Implementation of dynamic controllers using real-time middleware for a low-cost parallel robot

Abstract

As it is well known, robots are complex devices capable of performing very fast and precise movements. Developing robots and their controllers is a very challenge task due to the different technologies that are needed to be dealt with (access to peripherals, real-time operating systems, communications …) and the amounts of programming work that is needed. Moreover, this work needs to be repeated in most cases when a new robot is developed. A new way is needed for developing the code implemented for controlling these robots that allows to reuse it in a safe way.In this paper, the Orocos (Open Robot Control Software) middleware has been chosen for the controller development. Orocos is a real-time middleware, focused on control systems, especially those related to robotics and automation. Its greatest advantage over the other solutions available is the capability to provide an off-the-shelf hard real-time operation. This is essential in most of the robotics applications, making this middleware in a very suitable piece of software. Since Orocos is a component-based middleware, several CBSD (componentbased software development) techniques have been used to design and implement the control system. Thus, using a modular control structure, a number of advantages can be achieved such as code reusability, execution of the modules in a distributed way, ability to load or instantiate a module several times, easy following of flow execution and fewer programming errors. In addition, these components are configurable and reconfigurable in runtime.In fact, in a typical control application, there are three parts that can be thought as software components that are reading sensors, computing the control action, and sending it to the actuators. Besides this, in some applications it is also possible to find common parts to different control strategies that can be implemented as separate software components that are loaded, instantiated and configured depending on the control strategy that it is needed in a particular moment.The robot that has been controlled using Orocos modules is a low cost parallel-robot PRS. The parallel distinction means that the terminal end of the robot member is connected to the base with at least two kinematic lims, with the particularity that they all work in parallel. The main advantages of this type of robot are the high speed, accuracy, and the ability to carry heavy loads.