Vision-Based Hybrid Controller to Release a 4-DOF Parallel Robot from a Type II Singularity
José L. Pulloquinga,
Rafael J. Escarabajal,
Jesús Ferrándiz,
Marina Vallés,
Vicente Mata,
Mónica Urízar
Affiliations
José L. Pulloquinga
Departamento de Ingeniería de Sistemas y Automática, Instituto de Automática e Informática Industrial, Universitat Politècnica de València, 46022 Valencia, Spain
Rafael J. Escarabajal
Departamento de Ingeniería de Sistemas y Automática, Instituto de Automática e Informática Industrial, Universitat Politècnica de València, 46022 Valencia, Spain
Jesús Ferrándiz
Departamento de Ingeniería de Sistemas y Automática, Instituto de Automática e Informática Industrial, Universitat Politècnica de València, 46022 Valencia, Spain
Marina Vallés
Departamento de Ingeniería de Sistemas y Automática, Instituto de Automática e Informática Industrial, Universitat Politècnica de València, 46022 Valencia, Spain
Vicente Mata
Departamento de Ingeniería Mecánica y de Materiales, Instituto Universitario de Investigación Concertado de Ingeniería Mecánica y Biomecánica, Universitat Politècnica de València, 46022 Valencia, Spain
Mónica Urízar
Department of Mechanical Engineering, Faculty of Engineering in Bilbao, University of the Basque Country, 48013 Bilbao, Spain
The high accuracy and dynamic performance of parallel robots (PRs) make them suitable to ensure safe operation in human–robot interaction. However, these advantages come at the expense of a reduced workspace and the possible appearance of type II singularities. The latter is due to the loss of control of the PR and requires further analysis to keep the stiffness of the PR even after a singular configuration is reached. All or a subset of the limbs could be responsible for a type II singularity, and they can be detected by using the angle between two output twist screws (OTSs). However, this angle has not been applied in control because it requires an accurate measure of the pose of the PR. This paper proposes a new hybrid controller to release a 4-DOF PR from a type II singularity based on a real time vision system. The vision system data are used to automatically readapt the configuration of the PR by moving the limbs identified by the angle between two OTSs. This controller is intended for a knee rehabilitation PR, and the results show how this release is accomplished with smooth controlled movements where the patient’s safety is not compromised.
