Study on grain loss detecting sensor of combine harvester

A floating raft structure sensor using piezoelectric polyvinylidene fluoride (PVDF) film as sensitive material for grain loss detecting of combine harvester was presented in this paper. Double-layer vibration isolator was proposed to eliminate the vibration influence of combine harvester. Signal processing circuit which composed of a charge amplifier, band-pass filter, envelope detector, absolute value amplifier and square wave generator was constructed to detect the grain impact signal. According to the impact duration of grain on PVDF film, critical frequencies of band-pass filter were determined and the impact responses of filter under different impact durations were numerical simulated. Then, grain detecting experiments were carried out by assembling the sensor on the rear of vibrating cleaning sieve, the results showed that the grain impact can be identified effectively from vibrating noise and the sensor can output a standard square voltage signal while a grain impact is detected.