| In the process of high-speed grinding,the unbalance caused by the accumulation of grinding wheel wear and uneven distribution of coolant is an important factor that leads to the system vibration,the decline of grinding accuracy and the poor consistency of machining quality.The on-line active balancing method has the characteristics of non-stop,high balancing accuracy and short balancing time,which deeply meets the needs of modern production.Electromagnetic active balancing system has the advantages of non-contact between the executive system and the control system,short axial length and fast response speed.It is one of the most potential online balancing technologies at present.At present,this kind of commercial products can not meet the production demand in China.In this paper,the key technical problems such as less self-locking experiments,narrow driving current range,single driving mode and poor execution reliability in the current electromagnetic active balancing system are studied.(1)The finite analysis models of self-locking torque,electromagnetic driving torque and rotor vibration of balancing head are established.The finite element model of self-locking magnetic circuit was established by using the finite element analysis method and control variable method,and the influence of the geometric parameters(tooth number,tooth length,tooth margin,tooth opening angle,etc.)of the gear disk and the geometric parameters(diameter,length,material,axial air gap,etc.)of the permanent magnet on the self-locking torque was explored;the coupling finite element model of the driving magnetic circuit and the external circuit was constructed,and the driving current,the torque were analyzed.The influence of the diameter and length of the permanent magnet and the air gap between the moving and stationary rings on the driving torque was studied.With the help of the finite element analysis method,the vibration characteristics of the balancing head rotor system were studied,the vibration finite element analysis model of the balancing head rotor system was established,and the free modal frequency and constrained modal frequency of the rotor were analyzed,which provides a theoretical basis for the product design.(2)The development of the online dynamic balancing system prototype and test bed was completed.Based on the theoretical research rules and results,the design parameters were determined,and the prototype of online dynamic balancing system was developed through the analysis of function,machining,assembly process and other manufacturing feasibility;around the functional characteristics of the balancing head,the Lab VIEW test system,driver and power transmission system required for the experiment were designed,and the online dynamic balancing comprehensive experimental platform was completed.(3)The self-locking torque,driving current and the vibration characteristics of the balancing head of the on-line dynamic balancing system were experimentally verified.In view of the current situation that there were few self-locking experiments,the self-locking torque test was carried out based on the developed test system.The results show that the peak value of self-locking torque decreases with the increase of air gap length in a quasi exponential function.When the air gap is 0.15 mm,the maximum value is 1.95N·m.When the air gap increases from 0.1mm to 0.5mm,the peak value of self-locking torque decreases by42%,But overall,it is within 20%.In view of the single driving current value,the current pulse width of 20?45ms and the amplitude of 5?9A can be driven from the angle of work,and the small current narrow wave pulse electric conversion efficiency is high,and the large current wide wave pulse driving ability is strong.The first-order modal frequency of the rotor system is 665 Hz,and the error between theoretical analysis and experimental analysis is less than 4%.(4)The reliability test of the online dynamic balancing system was completed.In view of the current situation that the implementation depends on visual inspection,this paper presented a method of continuously changing the angle between the two counterweights to make the unbalance change according to the simple harmonic law,and monitored the rotor vibration at the same time.The experimental results show that the angle between the two counterweights ranges from 0 to 360 in the frequency range of 20?70Hz.During the change process,the amplitude of the same frequency vibration of the rotor is approximately harmonic,and there is no step loss phenomenon,which indicates that the online dynamic balancing system can achieve reliable drive and stable self-locking function at the speed of no more than 4200r/min.(5)The online dynamic balance of high speed grinder was realized.By adjusting the weight of the balancing rotor system and using the automatic balancing strategy to drive the counterweight to the designated position,it was verified that the online dynamic balancing system had effective vibration reduction ability.The experimental results show that the unbalance can be reduced by 88% through dynamic balancing. |
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