We propose a new mobile robot that uses three standing-wave-type ultrasonic motors (USMs). The USMs are composed of two stacked-type piezoelectric actuators. Recently, with the miniaturization of electronic and microelectromechanical system devices and progress in the biomedical sciences, the demand for multifunctional manipulation of chip parts and biomedical cells has increased. Conventional multiaxial stages are too bulky for multifunctional manipulation in which multiple manipulators are required. Using conventional precise mobile robots is feasible for miniaturization of multifunctional manipulation, although their cables influence positioning repeatability. USMs are feasible actuators for realizing cableless robots because their energy efficiency is relatively higher than that of other motors of millimeter scale. The aim of this study is to develop a new type of omnidirectional mobile robot driven by USMs. In experiments, we evaluated the feasibility by investigating velocity, positioning deviation, and achieving repeatability of translational movements under open-loop control. We determine the repeatability as a ratio of the standard deviation of the final points to the average path length. The proposed mobile robot achieves velocities of 18.6-31.4 mm/s and repeatability of 4.1%-9.1% with a 200-g weight.

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.