Optical hole seeking apparatus having dual spaced laser scanners

Optical hole seeking apparatus for webs advancing in a longitudinal direction, the apparatus comprising first and second deflection roller engaging the web so that the webs travel along a portion of the periphery of the roller, a first laser scanning device having first transverse scanning means directing a scanning beam onto a first surface of the advancing web and scanning the beam along a first scanning line which extends across a portion of the web engaged by the first roller transversely to the longitudinal direction, whereby light passing through a hole in the web is reflected by the first deflection roller, a first light receiving arrangement disposed parallel to the first scanning line and positioned to receive light reflected along the first scanning line, the first light receiving arrangement generating a first electrical signal, responsive to light reflected along the first scanning line and indicating, as a first fault signal, when a hole is present at the first scanning line, a second laser scanning device disposed at a spacing (A) in the direction of advance of the web from the first laser scanning device on the opposite side of the web from the first scanning device, the second scanning device having second transverse scanning means directing a second scanning beam onto a second surface of the advancing web along a second scanning line which extends across the web and is parallel to the first scanning line, the second scanning line being located to scan across a portion of the web engaged by the second deflection roller so that light from the second scanning beam passing through a hole in the web is reflected by the second deflection roller, the second deflection roller rotating in an opposite direction to the first deflection roller, a second linear photoelectric light receiving arrangement arranged parallel to the second scanning line and receiving light reflected along the second scanning line, the second photoelectric light receiving arrangement generating a second electrical signal responsive to light reflected along the second scanning line and indicating, as a second default signal, when a hole is present along the first scanning line, an electronic processing circuit means receiving the electrical signals from the first and second light receiving arrangements and processing the signals to determine the presence of fault signals, the processing circuit means further bringing the first and second electrical signals into correlation by intermediate storage of the first electrical received signal and generating a hole signal when substantially the same first and second fault signals at the same position of the web are received.