Abstract:
A joystick  50  comprising: a control shaft  52;  first and second reflecting surfaces, the surfaces each having a reflectivity that varies along a notional line on the surface; a first sensor assembly  70  comprising a first emitter operable to illuminate the first reflecting surface along said line with radiation, and a first detector arranged to detect radiation emitted by the first emitter and reflected by the first reflecting surface; and a second sensor assembly  72  comprising a second emitter operable to illuminate the second reflecting surface along the line with radiation, and a second detector arranged to detect radiation emitted by the second emitter and reflected by the second reflecting surface; wherein movement of said shaft  52  provides a relative movement between emitters of the first and/or second sensor assemblies  70, 72  and respective associated reflecting surfaces to vary the intensity of radiation reflected, and the detectors of the first and second sensor assemblies are each operable to output a voltage that is dependent on the intensity of radiation detected.

Description:
FIELD OF THE INVENTION  
         [0001]    This invention relates to joysticks, and in particular to optical joysticks.  
         DESCRIPTION OF THE PRIOR ART  
         [0002]    Joysticks are used for a variety of purposes in a variety of different circumstances. For example they are used in computer systems to control the position of a pointer on a screen, as well as being used in a variety of vehicles (such as a helicopter for example) to control the direction of motion of the vehicle.  
           [0003]    Whilst a variety of different types of joystick have previously been proposed, they all share a number of common features. For example, all joysticks have a shaft which can be gripped at one end by a user and pivoted about a fixed point in (at least) a two dimensional (X and Y) space. Coupled to the other end of the shaft is some sort of control system which is operable to convert movement of the shaft in the space into electrical signals.  
           [0004]    The earliest joysticks were mechanical joysticks, so called because they used a part-mechanical control system to convert movement of the shaft into electrical signals. FIG. 1 is a cross-sectional view through the base of one such mechanical joystick. As shown, the joystick  1  includes a pair of potentiometers  10 ,  12  which are mounted on a common frame  14 . A shaft  16  is provided, and one end of the shaft is coupled to a stationary member (such as the floor of the joystick) by a universal joint so that the other end of the shaft  16  can move in both X and Y directions. The control shafts of the potentiometers  10  and  12  are coupled to the shaft  16  by respective arm members  18  and  20  which each include an elongated opening  22 ,  24 .  
           [0005]    As the shaft is moved in the X direction it bears against the arm member  20  (without bearing on the other arm  18 ) and causes it to tilt about its axis. As the arm  20  tilts it rotates the control shaft of the potentiometer  12 , and so varies the resistance of that potentiometer. The change in resistance of the potentiometer  12  is directly proportional to the extent to which the control shaft is rotated and thus provides an accurate means to measure the amount of shaft deflection in the X direction.  
           [0006]    In a similar fashion, if the shaft is moved in the Y direction it bears against the arm member  18  (without bearing on the arm  20 ) and causes it to tilt about its axis to vary the resistance of the potentiometer  10  connected thereto.  
           [0007]    As will be apparent from FIG. 1, if the joystick is moved in directions other than along the X or Y axes, then both potentiometers  10  and  12  will be rotated simultaneously and the exact position of the shaft in the space can be read out based on the relative resistances of the two potentiometers.  
           [0008]    A problem with this previously proposed joystick is that as the potentiometers are mechanical devices, they are subject to wear and as a result will eventually fail. When this happens the potentiometers must be replaced if the user wishes to avoid having to purchase a new joystick. Another problem is that the greased control shafts of the potentiometers tend to attract fluff and other detritus which can impair smooth rotation of the control shafts.  
           [0009]    To alleviate these problems it has previously been proposed, in United Kingdom Patent Application No. 2334573 for example, to use optical components which are free from the problems which typically face corresponding mechanical components.  
           [0010]    [0010]FIG. 2 illustrates the joystick described in UK Patent Application No. 2334573. As shown, the shaft  2 ,  5  of the joystick  1  includes an optical emitter  3  which is adapted to illuminate a bank of optical detectors  9 ,  10 ,  11 ,  12  arranged on the floor of the joystick. As the shaft is moved about the two-dimensional space the emitter illuminates each of the detectors to a different degree, and hence the quantity of light detected by each of the detectors  9 ,  10 ,  11  and  12  varies. As the quantity (or intensity) of detected light varies the electrical signals output from the detectors also vary. Control electronics (not shown) interpret the signals output from the detectors to compute the position of the shaft in the space.  
           [0011]    Whilst the joystick of FIG. 2 avoids the problems associated with the joystick of FIG. 1, it has its own set of disadvantages.  
           [0012]    A first of these is associated with the fact that each of the detectors tend to detect an amount of light which can vary only to a small extent from that received by neighbouring detectors. As a result of this, the control electronics need to be quite sophisticated and carefully designed to enable position information to be accurately determined.  
           [0013]    A further problem with the joystick of FIG. 2, and indeed with that of FIG. 1, is that it is not easy to adapt the joystick to provide anything other than a linear response between shaft movement and signal output. One might want to do this, for example, if the joystick is to be used in a computer system for handicapped or otherwise disabled users where it would be useful for the joystick to have a response where the effect of involuntary hand movements (such as a tremor for example) on cursor movement is reduced. Similarly, a non-linear response would assist those persons who only have a relatively poor amount of movement to control the position of a cursor on a screen.  
           [0014]    U.S. Pat. No. 4,533,827 discloses another optical joystick which alleviates the first mentioned problem associated with the joystick of FIG. 2. As shown in FIG. 3, the joystick proposed in this US patent employs a number of emitter/detector pairs  20 - 26  spaced about the periphery of a central sphere  18 . The outside surface of the sphere is painted so that it varies smoothly from being wholly reflective (for example at the top of the sphere) to being wholly non-reflective (for example at the bottom of the sphere). As the joystick of FIG. 3 is moved, the sphere moves with it, and the quantity of light detected by each of the detectors varies accordingly. Since the emitter/detector pairs of the joystick of FIG. 3 are separated from one another, it is unlikely that illumination from any one emitter will have any real effect upon any other detector outside of its emitter/detector pair.  
           [0015]    However, a major disadvantage of the joystick shown in FIG. 3 is that as the sphere goes from reflective to non-reflective in front of one emitter/detector pair, it will tend to go from non-reflective to reflective in front of the other emitter/detector pair. This disadvantage is exacerbated if the reflectivity of the sphere varies non-linearly.  
           [0016]    The only way to avoid this disadvantage of the joystick shown in FIG. 3 is to adapt the control electronics so that one emitter/detector pair output is inverse to that of the other. This complicates the control electronics of the joystick, and hence increases the cost of the joystick.  
           [0017]    The present invention has been conceived with the aim of alleviating the above-described problems.  
         STATEMENT OF INVENTION  
         [0018]    In pursuit of this aim, one embodiment of the invention provides a joystick comprising: a control shaft; first and second reflecting surfaces, said surfaces each having a reflectivity that varies along a notional line on said surface; a first sensor assembly comprising a first emitter operable to illuminate said first reflecting surface along said line with radiation, and a first detector arranged to detect radiation emitted by said first emitter and reflected by said first reflecting surface; and a second sensor assembly comprising a second emitter operable to illuminate said second reflecting surface along said line with radiation, and a second detector arranged to detect radiation emitted by said second emitter and reflected by said second reflecting surface; wherein movement of said shaft provides a relative movement between emitters of the first and/or second sensor assemblies and respective associated reflecting surfaces to vary the intensity of radiation reflected, and said detectors of said first and second sensor assemblies are each operable to output a voltage that is dependent on the intensity of radiation detected.  
           [0019]    The joystick of this embodiment is advantageous over joysticks of the type shown in FIG. 1 because of the fact that the optical movement detection system is free from the problems that are characteristic of prior art mechanical joysticks. Furthermore, as the detector/emitter pairs are well spaced from one another so the likelihood of light from one emitter being detected by the detector of the other emitter/detector pair is significantly reduced, and thus the joystick of this embodiment is advantageous over the joystick of FIG. 2.  
           [0020]    The joystick of this embodiment is also advantageous over the joystick shown in FIG. 3 because of the fact that the control electronics do not need to be designed to compensate for outputs which vary in the opposite sense from one another. Unusually (and indeed contrary to normal expectations in the art) the joystick of this embodiment also provides advantages which result from the fact that it is more complicated than prior art optical joysticks of the type shown in FIG. 3. In particular, by increasing the number of reflecting surfaces it is possible to more easily provide different non-linear reflectivity variations. This is something that one might realistically want to do in circumstances where the user of the joystick is physically impaired only in one direction of movement.  
           [0021]    In accordance with a further embodiment of the invention, there is provided a joystick comprising: a control shaft moveable throughout a two dimensional space defined by X and Y axes; first and second reflectors each having a surface with a reflectivity that varies along one axis of the reflector; a first sensor assembly comprising a first emitter operable to illuminate portions of said first reflector surface with a beam of radiation, and a first detector arranged to detect radiation emitted by said first emitter and reflected by said first reflector surface; a second sensor assembly comprising a second emitter operable to illuminate portions of said second reflector surface with a beam of radiation, and a second detector arranged to detect radiation emitted by said second emitter and reflected by said second reflector surface; and means for transforming movement of the shaft into relative movement between emitters of the first and/or second sensor assemblies and respective associated reflectors; wherein said transform means is operable: on movement of said shaft along said X axis to establish a relative movement which causes said beam of said first emitter to track generally along said first reflector axis; on movement of said shaft along said Y axis to establish a relative movement which causes said beam of said second emitter to track generally along said second reflector axis; and on any other movement of said shaft to establish a relative movement which causes said beam of said first and second emitters to track generally along said first and second reflector axes, respectively.  
           [0022]    Other advantages of embodiments of the invention will be apparent once the following description has been read and understood. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0023]    Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which  
         [0024]    FIGS.  1  to  3  are schematic representations of previously proposed joysticks;  
         [0025]    [0025]FIG. 4 is a schematic isometric view of a joystick in accordance with an embodiment of the invention;  
         [0026]    [0026]FIG. 5 is a schematic isometric view of principal components of the joystick shown in FIG. 4;  
         [0027]    [0027]FIGS. 6 and 7 are schematic graphs of reflectivity versus Shaft Movement Distance;  
         [0028]    [0028]FIG. 8 is an elevation of the components shown in FIG. 5 as viewed in the direction “A” in FIG. 5; and  
         [0029]    [0029]FIG. 9 is an elevation of the components shown in FIG. 5 as viewed in the direction “B” in FIG. 5. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0030]    [0030]FIG. 4 is a schematic isometric view of a joystick  50  in accordance with a presently preferred embodiment of the invention.  
         [0031]    As shown, the joystick comprises a shaft  52  which is provided with a knob  54  at one end. The other end of the shaft extends into the interior of a housing  56 , and provided between the knob and the housing is a dust jacket  58  which is provided to help reduce the amount of dust, dirt and other detritus which might otherwise get inside the housing  56 .  
         [0032]    Located about the shaft  52  outside of the housing  56  and within the jacket  58  is a spring  60  which functions to return the shaft to a roughly dead-centre position.  
         [0033]    The housing  56  comprises a cage formed by an upper wall  62  which is connected to a lower wall  64  by four supporting pillars  66 . The lower wall  64 , in the preferred embodiment, comprises a printed circuit board to which sensing components (to be later described) are fixed and signals from the sensing components are output from the printed circuit board by means of an input/output interface  68 .  
         [0034]    The sensing components in the preferred embodiment comprise a first sensor assembly  70  for sensing movement of the shaft in an X axis direction and a second sensor assembly  72  for sensing movement of the shaft in a Y axis direction. Each sensor assembly  70 ,  72  comprises (as will later be described in detail) an optical emitter and an optical detector arranged so that light output from the optical emitter is reflected off a surface for detection by the optical detector. In the preferred embodiment, the surfaces for reflecting light each comprise an arcuate planar surface with a generally triangular or quadrant-shaped wall extending from one side thereof.  
         [0035]    Provided within the housing  56  is mechanical linkage indicated generally by reference numeral  74  which functions to convert movement of the shaft  52  into corresponding movements of one or both of the aforementioned reflecting surfaces as appropriate.  
         [0036]    [0036]FIG. 5 is a schematic isometric view of the joystick  50  shown in FIG. 4 but with the housing  56  and dust jacket  58  removed.  
         [0037]    As shown in FIG. 5, the joystick shaft  52  is coupled by an appropriate mechanical linkage  74  to an X axis reflector  80  and a Y axis reflector  82 . The X axis reflector  80  is snugly mounted on an X axis shaft  76  for joint rotation therewith, and the Y axis reflector  82  is directly coupled to the shaft  52  by means of an extension  75  of the Y axis reflector  82  which is provided with a longitudinal generally rectangular slot that enables the extension to be fitted over the end of the shaft  52 .  
         [0038]    Broadly speaking, the mechanical linkage  74  (to be later described) functions to convert movement of the shaft  52  in an X direction (as indicated in FIG. 5) into a rotation of the X axis shaft  76  and X axis reflector  80  mounted thereon. Similarly, the mechanical linkage also functions to convert movement of the shaft  52  in a Y direction (also indicated in FIG. 5) into a rotation of the Y axis reflector  82  which is pivotally mounted on the housing  56  by means of a pivot pin  78 .  
         [0039]    As mentioned before, the X and Y axis reflectors each comprise a generally arcuate planar reflecting surface  84  which is provided with an upstanding generally triangular web  86  which is apertured so that it can be received on the X axis shaft  76  or pivot pin  78 , as appropriate.  
         [0040]    The undersides of each reflecting surface  84  (i.e. the sides facing away from the aforementioned connecting webs  86  are coated with light reflective material and the coating is arranged so that the reflectivity of the surface varies from being substantially reflective at one end of the surface to being substantially non-reflective at the other end of the surface.  
         [0041]    As an example, if the aforementioned light emitters are infrared emitters then the reflecting surfaces could be graded from black to white along their longitudinal length. This arrangement would also prove workable if the light emitters where to emit visible white light.  
         [0042]    The grading of the reflectivity of the surfaces can, in one embodiment of the invention, be smooth in that the rate of change of reflectivity is constant along the longitudinal length of the reflecting surface. Alternatively, in another preferred embodiment of the invention, the grading of the reflectivity along the length of the surface can be arranged so that the rate of change of reflectivity is not constant and instead varies non-lineally.  
         [0043]    Providing a reflectivity which changes non-lineally can be advantageous in circumstances where a user of the joystick is only capable of relatively small hand movements, and hence relatively small movements of the shaft  52 .  
         [0044]    [0044]FIGS. 6 and 7 show representative graphs of reflectivity versus shaft movement distance either side of a centre point on the X axis.  
         [0045]    In particular, FIG. 6 illustrates an arrangement where the reflectivity of the surface varies lineally (i.e. the rate of change of reflectivity is constant) along the length of the reflecting surface. FIG. 7, on the other hand, illustrates an arrangement where the reflectivity of the reflecting surfaces varies non-lineally (i.e. the rate of reflectivity change is not constant) along the length of the reflecting surface.  
         [0046]    It can be seen by comparing FIGS. 6 and 7 that to attain a given reflectivity, say 0.75, the arrangement of FIG. 7 requires less joystick movement than the arrangement of FIG. 6. As a consequence the arrangement of FIG. 7 would be more appropriate for users who have some sort of physical disability which reduces the extent to which they can easily move their hands.  
         [0047]    Another advantage of the particular arrangement shown in FIG. 7 is that the reflectivity changes relatively slowly for relatively small movements of the shaft from a notional centre point. This is advantageous in that it provides a central dead band in which a small shaft movement (such as that which might be caused by an involuntary hand movement or tremor) will have little effect upon the reflectivity of the surface.  
         [0048]    The reflectivity&#39;s of each reflecting surface  84  can be arranged to change in a similar manner, or alternatively one surface can be arranged to have a change of reflectivity which is constant whilst the other surface has a non-lineally varying change of reflectivity.  
         [0049]    [0049]FIGS. 8 and 9 provide a schematic illustration of the mechanical linkage  74  shown in FIGS. 4 and 5. In particular, FIG. 8 is a view of the linkage in a direction “A” shown in FIG. 5, and FIG. 9 is a view of the linkage in a direction “B” also shown in FIG. 5.  
         [0050]    Referring firstly to FIG. 8, the shaft  52  is fitted in a longitudinal generally rectangular slot  94  that extends right through a generally cylindrical X axis sleeve  92  (as indicated by the dotted lines in FIG. 8). The shaft  52  is connected to the sleeve  92  by means of a pivot pin  91  which extends, although not visible in FIG. 8, from one side of the sleeve through a bore in the shaft  52  and out the other side of the sleeve. Movement of the shaft  52  in a Y direction  90  causes the shaft  52  to pivot about the pin  91  and a portion of the shaft  52  extending below the sleeve  92  to drive the aforementioned extension  75  of the Y axis reflector  82  (and hence to rotate the Y axis reflector about the pivot  78 ).  
         [0051]    [0051]FIG. 9 is a view in direction “B” of FIG. 5 and illustrates the X axis shaft  76  which, in the preferred embodiment, is formed as an extension of the above described X axis sleeve  92  (for example by machining the generally cylindrical sleeve to reduce its cross-sectional area). Movement of the shaft  52  back and forth in a direction  98  will cause the shaft  52  (as shown in FIG. 8) to abut against the edges of the longitudinal slot  94  and hence will cause the X axis sleeve  92  and X axis shaft  76  to rotate in unison with movement of the shaft  52  in the aforementioned direction  98 . Since the Y axis reflector extension  75  is longitudinally slotted, a movement of the shaft in direction  98  only will not drive the extension  75 , and thus will not cause the Y axis reflector  82  to pivot about pivot pin  78 .  
         [0052]    In operation, movement of the shaft  52  in the X direction  98  will give rise to a rotation of the X axis shaft  76 . Rotation of the X axis shaft will causes a corresponding rotation of the X axis reflector, and as the reflector moves so the reflectivity of the reflective surface  84  immediately opposite the emitter of the X axis sensor assembly  70  will change. Light emitted from the emitter of the X axis sensor assembly  70  is detected by the detector of the assembly and converted into a voltage signal which varies in magnitude in dependence upon the intensity of light detected, upon the portion of the reflective surface  84  illuminated by the emitter, and hence upon the position of the shaft  52  in the X axis.  
         [0053]    Movement of the shaft  52  in the Y direction  90  causes the shaft to pivot in the slot  94  about the pivot pin  91 , and causes the part of the shaft  52  extending below the X axis sleeve  92  to directly drive the Y axis reflector extension  75 , and hence to rotate the Y axis reflector  82  about the pivot axis  78 . As the Y axis reflector  82  is pivoted a change in voltage level is detected by the Y axis sensor assembly  72 .  
         [0054]    Movement of the shaft in both the X and Y directions results in voltage level changes at each of the sensor assemblies  70 ,  72  which are indicative of the position of the shaft  52 .  
         [0055]    As mentioned above, the preferred embodiment of the present invention (as described above) provides a number of advantages over the joysticks of the prior art. In particular, it is surprising that (given the general aim in the art of simplifying joystick construction) a complication of the joystick construction to include two reflectors actually leads to a simplification of the joystick as a whole.  
         [0056]    It will be understood that embodiments of the invention have been described above by way of example only, and that modifications may be made within the spirit and scope of the invention.  
         [0057]    For example, whilst it is mentioned above that the reflective surfaces are coated with reflective material it will be apparent that the surfaces could instead simply be painted with different shades of paint to achieve the same effect. It will also be apparent to persons skilled in the art that the particular arrangement of the sensor assemblies and associated reflectors may be reversed without departing from the scope of the invention. In such an arrangement the emitter and detector pairs would be carried and pivoted by appropriate mechanical linkage and the two reflectors would be stationary on the lower wall  64  of the housing  56 .  
         [0058]    As another example, it will be appreciated that whilst it is preferred for the reflective surfaces to be arcuate (to maintain a roughly constant distance between the emitter and the reflective surface) this may not actually be required, and thus that the reflective surfaces may be flat or have any other profile.  
         [0059]    It will also be apparent that any of a number of different light sources may be provided as the emitter of each sensor assembly. For example, the emitters could be white light emitters, infra-red LED (light emitting diode) emitters or any other type of emitter.  
         [0060]    If the emitters are chosen to be infrared emitters then the present invention may also make use of the temperature compensation circuitry disclosed in the aforementioned UK Patent Application No. 2334573.