Apparatus for detecting splices in the web of a printing press

An apparatus for detecting within a generally uniform sheet material of extended length that moves along a path, a variation, such as a splice, in the otherwise uniform sheet material, said apparatus comprising:

• transmitting means for generating a sound along the path opposite one face of the moving sheet material;
• receiving means located along the path opposite the other face of the moving sheet material for converting the sound after it passes through the sheet and is attenuated thereby into an oscillating electrical signal of corresponding frequency, whereby the sound passing through the generally uniform portion of the sheet material will create within the oscillating signal a succession of peaks having a generally uniform magnitude, whereas the sound passing through the variation will create within the oscillating signal peaks of a different magnitude;
• amplifier means for amplifying the oscillating signal produced by the receiving means so as to provide an amplified signal likewise having peaks of a generally uniform magnitude representing the uniform portion of the sheet material and peaks of a different magnitude representing the variation;
• detector means for producing a generally constant reference potential which is less than the magnitude of the generally uniform peaks in the amplified signal;
• and comparing means connected to the amplifying means and the detector means for comparing the amplified signal with the reference potential and for indicating when the magnitude of the peaks in the amplified signal undergoes a change with respect to the reference potential, whereby the presence of a variation in the moving sheet material is detected, the comparing means producing a signal having a succession of pulses when the amplified oscillating signal constitutes a succession of uniform peaks and a discontinuity in the succession of uniform pulses when the magnitude of the peaks in the amplified signal undergoes a change.

In combination with a moving paper web having generally uniform thickness, but also having a splice of increased thickness, an apparatus for detecting the splice, said apparatus comprising:

• a transmit driver for producing first oscillating electrical signals at an ultrasonic frequency;
• a transmitter located opposite one face of the moving web and being connected to the driver, the transmitter converting the first electrical signal into ultrasonic sound of an intensity great enough to pass through the moving web, whereby the uniform web attenuates the sound and the splice will attenuate it still further;
• a receiver located opposite the other face of the moving web where the attenuated sound from the transmitter impinges on it, the receiver converting the ultrasonic sound into a second electrical signal which corresponds in frequency to the sound and has generally uniform peaks representing the sound attenuated by the uniform web and peaks of lesser magnitude representing the sound attenuated by the splice;
• amplifying means connected to the receiver for amplifying the second oscillating signal so as to produce a third oscillating signal which is an amplification of the second signal;
• detector means connected to the amplifying means for producing a reference potential which is less than the peaks of the third signal by a predetermined proportion;
• and comparing means for comparing the third signal with the reference potential and for indicating when the peaks of the third signal falls below the reference potential, thus denoting the passage of a splice between the transmitter and the receiver.

A process for detecting a splice in a web of otherwise uniform thickness, said process comprising:

• directing ultrasonic sound through the web from a fixed location as the web moves past that location, whereby the web attenuates the sound;
• receiving the sound after it passes through the web and converting the sound into a first oscillating electrical signal;
• amplifying the first signal to produce a second oscillating signal;
• converting the second oscillating signal into a reference potential which is a predetermined proportion of the amplitude of the peaks in the second signal irrespective of the amplitude of such peaks;
• comparing the second signal with the reference potential;
• and detecting when the amplitude of the peaks for the second signal falls below the reference potential, thus indicating the further attenuation of the sound as the result of a splice moving through the sound.