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Ultrasonic based multiple web sensing for lateral control application

Haque, Jami
Winter, Darcy
Ploetz, William
As sensing requirements in guiding applications increase in complexity, innovation must increase to meets these needs. In applications with multiple webs, space restrictions often limit the placement of sensors. In this case, a single sensor that can sense multiple edges would be desired. Sensing multiple edges within the same sensor opens other new possibilities in guiding applications as well.
To address these needs, staggered arrays of ultrasonic transducers in a through-beam configuration can be employed using a combination of FPGA and microprocessor based technology. The transmit side consists of an array of ultrasonic transducers which are driven individually with a precisely timed signal. The receiver side consists of an identically arranged array of transducers diametrically opposed to the transmitter. To handle the concept of multiple edges, a methodology can be adopted to partition the sensor field of view into many individual "virtual sensors". Virtual sensors can further be selective about the type of edge polarity they sense. Because virtual sensors exist only mathematically, they can overlap each other in any conceivable manner and can be moved around to reposition their respective webs. This scheme has another advantage that is useful particularly in sensing and guiding applications. The entire sensor field of view is active at all times which open the possibility to provide multiple edge tracking within the complete sensor field of view.
Ultrasonic sensing technology is often preferred for its ability to sense wide varieties of materials such as opaque, clear and photosensitive type web materials. However it is often limited to smaller bandwidth because of transducer size. Those sensors that offer wider sensor field of view are typically limited to single edge detection. Multiple edge detection with edge polarity awareness is achieved by keeping all of the transducers active at all times. A sensor with these capabilities can operate like a conventional sensor with a single edge, or provide more advanced capability using multiple edge detection. Multi-edge applications include center or edge guiding one or more webs, multiple web width measurement, web position, and lane measurement (distance between webs).