Study On Active Vibration Control Of Press Section For A Modern Paper Machine

Engineering vibration problem has been one of the important research topics in the fieldsof science research and engineering technology. At present, the development of domesticpapermaking machinery towards higher speed, larger width, more complex, higher automation,more greening. The press section of paper machine which is a complex roll press system is verysensitive to vibration, thus, it is prone to vibrate. The vibration of press section will affect thequality of the paper if it is severe, the intense noise caused by vibration and vibration result in abad work environment of papermaking workshop, even prevent the normal operation of papermachine, at worst, it will cause unscheduled downtime. The vibration problem is gotten moreand more attentions of the people when designing and using this kind of papermakingmachinery. Based on this, this paper puts forward a variety of vibration control methods, andthen, study the active vibration control method which has a great potential for growth in details,in order to provide theoretical basis and technology solution for making and implementing theprogram of vibration reducing for press section, which is help to the operation of paper machinesafe and smoothly.At first, it analyzed the press section whose structure was compact and complex, includingthe process function, structure characteristics, vibration reasons, and consequences of vibration.And then on this basis, put forward many kinds of vibration control methods such as passivevibration control methods and active vibration control methods. Passive vibration controlmethods included reducing the amplitude of exciting force, vibration isolation, vibrationresistance, tuning, etc. The discussion of those kinds of vibration control methods was on in theview of vibration theory, in order to highlight the advantages of active vibration controlmethods applied in press section; Secondly, considering the fact of the press section composedof large rolls, active vibration control of press section focused on the study of vibration controlof press roll, and the vibration characteristics of press roll were studied using large finiteelement software ANSYS. Again, the simulation research of active vibration control for thepress roll was on with MATLAB7.0/Simulink platform. It included two cases, one case was inquality imbalance caused by centrifugal force of the press roll, and the other case was in theviscoelastic layer on the surface of the press roll. At last, a test model was designed, in order toverify the effectiveness of the proposed active vibration control methods.The results were as follows:（1） Through the investigation of a paper mill and the collection of related literatures, it was known that the roll press system of press section was prone to vibrate; the vibration signal wasvery complex, and the vibration intensity was bigger, which wound affect the quality of thepaper, the performance of equipment.（2） Among vibration control methods, the passive vibration control methods were usedwidely in practice. The research results of the paper indicated that active vibration controlmethods were more suitable to vibration reducing for press section of a paper machine.Through the analysations of active vibration control system composition and the analysis of itsworking principle for the press section, put forward the technological scheme of activevibration control for the press section.（3） The vibration characteristics of press rolls were studied using ANSYS software, itincluded that the first order natural frequency of press rolls was not much difference between itssecond order natural frequency, the corresponding vibration shapes were the same, and the gapof the maximum deformation for press rolls was very small. The third vibration shape of pressrolls was the small amplitude sway around its symmetry axis, the deformation in the middlewas much larger and the deformation of two ends was much smaller, the gyroscopic effect wasmore obvious. The fourth vibration shape of press rolls was torsion modal, the vibrationdirections of two ends were opposite, and the vibration deformation was obvious. Themaximum deformations of the first four modal vibration were:0.008774m、0.00877m、0.007446m、0.012378m. For the first four natural vibrations, the maximum deformation areaswere in the middle of press rolls, and it indicated that intermediate position was the stiffnessweak part. The operating line speed of press rolls was450m/min, and it got that the workingfrequency of press rolls was1.67Hz. This working frequency was far away with its first naturalfrequency79.360Hz, it didn’t appear the phenomenon of roll resonance.（4） Without considering the dynamic effects for the structure of sensor and actuator,through the simulation of active vibration control for a single roll with theMATLAB7.0/Simulink simulation software, it indicated that the direct velocity feedback andpositive position feedback control were both effective. Among them, the direct velocityfeedback in three different velocity gains （g=500、 g=1000、 g=1500） reduced vibrationdisplacement of press roll vibration system, especially, when g=1500, the vibrationdisplacement reduced to2.6×10^-3mfrom3.8×10^-3m, the reduced amplitude reached32%.When g=1000, the vibration displacement with the direct velocity feedback was3.08×10^-3m,however, when displacement gain g=1000for the positive position feedback, the vibrationdisplacement was3.38×10^-3m. Thus, the direct velocity feedback algorithm was more effectivewithout considering the dynamic performance of the actuator.（5） For double press rolls vibration system, it did some simulation studies on activevibration control whose vibration was caused by the viscoelastic of covers throughMATLAB7.0/Simulink software. The results showed that the maximum vibration displacementsof the top roll and the bottom roll was8.5×10^-5m、4×10^-5mrespectively after taking activedamping vibration control, compared with its original maximum vibration displacement1.1×10^-4m、6×10^-5m, and the vibration reduced23%、25%respectively; In addition, the vibration attenuation time of the top roll and the bottom roll was also reduced from0.22s and0.20s to0.12s and0.10s. It reduced the risk of getting damage for rolls because of the shortageof vibration time.