莲子机械自动去芯自适应定心技术与样机试验

针对莲子在自动化去芯过程中的钻偏问题,提出了莲子自适应定心方法,该方法基于一种由曲柄滑块机构与平行四边形机构组合而成的自适应定心装置,能实现去芯钻头位置随莲子大小变化而自动调整。利用随机优化算法对机构中的连杆参数进行了优化,实现去芯钻头轴线保持与莲子轴线同轴,理论定心偏差为0.0448 mm。研制了一种自适应莲子去芯机,进行了未分级莲子的去芯试验,结果表明:自适应莲子去芯机钻正率达91.25%,远高于现有去芯设备,初步验证了自适应定心方法的有效性与实用性。研究结果为莲子优质钻芯设备设计、与莲子形状类似物料的优质钻孔设备研发提供参考。

Study on self-adaptive centering method of removing core of lotus seed and prototype test

Abstract: Lotus seed has very high nutritional and medicinal value, which consists of lotus shell, lotus kernel and lotus core. Because of the bitter taste, the lotus cores need to be removed before eating. The existing equipment for removing core can remove the lotus core fast by operating the coring bit. Before drilling, the lotus kernel has to be centered in the centering working position. The centering device generally consists of two rotating rollers. Under the action of gravity and friction force, the lotus kernel can be centered in the rotating process. However, the position of the coring bit is fixed in the centering working position, and therefore the drilling deviation occurs due to the diameter variation of lotus kernels, and the lotus cores cannot be removed effectively, which lowers the quality of lotus kernels directly. To solve the above problems, the classification process is applied widely. However, it is ineffective owing to the inaccuracy of the classification process and the high requirement for staff and equipment. In order to avoid this situation, the shape parameters of lotus kernels are firstly measured and analyzed in this paper. The results show that the maximum cross section of the lotus kernel is almost round with a mean roundness deviation of 0.46 mm and the diameter ranges from 9 to 16 mm; the average chordwise curvature radius is 7.764 mm, and the average longitudinal curvature radius is 5.177 mm, therefore, the shape of a lotus kernel can approximate to an ellipsoid. Moreover, the centering deviation of the double roller rolling centering method presents a maximum value of 6.654 mm. Aiming at solving the problem of drilling deviation in the automated coring of lotus seeds, this paper proposes a self-adaptive centering method for lotus seeds based on a slider-crank mechanism and a parallel crank mechanism. By utilizing this method, the position of the coring bit can be automatically adjusted according to the lotus kernel size. A mathematical model of self-adaptive centering is established by the complex number vector method. Once the parameters of the linkages are selected, the centering deviation value is determined. For the self-adaptive centering mechanism, the optimization of the linkage parameters is complicated and difficult to meet the demand through traditional optimization methods. Therefore, in order to make the centering deviation minimum, by utilizing the stochastic optimization algorithm of Cuckoo Search, this paper optimizes the linkage parameters in MATLAB. The initial parameters are as follows: the nest number is 25, the probability of detection is 0.25, and the maximum iteration number is 4×105. The optimized parameters of connecting rod are 88.51, 135.72, 0.12828, and 125.35 mm respectively, and the coaxial deviation between the coring bit axis and lotus kernel axis is lower than 0.05mm. Based on the above study, a self-adaptive machine for removing core of lotus seed was developed and a coring experiment with 400 samples of lotus seeds was carried out. The experimental parameters were as follows: the working cycle was 1.5 s, the roller's rotating speed was 238 r/min, the pressure of the pressing wheel was 25 N, the coring bit diameter was 2.5 mm and the drill speed was 2800 r/min. By measuring the circle run-out value at the maximum cross section of the lotus kernel, the drilling accuracy of lotus seeds were calculated. The results show that the drilling accuracy of a self-adaptive machine for removing core of lotus seed is 91.25%, much higher than that of the existing equipment, which is 60%-70%; moreover, this machine can handle different sizes of lotus kernels. The experimental results verify the effectiveness and practicability of this self-adaptive centering method.