Position sensing for force feedback devices

A force feedback device coupled to a host computer, the force feedback device comprising:

• a manipulandum physically contacted and manipulable by a user;
• a linkage mechanism providing a degree of freedom to said manipulandum;
• at least one actuator coupled to said linkage mechanism, said actuator operative to output a force on said manipulandum in said degree of freedom;
• at least one sensor operative to sense a position of said manipulandum in said degree of freedom and to output a raw sensor value representing said position;
• and
• a local microprocessor, separate from and communicating with said host computer, said local microprocessor receiving said raw sensor value from said sensor and adjusting said raw sensor value based on a compliance between said sensor and said manipulandum in said force feedback device, said adjustment compensating for said compliance to provide a more accurate position of said manipulandum, and wherein said local microprocessor outputs said adjusted sensor value to said host computer as said position of said manipulandum.

A method for dynamically calibrating a sensed range of motion of a manipulandum of a force feedback device, said force feedback device being coupled to a host computer and including an actuator and at least one relative sensor, the method comprising:

• a) providing a predetermined initial range of movement for said manipulandum when said force feedback device is initially powered, said initial range including two boundary values, said boundary values including a maximum value and a minimum value;
• b) receiving a sensor value representing a position of said manipulandum of said force feedback device in said range of movement as said manipulandum is moved;
• c) setting said maximum value or said minimum value to said received sensor value if said received sensor value is outside said initial range;
• and
• d) adjusting said other of said boundary values not set in step c) to maintain said initial range between said maximum value and said minimum value unless said other of said boundary values has been previously detected to be outside said initial range.

A method for providing accurate sensing of position of a manipulandum in a force feedback device that includes compliance between said manipulandum and a position sensor of said force feedback device, the force feedback device including at least one actuator for outputting forces and being coupled to a host computer, the method comprising:

• reading a raw sensor value representing a position of a manipulandum of said force feedback device in a range of motion of said manipulandum, said manipulandum being phyisically contacted and manipulable by a user;
• filtering said raw sensor value for overshoot sensor values occurring at limits to said range of motion of said manipulandum;
• and
• dynamically calibrating said range of motion of said manipulandum by adjusting minimum and maximum values of said range of motion based on the extent of motion of said manipulandum up to a current point in time, wherein said dynamic calibration uses said filtered sensor values.

A method for compensating for sensing inaccuracies contributed to by compliance in the mechanical systems of a force feedback device, the force feedback device including at least one actuator for outputting forces and being coupled to a host computer, the method comprising:

• reading a raw sensor value representing a position of a manipulandum of said force feedback device in a range of motion of said manipulandum, said manipulandum being physically contacted and manipulable by a user;
• normalizing said raw sensor value to a normalized range of motion, said normalizing including providing a saturation zone at each end of said normalized range of motion that adjusts sensor values over a saturation level provided at said ends of said normalized range of motion to said saturation level;
• and
• reporting said normalized sensor value to said host computer, wherein said host computer updates an application program using said normalized sensor value.

A method for dynamically calibrating a sensed range of motion of a manipulandum of a force feedback device during usage of the device, said force feedback device being coupled to a host computer and including an actuator and at least one sensor, the method comprising:

• providing a sensing range of motion for said manipulandum less than a full range of motion of said manipulandum, said sensing range having a maximum value and a minimum value;
• reading a sensor value using said at least one sensor, said sensor value representing a position of said manipulandum of said force feedback device as said manipulandum is moved;
• outputting a force on said manipulandum by said actuator approximately concurrently with said reading of said sensor value;
• setting said maximum value of said sensing range to said sensor value if said sensor value is greater than said maximum value, wherein said maximum value is not set if said force is being output in a direction towards a maximum physical limit past said maximum value;
• and
• setting said minimum value of said sensing range to said sensor value if said sensor value is less than said minimum value, wherein said minimum value is not set if said force is being output in a direction towards a minimum physical limit past said minimum value.