GB2229016A

GB2229016A - Manufacturing cam ring of lens barrel

Info

Publication number: GB2229016A
Application number: GB8915590A
Authority: GB
Inventors: Makoto Iwamura
Original assignee: Asahi Kogaku Kogyo Co Ltd
Current assignee: Pentax Corp
Priority date: 1989-03-09
Filing date: 1989-07-07
Publication date: 1990-09-12
Anticipated expiration: 2009-07-07
Also published as: DE3922817A1; DE3922817C2; FR2644252B1; GB2229016B; FR2644252A1; GB8915590D0

Description

C CAM RING OF LENS BARREL AND METHOD FOR MANUFACTURING SMIE 1 The present

invention relates to a cam ring used in a lens barrel and a method for manufacturing the same.

A lens barrel having a cam ring is commonly used in a zoom lens. The cam ring has for example, two cam grooves in which guide pins of front and rear groups of movable lenses are fitted, so that when the 10 cam ring rotates, the movable lens groups are moved in accordance with profiles of the cam grooves to vary the focal length.

In the lens barrel as mentioned above, in case where the cam ring is driven to rotate by an electrical drive mechanism, it is necessary to provide a gear on the outer periphery of the cam ring. To this end, a separate gear ring is secured to the outer periphery of the cam ring in a conventional lens barrel. The cam grooves are usually in the form of through openings on which the gear ring is usually superimposed. It is therefore next to impossible to form the cam ring 20 integral with the gear rin g.

The assignee of the present application has proposed a zoom lens barrel in which a cam ring is supported so as to move in the optical axis direction in accordance with the rotation thereof to decrease the length necessary for accomodating the zoom lens barrel in a camera body (Japanese Patent application No. 63-137019). In this zoom lens barrrel, the cam ring is provided, on its outer periphery, with a male helicoid (thread) which serves as a rotational guide means and which is engaged by a stationary female helicoid. Also in this zoom lens barrel, the male helicoid is provided on a helicoid ring which 30 is made of a piece separate from the cam ring for the same reason as 1 -2that mentioned above. The helicoid ring must be secured to the cam ring later. It is also necessary to provide a gear for rotating the cam ring on the helicoid ring.

The primary object of the present invention is therefore to eliminate the above-mentioned drawbacks of the prior art in which the gear ring or the helicoid ring which is made of a separate piece from the cam ring must be secured later to the cam ring, by providing a cam ring which has a gear or helicoid formed integrally therewith.

Another object of the present invetion is to provide a method for effectively and precisely manufacturing such a cam ring having a gear and/or a helicoid integral therewith.

The inventor of the present invention has found that the rotational guide means (cam or helicoid) can be integrally formed on the outer periphery of the cam ring by providing inner cam grooves having closed outer surfaces (bottoms) on the cam ring, in place of the conventional cam grooves which are in the form of through openings.

To achieve the object inentioned above, according to.the present invetion, there is provided a lens barrel having a rotatable cam ring which has at least one cam groove, at least a part of which is in the form of an inner cam groove having a closed bottom located on the outer surface thereof, said cam ring being provided on its outer periphery with a gear and/or a rotational guide means formed integrally therewith.

The highly developed modern metal machining process makes it possible to mold or form the inner cam groove and the gear and/or the rotational guide means integral with the cam ring. If the cam ring is made of a synthetic resin material, such a integral molding can be -3more easily performed. As the rotational guide means can be used not only the above-mentioned helicoid but also a cam.

The cam groove can be either linear or non-linear. The present invention can be advantageously applied particularly to the non-linear cam groove.

A method for manufacturing a cam ring according to the present invetion is characterized in that the cam ring and the gear (and/or the rotational guide means) which are both made of synthetic resin are integrally molded at one time, and then, the cam groove is formed by a cutting operation.

In theory, the gear and/or the rotational guide means can be formed by the cutting operation after the cam ring is made. However, it has been found that the gear and/or the rotational guide means can be precisely formed at the same time as the formation of the cam ring.

Similarly, in theory, it is possible to form the cam grooves simultaneously with the formation of the cam ring by using split type molding dies. However, it should be taken into account that the cam groove which determine a track of the movement of the lens group is usually non-linear, and accordingly, must be more accurate than linear groove. Furthermbre, particularly in case where such non-linear cam groove is formed by using a split type of molding dies, the cam groove usually bridge the molding dies. It is, however, very difficult to make a smooth connection of the bridged portion.

In other words, the present invetion satisfies both the requirements of a reduced manufacturing cost and a high precision.

Namely, the former requirement can be achieved by a technical idea that the gear (and/or the rotational guide means) are formed by molding to reduce the manufacturing cost, since those portions do not need a high precision. On the other hand, the latter requirement can be achieved by forming the cam grooves which need higher precision by the cutting operation after the cam ring is molded.

Alternatively, it is also possible to form the cam groove in two steps, in which the first formation is effected by molding and the second formation (finishing machining) is effected by cutting. Note that in the present application, the term "cutting" of the cam groove also includes such a finishing machining.

The invention will be described below in detail with reference to the accompanying drawings, in which:

Figure 1 is a schematical sectional view showingsuccessive steps of manufacturing a cam ring according to the present invetion; Fig. 2 is a schematical sectional view showing another step of manufacturing a can ring according to the present invetion; Fig. 3 is a sectional view of an upper half of a lens barrel in which a cam ring shown in Fig. 1 is incorporated; Fig. 4 is a view of development of a cam ring according to another aspect of the present invetion; and, Figs. 5 through 7 are:ectional views of an upper half of a lens barrel in which a cam ring shown in Fig. 4 is incorporated, shown in an accomodated position, a wide extremity position and a tele-extremity position, respectively.

Fig. I is a schematical view showing how to manufacture a cam ring according to an aspect of the present invetion.

An injection molding die AA for resin material has an annular space Al corresponding to a cam ring, and a gear forming space A2 which is located on a part of the outer periphery of the cam ring l:

forming annular space Al to be connected thereto. Although the molding die AA is illustrated as a single piece, it is of a split type. The injection molding die AA is provided an injection port (not shown) through which a molten resin material is introduced into the cam ring forming annular space Al.

In the present invetion, a molten resin material is.injected in the cam ring forming annular space Al and the gear forming space A2 of the injection molding die AA to mold the whole cam ring I and the gear lc which is provided on a part of the outer periphery of the cam ring 1. After that, the cam ring I is removed from the molding die AA and is then cut by a cutting tool BB to form inner cam grooves la and lb on the inner surface of the cam ring 1. The inner cam grooves la and lb have closed bottoms and open to the inner surface of the cam ring 1. The inner cam grooves la and lb can be easily cut by a cutting operation perse known.

With the manufacturing processes as mentioned above, since the cam ring 1 and the gear lc are integrally injection-molded at one time, the manufacturing cost can be reduced. It should be appreciated that the gear which is formed by the injection molding has a practically satsfactory precision. The inner cam grooves which need higher precision than the gear can be precisely formed by the cutting operation.

Fig. 2 shows another embodiment in which a helicoid HH is formed on the outer periphery of the cam ring 1A by the injection molding.

The cam ring 1A has inner cam groove la on the inner surface thereof. The inner cam groove la can be formed by the cutting operation similarly to Fig. 1. Alternatively, it is also possible to form the inner groove in two steps. Namely, primary inner cam groove la' is first formed by injection molding and then secondary (finished) inner cam groove la is formed by cutting. Such a -6multi-step formation of the inner cam groove contributes to a decreased consumption of resin material and to an increased service life of the cutting tool BB due to a decreased amount of the cam ring to be cut.

As a synthetic resin material of which the cam ring 1 is made can be used a material having a good injection molding property and a high machinability (cutting property), such as polycarbonate, polyphenylensulfide, or polyphenylenoxide.

It is preferable to add to the synthetic resin material, fluorine or carbon as a lubricant and glass fiber or carbon as a reinforcement. The added carbon also contributes to a high precision of dimension and a high stability of dimension. Fig. 3 shows a lens barrel in which the cam ring I shown in Fig. 1 is incorporated. The cam ring 1 is rotatably supported between a front securing plate 2 and a rear securing plate 3. The front and rear securing plates 2 and 3 are interconnected by a guide rod 4 which extends in parallel with an optiocal axis of the lens. A front group of lenses (frame) 5 and a rear group of lenses (frame) 6 are movably supported on the gui4e rod 4. 20 In the inner cam grooves la and lb of the cam ring 1 are fitted guide pins 5a and 6a of the front lens group 5 and the rear lens group 6, respectively. The gear lc is engaged by a pinion 7 which is rotated by a motor 9 which is in turn driven through a zoom control circuit 8, so that when the motor 9 is driven to rotate, the cam ring 1 is rotated to move the front lens group 5 and the rear lens group 6 in the optical axis directions in accordance with the cam profiles of the inner cam grooves la and lb in order_to effect zooming. According to the present invetion, as mentioned aboVe, the cam grooves which are to be formed on the cam ring 1 are in the form of inner cam grooves with closed bottoms and the gear lc is integrally 1 -7formed on the outer periphery of the cam ring, thus resulting in a less number of components of the lens barrel and less number of assembling steps.

In Fig. 3, cam projection 10 as the rotational guide means provided on the outer pheriphery of the cam ring 1 is drawn by an imaginary line. The cam projection 10 engages with stationary recess (not shown) so that the cam ring 1 moves in optical axis directions while rotating.

A cam ring 22 which is shown in Fig. 4 by way of an'example is provided on its outer surface with a gear 22a and a helicoid 22b and on its inner surface with cam grooves which are partly in the form of inner cam grooves 22c and 22d with closed bottoms and partly in the form of through openings 22c' and 22d'. The inner cam grooves 22c and, 22d which have closed outer surface portions (bottoms) correspond to the gear 22a and the helicoid 22b and the through cam grooves 22c and 22d correspond to the remaining portion of the cam ring that has neither gear nor helicoid, so that each of the cam grooves has a non- linear profile.

The cam ring 22 is essentially formed by the same processes as mentioned above with reference to Fig. 1 or Fig. 2.

Figs. 5 through 7 show a zoom lens barrel in which the cam ring 22 shown in Fig. 4 is incorporated.

The basic construction of the zoom lens barrel shown in Figs. 5-7 is similar to that of the lens barrel as disclosed in the above-mentioned Japanese Patent Application No. 63-137019 proposed by the assignee of the present application except for the cam ring 22 with which the gear 22a and the helicoid 22c are integral. The constrcution and the operation of the lens barrel are as follows.

The camera body 11 of a lens shutter type of camera has a stationary barrel 12 secured thereto. The camera body has an outer -8rail 13 and an inner rail 14, both serving as a film guide.

An outer helicoid (which has helicoid teeth on its inner periphery) 18 is secured to the stationary barrel 12 through a machine screw 19. The cam ring 22 shown in Fig. 4 is located in the outer helicoid 18. The cam ring 22 has an inner peripheral helicoid 22a (which has helicoid teeth on its outer periphery) which is engaged by the outer helicoid 18, and a gear 22a which is inclined at a same inclination angle as that of the helicoid teeth of the inner helicoid 22a. The gear 22b is in mesh with a pinion 7 as shown in fig. 3, so that the forward and reverse rotations of the pinion 7 cause the rotations of the cam ring 22 in the same direcitons. Consequently, the cam ring 22 moves in the optical axis direction, in accordance with the lead of the helicoid 22a when the cam ring 22 rotates. The inclination of the gear 22b enables the axial movement of the cam ring 22.

In the cam ring is fitted a lens guide ring 24 which has a linear movement guide plate 26 secured to the rear end thereof by a set screw 25. The linear movement guide plate 26 is partially engaged, at its outer surface, in a lens linear movement guide groove 27 formed on the inner face of the stationary barrel 12. An inner flange 29 which is formed at the rear end of the cam rrng 22 is fitted in an annular groove 28 which is formed between the linear movement guide plate 26 and the rear end of the lens guide ring 24. Consequently, the rotational movement of the lens guide ring 24 is restricted by the lens linear movement guide groove 27, but the lens guide ring 24 can move with the cam ring 22 in the optical axis directions. The cam ring 22 is rotatable relative to the lens guide ring 24.

The front and rear lens groups 15 and 16 are secured to a front 30 lens group frame 30 and a rear lens group frame 31, respectively. The -gfront lens group frame 30 is engaged by a helicoid ring 33 which is secured to a shutter block 32. The shutter block 32 is secured to a front lens group moving frame 34 which is provided on its outer periphery with a plurality of guide pins 35. The rear lens group frame 31 is also provided on its outer periphery with a plurality of guide pins 36. Although the guide pins 35 and 36 are illustrated to be overlapped in Figs. 5 and 7 only for convenience's sake. they are actually located in different phases.

The shutter block 32 rotates a drive pin 32a by an angle 'corresponding to an object distance to be photographed detected by an object distance measuring device to rotate the front lens group frame 30 connected to the drive pin 32a in the same direciton in order to move the front lens group frame 30 in the optical axis directions in accordance with the helicoid thereby to effect an adjustment of focus. The shutter block 32 also actuates shutter blades 32b in accordance with a brightness signal of the object to be photographed.

Numerals 38 and 39 designate a cylindrical lens cover integral with the front lens group moving frame 34 and a decorative ring which protrudes from a body shell lla of the camera to cover the outer peripheries of the lens guide ring 24 and the cam ring 22, respectively. The guide pins 35 and 36 are inserted in the through cam grooves 22c' and 22d which are formed at the portions in which neither the helicoid 22a nor the gear 22b are positioned, as mentioned above. 25 The lens guide ring 24 is provided with lens linear movement guide grooves 43 and 44 corresponding to the front lens group cam grooves 22c and the rear lens group cam grooves 22d. The. guide pins 35 are inserted in both the lens linear movement guide grooves 43 and the front lens group cam grooves 22c. The guide pins 36 are inserted in both the lens linear movement guide grooves 44 and the rear lens group cam grooves 22d.

The profiles of the front lens group cam grooves 22c and the lens linear movement guide grooves 43 and the profiles of the rear lens group cam groove 22d and the lens guide grooves 44 are designed so that the movable lens groups 15 and 16 are moved along predetermined tracks in the optical axis directions by the axial movements of the cam ring 22 and the lens guide ring 24 which are caused by the rotation of the cam ring 22 and the relative rotation --of the cam ring 22 and the lens guide ring 24. In the front lens group cam grooves 22c and the rear lens group cam grooves 22d shown in Fig. 4, sections P, i, P, 2 and -e 3 are zooming section, macrotransferring section connected to tele-extremity of the zooming section P, i and lens accommodation section connected to the wide-extremity of the zooming section Q 1, respectively.

In the lens barrel as constructed above, when the cam ring 22 is rotated through the gear 22b in the forward and reverse directions, the cam ring 22 moves in the optical axis directions in accordance with the lead of the helicoid 22a while rotating, since the outer helicoid 18 which is engaged by the helicoid 22a is immovable, so that the lens guide ring 24 also moves in the optical axis directions. As a result of the axial movement of the lens guide ring 24, the cam ring 22 rotates relative to the lens guide ring 24 in accordance with a relationship between the cam grooves 22c, 22d and the lens linear movement guide grooves 43, 44. The relative rotation of the cam ring 22 and the lens guide ring 24 causes the lens groups 15 and 16 to move in the optical axis directions. This makes it possible to move the lens groups 15 and 16 from the lens accommodation position shown in Fig. 5 to the tele-extremity position shown in Fig. 7. It should be appreciated that in the lens accommodation position, the cam ring 22 and the lens guide ring 24 do 1 not protrude from the camera body, thus resulting in a decreased accommodation length.

In the modified embodiment as mentioned above, similarly to the embodiment shown in Figs. 1-3, since at least a part of each of the cam grooves formed on the cam ring 22 is an inner cam groove with a closed bottom, and since the gear 22b and the helicoid 22a are integrally formed with the cam ring 22, the number of separate components and the assembly processes can be decreased. In the,illustrated embodiment, it is possible to integrally provide only the jear 22b or the helicoid 22a on the cam ring 22.

According to the present invetion, since the cam ring and the gear and/or the helicoid are integrally molded of resin 'material at one time, and since the inner cam grooves are formed by cutting, the desired cam ring can be precisely and effectively manufactured at low cost. In particular, in case of non-linear cam groove, precise cam profile can be precisely formed by cutting.

Claims

CLAIMS:

1. A cam ring of a substantially annular shape for a lens barrel comprising at least one cam groove in which guide pins provided on lens group which is movable in optical axis directions'and a gear which is provided on the outer periphery of the cam ring to rotate the cam ring, wherein at least a part of said cam groove is in the form of an inner cam groove with a closed bottom located on the outer surface thereof, and said gear is integrally formed on the outer.-surface of the cam ring.

10.

2. A cam ring according to claim 1, wherein said gear is inclined with respect to the circumferential direction of the cam ring. -

3. A cam ring of a substantially annular shape for a lens barrel comprising at least one cam groove in which guide pin provided on lens group which is movable in optical axis directions and a rotational guide means, on the outer periphery of the cam ring for moving the cam ring in the optical axis directions in accordance with the rotation thereof, wherein at least a part of said cam groove is in the form of an inner cam groove with a closed bottom located on the outer surface thereof, and said rotational guide means is integrally formed on the outer surface of the cam ring.

4. A cam ring according to claim 3, wherein said-rotational guide means comprises a helicoid.

5. A cam ring according to claim 3, wherein said rotational guide means comprises a cam.

6. A cam ring of a substantially annular shape for a lens barrel comprising at least one cam groove in which guide pin provided on lens group which is movable in optical axis directions, a gear which is provided on the outer periphery of the cam ring to rotate the cam ring, and a rotational guide means on the outer periphery of the cam -13ring for moving the cam ring in the optical axis directions in accordance with the rotation thereof, wherein at least a part of said cam groove is in the form of an inner cam groove with a closed bottom located on the outer surface thereof, and both the rotational guide means and the gear are integrally formed on the outer surface of the cam ring.

7. A cam ring according to claim 6, wherein said rotational guide means comprises a helicoid.

8. A cam ring according to claim 6, wherein said rotational _kuide means comprises a cam.

9. A cam ring according to claim 6, wherein said gear is inclined with respect to the circumferential direction of the cam ring.

10. A cam ring according to claim 1, 3 or 6, wherein said cam ring, said gear and/or the rotational guide means a.re made of synthetic resin.

11. A cam ring according to claim 1, 3 or 6, wherein said cam groove is non-linear.

12. A lens barrel having a rotatable cam ring which has at least one cam groove, group of lenses which have guide pin engaged in the associated cam groove of the cam ring and which is moved in the optical axis directions in accrodance with the rotation of the cam ring, a gear which is provided on the outer periphery of the cam ring to rotate the cam ring, and/or a rotational guide means on the outer periphery of the cam ring for moving the cam ring in the optical axis directions in accordance with the rotation thereof, wherein at least a part of Said cam groove is in the form of an inner cam groove with a closed bottom located on the outer -surface thereof, and the gear and/or the rotational guide means is (are) integrally formed on the outer surface of the cam ring.

13. A cam ring according to claim 12, wherein said-rotational -14guide means comprises a helicoid.

14. A cam ring according to claim 12, wherein said rotational guide means comprises a cam.

15. A cam ring according to claim 6, wherein said gear is 5 inclined with respect to the circumferential direction of the cam ring.

16. A method for manufacturing a cam ring of a substantially annular shape for a lens barrel having at least one cam groove in which guide pin provided on lens group which is movable in optical axis directions, at least a part of said cam groove is in the form jo bf an inner cam groove with a closed bottom located on the outer surface thereof, and a gear which is provided on the outdr periphery of the cam ring to rotate the cam ring, comprising molding the cam ring and the gear at one time, both being made of synthetic resin.

17. A method according to claim 16, wherein said cam groove is is formed by cutting after the cam ring and the gear are molded.

18. A method according to claim 17, wherein said gear is inclined with respect to the circumferential direction of the cam ring.

19. A method for manufacturing a cam ring of a substantially annular shape for a lens barrel having at least one cam groove in which guide pin provided on lens group which is movable in optical axis directions, at least a part of said cam groove is in"the form of an inner cam groove with a closed bottom located on the outer surface thereof, and a rotational guide means on the outer periphery of the cam ring for moving the cam ring in the optical axis directions in accordance with the rotation thereof, comprising molding the cam ring and the gear at one time, both being made of synthetic resin and then forming the cam grooves by cutting.

20. A method according to claim 19, wherein said rotational guide means comprises a helicoid or a cam.

1 51

21. A method for manufacturing a cam ring of a substantially annular shape for a lens barrel having at least one cam groove in which guide pin provided on lens group which is movable-in optical axis directions, at least a part of said cam groove is in the form of an inner cam groove with a closed bottom located on the outer surface thereof, a gear which is provided on the outer periphery of the cam ring to rotate the cam ring, and a rotational guide means on the outer periphery of the cam ring for moving the cam ring in the optical axis directions in accordance with the rotation thereof, comprising molding the cam ring, the gear and the rotational guide means, of synthetic resin at one time, and then forming the cam grooves by cutting.

22. A method according to claim 21, wherein said rotational guide means comprises a helicoid or a cam.

23. A method according to claim 21, wherein said gear is inclined with respect to the circumferential direction of the cam ring.

24. A method according to claim 16, 19 or 21, wherein said cam groove is non-linear.

25. A method according to claim 16, 19 or 21, wherein said synthetic resin of which the cam ring, the gear and/or the rotational guide means are molded is selected from a group of polycarbonate, polyphenylensulfide and polyphenylenoxide.

26. A method according to claim 25, wherein fluorine is added to the synthetic resin material as a lubricant.

27. A method according to claim 25, wherein carbon is added to the synthetic resin material as a lubricant.

28. A method according to claim 26 or 27, wherein glass fiber is added to the synthetic resin material as a reinforcement.

29. A method according to claim 26 or 27, wherein carbon is added to the synthetic resin material as a reinforcement.

30. A method according to claim 16, wherein said cam groove is formed in two steps which comprise molding primarypam groove together with the cam ring and the gear at one time and then finishing the primary cam groove by cutting.

is z-0 Published 1990 a. The Patent Office. StateHouse.6571 High Holborn. London WCIR 4TP. Further copies maybe obtainedfromThefttentOffi(e Sales Branch, St Mary Cray. Orpington, Kent BR5 3RD. Printed by Multiplex techniques ltd. St Mary Cray, Kent, Con. 1187