Design and parameter optimization of the automatic reverse pulling type shift clamping device for ramie stripping machine

A ramie stripping machine has been commonly used in modern agriculture in recent years. However, the current manual feeding and back-pulling cannot fully meet the large-scale production, due to the high operational intensity, low safety, and unstable stripping quality. In this study, a double-drum stripping device was designed to replace the manual feeding and reverse-pulling in an automatic ramie fiber stripping machine. There were also the different mechanical properties between the ramie fiber layer and the woody part. Firstly, some measurements were performed on the physical dimensions and mechanical property parameters of "Chuanzhu No. 11" ramie stalks. Then, the technical solution of a double clamping mechanism was proposed with the synchronous belt clamping and conveying, motor-driven clamping mechanism flipping and changing position, and double-drum reverse stripping. The ramie stalks were fed directly, and then stripped at the base and tip of the ramie stalks in turn by the changing position of the clamps. The toothed rubber clamping plate was used to hold the stalks. The grooves and projections of the toothed rubber plate were firmly held to prevent the stalks crushed by the clamps and slipping out. The operation of the ramie stripping machine was divided into four steps: the straw feeding, base stripping, tip stripping, and collecting ramie skin. The key components mainly included the transposition clamping, lateral feeding, and ramie stripping device. The mechanical analysis of double-drum ramie stalk stripping showed that the stripping force was closely related to the drum speed. A mechanical test was carried out to investigate the relationship between the stalk feeding angle and stripping force. The results showed that the stalk feeding angle and stripping force shared a highly significant negative linear correlation. The structural design and theoretical analysis were performed on the main components in the ramie stripping device and clamping mechanism. After that, the structure and motion parameters of the ramie stripping machine were determined, including drum speed, reverse-pulling speed, and feeding angle. Furthermore, a single-factor simulation model was established using ANSYS/LS-DYNA to simulate the process of stripping and the amount of xylem removal, the loss of the bast fiber layer, and the force of the feeding direction. Previously, the ramie stalk actual stripping process was analyzed and a simulation model was developed. The structure of the ramie stalk was also analyzed during this time. The optimal ranges of parameters were achieved for a better stripping effectiveness: the roller speed of 350-650 r/min, the reverse-pulling speed of 0.2-0.4 m/s, and the feeding angle of 5°-15°. A three-factor and three-level orthogonal test was conducted, according to the Box-Behnken method. The results showed that the drum speed, reverse-pulling speed, and feeding angle posed the significant effects on the fiber percentage of fresh stalk, and the impurity rate of raw fiber using ANOVA and response surface analysis. In addition, a significant coupling effect was found in the interaction of drum speed and reverse-pulling speed, as well as each experimental factor, but there was no a simple linear relationship. The optimal operating parameters were obtained for the ramie stripping machine with the reverse-pulling clamping: the stripping drum speed of 450 r/min, the reverse-pulling speed of 0.32 m/s, and the feeding angle of 11°. Finally, the validation test of the ramie stripping machine prototype was carried out using the optimized parameters. A better performance was achieved in an average fresh stem fiber yield of 5.03% and an average impurity rate of 1.14% of raw ramie, fully meeting the national technical standards of the ramie stripping machine. The transposition clamping device can be expected to realize the ramie clamping and feeding, as well as the automatic reverse pulling. The simple and optimal structure of the ramie stripping machine was had improved the performance and quality of ramie stripping. The finding can provide a technical reference for the development of an automatic lightweight ramie stripping machine.