7. MILLILITERS COLLECTED = LITERS PER HECTARE BEING APPLIED
1.6.18. Electronic Sensors and Robotic Harvesting
Mechanical (contact) and electronic (γ-ray) sensors have been developed for selective harvest, such as that of lettuce by ripeness. In this case head compactness is the criterion for quality.
Optical sensors have been applied for color recognition and soil-clod separation in tomato harvesters. The development of electronic sensing has been great, but the application is mainly in handling equipment.
Robotic harvesting has been oriented for soft, fresh fruit that cannot be harvested with conventional machines, because of excessive mechanical damage. Therefore, it represents an alternative to the current mechanical harvesting systems, superior from
Table 1.73. Working capacities of mechanical aids and harvesters for some fruits Working Capacity Losses (%) Mechanical aids
Tree-fruits
Single-man positioner 130 kg/man h or 3
0.95 ha/100 h
Multiple (hedgerow) platform 140–220 kg/man h or 3–6 2–10 ha/100 ha
Strawberries, man carriers 10–12 kg/man h 5
Small fruits, hand combs 35 kg/man h 8
Harvesters
Grapes 2000–6500 kg/h 5–15
Nuts, ground sweepers 6000–7000 per meter width 2
Tree-fruit 40–60 trees/h 5–8
Trunk Shakers
Limb shakers 8–10 trees/h 5–15
Strawberries 200–600 kg/man h 10–20
Small fruits 500–1000 kg/man h 10–30
Sources: [1, 6–9, 11, 12, 14, 15].
a 6–8 pickers.
the point of view of fruit quality and with a clear projection to the future consisting of automated fruit picking with a robotic system that emulates the human picker.
Although much research has been oriented towards this goal, no commercial robot is yet (as of 1998) capable of replacing manual labor for picking fresh fruits. A fruit-picking robot should possess the capability to locate fruits on the tree in three dimensions, and in any light conditions (including the dark); to approach and reach for the fruit; to detach the fruit and transfer it to a suitable container; and to move by itself in the orchard from tree to tree and row to row without human help [16]. Several up-to-date technologies are involved in achieving these goals, such as artificial vision, image processing, robot kinematics, sensors, control, and computerized signal analysis. Prototypes for the robotic harvesting of commodities different from tree fruits, such as melons and grapes, also are being developed.
Looking into the future, it seems possible that the robot, equipped with the appropriate sensors, would be able to select the most suitable fruits on the tree itself (in terms of quality), to be picked concurrently with the fruit-identification process. In the case in which the system would be able to obtain the best quality, and operating in controlled spaces (e.g., high-density orchards and greenhouses, rather than in the open), there could be commercial fruit-picking robots available in some years’ time.
List of Symbols
c : damping factor (Nãs/m) Cr: air resistance coefficient
d : diameter (m)
e : coefficient of restitution
f : frequency (Hz) F : force (N)
g : acceleration of gravity (m/s2) (≈9.8 m/s2) k : elastic coefficient (N/m)
m,M : mass, kg NIR : nearinfrared
r : eccentricity (m) VIS : visible
v: speed (m/s)
ω: angular speed (rad/s) δ: density (kg/m3)
σ: pressure, stress (kPa, N/cm2)
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Tropical Crops