Space Robotics Dynamics Simulation Performance in Real-Time Environments

The integration of various hardware and software components to achieve an overall simulation capability for the dynamic behaviour of space robotic systems are reported, being all part of real-time, hardware-in-the-loop (HIL) system simulation environment. The investigations are focused on analysing the various items impacting real-time performance and on adapting an exisitng dynamics analysis tool for multibody systems (SIMPACK) to automatically generate real-time dynamics simulation code that can be configured and used in a variety of simulation environments (e.g. Matlab/Simulink). Our HIL simulation environment mainly consists of the following components: a) the SIMPACK model software simulating in both non-real and real-time the dynamic behavioour of the space robot, the base (chaser) and target satellites, b) an industrial robot (IR) being slaved by the calculated end effector trajectories of interest, c) and a force/torque sensor system attached to the IR gripper that measure the applied forces during contact. By feeding back the measured contact forces into the software simulation, modeling complexity will be reduced thus avoiding vey critical and time-consuming modeling effort of complex contact dynamics that otherwise would deteriorate or even make impossible real-time applications. However, the closed-loop simulation may get instable in cases where dead times in the overall HIL simulation are too large, arising predominatly from robot trajectory interpolation and force/torque sensor data acquisition and processing and depending very strongly upon the stiffness and damping behaviour of both, the simulated space manipulator and the measured contact dynamics. Intensive studies have been performed in order to understand and to remedy this problem. the results obtained are based on a typical space robotics scenario such as the Experimental Servicing Satellite system, a repair satellite demonstrating special servicing robotics functions of telecommunications satellite in geostationary orbit. A very important part of this study is dedicated to the performance assessment of the various simulation components integrated in the real-time environment