Technology of 2-DOF collision testing for rape pod shatter resistance

Abstract: The rape pod shatter resistance is the main factor affecting for mechanical harvesting loss. In order to choose more suitable varieties with strong pod shatter resistance for mechanized harvesting, the study proposed a testing technology with 2 degree of freedom(2-DOF) collision tester, it was simple and easy to move, so we could evaluating the pod shatter resistance real-time in field, and it also had the advantages of test results with good repeatability and high discrimination. To study the method of 2-DOF in detail, the tester structure principle and the parameters designed were analyzed, and the motion characteristics of the 2-DOF collision tester was calculated by Matlab. Then the different motion characteristics of steel ball under 2-DOF compound motion and shaking table reciprocating motion were simulated by EDEM, respectively. The simulation results showed that the steel ball's speed was higher and more uniform by 2-DOF collision, however, the velocity distribution was uneven comparatively under table collision, so we considered the 2-DOF collision was more reliable. Further the reasonable test parameters of 2-DOF was studied by testing, and 2-DOF collision testing and shaking table collision were compared. In order to study the importance of real-time test in the field, the pod shatter resistance index(SRI) of 15 varieties was tested, and the difference of SRI between the field pods and dried pods indoor under the same moisture condition was also analyzed. The results showed that the 60 r/min of swing motor speed and 75 r/min of moving motor speed were the suitable collision parameters. Under this collision condition, the SRI was 0.358 and the coefficient of variation of SRI was 8.35%. And the range of SRI by 2-DOF collision was 0.008-0.948 and average value was 0.370 under 15 varieties comparative test, but the table collision results performed higher, the range was 0.127-0.983 and average value was 0.549 correspondingly, meanwhile the mean standard deviation of 2-DOF was 0.020 3, accordingly result of shaking table collision was 0.025 6. This showed that the method of 2-DOF was more reliable and repeatable than the table collision. In addition, we found that the SRI of 4 varieties with strong shatter resistance was greater than 0.9, while the SRI of 2-DOF was 0.663-0.948, respectively. It indicated that the 2-DOF had a good effect on identifying cultivars with strong pods shatter resistance, but for the varieties with particular poor pod shatter resistance, the SRI were all less than 0.1 by 2-DOF collision, which could quickly and easily exclude pod varieties with poor pod crushing resistance. In addition, the correlation coefficient of the result between the two testing methods was analyzed(0.963 (P<0.05)), it indicated that the two methods had the same general trend of the evaluation result, so the identification method of 2-DOF was reliable and practicable. And last, we found the results of SRI range was 0.013-0.553 via the pod testing in field of 15 rape varieties, as well as the SRI was 0.008-0.948 by dried pods indoor. The results showed that pod resistance in the field was significantly smaller, indicating that water was not the only factor affecting pod resistance, so real-time field testing of pod was needed. In conclusion, the real-time test of 2-DOF SRI can reflect the actual situation of pods in mechanized harvesting period, screen out more reliable rapeseed varieties, and help to determine the optimal harvesting time for mechanized harvesting.