Development and Evaluation of a Roller-Type Onion Topper

During onion harvesting, removing leaves from the onion bulbs is a time- and energy consuming operation that is currently done manually on most Iranian farms. Roller-type toppers can be appropriate devices for onions that are already undercut and gathered. The machine parameters of rotational speed and clearance between rollers have significant impacts on machine performance. This study developed a rolling topper and evaluated the effects of rotational speed (100, 150, 200, 250 and 300 rpm) and the clearance between rollers (23, 33 and 43 mm) on the percentage of damaged bulbs, number of bulbs oriented in the appropriate direction and forward speed of the bulbs on the machine. Results showed that the greatest percentage of damaged bulbs (31.8%) occurred where clearance between rollers was set at 43 mm. Increasing the rotational speed enables movement of bulbs at higher forward speeds along the rollers; however, increasing the forward speed of bulbs increased the percentage of non oriented bulbs to 24% at a rotational speed of 300 rpm. A rotational speed of 200 rpm and 23 mm in clearance between rollers was found to be the optimum configuration for a roller-type topper. In this case, a two blade mechanism decreased the height of remaining leaves after cutting (6.52 mm) and increased the number of onions topped at the appropriate distance from bulb base (95.5%), which was more effective than blade and idler mechanisms.