JP2007205425A - Feed screw drive mechanism - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a feed screw drive mechanism allowing the use of a whole feed screw region as an effective drive region while eliminating the possibility of seizure between a nut and a feed screw. <P>SOLUTION: The feed screw drive mechanism comprises a motor for driving a feed screw shaft to be rotated, the nut having a screw hole to be threaded to the feed screw shaft and adapted to be moved forward/backward to the axial direction with the positive/reverse rotation of the feed screw shaft, a driven member to be guided to axial direction of the feed screw shaft in a linearly movable manner and thrust and moved to a first moving direction by the nut, and an energizing means for energizing the driven member to a second moving direction opposite to the first moving direction to move the driven member following the movement of the nut to the second moving direction. The nut has a nut energizing means for unthreading the nut from the feed screw shaft at the moving end in the second moving direction and for consistently energizing the nut toward the first moving direction even in the condition of either being threaded to the feed screw shaft or being unthreaded therefrom. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a feed screw drive mechanism.

  In a feed screw drive mechanism in which a feed screw (lead screw) is screwed into a rotation-restricted nut and the nut is advanced and retracted by the rotation of the feed screw, the nut reaches the end of the feed screw and the movement is restricted. Nevertheless, when the feed screw is further driven to rotate, there is a possibility that a problem called “biting” occurs in which the nut is tightened and becomes inoperable. When precise driving is required as in the case of a camera focusing motor, the movement accuracy (resolution) of the nut can be increased as the pitch of the feed screw is reduced, but on the other hand, biting tends to occur.

  In order to solve such a problem, in the normal use state, the nut and the driven member driven by the nut are set with a margin so that the nut does not reach the end of the feed screw. It is possible. However, in this configuration, the entire region including the vicinity of the end portion of the feed screw cannot be made an effective drive region, and there is a limit to downsizing the mechanism. In addition, if the software signal that operates the motor that drives the feed screw malfunctions, the nut will reach the end of the feed screw despite the allowance as described above, and biting will occur. There was a risk of it occurring.

In order to solve such a problem, in Patent Document 1, when the nut reaches the end of the feed screw, the screwing is released to prevent biting. There is an urging spring to which the nut abuts when the screw is disengaged, and this urging spring presses the nut in the direction of the feed screw, so if the feed screw is rotated in the opposite direction, the nut is turned into the feed screw. It can be re-threaded.
Japanese Patent Laid-Open No. 9-203849

  However, in the structure of Patent Document 1, the load applied to the nut suddenly changes when contacting the urging spring. In other words, because of the biasing spring, the linearity of the driving force applied to the nut is impaired, so that it is not suitable for equipment that requires precise driving. In other words, in the configuration of Patent Document 1, it is difficult to use the entire length of the feed screw as an effective precision drive region. Further, when the nut and the lead screw are unscrewed, if the nut is inclined, the nut cannot be smoothly re-screwed, and the screwed portion may be damaged in some cases.

  Therefore, an object of the present invention is to provide a feed screw drive mechanism that does not cause biting between a nut and a feed screw and can use the entire area of the feed screw as an effective drive region.

  The present invention has a motor that rotates the feed screw shaft in forward and reverse directions and a screw hole that is screwed into the feed screw shaft, and is rotated so that the feed screw shaft is moved forward and backward in the axial direction by forward and reverse rotation of the feed screw shaft. A regulated nut, a driven member that is guided so as to be linearly movable in the axial direction of the feed screw shaft, and is pressed and moved in the first moving direction by the nut; and the driven member is opposite to the first moving direction. In a feed screw driving mechanism having a biasing means for biasing in a second movement direction and moving the driven member following the movement of the nut in the second movement direction, the nut moves in the second movement direction. A nut that releases the screwing with the feed screw shaft at the end and constantly urges the nut toward the first moving direction when the nut is in either the screwed state or the screwed state with the feed screw shaft. It has a biasing means.

  In addition, a movement restricting member that determines a moving end of the driven member in the second moving direction is provided, and when the nut releases the screwing with the feed screw shaft at the moving end in the second moving direction, the nut is driven. It is good to comprise so that it may space apart from a member.

  It is preferable to set the urging forces of the driven members so that the urging force of the urging means of the driven member is stronger than the urging force of the nut urging means.

  The nut biasing means may be a compression coil spring disposed between a fixing member that supports the motor and the nut.

  Moreover, you may comprise so that a nut may cancel | release screw connection with a feed screw shaft further in the movement end in a 1st movement direction.

  Preferably, the nut is provided with a fall prevention hole that is continuous with the screw hole and into which the end of the feed screw shaft is fitted in a state where the screw screw is released.

  The present invention also has a motor that drives the feed screw shaft to rotate in the forward and reverse directions, and a screw hole that engages with the feed screw shaft, and rotates so that the feed screw shaft is moved forward and backward in the axial direction by forward and reverse rotation of the feed screw shaft. In a feed screw drive mechanism having a regulated nut and a driven member that is guided so as to be linearly movable in the axial direction of the feed screw shaft and is moved by the nut. The nut is provided with a hole for preventing the tip of the feed screw shaft from fitting into the nut in a state where the screw screw is released from the screw hole. It is characterized by that.

  The nut may be positioned with the screw hole interposed therebetween so that the nut is released from the screw screw shaft at both moving ends with respect to the feed screw shaft to form a pair of fall prevention holes.

  The driven member in the feed screw driving mechanism of the present invention described above can be, for example, a holding frame for an optical element that constitutes a photographing optical system of a camera. Furthermore, this optical element can be a focusing lens group, and the motor can be a focusing motor that moves the focusing lens group to a focus position in accordance with the subject distance.

  According to the feed screw drive mechanism of the present invention as described above, there is no possibility of biting between the nut and the feed screw, and there is no possibility of sudden load change caused by the nut biasing spring. It can be used as an effective driving region.

  FIG. 1 shows the appearance of a digital camera 200 to which the feed screw driving mechanism of the present invention is applied. A zoom lens barrel 201, an optical viewfinder 203, and a strobe 204 are provided on the front surface of the camera body 202, and a shutter button 205 and a main switch 206 are provided on the upper surface of the camera body 202.

  The zoom lens barrel 201 of the digital camera 200 whose side cross section is shown in FIGS. 2 and 3 is extended from the camera body 202 to the subject side as shown in FIG. 2 at the time of shooting, and as shown in FIG. 3 when shooting is not performed. The body 202 is accommodated (collapsed). In FIG. 2, the zoom lens barrel 201 shows a photographing state in which the upper half section is the wide end and the lower half section is the tele end. As shown in FIGS. 5 and 6, the zoom lens barrel 201 includes a second group straight guide ring 10, a cam ring 11, a third feed cylinder 12, a second feed cylinder 13, a straight guide ring 14, and a first feed cylinder 15. A plurality of substantially concentric annular (cylindrical) members such as a helicoid ring 18 and a fixed ring (movement restricting member, fixed member) 22 of a driven member, and a common central axis of these annular members is shown in FIGS. 3 is shown as the central axis Z0 of the lens barrel.

  The imaging optical system of the zoom lens barrel 201 includes a first lens group LG1, a shutter S and an aperture A, a second lens group LG2, a third lens group LG3, a low-pass filter 25, and a CCD 60 in order from the object side. Each optical element from the first lens group LG1 to the CCD 60 is located on a common photographing optical axis (common optical axis) Z1 in the photographing state. The photographing optical axis Z1 is parallel to the lens barrel central axis Z0 and is eccentric downward with respect to the lens barrel central axis Z0. Zooming is performed by moving the first lens group LG1 and the second lens group LG2 along a photographing optical axis Z1 along a predetermined locus, and focusing is performed by moving the third lens group LG3 in the same direction. In the following description, the “optical axis direction” means a direction parallel to the photographing optical axis Z1, and the subject side is the front and the image plane side is the rear.

  The fixed ring 22 is fixed in the camera body 202, and a fixed holder 23 is fixed to the rear part of the fixed ring 22. A CCD 60 and a low-pass filter 25 are supported on the fixed holder 23. An LCD 20 that displays images and shooting information is provided at the rear of the fixed holder 23.

  A third group lens frame (driven member) 51 that holds the third lens group LG3 is guided straight in a direction parallel to the photographing optical axis Z1 via guide shafts 52 and 53, and a third group frame biasing spring ( The driven member is biased forward by a biasing means 55). An AF nut 54 that is moved back and forth in the optical axis direction by the focusing motor 160 is applied to the third group lens frame 51. When the AF nut 54 is moved rearward by the focusing motor 160, the third group lens frame 51 is It is pressed by the AF nut 54 and moved rearward. Conversely, when the AF nut 54 is moved forward, the third group lens frame 51 is moved forward following the AF nut 54 by the biasing force of the third group frame biasing spring 55. A driving mechanism of the third group lens frame 51 will be described later.

  As shown in FIG. 4, a zoom motor 150 is supported on the fixed ring 22. The driving force of the zoom motor 150 is transmitted to the zoom gear 28 in FIG. 5 through the reduction gear mechanism. The zoom gear 28 is pivotally attached to the fixed ring 22 by a zoom gear shaft 29 parallel to the photographing optical axis Z1.

  A helicoid ring 18 is supported inside the fixed ring 22. The helicoid ring 18 is rotationally driven by a zoom gear 28, and the helicoid ring 18 rotates in the direction of the optical axis while rotating through the helicoid mechanism from the housed state in FIG. 3 to the photographing state in FIG. 2 (and vice versa). In the imaging state of FIG. 2 (between the wide end and the tele end), the helicoid ring 18 is rotated at a fixed position without moving in the optical axis direction. The first feeding cylinder 15 is coupled with the helicoid ring 18 so as to rotate and move in the optical axis direction.

  A straight guide ring 14 is supported inside the first feeding cylinder 15 and the helicoid ring 18. The rectilinear guide ring 14 is linearly guided in the optical axis direction through a linear groove formed in the fixed ring 22, and relative rotation is possible with respect to the first feeding cylinder 15 and the helicoid ring 18 in the optical axis direction. They are engaged so as to move together.

  As shown in FIG. 5, the linear guide ring 14 has a through guide groove 14 a penetrating the inner peripheral surface and the outer peripheral surface. The penetrating guide groove 14 a has a lead groove portion that is inclined with respect to the photographing optical axis Z <b> 1 and a circumferential groove portion that is centered on the lens barrel central axis Z <b> 0, and is provided on the outer peripheral surface of the cam ring 11. The outer diameter protrusion 11a is slidably fitted. The outer diameter protrusion 11a is further engaged with a rotation transmission groove 15a formed on the inner peripheral surface of the first feeding cylinder 15 and parallel to the photographing optical axis Z1, and the cam ring 11 is rotated together with the first feeding cylinder 15. . When the outer diameter protrusion 11a is engaged with the lead groove portion of the penetrating guide groove 14a, the cam ring 11 is advanced and retracted in the optical axis direction while rotating by receiving the guide of the lead groove portion, and the circumferential direction of the penetrating guide groove 14a. When the outer diameter protrusion 11a is engaged with the groove portion, it rotates in a fixed position without moving in the optical axis direction. Similar to the helicoid ring 18, the cam ring 11 is rotated and retracted between the retracted state of FIG. 3 and the shooting state of FIG. 2 (and vice versa), and in the shooting state of FIG. 2 (between the wide end and the tele end) The ring 11 is rotated in place.

  The rectilinear guide ring 14 linearly guides the second group rectilinear guide ring 10 and the second feeding cylinder 13 in the optical axis direction by linear grooves formed on the inner peripheral surface thereof and parallel to the photographing optical axis Z1. The second group rectilinear guide ring 10 linearly guides the second group lens moving frame 8 supporting the second lens group LG2 in the optical axis direction, and the second feeding cylinder 13 supports the third feeding cylinder supporting the first lens group LG1. 12 is guided straight in the direction of the optical axis. The second group rectilinear guide ring 10 and the second feeding cylinder 13 are supported so as to be relatively rotatable with respect to the cam ring 11 and to move integrally in the optical axis direction.

  A second group cam follower 8 a provided on the outer peripheral surface of the second group lens moving frame 8 is engaged with the second group guide cam groove 11 b formed on the inner peripheral surface of the cam ring 11. Since the second group lens moving frame 8 is guided linearly in the optical axis direction via the second group linear guide ring 10, when the cam ring 11 rotates, the second group lens moving frame 8 follows the shape of the second group guide cam groove 11 b. Moves along a predetermined locus in the optical axis direction.

  As shown in FIG. 6, the second group lens frame 6 that holds the second lens group LG <b> 2 is supported on the inner side of the second group lens moving frame 8 so as to be rotatable about the retraction rotation shaft 33. The retraction rotation shaft 33 is an axis parallel to the photographing optical axis Z1, and the second lens group LG2 is moved to the photographing position (FIG. 2) on the photographing optical axis Z1 when the second group lens frame 6 swings. It is moved to the retracted position (FIG. 3) retracted above the optical axis Z1. At this retracted position, the optical axis of the second lens group LG2 is displaced to a position indicated by Z2 in FIGS. The second group lens frame 6 is urged toward the photographing position by a torsion spring 39, and the second holder lens frame 6 is moved against the torsion spring 39 when the second group lens moving frame 8 is retracted to the fixed holder 23. A retracting guide protrusion 40 is provided for rotating to the retracted position.

  The second delivery cylinder 13 guided linearly in the optical axis direction by the second group linear guide ring 10 further guides the third extension cylinder 12 in the optical axis direction. The third feeding cylinder 12 has a first group cam follower 31 projecting in the inner diameter direction, and the first group cam follower 31 is slidably fitted in a first group guide cam groove 11 c formed on the outer peripheral surface of the cam ring 11. is doing. The first group lens frame 1 is supported in the third feeding cylinder 12 via the first group adjustment ring 2. The first group lens frame 1 holds the first lens group LG1.

  A shutter unit 100 having a shutter S and a diaphragm A is supported between the first lens group LG1 and the second lens group LG2. The shutter unit 100 is fixed inside the second group lens moving frame 8.

  The zoom lens barrel 201 having the above structure operates as follows. When the main switch 206 is turned on in the lens barrel storage state of FIG. 3, the zoom motor 150 is driven in the lens barrel feeding direction. The zoom gear 150 is rotationally driven by the zoom motor 150, and the helicoid ring 18 and the first feeding cylinder 15 are rotated forward by the helicoid. The rectilinear guide ring 14 moves straight forward together with the first feeding cylinder 15 and the helicoid ring 18. At this time, the cam ring 11 to which the rotational force is applied from the first feeding cylinder 15 has a lead structure (penetration guide groove) provided between the linear movement of the linear guide ring 14 forward and the linear guide ring 14. The combined movement of the lead groove portion of 14a and the feeding portion by the outer diameter projection 11a) is performed. When the helicoid ring 18 and the cam ring 11 are drawn out to a predetermined position in front, the functions of the respective rotary feeding structures (helicoid, lead) are canceled and only the circumferential rotation about the lens barrel central axis Z0 is performed. become.

  When the cam ring 11 rotates, on the inner side, the second group lens moving frame 8 guided linearly through the second group linear guide ring 10 is in the optical axis direction due to the relationship between the second group cam follower 8a and the second group guide cam groove 11b. Is moved along a predetermined trajectory. 3, the second group lens frame 6 in the second group lens moving frame 8 is held at a retracted position deviated from the photographing optical axis Z1 by the action of the retract guide protrusion 40 projecting from the fixed holder 23. The second group lens frame 6 is separated from the retracting guide projection 40 while the second group lens moving frame 8 is extended to the zoom region, and the optical axis of the second lens group LG2 is adjusted by the urging force of the torsion spring 39. It is rotated to a photographing position (FIG. 2) that coincides with Z1. Thereafter, the second group lens frame 6 is held at the photographing position until the zoom lens barrel 201 is moved again to the storage position.

  Further, when the cam ring 11 rotates, the third feeding cylinder 12 guided linearly through the second feeding cylinder 13 on the outside of the cam ring 11 is related to the first group cam follower 31 and the first group guiding cam groove 11c. Is moved along a predetermined locus in the optical axis direction.

  That is, the former positions of the first lens group LG1 and the second lens group LG2 with respect to the imaging surface (CCD light-receiving surface) are respectively the forward movement amount of the cam ring 11 with respect to the fixed ring 22, and the third position with respect to the cam ring 11. The sum is determined as the sum of the cam feed amount of the feed cylinder 12 and the latter is the sum of the forward movement amount of the cam ring 11 relative to the fixed ring 22 and the cam feed amount of the second group lens moving frame 8 relative to the cam ring 11. Determined. Zooming is performed by moving the first lens group LG1 and the second lens group LG2 on the photographing optical axis Z1 while changing the air interval between them. When the lens barrel is extended from the storage position of FIG. 3, first, the wide end extended state shown in the upper half section of FIG. 2 is obtained, and when the zoom motor 150 is further driven in the lens barrel extending direction, the lower half section of FIG. As shown in FIG. As can be seen from FIG. 2, in the zoom lens barrel 201 of the present embodiment, the distance between the first lens group LG1 and the second lens group LG2 is large at the wide end, and the first lens group LG1 and the second lens at the tele end. The group LG2 moves in the direction of mutual approach, and the interval is reduced. Such a change in the air gap between the first lens group LG1 and the second lens group LG2 is given by the locus of the second group guide cam groove 11b and the first group guide cam groove 11c. In the zoom region between the tele end and the wide end, the cam ring 11, the first feeding cylinder 15, and the helicoid ring 18 perform only the above-mentioned fixed position rotation, and do not advance or retreat in the optical axis direction.

  When the zoom lens barrel 201 is ready to shoot from the wide end to the tele end, the third lens group LG3 (third group) is driven by driving the AF motor 160 according to the subject distance information obtained by the distance measuring means. The lens frame 51) moves along the photographing optical axis Z1 to perform focusing.

  When the main switch 206 is turned off, the zoom motor 150 is driven in the lens barrel storage direction, and the zoom lens barrel 201 performs a storage operation opposite to the above-described feeding operation, so that the storage state shown in FIG. In the middle of the movement to the storage position, the second group lens frame 6 is rotated to the retracted position by the retraction guide projection 40 (see FIG. 10) and retracts together with the second group lens moving frame 8. When the zoom lens barrel 201 is moved to the storage position, the second lens group LG2 is stored at the same position as the third lens group LG3, the low-pass filter 25, and the CCD 60 in the optical axis direction (in the radial direction of the barrel). Overlap). Due to the retracting structure of the second lens group LG2 at the time of storage, the storage length of the zoom lens barrel 201 is shortened, and the thickness of the camera body 202 in the left-right direction in FIG. 3 can be reduced.

  Details of the drive mechanism of the third group lens frame 51 will be described. The third group lens frame 51 has a pair of guide arm portions 51b and 51c extending in a radial direction from a holding frame portion 51a that holds the third lens group LG3. A guide hole that is slidably fitted to the guide shaft 52 is formed in the vicinity of the end portion of the one guide arm portion 51b, and the end portion of the other guide arm portion 51c is slidable with respect to the guide shaft 53. A guide groove that fits in a movable manner is formed. The guide shaft 52 and the guide shaft 53 are each parallel to the photographing optical axis Z1, and the third group lens frame 51 is guided so as to move straight in a direction parallel to the photographing optical axis Z1. As shown in FIGS. 9 and 10, the front end portion and the rear end portion of the guide shaft 52 are supported by support holes formed in the fixed ring 22 and the fixed holder 23, respectively. The mechanical movable range of the third lens group frame 51 is until the front and rear end portions of the guide arm portion 51b are in contact with the support portion of the guide shaft 52.

  As shown in FIGS. 7 and 8, a rotation restricting groove 56 is formed in the vicinity of the end of the guide arm portion 51b. The rotation restricting groove 56 has a longitudinal direction substantially parallel to the extending direction of the guide shaft 52. The rotation restricting groove 56 has rotation restricting surfaces 56a and 56b that are spaced apart from each other in the vertical direction of the camera and face each other. The rotation restricting surface 56a and the rotation restricting surface 56b are parallel to each other. Inclined surfaces 56c and 56d are formed at the front end portions of the rotation restricting surface 56a and the rotation restricting surface 56b, respectively. The inclined surface 56c and the inclined surface 56d are inclined surfaces that gradually widen each other as they move forward, and the rotation restricting groove 56 is opened at the front ends of the inclined surface 56c and the inclined surface 56d. The rear end side of the rotation restricting groove 56 is closed by a nut engaging plate portion 57 that protrudes toward the side. The nut engaging plate portion 57 is formed with a through portion 57a in the optical axis direction and an annular groove 57b that is substantially concentric with the through portion 57a and faces forward.

  The focusing motor 160 has a main body portion 160 b fixed to the motor support portion 22 a of the fixed ring 22, and a drive shaft (feed screw shaft) 160 a extending into the space between the fixed ring 22 and the fixed holder 23. The drive shaft 160a has an axis oriented in a direction parallel to the photographing optical axis Z1, and the focusing motor 160 can drive the drive shaft 160a to rotate in the forward and reverse directions around this axis. A feed screw 160c is formed on the outer peripheral surface of the drive shaft 160a. A spring receiving groove 22b having an annular shape centering on the focusing motor 160 is formed on the rear surface side of the motor support portion 22a facing the fixed holder 23. In addition, a pair of rotation restricting protrusions 22c and 22d project from the motor support portion 22a toward the rear in the optical axis direction.

  The AF nut 54 is a plate-like member that is substantially parallel to the nut engaging plate portion 57, and includes a screw hole 54a that is screwed into the feed screw 160c of the drive shaft 160a, and a rear side (nut engaging plate portion) following the screw hole 54a. 57 b) projecting forward (57 side), an annular projecting portion 54 c projecting forward (motor support 22 a side) opposite to the annular projecting portion 54 b, and an annular spring receiving groove centering on the annular projecting portion 54 b 54d, an annular protrusion 54e that is located on the back side of the spring receiving groove 54d and can be engaged with the annular groove 57b of the nut engaging plate portion 57, a rotation restricting protrusion 54f that projects toward the side, and a sub rotation restricting member A protrusion 54g and an elastic deformation portion 54h located on the lower side of the rotation restricting protrusion 54f are provided. The elastic deformation portion 54h is a free end portion whose base end portion is connected to the main body portion of the AF nut 54 and the front end portion is not fixed, and can be elastically deformed in the vertical direction around the base end portion. ing.

  The AF nut 54 is screwed into the feed screw 160c of the drive shaft 160a and the rotation restricting projection 54f and the elastically deforming portion 54h are inserted into the rotation restricting groove 56. It is assembled between 22a and the nut engaging plate portion 57. The upper and lower surfaces of the rotation restricting protrusion 54f abut against the rotation restricting surface 56a and the rotation restricting surface 56b, and the AF nut 54 is restricted from rotating with respect to the third group lens frame 51 by this contact relationship (FIG. 16). Note that the distance between the upper surface of the rotation restricting projection 54f (the surface in contact with the rotation restricting surface 56a) and the lower surface of the elastic deformable portion 54h (the surface in contact with the rotation restricting surface 56b) is such that the elastic restricting portion 54h is in a free state. When inserted into the rotation restricting groove 56, the elastic deformation portion 54h is elastically deformed in a direction approaching the rotation restricting projection 54f by being pushed by the rotation restricting surface 56b when wider than the vertical width (interval between the rotation restricting surfaces 56a and 56b). (FIG. 16). Due to the elastic deformation of the elastic deformation portion 54 h, the AF nut 54 is held against the third group lens frame 51 without play.

  The third group lens frame 51 is urged forward in the optical axis direction by a third group frame urging spring 55, and the state in which the nut engagement plate portion 57 is in contact with the AF nut 54 is maintained by this urging force. At this time, as shown in FIGS. 9 and 10, the annular protrusion 54b enters the through portion 57a, and the annular protrusion 54e enters the annular groove 57b.

  Further, a nut biasing spring (nut biasing means) 61 made of a compression coil spring is inserted between the spring receiving groove 54d on the AF nut 54 side and the spring receiving groove 22b on the stationary ring 22 side. A biasing force acting backward in the optical axis direction is applied to the AF nut 54 by the biasing spring 61. As can be seen from FIGS. 9, 10, 13 and 14, the urging force of the nut urging spring 61 always acts regardless of the movement position of the AF nut 54. In the state where the AF nut 54 and the nut engaging plate portion 57 are in contact, the urging force in the direction opposite to the nut urging spring 61 acts on the AF nut 54 by the third group frame urging spring 55. The urging force of the third group frame urging spring 55 is set to be stronger than the urging spring 61.

  The AF nut 54 whose rotation is restricted by the engagement relationship between the rotation restricting protrusion 54f and the rotation restricting groove 56 moves forward and backward along the axis of the drive shaft 160a when the drive shaft 160a is driven to rotate forward and backward. FIG. 9 shows a state in which the AF nut 54 is moved to the front end portion of the feed screw 160c. The third group lens urged in the contact direction with the AF nut 54 by the urging force of the third group frame urging spring 55. The frame 51 is moved to the front moving end following the AF nut 54 while maintaining the state in which the nut engaging plate portion 57 is in contact with the AF nut 54. FIG. 10 shows a state in which the AF nut 54 presses the nut engaging plate portion 57 against the urging force of the third group frame urging spring 55 to move the third group frame urging spring 55 to the rearward movement end. ing. Therefore, when the AF nut 54 moves back and forth by the rotational drive of the drive shaft 160a, the third group lens frame 51 is moved in the optical axis direction together with the AF nut 54. Thereafter, the rotation direction of the drive shaft 160a for moving the AF nut 54 backward (the distal end side of the drive shaft 160a, the first movement direction) is rotated forward, and the AF nut 54 is moved forward (the proximal end side of the drive shaft 160a, the second The direction of rotation of the drive shaft 160a to be moved in the reverse direction is the reverse direction.

  In the lens barrel storage state (FIG. 3) with the main switch 206 turned off, the third group lens frame 51 is moved to the rearward movement end shown in FIG. 11 and 12 show the relationship between the drive shaft 160a and the AF nut 54 at this time. As can be seen from FIG. 11, the AF nut 54 is screwed between the feed screw 160c of the drive shaft 160a and the screw hole 54a. Has reached the rearward movement end. Even if the drive shaft 160a is driven in the forward rotation direction in this unscrewed state, the rearward movement of the third group lens frame 51 is limited because no backward movement force is applied to the AF nut 54. In addition, no biting occurs between the feed screw 160c and the screw hole 54a. Conversely, when the drive shaft 160a is driven in reverse from the state of FIG. 10, the AF nut 54 is biased toward the main end 160b of the focusing motor 160 by the biasing force of the third group frame biasing spring 55. Therefore, the screw hole 54a is re-engaged with the feed screw 160c, and the AF nut 54 moves forward. Here, the urging force of the nut urging spring 61 in the direction opposite to the urging force of the third group frame urging spring 55 is acting on the AF nut 54. Since the urging force is weaker than the urging force of the third group frame urging spring 55, the re-engagement of the feed screw 160c and the screw hole 54a is not hindered.

  The AF nut 54 in the photographing state is the front end moving position shown in FIG. 9, but the AF nut 54 further moves to the front moving end in FIG. 13 where the screw hole 54a and the feed screw 160c are disengaged. Can do. For example, there is a possibility that the drive shaft 160a is further reversely driven without stopping the AF nut 54 at the position shown in FIG. 9 due to a malfunction of software for operating the focusing motor 160. Then, as shown in FIG. 13, the AF nut 54 is moved to a position adjacent to the motor support portion 22a, and the screw hole 54a and the feed screw 160c are disengaged. Even if the drive shaft 160a is further reversely driven in the state of FIG. 13, the forward movement force is not applied to the AF nut 54 in the state where the screwing with the feed screw 160c is released. No biting occurs between the holes 54a. When the drive shaft 160a is driven to rotate forward in the unscrewed state of FIG. 13, the AF nut 54 is biased toward the distal end portion of the drive shaft 160a by the biasing force of the nut biasing spring 61. 54a can be re-engaged with the feed screw 160c.

  As described above, when further moving force is applied by the drive shaft 160a with the AF nut 54 reaching the both ends of the drive shaft 160a, the screw hole 54a is disengaged from the feed screw 160c of the drive shaft 160a. Therefore, there is no possibility that biting occurs at the threaded portion formed by the feed screw 160c and the screw hole 54a. When the screw hole 54a is disengaged from the feed screw 160c on the tip end side of the drive shaft 160a, the screw hole 54a contacts the end of the feed screw 160c by the biasing force of the third group frame biasing spring 55. Therefore, the feed screw 160c and the screw hole 54a can be re-threaded by rotating the drive shaft 160a in the reverse direction. When the screw hole 54a is disengaged from the feed screw 160c on the proximal end side of the drive shaft 160a, the screw hole 54a is in contact with the end of the feed screw 160c by the biasing force of the nut biasing spring 61. Therefore, the feed screw 160c and the screw hole 54a can be re-threaded by driving the drive shaft 160a to rotate forward. Here, not only the third group frame biasing spring 55 but also the biasing force of the nut biasing spring 61 always acts on the AF nut 54 (in the entire region from the front moving end in FIG. 13 to the rear moving end in FIG. 10). Therefore, when the AF nut 54 is driven, there is no sudden change in load, and the AF nut 54 can be driven with high accuracy in the entire region from the distal end portion to the proximal end portion of the drive shaft 160a. it can. Specifically, the nut biasing spring 61 is a biasing means for re-engaging the screw hole 54a of the AF nut 54 with the base end side of the drive shaft 160a shown in FIG. In addition to the state, the screw hole 54a and the feed screw 160c are screwed together as shown in FIG. 9, and the screw screw 54c and the screw hole 54a of the AF nut 54 are screwed on the tip end side of the drive shaft 160a as shown in FIG. Even in the state where the engagement is released, the urging force of the nut urging spring 61 acts on the AF nut 54. With the above configuration, the entire region of the feed screw 160c of the drive shaft 160a can be used as an effective (high-precision) driving region for focusing, and there is no waste.

  Further, as shown in FIG. 12, the inner peripheral surfaces of the annular protrusion 54b and the annular protrusion 54c of the AF nut 54 are cylindrical with no screw formed across the screw formation region of the screw hole 54a. The fall prevention holes 54m and 54n are formed. The inner diameter size of each of the fall prevention holes 54m and 54n corresponds to the outer diameter size of the feed screw 160c, and the AF nut 54 releases the threaded engagement with the feed screw 160c on the distal end side of the drive shaft 160a as shown in FIG. When this is done, a part of the drive shaft 160a on the tip side is fitted into the cylindrical inner surface 54n (FIG. 12). On the other hand, when the AF nut 54 is disengaged from the feed screw 160c on the base end side of the drive shaft 160a as shown in FIG. 13, a part on the base end side of the drive shaft 160a falls into the fall prevention hole 54m. Fit. In any of these states, the tilting of the AF nut 54 is prevented by the contact relationship between the fall prevention holes 54m and 54n and the outer edge portion of the feed screw 160c of the drive shaft 160a, so that the screw hole 54a is formed with respect to the feed screw 160c. It can be re-threaded smoothly.

  Normally, the third lens group frame 51 and the AF nut 54 move integrally in the optical axis direction, so that the moving end before and after the screw hole 54a and the feed screw 160c are disengaged as shown in FIGS. Even when the AF nut 54 is moved, the rotation restriction state of the AF nut 54 due to the engagement of the rotation restriction protrusion 54f and the rotation restriction groove 56 is not released. Therefore, when the drive shaft 160a is rotationally driven in the screw re-threading direction in each of the screw release states of FIGS. 10 and 13, the AF nut 54 and the feed screw 160c are not rotated. It can be re-threaded. However, as shown in FIG. 14, the third group lens frame 51 does not move following the AF nut 54 for some reason such as mechanical catching, and the AF nut 54 moves alone to the base end side of the drive shaft 160a. Then, the rotation restricting protrusion 54f slides and moves in the rotation restricting groove 56 to the front end side of the rotation restricting groove 56, and the rotation restricting state of the AF nut 54 by the third group lens frame 51 is released.

  Here, a pair of rotation restricting protrusions 22c and 22d project from the motor support portion 22a of the fixed ring 22 toward the rear in the optical axis direction, and as shown in FIGS. 15 and 17, the rotation restricting protrusion 54f. Is moved forward from the rotation restricting groove 56 and the rotation restricting state of the AF nut 54 by the third group lens frame 51 side is released, the rotation restricting protrusions 22c and 22d sandwich the outer periphery of the AF nut 54 and the AF nut 54 The rotation of 54 is restricted. Specifically, the rotation restricting protrusion 22c is provided at a position adjacent to the upper surface of the sub rotation restricting protrusion 54g, and the rotation restricting protrusion 22d is provided at a position adjacent to the lower surface of the elastic deformation portion 54h. As shown in FIG. 14, when the third group lens frame 51 is at the rearward movement end, in the axial direction of the drive shaft 160, the front end portion of the rotation restricting groove 56 and the rotation restricting protrusion 22c (not shown in FIG. The same applies to the tip of the restricting projection 22d). Therefore, when the rotation restricting protrusion 54f is removed forward from the rotation restricting groove 56, the rotation restricting protrusions 22c and 22d instead restrict the rotation of the AF nut 54. In other words, regardless of the movement position of the third group lens frame 51, either the rotation restricting groove 56 or the rotation restricting protrusions 22c and 22d are always located in the movable range of the AF nut 54, and the AF nut 54 is always attached. Can prevent rotation.

  As shown in FIG. 18, in the vertical direction of the camera, the rotation restricting projection 22d is provided at substantially the same height as the front end of the inclined surface 56d, that is, at a position lower than the rotation restricting surface 56b of the rotation restricting groove 56. ing. Therefore, when the rotation restricting projection 54f is disengaged from the rotation restricting groove 56, the pressing state of the rotation restricting surface 56b against the elastic deforming portion 54h is released, and the rotation restricting projection 22d does not press the elastic deforming portion 54h. The elastic deformation of the deforming portion 54h is released (FIG. 17). When the AF nut 54 is separated from the third group lens frame 51 and is not screwed with the feed screw 160c, the AF nut 54 controls the position of the third group lens frame 51 in the optical axis direction for focusing. Therefore, it is not necessary to strictly position the AF nut 54 using the elastic deformation portion 54h.

  When the drive shaft 160a is driven to rotate forward in the detached state shown in FIGS. 15 and 17, the AF nut 54, whose rotation is restricted by the rotation restricting protrusions 22c, 22d, re-threads the screw hole 54a with the feed screw 160c, and the drive It moves backward along the shaft 160a. When the AF nut 54 moves rearward to some extent, the rotation restricting projection 54f and the elastic deformation portion 54h enter the rotation restricting groove 56, and the third group lens frame 51 returns to the state in which the AF nut 54 is restricted. At this time, since the inclined surfaces 56 c and 56 d are formed at the front end portion of the rotation restricting groove 56, the rotation restricting protrusion 54 f and the elastic deformation portion 54 h can be smoothly guided into the rotation restricting groove 56. When the rotation restricting projection 54f is inserted into the rotation restricting groove 56 again, the elastic deforming portion 54h is elastically deformed so as to gradually approach the rotation restricting projection 54f along the inclined surface 56d. At the same time, it is moved into the rotation restricting groove 56.

  Thus, switching the rotation restricting means of the AF nut 54 from the third group lens frame 51 side to the fixed ring 22 side in a specific state has the following advantages. First, in order to accurately move the third group lens frame 51 in the optical axis direction without causing a tilt, a predetermined engagement length A in the optical axis direction is provided between the guide hole of the guide arm portion 51b and the guide shaft 52. (FIG. 9) is required. On the other hand, the distance in the optical axis direction between the fixed ring 22 and the fixed holder 23 at the support position of the guide shaft 52 is B (FIG. 9). Therefore, the mechanical movable range of the third group lens frame 51 is B-A. Here, unlike the present embodiment, the engagement of the rotation restricting projection 54f and the rotation restricting groove 56 is maintained even when the third group lens frame 51 does not follow the AF nut 54 as shown in FIG. Furthermore, if the rotation restricting groove 56 is extended longer than the illustrated embodiment, the guide arm portion 51b becomes longer in the optical axis direction, and the movable range of the third lens group frame 51 becomes shorter. Not preferable. If the distance between the fixed ring 22 and the fixed holder 23 in the optical axis direction is increased, the movable range of the third group lens frame 51 can be secured, but it is difficult to downsize the entire lens barrel, which is also not preferable. On the other hand, as in the present embodiment, when the rotation restricting protrusion 54f is removed from the rotation restricting groove 56, the rotation restricting protrusions 22c and 22d on the stationary ring 22 side have a structure that prevents rotation of the AF nut 54. It is not necessary to form the guide arm portion 51b of the third group lens frame 51 longer than necessary, and it is not necessary to widen the distance between the fixed ring 22 and the fixed holder 23 in the optical axis direction, so that the AF nut 54 is always in a rotation restricted state. be able to.

  As mentioned above, although this invention was demonstrated based on illustration embodiment, this invention is not limited to this. For example, although the illustrated embodiment is applied to a camera driving mechanism for focusing, the feed screw driving mechanism of the present invention can be applied to other devices.

It is a front view of a digital camera provided with a feed screw drive mechanism to which the present invention is applied. It is a sectional side view in the imaging state of the digital camera. FIG. 2 is a side cross-sectional view of the digital camera in a lens barrel storage state. It is a perspective view of the zoom lens barrel in the storage state of the digital camera. It is a disassembled perspective view of a part of zoom lens barrel. It is a disassembled perspective view of a different part of a zoom lens barrel. It is a perspective view which shows the relationship between a 3 group lens frame and AF nut. It is the perspective view which expanded the AF nut vicinity in FIG. FIG. 6 is a cross-sectional view of the vicinity of the focusing motor and the AF nut in a state where the third group lens frame is at the forward moving end. FIG. 10 is a cross-sectional view illustrating a state in which the third group lens frame and the AF nut are moved from the state of FIG. 9 to their rearward movement ends. FIG. 11 is a partial cross-sectional view showing only a focusing motor and an AF nut in the state of FIG. 10. FIG. 12 is an enlarged cross-sectional view of the vicinity of the AF nut in FIG. 11. FIG. 10 is a cross-sectional view illustrating a state in which the AF nut is further moved to the forward moving end from the state of FIG. 9 and the screwing with the feed screw is released. It is sectional drawing which shows the state by which AF nut is moved to the front movement end, and the 3rd group lens frame has stopped at the back movement end. It is the perspective view seen from the back which shows the positional relationship of the rotation control protrusion and the AF nut which protruded from the motor support part of the stationary ring. It is a rear view which shows the relationship between a rotation control protrusion and an AF nut in the state in which the AF nut is rotationally restricted by the rotation restriction groove of the third group lens frame. It is a rear view which shows the relationship between the rotation control protrusion and AF nut in the state by which the rotation control by the rotation control groove of a 3 group lens frame was cancelled | released. FIG. 18 is a cross-sectional view taken along the line D1-D1 with the addition of the third group lens frame to FIG.

Explanation of symbols

11 Cam ring 12 Third feed cylinder 13 Second feed cylinder 14 Linear guide ring 15 First feed cylinder 18 Helicoid ring 22 Fixed ring (movement regulating member, fixed member of driven member)
22a Motor support portion 22b Spring receiving groove 22c 22d Rotation restricting projection 23 Fixed holder 51 Third lens group frame (driven member)
51a Holding frame portion 51b 51c Guide arm portion 52 53 Guide shaft 54 AF nut 54a Screw hole 54d Spring receiving groove 54f Rotation restricting projection 54g Sub rotation restricting projection 54h Elastic deformation portion 54m 54n Fall prevention hole 55 Three-group frame biasing spring (covered Driving member urging means)
56 Rotation restriction groove 56a 56b Rotation restriction surface 56c 56d Inclined surface 57 Nut engagement plate portion 61 Nut biasing spring (nut urging means)
160 Focusing motor 160a Drive shaft (feed screw shaft)
160c Feed screw 200 Digital camera 201 Zoom lens barrel LG1 First lens group LG2 Second lens group LG3 Third lens group Z1 Shooting optical axis

Claims (10)

A motor that rotates the feed screw shaft in forward and reverse directions;
A nut that has a screw hole that engages with the feed screw shaft, and whose rotation is regulated so that the feed screw shaft is moved forward and backward in the axial direction by forward and reverse rotation of the feed screw shaft;
A driven member that is guided so as to be linearly movable in the axial direction of the feed screw shaft and is pressed and moved in the first moving direction by the nut;
Urging means for urging the driven member in a second moving direction opposite to the first moving direction and moving the driven member following the movement of the nut in the second moving direction;
In a feed screw drive mechanism having
The nut releases the screwing with the feed screw shaft at the moving end in the second moving direction;
Feeding means comprising nut urging means for constantly urging the nut toward the first moving direction when the nut is in either a screwed state or a screwed state with the feed screw shaft. Screw drive mechanism. 2. The feed screw driving mechanism according to claim 1, further comprising a movement restricting member for determining a moving end of the driven member in the second moving direction, wherein the nut is connected to the feed screw shaft at the moving end in the second moving direction. A feed screw driving mechanism in which the nut is separated from the driven member when the screwing is released. 3. The feed screw drive mechanism according to claim 1, wherein the biasing force of the biasing means of the driven member is stronger than the biasing force of the nut biasing means. The feed screw drive mechanism according to any one of claims 1 to 3, wherein the nut biasing means comprises a compression coil spring disposed between a fixing member supporting the motor and a nut. 5. The feed screw drive mechanism according to claim 1, wherein the nut further releases the screw engagement with the feed screw shaft at a moving end in the first movement direction. 6. The feed screw drive mechanism according to any one of claims 1 to 5, wherein the nut is continuous with the screw hole and prevents the end of the feed screw shaft from being fitted when the nut is released from the feed screw shaft. Lead screw drive mechanism with holes. A motor that rotates the feed screw shaft in forward and reverse directions;
A nut that has a screw hole that engages with the feed screw shaft, and whose rotation is regulated so that the feed screw shaft is moved forward and backward in the axial direction by forward and reverse rotation of the feed screw shaft;
A driven member that is guided so as to be linearly movable in the axial direction of the feed screw shaft and is moved by the nut;
In a feed screw drive mechanism having
The nut is disengaged from the feed screw shaft at at least one moving end with respect to the feed screw shaft,
A feed screw driving mechanism characterized in that the nut has a fall prevention hole into which the end of the feed screw shaft is fitted in a state where the nut is continuous with the feed screw shaft in a state where the nut is disengaged from the feed screw shaft. 8. The feed screw drive mechanism according to claim 7, wherein the nut releases a screw engagement with the feed screw shaft at both moving ends with respect to the feed screw shaft, and has a pair of the fall prevention holes positioned between the screw holes. Has a lead screw drive mechanism. 9. The feed screw drive mechanism according to claim 1, wherein the driven member is a holding frame for an optical element constituting a photographing optical system of a camera. 10. The feed screw drive mechanism according to claim 9, wherein the optical element is a focusing lens group, and the motor is a focusing motor that moves the focusing lens group to a focus position in accordance with a subject distance.

Images