Force control for automatic cashew shelling considering size variance

Abstract

Vietnam has the world's largest market share of cashew nuts, and hence a large number of workers are involved in the cashew processing industry. A shelling operation is necessary to acquire a kernel (edible portion) of a cashew. However, it is difficult to automate this operation because of the size variance of a cashew shell, although other cashew processing operations such as steaming and sorting are automated. When the cashew is manually shelled by a sharp blade cutter, not only is the shelling rate very low (when compared to other operations) but also labor conditions are strenuous and unsafe. In particular, the cashew belongs to the sumac family, and hence it should be cautiously handled by workers. This paper presents a machine design for cashew shelling to advance working conditions and production efficiency. The proposed design consists of a conveyor to transport cashews, milling cutters for shelling, and a wedge-shaped splitter for the milled shell. To accommodate for the size variance of cashews, we propose a force controller for milling operation that cuts a cashew shell without damaging the kernel. Experimental results exhibit the effectiveness of the proposed force controller for size variance. © 2014 The Japan Society of Mechanical Engineers.