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

270 M. Ruiz-Altisent et al.
for grain threshing, friction is used to separate the pea grain from their hulls. Friction
is applied by slow-rotating rubber rollers or bands against a drum, sometimes
also itself rotating, that behaves as the concave, as it sieves the peas through
it (Figure 7). From there, peas are cleaned by air, conveyed and loaded to (refrigerated)
bins.
3.2. Bushy structures
Such as small fruits, wine grapes. . . . As mentioned above, small fruits are at the
same time:
– difficult to detach by shaking (non-contact) due to their small mass; and
– damage susceptible to be detached by combing or stripping (contact), as described
for some vegetable harvesters.
Therefore, the detachment of small fruits has been solved by a combination of contact
and non-contact actions applied by vibrating tools.
3.2.1. Small fruits harvesters
With ‘small fruits’, a number of species are referred: Raspberries, blackberries
(Rubus species) and blackcurrant and redcurrant (Ribes species) along with gooseberries,
blueberries, boysenberries, etc. They have in common their way of growing
in bushy structures, their small size and their use mainly for processing. In the
last ten years there has been a considerable activity in the application of mechanical
harvesters to collect these fruits, which are the only fruit produced in some
cold (northern) areas. Contact principles (combing and stripping) have been tested
for the detachment of small fruits in bushy as well as tree structures, with little
success. Present small fruit harvesters use a combination of shaking with soft
combing, based on vertical, tilted or horizontal drums provided with:
Figure 7. Pea-threshing principle (dehulling) and pea harvester. C: concave drum; ω 1 and ω 2: rotating
speeds of bars and concave drum; AB: shearing effect on pod; 1; cleaning brush; 2: concave sieving
drum; 3: pulling bolt; 4: threshing cylinder; 5: inclined band; 6: air cleaner; 7: slope-adjustment
mechanism.