Fruit Phantoms for Robotic Harvesting Trials—Mango Example

Abstract

Experimental trials on the performance of end-effectors for the automated harvest of soft fruit are constrained by seasonal limitations on fruit availability and fruit perishability, necessitating the use of different sets of fruit across time. Consequently, the use of fruit and stalk phantoms, rather than real fruit, is an attractive proposition. In this paper, a process for the cost-effective production of stable fruit phantoms using silicone (polydimethylsiloxane, PDMS) and starch was presented. A preliminary consideration was also presented for the creation of a phantom fruit stalk, involving a wooden dowel or a magnetic latching. Mango fruit phantoms were benchmarked to mango fruit in terms of density, firmness, brittleness, etc.

Evaluation of End Effectors for Robotic Harvesting of Mango Fruit

“…The duration of a pick cycle was around 6 s. The torque specification of the rotary actuator was 2.6 N m, thus a force of approximately 65 N should be exerted at a fruit-stalk interface 40 mm from the axis of rotation. This estimate was consistent with forces measured using a dynamometer (FT 327, Wagner Instruments, Greenwich, CT, USA) following the method of Goulart et al [37].…”

“…Third, fruit size at harvest varies markedly with growing conditions and cultivars (Table 1). Fourth, harvesting mango fruit involves a sharp rotation of the fruit to break the stalk at the point of attachment to the fruit, requiring a tangential peak force at the stalk-fruit interface of at least 64 ± 10 N [37]. Fifth, as released sap burns the fruit skin, the fruit should be conveyed in an inverted orientation to allow sap to drip away from the fruit.…”

“…In a prequel study, Goulart et al [37] developed phantom mango fruit to enable comparative assessment of end effectors in the development of a robotic harvester given the limited seasonal availability and perishability of real fruit. In the current study, a set of metrics are proposed and implemented for the comparison of gripper effectiveness in harvesting mango fruit.…”

“…A common set of phantom mango fruit (of masses 378, 512, 636, and 836 g (Figure 2)) was used. Phantoms were produced from a starch-silicone mixture as described in Goulart et al [37]. A frame was used to suspend and translate a phantom fruit within a two-dimensional plane, parallel to the base plate of the gripper (i.e., horizontal and vertical movement (Figure 3a)).…”