A Ball Joint With Continuously Adjustable Load Capacity Based on Positive Pressure Method

Research on the variable load capacity method is crucial in promoting the application of soft robots. However, the effects on the performance of current structures are still limited. This letter proposes a ball joint with continuously adjustable load capacity based on the principle of friction with positive pressure. The proposed ball joint can rotate freely under the atmosphere. Once the ball joint is actuated to the reference position, the inner air chamber expands with high pressure, locking the ball joint with friction torque and achieving high load capacity. Since the friction torque is proportional to the input air pressure, the load capacity of the ball joint can be continuously adjusted along with the change of air pressure. The theoretical model is verified via the test of the ball joints. Experimental studies show that the ball joint has a significant advantage in maximum driving torque than other conventional variable stiffness ball joints of similar size. A six-module flexible arm is built for applications. The experiments show excellent flexibility and load capacity of the arm.