Abstract
This paper deals with a new control scheme for Parallel Kinematic Manipulators (PKMs) based on the L1 adaptive control theory. The original L1 adaptive controller is extended by including an adaptive loop based on the dynamics of the PKM. The additional model-based term is in charge of the compensation of the modeled nonlinear dynamics in the aim of improving the tracking performance. Moreover, the proposed controller is enhanced to reduce the internal forces, which may appear in the case of Redundantly Actuated PKMs (RA-PKMs). The generated control inputs are first regulated through a projection mechanism that reduces the antagonistic internal forces, before being applied to the manipulator. To validate the proposed controller and to show its effectiveness, real-time experiments are conducted on a new four degrees-of-freedom (4-DOFs) RA-PKM developed in our laboratory.
Highlights
Adaptive control of mechanical manipulators has gained an increased interest in the last few decades
The corresponding joint trajectories are computed by solving the inverse kinematics problem (IK), which is trivial in the case of parallel kinematic manipulators (PKMs)
A new adaptive control scheme for mechanical manipulators based on L 1 adaptive control theory is proposed
Summary
Adaptive control of mechanical manipulators has gained an increased interest in the last few decades. The proposed control law consists of a fixed PD feedback loop in addition to an adaptive loop intended to compensate for non-linearities of the system This controller was not suitable for real-time setups. The number of the controller parameters to be estimated was too large (11 parameters for a simple 3-DOFs manipulator, after simplification) In addition to these issues, MRAC inherently suffers from a major drawback; the estimation and the control loops are coupled (Hovakimyan and Cao, 2010). A new adaptive control scheme is proposed, it combines the benefits of both L 1 and model-based adaptive control It was shown in (Bennehar et al, 2015) that L 1 adaptive control applied to a 4-DOFs PKM outperforms the PD controller in terms of tracking performance.
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