Force interactive virtual reality using local joint error control

Robot manipulators are the natural choice for transmitting computer-generated dynamic forces from a virtual environment to a human user immersed in that environment. Control schemes for this type of interactive interface are extensions of the techniques used in teleoperation systems. with the forces applied between the master and the human generated by the dynamic model rather than measured from sensors on the slave. Stability problems arise when the robot inertia and dynamics are coupled to the complex and time-varying human dynamic characteristics. In this work, a new local feedback error control technique is applied to an interface robot to allow motion only in free directions in the virtual space. This virtual force interface does not require the use of an end effector force transducer. As in all local control schemes, the dynamic characteristics and cross-coupling effects of the manipulator are neglected, so that actual motion may deviate slightly from the desired trajectory during high speed operation. Experimental results are presented showing the use of this haptic device moving within a cubic space representing a fish tank. Motion of the hand controls the motion of virtual fish within the tank, and as the fish contact the walls of the virtual tank, the human feels the hard surface of the tank walls. Stability for this scheme is based on the stability of position error feedback for the manipulator.