Dynamic modeling and responses investigation of spatial parallel robot considering lubricated spherical joint

Lubricated spherical joint is widely used in spatial parallel robots, which significantly influences the dynamic response of the mechanism. Current research of mechanism dynamics considering lubricated kinematic joint mainly focuses on the plane mechanism with revolute joint, while that involves lubricated spherical joint of spatial mechanism is very few, especially, spatial parallel robot has not been reported. Dynamic modeling and responses investigation of spatial parallel robot considering lubricated spherical joint is realized in this paper. Combined with Reynolds' equation and Gumbel's boundary condition, dynamic modeling method of spatial parallel robot with lubricated spherical joint is proposed. The dynamic model of 4-UPS/RPS parallel robot with lubricated spherical joint is developed. Lubrication force model has been improved to provide better numerical stability for spatial parallel robots. The influences of lubricated joint and dry contact joint on dynamic response of the parallel robot are simulated by adjusting clearance size and driving speed. Results demonstrate that contact-impact at clearance joint is closely related to impact response of moving platform, and lubricated joint effectively weakens this effect. The deviation degree of acceleration is weak when clearance size is less than 0.4 mm, which means that the robot has good performance. It is of great significance to investigate influences of lubricated spherical joint on performance of parallel robots for dynamic prediction and structural optimization design of the system.