Design And Experiment Of Mechanical Characteristic Test System For Scallion Stalks

As one of the most important cash crops in China,welsh onion plays an irreplaceable role in its nutritional value,and its planting area and yield are increasing year by year.With the increase of production,it is also required that the welsh onion harvesting machinery achieve higher efficiency.At present,the harvesting efficiency of Chinese onion harvesting machinery is relatively low,especially in the process of transportation and holding of scallion,such as broken stem and clogging.In order to solve these problems,we must study and analyze the mechanical properties of the scallion stalks,and grasp their related mechanical properties,therefore,based on the physical characteristics of the onion stalk itself and the soil,combined with the stress characteristics of the welsh onion harvest,a set of testing system for the mechanical properties of the stem was designed and developed in the field.The control system was designed with three parts: mechanical,circuit and software,mainly include control section,executive body,information collection and HMI(Human-computer interaction interface).Through the integrated design and material selection of the clamping device,the sensor,the transmission device and the whole frame,the weight of the whole is lightened,the structure is simple and convenient to carry,it can be carried to field test.The clamping device is designed as an adjustable U grooved structure,and can be used for testing the scallion stalks of different diameters;The transmission device is designed with spiral transmission and controlled by stepper motor.It can achieve precise control of speed and reduce the test error caused by manual operation.The control system takes the STM32F103zet6 chip as the core,and develops the STM32 minimum system development board based on this,its integrated reset circuit,SPI interface,SD card interface,USART serial port,buzzer,EEPROM and so on;Signal amplifier is set up by OP07 chip;The design of A/D conversion circuit uses ADS8344 chip;The human-machine interaction interface is written in C# language on the Microsoft Visual Studio 2010 software platform.The whole system realizes the real-time acquisition,transmission,conversion,display and preservation of test data,and can automatically calculate the maximum pull force and other parameters.The field experiment was carried out with the test system,and the relationship between the lifting force of the scallion and the soil moisture content,soil bulk density,soil hardness,loading speed and the position of the pine soil was obtained.Field test results show that: the physical characteristics of soil have great influence on the extraction power of scallion.The greater the soil bulk density and hardness,the lower the water content,the greater the pulling force for the extraction of the onion;The pulling force of welsh onion increased with the increase of loading speed.When the loading speed was 2 mm/s,3 mm/s and 4 mm/s,the corresponding pulling force was 109.4 N,142.6 N,160.1 N respectively;After loosening,the average pulling force is 64.4 N,and the effect is very obvious.The closer the loosen distance is,the deeper the depth is,the smaller the pulling force needed to get the welsh onion.The optimum loosen range of scallion at harvest time is determined: the distance from the pine soil is 13~18 cm,and the depth of the pine soil is 25~30 cm.The experimental results provide the mechanical and structural parameters for the design of the conveying clamping device for the harvesting machinery of the scallion.At the same time,choosing the appropriate harvest time according to the condition of the soil is beneficial to reduce the power consumption and improve the production efficiency.