Patent Publication Number: US-2002011815-A1

Title: Motor control systems and methods employing force sensing resistors

Description:
FIELD OF THE INVENTION  
       [0001] In a general sense, the invention is directed to systems and methods for controlling electric motors to achieve propulsion or steering of vehicles.  
       BACKGROUND OF THE INVENTION  
       [0002] Vehicles that employ electric motor driven wheels for propulsion and steering are well known, e.g., for use as golf carts, personal mobility scooters, or wheel chairs. The operator is allowed to either ride on the vehicle, or walk behind the vehicle, or both.  
       [0003] Vehicles of this type often encounter uneven terrain, which complicates the task of maintaining uniform speed and steering control. For example, when traveling downhill, the vehicles are prone to suddenly pick up speed due to pull of gravity. Sensors are often employed to monitor the actual speed of the wheel in comparison to the motor speed command, to detect an over speed condition and cause automatic braking to slow the vehicle. These sensors, and the microprocessor-based devices associated with them, add to the overall complexity and expense of the vehicle.  
       SUMMARY OF THE INVENTION  
       [0004] The invention provides systems and methods that make it possible to control the propulsion and/or speed of electrically powered vehicles in a straight forward, inexpensive, and ergonomic manner.  
       [0005] One aspect of the invention provides a control system for an electric motor. The system comprises a controller operating to generate motor control signals in response to a command input. The system also comprises an interface including an actuator arranged for manipulation by an operator. The interface further includes a circuit coupled to the controller for generating the command input. The circuit includes at least one force sensing resistor coupled to the actuator, to vary the command input in response to manipulation of the actuator.  
       [0006] Another aspect of the invention provides a throttle interface for a vehicle. The throttle interface comprises a handle capable of being hand-held by an operator and an articulated mount, which is coupled to the handle for pivoting in response to force applied by the operator&#39;s hand. The throttle interface further includes a circuit for generating electrical command signals. The circuit includes a force sensing element, to which the articulated mount applies pressure in response to pivoting of the articulated mount. The force sensing element operates to vary the command signals in response to applied pressure.  
       [0007] In one embodiment, the force sensing element includes a force sensing resistor.  
       [0008] Another aspect of the invention provides a control system for an electric motor. The control system comprises an interface that includes an actuator arranged for manipulation by an operator. The interface also includes a circuit for generating command inputs. The circuit includes at least one force sensing element to which pressure is applied in response to manipulation of the actuator. The force sensing element operates to generate a first command signal in response to a first range of applied pressures and to generate a second command signal in response to a second range of applied pressures greater than the applied pressures in the first range. The control system also includes a controller that operates to generate a braking signal for the motor in response to the first command signal and to generate a drive signal for the motor in response to the second command signal.  
       [0009] In one embodiment, the force sensing element comprises a force sensing resistor.  
       [0010] In one embodiment, the actuator comprises a generally horizontal handle oriented to be hand-held by an operator when in a standing position.  
       [0011] In one embodiment, the braking signal conditions the motor for regenerative braking.  
       [0012] Features and advantages of the inventions are set forth in the following Description and Drawings, as well as in the appended Claims.  
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0013]FIG. 1 is a schematic view of a motor control circuit for a vehicle that includes at least one force sensing resistor to generate a voltage input to a motor controller;  
     [0014]FIG. 2 is a schematic view of a voltage generating circuit utilizing a force sensing resistor, which can be used in association with the motor control circuit shown in FIG. 1;  
     [0015]FIG. 3 is a schematic view of a voltage generating circuit utilizing two force sensing resistors, which can be used in association with the motor control circuit shown in FIG. 1;  
     [0016]FIG. 4 is a perspective view of one possible embodiment of a throttle interface, implemented as a joystick-type controller, that can form a part of the voltage generating circuit shown in FIG. 3;  
     [0017]FIG. 5 is a perspective view of another possible embodiment of a throttle interface, implemented as a touch membrane key pad, that can form a part of the voltage generating circuit shown in FIG. 3;  
     [0018]FIG. 6 is a top view of another possible embodiment of a throttle interface, implemented as dual flex arm handle bar assembly, that can form a part of the voltage generating circuit shown in FIG. 3;  
     [0019]FIG. 7 is a perspective view of another possible embodiment of a throttle interface, implemented as rotating tiller grip, that can form a part of the voltage generating circuit shown in FIG. 3;  
     [0020]FIG. 8 is a schematic view of a motor control circuit for two motors, which includes several force sensing resistors to generate a voltage input to a motor controller and makes possible both propulsion and steering control for a multiple wheel vehicle;  
     [0021]FIG. 9 is a schematic view of a voltage generating circuit utilizing several force sensing resistor, which can be used in association with the motor control circuit shown in FIG. 8;  
     [0022]FIG. 10 is a schematic view of one possible embodiment of a throttle interface, implemented as a joystick-type controller, that can form a part of the voltage generating circuit shown in FIG. 9;  
     [0023]FIG. 11 is a perspective elevation view of a walk-behind, multiple wheel cart which incorporates a motor control circuit as shown in FIG. 8, and which includes a throttle interface for the motor control circuit realized as a horizontal handle intended to be grasped by the operator walking behind the cart;  
     [0024]FIG. 12 is an exploded perspective view of the handle embodiment of the throttle interface shown in FIG. 11;  
     [0025]FIG. 13 is a top assembled view of the handle embodiment of the throttle interface shown in FIG. 11;  
     [0026]FIG. 14 is a perspective elevation view of the walk-behind, multiple wheel cart shown in FIG. 11, with equipment that enable hands-off operation;  
     [0027]FIG. 15 is a schematic view of a brake pedal assembly that includes a force sensing resistor to enable an electric regenerative braking effect, as well as a pivot link that enables a mechanical braking effect; and  
     [0028]FIG. 16 is a schematic view of a dual function motor control pedal that incorporates a potentiometer.  
     [0029] The invention may be embodied in several forms without departing from its spirit or essential characteristics. The scope of the invention is defined in the appended claims, rather than in the specific description preceding them. All embodiments that fall within the meaning and range of equivalency of the claims are therefore intended to be embraced by the claims. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     [0030]FIG. 1 schematically shows a control circuit  10  for a vehicle  12  or cart, which is driven by an electric motor  14 . The motor  14  can comprise, e.g., a direct current, shunt type electric motor with independently excited armature and field windings. The motor  14  is typically powered by a rechargeable battery  16  carried by the vehicle  12 .  
     [0031] The style and use of the vehicle  12  can vary. For example, the vehicle  12  can comprise a personal mobility scooter, or a golf cart of either a walk-behind or a riding category, or a wheel chair.  
     [0032] The vehicle  12  is supported on wheels  18  for movement on the ground. The motor  14  is conventionally coupled to the wheel  18  by a drive shaft  20 . Typically, the vehicle  12  includes at least two motor-driven wheels  18 . For purposes of illustration, FIG. 1 shows only one wheel  18 .  
     [0033] The control circuit  10  includes a motor driver device  22 . The device  22  can comprise, e.g., a conventional H-bridge/driver circuit. In this arrangement, the device  22  comprises a configuration of power switching devices (typically, transistors). The device  22  responds to prescribed control signals to apply voltage pulses to the armature and to vary the current in the field windings of the motor  14 , which cause the motor  14  to rotate the wheel at the rate and in the direction desired by an operator.  
     [0034] The control circuit  10  also includes a microprocessor-based controller  24 . The controller  24  supplies prescribed control signals to the motor driver device  22  according to rules programmed in the controller  24 . The controller  24 , in turn, responds to one or more analog voltage inputs, which, according to the programmed rules, cause the controller  24  to generate the control signals.  
     [0035] The control circuit  10  further includes a throttle interface  26 . The throttle interface  26  generates the analog voltage inputs for the controller  24 . The throttle interface  26  includes a manual actuator  28  that the operator manipulates in a predetermined manner. Manipulation of the actuator  28  generates the voltage inputs, which dictate desired speed and direction commands for the vehicle  12 .  
     [0036] The throttle interface  26  includes a voltage generating circuit VG coupled to the battery  16 , which generates analog voltage inputs for the controller  24 . According to one aspect of the invention, the circuit VG includes at least one force sensing resistor FSR coupled to the actuator  28 . The force sensing resistors can be commercially purchased, e.g., from Interlink Electronics.  
     [0037] The particular electrical configuration for the voltage generating circuit VG can vary. As represented in FIG. 2, the circuit VG comprises a typical parallel electrical circuit that includes fixed resistors R and the force sensing resistor FSR.  
     [0038] The resistor FSR possesses a resistance that varies in proportion to applied pressure. Variation in the resistance of the resistor FSR, in turn, varies the magnitude of the voltage inputs generated by the circuit VG. In the circuit VG shown in FIG. 2, a reduction in the resistance of the resistor FSR increases the magnitude of the voltage input, while an increase in the resistance of the resistor FSR decreases the magnitude of the voltage input.  
     [0039] The actuator  28  is linked to the resistor FSR to allow the operator to apply differential pressure to the resistor FSR. In the circuit VG shown in FIG. 2, incremental increases in pressure on the resistor FSR results in incremental decreases in resistance, and thereby generates incremental increases in voltage inputs by the circuit, and vice versa.  
     [0040] The rules programmed in the controller  24  prescribe the generation of different control signals to the motor driver device  22  in response to different analog voltage inputs. The rules programmed in the controller  24  can, or course, vary. For example, the rules can prescribe a control signal that causes the motor  14  to rotate the wheel  18  in a set direction in response to a threshold voltage input above analog zero, to thereby begin propelling the vehicle in a prescribed direction when a threshold pressure is applied to the resistor FSR by the actuator  28 . The vehicle can be propelled forward or backward, depending upon the direction of wheel rotation prescribed by the control signal. In this arrangement, further incremental increases in the magnitude of the voltage input (by incrementally applying more pressure to the resistor FSR via the actuator  28 ) can result in the generation of control signals that incrementally increase the rate of rotation, to incrementally increase the vehicle speed.  
     [0041] The throttle interface  26  can take different forms. For example, the interface  26  can comprise a joystick-type controller, in which displacement of the joystick in a prescribed direction applies differential pressure on the resistor FSR. As another example, the interface  26  can comprise a membrane key pad, in which finger or thumb pressure applied to a membrane button applies differential pressure on the resistor FSR. Other embodiments for the throttle interface  26  will be described later.  
     [0042] Each motor driven wheel  18  of the vehicle  12  can be coupled to a control circuit  10  of the type shown in FIGS. 1 and 2. The direction and rate of rotation of each wheel  12  can thereby be independently controlled by a force sensing resistor FSR. Pressure can be selectively applied to each resistor FSR by separate actuators  28  or by a common actuator  28 . Alternatively, a control circuit  10  of the type shown in FIGS. 1 and 2 can drive a single motor that is coupled by a differential to two wheels  18 .  
     [0043] Furthermore, more than one force sensing resistor FSR can be used to control a single motor. The motor can be linked to a single wheel or linked to two wheels by a differential.  
     [0044] A representative electrical configuration for this embodiment is shown in FIG. 3. As there shown, the throttle interface  26  includes a voltage generating circuit VG for the controller  24  having two force sensing resistor FSR 1  and FSR 2 . In this arrangement, the resistors FSR 1  and FSR 2  can be coupled to the same or different actuators  28  to affect differential pressure application.  
     [0045] In the electrical arrangement shown in FIG. 3, pressure applied to the resistor FSR 1  increases the voltage input to the controller  24 , while pressure applied to the resistor FSR 2  decreases the voltage input to the controller  24 . The rules programmed in the controller  24  prescribe the generation of different control signals to the motor driver device  22  in response to the magnitude of the analog voltage inputs. For example, pressure differentially applied to the resistor FSR 1  (increasing the voltage input) can serve, through the controller  24 , to drive the wheel  18  in a forward direction at different speeds, while pressure differentially applied to the resistor FSR 2  (decreasing the voltage input) can serve, through the controller  24 , to drive the wheel  18  in a reverse direction at different speeds. In this embodiment, a foot-actuated brake pedal can be provided, which can activate a mechanical braking action (through a mechanical link) or a regenerative braking action within the motor (through an electrical link), or both. For example, the brake pedal can be linked to a potentiometer, which varies the resistance of a voltage generating circuit linked to the controller, to vary the regenerative braking effect with increased depression of the brake pedal. Alternatively, as will be described in greater detail later, the brake pedal can be linked to a force sensing resistor to achieve a comparable variable regenerative braking effect.  
     [0046] As another example, pressure differentially applied to the resistor FSR 1  can serve, through the controller  24 , to drive the wheel  18  in a forward direction at different speeds, while pressure differentially applied to the resistor FSR 2  can serve, through the controller  24 , to apply a braking force to the wheel  18 , either by means of an external mechanical brake  32  or by means of electrical regenerative braking generated within the motor  14  itself.  
     [0047] The throttle interface  26  shown in FIG. 3 can also take different forms. For example, the interface  26  can comprise a joystick-type controller  34  (see FIG. 4), in which displacement of the joystick in a forward direction applies differential pressure on the resistor FSR 1  and displacement of the joystick in a rearward direction applies differential pressure upon the resistor FSR 2 . As another example, the interface  26  can comprise a membrane key pad  36  (see FIG. 5), in which finger or thumb pressure applied to a right hand membrane button  38  applies differential pressure on the resistor FSR 1  and finger or thumb pressure applied to a left hand membrane button  40  applies differential pressure on the resistor FSR 2 . In FIG. 5, the key pad is shown as being carried by a steering wheel  42  for the vehicle.  
     [0048] In another embodiment (see FIG. 6), the throttle interface  26  can include right and left horizontal flex arms  44  and  46 , which are mounted on a console  140  behind which the operator sits or stands. In use, the operator grasps the ends of each flex arm  44  and  46 , as one holds the handle bars of a bicycle.  
     [0049] Each flex arm  44  and  46  includes a plunger  48  aligned with a force sensing resistor FSR 1  and FSR 2 . Each flex arm  44  and  46  is normally biased to hold the plunger  48  out of contact with the corresponding resistor FSR 1  and FSR 2 . Flexure of a given arm  44  and  26  moves the respective plunger  48  into a pressure applying relationship with the corresponding resistor FSR 1  or FSR 2 .  
     [0050] As shown in FIG. 7, the throttle interface  26  can include a tiller  72  with a grip  74  that twists about the free end of the tiller  74 . As FIG. 7 shows, the tiller  72  carries a first force sensing resistor FSR 1  to which pressure is applied when the tiller grip  74  is twisted in one direction. The tiller  72  also carries a second force sensing resistor FSR 2  to which pressure is applied when the tiller grip  74  is twisted in the opposite direction. Twisting the tiller grip  74  can therefore impart, e.g., forward and rearward movement. Alternatively, twisting the tiller grip  74  in one direction can impart accelerated forward movement while twisting the tiller grip  74  in the opposite direction can impart regenerative or mechanical braking. In this arrangement, the tiller  72  itself can be mechanically linked to a steering mechanism, so that transverse movement of the tiller  72  steers the vehicle.  
     [0051] It should be appreciated that two function control as above described can also be implemented using a potentiometer, without employing force sensing resistors. As shown in FIG. 16, a centrally pivoted control pedal  132  is linked to a potentiometer  134 . The potentiometer  132  forms a part of voltage generating circuit  138  for a controller  136 . Force directed on the front of the control pedal  132  (arrow A in FIG. 16) seesaws the pedal  132  in a first direction, which operates the potentiometer  134  to increase the voltage input to the controller  24 . Force directed upon the rear of the control pedal  132  (arrow B in FIG. 16) see-saws the pedal  132  in a second direction, which operates the potentiometer  134  to decrease the voltage input to the controller  24 .  
     [0052] As before explained, the rules programmed in the controller  24  can serve to drive the wheel  18  in different ways depending upon the magnitude of the voltage inputs. For example, the controller  24  can drive the wheel  18  in a forward direction at different speeds in response to increased voltage inputs (with the pedal  132  swung in direction of arrow A), as well as to drive the wheel  18  in a reverse direction at different speeds (or to apply a regenerative braking effect) in response to decreased voltage inputs (with the pedal  132  swung in the direction of arrow B).  
     [0053] The use of force sensing resistors in a voltage generating circuit VG coupled in association with a preprogrammed motor controller also makes possible control of both propulsion and steering in multiple wheel vehicles.  
     [0054] For example, FIG. 8 shows a three-wheel vehicle  50  including an embodiment of a throttle interface  52  that also embodies features of the invention. The vehicle  50  comprises a swivel-mounted front wheel  54 , which is idle and not power driven. The vehicle  50  also includes left and right rear wheels  56 L and  56 R, which are each independently powered by a direct current motor  58 L and  58 R. The motors  58 L and  58 R are coupled to a motor control circuit  60  (see FIG. 9).  
     [0055] As FIG. 9 shows, the throttle interface  52  includes four voltage generating circuits VG 1  to VG 4 , each with a force sensing resistor FSR 1  to FSR 4 . As shown in FIG. 10, the resistors FSR 1  to FSR 4  are actuated by a single articulated actuator  62 , although multiple actuators can be employed. The pre-programmed rules of the controller  64  independently respond to analog voltage inputs from the circuits VG 1  and VG 3  to generate command signals to the motor driver  66 R of the right rear wheel  56 R. The pre-programmed rules of the controller  64  independently respond to analog voltage inputs from the circuits VG 2  and VG 4  to generate command signals to the motor driver  66 L of the left rear wheel  56 L.  
     [0056] As FIG. 10 shows, the actuator  62  is biased toward a neutral position N. In this position, force is not applied to any one of the resistors FSR 1  to FSR 4 , and the voltage inputs of each circuit VG 1  to VG 4  reflect zero analog voltage. As a result, no motor command signals are generated, and the vehicle  50  is at rest. Mechanical brakes  68 L and  68 R can be provided, which the controller  64  enables to lock the rear wheels  56 L and  56 R when the actuator  62  occupies the neutral position N.  
     [0057] As FIG. 10 also shows, the actuator  62  is articulated and can be moved by the operator from the neutral position N in a range of direct forward and rearward directions A and D, oblique forward directions B and F, and oblique rearward directions C and E. Movement of the actuator  62  applies differential forces to the resistors FSR 1 , FSR 2 , FSR 3 , and FSR 4 , thereby creating an array of differential voltage inputs to the microprocessor-based controller  64 . The controller  64  provides according to its preprogrammed rules different command signals to the motor drivers  66 L and  66 R based upon the different voltage inputs of the circuits VG 1  to VG 4 . In this way, the motors  58 L and  58 R of the right and left rear wheels  56 L and  56 R can be individually controlled to achieve forward and rearward travel as well as steering.  
     [0058] In this arrangement, the application by the operator of direct forward force to the actuator  62  in the direction A, applies equal pressure upon FSR 1  and FSR 2  and no pressure upon FSR 3  and FSR 4 . Equal voltage inputs based upon FSR 1  and FSR 2  and zero voltage inputs based upon FSR 3  and FSR 4  result. In response, the microprocessor-based controller  64  disengages the mechanical brakes  68 L and  68 R (if present) and also conditions the motor drivers  66 L and  66 R to rotate both rear wheels  56 L and  56 R in a forward direction and at essentially the same rate of rotation. As a result, the vehicle  50  moves forward and in an essentially straight path. As the distance in direction A increases from the neutral position N, progressively greater pressure is applied equally upon FSR 1  and FSR 2 . As the equal voltage inputs based upon FSR 1  and FSR 2  increase, the rate of equal forward rotation of the wheels  56 L and  56 R increases, thereby increasing the forward speed of the vehicle  50 .  
     [0059] Movement of the actuator  62  by the operator in the forward oblique direction B applies greater pressure upon FSR 1  than FSR 2 , but still continues to apply no pressure upon FSR 3  and FSR 4 . The microprocessor-based controller  64  receives a voltage input based upon FSR 1  that is greater in magnitude than the voltage input based upon FSR 2 . In response to the different voltage inputs, the microprocessor-based controller  64  conditions the motor drivers  66 L and  66 R to rotate the right rear wheel  56 R in a forward direction at a rate of rotation greater than the forward rate of the left rear wheel  56 L. As a result, the vehicle  50  moves forward and turns to the left. As the distance in oblique direction B increases from the neutral position N, progressively greater differentially pressure is applied upon FSR 1 , increasing the left turn rate and reducing the diameter of turning circle.  
     [0060] Movement of the actuator  62  by the operator in the forward oblique direction F applies greater pressure upon FSR 2  than FSR 1 . The microprocessor-based controller  64  receives a voltage input based upon FSR 2  that is greater in magnitude than the voltage input based upon FSR 1 . In response to the different voltage inputs, the microprocessor-based controller  64  conditions the motor drivers  66 L and  66 R to rotate the left rear wheel  56 L in a forward direction at a rate of rotation greater than the forward rate of the right rear wheel  56 R. As a result, the vehicle  50  moves forward and turns to the right. As the distance in oblique direction F increases from the neutral position N, progressively greater differentially pressure is applied upon FSR 2 , increasing the right turn rate and reducing the diameter of turning circle.  
     [0061] Also in this arrangement, applying direct rearward force by the operator to the actuator  62  in the direction D, applies equal pressure upon FSR 3  and FSR 4  and no pressure upon FSR 1  and FSR 2 . Zero voltage inputs based upon FSR 1  and FSR 2  and equal voltage inputs based upon FSR 3  and FSR 4  result. In response, the microprocessor-based controller  64  disengages the mechanical brakes  68 L and  68 R (if present) and also conditions the motor drivers  66 L and  66 R to rotate the rear wheels  56 L and  56 R in a rearward direction and at essentially the same rate of rotation. As a result, the vehicle  50  moves backward and in an essentially straight path. As the distance in direction D increases from the neutral position N, progressively greater pressure is applied equally upon FSR 3  and FSR 4 . The rate of equal rearward rotation of the wheels  56 L and  56 R increases, thereby increasing the rearward speed of the vehicle.  
     [0062] Movement of the actuator  62  by the operator in the rearward oblique direction C applies greater pressure upon FSR 3  than FSR 4 . The microprocessor-based controller  64  receives a voltage input based upon FSR 3  that is greater in magnitude than the voltage input based upon FSR 4 . In response to the different voltage inputs, the microprocessor-based controller  64  conditions the motor drivers  66 L and  66 R to rotate the right rear wheel  56 R in a rearward direction at a rate of rotation greater than the rearward rate of the left rear wheel  56 L. As a result, the vehicle  50  moves backward and swings to the right. As the distance in oblique direction C increases from the neutral position N, progressively greater differentially pressure is applied upon FSR 3 , increasing the backward right turn rate and reducing the diameter of turning circle.  
     [0063] Movement of the actuator  62  by the operator in the rearward oblique direction E applies greater pressure upon FSR 4  than FSR 3 . The microprocessor-based controller  64  receives a voltage input based upon FSR 4  that is greater in magnitude than the voltage input based upon FSR 3 . In response to the different voltage inputs, the microprocessor-based controller  64  conditions the motor drivers  66 L and  66 R to rotate the left rear wheel in a rearward direction at a rate of rotation greater than the rearward rate of the right rear wheel. As a result, the vehicle  50  moves backward and swings to the left. As the distance in oblique direction E increases from the neutral position N, progressively greater differentially pressure is applied upon FSR 4 , increasing the backward left turn rate and reducing the diameter of turning circle.  
     [0064] Alternatively, a single direct current drive motor can be coupled by a differential gear arrangement to the two rear wheels. In this arrangement, an additional direct current motor is provided for steering. A drive motor arrangement that can be use is shown, e.g., in Gaffney U.S. Pat. No. 5,853,346, which is incorporated herein by reference.  
     [0065] As shown in FIG. 10, the throttle interface  52  can be implemented as an articulated joystick-like controller  70  with four resistors FSR 1  to FSR 4 . It should be appreciated that a joystick-like controller  70  can include more than four force sensing resistors or less than four force sensing resistors, depending upon the control functions required. For example, a joystick-like controller  70  having only fore and aft force sensing resistors can be used to provide forward or rearward travel capabilities. In this arrangement, mechanical linkages can be provided to affect steering, or alternatively, a second joystick-like controller can be provided with right and left force sensing resistors that provide selective regenerative braking action to the motors to affect steering.  
     [0066]FIG. 11 shows a throttle interface  76  employing force sensing resistors that achieve ergonomic control of both propulsion and steering in a multiple wheel vehicle. The vehicle takes the form of a three wheel, walk-behind cart  78  for carrying golf bags  142  and the like. The cart  78  includes motor driven left and right rear wheels  80 L and  80 R and a single, swivelled front idle wheel  82 .  
     [0067] The throttle interface  76  includes a horizontally extending handle  84 , which is presented at generally chest to shoulder height to the operator. The handle  84  is intended to be grasped by the operator while walking behind the cart  78 . The operator manipulates the handle  84  to provide both speed and direction commands to the motor driven left and right rear wheels  80 L and  80 R.  
     [0068] As FIGS. 12 and 13 show, the throttle interface  76  includes a gimbal plate  86  that is coupled by a bracket  88  to the handle  84 . The gimbal plate  86  is coupled by a central spring washer assembly  90  to a sensor plate  92 . The sensor plate  92  is mounted upon spacers  94  to a support board  96 .  
     [0069] The gimbal plate  86  rocks on the spring washer assembly  90  relative to the sensor plate  92  in response to forces applied by the operator to the handle  84 . Upward and downward forces applied to the handle  84  rocks the top and bottom portions of the gimbal plate  86  toward and away from the facing top and bottom portions of the sensor plate  92 . Leftward and rightward forces applied to the handle  84  rocks the left and right side portions of the gimbal plate  86  toward the facing left and right side portions of the sensor plate  92 .  
     [0070] Four force sensing resistors FSR 1  to FSR 4  are carried at the four corners of the sensor plate  92 . Looking forward in the direction of the handle  84 , the resistor FSR 1  is located at the bottom right hand corner of the sensor plate  92 ; the resistor FSR 2  is located at the bottom left hand corner of the sensor plate  92 ; the resistor FSR 3  is located at the top right hand corner of the sensor plate  92 ; and the resistor FSR 4  is located at the top left hand corner of the sensor plate  92 .  
     [0071] The force sensing resistors FSR 1  to FSR 4  are each electrically coupled to an electrical connector  98  on the support board  96 . An electrical cable  100  attaches to the connector  98 , to electrically couple each of the FSR 1  to FSR 4  to a voltage generating circuit VG 1  to VG 4  of the type shown in FIG. 9.  
     [0072] Four corresponding rubber bumpers RB 1  to RB 4  are carried at the four corners of the gimbal plate  86 . As the gimbal plate  86  rocks relative to the sensor plate  92 , one or more of the bumpers RB 1  to RB 4  apply pressure to the corresponding force sensing resistors FSR 1  to FSR 4 . The orientation and magnitude of the pressure on the resistors FSR 1  to FSR 4  depends upon the direction and magnitude of the force applied to the handle  84 . In this way, selective manipulation of the handle by the operator changes the resistance of one or more of the resistors FSR 1  to FSR 4  and the magnitude of analog voltages generated by the corresponding circuit.  
     [0073] The spring washer assembly  90  orients the gimbal plate  86  in a neutral position N in the absence of force applied by the operator to the handle  84 . In the neutral position, no contact between the bumpers RB 1  to RB 4  and any resistor FSR 1  to FSR 4  occurs. This condition corresponds to neutral position N in FIG. 10, as already described. In this position, the voltage inputs of each circuit VG 1  to VG 4  to the microprocessor-based controller  64  are essentially zero. As a result, the cart  78  is at rest. As before described, magnetic brakes coupled to the microprocessor-based controller  64  can be provided, which lock the rear wheels  80 L and  80 R in the absence of force to the handle  84 .  
     [0074] When the operator applies a direct downward pressure to the handle  84 , the rubber bumpers RB 1  and RB 2  apply equal pressure, respectively, to resistors FSR 1  and FSR 2 , while the rubber bumpers RB 3  and RB 4  apply no pressure, respectively, to resistors FSR 3  and FSR 4  . This condition corresponds to the direction A condition shown in FIG. 10. Equal voltage inputs from VG 1  and VG 2  and zero voltage inputs from VG 3  and VG 4  cause the microprocessor-based controller  64  to disengage the mechanical brakes (if present) and also condition the motor drivers  66 L and  66 R to rotate both rear wheels in a forward direction and at essentially the same rate of rotation. As a result, the cart  78  advances forward in front of the operator in an essentially straight path.  
     [0075] Walking behind the cart  78 , downward force applied by the operator to the handle  84  will fluctuate naturally in relation to the relative speed relationship between the cart  78  and the operator. If the cart  78  travels slower than the operator, the cart  78  will draw nearer to the operator, and downward pressure on the handle  84  will naturally increase, to speed up the cart  78 . If the cart  78  travels faster than the operator, the cart  78  will draw away from the operator, and downward pressure on the handle  84  will naturally decrease, to slow down the cart  78 . The downward deflection of the handle  84  will tend to stabilize at an equilibrium position, in which the forward speed of the cart  78  matches the walking speed of the operator, during both uphill and downhill travel.  
     [0076] In this arrangement, complicated and expensive motor RPM sensors, wheel speed sensors, and the like are not required to electronically provide feedback information that, when processed by the controller  64 , keep the cart  78  and operator together. The pressure of the handle  84  in the hand of the operator provides tactile feedback, which the operator&#39;s brain processes to dictate natural voluntary muscle responses, which keep the operator and the cart  78  moving in synchrony.  
     [0077] To further enhance the ergonomic interaction between the operator and the cart  78 , particularly when traveling downhill, the controller  64  can be programmed to include a regenerative braking regime when downward pressure applied to the handle  84  generates analog voltage inputs that lay at or below an established minimum threshold value. The regenerative braking regime automatically slows cart speed when relatively low downward pressure is being applied to the handle  84 , as would occur, e.g., as cart speed increases due to gravity on a downhill slope. The regenerative braking regime counteracts the increase in speed due to gravity in such a situation, thereby preventing an over speed condition during travel upon downhill terrain, so that the cart will not tend to pull abruptly away from the operator. In this arrangement, controller  64  terminates the regenerative braking regime when downward pressure above the minimum threshold value is applied to the handle  84 , and instead commands the cart  78  to accelerate with increasing downward handle pressure. In this way, the cart  78  keeps pace with the operator when traveling on generally flat or uphill terrain.  
     [0078] While still applying a downward pressure, the operator can apply either a right or left oblique force to the handle  84 . The rubber bumpers RB 1  and RB 2  no longer apply equal pressure, respectively, to resistors FSR 1  and FSR 2 , and resistor toward which the oblique force is applied (FSR 1  for a right oblique force, and FSR 2  for a left oblique force) will experience a greater differential force. The oblique right condition corresponds to the direction B condition shown in FIG. 10, and the oblique left condition corresponds to the direction F condition in FIG. 10.  
     [0079] When resistor FSR 1  experiences a greater differential force than resistor FSR 2 , the voltage of VG 1  will be greater than the voltage of VG 2 . As a result, the right rear wheel rotates in a forward direction at a rate of rotation greater than the forward rate of the left rear wheel. The cart  78 , moving forward, turns to the left. As the force differential increases, the left turn rate increases and the diameter of turning circle is reduced.  
     [0080] Likewise, when resistor FSR 2  experiences a greater differential force than resistor FSR 1 , the voltage of VG 2  will be greater than the voltage of VG 1 . As a result, the left rear wheel rotates in a forward direction at a rate of rotation greater than the forward rate of the right rear wheel. The cart  78 , moving forward, turns to the right. As the force differential increases, the right turn rate increases and the diameter of turning circle is reduced.  
     [0081] From behind the cart  78 , the application of a direct upward lifting force to the handle  84  causes the rubber bumpers RB 3  and RB 4  to apply equal pressure, respectively, to resistors FSR 3  and FSR 4 , while the rubber bumpers RB 1  and RB 2  apply no pressure, respectively, to resistors FSR 1  and FSR 2  . This condition corresponds to the direction D condition shown in FIG. 10. Equal voltage inputs from VG 3  and VG 4  and zero voltage inputs from VG 1  and VG 2  cause the microprocessor-based controller  64  to disengage the mechanical brakes (if present) and also condition the motor drivers to rotate both rear wheels in a rearward direction and at essentially the same rate of rotation. As a result, the cart  78  backs up in an essentially straight path.  
     [0082] While still applying an upward lifting pressure, the operator can apply either a right or left oblique force to the handle  84 . The rubber bumpers RB 3  and RB 4  no longer apply equal pressure, respectively, to resistors FSR 3  and FSR 4 , and resistor toward which the oblique force is applied (FSR 3  for a right oblique force, and FSR 4  for a left oblique force) will experience a greater differential force. The oblique right condition corresponds to the direction C condition shown in FIG. 10, and the oblique left condition corresponds to the direction E condition in FIG. 10.  
     [0083] When resistor FSR 3  experiences a greater differential force than resistor FSR 4 , the voltage of VG 3  will be greater than the voltage of VG 4 . As a result, the right rear wheel rotates in a rearward direction at a rate of rotation greater than the rearward rate of the left rear wheel. The cart  78 , moving backward, swings to the right. As the force differential increases, the right swing rate increases and the diameter of turning circle is reduced.  
     [0084] Likewise, when resistor FSR 4  experiences a greater differential force than resistor FSR 3 , the voltage of VG 4  will be greater than the voltage of VG 3 . As a result, the left rear wheel rotates in a rearward direction at a rate of rotation greater than the rearward rate of the right rear wheel. The cart  78 , moving backward, swings to the left. As the force differential increases, the left swing rate increases and the diameter of turning circle is reduced.  
     [0085] When pressure applied to the handle  84  is released, the controller  64  can also be programmed to enter a ramp-down regime. During the ramp-down regime, the controller  64  commands a period of regenerative braking, which can be either linear or progressive over time. If mechanical brakes are present, the controller  64  can also activate the mechanical brakes at the end of the ramp-down regime.  
     [0086] In the illustrated embodiment (see FIGS. 12 and 13), the gimbal plate  86  holds a potentiometer  102 . The potentiometer  102  is electrically coupled to the resistors FSR 1  to FSR 4 . Adjustment of the potentiometer  102  adjusts the rate at which resistance of the resistors FSR 1  to FSR 4  changes in proportion to the magnitude of force applied. The potentiometer thereby allows the individual operator to electrically adjust the response sensitivity of the handle  84 . For example, for an individual who walks at a brisk pace and wants the cart  78  to travel accordingly, a high sensitivity, leading to a relatively rapid speed-to-pressure response, is indicated. Likewise, for an individual who walks at a more leisurely pace, a lower sensitivity, leading to a relatively slow speed-to-pressure response, is indicated.  
     [0087] As shown in FIG. 14, the throttle interface  76  can includes a momentary switch  106 . Upon pushing downward upon the handle  84  to create forward movement of the cart  78  at a desired speed, the operator can activate the momentary switch  106  and let go of the handle  84 . The momentary switch maintains the forward progress of the cart  78  at the current speed, allowing the operator to walk behind the cart  78  in a hands-free condition.  
     [0088] The hands-free operation continues until the operator touches the handle  84  to deactivate the momentary switch  106 .  
     [0089] In this arrangement, the throttle interface  76  can also include an ultrasonic sensor  104 . The sensor  104  monitors the presence of the operator within a field of view behind the cart  78 . The sensor  104  permits hands-free operation to continue (prior to touch-deactivation of the momentary switch  106 ) as long as the operator lays inside the view range of the ultrasonic sensor  104 .  
     [0090] Force sensing resistors FSR&#39;s can also be used in other ways to control a vehicle. For example, as shown in FIG. 15, a brake pedal assembly  108  includes a foot pedal  110 , which pivotally mounted on one end of a pivot link  112 . The opposite end of the pivot link  112  is coupled to a cable  116 , which is also coupled to a mechanical brake assembly  122  of the vehicle.  
     [0091] The pivot link  112  is itself pivotally mounted on a bracket  114  between its two ends. The swing radius R 1  of the foot pedal  110  is larger than the swing radius R 2  of the pivot link bar  112 . Force applied to the foot pedal  110  will therefore first swing the foot pedal  110  about its axis before the pivot link  112  swings about its axis.  
     [0092] The pivot link  112  carries a force sensing resistor FSR. The resistor FSR is part of a voltage generating circuit that supplies voltage inputs to a microprocessor-based controller  124  for an electric direct current motor  126 , which drives a wheel  128 .  
     [0093] A spring  118  normally biases the foot pedal  110  toward a rest position, as shown in FIG. 15. The foot pedal  110  includes a plunger  120 . The plunger  120  is normally spaced from contact with the resistor FSR when the foot pedal  110  is in its rest position.  
     [0094] Force applied to the foot pedal  110  will first cause pivotal swinging of the brake pedal  108  about its axis, as arrow A in FIG. 15 shows. This causes the plunger  120  to apply pressure to the resistor FSR. Pressure to the resistor FSR changes its resistance and, in turn, varies the voltage input to the controller  124 . The controller  124  commands a motor driver  130  to create a regenerative braking effect in the motor  126  in proportion to the amount of pressure applied by the foot pedal  110  to the resistor FSR.  
     [0095] Continued force applied to the foot pedal  110  will maximize the regenerative braking effect and eventually cause the pivot link  112  to swing about its axis, as shown by arrow B in FIG. 15. The swinging of the pivot link  112  operates the cable  116  to activate the mechanical brake assembly  122 .  
     [0096] The brake pedal assembly  108  shown in FIG. 15 therefore achieves electrical regenerative braking through a force sensing resistor FSR and mechanical braking through the pivot link  112 .  
     [0097] It should be appreciated that the various throttle interfaces and motor control schemes are not limited in their implementation to the use of force sensing resistors. Other electrical, mechanical, or electromechanical devices capable of providing variable electrical output in response to operator interaction, e.g., switches, strain gauges, Hall generators, and equivalents thereof, can be used in the place of the force sensing resistors.  
     [0098] Various features of the invention are set forth in the following claims.