The Communication and Computation Architecture for a Universal Space Robotic Joint

In the recent years the two main disciplines of space robotics have been exploration e.g. [1] as well as service and maintenance e.g. [2]. Depending on the application, the system level complexity differs significantly. Both disciplines comprise on the one hand dedicated robots for a very specific task (e.g, [3], [4]) and on the other hand highly complex systems (e.g, [5], [6]) with different levels of autonomy. However, independent of the complexity, all robotic systems can be described as a configuration of joints. Therefore, a joint can be considered as the smallest unit of a robot's configuration to setup a specific kinematic structure. We applied this joint based module approach for mechanic, electronics and software development already in several terrestrial robotic developments e.g. [7], [8] who even reached commercialization state. Hence the logical step was to apply this approach also to space robot development of CAESAR (Compliant Assistance and Exploration SpAce Robot) [9]). In this paper we focus on the electronics and software part by presenting the computation and communication architecture for a universal space robotic joint based on CAESAR's joint control unit (JCD). It comprises all aspects from the overlying high level control of multiple joints on a real-time host down to the synchronisation of communication participants on register transfer level (rtl). This involves also the used middleware implementation and fieldbus communication as well as actuator control and sensor data acquisition.