A sufficient condition for the kinematic stability of a robot hybrid position/force control scheme is defined. The test for the sufficient condition is a technique that uses only the kinematic information to determine system stability or to identify situations where possible stability problems may occur. The sufficient condition test is applied to an example, using the original hybrid position/force control scheme of J.J. Craig and M.H. Raibert (1979) and the corrected hybrid position/force control scheme proposed by W.D. Fisher and M.S. Mujtaba (1992). A root locus analysis showed the original hybrid control approach to be unstable. It is shown that the sufficient condition is also violated for this situation. In the corrected hybrid control approach, the sufficient condition is never violated for any manipulator and the same example is shown to be always stable. A root locus plot for the hybrid control approaches is included to confirm the results of the sufficient stability condition.>

The authors present an inverse kinematic algorithm for a four-revolute-joint (4-R) spherical wrist that provides for a complete set of spatial orientations, is nonsingular, and is simple to implement with existing technology. The algorithm is a rate-controlled method that depends on the required Cartesian rate. In the process of presenting the algorithm, the authors have developed the fundamentals of differential motion with n-revolute-joint spherical wrists. The method is outlined and applied to a 4-R regional structure. The goal is to combine the 4-R spherical wrist with the 4-R regional structure to develop an 8-R manipulator that is free of internal singularities.>

A graphical representation of admissible profile times for robot trajectories is presented from a kinematic perspective. Profile times are defined to be the acceleration time, slew time, and deceleration time for robot end effector motions. Given initial and final robot end effector locations, identical profile times are computed for all the joints in the manipulator, where each joint has different acceleration and velocity limits. Ratio-locked profile times occur when the robot motion is joint-coordinated, with all of the joints moving in a proportional manner relative to each other. A closed-form solution to compute the minimum ratio-locked profile times for robot trajectories is presented for the case when the acceleration limit for each joint is equal to its deceleration limit. The algorithm is implemented in the HAL robot control system at HP Labs. for controlling robots in a manufacturing environment.>