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Tests of the Ability to Orient Apples using their Inertial Properties

Narayanan, P., Lefcourt, A.M., Tasch, U., Rostamian, R., Kim, M.S.
Paper 2007 no.076246
apples, fruit quality, sorting, automatic detection, image analysis, stems, calyx
Machine vision has the potential to improve quality and safety of fruit available for consumption. However, lack of an effective and inexpensive method for appropriately orienting fruit for imaging has hindered development of optical technologies for sorting fruit. For example, it is difficult to differentiate stem and calyx regions from problem areas in images. One solution would be to orient fruit so that these regions are not imaged. We discovered that apples can be oriented using their inertial properties. Apples were rolled down two test tracks consisting of two parallel wooden rails (16.5° inclination, 3 m length). When the apples achieved sufficient angular velocity, they generally moved to an "oriented" position where the stem/calyx axis is perpendicular to the direction of travel and parallel to the plane of the rails. As transit time is about 1.5 sec, a monochrome camera was used to create movies of the orientation process (60 fps, non-interlaced, 1/500th sec exposure, 640 x 480 pixels) and software was written to slow the movies to six fps, and to identify the center of the apple in each frame and whether the apple was oriented. Tests were conducted using 100 Red and 100 Golden Delicious apples with three different initial positions of the stem/calyx axis: (1) perpendicular, (2) at 45°, and (3) parallel to the rails. Apples started in a perpendicular position were de facto oriented; however, the apples often showed effects of precession as runs progressed. Apples started at 45°almost instantly became oriented. Orientation for the parallel condition was not always successful; theoretically, for a balanced apple, there are no lateral forces generated during end-over-end rotation. Theoretical dynamics suggest that parallel loading will not occur if a random loading mechanism is used. Alternatively, potential methods for circumventing this problem case are discussed.