Hybrid force/position control for a 3-DOF 1T2R parallel robot: Implementation, simulations and experiments

Abstract

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.

Desarrollo de un Robot de Rehabilitación pasiva para la articulación de la muñeca mediante la implementación de un microcontrolador Arduino UNO

“…Selección de los motores actuadores, de los análisis cinemáticos y cinéticos previos se pudo obtener los siguientes valores de trabajo como los son: las velocidades angulares instantánea máximas del dispositivo en los planos de rotación se encuentran alrededor de los 432,42 °/s, y el valor del par mínimo necesario para lograr los movimientos de 184,5 N‧mm, al considerar estos valores se optó por seleccionar el motor paso-paso STM17, el cual se encuentra conformado con un sistema encoder que permitirá detectar la posición del dispositivo en cualquier instante de tiempo. Este modelo corresponde a un modelo de motor paso-paso de la serie NEMA 17, el cual puede alcanzar una velocidad máxima de 3600 °/s al conectarse a un controlador simple [22] o incluso uno avanzado si se quieren tomar en cuenta aspectos de control de fuerza [23], permitiendo generar un par de trabajo mayor a 480,18 N‧mm que es adecuado para las rutinas de rehabilitación al dispositivo.…”

Research on Foot Trajectory Tracking of Parallel Wheel-legged Robot based on Dynamic Model Predictive Control

“…In [6], the desired lengths of actuators of platform has been measured based on solving inverse kinetic problem of the desired trajectory in task space, which developed the joint space control. Task space control can be performed based on: (1) Position and rotation of the movable platform using position, orientation and vision sensors [7], (2) Solving forward kinematic problem (FKP) by the values of sensors [8]. The first approach is expensive and the latter method needs lots of calculations.…”

Development and Control of a Pneumatic-Actuator 3-DOF Translational Parallel Manipulator with Robot Vision

“…In the task space control, the forward kinematic problem can be effectively solved by using the measured lengths of the PM links. As compared to the joint speed control, the more precise position of the PM end-effector can be performed by using vision and position sensors [11,12]. In 2011, Chiang et al [13] developed a 3-prismatic-universal-universal (3-PUU) PM that is driven by three vertical-axial pneumatic actuators (PAs) and used servo control for path tracking.…”