2.3 Key operating parameters 2.3.1 Vacuum pressure A Cartesian coordinate system was established using the centroid of the tuber as the origin, the tangential direction of rotational linear velocity as the positive x-axis, perpendicular to the x-axis pointing in the direction of rotation center as the positive y-axis. Some assumptions were conducted for further analysis as the rotation angular velocity of the device was constant, the tuber was an ideal rigid sphere, and the tuber would remain relatively stationary with the nozzle after being sucked. Force conditions of tuber in the vacuum pressure area are shown in Figure 6. In sucking process, compared with carrying process, a bigger suction force is additionally required to overcome the collision and friction between tubers. Therefore, if the vacuum pressure is sufficient for sucking process, carrying process could be successfully completed. Enlarged force diagram of tuber in vacuum pressure area is shown in Figure 7 according which Equation (4) can be obtained.