Speaker:Prajjwal Jamdagni

Modeling of Fruit and Vegetable Cutting: Analysis, Algorithms, and Robot Experiments

There is a huge potential for automating the process of cutting fruits and vegetables in the food industry. The task is labor-intensive with a high risk of injury due to working in the proximity of sharp cutting tools. There has also been an increasing focus on hygiene and safety after the event of the recent pandemic. This thesis takes a first step to address the challenges of robotic cutting of fruits and vegetables (which often deform during the action).

For the robot to control the knife skillfully, estimates are needed for the various forces experienced by the knife as it fractures a soft food item. We leverage the finite element analysis (FEA) and energy-based linear elastic fracture mechanics (LEFM). FEA is used for calculating the deformation and cutting force, while LEFM is utilized for predicting when the fracture happens and how much the crack propagates for an amount of work done by the knife.

Use of a 3D mesh model in FEA can be computationally prohibitive for achieving a desired accuracy since numerous tiny elements are required near the knife's moving edge. Instead, we represent the object as evenly spaced slices normal to the cutting plane such that the fracturing of each slice is modeled with a 2D mesh based on plane strain.  Fracture, deformation, and involved forces are then interpolated between every two adjacent slices. In addition to the dimensional reduction, this scheme also enables parallelization to further reduce the time of modeling.

The robot needs to demonstrate skills such as slice, rock-chop, etc. to reduce the cutting effort and generate pieces of desired shapes.  We perform a strain-based analysis to characterize the reduction in force as a result of slicing in comparison with pressing by the knife. This approach is then used to model the effect of knife geometry on the cutting force for a translating knife. A further extension is carried out to explain the effect of the knife’s rotation via a piecewise linear approximation of its trajectory. The results are used to control the knife while rock chopping an eggplant. We have conducted experiments with an ADEPT robot and 4-DOF WAM arm to demonstrate accuracies of force and shape modeling, and in knife control.

Committee: Yan-Bin Jia (major professor), Jin Tian, Tichakorn (Nok) Wonpiromsarn, Ashraf Bastawros, and James Oliver

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