Patent Publication Number: US-6909205-B2

Title: Motor assembly allowing output in multiple degrees of freedom

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   The present application is a continuation application of U.S. patent application Ser. No. 09/953,662 filed Sep. 18, 2001 now U.S. Pat. No. 6,664,666, which is a continuation-in-part of U.S. patent application Ser. No. 09/470,077 filed Dec. 22, 1999, now U.S. Pat. No. 6,320,284, both entitled “Motor Assembly Allowing Output in Multiple Degrees of Freedom,” the teachings of these applications are incorporated herein by reference in their entirety U.S. application Ser. No. 09/953,662 is also a continuation in part of provisional application No. 60/286,894 filed Apr. 27, 2001, which is incorporated herein by reference in its entirety. This application claims benefit of PCT/US02/13859 filed May 3, 2002, which is incorporated herein by reference in its entirety. 

   STATEMENT REGARDNG FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
   The government has a paid-up license in this invention and the right in limited circumstances to require the patent owner to license others on reasonable terms as provided for by the terms of contract F33615-00-C-6009 awarded by U.S. Air Force. 

   FIELD OF THE INVENTION 
   The present invention relates in general to a motor assembly, and in particular to a force feedback motor assembly that provides an output in one or more degrees of freedom for use in joystick and other applications and more particularly to an improved force feedback joystick. 
   BACKGROUND OF THE INVENTION 
   Various force feedback motor designs providing multiple degrees of freedom are known in the art for use in a wide variety of applications. For example, multiple degrees of freedom in motor output are particularly useful in linear actuation and positioning applications. Another application in which such motors may be used is in joystick applications for real control of an associated apparatus, e.g., direct control of an aircraft, wheelchair, or other vehicle, or for simulation apparatus control, e.g. video games, flight simulation, virtual reality simulation, etc. In these applications a control system may be provided for sensing a user&#39;s manipulation of a joystick, i.e., the motor output shaft, and providing a signal for controlling the application. 
   Many applications also require force or tactile (“haptic”) feedback to the user. The need for the user to obtain realistic tactile information and experience tactile sensation is extensive in many kinds of simulation and other applications. For example, in medical/surgical simulations, the “feel” of a probe or scalpel simulator is important as the probe is moved within the simulated body. It would be invaluable to a medical trainee to learn how an instrument moves within a body, how much force is required depending on the operation performed, the space available in a body to manipulate an instrument, etc. In simulations of vehicles or equipment, force feedback for controls such as a joystick can be necessary to realistically teach a user the force required to move the joystick when steering in specific situations, such as in a high acceleration environment of an aircraft. Alternatively, when actually operating in a high acceleration vehicle environment, the force feedback can be used to counteract the effect of the acceleration induced forces on the hand and thus improve controllability and safety of the vehicle. In virtual world simulations where the user can manipulate objects, force feedback is necessary to realistically simulate physical objects; for example, if a user touches a pen to a table, the user should feel the impact of the pen on the table. An effective human/computer interface, such as a joystick, not only acts as an input device for tracking motion, but also as an output device for producing realistic tactile sensations. An interface that accurately responds to signals having fast changes and a broad range of frequencies as well as providing such signals accurately to a control system, is therefore desirable in these and other applications. 
   In addition, there is a desire to provide force feedback to users of computer systems in the entertainment industry. Joysticks and other interface devices can be used to provide force feedback to a user playing a video game or experiencing a simulation for entertainment purposes. Through such an interface device, a computer system can convey to the user the physical sensation of colliding into a wall, moving through a liquid, driving over a bumpy road, and other sensations. The user can thus experience an entire sensory dimension in the gaming experience that was previously absent. Force feedback interfaces can provide a whole new modality for human-computer interaction. 
   In typical multi-degree of freedom apparatuses that are capable of providing force feedback, there are several disadvantages. Generally conventional devices are cumbersome and complex mechanisms that are difficult and expensive to manufacture. In particular, the use of a transmission between the actuator motor and the joystick reduces the performance of the device and reduces the reliability and life of the device. Many transmission types can fail in a manner that renders the device unusable. For industrial and military applications, reliability and maintenance concerns are sometimes linked to the safety of personnel. If a force feedback device is not reliable or failsafe, then its use in these applications may be restricted or prevented even though the force feedback capability would enhance the performance and safety for that application. 
   In consumer markets, low-cost is highly desirable. For example, personal computers for the home consumer are becoming powerful and fast enough to provide force feedback to the typical mass-market consumer. A need is thus arising to be able to manufacture and market force feedback interfaces as cheaply and as efficiently as possible. The cost, complexity, reliability, and size of a force feedback interface for home use should be practical enough to mass-produce the devices. In addition, aesthetic concerns such as compactness and operating noise level of a force feedback device are of concern in the home market. Since the prior art feedback interfaces are mainly addressed to specific applications in industry, most force feedback mechanisms are costly, large, heavy, are easily broken, have significant power requirements, and are difficult to program for applications. The prior art devices require high-speed control signals from a controlling computer for stability, which usually requires more expensive and complex electronics. In addition, the prior art devices are typically large and noisy. These factors provide many obstacles to the would-be manufacturer of force-feedback interfaces to the home computer market. 
   Accordingly, there is a need in the art for a reliable motor allowing output in multiple degrees of freedom and capable of providing force feedback that may be efficiently and cost-effectively produced. 
   SUMMARY OF THE INVENTION 
   The present invention is organized about the concept of providing a reliable and cost-efficient force feedback motor allowing multiple degrees of output freedom. In particular, a force feedback motor consistent with the invention may include: a stator having an interior surface forming at least a portion of a sphere or curved surface and first and second substantially orthogonally positioned stator coils wound on the interior (or exterior) surface; and a rotor fixed to the output shaft and movably supported adjacent the stator with an air gap disposed between the rotor and the stator, the rotor including one or a plurality of magnetic field generators disposed thereon and being movable along the interior surface in directions defining at least first and second degrees of freedom. Upon energization of the first stator coil, a first magnetic field is established to force at least a first one of the magnets and the rotor in a direction in the first degree of freedom. Upon energization of the second stator coil, a second magnetic field is established to force at least a second one of the magnets and the rotor in a direction in the second degree of freedom. The first degree of freedom may be parallel to the second stator coil and the second degree of freedom may be parallel to the first stator coil. 
   The interior surface of the stator may be defined by a stator back iron comprising a ferromagnetic material. Each of the rotor magnets may also be arranged on a rotor back iron comprising a ferromagnetic material. The rotor magnets may be permanent magnets or electromagnets. 
   The rotor magnets may be arranged to form different sides of a parallelogram, with first and second ones of the magnets defining a first pair of parallel sides of the parallelogram parallel to the first stator coil, and third and fourth ones of the magnets defining a second pair of parallel sides of the parallelogram parallel to the second stator coil. The parallelogram defined by the magnets may be a square. Also, the first and third ones of the magnets advantageously may be configured with north poles disposed adjacent the stator coils, and the second and fourth ones of the magnets are configured with south poles disposed adjacent the stator coils. 
   The rotor may be supported adjacent the stator by a gimbal mechanism connected to the output shaft, e.g., a joystick handle, and supported on the stator. The gimbal mechanism may be configured to establish pivot points for the output shaft to allow motion of the rotor in the first and second degrees for freedom, the pivot points being substantially aligned with an equator of the sphere or curved surface. 
   According to the invention, there is also provided a method of providing force feedback to the joystick handle in response to manipulation of the handle by a user. The method includes: providing a motor consistent with the invention with the joystick being the output shaft; sensing a position of the joystick; energizing at least one of the coils based on the position to establish the feedback force against at least the first one of the magnets and the rotor. 
   It is an object of the present invention to provide a motor having an output shaft movable in multiple degrees of freedom. The motor comprising a stator and a rotor. The stator having an interior surface with first and second stator coils wound thereon, wherein the stator coils are positioned substantially orthogonally to each other. The rotor being fixed to the output shaft and movably supported adjacent the stator with an air gap disposed between the rotor and the stator, the rotor including at least one magnet disposed thereon and being movable along the interior surface in directions defining at least first and second degrees of freedom, wherein upon energization of the first stator coil, a first magnetic field is established to urge the rotor to rotate in a direction of the first degree of freedom, and upon energization of the second stator coil, a second magnetic field is established to urge the rotor to rotate in a direction of the second degree of freedom, the second degree of freedom substantially perpendicular to the first degree of freedom. 
   It is a further object of the invention to provide a motor having an output shaft movable in multiple degrees of freedom. The motor comprising a stator and a rotor. The stator having an interior surface and first and second stator coils wound in close proximity to the interior surface. The stator coils being positioned substantially orthogonally to each other. The stator comprising a plurality of laminations radially disposed about a center point with a plane of each lamination extending through the center point. The rotor being fixed to the output shaft and movably supported adjacent the stator with an air gap disposed between the rotor and the stator. The rotor including at least one magnet disposed thereon and being movable along the interior surface in directions defining at least first and second degrees of freedom. 
   It is a further object of the invention to provide a motor having an output shaft movable in multiple degrees of freedom. The motor comprising a stator and a rotor. The stator having an interior surface and first and second stator coils wound in close proximity to the interior surface. The stator coils positioned substantially orthogonally to each other. The stator comprising a first plurality and a second plurality of parallel laminations arranged in an arc about a center point, the first plurality arranged perpendicular to the second plurality. The rotor being fixed to the output shaft and movably supported adjacent the stator with an air gap disposed between the rotor and the stator. The rotor further comprising at least one magnet disposed thereon and being movable along the interior surface in directions defining at least first and second degrees of freedom. 
   It is a further object of the invention to provide a motor having an output shaft movable in multiple degrees of freedom. The motor comprising a stator and a rotor. The stator having an interior surface and first and second stator coils wound in close proximity to the interior surface. The stator coils positioned substantially orthogonally to each other. The stator comprising a first plurality and a second plurality laminations arranged in an arc about a center point, the first plurality arranged perpendicular to the second plurality. The rotor fixed to the output shaft. The rotor comprising a cross linkage having a first arm extending radially from the output shaft and a second arm extending radially from the output shaft with the first arm fixed to and orthogonal to the second arm. The rotor further comprising a first permanent magnet disposed at a distal end of the first arm and a second permanent magnet disposed at a distal end of the second arm. The first and the second magnets movably supported adjacent along the interior surface of the stator in directions defining at least first and second degrees of freedom. 
   It is a further object of the invention to provide a lamination for use in a stator. The lamination comprising a ferromagnetic material having an arcuate surface orthogonal to a side surface and a plurality of parallel slots. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a better understanding of the present invention, together with other objects, features and advantages, reference should be made to the following detailed description which should be read in conjunction with the following figures wherein like numerals represent like parts, and wherein: 
     FIG.  1 : is an isometric view of a first exemplary embodiment of a motor assembly consistent with the invention in a joystick application; 
     FIG.  2 : is a partial sectional view of the motor assembly shown in  FIG. 1  taken along lines  2 — 2 ; 
     FIG.  3 : is a top view of an exemplary rotor magnet assembly for a motor consistent with the invention; 
     FIG.  4 : is a top view of the motor magnet assembly of FIG.  1  and stator coil assembly for a motor consistent with the invention; 
     FIG.  5 : is a top view of an exemplary polyphase stator coil assembly for a motor consistent with the invention; 
     FIG.  6 : is a top view of the stator coil assembly shown in  FIG. 5  in position relative to the rotor magnet assembly as shown in  FIG. 3 ; 
     FIG.  7 : illustrates in block diagram form a control scheme for actuator control application for a motor consistent with the invention; and 
     FIG.  8 : illustrates in block diagram form a control scheme for a simulation control application for a motor consistent with the invention. 
     FIG.  9 : is a cutaway view of a second exemplary embodiment of a motor assembly consistent with the invention; 
     FIG.  10 : is a partial top view of the motor assembly shown in  FIG. 9  taken along lines  9 — 9 ; 
     FIG.  11 : is a partial sectional view of motor assembly shown in  FIG. 9  taken along lines  11 — 11  of  FIG. 10 ; 
     FIG.  12 : is a view of motor assembly shown in  FIG. 9  showing the location of copper windings; 
     FIG.  13 : is an isometric view of a third exemplary embodiment of a motor assembly consistent with the invention; 
     FIG.  14 : is a top view of the motor assembly of  FIG. 13 ; 
       FIG. 15A  is a side view of a single stator lamination of  FIG. 13 ; 
       FIG. 15B  is a top view of a single stator lamination of  FIG. 13  having parallel sides; 
       FIG. 15C  is a bottom view of a single stator lamination of  FIG. 13  having a wedge shape; 
     FIG.  16 : is a top view of a fourth exemplary embodiment of a motor assembly consistent with the invention; 
       FIG. 17  is a side view of the motor assembly of  FIG. 16 ; 
       FIG. 18  is a side view of an exemplary embodiment lamination having horizontal slots; 
       FIG. 18A  is a detail drawing of the lamination of  FIG. 18 ; 
       FIG. 19  is an isometric view of a plurality of the laminations of  FIG. 18 ; 
       FIG. 19A  is an isometric view of the plurality of laminations of  FIG. 19  with windings; 
       FIG. 20A  is a side sectional view of a fifth exemplary embodiment of a motor assembly consistent with the invention; 
       FIG. 20B  is a top view of the motor assembly of  FIG. 20A ; 
       FIG. 20C  is a side view of the motor assembly of  FIG. 20A  with a first winding configuration; 
       FIG. 20D  is a side view of the motor assembly of  FIG. 20A  with a second winding configuration; 
       FIG. 20E  is side section view of a sixth embodiment motor assembly consistent with the invention; 
       FIG. 20F  is side section view of a seventh embodiment motor assembly consistent with the invention; 
       FIG. 20G  is a bottom view of the motor assembly of  FIG. 20E ; 
       FIG. 20H  is a bottom view of the motor assembly of  FIG. 20F ; 
       FIG. 21  is a perspective view of an eighth embodiment motor assembly consistent with the invention; 
       FIG. 22  is a perspective view of a ninth embodiment motor assembly consistent with the invention; and 
       FIG. 23  is a side view of the motor assembly of FIG.  21 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   With reference now to  FIG. 1 , there is shown an exemplary embodiment of a motor assembly  10  consistent with the invention. In the illustrated embodiment, the assembly  10  is configured for operation as a joystick, which may provide force feedback to a user through the joystick handle. However, a motor assembly  10  consistent with the invention may be used in a wide variety of applications. The descriptions provided herein relate to use of an assembly in a joystick configuration are provided, therefore, by way of illustration but not of limitation. 
   As shown, the exemplary embodiment of  FIG. 1  generally includes a curved surface, hemisphere, or truncated sphere  12  of ferromagnetic material which will be simply referred to as the sphere for the purposes of discussion, but in reality may be nonspherical, which is lined on the interior  14  with coils  16  and  18  configured to carry electrical current provided from a power supply (not shown). In the illustrated embodiment the coils  16 ,  18  are substantially orthogonal to each other. In a joystick application, as shown, a moving joystick handle  20  has a shaft  22  extending from a bottom thereof. The shaft  22  is attached to a bar  24  by a pivot  26  so that the shaft may pivot within an opening  28  in the bar  24  about the pivot  26 . The bar  24  has first  30  and second  32  ends which are pivotally supported relative to the sphere, e.g. on an upper edge  34  of the sphere  12  as shown. The described system of constraint serves as a simple embodiment. It is to be understood, however, that a variety of means for constraining the moving components to the desired degrees of freedom may be employed. 
   The bar thus acts as a gimbal, and the position of the shaft  22  can be sensed by sensing the rotation of the ends  32  or  30  and the pivot pin  26 . A variety of means for sensing the rotational position of these elements, and therefore determining the position of the shaft  22  may be employed. However, for cost and simplicity considerations, however, it has been found that potentiometers may be coupled to the shafts to provide varying resistance depending on the position of the shaft. A control application can provide an output signal that varies according to the resistance provided by the potentiometers so that the output of the application is related in a known manner to the position of the shaft. It is to be understood, however, that a variety of means for providing shaft position information may be employed. 
   The end of the shaft distal from the handle  20  has a ferromagnetic back iron  36  rigidly affixed thereto. The back iron  36  has one or a plurality of magnets affixed thereto. The magnets may be permanent magnets or electromagnets. In the illustrated embodiment the magnets  38 ,  40 ,  42  and  44  are arranged to form a square pattern with their edges substantially parallel with and perpendicular to the coils  16 ,  18 . Although the square configuration is preferable, it is possible to arrange the magnets in any parallelogram configuration. 
   The bar  24  and the pivot mechanism formed thereby maintains an air gap between the magnets  38 ,  40 ,  42 ,  44 , and the coils  16 ,  18 . Energization of one or more of the coils produces a force upon corresponding ones of the magnets in either of the two axes perpendicular to the wires in the coils. Advantageously, therefore, the coils may be selectively energized, e.g. in dependence of a control algorithm provided by a user application such as a video game or simulation device or based on the position of the joystick, to provide a force output to the user through the handle  20 . Thus configured, the assembly  10  can be considered to include a stator defined by the coils on the sphere (or curved surface)  12  and a rotor defined by the magnets  38 ,  40 ,  42  and  44  positioned on the end of the shaft  22 . 
   Turning now to  FIG. 2 , there is provided a partial sectional view of the assembly of  FIG. 1  wherein the orientation of the rotor  50  and the stator  52  are more particularly shown. As illustrated, the gimbal mechanism provided by the bar  24  maintains an air gap  54  between the rotor  50  and the stator  52 . The air gap  54  may have a constant width, or may have a width that varies with rotation of the handle, depending on the application. 
   In the illustrated embodiment two degrees of freedom are achieved. The degrees of freedom represent two orthogonal coordinates similar to the x and y axis in a Cartesian coordinate system, i.e. the standard θ and φ of spherical geometry. One degree of freedom may be considered “left to right” movement in  FIG. 2 , and another degree of freedom may be movement into and out of the page in FIG.  2 . 
   Torque is created at the output of the motor, e.g. the handle  20 , by selectively energizing the windings using an internal or external power supply. In the embodiment illustrated in  FIG. 2 , electrical current runs into and out of the page in the lower coil  16 . The lower coil  16  is used for actuation left-to-right, i.e., lateral movement, producing a roll rotation direction. 
   In the upper coil  18 , which is positioned immediately above the lower coil, electrical current runs to the left and right of the page. The coil  18  is used for actuation of the motor into and out of the page. The positive electrical current in this coil travels from left-to-right in the leg of the coil shown in  FIG. 2 , and right to left on the far side of the coil, which is not shown in FIG.  2 . The actuation for force (torque) into and out-of the page is achieved using the magnets  40 ,  44 . The into- and out-of-page motion produces a pitch rotation in a joystick application. 
   The angles and sizes of the coils  16 ,  18  can be adjusted to provide different force capabilities in pitch and roll if desired. Additionally, the pitch and roll axes can be arranged at a 45-degree angle to the coils if desired. This requires a controller to mix the currents to the pair of coils to drive one axis, but may improve manufacturability by allowing the end turns to easily clear the gimbal pivots. Any angles of coils for the two axis can be used to provide any desired angles of actuation by controlling the current to each coil such that the net force produced (the vector sum of the forces) is in the desired direction. This remapping of the forces can be performed by the electronics and/or a computer and may allow a less expensive embodiment to perform a desired task. The substantially orthogonal coil arrangement is the preferred embodiment since it reduces the complexity of the control system. 
   The coils can be wound using standard winding techniques for copper coils. Generally it is easier to wind the coils on a flat surface. However, if a curved geometry is used, as shown in  FIGS. 1 and 2 , the windings may be press-fit or heated then press-fit to the desired shape. The windings may also be wound between curved forming plates (not shown), or wound directly onto a form. Also, the windings may be wound so that their positions are adjustable to allow for user adjustment or re-mapping of the motor degrees of freedom. If desired, the stator iron  12  can be formed with teeth in the form of pins and the coils can be laid in the notches between the teeth. This is useful for reducing the magnet size required, but makes manufacturing more complex. 
   The back iron  36  may be fabricated using laminations in order to achieve improved frequency response operation and reduce eddy current heating losses. Lamination stock of suitable thickness for high frequency response is commercially available from numerous commercial vendors. Also, the magnets  38 ,  40 ,  42  and  44  may be provided as permanent magnets, as shown due to the cost and performance considerations. 
   In operation, the permanent magnets create magnetic flux, B, which couples through the current, I, in the stator windings (or coils) of active length, L. This creates a force (or torque, if a rotational geometry is used) according to the Lorentz force law, F=I×L×B, T=r×F, which pushes the rotor to the left if the polarity of the currents and permanent magnets are as shown. 
   A top view of the complete set of rotor magnets is shown in FIG.  3 . The coils  16 ,  18  are omitted from  FIG. 3  for clarity. When the illustrated magnet array is overlaid on top of the coils  16 ,  18 , the arrangement is shown in FIG.  4 . For clarity of viewing, the back irons have been omitted from FIG.  4 . Four magnets utilized in this exemplary embodiment with polarities as shown. 
   As used herein, “N” represents the north pole and “S” represents the south pole of a magnet or electromagnet. Thus, in the illustrated embodiment first  38  and second  40  magnets forming adjacent sides of the square (or parallelogram) configuration are configured with south poles disposed adjacent the coils, i.e. north poles shown in the top view of FIG.  4 . Third  42  and fourth  44  magnets forming remaining adjacent sides of the square rotor magnet configuration are configured with north poles disposed adjacent the coils, i.e. south poles shown in the top view of FIG.  4 . Although use of back iron is not necessary for motor operation, the back iron  36 ,  12  in the rotor and stator, respectively, is used to efficiently couple the magnetic flux through the magnetic circuit and create a high force in the motor. 
   The electrical windings are shown as single coils  16 ,  18  that are perpendicular to each other to achieve actuation in both the lateral θ and the “fore-aft” φ directions. In this view, it can be seen that energization of the θ coil  18  will result in a force (torque) to the left while producing no force in the φ direction. This is due to illustrated unique coil and permanent magnet arrangement. Likewise, energization of the φ coil  16  will result in a force (torque) upward (in this view) while producing no force in the θ direction. 
   The embodiment in  FIG. 4  is illustrated using a single pair of coils  16 ,  18  for simplicity. However, it also is possible to design the motor using a 3-phase (or any other number of phases) set of windings. In  FIG. 5 , for example, there is shown the coil windings for a polyphase embodiment. The rotor magnet array is not shown in  FIG. 5  for simplicity. In this coil arrangement, energizing only the coils that are under the magnets during rotation of the rotor can reduce the power requirements and heating. Many standard coil-winding options are possible. The illustrated embodiment is, however, suitable for the limited-throw case (i.e., restricted angular movement) where the right side magnet never passes over the left side of the coils. 
     FIG. 6  presents a view of the arrangement of  FIG. 5  including the rotor magnet array. The back iron is not shown in  FIG. 6  for simplicity. As shown, the conductors can be wound in the form of three independent overlapped coils  16   a ,  16   b ,  16   c  and  18   a ,  18   b ,  18   c  that can be driven with a three-phase power supply. As the handle  20  moves, a commutation system  45  (e.g., including sensors, controls, and power supply) changes the distribution of currents in the coils to provide a desired force at any stick position. This can produce a motor with an increased electrical efficiency. Due to the specific geometry of the design, the forces on the two axes are independently controlled with negligible cross talk or influence between axes. 
   In addition to the torques produced by the electrical current, a centering force can be obtained by forming the center of the sphere  12  to be slightly above the center of the stick (i.e. the handle  20  and shaft  22 ) rotation so that the closest approach occurs when the stick is centered. The inherent attraction of the magnets  38 ,  40 ,  42 ,  44  to the ferromagnetic sphere  12  will then produce a centering force. 
   Similarly, if the center of the sphere  12  is located below the pivot point then the magnetic force is destabilizing and drives the stick towards the edge. A bias in any direction or no bias can be achieved by controlling the location of the center of the sphere  12  in relation to the center of the gimbal pivot system. Similarly, arranging the gimbal so that the axes do not cross at a point allows a bias of one axis to be different than the other. More complex modifications of the curved or spherical surface are useful. For example a dimple pattern at the bottom center would help achieve the strong at-center centering force that many joysticks available today have. For most applications the neutral condition is the best. In the neutral configuration all the pivot centers and sphere centers meet at a common point. Thus, as an alternative to the illustrated bar gimbal, a ball joint gimbal can be used if desired. 
   For small displacements, the coils  16 ,  18  can be substantially similar, but for large displacement designs the performance is enhanced if the coils are shaped to maintain parallelism with the edges of the magnets  38 ,  40 ,  42 ,  44  to the greatest extent possible. For the arrangement shown, the coils  16 , 18  can be wound with longitude and latitude alignment for large displacements if desired. 
   Alternatively, the pivot points on the sphere can be rotated 45 degrees about the vertical axis while maintaining the position of the magnets  38 ,  40 ,  42 ,  44  and the coils  16 , 18  to provide a mixed axis drive. This makes more space available for the bearings and coil end turns, but requires the two coil drive control currents be properly blended to provide the desired force vector. Since the output forces for each coil are now essentially at 45 degrees to the main axes of pitch and roll and still essentially orthogonal, this control is still very easily handled by a controller with or without a mathematical look-up table. 
   The coils  16 ,  18  can be wound in layers and commutated so that only those coils most suited to producing the desired forces (those under the magnets) can be activated. Another alternative is to inset the coils in slots in the ferromagnetic sphere. This can enhance the performance by increasing the magnetic flux from the permanent magnets and reducing the effective air gap. The slots then form a grid-like pattern of pins on the sphere. It is advantageous to space these pins relative to the edges of the magnets so that the magnet motion tends to cover a constant area of pins, thus minimizing cogging. As one edge moves over new pins the other edge leaves the old pins such that the overall area remains constant. The greatest cogging force comes from the magnets seeking the lowest reluctance position, which for this design tends to be that position in which the maximum tooth areas is under the magnets, thus one goal of the design is to maintain a constant tooth area coverage to the greatest degree possible. Cogging may not, however, be an important parameter for some configurations and control schemes. 
   For use as a joystick, the motor may be used in either a simulator application (in which the user controls a simulated device such as a computer game or a flight simulator) or a real control application where the user is either controlling a machine, vehicle or other such device. In addition, it will be recognized that the motor can be used for a variety of positioning tasks, for example, the motor could be used as a mirror control for precise angular control about two axis of rotation can be achieved with this motor. The control for these two applications can be arranged as conceptually shown below in block diagram form in  FIGS. 7 and 8 . 
   Turning to  FIG. 7  there is shown a functional block diagram identifying a control scheme for a motor consistent with the invention in an actuator application. A motor  60  consistent with the invention may include a component that is actuated by a user or machine. For example, the motor  60  may control the position of a mirror, a control surface, (such as the tail of a dart or aircraft), or a robotic surgical device. The position of the component may be sensed by potentiometers, for example, and output to a control application  62  for causing real time control of the apparatus. For example, the application may cause corresponding modification of an aircraft pitch and/or roll based on the motor position. 
   The modified position of the apparatus may be sensed by a sensor  64  and provided to a feedback control  66  for providing control of the motor  60  in dependence of the new position. Power supply  68  provides power to the entire system. 
   Turning now to  FIG. 8 , there is shown a control scheme for use of a motor  60  consistent with the invention in a simulator or generalized application including actual control of a device, vehicle, or aircraft. As shown, operator manipulation of a joy stick handle or other interface with the environment  70  is sensed by an interface sensor  72 , which may include, for example, potentiometers for sensing rotational position of gimbals. The position sensed by sensor  72  is provided as an input to an application controller  74 . The application controller may, for example, be a flight simulation computer running software for a simulation program. The output of the controller  74  is provided to a power conditioner/motor controller  76  which provides an output to a motor  78  consistent with the invention to energize the motor coils and provide an output force to the user  80  through the joystick handle  82  in the manner described above. The power supply  84  provides power to the entire system. 
     FIG. 9  shows a cutaway view of a second embodiment motor assembly  100 . In the illustrated embodiment, the assembly  100  is configured for operation as a joystick, which may provide force feedback to a user through a joystick handle  102 . The joystick handle  102  is coupled to a rotor  104 . The rotor  104  may be a sphere that can rotate in all directions relative to the stator  108 . The rotor  104  may be configured with four permanent magnets  106 A- 106 D arranged around the equator of the sphere. Three of these  106 A,  106 B, and  106 C are shown in FIG.  9  and the fourth magnet  106 D (see  FIG. 10 ) is hidden behind the magnet in front. These magnets are shown circular in cross section and have curved facets in order to match the sphericity of the stator  108 . The circle in the center of the sketch indicates the front facet of magnet  106 B. The two curved sections on the right and left depict cutaways of magnets  106 A and  106 C. 
   The stator  108  is positioned outside of the periphery of the magnets  106 A- 106 D. The stator  108  and the magnets  106 A- 106 D are separated by an air gap  120 . 
   Backiron (iron used to complete the flux path and increase the air gap field strength) is used in both the rotor  104  and the stator  108  in order to assure high performance of the motor by maximizing the magnet coupling between the stator  108  and the rotor  104 . 
     FIG. 10  shows windings/coils  110 , preferably copper, wound on the stator  108  positioned just outside the magnets  106 A-D. The magnet flux  112  is generated by the permanent magnets  106 A-D located on the rotor  104 . The magnetic flux  112  is coupled from the permanent magnet  106 A-D on the rotor  104  through the copper windings/coils  110  in the stator  108  via the backiron in the magnetic circuit with low reluctance to maximize performance. 
   A magnetic circuit is shown in  FIG. 11 , where the coils  110 A-D may be overlapped or not. This portion of the magnetic circuit is configured to provide force in the θ direction. This is achieved by energizing the four coils  110 A-D shown in the picture with current of the appropriate polarity. When current is driven in these coils with the polarity shown, the interaction of the magnetic fields of the stator  108  and the rotor  104  causes the rotor  104  to be pulled in the direction that aligns the magnetic field of the magnets  106 A-D with that of the coils  110 A-D. As can be seen, the magnet  106 A, on the left, may be pulled down towards coil  110 D and pushed away from coil  110 C, while the magnet  106 C, on the right, may be pulled upward towards coil  110 A and pushed away from coil  110 B. 
     FIG. 12  shows the magnetic circuit orthogonal to the magnetic circuit of FIG.  11 . Actuation of the joystick in the Φ direction is provided by the permanent magnets  106 B and  106 D and windings/coils  110 E-H oriented at 90° to the coils and magnets shown in  FIG. 11  (permanent magnet  106 D and windings/coil  110 G and  110 H are hidden behind the magnet and winding/coils in front). 
   One significant benefit of the motor configuration is a very low cross-coupling between the operation of the joystick in the two orthogonal axis, Φ and θ. This is achieved through the positioning of the four magnets at the equator of the sphere. 
     FIGS. 13-15  show a four-arm motor assembly  200 . The assembly  200  is configured for operation as a joystick, which may provide force feedback to a user through an output shaft  202 . The output shaft  202  may also be used as an input device. The output shaft  202  may have a longitudinal axis LA that extends perpendicularly from and is fixed to a cross linkage  204 . The cross linkage  204  has a first pair of diametrically opposed arms extending radially from the output shaft  202  and a second pair of diametrically opposed arms extending radially from the output shaft  202 , the first arms fixed to and orthogonal to the second arms. In  FIG. 13 , each of four permanent magnets  206 A-D is attached to one end of the cross linkage  204  (the rotor). The cross linkage  204  may be mounted to a ball joint, universal joint or gimbal at the center of the stator lamination stacks  214 A-D. Each stator lamination stack  214 A-D preferably has an upper copper winding  210 A-D and a lower copper winding  210 A′-D′. For simplicity, the end turns of the copper windings  210 A-D are drawn as sharp connections. The copper windings may be controlled such that diametrically opposed winding are wired in series or in parallel. For example the upper winding  210 A of stator stack  214 A may be wired in series or parallel with lower winding  210 C′ of stator stack  214 C and lower winding  210 A′ of stator stack  214 A may be wired in series or parallel with upper winding  210 C of stator stack  214 C. Alternatively, each individual winding may be individually controlled. 
   In  FIG. 14 , the individual stator laminations of the lamination stacks  214 A-D can be seen to be oriented radially about the output shaft  202  when viewed from the top (parallel to the longitudinal axis of the output shaft  202 ). The laminations may comprise a pair of parallel sides, as shown in FIG.  15 B. The lamination stacks may be made up of a plurality of parallel-sided laminations each separated by a spacer. The purpose of the spacer is to make the distance between adjacent laminations greater along the outside surface of the lamination stack than along the inside surface of the lamination stack. The spacer may be wedge shaped. The individual laminations may be separated by insulators. The spacer may be used to space and to insulate adjacent laminations. A plane of each lamination extends through the output shaft  202 . These laminations may be all cut identically with an arcuate inner surface perpendicular to the plane of the laminations (as shown in FIG.  15 A). An airgap  218  exists between the rotor and the stator of the motor. As shown, the magnetic flux generated by the permanent magnets  206 A-D couples into the lamination stacks  214 A-D of the stator and through the base plate  208  of the joystick. An inside surface IS of each lamination may be orthogonal to the sides surface of the lamination as shown in FIG.  15 B. As used in this specification, an arcuate surface may or may not have a fixed/constant radius. The laminations may a have a plurality of radially oriented slots S. 
   Alternatively, as shown in  FIG. 15C , each lamination may be wedge shaped when viewed parallel to a longitudinal axis of the output shaft. In this configuration, spacers may not be required. The individual laminations may be separated by insulators. The inside surface IS of each lamination may comprise an arc when viewed parallel to a longitudinal axis of the output shaft, as shown in FIG.  15 C. 
   The mechanical system to hold the joystick to the base may comprise one of several designs, including universal joints, ball joints, and 2 DOF gimbals. However, universal joints are preferred for use with the system due to their durability, simplicity and widespread use and availability. 
   A simplified drawing of a single lamination is presented in FIG.  15 A. As can be seen in  FIG. 15A , the slots in the laminations are also pointed radially when viewed from the side and are not parallel with each other. 
   By positioning these laminations radially about the output shaft  202 , when viewed from the top, with all the laminations pointing towards the center of the joystick, these laminations form a spherical motor stator that maintains a constant airgap as the joystick rotor is rotated along both axes. This design provides a high performance direct drive joystick. 
     FIG. 16  shows a top view of a four-arm pseudo spherical motor assembly  300 . The assembly  300  is configured for operation as a joystick, which may provide force feedback to a user through an output shaft  302 . The output shaft  302  may also be used as an input device. The output shaft  302  may have a longitudinal axis that extends perpendicularly from and is fixed to a cross linkage  304 . The cross linkage  304  has a first pair of diametrically opposed arms extending radially from the output shaft  302  and a second pair of diametrically opposed arms extending radially from the output shaft  302 , the first arms fixed to and orthogonal to the second arms. Each of four permanent magnets  306 A-D is attached to one end of the cross linkage  304  (the rotor). The cross linkage  304  may be mounted to a ball joint, universal joint or gimbal at the center of the stator lamination stacks  314 A-D. Each stator lamination stack  314 A-D preferably has an upper copper winding and a lower copper winding. 
   In this configuration, a plurality of laminations, preferably identical, are all stacked flat against each other (parallel to each other) and the laminations near the edge of the stack are disposed slightly closer to the rotor to form a stepped concave surface about the longitudinal axis of the output shaft  302  in a plane orthogonal to a side surface of the plurality of laminations. The laminations may be spaced by an insulator. The shape of the stepped concave surface of the plurality of laminations about an equator of the plurality of laminations approximates an arc having a constant radius in a plane orthogonal to a side surface of the plurality of laminations. This creates an inner stator surface that is almost the shape of a sphere. The pseudo spherical design provides advantages over the other designs in terms of manufacturing ease. The use of the laminations arranged like this results in an inner surface of the laminations that is almost, but not quite spherical (thus, the term pseudo-spherical). This maintains an airgap  318  that is almost, but not quite, constant. The assembly  300  is configured for operation as a joystick, which may provide force feedback to a user through an output shaft  302 . 
   Note that in  FIG. 16 , the laminations are stacked flat against each other. The stator laminations can be seen to be oriented parallel to a line extending radially from a center point of the stator when viewed from the top. The small spaces between laminations presented in  FIGS. 14 and 16  are exaggerated for illustration purposes only. Note, also, that this view contrasts with that presented in  FIG. 14 , where the laminations are all aligned radially. Use of this design greatly eases the manufacturing process in that the laminations can be stacked flat against each other. 
   A side view of the lamination stacks  314 A-D fabricated with the pseudo spherical configuration is presented in FIG.  17 . The lamination stacks  314 A-D are made from a plurality of individual laminations. As can be seen in  FIG. 17 , the slots S in the laminations are also aligned radially when viewed from the side and are not parallel with each other. A plurality of generally uniform spreaders  330  located adjacent the arcuate surface. Spreaders are pole tips for spreading the magnetic flux in the poles more uniformly around the arcuate surface. A portion of the slots S extend between the spreaders  330 . The slots extend generally radially away from the arcuate surface. The individual laminations may be symmetric about a horizontal line and adjacent spreaders  300  are generally identical.  FIG. 18  is a side view of an alternative single lamination  414  spaced from a permanent magnet  406  coupled to a cross linkage  404 . As shown, the slots S P  cut into the lamination  414  are all parallel to each other and parallel to the stator base plate. In one embodiment, when the output shaft is in a “neutral” position, the longitudinal axis of the output shaft is perpendicular to the parallel slots. The parallel slots S P  reduce the motor size and height for a given magnetic and torque performance due to the lack of angled backiron and copper windings  410 . A plurality of single laminations  414  may be combined in a stack. This single lamination  414  can be used in the laminations stacks  214 A-D,  314 A-D shown in  FIGS. 14 and 16 . 
     FIG. 18A  is detailed drawing of the single lamination  414  shown in FIG.  18 . The arcuate surface of the single lamination  414  may have a fixed radius R about a center point CP. A plurality of non-uniform spreaders  430 - 446  located adjacent the arcuate surface help spread the magnetic field. A portion of the parallel slots S P  extends between the spreaders  430 - 446 . The slots S P  extend away from the arcuate surface generally parallel to the base of the laminations. The individual laminations  414  may be symmetric about a horizontal line, but adjacent spreaders are generally not identical. A drawing of a 3D model of the lamination stack  314  with a plurality of laminations  414  with the horizontal slots and a pseudo spherical configuration is presented in FIG.  19 . An isometric view of the plurality of laminations of  FIG. 19  along with windings is shown in FIG.  19 A. When the laminations are formed into a stack  314  as shown in  FIG. 19 , the individual laminations may be arranged about a center point of the rotor such that the arcuate surface of the lamination stack is equally spaced from the center point of the rotor. The stack  314  has an equatorial arc  340  and a longitudinal arc  342 . The radius of the equatorial arc  340  being generally equal to the radius of the longitudinal arc  342 . 
   Further details of the invention are illustrated in  FIGS. 20A-20F .  FIG. 20A  shows a side sectional view and  FIG. 20B  is a top view of a motor assembly  500 . The assembly  500  has eight coils  506 ,  508  positioned around an equator  510  (as shown in  FIG. 20A ) of a rotor  504 . A first set of four upper coils  506  may be centered on a “tropic of cancer” and a second set of lower four coils  508  may be centered on a “tropic of capricorn”. The upper coils  506  and the lower coils  508  are permanently located. The upper and lower coils  506  and  508  do not have to be located within 23° of the equator  510 . A handle  502  may be coupled to the rotor  504  to operate as a joystick. The joystick may be used as an input device and may also provide force feedback to a user. In one embodiment the upper coils  506  and lower coils  508  are similar in size (same wire gauge and number of turns); in a second embodiment the upper coils  506  may be smaller in size than the lower coils  508 ; and, in a third embodiment the upper coils may be absent with all the force feedback being provided by the lower coils  508 . Alternatively, the lower coils  508  could be smaller than the upper coils  506  or absent with all the force feedback being provided by the upper coils  506 . 
     FIGS. 20C and 20D  show that the winding may be formed in different configurations depending on the intended application. Winding  510  as shown in  FIG. 20C  is somewhat oblong and the winding  510 ′ as shown in  FIG. 20D  is somewhat triangular. Other winding configurations will work.  FIGS. 20E and 20F  are side sectional views of a motor assembly  600  and  600 ′ and  FIGS. 20G and 20H  show a bottom view of the motor assemblies  600  and  600 ′ respectively.  FIGS. 20E and 20G  show four coils  608 A-D disposed about a plurality of permanent magnets  606 A-D centered on an “Antarctic circle”. The coils  608 A-D are shown rotated 90° about the longitudinal axis of the out put shaft relative to the permanent magnets  606 A-D. Upon energization of coil  608 B or  608 D, a first magnetic field is established to urge the rotor to rotate in the θ direction, a first degree of freedom. Upon energization of coil  608 A or  608 C, a second magnetic field is established to urge the rotor to rotate orthogonal to the θ direction, a second degree of freedom. 
     FIG. 20F  shows a pair of concentric permanent magnets  606 ′ and  616 ′ centered on an “Antarctic circle”.  FIG. 20H  shows four coils  608 A-′D′ disposed about the concentric permanent magnets  606 ′ and  616 ′. 
   The permanent magnets  606 A-D,  606 ′ and  616 ′ and the coils  608 A-D and  608  A′-D′ maybe combined with the motor assembly  500 , shown in  FIGS. 20A and 20B , to provide auxiliary output force to the handle  602  coupled to the rotor  604 . Alternatively, the magnets  606 A-D,  606 ′ and  616 ′ and the coils  608 A-D and  608 A′-D′ may be used as an input device for detecting movement of the handle  602  and  602 ′. The magnet  608  does not have to be positioned directly opposite the handle  602  for proper operation. 
     FIG. 21  shows an eighth embodiment motor assembly  700 . The motor assembly  700  may comprise a stator comprising a plurality of lamination stacks  714 A,  714 B,  714 C and  714 D and a rotor  704 . An output shaft  702  may be coupled to the rotor  704 . The rotor  704  may comprise a cross linkage having a first arm and a second arm. The output shaft  702  may be fixed orthogonally to the cross linkage of the rotor  704 . The first arm and the second arm may each have first and second distal ends that may be radially spaced from the centrally positioned output shaft  702 . The first arm may be orthogonal to the second arm. A permanent magnet  706 A-D may be disposed at distal ends of the first arm and the second arm. 
   Each lamination stack  714 A-D may comprise an interior surface and a first and a second stator coil wound in close proximity to the interior surface. Each of the permanent magnets  706 A-D may be spaced by an air gap from the interior surface of an associated lamination stack  714 A-D. The lamination stacks  714 A-D may be disposed about the longitudinal axis LA of the output shaft  702 . One or more of the lamination stacks  714 A-D may be oriented relative to the longitudinal axis LA of the output shaft  702 . As shown in  FIG. 21 , the lamination stack  714 D may be oriented such that a plane formed by a lamination in the lamination stack  714 D forms an angle with the longitudinal axis of the output shaft  702 . The angle is shown as being substantially 90°, but any angle relative to the longitudinal axis of the output shaft is conceivable. Lamination stack  714 B may be oriented such that a plane formed by a lamination in the lamination stack  714 B is substantially parallel with the longitudinal axis of the output shaft. Lamination stack  714 B and  714 D may be diametrically opposed. Lamination stacks  714 A and  714 C may also be oriented such that a plane formed by a lamination in the lamination stacks  714 A and  714 C respectively are substantially parallel with the longitudinal axis of the output shaft  702  or they may be oriented such that that a plane formed by a lamination in the lamination stacks  714 A and  714 C form a first and a second angle with the longitudinal axis of the output shaft  702 . The first and the second angle may be the same or may be different. 
   The stator coils in each of the lamination stacks  714 A-D, when energized, urge the associated permanent magnet to rotate in a plane parallel to a plane formed by a lamination in the associated lamination stack. The stator coils in lamination stack  714 D, when energized, urge the output shaft  702  to rotate about the longitudinal axis of the output shaft  702 , thereby creating a first degree of freedom. The stator coils in lamination  714 B, when energized, urge the output shaft  702  to rotate in a plane parallel to a plane formed by a lamination in lamination stack  714 B, thereby creating a second degree of freedom. Likewise, the stator coils in lamination stack  714 A and lamination stack  714 C, when energized, urge the output shaft  702  to rotate in a plane parallel to a lamination in lamination stacks  714 A and  714 C respectively thereby creating a third degree of freedom. 
     FIGS. 22 and 23  show a perspective view and side view respectively of a ninth motor assembly  800 . The motor assembly may comprise a stator comprising a plurality of lamination stacks  814 A,  814 B,  814 C and  814 D and a rotor  804 . An output shaft  802  may be coupled to the rotor  804 . The rotor  804  may comprise a cross linkage having a first arm and a second arm. The output shaft  802  may be fixed orthogonally to the cross linkage of the rotor  804 . The first arm and the second arm may each have first and second distal ends that may be radially spaced from the centrally positioned output shaft  802 . The first arm may be orthogonal to the second arm. A permanent magnet  806 A-D may be disposed at distal ends of the first arm and the second arm. 
   Each lamination stack  814 A-D may comprise an interior surface and a first and a second stator coil wound in close proximity to the interior surface. Each of the permanent magnets  806 A-D may be spaced by an air gap from the interior surface of an associated lamination stack  814 A-D. The lamination stacks  814 A-D may be disposed about the longitudinal axis LA of the output shaft  802 . One or more of the lamination stacks  814 A-D may be oriented relative to the longitudinal axis LA of the output shaft  802 . 
   As shown in  FIG. 23 , the lamination stack  814 D may be oriented such that a plane formed by a lamination in the lamination stack  814 D forms an angle θ 2  with the longitudinal axis of the output shaft  802 . The angle θ 2  may be between about 5° and about 85°. Preferably, the angle θ 2  is between 15° and 75°, and most preferably the angle is between 30° and 60°. Lamination stack  814 B may be oriented such that a plane formed by a lamination in the lamination stack  814 B forms an angle θ 1  with the longitudinal axis of the output shaft  802 . Lamination stack  814 B and  814 D may be diametrically opposed. Angle θ 1  and θ 2  may be the same or may be different. Lamination stacks  814 A and  814 C may be oriented such that a plane formed by a lamination in the lamination stacks  814 A form an angle θ 3  and θ 4  (not shown) respectively with the longitudinal axis of the output shaft  802  or may also be oriented such that a plane formed by a lamination in the lamination stacks  714 A and  714 C are substantially parallel with the longitudinal axis of the output shaft  802 . Lamination stack  714 A and  714 C may be diametrically opposed. Angles θ 3  and θ 4  may be the same or may be different. 
   The stator coils in each of the lamination stacks  814 A-D, when energized, urge the associated permanent magnet to rotate in a plane parallel to a plane formed by a single lamination in the associated lamination stack. The stator coils in lamination stack  814 D, when energized, urge the output shaft  702  to rotate in a plane at an angle θ 2  with the longitudinal axis of the output shaft  802 , thereby creating a first degree of freedom. The stator coils in lamination  814 B, when energized, urge the output shaft  802  to rotate in a plane at an angle θ 1  with the longitudinal axis, thereby creating a second degree of freedom. Likewise, the stator coils in lamination stack  814 A and lamination stack  814 C, when energized, urge the output shaft  702  to rotate in a plane at an angle at an angle θ 3  and at an angle θ 4  with the longitudinal axis thereby creating a third degree of freedom. 
   There is thus provided a motor that is capable of providing output in multiple degrees of freedom. The motor is simple and efficient in design and can be adapted for a variety of applications including joystick applications. The motor includes substantially orthogonally arranged stator coils wound thereon. A rotor including a plurality of magnets is provided adjacent the stator. The rotor may be provided at the end of an output shaft that is pivotally disposed relative to the stator for pivotal movement upon energization of the stator coils. 
   The embodiments described herein, however, are but some of the several which utilize this invention and are set forth here by way of illustration but not of limitation. For example, although a motor consistent with the invention can provide output in multiple degrees of freedom, it would be possible to operate the motor in only one degree of freedom by providing or energizing only a single coil. Another example of use of the invention is replacement of the joystick with a mirror; the mirror can then be tilted in two degrees of freedom for scanning or alignment purposes. Also, a wide variety of gimbal arrangements may be provided for pivotally supporting the stick to maintain an air gap between the stator and rotor. Yet other embodiments may be made without departing materially from the spirit and scope of the invention as defined in the appended claims.