GB2221016A

GB2221016A - Trackerball arrangement

Info

Publication number: GB2221016A
Application number: GB8817244A
Authority: GB
Inventors: Christopher James Veel
Original assignee: Marconi Electronic Devices Ltd
Current assignee: Marconi Electronic Devices Ltd
Priority date: 1988-07-20
Filing date: 1988-07-20
Publication date: 1990-01-24
Anticipated expiration: 2008-07-20
Also published as: GB2221016B; GB8817244D0

Abstract

A trackerball arrangement consists of a solid rotatable ball mounted within a housing and supported by a pair of orthogonal rollers 4, 5, which run in bearings. Rotation of the ball 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. The supports and bearings are prone to damage from vertical shocks received via the ball. To limit shock damage an additional resilient support allows the ball to move away from the bearings and absorb the shock. This resilient support consists of a rotatable wheel 10 on a pin 11 supported on a pair of guide rails 12. A pair of leaf springs 13 urges the wheel 10 against the trackerball. <IMAGE>

Description

Trackerball This invention relates to a trackerball arrangement of the kind in which rotation of a ball by hand movement causes the generation of corresponding electrical signals. Such arrangements are comnonly 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 orthognal x and y axes, and these signals are derived from the rotational motion of the 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 rotation 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. It has been found that the bearings and rollers are susceptible to shockS delivered via the ball.

According to this invention a tracker ball arrangement including a ball rotatably mounted with respect to a housing; a plurality of supports arranged to locate the ball in a predetermined position; at least one of the supports being resilientley mounted; whereby pressure above a threshold value which is applied via the ball to the supports causes movement of the resiliently mounted support which allows lateral movement of the ball away from the other supports. In this way excessive shocks applied to the top of the ball do not cause damage to the ball supports at the point of contact between them.

The lateral movement of the ball away from the other supports is arranged preferably to allow the ball to drop, such that shock impacts on the ball are largely absorbed by the downwards movement of the ball and the resilience of a support.

The invention is further described by way of example with reference to the accompanying drawing in which: Figure 1 is side view, and Figure 2 is a part plan view.

Referring to the drawings, a trackerball arrangement includes a solid ball 1 mounted in a housing 14 so that a small portion of the ball 1 protrudes through an aperture in a top plate 2 of the housing.

The ball 1 is free to rotate in all directions about its centre point 3 and may be rotated by 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 (of which only 4 is visible in the drawing) and a third support 6 positioned in a common horizontal plane 7. The rollers 4 and 5 are supported by bearings (not shown) which are attached to means for supporting them in a fixed position relative to the housing.

As the rollers 4 and 5 are in contact with the ball 1 the rotational movement of the ball 1 generates electrical signals representative of the rotation of the two rollers 4 and 5 via optical angle encoders (not shown) attached to the rollers in conventional manner.

In use,shock forces can be inadvertantly applied to the top of the ball and these are transmitted to the rollers 4 and 5 and the support 6. A vertically applied force F results in a force of F SinX on the supports where X is the angle between a horizontal plane through the centre point 3 and the position of the support.

The ball 1 rests on a number of supports of which one support 6 is resiliently mounted. The resiliently mounted support 6 consists of a rotatable wheel 10 having a pin 11 passing through its axis of rotation. The ends of the pin 11 which protrude either side of the wheel 10 are supported by a pair of guiding rails 12 which are attached to the housing 14. The outer ends of the guides 12 are shaped so as to provide a stop position for the pin 11. The pin 11 is urged against the end stop by a pair of leaf springs 13, the outer ends of which bear against the pin 11 and the inner ends are attached to the housing 14.

The springs 13 hold the pins 11 against the end stop provided no force greater than the threshold value F is applied to the top of the ball 1. The ball 1 is located in a predetermined position from which it is displaced when a force greater than F is applied. In order to prevent damage to the supports the resilience of the leaf springs 13 permits the wheel 10 to move so that the pin 11 travels along the guides 12 towards the housing 14. As the wheel 10 moves away so the ball 1 that was supported partly on the wheel is now free to move laterally away from the rollers 4 and 5 and then to fall against a circular rim 9, the position of which is offset from the position of the aperture of the top plate 2 such that the rim holds the ball out of contact with the rollers 4 and 5.

When the force F is removed the resilience of the support 6 causes the ball 1 to be restored to its original position.

When the ball is subject to an abrupt shock resulting in a downwardly applied force which is in excess of a threshold value, it is largely dissipated in the resilience of support 6 and the downward movement of the ball, thereby minimizing the risk of damage to the rollers 4 and 5.

Claims

1. A trackerball arrangement including a ball rotatably mounted with respect to a housing; a plurality of supports arranged to locate the ball in a predetermined position, at least one of the supports being resiliently mounted; whereby pressure above a threshold value which is applied via the ball to the supports causes movement of the resiliently mounted support which allows lateral movement of the ball away from the other supports.

2. A trackerball arrangement as claimed in claim 1 and wherein said other supports comprise a pair of rollers which are mounted in fixed positions relative to said housing.

3. A trackerball arrangement as claimed in claim 1 or 2 and wherein lateral movement of the ball allows the ball to drop.

4. A trackerball arrangement as claimed in claim 3 and wherein a stop is provided to limit vertical movement of the ball and to hold it out of contact with said other supports.

5. A trackerball arrangement as claimed in claim 4 and wherein said stop is positioned so as to hold the ball such that the centre of the ball is held above the position of the resiliently mounted support.

6. A trackerball arrangement as claimed in any of the preceeding claims and wherein resilient means are provided to urge said resiliently mounted support against a further stop, positioned to locate the ball in said predetermined position.

7. A trackerball arrangement as claimed in claim 5 and wherein said resilient means includesd an elongate leaf spring one end of which is fixed relative to the housing.

8. A trackerball arrangement as claimed in any preceeding claim and wherein said resiliently mounted support is in the form of a roller mounted on a guide along which it is free to move away from said ball when said threshold value is exceeded.

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

Amendments to the claims have been filed as follows 1. A trackerball arrangement including a ball rotatably mounted with respect to a housing; a plurality of supports arranged to locate the ball in a predetermined operable position, at least one of the supports being resiliently mounted; and said one of the supports being urged against a stop by the action of resilient means acting upon it; whereby pressure above a threshold value which is applied via the ball to the supports causes movement of the resiliently mounted support when the applied pressure exceeds a threshold value which overcomes the force exerted by said resilient means, said movement allowing lateral movement of the ball away from the other supports.

6. A trackerball arrangement as claimed in any of the preceding claims and wherein said resiliently mounted support is located in a guide along which it is allowed to move when displaced from its stop position.

7. A trackerball arrangement as claimed in claim 5 and wherein said resilient means includes an elongate leaf spring one end of which is fixed relative to the housing.

8. A trackerball arrangement as claimed in any preceding claim and wherein said resiliently mounted support is in the form of a roller mounted on the guide along which it is free to move away from said ball when said threshold value is exceeded, the leaf spring also serving to hold said roller in contact with said guide.