Comparative analysis of load and power characteristics according to mechanical mechanisms of tractor-mounted sweet potato harvesters

Rural areas in South Korea are experiencing a decline in agricultural labor due to ongoing population decrease and urban concentration. This issue is particularly critical in labor-intensive upland crop harvesting, where mechanization remains limited. Sweet potatoes, a major upland crop, are prone to mechanical damage during harvest due to their delicate skin and complex field conditions. The mechanical structure of harvesters directly influences the load on tractors, making it essential to identify optimal operating conditions for tractor-implement systems. This study quantitatively compares the load characteristics imposed on a tractor by two types of tractor-mounted sweet potato harvesters with different mechanisms: a vibrating digger and a vibrating digger combined with a conveyor. A 42kW instrumented tractor was used to collect real-time torque and rotational speed data from the engine and axle. The data were pre-processed using a FIR low-pass filter and a moving average filter. Equivalent torque and rotational speed were calculated based on the Palmgren-Miner cumulative damage rule and Wöhler curves, followed by equivalent power estimation. Results showed that the vibrating digger with conveyor required 5.19 kW of engine equivalent power, approximately 27% higher than the 4.07 kW required by the vibrating digger. The additional load was attributed to the combined mechanism. While the vibrating digger exhibited lower overall load, it showed periodic load fluctuations due to impacts between the digging blade and the soil. These findings provide foundational data for durability assessment and optimization of tractor-implement operation in upland crop harvesting.