Patent Publication Number: US-4096488-A

Title: Modular stylus assembly

Description:
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, in which: 
     FIG. 1 is a perspective view of a one-piece molded stylus module, having four sets of writing tips, each set consisting of five wires; 
     FIG. 2 is a side elevational view of the stylus module of FIG. 1 mounted on a connector assembly which is, in turn, mounted on two etched flexible circuit member or circuit boards; 
     FIG. 3 is a view similar to that of FIG. 2, and partly in section, showing a typical conductive wafer for connecting stylus wires to the upper side of a circuit board or flexible circuit member; 
     FIG. 4 is a view similar to that of FIG. 2 with the stylus module removed and showing a typical conductive wafer for connecting stylus wires to the underside of a circuit board or flexible circuit member; 
     FIG. 5 is an enlarged fragmentary sectional view of FIG. 3 taken along the line V--V and showing the contact between the stylus wires and spring tabs of the conductive wafers; 
     FIG. 6 is a fragmentary top plan view of a wafer stack mounted on a flex circuit or flexible printed circuit strip, and partly broken away to show the epoxy-filled central core; 
     FIG. 7 is a bottom view of the fragmentary wafer stack of FIG. 6 and showing the connection of appropriate conductive-wafer solder tabs to the bottom of the flexible circuit strip; and 
     FIG. 8 is a side elevational view of an alternate method of mounting the wafer stack. 
    
    
     PREFERRED EMBODIMENT 
     Referring now to FIG. 1, where is shown a stylus module 12 of the invention of the instant application. The module 12 is molded, in one piece, of an insulating plastic material such as nylon. The molding die utilizes continuous wire inserts. Long lengths of stylus wires 13, as many as are required for the number of stylus positions, are guided into the molding die. After molding, the module 12 and wires 13 are indexed a pre-set distance, the wires 13 are repositioned in the die, and the process of molding repeated so that successive modules 12 are molded of the same lengths of wires 13. Protruding stylus wires 13, between successive modules 12 are then cut to proper length. After cutting, the stylus wire tips are honed smooth to remove any burrs caused during trimming. Two side lugs 12a and 12b, extend along the entire length of the module 12 and are undercut to provide a snap-fit joint between the module 12 and a connector module 10 (FIG. 2). Two ribs 12c and 12d, are provided across the top of the module 12 and serve as a gripping surface for easier handling. Although the module 12 shown in FIG. 1 has four writing tips, a convenient module length is eight tips. 
     The underside of the center span 12e of the module 12 is transversely slotted on both sides of each stylus wire 13 so that the lower half of each stylus wire 13 is exposed and able to make contact with respective spring tabs 15b, 15c and 16b, 16c (FIGS. 3 and 4) of the connector module 10 which will be described hereinafter in greater detail with respect to FIGS. 3, 4 and 5. 
     The module 12 shown in FIG. 1 is used to print character-lines of alphanumeric information in a seven-row by five-column matrix. When the modules 12 are mounted linearly, each writing tip 13&#39; contains five stylus wires. Each writing tip 13&#39; prints a one-dot wide dot-line, normally a horizontal line. When the printing of each dot-line is sequenced with a seven-step vertical movement of the paper, a series of five by seven alphanumeric dot matrices or character-lines is printed. Stylus wires of tungsten are 7 mill diameter on 18 mill centers, each group of five wires are on 100 mill centers. The resulting printed characters are approximately 79 mills wide by 100 mills high, on 100 mill centers. Character lines of any length may be obtained by adding styli and connector modules. 
     Another configuration for alphanumeric character printing along with graphic and facsimile generating may be achieved by changing the spacing of the stylus wires from groups of five to an even spacing, so that a continuous dot-line may be generated. 
     A third variation of the stylus shown in FIG. 1 is usually alone and not in modular configuration. A single set of writing tips composed of nine evenly spaced stylus wires is used to print alphanumeric characters, one column at a time. Each character column is a matrix of seven-rows by five columns. The two extra rows are provided for an offset when lower case letters are printed. Printing and moving the paper or the print head five steps, generates characters 80 mills wide by 103 mills high. Character spacing and, to some extent, character width are optional. Character size in this case assumes stylus wire diameters of 7 mills on 16 mill centers. 
     Referring to FIG. 2, there is shown a stylus module 12 mounted on a connector module 10, which is formed of alternating conductive wafers 15 and 16 and insulating wafers 14. The conductive wafers 15 and 16 are soldered at 21 to the conductors of conventional flexible printed circuit strips 17 and 18 through the aid of solder tabs 15a and 16a. Flexible circuit strips 17 and 18 are bonded to a hardboard reinforcement 19. The insulating wafer 14 may be fabricated as a stamping of mylar or similar material. A typical thickness of the insulating wafer 14 is 10 mills. A tab 12a is necessary for providing support to the relatively lengthy adjacent solder tab 15a of the conductive wafer 15. The hardboard reinforcement 19 should be fabricated of an insulating material such as phenolic, glass-reinforced epoxy, or similar material. 
     A central epoxy fill 20 extending through aligned apertures formed, respectively in a stack of the wafers 14, 15 and 16 serves to bond the stack together. In addition to bonding, keying and providing structural support, the central epoxy fill 10 eliminates the general problems encountered with conventional laminating procedures. 
     FIG. 3 shows the conductive wafer 15 with the solder tab 15a thereof, the spring tabs 15b and 15c of the wafer 15 being visibly in contact with a stylus wire 13. The conductive wafers 15 and 16 may be fabricated as stampings of beryllium copper or phosphor bronze, or similar material. To effect a proper fit, the thickness of a conductive wafer 15, 16 should be slightly greater than the diameter of a stylus wire 13. For example, when 7-mill stylus wire 13 are desired, the conductive wafers 15 and 16 should be each 8 mills thick. This is readily apparent in the fragmentary sectional view of FIG. 5. 
     The conductive wafer 16 is shown in FIG. 4 with the stylus module 12 removed. The spring tabs 16b and 16c are identical to the spring tabs 15b and 15c of the conductive wafer 15 but are shown unloaded in FIG. 4. The spring effect is achieved by the upwardly sloping top surfaces indicated by angles φ1 and φ2 in FIG. 4. When a stylus module 12 is in operating position, the spring tabs 15b, 15c, 16b, 16c are forced from the position thereof shown in FIG. 4 into a horizontal position as shown in FIG. 3, thus maintaining a constant spring pressure contact between the respective stylus wire 13 and the respective conductive wafer 15, 16. 
     FIGS. 6 and 7 are fragmentary top and bottom views of a connector stack. The resulting configuration of the central epoxy filled core 20 is visible in the broken-away portion of FIG. 6. This cavity in which the epoxy core 20 is disposed results from the aligned triangular or square recesses respectively, of the adjacent wafers 14, 15 and 16. Conductors 24 and 24a are of copper, approximately 2 mills thick. Conductor width and spacing may vary but typical conductor widths are 20 mills, and the spacing therebetween is 12 mills. As may be seen, conductor width and spacing is directly related to conductive wafer spacing which, in turn, is related to the desired stylus spacing and current-carrying requirements. The flexible printed circuit strip or base film 25 and 25a may be of 2 mill-thick KAPTON, a registered trademark, polyamide film or any of a variety of similar materials. The coverlay material 26 and 26a may be of polyester, however, the coverlay 26 must be the same thickness as that of the conductor 24. This is necessary because the coverlay material 26 is also used as a spacer to keep the wafer stack level with the surface of the conductor 24. Such a requirement is not encountered on the bottom side of the wafer stack shown in FIG. 7, nor does such a requirement exist for the vertical-mounting configuration of FIG. 8. For additional strength of the entire structure, the wafer stack, prior to soldering may be bonded to the coverlay 26 which is, in turn, bonded to the base film 24, in turn, further bonded to the hardboard support 19. A variety of conventional adhesives are available for this application. 
     FIG. 8 shows a variation of the connector assembly that may be used in a vertical-mounting configuration. The assembly of FIG. 8 is similar to the horizontal-mounting connector shown in FIG. 2, except that the conductive wafer 16 is not required, the solder tab 15a of the conductive wafer 15 is removed, and the support tabs 14a and 14b of the insulating wafer 14 are removed. The wafer stack of FIG. 8 thus is formed of alternating modified conductive wafers 15&#39; and modified insulating wafers 14&#39;. The conductive wafers 15&#39; of FIG. 8 are alternately reversed in direction so that solder contact at 21 may be made with both circuits 23 and 23a. The conductors on flexible circuit 23 are symmetrically spaced so that the flexible circuit 23 and 23a are the same. The insulating hardboard support member 22 in this configuration of FIG. 8 is substantially stronger than in the horizontal configuration of FIG. 2.