Apparatus and method for counting repetitive marks on a running web

#This invention relates to the measurement of a reference length of a running web and is more particularly concerned with the measurement of "board length."

#In the manufacture of certain types of multi-layer printed documents, it is common practice to provide a row of punched holes along a longitudinal edge of a paper web (e.g., holes at half inch intervals) which are later used for collation of the sheets. During the punching operation, which may be performed concurrently with the printing operation, the paper is under tension. After the paper leaves the press, it relaxes somewhat, resulting in a small dimensional change in hole spacing and paper length. This change is dependent upon such factors as infeed tension in the press and the width, thickness, and modulus of elasticity of the paper.

#Although the dimensional changes are small, for example. +0.03%, the error in alignment between holes in the various sheet levels as the sheets are collated accumulates and is proportional to the length of paper being collated. Collators can compensate for some of the differences in hole spacing, but when the variance becomes excessive, rolls of paper may be unusable.

#The invention will be further described in conjunction with the accompanying drawings, which illustrate a preferred and exemplary embodiment, and wherein:

#FIG. 1 is a fragmentary diagrammatic perspective view illustrating apparatus of the invention employed on a printing press;

#FIG. 2 is a diagrammatic view showing the path of a running web through a sensor unit in accordance with the invention;

#For illustrative purposes, the invention will be described as employed in conjunction with a printing press, such as the press A shown diagrammatically in FIG. 1, but the invention may be employed in other types of web feed systems as well. In the preferred embodiment, the apparatus of the invention comprises a sensor unit B at the press and a remote main unit C. The printing press has a pair of frame members A1 upon which a roller assembly A2 may be mounted. The roller assembly may comprise a pair of frame plates A3 between which four rollers A4, A5, A6, and A7 (see FIG. 2) are rotatably mounted.

#In the form shown, rollers A4-A7 are arranged in an upper pair and a lower pair, with the web D passing under roller A4 and then over rollers A5 and A6 and under roller A7 as shown, but the precise arrangement of rollers is not critical to the invention. The web D, which will be referred to as "paper" (although other webs may be used), is provided with a row of holes or reference marks E spaced substantially equally along a longitudinal edge of the web. For purposes of illustration of the invention, it is assumed that the holes have half-inch spacing, although one inch or other appropriate spacing may be employed. The holes are preferably punched by a conventional punch roll F shown diagrammatically. The punch roll has a plurality of punches F1 equally spaced about the circumference of the roll, and cooperates with a mating roll G having a plurality of depressions G1 spaced equally about its circumference for receiving the punches in a conventional manner. As the web D advances through the press, rolls F and G rotate in synchronism with the movement of the web and punch the holes E.

#In general, the web may be fed past printing stations (not shown) of the press from a supply roll (not shown), past the punch roll and past the roller assembly A2 to a rewind unit (not shown). The rewind unit and various feed rollers of the press will normally be driven so as to provide desired tension in the web at various stations of the press which may be adjusted in a conventional manner, as by operation of a tension motor. The details of the press are not germane to the invention.