Yan Jihong, Xu Zhidong, Shi Peipei, Zhao Jie
State Laboratory of Robotics and System, Harbin Institute of Technology, Harbin, China.
Laboratory for Space Environment and Physical Sciences, Harbin Institute of Technology, Harbin, China.
Soft Robot. 2022 Apr;9(2):399-411. doi: 10.1089/soro.2020.0153. Epub 2021 Jun 7.
Elevating stiffness without compromising compliance and agility is a key problem for soft finger applications, especially for articulate ones. Inspired by human finger, a multijoint soft finger with dual morphing through active/passive variable rigidity is proposed. The fabricated soft finger weighs 27.4 g. Conductive thermoplastic starch polymers (CTPSs) are embedded in a U-shape-joint pneumatic soft actuator segmentally like biological phalanges. Their stiffness can be independently adjusted utilizing customized thermomechanical property. Yoshimura origami imitating ligaments can passively match deformation and stiffness of the joints. Through electrothemal activation of CTPSs, the finger can realize dual independent articulate morphing: stiffened phalanges (mode 1) for dexterous manipulation and heavy load, softened phalanges (mode 2) for large deformation contact and light load. Comparative experiments of bending angle, output force, and stiffness are carried out between the active and passive stiffness adjustment of mode 1 and mode 2. The results show that the output force and stiffness of the finger adopting mode 1 can be improved more than two times and five times, and its compliance using mode 2 is almost similar, compared with the pure soft one. To further demonstrate performances of dual-mode morphing, a three-fingered gripper is assembled for grasping and manipulating targets with different shapes, sizes, rigidity, and weight, including playing card, unshelled raw egg, grapes, and unscrewing the bottle cap. It can successfully lift a dumbbell weighing 1460 g with a 7.6 load/weight ratio through a two-mode switch.
在不影响柔顺性和灵活性的前提下提高刚度是软手指应用中的一个关键问题，尤其是对于有多个关节的软手指。受人类手指启发，提出了一种通过主动/被动可变刚度实现双重变形的多关节软手指。制作的软手指重27.4克。导电热塑性淀粉聚合物（CTPSs）像生物指骨一样分段嵌入U形关节气动软致动器中。利用定制的热机械性能可以独立调节它们的刚度。模仿韧带的吉村折纸可以被动地匹配关节的变形和刚度。通过对CTPSs进行电热激活，手指可以实现两种独立的关节变形：用于精确操作和承受重负载的变硬指骨（模式1），以及用于大变形接触和轻负载的变软指骨（模式2）。对模式1和模式2的主动和被动刚度调节进行了弯曲角度、输出力和刚度的对比实验。结果表明，与纯软手指相比，采用模式1的手指输出力和刚度可分别提高两倍多和五倍多，而采用模式2时其柔顺性几乎相似。为了进一步展示双模式变形的性能，组装了一个三指夹具，用于抓取和操作具有不同形状、尺寸、刚度和重量的目标，包括扑克牌、带壳生鸡蛋、葡萄以及拧开瓶盖。通过双模式切换，它能够以7.6的负载/重量比成功举起一个重1460克的哑铃。
