Mechatronic Design and Control of a Waste Paper Sorting System for Efficient Recycling

Abstract

Sorting of paper into compatible grades is a necessaryKeywords: Sorting, waste paper, lignin, stiffness, gloss, color, fuzzy logic INTRODUCTIONRecycling of paper and paper related products are very important for sustainable economic growth. It helps save landfill space and costs and reduces the energy requirements for paper manufacturing since the energy that is needed to produce recycled fibers is much lower than energy required to produce virgin fibers from wood. Paper recycling reduces the rate of consumption of precious natural resources (wood, water, minerals, and fossil fuel). It is estimated that one ton of paper fibers from recycled stock saves approximately 17 to 31 trees, 7000 gallons (26500 liters) of water, 4,000 KWh of electricity, and 60 pounds (27.2 Kg) of air pollutants that would otherwise be produced [1]. In the US 100 million tons of paper a year is consumed--for everything from daily newspapers to books and cardboard boxes. It has also been established that 50% of all the paper being produced is discarded immediately after the first use and that almost all of it can be recycled [2]. Current recycling rate is about 50%. Paper products are the number one contributor to landfill volume. This highlights the importance of having an efficient recycling system for paper. Before waste paper can be recycled, it has to be sorted into the various grades. Paper is broadly classified into the following grades for the purposes of recycling groups: Newsprint, Coated Sheet, Colored Free Sheet, White Free Sheet, Board, and Mixed Waste.Currently waste paper is either sorted by the consumer prior to disposal or not sorted at all. At the municipal waste sorting plants, it is mostly carried out manually. Here the paper waste is broadly classified as brown paperboard, newspaper, and mixed office waste. But the inability of the human eye to distinguish between coated inferior grades and good grades result in sorted office waste containing high-grade paper contaminated by similar looking low-grade paper, which reduces the overall fiber quality when they are recycled together. The throughput from these manual sorting facilities is also very low. A typical manual conveyor operates at 75 feet per minute (22.86 m/min). A recently conducted research has also concluded that laborers working at the manual sorting facilities are exposed to microorganisms, organic dust, fungi which cause severe infections [3]. Hence there is an important need to automate the sorting process for efficient recycling.To develop an efficient automated sorting system, robust sensors that can measure various physical and optical properties of paper are necessary. The physical characteristic of paperboard is its high stiffness compared to other grades of paper; the characteristic of newsprint is its high lignin content; coated papers have high gloss; and non-office papers are generally not white and have high color content. In order to sort the papers into various grades, one needs to measure the stiffness of specimens, the chemical conten...