| Small Length-Diameter Ratio Screw(SLDRS)is widely used in the assembly of electronic equipment,but at present,the SLDRS automatic locking screw machine on the market mostly relies on the mechanical structure to set the torque value for locking,lacking the quality detection module of locking,so it is easy to produce abnormal locking phenomena such as skew locking,floating locking,sliding teeth,and adhesion of locking tool with workpiece.At the moment,electronic equipment is developing towards precision and miniaturization,so the requirement of high quality locking for SLDRS is put forward.Based on the practical problems mentioned above,this paper discuss the locking quality of small aspect ratio screw under the engineering background of locking TV backboard lamp.Firstly,aiming at the eccentricity problem and the random occurrence of initial screw engagement point in the process of SLDRS,a theoretical correction model is proposed;Second,the upgrading of dynamic feedback is carried out on the basis of the existing equipment;Third,the lock experiment is carried out on the basis of secondary positioning combined with machine vision;finally,the appropriate lock-up strategy is set according to the lock-up curve,which improves.the lock quality of the SLDRS.The main contents of this paper are as follows:(1)On the basis of the original gantry three-axis locking screw machine,a set of torque feedback locking system based on real-time acquisition is designed and developed,including servo tightening mechanism controlled by industrial computer and motion control card,parameter acquisition system for high-precision torque sensor by data acquisition card.And a set of screw machine control program suitable for dynamic feedback is designed,which realizes inching,point to point,following,interpolation and other motion functions.(2)The magnetic suction is used instead of the original air suction method to absorb the screw.The screw axis coincides with the batch head axis in the process of taking out the screw from screw arrangement machine.The process of taking out the screw is optimized.The feasibility and stability of the magnetic suction scheme are proved by experiments.Adding industrial cameras and combining machine vision for secondary positioning can further reduce the lock-in positioning errors caused by manufacturing errors,and improve the positioning accuracy within 0.061 mm.(3)A theoretical tightening model is established,which according to the actual locking of SLDRS.The influence of initial screw-in point on the peak torque value is eliminated.Torque-time ratio algorithm is used to analyze the accuracy of pre-tightening force control.The theoretical model is verified to be in accordance with the actual situation by combining the experimental data.The characteristics of the lock curve of skew lock and the sliding teeth are analyzed,and the detection model is established.The detection of alarm functions with screw lock and sliding teeth are realized by real-time monitoring of the torque. |
