Method of making an endless forms feed tractor belt
DESCRIPTION 
     1. Background of the Invention 
     This invention relates to a method of making an endless forms feed tractor belt. More particularly, the tractor belt is to be used for moving a record medium having edge perforations. 
     2. Description of the Related Art 
     Forms feed mechanisms have been used for many years for moving paper through printers and the like. The paper conventionally utilized has pre-punched perforations along both sides. Tractor mechanisms, including an endless tractor belt, are mounted at an appropriate place on the printer so that drive members mounted on the belt are inserted into the paper perforations. Rotation of the belt causes the drive members to move, carrying the paper forward in the printer. Belt rotation can be activated by any form of belt drive mechanisms. 
     Tractor belts generally consist of a band with drive members mounted thereon. The drive members may be mounted on the band by molding. It is known to mold the entire belt, drive members and band, from a single moldable material in a single molding operation. However, this method of molding fails to optimize the individual material characteristics of each belt part. The drive members should be made from a hard, wear resistant material whereas the band material should be flexible and durable. 
     Another method of mounting drive members on the band consists of molding the drive members through perforations in the band. This method of mounting has several drawbacks. First, perforations in the band tend to act as stress concentrators during belt use. Stress concentration can lead to the formation of defects such as cracks which can cause premature failure. Another drawback is that drive members may be poorly fit to the perforations in the band. Subsequent movement of the drive members with respect to the band may also cause wear and premature failure. Still another drawback is that the perforations in the band must be close enough to the lateral center of the band to allow for a sufficient thickness of band material on all sides of the perforations. This limits the possible use of drive members mounted off-center laterally with respect to the band. 
     Past tractor belt designs have still other associated problems. Little protection is typically provided to prevent the paper from contacting the band. Excessive contact between the paper and the thin band can result in premature wear of the band. In addition, some drive member designs maintain a small gap between the base of the pin and the band. A paper edge can wedge into this gap and cause poor paper feeding. 
     It is therefore desirable to create a tractor belt in which the causes of band wear are minimized. This may be accomplished by the use of a proper belt design and method of belt making. 
     SUMMARY OF THE INVENTION 
     It is the principal object of this invention to provide an improved method of making an endless forms feed tractor belt. 
     This and other objects are accomplished by providing a method of making an endless forms feed tractor belt including drive members molded around a thin, flexible band at longitudinal intervals. The drive members consist of an upper pin portion, a shoulder portion, and a lower drive element portion. The pin portions are sized to engage perforations in the paper. The shoulder portions are integral to and inseparable from both the pin portions and the drive element portions of the drive members in order to prevent paper from wedging in gaps or contacting the band. The drive element portions are shaped to engage a sprocket. 
     The belt is produced by first punching slots in at least one side of a thin, flexible band at longitudinal intervals. Drive members are then molded around the band at each of the slots except for at least one drive memberless interval at each end of the band. The ends of the band are overlapped so that the slots of the drive memberless intervals at each end of the band coincide. Final drive members are then molded around the slots of each pair of coincided memberless intervals to complete the endless tractor belt. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is an isometric view of a tractor belt in a forms feed tractor mechanism. 
     FIG. 2 is a side view of the tractor belt. 
     FIG. 3 is a top view of the tractor belt according to the preferred embodiment of the invention. 
     FIG. 4 is a cross-sectional view of a drive member as mounted on the flexible band. 
     FIGS. 5 is a top view of the flexible band. 
     FIGS. 6, 7 and 8 are magnified top views of the slots in the flexible band shown in FIG. 5. 
     FIG. 9 is a top view of the flexible band with drive members mounted thereon prior to overlapping the band ends. 
     FIG. 10 is a top view of the flexible band with the band ends overlapped but prior to mounting of the final drive members. 
     FIG. 11 is a magnified view of FIG. 10. 
     FIG. 12 is a cross-sectional view of a drive member as mounted on the overlapping ends of the flexible band. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 shows a conventional tractor belt 9 as used in a forms feed tractor mechanism 10. The forms feed tractor belt of the present invention is illustrated in FIG. 2. The tractor belt 15 includes drive members 14 mounted on a thin flexible band 11. Referring to FIGS. 3 and 4, drive members 14 include three portions. The upper pin portion 16 is sized to engage the perforations in a record medium which is usually, although not limited to, paper. The lower drive element portion 17 is shaped to engage a sprocket. Activation of the sprocket causes the belt to rotate, thereby advancing the paper. The drive members also have shoulder portions 18a, 18b and 18c which are sufficiently raised above the band to prevent the paper from contacting the band. 
     In the preferred embodiment, drive members 14 are single molded units. Therefore, the shoulder portions 18a, 18b and 18c are integral to and inseparable from corresponding pin portions 16 and drive element portions 17 of the drive members. There are no gaps between the base of the pin portion and the band into which the edge of the paper can wedge. 
     FIGS. 3 and 4 also illustrate that drive members 14 are molded around, though not necessarily surrounding, band 11. There are no perforations in the band which can cause premature failure. Furthermore, the pin portions can be mounted off-center laterally with respect to the band, if desired. 
     Referring to FIGS. 5-8, slots 12a, 12b and 12c are at longitudinal intervals 21 along first and second sides of band 11. Each of these slots serves to anchor the drive members fixed to the band in all directions. Tabless slot 12c is also important in the method of making the tractor belt, as disclosed later in the specification in the discussion of the molding of the final drive members. Tabs 13 exist within slots 12b. Tabs 13 are deflected into drive members 14, as shown in FIG. 4. The tabs are also used in fixing the position of the drive members on the band. The size and shape of slots 12a, 12b, and 12c and tabs 13 are not limited to those shown in the drawing, but those skilled in the art will realize that they may be any shape capable of fixing the drive member position upon the band. 
     The method of making tractor belt 15 of FIG. 2 begins by providing flexible band 11. The band is preferably made from a material characterized by high flexibility, low moisture absorption, no creep, and high tensile strength. Additionally, the band should be made from a material capable of withstanding the processing temperatures required to manufacture the belt. Examples of suitable materials are plastic films of polyimide or polyester. 
     Slots 12a, 12b, and 12c are punched into the band at longitudinal intervals 21, leaving tabs 13 remaining in slots 12b as previously shown in FIG. 5. Referring to FIG. 9, drive members 14 are molded around band 11 at each of the slots except for drive memberless intervals 21a and 21b containing slots 12a, 12b, and 12c at opposite ends of the band. The drive members may be molded simultaneously, or one at a time. The drive members are preferably made from a moldable, wear-resistant material such as glass-filled nylon. Referring to FIG. 10, the ends of the band 11a and 11b are then overlapped so that the drive memberless intervals 21a and 21b, and slots therein 12a, 12b and 12c, coincide. FIG. 11 shows overlapped slots 12c and 12b. A final drive member is then molded around slots 12a, 12b, and 12c of coincided drive memberless intervals 21a and 21b to form an endless tractor belt. FIG. 12 illustrates a cross-sectional view of final drive member 19 molded around overlapped ends 11a and 11b of the band. Alternatively, several final drive members may be molded around the overlapped ends of the band to add belt strength. To accommodate additional final drive members, several tabless slots are initially punched at one end of the band at successive longitudinal intervals. The intervals containing these slots, and corresponding intervals at the opposite end of the band, remain memberless until the band ends are coincided and final drive members are molded. Tabs 13 are deflected into the drive members either before or during molding, and remain within the drive members after molding. Injection molding is used in the preferred embodiment, but other types of molding may be used. 
     While the invention has been particularly shown and described with reference to a preferred embodiment thereof, it will be understood by those skilled in the art that various changes in detail may be made therein without departing from the spirit, scope and teaching of the invention. For example, other drive element portion shapes may be used, provided they are compatible with the remainder of the mechanism. Accordingly, the apparatus and method herein disclosed is to be limited only as specified in the following claims.