Three dynamic characteristics of robot systems are discussed: rigid-body bandwidth, dynamically noncolocated flexible modes, and dynamically colocated flexible modes. All of these combine to limit the closed-loop bandwidth achievable in the individual joint control loops of the robot. They play a particularly important role in establishing performance limits for robots under force control.>

Three dynamic problems which arise in robot systems are discussed: rigid-body bandwidth; dynamically noncolocated flexible modes; and dynamically colocated flexible modes. These effects combine to set the closed-loop bandwidth achievable in the individual joint control loops. Simple models of robot systems are presented to illustrate these three dynamic effects. Some laboratory data are then presented and analyzed in these terms. Finally, the implications for robot system design is discussed in the hope that these issues will be considered in the development of the next generation of robot systems and machine tools.>

Dynamic models have been developed in an attempt to match the response of a robot arm. The experimental data show rigid-body and five resonant modes. The frequency response and pole-zero arrays for various models of structural flexibility are compared with the data to evaluate the characteristics of the models, and to provide insight into the nature of the flexibility in the robot. Certain models are better able to depict transmission flexibility white others describe types of structural flexibility.>

This paper provides an analytical overview of the dynamics involved in force control. Models are developed which demonstrate, for the one-axis explicit force control case, the effects on system closed-loop bandwidth of a) robot system dynamics that are not usually considered in the controller design; b) drive-train and task nonlinearities; and c) actuator and controller dynamics. The merits and limitations of conventional solutions are weighed, and some new solutions are proposed. Conclusions are drawn which give insights into the relative importance of the effects discussed.

A series of lumped-parameter models is developed in an effort to predict the dynamics of simple force-controlled robot systems. The models include some effects of robot structural dynamics, sensor compliance, and workpiece dynamics. A qualitative analysis suggests that the robot dynamics contribute to force-controlled instability.