Prediction of the mechanical performance of McKibben artificial muscle actuator

•We analyze the McKibben actuator by considering energy losses in the actuator deformation.•Equations are obtained for pressurization and decompression of the actuator.•Effects of sleeve geometry on the performance of actuator are discussed.•Cross-sectional area of the thread is an important factor for actuator performance.•Use of Pattern 2, instead of Pattern 1, will improve the maximum contraction ratio.

In this study, the deformation mechanism of McKibben artificial muscle actuator is investigated through experimental and theoretical approaches. Especially, the relationship among the applied load, the actuator's length and the internal pressure for the actuator is analyzed by considering several types of energy losses associated with the actuator's deformation. The relationship between the applied load and the internal pressure of the actuator under both pressurization and decompression process can be predicted well by using our theoretical model. Also the effects of the sleeve's geometry on the performance of the actuator are discussed by using the proposed model. The contraction ratio of the actuator is the key for evaluating the actuator's performance, but enhancing the contraction ratio may result in increasing the possibility of the rubber's protrusion between threads. Moreover, based on our results, the appropriate number of threads, the way of braiding and the cross-sectional shape of a thread are proposed for improving the performance of the actuator.