GB2318841A

GB2318841A - Bearing assembly

Info

Publication number: GB2318841A
Application number: GB9622796A
Authority: GB
Inventors: Douglas Sharp
Original assignee: PerkinElmer Ltd
Current assignee: PerkinElmer Ltd
Priority date: 1996-11-01
Filing date: 1996-11-01
Publication date: 1998-05-06
Also published as: GB9622796D0

Abstract

An optical scanning device 10 is mounted on a vertical shaft 15 supported by two bearing assemblies, each comprising a spherical or part-spherical member 24, 32 bonded to the shaft and located in a conical seat 26, 28. The upper seat 28 is supported on a spring member 29, which is secured to a mounting flange on the housing and extends into a slot 27 in a larger diameter portion 18 of the shaft. The shaft is arranged to undergo oscillatory movements through an angle of 25{ by means of a coaxial core and coil assembly 20. A magnet 22 generates an axial force which urges the members 24, 32 into their respective seats.

Description

BEARING ASSEMBL This invention relates to apparatus for imparting angular oscillatory movement to a device such as an optical scanning device. In particular, the invention is concerned with a bearing assembly for such an apparatus.

In optical devices such as optical interferometers used for example in IR spectroscopy it is common to employ a scanning mechanism in which one or more optical elements are caused to undergo an oscillatory angular movement. In devices such as interferometers it is important that the angular movement can be carried out extremely precisely and at an angular velocity which can be maintained with a high degree of accuracy. It is also important that the oscillatable elements are accurately aligned and that such alignment can be maintained during operation.

The present invention is concerned with an apparatus for imparting angular oscillatory movement to a device which can achieve these aims.

According to the present invention there is provided apparatus for imparting angular oscillatory movement to a device, such as an optical scanning device, comprising a shaft which in use is coupled to said device, means for imparting rotational movement to the shaft to cause it to oscillate angularly, and bearing means for supporting said shaft within a housing, said bearing means including a spherical or part spherical member carried by or fixed to the shaft and a generally conical seat for receiving said spherical or part-spherical member.

A bearing means in which a spherical or partspherical member locates within a generally conical seat has the advantage that there is a line contact at a relatively small circumferential radius and this provides a low frictional torque. In addition the bearing conical seat arrangement has the property of being self-aligning due to its geometry.

The bearing means may include two bearing assemblies, a first said assembly including a spherical or part-spherical member at the end of the shaft remote from the device, said member locating in a conical seat on an end face of said housing, and a second said assembly being located towards the other end of the shaft and located in a slot in said shaft, said second assembly including a spherical or part spherical member secured to the shaft and located in a seat supported in said slot.

The seat of the second assembly may be supported on a spring member extending radially into said slot from the housing. Preferably the spring is stiff in all directions except an axial direction whereby it can resist all movement of the seat other than movement along the axis of the shaft.

The means for driving the shaft may comprise an electromagnetic type arrangement including an electrically energisable coil disposed coaxially around the shaft.

The apparatus may include means for imparting a force to the shaft tending to urge the spherical or part spherical bearing members into their seats. The force may be a magnetic force generated by an annular magnet disposed coaxially around the shaft.

The force generated by the magnet acts to locate the bearings and to control both position and alignment of the bearing assembly.

The invention will be described now by way of example only, with particular reference to the accompanying drawings. In the drawings: Figure 1 is a plan view of an apparatus for imparting angular oscillatory movement to an optical scanning device in accordance with the present invention, and Figure 2 is a side elevation of the apparatus of Figure 1.

Referring to the drawings, apparatus for imparting angular oscillatory movement to oscillatable elements of an optical arrangement shown schematically at 10 comprises a tubular housing 11 which is closed at one end by a circular end face 12 and has at its other end an annular mounting flange 14. A shaft 15 is disposed axially within the housing and has a lower relatively narrow diameter portion 16 and an upper larger diameter portion 18, which extends through the central opening of the mounting flange 14 and is coupled to the optical arrangement 10. The shaft is disposed coaxially within an annular core and coil assembly 20, which can be used to generate the necessary electromagnetic field to rotate the shaft 15. Disposed above the assembly 20 is an annular magnet 22.

At its lower end the shaft 15 carries a spherical end piece 24, which locates within a conical seat 25 formed in seat member 24, which is secured within the end face 12. The seat member 26 can be formed of suitable bearing materials such as PTFE or an acetal resin loaded with PTFE. The spherical end 24 on the shaft 15 can be a steel ball bonded or swaged to the end of the shaft. The conical bearing preferably has an apex angle of approximately 900.

In the larger diameter portion 18 the shaft is formed with a diametrical through slot 27.

Accommodated within the slot 27 is a seat 28 which is carried on a spring member 29 secured at 30 to the mounting flange of the housing. A ball 32 which is bonded to the lip of the lower end of an axial bore in the upper part 18 of the shaft is seated in the seat member 30. The seat 28 can be formed from a material similar to that of the seat 24 and the cone angle can be the same as that of seat 24.

The spring 29 is arranged to be stiff in all directions other than the axial direction of the shaft. This arrangement means that the spring allows movement of the seat 28 only in the axial direction of the shaft.

The magnet 22 is arranged to generate an axial force on the shaft tending to urge the shaft in a direction which forces the bearings into their respective seats.

In use when the core and coil assembly 20 is energised under the control of a control system (not shown) the shaft 15 is caused to undergo an angular oscillatory movement through approximately 250. The movement is imparted to the optics 10 by virtue of their coupling to the upper end of the shaft 16. The bearing arrangements 24, 25 and 32, 28 shown in Figures 1 and 2 are capable of enabling the apparatus to provide a precise oscillatory movement which is accurately repeatable and which can be carried out at a very constant angular velocity. The geometry of the bearing arrangements in which a spherical bearing element seats within a conical seat means that there is a line contact at a small circumferential radius which provides a low frictional torque and which has a self-aligning characteristic. This means that the alignment of the arrangement is accurately maintainable. Furthermore, even when there is wear in the seat the arrangement effectively has wear compensation which maintains the axial alignment of the output shaft. Furthermore, the above characteristics are present irrespective of the orientation of the device.

Claims

CWUMS t

1. Apparatus for imparting angular oscillatory movement to a device, such as an optical scanning device, comprising a shaft which in use is coupled to said device, means for imparting rotational movement to the shaft to cause it to oscillate angularly, and bearing means for supporting said shaft within a housing, said bearing means including a spherical or part spherical member carried by or fixed to the shaft and a generally conical seat for receiving said spherical or part-spherical member.

2. Apparatus according to claim 1, wherein the bearing means include two bearing assemblies, a first said assembly including a spherical or part-spherical member at the end of the shaft remote from the device, said member locating in a conical seat on an end face of said housing, and a second said assembly being located towards the other end of the shaft and located in a slot in said shaft, said second assembly including a spherical or part spherical member secured to the shaft and located in a seat supported in said slot.

3. Apparatus according to claim 2, wherein the seat of the second assembly is supported on a spring member extending radially into said slot from the housing.

4. Apparatus according to claim 3, wherein the spring is stiff in all directions except an axial direction whereby it can resist all movement of the seat other than movement along the axis of the shaft.

5. Apparatus according to any preceding claim, wherein the means for driving the shaft comprise an electromagnetic type arrangement including an electrically energisable coil disposed coaxially around the shaft.

6. Apparatus according to any preceding claim, including means for imparting a force to the shaft tending to urge the spherical or part spherical bearing members into their seats.

7. Apparatus according to claim 6, wherein the force is a magnetic force generated by an annular magnet disposed coaxially around the shaft.

8. Apparatus for imparting angular oscillatory movement to a device substantially as hereinbefore described with reference to and as shown in the accompanying drawings.