Piezoelectric ultrasonic motors perform the advantages of compact design, faster reaction time, and simpler setup compared to other motion units such as pneumatic and hydraulic motors, especially its non-ferromagnetic property makes it a perfect match in MRI-compatible robotics systems compared to traditional DC motors. Hollow shaft motors address the advantages of being lightweight and comparable to solid shafts of the same diameter, low rotational inertia, high tolerance to rotational imbalance due to low weight, and tolerance to high temperature due to low specific mass. This article presents a prototype of a hollow cylindrical ultrasonic motor (HCM) to perform direct drive, eliminate mechanical non-linearity, and reduce the size and complexity of the actuator or end effector assembly. Two equivalent HCMs are presented in this work, and under 50g prepressure on the rotor, it performed 383.3333rpm rotation speed and 57.3504mNm torque output when applying 282$V_{pp}$ driving voltage.

Precise surgical procedures may benefit from intra-operative image guidance using magnetic resonance imaging (MRI). However, the MRI's strong magnetic fields, fast switching gradients, and constrained space pose the need for an MR-guided robotic system to assist the surgeon. Piezoelectric actuators can be used in an MRI environment by utilizing the inverse piezoelectric effect for different application purposes. Piezoelectric ultrasonic motor (USM) is one type of MRI-compatible actuator that can actuate these robots with fast response times, compactness, and simple configuration. Although the piezoelectric motors are mostly made of nonferromagnetic material, the generation of eddy currents due to the MRI's gradient fields can lead to magnetic field distortions causing image artifacts. Motor vibrations due to interactions between the MRI's magnetic fields and those generated by the eddy currents can further degrade image quality by causing image artifacts. In this work, a plastic piezoelectric ultrasonic (USM) motor with more degree of MRI compatibility was developed and induced with preliminary optimization. Multiple parameters, namely teeth number, notch size, edge bevel or straight, and surface finish level parameters were used versus the prepressure for the experiment, and the results suggested that using 48 teeth, thin teeth notch with 0.39mm, beveled edge and a surface finish using grit number of approximate 1000 sandpaper performed a better output both in rotary speed and torque. Under this combination, the highest speed reached up to 436.6665rpm when the prepressure was low, and the highest torque reached up to 0.0348Nm when the prepressure was approximately 500g.

Intra-operative image guidance using magnetic resonance imaging (MRI) can significantly enhance the precision of surgical procedures, such as deep brain tumor ablation. However, the powerful magnetic fields and limited space within an MRI scanner require the use of robotic devices to aid surgeons. Piezoelectric motors are commonly utilized to drive these robots, with piezoelectric ultrasonic motors being particularly notable. These motors consist of a piezoelectric ring stator that is bonded to a rotor through frictional coupling. When the stator is excited at specific frequencies, it generates distinctive mode shapes with surface waves that exhibit both in-plane and out-of-plane displacement, leading to the rotation of the rotor. In this study, we continue our previous work and refine the motor design and performance, we combine finite element modeling (FEM) with stroboscopic and time-averaged digital holography to validate a further plastic-based ultrasonic motor with better rotary performance.

While robots are becoming more diverse and capable, there's one component that hasn't changed much in the past half century: their actuators. A vast majority of robots use an electric motor coupled to a gearbox to move each of their wheels and joints. The motor spins rapidly, as it's optimized to do, while the gearbox reduces the rotation speed of the output shaft, increasing the torque in the process. This type of actuator powers robots as varied as industrial arms, walking humanoids, and Mars rovers. But it's far from perfect: Gear motors are often bulky and sluggish.

There's a reason why you don't see rotary motors or joints in nature: at anything above the molecular scale, too much stuff has to be permanently attached to too much other stuff for any of it to be freely rotating in the way a mechanical wheel or axle is. The more bioinspiration you want to work into a robot, the more of an issue this becomes, which is why it's particularly impressive that researchers at Rutgers University in New Brunswick, N.J., have managed to put four silicone-based wheels with air-powered motors inside of them on a robot that's as soft as a Crocs shoe. Most squishy robots with pneumatic muscles exert force on the environment through bending: a pneumatic chamber that's constrained on one side will curve when inflated, which generates enough motion that robots can walk around on legs and pick things up with grippers. Directional motion like this is very common in nature: most of your muscles work this way, exerting force one way over a finite distance, in cooperative opposition to another muscle that exerts force the other way. You also have muscles that work together in peristalsis, in which synchronized contractions and relaxations generates a propagating wave.