Agriculture Reference
In-Depth Information
of harvest to the road side trucks which will transport the fruit to the processor or
packinghouse. The harvesting systems can be equipped with additional functional-
ity using on-board grading systems that leave culls in the field, and yield monitoring
systems that georeference fruit harvest rates for precision agriculture applications and
traceability. Ultimately, each robotic system must have an internal communications
network based on Ethernet or a Controller Area Network (CAN Bus), which enables
interfacing of all component controllers to the systems supervisor that will monitor
individual component status and performance, and coordinate all system interactions.
In the following sections, more details will be provided on the unique character-
istics of robotic fruit harvesting.
7.4.2.1 Physical Properties and Fruit Removal
A robotic harvester must be able to quickly remove fruit without damaging the fruit or
the tree. An integral part of the harvester is the end-effector, which is a tool or device
attached to the end of the manipulator that grabs and removes the fruit from the tree.
Because of its direct interaction with the fruit and tree structure, it must be designed
with the specific physical properties of the commodity to be harvested in mind.
There are several ways that a robot might damage the fruit or tree: (1) end-effector
applying excessive positive/negative pressure or force to the fruit during pick and
place operations; (2) inappropriate stem separation techniques for the type of fruit;
(3) fruit damage during retraction from the tree canopy or conveyance to bulk stor-
age; or (4) manipulator contact with the tree structure. Fruit damage may not be
visually evident at harvest time. However, bruising, scratches, cuts, or punctures can
result in decreased shelf life and increase food safety risks. Consequently, a properly
designed end-effector must minimize or preferably eliminate fruit damage.
The fruit removal technique used is typically the largest cause of fruit injury. In the
case of oranges, the fruit must be harvested with the calyx intact and the stem removed
flush with the calyx. If the peel is torn away from the calyx, the resulting fruit is unusable
for the fresh fruit market because of contamination and reduced shelf life. This condition
is referred to as “plugging.” If a long stem remains on the fruit, the packer will either
reject the fruit or require stem removal after harvest. The rind of the oranges makes it
one of the more durable fruits, in contrast with more delicate skinned products, such as
tomatoes. They are still, however, susceptible to injury. Injury is more prevalent in less
mature oranges as was found by Juste et al. (1988). Flood et al. (2006) extended the work
of Juste et al. by conducting rind resistance tests over a broader range of punch sizes that
was more representative of robotic harvesting end effector contact areas. They deter-
mined contact pressure thresholds that would protect the fruit from puncture and bruis-
ing damage. Additional tests were conducted on various harvesting motions, resulting in
the identification of optimal pitch and rotational modes of detachment that significantly
reduced plugging (Flood, 2006).
When manually harvesting oranges, the fruit is detached using one of three meth-
ods depending on the variety and cultural practice. The laborer can use a set of
clippers to detach the fruit, usually leaving as short a stem as possible. Second, the
laborer can lift the fruit so that the stem axis is rotated 90° and then pull down so
that the force is perpendicular to the stem axis. Lastly, the laborer can add a twisting
motion to the second method. Although the end-effector does not necessarily have
