GB2322680A

GB2322680A - A compact cam drive assembly for moving a lens of an electrophotographic apparatus

Info

Publication number: GB2322680A
Application number: GB9704247A
Authority: GB
Inventors: Wil Meijer; Joseph H J Martens
Original assignee: Xerox Corp
Current assignee: Xerox Corp
Priority date: 1997-02-28
Filing date: 1997-02-28
Publication date: 1998-09-02
Also published as: GB9704247D0

Abstract

A cam drive assembly comprises at least two cam surfaces 42, 44 rotational driven by motor 49 via gear 48. As cams 42, 44 rotate they cooperate with cam follower 50, thereby causing lever 54 to pivot, either towards or away from the rotational axis of cams 42, 44, about shaft 56. Cam follower 50 is connected to a spring 66 via first wire 60 and pulley 64 which is in engagement with second pulley 76. As the lever 54 pivots the first wire 60 is drawn through pulley 64 causing it to rotate, this rotation is transmitted to the second pulley 76 thereby moving second wire 70. Both ends 72, 74 of second wire 70 are attached, via further pulleys 77, 78, 79, to an optical arrangement 20, eg a lens of a copying machine, so that movement of the second wire 70 causes translation of the lens 20 along non parallel guide edges 22a, 22b of support 21. This translation of the lens 20 allows for simple control of magnification.

Description

CAM DRIVE ASSEMBLY This invention relates to a cam drive assembly suitable for transmitting force to a movable body. The cam drive assembly is particularly suitable for use in an electrophotographic apparatus wherein the movable body is an optical arrangement comprising a lens.

In the well-known electrostatographic reproduction process, a uniform electric charge is provided to an electrostatographic plate. The plate typically comprises a photoconductive insulating material mounted on a conductive backing. A light image of the subject matter to be reproduced is projected onto the charged plate. Discharging occurs where the light image strikes the plate, thereby resulting in formation of an electrostatic latent image on the plate. The latent image is developed by applying a developer material, such as a toner, which electrostatically clings to the plate in a visual pattern corresponding to the latent image. Thereafter, the developed image is transferred from the plate to a support material, such as paper or a transparency, to which it may be fixed thereby forming a permanent print on the support material In the above process, the light image is typically generated by placing the document to be reproduced on the platen glass of the copying machine; illuminating the original document with an exposure lamp; and channelling the reflected light image to the charged plate by use of an optical system, typically involving mirrors and one or more lenses. As is well known, enlargement or reduction of the size of the light image projected onto the charged plate can be adjusted by adjusting the arrangment of the optical system. In particular, in a simple one lens system, adjustment of the ratio of the distance travelled by the light in going from the original document to the lens to that distance travelled on going from the lens to the charged plate allows for simple control of magnification.

It is desirable for a copying machine to provide a range of document image magnification possibilities. A machine might thus, for example, allow magnification options in the range from 50 to 200% at stepped intervals of for example, 1% throughout that range. Typically, to allow for such magnification options, the copying machine is provided with an operator directed means for adjusting the position of the optical arrangement relative to that of the platen glass upon which the original document is placed, and the charged plate. The operator inputs a desired magnification level, and the machine automatically adjusts the position of the optical arrangment to be in accord with that level. For accuracy of magnification and good resolution, accurate positioning of the optical arrangement is necessary.

It is known to use a motor driven cam assembly to acheive such positioning of an optical arrangement. A known assembly comprises a rotatably mounted cam; a motor driven pulley wheel for rotably driving the cam; a cam follower means movable in response to the rotation of the cam; a pivoted lever coupled to the cam follower means; and a wire arrangement coupled to the lever and connecting a lens assembly. The lens assembly is slidably mounted on a mounting arrangement having guide edges, and is translatable thereon. As the cam rotates, the cam follower means moves causing the lever to be moved about its pivot axis. This pivoted movement of the lever is translated to the lens assembly via the wire arrangement, thereby causing the lens assembly to be moved in the appropriate direction along the guide edges. The positioning of the lens is hence, dependent on the degree of rotation of the cam, which in turn is responsive to the instruction given to the drive motor by the machine control panel in response to the operator's selection of magnification.

A problem associated with positioning systems using such a cam drive assembly is in providing the required degree of resolution and accuracy of magnification over a wide range of magnification options. Such problem might be ameliorated by the use of a particularly large cam.

This solution however, is not optimum in view of the conflicting desire to have a relatively compact positioning system, which itself does not take up too much of the limited available space within the body of a copying machine, which has to accomodate many complex moving parts.

The Applicants have now found that an alternate solution to the above described problem is provided by use of a cam drive assembly employing a cam arrangement which comprises a plurality of cam surfaces, each rotatableabout the same rotational axis such that on rotation of the cam arrangement, the cam follower means contacts either one or a plurality of said cam surfaces.

US-A-5,437,210 describes a power cam drive assembly for use in an electrophotographic apparatus comprising a single cam.

Summary of the Invention According to one aspect of the present invention there is provided a cam drive assembly suitable for transmitting force to a movable body comprising a rotatably mounted cam arrangement; drive means for rotably driving said cam arrangement; cam follower means movable in response to the rotation of the cam arrangement; and translation means capable of translating movement of said cam follower means into a force communicable to said movable body, wherein said cam arrangement comprises a plurality of cam surfaces, each rotatable about the same rotational axis, such that on rotation of the cam arrangement the cam follower means contacts either one or a plurality of said cam surfaces.

According to another aspect of the present invention there is provided an electrophotographic apparatus comprising a cam drive assembly as described above wherein the movable body is an optical arrangement, preferably comprising a lens.

Brief Description of the Drawings Figure 1. is a perspective view, from above, of the interior of part of an electrophotographic apparatus comprising an optical arrangement, and in exploded view a cam drive assembly in accord with the present invention.

Figure 2. is a perspective view, from above, of a cam drive assembly in accord with the present invention.

Detailed Description of the Invention There is provided a cam drive assembly suitable for transmitting force to a movable body.

In a preferred aspect, the cam drive assembly is employed in an electrophotographic apparatus and said movable body is an optical arrangement, preferably comprising a lens. The optical arrangment can, for example be slidably mounted for translation along guide rails.

The cam drive assembly comprises a rotatably mounted cam arrangement. A cam is to be understood in its usual sense, to be an essentially planar mechanical part presenting an eccentric cam surface, which is typically provided with gear teeth. A central aperture is provided in the body of the cam to enable mounting of the cam for rotation. The distance from the axis of rotation to a particular point on the cam surface is herein, termed the cam diameter for that point.

In accord with the present invention, the cam arrangement comprises a plurality of cam surfaces, each rotatable about a common rotational axis. In a preferred aspect, the cam arrangement comprises a plurality of cams mounted in a stack, wherein more preferably each of said plurality of cams has a different range of maximum to minimum cam diameters and the stack is arranged in order of increasing maximum cam diameter. In a highly preferred aspect, each cam in the stack, other than the cam with the smallest minimum cam diameter, has a minimum cam diameter corresponding to the maximum diameter gf the cam immediately superior to it in the stack.

A drive means is provided for rotably driving the cam arrangement. Preferably, the drive means comprises a motor driven wheel coupled to said cam arrangement.

A cam follower means is provided which is movable in response to the rotation of the cam arrangement. On rotation of the cam arrangement, the cam follower means contacts either one or a plurality of the eccentric cam surfaces. A means is typically provided to urge the cam follower means against a cam surface. Thus, as the cam arrangement rotates, the cam follower is moved either towards or away from the axis of rotation of the cam arrangement.

A translation means capable of translating the movement of the cam follower means into a force communicable to the movable body is also provided. In a preferred aspect, the translation means comprises a lever means coupled to said cam follower means and a wire arrangement connecting with said movable body. More preferably, the wire arrangement is tensioned such as to urge the cam follower means against the cam arrangement.

Preferred embodiments of the invention will now be further described with reference to the accompanying drawings.

Referring to Figure 1. there is shown part of an electrophotographic apparatus comprising a frame 10 and an optical arrangement 20 slidably mounted to the frame 10 on mounting support 21 having guide edges 22a and 22b for guided movement therealong. The guide edges 22a and 22b are non-parallel to each other. Also present is a cam drive assembly shown in exploded view. Figure 2.

shows in detail, the cam drive assembly in assembled form. The cam drive assembly comprises a cam arrangment 40 which comprises a first cam 42 and a second larger cam 44, each mounted for rotation about spigot 46 wherein the second cam 44 sits in a fixed position on top of the first cam 42 in a two cam stack. The stack itself is fixed to a drive wheel 47 having gear teeth 48 which is also mounted for rotation about spigot 46. Rotation of the drive wheel 47, and hence of the cam arrangment 40 is driven by a motor 49. A cam follower 50 is provided, which engages with either one or both of the cam surfaces provided by the first 42 and second 44 cams respectively, as the cam arrangement 40 rotates. The cam follower is mounted at the end of lever 54, which is pivotally mounted about pivot 56. The cam follower is urged against a cam surface by tensioned first wire arrangement. The tensioned first wire arrangement comprises first wire 60 which is provided with a washer 62 at one end, which is looped over spigot 49 for attachement thereto. In another part of the tensioned first wire arrangement, the other end of the first wire 60 connects via first pulley wheel 64 to spring arrangment 66. There is also provided a second wire arrangment comprising second wire 70, which is fixedly attached at both ends of the wire 72, 74 to the optical arrangement 20. The second wire runs through second pulley wheel 76, which engages with the first pulley wheel 64, and further pulley wheels 77, 78 and 79 which are spatially separated from each other. It can be seen that movement of the second wire will result in movement of the optical arrangement 20 along the guide edges 22a and 22b.

On rotation of the cam arrangement 40, the cam follower 50 and end of the lever 54 are moved either towards or away from the rotational axis of the cam arrangement 40. The tensioned first wire 60 is thus drawn through pulley wheel 64 causing its rotation. The engagement of first pulley wheel 64 with second pulley wheel 70 causes it also to rotate (in the opposite direction) thereby moving the second wire, which itself causes the position of the optical arrangement 20 to be shifted along the guide edges 22a and 22b.

Claims

CLAIMS:

1. Cam drive assembly suitable for transmitting force to a movable body (20) comprising a rotatably mounted cam arrangement (40); drive means (49) for rotably driving said cam arrangement (40); cam follower means (50) movable in response to the rotation of the cam arrangement (40); and translation means (54, 60) capable of translating movement of said cam follower (50) means into a force communicable to said movable body (20), wherein said cam arrangement (40) comprises a plurality of cam surfaces (42,44), each rotatable about the same rotational axis, such that on rotation of the cam arrangement (40) the cam follower means (50) contacts either one or a plurality of said cam surfaces (42,44).

2. An assembly according to Claim 1 wherein wherein said cam arrangement (40) comprises a plurality of cams (42,44) mounted in a stack.

3. An assembly according to Claim 2 wherein each of said plurality of cams (42, 44) has a different range of maximum to minimum cam diameters and wherein said stack is arranged in order of increasing maximum cam diameter.

4. An assembly according to Claim 3 wherein each cam in said stack, other than the cam with the smallest minimum cam diameter, has a minimum cam diameter corresponding to the maximum diameter of the cam immediately superior to it in the stack.

5. An assembly according to any of Claims 1 to 4 wherein said translation means comprises a lever means (54) coupled to said cam follower means (50) and a wire arrangement (60) connecting with said movable body (20).

6. An assembly according to Claim 5 wherein said wire arrangement (60) is tensioned so as to urge the cam follower means (50) against said a cam surface (42,44).

7. An assembly according to any of Claims 1 to 6 wherein said drive means (49) comprises a motor driven wheel coupled to said cam arrangement (40).

8. Electrophotographic apparatus comprising a cam drive assembly according to any of Claims 1 to 7 wherein said movable body is an optical arrangement (20), preferably comprising a lens.

9. Electrophotographic apparatus according to Claim 8 wherein said optical arrangement (20) is slidably mounted on a mounting support (21) having guide edges (22a, 22b) for guided movement therealong

10. Electrophotographic apparatus according to either of Claims 8 or 9 having a range of magnification settings, preferably in the range of from 50 to 200% magnification, adjustable within said range by movement of said optical arrangement (20).