Patent Publication Number: US-8534151-B2

Title: Gearbox output switcher

Description:
BACKGROUND 
     The present disclosure relates to printer devices and more particularly to a gear clutch assembly and method for operating different rollers in the printer device using a single motor. 
     In many printer devices, an intermediate transfer surface, such as a transfer drum, is used to deliver printer ink from a print head to a print or receiving medium such as paper. More specifically, ink is ejected from jets in the print head onto the transfer drum creating a liquid layer of ink. The receiving medium is then brought into contact with the transfer drum and the ink image is transferred and fused or fixed to the receiving medium. 
     To assist in the transfer and fixing of the ink image, a transfix roller is often utilized to apply a pressure to the receiving medium thereby pressing the receiving medium against the transfer drum. When or around the time the receiving medium engages the transfer drum for transfixing of the image on the receiving medium, the transfix roller is moved from an unloaded or disengaged position toward a loaded or engaged position. In the loaded position, the receiving medium is sandwiched between the transfer roller and the transfer drum. After the ink image is transfixed on the receiving medium and the receiving medium is ready or about ready to disengage from the transfer drum, the transfix roller is moved from the loaded position toward an unloaded position to permit the receiving medium to exit from the transfix roller and transfer drum. The transfix roller remains in the unloaded position until the next transfix operation occurs. 
     After the ink is transfixed to the receiving medium from the transfer drum, the transfer drum requires conditioning for a subsequent ink jetting from the print head. Typically, a drum maintenance system is used to condition the transfer drum for receipt of the next ink image. The drum maintenance system, when activated, moves from staged or disengaged position to an operating or engaged position. In the engaged position, a roller included in the drum maintenance system applies oil or other similar functioning substance to the transfer drum. The oil reduces the probability that ink sprayed onto the transfer drum will stick to the transfer drum during the transfix operation. The drum maintenance system also includes an elastomeric or rubber blade that approaches or engages the transfer drum when the drum maintenance system is in the engaged position. The blade meters the oil being applied to the transfer drum. While the drum maintenance system is in the engaged position, the transfix roller remains in its idle unloaded position. Upon completion of the drum maintenance operation, the drum maintenance system is moved to its staged position. 
     Typically, the transfix roller and the drum maintenance system are cam driven. For instance, each of the transfix roller and the drum maintenance system may be driven by independent cam mechanisms, namely a transfix cam mechanism and a drum maintenance cam mechanism. In one prior art system, two separate motors were used to drive the individual cam mechanisms. The first motor drives the transfix cam mechanism and the second motor drives the drum maintenance cam mechanism, with appropriate switching to activate each motor when needed. A disadvantage of the two motor system is the cost for including two such motors in a print device and the spatial and volumetric constraints within print devices. 
     In a second prior art system, a single motor is used to drive both the transfix cam mechanism and the drum maintenance cam mechanism. Independent control of the cam mechanisms is achieved through the use of electromagnetic clutches or electromagnetic solenoids. There are several disadvantages in the single motor/electromagnetic clutch or solenoid system. First, electromagnetic clutches and solenoids are unreliable as they tend to fail and render their print devices inoperable. Second, although not always as costly as the two motor system, electromagnetic clutches and solenoids are still costly to include in competitive print devices. 
     Third, single motor/electromagnetic clutch or solenoid systems do not permit operation of the cam mechanisms simultaneously. Simultaneous or concurrent operation allows the drum maintenance system to be moved toward the engaged position at the same time that the transfix roller is moved from the loaded position to the unloaded position. Such simultaneous operation increases the speed and efficiency of the print device. 
     One solution to these problems of the prior single motor systems is shown in  FIGS. 1-3 .  FIG. 1  shows a print device  10  having a transfer drum  12  rotatably mounted therein. The print device  10  further includes a print head (not shown) for spraying ink onto the transfer drum  12 , a preheater (not shown) for heating a print or receiving medium, such as a sheet of paper, prior to said receiving medium engaging the transfer drum  12 , a transfix roller (not shown) for applying pressure to the receiving medium against the transfer drum  12  as the receiving medium passes the transfer drum  12 , and a drum maintenance system  16  ( FIG. 2 ). The drum maintenance system  16  includes a roller for applying an oil or like substance to the transfer drum  12  to prevent ink from sticking thereto and a rubber blade for metering the oil applied to the transfer drum  12 . A motor driven gear clutch assembly  20  operates or controls the engagement and disengagement of the transfix roller as well as the engagement and disengagement of the drum maintenance system  16 . 
     With reference to  FIG. 3 , the gear clutch assembly  20  is shown with a first housing piece  22  ( FIG. 1 ) removed to reveal the details of the gear clutch assembly  20 . Gears of the gear clutch assembly  20  are in meshing relation with a transfix driving gear  26  and a drum maintenance driving gear  28 . The transfix driving gear  26  is a component of a transfix cam shaft assembly  30  which includes a transfix cam shaft  32  and first and second cams  34 ,  36 . Rotation of the transfix driving gear  26  will rotate the cam shaft  32  and the cams  34 ,  36  mounted thereto. The drum maintenance driving gear  28  is a component of a drum maintenance cam shaft assembly  40  which includes a drum maintenance cam shaft  42  and first and second cams  44 ,  46  mounted to the cam shaft  42 . Rotation of the drum maintenance driving gear  28  will rotate the cam shaft  42  and the cams  44 ,  46 . A motor  48  is separately connected to the gear clutch assembly  20  to drive the gears of the gear clutch assembly  20 . 
     The gear clutch assembly includes a swing arm  50  that selectively engages one or both of the output gear trains  52 ,  54  to drive the corresponding transfix and drum maintenance driving gears  26 ,  28 . As described in more detail in U.S. Pat. No. 6,585,368, the disclosure of which is incorporated herein by reference, controlled pivoting of the swing arm selectively engages the output gear trains  52 ,  54  to the drive motor  48 . Certain movements of the swing arm  50  allow both forward and reverse rotation of each output gear. Rotation of the swing arm is produced by rotation of a driven gear of the swing arm and controlled by various pins and stops. Independent output gear engagement by the swing arm movement depends in part upon missing teeth in the two output gears. 
     There remains a need for a gearbox capable of switching between multiple output gears, especially in drive systems for devices like printing devices. The need is particularly acute for providing a low cost, quiet gearbox capable of high torque transmission. 
     SUMMARY 
     A gear switching mechanism is provided that may be used in a printing machine, for instance. In certain disclosed embodiments, the gear switching mechanism includes an axle defining a longitudinal axis, a gear supported by the axle for rotation about the longitudinal axis, and a rotational coupling supported by the axle for rotation about the longitudinal axis. The gear and the rotational coupling supported for axial movement relative to each other along the longitudinal axis between a first position in which the rotational coupling is in engagement with the gear to transmit a rotary force thereto and a second position in which the rotational coupling is disengaged from the gear. 
     In one aspect of the embodiments described herein, the rotational coupling includes a cam follower. In a further aspect of the disclosed embodiments, a shuttle is provided that defines at least one cam surface slidably engaged with the cam follower and configured to move the rotational coupling axially between the first and second positions as the cam surface and the cam follower move relative to each other. A drive mechanism is provided for imparting relative movement between the shuttle and the cam follower in a plane substantially perpendicular to the longitudinal axis. 
    
    
     
       DESCRIPTION OF THE FIGURES 
         FIG. 1  is a perspective view of a print device shown with a side cover of the print device removed to reveal a transfer drum and a gear clutch assembly operatively received within the print device. 
         FIG. 2  is a perspective view of select components of the print device of  FIG. 1  including the transfer drum, the gear clutch assembly and a drum maintenance system assembly. 
         FIG. 3  is perspective view of select components of the print device of  FIG. 1  including the gear clutch assembly, a motor, and first and second cam shaft assemblies operatively engaged with the gear clutch assembly. 
         FIG. 4  is a perspective view of a gear switching mechanism according to one embodiment disclosed herein. 
         FIG. 5  is a perspective view of a gear switching mechanism according to another embodiment disclosed herein. 
         FIG. 6  is a top view of a gear switching mechanism for use in a printing machine, such as the machine shown in  FIG. 1 . 
         FIG. 7  is a section view of the mechanism shown in  FIG. 6 , taken along line  7 - 7  as viewed in the direction of the arrows. 
         FIG. 8  is a section view of the mechanism shown in  FIG. 6 , taken along line  8 - 8  as viewed in the direction of the arrows. 
         FIG. 9  is a bottom view of the mechanism shown in  FIG. 6 , with the housing removed to reveal the gear trains within. 
         FIG. 10  is a perspective view of a shuttle cam according to a further disclosed embodiment. 
         FIG. 11  is a bottom perspective view of a gear switching mechanism according to another embodiment. 
         FIG. 12  is a top perspective view of the gear switching mechanism shown in  FIG. 11 . 
         FIG. 13  is a side cross-sectional view of the gear switching mechanism shown in  FIGS. 11-12 . 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     According to one disclosed embodiment, a gear switching mechanism  60  is operable to switch between first and second input gear components  62 ,  64  to selectively engage those components to corresponding first and second driven gear components  84 ,  86 , as illustrated in  FIG. 4 . The first input and driven gear components  62 ,  84  are preferably mounted on a common axle  63 , while the second gear components are similarly mounted on a common axle  65 . The axles  63 ,  65  may be integrated into one or the other of the input or driven gears, or the axles may be fixed with the gears rotatably mounted on the axles. 
     The input gear components include corresponding first and second input gears  68 ,  76  mounted on the corresponding axles  63 ,  65 . An engagement interface or rotational coupling is provided in the form of gear faces  70 ,  78 , each including a series of engagement cogs  72 ,  80  configured to transmit rotational movement or torque to a mating gear face when engaged or coupled. The gear face engagements may be integral with the corresponding first or second input gear  68 ,  76  or may be otherwise suitably affixed to the gear face to rotate with the gear. The engagement cogs  72 ,  80  are uniformly spaced around the circumference of the gear faces  70 ,  78 . 
     The first and second driven gear components  84 ,  86  include corresponding driven gears  88 ,  96  concentrically mounted on the axle  63 ,  65  common with the first and second input gears  68 ,  76 . Each driven gear also includes a gear face  90 ,  98  with cogs  92 ,  100  arranged to engage the cogs  72 ,  80  in a known manner. The faces of the cogs  72 ,  80 ,  92  and  100  may be configured as is known in the art to permit engagement while the input gear is rotating and the driven gear is stationary. For instance, the cogs may include angled faces that provide smooth engagement and disengagement. The gear faces  70 ,  78  mate with the corresponding gear faces  90 ,  98  in a known manner—i.e., by relative translation of the two gear faces toward each other. Likewise, the gear face engagements disengage by relative translation away from each other. In the illustrated embodiment, a bias spring  105 ,  107  is concentrically disposed on each axle  63 ,  65  between the opposing input and driven gear engagement pairs of gear faces  70 ,  90  and  78 ,  98 . The bias springs thus bias the two gear faces apart so that no rotational movement or torque is transmitted from input gear to driven gear, unless they are otherwise forced into engagement. 
     The gear switching mechanism  60  incorporates a translating shuttle cam  120  that is operable to selectively bring the gear face pairs into engagement. The shuttle cam  120  is formed by a perimeter wall  122  that defines a slot  128 . The axles  63 ,  65  extend through the slot, as shown in  FIG. 4 . The perimeter wall defines cam edges  123  on opposite sides of the shuttle cam and opposite end wall edges  124 . The cam edges  123  incorporate a number of profile segments  125 ,  126 ,  127 . Each driven gear component  84 ,  86  includes a cam follower  113 ,  115  that is configured to ride along the opposing cam edges  123  along the profile segments  125 - 127 . The profile segments are thus configured to raise or lower the cam followers as the shuttle cam  120  translates relative to the axles  63 ,  65 . 
     In one embodiment, the cam followers  113 ,  115  may be integral with a corresponding driven gear  88 ,  96 . However, in the embodiment illustrated in  FIG. 4 , engagement springs  109 ,  111  are interposed between the cam followers  113 ,  115  and the driven gears  88 ,  96 . The engagement springs  109 ,  111  facilitate the engagement of the cogs of the mating gear faces. For example, when the cam follower  115  of the second gear component  86  moves from the lower profile segment  126 , along the intermediate segment  127  to the higher end wall edge  124 , the cam follower is moved in an axial fashion to push the driven gear component  86  upward toward the rotating input gear face  78 . Since the input gear face is rotating, the cogs  80 ,  100  may not immediately engage. The engagement spring  111  compresses to create the force needed to cause the cogs to engage but in effect, “absorbs” the upward movement of the driven gear face until the cogs are aligned and engaged. It should be understood that the spring force of the engagement springs in their fully extended state is less than the spring force of the bias springs, otherwise the engagement springs would overpower the bias springs and draw the mating gear faces together. However, the spring force of the engagement springs when compressed, such as when the cam follower  113  is at the end edge  124 , is sufficient to compress the bias spring to push the mating gear faces together. 
     In another embodiment illustrated in  FIG. 5 , the shuttle cam  140  rotates, rather than translates as in the embodiment of  FIG. 4 . (It is noted that while the term shuttle most generally refers to linear or back and forth motion, for the present disclosure the term applies to any motion, including rotational and serpentine.) In this embodiment, the shuttle cam  140  includes a shuttle disc  142  that is mounted for rotation at its center  141 . The disc may define an opening at the center  143  for mounting on a pivot bolt or the like. The shuttle cam  140  defines an outer wall  144  and an opposite inner wall  145 , together which forms a slot  149  within which the axles  63 ,  65  reside in the manner describe above with respect to the shuttle cam  120 . The outer wall  144  defines a cam outer edge  146 , while the inner wall defines a corresponding cam inner edge  147 . As in the previous embodiment, the outer and inner edges  146 ,  147  define a profile that is essentially parallel to cam motion. In the embodiment illustrated in  FIG. 5 , this profile includes profile segments  150 ,  151 ,  152  and  153  that are, in the illustrated embodiment, mirrored at each half of the cam profile. The profile segments  151  gradually transition to the profile segment  150  that may preferably be flush with the plane of the shuttle disc  142 . 
     As with the shuttle cam  120 , movement of the shuttle cam  140  causes the engaging gear faces of the two gear components  62 ,  64  ( FIG. 4 ) to engage and disengage as the respective cam followers  113 ,  115  follow the profile segments  150 - 153 . In other words, as the shuttle cam  140  rotates, the profile segments sequentially move beneath the two cam followers  113 ,  115 . The cam followers move up and down with the profile segments, with upward movement causing the cogs of the corresponding gear faces to engage and transmit rotation/torque from the input gear  68 ,  76  to the driven gear component  84 ,  86 . 
     Another feature of the illustrated embodiments is shown in  FIG. 5 , namely the rear gear component  165  that is disposed on the rear face of the shuttle cam  140  relative to the other gear components  62 ,  64 . As shown in  FIG. 5 , this rear gear component  165  may reside on a common axle with one of the other gear components, such as on the axle  65 . The rear gear component  165  is configured like the other gear components with a cam follower (not shown) that translates the driven gear  168  into engagement with the input gear  166 . The cam follower for the rear gear component follows a cam profile defined at the rear cam outer and inner edges  155 ,  156 . Thus, the engagement/disengagement of the rear gear component may be governed by profile segments  160 ,  161 ,  162 , as shown in  FIG. 5 . It can be appreciated that the profile segments  160 - 162  need not parallel the profile segments  150 - 153 , so that the engagement/disengagement of the rear gear component need not coincide with the engagement/disengagement of gear component  64  that shares the common axle  65 . It can also be contemplated that the axle  63  of the other gear component  62  may include a similar rear gear component mounted thereon. Furthermore, a distinct rear gear component with its own axle may also be provided that is independent of the two gear components  62 ,  64 . 
     It should be understood that the arrangement of the gear components, whether on the front or rear of either shuttle cam  120 ,  140 , is dictated by the necessary profile segments, and the range of travel of the shuttle cam. In both shuttle cams, the slot  128 ,  149  through which the axles  63 ,  65  extend is closed at the opposite ends so that the relative travel of the axles within the slots is limited. 
     In accordance with the illustrated embodiments of  FIGS. 4-5 , the shuttle cams  120 ,  140  are driven so that the corresponding cam profile segments pass by each cam follower. Optimally, but not necessarily, the shuttle cam will be driven by a motor common to various gear components. The shuttle cam  120  is linearly translated along the axis of the slot  128 . As indicated above, the shuttle cam  120  must be driven forward and backward as one cam follower or the other reaches the end walls  124  of the shuttle cam. The shuttle cam  120  may thus be driven by a mechanism capable of producing linear movement, such as a rack and pinion gear arrangement or an eccentric arm on a rotating shaft. The shuttle cam  140  is rotated clockwise and counter-clockwise by an appropriate motor and/or transmission. The shuttle cam  140  may be rotated by a shaft affixed to at the center  143  of the shuttle disc  142 . Alternatively, the outer edge of the disc apart from the cam walls  144 ,  145  may define gear teeth for meshed engagement with a drive gear. 
     The gear switching mechanism of the disclosed embodiments may be used in a variety of applications that require switching or selecting among output gear trains. One particular application is in the printing machine  10  described above. The gear switching mechanisms disclosed herein may replace the gear clutch assembly  20  of the prior printing machine shown in  FIGS. 1-3 . More specifically, the shuttle cam  120 ,  140  can replace the swing arm  50  ( FIG. 3 ) as the mechanism for transferring rotation/torque from the motor  48  to one of the output gear trains  52 ,  54 . 
     Thus, as shown in  FIGS. 6-8 , a gear switching mechanism  200  may be provided within a housing  210  that is adapted to be mounted within any mechanical device, for example a printing machine such as the machine  10  shown in  FIG. 1 . A drive motor  212  rotates a drive gear  214  that is in constant engagement with two input gear components  216 ,  218 . Each input gear component is mounted on a corresponding common axle  224 ,  226  with a corresponding driven gear component  220 ,  222 , all as described above. Each driven gear component is in constant engagement with a corresponding output gear train  228 ,  229 , which in one example may drive a one of the transfix cam shaft assembly  30  ( FIG. 3 ) or the drum maintenance cam shaft assembly  40  ( FIG. 3 ) of the printing machine  10 . 
     Each input and driven gear pair includes an engagement interface  232 ,  234  that permits selective engagement of the driven gear to the input gear for the transmission of rotation and torque therebetween. This engagement interface  232 ,  234  may incorporate the engagement cog configuration described above. Alternatively, the engagement interface may incorporate some other suitable interface that is linearly actuated to transmit rotation between the gear components, such as opposing clutch surfaces. The nature of the interface is determined by the force required to maintain the engagement, the torque to be transmitted, cost of components and other factors. For the disclosed printing machine, an engagement cog arrangement is preferable because it requires minimal force to initiate and maintain and because it has high torque transmission capabilities. 
     Each driven gear component includes a cam follower  236 ,  238  that follows the cam profile  240  of a shuttle cam  230 . In the embodiment illustrated in  FIGS. 6-8 , the shuttle cam is a linear shuttle cam, such as the shuttle cam  120  shown in  FIG. 4 . Bias springs  242 ,  244  are positioned between the input and driven gears to bias the gear components in the non-engaged position, such as the input gear component  216  and drive gear component  220 . Engagement springs  242 ,  244  are disposed between the cam followers and the driven gear components and are operable to linearly translate the corresponding driven gear when the corresponding cam follower is elevated by the shuttle cam, such as the follower  238 , spring  248  and driven gear component  222  shown in  FIGS. 7-8 . 
     With particular reference to  FIGS. 7-8 , it can be seen that the driven gear components  220 ,  222  include driven gears  223  that have elongated splines. In particular, the splines are long enough so that the driven gears  223  remain in meshed engagement with the associated output gear train  228 ,  229  when the driven gear component is disengaged, such as the driven gear component  220 , or engaged, such as the driven gear component  222 . The length of the splines is dictated by the amount of axial travel of the driven gear component, which in turn is controlled in part by the height of the engagement cogs (such as cogs  72 ,  80 ,  92 ,  100  in  FIG. 4 ). In can be appreciated that in the disengaged position the opposing engagement cogs, such as cogs  72  and  92  in  FIG. 4 , the cogs cannot contact, and that when fully engaged the driven gear component must move upward by the height of the cogs. Thus, the length of the splines on the driven gears  223  must be at least equal to the height of the cogs. 
     The gear switching mechanism provides robust performance, particularly in high torque applications. The mechanism further permits the use of materials that provide low manufacturing costs. For instance, the sliding components, such as the engagement cogs, shuttle cam and cam followers can be formed of a lower modulus lubricious plastic, such as acetyl, nylon, polyethylene and polypropylene. Other less lubricious materials may be suitable depending upon load, duty cycle, switching speed and permissible noise level. Such other materials may include polyphenylene sulfide, polyurethane, aluminum and brass. The components are preferably molded, rather than machined. 
     The engagement cogs  72 ,  80 ,  92 ,  100  may be configured for shallow, rapid engagement with short travel required for engagement. On the other hand, increased engagement area necessary for higher torque applications can utilize a longer travel, and therefore cogs having greater height. The cogs themselves may have square engagement faces for maximum drive force with very little rotational friction or axial cam-out tendency. Alternatively, the drive faces of the cogs may be slightly angled for greater smoothness during engagement and quieter operation. The angled faces make cam-out more likely at higher loads, so the use of angled cog drive faces inherently limits the torque transmission capabilities of the engagement interface. Portions of the cogs may be angled for clearance to enable or enhance engagement and other portions may be straight or nearly so with minimal clearance for improved force transmission and/or slack or hysteresis control. 
     In accordance with certain embodiments, the cog engagement is facilitated by maintaining the rotation of the input gears while the shuttle cam is moving. In some applications, particularly where multiple engagements or disengagements are occurring, the rotational speeds may be reduced momentarily to facilitate complete engagement. In an alternative embodiment, gear positional and/or rotation angle detectors or sensors may be employed so that engagement may be accomplished without rotating one or the other of the gears. 
     In the illustrated embodiments, the input gear components  62 ,  64  do not translate along the axles  63 ,  65 , but simply rotate as the driven gears for the switching mechanism. However, the translated gear components may become the driven gears with rotational movement and torque being transmitted from the translated gear components, such as gear components  84 ,  86  in  FIG. 4 , to the axially stationary gear components, such as components  62 ,  64 . Elongated splines on the gears  88 ,  96  allow the translated gear components to continuously rotate even as the gears are elevated as the shuttle cams  120 ,  140  drive the cam followers  113 ,  115 . The drive can be configured so that either of the gears in a set can be an input with the other being the output. 
     One feature of the described embodiments is that the shuttle cams may be configured differently for different devices and applications. For example, as shown in  FIG. 4 , the shuttle cam  120  is configured so that one gear set is engaged while the other is disengaged—i.e., only one output is driven at a time. On the other hand, the cam profile for the shuttle cam  140  shown in  FIG. 5  is configured so that both gear sets are driven at one time, such as when the shuttle cam  140  is positioned with the profile segment  153  contacting both cam followers  113 ,  115  at the same time. In the embodiment of  FIG. 5 , it can be appreciated that the cam follower  115  will remain on the profile segment  153  even after slight counterclockwise rotation, while the other cam follower  113  will drop to the profile segment  150  to disengage the corresponding gear set  62  while the other gear set  64  remains engaged. Full clockwise rotation will similarly disengage the gear set  64  while the gear set  62  remains engaged; however, as the shuttle cam disc  142  rotates from the full counter-clockwise to the full clockwise position the two gear sets will be simultaneously engaged over at least the profile segments  152  and  153 . 
     The cam profiles may also be modified to control the torque transmission capability of a particular gear set. For instance, the engagement interface may constitute a clutch interface, rather than the cog arrangement shown in  FIGS. 4-5 . With a clutch interface the amount of torque transmission depends upon the axial force applied to press the clutch surfaces together. Limited slip may be permitted at certain axial loads. The cam profile may be calibrated to slightly reduce the axial force applied through the engagement spring to the driven gear, for instance, to continuously or selectively permit a limited slip condition, versus the no slip condition when the clutch is completely engaged. 
     The cam shuttles of the various embodiments disclosed herein may be driven by various devices. The drive device may be separate from the drive mechanism for the input gear components, such as a separate solenoid, pneumatic/hydraulic cylinder or motor. The drive device may be coupled to the shuttle in a number of ways suitable to impart the necessary translational or rotational motion to the shuttle. For instance, the drive coupling may be by a direct mechanical linkage, through a gear train or transmission, or by way of a driven lead screw, belt or chain. 
     In the illustrated embodiment shown in  FIGS. 6-8 , the translating shuttle cam  230  is driven by a rack and pinion arrangement. Thus, as illustrated in  FIG. 9 , the shuttle cam  230  is provided with a lateral extension  250  that defines a gear rack  252 . It can be appreciated that this lateral extension  250  runs essentially parallel to the base of the housing  210  and may be configured for low-friction sliding contact with the housing. The gear rack  252  meshes with a pinion gear  254  that may be integral with or affixed to a drive gear  256 . The drive gear  256  is driven by an output gear  258  of a motor  260 . The motor  260  is independent of the motor  212  used to drive the output gear trains  228 ,  229 , but is preferably commonly controlled. Dampers or bumpers may be provided at the ends of travel for the shuttle cam and/or rack component to minimize operational noise. Sensors may also be provided at the ends of travel to reverse the direction of operation of the drive device. 
     In the two previous embodiments, the slots  128 ,  149  are configured to simultaneously contain all the axles  62 ,  64  associated with the gear sets of the mechanism. This arrangement thus provides a self-guiding feature for the shuttle cams provided that the axles  63 ,  65  are held stationary. Alternatively the shuttle cam may be configured with separate slots or tracks for each axle. Thus, a shuttle cam  300  may be provided as shown in  FIG. 10  having two slots  302 ,  303  for receiving one each of the axles  63 ,  65 . The shuttle cam thus includes two perimeter walls  304 ,  306  that define cam profile edges  308 ,  310  that may be identical or different as depicted in  FIG. 9 . The two perimeter walls may be attached by a bridge piece  315  or may be flush with each other, depending upon the size and orientation of the gear components mounted within each slot. With this shuttle cam, the cam  150  is translated along an axis perpendicular to the common line between the axles  63 ,  65 , rather than collinear with that line as with the shuttle cam  120  shown in  FIG. 4 . The desirability of using one or the other of the linear shuttle cams  120  or  150  depend upon space requirements for the particular application. 
     In the illustrated embodiments, bias springs  105 ,  107  are situated between the gear face engagement pairs  70 ,  90  and  78 ,  98  that oppose the movements induced by the shuttle cams and that bias the engagement interfaces to the disengaged position. The bias springs may be replaced with other components capable of biasing to the disengaged position but also capable of being overcome by movement of the cam followers. Thus, alternative embodiments may utilize closed pneumatic/hydraulic cylinders, compression springs, extension springs, leaf springs, or torsion springs. Similarly, the engagement springs  109 ,  111  disposed between the cam followers  113 ,  115  and gear faces  90 ,  98  may be replaced by levers, screws or combinations of springs and similar devices. Gear faces illustrated are suggestive of a face engagement plate or an integrated flange with engagement cogs. Smaller gears may be configured in this fashion, however, it possible, even likely with larger gears, to incorporate face engagement features over an area smaller in diameter than the gear. 
     A multiplicity of cams and gears may be configured for applications that benefit from spatial separation of gear sets or multiple gear engagements. In such an applications, multiple cams may be used, coupled with integral or affixed links or external phasing means, such as gears. For simplicity, the surface of a profile defining a cam that interfaces with a cam follower can be termed a rib or cam rib. In another embodiment, one or more cam slots may be open at one end such that the cam ribs may appear fork like. Other cam configurations may be employed, such as, for example, a single rib running through a slot in a stationary shaft or a rotational cam with independent inner and outer cam ribs acting in unison on a cam follower, moved and phased by an external gear, chain or belt. The latter example would allow a unidirectional motion or any cam rotation angle, including greater than 360 degree rotations, with or without reversal. Cam profiles may be made up of one, two (such as the slotted example) or greater number of ribs. If the cam is formed from a molded component, the rib configuration may be controlled, in part, by features of the molding process to maintain optimum flow or minimize sink or other deformations while at the same time providing increased surface area for reducing force, pressure and/or wear. 
     An example of such a rotational cam with independent inner and outer cam ribs is shown in  FIGS. 11-13 . The gear switching mechanism  400  includes an outer ring shuttle  402  and an inner shuttle disc  404  that are concentrically mounted for rotation within a particular machine. The two shuttles  402 ,  404  define a continuous slot  408  between the two components through which the axles  63 ,  65  ( FIG. 13 ) extend in the manner described above. As shown in the figures, the gear switching mechanism  400  can be implemented with the gear components  62 ,  64  and  165  described above. Each gear component includes a corresponding cam follower  113 ,  115  and  169  that is configured to engage a cam surface as described herein. 
     The two shuttles  402 ,  404  may be synchronized in rotation by a phasing mechanism  410  that is operable to ensure a fixed rotational relationship between the cam surfaces on each of the two shuttles. Thus, in one embodiment, the phasing mechanism  410  may include an ring gear  412  defined on an interior surface of the outer ring shuttle  402 , a inner gear  414  mounted to the inner shuttle disc  404 , and a phasing gear  416  therebetween. A support bracket  418  is provided to rotationally support the gears of the phasing mechanism. It is contemplated that any one of the components may be rotationally driven to impart phased rotation to the remaining components. For instance, the phasing gear  416  may connected to a separate drive mechanism for controlled rotation of the two shuttle components. 
     The outer ring shuttle  402  includes a circumferential rim  420  that supports the cam surfaces or cam ribs. Thus, in one embodiment, a pair of upper cam ribs  422  project from one surface of the rim  420 , while lower cam ribs  424  project from an opposite face of the rim. Similarly, the inner shuttle disc  404  includes upper cam ribs  432  projecting from one surface of the disc, and lower cam ribs  434  projecting from the opposite surface. In one embodiment, a like number of upper cam ribs  422  and  432  is provided on the two shuttle components, with corresponding pairs of ribs facing each other across the continuous slot  408 . The facing pairs of cam ribs  422 ,  432 , support the cam followers  113 ,  115  of two gear components  62 ,  64 , as shown best in  FIG. 12 . 
     As seen in  FIGS. 11 and 13 , a similar correspondence may be implemented for the lower cam ribs  424 ,  434 . It can be appreciated that the upper and lower cam ribs can be variously positioned around the circumference of the concentrically rotated shuttles  402 ,  404 . In other words, the upper cam ribs  422 ,  432  may be aligned at 0° and 180° degree positions while the lower cam ribs  424 ,  434  may be arranged at 90° and 270° positions, for example. Of course, other angular arrangements are possible depending upon the needs of the particular application. Moreover, the shuttles may be provided with different numbers of cam rib pairs on the upper and lower surfaces. It can be appreciated that rotation of the outer ring shuttle  402  and inner shuttle disc  404  is operable to engage and disengage the gear components in the manner described above. It should be further understood that the concentric shuttles may be continuously rotated in a single direction or capable of reversing rotation, depending upon the particular application. 
     The gear switching mechanisms disclosed herein operate to select among multiple outputs from a common input. Alternatively, the mechanisms may be used to select among multiple inputs for a common output. Multiple inputs and/or outputs may also be accommodated with the cam shuttle concept. Similarly, engagement cogs may take various shapes other than circular segments, such as for example, triangular, square or round (pins or pin shape). Drive and driven gears may employ any combination of engaging cog configurations including protrusions and insets.