A method of designing and fabricating Mckibben muscles driven by 7 MPa hydraulics

Research has recently been increasing on light weight and high-power robot hands that use artificial muscles. By applying ultra high strength PBO fiber sleeves to McKibben artificial muscles, new hydraulic artificial muscles have been developed in our laboratory. In this research, to apply this technology to a high-power robot easily, we have developed new, thin, hydraulic artificial muscles. While the hydraulic artificial muscles reported in our previous paper were driven by a maximum water pressure of 4 MPa, the newly developed thin muscles are driven by water with a maximum pressure of 7 MPa, resulting in very high force capability. This paper details the materials and structure of the new artificial muscles and reports the results of experiments on them. The muscles developed in this work are based on a sleeve and rubber tube design. The movements of the muscles depend on the angle of the knit of sleeve: an angle of less than 54.5 deg produces contraction while an angle of more than 54.5 deg produces extension. Based on this idea, we optimize, using FEM analysis, the angle of knit of the sleeve of each muscle. As a result, a high powered artificial muscle 21 mm in diameter which generates 8 kN of contraction force has been successfully developed.