A variable stiffness method for pneumatic flexible arms

In this study, a three-degree-of-freedom pneumatic flexible arm with a braking function was designed to overcome the shortcomings of low bearing capacity and insufficient rigidity of existing flexible arms. The braking force was adjusted by controlling the air pressure entering the brake, changing the stiffness of the flexible arm, and enhancing the posture maintainability of the flexible arm. A theoretical model of the braking force and stiffness of a flexible arm was established, and applicable experiments were conducted. The theoretical data were consistent with the experimental results. The braking force linearly increased with the increase of braking pressure, at a brake air pressure of 0.40 MPa. The braking force of a single braking unit reached 276 N. The stiffness nonlinearly increased with an increase in the brake air pressure. At a brake air pressure of 0.4 MPa, the axial stiffness of the flexible arm in the initial state had the highest value of 20 kN/m. The stiffness change in the bending direction of the flexible arm in the spatial bending state was the largest and increased by 12.4 times. The proposed flexible arm exhibited high stiffness and flexible movement; thus, it can be used as a flexible arm to support other end effectors. The proposed variable stiffness method can be practically employed to maintain the posture of flexible robots, which has a high practical value.