Portable Weighing System for Determining Harvest Efficiency

The efficiency of labor during sweet cherry (Prunus avium L.) harvest is affected by many factors including orchard architecture, fruit yield, and capability of the worker, among others. For sweet cherry, harvest costs account for the majority of annual production costs and there is great interest to reduce these via horticultural and/or mechanical means. Our research program is studying the role of key harvest efficiency factors in tree fruit to better understand their relative importance and to develop more efficient harvest systems. This paper introduces a prototype system used to study labor efficiency by measuring and recording the weight of standard orchard bins over time. The system consists of a digital commercial platform scale (5' x 5') mounted on a custom steel frame fitted into a standard cherry harvest bin (4' x 4' x 1') to facilitate transport of the weighing system.  A standard harvest bin was placed on the scale to receive fruit as pickers empty their harvest bags. The digital interrogator controlling the platform scales and receiving weight data was interfaced to a wireless radio networked to a remote coordinator consisting of a Zigbee wireless radio and a custom data logger that collected and stored the data. System performance and reliability was tested in six orchards in cooperation with three commercial growers. We deployed the system with their commercial picking crews, using 3 systems in most orchards, with 3 or 4 pickers per system. The total bin weight, harvest rate per crew, the weight of each picker’s bucket drop into the bin, the time to pick a bin and the average labor cost per lb was determined using this system. Further, we compared the efficiency of harvesting ‘Skeena’ with or without pedicels (i.e., stem-free). The time required to fill a bin varied more than 2-fold across the orchards we studied. Picking rate (lbs/min/person) varied from about 1.1 to 3.0. The mean picking rates for stem-free and cherries with stems were 2.54 lbs/min (std 0.31) and 1.66 lbs/min (std 0.35) when picked by the same crew in the same orchard. Further, final fruit weight per bin ranged from 320 lbs to 418 lbs. Reasons for these differences, and strategies for improving efficiency, will be discussed.