Progressive Crop Consultant May/June 2021

Peak acceleration(g)
250
200
Day of bruise assessment
Drop height (ft) Day of drop After 14 days
150
2 11.4 16.2
3 100 14.4 19.7
4 20.3 25.6
2 50 3.1 4.9
3 3.7 2.0
0 0 6 12 18 24 30 36 42 48
4 2.9 6.6
0 0.6 2.0
Drop height (inch)
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Along with documenting fruit impacts
with a BIRD, a closeup video camera recorded
the harvesting to pinpoint critical
control points where most impacts were
created. The results showed that the drop
to the plastic catch plates on the harvester
accounted for over 30% of all impacts
on the BIRD, followed by the drop from
the grading belt on the harvester into an
empty lug (20%). When the lug is filled
with blueberries, fruit-to-fruit impacts
occur, which are much lower than when
the fruit fall into an empty lug.
Impacts created by the conveyor, including
secondary bounce from the catch
plates, and shaking rods combined for
another 25% of recorded impacts. The
remaining 25% of impacts that occurred
before the sphere contacted the catch
plate were classified as obscured impact
events which could not be identified
clearly from the video and were attributed
to contact with the shaking rod,
branches and the vertical tunnel panels.
These measurements suggested that
the most significant reduction in fruit
impacts could be achieved by 1) Modifying
the catch plates; 2) Reducing drop
heights, either by restricting bush size,
placing catching surfaces closer to the
fruit or decreasing drop heights at other
transition points; and 3) Placing softer
surfaces at the transition points (e.g.,
at transfer points in the fruit handing
equipment on the top of platform.)
The two parts of the impacts include
the number of encounters between the
sphere and different surfaces of the
harvester and the magnitude of these
impacts. In our study, the harvesting
process was documented with video that
recorded time-stamped impact events
with the larger, heavier BIRD I sensor.
Legend
Stainless steel plate
Glued foam pad on
stainless steel plate
Suspended foam pad
Suspended fabric net
Figure 6. The relationship between various contact surface materials and drop height. The
impacts were collected with a BIRD II sphere dropped from different heights.
Using these parameters, the OTR MH
process was divided into four phases:
Phase I (detachment and falling), Phase
II (fruit hitting the catch plate/conveyor
belt), Phase III (elevation from the
conveyor/transfer belt to the top platform
and conveyance through a trash blower)
and Phase IV (dropping from the conveyor
belt into the lug).
Results showed that for the rotary drum
shaker, the BIRD sensor recorded an
average of 18 impacts in Phases I to IV.
During Phase I, it is assumed blueberries
detached by fast-moving harvesting rods
that shake left and right, impact branches
as they fall and/or are flung out to the
side panel. There were about five impact
events in Phase I, but magnitudes of
these impacts proved to be less significant
than initially assumed. In Phase
II, the BIRD contacted the catch plate
and usually only one or two events were
recorded. The magnitude of the impacts
in Phase II was extremely high compared
to impacts recorded in Phases I, III and
IV. Our results strongly suggested that
the high impact that the falling blueberries
receive at the point of contact with
the catch plate injures the fruit, resulting
in fruit softening and larger bruise while
the fruit is in storage (Figures 3 and 4,
see page 5).
Further analysis was performed by
dropping the large, heavier BIRD I sensor
onto a hard-plastic catch plate from
different heights (6, 12, 24, 36 and 48 in)
(Figure 6). As expected, the impact values
(peak acceleration at impact (g) increased
sharply linearly with increasing
drop height, ranging from 280 g at 6 in
to about 800 g at 48 in (data not shown).
In subsequent studies, impact measurements
were made using the smaller and
lighter-weight BIRD II sphere by dropping
onto soft surfaces created by placing
Figure 5 . BIRD II (red sphere) connected
with a 4-pin connector to a laptop to
charge its internal battery, initiate impact
measurements or download collected data
to a laptop or mobile device.
cushioned padding on top of the hard
plastic plates or by suspending the soft
material (no hard surface underneath.)
A wide range of impact values were obtained
depending on the hardness of the
catch plate (Figure 6). Impacts greater
than 200 g were recorded on hard surfaces
such as a stainless-steel sheet and a
plastic catch plate even when the BIRD II
was dropped from a height less than 30
cm (12 in). Gluing a soft surface to a hard
surface reduced impact; however, this
type of surface still created high impact
above a one-foot drop height such that
blueberries falling 30 inches onto such a
surface would still be bruised. For example,
the suspended foam sheet we used
in our harvest-assist blueberry picking
machine in 2017 generated less than 200
g even when the drop height was 42 in,
but well above the 120 g at which ripe
blueberries can be bruised by impact
force. Only the netted fabric that acted
like a hammock produced low enough
impact force and kept the blueberries
from getting bruised even when the fruit
was dropped from a 48-in height. Thus,
it was thought that replacing the hard,
plastic fruit catching and collection surfaces
with soft and durable catching surface
materials and plate design features
that prevent soft surface from contacting
any hard surfaces underneath had the
potential to improve the quality of MH
blueberries and reduce bruise damage
associated with high mechanical impact.
In terms of mechanical impact to blueberry
fruit, our research has shown that
bruise damage and the loss of firmness
in MH fruit can be decreased by reducing
space between blueberries on
the bush and the catching surface to 12
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6 Progressive Crop Consultant May / June 2021