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Very High Force Hydraulic McKibben Artificial Muscle with a p-Phenylene-2,6-benzobisoxazole Cord Sleeve

Small and lightweight actuators that generate high force and high energy are strongly required for realizing powerful robots and tools. By applying ultra-high-strength p-phenylene-2,6-benzobisoxazole fiber sleeves to McKibben artificial muscles, new hydraulic artificial muscles have been developed. While conventional McKibben muscles are driven by a maximum pneumatic pressure of 0.7 MPa, the newly developed muscles are driven by a maximum water hydraulic of pressure of 4 MPa, resulting in very high force capability. This paper presents the materials and structure of the new artificial muscle and the experimental results. The developed muscles are evaluated by four parameters — force density per volume (FDV), force density per mass (FDM), energy density per volume (EDV) and energy density per mass (EDM) — for comparisons with other conventional linear actuators. The prototype artificial muscle, which is 40 mm in diameter and 700 mm in length, can achieve a maximum contracting force of 28 kN, FDV of 32.3 × 10–3 N/mm3, FDM of 9.44 × 103 N/kg, EDV of 2600 × 10–3 J/mm3 and EDM of 762 × 103 J/kg. These values are 1.7 to 33 times larger than those of the typical conventional actuators. As the result, a high force artificial muscle of 40 mm in diameter that generates 28-kN contracting force has been developed successfully.