Method and apparatus for wrapping a load using variable roller stretch

Abstract

A method and apparatus for wrapping the load at a desired wrap force are provided. The apparatus includes a dispenser for dispensing packaging material and means for providing relative rotation between the load and the dispenser. The dispenser has a prestretch portion and a post-stretch portion. The prestretch portion is configured to prestretch the packaging material within the dispenser to a point below the yield point of the packaging material. Preferably the packaging material is prestretched between first and second unpowered prestretch rollers. The post-stretch portion is configured to further stretch the prestretched packaging material to a point above the yield point of the packaging material as the packaging material moves from the dispenser to the load. Preferably, the post-stretch portion includes a friction element, such as a brake, to apply friction to one of the prestretch rollers.

What is claimed is:  
     
         1 . A method of wrapping a load, comprising: 
 placing a load on a load wrapping surface;    pulling a leading end of packaging material from a packaging material dispenser and attaching the leading end of packaging material to one of the load and the load wrapping surface;    providing relative rotation between the load and the packaging material dispenser to dispense the packaging material;    applying an initial force to prestretch the packaging material in the dispenser to a point below the packaging material yield point; and    applying a secondary force to further stretch the prestretched packaging material to a point above the yield point as the packaging material is applied to the load.    
     
     
         2 . The method of  claim 1 , wherein applying the initial force includes prestretching the packaging material to an elongation of between 30% and 60%.  
     
     
         3 . The method of  claim 1 , wherein applying the initial force includes prestretching the packaging material to an elongation of 30%.  
     
     
         4 . The method of  claim 1 , wherein applying the initial force includes prestretching the packaging material to an elongation of 45%.  
     
     
         5 . The method of  claim 1 , wherein applying the initial force includes prestretching the packaging material to an elongation of 60%.  
     
     
         6 . The method of  claim 1 , wherein applying the secondary force includes stretching the film to a total elongation of between 70% and 150%.  
     
     
         7 . The method of  claim 1 , wherein applying the secondary force includes stretching the film to a total elongation of 70%.  
     
     
         8 . The method of  claim 1 , wherein applying the secondary force includes stretching the film to a total elongation of 100%.  
     
     
         9 . The method of  claim 1 , wherein applying the secondary force includes stretching the film to a total elongation of 125%.  
     
     
         10 . The method of  claim 1 , wherein applying the secondary force includes stretching the film to a total elongation of 150%.  
     
     
         11 . The method of  claim 1 , wherein providing relative rotation includes actuating a turntable.  
     
     
         12 . The method of  claim 1 , wherein providing relative rotation includes rotating the dispenser around the load.  
     
     
         13 . The method of  claim 1 , wherein applying an initial force includes stretching the packaging material between first and second rollers.  
     
     
         14 . The method of  claim 1 , wherein applying a secondary force includes applying friction.  
     
     
         15 . The method of  claim 1 , wherein applying a secondary force includes applying a brake to a prestretch roller.  
     
     
         16 . The method of  claim 1 , wherein the initial force is less than the secondary force.  
     
     
         17 . A method of wrapping a load, comprising: 
 placing a load on a load wrapping surface;    pulling a leading end of film from a film dispenser and attaching the leading end of film to one of the load and the load wrapping surface;    providing relative rotation between the load and the dispenser to dispense the film;    as the film is dispensed, prestretching the film between two unpowered prestretch rollers in the dispenser to a point below the film yield point; and    applying friction to one of the two unpowered prestretch rollers to stretch the film between the load and the dispenser to a point above the yield point as the film is applied to the load.    
     
     
         18 . The method of  claim 17 , wherein providing relative rotation includes actuating a turntable.  
     
     
         19 . The method of  claim 17 , wherein providing relative rotation includes rotating the dispenser around the load.  
     
     
         20 . The method of  claim 17 , wherein applying friction includes applying a brake to one of the unpowered prestretch rollers.  
     
     
         21 . The method of  claim 17 , wherein prestretching the film includes prestretching the film to an elongation of between 30% and 60%.  
     
     
         22 . The method of  claim 17 , wherein prestretching the film includes prestretching the film to an elongation of 30%.  
     
     
         23 . The method of  claim 17 , wherein prestretching the film includes prestretching the film to an elongation of 45%.  
     
     
         24 . The method of  claim 17 , wherein prestretching the film includes prestretching the film to an elongation of 60%.  
     
     
         25 . The method of  claim 17 , wherein the film is stretched between the load and the dispenser to film to a total elongation of between 70% and 150%.  
     
     
         26 . The method of  claim 17 , wherein the film is stretched between the load and the dispenser to film to a total elongation of 70%.  
     
     
         27 . The method of  claim 17 , wherein the film is stretched between the load and the dispenser to film to a total elongation of 150%.  
     
     
         28 . The method of  claim 17 , wherein the film is stretched between the load and the dispenser to film to a total elongation of 100%.  
     
     
         29 . The method of  claim 17 , wherein the film is stretched between the load and the dispenser to film to a total elongation of 125%.  
     
     
         30 . The method of  claim 17 , further comprising releasing the friction to adjust the wrap force of the packaging material.  
     
     
         31 . The method of  claim 1 , further comprising ceasing application of the secondary force to adjust the wrap force of the packaging material.  
     
     
         32 . An apparatus for wrapping a load, comprising: 
 a dispenser for dispensing packaging material, the dispenser including: 
 a prestretch portion configured to prestretch the packaging material within the dispenser to a point below a yield point of the packaging material, and  
 a post stretch portion configured to further stretch the prestretched packaging material to a point above the yield point of the packaging material as the packaging material moves from the dispenser to the load; and  
 means for providing relative rotation between the load and the dispenser to wrap packaging material around the load.  
   
     
     
         33 . The apparatus of  claim 32 , wherein the means for providing relative rotation includes a turntable.  
     
     
         34 . The apparatus of  claim 32 , wherein the means for providing relative rotation includes a horizontal wrapping ring.  
     
     
         35 . The apparatus of  claim 32 , wherein the means for providing relative rotation includes an arm supporting the dispenser and configured to rotate around the load.  
     
     
         36 . The apparatus of  claim 32 , wherein the prestretch portion includes first and second unpowered prestretch rollers.  
     
     
         37 . The apparatus of  claim 36 , wherein the first and second prestretch rollers are connected to one another.  
     
     
         38 . The apparatus of  claim 32 , wherein the post-stretch portion includes a friction element.  
     
     
         39 . The apparatus of  claim 32 , wherein the post-stretch portion includes a brake.  
     
     
         40 . The apparatus of  claim 39 , wherein the brake is configured to apply friction to a portion of the prestretch portion.  
     
     
         41 . The apparatus of  claim 39 , wherein the post-stretch portion further includes a knob for adjusting tension of the brake.  
     
     
         42 . The apparatus of  claim 39 , wherein the brake is configured to apply friction to a prestretch roller in the prestretch portion of the dispenser.  
     
     
         43 . The apparatus of  claim 32 , wherein the prestretch portion is configured to be set at one of three levels of prestretch.  
     
     
         44 . The apparatus of  claim 43 , wherein the prestretch portion can be set for 30% prestretch, 45% prestretch, and 60% prestretch.  
     
     
         45 . The apparatus of  claim 43 , wherein the level of prestretch can be set by connecting first and second prestretch rollers.  
     
     
         46 . The apparatus of  claim 32 , wherein the post-stretch portion is configured to allow variation of the amount the prestretched packaging material is further stretched.  
     
     
         47 . The apparatus of  claim 46 , wherein the prestretched packaging material is further stretched to a total elongation of between 70% and 150%.  
     
     
         48 . The apparatus of  claim 46 , wherein the amount the prestretched packaging material is further stretched is varied by adjusting tension on a brake.  
     
     
         49 . The apparatus of  claim 32 , wherein the post-stretch portion is connected to a release lever to allow adjustment of wrap force on the load.  
     
     
         50 . An apparatus for wrapping a load, comprising: 
 a dispenser for dispensing packaging material, the dispenser including: 
 a prestretch portion having first and second unpowered rollers configured to stretch the packaging material between the rollers to a point below a yield point of the packaging material, and  
 a post stretch portion having an adjustable friction element configured apply friction to one of the first and second rollers to further stretch the prestretched packaging material to a point above the yield point of the packaging material as the packaging material moves from the dispenser to the load; and  
 means for providing relative rotation between the load and the dispenser to wrap packaging material around the load.  
   
     
     
         51 . The apparatus of  claim 50 , wherein the means for providing relative rotation includes a turntable.  
     
     
         52 . The apparatus of  claim 50 , wherein the means for providing relative rotation includes a horizontal wrapping ring.  
     
     
         53 . The apparatus of  claim 50 , wherein the means for providing relative rotation includes an arm supporting the dispenser and configured to rotate around the load.  
     
     
         54 . The apparatus of  claim 50 , wherein the first and second unpowered rollers are connected to one another.  
     
     
         55 . The apparatus of  claim 50 , wherein the adjustable friction element includes a brake.  
     
     
         56 . The apparatus of  claim 50 , wherein the prestretch portion is configured to be set at one of three levels of prestretch.  
     
     
         57 . The apparatus of  claim 56 , wherein the prestretch portion can be set for 30% prestretch, 45% prestretch, and 60% prestretch.  
     
     
         58 . The apparatus of  claim 56 , wherein the level of prestretch can be set by connecting first and second prestretch rollers.  
     
     
         59 . The apparatus of  claim 50 , wherein the prestretch portion is configured to be set at one of a high level of prestretch and a low level of prestretch.  
     
     
         60 . The apparatus of  claim 50 , wherein the post-stretch portion is configured to allow variation of the amount the prestretched packaging material is further stretched.  
     
     
         61 . The apparatus of claim  60 , wherein the prestretched packaging material is further stretched to a total elongation of between 70% and 150%.  
     
     
         62 . The apparatus of claim  60 , wherein the amount the prestretched packaging material is further stretched is varied by adjusting the friction element.  
     
     
         63 . The apparatus of  claim 50 , wherein the post-stretch portion is connected to a release lever to allow release of the friction element from the roller.