| Laser technology is one of the most important scientific and technological inventions since the 20th century,filling the gap in the field of physics and promoting the development of industrial system automation.Due to the characteristics of strong collimation,good coherence,stable physical properties and high precision,the laser has become more and more widely used.The laser leveling technology uses the rotating laser as the calibration plane,control the hydraulic system with the elevation deviation information to adjust the elevation position of the scraper to achieve accurate leveling,which can effectively reduce the elevation deviation of the field,save the irrigation water of farmland,improve the utilization rate of pesticides and fertilizers,improve the growth environment of crops,increase the yield and quality of agricultural products,and lay the foundation for agricultural mechanized production.The laser receiver is an important part of the laser leveling system,and the detection accuracy of its elevation will directly affect the leveling effect.Therefore,this article studies the transmission characteristics of laser beams and conducts photoelectric sensing system test,a new type of laser receiver with multi-level adjustable elevation detection accuracy is designed,and conducted the test verification,which can meet the differentiated needs of elevation detection accuracy in different fields.The main research contents and conclusions are as follows:（1）Research on the transmission characteristics of the laser beam,using a laser beam analyzer and a laser power meter to collect the laser beam spot image and spot power,the results of the comparative analysis of the spot power show that when the transmission distance is 10～100m,the spot power of laser transmitter A is less than the spot power of laser transmitter B.The spot image modeling analysis results show that when the transmission distance is 10～100m,the laser beam spot produced by the laser transmitter continues to spread,and form a multi-level magnified circular ring spot,the irradiance of laser transmitter A is significantly smaller than that of laser transmitter B.The result of the spot diameter fitting analysis shows that when the transmission distance is 10～100m,there is no obvious difference between the fitting curves of the spot diameters of the two laser transmitter and some curves overlap each other;when the transmission distance is 100～300m,the spot diameter of laser transmitter A is significantly smaller than that of laser transmitter B.The comparative analysis of the spot drift shows that when the transmission distance is 10～100m,the collimation of laser transmitter A is stronger than that of laser transmitter B.Based on the above analysis,a laser transmitter with good collimation of the laser beam,regular distribution of the spot image and a spot diameter diffusion rate of less than 1.2 should be selected for use with the laser receiver designed in this article.（2）Design photoelectric sensor experiment system,which is mainly composed of adjustable constant voltage source,adjustable constant current source,light source module,photoelectric detection module,illuminometer,voltmeter,ammeter and so on.The photoelectric characteristics of Cd S photoresistor,2CR silicon photocell,2CU photodiode,3DU phototransistor,PIN photodiode and APD photodiode were tested.Through comparative analysis,a PIN photodiode with a linear increase in the illumination characteristic curve,a nonlinear volt-ampere characteristic curve,a spectral response range of 450～975 nm,and a peak spectral response of 900 nm was selected as the photodetector of the laser receiver.（3）Design the hardware of the laser receiver,including the photoelectric conversion array structure,the filter amplification circuit,the shaping and stretching circuit,and the signal processing and transmission circuit,which can realize the detection,conversion,modulation,processing,transmission and display of rotating laser signal,and communicate with the controller in the laser levelling system.The test results of the effective photosensitive area of the PIN photodiode show that the photocurrent is linearly correlated with the effective photosensitive area,when the rotating laser signal illuminated the effective photosensitive area≥10%,it can trigger photoelectric conversion to generate a photocurrent signal.The test results of the effective spot diameter of the PIN photodiode show that the transmission and diffusion law of the effective spot diameter of the laser beam that can be detected by the PIN photodiode is significantly different from that of the laser beam spot diameter,when the transmission distance is 10～200m,the effective spot diameter variation range is6.85～28.53mm,which provided a theoretical basis for the photoelectric conversion array structure design and laser receiver software design.The calculation result of the effective light time of the PIN photodiode shows that when the transmission distance is 10～200m,the effective light time variation range is 2.214～16.385μs,which provided a theoretical basis for the design of the shaping and stretching circuit.（4）Designed the software for the laser receiver,introduced the overall structure and flow of the program.Study the algorithm of rotating laser elevation deviation calculation,communication protocol based on CAN bus and LED status display,realize the multi-level adjustment of the elevation detection accuracy of the laser receiver,and transmit the rotating laser elevation deviation information and implement elevation adjustment speed information to the grader controller.（5）Conducted a laser receiver performance test.The test results of elevation detection accuracy showed that when the laser receiver was within a radius of 90 m,the elevation detection accuracy was within±3 mm.When the laser receiver was used with the agricultural grader,the test results of farmland levelling showed that the standard deviation(（9） of the field surface decreased from 9.54 cm before levelling to 2.42 cm after levelling,and the percentage of sampling points with elevation absolute errors of≤3 cm was 84.06%.These outcomes meet the requirements of the high standard of farmland construction.When the laser receiver was used with the concrete leveller,the test results of the levelling showed that after levelling,the standard deviation(（9） of the sand bed surface was 0.881 mm,and the percentage of the sampling points of the absolute error of≤3 mm was 100%.These outcomes also met the construction standards of the concrete industry. |
