Multi-objective control systems for complex robots usually have to handle multiple prioritized tasks. Most existing hierarchical control techniques handle either strict task priorities by using null-space projectors or a sequence of quadratic programs; or non strict task priorities by using a weighting strategy. This paper proposes a novel approach to handle both strict and non-strict priorities of an arbitrary number of tasks. It can achieve multiple priority rearrangements simultaneously. A generalized projector, which makes it possible to completely project a task into the null-space of a set of tasks, while partially projecting it into the null-space of some other tasks, is developed. This projector can be used to perform priority transitions and task insertion or deletion. The control input is computed by solving one quadratic programming problem, where generalized projectors are adopted to maintain a task hierarchy, and equality or inequality constraints can be implemented. The effectiveness of this approach is demonstrated on a simulated robotic manipulator in a dynamic environment.
KeywordsRedundant robots Task hierarchy Priority switching Dynamics Torque-based control
We would like to thank the reviewers for their insightful comments on the paper. This work was partially supported by the European Commission, within the CoDyCo project (FP7-ICT-2011-9, No. 600716) and by the RTE company through the RTE/UPMC chair Robotics Systems for field intervention in constrained environments held by Vincent Padois.
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