Melon material properties and finite element analysis of melon compression with application to robot gripping

The moduli of elasticity of the inner, middle, and outer portions of melon flesh (Cucumis melo reticulatus L. cv. 'Superstar') were determined using flat plate compression of cylindrical samples. The modulus of elasticity of the melon rind was determined using a tensile loading test. These values were used in a Finite Element Analysis (FEA) of melon compression. The FEA predictions for deformations resulting from flat plat loading of half a melon were within 11% (average error) of the values measured in an Instron compression test at a strain rate of 25.4 mm/min. After this verification procedure, the FEA was used to predict the internal stresses and the deformations of melons handled by two types of robot grippers: a parallel plate gripper and a v-v notch gripper. The maximum equivalent stresses of 66 kPa (9.6 psi) and 28.2 kPa (4.1 psi) for the parallel plate and v-v-notch gripper, respectively, were located near the surface of the melon at the point of load application. These are well below the experimentally determined ultimate strength of the melon tissue, which was 132 kPa (19.1 psi) for the outer melon flesh. Effect on bruising could not be predicted because failure criteria for bruising were not available.