A Wide-Range Stiffness-Tunable Soft Actuator Inspired by Deep-Sea Glass Sponges

Abstract

Achieving both high compliance and stiffness is a key issue in stiffness-tunable soft robots. A wide-range variable-stiffness method keeping pure soft characteristic is proposed by bioinspired design of deep-sea glass sponges adopting thermoplastic starch. The stiffness-tunable mechanism is designed through force analysis and optimization of its bionic cellular structure. It is fabricated with load-weight ratio exceeding 470. Then, a widerange stiffness-tunable omnidirectional-bending soft actuator (WOSA) is realized, and the bending stiffness model is established. Comparative experiments of stiffness and deformation are conducted on WOSA and a pure soft actuator (PSA) with the same size. Results show that the WOSA can get 92.3 times initial bending and 70.8 times torsional stiffness variation range, of which the flexibility is even better than PSA. A gripper assembled by three WOSAs is verified through stiffness adjustment that it can grasp different weight fragile, soft items from the unshelled fresh egg, boiled egg yolk to grapes. It can even lift a dumbbell weighting 3.32 kg. Finally, a manipulator demonstrated its potential in future minimally invasive surgical applications due to its wide stiffness range and large deformation capacity.

A Novel Distal Hybrid Pneumatic/Cable‐Driven Continuum Joint with Variable Stiffness Capacity for Flexible Gastrointestinal Endoscopy

“…Thermoplastic PET [35] \ \ \ 22 3.5N (12.8%) 12s(F!R) 15 mm 2 (2) ϕ3.5 mm FE 15s(R!F) Thermoplastic starch [36] \ \ 92.3 4N (10%) 165s(F!R) 15.5 mm 0 \ MIS 28s(R!F) SMA [37] \ \ \ 1.4 1.45N (16.7%) 18s(F!R) 13 mm 0 \ SPS 60s(R!F)…”

“…The working principles for variable stiffness techniques can generally be dichotomized: the domains of materials and structures. The material-based approaches primarily realize tunable stiffness by changing the intrinsic material properties with external stimulation, including low melting point alloys (LMPA), [32][33][34] the thermoplastic polymer, [35,36] shape-memory materials, [37,38] rheological fluids (electro-and magneto-rheological fluids), [39,40] and so on. Despite the high stiffness-changing ratio values, the phase transition process is time consuming.…”

Printable multi-stage variable stiffness material enabled by low melting point particle additives

“…Composites synthesized with higher structural parameters can attain high stiffness and a large load capacity. 27 It is recommended that taking advantage of a material with an extremely low elastic modulus (involving LMPA and viscous TP) will satisfy the demand for high flexibility and interaction security. To date, the Kramer-Bottiglio Group has been working on the combination of Field's metal metal (FM) 28,29 and silicone and a silicone elastomer with their electrical conductivity 30 and stretchability, 31 in which FM is one type of LMPA.…”

A Novel Continuum Robot With Stiffness Variation Capability Using Layer Jamming: Design, Modeling, and Validation

“…Continuum robots (CRs) are recently becoming a research focus due to their novel inherent compliance, flexibility, and dexterity [1], [2]. Because of these advantages, CRs have the potential to be applied in many application scenarios, such as medical services [3], [4], non-destructive inspections [5], and general grasping tasks [6]. However, this type of robot may suffer from many problems, and one of them is the need to improve its stiffness variation capability while keeping the same dexterity level [1]- [3].…”