Dynamical behaviour of pneumatic artificial muscles

The mechanical response of pneumatic artificial muscles is analyzed in transient and periodic conditions, assuming the inextensibility of the sheathing fibres and considering the influence of the texture geometry, of the dissipation due to the mutual sliding between the braids and of the stress field inside the bladder thickness, where the constituent elastomer is regarded as a two-parameter Mooney–Rivlin material. The polytropic exponent of the thermodynamic air evolution inside the muscle during the charging and discharging phases may be properly chosen depending on the working frequency. The muscle end shape is taken into account profiling the meridian section by a simple m-degree parabolic law. The estimate of the mechanical and geometrical parameters of each individual muscle permits simulating its response in several unsteady operations and identifying its hysteretic behaviour under periodic pressure excitation. The comparison with several experimental results present in the literature shows a very acceptable agreement.