Abstract:
A mechanical architecture for a user interface system enables the use of the low cost commercial load cells. Force inputs to a user interface that is rotatable about two perpendicular axes are reacted in each axis by cantilevered load cells. Two load cells react the loads in each axis, thereby enabling the system to exhibit quadruple redundancy in the load cells.

Description:
TECHNICAL FIELD 
   The present invention generally relates to user interfaces and, more particularly to user interface system that includes a plurality of low-cost force sensing devices. 
   BACKGROUND 
   User interfaces that are used to translate human movements to machine movements are used in myriad industries. For example, some aircraft flight control systems include a user interface in the form of one or more control sticks, pedals, or other mechanisms. The flight control system, in response to input forces supplied to the user interface(s) from the pilot and/or co-pilot, controls the movements of various aircraft flight control surfaces. No matter the particular end-use system, the user interface preferably includes some type of mechanism to supply haptic feedback, through the user interface, to the user. 
   Many haptic feedback mechanisms are implemented using a force sensor as the primary input device to the feedback loop. In most instances, the force sensor drives some type of servo amplifier, which in turn drives a motor. The motor, which may be coupled to the user interface via a gearbox, supplies a feedback force to the user interface. Although these types of haptic feedback mechanisms are generally safe and reliable, they do suffer certain drawbacks. For example, the force sensor (or sensors) that are typically used are relatively high-fidelity force sensors, which increase overall system cost and complexity. Moreover, when redundancy and minimization of cross-axis coupling are employed to increase overall system reliability, the increased cost and complexity can be significant. 
   Hence, there is a need for a method of sensing the force in a user interface system that exhibits suitable fidelity, redundancy, and/or minimal cross-axis coupling, without significantly impacting overall system cost and complexity. The present invention addresses at least this need. 
   BRIEF SUMMARY 
   In one embodiment, and by way of example only, a user interface system includes a user interface and a plurality of load cells. The user interface is configured to rotate, from a null position, in first and second directions about a first rotational axis, and in first and second directions about a second rotational axis that is perpendicular to the first rotational axis. The user interface is adapted to receive an input force and, in response to the input force, to rotate, from the null position to a control position, about one or both of the first and second rotational axes. The plurality of load cells are coupled to, and extend in cantilevered manner from, the user interface. Each load cell is configured to at least selectively sense the input force supplied to the user interface. The plurality of load cells includes a first pair of load cells and a second pair of load cells. The first pair of load cells each extend along a respective first load cell axis that intersects the second rotational axis, and the second pair of load cells each extend along a respective second load cell axis that intersects the first rotational axis. The first pair of load cells are disposed such that when the user interface is rotated from the null position about the first rotational axis, the input force sensed by one of the first pair of load cells increases and the input force sensed by another of the first pair of load cells decreases. The second pair of load cells are disposed such that when the user interface is rotated from the null position about the second rotational axis, the input force sensed by one of the second pair of load cells increases and the input force sensed by another of the second pair of load cells decreases. 
   Other desirable features and characteristics of the user interface assembly will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention. 

   
     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 wherein: 
       FIG. 1  depicts a functional block diagram of an exemplary multi-axis user interface system; 
       FIG. 2  is a simplified top view representation of an exemplary user interface that may be used to implement the system of  FIG. 1 ; and 
       FIG. 3  depicts a partial cross section view of an exemplary embodiment of portions of a user interface system that may be used to implement the system of  FIG. 1 . 
   

   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. In this regard, although the following description may indicate an aircraft as an end-use environment, it will be appreciated that the invention may be used in any one of numerous environments, and with numerous products, in which a user interface may be included. 
   Turning now to  FIG. 1 , a functional block diagram of a multi-axis user interface system is depicted. The depicted system  100  includes a user interface  102 , a plurality of load cells  104  (e.g.,  104 - 1 ,  104 - 2 ,  104 - 3 , . . .  104 -N), a motor control  106 , and a plurality of motors  108  (e.g.  108 - 1 ,  108 - 2 ). The user interface  102  adapted to receive an input force and is movable from a null position  110  to any one of numerous control positions, along a random path, and with multiple degrees of freedom. More specifically, the user interface  102  is coupled to a gimbal assembly  105 , and as such is responsive to a supplied input force to rotate, from the null position  110  to a control position, about two perpendicular rotational axes—a first rotational axis  112  and a second rotational axis  114 . It will be appreciated that if the user interface  102  is implemented as an aircraft flight control user interface, such as a pilot (or co-pilot) inceptor, then the first and second rotational axes  112 ,  114  may be referred to as the pitch axis and the roll axis, respectively. No matter its specific end use, the user interface  102  is movable about the first axis  112  in a forward direction  116  and an aft direction  118 , and is movable about the second axis  114  in a port direction  122  and a starboard direction  124 . It will additionally be appreciated that the user interface  102  may be simultaneously rotated about the first and second rotational axes  112 ,  114  to move the user interface  102  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  110 . 
   The plurality of load cells  104  are each disposed adjacent the user interface  102 . The load cells  104 , particular embodiments of which are described in more detail further below, are preferably low cost commercial load cells that are operable to at least selectively sense the input force that a user is applying to the user interface  102 . In response, the load cells  104  supply force feedback signals representative of the sensed force to the motor control  106 . Preferably, the load cells  104  are spaced evenly around the user interface  102 . Although the number of load cells  104  may vary, in the depicted embodiment, and as shown most clearly in  FIG. 2 , the user interface assembly  100  includes four load cells  104  (e.g.,  104 - 1 ,  104 - 2 ,  104 - 3 ,  104 - 4 ), equally spaced 90-degress apart from each other. A first pair of the load cells  104 - 1 ,  104 - 2  selectively senses the input force when the user interface  102  is moved, fully or partially, in the forward and aft directions  116 ,  118 , and a second pair of the load cells  104 - 3 ,  104 - 4  selectively senses the input force when the user interface  102  is moved, fully or partially, in the port and starboard directions  122 ,  124 . No matter the specific number of load cells, the motor control  106 , upon receipt of at least the force feedback signals, supplies motor drive signals to one or both of the motors  108 - 1 ,  108 - 2 . 
   Returning once again to  FIG. 1 , the motors  108 - 1 ,  108 - 2 , which are each coupled to the user interface  102 , are each operable, upon receipt of motor drive signals, to supply a feedback force to the user interface  102 . It will be appreciated that, at least in some embodiments, non-illustrated gear sets may be disposed between each motor  108 - 1 ,  108 - 2  and the user interface  102 , if needed or desired. It will additionally be appreciated that, at least in some embodiments, the motor drive signals may be variable in magnitude, based on one or more user interface parameters and/or one or more external signals supplied to the motor control  106 . These parameters and/or external signals, if included, may vary depending, for example, on the actual end-use environment of the user interface system  100 . For example, if the user interface system  100  is used in a flight control system, the parameters may include the position of the user interface  102 , the slew rate of the user interface  102 , and the external signals may include various aircraft and control surface conditions, and the position of a non-illustrated co-pilot user interface. The user interface, in response to the feedback force supplied from the motors  108 - 1 ,  108 - 2 , supplies haptic feedback to a user via the user interface  102 . In a particular preferred embodiment, the motors  108 - 1 ,  108 - 2  are implemented as brushless DC motors. It will be appreciated, however, that other types of motors may also be used. 
   Turning now to  FIG. 3 , a partial cross section view of an exemplary embodiment of portions of the user interface system  100  are depicted. More specifically,  FIG. 3  depicts a portion of the user interface  102  and the first pair of the load cells  104 - 1 ,  104 - 2 . It is seen that the user interface  102 , at least in the depicted embodiment, includes a universal joint  302 , a base  304 , a grip  306 , a connector  308 , and a body  312 . The grip  306  is configured to be grasped by a hand of a user, and thus receive input force from the user. The connector  308  is coupled to the grip  306  and the body  312 . The body  312  is in turn coupled to the universal joint  302 . 
   The universal joint  302  is coupled between the base  304  and the body  312 , and provides for complete decoupling of cross-axis forces. For example, due to the presence of the universal joint  302 , if a force is applied to the grip  306  solely in a forward or aft direction (or solely in a port or starboard direction), then only two of the load cells  104 - 1 ,  104 - 2  (or  104 - 3 ,  104 - 4 ) will sense a change in force. If the universal joint  302  were not included, one or both of the other two load cells  104 - 3 ,  104 - 4  (or  104 - 1 ,  104 - 2 ) would sense a change in force, and supply one or more undesired signals. The universal joint  302  may be variously configured to implement this functionality. For example, it may be configured as a Cardon joint or any one of numerous other suitable devices. No matter its specific implementation, the universal joint  302  is coupled to the base  304 . In the depicted embodiment, the base  304  is adapted to be coupled to one or both motors  108  and to the gimbal assembly  105  (not depicted in  FIG. 3 ). 
   With continued reference to  FIG. 3 , it is seen that the load cells  104  are each coupled to the user interface  102  and each includes a beam  314  and a plurality of strain gages  316 . The beams  304  each include a fixed end  317  and a free end  318 . The beam fixed end  317 , as its name connotes, is coupled to the a first portion of the user interface  102 , and the beam free end  318  is disposed adjacent a second portion of the user interface  102 . It may thus be appreciated that the load cells  104  extend, in cantilevered manner, from the first portion of the user interface  102  toward the second portion of the user interface  102 . The first pair of load cells  104 - 1 ,  104 - 2  each extend, from its respective fixed end  317  to its respective free end  318 , along a respective first load cell axis  322 - 1 ,  322 - 2  that intersects the second rotational axis  114 . Similarly (although not depicted in  FIG. 3 ), the second pair of load cells  104 - 3 ,  104 - 4  each extend, from its respective fixed end  317  to its respective free end  318 , along a respective second load cell axis that intersects the first rotational axis  112 . In the depicted embodiment, the first load cell axes  322 - 1 ,  322 - 2  each intersect the second rotational axis  114  at a right angle, and the second load cell axes each intersect the first rotational axis  112  at a right angle. It will be appreciated, however, that first pair of load cells  104 - 1 ,  104 - 2  could alternatively be disposed so that the first load cell axes  322 - 1 ,  322 - 2  intersect the second rotational axis  114  at a non-right angle, and that second pair of load cells  104 - 3 ,  104 - 4  could alternatively be disposed so that the second load cell axes intersect the first rotational axis  112  at a non-right angle. It is noted that in the depicted embodiment the load cells  104  are each coupled to the base  304  and extend, in cantilever manner, toward the body  312 . It will nonetheless be appreciated that in an alternate embodiment, the load cells  104  may be coupled to the body  312  and extend, in cantilevered manner, toward the base  304 . 
   The strain gages  316 , as is generally known, are devices that exhibit variations in electrical resistance in response to deformation. The strain gages  316  are disposed on the beam  314 , and thus exhibit electrical resistance variations in response to deformation of the beam  314 . Preferably, the plurality of strain gages  316  on each beam  314  are configured to implement a Wheatstone bridge strain gage sensor. In some embodiments, where an added level of redundancy is needed or desired, the plurality of strain gages  316  on each beam  314  are configured to implement one or more pair of Wheatstone bridge strain gages sensors. 
   As  FIG. 3 , further depicts, each load cell  104  additionally includes a preload adjustment mechanism  326 . The preload adjustment mechanism  326  extends through the beam  314 , and engages at least a portion of the user interface  102 . In the depicted embodiment the preload adjustment mechanism  326  engages the body  312 . Preferably, the preload adjustment mechanism  326  is movable relative to the beam  314 , for example via mating threads on the beam  314  and the preload adjustment mechanism  326 . This configurations allows a preload on each load cell  104  to be an adjustably set. The particular preload value may vary, but in one particular embodiment, each load cell  104  is preferably preloaded, via its associated preload adjustment mechanism  326 , to approximately half of its maximum load value. Each adjustment mechanism  326  includes a rounded, or semispherical, section, that engages the body  312  at a contact point  328 . It is at this contact point  328  where the force is measured by each load cell  104 . 
   As noted above, each load cell  104  is configured to at least selectively sense the input force supplied to the user interface. More specifically, as may be seen with continued reference to  FIG. 3 , if a force is applied to the user interface  102  that moves the user interface  102  directly toward, for example, one of the first pair of load cells  104 - 1  ( 104 - 2 ), then that load cell  104 - 1  ( 104 - 2 ) will sense an increase in load. The other of the first pair of load cells  104 - 2  ( 104 - 1 ), however, will sense a corresponding decrease in load. If a force is applied to the user interface  102  that moves the user interface  102  in a direction between one of the first pair of load cells  104 - 1 ,  104 - 2  and one of the second pair of load cells  104 - 3 ,  104 - 4 , then those two load cells  104  will sense an increase in load, and the other two load cells will sense a corresponding decrease in load. 
   The total load at the contact point  328 , where the loads are sensed by each load cell  104 , may be determined using any one of numerous suitable techniques. For example, the total load may be determined from the square root of the sum of the squares of the positive load change measured by the two load cells  104  that sense increasing load. Alternatively, the total load may be determined by from the square root of the sum of the squares of the negative load change measured by the two load cells  104  that sense decreasing load. In yet another alternative embodiment, the motor control  106  could be a dual-channel control, and one of the first pair of load cells  104 - 1  ( 104 - 2 ) and one of the second pair of load cells  104 - 3  ( 104 - 4 ) could be used to supply force signals to one motor control channel, while the other one of the first pair of load cells  104 - 2  ( 104 - 1 ) and the other one of the second pair of load cells  104 - 4  ( 104 - 3 ) could be used to supply force signals to a second, redundant motor control channel. 
   While at least one exemplary embodiment has been presented in the foregoing detailed description of the invention, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment of the invention. It being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope of the invention as set forth in the appended claims.