Development Of Precision Automatic Adjusting System For Micro Thread

In precision assembly,threads are widely used in connection of multi-frame structures,such as gimbal.It is difficult to keep consistency of tightening and adjusting for operators.The gimbal is an ultra-low-speed mechanical servo system with a dual-frame structure.It is widely used in large and long-life or rapid pose maneuverability requirement spacecraft,such as space stations,satellites and missiles and it is necessary to use bolted shafts to connect multiple parts into components,belongs to the research field of precision assembly.During assembly process,later assembled bolted shafts will impact connected components.Therefore,it is not only necessary to control the tightening torque of a single screw shaft,but need to measure and analyze the overall performance of the assembled components after the assembly is completed,so the assembly process is complex.At present,manual assembly and adjustment of parts are used for gimbals,the automation level and efficiency are low,the product consistency is poor,and the requirement of operators’ technical level is high.Therefore,it is urgent to develop the precision automatic adjusting system for micro thread and further automatic research to improve the production capacity and quality.The main research work of this paper includes:Take the gimbal as an example to carry out the development of precision automatic adjusting system for micro thread.Firstly,Analyze the assembly and adjustment tasks and technical requirements,and carry out the overall plan design of the gimbal precision assembly and adjustment system.Respectively realize the dual-frame structure connections between the inner ring and the bracket,the inner ring and the outer ring by bolted shafts,and realize the automatic adjustment based on the pre-tightening force control of screw thread,and finally realize the control of the installation eccentricity,movement and other parameters to realize the automatic gimbal assembly and adjustment.Following the concept of systematic and modular design,structure design and system construction are carried out by functional modules.Based on the manual assembly process and precautions,an automatic assembly process is formulated.Combine adjustment process characteristics and processes,the system is divided into four functional structural units,including bolted shaft pick-up unit,inner or outer ring pick-up unit,screw thread assemble and adjust unit and worktable and feeding unit.And then,the supporting hardware control system and strategy are designed to realize accurate movement control.Based on force sensing and machine vision,the assembly data acquisition and feedback control are realized.Real-time collection and feedback of force sensor and torque sensor are used to come true automatic adjustment of parameters.In order to acquire the position and pose information of the target parts,we build a scientific and reasonable machine vision system,and propose a micro screw thread collection method to extract the contour and center feature.This method solves the problem of center position accurate measurement of asymmetric features,such as internal and external threads,and realizes automatic alignment between parts.Conduct hardware performance test and assembly experiments,to verify the functionality and reliability of gimbal automatic assembly system.Detect and calibrate the performance of the key hardware of the system;analyze the influence of key parameters on the performance of gimbal during the automatic adjusting process,and adopt the best adjusting parameters and strategies.Develop the eccentricity and dynamic stability of the components based on the interaction of force and visual information Detection and adjustment.Finally,we randomly chose six selected gimbals to conduct assembly and adjustment experiment,the data shows that precision assembly system for gimbal can realize tasks of the assembly,and the accuracy meets the technical requirements.