JPS597319A - Cam follower for zoom lens - Google Patents

Abstract

PURPOSE:To enable smooth zooming by using hollow cylinders having elasticity and a small coefft. of friction in making the cam followers of a zoom lens and fitting the same to a cam groove without clattering. CONSTITUTION:Cam followers 11, 12 are constituted into a hollow cylindrical shape by using a material such as a synthetic resin having a small coefft. of friction and elasticity. The followers 11, 12 are made to the outside diameter slightly larger than the groove width of cam grooves 2, 3 provided in a cam ring 1. Clatters between the grooves 2, 3 and the followers 11, 12 are eliminated and smooth movement is effected by the elastic deformation of the followers 11, 12.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a cam follower for a zoom lens, and particularly to a cam follower for a zoom lens that is made elastic so that no pressure fluctuation occurs between the cam follower and the cam groove.

Generally, a zoom lens includes a variable power lens for changing the focal length of the lens, and a correction lens that moves as the variable power lens moves and corrects aberrations caused by the movement of the variable power lens. A mechanism consisting of a cam follower embedded in a holding frame that holds these lenses, and a cam ring having a cam groove that engages with the cam follower allows the lenses to maintain a predetermined positional relationship and be moved from the lens. It is composed of

An example of a conventional cam follower for such a zoom lens will be described below with reference to the drawings.

1 and 2 are perspective views and sectional views of the main parts of a zoom lens including a cam follower and a cam ring according to the prior art. In FIGS. 1 and 2, 1 is a cam ring, 2 and 3
4 and 5 are cam followers, 6 is a variable power lens holding frame, 7 is a correction lens holding frame, 8 is a variable power lens, 9 is a correction lens, and 10 is a guide rod.

A zoom lens using a cam follower using conventional technology is
As shown in FIGS. 1 and 2, a variable power lens holding frame 6 holding a variable power lens 8 and a correction lens holding frame 7 holding a correction lens 9 are slidably supported by a guide rod 10. Cam followers 4 and 5 embedded in both holding frames 6 and 7 are fitted into cam grooves 2 and 3 of a cam ring 1 provided so as to surround both holding frames 6 and 7. The cam followers 4, 5 and the cam R1 are made of a non-elastic material such as metal, and when the cam ring 1 is rotated,
The variable power lens holding frame 8 and the correction lens holding frame 9 are moved by cam grooves 2 and 3 of the cam ring 1 via cam followers 4 and 5. Thereby, the zoom lens can change the focal length by simultaneously moving the variable power lens 8 and the correction lens 9 while maintaining the positional relationship defined by the cam groove of the cam R1.

The positional accuracy of the variable magnification lens 8 and correction lens 9 during movement depends on the accuracy of the cam grooves 2 and 3, so the accuracy of the cam grooves 2 and 3 must be extremely high. However, the cam grooves 2 and 3 are easily deformed and distorted during machining, making it difficult to obtain high accuracy, and it has been difficult to completely and accurately fit the cam followers 4 and 5.

For this reason, in a zoom lens using a cam 7 follower according to the prior art, for example, if the width of the cam grooves 2 and 3 of the cam ring 1 widens due to deformation during processing, the cam grooves 2 and 5 and the cam follower 4 and Due to this, the contact surfaces of the cam followers 4 and 5 and the cam grooves 2 and 3 are different from each other depending on the zooming direction, which deteriorates the performance of the zoom lens and causes damage to the lens. If the groove widths of the cam grooves 2 and 3 were narrowed, the torque required to rotate the cam ring 1 would increase, resulting in malfunction and failure.

SUMMARY OF THE INVENTION An object of the present invention is to provide a cam follower for a zoom lens that eliminates the drawbacks of the prior art described above and prevents rattling between the cam follower and a cam groove provided in a cam ring.

To achieve this objective, the present invention provides a hollow cylindrical structure for the cam follower and imparts elasticity to the cam follower in order to keep the cam follower always in contact with the cam surface of the cam groove provided in the cam ring. It is characterized by the following points.

Hereinafter, embodiments of a cam follower for a zoom lens according to the present invention will be described with reference to the drawings.

FIG. 3 is a cross-sectional view of the main parts of a zoom lens using a cam follower according to the present invention, and FIG. 4 is an enlarged perspective view of the cam follower according to the present invention, where 11 and 12 are cam followers, which correspond to FIG. 2. Parts are given the same reference numerals and some explanations are omitted.

The configuration of a zoom lens using a cam follower according to the present invention is exactly the same as that using the conventional cam follower shown in FIG. 2, as shown in FIG. 3, except for the structure of the cam follower itself. The cam follower according to the present invention is shown as cam followers 11 and 12 in FIG. 3, and as shown in the enlarged view in FIG. organized into shapes. The outer diameter dimensions of the cam followers 11 and 12 are configured to be slightly larger than the groove width dimensions of the cam grooves 2 and 3 provided in the cam ring 1. In this way, the cam followers 11 and 12 are made of a hollow cylindrical structure using an elastic material with a small coefficient of friction, and the outer diameter of the cam followers 11 and 12 is made slightly larger than the width of the cam grooves 2 and 3. H, cam follower 11 and h 12 cam grooves 2 and 3
When the cam followers 11 and 12 move along the cam grooves 2 and 5 VC, the cam followers 11 and 12 do not have backlash between them and the cam grooves 2 and 3 even in places where the groove widths of the cam grooves 2 and 3 are wider than the designed dimensions. The cam follower 11 can move along the cam grooves 2 and 3 without causing any
and 12 can be elastically deformed and smoothly moved along the cam grooves 2 and 3.

Next, an increase in the rotational force of the cam ring 1 during zooming operation in a zoom lens using the cam follower according to the present invention as described above will be considered.

Generally, the groove widths of the cam grooves 2 and 3 provided in the cam ring 1 vary by about ±10 μm from the design value. For this reason, the external dimensions of the cam followers 11 and 12 according to the present invention are such that the cams are designed so that no looseness occurs between the cam followers 11 and 12 and the cam grooves 2 and 3 even at locations where the groove widths of the cam grooves 2 and 3 are widened. The groove widths of grooves 2 and 3 were set to be approximately 0 μm larger than the designed values. Cam follower 11
and 12 are highly elastic because they are made of elastic synthetic resin or the like in a hollow cylindrical shape, as described above, but the cam ring in which the cam grooves 2 and 3 are provided is made of metal such as aluminum. and will not undergo elastic deformation. Therefore, when the cam followers 11 and 12 move along the cams n2 and 3, the cam followers 11 and 12 move up to the cam grooves 2 and 6 and receive a compressive force of up to 30μ? 7! It undergoes a degree of elastic deformation. Due to this elastic deformation, the cam follower 11
and 12 generate a drag force corresponding to the amount of elastic deformation, and this drag force becomes a load on the rotational force of the cam ring 1 when the cam followers 11 and 12 move along the cam grooves 2 and 3.

Now, if the aforementioned drag is P1 load is F1 and the friction coefficient between cam grooves 2 and 3 and cam followers 11 and 12 is μ, then
It can be expressed as F=μP.

On the other hand, the drag force P is a function of the elastic modulus E of the material constituting the cam follower, and if δ is the amount of deformation of the cam follower, then
It can be expressed as PocEδ, and the aforementioned negative load F is expressed as pcpcμEδ.

As an example, the cam followers 11 and 12 are made of polyamide (
Considering the case of nylon 6) resin,
The elastic modulus E of the polyamide resin is E = 83000f
1/J, and the outer diameter of the cam followers 11 and 12 is 40. If the wall thickness is 02yn hollow cylinder, 50m
The force P that causes the deformation of is of the order of P:140. Further, since the friction coefficient μ between the cams @2 and 3 of the cam R1 and the cam followers 11 and 12 is μ=0.3, the load F for the rotational force of the cam ring 1 described above is F: 4
It will be about 01. This load is approximately 1 of the rotational force of the cam ring 1 required for normal zooming in a general zoom lens.
It is 0%, and is not so large as to cause any particular problem in the operation of the zoom lens.

The material for the cam follower should be strong enough to move the variable magnification lens holding frame 6 and correction lens holding frame 7 in which the cam followers 11 and 12 are embedded into predetermined positions as the cam ring 1 rotates, and a smooth material. Cam groove 2 provided in cam ring 1
Any material may be used as long as it can move within the polyamide resin and 3.
Synthetic resins such as tetrafluoroethylene resin and polyacetal resin can be used.

FIG. 5, FIG. 6, and FIG. 7 each show a cross-sectional view of another embodiment of a cam follower for a zoom lens according to the present invention.

The cam follower shown in Fig. 5 is a hollow cylinder with one end closed to increase the strength of the buried part.
The cam follower shown in FIG. 5 has a screw provided in the buried part of the cam follower shown in FIG. 5 in order to further increase the strength of the buried part compared to the case of FIG. Additionally, the cam follower shown in FIG. 7 is constructed so that the inner surface of the hollow cylinder is provided with irregularities so that the cam follower is easily deformed and the elastic effect of the cam follower is increased.

As explained above, according to the present invention, the cam follower is made of an elastic synthetic resin material and is configured in a hollow cylindrical shape, so that there is no backlash between the cam groove and the cam follower, and smooth zooming operations can be performed. Therefore, it is possible to provide a cam follower for a zoom lens that allows stable photographing even when the zooming direction is different, and has superior functions not found in the above-mentioned prior art.

[Brief explanation of drawings]

1 and 2 are perspective views and sectional views of main parts of a zoom lens including a cam follower and a cam ring according to the prior art;
FIG. 4 is an enlarged perspective view showing an embodiment of the cam follower according to the present invention, and FIGS. FIG. 7 is a sectional view showing another embodiment of the cam follower according to the invention. 1...Cam ring 2, 3...Cam groove 4, 5.11.12...Cam follower 6...Variable lens holding frame 7...Correction lens holding frame 8...Variable lens 9・・・
・Correction lens 10...Guide rod Luc I Fig. 37 Fig. 2 Koma 4 Fig. 57 Fig. 6 Koma 7 (21

Claims (1)

[Claims] 1. A variable power lens holding frame holding a variable power lens, a correction lens holding frame holding a correction lens, a cam follower embedded in these holding frames, and the variable power lens holding frame and This zoom lens consists of a guide rod that slidably guides a correction lens holding frame, and a cam ring having a cam groove that fits into the cam follower, and moves the variable power lens and the correction lens to a predetermined position simultaneously by a zooming operation. A cam follower for a zoom lens, characterized in that the cam follower for a zoom lens is made of a hollow cylinder having elasticity and a small coefficient of friction, and is configured to be able to fit into the cam groove without rattling. 2. The cam follower for a zoom lens according to claim 1, wherein the elastic effect is increased by providing unevenness on the inner surface of the hollow cylinder.