This paper presents a novel compliant differential (CD) Shape Memory Alloy (SMA) actuator with improved performance compared to traditional SMA actuators. This actuator is composed of two antagonistic SMA wires and a mechanical joint coupled with a torsion spring. The torsion spring is employed to reduce the total stiffness of SMA actuator and improve the range of motion. The antagonistic wires increase the response time as one wire can be heated up while the other wire is still in the cooling process. Dynamic model of this actuator was established for control design. Experimental results proved that this new actuator can provide larger output range of motion and faster response speed than traditional SMA actuators under the same conditions. Sine wave tracking with 0.05 Hz, 0.08 Hz and 0.1 Hz were performed and our results demonstrated that this compliant actuator has good tracking performance under simple PID control.

We synthesize an adaptive motion control law for a free-flying robot with no external forces or moments. The basic idea is to make use of the articulated part of the space robot to control the position and orientation of the end-effector in an inertial frame. The inertia parameters for the robot end-effector and load are assumed to be a priori unknown. The articulated-body model is linear in the unknown parameters, so that an adaptive control law is developed. A novel feature of our approach is that the parameter estimates are obtained using momentum integrals only. In addition, we use unit quaternions to represent orientation errors. The stability properties of the adaptive control law is shown using Lyapunov stability theory. Computer simulations of an example 12 degrees of freedom space robot system are presented.

Contact between free-flying space robots, and the minimization of the impulse at contact are studied. A general approach for modeling systems with a moving base is presented. In particular, the formulation of the dynamical equations of motion for a space-based manipulator system with external applied forces are considered. The new equation of motion is then used to derive a dynamical contact model. Unlike previous approaches, the analysis takes into account both relative translational and rotational motions between contacting bodies. An analysis of the dynamical contact model reveals that the impulse at contact could be minimized by the optimization of a scalar cost function. Two approaches to the Cartesian space planning problem for space-based systems are discussed. A joint space planning strategy that achieves both trajectory tracking and impact minimization is proposed. Simulation results for a fifteen-degree-of-freedom (DOF) space robot are presented.>

The authors present a novel adaptive control method for space-based robots which achieves globally stable trajectory tracking in the presence of uncertainties in the inertial parameters of the system. They begin with a partitioning of the fifteen-degree-of-freedom system dynamics into two component: a nine-degree-of-freedom invertible portion and a six-degree-of-freedom noninvertible portion. The controller is then designed to achieve trajectory tracking of the invertible portion of the system. This portion of the system consists of the manipulator joint positions and the orientation of the base. The motion of the noninvertible portion is bounded but unpredictable. This portion of the system consists of the position of the robot's base and the position of the reaction wheels. Simulation results are presented on a space-based robot with five revolute joints and one prismatic joint.>

A control method is presented that achieves globally stable trajectory tracking in the presence of uncertainties in the inertial parameters of the system. The 15-degree-of-freedom (DOF) system dynamics are divided into two components: a 9-DOF invertible portion and 6-DOF noninvertible portion. A controller is then designed to achieve trajectory tracking of the invertible portion of the system, which consists of the manipulator joint positions and the orientation of the base. The motion of the noninvertible portion is bounded but otherwise unspecified. This portion of the system consists of the position of the robot's base and the position of the reaction wheels. A simulation is presented to demonstrate the effectiveness of the controller. A quadratic polynomial is used to generate the desired trajectory to illustrate the trajectory tracking capability of the controller.>