Compliant mechanisms actuated by pneumatic loads are receiving increasing attention due to their direct applicability as soft robots that perform tasks using their flexible bodies. Using multiple materials to build them can further improve their performance and efficiency. Due to developments in additive manufacturing, the fabrication of multi-material soft robots is becoming a real possibility. To exploit this opportunity, there is a need for a dedicated design approach. This paper offers a systematic approach to developing such mechanisms using topology optimization. The extended SIMP scheme is employed for multi-material modeling. The design-dependent nature of the pressure load is modeled using the Darcy law with a volumetric drainage term. Flow coefficient of each element is interpolated using a smoothed Heaviside function. The obtained pressure field is converted to consistent nodal loads. The adjoint-variable approach is employed to determine the sensitivities. A robust formulation is employed, wherein a min-max optimization problem is formulated using the output displacements of the eroded and blueprint designs. Volume constraints are applied to the blueprint design, whereas the strain energy constraint is formulated with respect to the eroded design. The efficacy and success of the approach are demonstrated by designing pneumatically actuated multi-material gripper and contractor mechanisms. A numerical study confirms that multiple-material mechanisms perform relatively better than their single-material counterparts.

翻译：受气动载荷驱动的柔性机构因其可直接作为利用柔性体执行任务的软体机器人而日益受到关注。采用多种材料制造此类机构可进一步提升其性能与效率。随着增材制造技术的发展，多材料软体机器人的制造正逐步成为现实。为充分利用这一机遇，亟需专门的设计方法。本文提出了一种系统化方法，通过拓扑优化开发此类机构。采用扩展SIMP方案进行多材料建模。基于达西定律及体积排水项，对压力载荷的设计依赖性进行建模。每个单元的流动系数通过平滑Heaviside函数插值得到。通过伴随变量法计算灵敏度。建立鲁棒性公式，其中基于侵蚀设计与蓝图设计的输出位移构建最小-最大优化问题。蓝图设计施加体积约束，而应变能约束则针对侵蚀设计建立。通过设计气动驱动多材料夹持器与收缩机构，验证了该方法的有效性及成功性。数值研究表明，多材料机构性能相对优于单材料机构。