Multi-material 3D Printing of Thermoplastic Elastomers for Development of Soft Robotic Structures with Integrated Sensor Elements

Embedded sensing can benefit soft robots with the ability to interact with their environment but producing embedded soft sensors can be challenging. Multi-material Fused Deposition Modeling (FDM) additive manufacturing allows producing complex structures, by combining more than one kind of polymeric material. For multi-material FDM, conductive thermoplastic elastomer filaments have been developed. This allows the printing of flexible functional structures, based on thermoplastic elastomer structures with conductive paths that are of great interest for stretchable electronics and soft robotic applications. In this study, stretchable piezoresistive elastomer strain sensor composites were successfully produced by using multi-material FDM. A piezoresistive thermoplastic elastomer was printed on the top of a nonconductive, flexible thermoplastic elastomer strip using FDM multi-material 3D printer. FDM elastomer filaments with different shore hardness as substrate materials for the gripper structure were used. The hardness of the elastomer affected the printability and the adhesion to the conductive elastomer material, which was used as a strain sensor material. The hardness affected the strain sensor properties too. The piezoresistive response, dynamic behavior, drift, relaxation and sensitivity of the printed multi-material strips were investigated by tensile tests. Soft robotic grippers with integrated sensing elements to detect deformation while touching the objective were selected as a case study. The soft grippers with the integrated sensors exhibited intelligent response by recognizing when they were griping a small or big object and when an obstacle was inhibiting their function.嵌入式传感可赋予软体机器人与环境交互的能力，但制备嵌入式软体传感器仍颇具挑战。多材料熔融沉积成型（Fused Deposition Modeling, FDM）增材制造技术可通过结合多种聚合物材料，制备复杂结构。针对多材料FDM工艺，研究人员已开发出导电热塑性弹性体丝材，这使得基于带有导电路径的热塑性弹性体结构的柔性功能结构的打印成为可能，此类结构在可拉伸电子学与软体机器人应用中极具研究价值。本研究通过多材料FDM工艺成功制备了可拉伸压阻式弹性体应变传感器复合材料。研究人员利用多材料FDM 3D打印机，将压阻型热塑性弹性体打印于非导电柔性热塑性弹性体条带的表面。本研究采用不同邵氏硬度的FDM弹性体丝材作为夹持器结构的基底材料，发现弹性体的邵氏硬度不仅会影响打印适配性以及与作为应变传感器材料的导电弹性体之间的粘附性能，同时也会对应变传感器的性能产生影响。研究团队通过拉伸测试，对打印得到的多材料条带的压阻响应、动态特性、漂移现象、弛豫行为与灵敏度进行了表征。本研究选取集成了传感元件、可在接触目标物体时检测形变的软体机器人夹持器作为案例研究对象，结果表明，搭载集成传感器的软体夹持器可通过识别夹持小/大物体时的状态，以及识别阻碍其工作的障碍物，实现智能化响应。