Method and apparatus for providing passive fluid force feedback

An interface device for use with a host computer updating a graphical environment in response to user manipulation of said interface device, said host computer commanding said computer interface device to generate force feedback sensations in coordination with events within said graphical environment, said interface device comprising:

• a user object contacted by a user;
• a support mechanism which supports said user object while allowing a degree of freedom of motion of said object with respect to a grounding surface;
• an actuator for providing resistance to motion of said user object along said degree of freedom of said user object, said actuator including a grounded portion and a non-grounded portion, wherein said grounded portion of said actuator remains stationary with respect to said grounding surface, and wherein said resistance to motion is varied by said actuator in response to commands from said host computer;
• a slotted yoke mechanism provided between said actuator and said user object, said slotted yoke mechanism allowing an inherent amount of play between said user object and said non-grounded portion of said actuator;
• and
• a sensor system, said sensor system being grounded wherein a portion of said sensor system remains stationary with respect to said grounding surface, and wherein a different portion of said sensor system is coupled to said user object and moves with respect to said grounding surface when said user object moves along said degree of freedom, wherein no substantial play is allowed between said user object and said portion of said grounded sensor system coupled to said user object, said motion of said coupled sensor portion resulting in signals representing a position of said user object along said degree of freedom, and wherein said inherent amount of play is detectable within a sensing resolution of said sensor system.

A force feedback interface device for use with a host computer displaying a graphical environment, said force feedback interface device providing force feedback sensations to a user, said interface device comprising:

• a user manipulatable object contacted by a user and moveable in two linear degrees of freedom, said two linear degrees of freedom substantially defining a plane, said user manipulatable object including a recess for contacting a tip portion of at least one finger of said user or a tip portion of a stylus;
• at least one sensor in communication with said host computer and coupled to said user manipulatable object for sensing positions of said user manipulatable object along at least one of said degrees of freedom;
• and
• a first and a second actuator, each in communication with said host computer, said first actuator comprising a first linear member mechanically coupled to said user manipulatable object to apply a force to said object along a first linear degree of freedom, and said second actuator comprising a second linear member mechanically coupled to said user manipulatable object to apply a force to said object along a second linear degree of freedom, wherein said actuators provide said forces as a resistance to motion by changing the flow rate of an electrorheological fluid having a viscosity changed by applying an electric field to said fluid.