Dynamic Emulation of Space Robot in One-g Environment using Hardware-in-the-Loop Simulation J.-C. Piedboeuf, F. Aghili, M. Doyon, Y. Gonthier and E. Martin Canadian Space Agency, 6767 Route de l’Aeroport, St-Hubert, Quebec, Canada, J3Y 8Y9 Jean-Claude.Piedboeuf@space.gc.ca Abstract To verify all robotic tasks involving a space robot interacting with environment, such as the Special Purpose Dexterous Manipulator (SPDM), one should appeal to a simulation technique because the space robot cannot operate in an 1-g environment. However, to simulate dynamical behavior of a robot interacting with environment creates difficulties due to complexity of the physical phenomenon involved during the interaction. In this work we develop an hardware-in-loop simulation (HLS) technique, where a simulation of the space robot dynamics is combined with emulation of the contact dynamics by using a rigid robot prototype performing contact task. The rigid robot is not dynamically or kinematically equivalent to the space robot, but it is controlled so that its endpoint dynamics replicates that of the space robot. Simulation and experimental results given from implementation on a six degrees of freedom manipulator are presented. 1 Introduction Canada’s contribution to the International Space Station (ISS) is the Mobile Servicing System (MSS) ([1]). A major com- ponent of the MSS is the Special Purpose Dextrous Manipulator (SPDM). While the Canadarm 2 (Space Station Remote Manipulator System) will assemble the ISS, the SPDM will be required for performing maintenance tasks. Essentially, the SPDM will manipulate the Orbital Replacement Units (ORU), the components of the ISS systems replaceable on orbit. The SPDM will operate directly connected to the ISS or to the tip of the Candarm 2. Both the Canadarm 2 and the SPDM are tele-operated by an operator located inside the ISS. Due to the important flexibility in the Canadarm 2/SPDM system, all insertion/extraction tasks involving the SPDM will be done using only one arm with the other arm grasping a stabilization point. The cost and risks associated with the execution of robotic tasks around the ISS require that all procedures be verified on earth prior to their execution in space. The Canadian Space Agency (CSA) is currently developing the SPDM Task Verification Facility (STVF). One of the main technical challenges with the STVF is the verification of the feasibility of the insertion/extraction tasks. Simulation is a viable tool to validate functionality of a space manipulator ([2]). A faithful model of the space robot is available, but accurate modeling of contact dynamics is difficult to obtain due to the complex nature of the physical phenomenon during the interaction. The main difficulty in emulating a space robot on ground is the fact that space manipulators cannot support their own weight on earth. Different possibilities exist for the ground emulation of a space robot. The first one is to use a flat floor as done for Shuttle Remote Manipulator System or European Robotic Arm validation. However, the limitation to a plane is not representative of real contact task. A second possibility is to use a scaled-down version of the space manipulator. While attractive in theory, this is very difficult to realize in practice especially for a robot having flexibility. The third option is to use counterweights to build a system that will be dynamically equivalent to the space robot as done by MD- Robotics for the engineering test of the SPDM. This is an interesting option but matching the frequency response of the space robot is difficult. In addition, the SPDM is mounted itself on the Canadarm 2 which is very flexible. A self-balancing system is not able to represent the flexible motion of the base. The last option is to use hardware-in-the-loop simulation (HLS)as done by the Canadian Space Agency ([3],[4]) but also by DLR ([5]) and NASA ([6]). It is a hardware-in-the-loop simulator consisting in a rigid robot with its control, a simulation of Canadarm 2/SPDM dynamics and a visualisation engine. An operator controls the motion of SPDM through the simulation engine which generates the endpoint motion of the SPDM. That is then used as a setpoint for the robot controller who ensures that the robot endpoint follows the same trajectory as the SPDM. The contact forces are measured using force/moment sensors and fed back into the simulator to allow the dynamic simulation engine to react to external contact forces. This concept 7th ESA Workshop on Advanced Space Technologies for Robotics and Automation 'ASTRA 2002' ESTEC, Noordwijk, The Netherlands, November 19 - 21, 2002 1