Apparatus for maintaining uniform paper tension in a graphical recording device

Claim 1

A graphical recording device of the type having main recording paper drive means for bidirectionally driving folded recording paper through said device where said folded recording paper has folds extending transversely to the direction of driving of the folded recording paper, a pair of spaced rotatable main drive sprockets connected to said drive means for engaging and driving the folded recording paper, a movable recording pen traversable between said drive sprockets, a chamber located below said drive sprockets approximately equal in width to the spacing between said drive sprockets and extending, at least, past either side of said drive sprockets, low pressure inducing means mounted in said chamber for drawing said folded recording paper uniformly over its entire width into said chamber, a plurality of level sensors mounted in said chamber for sensing the level reached by said folded recording paper in said chamber and further comprising: a. a platen disposed beneath said recording pen and between said rotatable drive sprockets for carrying the folded recording paper; b. a pair of recording paper support tubes, one each of said tubes disposed on opposite sides of the platen for carrying the folded recording paper to impend the recording paper into the chamber between each support tube and the platen; c. a plurality of tension sprockets fixedly mounted on each end of each of said support tubes for engaging and driving the folded recording paper; d. first servo means responsive to at least one of said level sensors and connected to at least one of said tension sprockets to rotatably drive one of said support tubes so that said folded recording paper reaches a predetermined level in said chamber between said driven support tube and said platen; e. second servo means responsive to at least one of said level sensors and connected to at least one other of said tension sprockets to rotatably drive the other of said support tubes so that said folded recording paper reaches a predetermined level in said chamber between said last mentioned driven support tube and said platen whereby actuation of said low pressure inducing means will uniformly tension said folded recording paper across its entire width about said platen and said support tubes irrespective of movement of said main drive sprockets; and f. a pair of roller assemblies, one each for engaging a first surface of the folded recording paper and disposed to urge engagement of the opposite surface of the folded recording paper with the tension sprockets of each respective support tube, each roller assembly disposed on a side of each respective recording paper support tube generally farthest from the platen disposed between the pair of recording paper support tube.