Repetitive learning control of a flexible whisker in tip contact with an unknown surface

Repetitive contact imaging uses a flexible whisker attached to a two-axis robot through a load cell. Assuming small deformations and rotations, the pitch axis decouples from the yaw. The yaw axis, under proportional-integral- derivative control, sweeps periodically back and forth across the object while the pitch axis, under repetitive learning (RL) control, maintains a uniform contact force. Once the RL controller converges, the three-dimensional contact points can be determined using an elastica algorithm. The RL controller is proven stable based on a distributed parameter beam model and is experimentally shown to provide a stable performance with improved moment regulation when compared with under proportional-derivative control.