Patent Publication Number: US-6982696-B1

Title: Moving magnet actuator for providing haptic feedback

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. Provisional Application No. 60/142,155, filed Jul. 1, 1999, entitled, “Providing Vibration Forces in Force Feedback Devices,” and which is incorporated by reference herein. 
    
    
     This invention was made with government support under Contract Number N00014-98-C-0220, awarded by the Office of Naval Research. The government has certain rights in this invention. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates generally to producing forces in force feedback interface devices, and more particularly to the output and control of vibrations and similar force sensations from actuators in a force feedback interface device. 
     Using an interface device, a user can interact with an environment displayed by a computer system to perform functions and tasks on the computer, such as playing a game, experiencing a simulation or virtual reality environment, using a computer aided design system, operating a graphical user interface (GUI), or otherwise influencing events or images depicted on the screen. Common human-computer interface devices used for such interaction include a joystick, mouse, trackball, steering wheel, stylus, tablet, pressure-sensitive ball, or the like, that is connected to the computer system controlling the displayed environment. 
     In some interface devices, haptic or tactile feedback is also provided to the user, also known as “force feedback.” These types of interface devices can provide physical sensations which are felt by the user using the controller or manipulating the physical object of the interface device. One or more motors or other actuators are used in the device and are connected to the controlling computer system. The computer system controls forces on the force feedback device in conjunction and coordinated with displayed events and interactions on the host by sending control signals or commands to the force feedback device and the actuators. 
     Many low cost force feedback devices provide forces to the user by vibrating the manipulandum and/or the housing of the device that is held by the user. The output of simple vibration force feedback requires less complex hardware components and software control over the force-generating elements than does more sophisticated haptic feedback. For example, in many current controllers for game consoles such as the Sony Playstation and the Nintendo 64, a motor is included in the controller which is energized to provide the vibration forces. An eccentric mass is positioned on the shaft of the motor, and the shaft is rotated quickly to cause the motor and the housing of the controller to vibrate. The host computer (console) provides commands to the controller to turn the vibration on or off or to increase or decrease the frequency of the vibration by varying the rate of rotation of the motor. These current implementations of vibrotactile feedback, however, tend to be limited and produce low-bandwidth vibrations that tend to all feel the same, regardless of the different events and signals used to command them. The vibrations that these implementations produce also cannot be significantly varied, thus severely limiting the force feedback effects which can be experienced by a user of the device. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to moving magnet actuators that provide haptic sensations in a haptic feedback device that is interfaced with a host computer. The present invention provides actuators that output high magnitude, high bandwidth vibrations for more compelling force effects. 
     More specifically, the present invention relates to an actuator for providing vibration forces in a haptic feedback device. The actuator includes a core member that is grounded to a ground member. A coil is wrapped around a central projection of the core member, and a magnet head is positioned so as to provide a gap between the core member and the magnet head. The magnet head is moved in a degree of freedom based on an electromagnetic force caused by a current flowed through the coil. An elastic material is positioned in the gap between the magnet head and the core member, where the elastic material is compressed and sheared when the magnet head moves and substantially prevents movement of the magnet head past a range limit, the range limit based on an amount which the elastic material may be compressed and sheared. 
     Preferably, the elastic material is a material such as foam. The actuator can be driven by a drive signal that causes said magnet head to oscillate and produce a vibration in the ground member. The ground member can be a housing of the haptic feedback device, such as a gamepad controller. In some embodiments, at least one flexible member can also be coupled between the magnet head and the ground member to allow the magnet head to move in the degree of freedom. The degree of freedom of the magnet head can be linear or rotary. 
     In another aspect of the present invention, an actuator for providing vibration forces in a force feedback device includes a core member that is grounded to a ground member, a coil wrapped around a central projection of the core member, and a magnet head positioned adjacent to the core member, where the magnet head is moved in a degree of freedom based on an electromagnetic force caused by a current flowed through the coil. At least one flexible member is coupled between the magnet head and the ground member, where the flexible member(s) flex to allow the magnet head to move in the degree of freedom and provide a centering spring force to the magnet head. The flexible members limit the motion of the magnet head such that the magnet head does not impact a hard surface. The flexible members can be coupled between the magnet head and a ground surface to which the core member is coupled, or can be coupled between the magnet head and a ground surface to a side of the core member. The flexible members can also be coupled to a housing of the actuator as the ground surface. The degree of freedom of the magnet head can be linear or rotary. An elastic material can also be positioned in a gap between magnet head and core member which is compressed and sheared when the magnet head moves. A haptic feedback device including any of the above embodiments of actuator is also described. 
     The present invention advantageously provides an actuator for a haptic feedback device that can output high quality vibrotactile sensations. Both the frequency and amplitude of the vibrations can be controlled using bi-directional control, and features such as the elastic material and flexures contribute to a high quality and high bandwidth vibration force output. 
     These and other advantages of the present invention will become apparent to those skilled in the art upon a reading of the following specification of the invention and a study of the several figures of the drawing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of a haptic feedback system suitable for use with the haptic feedback device of the present invention; 
         FIG. 2  is a side elevational view of one embodiment of a linear actuator of the present invention; 
         FIG. 3  is a side elevational view of one embodiment of a rotary actuator of the present invention; 
         FIG. 4  is a top plan view of the actuator of  FIG. 2  having flexures in a different location; and 
         FIG. 5  is a perspective view of another embodiment of the actuator of  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       FIG. 1  is a block diagram illustrating a force feedback interface system  10  for use with the present invention controlled by a host computer system. Interface system  10  includes a host computer system  12  and an interface device  14 . 
     Host computer system  12  can be any of a variety of computer systems, such as a home video game systems (game console), e.g. systems available from Nintendo, Sega, or Sony. Other types of computers may also be used, such as a personal computer (PC, Macintosh, etc.), a television “set top box” or a “network computer,” a workstation, a portable and/or handheld game device or computer, etc. Host computer system  12  preferably implements a host application program with which a user  22  is interacting via peripherals and interface device  14 . For example, the host application program can be a video or computer game, medical simulation, scientific analysis program, operating system, graphical user interface, or other application program that utilizes force feedback. Typically, the host application provides images to be displayed on a display output device, as described below, and/or other feedback, such as auditory signals. 
     Host computer system  12  preferably includes a host microprocessor  16 , a clock  18 , a display screen  20 , and an audio output device  21 . Microprocessor  16  can be one or more of any of well-known microprocessors. Random access memory (RAM), read-only memory (ROM), and input/output (I/O) electronics are preferably also included in the host computer. Display screen  20  can be used to display images generated by host computer system  12  or other computer systems, and can be a standard display screen, television, CRT, flat-panel display, 2-D or 3-D display goggles, or any other visual interface. Audio output device  21 , such as speakers, is preferably coupled to host microprocessor  16  via amplifiers, filters, and other circuitry well known to those skilled in the art and provides sound output to user  22  from the host computer  12 . Other types of peripherals can also be coupled to host processor  16 , such as storage devices (hard disk drive, CD ROM/DVD-ROM drive, floppy disk drive, etc.), communication devices, printers, and other input and output devices. Data for implementing the interfaces of the present invention can be stored on computer readable media such as memory (RAM or ROM), a hard disk, a CD-ROM or DVD-ROM, etc. 
     An interface device  14  is coupled to host computer system  12  by a bi-directional bus  24 . Interface device  14  can be a gamepad controller, joystick controller, mouse controller, steering wheel controller, or other device which a user may manipulate to provide input to the computer system and experience force feedback. The bi-directional bus sends signals in either direction between host computer system  12  and the interface device. An interface port of host computer system  12 , such as an RS232 or Universal Serial Bus (USB) serial interface port, parallel port, game port, etc., connects bus  24  to host computer system  12 . Alternatively, a wireless communication link can be used. 
     Interface device  14  includes a local microprocessor  26 , sensors  28 , actuators  30 , a user object  34 , optional sensor interface  36 , an actuator interface  38 , and other optional input devices  39 . Local microprocessor  26  is coupled to bus  24  and is considered local to interface device  14  and is dedicated to force feedback and sensor I/O of interface device  14 . Microprocessor  26  can be provided with software instructions to wait for commands or requests from computer host  12 , decode the command or request, and handle/control input and output signals according to the command or request. In addition, processor  26  preferably operates independently of host computer  12  by reading sensor signals and calculating appropriate forces from those sensor signals, time signals, and stored or relayed instructions selected in accordance with a host command. Suitable microprocessors for use as local microprocessor  26  include the MC68HC7111E9 by Motorola, the PIC16C74 by Microchip, and the 82930AX by Intel Corp., for example. Microprocessor  26  can include one microprocessor chip, or multiple processors and/or co-processor chips, and/or digital signal processor (DSP) capability. 
     Microprocessor  26  can receive signals from sensors  28  and provide signals to actuators  30  of the interface device  14  in accordance with instructions provided by host computer  12  over bus  24 . For example, in a preferred local control embodiment, host computer  12  provides high level supervisory commands to microprocessor  26  over bus  24 , and microprocessor  26  manages low level force control loops to sensors and actuators in accordance with the high level commands and independently of the host computer  12 . The force feedback system thus provides a host control loop of information and a local control loop of information in a distributed control system. This operation is described in greater detail in U.S. Pat. No. 5,734,373, incorporated herein by reference. Microprocessor  26  can also receive commands from any other input devices  39  included on interface apparatus  14 , such as buttons, and provides appropriate signals to host computer  12  to indicate that the input information has been received and any information included in the input information. Local memory  27 , such as RAM and/or ROM, can be coupled to microprocessor  26  in interface device  14  to store instructions for microprocessor  26  and store temporary and other data (and/or registers of the microprocessor  26  can store data). In addition, a local clock  29  can be coupled to the microprocessor  26  to provide timing data. 
     Sensors  28  sense the position, motion, and/or other characteristics of a user manipulandum  34  of the interface device  14  along one or more degrees of freedom and provide signals to microprocessor  26  including information representative of those characteristics. Rotary or linear optical encoders, potentiometers, photodiode or photoresistor sensors, velocity sensors, acceleration sensors, strain gauge, or other types of sensors can be used. Sensors  28  provide an electrical signal to an optional sensor interface  36 , which can be used to convert sensor signals to signals that can be interpreted by the microprocessor  26  and/or host computer system  12 . For example, these sensor signals can be used by the host computer to influence the host application program, e.g. to steer a race car in a game or move a cursor across the screen. 
     One or more actuators  30  transmit forces to the interface device  14  and/or to manipulandum  34  of the interface device  14  in response to signals received from microprocessor  26 . In one embodiment, the actuators output forces on the housing of the interface device  14  which is handheld by the user, so that the forces are transmitted to the manipulandum through the housing. Alternatively, the actuators can be directly coupled to the manipulandum  34 . Actuators  30  can include two types: active actuators and passive actuators. Active actuators include linear current control motors, stepper motors, pneumatic/hydraulic active actuators, a torquer (motor with limited angular range), voice coil actuators, and other types of actuators that transmit a force to move an object. Passive actuators can also be used for actuators  30 , such as magnetic particle brakes, friction brakes, or pneumatic/hydraulic passive actuators. Active actuators are preferred in the embodiments of the present invention. Actuator interface  38  can be connected between actuators  30  and microprocessor  26  to convert signals from microprocessor  26  into signals appropriate to drive actuators  30 , as is described in greater detail below. 
     Other input devices  39  can optionally be included in interface device  14  and send input signals to microprocessor  26  or to host processor  16 . Such input devices can include buttons, dials, switches, levers, or other mechanisms. For example, in embodiments where the device  14  is a gamepad, the various buttons and triggers can be other input devices  39 . Or, if the user manipulandum  34  is a joystick, other input devices can include one or more buttons provided, for example, on the joystick handle or base. Power supply  40  can optionally be coupled to actuator interface  38  and/or actuators  30  to provide electrical power. A safety switch  41  is optionally included in interface device  14  to provide a mechanism to deactivate actuators  30  for safety reasons. 
     Manipulandum (or “user object”)  34  is a physical object, device or article that may be grasped or otherwise contacted or controlled by a user and which is coupled to interface device  14 . By “grasp”, it is meant that users may releasably engage, contact, or grip a portion of the manipulandum in some fashion, such as by hand, with their fingertips, or even orally in the case of handicapped persons. The user  22  can manipulate and move the object along provided degrees of freedom to interface with the host application program the user is viewing on display screen  20 . Manipulandum  34  can be a joystick, mouse, trackball, stylus (e.g. at the end of a linkage), steering wheel, sphere, medical instrument (laparoscope, catheter, etc.), pool cue (e.g. moving the cue through actuated rollers), hand grip, knob, button, or other object. 
     In a gamepad embodiment, the manipulandum can be a fingertip joystick or similar device. Some gamepad embodiments may not include a joystick, so that manipulandum  34  can be a button pad or other device for inputting directions. In other embodiments, mechanisms can be used to provide degrees of freedom to the manipulandum, such as gimbal mechanisms, slotted yoke mechanisms, flexure mechanisms, etc. Various embodiments of suitable mechanisms are described in U.S. Pat. Nos. 5,767,839, 5,721,566, 5,623,582, 5,805,140, 5,825,308, and patent application Ser. Nos. 08/965,720, 09/058,259, 09/156,802, 09/179,382, and 60/133,208, all incorporated herein by reference. 
     Moving Magnet Actuator 
       FIG. 2  is a side elevational view of an actuator  100  of the present invention which can be included in a handheld controller  14  or coupled to manipulandum  34  as actuator  30  for providing force feedback to the user of the controller  14  and/or manipulandum  34  in the interface device  14  of  FIG. 1 . In one embodiment, the actuator  100  can be coupled to the housing of the interface device  14 , e.g. the housing of a handheld gamepad controller as used with console game systems or personal computers. In other embodiments, the actuator can be coupled to a manipulandum  34  or other member. 
     Actuator  100  is a moving-magnet actuator in which a grounded metal core  102  includes a wire coil  104  that is wrapped around a central projection of the core as shown (shown in cross section in  FIG. 2 ). A magnet head  105  includes two magnets  106  and  108  which have opposite polarities facing the coil  104  and are coupled together as shown and spaced from the coil  104  and core  102 . Magnet head  105  also includes a metal piece  110  coupled to the magnets  106  and  108  to provide a flux return path for the magnetic flux of the actuator. A plastic housing  112  provides a structure for the magnets and metal piece of the magnet head  105 . 
     The actuator  100  operates by producing a force on the magnet head  105  in the linear directions indicated by arrows  114  when a current is flowed through the coil  104 . The direction of the current dictates the direction of force on the head  105 . The operation of E-core actuators similar to the components  102 – 110  of actuator  100  is described in greater detail in co-pending application Ser. No. 60/107,267, incorporated herein by reference, and in U.S. Pat. No. 5,136,194. The magnet head  105  can be moved to either side from the center position shown in  FIG. 2 . 
     Actuator  100  is intended to be used in the present invention for producing vibrations which are transmitted to the housing of the interface device  14  and/or to a user manipulandum  34 . In other embodiments, the actuator  100  can be used to produce other force feedback effects. The motion of the head  105  is desired to be constrained to a particular range of motion to provide an oscillatory motion as desired for the bi-directional mode of operation as described above. However, if mechanical stops are provided to limit the range of motion of the magnet head  105 , the impact of the head  105  with the stops causes harmonics and disturbances in the vibration force feedback which the user can feel. 
     To reduce the disruptive effect of such hard stops, the present invention provides several features. Flexures  120  are coupled between the grounded core  102  and the moving magnet head  105 , and can flex in the directions shown to allow motion of the magnet head  105  in its linear degree of freedom. The flexures can flex to allow the magnet head to move to other positions, e.g. one different position is indicated by the dashed lines. The flexures  120  provide a spring resilience to the motion of the magnet head  105 , such that when the magnet head  105  moves closer to a limit of motion to either side, the flexures resist the motion like a spring and bias the head back toward the center position. This helps limit the motion of the magnet head  105  without using hard stops. 
     Furthermore, the actuator  100  of the present invention includes an elastic material  122  positioned between the grounded core  102  and the magnet head  105 , such as foam. The foam material may be physically coupled to either the core  102  or to the head  105 , or to neither the core or the head. The magnetic attractive force F between the core  102  and the magnets  106  and  108  causes slight compression of the foam and keeps it in position. The foam allows the magnet head  105  to move in its linear degree of freedom since the foam is a flexible, deformable material. As the magnet head  105  moves to one side, the foam compresses and shears and resists the motion of the head to a greater degree as the head moves a greater distance. The flexures  120  cause the magnet head  105  to move closer to core  102  as the head  105  moves to either side. At some point, the foam  122  is compressed to such an extent that no further motion of the head  105  is substantially allowed away from the center position, and the limit to motion is effectively reached. In other embodiments, other elastic or compressible materials having a modulus or otherwise similar to foam may be used, such as rubber, a fluid with viscoelastic properties, etc. 
     The foam and flexure structure described above provides limits to the motion of the magnet head without causing a disturbance in the force feedback that would be caused if the head  105  were to impact a surface. The foam  122  provides increasing resistance to motion of the head to provide an actuator limit, based on the compressibility and shear factor of the foam. Furthermore, the foam is an inexpensive material that is simple to assemble between the core  102  and the head  105 . In addition, the frequency response of the actuator  100  can be adjusted by selecting a particular foam type, e.g. a foam having a higher or lower compliance or compressibility. 
     Actuator  100  can be used to provide the oscillating vibrations for a bi-directional mode of vibration force feedback. In such a mode, the magnet head  105  is oscillated in the linear degree of freedom, producing a vibration that is transmitted from the actuator to the housing of the device  14  to which the actuator is coupled. A drive waveform that changes between positive and negative signs can be provided to the actuator to cause the oscillations. If a lower amplitude drive waveform is used, then the magnitude of vibration output is correspondingly lower. This allows the controller of the drive waveform to adjust the magnitude of vibration to a desired level within the allowed magnitude range by adjusting the magnitude of the waveform. The controller can also adjust the frequency of the drive waveform independently of the amplitude to adjust the frequency of vibration. This allows different frequency vibrations to be output independently of the magnitude of those vibrations. The drive waveform can be supplied by the local microprocessor  26 , actuator interface  38 , or host computer  12  directly. The drive signal can be supplied by a well-known H-bridge circuit or other amplifier circuit, as also disclosed in copending application no. 09/608,125, filed concurrently herewith, entitled, “Controlling Vibrotactile Sensations for Haptic Feedback Devices,” which is incorporated by reference herein. 
     The linear actuator  100  provides a greater magnitude of vibrations at higher frequencies (assuming the waveform magnitude is held constant). This gain at higher frequencies is due primarily to the vibration occurring at the resonance frequency of the mechanical system including actuator, foam, housing, etc., and, if desired, can be compensated for in other embodiments to obtain a more flat response by providing compensating frequencies that will provide the desired response (e.g. from a look-up table or firmware). 
       FIG. 3  is a side elevational view of an alternate embodiment  100 ′ of the actuator  100  shown in  FIG. 2 . Actuator  100  includes a core  102 ′, a coil  104 ′; and a magnetic head  105 ′ substantially similar to like components of the actuator  100  of  FIG. 2 . However, actuator  100 ′ provides rotational force and motion instead of the linear motion of actuator  100 . Thus, the core  102 ′ and the magnetic head  105 ′ have opposed curved surfaces, and the foam  122 ′ fills the gap therebetween. The magnet head  105 ′ rotates about an axis B when current is flowed through the coil  104 ′, and the foam  122 ′ compresses as described above to limit the range of the head  105 ′. The head  105 ′ can be rotatably coupled to a grounded member  130  to provide support for the head. Radial flexures similar to those of  FIG. 4  or  5  can also be used in the embodiment of  FIG. 3  to provide a spring resilience to the magnet head  105 ′ about axis B. 
       FIG. 4  is a top plan view of an alternate embodiment  150  of the actuator  100  shown in  FIG. 2 . The core, coil, and magnet head components are substantially similar as described with reference to  FIG. 2 . In this embodiment, flexures  152  are provided between the magnet head  105  and a grounded surface  154 . Grounded surface  154  can be the housing of the motor itself, the housing of the controller or interface device  14 , or other surface. The flexures  152  flex to accommodate the motion of the magnet head  105 , as shown by the dashed lines and arrows  156 . 
       FIG. 5  is a perspective view of one embodiment of an actuator  160  which is similar to actuator  100  and implements flexures similar to the flexures  152  of  FIG. 4 . Core  162  has a projecting portion  163  around which is wrapped coil  164 . Magnets  166  and  168  are provided in magnet head  165  which moves linearly above the core  162  and coil  164  as indicated by arrow  167 . A flexure  170  is positioned on either side of the core  162  and head  165 . Each flexure  170  is coupled to the housing  172  of the motor  160  at a point  174 . The other end of each flexure is coupled to the magnet head  165  by a frame or shuttle  176  (shown in dashed lines) which is coupled between the magnets  166 ,  168  and the flexures  170 . A foam layer as described above is also preferably positioned between core  162  and head  165 . When the head  165  is caused to oscillate quickly back and forth, the force is transmitted through flexures  170  to the motor housing, and from the housing to the interface device  14  held by the user. 
     In other embodiments of the present invention, yet other types of actuators can be used. For example, a solenoid having linear motion can be used to provide the bi-directional vibrations described above. 
     While this invention has been described in terms of several preferred embodiments, it is contemplated that alterations, permutations and equivalents thereof will become apparent to those skilled in the art upon a reading of the specification and study of the drawings. Furthermore, certain terminology has been used for the purposes of descriptive clarity, and not to limit the present invention.