It is well-known that iff the robot with its end-effector force control is passive, the closed loop system consisting of the robot and an arbitrary passive environment is asymptotically stable. Passive robot control, however, limits the achievable robot impedance reduction. Recently, investigated what performance can be achieved with nonpassive control when uncertainty bounds for the environment are known. The question of stability margins neglected in is treated in our companion paper. In this paper we report on experiments on a full scale industrial robot in order to identify six transfer functions from the velocity reference of the inner velocity loop to the end effector force output for six different environments, from solid wall to air. It is shown how the experimental data also makes it possible to compute the impedance of the controlled robot. Two controllers are designed: one marginally stable but with nonpassive and low-gain controlled robot impedance at low frequencies, and another controller respecting the stability margin of closed loop sensitivity gain less than 6 dB, but with a passive controlled robot impedance that has higher gain for low frequencies than that of the first controller. The designs are compared experimentally by having the robot interact with environments of different impedances, and with a human operator leading the robot The paper is concluded by a short discussion of the possible need of controller adaption when a robot operates in varying impedance environments, and interacts with a human operator.

In the field of comanipulation (i.e. a man and a robot sharing the same task), force amplification is an interesting function that can be achieved by using two force sensors. This technique is known in the literature but little attention has been paid so far to stability/passivity properties. We will explain how to deal with passivity based stability criteria, and point out performance limitations of such a control in case of noncollocated and bandwidth limited force sensors. Theoretical, as well as experimental results will be presented.

We focus on comanipulation, i.e. manipulation of an object simultaneously held by a robot and a human operator. In this domain, a major difficulty is raised by significant variations of human dynamics, which depend not only on the arm posture, but also on the muscular activity (muscular co-contraction) and more generally on the type of task being performed: fine positioning, gross and rapid movements, repeated movements, etc. An ideal comanipulation system should be able of adapting its behavior to the operator's functional intention, resulting in an intuitive assisting device. Toward this goal, we present in this paper first results of our research aimed at developing an instrumented handle mounted on a robot end-effector and held by an operator, that can be used for estimating the grasping force and for adapting the robot controller accordingly. We show first experimental evidences that changes in the grasping force drastically affect the robot controller performances. We thus propose a handle design and a gain scheduling strategy that result in a robot behavior adequate for any kind of grasps. This solution is successfully experimented with a 1 degree of freedom robot under largely variable comanipulation conditions, exhibiting a stable and efficiently adaptive behavior.