This article will show conclusively that "kinematic instability" is not inherent to the hybrid position/force control scheme of robot manipulators but is a result of an incomplete and inap propriate formulation. The inverse of the manipulator Jacobian matrix is identified as causing the kinematic instability of the hybrid position/force control scheme. Linear algebra is used to explain clearly the implications of mapping between vec tor spaces and to reveal why the inverse of the manipulator Jacobian matrix should not be used in hybrid position/force control. A generalized architecture for hybrid position/force control is presented that can influence both joint positions and torques. This generalized formulation also includes the control of redundant manipulators. Some sufficient conditions for kine matic stability are proposed to determine when a system may become unstable without requiring a complete system analysis. A stable hybrid position/force control scheme is given and is demonstrated using an example that was previously shown to be unstable.

The frequency response characteristics of the hydraulic shaking table show the same as that of a two degree of freedom (DOF) resonance system due to the structural flexibility of the hydraulic shaking table. The hydraulic shaking system induces an anti-resonant peak during the working frequency band, which substantially reduces band width of the shaking table. The frequency response influence factor like mass, stiffness, and damping of the reaction wall are studied in this paper. The feed-forward control strategy is proposed in shaking system, which eliminates the effect of zero points at the anti-resonant peak and poles nearly the imaginary axis, broadens the bandwidth, and improves the control precision of the system. The notch filter is used to reduce the magnitude of resonant peak at the nature frequency of servo valve. The experimental results show that the proposed algorithm properly compensates the effect of structural flexibility and improves the bandwidth of the shaking system. INDEX TERMS Hydraulic shaking table, structural flexibility, resonance system, feed-forward control, notch filter.

No abstract

A graphical representation of admissible profile times for robot trajectories is presented from a kinematic perspective. Profie times are defied to be the acceleration time, slew time, and deceleration time for robot end effector motions. Given initial and f i a l robot end effector locations, identical profile times are computed for all the joints in the manipulator, where each joint has merent 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.The ability to have ratio-locked profie times results in smooth, well behaved end effector motions that are path invariant at different robot speeds. A dosed 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 solution is straightforward and may be used to compute the profile times in real time. The algorithm is implemented in the HAL robot control system at HP Labs for controlling robots in a manufacturing environment.

No abstract