Abstract:
A spring assembly for a latch mechanism includes a spring, a first support, and a second support. The spring includes a first end, a second end, and a plurality of coils extending therebetween. The coils define an internal helical surface. The first support is configured to be coupled to a first pivoting member. The first support includes a grooved surface for threadingly engaging at least a portion of the internal helical surface of the spring proximate the first end. The second support is configured to be coupled to a second pivoting member. The second support includes a grooved surface for threadingly engaging at least a portion of the internal helical surface of the spring proximate the second end.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of prior-filed, co-pending U.S. Provisional Application No. 61/694,443, filed Aug. 29, 2012, the entire contents of which are incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    The present invention relates to the field of mining shovels. Specifically, the present invention discloses a dipper door latch mechanism. 
         [0003]    A conventional mining shovel includes a dipper having a dipper door pivotably coupled to a dipper body. During operation, the shovel operator releases a latch, thereby permitting the door to pivot to an open position and unload the contents of the dipper. The operator then moves the dipper into a tuck position so that the door falls back against the dipper body. The door slams shut, and a latch mechanism secures the door against the dipper body. The latch mechanism may include a linkage having multiple pivoting members and a tension spring biasing the linkage alternatively toward a locked state or an unlocked state. The spring is typically coupled to the links at its ends, creating a stress concentration at these points. Over time, the stress on the spring causes the spring to break, and the subsequent time for repair prevents the dipper from being used. The stress also alters the nominal tension force exerted by the spring, changing the response behavior of the spring and therefore changing the behavior of the latch mechanism. 
       SUMMARY 
       [0004]    In one embodiment, the invention provides a spring assembly for a latch mechanism including a first pivoting member and a second member pivotably coupled to the first member. The spring assembly includes a spring, a first support, and a second support. The spring includes a first end, a second end, and a plurality of coils extending therebetween. The coils define an internal helical surface. The first support is configured to be coupled to the first pivoting member. The first support includes a grooved surface for threadingly engaging at least a portion of the internal helical surface of the spring proximate the first end. The second support is configured to be coupled to the second pivoting member. The second support includes a grooved surface for threadingly engaging at least a portion of the internal helical surface of the spring proximate the second end. 
         [0005]    In another embodiment, the invention provides a latch mechanism for a dipper. The latch mechanism includes a first pivoting member, a second member pivotably coupled to the first member, a spring, a first spring support, and a second spring support. The spring includes a first end, a second end, and a plurality of coils extending therebetween. The first spring support includes a first end coupled to the first pivoting member and a second end having a first helically-grooved surface. The first helically-grooved surface engages an internal surface of at least a portion of the plurality of coils proximate the first end of the spring such that rotation of the first spring support relative to the spring threads the first helically-grooved surface into the plurality of coils. The second spring support includes a first end coupled to the second pivoting member and a second end having a second helically-grooved surface. The second helically-grooved surface engages an internal surface of at least a portion of the plurality of coils proximate the second end of the spring such that rotation of the second spring support relative to the spring threads the second helically-grooved surface into the plurality of coils. 
         [0006]    In yet another embodiment, the invention provides a dipper for a mining shovel. The dipper includes a body having an opening, a door pivotably coupled to the body to selectively close the opening, and a latch mechanism for releasably securing the door relative to the body. The latch mechanism includes a first pivoting member, a second member pivotably coupled to the first member, a spring, a first spring support, and a second spring support. The spring includes a first end, a second end, and a plurality of coils extending therebetween. The first spring support includes a first end coupled to the first pivoting member and a second end having a first helically-grooved surface. The first helically-grooved surface engages at least a portion of the plurality of coils proximate the first end of the spring such that rotation of the first spring support relative to the spring threads the first helically-grooved surface into the plurality of coils. The second spring support includes a first end coupled to the second pivoting member and a second end having a second helically-grooved surface. The second helically-grooved surface engages at least a portion of the plurality of coils proximate the second end of the spring such that rotation of the second spring support relative to the spring threads the second helically-grooved surface into the plurality of coils. 
         [0007]    Other aspects of the invention 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 shovel. 
           [0009]      FIG. 2  is a perspective view of a bail and a dipper. 
           [0010]      FIG. 3  is a perspective view of a portion of a dipper body. 
           [0011]      FIG. 4  is a perspective view of a portion of a dipper door. 
           [0012]      FIG. 5  is a perspective view of a latch mechanism. 
           [0013]      FIG. 6  is a perspective view of a spring assembly for use with the latch mechanism of  FIG. 5 . 
           [0014]      FIG. 7  is an exploded perspective view of the spring assembly of  FIG. 6 . 
           [0015]      FIG. 8  is a perspective view of a first spring support engaging a portion of a spring. 
           [0016]      FIG. 9  is a perspective view of a second spring support engaging a portion of the spring. 
           [0017]      FIG. 10  is a reverse perspective view of a portion of the latch mechanism of  FIG. 5 . 
           [0018]      FIG. 11  is a cross-section view of a portion of the latch mechanism taken along line  11 - 11  of  FIG. 10 . 
           [0019]      FIG. 12  is a perspective view of a portion of the latch mechanism of  FIG. 5 . 
       
    
    
       [0020]    Before any embodiments of the invention are explained in detail, it is to be understood that the invention 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 invention 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. 
       DETAILED DESCRIPTION 
       [0021]    As shown in  FIG. 1 , a mining shovel  10  rests on a support surface and includes a base  22 , a boom  26 , a handle  30  moveably coupled to the boom  26 , a dipper  34 , and a bail  38  coupled to the dipper  34 . The base  22  includes a hoist drum (not shown) for reeling in and paying out a cable or rope  42 . The boom  26  includes a first end  46  coupled to the base  22 , a second end  48  opposite the first end  46 , a boom sheave  50  coupled to the second end  48 , a shipper shaft  52  extending through the boom  26 , and a saddle block  54  pivotably coupled to the boom  26  via the shipper shaft  52 . The handle  30  is inserted into the saddle block  54  and is translationally and rotationally movable relative to the boom  26 . The dipper  34  is supported on an end of the handle  30 . The rope  42  passes over the boom sheave  50  and is coupled to the dipper  34  by the bail assembly  38 . The dipper  34  is raised or lowered as the rope  42  is reeled in or paid out by the hoist drum. 
         [0022]    Referring to  FIG. 2 , the dipper  34  includes a dipper body  58 , a dipper door  62  pivotably coupled to the dipper body  58  about a hinge pin  66 , a snubber (not shown) for dampening motion of the dipper door  62 , and a latch mechanism  70  for releasably securing the dipper door  62  to the dipper body  58 . In the illustrated embodiment, the dipper body  58  includes a first end, or a material receiving end  74 , and a second end, or a material discharging end  78 . The dipper door  62  pivots about the hinge pin  66  proximate the material discharging end  78  between a first, or open, position (shown in solid lines in  FIG. 2 ) and a second, or closed, position (shown in broken lines in  FIG. 2 ). In the embodiment illustrated in  FIGS. 2 and 3 , the latch mechanism  70  ( FIG. 2 ) is coupled to the dipper door  62  and engages a latch pin  80  coupled to the dipper body  58  and positioned proximate a lower edge of the dipper body  58 . In other embodiments, the latch mechanism  70  is coupled to the dipper body  58  and the latch pin  80  is coupled to the dipper door  62 . 
         [0023]    As shown in  FIGS. 4 and 5 , the latch mechanism  70  is positioned on the dipper door  62  ( FIG. 4 ). The latch mechanism  70  includes a primary cam or primary latch member  82 , a first link  86  pivotably coupled to the primary latch member  82 , a second link  90  pivotably coupled to the first link  86  at a pivot joint  92 , a spring assembly  94 , and a secondary cam or secondary latch  98 . The latch mechanism  70  is moveable between a locked state and an unlocked state. The primary latch member  82  includes a jaw  102  that is pivotable relative to the door  62 . The jaw  102  is positioned to engage the latch pin  80  ( FIG. 3 ) when the latch mechanism  70  is in the locked state and is positioned to release the latch pin  80  ( FIG. 3 ) when the latch mechanism  70  is in the unlocked state. 
         [0024]    The second link  90  is pivotable relative to the door  62 , and the first link  86  is pivotably coupled between the primary latch member  82  and the second link  90 . The spring assembly  94  is coupled between the first link  86  and the second link  90 , and exerts a spring force therebetween to pivot the first link  86  and the second link  90  about the pivot joint  92 . In the embodiment shown in  FIG. 5 , the spring assembly  94  biases the latch mechanism  70  toward the unlocked state. In one embodiment, the spring assembly  94  is positioned in an over-center configuration with the pivot joint  92 , and the spring force biases the latch mechanism  70  toward either the locked state or the unlocked state depending on the relative position of the pivot joint  92  with respect to the spring assembly  94 . Also, in the illustrated embodiment, the latch mechanism  70  includes a spring assembly  94  positioned on each side of the first link  86  and the second link  90 . 
         [0025]    The secondary latch  98  engages an end of the second link  90  to maintain the latch mechanism  70  in the locked state. The weight of the dipper door  62  and material supported within the dipper body  58  cause the latch pin  80  to exert a reaction force on the latch mechanism  70 . Actuating or releasing the secondary latch  98  permits the second link  90  to pivot, and the reaction force of the latch pin  80  causes the primary latch member  82  to pivot out of engagement with the latch pin  80 . The associated movement of the first link  86  and the second link  90  causes the pivot joint  92  to move, toggling the spring assembly  94  so that the spring force biases the latch mechanism  70  toward the unlocked state. 
         [0026]    When the operator desires to close the dipper door  62 , the dipper  34  is moved to a tuck position so that the door  62  pivots to the closed position. The latch pin  80  contacts with primary latch member  82 , pivoting the components of the latch mechanism  70  to the locked state. The movement of the pivot joint  92  toggles the spring assembly  94  so that the spring assembly  94  biases the latch mechanism  70  toward the locked state. The secondary latch  98  engages the end of the second link  90  to hold the latch mechanism  70  in the locked state. The operation of the latch mechanism  70  is described in further detail in U.S. patent application Ser. No. 12/986,933, filed Jan. 7, 2011, the entire contents of which are incorporated herein by reference. 
         [0027]    As shown in  FIG. 6 , the spring assembly  94  includes a first support  106 , a second support  110 , and a spring element such as a coil spring  114  extending between the first support  106  and the second support  110 . Referring to  FIG. 7 , the first support  106  includes a first plug  120 , a first bolt  124 , and a first retaining collar  128 . The first plug  120  is an elongated member having a first end  136 , a second end  140 , and a bore  144  extending longitudinally through the first plug  120  between the first end  136  and the second end  140 . The first plug  120  further includes a threaded or grooved portion  148  proximate the first end  136 . The first bolt  124  is inserted through the bore  144  from the first end  136  and extends through the first plug  120  so that an end of the bolt  124  is positioned away from the grooved portion  148 . The first retaining collar  128  is positioned on the first plug  120  proximate the second end  140 . 
         [0028]    Similarly, the second support  110  includes a second plug  152 , a second bolt  156 , a second retaining collar  160 , and a nut  164 . The second plug  152  is an elongated member having a first end  168 , a second end  172 , and a bore  176  extending longitudinally through the second plug  152  between the first end  168  and the second end  172 . The second plug  152  further includes a threaded or grooved portion  180  proximate the first end  168 . In the illustrated embodiment, the second bolt  156  is inserted through the bore  176  from the second end  172  and extends through the plug  152  so that an end of the bolt  156  is positioned proximate the grooved portion  180 . The nut  164  is threaded onto the end of the second bolt  156  to secure the bolt  156  to the second plug  152 . The nut  164  can be retained in various ways such as welding, for example. The second bolt  156  includes an opening or eye  184  for coupling the second support  110  to the first link  86  ( FIG. 12 ). The second retaining collar  160  is positioned on the second plug  152  proximate the second end  172  between the eye  184  and the grooved portion  180 . 
         [0029]    As best shown in  FIGS. 8 and 9 , the spring  114  is formed as stacked coils, which form an internal helical surface. As shown in  FIG. 8 , the first support  106  is coupled to the spring  114  by inserting the first end  136  of the first plug  120  into the spring  114  such that the grooved portion  148  receives the internal helical surface of a portion of the coils. The first plug  120  is rotated, thereby threading the grooved portion  148  into the coils of the spring  114 . Similarly, as shown in  FIG. 9 , the second support  110  is coupled to another end of the spring  114  by inserting the first end  168  of the second plug  152  into the spring  114 , threading the grooved portion  180  into the internal helical surface of the spring  114  as described above with respect to the first support  106 . 
         [0030]    In the illustrated embodiment, the first retaining collar  128  includes a pair of arms  192  forming a forked portion that receives one end of the spring  114 . Similarly, the second retaining collar  160  includes a pair of arms  196  forming a forked portion that receives the other end of the spring  114 . The retaining collars  128 ,  160  can be secured to the plugs  120 ,  152 , respectively, in various ways including welding, for example. The arms  192 ,  196  provide anti-rotation stops to prevent the spring  114  from unthreading or uncoiling from the first plug  120  or the second plug  154 , respectively. 
         [0031]    In the embodiment shown in  FIGS. 10 and 11 , the first bolt  124  ( FIG. 11 ) is inserted through a lug  204  coupled to the second link  90 . The first bolt  124  is secured to the lug  204  with a nut  208 . The connection between the first plug  120  and the second link  90  can be adjusted by threading or unthreading the nut  208  with respect to the first bolt  124 . In addition, one or more spacers  212  may be positioned on the first bolt  124  between the lug  204  and the plug  120  or between the lug  204  and the nut  208 . These adjustments permit the user to change the pre-load on the spring assembly  94  as necessary to produce the desired response behavior of the latch mechanism  70  during operation. 
         [0032]    As shown in  FIG. 12 , the eye  184  is positioned around a pin  216  coupled to the first link  86  to pivotably couple the second support  110  to the first link  86 . The eye  184  can be secured to the pin  216  in various ways, such as by a cotter pin inserted through a hole in the pin  216 . 
         [0033]    The threaded engagement between each plug  120 ,  152  and the spring  114  provides a secure coupling between the spring  114  and the supports  106 ,  110 . In addition, the threaded engagement between the grooved surfaces  148 ,  180  and the internal helical surface of the spring reduces stress concentrations during operation by distributing the load over multiple spring coils instead of applying the load only at the ends of the spring  114 . Reducing stress concentrations on the spring  114  prevents malfunction and improves reliability of the spring assembly  94 , which in turn reduces the amount of time required for maintenance of the latch mechanism  70 . 
         [0034]    Thus, the invention provides, among other things, a spring assembly for a latch mechanism. Although the invention has 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 of the invention as described. Various features and advantages of the invention are set forth in the following claims.