Method and apparatus for metered pre-stretch film delivery

Abstract

The present invention provides a method and apparatus for dispensing a predetermined substantially constant length of pre-stretched packaging material based upon load girth. Based upon the girth of the load to be wrapped, an amount of pre-stretched packaging material to be dispensed for each revolution of relative rotation between a packaging material dispenser and the load is determined. A rotational drive system used to provide the relative rotation is linked to a pre-stretch assembly portion of the packaging material dispenser. The linkage may be mechanical or electrical. The linkage controls a ratio of the rotational speed to the pre-stretch assembly dispensing speed, such that the predetermined substantially constant length of pre-stretched packaging material is dispensed for each revolution of the packaging material dispenser relative to the load regardless of the speed of the rotational drive. In the case of a mechanical linkage, the linkage also connects the rotational drive to the pre-stretch assembly portion such that the rotational drive also drives the pre-stretch assembly portion.

Description

[0001] This application claims priority under 35 U.S.C. §119 based on U.S. Provisional Application No. 60 / 775,779, filed Feb. 23, 2006, the complete disclosure of which is incorporated herein by reference.FIELD OF THE INVENTION [0002] The present invention relates to an apparatus and a method for wrapping a load with packaging material, and more particularly, stretch wrapping. BACKGROUND OF THE INVENTION [0003] Various packaging techniques have been used to build a load of unit products and subsequently wrap them for transportation, storage, containment and stabilization, protection and waterproofing. One system uses stretch wrapping machines to stretch, dispense and wrap stretch packaging material around a load. Stretch wrapping can be performed as an inline, automated packaging technique that dispenses and wraps packaging material in a stretch condition around a load on a pallet to cover and contain the load. Pallet stretch wrapping, whether accomplished by a turntable, rotating a...

AI Technical Summary

Benefits of technology

[0030] According to yet another aspect of the present invention, an apparatus for stretch wrapping a load includes a packaging material dispenser for dispensing a film web, the packaging material dispenser including an upstream pre-stretch roller and a downstream pre-stretch roller within a powered pre-stretch assembly, a rotational drive system providing relative rotation between the load and the dispenser during the wrapping cycle, an electronic control configured to maintain a predetermined ratio between a drive powering the pre-stretch portion and the rotational drive system during a primary portion of a wrap cycle, wherein the electronic control is configured to vary the predetermined ratio during at least one of initial acceleration and final deceleration of the wrap cycle, and a final roller positioned a predetermined distance from the downstream pre-stretch roller, the predetermined distance being such that at least a portion of a length of film extending between the downstream pre-stretch roller and the final roller acts to dampen variations in forces acting on the pre-stretched packaging material as it travels from the dispenser to the load.

[0032] According to another aspect of the present invention, a method for stretch wrapping a load includes providing relative rotation between the packaging material dispenser and the load, setting a ratio of relative rotational speed to pre-stretch speed, electronically maintaining the set ratio during a primary portion of the wrap cycle to dispense the predetermined substantially constant length of pre-stretched packaging material during each revolution of the packaging material dispenser relative to the load during the primary portion of the wrap cycle, electronically varying the set ratio upon sensing at least one of a film break and slack film, and damping variations in forces acting on the dispensed predetermined constant length of pre-stretched packaging material as it travels from the dispenser to the load.

Problems solved by technology

Historically, rotating ring style wrappers have suffered from excessive packaging material breaks and limitations on the amount of containment force applied to the load (as determined in part by the amount of pre-stretch used) due to erratic speed changes required to wrap “non-square” loads, such as narrow, tall loads, short, wide loads, and short, narrow loads.

The non-square shape of such loads often results in the supply of excess packaging material during the wrapping cycle, during time periods in which the demand rate for packaging material by the load is exceeded by the supply rate of the packaging material by the packaging material dispenser.

This leads to loosely wrapped loads.

In addition, when the demand rate for packaging material by the load is greater than the supply rate of the packaging material by the packaging material dispenser, breakage of the packaging material may occur.

However, when variations in the demand rate are large, fluctuations between the feed and demand rates result in loose packaging of the load or breakage of the packaging material during wrapping.

With the ever faster wrapping rates demanded by the industry, the rotation speeds have increased significantly to a point where the concept of sensing demand change and altering supply speed is no longer effective.

Use of high speed wrapping has therefore been limited to relatively lower wrap forces and pre-stretch levels where the loss of control at high speeds does not produce undesirable packaging material breaks.

Packaging material dispensers mounted on horizontally rotating rings present additional special issues concerning effectively wrapping at high speeds.

All of these devices suffer complexity, cost and maintenance issues.

But even more importantly they add significant weight to the rotating ring which impacts its ability to accelerate and / or decelerate rapidly.

Packaging material dispensers mounted on vertically rotating rings have the additional problem of gravity forces added to centrifugal forces of high-speed rotation.

High-speed wrappers have therefore required expensive and very heavy two part bearings to support the packaging material dispensers.

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