Development and test of fully automatic film-cleaning machine for Chinese greenhouses

Chinese greenhouses have been widely used with planting areas exceeding 810,000 hm² in northern China, due to heat preservation, low investment, and energy saving. The plastic film of greenhouses cannot be washed by less rain in the northern region for an extended period. The accumulation of more dust can also reduce the light conditions in the shed, leading to adverse effects on the growth and development of crops. Consequently, it is very necessary for regular shed cleaning. In this study, a fully automatic cleaning machine of greenhouse film was proposed for the labor-saving and high efficiency. The machine included a cleaning host, floor and roof lateral shifting devices, as well as a control system. The cleaning host consisted of a bracket, brush, support wheel, climbing motor, brush motor, and water spray pipe. The roof lateral shifting device comprised a hanging rail, stainless steel pulley assembly, hanger, roof lateral shifting motor, polyurethane wheel, and control system. The ground lateral shifting device was composed of a flip frame, bearing bracket, rear axle assembly, water tank, and control system. A 433 MHz wireless module was selected to communicate between the floor and roof lateral shifting device conveyor over a distance of up to 200 m. A double worm gear motor was used to drive the brush and climbing shaft of the cleaning host, in order to reduce the weight of the entire machine for cost saving. A ground lateral shifting device was designed to carry the cleaning host along the length of the greenhouse. The roof lateral shifting device was designed for automatic line wrapping cleaning. The installation height of the roof lifting rope was determined to avoid interference during the lateral shifting operation, even damage to the film. Multi-sensor fusion and data verification were utilized for the real-time, consistency, and reliability of cooperation between the cleaning host, roof and ground lateral shifting device. A model greenhouse was then made to verify the rationality and feasibility of the design. The prototype parameters of span, ridge height, and shoulder height were used at the scaling ratio of 10:1. The prototype was then processed and cleaned, according to the external dimensions at 5:1. Alignment, tilt deviation, and cleaning tests were conducted to verify the performance. The results showed that the horizontal offset during the lifting and lowering of the cleaning host was within ±3°, the left and right offset was within ±7 mm, and there was no offset during the lateral shifting. There was approximately 1 mm in the single and cumulative lateral shifting errors of the floor and roof lateral shifting devices. The average light intensities were 107 232.38, 77 866.77, and 112 377.26 lx with/without the cleaning shed and the cleaning reference, respectively. The relative transmittance of the film increased from 69.3% to 95.4% after cleaning, indicating the well-designed brush material and key parameters of the machine. A remarkable cleaning performance was achieved on the surface of the film. The cleaning machine with the large weight in the early stage can also be updated for the high automation level, less film damage and cleaning blind zone. The findings can provide a strong reference for the design and development of film-cleaning equipment in the greenhouse.