Patent Publication Number: US-3874288-A

Title: High speed impact printer

Description:
United States Patent 1191 Ellefson et al.  
 1 1 Apr. 1, 1975 1 HIGH SPEED IMPACT PRINTER [75] Inventors: Larry F. Ellefson; M. Ray Dilling,  
 both of Seattle, Wash.  
 [73] Assignee: Interface Mechanisms, lnc.,  
 Mountlake Terrace. Wash.  
 [22] Filed: Oct. 3, 1973 [21] App]. No.: 403,279  
 Primary E.\aminw&#39;Edgar S. Burr Assistant Examiner-Edward M Coren Attorney, Agent, or Firm-Christensen, OConnor, Garrison &amp; Havelka [57] ABSTRACT A high speed mechanical impact printer using a continuously rotating print wheel. Paper label stock is contained on a supply reel and fed through a print station comprising the print wheel and a print hammer by a motor and roller means positioned beyond the print station. Substantially constant tension is maintained between the supply reel and the print station by a spring assisted tension means operating in conjunction with the supply reel. The print wheel is secured to a beltdriven, printer drive member through a compressible plastic ring. In printing. a hammer impacts the label stock and an ink ribbon against the rotating print wheel under logic control. After printing. the stock proceeds through a mechanical means which permits the operator to conveniently strip the most recently printed label from the stock backing so that he may attach it to a commercial item or the like.  
 8 Claims, 11 Drawing Figures HIGH SPEED IMPACT PRINTER BACKGROUND OF THE INVENTION This imention relates generally to printing devices. and more specifically. to the art of high speed mechanical impact printers.  
  Mechanical impact printers are generally well-known in the art. although frequently such printers must be specially adapted for particular applications. The printing ol bar codes. such as that disclosed in US. Pat. No. 3.700.858 to Murthy. for purposes of high speed item identification. requires high resolution. accurately spaced. printing. The individual characters must be clear and precise. and the separation between charactcrs accurate and uniform. If such high resolution. uni form printing is not maintained. errors in reading the bar code will increase. to the detriment of the identification system using the code.  
  Futhermore. in the printing of label stock. the operator of prior art printers must peel off the individual labels manually from the stock backing after they are printed in order to affix them to the commercial item; e.g.. carton. which is to be identified. This manual stripping ol&#39; the labels from the stock backing is often im practical as it can only be accomplished some distance away from the rotating printing element.  
  Thus. there is a current need in particular printing applications for an impact printer. otherwise utilizing conventional impact printing principles. which is capable of printing high resolution. accurately spaced. characters lor particluar code printing applications. and in the case of label stock. for a means which presents the labels to the operator after printing in a condition such that they may be readily stripped and affixed to the item to he identified. In accordance with the above. it is a general object of the present invention to provide a mechanical impact printer which overcomes the dis advantages of the prior art.  
  It is another object of the present invention to provide an impact printer wherein the printing stock supply reel has a tensioning means in conjunction therewith for maintaining a substantially constant tension on the printing stock.  
  It is a further object of the present invention to provide an impact printer in which the time for actuation of the print hammer is substantially decreased.  
  It is yet another object of the present invention to provide a mechanical impact printer having a print wheel which is rotated by means of a compressible ring connection between the driving means and the print wheel.  
  It is a still further object of the present invention to provide a mechanical impact printer wherein labels may be individually stripped immediately after printing is accomplished.  
 SUMMARY OF THE INVENTION According. a compressible pad member is provided for use in coupling driving energy from a moving drive member to a print wheel. wherein the pad member is configured to mate with the drive member and thus move with it. and includes at least one compressible portion which extends away from one surface of the pad member to provide contact support for the print wheel. When the print wheel is forced toward the drive member. suficient friction contact between the drive member. the pad member and the print wheel is estab- Ill lished so that all three move together when the drive member is moved.  
 DESCRIPTION OF THE DRAWINGS A more thorough understanding of the invention may be obtained by a study of the following description olthe preferred embodiment taken in connection with the accompanying drawings in which:  
  FIG. I is a simplified isometric view of the impact printer.  
  FIG. 2 is an elevation icw of the label stripper mechanism of the present invention.  
  FIG. 3 is a plan \iew ol&#39; the label stripper mechanism of the present invention.  
  FIG. 4 is an isometric view of the tensioning means associated with the stock supply reel of the present invention.  
  FIG. 5 is a partial section elevation view of the print hammer actuator mechanism of the present im ention.  
  FIG. 6 is a section view of the print wheel of the present invention.  
  FIG. 7 is a simplified representation of the print hammer actuator mechanism of the present invention.  
  FIG. 8 is a graph of the motion of the print hammer against time during actuation.  
  FIG. 9 is a graph olthe current through the coil olthe print hammer actuator mechanism of FIG. 7 against time during actuator.  
  FIG. 10 is a top plan view of the compressible pad of the present invention.  
  FIG. [0a is a section view of the compressible pad. taken along lines Illa-Illa in FIG. II).  
 DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. I. an isometric view of the impact printer otthe present invention is shown. As in prior art printers. input power is supplied via a standard I20 volt line (not shown) to a power supply module 12. which in turn provides power for the printer. including the logic control circuit I4. Signals from peripheral equipment can be connected into the printer through connectors [6 to the motor drive circuit 18. and the logic control circuit I4. These two circuits I8 and [4 control, in conventional fashion. the operation of the printer. Printing stock I9 is typically stored on a supply reel 20. and is directed around arm 22. through stock sensor 24. through a print station. comprised of print hammer assembly 26 and a cylindrical print wheel 28. through a label stripper 30. and then through a stock stepper assembly 32. which typically contains a motor drive and a pair of rollers. for placing the printing stock under tension.  
  The ink ribbon 34 is typically stored on a supply reel 36.. first positioned partially around guide pin 38. then directed between the printing stock 19 and the circumferential surface of the print wheel 28 before going through a powered ribbon drive assembly 40. and finally wound up on a ribbon take-up reel 42 which is driven by motor 44. The print wheel 28 is cintinuously rotated in operation by means of drive motor 46 acting through a drive wheel 54 and belt 48.  
  In operation. print wheel 28. having a set of raised print characters arranged around its circumferential surface. continuously rotates by means of drive motor 46, and the ribbon 34 and printing stock 19 are pulled past the print station comprising print hammer assembly 26 and print wheel 28 by means of their respective take-up motors. The logic control board 14 issues signals commands to the print hammer assembly 26. which signal commands actuate the print hammer to impact the printing stock [9 and the ribbon 34 sufficiently against the circumferential surface of the print wheel 28 that a single raised character is imprinted on the stock 19. A system for synchronizing the operation of the rotating print wheel and the hammer assembly is disclosed in copending application Ser. No. H0517, filed Jan. 28, l97l. entitled &#34;High Speed Printer&#34; and is assigned to the same assignec as the present inven tion. Briefly, such a synchronization system utili7es a cylindrical code wheel. attached to the print wheel and rotating therewith, which code wheel has a plurality of coded holes patterns, one for each print character, located therein. Photoelectric means is used to detect the hole patterns, which data is in turn applied to a circuit which compares the code data with signals representing the desired character selected at a keyboard or similar device. When there is a coincidence. the print hammer is actuated. resulting in the desired character being printed.  
  Referring now to FIGv 6. a cross section view of the print wheel assembly of the present invention is shown. The print wheel assembly consists generally of: a housing 52. which is attached to the deck of the printer; a drive assembly comprising drive wheel 54, bearing 56 and drive shaft 58; print wheel 60; securing knob 62&#39;, and a compressible plastic ring pad 64. in operation, motor 46 (FIG. 1 rotates drive wheel 54 by means of the belt 48 (FIG. 1 connecting the motor 46 and the drive wheel 54. Shaft 58 does not rotate with the drive wheel 54. but is anchored into the housing 54 by end bolt 57.  
  The print wheel 60 is secured to the rotating drive wheel 54 by means of the compressible ring pad 64, which is positioned between the drive wheel 54 and print wheel 60. The print wheel 60 is forced toward the drive wheel, compressing ring pad 64, by means of screw-adjusted securing knob 62, which is turned into the drive shaft 58. Thus, the only contact between drive wheel 54 and the print wheel 60 is through the compressible polyurethane ring pad 64, shown in position in FIG. 6, and in more detail in FIGS. and a. The compressible pad 64 is in the shape of a ring having outer and inner boundary surfaces 65 and 67, respectively. A trough 68. formed in the ring pad 64 enables the ring pad to be fitted snugly over a mating ring 69 in drive wheel 54. Trough 68 substantially follows the shape of the outer and inner boundary surfaces 65 and 67. resulting in a compressible ring pad having two concentric edge members 6411 and 64h extending perpendicularly from a cross member 641&#39; connecting edge member 64a and 64h and one end thereof. Extending away from surface 64d of connecting member 64c are a plurality of integral compressible hemispheres 7070, which are of the same compressible polyurethane material as the remainder of the compressible ring pad.  
  Print wheel 60 rests on the plurality of compressible hemispheres 70-70, and these hemispheres are compressed by the action of tightening securing knob 62 into shaft 58. The friction fit between the print wheel 60. the compressible ring pad 64 and the ring portion 69 of drive wheel 54 is sufficient to rotate print wheel 60 by rotating drive wheel 54 by means of motor 46 and belt 48. without slippage between them. A hearing 66 is positioned between the print wheel and shaft 58 to provide rotational freedom of movement. The friction drive of print wheel 60 accomplished by compressible ring pad 64 eliminates the need for high tolerance machining and keying to mate a print wheel with a drive wheel, as is done in the prior art. The friction drive also significantly reduces the potential for printing inaccuracies due to wear or poor machining of the print wheel 60 or the drive wheel 54. Furthermore, such an arrangement allows for the print wheel to be easily removed for cleaning or exchange. as desired, without the necessity of time-consuming realignment of the printing wheel assembly.  
  The print station, as mentioned above, comprises print wheel assembly 28 and the print hammer assembly 26 (FIG. I) which is under the control of control logic circuit l4. Referring to FIG. 5. the print hammer assembly 71 is shown in a partial section view. When the hammer 7lu is to be actuated toward print wheel 72, a signal is applied from control logic 14 (not shown) to an electromagnct (not shown) within the assembly. When the electromagnct is energized by current flowing through its coil (not shown) lever arm 74 which is secured to the hammer assembly 71 by flexible member 76 at one end thereof, is drawn into contact with a portion 78 of the assembly electromagnct (otherwise not shown). As lever arm 74 moves toward the magnet portion 78, hammer arm 80 moves in the direction of the arrow toward the circumferential surface 73 of print wheel 72. At the other end 83 of hammer arm 80 is connected hammer 71a. When lever arm 74 is actuated, hammer 71a moves in the direction of the arrow toward circumferential surface 73 of print wheel 72 to such an extent as to impact the printing stock (not shown) and ink ribbon (not shown) positioned be tween the print wheel 72 and the print hammer 71 against a particular character 72a on circumferential surface 73.  
  When the current is discontinued through the electromagnct. lever arm 74 springs back away from engagement with magnet portion 78 by means of flexible member 76. The force of this sprng back is absorbed by spring loaded stop 84, and any oscillations of hammer arm 80 are quickly damped. Such a print hammer assembly is commonly referred to as a cantilever beam assembly.  
  A principal disadvantage to such print hammer assemblies has been the time heretofore required to actuate and retrieve the print hammer mechanism. The re sponse time ofthe mechanism is dependent on the rate of increase of current or di/dr. in the electromagnct coil. The greater the rate of increase in current over time. the faster the hammer will actuate. Heretofore, however, coil di/d! has been limited because high [Ii/d! values have been obtained only by using actuator circuits which produce a high value of coil current for much of the hammer travel time, which results in undesirable coil heating and drive transistor strain, ultimately resulting in failure of both elements.  
  To prevent high heat loss and coil failure, while significantly increasing coil (Ii/d! so as to provide faster actuation of the print hammer, the actuator circuit of the present invention has been developed. Referring to FIG. 7, a significantly higher actuating voltage V,, than is provided by the prior art I00 volts as opposed to approximately 25 volts) is connected through a transistor 90 and an RC circuit comprising capacitor 92 and resisitor 94 to the electromagnct coil 96. Transistor 90 is controlled by a signal from control logic circuit 14 (not shown). In operation, when transistor 90 is turned on by the logic control signal. current flows primarily through capacitor 92 and coil 96. A diagram of coil current v. time is shown in FIG. 9. As the charge on capacitor 92 approaches actuating voltage V,,. the current decreases to a value dependent on resistor 94. thus limiting the energy dissipated in coil 96 to a tolerable level and easing the load on transistor 90. Because of the high initial rate of current increase. however, the hammer 97 begins to move substantially sooner than previously. and actuation time is reduced. At 1.2 milliseconds from the start of current flow. hammer 97 intpacts the paper stock and ribbon against the desired character 99. A graph of distance v. time for the travel of the print hammer is shown in FIG. 8.  
  Referring again to FIG. I. printing stock 19 is directed through a print station comprising print hammer assembly 26 and print wheel 28 by means of a supply reel 20, and a label stepper 32. which exerts a pulling force on stock I9. However. in certain applications, such as label printing, where the movement of the printing stock is not uniform. slack will tend to occur in the printing stock between the supply reel 20 and the print station. Any such slack is ordinarily unsatisfactory. as it results in either distortion of the printed characters or variations in the character separation or both. The printed code is thus more difficult to accurately read and subject to an increased number of reading errors.  
  To overcome this tendency. a tensioning means is provided by the present invention in conjunction with the supply reel 20. as shown in FIG. 4. A printing stock supply reel I is positioned conventionally on a reel spindle 102. In operation, stepper 32 exerts a pulling force on stock I9. and hence pressure on roller guide 104. which roller guide is rotatably mounted on one end I of guide arm I06. The other end I07 of guide arm I06 is fixedly connected to a rotating arm assembly 108. which comprises a cylinder I10 fixedly mounted on plate I12, which arm assembly rotates with the rotation of guide arm 106 about a fixed central shaft II4 against the tension of spring I16. one end of which is secured to a fixed peg I18. and the other end to a peg I on the rotating arm assembly I08. As the force on the stock 101 increases in the direction of the arrow, thus forcing guide arm 106 to move counterclockwise about central shaft II4, the rotating arm asscmbly I08 also rotates counterclockwise. forcing the free end I22 of pivot arm I24 toward the periphery of supply reel I00 against the tension of spring I27. This movement of pivot arm I24 reduces the braking force of tension arm I26. which is secured to pivot arm I24, against supply reel spindle ring 128. allowing spindle 102 to rotate more freely. and thus feed printing stock I01 faster. Roller guide I04 and guide arm 106 will eventually reach an equilibrium angular position when a constant force is exerted on stock IOI. However, if the force on stock 101 varies. as in label printing, the angular position of guide I04 and guide arm I06. and hence, the remainder of the system will attempt to track the force. &#34;searching&#34; for an equilibrium position.  
  For instance. if the force on roller guide 104 is saddenly reduced, as would occur with the return of the stripper to its original position. the tension exerted by spring 116 will tend to rotate the arm assembly I08 in the clockwise direction. and along with it guide arm I06 and roller guide I04 until a system equilibrium is reached. Equilibrium is eventually achieved because the clockwise rotation of arm assembly I08 will allow pivot arm I24 to move in the direction of the spindle I02. under the tension of spring I27. This will increase the braking force on spindle ring I28 exerted by tension arm I26. and the supply reel will thus he increasing braked. Such a responsive tensioning device tends to maintain that portion of printing stock 101 located between the supply reel and the print station in substantially constant tension, thus increasing printing resolution and accuracy. and hencec. reducing code read ing errors.  
  Following the print station is located a label stripper 30, shown generally in FIG. I and in more detail in FIGS. 2 and 3. In operation. the label stock (when used) is passed between guide elements I30 and I32. connected by support member 133. The entire stripper 30 is rotatable about axis I34 I34 with respect to the deck of the printer. so that it may be conveniently taken out of operation. Guide elements I30 and I32. as well as support element I33 are rotatable about axis I35-I35. By rotating the stripper about axis I35-I35 in a clockwise manner from its original position by convenient means of rotation knob I42. peg I30 guides the label stock through a substantially U- shaped path before it comes to the label stepper 32. Although the stock backing follows such a path. the labels themselves do not, and separate from the backing when the backing begins to bend to follow the U-shaped path. By thus rotating label stripper knob 142 in such a fashion. the operator is able to strip a label in close proximity to the print mechanism. and then conveniently place them. if desired. on appropriate cartons or other commercial items. Located within rotation knob I42 is a spring I40. which is secured at one end thereof such that the knob. and hence, guide pins I30. I32 are rotated against the tension of the spring. When the knob I42 is released. the action of spring I38 returns the stripper elements to their rest position of FIG. I. Bendable stop MI is provided to lock the stripper in operating position. if desired. A spring I38 is positioned so as to place the stripper 30 and element I39 in tension along shaft I39a.  
  Thus, a mechanical high speed impact printer has been disclosed which utilizes a generally conventional configuration but which has several novel features to increase printing resolution. printing accuracy, and operational convenience in the printing of bar codes on labels or other printing stock.  
  Although an exemplary embodiment of the invention has been disclosed herein for purposes of illustration, it will be understood that various changes, modifications and substitutions may be incorporated in such embodiment without departing from the spirit of the invention as defined by the claims which follow.  
 What is claimed is:  
  I. An article useful in an impact printer for coupling rotational force generated by a drive member mounted to rotate about a central shaft to a print wheel mounted to rotate about said central shaft and movable there along by means mounted on said central shaft for moving said print wheel axially of said central shaft in the direction of said drive member, comprising a ring-like. generally flat pad having upper and lower spaced surfaces and a peripheral edge surface therebctween. the lower surface of which is adapted to mate with a portion of said drive memher so that the pad rotates therewith when so mated. the upper surface of which is presented in operation adjacent the print wheel such that said driie member. said pad. and said print wheel are positioned axially sequentially along said central shaft. the upper surface having one or more hump like integral portions thereof extending therefrom to contact a first surface of said print wheel. the remainder of said upper surface remaining out of contact with said first surface. said hump like portions being sufficiently compressible such that upon application of pressure on said print wheel axially of said central shaft in the direction of said drive member. said hump-like portions deform and engage said first surface to rotate said print wheel upon rotation of said drive member.  
  2. An apparatus of claim I. including a plurality of humplilse portions. positioned at regular intervals on said upper surface.  
  3. An article of claim I. wherein said pad and said hump-like portions are compressible. plastic material.  
  4. An article of claim I. wherein said ringlikc pad further includes first and second annular projections extending normally from the lower surface of said pad and integral therewith, said first and second annular projections defining an annular trough for engagement with said drive member.  
  5. A print wheel assembly for use in an impact printer. comprising in combination:  
 drive means mounted so as to be rotatable about a central shaft;  
 print means having a plurality of print characters on a peripheral surface thereof mounted to be rotatable about said central shaft and movable axially therealong;  
 a pad positioned between said dri\e means and said print means for coupling the rotational force of said drive means to said print means. said pad being ring-like and generally flat. and having upper and lower spaced surfaces with a peripheral edge surface thercbetween said lower surface adapted to mate with said drive means so that the pad rotates therewith. said upper surface being presented in operation axially adjacent said print means. such that said drive means. said pad. and said print means are positioned axially sequentially along said central shaft. the upper surface of said pad having one or more hump-like integral portions thereof extending therefrom to contact a first surface of said print means. the remainder of said upper sur face remaining out of contact with said first surface. said hump-like portions being sufficiently compressible such that upon application of pressure on said print means axially of said central shaft in the direction of said drive means. said hump-like portions deform and engage said first surface to rotate said print wheel upon rotation of said drive member. and.  
 means mounted on said central shaft for moving said print means axially of said central shaft in the direction of said drive means.  
  6. An apparatus of claim 5, including a plurality of hump-like portions. positioned at regular intervals on said upper surface.  
  7. An article of claim 5. wherein said pad and said hump-like portions are compressible. plastic material.  
  8. An article of claim 5. wherein said ring-like pad further includes first and second annular projections extending normally form the lower surface of said pad and integral therewith. said first and second annular projections defining an annular trough for engagement with said drive member.