Study On The Online Accurate Measurement Technology Of Basis Weight And Thickness Of High Basis Weight Paperboard

Due to the impacts of new media and national conomic macro-control in papermaking industry, the paper manufacturers are facing double pressure from falling demands and increasing production costs, so many papermaking enterprises have falls onto the urgent needs of reducing the unit product input and improving productivity relying on technological progress in papermaking process.During the process of high basis weight(BW) paperboard making, there are no mature BW sensors for paperboard with the wide range of 150g/m2-1500g/m2 to measure in domestic of China. And for the measurement technology of 300μm-1500μm paper board thickness was rarely reported. Therefore there is an urgent need for study of accurate BW and thickness measurements of high BW paperboard. In order to solve the questions of automatic sensor range switching, mechanical scanning clearance compensation and early warning of paper broken during the high BW paperboard BW and thickness measurement, the data form multi sensors or many times data from a single sensor need to be analyzed comprehensively. Data fusion technology can make full use of collaborative multi sensor or multiple data. It has a unique advantage of improving the measurement accuracy of some parameters or early warning to a target. DCS and QCS system of papermaking industry already has the hardware platforms which are needed by the data fusion technology. So it is necessary to carry out the study of using data fusion technology in papermaking industry. Data fusion technology can make full use of multi-sensor data which is readily available from the paper industry DCS and QCS, which can extend the function of DCS and QCS and improve the application value of DCS and QCS.This paper studied on accurate BW and thickness measurement technologies, related scanner box positioning precisely and paper broken early warning technologies. It is an important subproject of "Shaanxi Province Science and Technology Overall Innovation Engineering Plan Project-- Paper Quality Integrated Monitoring System of Energy Saving and Environmental Protection Type Middle-High Speed Paper Machine(2012KTCQ01-19)". Main achievements can be summarized as the following aspects:(1) Study on industrial data fusion model and dat fusion algorithmState of art of data fusion technology, process industry data fusion model and fusion algorithm were studied. This paper proposed a modified Dasarathy fusion model with optimizer and optimization rules. The optimizer converted the fusion decision into optimization rules. The optimization rules then have being feedback to data fusion process to optimize the system process.A hierarchical fusion model was proposed according to data fusion location based on improved Dasarathy fusion model through the analysis of the paper industry data fusion needs and combining with the DCS/FCS structure. Data fusion results were used as guidance for loop control optimization was also discussed.Traditional industrial simple filtering algorithm, Kalman algorithm, Gram algorithm and EMD algorithm were discussed to explore the sui Tab. data fusion algorithm for industrial field level and operation level. A data fusion and feature extraction algorithm was designed based on data density.(2) Study on accurate BW measurement technology of high BW paperboardThe measurement accuracy of BW sensor on paperboard at home and abroad is ±1.0%, while the enterprises expect to achieve ±0.5%. But for the wide range of 150g/m2-1500g/m2 paperboard, there are no mature BW sensors to measure in domestic. Therefore it is necessary to study the accurate BW measurement technology of high BW paperboard. The BW measurement of high BW paperboard had good sensitivity and accuracy by adopting imported ionization chamber, high accuracy amplifier, Z axis compensation, temperature compensation and range partitioning. Its relative error was ±0.5% at rang of 150g/m2-1500g/m2. Its performance index was about the same level of the imported BW sensor.In order to realize the automatic sensor range switching, ray energy modulation and multi on-line segment of BW signal amplification circuit were used on the the hardware according to range division. BW observation model was proposed based on multi-sensor data monitoring. A fusion framework of automatic range switching and recognition was presented, which was based on the proposed data fusion model. And fuzzy theory was used in decision making fusion to estimate the BW range. Field test showed that the quantitative observation model had a high reliability. Simulation results also showed that range automatic identification was accurate.Precise of the measuring points and the control points was the key to the cross machine direction(CD) control. A solution was proposed that based on a SIEMENS PLC and encoder. The positioning accuracy error was within ±0.5mm. It can fully meet the demand of the CD control.(3) Study on accurate thickness measurement technology of high BW paperboardCurrently, in order to improve the paper quality more and more, the papermaking enterprises pay attention to the measurement of the thickness of the paper. The measurement of paper thickness less than 300μm is fully mature, but for the measurement technology of 300μm-1500μm board thickness is rarely reported. In this paper, the 300μm-1500μm board thickness measurement was studied by using laser displacement sensor and eddy current sensor. The corresponding compensation measures were given after analyzing factors that affect thickness measuring precision. Through the analysis of the static test, a solution of paper types and color interference measurement accuracy was obtained. The mechanical scanning factors affecting on thickness measurement accuracy were analyzed with dynamic test. An optimal measurement method was selected from three different measurement methods. The measurement error caused by mechanical scanning factors was reduced to ±40μm by clearance compensation.In order to further reduce the error, a data fusion algorithm based on data density was used to get a scanner gap fusion curve by fusing the multiple scanner gap data. The fusion curve was more focused on the center of data-intensive area compared with the averaging method. The fusion algorithm based on data density was proved by using fusion curve to compensate scanner gap. The compensation curve peak amplitude was smaller and the error was reduced to ±20μm. The standard deviation was reduced by 12.8% compared with the averaging method.In order to achieve the manufacture requirements of paperboard measurement accuracy, a single scanning CD curve noise reduction algorithm was used. The single CD curve noise was reducedby using an EMD algorithm to analyze its frequency components. And then seven different algorithms were used for the CD curve noise reduction. Kalman filter and a sliding filter were used as the thickness measuring noise reduction algorithms after comprehensive comparison of the optimized single CD curve and difference compensation curve. The standard deviations for their compensation errors were within ±5μm. Actual measurement error was within ±40μm for the whole CD curve, the relative error was within ± 4% at range of 300μm-1500μm, and it meets the needs of measurement accuracy requirement from the enterprise manufactures.A paper board thickness measurement method and process algorithm based on laser displacement sensor was presented.(4) Study on early warning technology of paper brokenUnplanned downtime caused broken in paper production process not only reduces the production efficiency, but also causes energy waste and other direct economic losses. And early warning of paper broken can protect the QCS equipment and sensors. After the analysis of the domestic and foreign study status of early warning technology for paper broken, the factors which may cause paper breaking from pulping, stock preparing, flowing, driving, drying and QCS were analyzed. An early warning of paper broken method with the character of automatically optimizing warning threshold based on data fusion technique was proposed. Firstly, an early warning data fusion framework was designed based on the data fusion model proposed in this paper. Then the level 0 and level 1 fusion in automation station and level 2 fusion in operation station were described in detail. Optimization rules of warning threshold according to the break signal and decision fusion were presented in the section end. And the level 0-2 fusions were simplified to the binary operation. It can reduce the amount of calculation in the process of paper warning. By constructing the experimental simulation system, the early warning paper broken method proposed in this paper was verified that it was effective and could automatically optimize and adjust the early warning threshold.The study results showed that the intelligent of QCS and the prisision of were improved by adopting data fusion technologies. And it was practicable to measure the BW and thickness of high BW paperboard accurately. There were still many problems can be explored by using data fusion technology. We believe that this study upsurge of data fusion technology in papermaking industry will come in the near future. And then the automation level of the papermaking industry can be improved.