Sensor Detects Differences in Plastic Materials

At the center of a new, automated plastic sorting system is a sensor that can detect the differences among six types of detectable plastics: PET (polyethylene terephthalate), PE (polyethylene), PVC (polyvinyl chloride), PP (polypropylene), PS (polystyrene) and ABS (acrylonitrile butadiene styrene).

The sorting system relies on two sensors, a proximity sensor to detect the presence of an object in the system, and a new plastic material sensor from IDEC. According to Lanny Schuberg, IDEC product engineer manager, "The plastic sensor detects different grades of plastic based upon the resonant frequency of each plastic.  Different plastic molecules have different resonant frequencies and by tuning laser diodes to these frequencies, they excite the molecule of the plastic and are thus detected."

The IDEC plastic identification sensor used in the recycling system developed by IDEC, Osaka University, Mitsubishi Electric Engineering Co., Ishida Co. and Japan's Ministry of Economy, Trade and Industry. Source: IDEC.

The ability to sort plastics properly is a major issue for plastics recycling. Current methods involve manual, visual inspection and sorting, which is often not as accurate as needed or infrared spectroscopic analysis, an expensive option. Behind the push to develop this plastic sorting sensor is the desire to create a less expensive, more accurate, automated option. Schuberg notes that accurate plastic sorting is inherently a difficult process "because there are many different grades and materials of plastic in the market and different plastics recycle differently in terms of their use."

Automated Sorting
IDEC and its project partners (including Osaka University, Mitsubishi Electric Engineering Co., Ishida Co. and Japan's Ministry of Economy, Trade and Industry) worked together to design and create the sorting system; IDEC claims the system is the world's first plastic sorting system equipped with an industrial robot to be introduced at retail stores. The system has been introduced in Japan at the Nara Co-op and the Osaka University Co-op for people to turn in used plastics for recycling without having to first pre-sort the items. (See System Overview graphic.)

Sensor Specifics Preliminary specifications for the fiber-type IDEC plastic sensor: Power voltage: 24V Current draw: 500mA maximum Sensing range: 300-450mm Objects: PET, PVC, PE, PP, PS, ABS and other plastics Response time: 1msec maximum Light source: 5 infrared laser diodes Control output: RS232 Dimensions: Sensor head (100mm x 90mm x 40mm), Controller (200mm x 150mm x 75mm)

Using a six-axis articulated robot arm manufactured by Mitsubishi Electric Corp. and interfaced to an IDEC controller, the sorting system is able to transfer plastic items into specific boxes for recycling after sorting. The basic function of the system is to first analyze a plastic item against a reference by means of the sensor's photodiode receiving a signal captured from a mirror that directs the "image" created by laser diodes. These laser diodes provide the light source for the sensor. Data from the sensor is then sent to a control/signal processor in the system's controller before being output to direct the robot arm for sorting.

A major push behind the development of this sorting system is Japan's current policy initiative to promote the use of the "service robots" for lifestyle support. Osaka University is also a principal supporter of the move toward more plastic recycling as part of its goal of contributing to the creation of a low-carbon society.

Carbon Reduction
"This project started with a grant from the Japanese government to IDEC, which then started working with Osaka University researchers in this area," says Schuberg. Other partners, like Mitsubishi, were brought in to add their particular expertise.

Carbon reduction is a major component of this project because plastic production is one of the leading uses of petroleum. "By reducing the amount of plastics produced, we would use less oil, and therefore reduce the amount of CO₂ created to produce them," says Schuberg. Though this is a major issue of concern in Japan, Schuberg points out that California bill AB32 specifically calls for a reduction in greenhouse gasses, and a number of other Congressional bills are pending in this area, which could make plastics recycling in the U.S. as significant an issue here as it is now in Japan.

Source: IDEC

Schuberg says that IDEC is gauging the market potential for the sensor in the U.S. "At the moment, we have a very promising opportunity with the state of California to detect bio-plastics, but this is in the initial stage," he says. Potentially, the system could be used in recycling plants, as well as being set up in retail or collection centers.

Though the current vision for this sensor is plastic detection and recycling, "the sky is the limit for this detection technology," Schuberg says, "as the lasers can be tuned to detect resonant frequency of many different objects."

Laser and Photonics Expert Plays Leading Role
Satoshi Kawata, a professor in the Department of Applied Physics at Osaka University and the center director professor in The Photonics Advanced Research Center (PARC) at Osaka University, worked with IDEC and other partners on the development of the laser sensor application for plastic identification and sorting. Kawata is known for his work in nanophotonics (study of the interaction between photons and nanostructures). In his career, he has contributed to a number of inventions, publications, and conference organizations in fields including near-infrared spectroscopy, laser-scanning microscopy, near-field optics, plasmonics, biophotonics, laser nanofabrication and signal recovery.

PARC was established by the president of Osaka University in July 2007 and is sponsored by the Ministry of Education, Culture, Sports, Science and Technology, Japan (MEXT). For more information on PARC, visit: http://parc.eng.osaka-u.ac.jp/english/