Mango postharvest handling and firmness assessment with a robotic gripper

The mango fruit (Mangifera indica) is a highly appreciated fruit by the consumers. One of the most significant quality aspects of mango is its firmness as it represents ripeness. Destructive tests are still commonly used as an instrumental reference for texture measurements. However, during the last two decades there has been an increasing interest in nondestructive fruit quality inspection. This study describes a pneumatic robot gripper that has been developed and tested for this purpose in mango fruits. The gripper had three fingers and one suction cup. Every finger had an inertial sensor attached to it. One of the fingers with the jamming of granular materials adapts to the mango fruit shapes. The information registered from the inertial sensors was processed to obtain 16 different independent parameters. Three sets of mango fruits were prepared, including hard, soft, and very soft products to obtain three different firmness levels. The first set of mango fruit was just harvested whereas the second and third sets contained fruits stored at 22°C and 48% RH for 6 and 12 days respectively. Weight, diameter, length and firmness (using a Magness-Taylor pressure destructive tester) of the fruits were measured. The robot gripper capability for manipulating mango fruit in the pick and place operation was assessed. A logistic regression was developed in order to assess the physical parameters that mango fruits presented before the storage period. These parameters determined the gripper capability of grasping the fruit. The results obtained indicated that the volume, instead of weight, is the limiting parameter of the gripper capability to manipulate and classify the mango fruits by their firmness. A selective analysis showed a 93.6% of well-classified fruit according to the three firmness levels using the non-destructive parameters obtained from the inertial sensors of the gripper. As a conclusion, it has been proved that the hygienic non-destructive assessment of mango fruit firmness, while grasping in the pick and place operations, could be a good system to be implemented in postharvest mango fruit packaging processes.