Numerous systems exist in which vacuum or forced air must be distributed to various portions of the surface of a rotating member. For example, some systems require vacuum to be selectively applied through apertures at selected circumferential locations on a rotating roll in order to hold material to the roll for a desired time or along a desired path. Other systems may require air to be forced out of similar ports to manipulate material being processed. In still other applications, the distribution of vacuum or forced air to various portions of a rotating roll is necessary to retract, extend, engage, or otherwise actuate elements or assemblies upon the roll (e.g., retractable cutoff or perforation blade assemblies, retractable anvil blade assemblies, and the like). The following discussion is with reference only to a rotating cutoff roll having alternating longitudinal rows of vacuum ports and cutoff blades for making regularly-spaced cuts in a web of material passing the roll. Vacuum supplied through the vacuum ports holds the web of material to the cutoff roll during cutting operations and until the cut material is released to downstream equipment. However, it should be noted that the following discussion applies equally to the other types of rotating members such as those mentioned above. As used herein and in the appended claims, the term "web" means any material (including without limitation paper, metal, plastic, rubber or synthetic material, fabric, etc.) which can be or is found in sheet form (including without limitation tissue, paper toweling, napkins, foils, wapping paper, food wrap, woven and non-woven cloth or textiles, etc.). The term "web" does not indicate or imply any particular shape, size, length, width, or thickness of the material.
Conventional vacuum cutoff systems suffer from several disadvantages. First, many conventional systems typically can cut material only at set cut lengths. Therefore, to produce several different cut lengths, it is necessary to reconfigure the cutoff roll and system each time the cut length is changed. Even if such a process can be performed on the system at hand, the process is burdensome, time-consuming, and expensive, and usually cannot be performed on conventional systems without stopping the machinery, clearing product from the machinery, reconfiguring the blade arrangement, and then restarting the machinery. Otherwise, a different system must be purchased to run the different cut lengths desired--a clearly expensive and inefficient alternative. Furthermore, these machines require a significant amount of factory floor space. In light of the above, a significant investment in worker time and machinery and/or factory floor space is often required to provide machinery capable of cutting different lengths of material.
Another disadvantage of many conventional cutoff roll systems involves the manner in which vacuum or forced air is supplied to the cutoff roll. As mentioned above, existing cutoff rolls typically have a number of blades separated by a number of vacuum apertures between the blades. Regardless of the number and spacing of the blades upon the cutoff roll, vacuum supplied to the apertures therefore is sufficient to hold web material to the surface of the cutoff roll before, during, and/or after web cutting operations. Unfortunately however, such cutoff rolls require relatively large vacuum systems due to the large number of vacuum apertures. If a smaller vacuum system is desired, selected vacuum apertures need to be taped or otherwise covered or shut. Covering or shutting vacuum apertures is a tedious, time-consuming, and expensive process typically requiring system shutdown.
Furthermore, many cutoff roll systems repeatedly use a first cutoff blade located at, for example, a zero degrees position on the cutoff roll, along with a number of other blades located at specific cut lengths and corresponding angular positions from the first blade. The first blade is typically used in all cuts, while the other blades in the system are used periodically, depending upon the cut length. Thus, the first blade is subject to significantly more wear than the other blades in the system and requires frequent maintenance and/or replacement.
Conventional cutoff roll systems have minimal to no ability to easily control which vacuum holes on the cutoff roll are covered or shut and which are open, and which blades on the cutoff roll are extended and which are retracted. Even where such control does exist, conventional system users do not have the ability to quickly and easily select one of a number of extended cutoff blade patterns and one of a number of open vacuum aperture patterns. Therefore, conventional systems are largely unable to prevent excessive blade wear and/or to provide a large amount of web control without a using a relatively large vacuum system.
In light of the problems and limitations of the prior art described above, a need exists for a cutoff roll which can produce cut lengths of web material while avoiding uneven wear distribution between the various blades on the cutoff roll, which can be quickly and easily controlled to change the locations of extended blades and to open vacuum apertures on the cutoff roll without requiring significant machine downtime and manual changes to the system, which provides superior control of vacuum apertures and extended blade positions, and which requires a relatively small vacuum system to operate. Each preferred embodiment of the present invention achieves one or more of these results.