| Threshing device is one of the core components of the combine harvester.It is used to take off the seeds on the stalk and separate it.The threshing and separating performance of threshing device directly affects the working efficiency and performance of combine harvesters.In the case of excessive feeding rates or sudden changes in feeding rates,threshing device is easy to be blocked.Controlling the concave clearance actively to prevent threshing device plugging can improve the productivity,performance and reliability of the combine,therefore,it is of great theoretical significance and practical value to study the automatic control technology of concave clearance of combine harvesters.This paper takes multi-roller cereals combine harvester as the research object.On the basis of the theoretical analysis of the blocking process of the threshing device,an automatic control system for concave clearance is designed.The research work includes the following aspects:1.Design of adjustment device for concave clearance.Through previous research,it is known that the blockage of threshing cylinder usually occurs in the tangential flow threshing and separating device and the first transverse axial flow threshing and separating device.Therefore,the tangential flow concave and the first transverse axial flow concave are designed into the integral concave,and the corresponding adjusting mechanism is designed.The concave clearance is regulated by the four point support of the hydraulic cylinder.The hydraulic system is designed.The model of hydraulic cylinder is ROCR30X25,its diameter is 30 mm and stroke is 25 mm.The required flow rate of hydraulic system is 1.696L/min.Synchronous hydraulic motor is used as multi-cylinder synchronous device,its synchronous precision is 98%,which meets the need of the system.The hydraulic circuit was designed to adjust the concave clearance and its adjusting speed is 0~10mm/s.By analyzing the load of the hydraulic cylinder on rear side of concave in the process of threshing and separating,the load of the hydraulic cylinder on rear side of concave is selected to characterize the load of the threshing roller.The blockage of the threshing unit is analyzed from the angle of force.The increasing of feeding rates will increase the material thickness.As a result,the extrusion pressure of the threshing roller to the material will increase,the friction resistance of the material to the threshing cylinder will increase accordingly.If the resistance is consistently greater than the power,the cylinder speed will drop until blocked.Increasing the concave clearance properly can reduce friction to prevent blockage.2.Design of monitoring system for automatic adjustment of concave clearance of threshing roller.The overall plan of the automatic adjustment monitoring system for concave clearance is designed.The hardware circuit design is designed.The controller is STM32 single-chip microcomputer.The pressure sensor model is JLBM-500KG-BSQ-3.The hydraulic pressure sensor model is MIK-P300-10MPa-V1-B5-C3-J2P2.The displacement sensor model is KPC-50 mm.These output signals are 3.3V.The control circuit of the electromagnetic directional valve is designed.Finally,a software design was carried out to realize the receiving and displaying of the pressure and concave gap data in the host computer.The acquisition frequency is 5 Hz,and the buzzer can be activated when the concave gap exceeds the threshold.3.The test of concave load monitoring and threshing performance.The signals of pressure sensors and oil pressure sensors in the process of threshing and separation are compared,they are equal to each other,which means that pressure transmitters can replace pressure sensors to monitor the concave load.The pressure signals on the left and right sides of rear side of concave in the process of threshing and separation are compared and analyzed.The pressure of the two hydraulic cylinders on rear side of the concave is the same in the empty and uniform feeding.When the material is just fed,the pressure of the hydraulic cylinder on the rear side of concave will have a larger peak,and the pressure of the hydraulic cylinder on both sides is different.The oil pressure on the rear side of the concave tends to increase with the feeding rates.It is verified that the threshing and separating loss increase with the feeding rates increasing.More concretely,when the feeding rates increased from 3.4kg/s to 6kg/s,the oil pressure on the rear side of the concave increased from 732 N to 1114 N,and the threshing and separating loss increased from 0.54% to 1.08%.The oil pressure on the rear side of concave tends to decrease as the concave clearance increases.The threshing and separating loss increases as the concave clearance increases.In case that the feeding rates is 6.0kg/s and the concave clearance increased from 35 mm to 45 mm,the oil pressure on rear side of concave decreased from 1114 N to 758 N,and the threshing and separating loss increased from 1.08% to 1.31%.It proves that it is feasible to reduce the threshing cylinder load by increasing the concave clearance.The threshing and separating loss is under natural standard.Under the conditions that the feeding rates is 6kg/s and concave clearance is 35 mm,the threshing and separating system has the best performance,the corresponding pressure on rear side of concave is 900~1320N,the threshing and separating loss is 1.08%.4.Design of fuzzy controller for automatic adjustment of concave clearance and field test verification.According to the characteristics of the concave clearance adjustment device,the fuzzy is designed.According to the actual work requirements,the adjustment process of concave clearance is designed.Finally,field validation experiments are carried out.The results show that fuzzy control system can control concave clearance to adapt to the variation of feeding rates,so as to reduce the extrusion pressure of threshing cylinder to material and prevent the blockage of threshing cylinder. |
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