Six-Degree Virtual Pivot Controller

The present invention pertains to hand controllers and particularly to aircraft hand controllers. More particularly, the invention pertains to displacement aircraft or space vehicle hand controllers.

The related art involves conventional hand controllers which rotate about a fixed axis in the base, require movement of both the arm and the wrist, have a high force displacement gradient, and have either no or complex proprioceptive feedback.

In recent years, space and weight constraints in modern aircraft have resulted in compact fly-by-wire or fly-by-light control systems. Such systems reduce the size and weight of flight control hardware in the cockpit. In addition, these systems permit a side-arm controller configuration that reduces obstruction of the instrument panel area directly in front of the pilot. Two general configurations of those compact controllers have been developed--rigid and movable displacement. Rigid controllers measure the force of the control input and have no movement associated with input magnitude. Moveable controllers have a range of motion of about .+-.2 inches to .+-.4 inches associated with the magnitude of the control input. The force required to fully displace a moveable controller may be quite small, although the inclusion of a force-displacement gradient has been found to improve control performance.

Difficulties are associated with both types of hand controllers. Rigid controllers may produce severe operator fatigue due to a lack of proprioceptive feedback to tell the pilot how much force he is exerting. That difficulty can be reduced by allowing for a small (i.e., .+-.1/4 inch) amount of displacement or wobble unrelated to the force-output function. Further, rigid controllers provide fairly imprecise control and suffer from input axis cross-coupling, again due to the poor proprioceptive feedback provided to the operator.

Moveable controllers can provide reasonable control when a fairly heavy-force output gradient (i.e., .gtoreq..+-.15 pounds at full displacement) is used; however, these force requirements result in operator fatigue. At lower force requirements, control imprecision and axis cross-coupling are resulting problems.

Some of these problems were solved upon the conception and development of a moveable hand controller configuration that permits accurate control while requiring a relatively low force-displacement gradient. Also, such hand controller is useful in a side-arm configuration in that it allows the operator's arm to remain essentially motionless in an arm rest while control inputs are made about the fulcrum of the wrist. When the operator provides an input, such hand controller assembly is rotated in an arc having its center at the operator's wrist and/or center is translational. The hand controller also has the advantage of rotation about the operator's wrist joint, thus requiring movement of the wrist only. In other words, that hand controller has a "virtual pivot" that permits inputs to be made about any point in space and the controller translates movement of the controller grip about a point in space (such as the operator's wrist joint) into movements of a sensor about an internal reference point thereby permitting one hand controller to optimally function for all hand sizes. However, that controller has a grip and a sensor platform with a small-displacement and a motion base with spring-loaded legs for flexibility. Such hand controller is disclosed in U.S. Pat. No. 4,962,448, by DeMaio et al., issued Oct. 9, 1990, and entitled "Virtual Pivot Hand Controller," which is herein incorporated by reference.

The present invention is still yet a further improvement on the related art. Not only does the present invention have a virtual pivot which accommodates variations in operator action, have six degrees of freedom, and variable pivot point locations; the invention is adaptable for providing various forces and torques and displacements and rotations and provides force feedback which simulates spring-type feedback but having different rates, various stop positions, variable damping, and a variety of reflective conditions to the controller environment including impact, proximity, limits, etc. The system of the invention has a hand controller incorporating system actuators, system sensors and feedback actuators which are connected to system control and force feedback control mechanisms which implement a variable control algorithm. The controller has a hand grip platform which is supported by telescoping legs. Linear actuators drive the telescoping motion in the legs. Motors drive radial angular motion at the universal joints which attach the legs to the base plate. A force/torque sensor is attached to the hand grip platform and monitors control inputs from an operator of the hand controller. There are angular potentiometers, linear potentiometers, and motor tachometers associated with the telescoping legs. The potentiometers provide a measurement of the position and attitude of the platform with respect to the base. Signals from the force/torque sensor, angular potentiometers, linear potentiometers and motor tachometers are input into the control system. The control system sends signals to the motors to drive the hand controller to the commanded configuration with the appropriate force and feel characteristics at the hand grip.

The virtual pivot of the hand controller system accommodates a wide variety of operator sizes with a "floating" pivot point. Motors and controllers replace springs of the related art hand controller and yet provides force feedback or "feel". Spring rates, spring tension, damping rates, stop positions, the number of control axes, the dimensions and range of control axes, and force reflection characteristics may be programmed with various values based on specific requirements into the control system. The programmability and flexibility of the hand controller system permits the controlling of a large and varied range of devices with a single hand controller. The hand controller system may be programmed to compensate for various gravities, various gravity and inertial effects, or for gravity-free environments. Applications of the hand controller system include use in space stations, space vehicles, helicopters, fixed-wing aircraft, underwater vehicles, robotic vehicles, robotic arm controls, and other applications.

FIG. 1 is a drawing of hand controller.

FIG. 2 is an overview diagram of the hand controller, control system, and the controlled system.

FIG. 3 is a graph showing the relationship of hand grip-applied force/torque versus hand controller movement displacement profiles.

FIG. 4A-4C illustrates the vector relationships between base and platform coordinate frames of the virtual pivot hand controller.

FIG. 5a, 5b and 5c constitute a signal flow diagram of the control system and motor channels.

FIG. 1 reveals an adaptable six degree of freedom virtual pivot hand controller 10. Virtual pivot hand controller 10 has a hand grip 28 for the operator's input. Hand grip 28 is connected through grip platform 30 to six degree of freedom force and torque sensor 34. Force and torque sensor 34 is an F/T series, model 75/250 sensor from Assurance Technologies, Inc., of Garner, NC 27529. Grip platform 30 is connected to shafts 62 via ball joints 32. Three shafts 62 extend into three linear actuators 36, respectively. Linear actuators 36 cause shafts 62 to extend out of actuators 36 or to withdraw into actuators 36. The amount of shaft 62 extending out of linear actuator 36 is measured by linear potentiometer 38. Linear actuators 36 are driven by motors 40 thereby causing the extension or withdrawal of shafts 62. The withdrawal or extension of shafts 62 via ball joints 32 raise, lower, tilt, rotate and/or laterally move grip platform 30 and hand grip 28. The activity of motors 40 driving linear actuators 36 is monitored by tachometers 42. Linear actuators 36 are attached to universal joints 60, respectively. The other ends of the universal joints 60 opposite of linear actuators 36, are effectively attached to base plate 48. Six potentiometers 44 are, respectively, attached to universal joints 60 for measuring the angles of linear actuators 36 relative to base plate 48. The angle of linear actuator is 36, relative to base plate 48, is driven and set by motors 52 via gear heads 50 and worm and worm wheel assemblies 46. Gear heads 50 are attached to motors 52 through base plate 48 to worms 46. Worms 46 drive worm wheels 46 which are attached to the portions of universal joints 60 that are rigidly attached to linear actuators 36, respectively. Worms 46 driving worm wheels 46 set linear actuators 36 and shafts 62 to particular angles of inclination. Motors 52 are monitored by tachometers 54. Base plate 48 is supported by a surface 58 with structural supports 56. Surface 58 represents the place or area upon which hand controller 10 is situated and mounted.

FIG. 2 reveals an overall diagram of the adaptable six degree of freedom virtual pivot hand controller 10 system. Hand controller 10 outputs sensor signals 20 from six degree of freedom force and torque sensor 34, linear potentiometers 38, angular potentiometers 44, motor tachometers 42 and motor tachometers 54. Sensor signals 20 are input to control system 12 which is a processor and specifically a Motorola VMEbus 68020 single board microcomputer, having system control 14 and force feedback control 16. Force and torque sensor 34 which is attached to hand grip platform and hand grip monitors the control inputs from the operator. Control system 12, in response to sensor signals 20, sends feedback signals to motors 40 and 52 to drive hand controller 10 in accordance with the commanded configuration, having appropriate force and feel characteristics. The force and feel characteristics are determined by force feedback control 16 and response to sensor signals 20 revealing force, torque, position and rate, and signals from controlled system 18 sensors indicating proximity, force, field dynamics, etc., in response to driving signals 22 to system actuators such as motors, propulsion, etc. Hand controller 10 uses motor biasing to generate the sense the feel of springs, damping and mechanical deadbands as illustrated in FIG. 3. FIG. 3 is a graph of hand grip applied force and torque verses displacement profiles of hand grip 10.

Control interface 22 required to determine hand control 10 orientation and translation in six degrees of freedom contains nine potentiometer measurements (three per leg) that define three position vectors of grip platform 10, corresponding to three fixed ball joints 32, with respect to the three base leg pivot points at the ends of shafts 62. During system calibration, a fixed displacement vector (from the origin of platform 30 coordinate frame) of the operator's wrist joint is estimated. FIG. 4A-4C show the vector relationships between base 48 and platform 30 coordinate frames. Processor or control system 12, through force feedback control 16, returns three Euler angles and three linear translations from nominal platform 30 origin. Additionally, force and torque sensor 34 inputs are used in either position or rate mode to command a six degree of freedom velocity that motorized legs 36 and shaft drives 46 are to deliver. Thus, processor or control system 12 must first solve the geometric task of computing orientation an translation, and then compute the requisite leg or shaft rotational and linear velocities that result in the commanded and controller state.

Kinematic solutions to the hand grip platform Euler angles (defining attitude angles) and linear displacements from the center of the coordinate frame are obtained by use of nine potentiometers, 38 and 44. Fewer potentiometers can accomplish the same task of monitoring as the nine potentiometers. Telescoping legs or shafts 62 (whose links are actuator 36 driven) are attached to platform 30 by ball joints 32 and to base 48 by double-gimbaled motorized joints 60. Outer gimbals 60 are rigidly attached to base 48, are motor 52 driven, and cause a roll motion about the leg or shaft 62 motor axis of rotation. Outer gimbal 62 axis defines the leg or shaft 62 coordinate frame X-axis for each of the three legs or shafts 62. These three axes are each oriented along the radial directions with respect to the center of base 48. This results in the forward base 48 point having its motor axes along the X-axis of the base 48 coordinate frame. Azimuth angles .phi..sub.i to the other two base 48 points have constant values of 120 and 240 degrees, respectively. Inner gimbals 60 allow rotation about the respective leg or shaft 62 pitch axes. Designating the length of the three legs 62 d.sub.i, where i equals 1, 2, 3, and is defined 0<d.sub.imin <d.sub.i <d.sub.imax. Then the position vectors of platform 30 ball joints 32 with respect to base 48 frame S.sub.B : ##EQU1##

Processor of control system 12 is a Motorola VMEbus 68020-board microcomputer housed in a standard Motorola chassis having several analog-to-digital interface cards. Six tachometers 42 and 54 on three legs 62 measure motor speeds of leg-extending or retracting motors 40 and leg-angular rotating motors 52. There are two motors, 40 and 52, per leg 62. Linear potentiometers 38 measure leg 62 extension and two angular potentiometers 44 per leg 62 measure angles of each leg 62 relative to base 48. There is a total of nine potentiometers 38 and 44.

Rate and position control modes of hand controller 10 differ. In the position mode, removal of grip, force and torque commands from the operator causes hand controller 10 to remain at its latest attained attitude and linear displacement. Removal of input in the rate mode will cause a return of hand controller 10 to the initial displacement origin. Any of the six degrees of freedom of hand controller 10 may be locked out as desired. Software stops are provided to prevent hand controller 10 from running into hard stops which might cause damage.

FIGS. 5a, 5b and 5c constitute an overview signal flow diagram of hand controller 10 input and motor control channels. This diagram has correlation with the program listing at the end of this description. Force/torque sensor 34 is a strain gauge type of sensor for detecting applied force and torque to hand grip 28 of controller 10. Interface 13 provides for keyboard or other type of input to the processor which includes input command processing 68 and motor command 70. Interface 13 is a RS-232 terminal interface for operator inputs of the controller 10 processor. Control system 66 provides for needed interaction among force and torque sensor 34, input command processing 68 and interface 13. Control system 66 includes sensor 34 electronics and control and may incorporate a Lord preprocessor and a Lord controller for sensor 34, from Assurance Technologies, Inc., of Garner, NC 27529 Controller function 72 incorporates software to perform the calculations of required motor rates to equal commanded input velocities of translation and rotation by incorporation kinematic system equations. Orientation function 74 incorporates software to perform the calculations of the platform and/or virtual pivot translation and rotation with respect to the base coordinate system. Inputs represent shaft or leg lengths, elevations and azimuth angles obtained from the nine potentiometers 38 and 44 (three per shaft or leg). Function 74 incorporates reverse kinematic system equations in its calculations. External object or device 18 receives input for external control and outputs signals for providing reflected force or torque (i.e., "feel" dynamics), or alarms.

The following describes the geometric relationships. Position vectors of the pivots are defined by R.sub.Bi and R.sub.Pi, where i=1, 2, 3, in the two separate frames S.sub.B (the base 48 frame) and S.sub.P (the platform 30 frame), results in ##EQU2## The above dot represents a matrix dot product. Referring to FIG. 4, the platform 30 Xp unit vector is directed from the center toward P.sub.i. The Yp unit vector is parallel to the line from P.sub.3 to P.sub.2. Then, ##EQU3##

The direction cosines of the Xp, Yp, and Zp unit vectors are the components of the preceding vector equations. The Euler rotation matrix from S.sub.B to S.sub.p is then ##EQU4## The above dots represent vector dot products.

All information concerning the relative attitude orientation between the base 48 and platform 30 frames is contained in the Euler matrix E.sub.P/B. Euler angles can be defined in 24 different ways depending on the sequence of rotations (in a positive sense about each of three axes). There are 12 permutations starting with either frame S.sub.p or S.sub.B, or 24 total. Each set of three angels is not interchangeable (except for very small rotations). Each set does, however, result in the same rotation of one frame to another when applied in its specific sequence.

The following set arises from a yaw rotation about the SB z axis followed by a pitch rotation bout the y axis and a final roll about the x axis:

Each rotation assumes the right-hand rule for positive sense. The inverse transformation performs a roll-pitch-yaw transformation (in that order) which is not uncommon in the aircraft industry.

The following describes the platform velocity equations. Tachometers 42 and 54 mounted on the handcontroller 10 legs and roll axis shafts are used in a velocity feedback controller 16 that drives each motorized leg 62 to null a separate commanded velocity. These six velocities are in turn computed according to the six signals from force/torque sensor 34 (after biasing to provide reflected force or torque dynamics for the operator).

At present, handgrip 28 force signals are interpreted as referenced to the base 48 coordinate frame as a linear velocity command. The coordinate system used in arbitrary and can be easily redefined in processor code and provided as an optional handcontroller 10 operating mode at a later time if desired.

The inertial velocity V.sub.i of each leg 62 is composed of the linear velocity of the platform 30 center summed with the rotational velocity about the center, that is ##EQU5## where .theta..sub.i, .phi..sub.i, and d.sub.i are the time rate of change of angles .theta..sub.i .phi..sub.i, and leg length d.sub.i for each leg. Then, ##EQU6##

In the above equation, only the expressions for leg roll and length rates are of interest as the handcontroller 10 leg 62 pitching rates are automatically driven by mechanical constraints. This solution requires inversion of a 3 by 3 matrix, where ##EQU7##

The platform 30 angular velocity vector input commands, .omega..sub.p, above are referenced to S.sub.B ; if they are instead referenced to S.sub.p, they are simply converted by the inverse Euler transformation as follows: ##EQU8##

The inverse Euler matrix is the transpose of the matrix since the coordinate frame is orthogonal and Cartesian.

In summary, one feature of hand controller 10 is that the sensed location of the pivot point can be set arbitrarily. It can be sent through the center of grip 28, above or below it, or be centered inside the operator's wrist. For example, with a pivot point below grip 28, it would act like a conventional military aircraft hand controller having the pivot point where the control stick attaches to the floor or deck of the aircraft. However, with the pivot point above grip 28, the top of the grip would be seemingly attached to a point above it and the grip would swing freely below it. The programmability of the pivot point provides for maximum flexibility and adaptability of hand controller 10. These changes in location of pivot point can be made by entering the appropriate software commands in control system 12. An initial setting can be made by the operator through the movement of his or her wrist for setting the virtual pivot and control swing and rotation dimensions in accordance with and to match the wrist movement. Other operating characteristics can be changed simply by altering the software. Such things as break out forces, the degree of freedom available, damping rates, spring tensions and velocity rates can be modified without altering the hardware of control system 12 or hand controller 10. Based on information from the vehicle or object being controlled, the operator is given feedback through grip 28. This capability is force reflection and usually involves providing tactile feedback through grip 20 when the control object 18 (e.g., a robot arm or vehicle) contacts the target or other object. The combination of a programmable virtual pivot point having an active hand controller 10 allows the operator or user to configure hand controller 10 to match or meet the demands or needs of a particular task and user.

Motor-driven force feedback (microprocessor 12 control) replaces spring centering. Gradients of forces or torques versus displacements (in each of six axes), as shown in FIG. 2, are stored as parameters that can be modified by keyboard 13 input. Such modification provides adaptability or programmability of key hand controller 10 operating characteristics including sensed (virtual) pivot axes locations and range of motion in each axis, sensed spring force reflection or the feel of grip 28 (i.e., force/displacement gradients), the capability, as desired, to implement bilateral force feedback from system 18 being controlled (via motor control feedback) to the human operator and the capability of operator-mode control to introduce menu-driven commands (via the VMEbus single-board computer). ##SPC1##