Untethered Microrobots With Serpentine Actuators: The Role of Elastics Point Contact & Laser Beam Shape on Their Locomotion

Abstract

FEA simulations of 7 microrobots designed from asymmetric Chevron actuators are presented with in depth analysis of their resonance behavior due to fixed, as well as elastic supports at their contact points with underlying substrate. Experimental resonance frequencies of 3 different designs identified by frequency sweep experiments, excited by a 532 nm pulse laser, are in close agreement with the simulated values. Contact stiffness is estimated by comparing simulated and experimental resonance frequencies. Both in-plane and out of plane motion due to resonance is found in all of these structures that can be used to predict the stick-slip step size (locomotion mechanism) of these robots. In addition, modeling of differential thermal expansion is conducted to optimize the laser spot size that is used to drive these microrobots. Simulations of elliptic and circular laser spots with varying size suggest that covering only the actuators of the robot is sufficient for successful actuation. Using a circular laser spot increase the thermal expansion of the overall microrobot by 3.3 nm resulting in no significant gain in step size/gait of the robotic locomotion. This finding proves that the shape and size of the laser spot are insignificant as long as the actuators are under the laser beam.

Learning Control of a Laser-Driven Locomotive Microrobot for Dry Environments

“…Recently, a preliminary study [31], identified both theoretical and experimental methods to evaluate 7 different SerpenBot designs and led to the selection of best-fitting candidates for further investigation with regard to steering control. Typical design parameters for the dimensions of the SerpenBot and top and side views of the robot are presented Fig.…”

“…The resulting microrobot has a body with approximate dimension 647 𝜇𝑚 by 445 𝜇𝑚 , with serpentine width 5 𝜇𝑚 and 9 turns. This design is based on the consideration of the laser spot size, power, and pulse frequency, as detailed by our previous publications [26][27][28][29][30][31]. System Modeling…”

“…The motion of the SerpenBot is governed by complex opto-thermal-mechanical phenomena, where optothermal absorption effect can be described by a first order differential equation, and the thermo-mechanical part can be represented by a second order differential equations, leading to an overall third order system. The opto-thermal behavior can be described by the heat equation [31]:…”