| China is a big grain produce country,raw grain generally refers to the unprocessed grain.Raw grain packaging is the complete and efficient automatic bagging and packaging of raw grain after harvest to meet the needs of subsequent raw grain processing,storage,transportation and sales.Raw grain generally uses raw grain packaging machinery to achieve packaging through bagging,bag clamping and supporting,filling materials,conveying seals and other processes.However,the cold harvest period of raw grain in the northeast cold area has cold weather and long winter time,out of synchronization which is caused by respective cylinder drive of the bag clamping mechanism and bag supporting mechanism of the quantitative packaging machine in cold regions,poor efficiency,especially pneumatic system condensation or even ice formation triggered by low operating temperature during raw grain harvesting and packaging period and large dust in the working environment,thus lead to cylinder moving malfunction or sluggishness,further influence the packaging efficiency of raw grain packaging machines.Therefore,the development of high-quality and efficient raw grain packaging machines is of great practical significance to reduce the loss of raw grain packaging and ensure food security.Aiming at the above problems,in order to ensure and improve the working efficiency and reliability of raw grain packaging machine in production enterprises in the northern cold region,this paper carries out optimization design and in-depth theoretical analysis for the key component of raw grain quantitative packaging machine.It is proposed to replace pneumatic drive with motor drive to solve the problem of great influence of condensation and dust in the system.Using only one motor synchronously drives the bag clamping mechanism and a spatial cam bag supporting mechanism to achieve bag clamping,bag supporting and reset is completed.Optimizing the pressure angle,spatial cam working profile of the cam bag supporting mechanism and the design of the transmission mechanism,simulating and analyzing the bag supporting motion,bag clamping motion and the control system,testing the mechanical properties of packaging materials and the bag supporting mechanism,which aim to provide a theoretical basis for the optimal design of the raw grain packaging machine,improve the work efficiency and meet the actual needs of production.The main research contents and achievements are as follows:(1)This paper introduces the current situation of grain planting and packaging in China,as well as the research status of packaging machine and bag supporting and clamping mechanism at home and abroad.The analysis shows that the research of bag supporting mechanism of domestic packaging machine mostly uses air cylinder to drive independent actuator or cooperate with independent bag clamping mechanism to complete bag supporting and bag clamping work.It is difficult to synchronize bag supporting and bag clamping,which affects the packaging productivity.(2)Overall scheme design of bag supporting and clamping mechanism.Through the analysis of the raw grain packaging process,a bag supporting and clamping mechanism driven by motor instead of pneumatic drive is designed.The mechanism drives two groups of four-bar mechanisms through a motor to synchronously drive the bag clamping mechanism and cam bag supporting mechanism,so as to realize the movement of bag supporting,bag clamping and return reset.In order to realize the bag supporting movement,the cam bag supporting mechanism is configured on both sides of the bag clamping mechanism and fixed on the front nozzle splint of the bag clamping mechanism.(3)Optimization design of cam bag supporting mechanism.A bag supporting mechanism that moves synchronously with the front nozzle clamping plate of the bag clamping mechanism is designed.The sinusoidal acceleration motion is selected as the motion law of the bag supporting rod.Based on geometric coordinate transformation and vector method,the parameter equation of cam working profile of cam bag supporting mechanism is established.Through the force analysis of cam mechanism,the pressure angle model of spatial cam mechanism is established.Through single factor analysis,the optimal parameter combination of pressure angle is determined:R=6mm,lz’=120mm,φ0=4.5°,lOK=39mm,lON=88mm,θ0=-180°,θ=-170°,the linear relationship between φ and θ is θ=20(φ-90)/9+20,the maximum angular displacement of cam is δ0=16°.The motion law of bag support and the working profile of cam are obtained by optimization design.The maximum pressure angle 23°is less than the allowable pressure angle,which meets the working requirements of the mechanism,verifies the rationality of the mechanism design,and provides an optimal solution method of pressure angle of spatial cam mechanism.(4)Optimization design of transmission system of bag clamping mechanism.Based on the optimization design function of MATLAB,the hierarchical sequence method is used to optimize the design of two groups of four-bar transmission mechanisms pull rod four-bar mechanism and push rod four-bar mechanism.The optimization results show that the design of the two groups of four-bar transmission mechanisms can meet the requirements of rod length and minimum transmission angle(γmin≥40°～50°).The rotation angle of the rotating arm is reduced from 46° to 41°.Under the condition of constant motor speed,the opening and closing time of the bag clamping mechanism is reduced and the working efficiency is improved.(5)Simulation analysis of bag supporting motion and bag clamping motion based on ADAMS.The simulation results based on ADAMS show that the motion analysis of the bag support mechanism is consistent with the actual operation.When the cam angular displacement is δ=5.27° and δ=10.9°,the maximum errors of angular acceleration between simulation analysis values and the theoretical values of optimization design are 21.35°/s2 and-26.33°/s2.On the one hand,the errors are caused by the modeling error of cam working profile;On the other hand,due to the limitation of software conditions,there is a slight deviation between the theoretical contact point and the simulated contact point of cam mechanism.Simulation analysis verifies the rationality of the structural design of the cam bag supporting mechanism.Based on ADAMS,the bag clamping motion simulation analysis of the bag clamping mechanism is carried out.The simulation analysis shows that the angular displacement simulation result of the mechanism is consistent with the theoretical value,and the movement of the front and rear nozzle clamping plates is synchronous.The simulation results of the transmission angle of the mechanism are basically consistent with the theoretical design results.The simulation results of the minimum transmission angle of the mechanism meet the design requirements of the minimum transmission angle of the connecting rod mechanism,which verifies the rationality of the structural design of the bag clamping mechanism.(6)Experiment on mechanical properties of plastic woven packaging bag materials.According to the statistical experiment data,the average tensile failure load of packaging bag sample is(35.94±5.05)and the average tensile strength is(23.96±2.46)MPa.The friction coefficient measurement test device is designed according to the national standard Hg/T 2729-2012.The friction coefficient between packaging bag and rubber is measured.It is determined that the mean values of static friction coefficient and dynamic friction coefficient along the radial direction of packaging bag are 0.695 and 0.678 respectively;The mean values of static friction coefficient and dynamic friction coefficient along the weft direction of packaging bag are 0.697 and 0.642 respectively.The experiment provides a basis for the calculation of motor load parameters.(7)Control system design and simulation bench test of bag supporting and clamping mechanism.Based on the analysis of the working principle and process flow of the bag supporting and clamping device,according to its process requirements,the bag supporting and clamping control system is designed based on STM32 single chip microcomputer control.Based on the control function of STM32,the simulation test bench is built by using components such as pressure sensor,proximity switch and stepping motor,ect.The simulation results show that the functions of signal,display and data recording of the control system are normal in the process of simulation verification;It can judge the detection and accurate control of the detection function and function of the proximity switch through the predetermined value of the pressure sensor;The control system of bag supporting and clamping mechanism based on STM32 single chip microcomputer is feasible in principle,has high control accuracy and can meet the needs of practical operation.The research lays a foundation for the integration of the control system of the bag supporting and clamping mechanism into the overall control system of the whole machine.(8)Bench verification experiment of cam bag supporting mechanism.The experiment verifies that the cam bag supporting mechanism and the bag clamping mechanism of the bag supporting and clamping mechanism can realize synchronous movement,and examines the rationality of the design of the cam bag supporting mechanism and the law of bag supporting movement.The experiment shows that there will be elastic deformation along the direction of bag clamping in the process of bag supporting.The analysis shows that the deformation may be caused by the excessive pressure angle of the cam mechanism and the insufficient rigidity of the bag supporting rod,which provides a basis for the further optimization design of the cam bag supporting mechanism. |
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