At the forefront of
optical sorting by Masazumi Hara, Technical Division, Satake
he very first optical sorter for the rice milling industry in Japan was introduced on a trial basis in the early 1960s. As far as records show, it was a European sorter of small capacity with only three channels. This optical sorter did not become widely used in the Japanese rice milling industry for two reasons â€“ the purchase and running costs were high, and the market requirement was low. The 1960s were a period of very rapid growth in Japan. Demand for rice exceeded supply, mainly due to poor logistics, and discolored rice was not an issue at the time. In the late 1970s, the demandand-supply balance of rice was reversed and the supply exceeded the demand. The Government restricted the use of agrichemicals and controlled rice production. As a result, areas of fallow paddy field increased. Grass invaded even areas still under cultivation, and pests increased, causing rice discoloration. In the meantime, grass seeds often contaminated harvested rice due to insufficient weeding. Japanese rice mills began to require optical sorters. In response to the demand from Japanese rice mills, Satake started working on the development of optical sorters in 1978 and released the first one in 1979. It was a 10-channel monochromatic optical sorter using photo diodes. Subsequent models had greater and greater capacity, reaching 30 channels by 1981 and 80 channels by 1986. Originally used in large-scale rice mills, optical sorters are now used by even quite small rice retailers. In 1993, Satake optical sorters obtained a new camera â€“ a chargecoupled device (CCD) with near infrared (NIR) capability, which made it possible to identify and reject tiny specks and inorganic particles of the same or similar colour to the product rice kernels and which conventional sorters could not remove. Machine size was also increased to 160 channels. In 1994, Japan experienced its worst ever crop of rice, and decided to import rice. Since this was an emergency measure, and the diffusion rate of the optical sorters used in the countries sending the rice was relatively low, the rice imported into Japan contained a lot of discolored and foreign materials, which did
46 | Milling and Grain
not meet consumer demands in Japan. Rice exporters overseas who wished to sell rice to Japan introduced optical sorters to ensure their rice quality met market requirements; those rice mills inside Japan that milled imported rice did likewise. Indeed, rice exporters would make the point that a Japanese machine had sorted their rice, thereby guaranteeing the quality of their rice. In the same year, the Japanese Food Control Act was revised and the market demand for quality rice became stronger.
These two events helped the spread of optical sorters in the rice milling industry. Today, optical sorters sort almost all rice distributed in Japan, and rice in Japan is safe and reliable, without contamination by foreign materials such as glass or stones, and beautifully white. In recent years, due to the exponential advances made in information-communication technology (ICT), the performance of optical sensors has improved and processing units have been highly integrated and accelerated. It is the home appliance