Bidirectional Linear Motion by Travelling Waves on Legged Piezoelectric Microfabricated Plates

Abstract

This paper reports the design, fabrication and performance of MEMS-based piezoelectric bidirectional conveyors featuring 3D printed legs, driven by linear travelling waves (TW). The structures consisted of an aluminium–nitride (AlN) piezoelectric film on top of millimetre-sized rectangular thin silicon bridges and two electrode patches. The position and size of the patches were analytically optimised for TW generation in three frequency ranges: 19, 112 and 420 kHz, by the proper combination of two contiguous flexural modes. After fabrication, the generated TW were characterized by means of Laser–Doppler vibrometry to obtain the relevant tables of merit, such as the standing wave ratio and the average amplitude. The experimental results agreed with the simulation, showing the generation of a TW with an amplitude as high as 6 nm/V and a standing wave ratio as low as 1.46 for a device working at 19.3 kHz. The applicability of the fabricated linear actuator device as a conveyor was investigated. Its kinetic performance was studied with sliders of different mass, being able to carry a 35 mg silicon slider, 18 times its weight, with 6 V of continuous sinusoidal excitation and a speed of 0.65 mm/s. A lighter slider, weighting only 3 mg, reached a mean speed of 1.7 mm/s at 6 V. In addition, by applying a burst sinusoidal excitation comprising 10 cycles, the TW generated in the bridge surface was able to move a 23 mg slider in discrete steps of 70 nm, in both directions, which is a promising result for a TW piezoelectric actuator of this size.

Linear Motors Based on Piezoelectric MEMS

“…The generation of linear TW in beams by the combination of two flexural vibration modes was already reported using two symmetrically placed piezoelectric patches [10]. Here, we followed the same approach, obtaining the patch position and size that optimises the TW quality and amplitude with the targeted modes in Figure 1b.…”

“…Regarding leg position, those should be placed where the TW envelope is ideally constant to ensure an elliptical trajectory at the tip [12]. That condition is met at the central plateau of the TW envelope, the area between the two patches [10].…”

“…According to Reference [10], the optimal patches for TW generation could be suitable for SW generation too. Besides, in order to maximize excitation of the SW and taking advantage of the twopatch configuration, a phase optimisation was performed [14].…”

“…Different actuation techniques have benefited from Micro-electromechanical Systems (MEMS) technology, demonstrating locomotion or conveyance on the millimetre scale with speeds of a few millimetres per seconds and payloads below 50 mg [6][7][8]. However, to reach a step further into the miniaturisation of efficient motors, piezoelectric actuation becomes a promising alternative [9,10].…”

Sub-Gram In-Plane Vibration-Driven Robot with Inclined Legs

“…The combination of straight legs and SW was reported for the movement of sliders [1] or the locomotion of a platform [2]. Recent publications also demonstrated the use of TW and straight legs for conveyance applications [3], as well as robotic locomotion [4].…”