WO1995035576A1

WO1995035576A1 - Joystick assembly

Info

Publication number: WO1995035576A1
Application number: PCT/GB1995/001489
Authority: WO
Inventors: Leslie Arthur Birt
Original assignee: Penny & Giles Electronic Components Limited
Priority date: 1994-06-22
Filing date: 1995-06-22
Publication date: 1995-12-28
Also published as: GB9412504D0; GB2290600A; AU2748395A

Abstract

An electromechanical joystick assembly comprising an operating lever (10) which is pivotally mounted to a housing by means of an electrically conductive mounting member (23), which is in contact with an electrically conductive spring (32) mounted to the inner side wall of the housing. The operating lever (10) is pivoted to the mounting member (23) by a conductive pin (24). The inner side walls of the housing (20) have an electrically conductive coating and a ground conductor is provided on a printed circuit board (PCB 1 or PCB 2) which is in contact with a portion of the inner side wall. Thus the operating lever (10) is connected to ground by the conductive pin (24), the mounting member (23) and the spring (32). Because the lever is grounded in this way, it is prevented from acting as an aerial for any stray signals generated externally or within the assembly, and an electrostatic discharge path is provided from the operating lever to ground. The joystick assembly therefore exhibits effective electromagnetic compatibility.

Description

Joystick Assembly

This invention relates to an electromechanical joystick assembly, and more particularly to a joystick assembly which is electro agnetically compatible.

There is an increasing need for electromechanical joystick assemblies which are electromagnetically compatible, in that they do not malfunction in the presence of externally generated magnetic fields or emit stray electromagnetic radiation which might interfere with other electrical or electronic equipment situated nearby. This can be a particular problem with joystick assemblies which have non-contact switches or sensors, for example sensors of inductive type. Usually the joystick lever comprises a metal shaft and this can act as an aerial which can pick up and transfer externally generated electromagnetic radiation to the inside of the joystick or radiate stray signals which might be generated within the joystick assembly. Also, if a statically charged object or person comes into contact with the operating lever of the joystick assembly, the resulting electrostatic radiation may also be transferred to the inside of the joystick and cause malfunction.

We have now devised a joystick assembly which is protected against malfunctioning in the presence of externally generated electromagnetic fields and which emits negligible stray electromagnetic radiation and therefore exhibits effective electromagnetic compatibility (EMC) . It also ^•provides protection against contact by an electrostatically charged person or object.

In accordance with this invention, there is provided an electromechanical joystick assembly comprising a housing, an operating lever projecting upwardly through an aperture in the top of the housing, an arrangement which pivotally mounts the operating lever, and a sensor arrangement within the housing for detecting the angular position of the operating lever, the housing forming an electrically shielded enclosure and the pivotal mounting arrangement for the operating lever comprising at least one electrically conductive component which short- circuits the operating lever to ground.

In this joystick assembly, any stray signals which may be generated are conducted to ground and the operating lever is therefore prevented from acting as an aerial for any stray signals which it may pick up from the external environment and from within the assembly. The electrically conductive component also provides an electrostatic discharge path from the operating lever straight to ground. Preferably the pivotal mounting arrangement for the operating lever comprises an electrically conductive pivotal member which is mounted to the housing for pivoting about a first axis, and the operating lever is mounted to the pivotal member for pivoting about an axis perpendicular to the first axis (the operating lever extending perpendicular to both these pivotal axes) . Preferably a conductive pin (e.g. of steel or other metal) mounts the operating lever to the conductive pivotal member.

Preferably the pivotal member comprises a pair of oppositely-projecting spindles which are mounted in respective bearings. Preferably a spring presses against the end of one of the spindles, to electrically connect the pivotal member to ground and to remove free play from the pivot mechanism.

Preferably the pivotal member comprises an electrically conductive material which is also wear-resistant, so that it does not wear at its bearings relative to the housing or at its pivotal interconnection with the operating lever. Preferably the material of the pivotal member comprises a carbon reinforced thermoplastics material, e.g. a polyamide (such as nylon) : preferably the plastics material is filled with carbon fibre.

Preferably the sensors for the angular position of the operating lever comprise inductive sensors. Preferably the bottom end of the operating lever carries a member of magnetically permeable material, and a primary winding is mounted centrally below the bottom end of the operating lever, with secondary windings positioned at 90° intervals around the primary winding. The inductive coupling between the primary winding and the respective secondary windings varies according to the angular position of the operating lever: the output signals from the secondary windings are decoded, preferably by electronic circuitry enclosed within the housing, to determine the lever position. An embodiment of this invention will now be described by way of example only and with reference to the accompanying drawing, the single figure of which is a vertical section through an electrical joystick assembly in accordance with this invention. Referring to the drawing, there is shown an electrical joystick assembly which comprises an operating lever 10 pivotally mounted to a housing 20. The housing 20 is generally in the form of an inverted cup, having an aperture 21 through which the lever 10 passes. The lever 10 is pivotally mounted to the housing 20 via a pivot member 23 in the following manner: thus, the lever 10 passes through an aperture in the mounting member 23 and is pivoted thereto by a transverse pin 24. The pivot member 23 has spindles 25,26 projecting from it in opposite directions along an axis perpendicular to the axis of pin 24, and is mounted to the housing 20 by engagement of the spindles 25,26 in through-bores of respective bearing members 27,28 which are fixed to the underside of the top wall 29 of the housing 20.

Abutments 30,31 project downwardly from the top wall 29 of the housing 20, adjacent the outer ends of the respective spindles 25,26. An inverted, generally U-shaped spring 32 is located in a space between the abutment 30 and the side wall of the housing 20, the opposite limbs of the spring 32 pressing against the abutment 30 and the side wall of the housing 20 respectively to retain the spring in position. The spring 32 has a projecting spring finger 33 on one of its limbs, the finger 33 passing through a slot cut out of the abutment 30, to press against the end of spindle 25 of the pivot member 23: as shown, the end of spindle 25 is formed with a projecting, domed pip 25a against which the spring finger 33 rests. Thus, the spring finger 33 urges the pivot member 23 axially so that the end of its other spindle 26 is pressed against the corresponding abutment 31.

A plate 34 is located on the top of the housing 20 and is formed with a circular aperture through which the operating lever 10 passes. A sleeve 35 is slidably mounted on the lever 10 and has a conical lower end which seats against the rim of the aperture in the plate 34. A helical spring 36 is carried by the lever 10 and acts between a collar 37, which is fixed to the lever 10, and the top end of the sleeve 35. As the lever 10 is displaced from its centre, vertical position, the bottom end of the sleeve 35 slides on the rim of the aperture in the plate 34, and is urged upwardly against the bias of the spring 36. The biassing force provided by the spring 36, transmitted to the sleeve 35 and acting via the conical lower end of sleeve 35 against the rim of the aperture in the plate 34, tends to return the lever 10 to its vertical, centre position. The arrangement therefore provides for self-centring of the lever 10.

It will be noted that a tubular gaiter 38 of rubber or the like is provided, one end of the gaiter 38 being fitted around the lever 10 above the collar 37, whilst the other end (not shown) of the gaiter 38 is fitted around the housing 20. A generally conical member 39 is mounted to the lever 10 above the gaiter 38, to protect the latter.

A member 40 of magnetically permeable sheet material (e.g. mumetal) is mounted to a plastics carrier 46 which in turn is mounted to the bottom end of the lever 10, and preferably as shown has a bottom surface which is part of a sphere centred on the point at which the two pivotal axes of the lever 10 intersect. A first printed circuit board PCB1 is mounted in the housing 20, parallel to the top wall 29 and

■ spaced inwardly from the bottom end of the housing 20. A primary coil 41 is mounted centrally on the upper side of the printed circuit board PCB1, and four secondary windings are also mounted on the printed circuit board PCB1, only two such windings 42 and 43 being shown in the drawings. Thus, secondary windings 42,43 are mounted in complementary positions either side of the primary winding 41, at inclined orientations. The other two secondary windings, which are not shown, are similarly positioned either side of the primary winding 41, but on an axis perpendicular to the axis on which windings 42,43 are disposed. The arrangement is such that the inductive coupling between the primary winding 41 and each of the secondary windings varies depending upon the angular position of the operating lever 10. The output signals from the four secondary windings are decoded, to determine the position of the lever 10, by electronic circuitry mounted partly on the underside of printed circuit board PCB1 and partly on a second printed circuit board PCB2, which is mounted in the housing 20 below the first printed circuit board. The bottom end of the housing is closed by an end cap 45. In order to ensure electromagnetic compatibility (EMC) , the inner surfaces of the housing 20 (itself preferably formed of plastics material) are provided with an electrically conductive coating, and a connection is made from this coating to a ground conductor on either of the printed circuit boards. Further, the end cap 45 is of metal or alternatively of plastics but provided on either its inner or outer surface with an electrically conductive coating. Further still, the pivotal member 23 comprises an electrically conductive material, and is connected to the internal conductive coating of the housing 20 by the spring 32: the operating lever 10 is therefore connected to ground via its pivot pin 24, the mounting member 23, and the spring 32. Because the operating lever is grounded in this manner, it is prevented from acting as an aerial for any stray signals generated externally or within the assembly, and an electrostatic discharge path is provided from the operating lever to ground.

As noted previously, the pivotal member 23 preferably comprises a plastics material filled with carbon fibre to

• provide wear-resistance in addition to electrical conductivity. In the example shown, pivotal member 23 comprises nylon 6/6 filled to 30% with carbon fibre.

It will be appreciated that the joystick assembly which as been described exhibits effective electromagnetic compatibility and in addition its moving parts are highly wear- resistant, so that the assembly is ensured of a long and reliable life.

Claims

1) An electromechanical joystick assembly comprising a housing, an operating lever projecting upwardly through an aperture in the top of the housing, an arrangement which pivotally mounts the operating lever, and a sensor arrangement within the housing for detecting the angular position of the operating lever, the housing forming an electrically shielding enclosure and the pivotal mounting arrangement for the operating lever comprising at least one electrically conductive component which short-circuits the operating lever to ground.

2) An electromechanical joystick assembly as claimed in claim 1, wherein the pivotal mounting arrangement for the operating lever comprises an electrically conductive pivotal member which is mounted to the housing for pivoting about a first axis, and wherein the operating lever is mounted to the pivotal member for pivoting about an axis perpendicular to the first axis, the operating lever extending perpendicular to both these pivotal axes.

3) An electromechanical joystick assembly as claimed in claim 2, wherein a conductive pin mounts the operating lever to the conductive pivotal member.

4) An electromechanical joystick assembly as claimed in any preceding claim, wherein the pivotal member comprises a pair of oppositely-projecting spindles which are mounted in respective bearings.

5) An electromechanical joystick assembly as claimed in claim 4, wherein a spring presses against the end of one of the spindles to electrically connect the pivotal member to ground and to remove free play from the pivot mechanism.

6) An electromechanical joystick assembly as claimed in claim 2, wherein the pivotal member comprises an electrically conductive material which is also wear-resistant. 7) An electromechanical joystick assembly as claimed in claim 6, wherein the pivotal member comprises a carbon- reinforced thermoplastics material.

8) An electromechanical joystick assembly as claimed in claim 7, wherein the plastics material is filled with carbon fibre.

9) An electromechanical joystick assembly as claimed in any preceding claim, wherein the sensor arrangement for detecting the angular position of the operating lever comprises a plurality of inductive sensors.

10) An electromechanical joystick assembly as claimed in any preceding claim wherein, the bottom end of the operating lever carries a member of magnetically permeable material and wherein a primary winding is mounted centrally below the bottom end of the operating lever, secondary windings being positioned at 90° intervals around the primary winding.

11) An electromechanical joystick assembly as claimed in any preceding claim, wherein electronic circuitry is provided in the housing for decoding signals from the sensor arrangement in order to determine the angular position of the operating lever.