PHYSICAL PROPERTIES OF ORANGES IN RESPONSE TO APPLIED GRIPPING FORCES FOR ROBOTIC HARVESTING

In order to understand more fully how an orange would respond to a robotic harvester, studies were conducted that bridged the gap between previously conducted puncture studies and previously conducted burst studies. Field run (unwashed, unwaxed) Valencia oranges (Citrus sinesis cv. Valencia) were tested on March 30, May 15, and June 16, 2004, using an Instron universal testing machine. The punch sizes used for the puncture tests were 0.323, 0.632, 0.964, 1.27, 1.90, and 2.540 cm. Burst tests were also performed with the whole fruit under flat plate compression. As expected, the force required to puncture or burst a fruit is directly related to the contact area. This is a function of two variables: the punch diameter used, and the radius of curvature of the fruit. Based on the results of these tests, a model was developed that relates punch diameter to puncture force. It was also noted that as the punch diameter size increased, the punch diameter term in the model approached zero. This left the puncture force term as a function of the radius of curvature only. This correlated well with physical observations in that punch diameters beyond 2.540 cm approached the behavior of a flat plate, where puncture force was no longer a function of the punch diameter but solely of the fruit properties. Recommendations were then made as to the design of a grasping robotic citrus harvester end effector.