The working logic of the sieve belt grading system is clear, forming a closed loop from feeding to discharging, and operating fully automatically. The specific steps are as follows:

**Feed Pre-treatment:** Blueberries to be graded are poured into the equipment's feed hopper via a conveyor line or manually. The vibrating distribution trough at the bottom of the hopper is activated, gently vibrating to break up the blueberries and prevent clumping. Simultaneously, the tilt angle of the distribution trough and the vibration frequency work together to evenly transport the blueberries to the input end of the sieve belt.

Single-Layer Spreading Conveying: After entering the sieve belt, the blueberries are spread out in a single layer under the constraint of the belt's uniform speed (usually 8-15 m/min, adjustable according to fruit ripeness: low speed for soft fruit, high speed for firm fruit) and the side baffles. This ensures that each fruit fully contacts the belt surface, without obstruction or overlap.

Gradient sieve sorting: As the conveyor belt moves towards the output end, blueberries first pass through the smallest aperture sieve area—blueberries smaller than the sieve aperture diameter (e.g., a 12mm sieve corresponds to blueberries ≤12mm). Under their own gravity, they fall through the sieve and enter the first receiving channel below, completing the first stage of grading. Blueberries larger than the sieve aperture continue moving with the belt into the next larger aperture sieve area (e.g., 15mm), repeating the "gravity fall - channel collection" process.

Multi-stage grading: After sequential grading according to the sieve aperture, blueberries of different sizes fall into their corresponding receiving channels, ultimately achieving precise grading of 3-6 levels (e.g., ≤12mm, 12-15mm, 15-18mm, 18-21mm, ≥21mm). Oversized blueberries that do not pass through the last sieve aperture (largest aperture) are carried by the conveyor belt to the output end and fall into a dedicated "oversized fruit" receiving area, completing the full-process grading.

Cleaning and Reset: During the grading process, some residual fruit scraps and dust will fall through the sieve holes into the dust collection tank at the bottom of the machine body, which is convenient for regular cleaning; after the equipment is stopped, the sieve belt can be removed through the quick-release belt design for thorough cleaning and disinfection to avoid cross-contamination.