Collaboration of human pickers and crop-transporting robots during harvesting – Part I: Model and simulator development

Abstract

Some specialty crops, such as strawberries and table grapes, are harvested by large crews of pickers who spend significant amounts of time carrying empty and full (with the harvested crop) trays. A step toward increasing harvest automation for such crops is to deploy harvest-aid robots that transport the empty and full trays, thus increasing harvest efficiency by reducing pickers’ non-productive walking times. To that end, this work addresses human-robot collaboration modeling in a harvesting context. First, a modeling framework for all-manual and robot-aided harvesting was developed, which can be used for off-line simulation by system designers, but also as a representation model for robot control, during real-time operation. To serve both functions, the framework utilizes hybrid systems to model picker and robot activities. Finite state machines model discrete operating states, and difference equations describe motion and mass transfer within each discrete state. To capture the variability in human behavior and performance during harvesting, the human activity model utilizes stochastic parameters (e.g., picking time, walking speed) that can be estimated by measurements during harvesting. The stochastic model does not require direct yield measurements, which are not available for most specialty crops. Second, a stochastic simulator was developed based on the developed model. For a given field and crew size, the simulator samples all stochastic parameters to generate many instances of the harvest operation, and estimates metrics such as pickers’ non-productive time and harvest operation efficiency. Part II of this work presents the calibration and evaluation of the simulator based on field data, and a case study that evaluates the effect of various robot scheduling algorithms on harvest efficiency.