| The round baler is suitable for the harvesting of natural and planted grassland,and also can be used for the harvest of crop straw,which is widely used in Inner Mongolia of China.In recent years,the domestic scholars have took the small round baler(the bale diameter less than 1.0 m)as the research object,and have carried out the general engineering mechanics and rheology experimental studies of corn straw and rice straw during rotary compression,which has guiding significance for the optimization design of the round baler.The diameter of bales produced by large round baler is more than 1.0 m,which has a high market share.Therefore,this paper takes the large round baler as the research object,selects the forage which has large planting area in Inner Mongolia of China——alfalfa as the test material,and analyzes the rotary characteristics of alfalfa by using the self-designed test platform,gets the main effect factors and establishes the intrinsic model in the baling process by combining the finite element simulation results,and designs a baling process monitoring system of round balers based on Android platform,which can provide the theoretical basis and engineering realization platform for parameter optimization of round balers.According to the alfalfa rotary compression test requirements,the test platform of round balerwas designed and the data collection system of rotary pressure was built.Secondly,three factors and three levels of Alfalfa rotary compression experiments were carried out under the conditions of moisture content of 18.0,21.0 and 24.0%,feeding speed of 1.11,1.39 and 1.67 m/s,and steel roll speed of 106.0,126.0 and 146.0r/min,respectively.The nonlinear regression analysis of compression stress and compression density test data was carried out by least square method.The relationship between compression stress and compression density in alfalfa compression process can be described by quadratic polynomial function.Based on the analysis of stress relaxation test curve and model principle,the stress relaxation behavior of alfalfa under different moisture content,feeding speed and steel roll speed can be simulated by generalized Maxwell model composed of two Maxwell elements and one spring element in parallel.Through variance analysis of the orthogonal test results,it is concluded that the effects of the factors on the maximum compressive stress,stress relaxation time and minimum equilibrium stress are in the same order:water content>feeding speed>steel roller speed.The influence of each factor on the index was analyzed,the maximum compression force decreases with the increase of moisture content and increases with the increase of feeding speed.The stress relaxation time decreases with the increase of moisture content,feeding speed and steel roll speed.The minimum equilibrium stress decreases with the increase of steel roll speed and moisture content,and increases with the increase of feeding speed.In order to further understand the rotary compression theory and obtain the internal stress distribution and stress relaxation curve of bales,the finite element method was used to simulate the bale forming process.The simulation process was divided into two stages,compression and stress relaxation.In the compression stage,alfalfa was considered as an elastoplastic material and the modified Druker Prager Cap model was used to describe its elasto-plastic behavior.The uniaxial compression test was carried out with universal testing machine and self-made compression device,and the parameters ofthe modified Druker Prager Cap model of alfalfa.The compression process of alfalfa was simulated by using arbitrary Lagrange Eulerian method to control the material flow.During the stress relaxation stage,the viscoelastic behavior was described using the Prony series.The stress relaxation process was simulated by applying-0.001 m displacement load to the bale,the transient analysis was carried out.The simulation results showed that in the compression stage,the internal stress of alfalfa compression gradually decreases from the outside to the inside,and the intermediate stress in the outer layer of the bale is lower than the stress on both sides.In the stage of stress relaxation,the change law of stress with time obtained by simulation is consistent with that of test,and the coincidence degree is high.The t-test results showed that the predicted values of internal stress distribution and stress relaxation stress obtained from the finite element simulation have little difference with the experimental values.The result indicated that the finite element model constructed in this paper is able to describe the compression and stress relaxation process of alfalfa.Based on Android platform,a monitoring system for the baling process of round baler was designed.The system collects bale weight,number of bales,hydraulic pressure and round baler torqueby the collecting unit.The controlling unit sends the sensor data to the cloud platform through SIM800A module,and receives the control commands of the cloud platform through serial port interrupt,and controls actuator movement to realize processing control of baling by opening and closing chamber doors,rolling ropes and adjusting overflow pressure of relief valves.The Android platform realized the real-time monitoring of the baling process through the independent access to the cloud server.The simulation test showed that the system has stable performance with less than 5.0%data loss rate and less than 2.0 s delay time for information acquisition.The control is timely and correct,which meets the requirements of remote monitoring for baling of round balers. |
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