Abstract:
A gear and a method for combining a first gear with a second gear including the steps of moving the first gear relative to the second gear such that a first tooth of the first gear contacts a second tooth of the second gear, pressing the first tooth of the first gear against the second tooth of the second gear such that a resultant force is not directed to a center of at least one of the first gear or the second gear, wherein a torque is created by the resultant force, and rotating at least one of the first gear or the second gear based on the created torque until first teeth of the first gear mesh with second teeth of the second gear.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of Invention  
         [0002]     The invention relates to systems and methods that enables direct engagement between two gears.  
         [0003]     2. Description of Related Art  
         [0004]     Two gears can be structured such that they can become engaged with or disengaged from each other. The two gears can also be structured such that they become engaged with or disengaged from each other (i.e., engage/disengage) once or a plurality of times. For example, the two gears can engage each other once and remain engaged. Alternatively, the two gears can repeatedly engage/disengage each other.  
         [0005]     When the two gears engage/disengage each other, a first gear of the two gears moves relative to a second gear of the two gears. When the two gears engage each other, teeth located along an outer circumference of the first gear are placed between teeth located along an outer circumference of the second gear. The rotation of the first gear thus affects the rotation of the second gear and vice versa.  
       SUMMARY OF THE INVENTION  
       [0006]     The gears can be, for example, spur gears, helical gears, bevel gears or worm gears. For illustrative purposes, spur gears will be described. Spur gears include teeth that are parallel to the axis of rotation with top lands located on an outer surface of the teeth that is farthest from a center of the gear and bottom lands located between the top lands. When the first gear translates relative to the second gear along, for example, a linear or circular path, the top land of a tooth of the first gear can first come into contact with the top land of a tooth of the second gear. Tooth-to-tooth contact is thus created. The two gears do not engage each other because the top lands of both gears are in contact with each other. In other words, the teeth of the first gear are not located between the teeth of the second gear.  
         [0007]     When the top lands of the two gears come into contact with each other, a contact force is created. This happens with gears that are moving, non-rotating gears with translating gear centers. The contact force is a force created by the movement of the teeth of the first gear against the teeth of the second gear. The contact force, created by the tooth-to-tooth contact, is directed to the center of both gears because the center of radius of the top land is at the center of the gear. The resultant forces are thus directed from the surface of both of the top lands to the center of each gear. As such, the two gears do not rotate relative to each other and thus do not engage each other after contact has been made because of the direction of the resultant force toward the center of each gear. In other words, because the resultant force is directed to the centers of the gears, and not offset from the centers of the gears, a rotating force is not created. Damage can thus occur to the top lands of both teeth because of the force created by the tooth-to-tooth contact.  
         [0008]     Furthermore, the combined center-to-center distance between the two gears is increased because the top lands of both gears contact each other. In other words, the teeth of the first gear do not mesh with the teeth of the second gear. With the increased center-to-center distance, a drawer or assembly that is associated with the first gear may not fit into a slot that is associated with the second gear because of the increased distance. As such, the drawer or assembly may not position or lock correctly relative to the slot.  
         [0009]     One method of avoiding the tooth-to-tooth contact is to provide narrow teeth. Although the probability for tooth-to-tooth contact is decreased, tooth-to-tooth contact can still occur. Another method of mitigating the bad effects of the tooth-to-tooth contact is to provide a spring loaded or a gravity loaded idler gear that pivots around the center of a first gear. The idler gear pivots around the center of a first gear and moves out of the way of the teeth of the second gear in order to avoid the high forces associated with tooth-to-tooth contact. Spring-loaded shafts that allow the gears to take the impact of the tooth-to-tooth contact can also be used. As a result, the torque that can be transmitted is limited because of the spring. Furthermore, manufacturing costs are increased by using the idler gear or the spring-loaded shafts. Furthermore, in both cases the size of the gear mechanism is increased in order to accommodate the additional structure.  
         [0010]     Accordingly, the invention thus provides, among other things, a method and apparatus that allows direct engagement that is simple, inexpensive, increases the life span of the two gears, and allows assemblies to be located properly.  
         [0011]     According to one exemplary aspect of the invention, the invention includes a gear with a body with a center and at least one tooth formed on an outer circumference of the body, wherein the at least one tooth includes a top land with a center of radius that is not at the center of the body.  
         [0012]     According to another exemplary aspect of the invention, the invention includes a method for combining a first gear with a second gear, comprising moving the first gear relative to the second gear such that a first tooth of the first gear contacts a second tooth of the second gear, pressing the first tooth of the first gear against the second tooth of the second gear such that a resultant force is not directed to the center of at least one of the first gear or the second gear, wherein a torque is created by the resultant force, and rotating at least one of the gears based on the created torque until first teeth of the first gear mesh with second teeth of the second gear.  
         [0013]     According to another exemplary aspect of the invention, the invention includes a gear assembly with a shaft with a protrusion located at an end of the shaft, a gear comprising a body with a center and at least one tooth formed on an outer circumference of the body with the at least one tooth including a top land with a center of radius that is not at the center of the gear, wherein the shaft extends through the gear, a hub that is located on a first side of the gear between the protrusion and the first surface, the hub including a slot with a first end and a second end, wherein the protrusion extends through the slot, and an urging member that urges the shaft toward the first end of the slot.  
         [0014]     These and other features and advantages of this invention are described in, or are apparent from, the following detailed description of various exemplary embodiments of the systems and methods according to this invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]     Various exemplary embodiments of this invention will be described with reference to the following figures, wherein:  
         [0016]      FIG. 1  is a plan view of two gears before engagement;  
         [0017]      FIG. 2  is a plan view of two gears with tooth-to-tooth contact;  
         [0018]      FIGS. 3A and 3B  are plan views of two gears in accordance with an embodiment of the invention;  
         [0019]      FIG. 4  is a plan view of two gears before engagement according to an embodiment of the invention;  
         [0020]      FIG. 5  is a plan view of two gears that are engaged in accordance with an embodiment of the invention;  
         [0021]      FIG. 6  is a projection view of a gear in accordance with the modification of the invention;  
         [0022]      FIG. 7  is a plan view of two gears that are engaged in accordance with a modification of the invention;  
         [0023]      FIG. 8  is an enlarged view of  FIG. 7 ;  
         [0024]      FIG. 9  is a plan view of two gears that are engaged in accordance with a modification of the invention; and  
         [0025]      FIG. 10  is an enlarged view of  FIG. 11 . 
     
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS  
       [0026]     For a general understanding of two gears in accordance with the invention that can be incorporated into, for example, an image forming device, cars, appliances, or any structure currently available or later developed in which two gears are engaged or disengaged, reference is made to  FIGS. 3-10 , which depicts various embodiments of the invention.  
         [0027]     For clarification,  FIGS. 1 and 2  illustrate two gears that engage and disengage in accordance with the conventional art.  FIG. 1  illustrates two gears before engagement and  FIG. 2  illustrates the two gears that are in tooth-to-tooth contact.  
         [0028]     As shown in  FIGS. 1 and 2 , a first gear  100  and a second gear  150  are shown. The first gear  100  includes a center  102  and teeth  110  that surround a part of the outer circumference of the first gear  100 . The teeth  110  include top lands  112  located at an outer surface of the teeth  110  of the first gear  100  that is farthest from the center  102  of the first gear  100  and bottom lands  114  located between the top lands  112 . Similarly, the second gear  150  includes a center  152  and teeth  160  that surrounds a part of the outer circumference of the second gear  150 . The teeth  160  include top lands  162  located at an outer surface of the teeth  160  of the second gear  150  that is farthest from the center  152  of the second gear  150  and bottom lands  164  located between the top lands  162 .  
         [0029]     The teeth  110  of the first gear  100  and the teeth  160  of the second gear  150  are positioned such that they are opposite each other. Both of the teeth  110 ,  160  are also structured such that they have a standard involute gear profile.  
         [0030]     When the first gear  100  moves in a linear direction  170  toward the second gear  150 , the teeth  110  of the first gear  100  contact the teeth  160  of the second gear  150 . As the first gear  100  further attempts to move in the linear direction  170 , further pressure is applied by the teeth  110  of the first gear  100  against the teeth  160  of the second gear  150 . The teeth  110  of the first gear  100  do not move between the teeth  160  of the second gear  150  because both of the top lands  112 ,  162  have the standard profile where the center of radius of the top land profile of each tooth  110 ,  160  is at the center of each gear  100 ,  150 . Accordingly, the resultant force created by the contact forces between the two gears  100 ,  150  is directed to the centers  102 ,  152  of the gears  100 ,  150 . Further pressure applied between the teeth  110 ,  160  of the gears  100 ,  150  thus causes damage to the teeth  110 ,  160 .  
         [0031]     In order to avoid the negative effects of tooth-to-tooth contact and to thus reduce the possibility of damage to teeth, the invention thus provides gears with teeth whose top lands include a special or non-standard profile. By providing this profile, the resultant forces that are created by the teeth of two gears are not directed to the center of the gears. The resultant forces are not directed to the centers of the gears because there is no center of radius of each tooth top land that is at the center of each gear. Accordingly, the gears rotate in the direction in which the resultant forces are directed so that the teeth can mesh.  
         [0032]     As shown in  FIGS. 3A and 3B , two gears that include two modified profiles are shown. As shown in  FIG. 3A , a first gear  200  is shown with teeth  210 . Each tooth  210  includes a slanted top land  212 . In particular, the top land  212  includes a first end  214  that extends farther from a center  202  of the gear  200  than a second end  216 . As shown in  FIG. 3B , a second gear  250  is shown with teeth  260 . Each tooth  260  includes a curved top land  262 . In particular, the top land  262  includes a first end  264  that extends farther from a center  252  of the gear  250  than a curved second end  266 .  
         [0033]     By providing the slanted top land  212  or the curved top land  262 , the resultant forces that are created by two opposing teeth coming into contact are not directed toward the center of the gear because the resultant force is perpendicular to the contact surface. In other words, the resultant forces that are created provides a torque around the center of the gears so that a first gear rotates relative to a second gear so that teeth can mesh together. The torque is created because the resultant forces are not directed toward the center of the gear. As should be appreciated, almost any top land profile can be used as long as the center of radius of a top land of at least one tooth is not at the center of the gear so that the resultant forces are not directed toward the center of the gear.  
         [0034]      FIGS. 4 and 5  illustrate two gears that engage and disengage in accordance with an embodiment of the invention.  FIG. 4  illustrates two gears before engagement and  FIG. 5  illustrates the two gears wherein the teeth mesh together. As should be appreciated, the two gears of  FIGS. 4 and 5  are the same as the gear  250  of  FIG. 3B .  
         [0035]     In  FIGS. 4 and 5 , a first gear  300  and a second gear  350  are shown. The first gear  300  includes a center  302  and teeth  310  that surround a part of the outer circumference of the first gear  300 . The teeth  310  include top lands  312  located at an outer surface of the teeth  310  of the first gear  300  that is farthest from the center  302  of the first gear  300 . Similarly, the second gear  350  includes a center  352  and teeth  360  that surround a part of the outer circumference of the second gear  350 . The teeth  360  include top lands  362  located at an outer surface of the teeth  360  of the second gear  350  that is farthest from the center  352  of the second gear  350 .  
         [0036]     The teeth  310  of the first gear  300  and the teeth  360  of the second gear  350  are positioned such that they are opposite each other. Both of the teeth  310 ,  360  are also structured such that they have a curved top land  312 ,  362  that slopes from a first end  314 ,  364  to a second end  316 ,  366 . The curved top lands  312 ,  362  slope in the same direction. In other words, if the curved top land  312  slopes such that the first end  314  is in a counterclockwise direction from the second end  316 , the curved top land  362  also slopes such that the first end  364  is in a counterclockwise direction from the second end  366 .  
         [0037]     When the first gear  300  moves in a linear direction  370  toward the second gear  350 , the teeth  310  of the first gear  300  first contact the teeth  360  of the second gear  350 . As the first gear  300  further attempts to move in the linear direction  370 , further pressure applied by the teeth  310  of the first gear  300  against the teeth  360  of the second gear  350  creates a contact force with a tangential force component that is not directed toward the centers  302 ,  352  of the gears  300 ,  350 . By creating the tangential force, a torque around the centers  302 ,  352  of the gears  300 ,  350  is thus created. The tangential force and the resultant torque are directed in an opposite direction to a direction in which the top lands  312 ,  362  curve. In other words, if the top land  312  is curved such that the first end  314  is in a counterclockwise direction from the curved second end  316 , the gear  300  rotates in the counterclockwise direction. When the torque is created, both gears  300 ,  350  are urged to rotate relative to each other. Both gears  300 ,  350  rotate relative to each other until the teeth  310  mesh with the teeth  360 .  
         [0038]     During normal conditions when the teeth  310  mesh with the teeth  360 , the working length between the two sets of teeth  310 ,  360  should be maximized. In other words, the length of the teeth  310  between the top lands  312  and the bottom lands  318  should contact most of the length of the teeth  360  between the top land  362  and the bottom land  368 . The profiles of the top lands  312 ,  362  should not transmit torque between the gears  300 ,  350 . In order to maximize the working surface between teeth  310 ,  360 , the first end  314  of the teeth  310  of the first gear  300  is in contact with the first end  364  of the teeth  360  of the second gear  350 . As such, the contact surface between the gears  300 ,  350  is not reduced when the gear  300  rotates in the counterclockwise direction because the area of contact between the teeth  310 ,  360  is not reduced because the first end  314  of the teeth  310  contact the first end  364  of the teeth  360 . In other words, the working length in which the teeth  310 ,  360  contact an transmit torque is the same as the teeth  112 ,  162  of  FIGS. 1 and 2 . As should be appreciated, when the gear  300  is driven in the clockwise direction when the teeth  310 ,  360  mesh, the first ends  314 ,  364  would be located in the clockwise direction relative to the second ends  316 ,  366  in order to maintain the working length.  
         [0039]     As shown in  FIG. 5 , the final positions of the centers  302 ,  352  of the gears  300 ,  350  should have a predetermined engagement angle relative to each other and to the tangent of the direction  370 . The gears  300 ,  350  should have a predetermined pressure angle so that the direction in which the resultant force that acts between the two gears  300 ,  350  (i.e., pressure line) does not force the gears  300 ,  350  away from each other. In other words, the pressure angle should not exceed a predetermined range. In this embodiment, the engagement angle is an angle defined by a straight line from the center  302  of the gear  300  in the direction  370  and a line that connects the centers  302 ,  352  of the gears  300 ,  350 . If the engagement angle is equal to or smaller than a predetermined angle, then the gears can be easily disengaged. However, if the engagement angle is greater than the predetermined angle, the rotational force created by one gear against another gear does not drive the gears  300 ,  350  apart under a load.  
         [0040]     As described, at least one gear rotates relative to another gear in order for gears to engage each other. However, it may be difficult to rotate one of the gears. Typically, a shaft extends through or is attached to the center of one or both gears. It may also be difficult to rotate at least one of the shafts. For example, one of the shafts may be connected to a motor or to a rigid device. As such, a significant amount of torque may be required to rotate the gear and shaft connected thereto. When the second gear thus approaches the first gear, some play must exist between the shaft and the second gear so that the teeth of both gears engage with each other when tooth-to-tooth contact occurs.  
         [0041]      FIG. 6  illustrates an example of a shaft  420  and a gear  400  that is allowed a limited amount of rotation (i.e., play) relative to the shaft  420 . The gear  400  includes teeth  410  that surround the outer circumference of the gear  400 . Each tooth  410  also includes a top land  412  similar to the top lands  212  of  FIG. 3A .  
         [0042]     The shaft  420  extends through the center of the gear  400  and includes a pin  422  located at an end  424  of the shaft  420 . Attached to or integral with the gear  400  is a hub  430  with a U-shaped slot  432 . The U-shaped slot  432  includes a first end  434  that extends closer to the surface  414  of the gear  400  than the second end  436 . The slot is also designed so that the pin  422  comes into contact slot  432 .  
         [0043]     A biasing spring  440  is placed in contact with the gear  400  between a surface of the gear  400  opposite the hub  430  and a ring  442  or shoulder that is attached to or integral with the shaft  420 . The spring force of the spring  440  is applied such that the pin  422  is forced toward the surface  414  of the gear  400 . As such, the pin  422  moves toward the first end  434  of the slot  432 , which is closer to the surface  414  than the second end  436 .  
         [0044]     When the top lands  412  of the gear  400  come into contact with the top lands of another gear, the gear  400  rotates in the clockwise direction relative to the shaft  420 . When the gear  400  moves in the clockwise direction, the pin  422  against the urging force created by the spring  400  moves from the first end  434  of the slot  432  toward the second end  436 . When the gear  400  is loaded, the gear  400  rotates back to its original position relative to the shaft  420 . As such, the width of the slot between the first end  434  and the second end  436  thus allows for the necessary play. As should be appreciated, the minimum width of the slot  432  should be sufficient such that the gear  400  can rotate by the equivalent of at least one tooth.  
         [0045]     In yet other embodiments, the biasing spring  440  is a torsion spring. As should be appreciated, any device currently available or later developed can be used that provides for a limited amount of play with the gear and that returns the gear to a fixed position when disengaged from another gear.  
         [0046]      FIGS. 7 and 8  illustrates another embodiment of the invention. As shown in  FIGS. 7 and 8 , a first gear  500  and a second gear  550  are shown. In this embodiment, a significant amount of torque is required to rotate the shaft  502  and the first gear  500 . As such, some play must exist with the second gear  550 . Also in this embodiment, the structure of the gears  500 ,  550  is set so that a resultant force that is transferred from the gear  500  to the gear  550  is effectively transferred so that the gear  550  is not forced away from the gear  500 .  
         [0047]     The first gear  500  includes the shaft  502  that extends therethrough and teeth  510  that surround the outer circumference of the gear  500 . Each tooth  510  also includes a top land  512  similar to the top lands  212  of  FIG. 3A . The second gear  550  rotates about a shaft  552  of the gear  550 . The shaft  552  of the second gear  550  is attached to or integral with an arm  554  that is further attached to a shaft  556 . As such, the shaft  552  rotates around the center of the gear  550 .  
         [0048]     The second gear  550  also includes teeth  560  that surround the outer partial circumference of the gear  550 . As should be appreciated, by providing a second gear  550  that is a partial gear, the height of the overall mechanism is reduced when meshed. The second gear  550  also includes two sets of top lands. The first set of top lands  562  are located at the two left most teeth  560  as shown in  FIG. 7  and include a modified top land profile similar to the top lands  212  of  FIG. 3A . In this embodiment, only the two left most teeth  560  include the modified top land profile because when the second gear  550  is moved in the direction  570 , only the two left most teeth  560  contact the teeth  510  of the first gear  500 . As such, it is only necessary to modify the two left most teeth  560  so that the teeth  510  mesh with the teeth  560 . As should be appreciated, more or all of the teeth  560  can include the modified profile and not all of the teeth  510  require the modified profile.  
         [0049]     When the gear  550  moves in the direction  570 , the top land  562  of the teeth  560  come into contact with the top land  512  of the teeth  510 . When the gear  550  is moved further in the direction  570 , torque is created. When the torque is created, the gear  550  rotates in the clockwise direction. However, when using a partial gear for the second gear  550  and a top land  562  with a modified profile, the teeth  560  should preferably mesh with the teeth  510  such that when the gear  500  rotates in a clockwise direction, a sufficient torque is transmitted from the gear  500  to the gear  550  without pushing the gear  550  in a direction  580 .  
         [0050]     As shown in  FIG. 8 , when the gear  500  rotates in the clockwise direction because of torque applied by a motor (not shown), a resultant force Fg is exerted on the teeth  560  of the gear  550  by the teeth  510  of the gear  500 . This resultant force Fg is created based on the profile of the teeth  510 ,  560 , the position of the gear centers relative to the direction  570 , and the torque applied to the gear  500  by the motor. As shown in  FIG. 8 , the angle of the resultant force Fg is 95.2° created by the clockwise rotation of the gear  500 . As should be appreciated, the ideal resultant force angle may be 90°. By providing a resultant force angle between 90° and 95.2°, a minimal amount of force is directed toward the direction  580 . Disengagement of the gears  500 ,  550  is thus avoided. In order to obtain a resultant force between 90° and 95.2°, the gear center locations  502  and/or  552  and/or by changing the tooth face geometry may be modified.  
         [0051]     On the contrary, as shown in  FIGS. 9 and 10 , when the teeth  510  of the gear  500  mesh with the teeth  560  of the gear  550 , the teeth  560  contact the teeth  510  such that the angle of resultant force created by the clockwise rotation of the gear  600  is 109.9°. The larger angle for the resultant force Fg is created because the initial angle of the gear  550  is excessively rotated clockwise. This results in the working surface of the teeth  510  of the gear  500  hitting the tip of the teeth  560  of the gear  550 . This creates a resultant force angle of 109.9° and an additional force directed toward the direction  580 . Thus, the possibility of disengagement between the gears  500 ,  550  is increased.  
         [0052]     While this invention has been described in conjunction with various exemplary embodiments, it is to be understood that many alternatives, modifications and variations would be apparent based on the foregoing description. Accordingly, the exemplary embodiments of this invention, as set forth above are intended to be illustrative, and not limiting. Various changes can be made without departing from the spirit and scope of this invention.