GB2269630A - Code plate mounting device comprises elastic curved code plate and engaging projection - Google Patents

Abstract

A code plate mounting device for mounting a code plate (63) on an outer peripheral surface or on an inner peripheral surface of a cam ring (61) of a zoom lens comprises an engaging projection (67) provided on the outer peripheral surface or on the inner peripheral surface of the cam ring and an engaging hole (69) provided on the code plate. The code plate is made of an elastic or flexible plate which is curved at a curvature greater than that of the outer peripheral surface or less than that of the inner peripheral surface of the annular member. There may be engaging holes at both ends of the code plate. <IMAGE>

Description

CODE PLATE MOUNTING DEVICE The present invention relates to a mounting device of a code plate which is used to detect focal length data or the like, for example in a zoom lens camera.

In a conventional photographing lens, such as a zoom lens, a two-focus lens, or a macro lens, etc., a cam ring is rotated manually or automatically by a motor to move a group of variable power lenses provided in the cam ring in the optical axis direction so that the variable power lenses move towards and away from each other to change the focal length thereof or the like.In a known camera having such a photographing lens, lens information (data), such as the varied focal length or the open F-number which varies in accordance with the focal length are automatically detected to effect the necessary control A code plate which is provided on the outer periphery of the cam ring and which is selectively brought into contact with brushes has been used as an automatic detecting means for detecting the lens data which has been used; this has been done so that the position of the contact of the brushes with the code plate is read as position data. The position data thus read is converted to focal length data, etc. The code plate is usually attached to the cam ring by an adhesive tape with adhesive layers on the opposite surfaces thereof or by set screws.In this attaching mechanism, the precision of the detection of the position data largely depends on the precision of the attachment of the code plate.

However, it is very difficult to precisely attach the code plate to the outer cylindrical periphery of the cam ring with the adhesive tape. Furthermore, an undesirable displacement of the code plate on the cam ring tends to occur during the attachment, which is in any case a troublesome operation. If the code plate is reattached to the cam ring, for example, after a failure in attachment, the code plate tends to be detached from the cam ring due to a decrease in the adhesive force due to ageing.

On the other hand, in the case of the attachment of the code plate using set screws, there is no or less possibility of detachment due to ageing. However, the engagement of the set screws in the corresponding small threaded holes is a troublesome and time-consuming operation, thus resulting in decreased efficiency of assembly.

An object of the present invention is to provide a simple mounting device which can easily position and mount a code plate to an annular member (e.g. a cam ring) and which can prevent the attached code plate from being detached from the annular member due to ageing or the other factors.

According to the present invention there is provided a code plate mounting device for mounting a code plate on an outer peripheral surface or on an inner peripheral surface of an annular member in a lens barrel, comprising: at least one engaging portion which is provided on the outer periphery surface or on the inner peripheral surface of the annular member; a code plate which is made of an elastic or flexible plate and which is curved at a curvature greater than that of the outer peripheral surface or less than that of the inner peripheral surface of the annular member; and, an engaging portion which is provided on the code plate to engage with at least one of said engaging portions of the annular member.

With this arrangement the positioning of the code plate can be automatically and precisely effected.

In one embodiment, said annular member is provided with a recess in which the code plate is received.

Conveniently, at least one of said engaging portions is provided on the bottom of the recess.

It is preferred that said at least one engaging portions provided-on the bottom of the recess is a pin integral with the annular member.

In a particular case, said engaging portion of the code plate is an engaging hole in which the pin is engaged.

In another embodiment, said annular member provides two engaging portions which are spaced from one another at a predetermined distance in the circumferential direction.

Conveniently, the code plate is provided with two engaging portions to engage with the engaging portions of the annular member.

It is preferred that said two engaging portions are in the form of pins integral with the annular member.

In a particular case, said code plate is provided on its opposite ends with an engaging hole in which one of the pins of the annular member is engaged hole and an elongated hole which extends in the circumferential direction to engage therein the other pin of the annular member.

The present invention encompasses a lens barrel including an annular member and a code plate and code plate mounting device as herein above defined.

Reference is made to parent application number 2240132 from which the present application has been divided.

Examples of the present invention will be described below in detail with reference to the accompanying drawings, in which: - Fig. 1 is a perspective view of a main part of a mounting device of a first embodiment of the present invention; Fig. 2 is a perspective view of a main part of a mounting device of a second embodiment of the present invention; and, Fig. 3 is a perspective view of a main part of a mounting device of a third embodiment of the present invention.

Figs. 1 to 3 show different embodiments of the present invention in which a code plate is attached to a cam ring due to the flexibility (or elasticity) of the code plate.

In Fig. 1, which shows a main part of a zoom lens to which the present invention is applied, a cam ring 61 has an annular member rotatably supported in a stationary lens barrel secured to a camera body. A code plate 63 which codes the angular displacement of the cam ring 61 is mounted to the outer periphery of the cam ring 61.

A group of variable power lenses (not shown) is supported in the cam ring 61 through a known cam mechanism. The cam ring 61 rotates in association with the rotation of a zoom motor (not shown) to move the variable power lenses in the optical axis direction through the cam mechanism to perform the zooming.

The cam ring 61 is provided on its outer periphery with a circumferential recess 65 corresponding to the code plate 63.

An engaging projection 67 which serves as a positioning and engaging element is provided on the bottom of the recess 65.

The cam ring 61 is formed for example by an injection molding of synthetic resin or the like.

The width of the recess 65 is such that when the code plate 63 is received therein, no undesirable displacement of the code plate in the recess occurs. The circumferential length of the recess 65 is longer than the whole length of the code plate 63 so as to completely accommodate the code plate 63 in the recess 65.

The code plate 63 is made of a flexible or elastic thin plate or sheet and is generally C-shaped. The code plate 63 has at its one end a positioning and engaging hole 69 in which the engaging projection 67 on the recess 65 of the cam ring 61 is fitted.

The curvature of the inner peripheral surface of the code plate 63 is greater than that of the bottom of the recess 65. Namely, the diameter dl of the inner peripheral surface of the code plate 63 is smaller than the diameter D1 of the bottom of the recess 65 (dl < D1).

The circumferential length of the code plate 63 is longer than half the whole circumferential length of the cam ring 61 (or half the whole circumferential length of the bottom of the recess 65).

Thus, the code plate 63, which is elastically expanded when received in the recess 65? presses against the bottom of the recess 65 by the contracting (restoring) force due to the flexibility or elasticity of the code plate, especially at the opposite ends of the code plate, so that the code plate can be firmly held on and closely brought into surface contact with the bottom of the recess 65.

Even if the circumferential length of the code plate 63 is shorter than half the whole circumferential length of the cam ring 61, the code plate 63 can be brought into close surface contact with the bottom of the recess and firmly held therein by the elastic restoring force of the code plate and the frictional force between the code plate and the recess.

The code plate 63 has thereon codes (not shown) which code the angular displacement (angular position) of the cam ring 61 and which are read by brushes secured to the lens barrel. Alternatively, it is possible to provide the code plate 63 and the brushes on the stationary lens barrel and a rotary lens barrel (not shown), respectively.

The code plate 63 is mounted to the cam ring 61 as follows.

The generally C-shaped code plate 63 is elastically deformed to slightly widen the opening defined between the opposite ends thereof so that the code plate 63 can be fitted on the cam ring 61 in the axial direction to be brought into the recess 65. The engaging projection 67 of the cam ring 61 is fitted in the engaging hole 69 of the code plate 63. As soon as the external force is released, the code plate 63 is firmly fitted in the recess 65.

Namely, the position of the code plate 63 in the circumferential direction and in the axial direction is restricted by the engagement of the projection 67 and the engaging hole 69 at the end of the code plate 63 adjacent to the engaging hole 69. When the code plate 63 is completely received in the recess 65, the opposite side walls of the code plate 63 come into contact with the side walls of the recess 65 so that the axial position of the code plate 63 is fixed and no inclination of the code plate 63 in the recess 65 occurs.

As can be understood from the foregoing, with this embodiment of the present invention, since the attachment of the code plate 63 to the cam ring 61 is completed merely by fitting the code plate 63 on the cam ring 61 against the elastic force of the code plate and by fitting the projection 67 of the cam ring 61 in the engaging hole 69 of the code plate, the assembly can be simplified and effected with a high precision.

Although the projection 67 and the engaging hole 69 are provided on the cam ring 61 and the code plate 63, respectively in the illustrated embodiment, it is possible to provide the projection 67 and the engaging hole 69 on the code plate 63 and the cam ring 61, respectively.

Fig. 2 shows another embodiment of the present invention in which a code plate 83 is mounted to the inner peripheral surface of a cam ring 81.

In Fig. 2, a variable power lens group is supported in the cam ring 81 through a known cam mechanism, as mentioned before. The cam ring 81 rotates in accordance with the rotation of a zoom motor to move the variable power lens group in the optical axis direction, thereby to effect the zooming operation.

The cam ring 81 is provided on its inner periphery with a circumferential recess 85 corresponding to the code plate 83. The recess 85 has on its bottom an engaging and positioning projection 87.

The width of the recess 85 is such that when the code plate 83 is received therein, no undesirable displacement of the code plate in the recess occurs. The circumferential length of the recess 85 is longer than the whole length of the code plate 83 so as to completely accommodate the code plate 83 in the recess 85.

The code plate 83 is made of a flexible or elastic thin plate or sheet and is generally C-shaped. The code plate 83 has at its one end a positioning and engaging hole 89 in which the engaging projection 87 on the recess 85 of the cam ring 81 is fitted.

The curvature of the outer peripheral surface of the code plate 83 is less than that of the bottom of the recess 85. Namely, the diameter d2 of the outer peripheral surface of the code plate 83 is larger than the diameter D2 of the bottom of the recess 85 (d2 > D2).

The circumferential length of the code plate 83 is longer than half the whole circumferential length of the cam ring 81 (or half the whole circumferential length of the bottom of the recess 85).

Thus, the code plate 83* which is contracted when received in the recess 85,presses against the bottom of the recess 85 by the expanding (restoring) force due to the flexibility or elasticity of the code plate, particularly at the opposite ends of the code plate, so that the code plate can be firmly held on and closely brought into surface contact with the bottom of the recess 85.

The code plate 83 has, on its inner peripheral surface, codes (not shown) which code the angular displacement (angular position) of the cam ring 81 and which are read by brushes secured to the lens barrel.

The code plate 83 is mounted to the cam ring 81 as follows.

The generally C-shaped code plate 83 is elastically contracted to slightly reduce the distance between the opposite ends thereof so that the code plate 83 can be inserted in the cam ring 81 in the axial direction to be brought into the recess 85. The engaging projection 87 of the cam ring 81 is fitted in the engaging hole 89 of the code plate 83. As soon as the external force is released, the code plate 83 is firmly fitted in the recess 85.

Namely, the position of the code plate 83 in the circumferential direction and in the axial direction is restricted by the engagement of the projection 87 and the engaging hole 89 at the end of the code plate 83 adjacent to the engaging hole 89. When the code plate 83 is completely received in the recess 85, the opposite side walls of the code plate 83 come into contact with the side walls of the recess 85 so that the axial position of the code plate 83 is fixed and no inclination of the code plate 83 in the recess 85 occurs.

As can be understood from the foregoing, with this embodiment of the present invention, since the attachment of the code plate 83 to the cam ring 81 is completed merely by inserting the code plate 83 in the cam ring 81 while contracting the code plate 83 against the elastic force of the code plate and by fitting the projection 87 of the cam ring 81 in the engaging hole 89 of the code plate, the assembly can be simplified and effected with a high precision.

Although the positioning of the code plate 63 or 83 in the optical axis direction is mainly effected by the recess 65 or 85 provided on the cam ring 61 or 81 in the above mentioned embodiments, it is possible to provide guide projections for positioning the code plate in place of the recess 65 or 85.

Although the projection 87 and the engaging hole 89 are provided on the cam ring 81 and the code plate 83, respectively, in the illustrated embodiment , it is possible to provide the projection 87 and the engaging hole 89 on the code plate 83 and the cam ring 81, respectively.

There is no limitation to the number of the engaging projection(s) and the engaging hole(s).

The invention is not limited to the above mentioned embodiments in which the positioning of the code plate 63 or 83 is effected by one engaging projection 67 or 87 provided on recess 65 or 85 of the cam ring 61 or 81 and one engaging hole 69 or 89 formed on the code plate 63 or 83. For instance, it is possible to provide a pair of engaging projections and a pair of corresponding engaging holes on the code plate at the opposite ends thereof and on the cam ring, respectively, as shown in Fig. 3.

In Fig. 3, a cam ring 91 is provided on its outer peripheral surface with a pair of engaging projections 92a and 92b which are circumferentially spaced from one another. A code plate 93 is provided on its opposite ends with a pair of engaging holes 99a and 99b corresponding to the engaging projections 92a and 92b of the cam ring 91. One of the engaging holes 99a and 99b, for example, the engaging hole 99b is an elongated hole.

The basic construction of the code plate 93 is substantially the same as that of the code plate 63 shown in Fig. 1. Therefore, the curvature of the code plate 93 is greater than that of the cam ring 91.

In : the arrangement shown in Fig. 3, when the code plate 93 is attached to the cam ring 91, the generally C-shaped code plate 93 is widened at the opposite ends (free ends) thereof to fit it on the cam ring 91. After that, the projection 92b is first fitted in the corresponding engaging hole 99b. Thereafter, the engaging projection 92a of the cam ring 91 is fitted in the engaging hole 99a of the code plate 93. As soon as the external expanding force is released, the code plate 93 is elastically restored due to the elasticity or flexibility thereof so as to be fitted on the cam ring 91. The elongated hole 99b enables the code plate 93 to be elastically restored (contracted).

It should be appreciated that the concept shown in Fig. 3 can be applied to an alternative in which the code plate is mounted to the inner periphery of the cam ring.

As can be seen from the above discussion, with the embodiment shown in Fig. 3, the code plate 93 can be easily mounted to the cam ring merely by engaging the engaging projections 92a and 92b in the corresponding engaging holes 99a and 99b due to the flexibility or elasticity of the code plate 93. Furthermore, since the circumferential position of the code plate 93 is determined by the engagement of the projection 92a in the engaging hole 99a and since the engagement of the other projection 92b in the corresponding engaging hole 99b prevents the code plate from being twisted or displaced relative to the cam ring, the code plate 93 can be precisely mounted to the cam ring 91.

The elongated hole 99b can be replaced with a large circular hole or a U-shaped groove having an open end. The shape of the engaging projections and the engaging holes is not limited to being circular and can be polygonal. The number of the engaging projections and the engaging holes is not limited to two. For example, it is possible to provide -more than one pair of engaging projections and more than one pair of engaging holes which are aligned in the axial direction.

With the present invention, since the code plate is generally made of a C-shaped flexible or elastic plate substantially corresponding to the curvature of the annular member (cam ring), the code plate can be easily and firmly mounted to ' the annular member by the flexibility or elasticity of the code plate, resulting in no detachment of the code plate from the annular member due to aging.

Claims (11)

1. A code plate mounting device for mounting a code plate on an outer peripheral surface or on an inner peripheral surface of an annular member in a lens barrel, comprising: at least one engaging portion which is provided on the outer periphery surface or on the inner peripheral surface of the annular member; a code plate which is made of an elastic or flexible plate and which is curved at a curvature greater than that of the outer peripheral surface or less than that of the inner peripheral surface of the annular member; and, an engaging portion which is provided on the code plate to engage with at least one of said engaging portions of the annular member.

2. A code plate mounting device according to claim 1 wherein said annular member is provided with a recess in which the code plate is received.

3. A code plate mounting device according to claim 2 wherein at least one of said engaging portions is provided on the bottom of the recess.

4. A code plate mounting device according to claim 3 wherein said at least one engaging portions provided on the bottom of the recess is a pin integral with the annular member.

5. A code plate mounting device according to claim 4 wherein said engaging portion of the code plate is an engaging hole in which the pin is engaged.

6. A code plate mounting device according to any one of claims 1 to 3 wherein said annular member provides two engaging portions which are spaced from one another at a predetermined distance in the circumferential direction.

7. A code plate mounting device according to claim 6 wherein the code plate is provided with two engaging portions to engage with the engaging portions of the annular member.

8. A code plate mounting device according to claim 6 or 7 wherein said two engaging portions are in the form of pins integral with the annular member.

9. A code plate mounting device according to claim 8 wherein said code plate is provided on its opposite ends with an engaging hole in which one of the pins of the annular member is engaged and an elongated hole which extends in the circumferential direction to engage therein the other pin of the annular member.

10. A code plate mounting device for mounting a code plate on an outer peripheral surface or on an inner peripheral surface of an annular member in a lens barrel and substantially as herein described with reference to the accompanying drawings.

11. A lens barrel including an annular member and a code plate and code plate mounting device according to any preceding claim.