Reference Input Shaping to Reduce the Move Time of a Very Flexible One-Link Manipulator

When a robot manipulator is required to be light, long or to move quickly, its link tends to flex. When the link flexes, its end position is difficult to control. In fact, the flexibility brings about undesirable attributes such as non-minimum phase, tip vibration and complicated dynamics. As a result, in contrast to a rigid-link robot, control of the flexible-link robot is more challenging and is still an open research problem. This study aimed to design a two-degrees-of-freedom control system from a simple model. The controller ensured good tracking and proper disturbance rejection. The closed-loop natural frequency was then computed, with the reference input shaped such that its energy content was low around the natural frequency. The experiment showed that this proposed method reduced tip vibration significantly resulting in a faster move time.