This paper presents a methodology to synthesize robot compliant motions in environments that can move or oscillate due to random disturbances. Motions of the environment are taken into account in the task frame position which is considered unknown and time-varying but bounded. The position, velocity and force responses of the coupled robot/environment system are determined and tasks are expressed as inequality constraints on these expressions. A set of controller parameters is found by fitting the largest possible uncertainty box inside the region of the impedance parameter space that satisfies all task constraints. Experimental results demonstrate the validity and robustness of the approach.

This paper discusses the implementation and performance of the impedance control scheme on position controlled robot manipulators. The performance of such impedance controllers is very dependent on the behavior of the underlying position controller. Three different configurations are presented and compared with respect to their ability to follow the nominal impedance equation, as well as their ease of implementation. A very simple method based on the use of additional feedback signals is also proposed as a way of significantly improving the tracking performance of these controllers. Simulation as well as experimental results demonstrating the controller behaviors are presented.>

This paper presents a new approach to the problem of control synthesis and motion planning for compliant motions of manipulators. The scheme is based on decoupled linear impedance models of the robot and the environment, in which the errors due to control, task frame estimation, as well as environment uncertainty are explicitly taken into account. The technique consists of characterizing the position, velocity and force responses of the decoupled models, and expressing the task goals as constraints on these expressions. The impedance parameters of the controller are found by fitting uncertainty boxes inside the region of the parameter space that satisfies all task constraints. An experimental verification of this method is presented for the task of closing a circuit breaker.>

An investigation is reported of the design and implementation of a compliant control scheme based on damping control that can be used to perform position and force control of robot manipulators in teleoperation or autonomous control. The dynamic performance of such a system in constrained situations is very dependent on the environmental parameters. An adaptive controlled based on the model reference adaptive controller (MRAC) approach is developed for a single-axis manipulator model and is further extended to the multiaxis case using the concept of directional adaptation: the MRAC and the compliance are active only in the direction of the force constraints, thus allowing near-perfect velocity and force tracking in all directions. Simulation results show that the adaptive scheme can significantly improve the performance in force tracking and enhance stability at high stiffness by rendering the behavior independent of the environment and robot parameters. Some experimental implementation concerns are presented in light of a series of preliminary tests with a PUMA 560 manipulator.>

An expert system is developed which determines the best grasp configuration to pick up a rectangular box. This two-level system first chooses, from a predetermined set of grasps, the ones best suited for the task using a set of rules, and then computes a quality index for each possible configuration. The program is written in LISP and was tested for many different objects and situations. The grasps found are not necessarily optimal but are efficient since they are similar to the grasps a human would choose in the same situation. Because the program gives fast results and doesn't perform tedious computations, the best grip found can easily be used as a suboptimal solution or as a starting point for an optimizing program.>