Abstract:
A method is provided for removing slack in a chain conveyor driven between a first sprocket and a second sprocket, the first sprocket and the second sprocket rotating in a first direction. The method includes: locking the second sprocket to prevent rotation of the second sprocket in a second direction opposite the first direction; operating the first sprocket in the second direction to position a slack portion between the first sprocket and the second sprocket; and removing at least one chain link from the slack portion.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of co-pending, prior-filed U.S. Provisional Patent Application No. 62/348,378, filed Jun. 10, 2016, the entire contents of which are incorporated by reference. 
     
    
     BACKGROUND 
       [0002]    The present disclosure relates to conveyors, and particularly to chain conveyors. 
         [0003]    Mining operations typically include a cutting mechanism for breaking or cutting material from a mine face. In some embodiments, the material is deposited on one or more conveyors (e.g., a face conveyor) and carried away from the mine face. The conveyors may include one or more parallel chains driven by rotating sprockets. Over time, operation of the face conveyor may cause the chain(s) to wear and become elongated. 
       SUMMARY 
       [0004]    In one embodiment, a method is provided for removing slack in a chain conveyor driven between a first sprocket and a second sprocket, the first sprocket and the second sprocket rotating in a first direction. The method includes: locking the second sprocket to prevent rotation of the second sprocket in a second direction opposite the first direction; operating the first sprocket in the second direction to position a slack portion between the first sprocket and the second sprocket; and removing at least one chain link from the slack portion. 
         [0005]    In another embodiment, a conveyor system includes a first sprocket operable to rotate in a first direction and a second direction, a second sprocket operable to rotate in the first direction and the second direction, and a chain extending between the first sprocket and the second sprocket. The chain is nominally driven by at least one of the first sprocket and the second sprocket in the first direction, and the chain includes a plurality of flight to convey material. The conveyor system further includes a locking mechanism selectively engageable with the second sprocket to inhibit the second sprocket from rotating in the second direction 
         [0006]    In yet another embodiment, a conveyor system includes a first sprocket driven by a first motor and operable to rotate in a first direction and a second direction, a second sprocket driven by a second motor and operable to rotate in the first direction and the second direction, and a chain extending between the first sprocket and the second sprocket. The chain is nominally driven by at least one of the first sprocket and the second sprocket in the first direction, and the chain includes a plurality of flights to convey material. The conveyor system further includes a tensioner unit selectively engageable with the first sprocket and operable to drive the first sprocket in the second direction independently of the first motor. The conveyor system further includes a locking mechanism engageable with the second sprocket while the tensioner unit drives the first sprocket in the second direction, the locking mechanism inhibiting the second sprocket from rotating in the second direction. 
         [0007]    Other aspects will become apparent by consideration of the detailed description and accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a perspective view of a mining operation. 
           [0009]      FIG. 2  is an enlarged perspective view of a portion of the mining operation of  FIG. 1 . 
           [0010]      FIG. 3  is a perspective view of a portion of a conveyor and a roof support. 
           [0011]      FIG. 4  is a section view of the conveyor of  FIG. 3 , viewed along section  4 - 4 . 
           [0012]      FIG. 5  is a schematic view of the conveyor of the mining machine. 
           [0013]      FIG. 6  is a schematic view of a first drive assembly of the conveyor. 
           [0014]      FIG. 7  is a schematic view of a second drive assembly of the conveyor. 
           [0015]      FIG. 8  is a schematic view of the conveyor, illustrating a slack chain portion. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    Before any embodiments are explained in detail, it is to be understood that the disclosure is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The disclosure is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. Use of “including” and “comprising” and variations thereof as used herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Use of “consisting of” and variations thereof as used herein is meant to encompass only the items listed thereafter and equivalents thereof. Unless specified or limited otherwise, the terms “mounted,” “connected,” “supported,” and “coupled” and variations thereof are used broadly and encompass both direct and indirect mountings, connections, supports, and couplings. 
         [0017]    In general, this disclosure relates to a chain conveyor system including a mechanism for locking and preventing counter-rotation of one or more conveyor sprockets. A drive mechanism for one of the sprockets includes a pawl unit with a one-way clutch for engaging an input shaft of the sprocket. The pawl unit permits the input shaft and the sprocket to rotate in a forward direction during normal operation, but prevents any rotation in a reverse direction. When another sprocket is operated in the reverse direction, the one sprocket locks one end of the chain and can expose a slack portion of the chain. 
         [0018]      FIGS. 1 and 2  illustrate an excavation operation (e.g., a longwall mining operation). A mining machine  10  excavates material from a mine face  14  of a mineral seam  18 , and progresses through the seam  18  as material is removed. In the illustrated embodiment, the mining machine  10  is a conventional longwall shearer, and the structure and operation of the shearer may be readily understood by a person of ordinary skill in the art. In other embodiments, a different type of mining machine may be used. Roof supports  22  are aligned in a row along the length of the mine face  14  to provide protection (a portion of the roof supports  22  are removed in  FIGS. 1 and 2  to illustrate the mining machine  10  and mine face  14 ). As the shearer  10  removes material from the mine face  14 , the cut material is directed onto a face conveyor  46  that conveys the material generally parallel to the mine face  14  and toward a main gate conveyor  34  ( FIG. 1 ). In the illustrated embodiment, the face conveyor  46  deposits the cut material on a beam stage loader  38  positioned adjacent an end of the mine face  14 . In some embodiments, the cut material may pass through a sizer or crusher (not shown) before or after it is deposited on the beam stage loader  38 . 
         [0019]    With reference to  FIGS. 3 and 4 , the face conveyor  46  includes a conveyor pan structure and a conveying element. In some embodiments, the conveyor pan structure is formed as multiple individual pan sections  58  that are interconnected with one another. The conveying element may be a chain conveyor including a pair of chains  60  and flight bars  62  ( FIG. 4 ) coupled between the chains  60  at regular intervals. As the flight bars  62  are drawn by the chains  60 , the flight bars  62  move sequentially across each pan sections  58  and move cut material along the pan sections  58 . Each pan section  58  includes a pan  63  supported on a ground surface  48 . The pan  63  supports the structure of the face conveyor  46 , such as the flight bars  62  and the chains  60  extending between the flight bars  62 . In the illustrated embodiment, each pan section  58  is coupled to a rack  54 . The mining machine  10  may include a pinion (not shown) that engages the rack  54  to move the mining machine  10  along the mine face  14  ( FIG. 2 ). 
         [0020]    With reference to  FIGS. 5-7 , the face conveyor  46  further includes a first drive assembly  64  having a first sprocket  66  and a second drive assembly  68  having a second sprocket  70 . Each sprocket  66 ,  70  intermeshes with the chains  60  in order to drive the chains  60  in an endless loop between a first end and a second end. The sprockets  66 ,  70  are illustrated schematically in  FIG. 5  as multi-sided polygons (e.g., seven-sided polygons), and a person of skill in the art will understand that each side or vertex may represent a tooth for engaging links of the chains  60 . As shown in  FIGS. 6 and 7 , each sprocket  66 ,  70  may include two sets of teeth  66   a,    70   a,  respectively, with each set engaging a separate chain  60 . In other embodiments, the sprockets  66 ,  70  may include fewer or more sets of teeth, and each set of teeth may include fewer or more teeth. Also, although the sprockets  66 ,  70  are illustrated schematically as circles in  FIG. 8 , it is understood that the sprockets  66 ,  70  in  FIG. 8  include teeth for driving the chains  60 . 
         [0021]    In the illustrated embodiment of  FIGS. 5-7 , the first drive assembly  64  includes a first motor  72  ( FIG. 6 ) driving the first sprocket  66  and the second drive assembly  68  includes a second motor  74  ( FIG. 7 ) driving the second sprocket  70 . The first motor  72  drives the first sprocket  66 , for example, in a first direction  76  to pull a lower portion or lower run  78  of the chains  60  while the second motor  74  drives the second sprocket  70 , for example, in the first direction  76  to pull an upper portion or upper run  80  of the chains  60 . The first and second motors  72 ,  74  are also capable of driving the sprockets  66 ,  70  in a second direction  82  opposite the first direction  76 . In other embodiments, a single motor may be used to directly or indirectly drive one or more of the sprockets. 
         [0022]    With reference to  FIG. 6 , the motor  72  of the first drive assembly  64  includes a first drive shaft  84  coupled to a first gearbox  86  via a first gearbox input shaft  88 . A first coupling mechanism  90  couples the first drive shaft  84  to the first gearbox input shaft  88 . The first gearbox  86 , in turn, transmits power from the first gearbox input shaft  88  to the first sprocket  66 . The first drive assembly  64  also includes a first spur wheel  92  fixedly coupled to the first gearbox input shaft  88 . As illustrated, the first spur wheel  92  is engaged with a hydraulic tensioner unit  94  and integral brake  96 . However, the hydraulic tensioner unit  94  and the brake  96  may be disengaged from the first spur wheel  92 . The hydraulic tensioner unit  94  and integral brake  96  engages the first spur wheel  92  to drive and maintain an angular position of the first sprocket  66  relative to the second sprocket  70  when the first motor  72  is deactivated for purposes described in further detail below. 
         [0023]    With reference to  FIG. 7 , the motor  74  of the second drive assembly  68  includes a second drive shaft  98  coupled to a second gearbox  100  via a second gearbox input shaft  102 . A second coupling member  104  couples the second drive shaft  98  to the second gearbox input shaft  102 . The second gearbox  100  of the second drive assembly  68  transmits power from the second gearbox input shaft  102  to the second sprocket  70 . The second drive assembly  68  also includes a second spur wheel  105  fixedly coupled to the second gearbox input shaft  102 . The second spur wheel  105  is engaged with a locking mechanism  106  to inhibit the second sprocket  70  from rotating in the second direction  82  ( FIG. 5 ). However, the locking mechanism  106  may be disengaged from the second spur wheel  105 . The locking mechanism  106  engages the second spur wheel  105  when the second motor  74  is deactivated for purposes described in further detail below. 
         [0024]    In operation, the gearboxes  86 ,  100  of the first and second drive assemblies  64 ,  68  transmit power from the motors  72 ,  74  to drive the first and second sprockets  66 ,  70  in the first direction  76  ( FIG. 5 ). Accordingly, the chains  60  and flight bars  62  of the face conveyor  46  are driven to transport cut or “won” material away from the mining machine  10 . When the cut material is removed from the mine wall  34  and deposited on the face conveyor  46 , the cut material exerts a force Fl ( FIG. 5 ) on the upper run  80  of the face conveyor  46 . The force Fl is oriented generally perpendicular to the direction of motion of the chains  60 . The force Fl induces large tensile stress in the chains  60 . Over time, the tensile stress exerted on the chain links and the wear on the individual links causes the chains  60  to become elongated. As a result of the elongation, the chains  60  are no longer at an optimal tension to transport the cut material. When the chains  60  become elongated beyond a predetermined level, an operator shortens the chains  60  to increase the tension in the chain  60  to a desired level. 
         [0025]    Referring now to  FIG. 8 , in order to shorten the chains  60 , one or more links of the chains  60  are removed by exposing a slack portion  108  of the chains  60 . Prior to exposing the slack portion  108 , the motors  72 ,  74  of the first and second drive assemblies  64 ,  68  are deactivated. At this point, the hydraulic tensioner unit  94  and the integral brake  96  ( FIG. 6 ) engage the first spur wheel  92  and the locking mechanism  106  ( FIG. 7 ) engages the second spur wheel  105 . 
         [0026]    Once the hydraulic tensioner unit  94  is engaged with the first spur wheel  92 , the hydraulic tensioner unit  94  rotates the first spur wheel  92  to drive the first sprocket  66  in the second direction  82 . While the first sprocket  66  is rotating in the second direction  82 , the locking mechanism  106  is engaged with the second spur wheel  105  to inhibit rotation of the second sprocket  70  in the second direction  82 . In other words, the first sprocket  66  rotates relative to the second sprocket  70  when the hydraulic tensioner unit  94  drives the first sprocket  66 . As such, the first sprocket  66  applies a force F 2  on the lower run  78  to tension the lower run  78 , while the slack portion  108  is exposed in the upper run  80 . Meanwhile, the force F 2  is applied to the chains  60  via the first sprocket  66  and a force F 3  is applied to the chains  60  via the second sprocket  70 , as shown in  FIG. 8 . The integral brake  96  of the first drive assembly  64  maintains the angular position of the first sprocket  66  relative to the second sprocket  70  by holding the position of first spur wheel  92  while the second spur wheel  105  is locked via the locking mechanism  106 . 
         [0027]    Once the slack portion  108  is exposed in the chains  60 , an operator cuts and removes one or more links from each chain  60 . The chains  60  are subsequently re-joined together. While a majority of the slack  108  is removed from the chains  60 , a residual amount of slack may remain. The residual slack in the chains  60  may be dissipated, for example, by the tensioner unit  94  and integral brake  96  working together to gradually distribute the tension from the lower run  78  and forces F 2 , F 3  from the sprockets  66 ,  70  throughout the rest of the chain  60 . 
         [0028]    Chain conveyors typically are formed with large, strong individual links. The disclosed tensioner unit allows the chain to be tensioned without the use of conventional heavy, in-pan chain sprag devices or other heavy ancillary mechanisms. The tensioner unit includes a series of toothed wheels which decrease the required holding torque (when the lower run is tensioned) to a level which the locking mechanism can safely withstand. Also, the tensioner unit may be engaged by a screw thread to prevent inadvertent engagement with the spur wheel. Specifically, the screw thread is used to engage or disengage the tensioner unit with the spur wheel. Maneuvering the tensioner unit into and out of engagement is achieved by rotating a screw rod clockwise and counterclockwise. The screw rod provides a mechanism for positively engaging the tensioner unit and the spur wheel with low risk of the tensioner unit inadvertently engaging the spur wheel when the conveyor is running and disengaging when the tensioner unit is in use. 
         [0029]    Although aspects have been described in detail with reference to certain preferred embodiments, variations and modifications exist within the scope and spirit of one or more independent aspects as described.