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FIELD OF THE INVENTION 
       [0001]    The present invention pertains to a bucket for a universal dig and dump mining operation. 
       BACKGROUND OF THE PRESENT INVENTION 
       [0002]    Universal dig and dump (UDD) mining operations involve the use of dragline buckets that are controlled by UDD mining machines having front hoist lines, rear hoist lines and drag lines, such as disclosed in U.S. Pat. Nos. 6,705,031 and 6,826,466. While these operations have provided benefits, they have been particularly hard on the front hoist lines; i.e., the front hoist lines tend be damaged or to wear much faster than the rear hoist lines. Such wearing requires frequent replacement of the front hoist lines, which results in the use of more hoist line and in frequent downtime of the equipment. Moreover, the front hoist lines frequently wear at unequal intervals from the rear hoist lines resulting in even increased equipment downtime as the hoist lines are replaced separately. The front hoist motors also have more power, which can further lead to front hoist rope problems. 
       SUMMARY OF THE INVENTION 
       [0003]    The present invention pertains to a UDD mining machine that moves the bucket during the carry phase of a digging operation within a range of motion that is predetermined at least in part by the expected relative loads on the hoist lines. 
         [0004]    In one aspect of the present invention, the bucket is moved through a carry envelope for an improved UDD mining operation that reduces the loading on the front hoist line and enhances the efficiency of the mine. 
         [0005]    In one aspect of the invention, a control system for a UDD mining machine directs the movement of a loaded bucket within a prescribed carry envelope to limit unequal loading of the hoist lines. The control system directs the operator to move the UDD bucket within the prescribed carry envelope or, alternatively, move it directly under computer control. In one preferred construction, the control system directs the bucket to be moved within a range of motion where the loads on the hoist lines are kept within a prescribed variance of each other during the carry phase or most of the carry phase of a digging cycle. For example, movement of the bucket will be directed by the inventive control system so that the loads applied to the front hoist line are within, for example, 5%, 10% or 15% of the loads applied to the rear hoist line. This general equaling of the loads in the hoist lines results in longer wear life for the front hoist line, and generally equal wearing of the front and rear hoist lines to enable simultaneous replacement. 
         [0006]    In another aspect of the invention, the control system for a UDD mining machine directs the movement of the bucket within a carry envelope defined by borders that widen, and which preferably widen generally at an increasing rate, in a direction opposite to the pulling of the drag line. 
         [0007]    In another aspect of the invention, the control system for a UDD mining machine directs the movement of the bucket in the carry phase of a digging cycle to predominantly move under a prescribed datum having a generally bell-shaped curve. 
         [0008]    In another aspect of the invention, the control system for a UDD mining machine directs movement of the bucket in the carry phase of a digging cycle to move under a prescribed datum having a slope that generally increases in a direction opposite the pulling of the bucket during the digging phase. 
         [0009]    In another aspect of the invention, the control system directs the bucket during the carry phase to be moved predominantly below an upper datum where the variation between the loads on the hoist lines is at predetermined level. 
         [0010]    In another aspect of the invention, the control system directs the bucket to be predominantly moved during the carry phase in a range of motion which on average loads the front hoist line at a predetermined higher level than the loads on the rear hoist lines to control the replacement time for the front hoist line. 
         [0011]    In another aspect of the invention, the control system directs the bucket to be moved during the carry phase in a range of motion that depends on the expected relative loads on the hoist lines. 
         [0012]    In another aspect of the invention, the control system directs the movement of the bucket in a carry envelope where the overall magnitude of the loads on the hoist lines is reduced rather than equalizing the hoist line loads. 
         [0013]    In another aspect of the invention, a UDD machine commonly has more motors supporting the front hoist lines than the rear hoist lines. The control system can direct the bucket through a carry envelope that maximizes the carrying power of the additional motors. For example, the prescribed carry envelope may equalize the loads carried by each motor rather than in each hoist line. 
         [0014]    In another aspect of the invention, the bucket for a UDD mining operation is provided with a plurality of pairs of connection points for either or both of the front and rear hoist lines. In this way, the carry envelope for a particular bucket can be adjusted for a particular mining operation to maximize the equaling of the hoist line wear. Multiple connection points can also provide flexibility in accommodating and maximizing performance. 
         [0015]    In another aspect of the invention, the bucket for a UDD mining operation is formed with a bottom wall, a rear wall and a pair of sidewalls that are connected to define a front digging edge and a bucket cavity. The bucket is provided with connection points to facilitate the connection of front and rear hoist lines to the bucket. At least one of the connection points for coupling the rear hoist line to the bucket is located forward of the rear wall to provide improved carrying of the bucket during use for certain mining operations. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1  is a schematic illustration of a UDD mining operation. 
           [0017]      FIG. 2  is a side view of a UDD bucket. 
           [0018]      FIG. 3  is an enlarged side view of a trunnion for the UDD bucket. 
           [0019]      FIGS. 4-6  are graphs illustrating the operation of the control system of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0020]    The present invention pertains to a UDD mining machine wherein the bucket is controlled by independently operated front and rear hoist lines as well as a drag line, such as disclosed in U.S. Pat. Nos. 6,705,031 and 6,826,466, both of which are incorporated herein by reference. Briefly, a UDD operation is a dragline mining operation wherein the bucket is controlled solely by the attachment of flaccid lines, such as ropes, cables or chains. With reference to  FIG. 1 , a UDD operation  10  includes a machine  12  situated at a base location that is typically at or near ground level. The machine includes an elongate boom  14  that extends over the mining site, which typically is a large pit. One or more rear hoist line  16  extends downward generally from a free end  18  of the boom to engage a rear portion of bucket  20 . Similarly, one or more front hoist line  22  extends downward from boom  14  to connect to a front portion of bucket  20 . Hoist lines  16 ,  22  operate independently to carry and dump the bucket through each digging cycle. One or more drag line  24  connects to a front portion of bucket  20  to pull the bucket along the ground in order to fill the bucket. The UDD machine  12  further includes a control system with the appropriate motors, operator controls and computer for controlling the movement of the bucket via the hoist and drag lines. Ordinarily, other than the attitude of the bucket which is automatically controlled by the computer, the operator manually controls the movement of the bucket in a digging operation. For convenience, this application will discuss an operation that includes a single rear hoist line, front hoist line and drag line, though operations with a plurality of each kind of line or a mixed operation of single and multiple lines is possible. 
         [0021]    In one common digging cycle, the bucket is first set on the ground at the beginning of a pulling or digging phase in which the drag line pulls the bucket along the ground to fill it. Once the bucket is loaded, it is hoisted off the ground by the hoist line and moved from the terminus end of the digging phase to the dumping location, which is the carry phase of the digging cycle. The carry phase is followed by a dumping phase where the front hoist line is lowered relative to the rear hoist line to dump the earthen material out of the bucket via its open front end. The bucket is then returned, in a return phase, to the beginning of another digging phase. In the present invention, the operation of the hoist and drag lines in a UDD operation is directed by a computer  25  for the control system. Of course, the computer may be the same unit controlling the attitude of the bucket or a different unit. 
         [0022]    While UDD operations provide better control of the bucket than conventional dragline operations, they tend to suffer from undue damage, loading and wearing of the front hoist line. As a result, the front hoist line wears more quickly than the rear hoist line and, in some cases, as much as three to four times as fast. Premature wearing of the front hoist line results in increased usage of hoist line and in excessive downtime for the mining equipment. Moreover, the front and rear hoist lines frequently wear at uneven intervals requiring separate replacement of the front and rear hoist lines and even more equipment downtime. 
         [0023]    It has been determined that such excessive and unequal wearing of the front hoist line is caused primarily by unequal loading of the hoist lines during the carry phase of a digging cycle. Ordinarily, during the carry phase, the load on the rear hoist line tends to be relatively constant. In many potential positions during the carry phase, the pull of the drag line  24  will tend to generate high loads on the front hoist line  22 , particularly as the bucket nears boom  14 . When the bucket is at lower positions within the mine, the loads on front hoist lines  22  tend to be less as compared to many positions when the bucket is high in the mine. The pull of drag line  24  on front hoist  22  is reduced in some positions and in others actually bears some of the hoisting load to reduce the load on the front hoist line. While it is preferable to maintain generally equal loading of the front and rear hoist lines throughout the carry phase of the digging cycle, it is typically more important to do so in the higher reaches of the mine because of these higher loads. 
         [0024]    It has been determined that loading of the front and rear hoist lines, and particularly the front hoist line, is dependent on several factors including the position of the bucket under boom  14 , the center of gravity of the loaded bucket (i.e., the loaded center of gravity), and the location of the front and rear connection points relative to the loaded center of gravity. A change of any of these factors will result in more or less loading of the front hoist line. As noted above, the loads on the rear hoist line, though changing, generally tend to remain relatively constant through most carry positions. 
         [0025]    In one example, bucket  20  includes a bottom wall  26 , a rear wall  28 , and a pair of sidewalls  30  coupled together to define a front digging edge  32  and an inner bucket cavity. The digging edge includes a series of spaced apart teeth  34  for penetrating the ground and facilitating loading of the bucket when pulled along the ground by the drag line  24 . The drag line usually branches forward of the bucket to connect to each side of the bucket. An arch  36  couples the upper front ends of sidewalls  30 ; although an arch is not required. Front hoist line  22  is coupled to arch  36  via front connection point  38 . Rear hoist line  16 , which usually branches above the bucket, attaches to each sidewall  30  via rear connection points  40 . Nevertheless, connection points  38 ,  40  could be fixed to other parts of the bucket, and buckets having other designs could be used. As examples only, front connection points could be fixed to sidewalls  30 , such as disclosed in U.S. Pat. No. 6,705,301, and/or the rear connection points could be fixed to the rear wall  28 . In any event, the front connection point(s)  38  is fixed to a front portion  44  of bucket  20  and rear connection points  40  are fixed to a rear portion  46  of the bucket. Drag line  24  is coupled to the front edges  48  of sidewalls  30  via drag connection points  50 . 
         [0026]    During use, the bucket is loaded with earthen material in each digging phase. While the loaded center of gravity may shift slightly from load to load, an average loaded center of gravity  52  can be determined for each particular bucket. The loaded center of gravity  52  is also a factor of the density of the material to be gathered as denser loads will tend to shift the center of gravity rearward. The location of connection points  38 ,  40  can be determined in a two-dimensional format (i.e., height and length) relative to the loaded center of gravity  52 . With these three known location points  38 ,  40 ,  52 , the loads carried by each hoist line  16 ,  22  can be determined and mapped for all carry positions (i.e., positions where the bucket may be in a carry phase of a digging cycle) within the mine site. It has been determined that relatively equal loading of hoist lines  16 ,  22  can be achieved when the bucket is maintained within a prescribed carry envelope  54 . 
         [0027]    In one example, front hoist line  22  is coupled to front connection point  38  and rear hoist line  16  is coupled to rear connection points  40   a . In the carry phase of a loaded bucket, hoist lines  16 ,  22  will carry generally the same load (i.e., within about 5% of each other) if the bucket&#39;s loaded center of gravity  52  is kept within a carry envelope  54   a  defined by an upper datum or border  56   a  and a lower datum or border  58   a . With reference to  FIG. 4 , the zero point of the plot is the base position of boom  14 , i.e., where boom  14  is coupled to the base  13  of machine  12 . The vertical and horizontal axes in the plot represent the vertical and horizontal distances the bucket may be relative to the zero point. As can be seen ( FIG. 4 ), in this case, upper border  56   b  has a curved, generally bell-shaped configuration. In this example, the slope of the curve generally increases as the border extends away from the zero point and toward free end  18  of boom  14 . Further, carry envelope  54   a  generally widens and, in this example, generally at an increasing rate as it extends away from machine  12  base  13 . Borders  56 ,  58  extend into and out of the paper of the plot in  FIG. 4  to control the lift of the bucket irrespective of the lateral swinging of boom  14 . 
         [0028]    As one illustration, if the terminus of the digging phase locates bucket  20  at point  60 , bucket  20  will be directed by computer  25  for the control system to follow a carry path to the dump site  61  that stays beneath upper border  56   a  to ensure that the loads in each of the front and rear hoist lines remain relatively equal; i.e., the control system would direct the operator to move the UDD bucket within the prescribed carry envelope (e.g., with a light indicator or other indication of when the bucket is outside of the prescribed carry envelope). Alternatively, the bucket could be moved directly under computer control. As can be appreciated, this carry path  62  from point  60  to the dump site  61  (one example illustrated in  FIG. 4 ) will have an axial configuration (lateral motion of bucket  20  is not shown in the plot) that is generally bell shaped so that the bucket generally moves more horizontally in the earlier portion of the carry phase and generally more vertical in the later stages of the carry phase. The actual path may vary from what is shown depending on various factors such as the swing speed and swing angle. In the past, it was common for the bucket to generally follow a carry path  64  from point  60  to dump site  61  that was axially linear to reduce the overall length of travel. While the distance to the dump site is lessened, it causes the bucket to move outside of carry envelope  54   a , i.e., above upper border  56   a , and to thereby apply higher loads to front hoist line  22  as compared to rear hoist line  16 . This repeated additional loading causes front hoist line  22  to wear out more quickly than rear hoist line  16 . 
         [0029]    The position of carry envelope  54  can be adjusted in the mine site by changing the position of one or more of the connection points  38 ,  40 . In one example, front connection point  38  remains unchanged, and rear connection point  40  is moved rearward from location  40   a  to location  40   b . As seen in  FIG. 3 , connector  66  can be attached via a pin  68  to hole  70  to define a first connection point  40   a  or to hole  72  to define a second connection point  40   b  rearward of the first connection point. Of course, other ways of connecting or changing the connection points could be used. By moving rear connection point  40  rearward to location  40   b , the carry envelope  54  drops relative to the zero point so that upper and lower borders  56 ,  58  are lower relative to boom  14  and lower into a mining pit ( FIG. 5 ). As with the first connection points  38 ,  40   a , these second connection points  38 ,  40   b  define a carry envelope  54   b  with an upper border  56   b  and a lower border  58   b . Further, the carry envelope  54   b  generally widens, and in this example, generally at an increasing rate as it extends axially away from machine  12 . The carry path for bucket  20  with this second set of connection points  38 ,  40   b  is directed by the control system to stay between borders  56   b ,  58   b  so that the loads on hoist lines  16 ,  22  remain within about 5% of each other. This connection arrangement for this bucket may be preferred in a deeper mine site. Moreover, the connection points could be selectively chosen for a bucket that is designed for a particular mine in order to maximize the ability of the bucket to travel within the preferred carry envelope for that mine or mine plan. When designing the connection points for a bucket to be used in a particular mine site, greater attention will preferably be paid to the expected movement of the bucket through the higher regions of the mine. In a preferred embodiment for many mines, the rear connection points  40  are located forward of the rear wall  28  of the bucket to provide a more optimal carry envelope. Nevertheless, rear connections could be along rear wall  28 . 
         [0030]    As can be appreciated, the position of the carry envelope  54  can be adjusted up or down within the mine or its shape changed to narrow or widen depending on whether connection points  38 ,  40  are moved rearward/forward or up/down relative to the loaded center of gravity  52 . Irrespective of these changes, computer  25  for the control system, with the proper input of data, will direct the movement of the bucket for the carry phase to stay within the prescribed carry envelope to the dump site. The carry envelope will generally be defined by upper and lower borders  56 ,  58  that diverge generally at an increasing rate as the carry envelope extends away from machine  12 . Upper border  56  in many cases will generally have a configuration that resembles a bell shape (i.e., that flares upward at the outer range of the bucket&#39;s motion). The control system will often direct the bucket to move primarily in a horizontal direction in early portions of the carry phase and primarily in a vertical direction in later phases of the carry phase. Additional connection points can also be added to bucket  20  to provide further variations in the carry envelope. These additional connection points may be front and/or rear connection points. 
         [0031]    At times, however, a mine will have a certain layout that precludes the bucket from moving solely within a carry envelope wherein the loads on the hoist lines  16 ,  22  are kept generally equal (i.e., within about 5% of each other). This may occur, for example, when the mine pit is deeper than the operating carry envelope  54  so that the bucket ends its digging phase below lower border  58 . It may also occur, for example, when the dump site is higher than carry envelope  54  so that the bucket must travel above the upper border  56  to dump its load. In these cases, the control system directs the bucket to move predominantly within the desired carry envelope  54  so that the application of higher loads on the front hoist line is minimized. Under such circumstances, if the bucket included multiple connection points, the hoist lines would preferably be set to enable movement of the bucket beneath the upper datum  56  even if it meant substantial movement below the lower datum because of the difference in the magnitudes of the loads on the front hoist line at these different positions in the mines. 
         [0032]    Moreover, due to higher loads on the front hoist line in certain higher regions of a mine as compared to the lower regions, the control system can be set to direct the movement of the bucket along a carry path that is kept predominantly beneath an upper datum  56  without regard to a lower datum  58 . Under these parameters, the upper datum is defined in the same way, i.e., the boundary where the load on the front hoist line is within a predetermined load differential (e.g., within 5%, 10%, etc.) as compared to the load expected on the rear hoist line. 
         [0033]    Operation outside of a carry envelope that ensures generally equal loading of hoist lines  16 ,  22  may also occur, for example, when a bucket has only a single set of connection points that may not be able to maximize efficiency for a particular mine. In these cases, it may be necessary to operate the bucket for substantial periods outside of this desired carry envelope. In such cases, the control system can be set to direct the movement of the bucket within or at least predominantly within a carry envelope where the front and rear hoist lines are kept within a prescribed load percentage of each other which may be greater than a 5% difference. 
         [0034]    For instance, with reference to  FIG. 6 , carry envelope  54   c  for a particular bucket, with borders  56   c ,  58   c , defines a range of motion for the bucket where the loads on hoist lines  16 ,  22  remain within about 5% of each other. The particularities of the mine may dictate that for a particular bucket substantial portions of the carry phase may need to occur outside of carry envelope  54   c . In such cases, the control system can be set to direct the movement of the bucket within or predominantly within a carry envelope  54   d  with borders  56   d ,  58   d  where the loads on hoist lines  16 ,  22  are kept with a range of about 10% of each other. Alternatively, the control system could be set to direct the movement of the bucket within a carry envelope  54   e  with borders  56   e ,  58   e  where the loads on hoist lines  16 ,  22  are kept within 15% of each other. As can be appreciated, the control system can be set to dictate that the hoist lines stay within a certain prescribed load percentage of each other or as closely as possible to the desired variance to keep hoist line loads as close as possible. Such control alleviates as much as possible under the given circumstances unequal loading of the hoist lines and the premature wearing of the front hoist line. 
         [0035]    There are times also when it may be desirable to operate the UDD machine to balance the speed of the digging operation against the frequency of replacing the front hoist line. For instance, the digging cycle may be lengthened by having the control system direct the bucket to move in a range of motion where the loads in the front and rear hoist lines are predominantly within 5% of each other during the carry phase. As an alternative, the operator may set the control system to direct the movement of the bucket along a path where the loads in the front hoist line are within a predetermined difference of the loads in the rear hoist line by more than 5% in order to shorten the digging cycle and increase the production of the machine even if not required by the mine layout. 
         [0036]    In one example, the bucket is directed to move predominantly (at least in the upper regions of the mine) along a carry path where the load on the front hoist line is about 15% higher than the load on the rear hoist line. Further, the control system can be set so that the load on the front hoist line is kept within a certain variation of the carry path that approximates a 15% difference in the front and rear hoist line loads. For instance, the bucket can be moved within a range of motion wherein the hoist line loads vary upward or downward 5% (or other value) from the prescribed path—that is, the bucket predominantly moves within a range of motion where the load on the front hoist line is 10-20% higher than the loads on the rear hoist line. In this way, the operator can balance the downtime caused by replacing the front hoist line with the speed of the digging cycle in an effort to maximize the overall production of the mine. 
         [0037]    In another example, the control system can be set to permit even higher variations in hoist line loads (i.e., more than 15%) provided sufficient shortening of the digging cycle is gained. In other words, the overall production of the UDD machine mining can be maximized in some operations by accepting more frequent replacements of the front hoist lines and achieving a shorter digging cycle. The control system can achieve optimum bucket movement during the carry phase by factoring the duration of the digging cycle, the output production of each digging cycle, the variations in loads between the hoist lines, and the downtime caused by replacement of the front hoist line. 
         [0038]    Also, in certain mines, the front hoist line suffers abrasion wear near connection point  38  so that the terminal end of the front hoist becomes unacceptably worn even though the remainder of the hoist line has not worn as a result of the hoist loads. In such cases, the worn end of the front hoist line can be cut off and the front hoist line reattached in order to lengthen the use of the front hoist line, i.e., until the overall length of the front hoist line becomes too short to be used. Under these circumstances, the control system may be set to direct bucket movement along a path where the wearing of the hoist line due to uneven loading of the front hoist line corresponds with the time in which the front hoist line needs to be replaced due to shortening caused by abrasion wear. In this way, the operator may be able to shorten the time for the digging cycle and control front hoist line wear caused by hoist loads to correspond to the time when the front hoist line would need to be replaced for other reasons such as shortening caused by abrasion wear. 
         [0039]    As discussed above, the operation of the drag line affects the loads on the hoist lines. In another alternative, the bucket may be moved along a carry envelope to minimize the overall loads on the hoist ropes rather than equalizing the loads in the front and rear hoist lines. 
         [0040]    Also, as discussed above, it is common for UDD machines to have more motors supporting the front hoist lines than the rear hoist lines. As an alternative, the bucket can be directed to move through a carry envelope that generally equalizes the loads carried by each motor rather than in each line. 
         [0041]    Also, in a mixed line operation, e.g., where two front hoist lines are used but only one rear hoist line, the bucket can be moved through a carry envelope where the loads in each line are generally equal (i.e., where the overall load on the front hoist lines is twice the load in the single rear hoist line). 
         [0042]    Various other embodiments as well as many changes may be made without departing from the spirit and broader aspects of the invention as defined in the claims.

Summary:
A UDD bucket for a UDD mining operation provided with multiple hoist connection points that alternative couple to the front and/or rear hoist lines. The UDD mining machine includes a control system that directs the movement of the bucket within a prescribed carry envelope to limit unequal wearing of the hoist lines or minimize the magnitude of rope loads. In one construction, the control system directs the movement of the bucket with a range of motion where the loads on the hoist lines are kept within a prescribed variance of each other during the carry phase or most of the carry phase of a digging cycle. The bucket will be moved by the mining machine with the inventive control system so that, in the carry phase, the loads applied to the front hoist line are within, for example, 5%, 10% or 15% of the loads applied to the rear hoist lines. This general equaling of the loads in the hoist lines results in longer wear life for the front hoist lines, and generally equal wearing of the front and rear hoist lines to enable simultaneous replacement. The alternative connection points enables the carry envelope to be altered.