Combine harvester cleaning control and cleaning method

A combine harvester comprising:

• a sieve;
• a collecting auger,
• a grain auger;
• a grain cleaning system;
• a grain hopper;
• a grain loss monitoring sensor;
• a centrifugal fan;
• and
• a grain impurity ratio monitoring device, wherein:
• the grain loss monitoring sensor, an outlet plate and the collecting auger are located at a tail of the sieve;
• the sieve includes an adjustable tail, and comprises an upper jitter plate, a lower jitter plate, an upper vibrating screen, and a lower vibrating screen including a lower vibrating screen diving motor, wherein the upper jitter plate is located on the upper vibrating screen, and the sieve includes a serrated tail which is located on a tail of the upper vibrating screen;
• a power drive mechanism for the sieve adjustable tail is located at the tail of sieve;
• a lower shaker driving motor is connected to drive the sieve;
• and a lower vibrating screen drive shaft is connected to the lower vibrating screen driving motor, wherein:
• the combine harvester further comprises an on-line monitoring and control system, wherein an input of the on-line monitoring and control system, the grain loss monitoring sensor, and the lower vibrating screen driving motor, and an output of the on-line monitoring and control system is connected to the power drive mechanism for controlling the sieve adjustable tail, and to the centrifugal fan for controlling a degree of opening of the sieve adjustable tail and an air intake and an outlet direction of the centrifugal fan.