Design and Validation of a Multi-stage Adjustable-stiffness Rigid-flexible Coupled Bionic Manipulator

doi:10.3901/JME.2025.21.237

Abstract

Abstract: To address the challenges of variable stiffness control and the issues related to the bonding at the rigid-flexible interface caused by significant stiffness differences, a bionic multi-stage variable-stiffness manipulator and its rigid-flexible integrated fabrication process are proposed. A three-stage finger structure is designed based on the coordination mechanism of the human skeletal-muscular system, with rigid and flexible materials replicating the characteristics of bones and muscles, respectively. By combining the advantages of additive manufacturing and casting processes, a structural embedding and adhesive redundancy design is employed, resulting in a 120% improvement in the bonding strength at the rigid-flexible interface (106 N), with a transient fracture force reaching up to 2 400 times the self-weight of a single rigid-flexible segment. Structural physical constraints are reconfigured to replace biological muscle antagonism, and a stiffness modulation strategy based on multi-stage antagonistic lever arms is introduced. An independent flexor tendon is retained as the primary actuation element, while a ratchet-based locking mechanism is incorporated to enable multi-position adjustment of the tendon endpoint within the distal phalanx track. This allows for dynamic regulation of the antagonistic lever arm length and thus realization of tunable stiffness. The complexity associated with traditional multi-tendon coordinated control is effectively avoided, enabling wide-range stiffness modulation with a regulation ratio of 1:1.56 and controllable joint movement from 43.5° to 83.6°, covering a span of 92.2%, without reliance on complex control systems. A kinematic model is established using the Denavit-Hartenberg (D-H) parameter method, and the influence of the antagonistic lever on end-force and workspace is verified through static analysis. Experimental results demonstrate that the manipulator is capable of graded matching and adaptive grasping of objects ranging from 4 g to 234 g, including irregularly shaped, rigid, and flexible mixed items. The effective matching capability of the variable stiffness mechanism with varying load requirements is validated, and the grasping stability is verified through a series of predefined multi-condition and repetitive scenarios, showing its potential for applications in unstructured grasping tasks.

Key words: rigid-flexible coupled manipulator, variable stiffness, integrated fabrication, kinematic analysis, grasping experiments

CLC Number:

TP241

WANG Zhenyu, SUN Jianwei, ZHANG Meiling, CONG Ming, CHU Jinkui. Design and Validation of a Multi-stage Adjustable-stiffness Rigid-flexible Coupled Bionic Manipulator[J]. Journal of Mechanical Engineering, 2025, 61(21): 237-248.

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