Lens barrel

A lens barrel includes a lens barrel part generally cylindrical about an optical axis, a first driving part arranged to serve as a drive source for executing a focusing action, a second driving part arranged to serve as a drive source for executing a zooming action and a third driving part arranged to serve as a drive source for executing an aperture reducing action. The first, second and third driving parts are disposed externally of the lens barrel part and circumferentially of the optical axis, and may have arcuate outer surfaces which may not extend beyond the perimeter of the lens barrel part.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 This invention relates to a lens barrel having optical members including a
 zooming lens, a focusing lens and a diagram.
 2. Description of the Related Art
 For the lens barrel of the kind arranged to move some of various lens
 groups with a stepping motor which is employed as a drive source by
 transmitting its driving force through the meshing engagement of a feeding
 screw and a rack screw, the stepping motor has been arranged to be
 approximately in a cylindrical shape for the purpose of imparting
 universal applicability to the stepping motor.
 Further, a motor unit which is approximately cylindrical in appearance has
 been arranged as an actuator at a diaphragm driving part in cases where a
 linear movement is necessary, like in the case of the diaphragm driving
 part of a video camera.
 However, the conventional arrangement mentioned above has presented various
 problems as described below.
 An effort to minimize the size of a lens barrel without lowering its
 optical performance results in an approximately cylindrical shape of the
 lens barrel.
 However, in order to arrange a driving part for each of a zooming lens, a
 focusing lens and a diaphragm to have a sufficient torque, the outside
 diameter of the lens barrel increases with a driving load. The increase in
 the driving load makes the driving part hardly containable within the
 shape of the minimum size of the lens barrel.
 In the case of the conventional lens barrel which is shown in FIG. 6, an
 actuator unit 59 for driving a magnifying power varying system or a
 focusing system is formed with a U-shaped sheet metal member 59a arranged
 to support a motor 59b which is provided with a screw shaft 59c. The
 U-shaped sheet metal member 59a is screwed to the lens barrel 51. The lens
 barrel 51 has a cutout part 51a which is provided for mounting the
 actuator unit 59 thereon and extends over the whole moving range of the
 power varying system or the focusing system.
 However, the structure of making the U-shaped sheet metal member 59a
 support the actuator unit 59 and of screwing the U-shaped sheet metal 59a
 to the lens barrel 51 necessitates the cutout part 51a of the lens barrel
 51 to be large. The large cutout part 51a lowers the strength of the lens
 barrel 51 and also makes it difficult to attain a required degree of
 precision. The provision of the U-shaped sheet metal member 59a brings
 forth another problem which lies in that the meshing engagement of rack
 teeth (not shown) and the screw shaft 59c cannot be ascertained in their
 assembled state.
 Further, for the lens barrel of this kind, use is generally made of a
 diaphragm unit including, in one unified body, a plurality of diaphragm
 blades, a diaphragm base plate and a blade retaining member which are
 arranged to sandwich the diaphragm blades therebetween, and a diaphragm
 driving part. The diaphragm unit which is arranged in this manner is
 disposed and fixed in position within the lens barrel in a state of being
 completely independent of the lens barrel.
 However, the unitizing arrangement of the diaphragm device inevitably
 causes an increase in number of parts of the diaphragm device. The
 increased number of parts causes not only an increase in cost but also an
 increase in space required, and thus has resulted in a larger size of the
 lens barrel.
 Further, depending on the mounting precision, the diaphragm unit tends to
 cause a discrepancy between an optical axis and the center of the
 diaphragm and thus has caused one of four corners of an image plane to
 become dark or, in the worst case, to be eclipsed.
 SUMMARY OF THE INVENTION
 One aspect of this invention resides in the provision of a lens barrel
 which is arranged to permit reduction in size by making driving parts for
 a zooming system, a focusing system and a diaphragm respectively to be in
 an arc form i.e., circumferentially of the lens barrel optical axis with
 arcuate outer surfaces which may not extend radially outwardly of an outer
 circumference of a lens barrel part, and disposing the driving parts
 externally of the lens barrel which has approximately a cylindrical shape.
 Another aspect of this invention resides in the provision of a lens barrel
 of the kind arranged to move an optical member in the direction of an
 optical axis by rotating a screw shaft with a motor and by axially moving
 a meshing member which meshes with the screw shaft, wherein an aperture
 part is provided in an approximately tubular member so as to cause the
 meshing member to mesh with the screw shaft in a position of the aperture
 part.
 A further aspect of this invention resides in the provision of a lens
 barrel, wherein a diaphragm member is set in position in a state of being
 sandwiched in the direction of an optical axis with one of the sandwiched
 sides thereof supported by a lens holding member.
 These and other aspects and features of this invention will become apparent
 from the following detailed description of embodiments thereof taken in
 connection with the accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
 FIG. 1 shows the features of a lens barrel which is arranged according to
 this invention as a first embodiment thereof. Referring to FIG. 1, the
 lens barrel is arranged as follows. A first lens holding member 1 is
 arranged to hold a first lens group. A second lens holding member 2 is
 arranged to hold a second lens group and to vary a magnifying power by
 moving the second lens group. A third lens holding member 3 which is
 stationary is arranged to hold a third lens. A fourth lens holding member
 4 is arranged to hold a fourth lens group and to perform focusing by
 moving the fourth lens group. A rear fixed tube 5 is provided with a mount
 part 5a on which an image sensor is mounted.
 The second lens holding member 2 is movably supported by guide bars 6 and 7
 which have their two ends secured to the first and third lens holding
 members 1 and 3. The second lens holding member 2 is thus arranged to be
 movable in the direction of an optical axis.
 A rack teeth part 8 which is supported by holes 2a and 2b formed in the
 second lens holding member 2 is arranged to mesh with an output screw
 shaft 9a of a stepping motor 9 of an arc form having an arcuate outer
 surface which is secured to the third lens holding member 3 as a driving
 part for zooming. When the output screw shaft 9a of the stepping motor 9
 rotates, the second lens holding member 2 is driven to move in the
 direction of the optical axis.
 A protruding part 2c of the second lens holding member 2 constitutes a
 means for detecting the position of the second lens group in conjunction
 with a sensor switch 10 which is secured to the first lens holding member
 1. The initial position of the second lens holding member 2 is determined
 on the basis of the output of the sensor switch 10.
 The third lens holding member 3 is provided with guide pins (not shown)
 which are respectively inserted in holes 12a and 13a formed in diaphragm
 blades 12 and 13. The diaphragm blades 12 and 13 are arranged to be
 swingable on these guide pins in the direction of orthogonally
 intersecting the optical axis along guide rails (not shown) provided on
 the third lens holding member 3 and guide rails 11a provided on a blade
 retaining plate 11. The guide rails 11a are formed with parts of the blade
 retaining plate 11 caused to protrude in the shape of rails by press work.
 A diaphragm driving part 14 of an arc form is secured to the third lens
 holding member 3. The output shaft 14a of the diaphragm driving part 14 is
 inserted into slots 12b and 13b formed in the diaphragm blades 12 and 13.
 The diaphragm blades 12 and 13 are driven when the output shaft 14a swings
 along an arcuate hole 3a which is provided in the third lens holding
 member 3.
 The fourth lens holding member 4 is movably supported by guide bars 15 and
 16 which have their two ends secured to the third lens holding member 3
 and the rear fixed tube 5. The fourth lens holding member 4 is thus
 arranged to be movable in the direction of the optical axis.
 Similarly to the second lens holding member 2, a rack teeth part 17 which
 is supported by the fourth lens holding member 4 is arranged to mesh with
 an output screw shaft 18a of a stepping motor 18 having an arcuate outer
 surface which is secured to the rear fixed tube 5 as a driving part for
 focusing. The fourth lens holding member 4 is thus arranged to be driven
 in the direction of the optical axis when the output screw shaft 18a of
 the stepping motor 18 rotates.
 A protruding part 4a which is provided on the fourth lens holding member 4
 constitutes a means for detecting the position of the fourth lens group in
 conjunction with a sensor switch 19 which is secured to the rear fixed
 tube 5. The initial position of the fourth lens holding member 4 is
 determined on the basis of the output of the sensor switch 19.
 FIG. 2 shows the lens barrel which is the first embodiment of this
 invention as viewed from the side of the focal plane thereof. Referring to
 FIG. 2, the driving parts (or actuators or stepping motors) 9, 18 and 14,
 each having an arcuate outer surface, for zooming, focusing and the
 diaphragm are disposed between the diaphragm blades 12 and 13 and the
 image sensor (mounted on the mount part 5a) along an external form of the
 lens barrel having a cylindrical shape and in such positions where a light
 flux can be stopped down and where they permit reduction in size of the
 external form of the lens barrel. The lens barrel is thus can be arranged
 to have an approximately cylindrical external shape. Incidentally, the
 upper and lower positional relation between the zooming and focusing
 stepping motors 9 and 18 may be conversely arranged. Driving parts 9, 18
 and 14 will be seen to be disposed along respective individual axes spaced
 from and parallel to the optical axis.
 A lens barrel according to a second embodiment of this invention is
 arranged as shown in FIG. 3, which shows it as viewed from the side of a
 focal plane. Referring to FIG. 3, the actuators 9, 18 and 14, each having
 an arcuate outer surface for zooming, focusing and the diaphragm are
 disposed externally of the cylindrical lens barrel in such a way as to
 allow the lens barrel to have an approximately cylindrical external shape.
 In the case of the second embodiment, however, one side of the shape of
 the lens barrel which is opposed to the diaphragm actuator 14 is cut away
 for the purpose of reducing the dimension in the direction of the width of
 the lens barrel. Incidentally, the upper and lower positional relation
 between the zooming and focusing stepping motors 9 and 18 may be
 conversely arranged.
 FIG. 4 shows a lens barrel arranged as a third embodiment of this invention
 as viewed from the side of a focal plane. Referring to FIG. 4, the
 actuators 9, 18 and 14, each having an arcuate outer surface for zooming,
 focusing and the diaphragm are disposed along an external form of the
 cylindrical lens barrel in such a way as to allow the lens barrel to have
 an approximately cylindrical external shape. In the case of the third
 embodiment, however, one side of the shape of the lens barrel opposed to
 the actuator 9 is cut away for reducing the dimension in the direction of
 the height of the lens barrel. Incidentally, the upper and lower
 positional relation between the zooming and focusing stepping motors 9 and
 18 may be conversely arranged.
 Each of the first, second and third embodiments described above is arranged
 such that the driving parts for zooming, focusing and the diaphragm are
 made having an arcuate outer surface and disposed externally of the
 approximately cylindrical lens barrel. By virtue of this arrangement, the
 lens barrel can be saved from having protruding parts, thereby permitting
 reduction in size. Further, each of these driving parts is arranged
 between the image sensor and the diaphragm blades in a place where a light
 flux is stopped down. That arrangement permits minimization of the size of
 the lens barrel.
 This advantageous effect is enhanced further with the dimension in one
 direction of the lens barrel shortened in a manner as shown in FIG. 3 or
 4.
 FIG. 5 best represents the features of a fourth embodiment of this
 invention. In FIG. 5, all the parts that are arranged in the same manner
 as those of the first embodiment are indicated by the same reference
 numerals and the details of them are omitted from description.
 The fourth embodiment differs from the first embodiment in the following
 points.
 The front end of the output screw shaft 9a of the stepping motor 9 is
 supported by a bearing part 1b of the first lens holding member 1 and, the
 stepping motor 9 itself is secured to the third lens holding member 3, so
 that a U-shaped sheet metal member which has been needed according to the
 conventional arrangement is no longer required and is thus omitted from
 the structure of the fourth embodiment.
 The first lens holding member 1 is provided with an aperture part 1a which
 is arranged in a part of the moving range of the second lens holding
 member 2 to permit work for meshing the rack teeth part 8 and the output
 screw shaft 9a of the stepping motor 9 with each other and for
 confirmation of the meshing engagement. This aperture part 1a is used also
 as an escape part for the rack teeth part 8 during the process of assembly
 work (meshing engagement) on the rack teeth part 8 and the output screw
 shaft 9a of the stepping motor 9.
 A cover member 20 is formed in such a shape as to cover the aperture part
 1a of the first lens holding member 1 and is secured to the first lens
 holding member 1 by snap fitting with a hooked claw or by bonding. While
 the description given here applies to the magnifying power varying system,
 the moving members of the focusing (focus adjustment) system are also
 arranged in the same manner.
 The rear fixed tube 5 is provided with an aperture part (not shown) in a
 part of the moving range of the fourth lens holding member 4 for meshing
 the rack teeth part 17 and the output screw shaft 18a of the stepping
 motor 18 with each other. The aperture part is used also as an escape part
 for the rack teeth part 17 during the process of assembly work (meshing
 engagement) on the rack teeth part 17 and the output screw shaft 18a of
 the stepping motor 18.
 A cover member 21 is formed in such a shape as to cover the aperture part
 (not shown) of the rear fixed tube 5 and is secured to the rear fixed tube
 5 either by snap fitting with a hooked claw or by bonding.
 In the fourth embodiment described above, the cover members 20 and 21 which
 cover the aperture parts are either made of the same material as the first
 lens holding member 1 and the rear fixed tube 5 which are opaque, or
 adhesive tape pieces are applied to cover the aperture parts. Further, if
 there is no fear of leakage of light, the cover members 20 and 21 may be
 made of a transparent material. The use of a transparent material for
 these cover members 20 and 21 facilitates making a check for the meshing
 state of the output screw shafts 9a and 18a with the rack teeth parts 8
 and 17.
 Since it suffices to form the above-stated apertures just in small sizes in
 the case of the fourth embodiment, the lens barrel can be arranged to
 retain a sufficient strength and, therefore, can be made with an adequate
 precision. Further, since the meshing work can be done on the engaging
 members by utilizing the aperture parts, the assembly work can be
 efficiently carried out, because it is no longer necessary to mesh the
 meshing members with the output screw shafts within the lens barrel.
 While the stepping motor has been mounted by mounting a U-shaped sheet
 metal member according to the conventional method, the invented method
 obviates the necessity of mounting the U-shaped sheet metal member, so
 that the arrangement of the fourth embodiment is not only advantageous in
 terms of cost but also permits reduction in weight of the lens barrel.
 A fifth embodiment of this invention is next described as follows, FIG. 7
 shows in a sectional view the essential parts of a lens barrel which is
 arranged as the fifth embodiment. FIG. 8 shows the lens barrel in an
 exploded oblique view. The fifth embodiment is arranged almost in the same
 manner as the fourth embodiment which has been described above. Therefore,
 all parts that are of the same construction as those of the fourth
 embodiment are indicated by the same reference numerals and the details of
 them are omitted from description.
 Referring to FIGS. 7 and 8, the lens barrel includes diaphragm blades 12
 and 13. An ND filter 12c (not shown in FIG. 7) is attached to the
 diaphragm blade 12. The diaphragm blades 12 and 13 are interposed between
 the blade retaining plate (sandwiching member) 11 and the third lens
 holding member 3 and are arranged to be driven by the swinging movement of
 an output shaft 14a of the diaphragm driving part 14 in the directions of
 arrows as shown in FIG. 9, which is an oblique view showing in detail the
 essential parts of the diaphragm part. Guide pins 3b which are formed
 integrally with the third lens holding member 3 are inserted into round
 holes 12a and 13a which are formed in the diaphragm blades 12 and 13. The
 output shaft 14a of the diaphragm driving part 14 is inserted through an
 aperture part 3a of the third lens holding member 3 into slots 12b and 13b
 formed in the diaphragm blades 12 and 13. The blade retaining plate 11 is
 snap-fitted and carried by a claw part 3d, etc., of the third lens holding
 member 3. The diaphragm blades 12 and 13 are thus driven to stop down a
 light flux by swinging in the direction orthogonally intersecting the
 optical axis according to the movement of the output shaft 14a of the
 diaphragm driving part 14.
 In this instance, guide rails 3c which are formed integrally with the third
 lens holding member 3 and guide rails 11a which are formed integrally with
 the diaphragm retaining plate 11 enable the diaphragm blades 12 and 13 to
 smoothly move without coming into contact with each other.
 Further, a plurality of claw parts 14e which are formed on the outside part
 of the diaphragm driving part 14 enable the diaphragm driving part 14 to
 be secured to the third lens holding member 3 by fittingly engaging (snap
 fitting) hook parts (not shown) which are provided on the third lens
 holding member 3 in positions where they are opposed to to the claw parts
 14e. As shown in FIG. 7, the rear fixed tube 5 is provided with a
 protruding part 5b in the rear of the diaphragm driving part 14 on one
 side opposite to the side on which the rear fixed tube 5 is secured to the
 third lens holding member 3. The dimensional arrangement of the protruding
 part 5b is such that when any impact is applied, for example, in the
 direction of the optical axis, the rear end part of the diaphragm driving
 part 14 abuts on the protruding part 5b before the claw parts 14e
 completely disengage from the the third lens holding member 3 to prevent
 the diaphragm driving part 14 from pulling off.
 The diaphragm part can be arranged in the form of the conventional
 diaphragm unit by first mounting the diaphragm blades 12, 13, the blade
 retaining plate 11 and the diaphragm driving part 14 on the third lens
 holding member 3 during the process of assembly work. The assembly work
 can be further facilitated by arranging the third lens group III to be set
 in place by inserting it from a direction opposite to the diaphragm blades
 12 and 13.
 Further, the arrangement of mounting the diaphragm blades 12 and 13
 directly on the third lens holding member 3, as mentioned in the
 foregoing, dispenses with the conventional diaphragm base plate and gives
 some space allowance in the direction of thrust to an extent corresponding
 to a space required for the diaphragm base plate.
 The arrangement of having the guide pins 3b for the diaphragm blades 12 and
 13 formed integrally with the third lens holding member 3 ensures that the
 center of diaphragm aperture defined by the diaphragm blades 12 and 13
 deviates from the optical axis only to an extent less than the
 conventional lens barrel, so that the optical performance can be greatly
 enhanced.
 While the embodiment has each of the motor driving parts formed with
 arcuate outer surfaces for the purpose of making the whole lens barrel
 compact, it goes without saying that the same advantageous effect is
 attainable in this respect by using circular actuators (driving parts)
 instead of using actuators with arcuate outer surfaces. Further, while the
 embodiment uses the diaphragm blades of a swinging type, the diaphragm
 blades may be replaced with linearly moving diaphragm blades.
 The rear fixed tube 5 is provided with the protruding part 5b for
 preventing the diaphragm driving part 14 from pulling off from the lens
 barrel, with a predetermined amount of clearance provided there. This
 arrangement may be changed to impart some resilience to the protruding
 part 5b in such a way as to charge the diaphragm driving part.
 According to the structural arrangement of the lens barrel of the fifth
 embodiment, as described above, the diaphragm blades, the blade retaining
 plate and the diaphragm driving part are assembled to be located within
 the lens holding member. This arrangement not only effectively permits
 reduction in number of parts for cost reduction but also permits effective
 space utilization for reduction in size of the whole lens barrel. Further,
 apposite procedures for assembly permit the diaphragm part to be
 discretely handled as a diaphragm unit, so that the advantage of the
 conventional arrangement of handling the diaphragm part as a diaphragm
 unit can be retained without impairing it.
 Further, the structural arrangement of the lens barrel permits the aperture
 center of the diaphragm blades to be easily set in precise alignment with
 the optical axis and not to easily deviate from the latter. This
 effectively prevents an image plane from being eclipsed and enables its
 four corners to have approximately equal luminance, so that a picture of
 high quality can be obtained. Further, the diaphragm driving part is
 arranged to be not deviating from its position, fixed in place by means of
 claw parts and prevented from pulling off by means of a pulling-off
 preventing mechanism provided on a separately arranged fixed member. The
 arrangement thus not only permits reduction in number of manufacturing
 processes but also ensures a sufficient impact resistance.