Geometric constraint-based modeling and analysis of a novel continuum robot with Shape Memory Alloy initiated variable stiffness

Abstract

Continuum robots exhibit promising adaptability and dexterity for soft manipulation due to their intrinsic compliance. However, this compliance may lead to challenges in modeling as well as positioning and loading. In this paper, a virtual work-based static model is established to describe the deformation and mechanics of continuum robots with a generic rod-driven structure, taking the geometric constraint of the drive rods into account. Following this, this paper presents a novel variable stiffness mechanism powered by a set of embedded Shape Memory Alloy (SMA) springs, which can make the drive rods become ‘locked’ on the body structure with different configurations. The resulting effects of variable stiffness are then presented in the static model by introducing tensions of the SMA and friction on the rods. Compared with conventional models, there is no need to predefine the actuation forces of the drive rods; instead, actuation displacements are used in this new mechanism system with stiffness being regulated. As a result, the phenomenon that the continuum robot can exhibit an S-shaped curve when subject to single-directional forces is observed and analyzed. Simulations and experiments demonstrated that the presented mechanism has stiffness variation of over 287% and further demonstrated that the mechanism and its model are achievable with good accuracy, such that the ratio of positioning error is less than 2.23% at the robot end-effector to the robot length.

Nonlinear energy-based control of soft continuum pneumatic manipulators

“…The flexible micro actuator (FMA) has been one of the first designs to achieve bending on any plane due to pressurization of its internal chambers [37] so that a manipulator can be constructed with a single FMA, thus it has inspired various subsequent versions [17]. Other actuation strategies include dielectric elastomers [26,45], cables [32], and shapememory alloy [23,42]. In general, not all degrees of freedom (DOFs) in soft continuum manipulators are actuated.…”

Recent Advances in Design and Actuation of Continuum Robots for Medical Applications

“…Mechanism-based variable stiffness methods (MVSMs) have been used in many previous works, including antagonistic actuation, rack-locking mechanism, drive-rod-locking mechanism, central-cable-tensioning mechanism, layer jamming and granular jamming [53]. The principle of antagonistic actuation is to add the internal stress by applying a couple of forces in opposite directions.…”

“…In addition, these kinds of mechanisms would take up the central passage of CMs, making the path of the tube to the end-effector difficult. Yang et al [53] proposed a MVSM based on SMA-spring for a novel rod-driven CR. The friction along the drive rods is then adjusted by electric current applied to the SMA springs, so that the desired robot configuration can be maintained.…”

Dynamic Modeling and Experimental Verification of A Cable-Driven Continuum Manipulator With Cable-Constrained Synchronous Rotating Mechanisms

“…Yuan et al [35] presented a comprehensive static model for cable-driven multi-section continuum manipulators. Yang et al [33] established a virtual work-based static model to study the deformation of a continuum robot with a generic rod-driven structure. Li et al [14] compared three designs of continuum manipulator at the mechanism level from the kinematics point of view.…”