Rigid–flexible coupling dynamics analysis with joint clearance for a 5-DOF hybrid polishing robot

SUMMARY Considering the polishing requirements for high-precision aspherical optical mirrors, a hybrid polishing robot composed of a serial–parallel manipulator and a dual rotor grinding system is proposed. Firstly, based on the kinematics of serial components, the equivalent load model for the parallel manipulator is established. Then, the elastodynamic model of kinematic branched-chains of the parallel manipulator is established by using the spatial beam element, and the rigid–flexible coupling dynamic model of the polishing robot is obtained with Kineto-elasto dynamics theory. Further, considering the dynamic properties of the joint clearance, the rigid–flexible coupling dynamic model with the joint clearance for the polishing robot is established. Finally, the equivalent load distribution of the parallel manipulator is analyzed, and the effect of the branched-chain elasticity and joint clearance on the motion error of the polishing robot is studied. This article provides a theoretical basis for improving the motion accuracy and dynamic performance of the hybrid polishing robot.

Dual Nozzle Weapon Power Couple Vibration Controller With Delayed Rear Nozzle

Aiming at the problem that the firing accuracy of barrel weapon is affected by the violent vibration during continuous firing, a double-nozzle vibration controller using the energy of gunpowder gas in the chamber is proposed. The synchronous external injection of the double nozzles of the controller is realized by the delayed ejection of the rear nozzles, so as to generate a power couple to balance the recoil flipping torque of the barrel weapon to achieve the stable firing effect of reducing the bore vibration. A double-nozzle vibration controller with a delayed rear nozzle for a chain gun is designed. The rigid-flexible coupling dynamic model of a chain gun with a double-nozzles vibration controller was established considering the two-phase flow of propellant gas in the barrel and airway. The numerical simulation of the muzzle vibration characteristics of the original weapon and a chain gun equipped with a double-nozzles vibration controller is carried out respectively, and the effectiveness of the double-nozzles dynamic couple vibration controller for the continuous firing vibration control of the barrel weapon is verified.

Application of Multi Body System Coupling Dynamic Model in Posture Stability Evaluation of Sports

Due to the lack of more precise and complete data support, the reliability of posture stability evaluation method based on common technology is poor. In the face of such problems, the application of multi-body system coupling dynamic model in the evaluation of sports posture stability is proposed. The coupling dynamic model of human motion posture is established, and the relevant data of human motion posture is collected. The complete data of human motion posture is obtained by solving the dynamic model. Choose the appropriate stability evaluation index, calculate the stability evaluation index, divide the stability level, and realize the evaluation of posture stability. The experimental results show that: the application of multi-body system coupling dynamic model in the stability evaluation method makes the time delay and data error of the evaluation method small, and its overall reliability is improved.

Thermos-Solid-Gas Coupling Dynamic Model and Numerical Simulation of Coal Containing Gas

Based on gas seepage characteristics and the basic thermo-solid-gas coupling theory, the porosity model and the dynamic permeability model of coal body containing gas were derived. Based on the relationship between gas pressure, principal stress and temperature, and gas seepage, the thermo-solid-gas coupling dynamic model was established. Initial values and boundary conditions for the model were determined. Numerical simulations using this model were done to predict the gas flow behavior of a gassy coal sample. By using the thermo-solid-gas coupling model, the gas pressure, temperature, and principal stress influence, the change law of the pressure field, displacement field, stress field, temperature field, and permeability were numerically simulated. Research results show the following: (1) Gas pressure and displacement from the top to the end of the model gradually reduce, and stress from the top to the end gradually increases. The average permeability of the Y Z section of the model tends to decrease with the rise of the gas pressure, and the decrease amplitude slows down from the top of the model to the bottom. (2) When the principal stress and temperature are constant, the permeability decreases first and then flattens with the gas pressure. The permeability increases with the decrease of temperature while the gas pressure and principal stress remain unchanged.

Research on Identification and Suggested Control Value of Continuous Multi-Wave Track Alignment Irregularities in High-Speed Railway

Continuous multi-wave irregularity can easily lead to train vibration, which will influence the safety and comfort of vehicle. Due to the influence of bridge creep and track plate deformation, continuous multi-wave irregularity has appeared in high-speed railway lines, but the management value of continuous multi-wave irregularity is not given in the geometric dynamic detection standard of high-speed railway tracks in China at present. Therefore, it is necessary to continue to improve the standard. Based on the dynamic detection data of high-speed railway, the typical characteristics of continuous multi-wave track alignment irregularity are extracted, its automatic recognition model is established, and the amplitude distribution and variation trend of continuous multi-wave track alignment irregularity were statistically analyzed. The vehicle-track coupling dynamic model is established, and the relationship between continuous multi-wave track alignment irregularity and vehicle dynamic response is simulated and analyzed. The control limit of continuous multi-wave track alignment irregularity at different speed levels of high-speed railway in China are put forward.

Vibration analysis of a flexible gearbox system considering a local fault in the outer ring of the supported ball bearing

Ball bearings are key components in the gear transmission system. Supported ball bearings have great influences on the vibrations of the gear transmission system, especially the presence of the local faults. Although some reported works formulated the local fault in the supported bearings of the gear transmission system, the box and shaft were considered as rigid bodies. To overcome this problem, a rigid-flexible coupling dynamic model for a flexible gearbox with the supported ball bearings is developed, which cannot be described by the previous multibody models. The local fault in the supported bearing is described by a time-varying impact force model with a half-sine profile. The bearing clearance, flexible shaft, and box are considered in the rigid-flexible coupling dynamic model. The flexible shaft and box are formulated by a finite element method. The damping and contact stiffness in the bearings and gears are obtained by the previous methods in the listed works. The frictions between the mating components are formulated by the Coulomb friction model. An experimental study is applied to validate the rigid-flexible coupling dynamic model. The effects of the faults on the vibration transmission characteristics are investigated. The results provide that the local fault in the supported bearings will greatly affect the vibrations of the gearbox system. Moreover, it depicts that the vibration collection point for the defective bearings should be located at the same side to obtain better singles. This work can provide a more reasonable method for understanding the vibration transmission characteristics of the gearbox system with the local faults in the supported bearings than the reported multibody models.

The Study on Nonlinear Model of Pantograph-catenary Coupling system for Straddle-type Monorail

Based on the Lagrange equation, the linear and nonlinear dynamic models of straddle monorail pantograph considering the lateral vibration of bogie are derived. On this basis, the lateral coupling dynamic model of pantograph-catenary is established. Newmark method is used to solve the pantograph-catenary coupling dynamic model. In order to evaluate the applicability of the two models，this paper analyzed the contact force response of two model with different speeds. The reasearch show that when the speed is below 40 km/h, the contact forces of nonlinear model and linear model can reflects the lateral excitation of the finger plate. When the speed exceeds 40 km/h, only the nonlinear model can reflect the lateral excitation of finger palte, the nonlinear pantograph-catenary coupling dynamics model is more suitable to the straddle-type monorail pantograph-catenary coupling research.