High speed trajectory control of a direct-drive manipulator

The trimming of three dimensional parts using laser cutting industrial robots raises a control challenge particularly when high speeds and precision are required. The precise control of robot movement along predetermined trajectories is thus necessary in order to achieve satisfactory quality cuts. This paper focuses on the control system design for direct-drive manipulators specially designed for high speed trajectory control applications. First, the concept of decoupled and invariant dynamics is discussed for a specific manipulator. Second, a simple procedure of system identification and control system design is presented. It is demonstrated that through arm mechanism design, the control system is greatly simplified and satisfactory control performance is achieved. The arm mechanism design and control system are evaluated through simulations and experiments. The experimental tracking performance achieved is 3 m/s in speed, 3.8G in acceleration with a mean tracking error of 0.055 degrees.