DESIGN AND EVALUATION OF PRINCIPLES FOR MECHANICALLY HARVESTING SWEET ONIONS

The principles of operation of a mechanical harvester for sweet onions were developed. The key features included: a lifting-head for each row comprised of guides for lifting the tops, gathering-wheels, an undercutter, liftingbelts, depth-gage wheels, a shaker of soil from the roots of the bulb and a topper to cut tops from the bulb; a conveyor to move the onions from the lifting-head to a container; and a conveyor to dispose of the tops. In addition to the driver, a machine operator was seated in such a position as to have a clear visibility of the lifting-head during the harvesting operation. An automatic lifting-head height control accommodated bed surface undulations. The machine operator controlled the mean height of the lifting-head as well as lifting-belt drive and undercutter depth, while the machine was operating, these in accordance with variations in onion bulb height and root length. Successful machine operation required the onions to be drilled in singular, uniform rows on a uniform bed, a bed that was free from weeds and other trash. A desirable soil type was found to be sandy loam, soil that could be penetrated by the undercutter and would easily shake loose from the roots. Undercutting provided trimming of the roots. It was necessary to correctly grasp the onion top in order for other operations to appropriately take place. The onions needed to be of optimum maturity. A maximum ground speed of 2.4 km/h, a lifting-belt speed equal to 125% of ground speed, an onion bulb neck length of 40 to 60 mm and an onion bulb root length of 10 to 40 mm were chosen for appropriate harvester operation.