Unit load wrapping with uniform wrap tension along the periphery of the wrapped load

Claim 1

In an apparatus of the type which wraps a unit load, at a wrapping station, with a resiliently stretchable film wrap advanced along a feed path from a supply of such film wrap to the wrapping station, with the film wrap tensioned to a desired tension, by advancing the unit load along a path of travel into a curtain of said film wrap extending laterally across the path of travel from one side to the other side thereof and closing said film wrap behind the unit load to complete a sleeve of said film wrap around the unit load, the unit load having a given lateral width between longitudinal sides, an improvement for attaining essentially uniform tension in the completed sleeve, said improvement comprising: opposed jaws located at the sides of the path of travel and juxtaposed with the curtain, the jaws being spaced apart a distance greater than the width of the unit load; jaw-moving means for moving at least one of the opposed jaws toward the other of the opposed jaws at a rate of movement to close the film wrap behind the unit load, the movement of said one jaw being from an initial position spaced away from the corresponding side of the unit load to an intermediate position juxtaposed in generally longitudinal alignment with said corresponding side of the unit load and thence into engagement with the other of the jaws at a closed position behind the unit load; Position detecting means for detecting the position of at least said one of the opposed jaws relative to the unit load during said movement of said one jaw for determining the location of the one jaw at said intermediate position; and feed means for advancing the film wrap at a first rate of advancement relative to the rate of movement of the one jaw during movement of said one jaw from the initial position to the intermediate position and responsive to the position detecting means for advancing the film wrap at a second rate of advancement in response to the location of said one jaw at the intermediate position, as determined by the position detecting means, which second rate of advancement, relative to the rate of movement of the one jaw, is greater than the first rate of advancement during movement of said one jaw from the intermediate position to the closed position.