# 3D Printed Proprioceptive Soft Fluidic Actuators with Graded Porosity

## TL;DR

This paper presents a novel 3D printing method for creating soft, porous actuators with integrated sensing and models their strain estimation, enabling tailored actuation and sensing with hysteresis compensation.

## Contribution

Introduces a manufacturing approach for 3D printed soft porous actuators with integrated piezoresistive sensing and nonlinear hysteresis modeling.

## Key findings

- Porosity enables customization of stroke and resistance change.
- Wiener-Hammerstein models estimate strain with high accuracy.
- Models outperform linear approaches significantly.

## Abstract

Integration of both actuation and proprioception into the robot body would provide actuation and sensing in a single integrated system. Within this work, a manufacturing approach for such actuators is investigated that relies on 3D printing for fabricating soft-graded porous actuators with piezoresistive sensing and identified models for strain estimation. By 3D printing, a graded porous structure consisting of a conductive thermoplastic elastomer both mechanical programming for actuation and piezoresistive sensing were realized. Whereas identified Wiener-Hammerstein (WH) models estimate the strain by compensating the nonlinear hysteresis of the sensorized actuator. Three actuator types were investigated, namely: a bending actuator, a contractor, and a three DoF bending segment (3DoF). The porosity of the contractors was shown to enable the tailoring of both the stroke and resistance change. Furthermore, the WH models could provide strain estimation with on average high fits (83%) and low RMS errors (6%) for all three actuators, which outperformed linear models significantly (76.2/9.4% fit/RMS error). These results indicate that an integrated manufacturing approach with both 3D printed graded porous structures and system identification can realize sensorized actuators that can be tailored through porosity for both actuation and sensing behavior but also compensate for the nonlinear hysteresis.