| The study of the deadweight force standard machine with wide-range is the leading edge in the field of force metrology.Optimizing the performance of deadweight force standard machine is always a hot topic.The range of 2MN deadweight force standard machine is the largest at present in China was regarded as the research object.The weight loading and unloading process was deeply analyzed and studied,The dynamic response law of each parameter to the output end and the hanging system was revealed and on this basis,the weight loading and unloading method and the weight loading configuration scheme were optimized.Specific work is distributed as follows.Firstly,the mechanical structure and working principle of 2MN deadweight force standard machine were introduced and analyzed,and relevant force components were checked.According to the design scheme and the actual situation of the machine,the three-dimensional simplified model of the main force components was established,and the finite element method was used to check the strength,stiffness and stability of each component under extreme working conditions.The results show that the main components of the machine meet the safety requirements.Then,the influences of various parameters on the longitudinal vibration of the output during the loading and unloading process were studied in this paper.The dynamic theoretical model was established and the loading and unloading curve was taken as a straight line as the excitation of the model.The numerical results show that the curve tip is easy to cause longitudinal impact on the system,and the slower the loading and unloading speed,the longer the loading and unloading time,the smaller the impact.In addition,as the equivalent stiffness of the hanging system or the weight driving assembly increases,the impact increases.And the influence law of each parameter in the process of weight loading and unloading on hanging system swing was studied.The dynamic model of hanger system swing was established and the numerical calculation was carried out.The results show that the decrease of radius of load pad or the increase of rolling resistance coefficient in load pad will lead to the enhancement of the swing.In addition,the closer the weight loading position is to the upper end of the hanging system,the weaker the swing of the hanging system is.In further,the method of smooth loading and unloading of weights was studied.Firstly,through comparative analysis,the reasonable weight loading and unloading device was selected.Then,the smooth loading and unloading curve was designed and used as the preset loading and unloading curve of 2MN deadweight force standard machine to ensure that the machine can be smoothly loaded and unloaded within the specified time.Finally,the method of displacement-force combined control was proposed to realize the rapidity and stability of the whole process of weight loading and unloading.Through theoretical modeling and simulation,it was verified that the longitudinal impact of the output terminal was extremely small.Finally,aiming at the optimization problem of weight loading configuration of 2MN deadweight force standard machine,an optimal configuration scheme was proposed.And the scheme was analyzed by experiment.The experimental results show that the repeatability of force transducer under the optimal configuration scheme is obviously better than that under the other two random configuration schemes,and the deviation of the repeatability curve under the optimal configuration scheme is less than 0.001%.Compared with the other two random schemes,the deviation of linearity of force transducer in the optimal configuration scheme is reduced by about 10%at most.The superiority of the optimal configuration scheme is proved. |
