CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the U.S. National Phase under 35 U.S.C. § 371 of International Patent Application No. PCT/EP2019/061145, filed on May 1, 2019, which in turn claims the benefit of Denmark Patent Application No. PA201870262, filed on May 2, 2018 the entire disclosures of which Applications are incorporated by reference herein for all purposes.

FIELD OF THE INVENTION

The present invention relates to a cutting apparatus for the manufacturing of bags, wherein e.g., a thermoplastic film or other suitable material film, such as film coated paper/foils or of a biodegradable material, is passed between two rotary rollers for making cuts through the film, of the type including an apparatus frame and a cutting station with a rotary anvil mounted to a first frame structure and a rotary cutting die including a rotatable cylindrical shaft carrying a die blade disposed adjacent to the rotary anvil mounted to a second frame structure. The first frame structure or the second frame structure preferably is stationary relative to the apparatus frame, and may even be a part thereof, one of the frame structures being movably supported by the apparatus frame to allow it to be moved towards the other.

BACKGROUND

In one common method for manufacturing plastic bags, an elongated web in the form of a collapsed tube of a thermoplastic film is run in a longitudinal machine direction. The collapsed tube proceeds to a heat sealing station and a cutting station that, respectively, form parallel transverse heat seals at bag-length distances apart and transverse perforation lines defining lines of weakness for individualization of the plastic bags by an end-user, as wells as cut-outs for the purpose of forming a pair of handles in each of the plastic bags, see e.g., WO 00/23264.

An example of a cutting apparatus with such a cutting station includes a rotary cylindrical anvil and a rotary cutting die mounted parallel and adjacent to each other. The rotary cutting die includes a cylindrical shaft and a die blade mounted around the surface of the shaft. As the thermoplastic film passes between the rotary anvil and the rotary cutting die, the die blade of the rotating cutting die contacts and cuts through the plastic material, thereby creating perforations/cuts, see U.S. Pat. No. 5,935,367.

In use of such a cutting apparatus, the die blade is continuously worn, requiring adjustments to ensure the distance between the anvil and the cutting die remains essentially the same, up until the point where the die blade eventually must be replaced. To this end, an adjustment mechanism is provided.

It is, however, a problem that the prior art adjustment mechanisms only allow the operator to carry out a rough adjustment of the distance between the anvil relative and the cutting die; hence, either a substantial over- or under-compensation for wear may result.

SUMMARY

The present invention provides a cutting apparatus with an improved adjustment mechanism whereby an operator may reduce over- or under-compensation for wear by being able to finely adjust the distance between the anvil and the cutting die, when applying—either through a motor or manually—a relatively large control input to the mechanism. In addition, adjustments may conveniently be carried out while the apparatus is running, i.e., when the anvil/cutting die is rotating and processing the film.

More specifically, the aforementioned problems are solved through the use of an adjustment mechanism including a rotatable spindle having a first threaded portion and a second threaded portion, the pitch of the first threaded portion being different, i.e., larger or smaller, from the pitch of the second threaded portion, the first threaded portion engaging a threaded portion of the first or said second frame structure and the second threaded portion engaging a threaded portion of the apparatus frame. This allows fine adjustments, by moving the movable frame structure, of the position of the anvil or the cutter relative to the apparatus frame and, hence, of the distance between the anvil and the cutter die as the die blade is worn. The pitch is the distance along the axis of the spindle that is covered by one complete rotation of the spindle (360°). The adjustment made by the mechanism may of course also be so as to position the anvil in the start position.

Based on a knowledge of die blade wear stored in a computer memory, a motor driving the spindle may perform adjustments automatically from the point a new die blade is put into operation until it must finally be replaced; automated adjustments may also be carried out on the basis of measured machine temperature or other process parameters.

Embodiments of the invention are defined in the appended claims.

In one embodiment, the first frame structure carrying the anvil, or the second frame structure carrying the cutting die, is pivotally connected to the apparatus frame, the other frame structure being fixed relatively to the apparatus frame.

In another embodiment, a spring connected with the apparatus frame supports the first frame structure or the second frame structure. This spring prevents or limits undesired movements resulting from any play, such as within the hinge pivotally coupling the frame structure to the apparatus frame or within the adjustment mechanism proper, whereby the anvil is maintained as close to the cutting die as allowed for by the adjustment mechanism, which balances the force applied by the spring.

Preferably, the mechanism additionally comprises in one embodiment a first part including a motor, the spindle being directly or indirectly driven for rotation by the motor, the threaded portions being arranged next to each other, possibly spaced apart, along the length of the spindle, the second threaded portion being closer to the motor and optionally/preferably having the larger thread pitch, and a second part comprising two internally threaded structures, preferably nuts, engaging a respective one of the threaded portions of the spindle and being fixed against rotation to the first frame structure or to the second frame structure, and to the apparatus frame, respectively, the first threaded portion being distal from the motor and optionally/preferably having the smaller thread pitch. This allows for a construction that may be easily assembled while permitting motor controlled adjustments, with the ability to finely adjust the distance between the anvil and die cutter even with a large motor input rotating the spindle.

In yet another embodiment the spindle comprises a tubular wall, the first threaded portion being formed on the outside thereof and the second threaded portion being formed on the inside thereof, the threaded portion of the first or said second frame structure being internally threaded and the threaded portion of the apparatus frame being externally threaded, the spindle preferably including a manually engageable portion for rotation thereof and the first (outside) threaded portion preferably having a larger thread pitch compared to the thread pitch of the second threaded portion.

