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SUMMARYThis paper presents the design, kinematics, dynamics and control of a low-cost parallel rehabilitation robot developed at the Universitat Politècnica de Valencia. Several position and force controllers have been tested to ensure accurate tracking performances. An orthopedic boot, equipped with a force sensor, has been placed over the platform of the parallel robot to perform exercises for injured ankles. Passive, active-assistive and active-resistive exercises have been implemented to train dorsi/plantar flexion, inversion and eversion ankle movements. In order to implement the controllers, the component-based middleware Orocos has been used with the advantage over other solutions that the whole scheme control can be implemented modularly. These modules are independent and can be configured and reconfigured in both configuration and runtime. This means that no specific knowledge is needed by medical staff, for example, to carry out rehabilitation exercises using this low-cost parallel robot. The integration between Orocos and ROS, with a CAD model displaying the actual position of the rehabilitation robot in real time, makes it possible to develop a teleoperation application. In addition, a teleoperated rehabilitation exercise can be performed by a specialist using a Wiimote (or any other Bluetooth device).

A robot interacting with the environment requires that the end effector position is tracked and that the forces of contact are kept below certain reference values. For instance, in a rehabilitation session using a robotic device, the contact forces are limited by the allowed strength of the human limbs and their complex-joints. In these cases, a control scheme which considers both position and force control is essential to avoid damage to either the end effector or the object interacting with the robot. This paper therefore develops a real-time force/position control scheme for a 3-DOF parallel robot whose end effector holds a DOF one translation (1T) and two rotations (2R). The implemented hybrid force/position control considers, as a reference, the normal force on the mobile platform, which is measured by means of a load cell installed on the platform. The position control is designed to track the orientations of the robot either in joint or task space using a model-based control scheme with identified parameters. Moreover, the force control is based on a PD action. The control scheme is developed through simulations, before being applied to an actual parallel robot. The findings show that with the implemented controller, the actual robot accomplishes the reference values for the normal force on the mobile platform, while at the same time the platform accurately follows the required angular orientation.

La complejidad actual de los sistemas robotizados y de las aplicaciones queéstos deben realizar requiere que los robots dispongan de un control automático que permita la ejecución de las distintas tareas que forman parte del algoritmo de control y que tenga en cuenta cuestiones relacionadas por ejemplo con la periodicidad, el modo de ejecución, el hardware que se utilizará, etc. Para el desarrollo de este tipo de aplicaciones de control en losúltimos años se tiende a la programación basada en componentes puesto queésta permite obtener código reusable. Así mismo también se está incrementando la utilización de middlewares que permiten la abstracción de los sistemas operativos, el soporte de tiempo real y la infraestructura de comunicaciones. En el presente artículo se propone la utilización de un middleware orientado especialmente a la robótica: OROCOS. Así se describe cómo haciendo uso de una de sus librerías, Orocos Toolchain, se han desarrollado una serie de componentes correspondientes a distintos algoritmos para el control dinámico de robots, aplicándose a un robot paralelo de 3 grados de libertad (DOF).

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.

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Force platforms are the basic equipment to measure ground reaction forces and moments in biomechanical studies. So, accurate in situ calibration of force platforms is critical for ensuring the accuracy and precision of the results of experimental studies. Although there are different avaliable approaches for in situ calibration, most of the existing methods do not use realistic and repeteable force patterns to calibrate platforms. In this paper, a new technique based on the use of a 3PRS parallel robot for applying a predefined dynamical load is proposed, where force patterns can be reproduced in a similar way as the used during actual experimental measures. This robot can be programmed to apply force patterns simulating the conditions of human gait, running or jumping. Calibration is performed by comparing the forces measured by the platform and the ones measured by a calibrated load cell. A new algorithm was developed for correcting the sensitivity coefficients, including an estimation of errors in the orientation of the load cell. This method has been validated by means of an specific experiment.