US 4,877,323 A · Method and apparatus for inspecting a high speed web

Abstract

Printed webs leaving a printing press at speeds above 500 feet per minute are inspected with precision across the full width of the web by a stroboscope method and apparatus. Each repetitive image or design imprinted on the high speed web is rendered stationary relative to the eyes of a viewer at a web inspection station by bright short flashes of light emitted by an elongated xenon flash tube or tubes spanning the web transversely of its path of movement. Light flashes triggered by an improved strobe circuit which is synchronized with the images at all times permits an inspector to inspect any number of images, spaced around the press cylinder, whether or not the images are equally spaced. Additionally, the system can be used in either an image lock mode for side-by-side comparison with a standard or in a controlled pan or scroll mode to allow optimal inspection of entire impression sequences. Also, when desirable, both sides of the web can be inspected by utilizing a second flash tube configuration located behind the web.

Claims17

Dependent claims

A method of inspecting a high speed printed web having spaced repetitive impressions printed thereon, comprising the steps of:

translating said web past a flash tube assembly including at least one flash tube adapted to be stroboscopically excited and a photocell for sensing light transitions;
sensing at least one light transition in each printed impression on the portion of the web which passes said photocell;
generating an electrical signal for each sensed transition;
generating one strobe trigger pulse per repetition of the printed impression by dividing the frequency of occurrence of said generated electrical signals by the number of transitions in the photocell sensed portion of one impression;
exciting said at least one flash tube with the trigger pulse to produce light flashes;
directing said light flashes to one surface of the web whereby a stroboscopic effect is produced to produce a virtually stationary image of the impression of the web ;
generating a steady stream of pulses proportional to the speed of said web;
counting the number of pulses of said steady stream of pulses between two contiguous strobe trigger pulses;
and
storing the value of said number of counting steady stream pulses.

7 more elements

Dependencies are inferred from the claim text.

Method and apparatus for inspecting a high speed web

Life of this patent

Method and apparatus for inspecting a high speed web

Life of this patent

Abstract

Claims17