In this paper, we describe a newly proposed design of an integrated three-degrees-of-freedom (3DoF) inner position sensor for an omnidirectional and holonomic inchworm mobile mechanism. The mechanism has two Y-shaped electromagnets and six piezoelectric actuators for obtaining 3DoF inchworm motion on well-polished ferromagnetic surfaces. We calculate conversion equations from four measured distances to X-, Y-, and θ-axis motion. We also explain how to make the input signals to realize the minimum time trajectory of free electromagnets with a newly proposed special kinematic model as an additional condition for energy-efficient control. Details of the design and performance are also described to realize flexible, compact, and high-accuracy positioning in precision engineering.