Agriculture Reference
In-Depth Information
mixture of brown rice and paddy rice bounce up and down on the trays. There are
three discharge gates from the tray of the paddy separator: brown rice, paddy rice,
and a mixture of brown rice and paddy rice. Paddy rice and the mixture need to be
recycled to the huller and to the paddy separator, respectively. The position of the
border of the discharge gate is a very important factor to obtain a high performance
of separation. The position of the border is automatically controlled by using a CCD
(charge-coupled device) camera because of the color differences between brown rice
and paddy rice.
14.2.6 S
ORTING
S
YSTEMS
After hulling, a thickness grader is used for sorting brown rice to remove immature
kernels. The sieve slot width of the thickness grader has gradually become larger
to increase the percentage of sound whole kernels and to improve rice grade. For
example, the standard sieve slot widths have been set to 1.95 mm for Hoshinoyume
cultivar (Japonica type and non-waxy rice). However, even if a sieve with a larger slot
width is used, it is still difficult to process no. 1 grade rice. Moreover, a sieve with a
larger slot width decreases the sorting yield.
A color sorter has been recently used for sorting brown rice to improve rice grade.
Figure 14.3 shows a schematic diagram of a color sorter. Each single brown rice
kernel slides down on an inclined chute, and then the kernel freely falls down from
the end of the chute of the color sorter. Color and moisture of the kernel are detected
using visible-light and NIR rays during the free fall of each kernel. Immature,
chalky, damaged (with dark color) and discolored kernels and foreign materials such
as small stones, pieces of grass, and plastic (with no moisture) are removed from the
raw brown rice using an air ejector based on the color and moisture information.
Raw brown rice
Chute
Sensor
Light
Light
Air ejector
Good product
High quality
Bad product
Low quality
FIGURE 14.3
Schematic diagram of a color sorter.
