Smooth continuous transition between tasks on a kinematic control level: Obstacle avoidance as a control problem

• A new simple formulation for the null-space projection is proposed.
• Undisturbed motion of the secondary task if the primary task is not active.
• Avoiding obstacles without changing initial trajectory.
• Smooth transition between primary and secondary tasks.

Kinematically redundant robots allow simultaneous execution of several tasks with different priorities. Beside the main task, obstacle avoidance is one commonly used subtask. The ability to avoid obstacles is especially important when the robot is working in a human environment. In this paper, we propose a novel control method for kinematically redundant robots, where we focus on a smooth, continuous transition between different tasks. The method is based on a new and very simple null-space formulation. Sufficient conditions for the tasks design are given using the Lyapunov-based stability discussion. The effectiveness of the proposed control method is demonstrated by simulation and on a real robot. Pros and cons of the proposed method and the comparison with other control methods are also discussed.