as shown in fig1 the ink jet printer includes a rotatable imaging drum , generally indicated at 2 , that is driven by a stepping motor 3 . an ink jet printing head assembly 4 is mounted for longitudinal movement along tracks 5 and 5a . the imaging paper or other sheet material 6 envelopes the outer surface of the drum 2 during the imaging process and , at its conclusion , is ejected across a cutter bar 7 where it is sheared by a cutter mechanism , generally indicated at 8 . the term &# 34 ; sheet material &# 34 ; as used in this application includes the various flexible media on which images can be recorded , such as paper , transparencies and photographic materials , which are supplied in long lengths . while the drum 2 rotates , the print head 4 moves longitudinally along the drum 2 tracing a spiral path on the paper 6 to produce the desired image . during the imaging process , it is necessary that the ejecting orifices of the print head 4 remain a fixed distance , in this example about 30 mils , from the surface of the paper . if the paper is not maintained snugly against the surface of the drum 2 , poor imaging will result . as the completed image is ejected , a length of unused paper is simultaneously drawn from the interior of the drum 2 and positioned around the outside of the drum . as illustrated diagrammatically in fig2 and 4 , the rotatable drum 2 supports within it a rotatably mounted spool , generally indicated at 9 , that carries a roll of paper 6 . the drum 2 also carries three rollers : an idler roller 10 , a tension roller 12 , and a drive roller 14 . the path of the paper around and between these rollers is illustrated in fig3 and 4 where the rollers 10 , 12 and 14 have been spaced apart only for the purpose of illustration . the paper 6 from the spool 9 passes between the drive roller 14 and the tension roller 12 , as illustrated by the arrow 16 , partially around roller 12 and then around the outer circumference of the drum 2 . after passing around the surface of the drum 2 , the paper passes between the idler roller 10 and the drive roller 14 , partially around the inner surface of the roller 14 and then between the rollers 12 and 14 where one surface of the paper engages the roller 14 and the other surface engages the length of paper already between the same pair of rollers . a short stub 18 ( fig3 ) of paper extends from between the rollers 12 and 14 . if the paper is allowed to remain without tensioning , the intermittent separation of the paper from the surface of the drum 2 will interfere with the proper functioning of the print head 4 . as will be described later , the tension is produced by reverse rotation of the tensioning roller 12 while the drive roller 14 is locked in position . when the tensioning is complete , the rollers 12 and 14 are locked in position . the imaging process is then performed to produce an image on the surface of the paper 6 on the drum . when the imaging is completed , the drum is stopped at a predetermined rotary position and a drive mechanism , to be described later , is connected to the roller 12 . to eject the imaged paper , the rollers 12 and 14 are driven in the directions indicated by the arrows 22 and 24 in fig3 . this action causes additional paper to be drawn from the spool 9 and travel around the drum while the rollers 12 and 14 eject the imaged paper . when a sufficient length of paper has been ejected , the imaged portion of the paper extends beyond the cutter mechanism 8 ( fig4 ), which may be located some distance from the drum 2 . the length of the paper ejected may be measured by any appropriate mechanism such as by the rotation of a disk 25 ( fig5 ) that is secured to and rotates with the idler roller 10 . the disk 25 has radial non - reflecting stripes that are detected and counted by an infrared detector 27 . the paper is then sheared by the cutter mechanism 8 to separate the imaged portion . at this time , a length of paper extends from the drum 2 to the cutter bar 7 . the drive mechanism is arranged to drive the rollers 12 and 14 in the directions indicated by the arrows 28 and 32 in fig4 . this action draws the paper back between the rollers 12 and 14 , partially around the surface of roller 14 , between roller 14 and the idler roller 10 , around the outer surface of the drum 2 , and again between the rollers 12 and 14 into the interior of the drum . this motion is continued until the paper is withdrawn to again leave the short stub 18 projecting from between rollers 13 and 14 as measured by reverse rotation of the disk 25 . as state above , during the imaging process , it is of critical importance that the paper 6 be in close contact with the surface of the drum 2 . this is achieved by locking the roller 14 and driving the tensioning roller 12 in the direction indicated by the arrow 32 in fig4 . the driving surfaces of the rollers 12 and 14 , which may be rubber , have relatively high friction so that when the roller 12 is driven in the reverse direction indicated by arrow 32 , it tensions the paper around the drum by returning a short length of paper into the drum 2 while the paper 6 at the other end of the drum surface is restrained because of the surface friction of the locked drive roller 14 . during this motion , the stub 18 is prevented from being withdrawn into the drum because the friction between the surface of the roller 14 , which is locked , and the paper is substantially greater than the friction between the two adjacent surfaces of the paper . during and subsequent to this tensioning process , the roller 12 is driven through a one - way clutch , to be described later , which permits rotation of the roller 12 only in the direction of the arrow 32 relative to the gear that drives this roller . thus , when the tensioning action is complete and the drive is released from the roller 12 , the paper remains under tension . the tensioning process is not controlled by the length of the paper withdrawn , but instead the tensioning roller 12 is merely allowed to operate for some prefixed period of time , for example , five seconds . alternatively , a tension responsive switch can be used to disconnect the drive , but is more complicated and not as convenient as the timing procedure . when the tensioning process has been completed , the drive mechanism is disconnected from the drum which is then rotated to produce the next imaging sequence . this arrangement permits an automatic continuing sequence of imaging processes . fig5 and 8 - 12 illustrate a drive assembly , generally indicated at 36 , ( fig9 ) for the rollers 12 and 14 . the position of this drive assembly controls the three operating modes : the rest mode during which the drum 2 is free to rotate ; the drive mode for ejecting and retracting the paper 6 ; and the tensioning mode when the paper is tensioned around the drum 2 . during the rest mode , the drive assembly 36 is disconnected from the roller 12 by moving the drive mechanism to its position farthest removed from the drum 2 leaving the drum free for rotation . this is illustrated by the diagrammatic representation of fig8 in which the coupling is viewed from the front of the printer . in the driving mode , the drive assembly is moved to its position nearest the drum 2 and is arranged to drive rollers 12 and 14 , mounted on shafts 42 and 48 respectively , ( fig5 ) by means of a spur gear 44 , carried by the shaft 42 , and a similar gear 46 carried by the shaft 48 of the drive roller 14 . in the tensioning mode , the drive assembly 36 is positioned at an intermediate station where it is arranged to drive the roller 12 while the roller 14 is locked against reverse rotaion by the drive assembly . when the drum 2 is rotating , as during the imaging mode , the roller 12 is disconnected from the drive assembly 36 by a lever 52 ( fig1 and 9 - 11 ) which is hinged at 54 on one end and carries a bumper 56 on the opposite end . the position of the lever 52 is controlled by the position of a housing 58 ( fig1 ) that carries the cutter mechanism 8 . when the printer is in the imaging mode and the drum 2 is rotating , the lever 52 retains a motor 60 and its associated assembly in its rest position , far right as viewed in fig1 and 9 . in this rest position , a plunger 62 , controlled by the lever 52 , maintains a spring 64 under maximum compression within a stationary mounting case 65 . a drive sleeve 66 connected to the motor 60 , and which contains three splines 68 ( fig8 and 12 ) positioned circumferentially 120 ° apart within the sleeve 66 , is spaced from the drum 2 leaving it free for rotation . the drum 2 is driven by the direct drive stepping motor 3 ( fig1 ) which by means of a central processor ( not shown ) stops the drum 2 at the end of the imaging cycle . the drum is then caused to rotate slowly until a radial mark 71 , carried by a disk 70 ( fig5 ), which rotates with the drum 2 , indicates through an infrared detector 73 that the drum 2 is in the correct position for coupling the drive 36 to the roller 12 . when the imaging operation is completed and the drum 2 has been stopped in its drive position , the housing 58 is moved to the position that causes the drive motor assembly 36 to be coupled to the tensioning roller 12 through the sleeve 66 to eject the imaged paper 6 . in this position , the splines 68 engage the teeth of a spur gear 72 ( fig5 and 8 ) that extends within the sleeve 66 . the spur gear 44 is secured to gear 72 but is not secured to the shaft 42 other than through the gear 72 . as shown in fig8 a collar 88 , that forms the end of the mechanism by which rollers 12 and 14 are driven , and the interior of the sleeve 66 are tapered so that the drive sleeve 66 is brought into engagement with the gear 72 in spite of slight variations in the rotary position of the drum 2 . the gear 72 is secured to the shaft 42 that carries the roller 12 through a conventional one - way clutch 74 that permits rotation of the shaft 42 in the direction of the arrow 32 of fig4 relative to the gear 72 but prevents relative rotation in the opposite direction . the gear 72 is normally locked from rotation by a pin 76 ( fig6 and 8 ) carried in the end of an arm 78 and which extends into the space between adjacent teeth on the gear 72 . the arm 78 is hinged at 82 and is biased toward the locking position by a coil spring 84 positioned between the end of the drum 2 and the arm 78 . in the position when the gear 72 is engaged by the drive sleeve 66 , the end of the sleeve 66 abuts the arm 78 and moves it toward the right , as viewed in fig8 so that the pin 76 no longer engages the gear 72 . when the paper has been ejected to the desired length , as determined by a counter to be described , the drive motor 60 is stopped which prevents movement of the rollers 12 and 14 while the paper is sheared by the cutter mechanism 8 . after the paper has been sheared , the motor assembly 36 , while in the drive position , is driven in the reverse direction , by reversing the motor 60 , to withdraw the paper until only the short stub 18 projects from between the rollers 12 and 14 . the housing 58 is then moved , against the force of the spring 64 ( fig9 ), to move the lever 52 and the motor assembly 36 to its intermediate or tensioning position . in this position , the end of the sleeve 66 , which abuts the lever 78 , has moved away from the drum 2 allowing the pin 76 ( fig6 and 8 ), to lock the roller 14 by engaging the teeth of the gear 72 , while the roller 12 is driven in the direction of the arrow 32 ( fig4 ). this is accomplished by a drive pin 86 ( fig5 and 8 ) that extends through the collar 88 in the end of the shaft 42 of the roller 12 . one of the splines 68 in the drive sleeve 66 engages the drive pin 86 , but not the teeth of gear 72 , while the gear 72 , and thereby the gears 44 and 46 and the roller 14 , are locked by the locking pin 76 . in this state , while the gear 72 is locked , shaft 42 is free to rotate in the direction of arrow 32 of fig4 because of the one - way clutch 74 . the shaft 48 of the drive roller 14 is rotatably supported on the drum 2 by any suitable means such as that described in the cleary application . only the center portion of the shaft 48 is covered with a resilient sleeve 92 , for example about two inches in length , that engages the rollers 10 and 12 . this arrangement applies driving force to the paper only along the center strip of the paper and prevents the skewing that would occur if the driving forces were applied across the width of the paper . the contour of the paper on each side of the sleeve 92 is controlled by a series of spaced plastic bushings 94 which are smaller in diameter than the sleeve 92 . the bushings 94 , which have non - traction surfaces , do not touch , or may touch very lightly , the surface of the tension roller 12 the shaft 42 of the tensioning roller 12 is supported by the drum 2 in any suitable manner such as that described in the cleary application . this roller is similar in construction to the idler roller 10 and carries a resilient sleeve that extends most of the distance along the shaft 42 and substantially spans the width of the imaging paper . other essential parts of a printer of this kind , such as the construction of the cutter mechanism 8 , the imaging drum 2 , and the central processor unit that controls the sequence of operations , and the like are described more fully in the cleary application .