A singularity-robust LQR controller for parallel robots

Conference Article


IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS)





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Parallel robots exhibit the so-called forward singularities, which complicate substantially the planning and control of their motions. Often, such complications are circumvented by restricting the motions to singularity-free regions of the workspace. However, this comes at the expense of reducing the motion range of the robot substantially. It is for this reason that, recently, efforts are underway to control singularity- crossing trajectories. This paper proposes a reliable controller to stabilize such kind of trajectories. The controller is based on the classical theory of linear quadratic regulators, which we adapt appropriately to the case of parallel robots. As opposed to traditional computed-torque methods, the obtained controller does not rely on expensive inverse dynamics computations. Instead, it uses an optimal control law that is easy to evaluate, and does not generate instabilities at forward singularities. The performance of the controller is exemplified on a five-bar parallel robot accomplishing two tasks that require the traversal of singularities.


linear quadratic control, manipulators, optimal control, robot dynamics, robot kinematics.

Author keywords

LQR, Optimal Control, Parallel Robots, Manifold, Singularites, Singularity-Robust

Scientific reference

R. Bordalba, J.M. Porta and L. Ros. A singularity-robust LQR controller for parallel robots, 2018 IEEE/RSJ International Conference on Intelligent Robots and Systems, 2018, Madrid, Spain, pp. 270-276.