Abstract:
An apparatus and method is provided for operating an aircraft control stick in an active mode and a passive mode. The method comprises subjecting the control stick to an a resilient restoring force in the passive mode, and neutralizing the restoring force in the active mode. A spring assembly is provided for exerting and neutralizing the restoring force, which may be varied between minimum and maximum values.

Description:
FIELD OF THE INVENTION 
     Embodiments of the subject matter described herein relate generally to an aircraft control stick operable in first and second modes and, more particularly to a method and apparatus for providing an adjustable restoring force to releasably secure an aircraft control stick in a predetermined position in a passive mode and for neutralizing the restoring force for operation in an active mode. 
     BACKGROUND 
     On some devices, there is a need to bias a rotatable object toward a predetermined position on its rotational axis. For example, some aircraft flight control systems utilize a gimbal assembly to translate any movements of a flight control stick into the rotation of a plurality of shafts about two rotational axes. These shafts may be biased to a predetermined position to enable the flight control stick to return to a null position when it is released by the pilot or co-pilot. 
     In this passive mode, a force is required to release the object from the predetermined position, providing physical feedback to the user of the object and indicating to the user that the mechanism is in the predetermined position. Thus, the control stick that is coupled to a gimbal assembly may be releasably secured in its null position by securing each of the shafts in a predetermined position about its axis of rotation, and preventing the control stick from moving unless the pilot or co-pilot applies enough force to allow rotation of one or both of the shafts. 
     Active control sticks, however, are capable of operation in a passive mode, as above described, and in an active mode that does not require automatic return to the null position. To this end, it is known to utilize centering springs that are configured to return the control stick to its null position when there is no pilot exerted force on the control stick. However, these springs are not required in the active mode, and the presence of these centering springs when operating in the active mode requires the drive motors or electro-mechanical actuators to be larger, complicates the control laws relating to control stick inertia, friction, and force discontinuities, and makes it more difficult to achieve acceptable tactile characteristics in the active mode. 
     Considering the foregoing, it would be desirable to provide a control stick assembly that may be continuously adjusted between first and second positions so as to operate (1) in the passive mode, utilizing a restoring system, and (2) in the active mode by neutralizing the restoring forces. 
     Furthermore, other desirable features and characteristics of the present invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings, this Background, and the appended Claims. 
     BRIEF SUMMARY 
     In accordance with the above, there is provided an aircraft control stick assembly, comprising a control stick, and a first spring assembly for exerting an adjustable restoring force to releasably secure the control stick in a predetermined position in a first mode and for neutralizing the first restoring force in a second mode. 
     Also provided is an aircraft control stick assembly, suitable for use in an active mode and a passive mode, comprising a control stick, first and second spring assemblies coupled to the control stick for exerting first and second adjustable restoring forces, respectively, to releasably secure the control stick in a predetermined position in a passive mode, and for removing the first and second restoring forces in an active mode. 
     A method is also provided for operating an aircraft control stick in an active mode and a passive mode. The method comprises subjecting the control stick to an adjustable resilient restoring force in the passive mode, and neutralizing the restoring force in the active mode. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and: 
         FIG. 1  is an isometric view of an exemplary human-machine interface assembly; 
         FIGS. 2 and 3  are functional and graphical representations, respectively, of a passive return-to-center control stick arrangement; 
         FIG. 4  is a functional representation of another passive, return-to-center control stick arrangement; 
         FIGS. 5 ,  6 , and  7  are partial isometric, first side, and second side views, respectfully, of a gimbal box assembly utilizing the concepts discussed above, which allows motion in pitch and roll orthogonal axes as is typical for aircraft control; 
         FIG. 8  illustrates a first exemplary embodiment for providing a restoring force to releasably secure an aircraft control stick in a predetermined position in a passive mode and for neutralizing the restoring force for operation in an active mode; 
         FIGS. 9 and 10  are functional and graphical representations, respectively, of a second exemplary embodiment for providing an adjustable restoring force to releasably secure an aircraft control stick in a predetermined position in a passive mode and for neutralizing the restoring force for operation in an active mode; 
         FIGS. 11 and 12  are functional and graphical representations, respectively, of a third exemplary embodiment for providing an adjustable restoring force to releasably secure an aircraft control stick in a predetermined position in a passive mode and for neutralizing the restoring force for operation in an active mode; and 
         FIGS. 13 ,  14 , and  15  are functional representations of fourth, fifth, and sixth exemplary embodiments for providing an adjustable restoring force to releasably secure an aircraft control stick in a predetermined position in a passive mode and for neutralizing the restoring force for operation in an active mode. 
     
    
    
     DETAILED DESCRIPTION 
     The following Detailed Description is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. Furthermore, there is no intention to be bound by any theory presented in the preceding Background or the following Detailed Description. 
     Embodiments of the present invention may be utilized in conjunction with devices that have multiple shafts, to bias the shafts toward, and releasably retain them in, a predetermined position. For example,  FIG. 1  depicts an exemplary embodiment of a human-machine interface assembly  150 . The human-machine interface assembly  150  includes a user interface  152  and a gimbal assembly  154 . The user interface  152  is coupled to the gimbal assembly  154  and is configured to receive an input force from a user. The user interface  152  may be implemented as a grip or control stick that is preferably dimensioned to be grasped by the hand of a user, such as the pilot or co-pilot of an aircraft. 
     The gimbal assembly  154  is preferably mounted within a suitable, non-illustrated housing assembly, and is configured to allow the user interface  152  to be moved from a null position, which is the position depicted in  FIG. 8 , to a plurality of control positions in a plurality of directions. More specifically, the gimbal assembly  154 , in response to an input force supplied to the user interface  152 , allows the user interface  152  to be moved from the null position to a plurality of control positions, about two perpendicular rotational axes (e.g., a first rotational axis  156  and a second rotational axis  158  as shown). It will be appreciated that the human-machine interface assembly  150  may be implemented as an aircraft flight control system, with the user interface  152  functioning as a flight control stick. In such an embodiment, the first and second rotational axes  156 ,  158  may be referred to as the roll and pitch axes, respectively. 
     The gimbal assembly  154  includes a first roll shaft  160 , second roll shaft  162  and a pitch shaft  164 . The first and second roll shafts  160 ,  162  are each fixably coupled to opposing ends of the gimbal assembly  154 , for rotation therewith about the first rotational axis  156 . The pitch shaft  164  is coupled to the gimbal assembly  154  for rotation therewith about the second rotational axis  158 . 
     The gimbal assembly  154  is configured to permit the user interface  152  to be movable about the first and second rotational axes  156 ,  158  and to translate any movement of the user interface  152  into a corresponding rotation of the first and second roll shafts  160 ,  162  and/or the pitch shaft  164 . For example, movement of the user interface  152  about the first rotational axis  156  in the port direction  166  and starboard direction  168  result in a rotation of the gimbal assembly  154  and the first and second roll shafts  160 ,  162  about the first rotational axis  156 . Further, movement of the user interface  152  about the second rotational axis  158  in a forward direction  170  or an aft direction  172 , result in the rotation of the gimbal assembly  154  and the pitch shaft  164  about the second rotational axis  158 . It will be appreciated that the gimbal assembly  154  is configured to allow the user interface  152  to be moved in a combined forward-port direction, a combined forward-starboard direction, a combined aft-port direction, or a combined aft-starboard direction, and back to or through the null position, resulting in the rotation of the first and second roll shafts  160 ,  162  about the first rotational axis  156 , and the pitch shaft  164  about the second rotational axis  158 . It will additionally be appreciated that the gimbal assembly  154  may be configured using any one of numerous gimbal assembly implementations now known. 
       FIGS. 2 and 3  are functional and graphical representations, respectively, of a passive return-to-center control stick arrangement  200  wherein a restoring force is provided by a coil spring assembly  202  comprised of a coil spring  204  compressed between end plates  206  and  208 . The spring assembly  202  is mounted for slidable movement on shaft  210  and constrained between fixtures  212  and  214 . However, shaft abutments  216  and  218  are free to move through fixtures  212  and  214  respectively. Shaft  210  is pivotably coupled to control stick  220  at pivot  222 , and control stick  220  is coupled for rotation about an axis  224 . Thus, control stick may be moved clockwise or counterclockwise about axis  224  as is indicated by arrow  226 . 
     It should be appreciated that the pre-compression of spring  204  between abutments  216  and  218  will exert an opposing force of expansion |f| upon fixtures  212  and  214  that resists movement of shaft  210 . Before control stick  220  may be rotated either clockwise or counterclockwise a translational force |f| must be exerted on shaft  210 . Thus, referring to  FIGS. 2 and 3 , before control stick  220  may be rotated counter-clockwise, sufficient pressure must be exerted on control stick  220  in the counterclockwise direction to exceed the opposing force of expansion exerted by spring  204 . That is, until the opposing force of expansion is exceeded, there will be no linear displacement of shaft  210  in the x direction. After the opposing force is reached, the application of additional force of rotation on control stick  220  will result in linear movement of shaft  210  in the x direction. This is illustrated in  FIG. 3  which is a graph of displacement (x) as a function of applied force (F). In a similar fashion, clockwise rotation of control stick  220  will require sufficient pressure to exceed a force on shaft  210  in the opposite direction (−x) after which the displacement (−x) as a function of force (−F) will be substantially linear. 
       FIG. 4  is a functional representation of another passive, rerun-to-center control stick arrangement  400  wherein the restoring force is provided by leaf springs  402  and  404 . Leaf spring  402  is maintained in a first stressed position by fixed points  406 ,  408 , and  410 , and leaf spring  404  is maintained in a first stressed position by fixed points  412 ,  414 , and  416 . Control stick  418  is configured to be rotatable in clockwise and counterclockwise directions (as indicated by arrow  420 ) about a pivot  422 . Control stick  418  terminates with a transverse member  424  having a first leg  426  that rolls or slides along an inner surface of leaf spring  402 . Similarly, a second leg  428  has a terminus  427  that rolls or slides along an inner surface of leaf spring  404 . 
     Operationally, if control stick  418  is rotated in a clockwise direction, leaf spring  402  will be deflected off and away from fixed point  410  by leg  426 . The resulting energy stored in deflected leaf spring  402  provides the restoring force necessary to return the control stick  418  to its neutral position when it is released. Similarly, when control stick  418  is rotated in a counterclockwise direction, leaf spring  404  is deflected off and away from fixed point  416  by leg  428 . The energy stored in the deflected leaf spring is sufficient to provide a restoring force and return control stick  418  to its neutral position when released. 
     The principles described in connection with  FIGS. 1-4  may be utilized to provide a passive mode control stick assembly suitable for controlling aircraft roll and pitch. For example,  FIGS. 5 ,  6 , and  7  are partial isometric, first side, and second side views, respectfully, of a gimbal box assembly utilizing the concepts discussed above. Referring to these figures, a gimbal box assembly  500  includes an aircraft control stick assembly  502  that is rotatable about a first axis  504  (the roll axis) as indicated by arrows  506 , and a second axis  508  (the pitch axis) as indicated by arrows  510 . The gimbal box assembly comprises first and second pairs of leaf springs  512  and  514  of the type previously described in connection with  FIG. 4 . As can be seen, leaf springs  512  are anchored in the gimbal box housing as is shown at  516  in  FIG. 6 , and leaf springs  514  are anchored in an external housing  518  as is shown at  520 . 
     Leaf spring pairs  512  and  514  each provide a restoring force of the type described above. That is, at any given pitch and/or roll (other than null), the forces exerted on control stick  522  by spring pairs  512  and  514  will urge control stick  522  to its null position as described above. 
     As alluded to previously, it is contemplated that embodiments described herein provide a control stick assembly that may be operated in a passive mode utilizing a return-to-center restoring force, and in the active mode wherein the restoring force may be substantially eliminated or at least significantly reduced.  FIG. 8  illustrates such an arrangement wherein like elements are denoted with like reference numerals. 
     Once again, a control stick  418  is configured to be rotatable in clockwise and counterclockwise directions (as indicated by arrow  420 ) about a pivot  422 . Control stick  418  terminates with a transverse member  424  having a first leg  426  having a terminus  425  that rolls or slides along an inner surface of leaf spring  402 . Similarly, a second leg  428  has a terminus  427  that rolls or slides along an inner surface of leaf spring  404 . Leaf spring  402  is restrained, in part, by fixed points  406  and  410 , and leaf spring  404  is restrained, in part, by fixed pins  412  and  416 . 
     In the embodiment shown in  FIG. 8 , however, fixed pin  414  ( FIG. 4 ) has been replaced by eccentric cam assembly  802  having an off-center axis of rotation  806  and, if desired, a marker  808 . In the same manner, fixed pin  408  ( FIG. 4 ) has been replaced by eccentric cam assembly  804  having an off-center axis of rotation  810  and, if desired, a marker  812 . 
     For purposes of illustration only, cam assembly  802  is positioned to stress spring  404  and thus provide an adjustable restoring force to control stick  418  via leg  428  as previously described. Cam assembly  804 , in contrast, is positioned so as to permit spring  402  to remain in an unstressed condition; thus, leaf spring  402  will not provide a restoring force to control stick  418 . It should be clear that in practice, cam assemblies  802  and  804  will both be in either the restoring position or the non-restoring position. Thus, the system may be operating the passive mode (i.e. the restoring mode) or the active mode (i.e. the non-restoring mode). It should be clear that transitioning between these modes may be accomplished by adjusting cam assemblies  802  and  804 ; e.g. electronically or mechanically. It should also be noted that the restoring force may be adjusted by positioning the cams in an intermediate position. 
       FIGS. 9 and 10  illustrate yet another embodiment of a control stick assembly that may be operated in (1) a passive mode utilizing an adjustable return-to-center restoring force, and (2) in an active mode wherein the restoring force may be neutralized. Once again, like elements are denoted with like reference numerals. Control stick  418  includes a channel  900  therein that houses (1) a spring  902  and (2) a first end of a post  904  slidable mounted in channel  900 . The second end of post  904  is coupled to a roller-ball assembly  906  that may freely rotate in any direction. A first housing  908  (e.g. substantially circular in cross-section) includes (1) a lower portion  910  that houses a solenoid  912  and (2) an upper hollow section  914  including an upper, outwardly extending rim  916 . A second housing  918  is slidably received within the first housing  908  and includes a conical cavity  920  in an upper surface thereof that receives, to a greater or lesser extent as will be described below, roller-ball assembly  906 . Housing  918  likewise includes an upper, outwardly extending circular rim  922  that resides above rim  916  of housing  908 . 
     A resilient assembly (e.g. a spring)  924  is coupled between rims  916  and  922  and is chosen, along with spring assembly  902 , to assure that roller ball  906  remains in contact with the surface  926  of cavity  920  when the control stick assembly is being operated in the passive mode. In this manner, post  924 , and therefore control stick  418 ,| are biased toward center. That is, as control stick  418  is moved off center and upward on conical wall  926 , spring assembly  902  is compressed thus creating a restoring force that returns the control stick to the center position when the control stick  418  is released. Thus, an initial force |f| is required to initially move control stick  418  that corresponds to the preloaded force stored in spring assembly  902  after which the control stick  418  may be moved. This is represented by curve  930  in  FIG. 10  and corresponds to a passive mode of operation. 
     When active mode operation is desired, a control  932  coupled to power source  934  is activated. Power source  934  is coupled to a switch such as a solenoid  912  which, when activated, draws housing  918  downward overcoming the force of spring assembly  924  and to a position beyond the reach of conical surface  926 . In this mode (i.e. the active mode), spring assembly is no longer compressed and no restoring force is generated. Operation is then characterized by curve  936  in  FIG. 10  (i.e. zero restoring force). Thus, there has been provided a control stick assembly that may be operated in a passive mode utilizing a return-to-center restoring force, and in the active mode wherein the restoring force may be substantially eliminated or at least significantly reduced. 
       FIGS. 11 and 12  illustrate yet another embodiment of a control stick assembly that may be operated in (1) a passive mode utilizing an adjustable return-to-center restoring force, and (2) in an active mode wherein the restoring force may be neutralized. Once again, like elements are denoted with like reference numerals. In this embodiment, however, the restoring force may be adjusted continuously or in discreet increments between a predetermined minimum (including zero) and a predetermined maximum. For example, a cam assembly  936  (e.g. motorized or manually adjustable) is rotatable around axis  938  and is coupled to a lower portion of housing  918  at  940 . When cam  936  is positioned as shown at shown solid line, spring  902  is compressed, thus creating a restoring force that returns the control stick to the center position when the control stick  418  is released. Thus, an initial force |f| is required to initially move control stick  418  that corresponds to the preloaded force stored in spring assembly  902  after which the control stick  418  may be moved. This is represented by curve  942  in  FIG. 12  and corresponds to a passive mode of operation. As cam  936  is rotated to position  944 , spring  902  expands to an uncompressed state. There is no longer a restoring force, and the force characteristic is as shown by curve  946  in  FIG. 12 . As cam  936  is further rotated to position  948 , housing  918  is lowered further, and roller ball  906  disengages from the surface  926 . However, as control stick  418  pivots, roller ball may again engage cavity surface  926 . The force characteristic will then appear as curve  950  in  FIG. 12 , which indicates no force until roller ball  906  engages cavity surface at an upper region thereof. Of course, housing  918  may be lowered sufficiently such that roller ball  906  of control stick  418  does not engage surface of cavity  920  at all; i.e. the active mode. In  FIG. 13 , housing  918  is shown as being raised and lowered by a motor  952  and linkage assembly  954 , whereas in  FIG. 14 , a motor and screw assembly  954  raises and lowers housing  918 . 
       FIG. 15  illustrates yet another embodiment of a control stick assembly that may be operated in (1) a passive mode utilizing a return-to-center restoring force, and (2) in an active mode wherein the restoring force may be neutralized. Once again, like elements are denoted by like reference numerals. A spring  956  spring loads a roller ball  958  that is configured to engage and roll along the inner surface of a spherical cavity  960 . A linear screw drive  962  is configured to move cavity  960  into and out of abutment with the surface  964  as is indicated by arrow  966 . Moving surface  964  up and down changes the preload on spring  956 , which is now shown in the unloaded state. The radius of spherical surface  960  is less than the radius of the path of the unloaded roller ball  960  as it is caused to rotate about pivot  422 . Thus, cavity  960  may be lowered to a point where it does not engage surface  964 , and therefore no restoring force is created for operation in the active mode. As cavity  960  is raised, roller ball  958  will increasingly engage surface  964  creating an increasing restoring force as spring  956  is further compressed. 
     In view of the above, there has been provided several embodiments of a control stick assembly that may be continuously adjusted between first and second positions so as to operate (1) in the passive mode, utilizing a restoring force generating system, and (2) in the active mode by neutralizing the restoring force. 
     While at least one exemplary embodiment has been presented in the foregoing detailed description, it should be appreciated that a vast number of variations exist. For example, various biasing techniques and methodologies may be utilized to achieve the desired objectives. It should also be appreciated that the exemplary embodiment or embodiments described herein are not intended to limit the scope, applicability, or configuration of the claimed subject matter in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing the described embodiment or embodiments. It should be understood that various changes can be made in the function and arrangement of elements without departing from the scope defined by the claims, which includes known equivalents and foreseeable equivalents at the time of filing this patent application.