To reduce the labor involved in strawberry production in Japan, we have developed an automatic packing system for strawberries that packs the fruits methodically in returnable trays or in single-layer trays. The system comprises a supply unit and a packing unit. Each unit has machine vision system, a manipulator, and a suction hand that are operated in parallel. The supply unit is in charge of detecting a fruit in a random posture in a harvesting container, picking it up, and gently placing it on the conveyer. The packing unit then locates the orientation and the position of the supplied fruit on the conveyer, grades it according to its estimated weight, picks it up, and places it in the shipping tray. Performance tests in a production area showed the task success rate of the automatic packing system to be 97.3%, with a process time per fruit of 7.3 s. Matching the rates of manual grading and by machine vision system, however, showed variation from 59.0% to 85.2% depending on grade, while the estimation error of fruit weight ranged  from70711
 

-1.9 g to +2.0 g. We also conducted performance tests for inpidual units. The rate of damaged fruits was 4.1% at the supply unit and 2.7% at the packing unit. The postures of packed fruits were analyzed, showing a significant difference between the results from the packing unit and those from manual operation. Further study should be needed especially for the reduction of bruises on fruits and the uniformity of postures of packed fruits.

Keywords. Strawberry, Packing, Machine vision, Soft handling.

Technological level of postharvest sorting and packing operation directly affects the market value of agricultural products such as fruits and vegetables. From a quality perspective, a wide range of research to automate the sorting operation of various fruits and vegetables has been reported in literature, including work on apples (Rehkugler and Throop, 1986; Shahin et al., 2002; Xiaobo et al., 2010), fresh market tomatoes (Sarkar and Wolfe, 1985; Laykin et al., 2002), and eggplant (Chong et al., 2008). Furthermore, soft handling technique for deciduous fruit such as peaches, pears, and apples to inspect all sides of fruit was studied for more precise grading (Ishii et al., 2003).

The value of the wholesale market for strawberries (Fragaria x ananassa Duch.) in Japan was approximately USD1.9 billion in 2009 (MAFF, 2011), equivalent in size to that for  staple vegetables such as tomatoes and cucumbers. The market price for strawberries is about   USD12

/kg, high enough to allow long-term management. However, every 0.1 ha of strawberry production requires 2,100 man-hours of labor: twice that needed for tomato or cucumber production,and more than 60 times that for fully mechanized rice production (MAFF, 2009). Sorting  and  packing  of  strawberries  accounts  for  26%  of  labor  costs.  This,  in  addition     to

harvesting, is the so-called the  ‘bottleneck’ in strawberry production. Farmers usually   start

harvesting operation in the early morning, before the pericarp softens with the day’s heat. After precooling the harvested fruits, farmers start the sorting and packing tasks. The strawberry fruits are methodically laid by hand in plastic boxes that have two layers to protect them from vibration during transport to the market and to provide visual appeal. This two-layer packing is the type most commonly used in Japan. Since sorting and packing continues into the night during the peak harvesting season, a great deal of human labor is required. To maintain the high quality of     the fruits and avoid damaging them, farmers and employees have to work in cold conditions  for

many hours.

A number of studies on autonomous sorting techniques have been pursued over the years with the aim of reducing the labor involved in strawberry production. Grade classification techniques based on the geometric features of a projected image of the fruit and automatic sorting systems have been proposed (Cao et al., 1996; Nagata et al., 1996; Bato et al., 2000). Recently, Yamada et al. (2009) developed a nondestructive analyzer of strawberry quality, which they applied to a large-scale strawberry packing center in a production area. Their analyzer achieved a processing performance of three fruits per second. They reported that the packing speed was 26.2 packages per hour, a marked improvement over the conventional speed of 16 to 19 packages achieved manually. However, the fruits still have to be supplied manually to the sorting instrument, and packing still has to be done by hand.Since even automated sorting systems still require a lot of manual labor (20 people per sorting line), there is a compelling need to reduce labor costs.