Abstract:
Grapevines can be prevented from winter freezing damage on the open-field trellis in the grape planting areas of northern China. It is necessary to prune and lay down the vines, then bury them in the soil for cold protection. Once the climate warms in spring, it is often required for the soil clearing and vine unearthing operations before the grape buds sprout after the temperature warms up. The traditional clearing can be implemented on the soil first, and then unearthing vines. The critical issues can suffer from: the low manual operation efficiency, a narrow operation window (typically limited to 1 week), and a high risk of vine damage. However, it is unclear about the positions of the buried vines during soil clearing. Additionally, the timing constraint (while unearthing too early risks frosted the injury, while too late caused the bud germination in the soil) exacerbated the labor intensity and operational pressure in vineyards. In this research, the unearthing machine was developed to improve the operational efficiency for the reduction of the vine injury and extend the time window for the subsequent soil-clearing tasks. A double-spade side-mounted grapevine excavating machine was designed using an unearthing strategy. The vines were extracted from the soil ridges before removing protective soil. The key components included a crank-rocker mechanism with dual spades, a spring-loaded suspension system, and adjustable depth wheels. The trajectory of the spade tip was optimized for the effective penetration and lifting of the vines. The kinematic parameters of the mechanism were determined to consider some constraints, such as the minimum transmission angle and soil ridge geometry, according to the coordinate system and mathematical modeling. A RecurDyn-EDEM coupling simulation was conducted to validate the design. The multi-body dynamics (MBD) and discrete element method (DEM) were integrated into the soil-spade interactions. A Plackett-Burman experiment was carried out to screen seven parameters (e.g., spade angles and operating speed) for their impact on the maximum crank torque. Significant factors (end angle, digging angle, and excavating angle) were further optimized using the Box-Behnken test. The torque was then optimized to minimize using the response surface method. A prototype was fabricated and then tested in field conditions with the sandy loam soil (moisture 8-14%, and compactness 56-133 kPa). Performance metrics included the crank torque, vine exposure rate, and damage rate. Torque data were collected using a ZH07 sensor. While the vine exposure rate and damage rate were visually inspected post-operation. The optimal parameters of the spade were achieved in the end angle of 130°, digging angle of 3°, and excavating angle of 15°. Simulation results showed the minimum average crank torque of 62.3 N·m. Field trials verified the efficacy of the machine, with an average torque of 64.9 N·m (4.2% error from simulation). The vine exposure rate reached 86.8%, with a damage rate of 6.9%, due primarily to the vine entanglement during lifting. The machine was 10 times more efficient than manual work. A vine excavation was realized in 3 seconds. The vines were visibly exposed during post-unearthing, indicating the safer and more efficient subsequent soil removal. A double-spade side-mounted excavating machine was successfully developed and validated for the grapevine unearthing. The optimal design balanced the mechanical efficiency and vine protection, fully meeting the operational requirements in the northern Chinese vineyards. The finding can offer a practical solution to reduce the labor intensity, in order to extend the unearthing window for minimal crop damage.