Enhanced static modeling of commercial pneumatic artificial muscles

Purpose This paper aims to propose an enhanced static model of commercial braided pneumatic artificial muscles (PAMs), which is fully analytical without the need for experimentally determined parameters. Design/methodology/approach To address the highly nonlinear issues of PAMs, the enhanced model is derived considering the irregular shapes close to their end-fittings, as well as the elastic energy stored in both their braids and rubber bladders. The hysteresis characteristics of PAMs are also explored by analyzing the friction in the crossovers of the interlacing braided strands, together with that between the strands and their surrounding bladders. The isobaric and isometric experiments of a commercial PAM are conducted to demonstrate the enhancement, and the model accuracy is evaluated and compared with some existing models in terms of root mean square errors (RMSEs). Additionally, the proposed model is simplified to facilitate the applications that entail high computational efficiency. Findings The proposed model agrees well with the experimental results, which indicates its viability to accurately predict the static behaviors. An overall RMSE of 5.24 N shows that the enhanced model is capable of providing higher accuracy than the existing analytical models, while keeping the modeling cost at a minimum. Originality/value The proposed model, taking account of non-cylindrical shapes, elastic energy and friction, succeeds in enhancing the static predictions of commercial PAMs. The fully analytical model may accelerate the development of novel PAM-based robots for high-precision control, while giving a deeper understanding of commercial PAMs.