Exploring and analyzing the influence of hinge gap and component flexibility on the dynamic performa1

The problem of mechanism clearance, caused by manufacturing errors and normal wear and tear during operation, can lead to severe collisions and impacts between the sub-elements of connected components. This increases dynamic stress, wears down rods, increases elastic deformation, generates noise and vibration, and reduces overall mechanical system efficiency. Many researchers have studied the dynamics of parallel mechanisms with hinge gaps and flexibility, but further in-depth analysis is still needed.

For example, BAUCHAU et al. proposed a typical clearance hinge method for describing flexible multi-body systems using kinematics. ZHAO et al. discussed the influence of hinge gap size on the dynamic performance of space series robots. Chen Jiangyi et al. analyzed the dynamics of parallel mechanisms with hinge gaps. KAKIZAKI et al. studied the dynamics of space mechanisms with hinge gaps, considering the flexibility of the rod. He Baiyan et al. proposed and established the dynamic model of the rigid-flexible manipulator in the case of hinge gaps. These studies provide valuable insights into the dynamics of parallel mechanisms with hinge gaps and flexibility.

To address the issue of mechanism clearance, a dynamic model of the mechanism with hinge gap is established. Since hinges with gaps will collide during motion and metal parts have elastic and damping characteristics, a nonlinear spring damping contact force model and a modified Coulomb friction model are used. The nonlinear spring damping contact force model calculates the contact force between the hinge pin and sleeve based on the Hertzian contact model and considers energy loss caused by damping. The modified Coulomb friction model accurately describes friction from static friction to dynamic friction, considering Coulomb friction, static friction, and viscous friction.

When analyzing the dynamic characteristics of mechanisms with hinge gaps, it is necessary to consider the flexibility of the components. In ADAMS software, flexible components can be constructed using three methods: discretizing the flexible body into multiple rigid bodies, creating flexible bodies directly with ADAMS/Auto Flex module, or combining ANSYS software with ADAMS to build flexible components. The third method is chosen in this study because it can better reflect the actual movement of flexible bodies. ANSYS is used to model the flexible component, perform modal analysis, and generate a mode-neutral file that includes various parameters and information about the flexible member.

To demonstrate the analysis, a 3-RRRT parallel mechanism is used as the research object. Modal analysis is conducted on the branch chains of the mechanism using ANSYS, and the results are converted into flexible members in ADAMS. The mechanism consists of a fixed platform, three branch chains, and a moving platform. Each branch chain is composed of rods, rotating hinges, and moving pairs. The flexibility of the rods is considered, while other components are treated as rigid bodies. The driving pairs are set as the driving part, and the mechanism is simulated at low and high speeds.

The analysis reveals that hinge gaps have a significant influence on the speed and contact force of rigid mechanisms, while flexibility primarily affects the speed and acceleration of the mechanism. The larger the hinge gap, the greater the amplitude of velocity and acceleration changes. Driving speed also affects the dynamic performance of the mechanism, with higher speeds resulting in larger changes and less stability. However, regardless of the influencing factors, the contact force, velocity, and acceleration gradually reach a steady state after undergoing amplitude changes.

In conclusion, the dynamics of parallel mechanisms with hinge gaps and flexibility are crucial considerations in design and manufacturing. The flexibility of large deflection components must be taken into account, and hinge clearance cannot be ignored, especially for mechanisms that operate at high speeds. By understanding and addressing these factors, the performance and efficiency of the mechanical system can be significantly improved.