Optimum design of grain impact sensor utilising polyvinylidene fluoride films and a floating raft damping structure

Grain losses are unavoidable during harvesting. In order to improve the efficiency and reduce grain losses, the major structural and operational parameters of combine harvesters need to be adjusted accordingly. So, it is important to develop a sensor which can monitor the grain losses real-time. A sensor using piezoelectric polyvinylidene fluoride (PVDF) film as sensitive material for monitoring grain losses of combine harvesters is described. A floating raft damping structure was used to construct the sensor to suppress the influence of vibrations. Based on a dynamic analysis of sensor model, response properties of the sensor under working conditions were calculated. The results indicated that the amplitude and frequency of vibration interference were both decreased by optimising the isolators. A signal processing circuit composed of charge amplifier, high-pass filter, absolute value amplifier, envelope detector and voltage comparator in series was designed to detect grain impact signal. A square wave voltage signal was produced while grain impact was detected, and the mean time width was <2.5 ms. Grain cleaning loss tests were carried out during harvesting rice and wheat by mounting the sensor at the rear of cleaning sieve, the results showed that the grain impact could be identified effectively from vibration noise. The measurement errors of grain cleaning loss recorded by the sensor, relative to the loss checked manually, were less than 15%.

► A grain impact sensor using PVDF films as sensitive material was developed.
► Floating raft damping structure was used to suppress vibration influences.
► Sensor parameters were optimised by analysis of vibration performance.
► Cleaning loss monitoring performance of the sensor was verified by field tests.