JPH075450Y2 - Cam device for lens barrel - Google Patents

Description

[Detailed description of the device] [Industrial applications]

The present invention relates to a cam device in a lens barrel of a camera, and more particularly to a cam device in a lens barrel of a zoom lens.

[Prior art]

As is well known, the movement of a movable lens in a zoom lens can be performed by rotating or linearly moving a zoom operation ring by fitting a cam pin and a cam groove, or by moving a cam surface and a cam follower contacting the cam surface. The lens is transmitted to a movable frame that holds the lens, and the movable frame is moved in the optical axis direction. Conventionally, most of the cam barrels used in zoom lens barrels are made of a metallic cylindrical material, and NC machining of these has been used to form a highly accurate cam with a complicated shape. Whether the cam device has the former structure or the cam device having the latter structure, the cam surface with which the cam follower abuts is finished with high accuracy, so that the cost increase of the cam cylinder cannot be avoided. On the other hand, in recent years, a proposal has been made to integrally mold the cam and the cam barrel main body using a plastic material. In this case, in order to form the cam portion with a two-sided mold configuration of a fixed mold and a movable mold, which is advantageous for dimensional accuracy and mold configuration, it is advantageous that the shape is convex. However, even if such a convex cam is formed at low cost, there remains a problem of how to configure a cam follower guided by the cam. In other words, the prevention of "backlash" in the cam device greatly contributes not only to the improvement of the optical performance but also to the improvement of the operability and operation feeling of the zoom operation. Therefore, the structure of the cam follower for the cam is closely related to the backlash prevention. There is. Many configurations for preventing this "backlash" have already been proposed. For example, in the disclosed example disclosed in Japanese Utility Model Application Laid-Open No. 57-84507, a pair of cam followers is arranged on a convex cam, and the pair of cam followers are biased in parallel with the optical axis by a spring to form a convex cam. It is designed to be guided by the cam surface on one side. Another disclosed example (Japanese Patent Publication No. 61-20843)
In Japanese Patent Laid-Open Publication No. 2004-242, a straight key is provided with a pair of cam followers that come into contact with the cam surface of the cam, and the straight key is urged by a spring in the optical axis direction. In addition, Japanese Examined Sho 61-208
In the example disclosed in Japanese Patent Publication No. 42, a pair of cam followers is arranged so as to sandwich the convex cam, one of the pair of cam followers is fixed, and the other is urged by a spring or the like to the convex cam to move the cam to one side. It is designed to be held down by the cam follower. In these cam devices, a pair of cam followers use springs or the like to elastically contact the convex cams to prevent "backlash" from occurring. Alternatively, in the disclosed example of Japanese Utility Model Publication No. 60-41533, instead of using the biasing means, a pair of pins at least one of which is an eccentric pin (the distance between the pins is fixed) is used, and the convex cam is used. The pair of pins sandwiches each other to prevent "backlash" between the cam and the pins in the optical axis direction.

[Problems to be solved by the device]

Although the above-mentioned disclosure examples are effective in preventing the above-mentioned "backlash", there is a drawback in that the structure for that is complicated. In addition, since the springs are used for biasing, strength problems and reliability remain uncertain. Also, in the eccentric pin method, the eccentric pin is brought into contact with the cam surface at a position where there is no "play", and this pin is fixed with a set screw.
Although the structure for preventing backlash is simplified, looseness of the set screw may cause "backlash" even with an eccentric pin. Further, it is difficult to apply this method to a cam having a non-linear cam surface curved in a concave or convex shape in the optical axis direction. As described above, the conventional example has problems to be further improved, and the present invention has been made to eliminate these problems. Therefore, the present invention effectively suppresses "backlash" between the convex cam and the cam follower guided by the cam with a simple structure, and obtains high reliability and good operability as a cam device. It is an object of the present invention to provide a cam device for a lens barrel capable of performing the above.

[Means for solving the problem, and action / effect]

(Structure) In order to achieve the above object, the present invention has the following structure. That is, the cam device of the lens barrel of the present invention is held immovably in the optical axis direction, and has a convex cam formed on the inner peripheral surface of a rotating cylinder rotatably provided around the optical axis. A cam device provided with a cam follower mounted on the inside of the rotary cylinder so as to be movable in the optical axis direction so as to cooperate with the convex cam, and a cam follower provided on an outer peripheral surface of a movable frame for holding a lens. A cam follower main body in which the cam follower is rotatably supported by the movable frame, and a pair of contacts provided on the cam follower main body and having a curved cam corresponding surface that abuts the cam surface of the convex cam. Is equipped with
The cam corresponding surface is positioned symmetrically with respect to the rotation center axis of the cam follower body. The contactor may be a cylindrical pin member or roller member. Alternatively, it may be a protrusion protruding in the rotation center axis direction. That is, the contact itself should have at least the cam corresponding surface. (Operation) According to the above configuration, when the rotary cylinder is rotated, the cam follower moves in the optical axis direction while being guided by the convex cam formed on the rotary cylinder. Therefore, the movable frame supporting the cam follower also moves in the optical axis direction. Moreover, since the cam follower is rotatably supported by the movable frame with respect to the movable frame, it is guided by the convex cam so as to follow the shape of the cam surface of the convex cam. That is, even if the cam is a convex cam that is curved with respect to the optical axis direction, the cam follower is rotatable with respect to the support member that supports the cam, that is, the movable frame. You will be guided as if you are sandwiched. (Effect) Therefore, the cam device of the present invention realizes highly accurate movement by the cam follower following the shape of the predetermined cam surface formed on the convex cam. Further, since the cam follower can be brought into contact with the cam surface without looseness even if it is not biased using a spring or the like as in the conventional example, the structure is simple as a cam device, At the same time, the strength and reliability of the cam cylinder with respect to shocking external force are improved. That is, the cam device is not limited to the linear cam,
For a cam device with a non-linear cam, its operability,
It is a suitable device for increasing reliability.

【Example】

An embodiment of the present invention will be specifically described below with reference to FIGS. FIG. 1 is a partially omitted sectional view showing a lens barrel according to an embodiment. 2 is a perspective view for explaining a cam follower in the cam device, FIG. 3 is a development view showing a state in which the lens barrel is expanded for explaining the operation of the cam follower, and FIG. 4 is a cam barrel. A sectional view and FIG. 5 are perspective views showing a modification of the cam follower. In FIG. 1, reference numeral 1 denotes a lens mount, and inside the fixed barrel 2 that is integrally provided with the lens mount 1,
First movable frame 5 and second lens group holding the first lens group L ₁
A second movable frame 6 holding L ₂ is fitted. further,
The fixed barrel 2 has a first rectilinear groove 21 and a second rectilinear groove 22 formed in parallel with the optical axis direction, and the first and second cam followers 7, which will be described later, are provided in the grooves 21, 22. By fitting 8 to each other, the first and second cam followers 7 and 8 are guided to move in the optical axis direction. On the other hand, a cam barrel 3 which is a rotatable barrel is attached to the outer periphery of the fixed barrel 2. As shown in FIG. 4, a convex first cam 31 for moving the first lens group is provided on the inner peripheral surface of the cam barrel 3.
And a groove-shaped second cam 32 for moving the second lens group. The first cam 31 is a cam that protrudes inward and is curved with a predetermined curvature in the optical axis direction, and has a pair of cam surfaces 31a, 31a on the front and rear sides in the optical axis direction. Also, the second cam 32
Is a linear grooved cam formed behind the first cam 31. As well shown in FIG. 2, the first movable frame 5 has the frame 5
The first cam follower 7 is attached with attachment screws 9 so as to be rotatable with respect to. The first cam follower 7 is composed of a first cam follower main body 72 and a pair of columnar cam follower pins 71, 71 arranged to face the main body 72, as shown in FIG. The pair of cam follower pins 71, 71 sandwich the convex first cam 31. That is, the peripheral surface of the cam follower pin 71 becomes the cam corresponding surface 71a. or,
The first cam follower body 72 is rotatably fitted in the first rectilinear groove 21. The first cam follower 7 is attached by forming a seat surface 5a, which is substantially parallel to the optical axis, on the outer peripheral surface of the first movable frame 5 corresponding to the first cam by counterbore processing, and the seat surface 5a has the first The cam follower main body 72 is fitted and loosely fitted in the cam follower fitting portion 91 of the mounting screw 9 so as to be rotatably screwed to the first movable frame 5. The pair of cam follower pins 71, 71 are arranged symmetrically with respect to the rotation center axis of the first cam follower main body 72.
The intervals of 1,71 are sized and configured so that the first cam 31 can be inserted without play. Therefore, when the cam barrel 3 is rotated, the first cam follower 7, which is rotatably mounted on the first movable frame 5 by sandwiching the first cam 31, is guided by the first cam 31, and the cam surface 31a, It moves in the optical axis direction while following the shape of 31a. The first cam follower does not have to have the above-described configuration. That is, FIG. 5 shows a modification of the cam follower. This cam follower 7'is configured such that the contactor that abuts on the cam surface is integrated with the cam follower body. That is, a pair of protrusions 71 ', 71' having opposing curved surfaces, that is, the cam corresponding surface 71a ', may be integrally formed on the cam follower main body 72' at a predetermined interval. In this case as well, it goes without saying that the pair of cam-corresponding surfaces 71a 'are positioned symmetrically with respect to the rotation center axis of the cam follower body 72'. Also, as shown in FIG. 1, the second cam follower 8
Are planted in the second movable frame 6, and penetrate the second rectilinear groove 22 and are fitted with the groove-shaped second cam 32. In the figure, 4 is a cam barrel 3
Is a holding plate that regulates the plate so that it does not move back and forth in the optical axis direction. Next, the operation of this embodiment will be described with reference to FIG. When the cam cylinder 3 is rotated, the first and second cam followers 7 and 8 are moved along the optical axis by the first and second cams 31 and 32 provided on the cam cylinder 3. Each of these cam followers 7,8
Is connected to the first and second movable frames 5 and 6, so that each movable frame 5 and 6 also moves along the optical axis direction. That is, the focal length of the lens changes. FIG. 3A shows the positional relationship between the first and second cam followers 7, 8 at the short focal length position. FIG. 3B shows the positional relationship between the cam followers 7 and 8 at the intermediate focal length position.
Figure (C) shows each cam follower at the long focal length position.
8 shows the positional relationship. As described above, when the cam barrel 3 is rotated in the long focal length position direction from the position shown in FIG. 3A, the first cam follower 7 is guided by the first cam 31 to move from the position (A) to (B). ) Position and then to (C) position. Similarly, the second cam follower 8 is also guided by the second cam 32 and moves to each position of (A) → (B) → (C). Here, focusing on the first cam follower 7, the angle formed by the pair of cam follower pins and the optical axis is
As shown in the figure, θ ₁ ° → 0 ° (that is, parallel to the optical axis) → θ ₂
The first cam follower 7 rotates by (θ ₁ + θ ₂ ) ° with respect to the change in the focal length from the wide-angle range to the telephoto range.
This is possible because the first cam follower 7 is rotatable with respect to the first movable frame 5. That is, in the case of the cam curved along the optical axis as in the present embodiment, the cam follower holds the cam follower if the pin spacing of the pair of cam follower pins arranged so as to sandwich the cam is fixed. It must be rotatable with respect to the member to be rotated. With such a configuration, the cam follower can be guided in accordance with the shape of the cam surface machined into a predetermined shape without interposing "play" between the cam and the cam follower. Moreover,
The cam follower moves smoothly. As is apparent from the above description, the cam device for the lens barrel of the present embodiment eliminates "backlash" and realizes a smooth operation, and the cam follower acts on the lens barrel by always sandwiching the cam. It can be said that the device is suitable and has a simple structure, which protects the cam barrel from an impact force and improves the reliability of the cam device.

[Brief description of drawings]

1 to 5 show a cam device for a lens barrel according to an embodiment of the present invention, FIG. 1 is a partially omitted sectional view showing the lens barrel, and FIG. 2 is a cam follower in the cam device. FIG. 3 is a development view showing a state in which the lens barrel is expanded for explaining the operation of the cam follower, FIG. 4 is a sectional view of the cam barrel, and FIG. 5 is one of the cam followers. It is a perspective view which shows a modification. 1 ... Lens mount, 2 ... Fixed barrel, 3 ... Rotating barrel (cam barrel), 4 ... Holding plate, 5 ... Movable frame (first movable frame), 5a ... Seat surface, 6 ... 2 movable frames, 7,7 '... Cam follower (first cam follower), 8 ... Second cam follower, 9 ... Mounting screw, 21 ... First straight groove, 22 ...
… Second straight groove, 31 …… Convex cam (first cam), 31a ……
Cam surface, 32 ... Second cam, 71,71 '... Contact (cam follower pin), 71a, 71a' ... Cam corresponding surface, 72,72 '...
… Cam follower body, 91 …… Cam follower fitting part,
L ₁ ... the first lens group, L ₂ ... the second lens group.

Claims (1)

[Scope of utility model registration request] 1. A convex cam (31) formed on the inner peripheral surface of a rotary cylinder (3) which is held immovably in the optical axis direction and is rotatable around the optical axis; A cam that is mounted inside the barrel (3) so as to be movable in the optical axis direction and that is provided on the outer peripheral surface of the movable frame (5) that holds the lens (L ₁ ) and that cooperates with the convex cam (31). In a cam device for a lens barrel including a follower (7), the cam follower (7) includes a cam follower body (72) rotatably supported by the movable frame (5), and the cam follower body (72). 72) and above the convex cam (31)
Curved surface (71a) that contacts the cam surface (31a) of the
And a pair of contacts (71, 71) each having a cam, and the cam corresponding surface (71a) has the cam follower body (7).
A cam device for a lens barrel characterized in that it is symmetrically positioned with respect to the rotation center axis of 2).