Abstract
A novel two degree-of-freedom (DOF) ball-joint-like hydraulic spherical motion mechanism (SMM) for use in robotic applications is proposed to achieve smooth spherical motion in all directions. Unlike traditional systems that use serial or parallel mechanisms for generating multi-DOF rotations, the proposed SMM is capable of producing continuous 2-DOF rotational motions in a single joint without intermediate transmission mechanisms. The proposed SMM has a compact structure, low inertia, and high stiffness. First, the architecture and operating principle of the proposed SMM is introduced. Then, the kinematic model is established using Euler transformation, following which factors (such as workspace and dexterity) that have an impact on motion performance are evaluated. As the foundation of dynamics analysis and controller design, the Lagrange’s equations of the second kind are used to establish the dynamic model. To achieve high tracking accuracy, the radial basis function neural network–based sliding mode controller is applied to the mechanism. The simulation results indicate that the designed controller not only improves trajectory tracking capability but also enhances robustness against external disturbance and system uncertainty. Finally, experiments are performed on a prototype SMM to validate the performance of the proposed SMM and evaluate the control method.
Highlights
Spherical motion, which is probably the most important type of motion after rotary motion, is a multi-DOF rigid body motion along a spherical surface with a permanent center of rotation
This paper presents a novel 2-DOF ball-joint-like hydraulic spherical motion mechanism (SMM)
The SMM could be used in the field of robotics; it could be used as a robotic wrist joint, shoulder joint, hip joint, etc
Summary
Spherical motion, which is probably the most important type of motion after rotary motion, is a multi-DOF rigid body motion along a spherical surface with a permanent center of rotation. A novel 2-DOF ball-joint-like hydraulic SMM with an RBFSMC is proposed in this study to achieve spherical motion. The rudder blade, which is supported concentrically by the lower stator via a spherical pair, can rotate around the X1 axis. The stator, the rotor, and the rudder blade form two closed oil chambers A and B, which are the working chambers of the swing hydraulic motor. The working principle of the swing hydraulic motor is that the rudder blade and the rotor tilt an angle β around the X1 axis when the pressure in oil chamber A is not equal to that in oil chamber B. The rotor spins an angle α around the z axis relative to the rudder blade. Equations (4)–(6) indicate the relationships among rotation angles of the X rail, the Y rail, the rudder blade, and the rotor. The modeling process includes selecting the generalized coordinates, formulating the kinetic and potential energy, and calculating Lagrange’s equations
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