Tractor for engaging and advancing a web of paper

Claim 1

A tractor 10 for engaging and advancing a paper web 20 across the print station of a printer, said paper web 20 having spaced holes 21 along at least one edge thereof, said tractor 10 including a pair of generally planar side plates 12, 14 being spacially and parallely positioned, an elongated guide shoulder 32 defining a continuous guide surface 34 positioned between said side plates 12, 14 so as to define a guide channel 36 in cooperation with said guide plates 12, 14, a drive belt assembly 22 including a continuous belt 62 carrying a plurality of spaced drive members 38, said belt 62 having a plurality of spaced holes 63 with each of said drive members 38 located at selected ones of the holes on said belt 62 and adapted to engage the holes 21 along the edge of said paper web 20, a drive sprocket 33 defining a generally circular shape and rotatably positioned between said side plates 12, 14 and located at one end of said elongated shoulder 32, the surface of said drive sprocket 33 being adapted to releasably engage said drive members 38 so as to provide linear movement to the belt 62 as the drive sprocket 33 is rotated, said guide channel 36 and said drive sprocket 33 defining a continuous path for said drive belt assembly 22, CHARACTERIZED BY: each of said drive members 38 having a substantially hemicylindrically shaped base 64, the longitudinal axis of the base 64 is oriented transverse to the direction of travel of the belt 62, the longitudinal edges of said hemicylindrical base 64 being relieved 68, 68a to allow the belt 62 to conform to the curved contour of the drive sprocket 33 and the guide channel 36 as the base 64 of the drive members 38 are engaged by the drive sprocket 33 and the drive belt assembly 22 is thereby moved along the guide channel 36.