Precise Position Control of Holonomic Inchworm Robot Using Four Optical Encoders

Abstract

In this study, an XYθ position sensor is designed/proposed to realize the precise control of the XYθ position of a holonomic inchworm robot in the centimeter to submicrometer range using four optical encoders. The sensor was designed to be sufficiently compact for mounting on a centimeter-sized robot for closed-loop control. To simultaneously measure the XYθ displacements, we designed an integrated two-degrees-of-freedom scale for the four encoders. We also derived a calibration equation to decrease the crosstalk errors among the XYθ axes. To investigate the feasibility of this approach, we placed the scale as a measurement target for a holonomic robot. We demonstrated closed-loop sequence control of a star-shaped trajectory for multiple-step motion in the centimeter to micrometer range. We also demonstrated simultaneous three-axis proportional–integral–derivative control for one-step motion in the micrometer to sub-micrometer range. The close-up trajectories were examined to determine the detailed behavior with sub-micrometer and sub-millidegree resolutions in the MHz measurement cycle. This study is an important step toward wide-range flexible control of precise holonomic robots for various applications in which multiple tools work precisely within the limited space of instruments and microscopes.

Automatic Holonomic Mobile Micromanipulator for Submillimeter Objects Inspired by the Rhinoceros Beetle

“…Many of the presently documented precision holonomic mobile robots utilizing piezoelectric actuators rely on “sliding” movements, such as stick‐slip [ 38,41 ] or sliding feet movements. [ 55,60 ] In contrast, the HB has the theoretical capability to walk without slipping. This is achieved by raising and lowering its legs through a specially designed vertical actuator, distinguishing it significantly from other precision mobile robots driven by piezoelectric actuators.…”

“…Table 10 lists the performances of the measuring instruments. [60] To ensure simultaneous three-point contact with the floor, the scale stand, made of duralumin, weighed approximately 80 g. In addition, among the several floor materials tested, we chose a protective film on the tablet screen cover glass to achieve optimal walking performance.…”

“…The investigation of the displacement resolution and measurement method will be performed in our future work. Physical Quantity HB USM [55] Inchworm [60] MyCRoN [41] PER-hexpod [38] Principle…”

“…Holonomic mobile robots driven by resonance mechanisms [55][56][57] and based on inchworm principles [58][59][60][61] have also been devised. Stick-slip holonomic mobile robots have been reported as well, [38,41] influenced by the kinetic friction between legs and surfaces.…”

Editorial for the Special Issue on Flexible Micromanipulators and Micromanipulation

“…They found a linear relationship between the moduli of the whole microcapsule and the shell material. Tanabe et al [ 12 ] designed a holonomic inchworm robot that can be precisely controlled using four optical encoders. The robot moves in any direction, making it suitable for tasks such as inspection, assembly, and maintenance in tight spaces.…”