Parameter optimization and experiment of grapevines picking-up mechanism using multi-flexible-body dynamics

Grapevine picking-up machinery is a high demand in the open-field grape-producing regions of northern China during spring. In this study, the grapevine picking-up mechanism was proposed for the lifting operation using a crank-rocker mechanism. The mechanism was mainly consisting of a frame, crank rocker structure, pushing bar, picking bar, spring, and vine fender. Grapevines were lifted from the ground to the given angle with a simple and reliable structure. The structure of crank rocker was used to constrain the movement trajectory of the picking bar. The pushing bar was used to gather the grapevines, and then the picking bar was lifted them. MATLAB software was also utilized to optimize the parameters of the trajectory curve. An optimal set of structural parameters was achieved for the picking bar. The length of the crank was 160 mm, the length of the link-rod was 480 mm, the length of the rocker was 340 mm, and the length of the base frame was 600 mm. The endpoint coordinates of picking bar were relative to the uBv coordinate system as (1 070 mm, -250 mm). According to multi-flexible-body dynamics (MFBD) simulation, the finite element (FE) flexible body model was established for the grapevines and picking-up operation. A Box-Behnken simulation experiment was designed to analyze the impact of three parameters (forward speed, spring preload force, and crank rotational speed) on the grapevine picking-up through the software RecurDyn. Regression significance analysis of the experimental data was conducted using Design-Expert software, with the average angle and the coefficient of angle variation as the evaluation indices. The results showed that all three test factors shared a significant effect on the average angle, while the forward speed posed a significant effect on the coefficient of angle variation. Among the interaction factors, the spring preload force and the crank rotation speed had a significant impact on the average angle, while the spring preload force and the crank rotational speed had a significant impact on the coefficient of angle variation. Among the quadratic factors, only the square of the forward speed and the crank rotational speed had a significant effect on the coefficient of angle variation, while the rest factors had no significant effect. The maximum average angle and the minimum coefficient of angle variation were obtained after optimization. Consequently, the best combination of working parameter was determined for the machine: the forward speed was 0.2 m/s, spring preload force was 128 N, and crank rotation speed was 67 r/min. As such, the average angle of grapevines was 40.6° in RecurDyn, and the coefficient of angle variation was 6.0%. Finally, the prototype was manufactured to conduct the soil bin tests. There was the essentially consistent data with the optimization. The relative error between soil bin tests and simulation was 6.4%, and the mean of the coefficient of angle variation was 14.8%, fully meeting the operational requirements for picking up grapevines. This finding can be expected to serve as a strong reference in the integrated machines for grapevine lifting and tying.