Characteristic analysis and motion control of a novel ball double-screw hydraulic robot joint

The hydraulic joint is the key driving component of a robot. To reduce the joint size of the hydraulic robot, and improve the control accuracy and dynamic response performance, this paper proposes a novel joint structure and control method of a ball double-screw hydraulic robot. Using ball and circular arc spiral groove transmission, the hydraulic joint has a small transmission friction coefficient, compact overall structure and higher transmission accuracy. Aiming to resolve the problems of low control accuracy and motion instability caused by temperature drift in valve-controlled hydraulic systems, the high-precision joint control method based on adaptive fuzzy control compensation is used to improve the control accuracy and stability. The static and dynamic characteristics of the designed hydraulic joint are analyzed by simulation. A test platform was built, and the physical prototype of the hydraulic joint underwent static testing, dynamic control, amplitude frequency response and trajectory tracking tests. The experimental results were similar to the simulation results. The ball double-screw hydraulic robot joint has the characteristics of low starting pressure, high energy density, fast dynamic response, small amplitude frequency attenuation and high control accuracy. The starting pressure is 0.5 MPa, maximum swing frequency is 3 Hz, positioning accuracy is ± 0.03°, tracking accuracy is ± 3.9° and maximum angular velocity at 10 MPa is about 7.6 rad/s, which is close to the angular velocity of the actual human joint.