At the Cleveland Clinic, a novel means of cancer treatment, image-directed radiation therapy (IDRT), is being explored experimentally. Using a linear accelerator manipulated by a robot and computed tumor coordinates based on machine vision, this treatment means offers the potential for more highly targeted radiation dose delivery to tumors, reducing the collateral damage to surrounding healthy tissues. This paper presents the motivation for IDRT, identification of the challenges in accomplishing IDRT, and simulated and experimental results for evaluating the potential benefits of IDRT, specifically with respect to lung cancer treatment.

This research focuses on the implementation of a natural admittance controller on an industrial manipulator. Natural admittance control is a particular type of interaction controller which guarantees stability with any passive environment. The admittance criterion is presented along with methods of control. A robot model is proposed and the model parameters are found experimentally. A controller is designed which takes into consideration the aforementioned model. Also, a convenient technique that allows "on the fly" modification of controller gains and desired dynamics has been developed. The controller was designed and implemented on an industrial robot and performance results are presented. The implemented scheme is shown to offer high performance and guaranteed stability with good friction rejection.>

The authors present an analysis of why control systems are ineffective in compensating for acceleration disturbances due to Coulomb friction. Linear arguments indicate that the effects of Coulomb friction on a body are most difficult to reject when the control actuator is separated from the body of compliance. The linear arguments were illustrated in a nonlinear simulation of optimal linear tracking control in the presence of nonlinear friction. The results of endpoint acceleration measurements for four robot designs are presented and are compared with simulation and with equivalent measurements on a human. It is concluded that Coulomb friction in common bearings and transmission induces unacceptable levels of endpoint acceleration, that these accelerations cannot be adequately attenuated by control, and that robots for microgravity work will require special design considerations for inherently low friction.>