresistive element 24 can be arranged closer to each other.

  Furthermore, according to the camera 1 of the present embodiment, the guard yoke portions 36a and 36b are arranged on the side close to the magnetoresistive element 24 of the base yokes 26a and 26b so as to cover at least a part of the drive magnets 30a and 30b. Since it is provided, the influence of the magnetic field of the driving magnet can be suppressed while the linear actuator is configured to be relatively small.

  Further, according to the camera 1 of the present embodiment, since the magnetoresistive element 24 is disposed on the straight line M3 that bisects the angle α formed by the two voice coil motors 22a and 22b, each voice coil motor. While the 22a and 22b and the magnetoresistive element 24 are arranged close to each other, the influence on the magnetic sensor from each voice coil motor can be minimized.

Next, a camera according to a second embodiment of the present invention will be described with reference to FIGS.
The camera of this embodiment is different from the above-described first embodiment in that a base yoke and a guard yoke portion constituting a built-in linear actuator are integrally formed. Accordingly, here, only the points of the present embodiment that are different from the first embodiment will be described, and description of similar configurations and operations will be omitted.

  As shown in FIG. 6, the linear actuator built in the camera of this embodiment has a voice coil motor 122a. The voice coil motor 122a includes a base yoke 126a, a counter yoke 28a, and a driving coil 32a. And have. The base yoke 126 a is provided with a guard yoke portion 136 a on the side close to the magnetoresistive element 24. Note that, in another voice coil motor (not shown), the guard yoke portion is formed integrally with the base yoke. In the present embodiment, the guard yoke portion 136a is formed integrally with the base yoke 126a by plastic processing of the base yoke 126a.

  Specifically, as shown in FIG. 7A, first, in the base yoke 126a before plastic working, a portion where the guard yoke portion 136a is to be formed is formed as an overhang portion 138. Next, as shown in FIG. 7B, the overhanging portion 138 is so-called “half-punched” by the punch 140 and the die 142 to create a step between the guard yoke portion 136a and the guard yoke portion 136a. Form. Thus, a guard yoke portion 136a that covers a part of the side surface of the driving magnet 30a is formed integrally with the base yoke 126a. Finally, both ends of the base yoke 126a (two opposite sides orthogonal to the optical axis A of the base yoke 126a) are bent to form the base yoke 126a in a gate shape.

  For forming the guard yoke portion 136a by plastic working, “half-punching” as in this embodiment is preferable to bending. That is, as shown in FIG. 7C, when the guard yoke portion 144 is formed by bending, a curved surface having a relatively large curvature radius is formed at the bent portion. Due to the curved surface, the driving magnet 30a cannot be mounted close to the guard yoke portion 144, and a relatively large gap G is generated between the guard yoke portion 144 and the driving magnet 30a. This gap G reduces the effect of reducing the influence of the magnetism of the driving magnet 30a by the guard yoke portion 144, and increases the size of the base yoke.

  On the other hand, in this embodiment, as shown in FIG. 6, it is possible to attach the driving magnet 30a in the vicinity of the guard yoke portion 136a formed by plastic working, and the base yoke is downsized. be able to. This is advantageous for placing the linear actuator in a narrow space of the generally cylindrical lens barrel 6. In particular, in this embodiment, the end portion of the base yoke on which the guard yoke portion 136a is formed falls toward the driving magnet 30a, so that the linear actuator can be housed in a smaller lens barrel.

  According to the camera of the second embodiment of the present invention, since the guard yoke portion 136a is formed integrally with the base yoke 126a, the guard yoke portion 136a can be formed without increasing the number of parts. Further, since the guard yoke portion 136a is formed by forming a step on one side of the base yoke 126a, interference with the inner wall surface of the lens barrel of the base yoke 126a is avoided, and the linear actuator is placed in the lens barrel 6; It becomes possible to store more compactly.

  As mentioned above, although preferable embodiment of this invention was described, a various change can be added to embodiment mentioned above. In particular, in the above-described embodiment, the linear actuator is applied to the lens unit provided in the film camera. However, the linear actuator of the present invention is applied to various cameras such as a digital camera and a video camera, and a replacement lens. Can be applied to units.

  In the above-described embodiment, the yoke is configured by the gate-shaped base yoke and the flat counter yoke. However, the base yoke and the counter yoke are integrally formed by a flat plate bent into a U shape, a C shape, or the like. It can also be configured. Furthermore, in the above-described embodiment, a magnetoresistive element is used as the magnetic sensor, but any magnetic sensor such as a Hall element can be used.

DESCRIPTION OF SYMBOLS 1 Camera of embodiment of this invention 2 Lens unit 4 Camera main body 6 Lens barrel 8 Imaging lens 10 Linear actuator 14 Lens holder 14a Bearing part 14b U-shaped groove 16 Focus adjustment lens 18 Main guide shaft (guide shaft)
20 Sub-guide shafts 22a and 22b Voice coil motor 24 Magnetoresistive element (magnetic sensor)
26a, 26b Base yokes 28a, 28b Opposing yokes 30a, 30b Driving magnets 32a, 32b Driving coils 34 Position detecting magnets 36a, 36b Guard yoke portion 122a Voice coil motor 126a Base yoke 136a Guard yoke portion 138 Overhang portion 140 Punch 142 Die 144 Guard yoke

Claims (7)

A linear actuator that drives the lens in the direction of its optical axis,
A lens holder to which the above lens is attached;
A guide shaft for guiding the lens holder so as to move in the optical axis direction;
A drive coil, a drive magnet, and yokes for guiding the magnetism of the drive magnet to the drive coil, respectively, and two voice coil motors disposed on both sides of the guide shaft so as to be substantially perpendicular to each other; ,
A magnetic sensor disposed between the two voice coil motors and detecting the position of the lens holder;
A linear actuator, wherein the yoke is provided with a guard yoke portion that suppresses magnetism that leaks from the driving magnet and affects the magnetic sensor.   The linear actuator according to claim 1, wherein the guide shaft is made of a magnetic material, and magnetism that leaks from the driving magnet and affects the magnetic sensor is further suppressed by the guide shaft.   The yoke is arranged inside the winding of the driving coil so as to extend substantially parallel to the optical axis, and arranged outside the winding so as to extend substantially parallel to the opposing yoke. The drive magnet is attached to the base yoke so as to face the winding, and the guard yoke portion covers at least a part of the drive magnet. The linear actuator according to claim 1, wherein the linear actuator is provided on a side of the base yoke adjacent to the magnetic sensor.   4. The guard yoke portion according to claim 1, wherein the guard yoke portion is integrally formed with the base yoke by plastically deforming the base yoke so that a step is formed on one side of the base yoke. Linear actuator described in 1.   The magnetic sensor is arranged on a straight line that bisects an angle formed by two straight lines connecting the optical axis and the two voice coil motors. The magnetic sensor and one voice coil motor The linear actuator according to any one of claims 1 to 4, wherein the guide shaft is disposed between the first and second guide shafts. A lens unit,
A lens barrel;
An imaging lens arranged in the lens barrel;
The linear actuator according to any one of claims 1 to 5, which is attached to the lens barrel;
A lens unit comprising: A camera,
A lens unit according to claim 6;
A camera body to which this lens unit is attached;
A camera characterized by comprising:

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