Abstract: A positive pressure operated servo apparatus for lateral alignment of a continuous web of paper, plastic, textiles and other materials which are being processed at windup, unwind, printing, coating, folding and slitting stations, or other intermediate points in the machine process. The apparatus includes an air source communicating with a sensor and servo valve which regulates a double-acting air actuator having an output member to move a web positioning assembly. The servo valve is regulated by a diaphragm that is controlled by a pneumatic correction signal force from a low pressure sensor circuit and is arranged under the influence of such signal force to selectively position a valve element relative to two orifice openings to provide differential air pressure proportional to error to operate the actuator to produce actuator movement proportional to the error to correct and maintain the position of the web.

Abstract: A positive pressure operated control apparatus for lateral alignment of a continuous web of paper, plastic, textiles and other materials which are being processed at windup, unwind, printing, coating, folding and slitting stations, or other intermediate points in the machine process. The apparatus includes an air source communicating with a combination sensor and controller which regulates a double-acting air actuator having an output member to move a web positioning assembly. The controller is regulated by a sensor paddle which is spring loaded to be maintained in engagement with the web edge. As the web wanders or becomes misaligned, the paddle moves in proportion to the misalignment and results in movement of a valve element relative to two orifice openings to provide differential air pressure proportional to error to operate the actuator to produce actuator movement proportional to the error to correct the position of the web.