Abstract
Inspired by the structure of human arms, a modular cable-driven human-like robotic arm (CHRA) is developed for safe human–robot interaction. Due to the unilateral driving properties of the cables, the CHRA is redundantly actuated and its stiffness can be adjusted by regulating the cable tensions. Since the trajectory of the 3-DOF joint module (3DJM) of the CHRA is a curve on Lie group SO(3), an enhanced stiffness model of the 3DJM is established by the covariant derivative of the load to the displacement on SO(3). In this paper, we focus on analyzing the how cable tension distribution problem oriented the enhanced stiffness of the 3DJM of the CHRA for stiffness adjustment. Due to the complexity of the enhanced stiffness model, it is difficult to solve the cable tensions from the desired stiffness analytically. The problem of stiffness-oriented cable tension distribution (SCTD) is formulated as a nonlinear optimization model. The optimization model is simplified using the symmetry of the enhanced stiffness model, the rank of the Jacobian matrix and the equilibrium equation of the 3DJM. Since the objective function is too complicated to compute the gradient, a method based on the genetic algorithm is proposed for solving this optimization problem, which only utilizes the objective function values. A comprehensive simulation is carried out to validate the effectiveness of the proposed method.
Highlights
Unlike conventional robots that work in structured environments, safe human–robot interactions have been a key element for the robots that work in unstructured and unpredictable environments.Inspired by the structure of human arms, a modular cable-driven human-like robotic arm (CHRA) is developed for safe human–robot interaction, which employs cables to mimic the functionality of the human muscles
The cable tension distribution problem becomes a key element for the stiffness adjustment of the CHRA
3-DOF joint module (3DJM) of the CHRA is a curve on Lie group SO(3), the stiffness of the 3DJM was evaluated by the covariant derivative of the load to the displacement on SO(3), called an enhanced stiffness model of the 3DJM
Summary
Unlike conventional robots that work in structured environments, safe human–robot interactions have been a key element for the robots that work in unstructured and unpredictable environments. In [28], the SCTD problem of a CDM was studied by formulating it as an optimization model, and a gradient-projection-based algorithm was presented to solve the optimization problem It utilized the determinant of the stiffness matrix as the objective function. In [29], the SCTD problem of a 3-DOF cable-driven spherical mechanism was studied and it established the optimization model with all entries of the stiffness matrix, the determinant of the stiffness matrix. It employed the conventional stiffness model of the CDM, which was derived by the conventional differential formula of the load to the displacement. The main contribution of this paper is solving the cable tension distribution problem with the enhanced stiffness model of the
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