2.1.2. Principle of Operation

The motion of the spring-finger in the picking mechanism is a combination of linear motion in the direction of operation of the machine and rotary motion controlled by a cam slide. The cam chute constrains the movement of the rollers and at the same time constrains the different attitudes of the spring-finger during rotation, the different picking attitudes of the spring-finger correspond to different picking phases. For each week of rotation of the roller in the cam slide, the picking spring-finger correspond to four phases, i.e., "pickup", "lifting", "push" and "quick-return". The pickup cycle is shown in Figure 2.

**Figure 1.** Schematic diagram of the complete assembly of the picking device: (1) frame (2) curved housing (3) popping gear (4) spindle (5) roller (6) crank handle (7) spring-finger shaft (8) roller disc (9) inner and outer cam (10) potato collection box.

**Figure 2.** Diagram of the spring-finger picking process.

(1) Pickup stage: at the start of the pickup phase, the drum rotates and at the same time moves the spring-finger underneath the drum, the end of the spring-finger start to protrude through the gap in the curved hood and then are inserted into the ground at a certain angle of entry, then the spring-finger continue to move, as the machine advances and the drum disc rotates, the spring-finger continue to move upwards to pick up the potatoes laid on the ground.

(2) Lifting stage: at the start of the lifting stage, the direction of spring-finger swing is controlled by the rollers in the cam chute and the lifting stage starts in a horizontal position. The drum disc continues to rotate and the end of the spring-finger begin to move backwards and upwards, transporting the pickup potatoes to the top of the curved hood.

(3) Push stage: the phase starts with the pickup spring-finger located at the back front, the relative speed direction is horizontal backwards, pushing the potatoes backwards, in the pushing phase, the pickup spring-finger and the drum disc maintain a large backward angle of inclination between the pickup spring-finger and the curved hood shell to prevent a clamping angle between the pickup spring-finger and the curved hood shell, which is not conducive to backward movement of the potatoes or wounded potato to the potatoes.

(4) Quick-return stage: after the pickup spring-finger have finished picking up, lifting, pushing and unloading potatoes, with the continuous rotation of the drum disc, there is an idling stage before the spring-finger return to the initial position of the pickup stage, this stage does not touch the potatoes and the ground, but the spring-finger rotate with great acceleration in order to quickly return to the starting position of the next pickup stage, shortening the rush back stage and improving the pickup rate.
