Soft pneumatic actuators with integrated resistive sensors enabled by multi-material 3D printing

The concept of soft robots has garnered significant attention in recent studies due to their unique capability to interact effectively with the surrounding environment. However, as the number of innovative soft pneumatic actuators (SPAs) continues to rise, integrating traditional sensors becomes challenging due to the complex and unrestricted movements exhibited by SPA during their operation. This article explores the importance of utilising one-shot multi-material 3D printing to integrate soft force and bending sensors into SPAs. It highlights the necessity of a well-tuned and robust low-cost fabrication process to ensure the functionality of these sensors over an extended period. Fused deposition modelling (FDM) offers a cost-effective solution for embedding sensors in soft robots, directly addressing such necessity. Also, a finite element method (FEM) based on the nonlinear hyper-elastic constitutive model equipped with experimental input is developed to precisely predict the deformation and tip force of the actuators measured in experiments. The dynamic mechanical test is conducted to observe and analyse the behaviour and resistance changes of conductive thermoplastic polyurethane (CTPU) and varioShore TPU (VTPU) during a cyclic test. The flexible sensor can detect deformations in SPAs through the application of air pressure. Similarly, the force sensor exhibits the ability to detect grasping objects by detecting changes in resistance. These findings suggest that the resistance change corresponds directly to the magnitude of the mechanical stimuli applied. Thus, the device shows potential for functioning as a resistive sensor for soft actuation. Furthermore, these findings highlight the significant potential of 3D and 4D printing technology in one-shot fabrication of soft sensor-actuator robotic systems, suggesting promising applications in various fields like grippers with sensors and rehabilitation devices.