Contact stability in model-based force control systems of robotmanipulators

摘要

The authors address the stability problem in force control ofrobot manipulators. They analyze the stability of four well-knownmodel-based force control systems: hybrid force control, resolvedacceleration based force control, stiffness control, and impedancecontrol. The analysis is based on linearized models and uses theRouth-Hurwitz criteria. The results show that the stability of the fourcontrol systems studied depends upon the feedback gains as well as themanipulator configuration. When an arm engaged in a contact taskunexpectedly loses contact with the environment, all control systemsstudied except the hybrid control remain stable. The cause ofinstability in contact tasks is that the environmental stiffness matrixincreases the equivalent position gain in the control system. If thevelocity gain is chosen based only on the position gain neglecting alarge environmental stiffness, the resulting system will be highlyunderdamped and possibly unstable