An Open Source Distributed Platform for the Control of the PUMA 560 Manipulator

In this paper, an RTAI-Linux based distributed platform for the control of the PUMA 560 robotic manipulator is presented. From the mechanical point of view, the PUMA 560, besides being one of the first and most popular 6-DOF anthropomorphic manipulator, is still a very good example of implementation of small size robotic arms. On the other hand, its original control system, if compared to modern controllers, is an old piece of computer science history. Our goal is to preserve the mechanics and the power electronics of the PUMA 560 and replace the original control system with a modern and flexible platform based on RTAI-Linux. A PC/104 embedded system equipped with two DAQ boards is used to manage the I/O signals of the robot and to control the low level security functions, bypassing the original Mark III controller, while the high-level controller and the user interface run on a standard PC. With the aim of comparing the behaviour of the robotic device with a simulation of the system, useful for task planning and fault detection, the controller of the robot communicates also with a real-time simulation of the PUMA 560 that runs on a third PC. These three real-time systems are based on RTAI-Linux, and RTNet is used for the implementation of low-latency deterministic network communications needed in distributed control applications. In the paper, after the description of the architecture of the proposed control platform, the performances of the system are analyzed with particular attention to the execution time of the various tasks, communication delays due to network communication and comparison between the response of the real and the simulated robot.