Modeling and primary experiment of a 3-axis PID control with 50 nm resolution for a holonomic precision inchworm robot

In this paper, we describe design and development of a 3-axis proportional-integral-derivative (PID) controller for a holonomic precision inchworm robot. The mechanism has two Y-shaped electromagnets and six piezoelectric actuators (PAs) for obtaining 3-degrees-of-freedom (3DoF) motion on well-polished ferromagnetic surfaces. To measure its 3DoF position simultaneously, an integrated 3DoF inner position sensor composed of 4 linear encoders are developed. In experiments, we have checked that this arrangement of the encoders is valid for measuring the 3DoF motion under a condition without disturbance. To be robust against the disturbance, we also discuss requirement of an acceleration feedforward controller with 3 motion sensors to detect disturbance and slips of supporting electromagnet. This paper is first article which demonstrates simultaneous 3-axis PID control with nanometer-scale positioning resolution of miniature mobile robot driven by PAs. We also discuss about the future direction of the realization of compact, precise, fast, flexible, and energy-efficient mobile robotic factory.