GB2204712A

GB2204712A - Lens moving apparatus

Info

Publication number: GB2204712A
Application number: GB08808895A
Authority: GB
Inventors: Hisashi Suwa; Seiji Sato; Eiji Yano
Original assignee: Sony Corp
Current assignee: Sony Corp
Priority date: 1987-05-15
Filing date: 1988-04-15
Publication date: 1988-11-16
Also published as: DE3816482A1; JPS63282712A; KR880014804A; JP2832930B2; GB8808895D0; CA1312758C

Description

4 220,4712 1 LENS MOVING APPARATUS This invention relates to lens moving

apparatus.

A zoom lens unit for use with a video camera normally includes a variator lens and a compensator lens, both disposed between a focus lens and a master lens. The variator lens and the compensator lens are individually movable in a certain mutual relation in the direction of the optical axis of the unit, to effect a zooming operation. The individual movements of the variator lens and the compensator lens for zooming operation are provided by a helicoid gear incorporated in a cylindrical lens holder.

With this unit, the helicoid gear necessarily has a diameter substantially equal to that of the focus lens. Accordingly, the unit is comparatively large, while the variator lens and the compensator lens individually are comparatively small. Moreover, in a power zoom system a drive motor has to be mounted on the outside, so increasing the size of the unit.

An improved arrangement is disclosed, for example, in US patent specification US-A-4 853 827. In that arrangement, a sectoral driving plate is mounted for pivotal motion in a plane parallel to the optical axis of the system, and a compensator lens and a variator lens are individually moved in the direction of the optical axis by two cams provided on the driving plate. To increase the stroke of movement of the variator lens, the size of the driving plate must be increased, which hinders reduction in the size of the entire arrangement. Moreover, since the two cams are provided on the common driving plate, possible interference between the two cams must be prevented. Accordingly, the degree of freedom in design is reduced. It is also difficult to realize a structure to enable movement only of the compensator lens, while maintaining_ the variator lens stationary to effect a macro operation. 1 According to the present invention there is provided a lens moving apparatus comprising:

a driving disc mounted on a frame and rotatable in a plane parallel to an optical axis; cam and an engaging pin on sa.t.,i disc, first lens holder supported for movement in the direction of said 0 f 1 1 2 optical axis on said frame, and having a cam follower thereon for engagement with said cam; and a second lens holder supported for movement in the direction of said optical axis on said frame, and having a guide thereon for engagement with said engaging pin.

With embodiments of the present invention, only the cam for moving the first lens holder is provided on the disc, and the cam will not interfere with another cam for driving the second lens holder, that is, the guide on the second lens holder. Accordingly, two lenses which may be provided on the first and second lens holders can individually make desired movements. Moreover, the first lens holder on which a compensator lens may be mounted can be moved without moving the second lens holder on which a variator lens may be mounted, so permitting a macro operation for close-up photographs. In addition, the driving torque of the disc can be reduced, and consequently miniaturization of the driving means can be attained. The invention will now be described by way of example with reference to the accompanying drawings, throughout which like parts are referred to by like references, and in which: 20 Figure 1 is a partial fragmentary perspective view of a zoom mechanism of an optical system of a video camera, showing a preferred embodiment of the present invention; Figure 2 is a vertical sectional view of the optical system; Figure 3 is a bottom plan view, partly broken away, showing a driving system of the zoom mechanism; Figure 4 is a front elevational view of the optical system; Figure 5 is a rear elevational view of the optical system; Figure 6 is a plan view of the optical system in wide-angle operation; Figure 7 is a side elevational sectional view of the optical system of Figure 6; Figure 8 is a plan view of the optical system in tele-angle operation; Figure 9 is a side elevational sectional view of the optical system of Figure 8;' Is a, plan view of the optical system in macro Figure 10 operation; and k 3 Figure 11 is a side elevational sectional view of the optical system of Figure 10.

Referring first to Figures 2 and 3, there is shown an optical system of a video camera. The optical system includes a focus lens 10 provided at the forward end thereof and supported on a holding member 11. The member 11 is supported on a frame 14 by a pair of guide rods 12 and 13. A male thread 15 is formed on the outer periphery of the guide rod 12 and is held in thr eaded engagement with a female thread of a sleeve 16. A pulley 17 is f itted on the outer periphery of the sleeve 16. The pulley 17 is coupled with a focus motor (not shown) provided on the frame 14 near the pulley 17, by means of a belt (not shown), so that it may be driven by the motor.

A variator lens 20 and a compensator lens 21 are disposed on the frame 14 behind the focus lens 10. The lenses 20 and 21 are supported on a pair of holding members 22 and 23, respectively. The members 22 and 23 are supported by three guide rods 24, 25 and 26 as seen in Figure 1. In particular, referring to Figure 1, the member 22 on which the variator lens 20 is mounted is supported by the guide rods 24 and 26, while the member 23 on which the compensator lens 21 is mounted is supported by the guide rods 25 and 26.

Now, a mechanism for moving the members 22 and 23 on which the lenses 20 and 21 are mounted, will be described with reference to Figures 1 to 3. The mechanism includes a driving disc 30 supported for rotation on the frame 14. A pin 31 is mounted on the disc 30 for engagement with a cam groove 32 formed on a lower face of the member 22 on which the variator lens 20 is mounted. The upper end of the cam groove 32 terminates in an actuate guide face 33. A cam follower pin 34 is provided on a lower face of the member 23 on which the compensator lens 21 is mounted. The cam follower pin 34 normally engages with a cam 35 formed on the disc 30.

A motor 36 is mounted on a side portion of the frame 14. A pulley 37 is secured to an output power shaft of the motor 36, and is coupled to a pulley 38 by a belt 39. A worm 40 is mounted on the pulley 38, and is held in meshing engagement with a worm wheel 41. A driving gear 42 is mounted on the worm wheel 41 and is held in meshing engagement with a gear 43 formed on the outer periphery of the disc 30.

j f 4 An iris unit 45 is disposed behind the compensator lens 21. A cylindrical lens holder 46 is mounted on the frame 14 behind the iris unit 45, and a master lens set 47 including a plurality of lenses is mounted in the cylindrical lens holder 46. A frame 48 is securely mounted at the rear end of the lens holder 46, and a charge coupled device (CCD) imager 49 is mounted on the frame 48 (see also Figure 5).

The operation, particularly a zooming operation, of the apparatus will now be described. For wide-angle operation, to widen the angle of view, the disc 30 is rotated in the counter -clockwise direction in Figure 6 by the motor 36 by way of the pulley 37, the belt 39, the pulley 38, the worm 40, the worm wheel 41, and the gears 42 and 43. Thereupon, the member 22 is pushed at the cam groove 32 thereof by the pin 31 on the disc 30 to move the variator lens 20 towards the focus lens 10. Simultaneously, the compensator lens 21 is moved towards the CCD imager 49 by the cam 35 of the disc 30 by way of the cam follower 34 on the member 23. Thus, in wide-angle operation, the variator lens 20 and the compensator lens 21 are moved away from each other.

For tele-angle operation, to narrow the angle of view, the disc 30 is rotated in the clockwise direction in Figure 8 so that the member 22 is moved rearwardly by the pin 31 on the disc 30 to move the variator lens 20 back to a position directly in front of the compensator lens 21 as seen in Figures 8 and 9. Thus, the variator lens 20 and the compensator lens 21 are both moved away from the focus lens 10.

A macro operation for close-up photography will now be described with reference to Figures 10 and 11. In this case, the disc 30 is rotated further in the counter-clockwise direction than the most wide-angle position thereof. Thereupon, the pin 31 on the disc 30 is disengaged from the cam groove 32 of the member 22, and is now brought into engagement with the arcuate guide face 33 contiguous to the earn groove 32. The variator lens 20. is not thereupon moved in the direction of the optical axis, because here the arcuate guide face 33 has a profile which coincides with a locus of turning movement of the pin 31. While the variator lens 20 remains stationary, the member 23 on which. the compensator lens 21 is mounted is advanced a small distance towards the focus lens 10 by an end portion of Lhe cam 35 on Q 1 the disc 30. In this manner, only the compensator lens 21 is moved, while the variator lens 20 remains stationary, thereby enabling a macro operation of the optical system for close-up photography. With this apparatus, it is possible to move the compensator 5 lens 21 directly by the cam 35 formed on the disc 30, and to move the variator lens 20 in the direction of the optical axis through engagement of the pin 31 on the disc 30 with the cam groove 32 of the member 22 as described above. The members 22 and 23 holding the lenses 20 and 21 are guided for movement in the direction of the optical axis by the three guide rods 24 to 26. Accordingly, the' zoom lens unit does not necessitate a cylindrical lens holder, and it is possible to dispose a driving means such as the disc driving motor 36 in a space which is provided by omission of such a lens holder. As a result, miniaturization of the optical system of a video camera, particularly the zoom lens unit thereof, is possible.

Moreover, the member 11 for the focus lens 10 is guided by the two guide rods 12 and 13, and the focus lens 10 is moved in the direction of the optical axis by the thread 15 of the guide rod 12, to effect focusing of the optical system. Since the driving mechanism for the focus lens 10 is also disposed in the surplus space around the outer periphery of the zoom lens unit, no component of the driving means extends outwardly further than the outer periphery of the focus lens 10. Upper and lower end portions of the focus lens 10 are out, in order to reduce the vertical dimension, as seen in Figure 4. Since fixing of the focus lens 10 is attained not by means of a ring nut, but by means of fastening screws 52 mounted at the four corners of the member 11 as shown in Figure 4, it is possible to assure a comparatively large aperture for the lens 10. By combination of the structures, it is possible to accommodate all the mechanisms, even including an electric driving means, within the area of the outer diameter of the focus lens 10, which is cut at the upper and lower portions thereof as described above, and consequently to make the entire arrangement compact.

Again, in the present embodiment, the variator lens 20 is moved as the member 22 is pushed at the cam groove 32 thereof by the pin 31 on the disc 30. Accordingly, even if the disc 30 is rotated to a position in which a radial line passing the pin 31 extends parallel to 6 the optical axis, a large load is not applied to the disc 30. Incidentally, if the variator lens 20 is moved by a cam which is provided otherwise than on the disc 30, a high lateral pressure will be applied to the cam, depending upon the rotational position of the disc, which will consequently necessitate a very high driving torque for the disc 30. On the contrary, with the present embodiment, such a defect is eliminated, and it is possible to drive the disc 30 to rotate with a low torque, so as to move the two lenses 20 and 21 smoothly in the direction of the optical axis to effect an accurate zooming operation, 7

Claims

1. A lens moving apparatus comprising: a driving disc mounted on a frame and rotatable in a plane parallel to an optical axis; cam and an engaging pin on said disc; first lens holder supported for movement in the direction of said optical axis on said frame, and having a cam follower thereon for engagement with said cam; and a second lens holder supported for movement in the direction of said optical axis on said frame, and having a guide thereon for engagement with said engaging pin.

2. Apparatus according to claim 1 wherein said first lens holder supports a compensator lens thereon while said second lens holder supports a variator lens thereon, and said disc is coupled to a motor for driving said disc for a zooming operation.

3. Apparatus according to claim 2 wherein said cam has a zooming operation area and a macro operation area provided adjacent to each other, and also said guide has a zooming operation area and a macro operation area adjacent to each other.

4. Apparatus according to claim 2 further comprising a third lens holder provided in front of said first and second lens holders for carrying a focus lens thereon, and a fourth lens holder provided to the rear of said first and second lens holders for carrying a master lens thereon.

5. Apparatus according to claim 4 wherein said focus lens has a substantially rectangular shape, and said third lends holder is supported on a plurality of supporting rods which extend through a front wall of said frame.

6. A lens moving apparatus substantially as hereinbefore described with reference to the accompanying drawings.

Published 1988 at The Patent Off-lee, State House, 66.11 High Holborn, London WClR 4TP. Further copies may be obtained from The Patent Office, Sales Branch, St Mary Cray, Orpington, Kent BR5 3ILD. Printed by Multiplex techniques ltd, St Mary Cray, Kent. Con. 1/57.