Sensor system and method for web manufacturing

This application claims priority under 35 U.S.C. §120 to provisional application Ser. No. 60/980,318 filed Oct. 16, 2007, herein incorporated by reference in its entirety.

The present invention relates to articles of manufacture prepared from a material web, and in particular to the manufacture of plastic bag rolls suitable for use in most application, including for example, trash can liners, produce bags, and the like. Plastic bag rolls are typically built by continuously extruding plastic film through a die to form a bubble. The bubble, tubular in shape, is later reduced in width to that of the desired bag by flattening the shape and introducing folds known as gussets using rollers. Once flat, the web may be printed before conversion into bags. Timing marks may be incorporated into the print.

Two types of machines are usually involved in the final step, known as conversion. The first machine, commonly referred to as the ‘bag machine,’ perforates and seals the bag web at intervals that determine the length of the final bag. The seals and perforation are approximately perpendicular to the web. The second machine, commonly known as the ‘winder,’ separates the web at the perforation if an overlapped bag is being built but always winds the web into a roll while counting the bags. The ‘winder’ automatically transfers a new spindle into the web to continue winding bags when a roll has been completed.

Because the perforation is introduced onto the web in a different machine than the machine that winds the roll, the ‘winder’ must synchronize its operation to the location of the perforation and seal. The device used to determine the location of the perforation on the web is referred to as the ‘counter.’ The most prevalent form of counter is a perforation spark gap detector. This design incorporates two electrodes at a high voltage potential, one on each side of the web, at close proximity. When the plastic bag is between the electrodes, it acts as an insulator. However, when the perforation section passes the electrodes, the insulator is compromised and a spark can jump the gap between the electrodes. Such a design is not always satisfactory, as the high voltage used for sensing also induces a static bond between the layers of the plastic bag. This effect increases the difficulty that a person will have in opening the bag. Furthermore, the presence of an exposed high voltage device on the input of the winding machine often causes operator shocks. Moreover, the sensor can only detect the perforation, and not any other features of the bag and/or plastic bag web.

Therefore, a need in the art has been identified to provide a sensor system to identify, track, locate, and/or measure features associated with a plastic bag web, such as bag seals, perforations, printed markings, skirt length, or other features on the plastic roll, bag or bag web.

These particular objects and advantages may apply to only some embodiments falling within the claims and thus do not define the scope of the invention. In one aspect of the present invention a sensing system adapted for use in monitoring and detecting features of a web for manufacturing is disclosed. The sensing system includes an energy source adapted to project an energy beam onto the web and a sensor positioned relative to the web and the energy source to sense attenuation of the energy beam from the energy source to detect, locate or measure the web or features of the web. In a preferred form, the energy source is a light source and the energy beam is a light beam. The energy source is positioned on one side of the web and the sensor is aligned with the energy source on an opposite side of the web so that the web passes between the energy source and the sensor. In a preferred form, at least a portion of the energy beam is transmitted through the web so that the portion of the energy beam passing through the web is sensed by the sensor. The sensing system also includes a comparator in data communication with the sensor to measure a difference in energy between the energy beam and the portion of the energy beam that passes through the web. The sensing system identifies the difference as energy signatures for the web and/or a feature of the web, which may include but are not limited to: a) a perforation of the web; b) a seal of the web; c) a timing mark of the web; d) a skirt length of the web; or e) any part or dimension of the web ascertainable by measuring attenuation of the energy beam.

In another aspect of the present invention, a plastic bag manufacturing machine adapted to detect the existence and/or location of one or more features in the bag is disclosed. The machine includes a machine frame with one or more components for supporting and handling a plastic bag web, an energy source on the machine proximate the plastic bag web to project an energy beam onto the plastic bag web, and a sensor on the machine proximate the plastic bag web and the energy source to sense attenuation of the energy beam projected onto the plastic bag web from the energy source. In a preferred form, the energy source is a light source, the energy beam is a light beam and the light source is adjustable in intensity or frequency to be tuned to each specific plastic bag web or to filter out background light. The energy source may be positioned on the machine on one side of the plastic bag web and the sensor aligned with the energy source on the machine on an opposite side of the plastic bag web to sense at least a portion of the energy beam passing through the plastic bag web, or the energy source and the sensor may be positioned on the machine on one side of the plastic bag web so that the sensor is positioned relative the energy source and the plastic bag web on the machine on the one side to sense at least a portion of the energy beam reflected off of the plastic bag web.

A method of the present invention for detecting and measuring one or more features of a bag web is also disclosed. The method includes the steps of passing the bag web through a light from a light source, measuring attenuation of the light from the light source with an optical sensor, and identifying an optical signature as a function of attenuation for characterizing the bag web and/or its features. In a preferred form, the method includes the steps of: a) acquiring the optical signature from the optical sensor with a controller for comparing with a record describing what optical signatures should have been acquired; and, b) associating the line speed of the bag web with the record of detections for each optical signature for: i) confirming the presence of each feature of the bag web, ii) measuring one or more of the features of the bag web, and/or iii) determining false/positive readings from the optical sensor.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way.

FIG. 1 is a front elevation view of a plastic bag manufacturing machine of the prior art with the sensing system of the present invention.

FIG. 2 is a top view of the plastic bag web taken along line 2-2 in FIG. 1

FIG. 3A is a side view of the plastic bag web taken along line 3A-3A in FIG. 1.

FIG. 3B is another exemplary embodiment of the sensing system of the present invention shown in FIG. 3A.

FIG. 4 is a simplified electrical block diagram of the sensor system according to an exemplary embodiment of the present invention.

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