Design and field experiment of drawing resistance measurement system for cotton stalk

Abstract: The annual production of cotton stalks is about 22.8 million tons in China. As a by-product of cotton industry, cotton stalks not only can be used in the production of renewable biomass energy, but also can be utilized in papermaking or production of wood-based panels and so on. Because of the varying diameters of cotton main stalks, and the higher harvesting intensity and power consumption associated with thicker stalks, studies on cotton stalk mechanical harvesting technology have been one of the key problems in cotton mechanization technology research in recent years. In order to study the influence of factors such as soil, cotton stalk diameter, and draft angle on the stalk drawing resistance, a set of real-time drawing resistance measurement programs for cotton stalk was designed based on virtual instrument technology, and a kind of adjustable motor drawing device for cotton stalk was developed. The stalk draft resistance was tested with the system, which consisted of the software and the device. The system was programmed with LabVIEW graphical editor language to automate data collection and reading, data analysis and computing, real-time display, and archival. The drawing device was made up of a pair of drawing clips, a drawing sleeve, a tension sensor, a drawing rod, a reel, a wire rope, a frame, a pulley, and a support frame. The universal material mechanical performance testing machine was used to calibrate the drawing resistance measurement system. Experimental results showed that the measurement system was able to accurately measure the output signal of the tension sensor, with a maximum error was 0.405% between the output load from universal testing machine and the input load from measurement program, which had a high value for practical application. The field experiments of pulling the cotton stalks were conducted in the experimental field of Huazhong Agricultural University. The row spacing of cotton stalks in this experimental plot was 800 mm, and the plant spacing was about 450mm. The experiments were conducted during the period of January to March in 2013. The field experiments of pulling the cotton stalks involved variable soil moisture (26.93%, 28.13%, and 25.44%), cotton root diameter, draft angle (30°, 40°, and 50°), and draft speed (9.42 mm/s and 6.28 mm/s) as influencing factors. The stalk branches were excised and the main stalk was reserved with length of 300 mm before the experiments. After putting the stalk into the drawing sleeve and locking onto it, the stepper motor was turned on, and the reel pulling the rope which pulled the sleeve, and the sensor was set between the rope and sleeve to measure the draft resistance. The field experiment results showed that there was a positive linear correlation between cotton root diameter and cotton stalk draft resistance in the same soil condition, and there existed a negative linear relationship between the draft resistance and soil moisture. Changes in soil moisture had an enormous influence on drawing resistance. The regression analysis showed the fitting equation was significant, and its R2 was 0.764. The draft angle had significant influence on the stalk draft resistance, and the optimal draft angle was 30° under the test conditions. The influence of draft resistance on the draft speed was related to the soil condition, which was no significant impact on the drawing resistance with high soil moisture and low soil firmness, but the effect was opposite with the low soil moisture and high soil compactness when the optimal drawing speed was 6.28mm/s under the test conditions. We conclude that it is quite favorable for reducing power consumption and improving harvest efficiency byto select the appropriate harvest time according to soil conditions. The measurement system was able to quickly complete the draft resistance measurement during the whole process of the draft test. The measurement system was easy to operate and control, it was able to quickly complete the draft resistance measurement during the test, and the data collected were accurate and effective, which could provide mechanics and structural parameters for the study of cotton stalk harvest machinery and the research of cotton stalk draft resistance.