Design, test, and improvement of a low-cost apple harvest-assist unit

Open Access
Zhang, Zhao
Graduate Program:
Agricultural and Biological Engineering
Doctor of Philosophy
Document Type:
Date of Defense:
June 09, 2015
Committee Members:
  • Paul Heinz Heinemann, Committee Chair
  • Jude Liu, Dissertation Advisor
  • Andris Freivalds, Committee Member
  • James Rawlinson Schupp, Special Member
  • Rapid Upper Limb Assessment (RULA)
  • apple harvest
  • safety
  • ergonomic analysis
  • harvest assist-unit
  • awkward postures.
The U.S. is the second largest producer of apples in the world, with a wholesale value of $2.7 billion each year. Currently, apples are grown in 32 states in the U.S. However, the U.S. apple industry is in crisis mainly stemming from close dependence on a large seasonal workforce, coupled with a reduced labor pool and increased labor costs. Apple harvest is labor intensive, and currently, during apple harvest season, approximately 45,000 – 50,000 pickers use buckets and ladders and pick each apple manually throughout the U.S. Apple harvest work includes considerable awkward postures, prone to causing occupational injuries. In addition, pickers are at risk of fall hazards when working on a ladder. In this project, a harvest-assist unit, aimed at fresh market apples, was developed and field tested. Considerable research utilizing various concepts was conducted on mechanical apple harvesting since the 1950s, such as “shake-and-catch” harvesters, “combing fingers” machines, “rod press” mechanism, “air jets” machines, harvest robots, and harvest-assist systems. Based on literature review, the harvest-assist concept was selected to solve the U.S. apple industry issues. An apple harvest-assist unit was designed, fabricated, and field tested in 2013, during which the unit performed reliably. However, the unacceptably high apple bruising incidence of 48% was a main problem, especially considering this unit was targeting fresh market apples. The major component causing bruising was determined as the distributor for the following reasons: 1) the distributor itself caused 19% of the total apple bruising; 2) the distributor unsatisfactorily reduced apple speed, resulting in apples having high speeds when exiting the distributor, and the high apple speeds were prone to causing apple bruising. Two individual designs, the cone-shaped distributor and the brush mechanism, replaced the original distributor. Field tests demonstrated that the harvest-assist unit with the cone-shaped distributor and the brush mechanism mounted, resulted in 100% and 99% of harvested apples remaining in the Extra Fancy grade, respectively, after passing through the complete harvest-assist unit. While addressing the apple bruising issue, it was observed that padding was a key approach in decreasing apple bruising. Hence, research on establishing a model based on energy absorbed by one-layer and three-layer padding materials was established. The model was validated by the energy absorbed by a two-layer padding material. Correlation between predicted and actual absorbed energy yielded an r2 value of 99.17%, and slope and intercept of the predicted vs. actual absorbed energy linear regression curve were 1.0084 and 0.0210 Joule, respectively. Apple harvest work was first categorized into 12 activities, and the Rapid Upper Limb Assessment (RULA) method was used to analyze apple harvest activities and identify awkward activities that occurred during harvest. Awkward activities were determined as: ladder descending, dumping apples, picking high apples while standing on a ladder, picking low apples while standing on a ladder, picking high apples while standing on the ground, picking low apples while standing on the ground, and moving a ladder. It was also observed that pickers spent 63.5% of working time under awkward postures that needed to be changed soon or immediately. When working on the harvest assist-unit, awkward activities of ladder descending, moving a ladder, picking low apples while standing on a ladder and picking high apples while standing on a ladder were eliminated. Time percentage of awkward postures was decreased from 65.3% of the whole harvest time in conventional apple harvest approach to 43.3% of the whole harvest time using harvest-assist unit. In addition, this harvest-assist unit increased the overall apple harvest efficiency by 28.6%.