Abstract:
A self centering, angularly displacable joystick allowing multiple compound torque profiles is provided. The self centering joystick includes a first mount and a base. The first mount located a fixed distance away from the base. The joystick extends from a restoring plate having an upper surface and a multi-faceted lower surface pivotally mounted to said first mount to partially rotate about a first axis. A linearly displaceable force plate having a substantially flat upper surface is disposed between said base and said multi-faceted surface, and a spring is provide between the base and the force plate, the spring biasing the force plate against the multi-faceted surface to provide a centering force there against. The multifaceted surface includes a center position facet oriented such that the centering force applied by the force plate is evenly distributed on each side of the first axis when said center position facet is aligned parallel with the upper surface of the force plate.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a self-centering “joystick” input device capable of supporting multiple compound torque profiles for returning the joystick to the center position. Joystick input devices are well known in the art, and have been employed in a wide range of applications, from aircraft control to video game inputs. Joysticks may be provided to supply directional input information related to a single rotational axis, or to multiple axes. More sophisticated joystick instruments may provide magnitude data as well. 
     In operation, an operator will manually displace the joystick relative to one or more of its rotational axes in order to issue directional commands to other equipment. Sensors within the joystick will sense the angular displacement of the joystick and develop input signals accordingly, which may be transmitted to the equipment to be controlled. The sensors and the signals they produce may operate electronically, hydraulically, or otherwise. 
     In many applications it is desirable that the joystick return to a center or neutral position after it has been released by the operator. Many joysticks are designed to be displaced about two perpendicular axes, so that directional information may be detected through 360°. Thus, in order to return the joystick to a center position on both axes, many designs have required two or more springs to provide a centering force relative to each axis. Some designs, for example that disclosed in U.S. Pat. No. 4,124,787 require two springs per axis. A problem with multiple spring designs is their complexity and higher cost. Also, most multiple spring designs include a significant amount of backlash around the center position. Backlash around the center position allows the joystick to be displaced by a small amount without developing an adequate restoring force to return the joystick to center. Thus, prior art instruments often include a slight wobble around the center position that can lead to inaccurate input measurements. The backlash problem is especially troublesome in applications where a high degree of accuracy and sensitivity is required. 
     A number of single spring designs have been developed in order to simplify the design of self-centering joysticks and reduce backlash. U.S. Pat. Nos. 4,479,038 and 5,724,068, for example, each employ a single spring to bias a thrust plate, or force plate, against a restoring member which is attached to the joystick itself. These designs prove simpler, and improve backlash around the center position, however, they are limited to providing a uniform restoring torque that is substantially equal in all directions. 
     In some applications it is desirable that the restoring torque for returning the joystick to the center position be greater in some directions than it is in others. Further, it may also be desired that the torque profile have a step such that the restoring torque is significantly increased if the joystick is displaced beyond a certain amount. Prior art joystick designs include no provisions for such multiple compound force profiles. 
     SUMMARY OF THE INVENTION 
     In light of the background given above, a primary object of the present invention is to provide a self centering joystick that may be angularly displaced relative to at least one axis and automatically and accurately returned to a center position. 
     A further object of the invention is to provide a self-centering joystick having compound torque profiles wherein a restoring torque for returning the joystick to the center position varies significantly depending on the angular displacement of the joystick. 
     Yet another object of the present invention is to provide a self-centering joystick having multiple torque profiles, compound or otherwise, provided by a single biasing spring. 
     These objects, as well as others that will become apparent upon reading the detailed description of the preferred embodiment are accomplished by the Self-Centering Joystick as herein disclosed. 
     The present invention provides a centering device for returning an angularly displaceable joystick to a center position, and retaining the joystick in the center position until it is acted upon by an external force. The centering device provides multiple compound torque profiles for restoring the joystick to the centered position. The compound force profiles are such that as the joystick is angularly displaced, the magnitude of the restoring torque is dependent on the direction and angular distance that the joystick is displaced. Furthermore, the multiple compound torque profiles are provided by a single biasing spring. 
     The joystick-centering device of the present invention includes a support fixture which supports the joystick. The support fixture includes a mounting bracket which supports the joystick above the base of the fixture. A restoring plate is attached to a lower end of an elongate member that comprises the joystick itself, and the restoring plate is pivotally mounted to the mounting bracket. The self-centering joystick mechanism of the present invention may be employed on a joystick rotatable about a single axis or multiple axes. In a preferred embodiment the restoring plate is mounted within a two axis gimbal which allows the joystick to be rotated independently about two perpendicular axes. 
     A lower surface of the restoring plate is formed of a plurality of adjacent planar segments or facets. Included among the plurality of facets are a center facet and angularly displaced lateral facets abutting the center facet. The junction between the lateral facets and the center facet form distinct straight primary contact lines between the adjacent facets. The center facet is positioned such that pairs of primary contact lines are laterally offset an equal distance from each axis. Secondary lateral facets are formed adjacent the lateral facets. The secondary lateral facets abut the lateral facets to form secondary contact lines. The secondary contact lines are offset further from their associated axes than are the parallel primary contact lines. 
     A force plate is disposed between the base of the fixture and the restoring plate. A compression spring is compressed between the base and the force plate to bias the force plate against the multi-faceted lower surface of the restoring plate. The compressed spring provides a restoring force which biases the force plate against the restoring plate. When the joystick is in the center position, the center facet abuts the surface of the force plate, parallel thereto. The centering force applied by the force plate is evenly distributed against the center facet such that no net torque is transmitted to the joystick. However, when the joystick is displaced by a relatively small angle about a first axis, the centering force is concentrated against only one of the primary contact lines surrounding the center position facet. When the joystick is displaced further, the centering force is applied against one of the secondary contact lines. Because the secondary contact lines are located further from the first axis than are the primary contact lines, a first relatively smaller centering torque is developed when the centering force acts against one of the primary contact lines, and a second relatively larger centering torque is developed when the centering force is acting against one of the said secondary contact lines. 
     The arrangement of the lateral and secondary facets, and the subsequent formation of primary and secondary contact lines, may be repeated for each axis of rotation of the joystick. Thus, multiple compound torque profiles may be provided for centering the joystick about each axis. Furthermore, such multiple compound force profiles are provided by a single biasing spring compressed between the support fixture base and the force plate, providing a significantly less complex multi-axis self centering joystick than has heretofore been available in the art. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a self centering joystick having compound torque profiles according to a preferred embodiment of the invention; 
     FIG. 2 is a perspective view of the self centering joystick of FIG. 1 shown mounted in a two axis gimbal; 
     FIG. 3 is a perspective view of restoring plate; 
     FIG. 4 is a plan view of the self centering joystick of FIG. 1 shown in the centered position looking down the y-axis; 
     FIG. 5 is a plan view similar to FIG. 3, but with the joystick displaced relative to the y-axis; 
     FIG. 6 is a plan view of the self centering joystick of FIG. 1 shown in the centered position looking down the x-axis; 
     FIG. 7 is a plan view similar to FIG. 5, but with the joystick displaced relative to the x-axis by an amount less than the angle β; 
     FIG. 8 is a plan view similar to FIG. 6, but with the joystick displaced relative to the x-axis by an amount equal to the angle β; 
     FIG. 9 is a torque profile for the self centering joystick of FIG. 1 about the y-axis; 
     FIG. 10 is a torque profile for the self centering joystick of FIG. 1 about the x-axis. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIGS. 1 and 2, a joystick centering device according to the preferred embodiment is shown at  100 . The device acts to return an elongate member joystick)  102  to a center position after the joystick has been angularly displaced therefrom. The centering device includes a restoring plate  104  rigidly attached to the base of the joystick. 
     Angular displacement of the joystick is translated to rotation of the restoring plate and vice-versa. A spring loaded force plate  106  is disposed below the restoring plate. The force plate is guided by a linear bearing  108  disposed between the force plate and the base  114  of a support fixture configured to support the joystick and centering device. A coil spring  110  is compressed between the force plate and support fixture base  114 , biasing the force plate against a lower surface of the restoring plate. 
     FIG. 2 shows the joystick centering device mounted in a two axis gimbal. The two axis gimbal allows the restoring plate and the joystick to rotate simultaneously about two perpendicular axes. The support fixture includes a pair of mounting brackets  112  which are spaced apart from the fixture&#39;s base  114 . The outer gimbal  116  is pivotally mounted to the mounting brackets  112  such that the outer gimbal is free to rotate about the x-axis  118 . The inner gimbal  120  is pivotally mounted within the outer gimbal  116  at inner mounts  121  so that the inner gimbal is free to rotate about a y-axis  122  which is perpendicular the x-axis  118 . Restoring plate  104  is fixed within the inner gimbal  120  so that the restoring plate may be rotated about both the x-axis and y-axis. Thus, by a combination of rotation about both the x-axis and the y-axis, the joystick  102  attached to the restoring plate may be angularly displaced in any direction. 
     It should be noted that the two axis gimbal just described merely represents a bearing system for a self centering joystick. The present invention should not be considered limited to joysticks employing a two axis gimbal support bearing. Any support system capable of allowing an elongate member to be angularly displaced relative to a fixed mounting bracket may be employed in place of the two axis gimbal just described. Further, the present invention should not be limited to only two axis joysticks. For example, the self centering function of the present invention my be practiced on a joystick that pivots about a single axis only, or one that pivots about more than two axes. 
     Turning to FIG. 3, the underside of the restoring plate  104  is shown. The underside of the restoring plate forms a cam-like surface comprised of a plurality of adjacent planar segments, or facets. In the preferred embodiment, the multi-faceted surface includes a total of seven facets including a center position facet  128 , lateral facets  126 ,  130 ,  134  and  136 , and secondary lateral facets  124 ,  132 . Adjacent facets intersect along sharp, well defined contact lines between each angled surface. In the preferred embodiment there are a total of ten contact lines labeled  138 - 156  (even numbers only) in FIG.  3 . The vertical lines  158 ,  160 ,  162 , and  164  forming the four comers of the restoring plate  104  may also be considered contact lines if the joystick is allowed to pivot to such an extent that facets  124  and  134  are allowed to contact the force plate  106 . As will be described in more detail below, contact lines  138 ,  140 ,  142 , and  144  affect the rotation of the force plate  104  about the x-axis  118 , and contact lines  146 ,  148 ,  150 , and  152 ,  154 ,  156  affect rotation about the y-axis. The comers  158 ,  160 ,  162 , and  164  will also affect the rotation of the restoring plate  104  about the y-axis, if the joystick is allowed to rotate sufficiently to allow the comers to contact the force plate. 
     Facet  128 , located in the center of restoring plate  104 , defines the center position of the joystick. FIGS. 4 and 6 show the joystick in the centered position with facet  128  abutting the surface of force plate  106 . FIG. 4 is a plan view looking down the y-axis  122 , and FIG. 6 is a plan view looking down the x-axis. In FIG. 4 primary contact lines  148 ,  154  frame the left and right edges of facet  128 . Each contact line  148 ,  154  is laterally offset an equal distance from the y-axis  122 . Force plate  106  is biased against the restoring plate by compressed coil spring  110  (FIGS.  1  &amp;  2 ), which generates a centering force acting against the lower surface of the restoring plate. With the joystick in the centered position, the centering force acts against the center position facet  128  uniformly on each side of the y-axis, and the net torque developed about the y-axis is approximately zero. Due to the absence of applied torque, the restoring plate will tend to remain in the centered position relative to the y-axis. 
     Referring to FIG. 6, the center position relative to the x-axis is determined in the same manner. Contact lines  140 ,  142  frame the left and right edges of facet  128 , and are laterally offset an equal distance from the x-axis  118 . The restoring force exerted by force plate  106  acts uniformly against facet  128  on each side of the x-axis. Thus, no torque is developed tending to rotate the restoring plate about the x-axis. Again, as with the y-axis center position, the restoring plate will tend to remain in the center position relative to the x-axis until an external displacement force is applied to the elongate member  102 . 
     In contrast to the centered position, when the restoring plate is angularly displaced with regard to either the x-axis or the y-axis, the restoring force exerted by force plate  106  is concentrated along lines or at points that are laterally offset from one or both of the x and y axes. This generates a restoring torque which tends to return the restoring plate to the center position. Thus, when the joystick is displaced by an external force, the restoring torque tends to re-center the device as soon as the external force is removed. Conversely, the joystick tends to remain stable in the centered position until an external force is applied. 
     Angular displacement of the restoring plate  104  relative to the y-axis is depicted in FIG.  5 . Contact line  148 , here shown in end view, forces the force plate  106  downward, further compressing spring  110 . As is clear from the drawing, the points along contact line  148  represent the only points of contact between the force plate  106  and the restoring plate  104  relative to the y-axis. Therefore, the restoring force exerted by force plate  106  acts exclusively against contact line  148  which is offset from the y-axis. Thus, a restoring torque is developed which tends to rotate the restoring plate (and therefore elongate member  102 ) back toward the center position. The magnitude of the torque will be equal to the spring force exerted against the force plate  106  multiplied by the distance D y . D y  equals the horizontal distance from the y-axis to the contact line  148 . As the angular displacement of the restoring plate changes, the distance D y  will also change, as contact line  148  is rotated closer to vertical alignment with the y-axis. However, if the displacement of the joystick is restricted to a small angle, for example, between 5° to 10°, the distance D y  will not change significantly, and the restoring torque will vary approximately proportionately with the displacement of the force plate. 
     The torque profile for rotation of the restoring plate about the y-axis is shown in FIG.  9 . As can be seen, the torque increases in a substantially linear manner as the angle of displacement increases. This corresponds to the linear increase in the spring force as the coil spring  110  is further compressed by the downward rotation of contact line  148  shown in FIG.  5 . Because contact line  154  is located on the opposite side of the y-axis the same distance away as contact line  148 , the torque profile appears the same when the restoring plate is rotated in the opposite direction. A steeper or shallower torque profile may be provided by altering the width of the restoring plate, thereby altering the perpendicular distance D y  from the y-axis to the contact lines  146 ,  154 . 
     Contact lines  146  and  150 , as well as comers  158  and  160  form parallel extensions of contact line  148 . Similarly contacts lines  152  and  156  and comers  162  and  164  form parallel extensions of contact line  154 . When viewed from the side (FIGS. 6,  7 , and  8 ) these contact lines extend at various angles relative to contact lines  148 ,  154 , however, when viewed from the end, as in FIGS. 4 and 5, these additional contact lines extend parallel to the contact lines  148 ,  154 , at the same lateral distance from the y-axis. These additional contact lines and comers only have an affect when the restoring plate is simultaneously displaced relative to the x-axis and the y-axis. For example, when the restoring plate has been rotated about the x-axis so that facet  126  is parallel with the force plate  106  as shown in FIG. 8, contact lines  146  and  152  will be adjacent the force plate. Although the restoring plate has been rotated about the x-axis, there has been no displacement relative to the y-axis. The force plate continues to act uniformly against facet  126  on each side of the y-axis, and no restoring torque is generated about the y-axis. If however, the joystick is rotated with respect to the y-axis as well as with respect to the x-axis, contact line  146 , or  152  will be rotated against the force plate  104  in the same manner as contact lines  148 ,  158  when the restoring plate was centered relative to the x-axis. The same holds true for contact lines  150  and  156  if the restoring plate is rotated about the x-axis in the opposite direction. Comers  158 ,  162 , and  160 ,  164 , will act in a similar capacity depending on how far the restoring plate is pivoted about the x-axis. Because each of the contact lines and comers,  158 ,  146 ,  148 ,  150 ,  160 , and  162 ,  152 ,  154 ,  156 ,  164  are all located the same distance from the y-axis, and are parallel thereto, the torque profile about the y-axis shown in FIG. 9 will be that same regardless of which contact line the force plate is actually acting against. 
     Turning now to FIGS. 3,  6 - 8 , and  10 , rotation of the restoring plate about the x-axis will now be described. In the centered position shown in FIG. 6, the center facet  128  lies parallel to the surface of force plate  106 . Both contact lines  140  and  142  (shown in end view in FIGS. 6-8) lie parallel to the surface of force plate  106 . In this position, the force applied by the force plate against the restoring plate is evenly distributed on each side of the x-axis. Therefore, no torque is developed tending to rotate the restoring plate about the x-axis. Thus, the joystick tends to remain centered with respect to the x-axis. 
     In FIG. 7, the joystick is displaced a small distance to the right, causing the restoring plate to rotate a small amount in the clockwise direction. Contact line  140  is rotated away from the force plate  106 , and contact line  142  is rotated into the force plate, further compressing the spring  112 . Contact line  142  is offset from the x-axis by a lateral distance D x1 . Thus, rotation of the restoring plate about the x-axis generates a restoring torque equal to the spring force applied to against contact line  142 , multiplied by the distance D x1 . As with rotation about the y-axis, the distance D x1  will vary little during the course of the limited angular displacement of the joystick envisioned in the preferred embodiment of the invention. Therefore, the restoring torque for all practical purposes will be proportional to the linear displacement of the force plate due to the downward rotation of contact line  142 . Rotation of the of the restoring plate  104  in the opposite direction of that shown in FIG. 7 will have the same effect, only the force plate will act against contact line  140  and the restoring torque will be directed in the opposite direction. 
     When either of the contact lines  140 ,  142  are engaging the force plate  106 , the torque profile for the x-axis will look very similar to the torque profile for the y-axis shown in FIG.  9 . However, as can be seen best in FIG. 6, the facets  126  and  130  form angles α and β on each side of the center facet  128 . When the joystick is displaced further such that the restoring plate is rotated an amount greater than α or β, the primary contact lines  140  or  142  are rotated away from the surface of the force plate, and one of the secondary contact lines  138  or  144  engage the force plate. The secondary contact lines  138 ,  144  are located further from the x-axis and therefore the restoring torque tending to rotate the restoring plate back to the center position will be increased when the force plate engages the secondary contact lines  138 ,  140 . This can be seen in FIG.  8 . In FIG. 8, the joystick has been displaced to the right by an amount causing the restoring plate to rotate in the clockwise direction by an amount equal to the angle β. Thus, facet  130  lies parallel to the surface of the restoring plate  106 . If the joystick is rotated further to the right, contact line  142  will be rotated clear of the surface of the force plate  106 , and contact line  144  will rotate against the force plate, further compressing the coil spring  112 . Contact line  144  is located a distance from the x-axis equal to D x2  which is greater than D x1 . When the secondary contact line  144  engages the force plate  106 , the force applied against the restoring plate is offset further from the x-axis, and the restoring torque is increased proportionally. 
     The compound nature of the torque profile relative to the x-axis may be seen graphically in FIG.  10 . When the angular displacement of the restoring plate is less than α or β, the restoring torque increases in a substantially linear manner with increasing angular displacement as in FIG.  9 . However, when the angular displacement exceeds α or β, the restoring torque jumps to a higher level as the more distant secondary contact lines engage the force plate. Once the angular displacement exceeds α or β, the restoring torque again increases linearly with further angular displacement of the restoring plate. 
     FIG. 10 represents a compound force profile. With the present invention, such compound force profiles may be created in any direction by altering the lower surface of the restoring plate. For example, the angular position where the restoring torque jumps to a higher level may be manipulated by altering the angles α and β. Further, the size of the jump may be controlled by carefully selecting the width of the lateral facets. With the restoring plate profile shown in FIGS. 6,  7 , and  8 , as the width of lateral facets  126  and  130 , is increased, the distance D x2  between the primary contact lines  140 ,  142  and the secondary contact lines  138 ,  144  will increase. Thus, the greater the width of the lateral facets  126 ,  130 , the greater will be the increase in the restoring torque at angles greater than α or β. The present invention thereby provides a self centering joystick capable of having multiple complex compound force profiles. 
     It should be noted that various changes and modifications to the present invention may be made by those of ordinary skill in the art without departing from the spirit and scope of the present invention which is set out in more particular detail in the appended claims. Furthermore, those of ordinary skill in the art will appreciate that the foregoing description is by way of example only, and is not intended to be limiting of the invention as described in such appended claims.