Abstract
Pneumatic artificial muscle (PAM) is attractive in rehabilitation and biomimetic robots due to its flexibility. However, there exists a strong hysteretic nonlinearity in PAMs and strong coupling between the output displacement and the output force. At present, most commonly used hysteresis models can be treated as two-dimensional models, which only consider the nonlinearity between the input and the output displacement of the PAM without considering the coupling of the output force. As a result, high-precision modeling and estimation of the PAM’s behavior is difficult, especially when the external load of the system varies significantly. In this paper, the influence of the output force on the displacement is experimentally investigated. A three-dimensional model based on the modified Prandtl–Ishlinskii (MPI) model and the Nonlinear AutoRegressive Moving Average with eXogenous inputs (NARMAX) model is proposed to describe the relationship and couplings among the input, the output displacement, and the output force of the PAM. Experiments are conducted to verify the modeling accuracy of the proposed model when the external load of the PAM varies across a wide range. The experimental results show that the proposed model captures well the hysteresis and couplings of the PAM and can precisely predict the PAM’s behavior.
Highlights
Pneumatic artificial muscle (PAM), a flexible actuator, mainly consists of an inner elastomeric tube and an outer braided mesh [1]
modified Prandtl–Ishlinskii (MPI)-Nonlinear AutoRegressive Moving Average with eXogenous inputs (NARMAX) successfully captures the influence of the external load and improves the prediction accuracy on the output displacement of the PAM
The effectiveness of the identified MPI-NARMAX model is verified on another testing dataset, where the PAM is confronted with stronger external forces
Summary
Pneumatic artificial muscle (PAM), a flexible actuator, mainly consists of an inner elastomeric tube and an outer braided mesh [1]. PAM shows good flexibility because it generates an output force and displacement based on its elastic deformations [3]. This helps to guarantee the safety in human–machine interactions. In the research work of Sofla et al [9], a PAM-driven multi-section-compliant robotic manipulator was developed, where the Bouc–Wen model was modified based on the constant curvature method and the concentrated masses to compensate the asymmetric hysteresis. The effect of the output force is not considered in the above 2D models They cannot precisely predict the PAM’s behavior if confronted with varying loads or strong disturbances. The proposed MPI-NARMAX model achieves higher modeling accuracy and applicability
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