Soft Microrobotic Transmissions Enable Rapid Ground-Based Locomotion

In this paper we present the design, fabrication, testing, and control of a 0.4 g milliscale robot employing a soft polymer flexure transmission for rapid ground movement. The robot was constructed through a combination of two methods: smart-composite-manufacturing (SCM) process to fabricate the actuators and robot chassis, and silicone elastomer molding and casting to fabricate a soft flexure transmission. We actuate the flexure transmission using two customized piezoelectric (PZT) actuators that attach to the transmission inputs. Through high-frequency oscillations, the actuators are capable of exciting vibrational resonance modes of the transmission which result in motion amplification on the transmission output. Directional spines on the transmission output generate traction force with the ground and drive the robot forward. By varying the excitation frequency of the soft transmission we can control locomotion speed, and when the transmission is oscillated at its resonance frequency we achieve high speeds with a peak speed of 439 mm/s (22 body lengths/s). By exciting traveling waves through the soft transmission, we were able to control the steering direction. Overall this paper demonstrates the feasibility of generating resonance behavior in millimeter scale soft robotic structures to achieve high-speed controllable locomotion.