This paper describes a simple control strategy for stable hard-on-hard contact of a manipulator with the environment. The strategy is motivated by recognition of the equivalence of proportional gain explicit force control and impedance control. It is shown that negative proportional force gains, or impedance mass ratios less than unity, can equivalently provide excellent impact response without bouncing. This result is indicated by an analysis performed with an experimentally determined arm/ sensor / environment model. The results are corroborated by experimental data from implementation of the control algorithms on the CMU DD Arm II system. The results confirm that manipulator impact against a stiff environment without bouncing can be readily handled by this novel control strategy. 1 Introduction There are two extreme modes of operation for a manipulator: position controlled motion through free space, and force controlled interaction while constrained by the environment. Obviously th...

This paper discusses computational and experimental details necessary for successfully implementing and evaluating a wide variety of force control strategies. First, a review of both explicit force and impedance control strategies is provided. Second, the basic computational requirements of these schemes are discussed, and the hardware and timing information for our implementation is provided. Third, computational problems such as noise filtering and sampling rates are explained and discussed in detail. Finally, a review of the experimental results obtained is provided. These results support the previous discussions by demonstrating the importance of fully considering the implementational details required for successful force control of robotic manipulators.

This thesis presents a new actuator system consisting of a micro-actuator and a macroactuator coupled in parallel via a compliant transmission. The system is called the Parallel Coupled Micro-Macro Actuator, or PaCMMA. In this system, the micro-actuator is capable of high bandwidth force control due to its low mass and direct-drive connection to the output shaft. The compliant transmission of the macro-actuator reduces the impedance (stiffness) at the output shaft and increases the dynamic range of force. Performance improvement over single actuator systems was expected in force control, impedance control, force distortion and reduction of transient impact forces. A set of quantitative measures is proposed and the actuator system is evaluated against them: Force Control Bandwidth, Position Bandwidth, Dynamic Range, Impact Force, Impedance ("Backdriveability"), Force Distortion and Force Performance Space. Several theoretical performance limits are derived from the saturation limits of ...

This paper presents the analysis and experimental verification of a fourth order model of the arm/ sensor / environment system plant, to be use in evaluation of force control strategies. Both the undamped and underdamped cases are investigated. Approximations and qualifications, based on the reality of our experimental system, help reduce the solution to just a few dominant terms. Comparing these terms with experimental data of the system undergoing small oscillations yields approximate values for all of the parameters in the model. To justify the obtained values, and thereby the approximations used, two measures are taken. First, a simulation of the fourth order model is performed, and compared against experimental data obtained from the CMU DD Arm II system. Second, a stability analysis of several force control schemes acting on the modelled plant is reviewed and compared against experimental tests of the controllers. In both cases, the simulation and analysis match closely with the ...