Production Practices and Quality Assessment of Food Crops. Vol. 1

264 M. Ruiz-Altisent et al.
Table 2. Detachment forces for selected fruits.
– length and
– inclination angle of the share and working speed and cutting depth, determined
by the location of the recoverable product in soil, together with the abovementioned
parameters, constitute the regulations of the system.
Following the coulter(s), a vibrating rod-chain conveyor is needed to clean and
to feed the product to the complementary operations of handling, cleaning and
loading units. The above-ground plant parts, very fragile in comparison with the
subsurface parts, may be recovered or dispersed, before or at the same time of
harvesting the roots. This harvesting system is appropriate for any roots or tubers
(e.g. carrots or potatoes), below-ground fruits (e.g. peanuts) or bulbs (e.g. onions
and garlic).
Pulling the aerial portion of the plants is often used for the harvest of some
root crops (e.g. carrots) and also some surface crops (e.g. leeks and salad greens);
the structure and the strength of the plants must permit in this case the engagement
of the above-ground leaves and the uprooting of the entire plant, aided by a
subsurface coulter; the big advantage is that very little soil is extracted with the
product (Figure 1).
Pulling force: F p = 2µN
Pulling speed: v¯ p = v¯ a + v¯ r
Detachment force (N) Observations
Apple, pear 40 a
Almond 1.5 a
Cherries 12–16 8–10 N a
Grape 3–5 Single berry
25–50 clusters
Peach, apricot 1–5 9–15 N a
Tomato 20–30
Orange 20–30
Lemon 30–40
Strawberries 4–9
Small fruits 0.5–2.5
Olive 2–8
where
µ = friction coefficient
N = normal force exerted by the belts on the plant
v¯ a = working speed
v¯ r = speed of belts
The aerial parts have to be well aligned in the row and uniformly spaced, and
they are engaged and grasped by a pair of elevating belts, which, due to the combination
of the effects of: advance speed, velocity of the belts and their inclination,