Optimum design of an array structure for the grain loss sensor to upgrade its resolution for harvesting rice in a combine harvester

Grain loss is an inevitable part of the working process of a combine harvester and is influenced by a wide range of parameters. Since the 1960s researchers have engaged in developing grain loss auto-detection technology. Monitoring of grain loss has been achieved by quantifying grain impacts during occurring over a fixed interval based on the piezoelectric effect. However, saturation phenomena, originating from impact-based measurement principle, occur with existing grain loss sensors when they deal with high impacts rates. There is a need to optimise structure of the grain loss sensors to improve their resolution to meet requirements in rice harvesting. To establish a proper position for the developed sensor, an experiment was carried out on a test-bench in the laboratory using rice fed at different rates. The geometry of the instrumented plate had a significant influence on the performance of the sensor. To analyse the effect of the structure of the plate on detecting performance, a modal analysis and grain collision tests were carried out using different structural forms of instrumented plate. An array structure for the grain loss sensor was proposed which should enhance its reliability by providing further complementary data from the monitoring array. Calibration experiment results showed that the instrumented plate with a length of 150 mm, width of 40 mm, and a thickness of 1.0 mm was the optimum size and could monitor and discriminate rice grains effectively. Field test results showed that the averaged relative measurement error was <3.83%.