Design And Experiment Of Portable Mechanical Characteristic Tester For Crop Stalks

The tendency of modern agriculture needs a batch of modern equipments as guarantee.For this reason, we designed a kind of mechanical characteristic tester for crop stalks.Mechanical parts of the tester was designed with the integration of blade, sensor and cropstalk. With the whole structure optimization, the size and the weight of the tester weredecreased. The tester is easy to carry about and beneficial to experiment which is done in thegrowing field of crop stalks. The AC motor was used as actuator, by this way, the speed ofexperiment was kept at a constant speed and avoided the error which was incured by speedchange when was done by hand operation. The tester consisted of shear module, puncturemodule, modulus of elasticity module and stem stiffness module. The blade of shear modulewas made by1mm-thickness stainless steel. In order to acclimatise to the experiment ofdifferent diameters, the cutting edge of the blade was designed as5grades and the shear forceexperiments of wheat stalk, sorghum stalk and corn stalk could be done. The puncture probehad different diameters of0.5mm,1.0mm and1.5mm. The modulus of elasticity moduleconsisted of stand and digital dialgauge, and the stalk deflection can be displayed real-time.The stem stiffness experiment could be done when the digital dialgauge was removed.BSQ-2transmitter was selected as signal amplification module and AD620chip wasused as amplifier in this module. ADS8344chip was used as A/D converter. In order to gainhigher circuit stability, the AD586BR chip was used as reference voltage to supply steadyvoltage. The control system was designed based on STM32F103ZET6which was producedby STMicroelectronics corporation and this is the highest-performance chip based on ARMCortex-M3. A single chip microcomputer development system based on STM32F103ZET6was made and it consisted of EEPROM, serial port, SD card, buzzer, TFT screen and so on.The output signal of pressure sensor could be collected by the control system and experimentresults can be displayed real-time or be stored by SD card. The work and maximum valuescan also be calculated concurrently.Upper computer data acquisition interface was programed with Microsoft Visual C++6.0software and C++language. This interface had functions of data display, data query, datadownload, curve drawing and so on. At the same time, the data which was stored by SD cardcan be readed by the upper computer and the pressure curve also could be drawn through thedata. Shear force test and modulus of elasticity test of corn stalks were done by this tester. Theratio between loading and defection was replace by the slope of coupling line betweenpressure and defection, and it increased the reliability and repeatability of the experiment.Theresults indicate that in the certain range, elastic modulus increases with the rise of moisturecontents. This system was credible and stable, the accuracy could reach0.84%and it willbring more convenience in the studying of mechanical characteristics for crop stalks.