Patent Publication Number: US-6992602-B2

Title: Joystick controller

Description:
PRIORITY CLAIM 
   This application is a 35 U.S.C. §371 of PCT International Application Number PCT/GB01/00710, which was filed 21 Feb. 2001 (22.02.01), and was published in English. 
   This invention relates to a joystick controller and more particularly to a joystick controller utilising a non-contact principle for sensing joystick position, for example utilising a Hall or other magnetic proximity effect device. 
   It is an object of the present invention to provide an improved joystick controller which is capable of being produced in a cost-effective manner and which can be made in suitably miniaturised form and of high strength for use in rugged industrial applications and, in particular, also for use on a wheel chair. 
   According to a first aspect of the present invention, there is provided a joystick controller comprising:
     a body;   an operating shaft having a longitudinal axis;   a ball-and-socket joint mounting the operating shaft for universal pivotal movement relative to the body about a pivot centre;   a first member mounted for movement by the operating shaft relative to the body about a first axis;   a second member mounted for movement by the operating shaft relative to the body about a second axis which is substantially perpendicular to the first axis;   a third member mounted for movement relative to the body about a third axis substantially perpendicular to the first and second axes upon rotation of the operating shaft about its longitudinal axis; first detecting means for producing an output signal indicative of the position of the first member about the first axis;   second detecting means for producing an output signal indicative of the position of the second member about the second axis; and   third detecting means for producing an output signal indicative of the position of the third member about the said third axis;   wherein the first, second and third detecting means are fixed relative to the body.   

   The output signal produced by the third detecting means enables a third degree of control to be achieved simply by rotation of the operating shaft about its longitudinal axis. Thus, it is possible to avoid the trouble and expense of providing an additional control on top of the operating shaft with associated lead wires passing along the operating shaft requiring shielding and protection against damage and wear and tear, and also associated connections. 
   It is within the scope of the present invention for the rotatable operating shaft to take the form of an inner shaft which is rotatable in bearings within an outer tube which is non-rotatable but which is pivotable with the operating shaft about the first and second axes. However, it is preferred to avoid the additional expense which this entails by having a single operating shaft which is manually pivoted in the first and second axes to effect the first and second degrees of control and which is rotated about its own longitudinal axis to effect the third degree of control. 
   The means for mounting the operating shaft preferably comprises a ball-and-socket joint, in which part of the ball-and-socket joint is prefereably movable with the operating shaft about the longitudinal axis of the latter and forms part of connecting means operatively connecting the operating shaft with the third member. 
   The connecting means may comprise an interengaging pin and groove arrangement, or a pair of interengaging pin and groove arrangements which are disposed on diametrically opposite sides of the ball-and-socket joint. The groove of the or each pin and groove arrangement is preferably provided in the ball. 
   The connecting means is arranged so that movement of the third member about the third axis is independent of the position of the operating shaft ( 12 ) in relation to the first and second axes. 
   Whilst it is within the scope of the present invention for the operating shaft to be connected with the socket of the ball-and-socket joint so that the socket is pivotable relative to the body on a fixed ball about the pivot centre when the operating shaft is moved, it is preferred for the ball of the ball-and-socket joint to be movable with the operating shaft about the longitudinal axis of the latter. 
   Preferably, the operating shaft is rotatable by approximately 20° either side of a neutral rotary position. 
   Preferably, stop means are provided for limiting rotary movement of the shaft on either side of the neutral rotary position. 
   Preferably, means are provided for resiliently restoring the operating shaft to its neutral rotary position after rotary movement of said shaft. 
   Preferably, the resilient restoring means includes a return spring. More preferably, the return spring is curved so as to extend around the longitudinal axis of the operating shaft and has opposite ends which engage with the third member. 
   In a preferred embodiment, at least one, and preferably all, of the first, second and third detecting means is/are non-contact detecting means preferably comprising first, second and third magnets mounted, respectively, on the first, second and third members, and first, second and third Hall effect, magneto-resistive or other magnetic field sensing devices in operative proximity to the respective first second and third magnets. Other field sensing devices such as electrical field sensing devices may be used, these including capacitance and induction devices. 
   Preferably, the first, second and third field sensing devices are mounted on a substantially planar support. 
   According to a second aspect of the present invention, there is provided a joystick controller comprising:
     a body;   an operating shaft having a longitudinal axis;   means mounting the operating shaft for universal pivotal movement relative to the body;   a first member mounted for movement by the operating shaft relative to the body about a first axis;   a second member mounted for movement by the operating shaft relative to the body about a second axis which is substantially perpendicular to the first axis;   first detecting means for producing an output signal indicative of the position of the first member about the first axis; and   second detecting means for producing an output signal indicative of the position of the second member about the second axis;   wherein said first and second detecting means are non-contact sensing devices mounted on a substantially planar support.   

   Preferably, the detecting means are mounted within a magnetically soft cup-shaped member or cover engaged with the body. With such an arrangement, the magnetic cup-shaped body or cover not only protects delicate parts within the body but also, being magnetically soft, acts as a pole piece to concentrate flux from the magnets to the respective devices, and further acts to shield the devices from external magnetic fields which might otherwise adversely affect operation of the devices. Additionally, such a magnetically soft cover also reduces the amount of magnetic flux emanating from the joystick controller. 
   Preferably, connecting means are provided for operatively connecting the operating shaft to the first second and third members and are preferably formed of an insulator or are insulated from the operating shaft to reduce radiated electromagnetic interference being conducted along the operating shaft to the outside environment and to minimise susceptibility of the magnetic field sensing devices to electromagnetic interference from the outside. 
   Conveniently, the construction of the joystick provides a defined path for electrostatic discharge currents from the operating handle, the operating shaft, the magnetic cover or other externally contactable parts to an earthing conductor which prevents these currents from reaching the magnetic field sensing devices, but which includes a spark gap or other voltage-dependent breakdown device to maintain low voltage electrical isolation between these parts and the earthing conductor. 
   Preferably, means are provided for resiliently restoring the operating shaft to a neutral position about the axis of the ball, said means comprising a member slidable on the shaft and having a frusto-conical surface resiliently urged against an annular formation on the body. 
   The resilient restoring means preferably has a metallic liner so as to provide an accurate low backlash sliding fit with the operating shaft under normal operating environmental conditions, particularly temperature extremes. 

   
     Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which 
       FIG. 1  is an underneath plan view of a joystick controller according to the first aspect of the present invention shown with a magnetic cover and printed circuit board thereof removed; 
       FIG. 2  is an axial section taken on the line L—L of  FIG. 1  with the magnetic cover and printed circuit board in place; 
       FIG. 3  is an axial section taken on the line W—W of  FIG. 1  with the magnetic cover and printed circuit board in place; 
       FIG. 4  is a perspective view of a joystick controller according to the second aspect of the present invention shown with a magnetic cover thereof removed; 
       FIG. 5  is an axial section taken on the line L—L of  FIG. 4 ; and 
       FIG. 6  is an axial section taken on the line W—W of  FIG. 4 . 
   

   Referring now to the  FIGS. 1 ,  2  and  3 , the joystick controller includes a diecast aluminium alloy body  10 , a metal operating shaft  12  on which a handle (not shown) is mounted, a ball-and-socket joint  14 , and first, second and third carrier members  16 ,  17  and  19 . Instead of being formed of aluminium alloy, the body  10  may be formed of zinc alloy or a moulded polymer such as ABS or a glass-filled thermoplastic polyester or acetal resin. 
   The body  10  includes a mounting flange  10   a  and a sleeve  10   b  extending from the mounting flange  10   a . The body  10  further includes an internal transverse wall  10   c  through which there is a central aperture  18 . Integrally formed in that surface of the transverse wall  10   c  which faces the sleeve  10   b  is a square recess  10   d  bounded by a low wall  10   e . The sleeve  10   b  has a series of four equi-spaced apertures (not shown) therethrough to provide clearance for magnets (to be described hereinafter) when they are at the ends of their travel. 
   An annular socket member  22  is secured within the square recess  10   d  by screws (not shown). In its outer surface, the socket member  22  has a series of four part spherical recesses  22   a ,  22   b ,  22   c  and  22   d . The recesses  22   a  and  22   b  are illustrated in  FIG. 2  and lie diametrically opposite one another. The recesses  22   c  and  22   d  are illustrated in  FIG. 3  and lie diametrically opposite one another. 
   The aperture  18  in the transverse wall  10   c  has a collar  30  mounted therein. The axis of the collar  30  coincides with the longitudinal axis of the body  10 . The ring  30  has a lower widened part  30   a  of part spherical or conical shape so as to form part of the socket of the ball-and-socket joint  14 . 
   The first carrier member  16  is disposed within the sleeve  10   b  remote from the transverse wall  10   c . The first member  16  has an arcuately curved transverse region  16   a  from each end of which extends a respective support leg  16   b ,  16   c . The support legs  16   b  and  16   c  are mutually opposed and, have respective inwardly directed part-spherical pivot regions  16   d  and  16   e . The pivot regions  16   d  and  16   e  are engaged with the respective recesses  22   a  and  22   b . The support legs  16   b  and  16   c  have planar outer surfaces which are a close sliding fit against the adjacent region of the inner surface of the low wall  10   e . Thus, it will be appreciated that rocking movement of the first member  16  relative to the body  10  and the socket member  22  is permitted about a first axis which passes through both of the pivot regions  16   d  and  16   e.    
   The transverse region  16   a  of the first member  16  has a longitudinally extending slot  16   f  therethrough. At each end of the transverse region  16   a  there is provided a respective square section sleeve  16   g ,  16   h . Each sleeve  16   g  and  16   h  carries a respective magnet  24 ,  25 . 
   The second carrier member  17  is of similar construction to the first member  16  and similar parts are accorded equivalent references. Thus, the second member  17  has an arcuate transverse region  17   a  with longitudinal slot  17   f  therein, support legs  17   b  and  17   c , part-spherical pivot regions  17   d ,  17   e . However instead of being provided with two sleeves supporting respective magnets, it only possess one sleeve  17   g  and a single magnet  26  proximal to low wall  10   e . Only one magnet is usually needed on each carrier member  16 ,  17 , but a second magnet is provided on carrier member  16  in this embodiment and is used for applications which require independent outputs for integrity reasons. Thus, it will be appreciated that rocking movement of the second member  16  relative to the body  10  and the socket member  22  is permitted about a second axis which passes through both of the pivot regions  17   d  and  17   e  and which is perpendicular to the first axis. 
   The third carrier member  19  is also disposed within the sleeve  10   b  and situated on the opposite side of the sleeve  10   b  to the sleeve  17   g . The third member  19  comprises an annular region  19   a  and a web region  19   b  which lie parallel to the transverse wall  10   c , and a support arm  19   c  which is substantially perpendicular to the regions  19   a  and  19   b  and which is a close sliding fit with the sleeve  10   b . The web region  19   b  connects the support arm  19   c  with the annular region  19   a  which encircles the ball  32  of the ball-and-socket joint  14 . In this embodiment the annular region  19   a  is disposed between the transverse wall  10   c  and the annular socket member  22  so as to be pivotable relative thereto about the centre of the ball  32 . The annular region has diametrically opposed, inwardly directed pivot regions  19   d  and  19   e  disposed on an axis passing through the pivot centre of the ball-and-socket joint  14 . The support arm  19   c  carries a magnet  29  at its lower end. 
   The ball  32  is a part-spherical ball which engages the part-spherical wall  30   a  of the collar  30  and a part-spherical region of the annular socket member  22  so as to be universally pivotable relative thereto about its centre. The centre of the ball  32  lies on a third axis which, in this embodiment, is coincident with the longitudinal axis of the body  10 . The third carrier member  19  rotates about the third axis which is also perpendicular to both of the first and second axes. The mutually perpendicular first and second axes about which the first and second carrier members  16  and  17  respectively rock also pass through the pivot centre of the ball  32 . The inner end of the operating shaft  12  is anchored in a recess in the ball  32 . Thus, universal pivotal movement of the ball  32  is effected by appropriate manipulation of a handle (not shown) mounted on the upper, outer end of the shaft  12 . The inner surface of the collar  30  is outwardly flared away from the socket member  22  so as to increase the permitted degree of movement of the operating shaft  12 . The socket member  22  serves to retain the ball  32  in place. 
   The ball  32  is provided with an operating member  34  which is aligned with the operating shaft  12  and which is unitary with the ball  32 . The operating member  34  is of cylindrical form and projects through the slots  16   f  and  17   f  in the first and second carrier members  16  and  17 . The operating member  34  has a diameter which is a close sliding fit in the width of the slots  16   f  and  17   f  so that the operating member  34  can slide longitudinally of the slots  16   f  and  17   f  when moved in the appropriate direction, as will be described hereinafter. The ball  32  is also provided with a pair of diametrically opposed grooves  60  extending in the direction of the longitudinal axis of the operating shaft. The cylindrical pivot regions  19   d  and  19   e  of the third carrier member  19  engage with the respective grooves  60  and form a close sliding fit. Thus rotation of the operating shaft  12  about its longitudinal axis causes the ball  32  to move the third carrier member  19  about the third axis by virtue of the engagement of the pivot regions  19   d  and  19   e  in the grooves  60 . 
   Slidably mounted on the shaft  12  is a centering sleeve  36  having a frusto-conical surface  36   a  facing the collar  30 . The frusto-conical surface  36   a  is urged into engagement with the collar  30  by means of a compression spring  38  which is lodged between the centering member  36  and an abutment  40  which is secured to an intermediate region of the operating shaft  12 . The inner surface of the centering member  36  has a metallic liner to give an accurate low back lash sliding fit with the operating shaft  12  under all normal operating environmental conditions, particularly temperature extremes, and life. 
   The operating shaft  12  is maintained in a rotationally neutral position by means of a circular return spring  66  which extends around the longitudinal axis of the operating shaft internally of the sleeve  10   b . The spring  66  has opposite ends  68  that engage with opposite sides of the support arm  19   c  of the third carrier member  19  and act to restore this, and thereby the operating shaft  12 , to the neutral position. The operating shaft  12  has its arc of rotation limited by the provision of stops  64  on either side of the neutral position and stop  64   b  at the rotationally neutral position. In the embodiment shown, this rotation is limited to about 20 degrees either side of the neutral position. The stops  64  are disposed on the inner surface of the sleeve  10   b  in the path of movement of the support arm  19   c  of the third carrier member  19 . The stop  64   b  is also disposed on the inner surface of the sleeve  10   b  and has opposed surfaces against which the opposite ends  68  of the spring  66  are respectively engaged. 
   A flexible gaiter  42  surrounds the lower end of the operating rod  12 , the spring  38  and the centering member  36  and is secured in place on a ring  44  engaged in an upper recess  46  in the body  10 . The upper end of the gaiter  42  is secured to the abutment  40  on the shaft  12 . 
   The lower end of the sleeve  10   b  of the body  10  is closed by a planar printed circuit board  48  which is retained in place by locating pins (not shown) which may be riveted, formed or heat-staked for extra security. A cup-shaped end cap  50 , made of magnetically soft material such as low carbon steel or nickel iron is adhesively fixed to, or snap-engaged with, the outer surface of the sleeve  10   b.    
   The planar printed circuit board  48  carries first, second and third Hall-effect devices  52 ,  54  and  56  which are associated with the respective magnets  24 ,  26  and  29 . The devices  52 ,  54  and  56  are mutually coplanar. It is within the scope of the present invention to provide additional Hall-effect devices to provide dual independent safety outputs on each axis for system integrity. 
   The printed circuit board  48  may also carry components (not shown) which may be used to ensure compliance with any Electro-Magnetic Compatibility (EMC) legislation that may be required. The printed circuit board  48  may also carry a connector to enable the joystick controller to be connected into external circuitry which it is intended to control, but in certain applications a direct cable connection may be used. 
   The Hall-effect devices  52 ,  54  and  56  have their sensitive axes perpendicular to the axes about which the respective magnets are arranged to rock or rotate as the case may be. The axis of polarisation of each magnet  24 ,  26 ,  29  (characterised by its north and south magnetic poles) is aligned perpendicular to the pivot axis of the carrier member to which it is attached. 
   In use, it will be appreciated that the action of the spring  38  on the centering member  36  and of spring  66  on the third carrier member  19  causes the operating shaft  12  to be urged into a central or null position as illustrated in  FIGS. 2 and 3 . 
   When the operating shaft  12  is moved in a plane perpendicular to  FIG. 2 , the operating member  34  engages the appropriate side of the slot  16   f  so as to pivot the first carrier member  16  about the first axis. This moves the magnet  24  relative to the closely adjacent Hall-effect device  52  which produces a signal output corresponding to the position of the magnet  24  and thus the position of the operating shaft  12  in the direction under consideration. During such movement of the operating shaft  12 , the operating member  34  slides longitudinally in the slot  17   f  of the second carrier  17  so that no rocking motion of the latter occurs. Consequently, there is no movement of the magnet  26  relative to the Hall-effect device  54 . There is also no movement of the third carrier member  19  as the shaft  12  is moved so as to effect movement of the carrier member  16 . As the ball  32  moves, the position of the third carrier member  19  is maintained due to provision of the grooves  60  which slide longitudinally relative to the cylindrical pivot regions  19   d  and  19   e . Accordingly there is no movement of the magnet  29  relative to the Hall-effect device  56 . 
   Likewise, when the operating shaft  12  is moved perpendicular to the plane of  FIG. 3 , the operating member  34  slides longitudinally in slot  16   f  but is moved laterally of slot  17   f  with the result that the second member  17  is rocked about the second axis to cause movement of the magnet  26  relative to the Hall-effect device  54  to provide a signal output which is proportional to the amount of such movement of the operating shaft  12 . There is no movement of the shaft  12  about its longitudinal axis, and the movement of the ball  32  about its centre of rotation is about the axis on which the pivot regions  19   d  and  19   e  lie and so no movement of the third carrier member  19  occurs. 
   When the operating shaft  12  is released, the spring  38  acting through the centering member  36  serves to move the operating rod and thereby the ball  32  and the operating member  34  into the null or centre position. 
   When the operating shaft is moved in a plane between the two above-mentioned planes, there is a proportional movement of both carrier members  16  and  17  to cause a corresponding change in the output signals from both Hall-effect devices  52  and  54 , but still no movement of the third carrier  19  due to the positioning of the pivot regions  19   c  and  19   d  in the grooves  60 . 
   Rotational movement of the operating shaft  12  about its longitudinal axis, against the action of the spring  66 , causes rotation of the ball  32  and the operating member  34  about the longitudinal axis of the shaft  12 , but results in no movement of either carrier member  16  or  17 . However, the third operating member  19  connected to the ball  32  through pivot regions  19   d  and  19   e  and grooves  60  is caused to rotate about said third axis, resulting in movement of the third magnet  29  relative to the Hall-effect device  56 , thus providing a signal output which is proportional to the amount of such rotational movement of the operating shaft  12 . When the operating shaft  12  is released, it is returned to its neutral position by the restoring force of the spring  66  acting between the support arm  19   c  and the stop  64   b.    
   The cup-shaped end cap  50  serves to protect the internal parts such as the first, second and third carrier members  16 ,  17  and  19 , the magnets  24 ,  26  and  29  and the Hall-effect devices  52 ,  54  and  56  from physical and environmental damage. The flat closed end of the end cap  50  near to each of the devices  52 ,  54  and  56  acts as a pole piece concentrating the flux from the respective magnets in the direction of the sensitive axis of the devices  52 ,  54  and  56 , thereby improving sensitivity and performance. The end cap  50  also acts to shield the Hall-effect devices  52 ,  54  and  56  from the effects of external magnetic fields and also reduces the amount of flux from the magnets appearing outside the joystick controller. 
   The operating member  34  is an insulator or is insulated from the operating shaft  12  so as to reduce the risk of radiated electromagnetic interference (EMI) or electrostatic discharge (ESD) being conducted along the operating shaft  12  to the printed circuit board  48 . This also minimises any EMI from the Hall-effect devices  52 ,  54  and  56  being conducted to the outside environment. 
   Electrostatic discharges to the metal end cap  50  are conducted via a well defined static discharge path to an earthing conductor (not shown) in the connecting lead of the joystick and hence to system earth,. A high value resistor (e.g, 1 MΩ) in the static discharge path is provided in parallel with a high voltage breakdown device. The high value resistor permits lower voltage discharges of the static, but only at a low enough electrical current to avoid nuisance shocks. If the voltage is high enough, however, the high voltage breakdown device will conduct and reduce the high voltage rapidly. The high voltage breakdown device can be a non-linear resistor or semiconductor, or it can take the form of a small air gap (e.g. 0.2 to 0.5 mm) in the static discharge path. This gap can be made to break down before any other potential path within the controller by ensuring that all other potential paths have a larger air gap. 
   Referring now to  FIGS. 4 ,  5  and  6 , the joystick controller is primarily intended for mounting on an arm of a motorised wheelchair to control movement of the latter. 
   The joystick controller includes a diecast aluminium alloy body  10 , a hollow metal operating shaft  12  on which a handle (not shown) is mounted, a ball-and-socket joint  14 , and first and second carrier members  16  and  17 . Instead of being formed of aluminium alloy, the body  10  may be formed of zinc alloy or a moulded polymer such as ABS or a glass-filled thermoplastic polyester or acetal resin. 
   The body  10  includes a mounting flange  10   a  and a sleeve  10   b  extending from the mounting flange  10   a . The body  10  further includes an internal transverse wall  10   c  through which there is a central aperture  18 . A lower part  20  of the wall of the aperture  18  is of part-spherical or conical shape so as to form part of a socket of the ball-and-socket joint  14 . Integrally formed in that surface of the transverse wall  10   c  which faces the sleeve  10   b  is a square recess  10   d  (see  FIG. 5 ) bounded by a low wall  10   e  (see  FIG. 6 ). The sleeve  10   b  has a series of four equi-spaced apertures  10   f  therethrough to provide clearance for magnets (to be described hereinafter) when they are at the ends of their travel. 
   An annular socket member  22  is secured within the square recess  10   d  by screws (not shown). In its outer surface, the socket member  22  has a series of three part spherical recesses  22   a ,  22   b  and  22   c . The recesses  22   a  and  22   b  are illustrated in  FIG. 5  and lie diametrically opposite one another. The recess  22   c  is illustrated in  FIG. 6  and lies diametrically opposite a bore  22   d  through the socket member  22 . The outer ends of the recesses  22   a ,  22   b  and  22   c  and of the bore  22   d  are outwardly frusto-conically flared. 
   The aperture  18  in the transverse wall  10   c  has a collar  30  mounted therein. The axis of the collar  30  has an annular recess therein receiving a ring  30  whose axis coincides with the longitudinal axis of the body  10 . 
   The first carrier member  16  is disposed within the sleeve  10   b  adjacent the end of the latter remote from the transverse wall  10   c . The first member  16  has an arcuately curved transverse region  16   a  from each end of which extends a respective support legs  16   b ,  16   c . The support legs  16   b  and  16   c  are mutually opposed and have respective inwardly directed part-spherical pivot regions  16   d  and  16   e . The pivot regions  16   d  and  16   e  are engaged with the respective recesses  22   a  and  22   b  and have frusto-conically shaped root regions for mating with the frusto-conically flared ends of the recesses  22   a  and  22   b . The support legs  16   b  and  16   c  have planar outer surfaces which are a close sliding fit against the adjacent region of the inner surface of the low wall  10   e . Thus, it will be appreciated that rocking movement of the first member  16  relative to the body  10  and the socket member  22  is permitted about a first axis which passes through both of the pivot regions  16   d  and  16   e.    
   The transverse region  16   a  of the first member  16  has a longitudinally extending slot  16   f  therethrough. At each end of the transverse region  16   a  there is provided a respective square section sleeve  16   g ,  16   h . Each sleeve  16   g  and  16   h  carries a respective magnet  24 ,  25 . 
   The second carrier member  17  is of similar construction to the first member  16  and similar parts are accorded equivalent references. Thus, the second member  16  has an arcuate transverse region  17   a  with longitudinal slot  17   f  therein, support legs  17   b  and  17   c , part-spherical pivot region  17   e , and sleeves  17   g  and  17   h  supporting respective magnets  26  and  27 . However, instead of being provided with another pivot region like pivot region  16   d , the second member  17  is provided with a bore  17   d  which is aligned with the bore  22   d  and which supports a transverse pin  28 . The pin  28  projects through the bore  22   d  so as to protrude from the inner surface of the socket member  22 . Only one magnet is usually needed on each carrier member  16 ,  17 , but the second magnet is provided in this embodiment and is used for applications which require independent outputs for integrity reasons. It will be appreciated that rocking movement of the second member  17  relative to the body  10  and the socket member  22  is permitted about a second axis which (i) passes through the pivot region  17   e , (ii) is coincident with the longitudinal axis of the pin  28  and (iii) is perpendicular to the first axis. 
   The ball  32  is a part-spherical ball which engages the part-spherical wall  20  of the aperture  18  and a part-spherical region of the annular socket member  22  so as to be universally pivotable relative thereto about its centre. The centre of the ball  32  lies on the longitudinal axis of the body  10 . The mutually perpendicular first and second axes about which the first and second carrier members  16  and  17  respectively rock pass through the pivot centre of the ball  32 . The inner end of the operating shaft  12  is anchored in a recess in the ball  32 . Thus, universal pivotal movement of the ball  32  is effected by appropriate manipulation of a handle (not shown) mounted on the upper, outer end of the shaft  12 . The inner surface of the collar  30  is outwardly flared away from the socket  22  so as to increase the permitted degree of movement of the operating shaft  12 . The socket member  22  serves to retain the ball  32  in place. 
   If desired, the handle on the end of the operating shaft may be rotatable relative to the shaft so as to enable a switch or the like to be controlled. However, it is also possible to adapt the end of the shaft  12  so that it is capable to receiving a variety of different types of handle or operating knob. 
   The ball  32  is provided with an operating member  34  which is aligned with the operating shaft  12  and which is unitary with the ball  32 . The operating member  34  is of cylindrical form and projects through the slots  16   f  and  17   f  in the first and second carrier members  16  and  17 . The operating member  34  has a diameter which is a close sliding fit in the width of the slots  16   f  and  17   f  so that the operating member  34  can slide longitudinally of the slots  16   f  and  17   f  when moved in the appropriate direction, as will be described hereinafter. 
   Slidably mounted on the shaft  12  is a centering sleeve  36  having a frusto-conical surface  36   a  facing the collar  30 . The frusto-conical surface  36   a  is urged into engagement with the collar  30  by means of a compression spring  30   a  which is lodged between the centering member  36  and an abutment  40  which is secured to an intermediate region of the operating shaft  12 . The inner surface of the centering member  36  has a metallic liner to give an accurate low back lash sliding fit with the operating shaft  12  under all normal operating environmental conditions, particularly temperature extremes, and life. However, for very low cost applications, the liner may be omitted. 
   A flexible gaiter  42  surrounds the lower end of the operating rod  12 , the spring  38  and the centering member  36  and is secured in place on a ring  44  engaged in an upper recess  46  in the body  10 . The upper end of the gaiter  42  is secured to the abutment  40  on the shaft  12 . 
   The lower end of the sleeve  10   b  of the body  10  is closed by a planar printed circuit board  48  which is retained in place by locating pins (not shown) which may be riveted, formed or heat-staked for extra security. A cup-shaped end cap  50 , made of magnetically soft material such as low carbon steel or nickel iron is adhesively fixed to, or snap-engaged with, the outer surface of the sleeve  10   b.    
   The planar printed circuit board  48  carries first and second Hall-effect devices  52  and  54  which are associated with the respective magnets  24  and  27 . The devices  52  and  54  are mutually coplanar. In this embodiment, the other magnets  25  and  26  are not used. However, it is within the scope of the present invention to provide additional Hall-effect devices associated with these magnets  25  and  26  to provide dual independent safety outputs on each axis for system integrity. 
   The printed circuit board  48  may also carry components (not shown) which may be used to ensure compliance with any Electro-Magnetic Compatibility (EMC) legislation that may be required. The printed circuit board  48  may also carry a connector to enable the joystick controller to be connected into external circuitry which it is intended to control, but in certain applications a direct cable connection may be used. 
   The Hall-effect devices  52  and  54  have their sensitive axes perpendicular to the axes about which the respective magnets  24  and  27  are arranged to rock. The axis of polarisation of each magnet  24 ,  27 , (characterised by its north and south magnetic poles) is aligned perpendicular to the pivot axis of the carrier member to which it is attached. 
   In use, it will be appreciated that the action of the spring  38  on the centering member  36  causes the operating shaft  12  to be urged into a central or null position as illustrated in  FIGS. 5 and 6 . 
   When the operating shaft  12  is moved in a plane perpendicular to  FIG. 5 , the operating member  34  engages the appropriate side of the slot  16   f  so as to pivot the first carrier member  16  about the first axis. This moves the magnet  24  relative to the closely adjacent Hall-effect device  52  which produces a signal output corresponding to the position of the magnet  24  and thus the position of the operating shaft  12  in the direction under consideration. During such movement of the operating shaft  12 , the operating member  34  slides longitudinally in the slot  17   f  of the second carrier  17  so that no rocking motion of the latter occurs. Consequently, there is no movement of the magnet  27  relative to the Hall-effect device  54 . 
   Likewise, when the operating shaft  12  is moved perpendicular to the plane of  FIG. 6 , the operating member  34  slides longitudinally in slot  16   f  but is moved laterally of slot  17   f  with the result that the second member  17  is rocked about the second axis to cause movement of the magnet  27  relative to the Hall-effect device  54  to provide a signal output which is proportional to the amount of such movement of the operating shaft  12 . 
   When the operating shaft  12  is released, the spring  38  acting through the centering member  36  serves to move the operating rod and thereby the ball  32  and the operating member  34  into the null or centre position. 
   When the operating shaft is moved in a plane between the two above-mentioned planes, there is a proportional movement of both carrier members  16  and  17  to cause a corresponding change in the output signals from both Hall-effect devices  52  and  54 . 
   In this embodiment rotation of the operating shaft  12  about its longitudinal axis is prevented because the pin  28  engages in slot  32   a . Slot  32   a  is arcuate and centred on the centre point of the ball  32 , with the longitudinal dimension of the slot lying in the same plane as that of the slot  17   f . The provision of the slot  32   a  permits pivoting movement of the operating shaft  12  in a direction to rock the first carrier member  16 . 
   The cup-shaped end cap  50  serves to protect the internal parts such as the first and second carrier members  16 , the magnets  24  to  27 , and the Hall-effect devices  52  and  54  from physical and environmental damage. The flat closed end of the end cap  50  near to each of the devices  52  and  54  acts as a pole piece concentrating the flux from the respective magnets in the direction of the sensitive axis of the devices  52  and  54 , thereby improving sensitivity and performance. The end cap  50  also acts to shield the hall-effect devices  52  and  54  from the effects of external magnetic fields and also reduces the amount of flux from the magnets appearing outside the joystick controller. 
   The operating member  34  is an insulator or is insulated from the operating shaft  12  so as to reduce the risk of radiated electromagnetic interference (EMI) or electrostatic discharge (ESD) being conducted along the operating shaft  12  to the printed circuit board  48 . This also minimises any EMI from the Hall-effect devices  52  and  54  being conducted to the outside environment. 
   Electrostatic discharges to the metal end cap  50  are conducted via a well defined static discharge path to an earthing conductor (not shown) in the connecting lead of the joystick and hence to system earth. A high value resistor (e.g, 1 MΩ) in the static discharge path is provided in parallel with a high voltage breakdown device. The high value resistor permits lower voltage discharges of the static, but only at a low enough electrical current to avoid nuisance shocks. If the voltage is high enough, however, the high voltage breakdown device will conduct and reduce the high voltage rapidly. The high voltage breakdown device can be a non-linear resistor or semiconductor, or it can take the form of a small air gap (e.g. 0.2 to 0.5 mm) in the static discharge path. This gap can be made to break down before any other potential path within the controller by ensuring that all other potential paths have a larger air gap. 
   It is within the scope of the present invention for one or more switches or controls to be mounted in the operating knob and for connections to them to be via a cable passing through the hollow operating shaft ( 12 ). This cable (not shown) passes through the operating shaft  12  from the handle and exits through a slot (not shown) in cylindrical extension  32   b  to the ball  32 . From there, the cable is coiled around the extension  32   b  for strain relief and then passes under a clip (not shown) in the body  10  before passing through one of the apertures  10   f  in the sleeve  10   b . From there, the cable passes along L-shaped recess  10   g  in the sleeve  10   b  for connection to the printed circuit board  48 . 
   This cable introduces a potential ESD or EMC path from the handle mounted electrical components. In order to prevent damage to the sensitive electronic parts of the joystick controller via this route, these components may be well insulated and provided with RF decoupling components and an earthing conductor (not shown) provided in the form of a dedicated wire in this cable to provide a suitable discharge path for static build-up. 
   However, it is within the scope of the present invention, when there is no need to provide sensors in the handle, to use a solid operating shaft. 
   In the above described embodiments, the axes about which the first, second and third carrier members  16 ,  17  and  19  are coincident with the pivot centre of the ball-and-socket joint  14 . However, it is within the scope of the present invention for any of these axes to be slightly offset from this pivot centre by an amount which does not have a material effect on successful operation of the joystick. For example, it may be convenient from a constructional standpoint for the axis about which the second carrier member  17  is pivotable to be displaced one or two mm below the pivot centre (as shown in  FIG. 3 ).