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

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

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276 M. Ruiz-Altisent et al.<br />

Table 3. Frequencies <strong>and</strong> amplitudes used in fruit <strong>and</strong> nut harvesters.<br />

Harvested crop Frequency (Hz) Amplitude (mm) Observations<br />

Strawberries 05–15 20–40 Mass: 6–9 g<br />

Cherries 10–20 15–60<br />

Apricots 15–30 08–12<br />

Almonds 15–30 08–12<br />

Apples 15–30 08–12<br />

Prunes 15–30 10–14<br />

Peaches 15–30 12–16<br />

Olives 20–35 50–75<br />

Oranges 10–15 12–16<br />

Grapes 09–10/10–20 80–140 See text<br />

15–23 25–70<br />

Tomatoes 05–10 30–50<br />

Small fruits<br />

Rubus 05–10 40–75<br />

Ribes 10–25 40–75<br />

spread application due to the high cost, <strong>and</strong> to problems related to timeliness <strong>of</strong><br />

application, as well as to concerns about chemicals residues on the fruits.<br />

Kinematics <strong>of</strong> the inertial shaker<br />

If only one rotating mass, m, is considered (Ortiz-Cañavate <strong>and</strong> Hernanz, 1989)<br />

(Figure 13a), rotating at a constant angular speed ω, the centrifugal force has the<br />

following expression:<br />

F – = mr ω 2 exp(iωt)<br />

where r is the eccentricity <strong>of</strong> the rotating mass. This type <strong>of</strong> orbital shaker is the<br />

appropriate for some fruits, like almonds.<br />

If two eccentric masses are considered, m 1 <strong>and</strong> m 2 (Figure 13b), rotating at different<br />

angular speeds, ω 1 <strong>and</strong> ω 2, in the same or in opposite directions, <strong>and</strong> mounted<br />

in one or in two different axles, the forces generated by their rotations are:<br />

F – 1 = m 1r 1 ω 2<br />

1 exp(iω 1t)<br />

F – 2 = m 2r 2 ω 2<br />

2 exp(iω 2t)<br />

The usual output <strong>of</strong> inertia shakers is a relatively high frequency <strong>of</strong> vibration<br />

(12–40 Hz), <strong>and</strong> a short stroke (5–20 mm) delivered to the tree. The resultant<br />

force F – 1 + F – 2 can be adjusted for magnitude <strong>and</strong> pattern in any desired way by<br />

changing the relative masses <strong>of</strong> the eccentrics <strong>and</strong> by modifying their respective<br />

rotating speeds (Figure 14).<br />

The force generated by the shaker is (Figure 15):<br />

F(t) = Mx + cx + kx

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