Feedback controlled stretch wrapping apparatus and process

Claim 1

An apparatus for making a unitary package using a web of stretchable plastic material to form an overwrap, comprising a frame, plastic material dispensing means mounted to said frame, drive means to provide relative rotation between said load and said material dispensing means thereby to pull said plastic material from said material dispensing means and wrap said load, material elongation means positioned between said dispensing means and said load, said material elongation means comprising at least a rotating upstream roller and a rotating downstream roller to receive said plastic material and elongate said plastic material pulled across said rollers to wrap said load, and material elongating control means connected to said material elongation means and comprising means to determine and apply a restraint force on said upstream roller, to determine actual elongation of said material by sensing speeds of said rollers in said material elongation means, and to vary said restraint force to maintain elongation of said material within said material elonation means substantially at an infinitely variable predetermined constant elongation level, and means to apply to and sense at said downstream roller a power assistance force and means to vary said power assistance force so that said varied restraint force less said varied power assistance force, which equal wrapping force on said load, is maintained substantially at an infinitely variable predetermined constant force level.

Claim 2

An apparatus for making a unitary package using a web of stretchable plastic material to form an overwrap, comprising a frame, plastic material dispensing means mounted to said frame, drive means to provide relative rotation between said load and said material dispensing means thereby to pull said plastic material from said material dispensing means and wrap said load, material elongation means positioned between said dispensing means and said load, said material elongation means comprising at least a rotating upstream roller and a rotating downstream roller to receive said plastic material and elongate said plastic material pulled across said rollers to wrap said load, and material elongating control means connected to said material elongation means and comprising means to determine and apply a restraint force on said upstream roller, to determine actual elongation of said material by sensing speeds of said rollers in said material elongation means, and to vary said restraint force to maintain elongation of said material within said material elonation means substantially at an infinitely variable predetermined constant elongation level, and means to apply to and sense at said downstream roller a power assistance force and means to vary said power assistance force so that said varied restraint force less said varied power assistance force, which equal wrapping force on said load, is maintained substantially at an infinitely variable predetermined constant force level.

Claim 14

An apparatus for making a unitary package from a load using a single web of stretchable plastic material to form an overwrap, comprising a frame, a dispenser means mounted to said frame, said dispenser means being adapted to hold and dispense a roll of stretchable material, a rotatable turntable adapted to receive and support a load located adjacent to said frame, drive means connected to said turntable and adapted to rotate said turntable and said load placed on said turntable, elongation means connected to said frame adapted to receive stretchable material pulled from said dispenser means by rotation of said load and elongate the material beyond its yield point, said elongation means comprising at least an upstream roller and a downstream roller spaced apart and rotated by the material pulled from the dispenser means by rotation of the turntable, a brake coupled to said upstream roller applying a variable restraining force to said upstream roller so that the downstream roller transports the material faster than the upstream roller, powered torque means connected to said downstream roller to apply a variable positive force to said downstream roller, regulatory means coupled to said upstream and downstream rollers to calculate an actual elongation ratio of said material by sensing speeds of said upstream and downstream rollers, said regulatory means having means to determine said restraining force from the sensed speeds of the rollers, to sense said positive force and to determine the actual force on the load by calculation the difference between said restraining force and said positive force, said regulatory means having means for varying said restraining force of the brake to restrain said material and maintain actual elongation ratio between said rollers substantially equal to a predetermined constant ratio, and means for varying said positive force of the powered torque means so that the difference between the varied restraining force of the brake and the varied positive force of the powered torque means and therefore the actual force on the load is maintained substantially equal to a predetermined constant level less than force exerted on the material between the upstream and downstream rollers.

Claim 15

An apparatus for making a unitary package from a load using a single web of stretchable plastic material to form an overwrap, comprising a frame, a dispenser means mounted to said frame, said dispenser means being adapted to hold and dispense a roll of stretchable material, a rotatable turntable adapted to receive and support a load located adjacent to said frame, drive means connected to said turntable and adapted to rotate said turntable and said load placed on said turntable, elongation means connected to said frame adapted to receive stretchable material pulled from said dispenser means by rotation of said load and elongate the material beyond its yield point, said elongation means comprising at least an upstream roller and a downstream roller spaced apart and rotated by the material pulled from the dispenser means by rotation of the turntable, a brake coupled to said upstream roller applying a variable restraining force to said upstream roller so that the downstream roller transports the material faster than the upstream roller, powered torque means connected to said downstream roller to apply a variable positive force to said downstream roller, regulatory means coupled to said upstream and downstream rollers to calculate an actual elongation ratio of said material by sensing speeds of said upstream and downstream rollers, said regulatory means having means to determine said restraining force from the sensed speeds of the rollers, to sense said positive force and to determine the actual force on the load by calculation the difference between said restraining force and said positive force, said regulatory means having means for varying said restraining force of the brake to restrain said material and maintain actual elongation ratio between said rollers substantially equal to a predetermined constant ratio, and means for varying said positive force of the powered torque means so that the difference between the varied restraining force of the brake and the varied positive force of the powered torque means and therefore the actual force on the load is maintained substantially equal to a predetermined constant level less than force exerted on the material between the upstream and downstream rollers.

Claim 28

An apparatus for making a unitary package by wrapping a load with a web of stretchable plastic material, comprising a frame, a stretchable plastic material dispenser mounted to said frame, prestretching means connected to said frame, said prestretching means comprising an upstream roller and a downstream roller, a restraint means applying a restraint force F 1 to said upstream roller and a power assistance means applying a positive force F T to said downstream roller to stretch a film web drawn from said material dispenser substantially above the yield point of said web, turntable means positioned adjacent said frame to support and rotate a load, said web being drawn from said dispenser through said prestretching means and around said load by rotation of said turntable means, first feedback means coupled to said prestretching means to sense the speed V 1 of said upstream roller and the speed V 2 of said downstream roller and restrain the upstream roller and its resultant V 1 by determining and applying F 1 through said restraint means so that (V 2 -V 1 )/V 1 becomes equal to a predetermined constant elongation ratio, and second feedback means coupled to said prestretching means to sense said F T on said downstream roller and adjust F T through said power assistance means so that said varied F 1 less said varied F T becomes equal to a predetermined constant force on the load.

Claim 29

An apparatus for making a unitary package by wrapping a load with a web of stretchable plastic material, comprising a frame, a stretchable plastic material dispenser mounted to said frame, prestretching means connected to said frame, said prestretching means comprising an upstream roller and a downstream roller, a restraint means applying a restraint force F 1 to said upstream roller and a power assistance means applying a positive force F T to said downstream roller to stretch a film web drawn from said material dispenser substantially above the yield point of said web, turntable means positioned adjacent said frame to support and rotate a load, said web being drawn from said dispenser through said prestretching means and around said load by rotation of said turntable means, first feedback means coupled to said prestretching means to sense the speed V 1 of said upstream roller and the speed V 2 of said downstream roller and restrain the upstream roller and its resultant V 1 by determining and applying F 1 through said restraint means so that (V 2 -V 1 )/V 1 becomes equal to a predetermined constant elongation ratio, and second feedback means coupled to said prestretching means to sense said F T on said downstream roller and adjust F T through said power assistance means so that said varied F 1 less said varied F T becomes equal to a predetermined constant force on the load.