This invention relates to a joystick of the type intended particularly but not exclusively for use with computers for providing directional control of an object on the computer screen.

The term "joystick" was originally coined with reference to the control-lever of an aeroplane. It has also been applied in computer jargon to refer to the control handle connected to a computer, via the "joystick port", which is used as a man-machine interface. The joystick generally provides eight different control signals which are commonly used to provide directional control in eight directions, generally referred to as the primary directions (as in the cardinal points of a compass) and the diagonal directions.

The "joystick" method of control is frequently associated with computer games, where objects on the monitor screen are manipulated to perform various tasks.

A joystick usually comprises a short shaft, or "stick", mounted for multi-directional movement in a base, the shaft having a handgrip at one end and electrical or electronic contacts at the other end; the contacts cause changes in the circuit which will produce a known result in the computer interface. The shaft may be mounted in the base in a resilient block which permits movement in a prescribed radius. The conventional joystick usually employs four micro-switches to perform the required circuit control and a "fire switch". However, the shafts of such joysticks are generally

lacking in ease of movement, resulting in the need for two-handed operation where one hand is used to restrain the base against movement with the shaft; furthermore, the generation of a control signal for the four diagonal directions requires the simultaneous closing of two adjacent micro-switches and this is not always readily achieved in practice. Such conventional joysticks are in addition susceptible to damage occurring as a result of excessive operator forces being used.

It is an object of the present invention to provide an improved joystick, particularly one which is suitable for single-handed operation and which may additionally permit of easier generation of a control signal for all eight positions than is the case with existing joysticks.

According to one aspect of the invention, a joystick comprises a base including a plurality of switch means and an operating shaft pivotally mounted therein for movement about a normal position in any direction within a prescribed radius to activate a selected switch means, in which the joystick includes magnetic means which operatively bias the shaft towards the said normal position.

Preferably, the switch means comprise magnetic reed switches, thereby removing the element of unreliability often associated with micro-switches. It is also preferred that eight such switches are utilized, adjacent switches being angularly spaced at an angle of substantially 45 therebetween, whereby the generation of a signal in any one of the eight directions requires the closure of only a single switch. Hand control is

thereby improved and a more positive action is achieved compared with existing joysticks.

The pivotal connection of the operating shaft to the base may be by way of a ball and socket bearing, thereby enabling the shaft to exhibit the required freedom of movement in any direction. Preferably the ball is mounted at an intermediate position along the shaft and the lower end region of the shaft operates the switch means, although in an alternative arrangement the ball could be formed at the lower end of the shaft with the switch means mounted at an intermediate position.

In a preferred arrangement, the ball is mounted at an intermediate position on the shaft, the lower end region of which comprises a permanent magnet of opposite polarity to a further permanent magnet mounted in the base of the joystick directly beneath the shaft when in the normal position, thereby providing the biassing force. The permanent magnet of the shaft is also used to operate the reed switches, which are spaced with respect to each other so that only one reed switch can be operated by movement of the shaft at any one time. The biassing magnet also operates to concentrate magnetic flux towards a central position away from the reed switches, thereby reducing ambient magnetic forces acting on the switches and effectively rendering them more sensitive to magnetic forces derived from the shaft when in proximity to a switch.

Joysticks according to the invention may include means to restrict the radius of movement of the operating shaft. Such means may comprise an annular ring or wall which surrounds, the lower end region of the operating

shaft and an annular preferably resilient projection carried by or formed towards the lower end of the shaft whereby to prevent the shaft magnet from physically contacting the annular wall.

The joystick base is also provided with operating circuitry, for example logic circuitry in one embodiment, to transmit signals derived from the switch means to the computer. In another embodiment, the circuitry comprises a diode associated with each successive pair of adjacent switches, the diodes being provided to isolate electrically the primary and diagonal switches, the diodes and switches being mounted on a printed circuit board; the board may have a central aperture formed therein, within or below which is mounted the biassing magnet. The position of the biassing magnet in relation to the shaft may be adjustable to enable a pre-determined air gap to be established between them, in order to adjust the biassing strength.

Joysticks according to the invention may include a conventional fire switch, generally operated by a button which may be mounted as part of either the base or the shaft.

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings, of which

Figure 1A is a side elevation in partial cross-section snowing a conventional joystick;

Figure IB is a plan diagram showing parts of the j ystick of Figure 1A; *

Figure 2 is a circuit diagram for a conventional joystick;

Figure 3 is a cut-away perspective view of a joystick according to the present invention; and

Figure 4 is a circuit diagram of the joystick of Figure

3.

With reference to Figure 1A, a conventional joystick consists essentially of a shaft 11 having a control knob 12 and carried in a resilient rubber or composite material block 13 mounted in the top of a base 14; the block 13 permits pivotal movement of the shaft 11 and resiliently biasses it to a vertical portion. The lower extremity of the shaft 11 can move in a circular path, relative and opposite to the movement of the knob 12, and will cause one or two of the four micro-switches 15 to function. Figure IB illustrates the positional relationship of the shaft 11 with the four micro-switches 15, indicating the small gap between shaft 11 and the said switches when the shaft is in the vertical position. It can be seen that any movement of the knob 12 in one direction produces an opposite directional movement of the lower end of the shaft 11 such that, for example, movement to the left of the knob 12 would cause the micro-switch 15a to be contacted. Diagonal control is achieved by operating two adjacent switches simultaneously.

Figure 2 illustrates an appropriate circuit diagram for a conventional joystick such as is illustrated in Figures 1A and IB.

Referring to figure 3, a joystick according to the

invention consists essentially of a shaft 16 with a manipulating knob or handgrip 17 at the upper, outward extremity and a spherical projection 18 in an intermediate position which is engaged with a socket 19 to provide pivotal movement of the shaft in any direction. The shaft 16 extends below the ball and socket joint 18, 19 and carries at its base a permanent magnet 20. The socket 19 is set into the centre of the upper wall of a base housing 26. An annular, preferably resilient, projection 27 is attached to the lower end of the shaft above magnet 20 and an annular ring member 21 surrounds but is spaced from the lower end of the shaft when in the vertical position; the ring member 21 is engaged by the projection 27 on pivotal movement of the shaft 16 and serves to restrict the permitted pivotal movement thereof. Below the permanent magnet 20 and spaced from it by a pre-determined distance is a second permanent magnet 22, carried by the lower part 29 of the housing. A printed circuit board 23 is also carried in the lower part 29 of the housing, below the ring member 21 and below the lower end of the shaft 16; the board carries eight reed switches 24 suitably equidistantly spaced, the reed blade closest to the magnet 22 being set lowermost and horizontal in each reed switch. Between each adjacent pair of reed switches 24 is a diode 25, provided to isolate the primary direction switches from the diagonal direction switches. The board 23 is formed with a central aperture within or slightly below which is located the magnet 22.

The ball and socket joint 18, 19 permits easy movement of the shaft in relation to the base housing. The lower extremity of the shaft 16 can move in a circular or radial path above the plane of the printed circuit

board 23 and opposite to the movement of the control knob 17. The control knob 17, if moved to its limit of travel in any direction, causes the magnet 20 to operate the one reed switch 24 nearest thereto and the appropriate control signal is sent via the conventional interface circuitry. The shaft will self centre, when the control knob 17 is released, under the influence of the mutual attraction of the shaft magnet 20 and the biassing magnet 22, which are arranged with opposite poles facing. The ring member 21 limits shaft travel and the projection 27 absorbs impact and prevents the magnet 20 from connecting with the ring member 21.

As shown, the joystick is operating reed switch 24a and the upper part 26 of the base housing, the lower part 29, the ring member 21 and the socket 19 are all shown in part, to reveal the other components. A conventional fire button 30 is incorporated in the upper part 26 of the base housing.

It is possible to make shaft travel variable for example by introducing a frusto-conical ring member 21 which is vertically adjustable; reed separation adjustment may be achieved for example by springing the reeds against the outer edge of the same frusto-conical ring member. Biassing strength can be varied by adjusting the height of magnet 22 thereby altering the air gap between the magnet and the sh ft magnet 20.

Figure 4 illustrates a circuit diagram of the joystick of Figure 3 and shows each reed switch to be in open circuit.

Directional switching is achieved using eight switches (SI to S8) , these may be conventional micro switches

but are preferably reed switches.

The primary direction switches SI, S3, S5 and S7 are electrically isolated from the diagonal direction switches S2, S4, S6 and S8 by diodes Dl to D8 at contact 1 of each switch. Each diode has its cathode connected to the diagonal switch and its anode connected to the primary switch. Contacts 2 of each switch are connected in common.

The switches are connected to the computer via a flexible lead and a standard 9 pin D plug (female) .

The switch common (contact 2) is connected to ground on pin 8 of the D plug. The "down", "left", "up", and "right" control leads are on switch SI, S3, S5 and S7 contacts 1 and appear on the D plug pins 2, 3, 1, and 4 respectivel .

Operation of any one primary direction switch will place an earth condition on the D pin appropriate to that switch. The operation of any one diagonal switch will place earths on the two adjacent primary switch leads corresponding to that direction via the two diodes. It is to be noted that the diodes prevent current flow from primary to diagonal switch and allow current flow from diagonal to primary switch.

A conventional "fire" switch S9 is connected with contact 1 to common and contact 2 to D plug pin 6.

It can be thus seen that the joystick according to the invention achieves directional switching in eight directions using a separate switch for each direction and does not rely on making two switches at once to

achieve diagonal control, as is the case with conventional joysticks, and that the inventive joystick can return to the normal or vertical position under the influence of the mutual attraction achieved by the opposite poles of permanent magnets. The amount of shaft travel, reed switch spacing and biassing strength are all easily adjustable to suit individual applications. It can also be seen that the directional control assembly contains only one moving part and that no physical contact with the switches occurs. There is therefore no risk of damage to the switches caused by excessive operator forces being used.