Patent Publication Number: US-9884722-B2

Title: Apparatus and method for tracking conveyor belts

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of prior application Ser. No. 13/791,729, filed Mar. 8, 2013, which claims benefit under 35 U.S.C. §119 (e) to U.S. Provisional Application No. 61/608,333 entitled “Apparatus and Method for Tracking Conveyor Belts” filed Mar. 8, 2012. The contents of each patent application identified above is incorporated herein by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to tracking apparatuses and methods for tracking conveyor belts. 
     BACKGROUND OF THE INVENTION 
     Rollers for conveyor belts are arranged so that the conveyor belt travels thereover in a downstream belt travel direction and path. However, conveyor belts can tend to meander or mistrack laterally toward one side or the other of the rollers due to reasons such as uneven loads carried by the belt. Conveyor belt tracking devices have been developed that respond to belt mistracking to attempt to redirect the belt back to its correct travel path substantially centered on the conveyor rollers. 
     One type of belt tracking device configured to correct a misaligned belt has sensor rollers that are mounted to arms that are each operationally connected to a frame for tracking or training rollers under a belt. If the belt becomes misaligned, it will forcefully engage the sensor roller at the misaligned side, which will cause the arms to force the belt training roller to pivot for steering the belt back toward its proper downstream travel path. However, the sensor rollers are generally located upstream or downstream of the training rollers to create the necessary moment arm for pivoting the rollers. This upstream or downstream mounting of the sensor rollers means that the correcting mechanism is limited to use when the belt travels in a single direction. Furthermore, this solution requires the edge of the belt to forcefully make contact with the sensor rollers, which can undesirably damage the belt. 
     One type of belt tracker that avoids the use of sensor rollers is disclosed in U.S. Pat. No. 6,405,854 to Cumberlege. The Cumberlege system includes a pair of rollers mounted to an elongate support shaft that is pivotable about its center relative to a support frame. The shaft includes a vertical post that pivots within a cylindrical bushing mounted to the support frame. The rollers include an outwardly decreasing taper at the outer ends, which operate to cause the rollers mounted to the elongate shaft to pivot in a horizontal plane about the vertical axis to steer a misaligned belt back toward its proper downstream travel path. The rollers can be mounted to the shaft either in a trough configuration or in a non-troughed or flat configuration. In the troughed configuration, the rollers pivot about the vertical axis while maintaining their orientation relative to the vertical pivot axis. This configuration is limited, however, because when the belt is in a flat configuration, the belt may become misaligned and include laterally outer portions that track off the end of the rollers, reducing the amount of contact between the belt and the rollers and reducing the effectiveness of the steering. 
     Another belt tracking device that avoids the use of sensor rollers has an inclined pivot axis of the rollers located upstream of the rollers. This belt tracker is disclosed in U.S. Pat. No. 2,225,276 to Parker and includes an idler roller that is pivotal about a pivot axis that is upwardly inclined in the downstream direction. In this regard, when a conveyor belt mistracks toward one end portion of the idler roller, the drag forces acting downstream on the idler roller end portion increase, urging the end portion to shift downstream, while the downstream tilt of the pivot axis causes the idler roller end portion to also shift downwardly under the increased weight of the mistracked belt passing over the end portion. Thus Parker&#39;s belt tracker utilizes the weight of the conveyor belt and drag forces acting on the end portion toward which the belt is mistracking to energize the idler roller to pivot about the pivot axis. However, the Parker belt tracker is limited because the tilt of the pivot axis restricts its use to belts that travel in a single direction. 
     Applicants&#39; assignee herein also discloses a belt tracking apparatus in U.S. Patent Application Publication No. 2011/0272250 that has an inclined pivot axis. However, the pivot axis is located downstream of the idler tracking roller so that when the tracking roller pivots about the included pivot axis, the one end portion of the roller that shifts downstream will also shift upwardly for urging the mistracking belt back toward its correct travel path. The belt tracking apparatus of the &#39;250 publication also relies on engagement between an edge of the belt and the corresponding one of the sensor rollers to generate the energizing force for pivoting the tracking roller so that its end portion is shifted downstream and upwardly. Further, because the tracking roller pivots about an inclined pivot axis, shifting of the roller end portion upwardly will be dictated by the angle of the inclination of the pivot axis and the amount of downstream shifting of the roller end portion. In other words, the inclination of the pivot axis defines a predefined relationship between the amount of downstream shifting of the tracking roller end portion and the amount of upward shifting thereof when the tracking roller is pivoted for correcting a mistracking conveyor belt. This can require that greater energizing force be generated from the sensor roller for actuating the pivoting of the tracking roller since it simultaneously has its end portion shifted both downstream and upwardly. In addition, the use of sensor rollers and an inclined pivot axis restricts use of the &#39;250 publication tracking apparatus to conveyor belts that travel in a single direction. 
     SUMMARY OF THE INVENTION 
     A tracking apparatus and method for urging a mistracking conveyor belt back towards a correct travel path are provided. The apparatus and method both utilize downstream shifting of an end portion of an idler roller due to mistracking of the conveyor belt for directing or steering the belt back toward its correct travel path and a reaction force from the belt due to the steering thereof for energizing a tilting action of the idler roller to raise the downstream end portion thereof. In this manner, the tilting of the idler roller is not mechanically coupled to the downstream shifting of the roller end portion since it is the steering action that first generates the reaction force in the belt against the shifted idler roller which is used as the actuation or energizing force for tilting the idler roller. By mechanically separating the downstream shifting and tilting actions of the roller, an inclined pivot axis for the idler roller such as provided in prior belt tracking devices is avoided allowing the belt tracking apparatus herein to be bi-directional for use with conveyor belts that may be run in opposite travel directions. 
     Also, the energizing force for tilting the idler roller is independent of the energizing force for downstream shifting of the idler roller end portion thus allowing the tracking apparatus to generate an amount of tilting of the idler roller that is in proportion to the resistance of the belt being steered by the shifted idler roller. In other words, if the belt provides little resistance to being steered back toward its correct travel path by the shifted idler roller, then the idler roller will not be tilted to the same degree as when there is greater resistance by the mistracking belt to the steering action. In this instance, the tilting of the idler roller will be greater so that the tilted idler roller creates another influence on the mistracking belt, in addition to the steering action, that will urge it back towards it correct travel path. 
     In one aspect, a tracking apparatus is provided that includes at least one idler roller for supporting the conveyor belt and a frame assembly that is configured to operatively mount the idler roller to conveyor structure. The frame assembly is further configured to allow the idler roller to shift when the conveyor belt is mistracking so that one end portion of the idler roller is further downstream than the other end portion thereof for directing the belt back toward the correct travel path. The frame assembly is also configured to allow the idler roller to use a reaction force from the belt as the belt is being directed by the shifted idler roller to actuate the idler roller to be tilted for urging the belt back toward the correct travel path. Rather than defining a predetermined relationship between the amount of downstream shifting of the idler roller and the amount of upward shifting thereof as in prior tracking apparatuses, the tracking apparatus herein utilizes a reaction force from the belt as it is being directed by the idler roller that is shifted to have one of its end portions further downstream than the other end portion as the actuation force for tilting the idler roller for urging the belt back toward the correct travel path. In this manner, the tilting action of the idler roller is in proportion to the amount of resistance generated by the belt to the steering action undertaken by the shifted idler roller. 
     In another aspect, a bi-directional, self-energizing tracking apparatus for redirecting a mistracking conveyor belt back toward a correct travel path whether the conveyor belt is traveling in one direction or in an opposite direction is provided. The tracking apparatus has an idler roller device including a pair of outer idler rollers that support outer side portions of the conveyor belt, and a tilt device which mounts the idler roller device for shifting relative thereto. The outer idler rollers each include an outer end portion that tapers down toward a reduced diameter end thereof to cause the idler roller device to shift relative to the tilt device so that one of the outer idler rollers is further downstream than the other idler roller when the conveyor belt mistracks toward the one outer idler roller for steering the conveyor belt back toward the correct travel path. A base frame extends across the conveyor belt and is configured to be mounted to conveyor structure along the outer side portions of the conveyor belt. Linkage members interconnect the tilt device to the base frame for allowing the tilt device to tilt relative to the base frame upon receiving a reaction force from the conveyor belt when the idler roller device is shifted for steering of the mistracking conveyor belt so that the idler roller device is tilted and the downstream, one outer idler roller is raised relative to the other idler roller to urge the conveyor belt towards the correct travel path. 
     The self-energizing tracking apparatus does not rely on sensor rollers for generating either the actuation or energizing force for shifting of the idler rollers for steering the conveyor belt back towards the correct travel path or for tilting of the idler rollers for urging the conveyor belt back towards the correct travel path. Instead, it is the frictional engagement of the mistracking conveyor belt with the idler rollers that include tapered outer end portions that generates the actuation force for shifting thereof when the belt mistracks. In addition, the tilt device and the base frame are interconnected by linkage members such that when the idler rollers are shifted for steering the mistracking conveyor belt, a reaction force from the conveyor belt is received by the idler rollers which is used as the actuation force for causing the tilt device to tilt relative to the base frame. In this manner, the idler roller that is shifted further downstream due to mistracking the conveyor belt is also raised relative to the other upstream idler roller so that in addition to being steered back toward the correct travel path, the idler rollers are tilted to urge the conveyor belt back toward the correct travel path. Since the tracking apparatus does not need to employ sensor rollers for generating its energizing or actuation forces for shifting and tilting the idler rollers, the tracking apparatus is bi-directional in that it can be used without being reconfigured for correcting the travel path of the belt whether it is traveling in one direction or in a direction opposite to the one direction. 
     In one form, the idler roller device and the tilt device have a rotatable connection therebetween to allow the idler roller device to rotate relative to the tilt device. The rotatable connection can be in the form of a central pivot assembly that allows the idler roller device to pivot relative to the tilt device. Alternatively, the rotatable connection can be in the form of a central spherical bearing that allows the idler roller device to rotate relative to the tilt device. 
     In the form having the central pivot assembly, the tilt device can include a tilt frame member for extending across the conveyor belt. The tilt frame member pivotally carries the idler roller device thereon, and the central pivot assembly can include a pivot axis substantially normal to the tilt frame member and about which the idler roller device is pivotal. Because the pivot axis is not inclined, the tracking apparatus in this form has the ability to correct mistracking conveyor belts that travel in either of opposite travel directions relative thereto. 
     In one form, the idler roller device and the tilt device have rollers therebetween with the rollers rolling along the tilt device to provide low friction support to the idler roller device as the idler roller device shifts relative to the tilt device and as the tilt device tilts the idler roller device. 
     In another form, the idler roller device and the tilt device have stops therebetween that limit the shifting of the idler roller device relative to the tilt device by a predetermined amount. 
     In one form, the tilt device is hung from the base frame via the linkage members such that the linkage members are in tension. Alternatively, the tilt device is supported in an elevated orientation relative to the base frame such that the linkage members are in compression. 
     In another form, the idler roller device includes an idler roller frame, the tilt device includes a tilt frame member to which the idler roller frame is pivotably mounted, the base frame includes spaced lateral support members, and the linkage members pivotably interconnect the tilt frame member to the spaced lateral support members so that the tilt frame member and the idler roller frame are generally between the spaced lateral support members with the tilt frame member hanging from the lateral support members to extend generally therebelow and the idler roller frame pivotably mounted to the tilt frame member to extend generally above the lateral support members. 
     The idler roller device can include a central idler roller, and the idler roller frame can be configured to adjustably orient the outer idler rollers at a selected upward incline relative to the central idler roller for supporting a troughed upper run of the conveyor belt. 
     In another aspect, a method for urging a mistracking conveyor belt back toward a correct travel path is provided including mounting idler rollers having tapered outer end portions under outer side portions of the conveyor belt, shifting the idler rollers so that one of the idler rollers is further downstream than another idler roller in response to conveyor belt mistracking toward the one idler roller due to greater engagement of the corresponding belt outer side portion with the tapered outer end portion of the one idler roller, steering the conveyor belt back toward the correct travel path with the shifted idler rollers, tilting the idler rollers so that the one idler roller that has been shifted downstream is raised relative to the other idler roller in response to a reaction force received from the conveyor belt being steered by the idler rollers, and urging the conveyor belt to generally shift in a lateral direction away from the raised, one idler roller back towards the correct travel path due to the tilting of the idler rollers. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a belt tracking apparatus in accordance with the present invention showing a roller assembly mounted to a tilt channel device that is, in turn, mounted to a support frame; 
         FIG. 2  is a plan view of the belt tracking apparatus of  FIG. 1  showing the apparatus in a neutral position with a pair of rollers of the roller assembly extending laterally orthogonal to the belt travel direction; 
         FIG. 3  is an elevational view of the belt tracking apparatus of  FIG. 1  in the neutral position showing the tilt channel device in a non-tilted orientation relative to the support frame; 
         FIG. 4  is a partial cross-sectional view showing the interior of one of the rollers and a spherical bearing connection between the roller assembly and the tilt channel device; 
         FIG. 5  is a partial cross-sectional view of the spherical bearing connection; 
         FIG. 6  is a partial cross-sectional view of the tilt channel device and the support frame showing a center mount therebetween; 
         FIG. 7  is a bottom perspective view with the support frame removed showing the interior of the tilt channel device; 
         FIG. 8  is a perspective view with the roller removed showing an outboard end of a roller shaft having an exterior bearing and an upstanding retainer bracket member mounted to the end of the tilt channel device; 
         FIG. 9  is a plan view of the belt tracking apparatus in a partially shifted position with the belt mistracking to the right lateral side showing the rollers pivoted so that the right lateral portions thereof are pivoted further downstream; 
         FIG. 10  is an elevational view of the belt tracking apparatus in the partially shifted position of  FIG. 9  showing the tilt channel of the roller assembly pivoted or tilted up so that the right lateral portions thereof are tilted higher; 
         FIG. 11  is a plan view of the belt tracking apparatus in a fully shifted position with the belt mistracking to the right lateral side showing the rollers pivoted so that the right lateral portions thereof are further downstream than shown in  FIG. 9 ; 
         FIG. 12  is an elevational view of the belt tracking apparatus in the fully shifted position of  FIG. 11  showing the tilt channel of the roller assembly pivoted or tilted up so that the right lateral portions thereof are tilted higher than shown in  FIG. 10 ; 
         FIG. 13  is a cross-sectional elevational view of an alternative embodiment of the belt tracking apparatus of  FIGS. 1-12  showing a lower flange member mounted to the upstanding retainer bracket and located below the exterior bearing; 
         FIG. 14  is a perspective view of an alternative belt tracking apparatus showing idler rollers including inclined, tapered outer idler rollers that are supported in a troughed configuration by a frame assembly configured for allowing for shifting and tilting of the idler rollers when an upper, carry run of a conveyor belt is mistracking; 
         FIG. 15  is perspective view of the frame assembly of the belt tracking apparatus of  FIG. 14  with the idler rollers removed showing a support base frame, idler roller frame and a tilt frame of the frame assembly; 
         FIG. 16  is a perspective view of the idler roller frame of an idler roller device configured for supporting the idler rollers in the troughed configuration; 
         FIG. 17  is a perspective view of a tilt device including the tilt frame of the frame assembly showing a central pivot assembly for pivotally mounting the idler roller device thereto and linkage members for tilting of the tilt device and the idler roller device; 
         FIG. 18  is a perspective view of the tilt device of  FIG. 17  pivotally mounted to a support base frame via the linkage members for tilting relative thereto and showing stops of the tilt device for limiting pivoting of the idler roller device relative thereto; 
         FIG. 19  is an enlarged perspective, sectional view of the center pivot assembly secured to the tilt frame and to a laterally extending base member of the idler roller frame pivotally mounting the idler roller frame to the tilt frame; 
         FIG. 20  is a perspective view of the idler roller frame showing rollers rotatably mounted at the bottom of the base member thereof; 
         FIG. 21  is an enlarged perspective, fragmentary view showing the rollers of the idler roller frame engaged on a rolling surface of the tilt frame; 
         FIG. 22  is a perspective view of the support base frame of the frame assembly showing a pair of spaced laterally extending support members having mounting lugs secured thereto to which upper ends of the linkage members are pivotally connected; 
         FIG. 23  is an enlarged end perspective view of the frame assembly showing a single pivot shaft extending through an end of the tilt frame and having the lower ends of a pair of the linkage members pivotally secured at either end thereof for pivotally connecting the linkage members to the tilt device; 
         FIG. 24  is an end perspective, sectional view of the belt tracking apparatus showing pivot shafts extending between upper ends of the linkage members and the mounting lugs for pivotally connecting the linkage members to the support base frame; 
         FIG. 25  is a plan view of the belt tracking apparatus of  FIG. 14  showing the conveyor belt mistracking toward the right and the right, inclined idler roller shifted further downstream than the left, inclined idler roller; 
         FIG. 26  is a front elevation view of the belt tracking apparatus of  FIG. 14  showing the tilting of the tilt frame when the belt has mistracked as in  FIG. 25  with the right, inclined idler roller raised relative to the left, inclined idler roller; 
         FIG. 27  is a cross-sectional view of the belt tracking apparatus of  FIG. 14  showing the shafts for the tapered, outer inclined idler rollers and the opposite stub shaft portions for the center idler roller; 
         FIG. 28  is a front elevational view of the idler roller frame showing mounting brackets for the outer idler rollers adjustably secured at an intermediate adjusted position for conveyor belts having upper runs with an intermediate troughed configuration; 
         FIG. 29  is a front elevational view of the idler roller frame showing mounting brackets secured at a maximum lowered position for conveyor belts having an upper run having a minimally troughed configuration; 
         FIG. 30  is a front elevation view of the idler frame showing the mounting brackets secured at a maximum raised position for conveyor belts having upper runs with a maximum troughed configuration; 
         FIG. 31  is a front elevational view of an alternative conveyor belt apparatus tracking for use along the return run of a conveyor belt showing a linear arrangement of the idler rollers but otherwise similar to the conveyor belt tracking apparatus of  FIG. 14 ; 
         FIG. 32  is a plan view of the belt tracking apparatus of  FIG. 31  showing the idler rollers extending orthogonally to the travel path of the centered, conveyor belt thereon; 
         FIG. 33  is a perspective view of the idler roller device with the idler rollers removed showing the idler roller frame of the frame assembly of the belt tracking apparatus of  FIG. 31 ; 
         FIG. 34  is a plan view of the belt tracking apparatus of  FIG. 31  showing a conveyor belt traveling in an opposite direction to that depicted in  FIG. 25  with the belt mistracking toward the right idler roller and the idler rollers shifted so that the right idler roller is further downstream than the left idler roller; 
         FIG. 35  is a front elevational view of the belt tracking apparatus of  FIG. 31  showing the tilt frame tilted when the belt has mistracked as in  FIG. 34  so that the right downstream idler roller is raised relative to the left upstream idler roller; 
         FIG. 36  is a perspective view of an alternative, return run belt tracker apparatus showing the tilt device pivotally supported by linkage members at an elevated position relative to the support base frame similar to the belt tracking apparatus of  FIG. 1 ; 
         FIG. 37  is a perspective view of the idler roller device with the idler rollers removed showing an idler roller frame of the frame assembly of  FIG. 36  configured to support the idler rollers in a linear configuration; 
         FIG. 38  is a perspective view of the tilt device showing a central pivot assembly secured thereto for pivotally securing the idler roller frame thereto similar to the central pivot assembly of  FIG. 17 ; 
         FIG. 39  is a perspective view of a support base frame showing a beam member thereof having center rollers rotatably mounted on an axle similar to that shown in  FIGS. 6 and 7 ; 
         FIG. 40  is a plan view of the belt tracking apparatus of  FIG. 36  showing the conveyor belt traveling in the same direction as depicted in  FIG. 34  with the belt mistracking toward the right idler roller and the right idler roller shifted further downstream relative to the left idler roller; and 
         FIG. 41  is a perspective view of the belt tracking apparatus of  FIG. 36  showing the tilt frame device tilted when the belt has mistracked as in  FIG. 40  to raise the right idler roller relative to the left idler roller. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As illustrated in  FIGS. 1-12 , a conveyor belt tracking apparatus  10  is adapted to be used with an endless conveyor belt system positioned under a conveyor belt  12  thereof to track the belt  12  along a generally longitudinal belt travel path, the center of which is indicated at broken line  14  in  FIG. 2 . To this end, the belt tracking apparatus  10  will be described with respect to correcting lateral misalignment of the belt  12  relative to the center line  14 . The belt tracking apparatus  10  is generally symmetrical such that the structure and function and of the apparatus  10  on one lateral side will be applicable to the opposite side as well. 
     As shown in  FIGS. 1-4 , the belt tracking apparatus  10  includes a roller assembly  16  having a pair of rollers  18 , with each roller  18  being mounted for rotation on an elongate shaft  20  extending therethrough. The rollers  18  each include a cylindrical main portion  21  and a tapered outer end portion  22 . The tapered outer end portion  22  has an outwardly decreasing diameter relative to the main portion  21 . 
     The shafts  20  are coupled to a center coupling member  24  having a spherical portion or bearing  26  at the center thereof. The spherical bearing  26  is received within a spherical socket  28  of a housing  30  to provide a universal type joint therebetween such that the coupling member  24  can rotate and swivel about a plurality of axes relative to the housing  30  for optimized adjustability of the orientation of the roller assembly  16  during conveyor belt operations. Thus, rather than pivoting about a single, fixed vertical axis, the roller assembly  16  can undertake compound rotating or swiveling motion. 
     The housing  30  is fixedly mounted to an elongate tilt channel device  32  generally centrally along the length thereof. The tilt channel device  32  is mounted to a support frame  34  so that the tilt channel device  32  can shift and tilt relative to the support frame  34 . The support frame  34  is adapted for mounting to the frame structure of the endless belt conveyor system. 
     The roller assembly  16  is thus capable of compound rotary motion relative to the housing  30  and tilt channel device  32 , with the tilt channel device  32  being capable of translation and tilting relative to the support frame  34 . The rotary motion of the roller assembly  16  and the translation and tilting of the tilt channel device  32  combine to urge the belt  12  back toward the center to correct a misalignment in the event the belt  12  becomes misaligned to one side. As will be described in further detail below, the self-correcting ability of apparatus  10  can be accomplished without requiring the belt  12  to actively contact sensor rollers to force a change in orientation of the rollers  18 . This form of belt correction is known as “self-energizing,” and preserves the integrity of the belt edges more effectively than the non self-energizing types of belt trackers that require contact with sensor rollers or the like. Furthermore, the symmetrical nature of the apparatus  10  allows for the apparatus to be used with a belt travelling in both a first longitudinal belt travel direction and a reversed longitudinal direction opposite the first direction. 
     It should be noted that the term “symmetrical” refers to the general orientation of the components of the apparatus  10  when the apparatus is in a neutral position, and refers to the symmetry on the left and right side of a central longitudinal axis Z that is generally parallel to the direction of belt travel, as well the symmetry on the fore and aft side of a lateral axis X that is generally parallel to the length of the support frame  34 . As will be described in further detail, when the belt  12  becomes misaligned to one side, the roller assembly  16  will rotate about its connection to the housing  30 , which ultimately causes the tilt channel device  32  to translate laterally to the side of the misalignment relative to the support frame  34 . However, the housing  30  and tilt channel device  32  do not become offset in the longitudinal direction of the travel of the belt  12 . In such a condition, the overall apparatus  10  will no longer be symmetrical, but will return to its symmetrical orientation after the belt  12  has returned to its intended path of travel. The symmetrical orientation allows for correcting the belt  12  in the same manner regardless of the direction of travel of the belt  12  or the particular side to which the belt  12  becomes misaligned. 
     Furthermore, the terms “lateral” or “laterally” refer to a lateral direction along the axis X. The terms “fore,” “forward,” “aft,” and “rearward” refer to a longitudinal direction along the axis Z, and relative to the direction of belt travel, so that forward refers to the direction of belt travel and rearward refers to the direction opposite belt travel. 
     One of the rollers  18  of the roller assembly  16  is shown in further detail in  FIG. 4 . As previously mentioned, the apparatus  10  and the roller assembly  16  are generally symmetrical, so the description of one roller  18  will correspond to the other roller  18 , as well. The roller  18  is mounted for rotation to the shaft  20 , with an axis  40  of rotation for the roller  18  running along the central axes of both the roller  18  and the shaft  20 . The roller  18  includes a laterally inboard end  18   a  and a laterally outboard end  18   b . The rollers  18  have a cavity or bore  42  extending therethrough, through which the shaft  20  extends. The rollers  18  thus include an inboard opening  42   a  and an outboard opening  42   b . Annular end cap assemblies  44  are mounted at both the inboard opening  42   a  and outboard opening  42   b . The end cap assemblies  44  are sized such that the outer diameter of an inner portion  44   a  generally corresponds to the inner diameter of the openings  42   a  and  42   b . The inner portion  44   a  is received within the openings  42   a  and  42   b  at each end of the roller  18 . The end cap assemblies  44  also include an opening  44   b  through which the shaft  20  extends. The end cap assemblies  44  include a bearing  46 . The bearing  46  is mounted between the end cap assembly  44  and the shaft  20  so that the rollers  18 , with the end cap assemblies  44  mounted thereto, can rotate via the bearings  46  about the shaft  20 . The bearings  46  are generally in the form of a ball bearing assembly or the like, but other types of rotatable bearings can also be used. The roller  18  is held in place axially by a pair of disc retainer members  48  that radially extend from the shaft  20 . The disc retainer members  48  are disposed to the outside of the end cap assemblies  44 , and may be snap fit in place in grooves  48   a  of the shaft  20 . 
     The shaft  20  includes both an inboard end  20   a  and an outboard end  20   b . The inboard end  20   a  includes annular sleeve connection portion  20   c  configured for being coupled with the center coupling member  24 . An outer bearing  50  is mounted to the outboard end  20   b  of the shaft  20 . The outer bearing  50  may have a generally annular ring shaped form. The outboard end  20   b  of the shaft  20  has a reduced outer diameter relative to the remainder of shaft  20  to form a radially extending shoulder surface  20   d . The outer bearing  50  is held in place axially by a disc retainer member  50   a , similar to the disc retainer members  48 , and the shoulder surface  20   d  of the shaft  20 . The outer bearing  50  may be a ring or wheel bearing that can rotate about the shaft  20 , which will be further described below. The outer bearing  50  is preferably made from a low friction plastic material such as Acetal; however, other materials may also be used. 
     As shown in further detail in  FIG. 5 , the center coupling member  24  is in the form a shaft  24   a  with threaded opposite end portions  24   b  that are threaded into the annular sleeve connection portions  20   c  of the inboard end  20   a  of each shaft  20 . An undercut portion  24   c  is formed in the shaft  24   a  that corresponds to the shoulder surface  20   d  when the roller shafts  20  are fully installed on the coupling member  24  to eliminate a stress concentration at the termination of the threads. The spherical bearing  26  includes a ball portion  26   a  having a through bore through which the shaft portion  24   a  extends. The spherical bearing  26  is received within the spherical socket member  28 , which is fixedly mounted within the housing  30 . The housing  30  is fixedly mounted to the tilt channel device  32  via a welding bead, and extends upwardly from the tilt channel device  32  at the center thereof. Thus, the rollers  18  are each ultimately mounted for rotary motion about a central spherical connection  60  formed by the interface between the spherical bearing ball portion  26   a  and the socket member  28 , with the spherical connection  60  having a generally consistent location upward of the center of the tilt channel device  32 . 
     The tilt channel device  32  is mounted to the support frame  34  to allow for translation of the elongate tilt channel device  32  along the fixed elongate support frame  34  therebetween. More specifically, and with reference to  FIGS. 6 and 7 , the tilt channel device  32  is connected to the support frame  34  at a plurality of locations. The tilt channel device  32  can include a channel member  321  having an inverted generally C-shape cross-sectional configuration. The channel member  321  has an upper wall  322  with depending leg portions  323  and  324  on either side thereof. The support frame  34  is in the form of a cross beam  34   a  having a tubular configuration with a generally rectangular cross-sectional configuration to include upper and lower walls  341  and  342  interconnected by opposite sidewalls  343  and  344 . The cross-beam upper wall  341  has an upper surface  34   b  with a center mount portion  62  fixedly mounted thereto. The C-shaped configuration of the channel member  321  is configured so that the width of the upper wall  322  is wider than the width of the cross beam  34   a , such that the depending leg portions  323  and  324  can tilt downward and past the cross beam upper wall  341  when the tilt channel device  321  becomes tilted. This position is illustrated in  FIG. 12 . 
     The center mount portion  62  includes an upstanding mounting block  62   a  having a through-hole  64  through which an axle  66  extends in a fore and aft direction  66   a  when the apparatus  10  is mounted to generally extend laterally under and across the belt  12 . A pair of roller bearings  68  are mounted to the axle  66  both fore and aft of the center mount portion  62 . The roller bearings  68  are configured to contact a lower surface  32   a  of the channel member upper wall  322  of the tilt channel device  32 . Thus, when the tilt channel device  32  shifts or translates laterally along the support frame  34 , the lower surface  32   a  of the channel member upper wall  322  will roll across the roller bearing  68 . The tilt channel device  32  also includes a laterally extending slot  69  in each of the depending leg portions  323  and  324  through which the axle  66  extends. As the tilt channel device  32  shifts laterally, the axle  66  will ultimately contact one of end surface portions  69   a  of the slot  69  to limit the amount that the tilt channel device  32  can shift laterally relative to the support frame  34 . In one form, the slot  69  has a length of about three inches; however, other lengths could also be used. The translation of the tilt channel device  32  along the support frame  34  shifts the roller assembly  16  so that it is no longer centered relative to the support frame  34 . While this could impact the sensitivity of the belt tracking provided by the rollers  18 , the tilt channel device  32  is also operable to generate tension in the belt  12  for correcting its travel path as described further below. 
     With reference to  FIGS. 1, 3, 4, 8, and 9-12 , the tilt channel device  32  is mounted to the support frame  34  via a linkage system which can include linkage bars  70  disposed at four locations. The linkage bars  70  are operable to cause the tilt channel device  32  to tilt relative to the support frame  34  in response to a lateral reaction force acting upon the tilt channel device  32  that is caused by the skewed orientation of the rollers  18  as further described below. 
     More specifically, the linkage system includes an upper pivot shaft that  72  extends in the fore and aft direction between the fore and aft depending leg portions  323  and  324  of the tilt channel device  32  and is mounted thereto via retaining rings  72   a  at the exterior surfaces of the fore and aft depending leg portions  323  and  324  of the tilt channel device  32 . The upper shaft  72  is connected to the linkage bar  70  by extending through upper aperture  72   a . The support frame  34  has a linkage lug  74  fixed thereto to depend from a lower surface  34   c  of the lower wall portion  342  of the support frame cross beam  34   a  and generally extending in the fore and aft direction generally between the sidewalls  343  and  344  of the support frame cross beam  34   a . The linkage lug  74  includes a through aperture  74   a  through which a lower pivot shaft  76  extends. The lower shaft  76  is connected to the linkage bar  70  by extending through a slot  78  of the linkage bar  70 . As shown, the upper shaft  72  is located above and inboard of the lower shaft  76 . Thus, the linkage bar  70  extends upwardly and laterally toward the centerline  14  from the support frame  34  to the tilt channel device  32 . There is a pair of linkage bars  70  located on either side of the centerline  14 . One linkage bar  70  of each pair is located at the forward side of the support frame  34 , with the other located at the rearward side of the support frame  34 . When the tilt channel device  32  translates along the support frame  34  to the right, the right side linkage bars  70  will be put in compression, causing an upper end portion  78   a  of the slot  78  to contact the lower shaft  76 , thereby causing the linkage bar  70  to rotate about the lower shaft  76 . The rotation of the linkage bar  70  about the lower shaft  76  will cause the tilt channel device  32  to lift upwardly at the right side and become tilted relative to the support frame  34 . This tilted orientation can be seen in  FIGS. 10 and 12 , as is discussed in further detail below. In one form, the length of the slot can be approximately 1.35 inches; however, other slot lengths can also be used. 
     Additionally, and as illustrated in  FIGS. 6 and 7 , four guide blocks  80  are mounted to the support frame  34  via a pair of U-shaped brackets  82 . The brackets  82  are fixedly mounted to the upper surface  34   b  of upper wall  341  of the support frame  34 , similar to the center mount  62 , symmetrically at both the right and left side of the centerline  14 . The brackets  82  have a pair of upwardly extending mounting flanges  82   a  to which the guide blocks  80  are secured. One bracket  82  holds two guide blocks  80 , one at the forward side thereof and one at the rearward side thereof. The guide blocks  80  are configured to fit between and slide along interior surfaces  32   b  and  32   c  of the fore and aft depending leg portions  323  and  324  of the tilt channel device  32  as the tilt channel device  32  travels along the support frame  34 . The guide blocks  80  help to ensure that the tilt channel device  32  translates in the lateral direction and limits pivoting of the tilt channel device  32  relative to the support frame  34 . 
     As shown in detail in  FIG. 8 , the tilt channel device  32  also has a pair of upstanding retainer bracket members  90  mounted at each end. The upstanding retainer bracket members  90  include a pair of upwardly extending sidewall portions  90   a  extending generally upwardly from the opposite ends of the tilt channel device  32  so that the sidewall portions  90   a  are disposed both fore and aft of the outer bearing  50 . An end wall portion  90   b  extends in the fore and aft direction between the upwardly extending sidewall portions  90   a . An inwardly extending upper flange portion  90   c  extends laterally inwardly toward the centerline  14  from the end wall portion  90   b  so that the flange portion  90   c  is disposed above the outer bearing  50  of the shaft  20 . Thus, the outer bearing  50  has a fixed surface forward, rearward, and above. If the roller assembly  16  spherically rotates about the spherical connection  60  relative to the tilt channel device  32 , the outer bearing  50  can contact the upwardly extending sidewall portions  90   a  or the inwardly extending upper flange portion  90   c  to restrict the amount of fore and aft movement or upward movement that occurs at the outboard end  20   b  of the shaft  20 . As will be further discussed below, the upstanding retainer bracket members  90  bear a portion of the load in the apparatus  10  during operation. For example, when a downward load is exerted at the right side of the roller assembly  16  during a lateral misalignment of the belt  12  to the right, the roller assembly  16  will tend to tilt downwardly at the right side via the spherical connection  60 , causing the left side to tend to tilt upwardly at the left side. However, the left side flange portion  90   c  that extends over the corresponding outer bearing  50  will stop the upward movement of the outer bearing  50  at the left side and will thereby provide support to the roller assembly  16 , which will tend to limit the amount that the roller assembly  16  will tilt relative to the tilt channel device  32 . As can be seen in  FIGS. 10 and 12 , when the tilt channel device  32  is tilted relative to the support frame  34 , the axis of the roller assembly  16  will extend substantially parallel to the tilt channel device  32  along the length thereof. 
     The support frame  34  is configured for mounting to the belt conveyor system, as previously described. More specifically, and as shown in  FIG. 8 , the support frame  34  includes a pair of laterally outer telescoping portions  100  that are slidably received within a rectangular hollow bore  34   f  of the hollow cross beam  34   a . The hollow bore  34   f  is defined by the upper and lower walls  341  and  342  and the sidewalls  343  and  344 . The telescoping portions  100  are capable of sliding in the lateral direction in the bore  34   f  to adjust the width of the overall support frame  34 . The telescoping portions  100  are frictionally held in place by a screw and jam nut combination  100   a , although other known methods of securing a telescoping member can also be used. A mounting bracket  102  extends upwardly from the telescoping member  100  for mounting the apparatus to the conveyor belt system structure such as side stringer members  104  ( FIGS. 10 and 12 ) that extend along either side of the belt  12 . 
     Having described the structure of the belt tracking apparatus  10  above, the operation of the apparatus  10  is described below. 
     As previously described, the belt tracking apparatus  10  is mounted to the belt conveyor structure via the mounting brackets  102 . The belt  12  is in the form of an endless belt having an upper carry run and a lower return run with the belt tracking apparatus  10  mounted below the lower return run of the belt  12 . The apparatus  10  supports the belt  12  via contact with the roller assembly  16 . When the center of the belt  12  is aligned along the centerline  14 , the belt  12  will contact the generally cylindrical central portions  21  of each roller  18 , while generally not contacting the tapered outer end portions  22 . As the belt  12  is driven along its path, the contact between the belt  12  and the rollers  18  will cause the rollers  18  to rotate about their central axis. More specifically, the rollers  18  will rotate about the shafts  20  via the rotation of the bearings  46  that are housed in the end cap assemblies  44 . While the belt remains generally centered on the centerline  14 , the rollers  18  will rotate in a generally forward direction, and the rollers  18  will be oriented generally parallel to the support frame  34 . With the belt  12  centered on the centerline  14 , the rollers  18  may be referred to as being in the neutral position, which is shown in  FIGS. 1-8 . 
     In the neutral position, the tilt channel device  32  is also oriented generally parallel to the support frame  34  and rollers  18 . The tilt channel device  32  is generally not translated or tilted relative to the support frame  34  as long as the apparatus  10  remains in its neutral position. The linkage bars  70  are each oriented at approximately the same angle relative to the center of the apparatus  10 . 
     As shown in  FIGS. 9-12 , in the event the belt  12  begins to track off center, or become misaligned, the belt tracking apparatus  10  will operate to urge the belt  12  back toward its centered position as further described below. As the belt tracking apparatus  10  is generally symmetrical, the operation of the correcting features of the apparatus  10  is generally the same whether the belt becomes misaligned to the right or the left. For purposes of illustration, the operation of the apparatus  10  will be described with respect to a lateral misalignment to the right. For reference, a right misalignment refers to the belt  12  becoming misaligned laterally to the right relative to the direction of the belt travel. While the description of the misalignment will be described with respect to a right misalignment, it will be appreciated that a misalignment to the left operates in the same manner.  FIGS. 9 and 10  illustrate a partial misalignment of the belt  12  to the right.  FIGS. 11-12  illustrate a larger misalignment of the belt  12  to the right, with the belt tracking apparatus  10  fully shifted, tilted, and rotated to correct the misalignment. 
     As the belt  12  begins to track off center and to the right, the frictional contact between the between the belt  12  and the right tapered outer end portion  22  of the right roller  18  will cause the roller assembly  16  to have its right distal end be pulled downstream in the direction of the travel of the belt  12 , as described in further detail below. Because the device is rotating about the spherical connection  60  in the housing  30  to steer the belt  12  back to the left toward its intended path of travel, a reaction force from the belt  12  is generated to the right and transverse to the direction of belt travel. This causes the tilt channel device  32  to be translated to the right, with the linkage bars  70  causing the tilt channel device  32  to tilt upward at the right side against the bottom side of the belt  12 . 
     As the tilt channel device  32  is pushed to the right, the tilt channel device  32  will shift relative to the support frame  34 , which remains fixed to the conveyor structure. More specifically, the tilt channel device  32  will translate across the roller bearings  68  carried by the center mount portion  62 , which is fixedly mounted to the support frame  34 . Both the fore and aft roller bearings  68  will rotate as the tilt channel device  32  shifts. 
     With the tilt channel device  32  shifting to the right, the two linkage bars  70  located on the right of the apparatus  10  will be put in compression with the upper end surface portion  78   a  of the slot  78  being urged against the lower pivot shaft  76 . The lateral force exerted at the upper shaft  72  will cause the linkage bar  70  to rotate about the lower shaft  76 , thereby causing the upper shaft  72  to move upward as it moves to the right with the tilt channel device  32 . This rotation and lifting at the linkage bars  70  occurs at both the fore and aft linkage bars  70  on the right. With the linkage bars  70  lifting the right end of the tilt channel device  32 , the tilt channel device  32  thereby becomes tilted relative to the support frame  34  and the centrally located roller bearings  68 . The roller bearings  68  continue to support the tilt channel device  32  when it is in this shifted and tilted orientation. 
     With the right side of the tilt channel device  32  lifted upward, the left side of the tilt channel device  32  thereby moves downward. At the left side of the tilt channel device  32 , the linkage bars  70  at that location are pulled along as the tilt channel device  32  shifts to the right. More specifically, the lower pivot shaft  76  slides in slot  78 , with the length of the slot  78  allowing the tilt channel device  32  to translate laterally from the left to the right. The linkage bar  70  will rotate slightly about the upper pivot shaft  72  as the left side of the tilt channel device  32  tilts downward. Thus, the linkage bars  70  at the left side have a more horizontal orientation than in the neutral position, while the linkage bars  70  at the right side have a more upright orientation. This orientation of the linkage bars  70  is shown in  FIG. 12 . 
     The length and orientation of the linkage bars  70  determines the amount of tilting as the tilt channel device  32  shifts. A relatively longer linkage bar  70  would result in a larger amount of lifting due to the increased radius and rotation about the lower shaft  76 . Likewise, a shorter linkage bar  70  would result in a smaller amount of lifting. Furthermore, the length of the slot  69  operates to limit the maximum amount that the tilt channel device  32  can shift laterally, thereby limiting the maximum amount that the linkage bars  70  can lift the tilt channel as a result of the translation. 
     The amount that the tilt channel device  32  can translate to the right is limited by the laterally extending slot  69  and the axle  66  extending therethrough. As the tilt channel device  32  shifts to the right, the axle  66  will slide within the slot  69 . As the tilt channel device  32  continues translating to the right, the axle  66  will contact the left end surface portion  69   a  of the slot  69 , preventing additional shifting. Thus, the length of the slot  69  generally determines the maximum distance that the tilt channel device  32  can shift to either side. The longer the slot  69 , the further the tilt channel device  32  can translate before the end surface portion  69   a  of the slot  69  contacts the axle  66 . Likewise, a shorter slot  69  would limit the amount the tilt channel device  32  can translate.  FIG. 12  illustrates the tilt channel device  32  having shifted its maximum amount to the right. In one form, the outermost end of the tilt channel device  32  at the raised end is approximately 1.75 inches higher than opposite lowered end of the tilt channel device  32  when the tilt channel device  32  has translated its maximum lateral distance. 
     Alternatively, the amount of translation could be limited by the length of the slot  78  in the linkage bar  70 . The length of the slot  78  is generally long enough such that the lower pivot shaft  76  will not contact a lower end surface  78   b  of the slot  78  prior to the tilt channel device  32  shifting being stopped by the slot  69  and axle  66 . However, the length of the slot  78  of the linkage bar  70  could be configured such that the lower pivot shaft  76  contacts the lower end surface  78   b  end of the slot  78  in the linkage bars  70  that are being pulled before the end surface  69   a  of the slot  69  contacts the axle  66 . 
     With the tilt channel device  32  tilted due to the misalignment to the right, the downward gravitational force and the tension on the belt  12  caused by the tilting will tend to urge the belt  12  back to the left and toward the center. However, the apparatus  10  will also operate to correct the belt by rotating the roller assembly  16  via the spherical connection  60  so that the distal end of the roller  18  at the side of the misalignment is dragged forward along the direction of the travel of the belt  12 , as further described below. 
     As previously described, when the belt  12  is travelling along its intended path and centered on the roller assembly  16 , the belt  12  contacts and is supported by the rollers  18 . When the belt  12  becomes misaligned to one side, the misaligned side of the belt  12  will contact more of the tapered outer end portion  22  of the roller  18  at that side, causing the outboard end  18   b  of the roller  18  to be pulled forward or downstream along the direction of belt travel. 
     More specifically, as the rollers  18  are rotating about their axes in response to the belt  12  travelling across the top of the belt tracking apparatus  10 , each roller  18  has a given rotational velocity. However, the linear velocity of the roller  18  at the cylindrical main portion  21  is greater than the linear velocity at points on the tapered outer end portion  22  due to points on the tapered outer end portion  22  having a decreased diameter relative to the cylindrical main portion  21 . 
     The belt  12  is traveling at a generally constant speed across its width, which generally corresponds to the linear velocity of the cylindrical main portion  21 . When the belt  12  becomes misaligned to the right, the belt  12  will still be travelling at its previous linear speed. However, the points along the tapered outer end portion  22  are travelling at a linear speed that is less than the belt  12 . Thus, when the belt  12  contacts the tapered outer end portion  22  on the right side, the belt will pull the tapered outer end portion  22  in the direction of the belt travel. As a result, the outboard end  18   b  of the roller  18  on the right side moves forward or downstream. With the roller assembly  16  mounted at its center to the spherical connection  60 , the roller assembly will thereby rotate about the spherical connection  60  so that when the roller  18  on the right moves forward, the roller  18  on the left moves rearward. This results in the rotational direction of the rollers  18  being directed toward the left. The rollers  18  will exert a leftward force on the belt  12  in this orientation, thereby causing the belt  12  to move to the left toward its centered position and, as previously described above, the belt  12  will exert a reaction force to the right transverse to the direction of the travel of the belt  12 , which causes the tilt channel device  32  to translate to the right, with the linkage bars  70  operating to lift the right side of the tilt channel device  32 .  FIGS. 9 and 10  illustrate a partial rotation of the roller assembly  16  with the belt  12  partially shifted to the right.  FIGS. 11 and 12  illustrate a larger amount of rotation of the roller assembly  16  with the belt  12  shifted further to the right. 
     As the belt  12  moves back to the left, the belt  12  will travel off of the tapered outer end portion  22 , and the direction of the belt travel will tend to re-orient the rollers  18  so that the rollers  18  are rotating in the direction of belt travel and the belt  12  will run along its intended path. In the event the belt  12  shifts too far to the left as it is being corrected from its misalignment to the right, the belt  12  will contact the tapered outer end portion  22  of the left roller  18 , causing the left side roller  18  to be pulled forward, thereby correcting the belt  12  in a similar manner to that described above. 
     The amount that the roller assembly  16  will be able to rotate about the spherical connection  60  is limited by the upstanding retainer bracket members  90  mounted on the tilt channel device  32 . As previously described, the upstanding retainer bracket members  90  include upwardly extending sidewall portions  90   a  that are located both forward and rearward of the outer bearing  50  that is mounted at the outboard end  20   b  of the shaft  20 . As the roller  18  is pulled forward at the side of the misalignment, the outer bearing  50  translates in the forward direction. When the outer bearing  50  contacts the forward upwardly extending portion  90   a , the roller  18  will become restricted from further forward travel and thereby restricted from further rotation about the spherical connection  60 . Thus, the interface between the outer bearing  50  and the upwardly extending portion  90   a  prevents the roller assembly  16  from being pulled too far forward by the misalignment. In addition to the outer bearing  50  being stopped when moving in the forward direction at the side of the misalignment, the outer bearing  50  at the opposite side of the roller assembly  16  is also stopped from moving in the rearward direction. Thus, as the roller assembly  16  rotates in both directions during misalignments to both the right and the left, the outer bearings  50  at each side will move forward and rearward in response to the rotation, and contact the upwardly extending sidewall portions  90   a  both forward and rearward. 
     When the roller assembly  16  rotates about the spherical connection  60  so that the outboard end  18   b  of the roller  18  moves forward or rearward and contacts the upstanding retainer bracket members  90 , the rollers  18  thereby exert a force on the upstanding retainer bracket members  90 , which are mounted to the tilt channel device  32 . This force is therefore transferred to the tilt channel device  32 . Thus, when the roller  18  on the right side of the apparatus  10  moves forward, and the roller  18  on the left side moves rearward, these forces would tend to cause the tilt channel device  32  to rotate about the center in the same direction. However, the tilt channel device  32  is restricted form such rotation by the guide blocks  80  that are fixedly mounted to the support frame  34 . Thus, the tilt channel device  32  will be generally stopped from rotation, and generally limited to translating and tilting, as previously described. 
     As mentioned previously, the roller assembly  16  is mounted via a spherical connection  60  to the tilt channel device  32 . The spherical connection  60  allows for polyaxial adjustment and orientation of the roller assembly  16  relative thereto. As such, the roller assembly  16  is not limited by its connection at the center of the apparatus  10  to merely pivoting about a vertical axis. Rather, the spherical connection  60  allows for adjustment about multiple axes of rotation. The spherical connection  60  reduces the strain at the center of the apparatus  10  relative to a typical pivot connection. When the belt  12  becomes misaligned to the right, there is additional weight on the right roller  18 . Because of the spherical connection  60 , the roller  18  will tend to tilt downward due to the additional weight on the right side relative to the left side. This potential downward tilt is limited by the outer bearing  50  and the upstanding retainer bracket member  90 . As previously described, the upstanding retainer bracket member  90  includes an inwardly extending upper flange portion  90   c  that is disposed above the outer bearings  50  on each side of the apparatus  10 . Thus, when the roller  18  on the right side is forced downward due to increased weight, the roller  18  on the left side will be urged upward. The outer bearing  50  at the left side of the roller assembly  16  will translate upward and contact the inwardly extending upper flange portion  90   c  limiting the upward movement. The gap between the outer bearing  50  and the inwardly extending upper flange portion  90   c  is small when the rollers  18  are in the neutral position, so the amount that the roller  18  will tilt relative to the spherical connection  60  is thereby small, as well. However, rather that supporting the increased load caused by the misaligned belt  12  at a central connection like a typical pivot connection, the spherical connection  60  allows the load to be supported at both the spherical connection  60  and the outer bearing  50  and inwardly extending upper flange portion  90   c  connection at the opposite side. Furthermore, while the outer bearing  50  may be contacting the inwardly extending upper flange portion  90   c , the outer bearing  50  can still rotate about the shaft  20  to move forward and rearward by rolling across the upper flange portion  90   c.    
     In another form, the upstanding retainer bracket members  90  may include an inwardly extending lower flange member  90   d  ( FIG. 13 ) mounted to the upstanding retainer bracket member and operating similarly to the inwardly extending upper flange portion  90   c . The inwardly extending lower flange portion  90   d  can operate similarly to limit the tilting of the roller assembly  16  relative to the tilt channel device  32 . Instead of counteracting a load at the right with the left side outer bearing  50  contacting the inwardly extending upper flange  90   c  at the left, a load at the right side can be supported by the right inwardly extending lower flange  90   d , which is located below the outer bearing  50 . As a force is applied the right, the outer bearing  50  at the right side will tend to cause right side of the roller assembly  16  to tilt downward, but the inwardly extending lower flange portion  90   d  will contact the outer bearing  50 , limiting the tilt and supporting the right roller  18  at its outboard end  18   b.    
     The apparatus  10  also includes linkage bar shield members  106  that are fixedly mounted to the tilt channel device  32  that help to protect the connection between the upper pivot shaft  72  and the aperture  72   a  from dirt or other debris. Similarly, central shield member  108  is fixedly mounted at the center of the tilt channel device  32  to help protect the interface between the slot  69  and axle  66  from dirt and other debris. A housing shield member  110  is mounted over the housing  30  at the center of the tilt channel device  32  and sized to correspond to the general shape of the housing member  30 . In one form, the housing member is made from a urethane material or the like that is generally flexible, but other materials could also be used. 
     Thus, the belt tracking apparatus  10  described above operates to correct a belt misalignment by tilting the roller assembly  16  via the translation and tilting of the tilt channel device  32 , and also by rotating the roller assembly  16  about the spherical connection  60  to direct the belt  12  back toward center. This combined tilting and rotation of the roller assembly  16  provides a robust solution to conveyor belt systems that become misaligned. The correcting features of tilting and rotating are caused by the contact between the belt  12  and the rollers  18 , and do not require the edge of the belt  12  to contact any sensor rollers to cause the correction as in other configurations. 
     A further benefit of the belt tracking apparatus  10  is achieved by the symmetrical nature of the configuration. Because the apparatus  10  is symmetrical about its center while in the neutral position, the apparatus  10  can be installed on a conveyor belt system and operate on a belt  12  traveling in both a forward and rearward direction. The housing  30  having the spherical connection  60  is fixedly mounted at the center of the tilt channel device  32 , extending upwardly therefrom. As the apparatus  10  adjusts to provide the self-energizing correction of the misalignment, the housing  30  and spherical connection  60  remain generally at the same longitudinal position relative to the direction of the travel of the belt  12 , with the roller  18  remaining symmetrically disposed about the spherical connection  60 . This means that the belt tracking apparatus  10  is reversible. The belt  12  may be run in a first longitudinal belt travel direction to carry its payload in that direction, and may be subsequently reversed to deliver payload in the opposite direction. The belt tracking apparatus  10  may be installed at various points along the conveyor system without regard to the intended direction of the belt  12 . 
     An alternative conveyor belt tracking apparatus  400  is shown in  FIG. 14 . As can be seen, the apparatus  400  includes a frame assembly, generally designated  402  (see  FIG. 15 ), configured to support idler rollers  404  and operatively mount the rollers  404  to conveyor belt structure such as the previously described side stringer members  104 . The idler rollers  404  of the apparatus  400  are shown arranged in a troughed configuration so that there is a lower center idler roller  406  disposed between the outer idler rollers  408  and  410  on either side of the center roller  400  that extend at an upper incline therefrom. The troughed configuration of the idler rollers  404  is for supporting an upper run  412  of a conveyor belt  414  as depicted in  FIGS. 25 and 26  that is troughed for transporting material thereon. 
     The belt tracking apparatus  400  operates similarly to the belt tracking apparatus  10  in that a reaction force from the belt  414  against the idler rollers  404  that have been shifted for steering the mistracking belt  414 , such as shown in  FIG. 25 , back towards its correct, centered travel path on the idler rollers  404  is used as an energizing or actuation force for generating a tilting action of the idler rollers  404 , such as shown in  FIG. 26 . 
     The belt tracking apparatus  400  has an idler roller device  416  including an idler roller frame  414  rotatably mounted to a tilt device  420 , and more specifically tilt frame  422  thereof. The idler roller frame  414  and tilt frame  422  are supported by support base frame  423  that is configured to be secured to the conveyor structure. In the belt tracking apparatus  400 , the frame assembly  402  includes the idler roller frame  414 , the tilt frame  422  and the base frame  423 . 
     The idler roller device  416  and the tilt device  420  have a rotatable connection therebetween in the form of a central pivot assembly  424 , as shown in  FIGS. 17-19 . As can be seen in  FIGS. 14, 25 and 26 , the inclined, outer idler rollers  408  and  410  have their respective outer end portions  426  and  428  tapered. The rollers  408  and  410  taper from respective cylindrical portions  430  and  432  down to their reduced diameter outer end via the tapered end portions  426  and  428  thereof. By way of example and not limitation, the taper can be at approximately four degrees 4°. 
     As previously described with respect to rollers  18  having tapered end portions  22 , when the belt  414  mistracks toward one or the other of the outer idler rollers  408  or  410 , the increased engagement of the belt  414  with the tapered end portion  426  or  428  will cause that roller to be pulled downstream because of the increased drag force due to the reduced linear speed of the tapered end portions  426  and  428  relative to the larger diameter cylindrical portions  430  and  432  of the respective idler rollers  408  and  410 . In this regard, the idler roller device  416  will be shifted relative to the tilt device  420  as by being rotated, and more specifically pivoted, via the central pivot assembly  424  therebetween. At a taper of 4°, it has been found that the rollers  408  and  410  will generate sufficient frictional drag forces for shifting of the idler roller device  416  while not causing the belt  414  to simply slip thereover. 
     Alternatively, sensor rollers that engage the side edges of the conveyor belt could be used to generate the energizing force for shifting the idler rollers  404  as described above. However, this would not readily allow the belt tracking apparatus  400  to be used with conveyor belts  414  that can travel in opposite directions without having to disassemble the apparatus  400  from the conveyor structure and reorient the apparatus  400  for being operable to correct the belt  414  when it mistracks and is traveling in the opposite direction. Accordingly, for reversing conveyor belt applications, the belt tracking apparatus  400  having an idler roller or rollers  404  with tapered outer end portions  426  and  428  is preferred. 
     This shifting of the idler rollers  404  is depicted in  FIG. 25  where the belt  414  has mistracked toward the outer roller  410 . In this instance, the outer roller  410  has been shifted so that it is further downstream than the center roller  406  and the opposite outer roller  408 . As mentioned, this shifting occurs by pivoting of the idler roller frame  418  about the central pivot assembly  424 , and specifically about pivot axis  424   a  thereof ( FIG. 17 ). As can be seen in  FIG. 25 , since the idler rollers  404  maintain their orientation relative to one another as mounted to the idler roller frame  414 , the tapered end portion  428  of the idler roller  410  is shifted further downstream than the cylindrical portion  432  of the idler roller  410 , as well as being further downstream than the center roller  406  and the outer roller  408 . 
     The tilt frame  422  includes a main, laterally extending frame member  434 . The main tilt frame member  434  can be extruded to have a substantially square cross-sectional shape so that it includes an upper wall  434   a , a lower wall  434   b  and opposite side walls  434   c  and  434   d  interconnecting the upper and lower walls  434   a  and  434   b , as can be seen in  FIG. 17 . The ends of the main frame member  434  are closed by end wall caps  435  and  436  welded thereto to seal the interior of the main frame member  434  from fouling such as due to debris from the conveyor belt  414 . 
     The central pivot assembly  424  includes an inverted generally U-shaped mounting bracket  438  that is secured centrally along the length of the main frame member  434  as by fasteners  440 . The mounting bracket  438  has an upper plate portion  442  from which opposite leg portions  444  and  446  depend. As shown, the mounting bracket  438  is sized so that the upper plate portion  442  is fastened to the upper wall  434   a  of the main frame member  434  by a pair of fasteners  440  with the leg portions  444  and  446  extending down along either side wall  434   c  and  434   d  with each being secured to the corresponding side walls  434   c  and  434   d  by a pair of fasteners  440 . 
     Referring specifically to  FIG. 19 , the upper plate portion  442  of the mounting bracket  438  has a central aperture  448  into which the bottom of a flanged axle stud  450  is seated. The stud  450  is secured to the plate portion  442  as by welding and acts as the pivot shaft for the central pivot assembly  424 . A wedge-shaped pivot block  452  is rotatably mounted to the stud  450  by a bearing in the form of bushing  454  that extends along and about the stud  450 . Further, the stud  450  includes a lower, radially extending flange portion  456  that is seated on the plate portion  442  of the mounting bracket  438 . A bearing for taking axial loads in the form of a thrust washer  458  is disposed between the flange portion  456  and the bottom of the pivot block  452 . The pivot block  452  is retained on the stud  450  by a retaining clip  460  at the upper end of the stud  450 . 
     The idler roller frame  418  includes a laterally extending base member  462 , as shown in  FIG. 16 . The base member  462  can be extruded to have an inverted V cross-sectional configuration with a pair of inclined wall portions  464  and  466 , as best seen in  FIG. 24 . The inclination of the wall portions  464  and  466  substantially matches that of opposite inclined surfaces  468  and  470  of the wedge-shaped pivot block  452  for being secured thereto. Referring to  FIGS. 19 and 21 , fasteners  472  are received in aligned apertures  474  and  476  ( FIGS. 16 and 17 ) of the base member  462  and the pivot block  452 , respectively, for securing the pivot block  452  and base member  462  together. In this manner, the idler roller device  416  is pivotally mounted to and carried on the tilt device  420  for pivoting about pivot axis  424   a . In addition, the inverted V cross-sectional configuration of the base member  462  provides the advantage of substantially covering the underlying tilt frame member  434  to keep debris from the conveyor belt operations from accumulating thereon and does not present a horizontal surface for the accumulation and build-up of such debris on the base member  462  itself. 
     As can be seen in  FIG. 17 , the pivot axis  424   a  generally extends normal to the main frame member  434 , and specifically to the upper wall  434   a  thereof. Typically, the pivot axis  424   a  will extend normal to the conveyor belt  414  when the conveyor belt tracking apparatus  400  is mounted to the conveyor structure so that the apparatus  400  can be used in a bi-directional manner with respect to the travel directions of the conveyor belt  414 , as will be described further hereinafter. 
     For additional load bearing support for the idler roller device  416  over that provided by the central pivot assembly  424 , base member  462  has roller assemblies  478  and  480  secured to the underside thereof, as can be seen in  FIG. 20 . As shown, the roller assemblies  478  and  480  are spaced on either side of the central location at which the central pivot assembly  424  is secured to the base member  462 . Preferably, the roller assemblies  478  and  480  are disposed directly under upstanding mounting brackets  482  and  484  configured for supporting the center idler roller  406  extending therebetween. The center idler roller  406  supports the lower portion  486  of the troughed conveyor belt  412 , as shown in  FIG. 26 . It has been found that the lowered belt portion  486  and the center idler roller  406  thereunder can generally support approximately 70% of the loading generated by the material carried on the upper run  412  of the conveyor belt  414 . Thus, by positioning the roller assemblies  478  and  480  under the brackets  482  and  484  supporting the center idler roller  406  and the lowered belt portion  486  thereon, the majority of the load carried by the conveyor belt  414  can be transferred directly to the tilt frame main member  434 , as described further below. 
     More specifically, the roller assemblies  478  and  480  each include a mounting plate  488  that is configured to be secured to the underside of the base member  462 . The mounting plates  488  can have a generally triangular configuration for being secured to the inclined wall portions  464  and  466  as by welding thereto. Referencing  FIGS. 20 and 27 , the mounting plates  488  have a through aperture  490  for receiving a shaft  492  of a roller  494  extending therethrough. The shaft  492  is rotatably received in the through aperture  490  and can have a threaded end for receiving a nut  496  thereon to rotatably secure the roller  494  to the associated mounting plate  488 . 
     A pair of engagement plates  498  and  500  are secured to the upper wall  434   a  of the tilt frame member  434  with fasteners  501 . The engagement plates  498  and  500  are on either side of the central pivot assembly  424  positioned to be aligned with the corresponding overlying rollers  494  of the roller assemblies  478  and  480 , as best seen in  FIGS. 21 and 27 . The engagement plates  498  and  500  provide a smooth, flat surface across the upper wall  434   a  of the main frame member  434  so that as the idler roller frame  418  pivots relative to the tilt frame  422 , the rollers  494  roll along the smooth, flat surface of the engagement plates  498  and  500  to provide low friction support for the pivotal idler roller device  416  having the idler rollers  404  supporting the load of the conveyor belt  414  thereon. Thus, the rollers  494  are operable to transfer load directly to the tilt frame  422  and the main frame member  434  thereof while keeping rotational friction due to their engagement with the smooth, flat engagement plates  498  and  500  to a minimum. In this regard, the rollers  494  can have a crowned configuration to reduce the contact area between the rollers  494  and the associated engagement plates  498  and  500  for further friction reduction. 
     The pivoting of the idler roller  416  is limited by stops  502  between the idler roller frame  418  of the idler roller device  416  and the tilt device  420 , and specifically the main frame member  434  thereof. It has been determined that there is a point at which shifting of the rollers  404  in response to conveyor belt mistracking loses effectiveness in terms of the steering action the shifted rollers  404  provide as a corrective influence on the travel path of the belt  414 . In this regard, the stops  502  are positioned to limit the pivoting of the idler roller device  416  relative to the tilt device  420 , as can be seen best in  FIGS. 17 and 18 . 
     The stops  502  can be integral with the engagement plates  498  and  500  in the form of extension arm portions  503  that have upwardly bent end tab portions  504 . The arm portions  503  extend out beyond the width of the tilt frame member  434  in a longitudinal, fore-and-aft direction generally transverse, and more specifically orthogonal, to the length of the belt tracking apparatus  400  as it extends across the conveyor belt  414 . In this manner, there are upstream and downstream stop tab portions  504  that are in position to engage the wall portions  464  and  466  of the idler roller frame base member  462 , as shown in  FIGS. 21 and 24 . The stops  502  are adapted to limit the pivoting of the idler roller frame  418  to a predetermined angular amount so that over rotation of the idler roller device  416  is avoided. A stop  502   a  having an alternative confirmation is shown in  FIG. 27  and will be described in detail hereinafter. By way of example and not limitation, the stops  502  or  502   a  can limit the pivoting of the idler roller frame  418  to approximately four degrees (4°) in either direction from the non-pivoted, neutral position shown in  FIG. 14  where the idler roller frame  418  generally extends in alignment with the tilt frame  422 . The bottom edges of the base member wall portions  464  and  466  can have notches  505  to provide the wall portions  464  and  466  with clearance so that the fasteners  501  do not create interference with the pivoting of the base member  462 . 
     The tilt device  420  is shown best in  FIGS. 17 and 18 . The tilt device  420  is mounted to the support base frame  423  such that after the idler roller device  416  has been pivoted relative to the tilt device  420  and a reaction force has been applied to the idler rollers  404  by the mistracking conveyor belt  414 , the tilt device  420  is operable to tilt such that the downstream idler roller  410  ( FIG. 25 ) is raised as shown in  FIG. 26  relative to its position prior to being tilted such as in the neutral configuration of the belt tracking apparatus  400 . Thus, in addition to providing a steering action with the pivoted idler rollers  404  as shown in  FIG. 25 , the tilted rollers  404  will urge the mistracking conveyor belt  414  back towards its correct travel path to be centered on the idler rollers  404 . 
     For this purpose, the tilt frame  422  has the main frame member  434  thereof hung from the support base frame  423 , and specifically from a pair of laterally extending support members  506  and  508  thereof via a linkage system, as shown in  FIG. 18 . The linkage system includes linkage members or bars  510  pivotally connected to the tilt frame member  434  at their lower ends and to the support members  506  and  508  at their upper ends, as shown in  FIGS. 17 and 24 . 
     There are a pair of linkage bars  510  at either end of the tilt frame member  434 . The linkage bars  510  in a pair are interconnected at their lower ends by a single, lower axle member  512 . The linkage bars  510  have lower through apertures  514 , and the lower axle member  512  is provided with reduced opposite ends  516  that extend through the apertures  514  and are rotatably mounted therein by bushings  518 , as can be seen in  FIG. 24 . The projecting portions of the axle reduced ends have retaining clips  519  ( FIG. 21 ) thereon to keep the lower axle  512  members properly assembled to the linkage bars  510  at their lower ends. Each of the axle members  512  extend in clearance through corresponding sets of laterally aligned openings  520  and  522  formed in respective side walls  534   c  and  534   d  adjacent the opposite ends of the tilt frame member  434 . 
     The linkage bars  510  each also include an upper through aperture  524  that each receive an upper axle member  526  extending therethrough and are rotatably mounted to the linkage bar  510  via bushing  528  in the aperture  524 . Referencing  FIG. 22 , the support members  506  and  508  each have a pair of mounting lugs  530  that are mounted adjacent opposite ends thereof and aligned with a corresponding one of the pair of lugs  530  on the opposite one of the support members  506  or  508 . The mounting lugs  530  are fixed to the support members  506  and  508  as by welding and each include a through opening  532  having a corresponding one of the axle members  526  extending therethrough. At the projecting ends of the upper axle members  526  opposite to the ends extending through the linkage bars  510  and which projects beyond the mounting lugs  530 , retaining clips  534  are mounted for keeping the axle members  526  properly assembled to the mounting lugs  530 , as shown in  FIG. 24 . 
     The mounting lugs  530  are fixed to the support members  506  and  508  of the support base frame  423  to be laterally inward of the corresponding aligned openings  520  and  522  adjacent the ends of the underlying tilt frame member  434 . In this manner, when the linkage bars  510  are pivotally connected to the tilt frame member  434  and the support members  506  and  508  via the axle members  512  and  526 , the linkage bars  510  extend obliquely, upward and laterally inward between the lower tilt frame member  434  and the upper support members  506  and  508 , as shown in  FIGS. 14 and 15 . Thus, when a reaction force from the steered conveyor belt  414  is applied to the idler rollers  404 , the lateral component of this reaction force will cause the tilt frame  422 , and specifically the tilt frame member  434  thereof, to swing on the linkage bars  510 . This swinging action generates both a lifting and lowering movement of opposite ends of the tilt frame member  434  but also lateral shifting thereof toward the raised end, as can be seen in  FIG. 26 . To optimize the lift against the amount of lateral shifting of the tilt frame member  434  and thus the idler rollers  404  carried thereby, it has been found that when the apparatus  400  is in its neutral configuration, an angle of 120° between the linkage bars  510  and the support members  506  and  510  can be utilized, as depicted in  FIGS. 14 and 15 . 
     Referring to  FIG. 25 , with the belt traveling in the downstream travel direction  536  and mistracking to the right toward the outer idler roller  410 , the idler rollers  404  are pivoted so that the end portion  428  of the idler roller  410  is shifted downstream further than the cylindrical portion  432  of the idler roller  410  and further downstream than the center roller  406  and the other idler roller  408 . This provides the belt  414  with a steering action back towards the left and generates a reaction force in the belt  414  that has lateral force component back toward the right which, in turn, causes tilting of the tilt frame  422  via the linkage bars  510 . Referencing  FIG. 26 , it can be seen that the left pair of linkage bars  510  will swing the left end portion of the tilt frame member  434  downward while the right pair of linkage bars  510  will swing the right end portion of the tilt frame member  434  upwardly thereby lowering the left outer idler roller  408  and raising the right outer idler roller  410  from their positions in the non-tilted or neutral configuration of the belt tracking apparatus  400 . Thus, the tilting action generated by the belt tracking apparatus  400  is a result of and subsequent to the rotation or pivoting action of the rollers  404  for steering the belt  414  back towards its correct travel path. 
     To avoid fouling of the pivot locations for the axle members  512  and  526 , the axle member  512  has seal rings  536  and  538  mounted thereto on either side of the reduced end  516  thereof extending through the lower aperture  514  in the linkage bar  510 , as can be seen in  FIG. 21  which has the linkage bar  510  removed and in  FIG. 24 . The upper axle members  526  each have a cover member  540  secured to the corresponding mounting lug  530  and configured to extend over the mounting lug  530  and the upper end portion of the associated linkage bar  510  to cover the upper axle member  526  that pivotally connects the linkage bar  510  to the mounting lug  530 , as shown in  FIG. 24 . 
     For utilizing the conveyor belt tracking apparatus  400  with the upper run  412  of a conveyor belt  414  have a troughed configuration, the apparatus  400  has to be sized to fit into the relatively compact vertical space formed between the upper carry run  412  of the belt  414  and the lower return run  413  thereof, as depicted in  FIG. 26 . To this end, the belt tracker apparatus  400  has the main frame member  434  of the tilt frame  422  hung from the support base frame  423 , rather than supported in an elevated position relative thereto as with the previously described tracking apparatus  10  that is more suitable for use with the return run of the belt  12 . The belt tracking apparatus  400  is configured so that the tilt frame  422 , and particularly the main frame member  434  thereof, is mounted to the support base frame  423 , and specifically the laterally extending support members  506  and  508  thereof, to generally be below the support members  506  and  508  of the support base frame  423  when the apparatus  400  is in its non-tilted or neutral configuration, as shown in  FIGS. 14 and 15 . On the other hand, the idler roller frame  418  is pivotally mounted to the tilt frame member  434  so that it primarily extends above the support members  506  and  508  of the support base frame  423 . In this manner, the belt tracking apparatus  400  having the idler roller frame  418  pivotally carried on the tilt frame  422  does not also stack the tilt frame  422  on the support base frame  423 , and instead hangs the tilt frame  422  therefrom so that the support members  506  and  508  extend generally intermediate the idler roller frame  418  and the tilt frame  522  in the vertical direction. 
     In addition, the laterally extending support members  506  and  508  are spaced from each other in the fore-and-aft direction so that the idler roller frame  418  and the tilt frame  422  fit therebetween while allowing sufficient room for pivoting of the idler roller frame  418  through its full angular range of motion and for tilting of the tilt frame  422  without interference from the support members  506  and  508 . The linkage bars  510  can each have a bearing plate  541  ( FIG. 17 ) of low friction material secured thereto to be in facing and engaging relation with the adjacent one of the support members  506  and  508 , as shown in  FIGS. 23 and 24 . Because there will be a force acting on the apparatus  400  during belt operations in the downstream direction  536 , the bearing plates  541  take up space between the linkage bars  510  and the support members  506  and  508  to avoid play therebetween that could generate wear and damage to the apparatus  400 . Thus, the bearing plates  541  act to provide a durable wear surface and a load bearing member between the linkage bars  510  and the support members  506  and  508 . It should be noted that all of the linkage bars  510  are provided with bearing plates  541  since depending on the direction in which the belt upper run  412  is traveling, either the bearing plates  541  engaging the support member  506  or the bearing plates  541  engaging the support member  508  will be required to take the loading due to downstream travel forces generated by the belt  414 . 
     Referencing  FIG. 27 , the interiors of the idler rollers  404  are shown. Each idler roller  404  of the idler roller device  416  includes an outer shell  542  that is supported for rotation about a shaft  544  via roller bearing assemblies  546  at corresponding ends of the shell  542  and shaft  544 . As previously described, the outer idler rollers  408  and  410  are constructed in a manner similar to the rollers  18  of the belt tracking apparatus  10  in that they include tapered end portions  426  and  428 . 
     The outer shell  542  can generally be of nylon material. However, it has been found particularly in lower temperature environments that the nylon material may not provide the desired level of friction for the tapered idler rollers  408  and  410  with the conveyor belt  414 . In this regard, the outer idler rollers  408  and  410  are provided with a urethane sleeve  548  that extends about the shell  542 . With the shell  542  coated with the urethane material of the sleeve  548 , a more resilient interface is provided between the idler rollers  408  and  410  and the conveyor belt  414 , which is of particular significance along the respective outer tapered portions  426  and  428  thereof where the frictional engagement with the belt  414  is used to create the drag forces for shifting of the idler roller device  416  when the belt  414  is mistracking. The resilient interface with the belt  414  provided by the urethane material provides a better frictional grip therebetween so that the belt  414  traveling at the fastener linear speed at which the cylindrical portions  430  and  432  of the idler rollers  408  and  410  also travel will not simple slip past the tapered portions  426  and  428 , but instead will frictionally engage and pull either the tapered end portion  426  or  428  further downstream when the belt is mistracking toward the respective idler roller  408  or  410 . 
     Because the conveyor belt tracking apparatus  400  is configured for use under the upper troughed, carry run  412  of the conveyor belt  414 , and the troughing configuration and specifically the angle at which the belt outer side portions  412   a  and  412   b  are inclined relative to the lowered central portion  486  can vary from one conveyor system to another, the idler roller frame  418  is made to be adjustable to accommodate different troughing configurations. Referring to  FIG. 16 , the idler roller frame  418  includes a pair of outer idler roller subframes  550  and  552  for rotatably mounting the respective outer idler rollers  408  and  410  thereto. The laterally extending base member  462  along with the upstanding brackets  482  and  484  form a subframe  556  for rotatably mounting the center idler roller  406  thereto. Together, the subframes  550 - 556  cooperate to form the idler roller frame  418 . 
     To accommodate the different troughing configurations, the outer idler subframes  552  and  554  are adjustably connected to the center idler subframe  556  via adjustment mechanisms  558  and  560 . As shown in  FIG. 16 , the adjustment mechanism  556  extends between the subframe  550  and the subframe  554  and is operable to adjust the inclination of the subframe  550  relative to the subframe  554 . Similarly, the adjustment mechanism  558  extends between the subframe  552  and the subframe  554  and is operable to adjust the inclination of the subframe  552  relative to the subframe  554 . 
     More particularly, the subframes  550  and  552  are each constructed identically with each including an elongate base frame member  560  having upstanding brackets  562  and  564  at either end thereof. Like the brackets  482  and  484 , all of the brackets including brackets  562  and  564  have upwardly opening slots  566  to allow the idler rollers  404  to be lowered into operative position therein with the projecting ends of the shafts  544  of the idler rollers  404  seated at the bottom of the slots  566 , as shown in  FIG. 27 . 
     The adjustment mechanisms  556  and  558  likewise are identically constructed each including a pair of tie bars  568  that are pivotally connected to the base member  462  at either end thereof and to the corresponding end of the subframe  550  or  552  extending beyond the base member  464 , as shown in  FIGS. 16 and 20 . For this purpose, a pivot mounting block  570  is fixed at either end of the base member  462  to project outwardly therefrom. The pivot mounting block  570  fits between the lower ends of the tie bars  568  and has a through bore opening  572  through which lower pivot shaft  574  extends. The projecting ends of the pivot shaft  574  project through corresponding apertures (not shown) at the lower ends of the tie bars  568  for pivotally connecting the tie bars  568  to the base member  462 . Similarly, the base members  560  each have a pivot mounting block  576  fixed thereto at their distal ends sized to fit between the corresponding tie bars  568  and which include a through bore  578  through which pivot shaft  580  extends. Each pair of tie bars  568  is provided with three sets of aligned apertures, generally designated  582 . The sets of apertures  582  can include an upper set of apertures  528   a , an intermediate set of apertures  582   b , and a lower set of apertures  582   c . The trough configuration of the idler rollers  404 , and specifically the angle of inclination of the outer idler rollers  408  and  410  is dictated by which of these sets of apertures  582  are utilized for receiving the projecting ends of the pivot shaft  580  therethrough. Further, to allow the subframes  550  and  552  to be pivotally adjusted, the brackets  564  are pivotally connected with the brackets  482  and  484  of the subframe  554  adjacent their corresponding upper end via pivot shafts  584 . 
     Referring to  FIG. 28 , when the upper pivot shaft  580  of the adjustment mechanisms  556  and  558  is received in the intermediate set of apertures  582   b , the idler frame  418  is in its intermediate troughed configuration, which could nominally be set at a standard thirty-five degree angle for a conveyor belt  414  having outer side portions  412   a  and  412   b  with an intermediate angle troughed configuration. With the lowest aperture set  582   c  receiving the projecting ends of the upper pivot shaft  580  as shown in  FIG. 29 , the idler frame  418  is in its minimally troughed configuration, which could nominally be set at a standard twenty degree angle for a conveyor belt  414  having outside portion  412   a  and  412   b  with a minimum angle troughed configuration. With the uppermost set of apertures  582   a  receiving the projecting ends of the upper pivot shaft  580  as shown in  FIG. 20 , the idler frame  418  is in its maximum troughed configuration, which could nominally be at a standard forty-five degree angle for a conveyor belt  414  having its outer side portions  412   a  and  412   b  with a maximum angle trough configuration. 
     It has also been found that with the belt tracking apparatus  400  having the tapered outer idler rollers  408  and  410 , the distal end of the shafts  544  of the idler rollers  408  and  410  supported by the brackets  562  can advantageously be slightly raised relative to the laterally inward proximal ends supported by the bracket members  564 . This slight cant of the rollers  408  and  410  from their nominal troughed orientation provides benefits in terms of the engagement of the idler rollers  408  and  410 , and particularly their outer tapered end portions  426  and  428  with the troughed upper belt run  412  of the belt  414 . In certain instances, the troughed upper belt run  412  can tend to cup at the outer side edges thereof which lifts the edge portions away from engagement with the tapered end portions  426  and  428  of the idler rollers  408  and  410 . By raising the distal ends of the shafts  544 , e.g. by approximately two inches, and thus the tapered end portions  426  and  428 , this will essentially push the end portions  426  and  428  into engagement with the outer edge portions of the belt  414  which will act to flatten them out to overcome any cupping tendency at the belt edge portions. 
     The slight canting of the idler rollers  408  and  410  can be achieved in any number of ways. For instance, bottoms of the slots  566  of the inner, proximal brackets  564  can be slightly lowered or the bottoms of the slots  566  of the outer distal brackets  562  can be slightly raised. Alternatively, the positioning of each set of the apertures  582  can be slightly shifted to be closer to the distal ends of the tie bars  568 . 
     An alternative version of the conveyor belt tracking apparatus  400  is shown in  FIG. 31 . The alternative conveyor belt tracking apparatus  600  is substantially the same as the belt tracking apparatus  400  (as well as apparatus  10 ) in terms of its operating principles except it is adapted for use along a flat run of the conveyor belt  414  such as along the flat return run  413  of conveyor belt  414  similar to apparatus  10 . Since the structure is substantially the same as the structure for the belt tracker apparatus  400 , only the differences will be described in detail hereinafter. 
     The conveyor belt tracking apparatus  600  has idler rollers  602  that are arranged to extend in a linear configuration as viewed in elevation in  FIG. 31  so as to present an upper substantially linear line of contact for the conveyor belt flat return run  413  except at the roller tapered end portions. Thus, a pair of idler rollers  602  having identical configurations each with a tapered end portion  604  similar to the rollers  18  of the previously described belt tracking apparatus  10  are provided. To arrange the rollers  602  in their linear configuration, idler roller frame  606  is provided, as shown in  FIG. 33 . The idler roller frame  606  includes an elongate base member  608  with two sets of bracket members  610  that are each of equal height, as shown. Thus, as mentioned the belt tracker apparatus  600  will operate substantially the same as the belt tracker apparatus  400  so that when the return run  413  of the belt  414  is centered on the idler rollers  602  as shown in  FIG. 32 , the idler rollers  602  will extend substantially orthogonal to the downstream travel direction  612  of the belt  414 . However, when the belt  414  mistracks toward the right idler roller  602  as shown in  FIG. 34 , the idler roller frame  606  will be pivoted so that the rollers  602  are skewed with the right idler roller  602  shifted further downstream than the left idler roller  602 . This shifting of the idler roller frame  606  will cause the rollers  602  to provide the belt  414  with a steering action back to the left toward its correct travel path centered on the rollers  602 . The resistant provided to this steering action by the lower run  413  of the belt  414  will generate a pivoting action as has been described for apparatus  400  where the right idler roller  602  will be raised relative to the left idler roller  602  which is lowered, as shown in  FIG. 35 . 
     Another alternative belt tracking apparatus  700  is shown in  FIG. 36 . The belt tracking apparatus  700  is substantially the same in terms of its operating principles as the previously described belt tracking apparatuses  10 ,  400 , and  600  herein. However, its structural features are a combination of those used in each of the previously described apparatuses  10 ,  400  and  600 . 
     In the first instance, it should be noted that the tracker apparatus  700  has idler rollers  702  configured in identical manner to the rollers  18  of apparatus  10  and the rollers  602  of apparatus  600  to be arranged in a linear configuration as viewed in elevation for presenting a substantially straight line contact (except at their tapered end portions) to the underside of the flat return run  413  of the belt  414 . Accordingly, the idler roller frame  704  is identical to the idler roller frame  606  of apparatus  600  and need not be described further herein. However, the belt tracker apparatus  700  utilizes a different arrangement of its tilt device  706  relative to its support base frame  708  when compared to the corresponding structures in the belt tracker apparatuses  400  and  600 . Instead of hanging the tilt device  706  from the support base frame  708  via a linkage system, the tilt device  706  is supported in an elevated orientation relative to the support base frame  708  via its linkage system in a manner similar to corresponding structure of the previously described belt tracker apparatus  10 . 
     Referring to  FIGS. 38 and 39 , the tilt device  706  includes a main tilt frame member  710  that has pairs of linkage bars  712  pivotally mounted thereto adjacent either end thereof via upper axle members  714  extending therebetween. The support base frame  708  includes an elongate support member  715  that has mounting lugs  716  depending therefrom adjacent either end thereof. The mounting lugs  716  are operable to receive a lower axle member  718  extending therethrough and secured in the lower slots  720  of the linkage bars  712 . The slots  720  in the linkage bars  712  provide for travel of the ends of the lower axle members  718  along the slots  720  for tilting of tilt frame member  710 . The mounting lugs  716  are positioned laterally outward relative to the corresponding pivot connections formed by the upper axle members  714  as received in apertures of the channel member legs  722 . Like the linkage bars  70 , the linkage bars  712  extend obliquely, downward and lateral outward from the tilt frame member  710  to the support member  715 . In this regard, like the apparatus  10 , in the neutral configuration the apparatus  700  has its tilt frame member  710  elevated with respect to the support base from  708  so that the linkage bars  712  are in compression versus the linkage bars in the belt tracking apparatuses  400  and  600  having hanging tilt frame members so that they are in tension. 
     Thus, when the belt  414  mistracks, for example, to the right as it travels in its downstream travel direction  612 , the right idler roller  702  shifts downstream and the skewed idler rollers  702  act to steer the belt  414  back to the left toward its correct travel path, as shown in  FIG. 40 . The reaction force from the belt  414  to this steering action causes the tilt frame member  710  to shift toward the right and become tilted with the right end thereof raised and the left end lowered from their position in the neutral configuration of the apparatus  700 , as shown in  FIG. 41 . This generates another influence on the conveyor belt  414  that urges it back toward its correct travel path. 
     Similar to the belt tracker apparatus  10 , referencing  FIGS. 36, 38 and 39 , the main frame member  710  is formed as a downwardly open channel member so that depending legs  722  thereof fit along either side of the support member  715 . The support member  715  has a pair of brackets  724  fixed to the upper surface thereof with guide blocks  726  secured thereto for engaging the interior surfaces of the channel member legs  722 . In this manner, the tilt device  706  is kept in alignment with support member  712  and will not become skewed relative thereto. 
     Also like belt tracker apparatus  10 , support rollers  728  are mounted for rotation relative to a mounting block  730  secured centrally along the upper surface of the elongate support member  715 . The rollers  728  engage the interior lower surface of the upper wall  732  of the frame channel member  710  for rolling therealong during lateral shifting and tilting of the member  710 . However, unlike the apparatus  10 , the axle for the rollers  728  does not extend in laterally extending slots in the channel member legs  722 . No such slot is provided for limiting the lateral movement of the tilt frame member  710  of the apparatus  700 . Instead, the guide blocks  726  are used to limit the lateral shifting of the tilt frame member  710 . Accordingly, when the tilt frame member  710  is shifted laterally such as shown in  FIG. 41 , the left pair linkage bars  712  can engage with the corresponding left pair of guide blocks  726  so that any further lateral shifting and tilting of the tilt frame member  710  is restricted. 
     Referring to  FIG. 38 , alternative stops  502   a  are illustrated. The stops  502   a  have a triangular configuration similar to the inverted V configuration of the elongate base member  734  of the idler roller frame  704 . The inclined surfaces of the triangular stops  502   a  are spaced sufficiently from the inclined walls  736  and  738  of the base member  734  to allow the predetermined amount of angular rotation as previously described with respect to stops  502 . Further, because the stops  502   a  are located entirely under the base member  734 , they will not present a surface on which debris from the conveyor belt  414  can accumulate. 
     While there have been illustrated and described particular embodiments of the present invention, it will be appreciated that numerous changes and modifications will occur to those skilled in the art, and it is intended in the appended claims to cover all those changes and modifications which fall within the true spirit and scope of the present invention.