Abstract Apparatus and method of cyclic or intermittent feeding and unwinding of sheet material includes a pneumatic motor that drives the rotary web roll support and a brake that serves to stall out the motor when the predetermined length of material has been unwound. Draw means is provided to draw the predetermined length of film in a manufacturing process, such as packaging, with a slack loop being formed between the draw means and the web roll. The pneumatic motor is preferably a cylinder and rack combination with a drive stroke producing a capability greater than said predetermined length with the brake stalling out the motor at the end of the stroke to assure proper feed during each cycle and to maintain the tension in the web at a minimum and substantially constant during the complete operation. The slack loop is formed by a dancer assembly with linkage means comprising a cam and leaf spring applying the brake in a progressive manner only during the final moments of unwinding of the material. The dancer assembly desirably has insufficient pulling or tensioning power to pull film from the web roll so that complete reliance for feeding is put on the positive drive. The drive means and the draw means are operated at mutually exclusive times and are coordinated by first and second valves that actuate the drive means as the draw means are withdrawn to complete the drawing step.
The method of cyclic or intermittent feeding and unwinding of sheet material from a web roll comprising the steps of intermittently drawing a predetermined length of sheet material of said web roll supported on spaced support rollers, intermittently directly driving said web roll through said support rollers to the final turn of said roll to unwind a predetermined length of material substantially equal to that drawn and concurrently forming a slack loop between said web roll and said draw means varying from a minimum to a maximum slack loop, said direct driving step being initiated and performed substantially independently of the tension in said web, whereby the tension in said web remains at a minimum and substantially constant as determined by the formation of said slack loop and the duration of the driving step is substantially the same during each cycle regardless of the diameter of the web roll.
Claim 2
Independent Claim
149 words
The method of cyclic or intermittent feeding and unwinding of sheet material from a web roll comprising the steps of intermittently drawing a predetermined length of sheet material of said web roll supported on spaced support rollers, intermittently directly driving said web roll through said support rollers to the final turn of said roll to unwind a predetermined length of material substantially equal to that drawn and concurrently forming a slack loop between said web roll and said draw means varying from a minimum to a maximum slack loop, said direct driving step being initiated and performed substantially independently of the tension in said web, whereby the tension in said web remains at a minimum and substantially constant as determined by the formation of said slack loop and the duration of the driving step is substantially the same during each cycle regardless of the diameter of the web roll.
Claim 3
Dependent Claim
32 words
The method of feeding and unwinding of claim 1 wherein the drawing step anD the driving step are at different times and the driving step is terminated prior to said drawing step.
Claim 4
Dependent Claim
23 words
The method of feeding and unwinding of claim 2 wherein the driving step is commenced concurrently with the completion of the drawing step.
Claim 5
Dependent Claim
42 words
The method of feeding and unwinding of claim 1 wherein said driving step lasts longer than necessary to produce the predetermined length of material and braking is applied with respect to said roll to override said driving to produce said predetermined length.
Claim 6
Dependent Claim
33 words
The method of feeding and unwinding of claim 1 wherein tension is placed on said web in said slack loop that is limited to a value insufficient to unwind said material by itself.
Claim 7
Dependent Claim
33 words
The method of claim 1 wherein said maximum slack loop is provided at the start of the drawing step and the minimum slack loop is provided at the start of said driving step.
Claim 8
Dependent Claim
48 words
The method of claim 1 wherein is provided a progressive braking of said web roll only during the final moments of unwinding, whereby free rotation at other times allows minimum tension, and progressively reducing said tension further during braking to avoid stretching of said material during down time.