Abstract:
The invention is a silent chain with a profile capable of corresponding with the profiles of both sprockets and racks. The purpose of the invention is to convert rotational motion to linear motion in a way that is superior to the traditional rack and pinion device by allowing for more surface area contact with the rack through the use of, rather than a pinion, a silent chain that is capable of engaging with a rack. The invented silent chain comprises link plates of a particular shape stacked in alternating rows and joined together by connecting pins in such a way as to be bendable. The link plates are shaped such that the teeth of the link plates are offset when the chain is straightened, which allows the profile of the silent chain to correspond with the profiles of both sprockets and racks.

Description:
CROSS-REFERENCES 
     Technical Field 
       [0001]    This invention relates to a silent chain, and more specifically to a silent chain profile for linear motion. 
       Background 
       [0002]    The lifting capacity of an average person amounts to not more than a few hundred pounds. For this reason, people have turned for centuries to mechanical means of lifting heavy items. Some of the means devised include pulley systems, cranes, scissor lifts, or linear actuators. One type of linear actuator of particular interest here is a rack and pinion device. 
         [0003]    Rack and pinion devices are configured to convert rotational motion to linear motion. They are often used for creating horizontal linear motion, such as in transport, packaging, and assembly machines, but rack and pinion devices can also be used for vertical linear motion. An advantage of using a rack and pinion device, as opposed to other devices like cranes or pulleys, is that the rack and pinion device can drive and therefore lift from the bottom. However, when lifting heavy items vertically, rack and pinion devices have one significant disadvantage. 
         [0004]    Rack and pinion devices normally have only a few points of contact between the rack and the pinion. If a rack and a pinion have contact at only a few points, those points of contact may be put under undue amounts of stress when lifting, which could cause the rack and pinion device to fail. In contraptions in which reliability or safety are significant concerns, such as in an elevator, taking chances with parts that might break under load could lead to disastrous results. This problem is sometimes solved by increasing the size and, therefore, the load capacity of the rack and pinion, but larger parts are harder to manufacture, require more space, cost more, and might require larger motors, all of which lead to decreased efficiency. This is especially undesirable if trying to create a green or sustainable product. 
         [0005]    The disadvantage of a rack and pinion device could conceivably be resolved through the use of a silent chain in place of a pinion. Silent chains, like pinions, are generally built for rotational motion. However, if the rotational motion of a silent chain could be converted to linear motion, because of the longer profile of a silent chain, numerous points of contact between a silent chain and a rack could be established, rather than the few points of contact established between a pinion and a rack. 
         [0006]    Unfortunately, the profile of a typical silent chain is designed to engage only on one side, on the inner side, with a sprocket. Sometimes silent chains will have internal and external profiles, so that they can engage with sprockets inside and outside the silent chain. However, the profile of a silent chain cannot engage with a rack. More especially, a silent chain profile cannot engage with a rack on the outside and a motor-driven sprocket on the inside. 
         [0007]    In light of the foregoing, what is needed is a silent chain with a profile that would allow it to engage with a rack. In particular, the silent chain profile should allow the chain to engage with both a sprocket on the inside and a rack on the outside, so that the silent chain&#39;s rotational motion can be converted to linear motion. 
       SUMMARY OF THE INVENTION 
       [0008]    The disclosed invention has been developed in response to the present state of the art and, in particular, in response to the problems and needs in the art that have not yet been fully solved by currently available components and methods. Accordingly, efficient structural components and methods have been developed to allow a chain profile to configure to a linear rack. 
         [0009]    Consistent with the foregoing, a silent chain is disclosed. In one embodiment, the silent chain comprises a plurality of link plates, each link plate having at least four teeth and a first pin hole and a second pin hole. The link plates are stacked in alternating rows, where the first pin holes of a first row selection of link plates are aligned with the second pin holes of a second row selection of link plates. The silent chain further comprises a plurality of connecting pins inserted through the first pin holes and the second pin holes of the link plates to join the link plates together in such a way as to be bendable. The teeth of the link plates are shaped in such a way that the teeth of the first row selection of link plates and the teeth of the second row selection of link plates are offset when the silent chain is straightened, so that a profile of the silent chain can correspond with a profile of a sprocket and a profile of a rack. In some embodiments, the silent chain also comprises center guide link plates. The center guide link plates, which are stadium-shaped and have no teeth, are positioned centrally between the rows of link plates to prevent the silent chain from slipping. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    A more particular description of the invention briefly described above is made below by reference to specific embodiments depicted in drawings included with this application, in which: 
           [0011]      FIG. 1  depicts an exploded view of a link plate; 
           [0012]      FIG. 2A  depicts an exploded view of a link plate of a prior art silent chain; 
           [0013]      FIG. 2B  depicts an exploded view of a link plate of the silent chain built in accordance with the invention; 
           [0014]      FIG. 3A  depicts an exploded view of link plates arranged for stacking in alternating rows; 
           [0015]      FIG. 3B  depicts an exploded view of link plates stacked in alternating rows; 
           [0016]      FIG. 4A  depicts an exploded view of link plates of a prior art silent chain stacked in alternating rows; 
           [0017]      FIG. 4B  depicts an exploded view of link plates of a silent chain built in accordance with the invention stacked in alternating rows; 
           [0018]      FIG. 5  depicts an exploded view of connecting pins inserted through the first pin holes and the second pin holes of the link plates; 
           [0019]      FIG. 6  depicts an exploded view of a center guide link plate; 
           [0020]      FIG. 7A  depicts a perspective view of a complete silent chain built in accordance with the invention; 
           [0021]      FIG. 7B  depicts a side view of a silent chain built in accordance with the invention; 
           [0022]      FIG. 8  depicts a perspective view of the silent chain profile corresponding with a profile of a sprocket; 
           [0023]      FIG. 9A  depicts a perspective view of a prior art silent chain profile not engaging with a profile of a rack; 
           [0024]      FIG. 9B  depicts a perspective view of a prior art silent chain profile not engaging with a profile of a rack; 
           [0025]      FIG. 10  depicts a perspective view of the invented silent chain profile engaging with a profile of a rack; 
           [0026]      FIG. 11  depicts a perspective view of the invented silent chain profile engaging with both a profile of a sprocket and a rack; 
           [0027]      FIG. 12A  depicts a perspective view of points of contact between a rack and a pinion; and 
           [0028]      FIG. 12B  depicts a perspective view of points of contact between a rack and the invented silent chain. 
       
    
    
     DETAILED DESCRIPTION 
       [0029]    A detailed description of the claimed invention is provided below by example, with reference to embodiments in the appended figures. Those of skill in the art will recognize that the components of the invention as described by example in the figures below could be arranged and designed in a wide variety of different configurations. Thus, the detailed description of the embodiments in the figures is merely representative of embodiments of the invention, and is not intended to limit the scope of the invention as claimed. 
         [0030]      FIG. 1  depicts a single link plate  100 . Each link plate  100  has at least four teeth  110  and a first pin hole  120  and a second pin hole  130 . In one embodiment, each link plate is bow-shaped. In one embodiment, a tip of each of the teeth  110  of the link plate  100  forms an angle between about thirty and eighty degrees, preferably an angle between about fifty-five and sixty degrees. Each of the teeth  110  of the link plate  100  extends from a vertical waist  140  of each link plate  100  at an angle between about one hundred and one hundred fifty degrees, preferably an angle of between about one hundred twenty-five and one hundred thirty degrees. A distance between central pivot points within each first pin hole  120  and each second pin hole  130  measures 0.5 inches. A distance between central points of two teeth  110  that are pointing a same direction measures between about 0.345 and 0.79 inches, preferably measuring between about 0.49 and 0.68inches, more preferably measuring between about 0.55 and 0.645 inches. These measurements offset the link plates  100  when stacked on top of each other in a straight line. 
         [0031]      FIG. 2A  and  FIG. 2B  depict a comparison between a link plate  200  of a prior art silent chain and the link plate  100  of the silent chain built in accordance with the invention.  FIG. 2A  depicts the link plate  200  of a prior art silent chain. There are two important measurements of note on link plate  200 . A distance  210  between central pivot points within each first pin hole and each second pin hole measures about 0.5 inches. A distance  220  between central points of two teeth pointing a same direction measures about 0.52 inches. The difference between these two measurements is very small. Therefore, when two or more of these link plates  200  of a prior art silent chain are stacked on top of each other in a straight line, the teeth of each link plate nearly align.  FIG. 2B  depicts the link plate  100  of the silent chain built in accordance with the invention. Again, in one embodiment, a distance  230  between central pivot points within each first pin hole and each second pin hole measures about 0.5 inches. The distance  240  between central points of two teeth pointing the same direction measures between about 0.345 and 0.79 inches, preferably measuring between about 0.49 and 0.68 inches, more preferably measuring between about 0.55 and 0.645 inches. The difference between these two measurements is larger than the difference between the two corresponding measurements of the link plates  200  of a prior art silent chain. Therefore, when two or more of these link plates  100  of the silent chain built in accordance with the invention are stacked on top of each other in a straight line, the teeth of each link plate are offset. 
         [0032]      FIG. 3A  and  FIG. 3B  depict the link plates  100  of the silent chain built in accordance with the invention stacked in alternating rows. In  FIG. 3A , the first pin holes  120  of a first row selection  300  of link plates  100  are aligned with the second pin holes  130  of a second row selection  310  of link plates  100 . In  FIG. 3B , the link plates  100  are stacked on top of each other. As depicted in  FIG. 3B , the teeth of the link plates  100  are shaped in such a way that the teeth  320  of the first row selection  300  of link plates  100  and the teeth  330  of the second row selection  310  of link plates  100  are offset when the silent chain is straightened. Though the teeth are offset when the silent chain is straightened, the upper teeth align when it is bent. This allows the profile of the silent chain to correspond with a profile of a rack, which is a linear gear interface, and also with a profile of a sprocket, which is a circular gear interface. In one embodiment, the silent chain has eight alternating rows of link plates. In other embodiments, the silent chain has two, three, four, five, six, seven, nine, ten, or more alternating rows of link plates. A large number of alternating rows makes the silent chain stronger. 
         [0033]      FIG. 4A  and  FIG. 4B  depict a comparison of the link plates  200  of a prior art silent chain stacked in alternating rows and the link plates  100  of the silent chain built in accordance with the invention stacked in alternating rows.  FIG. 4A  depicts the link plates  200  of a prior art silent chain stacked in alternating rows. When the link plates  200  are stacked on top of each other in a straight line, the teeth of each link plate  200  nearly align.  FIG. 4B  depicts the link plates  100  of a silent chain built in accordance with the invention stacked in alternating rows. When the link plates  100  are stacked on top of each other in a straight line, the teeth of each link plate are offset. 
         [0034]      FIG. 5  depicts a plurality of connecting pins  500  inserted through the first pin holes  120  and the second pin holes  130  of the link plates  100  of the silent chain built in accordance with the invention, to join the link plates together in such a way as to make the silent chain bendable. In one embodiment, the connecting pins are rocker pins. In one embodiment, the pins are secured with washers. The washers are placed over top and bottom ends of the connecting pins  500 , and the ends of the connecting pins  500  are smashed down to hold the connecting pins  500  in place.  FIG. 5  depicts only two alternating rows of link plates  100 . In one embodiment, however, the silent chain has eight alternating rows of link plates. In other embodiments, the silent chain has two, three, four, five, six, seven, nine, ten, or more alternating rows of link plates. 
         [0035]      FIG. 6  depicts a center guide link plate  600 . The center guide link plates  600  are stadium-shaped and have no teeth. The center guide link plates  600  are positioned centrally between the rows of link plates. They are designed to align with center guide indentations on a rack, so that the silent chain built in accordance with the invention is guided and prevented from slipping. 
         [0036]      FIG. 7A  and  FIG. 7B  depict a complete silent chain  700  built in accordance with the invention. The chain has a variable length and a variable amount of alternating link plates.  FIG. 7A  depicts one embodiment, in which the center guide link plates  600  can be seen centrally positioned between alternating rows of link plates.  FIG. 7B  depicts a side view of silent chain  700 . In one embodiment, there are eight alternating rows of link plates. In other embodiments, the silent chain has two, three, four, five, six, seven, nine, ten, or more alternating rows of link plates. 
         [0037]      FIG. 8  depicts the silent chain  800  built in accordance with the invention engaged with a sprocket  810 . The profile of the silent chain  800  corresponds with the profile of the sprocket  810 . The teeth of the link plates of silent chain  800  are shaped in such a way that the teeth of each link plate are offset when the silent chain  800  is straightened. When the silent chain  800  is bent, just as with prior art silent chains, lower teeth  820  are drawn apart, and so they continue to be offset. However, unlike prior art silent chains, when the silent chain  800  built in accordance with the invention is bent, upper teeth  830  align. Still, because of the amount that the lower teeth  820 , which are the teeth that engage with the sprocket  810 , offset when the silent chain  800  is bent, the profile of the silent chain  800  built in accordance with the invention corresponds with a profile of sprocket  810 , functioning just like prior art silent chains. 
         [0038]      FIG. 9A  and  FIG. 9B  depict a prior art silent chain profile  900  not engaging with a profile of a rack  910 .  FIG. 9A  demonstrates a problem that is encountered when trying to interface a prior art silent chain  900  with a rack  910 . The circle in  FIG. 9A  draws attention to the area of problem. In a prior art silent chain  900 , as the silent chain  900  is bent so that the teeth  920  approach the rack  910  to engage with the rack  910 , the teeth  920  draw apart, such that they are offset. Because the teeth  920  draw apart such that they are offset, the teeth become too big to fit within a groove  930  of the rack  910 . Therefore, the teeth  920  cannot fit within the groove  930 , and they cannot engage with the rack  910 . This problem could conceivably be corrected by increasing the size of the groove  930  in the rack  910 . However,  FIG. 9B  depicts what happens when the size of the groove  930  in the rack  910  is increased. When the silent chain  900  is bent, the teeth  920  are drawn apart, such that they are offset. Because of the expanded size of the groove  930  in the rack  910 , the teeth fit within the groove  930  as the teeth approach the groove  930 . However, after the silent chain  900  is straightened, the teeth  920  align again. When the teeth  920  align, they are too small to fit within the groove  930 . Consequently, the teeth  920  are unable to engage with the rack  910 . In order to correct this problem, a silent chain profile is needed in which the teeth  920  align as they are bent to approach the rack  920 , and in which the teeth  920  are drawn apart such that they are offset when the silent chain  900  is straightened. 
         [0039]      FIG. 10  depicts the profile of silent chain  1000  built in accordance with the invention engaging with a profile of rack  1010 . The profile of silent chain  1000  corresponds with the profile of rack  1010 . The teeth  1020  of the link plates of silent chain  1000  are shaped in such a way that the teeth are offset when the silent chain  1000  is straightened. However, as the silent chain  1000  is bent so that the teeth  1020  approach the rack  1010  to engage with the rack  1010 , the teeth  1020  align. Because the teeth  1020  align, the teeth become small enough to fit within a groove  1030  of the rack  1010 . After the silent chain  1000  is straightened, the teeth  1020  are drawn apart, such that they return to their original offset position. In this way, the teeth  1020  are able to engage with rack  1010 . 
         [0040]      FIG. 11  depicts the profile of silent chain  1100  built in accordance with the invention engaging with both a profile of a sprocket  1110  and a rack  1120 . Due to the profile of silent chain  1100 , in which the teeth of the link plates are offset when straightened, the silent chain  1100  is able to engage with a sprocket  1110  on the inside and a rack  1120  on the outside at the same time. The sprocket  1110  can be connected to a motor. The motor drives sprocket  1110  and the silent chain  1100 , such that the silent chain  1100  moves up the rack  1120 , converting rotational motion into linear motion. 
         [0041]      FIG. 12A  and  FIG. 12B  depict a comparison of points of contact between a rack and pinion device and points of contact between a rack and the silent chain built in accordance with the invention.  FIG. 12A  depicts an ordinary rack and pinion device. Only a few teeth  1210  of the pinion  1200  make contact with the rack  1220 . Due to the small number of points of contact, these points of contact may be put under undue amounts of stress when lifting heavy loads, which could cause the rack and pinion device to fail. On the other hand,  FIG. 12B  depicts the silent chain  1230  built in accordance with the invention engaged with a rack  1240 . In this case, multiple points of contact exist between the rack  1240  and the silent chain  1230 . For this reason, the rack and silent chain device is stronger and able to hold more weight. In addition, only small parts are needed, thus increasing the efficiency and decreasing the cost of lifting heavy loads from underneath.