Research Of Methods For Material Volume Flow Measurement Based On Laser Triangulation

With the rapid development of industrial production and the refinement of processing equipment,the demand for accurate metering of batching system is increasing.At the same time,in order to achieve the best match between belt speed and load condition,the instantaneous flow of material need getting more accurately and realtime.At present,the device for measuring material flow on conveyor belts mainly includes electronic belt scale,nuclear belt scale and so on.Among them,the electronic belt scale has many shortcomings,such as many error sources,low actual measurement accuracy,frequent calibration and frequent maintenance work.The nuclear belt scale can not avoid the serious influence of material shape on the accuracy of measurement.Based on the principle of material volume flow measurement by laser triangulation method,the real time,continuous and accurate measurement method of the instantaneous volume flow of material on the conveyor belt is studied.The main research work is as follows:1.According to the calibration of the measurement system,the calibration method based on the laser triangle and the camera model principle is analyzed.In the measurement accuracy,the calculation results based on the camera model calibration are slightly better than the laser triangulation,but in terms of time,the former is far greater than the latter.Considering the real time requirement of the measurement system,the calibration method based on the vertical incident laser trigonometry is adopted.2.In view of the limited adaptability of the traditional optical center line extraction method,a double threshold barycenter method is proposed.On the basis of the traditional barycenter method,the center point coordinates of the gray value are too small are corrected.The method effectively reduces the noise interference and improves the extraction precision of the line structure light center line.Experimental results show that the method is better than the extreme value method,threshold method and barycenter method,which lays the foundation for improving the accuracy of material volume measurement.3,In view of the problem that the belt vibration affects the belt surface height,the method for calculating the height of the belt surface is studied.The analysis of multi space belt images shows that the height of the belt is different at different times,but the change trend is consistent.According to this characteristic,three methods are proposed,mean method,first time fitting method and proportional transformation method.These methods are used to deal with 300 empty belt images.By contrast,it is found that the maximum error of the calculated belt height is-1.862 mm and the average error is 0.331 mm by first time fitting method.By this method,the error of the belt height can be reduced,and the accuracy of the actual volume of the material can be further improved.4.On the basis of analyzing the traditional laser layouts,a slash measurement method is proposed.The angle between the laser line and the moving direction of the conveyor belt is less than 90 degrees.Through this method,more material contour information can be obtained on single image,and the requirement of frame rate is reduced.The volume of the regular material and the irregular material are measured by the two laser layout methods.The experimental results show that the volume measurement accuracy of the the slant line method is higher than the traditional laser arrangement under the condition of the same frame rate.And the volume of the material is measured under the condition of the different frame rate.The result shows that the slant line method can effectively reduce the requirement of camera frame rate when the measurement accuracy is guaranteed.5.A real time measurement system for measuring volume flow and cumulative volume of material is developed.The volume flow of sand pile and low sodium carnallite is measured in laboratory and production site.The maximum error of volume measurement is 2.80%.At the same time,the flow of low sodium carnallite in production site is measured for 120 minutes.The experimental verification shows that the measurement system can realize real-time,accurate and stable measurement of material volume flow on the conveyor belt.