Abb Process Automation, Inc.

Ralph S Lorenz

In a scanning head position sensing method and apparatus, a plurality of distinct electromagnetic signals are transmitted from a corresponding plurality of transmitter sites surrounding a central position on one side of a web of material. The signals are transmitted through the web and are received by an electromagnetic energy sensor on the opposite side of the web of material. The electromagnetic energy sensor is positioned to receive approximately equal signal energies from all the transmitters when the energy sensor is positioned substantially opposite to the central position across the web. The transmitters and the sensor are fixedly positioned relative to the first and second sensor heads such that the relative positioning of the heads is determined by combining the signals with one another. Pairs of transmitters are provided at two locations along each of two axes which cross on the central position such that the positioning of the sensor heads can be determined for machine and cross directions and also along the axes. Preferably, the axes are oriented at 45.degree. and 135.degree. relative to the machine direction such that information regarding the positioning of the sensor heads can be determined in the machine direction, the cross direction and along 45.degree. and 135.degree. directions relative to the machine direction.

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Columbus, OH, United States of America

Ralph S Lorenz