In a flat table drawing plotter, an image is drawn on the portion of a continuous work piece, e.g., a sheet of paper, located on a drawing table. Upon completion of the drawing of the image, a trace line is drawn at the rear end location of the image. The drawing carriage, having an optical detector means mounted thereon, is moved to the forward end of the table. The work piece is advanced with the optical detector means in continuous contact therewith. The advance of the work piece is stopped when the optical detector means detects the trace line. Then, the drawing carriage is slowly moved until the optical detector means again detects the trace line thereby identifying where the prior drawing of the image was completed. Drawing of the image is then recommenced.

An X, Y plotter particularly adapted to use both cut paper and strip paper. A driven roller provides motion of the paper back and forth according to one signal. A moveable pen block containing the pen is moved transverse the path of the paper in response to the second signal, thus providing controlled motion in the X and Y directions. According to one aspect, an idler roller is provided parallel to the driven roller around which an endless belt is disposed to be driven in combination with the drive roller by two pairs of rows of sprockets on the driven roller adapted to mate with holes provided therefor in the belt. Cut paper temporarily attached to the belt with drafting tape or the like is moved beneath the pen for plotting purposes. The inner row of sprockets is adapted for engaging holes in strip paper for moving it beneath the pen. According to another aspect, a pair of supply/takeup driven rollers are positioned with the driven roller therebetween with a single vacuum chamber divided into two compartments for receiving respective loops on either side of the driven roller. In the preferred embodiment, the two vacuum chamber portions are disposed such that the respective loops are substantially at right angles to one another.

A graphic recorder of the vacuum column buffer type has a pair of wells into which the two loops on the sheet material are drawn down. Top and bottom sensors are provided in each well for maintaining the loops within a predetermined range of movement; but in addition, the supply and take-up rolls are slaved to the speed of the drum. Cross-coupling is provided between the two wells to tend to equalize the vacuums therein.

A buffer system for isolating a supply of paper web from a processor operating on the paper web. The buffer system comprises a vacuum chamber and vacuum pump creating a pressure differential across a portion of the paper web forcing the web into the vacuum chamber in the form of a loop having suitable tension. The loop rises and falls within the vacuum chamber to either store or deliver web to the processor in response to the paper supply delivering more or less web than the processor can accommodate. In one embodiment, the vacuum chamber is provided with a movable wall to accommodate paper webs of different widths and a foot extending from the movable wall communicates with orifices to change the pressure differential.