Trajectory Tracking and Impedance Control of Hybrid Manipulators

Abstract

Usually, industrial robots are made up of serial manipulator architecture having large workspace but these suffer from several drawbacks such as low accuracy and heavy structural vibration. Similarly, the parallel architecture robots have better accuracy but small workspace. Therefore, in the last two decades, hybrid manipulators addressed great attention as a combination of serial and parallel chain architectures. In an effort to combine the advantages of serial and parallel chains in these manipulators, a brief introduction of hybrid manipulators is discussed here. These manipulators offer the possibility of having advantages of both architectures and reduce their drawbacks. A comprehensive literature review of kinematic and dynamic analysis of hybrid manipulators is done. Literature review on the overwhelming controller and impedance control is also done. Accordingly, the objectives of work are defined after this. A three dimensional hybrid manipulator with six degrees-of-freedom is proposed in the Thesis and this manipulator is made by placing a three degrees-of-freedom parallel manipulator over the other in series so as to increase its workspace and load carrying capacity. The forward and inverse dynamic models for planar hybrid manipulator as well as for 3D hybrid manipulator are developed. All the models are simulated in bond graph domain. The planar hybrid manipulator is validated for a practical application of lateral bending of human vertebrae and the path followed by the thumb of human hand while picking and placing an object. The 3D hybrid manipulator is also tested for trajectory tracking of the thumb of human hand during drawing an arc on white board with a marker pen. The physical models for planar parallel and hybrid manipulators are also reduced with Eigen value sensitivity method to reduce simulation time and complexity of the system. The response of reduced models is compared with full models to track a circular path. The workspace analysis of planar parallel and hybrid manipulators is done additionally and this illustrates that workspace is increased by connecting two parallel manipulators than a single parallel manipulator. Afterwards, the theory of impedance control with some changes is applied for an operation on a three dimensional L-shaped path having some restrictions imposed on the interactive forces when the manipulator is interacting with an object in its environment along with an approach to eliminate amnesia. Finally, the conclusions of the Thesis are presented in the end with scope for future research work.