Theoretical Analysis And Experimental Research On Boom Vibration Of Large-scale High Clearance Sprayer

The large-scale high clearance sprayer with a spray boom is an important plant protection machine to achieve high precision and high efficiency spray,in which,the spray boom is the key working part.At present,the spray boom oscillates,flips and shakes during the operation,resulting in poor stability,non-uniformity spray and low spray quality.On the basis of the current application and technical research status of the spray boom,by the combination of spring and damper,a spray-boom suspension structure was designed and applied to the high ground clearance sprayer with the spray boom of the 18-m triangular cross section.The modal frequency and mode shape of the spray boom were obtained by analyzing the dynamic and kinematic vibration characteristics of the spray boom,dynamic modal simulation and field tests.The optimal combination of vibration reduction parameters of spring and damper and the fatigue life of the spray boom were obtained by the single factor test of the vibration reduction element,regression analysis of vibration characteristics of the spray boom and field tests of vibration reduction combination.The main results obtained are as follows:1.A suspension structure based on the combination of spring and damper and a spray-boom structure with an 18m triangular cross section were designed.When the vibration amplitude at the end of the spray boom was±150 mm and the maximum horizontal inclination angle of the spray boom suspension was ±0.617° with the analysis of the suspension structure parameters,the vibration deformation of the cable-stayed spring was±3 mm,the rigidity coefficient of cable-stayed spring in the damping device was 17～20 N/mm,and that of the vertical damping spring was 55.1～110.2 N/mm.2.The vibration model of the spray boom was established.Based on the analysis of the general viscous damping theory,the mathematical model of the frequency,damping ratio and vibration mode under the complex mode of spray boom was developed.The modal frequency and mode shape of each vibration direction were achieved by the modal simulation analysis with the ANSYS 13.0.The dynamic modal test of the spray boom with the method of multipoint excitation and multipoint acquisition was carried out.The simulation and test results showed that the frequency difference was smaller than 7%,indicating that the simulation result was credible.3.Performance tests of cable-stayed spring,vertical spring,vertical damper and horizontal damper were carried out.Vertical springs with stiffness coefficients of 91.26 N/mm,71.80 N/mm and 57.68 N/mm,vertical dampers with restoring damping coefficients of 9.48 N·s/mm,7.66 N·s/mm and 5.84 N·s/mm and original damping coefficients of 87.42 N·s/mm,7.41 N·s/m and 6.07 N·s/mm were chosen to be used for single factor transient roll,transient response tests and field vibration tests,the results showed that the horizontal damper had a significant impact on the transient turnover response,vertical spring had a significant impact on the transient vibration,and vertical spring and vertical damper had a significant impact on the low-frequency vibration for the spray boom.4.In order to achieve the optimum of structure and working parameters,the field vibration experiments of high ground clearance sprayer in cotton,wheat and corn plots were designed by the Box-Benhnken Design(BBD)response surface method.An orthogonal rotary combination experiment was conducted with the driving speed,the vertical spring stiffness coefficient,the vertical damper damping coefficient and the damping level of horizontal damper as four independent variables,while the horizontal angle,the moving direction and the boom vertical amplitude were taken as three dependent variables.The Design-Expert software was employed to conduct the regression model analysis and optimization analysis of the test results.The optimal combination of vibration reduction operating parameters of the test block was obtained as follows:the driving speed of the sprayer was 2.10 m/s,the vertical spring stiffness coefficient was 77.77 N/mm,the vertical damper recovery damping coefficient was 8.33 N·s/mm,and the horizontal damper damping coefficient was 8.74 N·s/mm.Comparing to the optimal parameters combination and orthogonal test results,it was indicated that,in the moving direction,the vibration acceleration between 0 and 6 m/s2 segment was increased by more than 4%,in the vertical direction,the proportion of the vibration acceleration between 0 and 6 m/s2 segment was increased by more than 3%,the proportion in the roll angle between 0 and 0.6° segment was increased by more than 4%,and the reduction performance of the spray boom was improved.5.The comparative test of the strain under the optimal and no damping combination was carried out on the corn field.The results showed that the average life of the optimal vibration reduction combination was 28.28%longer than that of the non-vibration reduction combination according to the rain-flow counting method.The reasonable setting of the damping device parameters can effectively improve the operation life of the spray boom.