Abstract:
A printer including a single motor which provides rotary motion to a feed drum having an outer surface which frictionally engages and pulls a web material from a roll rotatably mounted on a supply shaft. First and second pendulum systems, each including two pendulums independently mounted to the frame, pivotally mount a take-up shaft and a tension roller to tension the web as it comes off the feed drum and the roll, respectively. A print head carriage assembly is moveable along a pivot beam which extends orthogonally across the linear path from a first end position to a second end position. The single motor is coupled to the print head carriage assembly for reciprocally pushing and pulling the print head carriage assembly between first and second end positions. An actuator selectively pivots the pivot beam such that the first end portion of the pivot beam is pivoted in the direction of the linear path when the print head carriage assembly is disposed for moving from the second end position to the first end position and the second end portion of the pivot beam is pivoted in the direction of the linear path when the print head carriage assembly is disposed for moving from the first end position to the second end position.

Description:
Applicant incorporates by reference and claims benefit pursuant to 35 U.S.C. 119(e) for Provisional Patent Application titled Synchronized Motion Printer With Continuous Paper Movement, Ser. No. 60/154856, filed Sep. 20, 1999. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates generally to printers for use with a web of paper or other sheet material which travels along a fixed linear path. More particularly, the present invention relates to printers of the type where a print device or other drawing instrument is traversed across the width of the web, in a direction perpendicular to the direction of the linear path of the web, to draw figures, characters, and other graphics on the sheet material. 
     Traditional printers utilizing a traversing head mechanism cause the print head to traverse across the web of paper while moving paper in one of three operational modes: 1) intermittent paper movement; 2) continuous paper movement; or 3) a combination of intermittent paper movement combined with continuous paper movement. In each of these three operational modes to date, the linear paper movement and the traversing movement are monitored independently and utilize electronic means for controlling each of these motions while also providing a means for electronically interlocking the two motions. 
     In the first mode of operation, the print head accelerates to a printing velocity while traversing across the paper web perpendicular to the length of the web while the paper remains stationary. A position encoder driven by the print head drive motor is used to provide timing information for the incremental placement of the print pattern on the paper. When the print head reaches the end of the printable band, the motor controlling the traversing motion of the print head brings the print head to a controlled stop. While the print head is being stopped, the paper is advanced an amount equal to the vertical height of the printed band. This motion is controlled by an independent motor drive and is monitored by an independent encoder or position transducer which directly or indirectly measures paper movement. When the paper reaches the next print position, the print head motor reverses the traversing direction and then repeats the acceleration, print and deceleration process. This cycle repeats for each required print band. The paper advance motor or an independent paper take-up motor is used to rewind the printed web while a separate means for tension control of the web is provided in most systems. 
     In the second operational mode, the paper is first placed in motion in one direction prior to or simultaneously with the beginning of the print head traversing cycle. The traversing angle in this case is not horizontal or zero degrees as in the first case, but is determined by the ratio of the linear paper speed and the traversing speed of the print head. This angle is required in order to generate a horizontal print band on the moving paper and is obtained by driving the print head with an x-direction and a y-direction drive mechanism. The traversing motor driving the print head in the x-direction will have the same acceleration, print, deceleration, stop, and reverse characteristics as the first case. Electronic synchronization of the paper feed and the traversing feed (x-direction) motors along with an additional means for controlling and synchronizing the displacement of the print head in the paper direction (y-direction) for creating the required traversing angle is required. At the end of two traversing passes or one complete right and left traversing pass across the web, the y-direction drive mechanism that creates the traversing angle must be reset to it&#39;s original home position to enable the cycle to repeat. This function usually utilizes a separate actuating device and requires high acceleration forces. 
     The third operational mode uses mode  2  but permits the paper and traversing mechanism to stop at the end of any printed line. 
     All three of the operational modes described above utilize relatively expensive servo mechanisms for synchronizing two or more axis of motion in order to obtain the required printing precision at high speeds. In addition, as the speed requirement of the printer increases, significantly higher accelerations for starting, stopping, and reversing the traversing motion require even more expensive mechanisms and typically reduce the reliability of the printer due to the increased loads resulting from the high accelerations associated with this type of traversing motion. 
     SUMMARY OF THE INVENTION 
     Briefly stated, the invention in a preferred form is a printer for printing on a web of material moving continuously in a single direction along a linear path. The printer includes means for advancing the web of material along the linear path and means for printing on the web of material along a print path extending across the linear path. A single motor provides the motive power for advancing the material along the linear path and for reciprocally pushing and pulling the print means between first and second end positions adjacent the opposite first and second sides of the linear path. 
     The advance means includes a feed drum which is rotatably mounted to the frame of the printer and has an outer surface which frictionally engages and pulls the web material along the linear path. The printer also includes means for tensioning the web of material as it is advanced along the linear path. The tensioning means includes a take-up shaft and means for moveably mounting the take-up shaft to the frame. A leading end of the web of material extending between the take-up shaft and the feed drum is mounted to the take-up shaft such that the web material is wound on the take-up shaft during the printing operation. 
     The advance means further includes a supply shaft which is mounted to the frame for rotatably mounting a supply roll of web material. The tensioning means further includes a paper tension roller and means for moveably mounting the paper tension roller to the frame. The paper tension roller has an outside surface adapted which engages the web material disposed intermediate the supply shaft and the feed drum. 
     The means for moveably mounting the take-up shaft and the means for moveably mounting the paper tension roller each include a pair of pendulum arms. Each of the pendulum arms has oppositely disposed first and second end portions, with the first end portion of each pendulum arm being independently pivotally mounted to the frame. The take-up shaft and the paper tension roller are each rotatably mounted to the second end portions of the respective pendulum arms. 
     The print means includes a pivot beam which extends orthogonally across and adjacent to the linear path of the web. At least one print head is supported on the pivot beam and is moveable along the pivot beam between the first and second end positions. Means are provided for selectively pivoting the pivot beam such that a first end portion of the pivot beam is pivoted in the direction of the linear path when the print head is disposed for moving from the second end position to the first end position and a second end portion of the pivot beam is pivoted in the direction of the linear path when the print head is disposed for moving from the first end position to the second end position. 
     A drive pulley and an idler pulley are rotatably mounted at the first and second end portions of the pivot beam, respectively, with the output of the motor being coupled to the drive pulley. A drive belt carried on the drive and idler pulleys is driven by the drive pulley in a single direction. The drive belt is linked to the print means for reciprocally pushing and pulling the print head between the first and second end positions. 
     First and second eccentric cams are rotatably mounted at the first and second end portions of the pivot beam, respectively, and engage with fixedly mounted first and second cam supports, respectively. The first and second eccentric cams each have a cam lobe, with the cam lobe of the second eccentric cam being located 180° from the cam lobe of the first eccentric cam. Trip means connected to the drive belt selectively rotates the first and second eccentric cams such that the cam lobe of the first eccentric cam engages the first cam support to pivot the first end portion of the pivot beam in the direction of the linear path when the print head is disposed for moving from the second end position to the first end position and the cam lobe of the second eccentric cam engages the second cam support to pivot the second end portion of the pivot beam in the direction of the linear path when the print head carriage assembly is disposed for moving from the first end position to the second end position. 
     It is an object of the invention to provide a new and improved printer for printing on a web of continuously moving material. 
     It is also an object of the invention to provide a printer having a paper advance system which provides a constant tension on the paper web in spite of variations in web tension and thickness. 
     It is further an object of the invention to provide a printer having horizontal print density and accuracy of the printed horizontal line which is independent of the throughput. 
     It is also further an object of the invention to provide a printer having a significantly lower power consumption than conventional printers. 
    
    
     Other objects and advantages of the invention will become apparent from the drawings and specification. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention may be better understood and its numerous objects and advantages will become apparent to those skilled in the art by reference to the accompanying drawings in which: 
     FIG. 1 is an isometric view of a printer in accordance with the invention, with all external covers removed; 
     FIG. 2 is a simplified version of FIG. 1, showing only those elements supported by the pivoting beam; 
     FIG. 3 is a plan view of the printer of FIG. 1, with the pivoting and fixed beams removed to illustrate the elements of the invention behind the beams; 
     FIG. 4 is a side view of the printer of FIG. 1, with the support channel removed to illustrate the means for paper feed and paper take; 
     FIG. 5 is a plan view of the means for detenting the link arm to the print head carriage assembly; 
     FIG. 6 is a side view of the means for detenting the link arm to the print head carriage assembly; 
     FIG. 7 is a top view of the pivoting beam and cams illustrating the means for detenting the cams to the pivoting beam; and 
     FIG. 8 is a plan view of the timing belt and pulleys dimensioned to identify the various timing regions defined for the printer. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     With reference to the drawings wherein like numerals represent like parts throughout the several figures, a synchronized motion printer with continuous paper movement in accordance with the present invention is generally designated by the numeral  10 . A synchronized motion printer  10  with continuous paper movement (hereinafter a “synchronized motion printer”) is a printer where a drawing of great length is produced by placing a web  12  composed of paper in a continuous linear motion while simultaneously traversing the print head across the web  12  of paper at an angle which is determined by the ratio of the paper speed and the traversing speed of the print head, without the need to independently measure, control, and synchronize these motions. It should be appreciated that synchronized motion printers  10  are useful for printing on webs consisting of materials other than paper, for example plastic or fabric. 
     Synchronized motion printers  10  are useful, for example, in the garment industry for drawing markers showing pattern pieces to be cut from a length of fabric. In such applications, the printer  10  may be part of a computer assisted pattern grading and marker making system. In this case the sheet material on which the drawing or marker is made is usually paper and the writing instrument is usually a multi-nozzle ink jet print head. Therefore, for convenience, in the following description and in the accompanying drawings, the sheet material referred to and shown is paper, and the writing instrument referred to and shown is an ink jet print head consisting of a vertical array of 128 nozzles placed on 0.0054 inch centers. Other sheet materials and conventional writing instruments may however be used without departing from the invention. 
     With reference to FIGS. 1 and 2, the synchronized motion printer  10  includes a paper advance system  14  having a single drive source for the printer  10 , motor  16 , which is mounted on the left printer support channel  18  via a support block  20 . In a preferred embodiment, the motor  16  is directly coupled to the main drive shaft  22  and drives a paper advance worm gear  24  through a worm drive  26  pinned to drive shaft  22  at a 100:1 speed ratio. The paper advance worm gear  24  is attached to the end of a rubber coated paper feed drum  28  that advances the paper web  12 , which is partially wrapped around paper feed drum  41 . This high reduction ratio provides for the slow and continuous movement of paper web  12  while significantly reducing the reflected inertia and torque requirements seen by drive motor  16 . 
     The friction force needed to advance the paper web  12  is applied to the paper web  12  as a result of the normal force created by the weight of the rewound paper  44  and the weight of the paper take-up shaft  30  resting on the paper feed drum  28 . A high-resolution encoder  32  is coupled to the print head carriage assembly  58  and precisely monitors the horizontal print head movement. 
     The two ends of the take-up shaft  30  are mounted to the support channels  18 ,  78  by a first free-floating mount system  33  which allows each end of the take-up shaft  30  to move independently, relative to the feed drum  28 . In a preferred embodiment, the first free-floating mount system  33  is a first pendulum system  34  (FIG.  4 ), consisting of first and second pendulum arms  36 ,  38 , pivoting independently at each end of the printer on pendulum pivot bearings  40  supports paper take-up shaft  30 . The leading edge of the paper web  12  exiting between the paper take-up shaft  30  and the paper feed drum  28  is attached to the paper take-up shaft  30 , such that the paper web  12  is automatically rewound on the paper take-up shaft  30  whenever the paper feed drum  28  rotates. The portion of the rewound paper  44  disposed intermediate the take-up shaft  30  and the paper feed drum runs in contact with both the take-up shaft  30  and the paper feed drum  28 , such that the displacement of the paper web  12  exiting the paper feed drum  28  is equal to the displacement of the rewound paper  44  winding on the takeup shaft  30 , rewinding the paper web  12  with minimal tension. The independently pivoting pendulum arms  36 ,  38  minimize paper feeding errors due to variations in web tension and paper thickness along the width of the web  12 . Higher tension or thinner paper along the width of the web  12  result in variations in the diameter of the rewound paper  44  (from side to side) on the take-up shaft  30 . In a system which does not have independently moving pendulum arms, portions of the rewound paper  44  having reduced diameter, as compared with other portions of the rewound paper  44 , will lose contact with the feed drum, resulting in movement of the web  12  in the smaller diameter portions and uneven windup. Alternatively, the free-floating mount system  33  may comprise a slot (not shown) in each support channel  18 ,  78  which allow the ends of the take-up shaft  30  to be displaced relative to the feed drum  28 . 
     With reference to FIG. 4, the pendulum configuration of the first pendulum system  34  also provides a self compensating system that applies a relatively constant normal force to the paper web  12  as the weight of the rewound paper  44  on the take-up shaft  30  increases. The normal force applied to the paper web  12  is a function of the sum of the weight of the paper take-up shaft  30  and the rewound paper  44  on the take-up shaft  30 , the coefficients of friction of the paper feed drum  28  and the paper web  12 , the tension applied to the supply end of the paper web  12 , and the effective angle of contact a between the outside diameter of the rewound paper  44  on the paper take-up shaft  30  and the paper feed drum  28 . When there is little or no rewound paper  44  on the paper take-up shaft  30 , the angle of contact a is very small and the resulting normal force is magnified and becomes greater than the combined weight of the paper take-up shaft  30  and the rewound paper  44 . 
     As the paper web  12  winds onto the paper take-up shaft  30 , the diameter of the rewound paper  44  continues to increase along with the weight of the rewound paper  44 . The increasing diameter of the rewound paper  44  causes the pendulum arms  36 ,  38  to rotate around the center of the pendulum pivot bearings  40  increasing the angle of contact a between the rewound paper  44  on the paper take-up shaft  30  and the paper feed drum  28 . This increasing angle compensates for the increased weight of the rewound paper  44  on the paper take-up shaft  30 , and maintains a relatively constant force on the paper feed drum  28 , independent of the amount of rewound paper  44  on the paper take-up shaft  30 . 
     The length of the pendulum arms  36 ,  38 , the location of the pendulum pivot bearings  40 , the initial contact angle without rewound paper  44 , and the contact angles defined by the rewound paper  44  provide the variables that enable the first pendulum system  34  to maintain a relatively constant normal force for all rewound paper  44  take-up diameters. This constant normal force is essential to maintain consistency of paper feeding. An alternative embodiment for the takeup function is to permit the paper web  12  to exit directly from between the paper take-up shaft  30  and the paper feed drum  28 . The paper web  12  can then be fed directly to the floor, to a take-up tray, or to an auxiliary take-up device. 
     A second free-floating mount system  45  which allows each end of a paper tension roller  54  to move independently, relative to the paper supply roll  56 . In a preferred embodiment, the second free-floating mount system  45  is a second pendulum system  46 , consisting of third and fourth pendulum arms  48 ,  50 , pivoting at each end of the printer on pendulum pivot bearings  52 , supports paper tension roller  54 . The paper tension roller  54  is positioned intermediate the paper supply roll  56  and the print head carriage assembly  58  and engages the paper web  12  as it comes off of the paper supply roll  56 . The pivoted connections allow either end of the paper tension roller  54  to be displaced relative to the paper supply roll  56  to allow for takeup variations in the tension of the web of paper wound on the roll  56  and thereby provide a constant tension on the paper web  12  in spite of such variations. The first and second pendulum systems  34 ,  46  apply a constant tensioning force to the paper web  12 , thereby eliminating paper stretch and preventing the formation of waves, thereby maintaining the accuracy of the print data along the length of paper web  12 . 
     In summary, paper web  12  is driven continuously in one direction by applying power to the drive motor  16  under the control of the printer controller  60 . The diameter of the paper feed drum  28  and the speed of the main drive shaft  22  determine the advance speed of the paper web  12 . Paper tension is obtained from the friction created between the paper supply shaft  62  and the tension support blocks  64  resulting from the weight of the paper supply roll  56  and the paper supply shaft  62  resting on the tension support blocks  64 . Additional tension of the web is achieved with adjustable pressure rollers  65  that engage shaft  62  within each support block  64 . The printing on the paper web  12  is performed while the paper web  12  is in motion. 
     Referring to FIGS. 2 and 3, the main drive shaft  22  drives a primary drive sprocket  66  that is attached to the end of the main drive shaft  22 . The primary drive sprocket  66  is coupled to the driven sprocket  68  through a drive chain  70  with a 6:5 ratio. The drive chain  70  is of sufficient length to permit the driven sprocket  68  to be displaced vertically as the driven sprocket  68  and the print guidance system are pivoted around pivot shaft  72 , seen in FIG. 1, and repositioned at the end of each printed line. 
     In a preferred embodiment, the pivot beam  74  is supported by a rigid fixed beam  76 , which is attached to the two printer side channels  18 ,  78 , and pivots about the pivot shaft  72 . The pivot beam  74  supports the print head carriage assembly  58  shown in FIG. 3, the linear guide rails  80 ,  82  (best viewed in FIG.  3 ), the print head idler and drive pulleys  84 ,  86 , the print head drive timing belt  88 , and the pivot control eccentric cams  90 ,  92 . As described in greater detail below, the pivot control eccentric cams  90 ,  92  rest on cam supports  94  and  96 . Therefore, it should be appreciated that the pivot beam  74  is not required to be pivotally connected to the fixed beam  76 . 
     As shown in FIG. 3, the print head carriage assembly  58  is guided parallel to the centerline of the pulleys  84 ,  86  by four linear bearings  98  attached to the print head carriage plate  100  and running on two parallel linear guide rails  80 ,  82 . The linear guide rails  80 ,  82  are supported on the pivot beam  74  by means of several “C”-channel brackets  102 . Attached to the print head carriage plate  100  is the ink jet print head  104  oriented with the print nozzles  106  (FIG. 5) along the vertical length or motion of the paper web  12 . Also attached to the print head carriage plate  100  is the ink reservoir  108 . 
     Referring to FIG. 2, the timing belt  88  is driven by the left, first print head drive pulley  86 , which is coupled to the driven sprocket  68 . Attached to the timing belt  88  are two trip pins  110 ,  112  which are located exactly  180  degrees apart from one another along the circumference of the timing belt  88 . Both trip pins  110 ,  112  have a cam actuating bearing  114 ,  116  attached to one end. The primary trip pin  110  also has a link arm  118  attached to the side opposite the cam actuating bearing  114 . The link arm  118  alternately pushes and pulls the print head carriage plate  100  along the linear guide rails  80 ,  82  as the timing belt  88  rotates in a clockwise direction as viewed from the front of the printer  10 . The right end of the link arm  118  is attached to the primary trip pin  110  through a trip pin link bearing  120 , while the left end is attached to the print carriage plate  100  through a carriage support bearing  122  with the location of this bearing set along the horizontal center line  124  defined by the axis  126 ,  128  of the print head idler and drive pulleys  84 ,  86 . It should be appreciated that drive means other than a timing belt  88  may also be used. For example, one or more trip pins may be carried on a rod having both right-hand and left-hand threads, where the trip pin(s) alternately engage the right-hand and left-hand threads to reverse direction of travel. 
     The above-described setup enables the timing belt  88  to be driven continuously with the left end of the link arm  118 , which is attached to the print carriage plate  100 , remaining on centerline  124 , while the other end of the link arm  118  follows the timing belt path by pivoting around the trip pin link bearing  120 . The continuous rotation of the link arm  118  on the trip pin link bearing  120  creates a reciprocating linear motion of the print head carriage assembly  58 . The length of linear travel is determined by the center distance between the print head idler and drive pulleys  84 ,  86  and the their pitch diameter. Printing occurs while the primary trip pin  110  that holds the link arm  118  is moving along the horizontal section of the timing belt  88 . In order to prevent sag and or vertical oscillation of the timing belt  88 , which could incrementally impact the horizontal location of the print head carriage assembly  58  through the horizontal component of the movement of the link arm  118 , a detenting mechanism is provided by means of the spring ball plungers  130  that detents the link arm  118  and the print head carriage plate  100  when the print head  104  is in the printable area. FIGS. 5 and 6 illustrate this detenting mechanism. 
     In order to print a horizontal line with the web  12  of paper in continuous linear motion, the print head  104  must travel across the web  12  of paper at an angle proportional to the ratio of the linear speed of the paper web  12  and the linear speed of the print head  104  traversing the paper web  12 . This “print angle” is positive for the print head  104  moving from left to right and negative for the print head  104  moving from right to left. The sign of the print angle is set such that the angle of the linear guide rails  80 ,  82 , relative to a horizontal line across the paper web  12 , provides for a displacement of the print head  104  in the same direction as the paper motion an amount equal to the paper displacement. Therefore, when looking at the linear guide rails  80 ,  82  from the front of the printer  10 , with the print head  104  moving from left to right and the paper web  12  moving from the bottom to the top of the printer  10 , the angle for the linear guide rails  80 ,  82  is positive and provides a vertical component of motion for the print head  104  which tracks the paper movement. When the traversing motion reverses direction and the print head  104  moves from the right to the left, the angle for the linear guide rails  80 ,  82  is negative again providing a vertical component of motion for the print head  104  which continues to track the paper movement. The center of the pivoting action for the linear guide rails  80 ,  82  is at the center of the maximum printable width across the paper web  12  using pivot shaft  72 . 
     While the print head carriage assembly  58  traverses from left to right, the two eccentric cams  90 ,  92  are positioned as shown in FIG. 3, with the left eccentric cam  92  having the smaller radius of the eccentric resting on the left cam support  96  and the right eccentric cam  90  having the larger radius of the eccentric resting on the right cam support  94 . These cam supports  96 ,  94  are fixed in position on the fixed beam  76  using mounting plates  132  (FIG.  1 ). As the timing belt  88  rotates clockwise, the trip pins  110 ,  112  eventually reach their respective drive pulleys  84 ,  86  and begin to rotate around the pulleys  84 ,  86  causing the trip pins  110 ,  112  to engage with and rotate the eccentric cams  90 ,  92  by  180  degrees. The cam rotation is very smooth and close to sinusoidal in motion resulting in a very low acceleration load on the print head  104  during each direction reversal. The shape of the eccentric cams  90 ,  92  rotating over the cam supports  94 ,  96  gradually repositions the pivot beam  74  to the negative print angle required for printing from right to left. The eccentric cams  90 ,  92  are detented in the print position by two cam detent ball springs  134 , shown in FIG. 7, as the trip pins  110 ,  112  exit the pulleys  84 ,  86  and the print head  104  moves into the print position. The two cam detent ball springs  134  are rigidly supported by the pivot beam  74 . 
     It should be appreciated that the link arm  118  imparts a force F on the print carriage assembly  58  having a vector component Fx in the direction of movement of the timing belt  88  and a vector component Fy which is perpendicular to direction of movement of the timing belt  88 . The link arm  118  and the horizontal center line  124  define an angle θ. Increasing the length of the link arm  118  reduces the value of angle θ, decreasing Fy and increasing Fx, thereby increasing the efficiency of the apparatus. Conversely, reducing the length of the link arm  118  increases the value of angle θ, increasing Fy and decreasing Fx, thereby decreasing the efficiency of the apparatus. Therefore, the minimum length of the link arm  118  is constrained by efficiency factors. 
     It should also be appreciated that the print head carriage assembly  58  is laterally offset from the primary trip pin  110  by the distance between cam actuating bearing  114  and carriage support bearing  122 . Consequently, when the print head carriage assembly  58  traverses from left to right, the primary and secondary trip pins  110 ,  112  engage the right and left eccentric cams  90 ,  92  respectively, after the print head carriage assembly  58  completes its travel through the print area. Conversely, the print head carriage assembly  58  completes its travel through the print area when traversing from right to left before the primary and secondary trip pins  110 ,  112  engage the left and right eccentric cams  92 ,  90 , respectively. In the case where the frame width is fixed, the maximum length of the link arm  118  is constrained by the ability to compensate for the offset between the primary trip pin  110  and the print head carriage assembly  58 , as explained below. In the case where the frame width is not fixed, the only constraint is that pivot  72  must be on the center of print head stroke. 
     For frames having a fixed width, the offset between the primary trip pin  110  and the print head carriage assembly  58  may be compensated for by moving the pivot beam  74  a distance to the right which is equal to the length of the offset. As best shown in FIGS. 1 and 3, the pivot shaft  72  is located at a position which is at the center of print head stroke and at a position which is to the left of the midpoint  140  of the pivot beam  74 . Further, the left end portion  142  of the pivot beam  74  is located at a position which is to the right of the left-hand edge of the paper web  12  and the right end portion  144  of the pivot beam  74  is located at a position which is to the right of the right-hand edge of the paper web  12 . Consequently, the print head  104  is positioned at one of the print margins of the paper web  12  when the print head carriage assembly  58  completes each traversing pass. 
     Printing occurs when any one or more of the nozzles  106  on the print head  104  is fired. In a preferred embodiment, print head  104  has  128  vertical nozzles  106 , providing a vertical print band which is 0.691 inches high. As the print head  104  traverses across the paper web  12 , the nozzles  106  repeatedly fire based on an encoder count determined by the rate of pulses provided by the encoder  32 . The maximum acceleration or “g-force” limitation for the print head  104  is not a limitation in this design since the maximum acceleration experienced by the print head carriage assembly  58  (which is reached at the end of it&#39;s cycle for each traversing pass) is well below this limitation. The maximum g force experienced by the print head  104  may further be kept below the maximum allowable g force by increasing the diameter of the idler and drive pulleys  84 ,  86 . Since the paper web  12  and the print head  104  are physically interlocked to a single motor  16 , a change in motor speed results in proportional changes to the paper movement, print head movement, and frequency of the encoder generated firing pulses. Therefore, the horizontal print density and the accuracy of the printed horizontal line is independent of the actual motor speed. In other system, which utilize servo mechanisms for each axis, the print head speed and inertial loads must be limited to maintain print accuracy. 
     For each complete revolution of the timing belt  88 , the printer  10  will generate two sequential and contiguous print passes, each of the print passes having a height of 0.691 inches. As shown in FIG. 8, each complete revolution of the timing belt  88  can be divided into four regions, based upon the position of the primary trip pin  110 . Regions T 1  and T 3  represent printable regions and regions T 2  and T 4  represent unprintable regions. The length of each region can be defined by the number of timing belt pitches or teeth in each region. In the preferred embodiment, the entire timing belt  88  has  400  teeth, with regions T 1  and T 3  each containing  185  teeth, and regions T 2  and T 4  each containing 15 teeth. 
     Since one revolution of the belt  88  is equal to 2×0.691 inches or 1.382 inches of vertical paper displacement, then T 1  and T 3  each represent (185/200)×0.691 inches or 0.639 inches of paper displacement while printing lines either left or right and T 2  and T 4  each represent (15/200)×0.691 inches or 0.052 inches of paper displacement and is the time it takes for the print head  104  to reverse direction and for the pivot beam  74  to reposition to the print angle. The sum of the paper displacement in the T 1  region and the T 2  region is equal to the vertical print height or 0.691 inches. Similarly, the sum of the paper displacement in the T 3  region and the T 4  region is 0.691 inches. Since the printer  10  can print during the T 1  and T 3  time, the maximum print efficiency for this printer  10  is ((T 1 +T 3 )/(T 1 +T 2 +T 3 +T 4 ))×100=92.5%. This is a significant improvement over traditional printer systems and does not change as the speed of the printer is increased. This embodiment uses a configuration where T 2  and T 4  are equal. Other embodiments are practical using unequal regions. For a given width printer  10 , running the motor  16  will result in an increased throughput without a loss of efficiency. 
     The timing belt  88  rotates clockwise when viewing the machine from the front. The print head  104  is parked at it&#39;s “home” position prior to moving. When the print head  104  begins to move for printing left to right, the left sensor  146 , shown in FIG. 3, detects the start of the print line by sensing a flag  148  attached to the print head carriage plate  100 . moving from left to right. The printer controller  60  then provides a programmable delay based upon encoder counts required to produce the left side print margin the user selects. Following this delay, the printer controller  60  uses the encoder pulses to generate firing pulses for the print head for one complete horizontal print band. After the trip pins  110 ,  112  rotate the eccentric cams  90 ,  92  and reverses. the angle of the pivot beam  74  for printing from right to left, the direction of the print head carriage assembly  58  is reversed. The printing begins again from right to left after the right sensor  150  detects the carriage flag  148 . The left and right sensors  146 ,  150  are located at a position which is immediately after the trip pin  110 ,  112  comes off the pulley  84 ,  86  to eliminate encoder variations due to backlash and non-linearity in the pulley region. 
     The advantages of this invention is that only a single drive motor  16  is required for the entire system. This motor  16  requires a fraction of the power of conventional printer systems because of the elimination of the high accelerations and decelerations by using a unidirectional continuous motion drive traversing the print head carriage assembly  58 . The effective speed for this system is only limited by the maximum print head firing rate. 
     The high-resolution encoder  32  may alternatively be coupled to motor  16 . As the print head  104  traverses across the paper web  12 , the nozzles  106  repeatedly fire based on an encoder count determined by the rate of pulses provided by the encoder  32 , the motor gear ratio, the ratio of the number of teeth on the primary drive sprocket  66  to the number of teeth on the driven sprocket  66 , and the pitch diameter of the driver pulley  86 . 
     There are many other embodiments possible for this invention. The actuation function performed by the eccentric cams  90 ,  92  can be replaced by other actuators, including solenoids and hydraulics, controlled by either the mechanical position of the timing belt  88  or by electronic sensors and/or counters. The basic concept that is present in all embodiments is the use of a pivoting beam  74  for establishing the positive and negative print angle for each reciprocating direction of the print head  104 . These alternative embodiments eliminate the requirement for independent x and y drives by means of positioning the print head guidance system at the required print angle for each traversing direction. 
     In other embodiments, multiple print head configurations can also be used. These heads can be positioned one over the other, staggered side-by-side, or evenly spaced across the width of the web  12  of paper in order to increase the band being printed on each traversing path or to increase the frequency with which the overall print pattern can be fired. 
     While preferred embodiments have been shown and described, various modifications and substitutions may be made thereto without departing from the spirit and scope of the invention. Accordingly, it is to be understood that the present invention has been described by way of illustration and not limitation.