Elastomeric Strain Limitation for Design of Soft Pneumatic Actuators

Abstract

Modern robots embody power and precision control. Yet, as robots undertake tasks that apply forces on humans, this power brings risk of injury. Soft robotic actuators use deformation to produce smooth, continuous motions and conform to delicate objects while imparting forces capable of safely pushing humans. This thesis presents strategies for the design, modeling, and strain-based control of human-safe elastomeric soft pneumatic actuators (SPA) for force generation, focusing on embodied mechanical response to simple pressure inputs. We investigate electroadhesive (EA) strain limiters for variable shape generation, rapid force application, and targeted inflation trajectories. We attach EA clutches to a concentrically strain-limited elastomeric membrane to alter the inflation trajectory and rapidly reorient the inflated shape. We expand the capabilities of EA for soft robots by encasing them in elastomeric sheaths and varying their activation in real time, demonstrating applications in variable trajectory inflation under identical pressure sweeps. We then address the problem of trajectory control in the presence of external forces by modeling the pressure-trajectory relationship for a concentrically strain-limited class of silicone actuators. We validate theoretical models based on material properties and energy minimization using active learning and automated testing. We apply our ensemble of neural networks for inverse membrane design, specifying quasi-static mass lift trajectories from a simple pressure sweep. Finally, we demonstrate the power of multiple pressure-linked actuators in a proof-of-concept mannequin leg lift.

Figures (33)

• Figure 1: A. Actuator expansion formed into three different shapes; shape chosen by clutch activation. Top-view presented over side-view. B. Expansion of soft, elastomeric actuator to 3.1 kPa under three different clutch activation configurations. C. Soft actuator manipulation of 3.7 g ball. D. Manipulation of 820 g textbook.
• Figure 2: System Overview. A. Overview of actuator test system with labels. B. Model of silicone membrane with clutch locations superimposed. Model includes stiff silicone reinforced with fabric, soft unsupported silicone, four outboard clutches, and one inboard clutch. C. Clutch is highlighted with yellow. i) Outboard clutch is activated and restricts membrane expansion. ii) Outboard clutch is deactivated and membrane is free to expand.
• Figure 3: Circuit Diagram. Clutch circuit diagram, building upon Diller et al.'s diller2018.
• Figure 4: Depth camera data (left), simulation (center), and experimental system (right) for actuator shape comparison at 3.1 kPa. A. Plateau shape. B. Round shape. C. Pyramidal shape.
• Figure 5: Mode 1 Actuator Characterization. A. Plot of actuator workspace along 4 DoF, looking at the actuator from a top-down view. Each DoF is accessed by activating a different set of clutches. Photos of corresponding positioning of 40 mm diameter ball. B. Plot that tracks position of ball once it has been placed on the actuator. The actuator lifts it to the specified direction and then releases the inboard clutch to rapidly apply force to the ball in the desired direction. Photos of corresponding projectile motion for 40 mm diameter ball. C. Labeled photo of actuator with directions and DoFs.