Dynamic Structural and Contact Modeling for a Silicon Hexapod Microrobot

Abstract

This paper examines the dynamics of a type of silicon-based millimeter-scale hexapod, focusing on interaction between structural dynamics and ground contact forces. These microrobots, having a 5 mm × 2 mm footprint, are formed from silicon with integrated thin-film lead–zirconate–titanate (PZT) and high-aspect-ratio parylene-C polymer microactuation elements. The in-chip dynamics of the microrobots are measured when actuated with tethered electrical signal to characterize the resonant behavior of different parts of the robot and its piezoelectric actuation. Out-of-chip robot motion is then stimulated by external vibration after the robot has been detached from its silicon tethers, which removes access to external power but permits sustained translation over a surface. A dynamic model for robot and ground interaction is presented to explain robot locomotion in the vibrating field using the in-chip measurements of actuator dynamics and additional dynamic properties obtained from finite element analysis (FEA) and other design information. The model accounts for the microscale interaction between the robot and ground, for multiple resonances of the robot leg, and for rigid robot body motion of the robot chassis in five degrees-of-freedom. For each mode, the motions in vertical and lateral direction are coupled. Simulation of this dynamic model with the first three resonant modes (one predominantly lateral and two predominantly vertical) of each leg shows a good match with experimental results for the motion of the robot on a vibrating surface, and allows exploration of influence of small-scale forces such as adhesion on robot locomotion. Further predictions for future autonomous microrobot performance based on the dynamic phenomena observed are discussed.

Impact-Based Amplification and Frequency Down-Conversion of Piezoelectric Actuation for Small Robotics

“…Their combination of high force generation, fast response time, and modest power consumption has made piezoelectric actuators promising for small-scaled robotics. For example, piezoelectric actuation has been used in miniature walking robots [2][3][4][5] and in anthropomorphic robotic hands [6]. However, when it becomes necessary to generate large displacement amplitudes, piezoelectric actuators are rarely ideal due to low intrinsic strain.…”

Synthesis of Micro-robotic Appendages Considering Different Performance Properties

“…The use of micro-robots offers many advantages including minimal disturbance to users, small power requirements, portability, disposability, and ability to work in large teams and exploit swarm intelligence. Thus, micro-robotics is a very relevant and ongoing research topic that has received much attention in recent years [1][2][3][4][5][6][7][8]. Among many different types of micro-robots [1,2], MEMS-based terrestrial micro-robots are of special interest in this paper (Fig.…”

“…The realization of MEMS micro-robots or more specifically micro-robotic appendages with thin-film PZT as actuators (Fig. 1b) were of special interest in the authors' past work [7,8]. Thin-film piezoelectric materials (PZT) offer many advantages including high actuation speeds, small power consumption, high work density per unit area, and reasonable efficiency as small capacitive loads [5], relative to other MEMS transducers.…”

“…But this raises the question of how to design such micro-robotic appendages. Typically, microrobotic appendages are designed based on designer experience, through a trial-anderror approach or taking inspiration from nature (mostly insects) [3,7,8]. Realizing micro-robotic appendages in such a way often leads to non-optimized designs where the appendages' range of motion and performance are limited.…”

Topology Optimization of Micro-robotic Appendages Combining Piezoelectric, Polymer, and Silicon Beams

“…Recently, appendages based on combinations of thin-film PZT, high-aspect ratio parylene-C beams, and rigid silicon links (Fig. 1) have been demonstrated that greatly improve robot leg resilience and leverage PZT displacement into a combination of larger-angle inplane or out-of-plane motions [7,8].…”