High speed shuttle printer
BACKGROUND OF THE INVENTION 
     The present invention relates to dot matrix printers and, more particularly, in a dot matrix printer of the shuttle variety wherein a plurality of printheads are disposed across the width of a shuttle which is oscillated from side to side within a printer base, to the improvement comprising, the shuttle being disposed within a ballistic energy transfer device mounted for oscillating movement from side to side in the opposite direction to the instantaneous movement of the shuttle; first spring means operably connected between the ballistic energy transfer device and the shuttle for exerting a rebounding force against the shuttle to aid it in reversing direction; and, second spring means operably connected for exerting a centering force against the ballistic energy transfer device. 
     Dot matrix printers have provided a simple and economical apparatus for computer-driven printing. In a dot matrix printer, a printhead such as that labelled as 10 in FIGS. 1 and 2 has a magnetic drive unit 12 connected to a print face 14 such as those shown by way of example in FIGS. 3 and 4. One or more print pins 16 are connected between the drive unit 12 and the print face 14. For example, FIG. 3 depicts a single print pins 16 while FIG. 4 depicts twelve print pins 16 configured in a 3×4 matrix. A print ribbon (not shown) is disposed between the print face 14 and the writing paper upon which printing is to take place. When the magnetic drive unit 12 pushes the pin(s) 16 out of the print face 14, the end(s) push the print ribbon against the paper causing a dot to be printed. Dot matrix printers are powerful in capability since they can produce both text (i.e. alpha-numeric characters) and graphics as a matrix of dots on the page. The process is depicted in FIGS. 5-7. The printhead 10 is moved back and forth transversely over the paper 18 as the paper is moved vertically under the support bar 20 carrying the printhead 10. The printhead 10 and paper 18 are moved by apparatus well known in the art which is, therefore, not shown for simplicity. Likewise, the magnetic drive unit 12 is activated under computer control in a manner well known to those skilled in the art which requires no further explanation. The printhead 10 is moved across the bar 20 from a starting position at the left side of the paper 18 as shown in FIG. 5 to the opposite side of the paper 18 where it reverses direction as depicted in FIG. 6. It continues across the paper in the opposite direction as depicted in FIG. 7 until it reaches its starting point once again. The process then repeats. As the printhead 10 moves across the paper 18, the magnetic drive unit 12 is activated to create one or more lines of dots (depending on the number of print pins 16) which comprise the graphics and/or text 22. The more pins 16, the fewer passes of the printhead 10 are required. 
     As with anything else, dot matrix printers are subject to numerous tradeoffs. A printer with only a few pins 16 is simple and inexpensive to build. Typically, these are very slow. A printhead 10 with a greater number of pins will be faster for a given quality; however, the cost is high and the printhead is large. To move the high mass of such a printhead across the paper rapidly and then quickly reverse its direction requires a large and expensive drive mechanism. Even then, there are limitations as to how fast one can make the printhead traverse a wide sheet of paper (e.g. fourteen inches) and then reverse direction. 
     In commercial printers where cost is not a major factor (as compared to the &#34;home&#34; market), shuttle printers such as that depicted in FIGS. 8-10 have been introduced as an answer to the above-mentioned problems of single printhead dot matrix printers. In a shuttle printer, a plurality of printheads 10 are disposed side-by-side on a shuttle 24. The shuttle 24 is then oscillated or shuttled from side to side a shuttle distance &#34;d&#34; as depicted in the figures. Each head 10 covers only a narrow vertical strip on the paper. For example, with eight printheads 10 as shown in FIG. 10, the shuttle 24 only has to move one-eighth the distance required to traverse the whole width of the paper with one printhead. Typically, the side-to-side movement of the shuttle 24 has been created by a rotating motor 26 driving a crank 28 which, in turn, reciprocates a link 30 connected to the shuttle 24. A position wheel 32 attached to the end of the motor shaft 34 is sensed by a sensor 36 to provide a signal of the position of the shuttle 24 as function of the rotation of the crank 28. 
     As can be appreciated, while solving some problems, shuttle printers have created problems of their own. Principally, the shuttle 24 with its multiple printheads 10 has a high inertial mass. Thus, it is hard to reverse to create the desired shuttle motion. Additionally, the sensor 36 is inexact since it is at the far end of a chain of additive errors from the shuttle 24 itself. To keep the mass low, shuttle printers have typically employed single pin printheads as depicted in FIG. 3. This, of course, means that many more passes or &#34;shuttles&#34; are required to create a finished &#34;line&#34; of text or the like. 
     Wherefore, it is an object of the present invention to provide a shuttle printer which is able to quickly reverse directions. 
     It is another object of the present invention to provide a shuttle printer which operates with larger, multiple pin printheads so as to require fewer shuttle motions to create a line of text or the like. 
     It is yet another object of the present invention to provide a shuttle printer which can be dynamically adjusted for maximum performance. 
     It is still another object of the present invention to provide a shuttle printer which does not impart high impact forces from the moving shuttle to the printer base. 
     It is a further object of the present invention to provide a shuttle printer having a position feedback system for the shuttle which accurately reflects the position of the shuttle. 
     It is still a further object of the present invention to provide a shuttle printer having low friction in the components whereby to achieve maximum benefit from the driving power. 
     Other objects and benefits of the present invention will become apparent from the description which follows hereinafter when taken in conjunction with the drawing figures which accompany it. 
     SUMMARY 
     The foregoing objects have been achieved in a dot matrix printer of the shuttle variety wherein a plurality of printheads are disposed across the width of a shuttle which is oscillated from side to side within a printer base by the improvement of the present invention comprising, the shuttle being disposed within a ballistic energy transfer device mounted for oscillating movement from side to side in the opposite direction to the instantaneous movement of the shuttle; first spring means operably connected between the ballistic energy transfer device and the shuttle for exerting a rebounding force against the shuttle to aid it in reversing direction; and, second spring means operably connected for exerting a centering force against the ballistic energy transfer device. Preferably, the ballistic energy transfer device is of a mass which is at least several times the mass of the shuttle. 
     In one version, there are a pair of spaced, parallel support rods carried by the printer base; means for slidably mounting the shuttle to the support rods; and, means for slidably mounting the ballistic energy transfer device to the support rods. Additionally, there is a linear motor operably connected between the shuttle and the ballistic energy transfer device for driving the shuttle back and forth in an oscillating motion with respect to the ballistic energy transfer device. According to one aspect, the linear motor comprises a linear armature carried by the shuttle and a linear coil assembly carried by the ballistic energy transfer device. 
     In the preferred embodiment, the invention additionally comprises a first linear encoder fence carried by the printer base to be parallel to a path of movement of the shuttle, the first fence having sensible positional indicia thereon and first sensor means carried by the shuttle for sensing the positional indicia of the first encoder fence as the shuttle moves back and forth and for producing a signal at an output thereof reflecting the position of the shuttle with respect to the printer base. Preferably, the first encoder fence is of a transparent material and the first sensor means includes a light emitting diode disposed on one side of the first fence and a phototransistor disposed on the opposite side of the first fence so as to develop the signal as a function of light passage through the positional indicia on the first fence. 
     In the instances where the linear motor is a stepper motor, there is also a second linear encoder fence carried by the shuttle having sensible positional indicia thereon and second sensor means carried by the ballistic energy transfer device for sensing the positional indicia of the second encoder fence as the shuttle moves back and forth and for producing a signal at an output thereof reflecting the position of the shuttle with respect to the ballistic energy transfer device whereby the linear motor is more easily controlled. 
     Also in the preferred embodiment, speed control circuit means are operably connected to the linear motor for adjustably controlling the speed of the shuttle. The preferred speed control circuit means includes means for adjusting the speed of the shuttle from between 5 inches per second and 100 inches per second. 
     The preferred first spring means comprises a pair of impact pads carried by respective ends of the shuttle and a pair of second springs carried by the ballistic energy transfer device at the ends of a span of movement of the shuttle to be contacted by respective ones of the impact pads whereby the second springs are compressed and then rebound to urge the shuttle in the opposite direction. For optimum energy conservation, the impact pads are disposed on a line running through the center of gravity of the shuttle whereby sideward, friction producing forces against the shuttle by the second springs are minimized. Also preferably, the second springs are leaf springs supported by the ballistic energy transfer device at ends thereof; the second springs are positioned transverse the path of travel of the shuttle to be impacted and deflected at a center thereof by the impact pads; and, the second springs have a spring constant chosen to turnaround the movement of the shuttle in less than 3 milli seconds. 
     Additionally for the purposes of energy conservation, first balancing means are connected to the ballistic energy transfer device for eliminating forces therefrom sideward to the path of movement thereof and second balancing means are connected to the shuttle for eliminating forces therefrom sideward to the path of movement thereof. Also, there are first support means for frictionlessly supporting a portion of the weight of the shuttle to reduce the frictional drag thereon during movement thereof and second support means for frictionlessly supporting a portion of the weight of the ballistic energy transfer device to reduce the frictional drag thereon during movement thereof. The preferred first support means comprises a magnetically attractable plate attached to a top surface of the shuttle and a magnet supported above the shuttle close adjacent the plate to attract the plate and thereby support a portion of the weight of the shuttle. The preferred second support means comprises a coil spring disposed vertically between a bottom of the printer base and the ballistic energy transfer device. 
     An alternate version of the linear motor comprises a vertical member carried by the shuttle and a solenoid assembly carried by the ballistic energy transfer device and having a moving member operably connected to the vertical member. 
     In one variation, the ballistic energy transfer device is part of the printer base. To accomplish that, there is an embodiment wherein there is a support rod carried by the ballistic energy transfer device; means for slidably mounting the shuttle to the support rod; and, means for supporting the ballistic energy transfer device for the oscillating movement wherein the means for supporting the ballistic energy transfer device for the oscillating movement comprises a pair of leaf springs disposed vertically between a bottom portion of the printer base and the ballistic energy transfer device. In another variation, the entire printer base is the ballistic energy transfer device with the printer base mounted on compliant rubber feet to accomodate the movement of the printer base. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a simplified side view of a prior art dot matrix printhead. 
     FIG. 2 is a rear view of the printhead of FIG. 1. 
     FIG. 3 is a front view of the printhead of FIG. 1 in an embodiment wherein the printhead only has one print wire emerging therefrom. 
     FIG. 4 is a front view of the printhead of FIG. 1 in an embodiment wherein the printhead has a plurality of print wires emerging therefrom. 
     FIG. 5 is a simplified drawing showing the way in which a prior art dot matrix printer of the non-shuttle variety starts the movement of its printhead across a page to be printed. 
     FIG. 6 shows the prior art dot matrix printer of FIG. 5 at the end of movement of its printhead across a page to be printed and returning in the opposite direction. 
     FIG. 7 shows the prior art dot matrix printer of FIGS. 5 and 6 with its printhead returning across a page to be printed towards the point cf origin with a line of text printed. 
     FIG. 8 is a simplified drawing showing the way in which a prior art dot matrix printer of the shuttle variety starts the movement of its multiple printheads in one direction across a page to be printed. 
     FIG. 9 shows the prior art shuttle printer of FIG. 8 returning in the opposite direction. 
     FIG. 10 is a plan view of the shuttle of a typical prior art dot matrix printer of the shuttle variety and its manner of generation of shuttle motion of the multiple printheads carried thereby by means of a rotary motor and crank. 
     FIGS. 11-13 are simplified drawings depicting the basic manner of operation of the present invention. 
     FIG. 14 is a more detailed front view of a shuttle printer according to the present invention in a first embodiment wherein only the shuttle is motor driven. 
     FIG. 15 is a partially cutaway drawing of the shuttle printer of FIG. 14 showing the manner in which the shuttle and inertia ballistic energy transfer device are slidably mounted on common shafts carried by the printer base. 
     FIG. 16 is a more detailed front view of a shuttle printer according to the present invention in a second embodiment wherein both the shuttle and inertia ballistic energy transfer device are motor driven. 
     FIG. 17 is a cutaway end view through the shuttle printer of FIG. 15 in the plane XVII-XVII. 
     FIG. 18 is a simplified front view showing one way of causing a variable rebound force and turnaround point in apparatus according to the present invention. 
     FIG. 19 is a simplified front view showing another way of causing a variable rebound force and turnaround point in apparatus according to the present invention. 
     FIG. 20 is a more detailed drawing of how a solenoid carried by a moving member can be employed to cause a variable rebound force and turnaround point in apparatus according to the present invention. 
     FIG. 21 is a more detailed drawing of how a solenoid carried by a stationary member can be employed to cause a variable rebound force and turnaround point in apparatus according to the present invention. 
     FIG. 22 is a drawing of a shuttle according to the present invention adapted for used in a &#34;focused&#34; mode of operation wherein a plurality of multi-pin printheads are employed across the width of the shuttle. 
     FIG. 23 is a partially cutaway, simplified, front view of a printer according to the present invention in a first preferred embodiment thereof. 
     FIG. 24 is a cutaway end view through the printer of FIG. 23 in the plane XXIV--XXIV. 
     FIG. 25 is a partially cutaway, simplified, front view of a printer according to the present invention in a second preferred embodiment thereof. 
     FIG. 26 is a cutaway end view through the printer of FIG. 25 in the plane XXVI--XXVI. 
     FIG. 27 is a motion and timing diagram of the operation of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The basic philosophy of the present invention is depicted in simplified form in FIGS. 11-13. Rather than slidably connecting the shuttle 24 to the printer base 38 as in the prior art, the shuttle printer 40 of the present invention employs a ballistic energy transfer device 42 to carry the shuttle 24. The ballistic energy transfer device 42 is of a mass which, preferably, is (but need not be) at least several times the mass of the shuttle 24. Preferably, the ballistic energy transfer device 42 is about five times the mass of the shuttle 24. There is a tradeoff which the designer must take into consideration when designing a printer employing the present invention. The distance and speed of movement of the ballistic energy transfer device 42 is in the same ratio as its mass is to the mass of the shuttle 24; that is, in the case where the ballistic energy transfer device 42 is ten times the mass of the shuttle 24, the ballistic energy transfer device 42 will move 1/10 the distance at 1/10th the speed of the shuttle 24. Thus, by making the mass of the ballistic energy transfer device 42 very large, it can be made to move very slightly from side to side at a lower velocity while the shuttle 24 moves quickly through its full oscillation cycle to produce the lines of printing. The ballistic energy transfer device 42 acts to greatly reduce the energy required to drive the shuttle 24. In embodiments tested by the inventors herein, a 90% energy transfer (i.e. only 10% of the energy is lost) appears to be attainable. 
     The shuttle 24 is directly driven longitudinally by a linear motor 44 (or other linear drive device) instead of by the crank and link system of the prior art as described earlier herein. The coils 46 are carried by the ballistic energy transfer device 42 and the armature 48 is carried by the shuttle 24 as shown in the figures. Note that the preferred configuration is with the ballistic energy transfer device 42 rectangular in shape with a rectangular opening 50 in the center thereof into which the rectangular shuttle 24 is disposed. As will be seen in one embodiment to be described hereinafter, it is possible to employ the printer base 38 as the ballistic energy transfer device 42 if desired. The shuttle 24 is positioned between a pair of rebound springs 52. In the preferred embodiment, the spring constant of the springs 52 is chosen so as to be able to impart a force to the shuttle 24 which can affect turnaround cf the shuttle 24 in less than 3 ms. Turnaround times of less than 1 ms have already been achieved with this mechanism in tested embodiments thereof. It should be noted in this regard that the turnaround time of the shuttle 24 is independent of the speed thereof--within the safe stress limits of the springs 52. In similar manner, the ballistic energy transfer device 42 is positioned between a pair of centering springs 54 carried by the end walls 56 of the printer base 38. The spring constant cf the springs 54 is chosen so as to only center the ballistic energy transfer device 42 in the static state. That is their only function and their spring constant should not be large enough to affect the operation of the mechanism in other ways. As can be appreciated, the above-described configuration results in a quick reversal of the shuttle 24 at the ends of its oscillation (e.g. under 3 ms) without the transfer of forces into the printer base 38. The shuttle 24 and ballistic energy transfer device 42 move in opposite directions as depicted in the drawing figures. Note that, for simplicity, the drawings are not to scale in this regard. The ballistic energy transfer device 42 and the shuttle 24 are easily reversed without the imparting of large forces into the printer base 38. Most of the kinetic energy is transferred by the ballistic energy transfer device 42 back to the shuttle 24 and never reaches the printer base 38. It should be noted at this point that while springs are shown and described herein for various functions, it is anticipated that magnet pairs could be substituted for the springs, if desired, with like poles adjacent one another so as to create and employ a magnetic repulsion force in lieu of a spring force. 
     The shuttle printer 40 of the present invention is shown in greater detail in FIGS. 14, 15 and 17 with an alternate embodiment, 40,, employing a power drive for the ballistic energy transfer device 42 instead of for the shuttle 24 shown in FIG. 16. As those skilled in the art will appreciate, either device (i.e. the ballistic energy transfer device 42 or the shuttle 24) can be the driven device in a printer according to the present invention. In all other regards, the embodiment of FIG. 16 is virtually identical to the embodiment of FIGS. 14, 15 and 17 and, therefore, &amp;.he embodiment of FIG. 16 will not be addressed further herein in the interest of simplicity and the avoidance of redundancy. 
     The shuttle 24 and ballistic energy transfer device 42 are slidably mounted on a pair of shafts 58 carried by the printer base 38. To date, acceptable performance has been achieved by having narrow points of contact with the shafts 58 and the use of phosphor bronze bushings, or the like. If desired, other forms of low friction mountings or support could be employed in lieu of or in addition to the mountings shown. For example, magnetic fields and/or springs could be disposed to support the weight of the ballistic energy transfer device 42. This will be shown in other embodiments to be described later herein. 
     The preferred ballistic energy transfer device 42 is an open rectangle in shape and, therefore, already suited for the low contact mounting on the shafts 58 described above. The shuttle 24 is generally &#34;H&#34; shaped having a rectangular body portion 60 carrying a plurality of pin drivers 62 disposed in side-by-side relationship. Four legs 64 extend outward from the corners of the body portion 60. The shafts 58 pass through respective pairs of the legs 64 as shown. The linear motor armature 48 is attached to the two bottom legs 64. The coils 46 are linearly attached to the bottom 66 of the ballistic energy transfer device 42 to position the coils 46 along the armature 48 in close spaced relationship thereto. The coils 46 are operably connected to a power source (not shown) through speed control circuit 47 which allows the speed of movement of the shuttle 24 to be varied for different printing conditions. For example, the inventors herein have determined that &amp;:he speed of the shuttle 24 should be variable from 5 inches/sec to 100 inches/sec in order to allow for a wide range of font selections and graphics resolutions. The preferred centering springs 54 are weak coil springs carried between holes 68 in the printer base 38 and the ballistic energy transfer device 42 provided therefor. The preferred rebound springs 52 are leaf springs which are contacted by impact pads 69. The rebound springs 52 are much more critical and will be returned to in greater detail shortly. 
     As best seen from the cutaway view of FIG. 17, the pin drivers each comprise a coil 70 for attracting a spring-loaded armature 72. The end of the armature 72 is connected to one end of a print pin 16 which passes through a bore 73 in the body portion 60 provided therefor. The other end of each print pin 16 emerges close adjacent an adjustable platen 74 carried by block 76 attached to the printer base 38. A plastic encoder &#34;fence&#34; 78 is also carried by the printer base 38 to be parallel to the path of movement of the shuttle 24. A sensor 36&#39; is carried by the shuttle 24 to sense the encoder fence 78 as the shuttle 24 moves back and forth and develop a positional signal on its output wires 79 indicating the position of the shuttle 24 with respect to the printer base 38. In its preferred embodiment, the encoder fence 78 is of transparent plastic and the sensor 36&#39; is of the type that has a light emitting diode on one side of the fence 78 and a phototransistor on the opposite side so as to develop an electrical position signal on wires 79 as a function of light passage through positional indicia on the fence 78. 
     In initial testing of the present invention, it has been found to be beneficial to be able to adjust the length of travel of the shuttle 24. While not determined to be as important as of this time, it may also be desirable to apply the same provision with respect to the ballistic energy transfer device 42 and its centering springs 54. Therefore, it is preferred that such provisions be included within a shuttle printer made and operating in accordance with the teachings of the present invention. Several methods and associated apparatus for this purpose will now be discussed. 
     In the approach of FIG. 18, a single leaf spring 80 adapted for bilateral movement as indicated by the arrows is carried by the moving member 82. The bilateral leaf spring 80 is provided with an impact pad 69 on either side at the intended points of contact. The stationary member 84 is provided with a stop block 86 at each end of the span of travel of the spring 80. The stop block 86 is provided with one or more removable stops 88. If desired, the stops 88 can be added or removed by a solenoid (not shown) or the like. Note in this embodiment that the length of the span is changeable in a fixed amount while the spring constant, k, of the spring 80 remains the same. 
     A variation of the approach of FIG. 18 is shown in FIG. 19. In this embodiment, the length of the span is again changeable while the spring constant of the spring 80 remains the same. A pair of unidirectional single leaf springs 90 are attached to the stationary member 84 at each end of the span of travel. Each leaf spring 90 is provided with an impact pad 69 on its inside face at the intended point of contact. Each end of the moving member 82 is provided with a stop block 86&#39; which, in turn, is once again provided with one or more removable stops 88. As in the previous embodiment, if desired, the stops 88 can be added or removed by the solenoid 96 or the like. 
     A pair of preferred approaches are shown in FIGS. 20 and 21. The approach of these figures is similar to the approach of FIG. 19 above. In these embodiments, however, the change in span of travel is precipitated by changing the spring constant, k, of the associated spring. With reference first to FIG. 20, a unidirectional, variable spring constant leaf spring 90&#39; is once again carried by the stationary member 84 at each end of the span of travel (only one being shown in the drawing for simplicity). The stop block 86, of this embodiment is a movable block carried on the end of a rod 92 carried by the armature 94 of a solenoid 96. By activating the solenoid 96, the contact position of the impact pad 69 carried by the stop block 86&#39; can be changed so as to contact the spring 90, along its length at a low k position or a high k position. As those skilled in the art will readily recognize and appreciated, by replacing the two position solenoid 96 with a variably positionable device, of course, more variations in the k of the spring 90, (and, therefore, variations in the span of the moving member 82) can be achieved. 
     A variation of this general approach is shown in FIG. 21 where the solenoid 96 is mounted above the spring 90&#39;. A force transfer ball 98 is attached to one end of a flexible vane 100 carried on the other end by the armature 94 of the solenoid 96 (or, optionally, a variable position device as mentioned above). The ball 98 can be moved along the spring 90, between positions of low k and high k as indicated in the drawing. A force transfer spring 90&#34; is positioned on the other side of the ball 98 to be contacted along its length by the impact pad 69 carried by the end of the moving member 82. As can be appreciated, the spring constant of the springs 90&#39; and 90&#34; is additive and should be considered when calculating the parameters of each. When the impact pad 69 strikes the spring 90&#34;, it (at a constant k) transfers the force to the ball 98 at its point of contact with the spring 90&#34;. The ball 98, in turn, transfers the force to the spring 90&#39; at its point of contact. The spring 90&#39;  provides a variable k of resistive force as a function of the position of the ball 98 on its length. 
     Another important aspect of the present invention determined by testing of the inventors herein is the need to balance the system in order to minimize energy loss during operation. As shown in FIG. 14, balancing of both the ballistic energy transfer device 42 and shuttle 24 is preferably accomplished by adding weights 65 at appropriate locations so that the rebound force is through the center of gravity. This results in virtually no sideward, friction producing components of the energy force within the sliding surfaces of the system with resultant rebound energy loss. As a consequence, energy conservation is maximized and driving energy requirements are minimized. The weights 65 can be of fixed weight or made to be adjustable, as desired. Alternatively, of course, instead of adding weight at light points to balance the system, weight could be removed from heavy points (as by drilling) to accomplish the same result. 
     Turning now to FIGS. 23-26, two embodiments of the present invention in its best mode as presently contemplated following testing of various approaches will now be described. In the embodiment of FIGS. 23 and 24, the shuttle 24 is still slidably mounted between the pair of shafts 58. The legs 64,, however, have been reduced to a thin web 102 where they contact the shafts 58 so as to reduce possible friction. The tops of the upper legs 64&#39; have a ferrous plate 104 attached thereto. The printer base 38 has a pair of horizontal arms 106 extending out over the top of the ballistic energy transfer device 42 and parallel thereto. The arms 106 each carry a magnet 108 which passes through a slot 110 in the ballistic energy transfer device 42 into close-spaced proximity to the adjacent plate 104 to create an attracting and lifting force therein which tends to frictionlessly support a portion of the weight of the shuttle 24 and thereby reduce the friction associated with its sliding movement along the shafts 58. In like manner, the ballistic energy transfer device 42 is supported on a pair of vertically mounted coil springs 112 which frictionlessly support a portion of the weight of the ballistic energy transfer device 42 while allowing side to side movement thereof and thereby reduce the friction associated with its sliding movement along the shafts 58. This in combination with the balancing described above minimizes the energy loss of the shuttle 24 and the ballistic energy transfer device 42 through friction. Note also that the size of the armature 48 has been reduced and it is mounted vertically between two opposed rows of coils 46 to provide the linear motor 44. In addition to reducing the amount of area which is in sliding contact with the shafts 58, the construction as shown concentrates the majority of the mass of the shuttle 24 along the center line thereof passing through the contacting impact pads 69. Note that in this embodiment the rebound springs 52, are flexure springs supported at both ends so as to provide a stiff, quick acting, flicking action in rebounding the shuttle 24 for minimization of the turnaround time. Note also that in this embodiment the centering springs 54 are disposed along the centerline of the system between the shafts 58 so as to impart virtually no sideward forces (even minimal ones) against the ballistic energy transfer device 42 which might cause friction producing results. 
     In the embodiment of FIGS. 25 and 26, there is a substantial change from the implementation of the present invention as hereinbefore described. Note, however, that the basic manner of operation is still present. The first major deviation is that the ballistic energy transfer device 42 is no longer mounted for sliding motion on the shafts 58. Rather, it is supported at its top (i.e. it hangs) between the tops of a pair of spaced, vertical leaf springs 114 extending upward from and carried by the printer base 38. As will be recalled, it was mentioned earlier that the printer base 38 could be used as the ballistic energy transfer device 42 if desired. As those skilled in the art will readily appreciate, it is this embodiment that could be so configured in various ways. A large, heavy printer base 38 mounted for lateral movement on a support base would energy transfer device 42. As in the previous embodiment, the upper legs 64&#39; have a ferrous plate 104 attached thereto and a pair of magnets 108 are carried by the upper portion of the ballistic energy transfer device 42 in close-spaced proximity to respective ones of the adjacent plates 104 to create an attracting and lifting force therein which tends to frictionlessly support a portion of the weight of the shuttle 24 and thereby reduce the friction associated with its sliding movement along the shaft 58. Note that in this embodiment, as in the previous embodiment, the rebound springs 52&#39; are flexure springs supported at both ends so as to provide a stiff, quick acting, flicking action in rebounding the shuttle 24 for minimization of the turnaround time. 
     In this embodiment, the linear motor 44 has been replaced by a solenoid drive system generally indicated as 116. As those skilled in the art will appreciate, the solenoid drive system 116 is a form of linear drive and, therefore, the linear motor 44 as described with respect to the previous embodiments could be employed with this embodiment. Likewise, the solenoid drive system 116 of this embodiment could be substituted for the linear motor 44 in any of the previously described embodiments. As shown in the drawings, the solenoid drive system 116 includes a U-shaped mounting plate 118 attached to the bottom of the ballistic energy transfer device 42 under the shuttle 24. The shuttle 24, in turn, has a mounting plate 120 attached to the bottom thereof with a vertical member 122 extending downward therefrom between the two vertical ends of the mounting plate 118. The bottom of the mounting plate 118 has a longitudinal slot 124 therein into which a guide finger 126 extending from the bottom of the member 122 fits for sliding motion. If desired, the guide finger 126 can have a roller bearing fitted thereon for virtually frictionless movement in the slot 124. The finger 126 in the slot 124 replaces the bottom shaft 58 of the prior embodiments in keeping the shuttle moving back and forth in a constant plane and not tending to rotate about the single shaft 58 from which it is hung. A pair of solenoid coils 128 are mounted to respective ones of the two vertical ends of the mounting plate 18. An armature core 130 extends from each of the coils 128 to the vertical member 122 where it is attached by a pin 132. As those skilled in the art will readily recognize and appreciate, the solenoid drive system 116 can be of the stored energy type or the moving coil (i.e. voice coil) type, as best fits the particular application. As with the linear motor 44, the solenoid drive system 116 is operably connected to the speed control circuit 47 to be controlled thereby. It should also be noted with respect to the choice of drives (i.e. a D.C. stepper motor or a D.C. linear motor such as a solenoid or the like) that when a stepper motor is employed, a second encoding device such as that described above (e.g. encoder fence 78 and sensor 36&#39;) mounted between the ballistic energy transfer device 42 and the shuttle 24 is preferred so as to obtain the position of the shuttle 24 within the ballistic energy transfer device 42 for optimum driving thereof. With a D.C. linear motor (linear actuator, solenoid, or the like), the second encoding device is not necessary since the device does not move step by step, but rather, once activated moves towards the extent of its movement as long as power is applied. 
     As those skilled in the art will readily recognize and appreciate, a variation of the foregoing approach would be to employ the entire printer including cover, electronics, etc. (with the exception of the shuttle 24 itself) as the ballistic energy transfer device 42. A large, heavy printer could be mounted for the necessary lateral movement on compliant rubber feet that would allow the printer to move slowly a slight distance from side to side during operation thereof. In such an embodiment, the shuttle 24 could again hang from a pair of thin-webbed legs 64&#39; slidably mounted on a single shaft 58 carried by the printer. 
     Another aspect of the present invention is also shown with respect to FIG. 25; however, the various techniques now to be described may be adopted for any of the embodiments herein. As can be appreciated, the speed control circuit 47 requires positional input information with respect to the shuttle 24 in order to effect proper control of the reversal drive forces applied thereto. This can be accomplished with an optical fence and sensor arrangement as previously described herein. Additionally, however, the rebound springs 52 in their various embodiments can also be employed for this purpose. For example, by suspending the shuttle 24 from a pair of insulating legs 64&#39; slidably mounted on the shaft 58, the rebound springs 52&#39; and impact pads 69 can be employed as the two contacts of a switch providing the signal of interest. In such case, the legs 64&#39; could be molded of glass-filled Nylon, or the like, with carbon bearings sliding on the shaft 58. Another possibility would be to mount a strain gauge 71 on the rebound spring 52&#39; to provide the signal of interest at an output thereof as a function of the flexing of the spring 52&#39;. Also, an accelerometer 73 could be mounted directly to the shuttle 24 to provide the signal of interest at an output thereof as a function of the acceleration and deceleration of the shuttle 24. 
     Having now discussed the construction and operation of a shuttle printer according to the present invention in general according to several embodiments thereof, some of the criteria to be considered in actually constructing a printer according to the teachings herein will now be addressed with particularity. In this regard, reference should also be made to the timing and motion chart provided as FIG. 27 herein. 
     As described hereinbefore, the shuttle printer of the present invention employs uniformly spaced pins across a print line moving at a constant speed while printing with a very fast turn around time. It is anticipated that turn around times in the order of 1 to 2 MS can be achieved. This is accomplished by a novel design that employs a linear shuttle motor and a kinetic energy transfer system. The design has the advantage of transmitting no inertial forces to the case or platen. The design also allows the turn around time to be varied. This feature can be employed, for example, to provide time to feed between lines of text without another pass of the printheads. In other word, if the shuttle carrying the printheads is turned around and begins its return trip before the paper can be fed to its next print position, the trip is a lost one and the printer will operate in a unidirectional mode. If the turn around time is adjusted so that the paper is in position for printing before the shuttle begins its return trip, the faster approach of bidirectional printing can be applied. 
     Another tradeoff that can be employed to good advantage in a shuttle printer according to the present invention is that of shuttle speed v. number of pins per printhead position. That is, while the prior art employs single pin printheads at each print position across the shuttle to keep the mass that must be accelerated and reversed to a minimum, the present invention allows one to select the best combination for optimum printer throughput. In this regard, initial investigation indicates that such optimum throughput is probably attained using printheads with multiple print pins vertically disposed above one another. For reference purposes, the single line of print pins spaced along the shuttle as depicted in the drawing figures described earlier herein is referred to as an &#34;unfocused&#34; approach while the use of multiple vertical print pins at each position, as represented by the shuttle 24&#39; of FIG. 22, is referred to as the &#34;focused&#34; approach. Some representative findings are shown in the following tables. 
     
                       TABLE 1                                                     
______________________________________                                    
2800 Hz Printhead Performance                                             
          24 Pins                                                         
                 33 Pins   48 Pins   66 Pins                              
______________________________________                                    
10 CPI (48 DPI)                                                           
            800 l pm 1052 l pm 1345 l pm                                  
                                       1800                               
l pm                                                                      
Shuttle Frequency                                                         
            48 Hz    64 Hz     86 Hz   113 Hz                             
Printing Efficiency                                                       
            90.5%    87.3%     82.7%   77.4%                              
10 CPI (60 DPI)                                                           
            656 l pm 870 l pm  1176 l pm                                  
                                       1538                               
l pm                                                                      
Shuttle Frequency                                                         
            39 Hz    52 Hz     71 Hz   95 Hz                              
Printing Efficiency                                                       
            92%      87.3%     82.7%   77.4%                              
Shuttle Motion                                                            
            .55&#34;     .4&#34;       .28&#34;    .2&#34;                                
Print Line  13.2&#34;    13.2&#34;     13.44&#34;  13.2&#34;                              
______________________________________                                    
 ##STR1##                                                                 
Time                                                                      
______________________________________                                    
 
    
     
                       TABLE 2                                                     
______________________________________                                    
Linear Shuttle Throughput (Non Focused)                                   
           28 Pins                                                        
                  28 Pins  49 Pins  49 Pins                               
______________________________________                                    
10 CPI (48 DPI)                                                           
             888 1pm  804 1pm  1415 1pm                                   
                                      1214                                
1pm                                                                       
Shuttle Frequency                                                         
             52 Hz    47 Hz    87 Hz  89 Hz                               
Printing Efficiency                                                       
             86.5%    70.4%    78.3%  61.1%                               
10 CPI (60 DPI)                                                           
             732 1pm  674 1pm  1188 1pm                                   
                                      1043                                
1pm                                                                       
Shuttle Frequency                                                         
             43 Hz    39 Hz    69 Hz  71 Hz                               
Printing Efficiency                                                       
             88.9%    73.3%    81.8%  65.0%                               
Shuttle Motion                                                            
             .48&#34;     .48&#34;     .27&#34;   .27&#34;                                
Print Line   13.44&#34;   13.44&#34;   13.23&#34; 13.23&#34;                              
LF/TurnAround                                                             
             1 MS     2 MS     1 MS   2 MS                                
______________________________________                                    
 
    
     
                       TABLE 3                                                     
______________________________________                                    
Linear Hybrid Shuttle Throughput (Focused)                                
Pins       2 × 7 Pins                                               
                     3 × 7 Pins                                     
                               4 × 7 Pins                           
                                       7 × 7                        
______________________________________                                    
10 CPI (48 DPI)                                                           
           497 1pm   723 1pm   935 1pm 1495                               
1pm                                                                       
Shuttle    4 Hz      6 Hz      8 Hz    12 Hz                              
Frequency                                                                 
Printing   94.2%     91.5%     89.1%   82.3%                              
Efficiency                                                                
10 CPI (60 DPI)                                                           
           402 1pm   588 1pm   765 1pm 1239                               
1pm                                                                       
Shuttle    3 Hz      5 Hz      6 Hz    10 Hz                              
Frequency                                                                 
Printing   95.3%     93.0%     91.0%   85.3%                              
Efficiency                                                                
Shuttle Motion                                                            
           6.6&#34;      4.4&#34;      3.3&#34;    1.9&#34;                               
Print Line 13.2&#34;     13.2&#34;     13.2&#34;   13.3&#34;                              
LF/TurnAround                                                             
           7 MS      7 MS      7 MS    7 MS                               
______________________________________                                    
 
    
     Where &#34;2×7 pins &#34; two 7-pin heads on the shuttle. 
     As those skilled in the art will appreciate, this invention is an improvement over the printer of Meloni as disclosed in U.S. Pat. No. 4,534,287 in that the Meloni apparatus employs a mechanical drive incorporating a motor-driven wobble plate or disk (designated as track 74) to oscillate a multi-pin print head to effect shuttle printer operation in much the same manner as the prior art apparatus shown in FIG. 10. 
     Thus, it can be seen from the foregoing that the present invention has truly met its stated objectives by providing a shuttle printer that can provide high quality output while printing at a much higher speeds than prior art dot matrix printers.