An untethered ring-shaped miniature robot with axisymmetric vibrations and non-axisymmetrically arranged feet

Background

Miniature robots have become a research focus in the field of robotics due to their small size, light weight, and agile motions, making them suitable for applications in environmental reconnaissance and rescue exploration. Conventional electromagnetic actuation can achieve fast and agile motions. However, its further miniaturization is constrained by the relatively complex transmission mechanisms and the sharp decrease in output power during component scaling. Piezoelectric robots are featured by flexible structural design and miniaturization, and inherited advantages of high precision, fast response, and excellent electromagnetic compatibility from piezoelectric actuation technology, have attracted considerable research attention worldwide. Among them, resonant piezoelectric robots achieve motions through the high-frequency vibration of piezoelectric elastic bodies. They can achieve high speeds of several hundred millimeters per second and submicrometer-level resolution, enabling cross-scale motion. However, there is a design conflict between vibration decoupling among multiple piezoelectric elastic bodies and structural connection strength, making it difficult to achieve both agile motions and high load capacity. Therefore, achieving cross-scale motion that combines high agility and large load capacity remains an important challenge for miniature piezoelectric robots.

Research Progress

To address this challenge, Prof. Yingxiang Liu's team at the State Key Laboratory of Robotics and Systems, Harbin Institute of Technology, developed a unique tripodal piezoelectric robot driven by a high-stiffness ring-shaped elastic body. By combining axisymmetric vibration modes with an asymmetric foot arrangement, the proposed robot achieves both planar agile motions and high load capacity. On one hand, a single high-stiffness ring-shaped structure is adopted to enhance the load capacity. On the other hand, the correspondence between the modal nodes of the ring structure and the positions of the driving feet is analyzed, and an asymmetric foot arrangement is designed. The third-order and fourth-order axial modes of the ring structure were used to realize rotational and linear motions, respectively. In addition, the speed of linear motion was improved by introducing differentiated spacings between different driving feet and vibration nodes. The approach provides an effective strategy for miniature piezoelectric robots to achieve both agile motions and high load capacity.

The effects of key structural parameters on the resonant frequency and foot-end displacement are investigated by using the Finite Element Method (FEM). The structural parameter design of the robot is completed, and a prototype is developed, with dimensions of approximately 38×38×15.5 mm³ and a weight of about 9.2 g. The experimental results showed that, under continuous ultrasonic excitation, the robot achieved maximum linear and rotational speeds of 338 mm/s and 944 °/s, respectively. The load capacity reached 400 g, exceeding 40 times its own weight. Under pulsed ultrasonic excitation, the linear and rotational resolutions were 0.81 μm and 36.14 μrad, respectively. To further enhance the mobility, a compact driving power supply was developed and integrated into the robot. The untethered robot achieved a linear speed of 93 mm/s and a rotational speed of 438 °/s. The load capacity reached 200 g and the resolution was 0.63 μm. The results demonstrate wireless cross-scale motion with both agile motions and high load capacity, indicating promising application potential in large-range transportation and inspection of miniature devices.

Future Prospects

In the future, miniature piezoelectric robots will continue to develop towards intelligence and integration. By further integrating functional units such as operation, sensing, and control, a closed-loop feedback system is constructed to achieve target recognition and autonomous switching of motion modes for robots in complex scenes. The autonomous cross-scale motion and operation capabilities of piezoelectric robots from macroscopic motion to microscopic operation will be enhanced. Besides, these piezo robots are expected to play an important role in tasks such as precision assembly, chip inspection, and micro/nano operations.

Sources: https://spj.science.org/doi/abs/10.34133/research.1158