A Small and Agile Ring-Shaped Tripodal Piezoelectric Robot Driven by Standing and Traveling Mechanical Waves

For miniature piezoelectric robots, it is difficult to realize multi-degree-of-freedom motion with a simple structure. In this article, a novel ring-shaped tripodal piezoelectric robot (RTPR) is proposed to solve the above difficulty. Multiple motion modes, based on the propagation of mechanical waves on the rigid ring-shaped structure, are designed to realize continuous/step linear and in-situ rotational motions. The prototype is fabricated with a weight of 2.2 g and a size of 20 mm × 20 mm × 4.6 mm, and the performance is tested. The test results show that RTPR can achieve a maximum linear speed of 39.3 mm/s (2 BL/s) and a maximum in-situ rotational speed of 16.5 rad/s. In addition, RTPR also shows strong load capacity (22 times of its weight) and submicrometer linear resolution (0.38 μm). In the experiment, RTPR also shows the capability of moving on narrow and curved roads with its multiple motion modes. RTPR has the characteristics of simple structure, agile motion, strong load capacity, and high resolution, which provides a new idea for achieving the multi-degree-of-freedom motion of miniature robots.

I. Introduction

Miniature robots with the advantage of small size can enter some space-limited environments to perform various tasks. For example, they can perform small pipeline inspections in high temperature, high pressure, or toxic gas environments where humans or large robots are difficult to enter; they can also be competent for remote reconnaissance operations carrying camera and power supply equipment [1], [2], [3], [4]. To be competent for these works, miniature robots should be designed with characteristics of small volume, high mobility, high load-carrying capacity, high durability, and so on [5], [6], [7]. Generally, the electromagnetic motor is the most common driving method for miniature robots. There are many advantages to using electromagnetic motors as actuators, such as the convenience of robot design and control with the in-depth study of electromagnetic motors [8], [9], [10], [11]. In addition, miniature robots driven by electromagnetic motors can easily obtain high speed and autonomous motions [12]. However, the existence of coils, bearings, and transmission mechanisms matched with electromagnetic motors limits the further miniaturization of such robots. So that researchers focus on robots driven by actuators that can eliminate these components, including shape memory alloys (SMAs) [13], [14], [15], dielectric elastomers actuator (DEA) [16], [17], [18], magnetostrictive actuator (MA) [19], [20], [21], [22], photo actuators [23], [24], [25], [26], [27], piezoelectric actuators (PA) [28], [29], [30], and so on. SMAs have the defect of slow response speed and poor environmental adaptability; DEAs require high voltage excitation of several thousand volts, which makes it challenging to realize untethered moving; photo actuators are used with external light sources; the huge electrical source equipment is needed to provide external magnetic fields for MAs. All the defects mentioned above have brought difficulties in applying these types of robots in complex environments.