DESIGN AND EVALUATION OF PRINCIPLES FOR MECHANICALLY HARVESTING SWEETONIONS

The principles of operation of a mechanical harvester for sweet onions were developed. The key features included: a lifting-head for each ro w comprised of guides for lifting the tops, gathering-wheels, an under cutter lifting-belts, depth-gage wheels, a shaker of soil from the roo ts of the bulb and a topper to cut tops from the bulb; a conveyor to m ove the onions from the lifting-head to a container; and ii conveyor t o dispose of the tops. In addition to the drivel; a machine operator w as seated in such a position as to have a clear visibility of the lift ing-head during the harvesting operation. An automatic lifting-head he ight control accommodated bed surface undulations. The machine operato r controlled the mean height of the lifting-head as well as lifting-be lt dl-ive and undercutter depth, while the machine was operating, thes e in accordance with variations in onion bulb height and root length. Successful machine operation required the onions to be drilled in sing ular 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 learn, soil t hat could be penetrated by the undercutter and would easily shake loos e from the roots. Undercutting provided trimming of the roots. It was necessary to correctly grasp the onion top in order for other operatio ns to appropriately take place. The onions needed to be of optimum mat urity. 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 h arvester operation.