Available at: https://digitalcommons.calpoly.edu/theses/3174
Date of Award
12-2024
Degree Name
MS in Agriculture - BioResource and Agriculture Systems
Department/Program
Bioresource and Agricultural Engineering
College
College of Agriculture, Food, and Environmental Sciences
Advisor
Mohammad Sadek
Advisor Department
Bioresource and Agricultural Engineering
Advisor College
College of Agriculture, Food, and Environmental Sciences
Abstract
43% of California’s vast land is consumed for agricultural production to feed the United States and other nations Lettuce production alone brought in over $3 billion in 2022 in California. Most of the lettuce today is still harvested by hand using large groups of seasonal laborers; however, this has become increasingly difficult with an immigrant labor shortage. The objective of this study was to design a low-cost autonomous lettuce harvester prototype and evaluate the performance of the harvester capable of harvesting romaine lettuce preciously on a raised bed.
The harvester is equipped with an electrohydraulic control system that is used to control navigation and the cutting height adjustment to ensure harvest consistency. Control systems were designed using the Danfoss plus+1 Guide platform and subsequent components. Cutting height is adjusted via a PID controller that uses the continuous output from a pair of linear potentiometers onboard. The harvester will be tested using three different types of cutting methods at varying cutting and approach speeds. The three cutting implements tested were a 24-inch linear reciprocating beef blade with a serrated edge, a 10-inch non-serrated disc blade, and a 10-inch serrated disc blade. Both laboratory and field tests were conducted to evaluate the performance of the system.
Lab results indicate that the harvester prototype may outcompete traditional hand harvesting methods. The prototype could harvest successfully at speeds up to 0.743 mph. Field results indicate that the harvester is not productive at any approach or blade speed combination. A significance threshold of 0.05 was established in this study. Harvest results for field testing were above this threshold throughout all trials, suggesting that neither blade nor approach speed had any effect on the quality of harvest of romaine lettuce hearts. Successes in lab testing suggest that the concept behind the prototype is effective, however, a system redesign is recommended to better validate field testing.