Demand throttle methods and apparatuses

Abstract

An apparatus for wrapping a load with packaging material may include a packaging material dispenser for dispensing packaging material. The apparatus may also include a relative rotation assembly for providing relative rotation between the load and the packaging material dispenser. The apparatus may further include a mechanical connection operatively coupling the packaging material dispenser to the relative rotation assembly. The relative rotation assembly may be configured to drive the packaging material dispenser through the mechanical connection. The apparatus may further include a force exerting mechanism operatively coupled to the mechanical connection. The apparatus may further include a sensing element configured sense a characteristic of dispensed packaging material. The sensing element may be operatively coupled to the mechanical connection. The force exerting mechanism and the sensing element may be configured to control the mechanical connection to maintain a selected ratio of packaging material dispensed to demand for packaging material at the load for at least a portion of a wrap cycle.

Description

[0001]This application claims priority under 35 U.S.C. §119 based on U.S. Provisional Application No. 61 / 297,709, filed Jan. 22, 2010, the complete disclosure of which is incorporated herein by reference.TECHNICAL FIELD[0002]The present disclosure relates to methods and apparatuses for wrapping a load with packaging material, and more particularly, stretch wrapping.BACKGROUND[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 wrapping machines to stretch, dispense, and wrap packaging material around a load. The packaging material may be pre-stretched before it is applied to the load. 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. Stretch wrapping, whether accomplished by a turn...

AI Technical Summary

Benefits of technology

[0018]By controlling the mechanical connection operatively coupling the rotational drive system and the packaging material dispenser based at least in part on the instantaneous demand, adjustments can be made in response to the variations described above. By making such adjustments, it may be possible to reduce costs by decreasing the likelihood of film breaks and ensuring that excess packaging material is not dispensed; wrap a wide variety of loads regardless of shape and / or size, or placement on a load wrapping surface; and improve throughput by allowing adjustments to settings to be made automatically. It may also be possible to obtain a more consistently wrapped load, since a selected payout percentage may be maintained for at least a portion of a wrapping cycle, and / or from one wrapping cycle to the next.

Problems solved by technology

Historically, wrappers have suffered from packaging material breaks and limitations on the amount of 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.

Variations in demand may make it difficult to properly wrap the load.

The problem with variations is exacerbated when wrapping a load having one or more dimensions that may differ from one or more corresponding dimensions of a preceding load.

The problem may also be exacerbated when wrapping a load having one or more dimensions that vary at one or more locations of the load itself.

With the ever faster wrapping rates demanded by the industry, the rotation speeds have increased significantly to a point where the concept of sensing changes in force and altering supply speed in response loses effectiveness.

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 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 vertical rotating rings have the additional problem of gravity forces added to centrifugal forces of high-speed rotation.

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