Analysis on variable stiffness of a cable-driven parallel–series hybrid joint toward wheelchair-mounted robotic manipulator

Abstract

The design of variable stiffness mechanism is of great importance to wheelchair-mounted robotic manipulators. In this article, the authors propose a cable-driven parallel-series hybrid joint toward wheelchair-mounted robotic manipulators with adjusting the system stiffness actively. The joint is a cable-driven, compression-spring-supported hybrid mechanism. Then, the kinematic analysis and cable tension analysis through static modeling are established to derive the joint stiffness model. Finally, cable-driven parallel-series hybrid joint stiffness adjustment ability analysis is carried out in four different load cases with MATLAB. Featured with light structure, stiffness adjustability, and large workspace, the proposed cabledriven parallel-series hybrid joint proves to be of great potential use for wheelchair-mounted robotic manipulators.

Spring Effects on Workspace and Stiffness of a Symmetrical Cable-Driven Hybrid Joint

“…The key to cable tension analysis and CDHJ stiffness is spring lateral bending and compression model. In most engineering applications, the coil spring under lateral buckling could be treated as an elastic beam [5,36,47,49,51]. Based this concept of an equivalent beam of helical spring, although wrenches of the spring exerted on the moving platform can be calculated, the influence of different springs on the performance of the mechanism cannot be analyzed by using this model.…”

“…In this paper, the mentioned stiffness is static stiffness. However, the vibration analysis is the purpose of dynamic stiffness analysis of CDM in those applications [32,33], requiring high performances [35], especially dynamic performances [36]. Most researchers took cables as massless springs which just considered axial stiffness of cables when CDM is with the light-weighted [34], low speed [33], and small size [37,38], and used the Jacobian-based stiffness analysis method [32,[39][40][41][42] to make static stiffness analysis to describe the Cartesian stiffness matrix which is the function of the manipulator's configuration and mechanism stiffness values.…”

“…In [5,36,47,48], they proposed a CDM with a linear compression spring spine which presents the nonlinear stiffness characteristics under bending and compression, but they did not analyze the impact of adding springs on the workspace and stiffness of CDM in detail. Gao et al [47], Zhang et al [5], and Zhang et al [36] treated the helical spring as a spatially curved bar. This concept of an equivalent column of helical spring is in most engineering applications in [49].…”

Stiffness analysis of cable-driven parallel mechanisms with cables having large sustainable strains

“…14,15 Since the stiffness model of a CDPM established based on such an assumption works well in practice, 2–5 it is believed that the assumption of modeling cables as unidirectional extension springs is valid. 16,17 Researchers proposed that the overall stiffness of a CDPM can be divided into the antagonistic stiffness and the elastic stiffness. 14,15 The antagonistic stiffness is due to cable tensions while the elastic stiffness due to the stiffness of cables.…”

“…The above stiffness analyses 14–22 of CDPMs mainly relied on the analyses of cable tensions. How cable strains play the role in determining the overall stiffness of a CDPM has seldom been reported.…”