Design Of Grain Volume Flow Measurement System For Screw Conveyor Based On Structured Light 3D Vision

Screw conveyor is a kind of continuous conveying equipment which is widely used in medium and short distance transportation of grain material in industry,agriculture,food processing,pharmacy and other fields.The screw conveyor has the advantages of simple structure,low maintenance cost and stable working performance.Current measurement solutions applied to screw conveyors:(1)The material flow calculating formula method,which can estimate the volume of material particles conveyed by screw conveyor,has the limitation of only being used in GX screw conveyors;(2)The method of manually weigh the material transported at the outlet of screw conveyors can result in errors of measurement result,due to different recording and weighing methods used by different metrologists.(3)Quantitative screw conveyor requires either major modifications to the equipment,such as the structure parameters of screw conveyor and controlling the rotational speed,or accurate control of the feed volume in order to measure the volume of material particles.(4)Nuclear scale has radioactive hazards and is used mostly in heavy industry.(5)Screw scale requires dynamic zero-settings and complex filtering algorithms under unstable conditions in order to measure the volume of material particles.With the rapid development of modern science and technology,non-contact measurement solutions have gradually entered people’s lives.3D vision technology is frequently used in non-contact weighing solutions.In view of the above problems in the measurement solutions of screw conveyor,a grain volume flow measurement system of screw conveyor based on structured light three-dimensional vision was designed.Combined with the developed measurement system software,and by extracting the Center Line of Grain Flow Structured Light Contour,the disturbance of agitator blade on structured light plane can be determined and processed.By establishing a calculation model applied of cross section area and volume applied to screw conveyor,the volume flow rate of grain conveyed by screw conveyor can be calculated.The main research work is as follows:(1)LS140 screw conveyor was selected as grain transportation platform,and hardware such as Daheng Mercury industrial camera,linear laser transmitter with 650 nm wavelength,frequency conversion controller and computer were used.A 3D vision measurement system based on structured light was built by applying direct laser triangulation method.The whole system has the advantage of simple structure,easy maintenance,low cost,and a good effect on collecting structured light contour of particulate matter pushed by screw conveyor;(2)By studying the calibration principle of Zhang Zhengyou’s checkerboard lattice calibration method,the checkerboard calibration board was made and used to completed the calibration of industrial cameras.According to the principle of laser triangulation,a cross laser calibration method was designed to calibrate the measurement system.The least square method was used in order to obtain calibration curve by fitting the calibration test data,which improves the calculation speed of cross-sectional area model.Verified by experiments,the average relative error between the fitting calibration curve and the test data was 0.93%,satisfying calibration requirements;(3)The image preprocessing technologies such as spatial filtering,frequency filtering and edge detection were studied.By comparing the effects of image processing,the median filter with a template of 5*5 was finally selected as the filter used in the processing method in this paper.The Gray centroid method,Geometric center method,Skeleton thinning method and Improved extremum method were applied to extract the centerline of the collected structured light image,and the Improved extremum method was used to extract the centerline of structured light contour.Due to the contour interference of the extracted contour centerline with the material groove wall,a threshold determination method was designed to extract the contour centerline of grain logistics;(4)Aiming to solve the disturbance of Dragon Blade on the plane of structured light,an image processing method and a function analysis method were designed to determine the bareness of the blade respectively.The obscured part of the grain flow contour can be fitted by applying least square method.Finally,the grain flow section calculation model and volume calculation model applied to the screw conveyor were separately established by applying trapezoidal calculus summation to the grain flow contour;(5)By using Windows 10 system and Visual Studio 2010 platform,and applying MFC library and C++ language,the software of grain volume flow measurement system was developed.The software has three modules:device control module,picture ROI adjustment module and volume calculation module.The whole software has the advantages of clear structure,simple operation and easy maintenance;(6)For two kinds of grains:rice and sorghum,the experiments were carried out under three different volumes of V1=11.6L,V2=17.4L,V3=23.2L,six agitators’ rotational speeds of n1=13.2r/min,n2=19.7r/min,n3=26.3 r/min,n4=32.8 r/min,n5=39.4 r/min,n6=46 r/min.And each condition was repeated ten times in the experiment.By using the same grain measurement volume,with the increase of agitator speed,the average relative error has the trend of decreasing at first and then increasing.The minimum errors of paddy and sorghum occur at 32.8r/min agitation speed under 11.6L measurement volume.Rice measurement:The minimum error of image processing method is 1.73%,and that of function analysis method is 1.97%.Sorghum measurement:The minimum error of image processing method is 1.99%,and that of function analysis method is 2.08%.While the rotational speed of agitator was 26.3r/min-46r/min,the average relative error was less than 5%,and CV was less than 0.03,RMSE is less than 1.161;Comparing the results of two kinds of grain test between paddy and sorghum,the average relative error of image processing method was smaller.The validity,accuracy and reliability of the grain volume flow measurement method and system studied in this paper were verified.The test results show that,the measurement system and method studied in this paper can meet the online measurement requirements of screw conveyor.