A simplified dynamic model for a one-link tip force-controlled flexible manipulator is simulated. Experimental work is then carried out and comparisons are made with the theoretical dynamic simulations. Results show that, during the initial contact process, separation between the manipulator and the environment occurs to the link elastic motion. This nonlinear effect causes a delay of force actuation and the occurrence of impacts, which are significant and detrimental to the system dynamic stability. It is shown that the nonlinear effects can be minimized by preloading an initial contact force through open-loop control.>

The effect of link flexibility on the dynamic stability of a two-link force-controlled robot manipulator is investigated. Assuming that the contact point is locked, the nonlinear open-loop equations for the compliant motion are derived. By using the hybrid force-position control law, the closed-loop dynamic equations are explicitly derived and linearized about some equilibrium configuration. Stability analyses are carried out by computing the eigenvalues of the linearized system equations. Results are verified by numerical simulations using the complete nonlinear dynamic equations. The effect of the wrist force sensor stiffness on the dynamic stability is also investigated. Results show that the link flexibility is an important source of dynamic instability in the motion of force-controlled manipulators. Moreover, the system stability is dominated by the effect of the distributed flexibility of the first link.>

The effects of joint and link flexibilities on the dynamic stability of two-link force-controlled manipulators are investigated. The complaint equations of motion involving joint and link flexibilities are presented. Three force control methods, which include the stiffness method, the damping method, and the hybrid method, are considered for the analysis. The linearized equations of motion about the equilibrium positions are used for stability analysis. Depending on the control method used and the distribution of system flexibility, different dynamic behaviors are predicted. Flexibility, which causes the instability problem of force-controlled manipulators, is inherent in every robotic structure. Thus, more sophisticated control strategies using different sensors which can compensate the flexibility effects are needed to improve the dynamic performance of force-controlled flexible-joint manipulators.>