Abstract:
A printer apparatus has a frame member supporting an endless revolving type band in alignment with a row of print hammers with a gap therebetween. Ribbon spools with ribbon wound thereon are rotatably supported in spool housings at either end and on opposite sides of the frame member. The spool housings each have a receptacle portion and a cover portion which enclose the spool. A gap in the spool houses enables the ribbon to extend between the housing and through the gap. The ink ribbon is guided through the gap in parallel with the row of hammers and at an angle to the print line by a set of guide pins on the cover of one spool housing and a set set of guide pins mounted on the frame member in proximity with the other spool housing. Both sets of guide pins engage the same side of the ink ribbon in a manner whereby touching the ribbon is not required to install or remove the ribbon from the printer apparatus. Individual drive motors for rotating the ribbon spools are mounted on the receptacles of the spool housings.

Description:
This invention relates to printer apparatus and particularly to a ribbon guide system for a line printer. The invention has utility in high speed line printers but in not necessarily limited thereto. 
     BACKGROUND OF THE INVENTION 
     High speed impact line printers comprise an endless type carrier band with a single row of characters moving parallel with a row of print hammers. The band is trained on spaced drive and idler or tension pulleys which are motor driven to revolve the band at constant speed. The band drive, as it is commonly called, is generally mounted on a support or frame member that holds the band in proximity to the row of print hammers mounted on another frame member. The hammers and the band are separated by a gap or throat which defines a passageway for a print medium such as paper forms and an ink ribbon. 
     The printing ribbon is sometimes a narrow strip wound on two widely separated spools with a section extending across the paper and lengthwise through the gap. Commonly the ribbon path is slanted relative to the line of the hammers and type band so that the entire width of the ribbon is presented for printing. Ribbon drive motors rotate the spools to feed the ribbon through the gap. Guide means between the spools is provided for maintaining the ribbon in proper alignment as it travels through the gap. The guide means necessarily are also widely separated to avoid interference with the hammer and paper feed operations and hence maintaining the ribbon on track presents a problem. The structures and arrangement of the guide means and the spool mountings have made it necessary to manually touch the ribbon when the ribbon is replaced and/or installed. The publication in the IBM Technical Disclosure Bulletin Vol. 31, No. 10, March 1989 pp. 32-33, shows a printer unit in which the type band drive is mounted on a frame above the horizontal paper path. A stretch of the ribbon between ribbon spools passes horizontally between the type band and paper. No guidance structure is shown. The ribbon spools are inserted into enclosures on either side of the paper path frame. Such an arrangement is not convenient because of space limitations if the print unit is located within a cabinet and the direction of paper feeding is from side to side instead of front to back. 
     SUMMARY OF THE INVENTION 
     The invention provides a printer apparatus having a printing ribbon drive and guidance system that does not require finger contact with the ribbon itself when installing the ribbon. Basically this is accomplished in accordance with the invention by providing an assembly in which the band drive and the ribbon drive are mounted on a common support member which supports the band drive above a horizontal row of print hammers. The support for the band drive and the ribbon drive comprises a frame member with gap therebetween. The ribbon drive comprises spaced apart ribbon spool housings mounted on either side of the frame member at opposite ends of the type band. A ribbon guidance system comprises movable ribbon guide means mounted on one spool housing and a fixed guide means mounted on the frame member. Each ribbon guide means comprises a series of guide elements with guide surfaces arranged to maintain the ribbon aligned with the spools and parallel within the gap with the type band and row of print hammers. The guide means includes a transition guide element between the other guide elements so that the ribbon can move therebetween in such a way that the configuration of the ribbon is distortion free and compatible with stable ribbon tracking. 
     It will be seen that the invention provides a ribbon drive assembly arrangement which is simple in construction and easy to use to assemble and remove ink ribbon from a printer apparatus. Other advantages will become apparent from the detailed description which follows. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an exploded three dimensional view of a printer apparatus of the type in which the invention can be used; 
     FIG. 2 is a perspective view of the print unit portion of the printer apparatus of FIG. 1; 
     FIG. 3 is a perspective view of the ribbon drive and band drive assembly portion of the print unit of FIG. 2; 
     FIGS. 4 and 5 are sequential perspective views of the ribbon drive and band drive assembly of FIG. 3 for illustrating the process for manually removing and installing a ribbon in accordance with the invention; 
     FIG. 6 is a bottom plan view of the ribbon drive and band drive assembly of FIG. 3; 
     FIG. 7 is a perspective view of the ribbon and spools only for the purpose of illustrating the ribbon guide system of the invention; 
     FIG. 8 is an elevational view showing one of the ribbon spool housings with the ribbon spool housed therein; 
     FIG. 9 is an enlarged perspective view showing the fixed ribbon guide; 
     FIG. 10 is a three dimensional exploded view of the ribbon spool housing of FIG. 8; 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As seen in FIG. 1, a printer apparatus comprises cabinet 10 within which is installed a print unit 11. The cabinet 10 has side walls 12 on which top door 13 and a pair of front doors 14 are hingedly attached. A pedestal 15 on bottom wall 16 supports print unit 11 within the cabinet 10. When installed in cabinet 10, print unit 11 prints on paper fed from side to side so that stacks of folded paper (not shown) would rest on bottom wall 16 on the right and left sides of pedestal 15. 
     Print unit 11 includes a casing having a base 17 and cover 18 on which is mounted a hammer unit 19. Mounted on hammer unit 19 is band and ribbon drive assembly 20 which in accordance with this invention comprises frame member 20a on which is supported both the type band drive and ink ribbon drive system. As described in copending application Ser. No. 07/664,255 filed Mar. 4, 1991, now U.S. Pat. No. 5,108,205 issued on Apr. 28, 1992, frame member 20a has pivot arms 20b and 20c pivotably mounted on hammer unit 19 so that an adjustable gap exists for the passage of the ink ribbon and paper to be printed on. The gap adjustment mechanism includes levers 21 and 22 for rotating cam 23 as more fully described in said copending application. The paper feed mechanism comprises pin belt tractors 24 and 25 which engage edge perforations in the paper and which are adjustably spaced along drive shaft 26 by dual coaxial rotatable lead screws 27 and 28 operated by knob 29 as more fully described in copending application Ser. No. 7/662,863 filed on Mar. 1, 1991. The tractors 24 and 25 feed paper across the top of cover 18 and over the hammer unit so that the paper movement is from side to side through the print unit as previously mentioned. 
     As best seen in FIG. 3, frame member 20a is a plate-like casting on which are mounted both the band drive and the ribbon drive. The band drive comprises endless type band 30 wrapped around a pair of drive pulleys 31 and 32 mounted on one side 20d of frame member 20a and could include an electric motor (not shown) mounted on the other side of frame member 20a and connected to one of the drive pulleys for rotating type band 30 at constant speed. A shelf-like platen 33 between the pulleys 31 and 32 at the bottom edge of the casting 20a provides backup to the type band 30. Platen 33 has a surface which, when frame member 20a is mounted on cover 18 of print unit 11, extends over a distance which is at least co-extensive with the row of print hammers 19. 
     As seen in the various figures, the ribbon drive comprises ribbon spool housings 34 and 35 mounted on opposite sides of frame member 20a at opposite ends of the type band 30. This enables ribbon 14 to be fed lengthwise through the gap at an angle to the print line formed by the row of hammers and the single row of characters on band 30 so that substantially the entire width of the ribbon 14 is presented for printing. Ribbon spool housings 34 and 35 are also tilted at an angle away from the vertical plane of frame member 20a. The degree of tilt can vary depending on the amount of space available between the top of the print unit 11 and the cover of cabinet 10. Tilting also enhances positioning and directing of ribbon 14 toward the path of travel as will be more fully understood hereinafter. When print unit 11 is contained in cabinet 10 as previously described, spool housings 34 and 35 are the back and front ribbon housings respectively. Mounting spool housings 34 and 35 on frame member 20a makes them more accessible for installing and replacing ribbon 14 within the print unit 11. Located within the spool housings 34 and 35 are spools 36 and 37 on which ink ribbon 14 is wound with a stretch of ribbon extending therebetween (see FIG. 7). Spools 36 and 37 are any well known type having flanges 36a and 37a with external gears 36b and 37b and stub shafts. Mounted on spool housing 35 is drive motor 38 having a pinion gear (not shown) which engages gear 37b on spool 37. Similarly, a drive motor (not shown) is mounted on ribbon spool housing 34 with the same gearing for engaging gear 36b on spool 36. 
     As seen in FIGS. 8 and 10, back spool housing 34 comprises housing or receptacle member 34a and cover member 34b hingedly connected thereto so that ribbon housing 34 can be opened and closed. Housing member 34a has parallel sidewalls 34c and 34d with saddle bearings 34e and 34f in which stub shafts on spool 36 rest when spool 36 is installed between sidewalls 34c and 34d. Pins 34g on sidewall 34c around opening 34h serve as the mount for a drive motor so that gearing on the motor shaft extending through opening 34h makes a drive connection with the gearing 36b on spool 36 when spool 36 is placed in housing member 34a. Between sidewalls 34c and 34d is cross member 34i with bearing edge 34j which engages the bottom side of ribbon 14 where it exits from inside the spool housing 34. Bearing edge 34j is concave to center the ribbon relative to the spool 36. 
     Cover member 34b comprises parallel side walls 34k and 341 and curved end wall 34m. The hinge connection for movement of cover member 34b between closed and open positions comprises hinge pins 34n on sidewalls 34k and 341 of cover member 34b and hinge elements 34o and 34p on sidewalls 34k and 341. Cover member 34b is locked in closed position or unlocked by operating latch element 34q pivoted on the sidewalls of cover member 34b and which has hooks 34r which engage housing member 34a in closed position. When closed, bearing edges 34s and 34t on the sidewalls 34k and 341 of cover member 34bx close the saddle bearings 34e and 34f so that spool gear 36b is brought into engagement with gearing on the drive motor shaft and the stub shafts on spool 36 are captured in place. 
     In accordance with this invention, a movable ribbon guide is provided at one end of the type band 30 which, in the preferred embodiment, comprises a series of guide pins 39, 40 and 41 fixedly attached between external flanges 34u and 34v at the swing end of cover member 34b. Flanges 34u and 34v form a ribbon channel in which the stretch of ribbon 14 proximate spool housing 34 is caught for engagement with and positioning by the guide pins 39-41 when cover member 34b is swung from open to closed position. Conversely, when cover member 34b is unlocked and swung open, the ribbon 14 in proximity with spool housing 34 is disengaged from guide pins 39-41 and removed from the ribbon channel formed by flanges 34u and 34v on cover member 34b and is thereby removable without hindrance when spool 36 is removed from housing member 34a. Likewise, when cover member 34b is opened, flanges 34u and 34v present no hindrance to the ribbon 14 when spool 36 is to be installed into housing member 34a. 
     As seen in the various figures, guide pins 39-41 have different angular orientations. Pin 39 is attached to flanges 34u and 34v so as to present a guide surface parallel with the axis of spool 36. This parallelism assures ribbon is properly aligned with the spool 36 in housing 34. Pin 39 is also located when cover 34b is closed so that it coacts with bearing edge 34j to engage opposite surfaces of ribbon 14 so that ribbon 14 moves through a bend which applies some amount of tautness to ribbon 14 as it leaves spool housing 34. Guide pin 40, mounted on the brackets 34u and 34v so that when cover member 34b is closed, pin 40 presents a guide surface that is normal to ribbon 14 and that is parallel with the surface of the row of hammers 19 and the face of type band 30 and since ribbon 14 is slanted at an angle relative to the print line as previously described, guide pin 40 in being normal to ribbon 14 is also slanted a corresponding amount relative to the print line. Guide pin 41 serves as a transition pin for guiding the ribbon 14 from the plane of pin 39 to the plane of pin 40 and is slanted in such a way that the ribbon 14 moves through the guide without wrinkling, folding or tearing at the edges. The proper orientation is determined by requiring that when the ribbon 14 is stretched over 39-41 with opposite forces perpendicular to pins 39 and 40 respectively, the resulting tension will not urge the ribbon to move up or down along the pins 39 or 40. 
     The front spool housing 35 comprises housing or receptacle member 35a and cover member 35b hingedly connected thereto. Spool housing 35 is the same as back spool housing 34 in all respects except that cover member 35b has a bearing edge near the swing end which when closed coacts with a concave bearing edge of the housing member 35a to provide for reverse bending of the ribbon 14 as it leaves spool housing 35 and no ribbon guide is attached to cover member 35b. Instead a fixed ribbon guide is provided at the end of type band 30 for engaging ribbon 14 proximate spool housing 35. As best seen in FIG. 9, the fixed ribbon guide comprises pin like guide elements 42, 43 and 44 on a bracket 45 attached to the frame member 20a between the end of type band 30 and front spool housing 35. As in the case of the guide pin 39 of the movable ribbon guide means, guide element 42 is parallel with the axis of spool 37 to maintain ribbon 14 in proper alignment with spool 37. Guide element 43, like guide pin 40 has a surface normal to ribbon 14 and parallel with the surface of type band 30. Guide element 43 is also parallel with guide pin 40 when cover member 34b is closed. Guide element 44 like guide pin 41 is a transition pin and is slanted in the same manner as previously described for guide pin 41. 
     Referring to FIG. 5, ribbon is installed in print unit 11 by opening cover member 34b on back spool housing 34 and cover member 35b on front cover member 35, and holding both spools 36 and 37 by their flanges, spool 36 is dropped into housing member 34a so that spool gear 36b engages the gearing on the drive motor and then cover member 34b is swung closed and locked. When closing, the ribbon guide, formed by flanges 34u and 34v, catches and and the guide pins 39-41 engage the top of the ribbon 14 as previously described and positions ribbon 14 at the proper level so as to be aligned with the gap at the back of frame member 20a. Holding the spool 37 by the flanges 37a, a stretch of ribbon 14 is drawn from spool 36 along the side of frame member 20a and, while holding the ribbon somewhat taut, ribbon 14 is brought under, aligned with and wrapped around the guide elements 42-44 of the fixed guide and spool 37 is dropped into the housing member 35a of front spool housing 35 on the other side of frame member 20a. Cover member 35b is swung closed and locked to complete the installation process. For replacement, the process is reversed by removing spool 37 from housing 35 and, after opening cover member 34b of back spool housing 34, removing spool 36 from housing member 34a. 
     Thus it can be appreciated that the invention provides a ribbon drive system in which the ribbon is accurately guided along the print line and in which the ribbon and spools therefor can be easily and cleanly installed and removed from the ribbon drive system. While the invention has been described with reference to a single embodiment, it will readily occur to a person skilled in the art that various changes can be made for uses in the same or other embodiments and printer devices without departing from the scope of the invention as defined in the following claims.