Research On Multi-axis Thread Tightening Control System

In modern industrial production,it is often encountered that a joint requires multiple bolts for fastening.When tightening a bolt group,the effect of the elastic interaction between bolts results in the decrease of preload,The best solution is to tighten a set of bolts to the desired preload at the same time.Multi-axis synchronous tightening not only requires the control of pretightening force of single bolt to be accurate,but also puts forward high requirements on the synchronization of tightening time of multiple bolts and the dispersion of pre-tightening force between multiple bolts.According to the control requirements of multi-axis synchronous tightening,this thesis first selects the torque method as the tightening process.First,the tightening process is modeled and theoretically analyzed.After analyzing the torque method of the current mainstream tightening equipment and its motor control scheme,an improved torque method and its motor control scheme are proposed.Based on this,a multi-axis synchronous tightening scheme that can be divided into coupling synchronization and phase synchronizationis is proposed,and a multi-axis synchronous tightening quality evaluation standard for judging the dispersion of the pre-tightening force based on the dispersion of the tightening angle is formulated.Secondly,the multi-axis coupling synchronization algorithm is analyzedand compared,and a simplified structure of coupling synchronization control is proposed.In the simplified structure,all coupling algorithms differ only in the definition of synchronization error.After the simulation analysis and comparison of the simplified coupling synchronization algorithms,the mean deviation coupling synchronization algorithm is selected as the synchronization algorithm in the multi-axis thread synchronization tightening control scheme.Then,the first order LADRC controller of velocity loop,the improved PID controller of position loop and the torque loop PID controller to prevent torque overshot are designed for the motor control scheme of the improved torque tightening process.The torque feedback of the torque ring is calculated by the current of the motor's q-axis,and the calibration method of the overall torque coefficient of the tightening shaft is proposed to reduce the cost of the torque sensor.Through simulation analysis,it is verified that the velocity loop LADRC has excellent dynamic performance and anti-interference,and it is proved that the PID controller with improved position loop can realize the compound precise control of position and speed.Finally,the hardware and software architecture of the multi-axis thread synchronous tightening experiment system is designed.The improved torque method tightening process was used for multiple tightening experiments.The experimental results show that the improved torque method tightening process has higher torque control accuracy and good stability of the tightening results.Carry out the multi-axis thread synchronous tightening experiment,compare whether to adopt the multi-axis thread synchronous tightening control scheme,and the analysis of the experimental results verifies that the multi-axis thread synchronous tightening control scheme based on the improved torque method tightening process can achieve multiple simultaneous The bolt is tightened to the target torque,and the dispersion of the pre-tightening force is smaller.