GB2220466A

GB2220466A - Trackerball arrangement

Info

Publication number: GB2220466A
Application number: GB8816070A
Authority: GB
Inventors: Christopher James Veel
Original assignee: Marconi Electronic Devices Ltd
Current assignee: Marconi Electronic Devices Ltd
Priority date: 1988-07-06
Filing date: 1988-07-06
Publication date: 1990-01-10
Anticipated expiration: 2008-07-06
Also published as: GB2220466B; GB8816070D0

Abstract

A trackerball arrangement consists of a solid rotatable ball mounted within a housing and supported by a pair of rollers which run in bearings. Rotation of the ball by hand causes corresponding rotation of optical encoders attached to the rollers so that electrical signals are generated representative of the x and y rotation of the ball. As it is important for the bearings to operate freely with low friction, a tubular shield 10 is placed around the ball so as to prevent any liquid which splashes onto the top of the ball reaching the bearings. The rollers contact the ball via apertures in the shield. An upper plate 2 is provided with a lip 14 on its underside, which follows the curvature of the ball and prevents liquid from travelling onto the undersurface of the top plate 2. <IMAGE>

Description

Trackerball Arrangement.

This invention relates to a trackerball arrangement of the kind in which rotation of a ball by handmovement causes the generation of corresponding electrical signals. Such arrangements are commonly used in conjunction with display screens for the purpose of moving a cursor or the like around the screen. The electrical signals may be indicative of the extent of rotation of the ball or merely of its sense. It is customary for separate electrical signals to be generated which are respectively indicative of rotation about orthogonal x and y axes, and these signals are derived from the rotational motion of rollers which bear against the surface of the ball.As the ball has a smooth surface, the frictional grip between the ball and a roller is very low, and any resistance by a roller to rotate will result in the roller slipping against the surface of the ball so that the resulting electrical signals do not faithfully represent the movement of the ball.

Any imperfection in the operation of the bearings by which a roller is supported degrades the operation of the trackerball arrangement, and it has been found that the bearings are adversely affected by the presence of liquids which may for example be spilt over the ball. The present invention seeks to provide an improved trackerball arrangement.

According to this invention a trackerball arrangement includes a ball rotatably mounted with respect to a housing; a roller mounted in a bearing and arranged to be in contact with the surface of the ball so as to rotate therewith; and means positioned between the ball and the bearing so as to provide a shield for the bearing against liquid.

The shielding means is positioned between the bearing and the ball, so as to reduce the likelihood of liquid on the surface of the ball reaching the bearing. In use, liquid such as a beverage can easily be spilt over the trackerball arrangement, and the liquid can enter the housing via the surface region of the ball which is contacted by the hand. Contamination of the bearing by such a liquid can seriously restrict its freedom to rotate, and impair the correct operation of the arrangement.

The invention is further described by way of example with reference to the accompanying drawings in which: Figure 1 is a part sectional elevation of a trackerball arrangement, and Figure 2 is a plan view.

Referring to the drawings a trackerball arrangement includes a solid ball 1 mounted in a housing so that a small portion of the ball 1 protrudes through an aperture in a top plate 2 which forms part of the housing. The ball 1 is free to rotate in all directions about its centre point 3 and may be moved using the fingertips or the palm of the hand. The ball 1 is supported, below its centre point 3, by two orthogonal rollers 4 and 5 and a third support 6 positioned in a horizontal plane 7 below the centre point 3. The rollers 4 and 5 are supported by pairs of bearings 8 and 9 which are attached to a cylindrical shield 10 with the contact points 11 between the rollers 4 and 5 occurring in the region of respective apertures in shield 10.

As the rollers 4 and 5 come into contact with the ball the movement of the ball provides the rollers 4 and 5 with the torque to turn the bearings 8 and 9. Electrical signals representative of the rotation of the two rollers 4 and 5 are generated by respective optical angle encoders 12 and 13.

The amount of the torque provided by these rollers 4 and 5 is small as the surfaces of the ball 1 and the rollers 4 and 5 are very smooth and have little frictional grip and the bearings are very prone to contamination by liquids and dust.

The most likely way in which liquids can reach the bearings 8 and 9 is via the gap between the upper plate 2 and the ball 1. The upper plate 2 is provided with a lip 14 on its underside, which follows the curvature of the ball 1 and prevents liquid from travelling onto the undersurface of the top plate 2. Thus liquid entering the arrangement via the gap is retained within the cylindrical shield 10 which acts to shield the bearings 8 and 9 from direct contact with the liquid.

The rollers 4 and 5 provide a possible route for the bearings to be contaminated by liquid running down the ball surface. In order to prevent this, collars 15 are attached to the rollers 4 and 5 directing the drips down the outside of the cylindrical shield 10 and away from the bearings 8 and 9. A perforated base plate 16 is provided below the shield 10 at the base of the housing to allow the unwanted liquid to drain away.

Claims

1. A trackerball arrangement Including a ball rotatably mounted with respect to a housing; a roller mounted in a bearing and arranged to be in contact therewith; and means positioned between the ball and the bearing so as to provide a shield for the bearing against liquid.

2. A trackerball arrangement as claimed in Claim 1 and wherein the shield surrounds the ball and is provided with a localised opening in the region of the contact between the roller and the ball.

3. A trackerball arrangement as claimed in Claim 1 or 2 and wherein two rollers are provided in mutually orthogonal positions with respect to the ball, with respective bearings being arranged to support each end of each roller.

4. A trackerball arrangement as claimed in Claim 3 and wherein the shield takes the form of a vertically disposed tubular member having a pair of localised openings at which the respective rollers contact the ball, with said bearings being mounted on the outer surface of said tubular member.

5. A trackerball arrangement as claimed in Claim 4 and wherein the tubular member Is in the form of a thin walled cylinder.

6. A trackerball arrangement as claimed in Claim 4 or 5 and wherein a portion of said ball projects through a circular aperture in a top plate of said housing, with means being provided for directing liquid falling onto the protecting portion of said ball to the interior of said tubular member.

7. A trackerball arrangement as claimed in Claim 6 and wherein said means comprises a downwardly projecting lip which follows the edge of said aperture.

8. A trackerball arrangement as claimed in any of the preceding claims and wherein means are provided in the base of said housing for allowing liquid collecting within the housing to drain away.

9. A trackerball arrangement substantially as illustrated in and described with reference to the accompanying drawings.