TECHNICAL FIELD 
       [0001]    This application relates generally to food handling systems and more particularly to a trough hoist system for lifting large amounts of dough. 
       BACKGROUND 
       [0002]    Trough hoists are used to raise, dump and lower dough troughs for feeding mixers, dough dividers or overhead forming equipment, as examples. For some commercial applications, bakeries may produce in the range of thousands of loaves of bread and other pastry items or hundreds of loaves of bread or pastry items per day. For bakeries on having the higher volumes, the trough hoists may have lifting capacities of up to 3,800 pounds or more. Lifting such large amounts of dough can put strain on load bearing members of the trough hoists. 
       SUMMARY 
       [0003]    In an aspect, a trough hoist apparatus that raises, dumps and lowers dough troughs includes a column assembly comprising a first column and a second column spaced laterally from the first column. A first externally threaded screw is mounted within the first column such that the first threaded screw extends vertically along a height of the first column. A second externally threaded screw is mounted within the second column such that the second threaded screw extends vertically along a height of the second column. A first drive assembly includes a first internally threaded drive nut internally receiving the first threaded screw. The first drive assembly is configured to rotate the first drive nut relative to the first threaded screw to move the first drive assembly vertically along the first threaded screw. A second drive assembly includes a second internally threaded drive nut internally receiving the second threaded screw. The second drive assembly is configured to rotate the second drive nut relative to the second threaded screw to move the second drive assembly vertically along the second threaded screw. A trough carriage assembly is located between the first column and the second column. The trough carriage assembly is mounted to the first drive assembly and the second drive assembly for vertical movement therewith. The trough carriage is configured to receive a dough trough. 
         [0004]    In another aspect, a method of moving dough using a trough hoist apparatus is provided. The method includes placing a dough trough in a trough carriage assembly located between a first column and a second column of a column assembly comprising the first column and the second column spaced laterally from the first column. A first drive assembly to which the trough carriage assembly is mounted is driven. The first drive assembly includes a first internally threaded drive nut internally receiving a first threaded screw mounted in the first column. The first drive assembly rotates the first drive nut relative to the first threaded screw thereby moving the first drive assembly vertically along the first threaded screw. A second drive assembly to which the trough carriage is mounted is driven. The second drive assembly includes a second internally threaded drive nut internally receiving a second threaded screw mounted in the second column. The second drive assembly rotates the second drive nut relative to the second threaded screw thereby moving the second drive assembly vertically along the second threaded screw. 
         [0005]    The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  is a side view of an embodiment of a trough hoist assembly that is used to feed a dough mixer with a trough carriage assembly of the trough hoist assembly in a lowered position; 
           [0007]      FIG. 2  is a side view of the trough hoist assembly of  FIG. 1  with the trough carriage assembly in a raised position; 
           [0008]      FIG. 3  is a perspective view of the trough hoist assembly of  FIG. 1 ; 
           [0009]      FIG. 4  is a front view of the trough hoist assembly of  FIG. 1 ; 
           [0010]      FIG. 5  is a side view of an embodiment of a support column including drive assembly of the trough hoist assembly of  FIG. 1 ; 
           [0011]      FIG. 6  is a side view of an embodiment of a drive assembly for use with the trough hoist assembly of  FIG. 1 ; 
           [0012]      FIG. 7  is a diagrammatic, section view of the drive assembly of  FIG. 6 ; 
           [0013]      FIG. 8  illustrates a system and method of controlling the drive assemblies; 
           [0014]      FIG. 9  is a perspective view of an embodiment of a clamp assembly; 
           [0015]      FIG. 10  is an exploded view of the clamp assembly of  FIG. 9 ; 
           [0016]      FIG. 11  is a side view of the clamp assembly of  FIG. 9 ; and 
           [0017]      FIG. 12  is a side view of the clamp assembly received within an opening in the top of a support column. 
       
    
    
     DETAILED DESCRIPTION 
       [0018]    Referring to  FIGS. 1-4 , a trough hoist assembly  10  is used to raise, dump and lower dough troughs for feeding mixers, dough dividers or overhead forming equipment, as examples. In the illustrated example, the trough hoist assembly  10  is used to feed a dough mixer  12 . A suitable dough mixer is a Roller Bar Mixer (e.g., model HS13FD or HS20FD), commercially available from Peerless Machinery Corp., Sidney, Ohio. Dough mixers can have various mixing capacities, for example, from 400 pounds to 3,200 pounds and can be suitable for mixing dough delivered from the trough hoist assembly  10  for making breads, rolls, buns, donuts, flour tortillas, croissants, sweet goods, pizza, English muffins and mixing low-absorption frozen doughs. The dough mixer  12  may include a refrigerated assembly such as that described in U.S. Pat. No. 6,047,558, the details of which are incorporated by reference. The refrigerated assembly can provide substantial temperature stabilization within the mixer during a dough mixing operation. 
         [0019]    The trough hoist assembly  10  includes a column assembly  14  including a first support column  16  and a second support column  18  that is spaced laterally from the first support column. The first support column  16  is substantially the same height as the second support column  18 , such as between about 150 inches to about 300 inches, such as about 210 inches. 
         [0020]    The first and second support columns  16  and  18  include bases  20 ,  22  at a bottom  24 ,  26  of the support columns that maintain the hoist assembly  10  in its upright, vertical orientation. The support columns  16  and  18  are also connected together by a support bar  28  that is connected at a top  30 ,  32  of the first and second support columns. Secondary support columns  34 ,  35 ,  36  and  37  are provided for additional support, particularly during a dumping operation, which will be described in greater detail below. 
         [0021]    A trough carriage assembly  38  is located between the first support column  16  and the second support column  18 . The trough carriage assembly  38  includes a welded carriage  40  that removably receives and supports a dough trough  42 . A dough trough is generally an elongated tub-like structure, which may include wheels and holds large amounts of dough to transport from one location to another. 
         [0022]    The trough carriage assembly  38  is moved vertically along the heights of the first and second support columns  16  and  18 .  FIG. 1  shows the trough carriage assembly  38  in a lowered position and  FIG. 2  shows the trough carriage assembly in a fully raised, dumping position. In some embodiments, a dough chute  39  is provided to guide the dough into the dough mixer  12  during the dumping operation. 
         [0023]    The support columns  16  and  18  include a channel  44  and  46  (see  FIG. 3 ) that extends vertically along the heights of the first and second support columns between their tops  30 ,  32  and bottoms  24 ,  26 . A first drive assembly  48  is located in the channel  44  of the first support column  16  and a second drive assembly  50  is located in the channel  46  of the second support column  18 . The trough carriage assembly  38  is mounted to the first drive assembly  48  and the second drive assembly  50 . The first and second drive assemblies  48  and  50  move the trough carriage assembly  48  along the heights of the first and second support columns  16  and  18  from the fully lowered position to the dumping position. 
         [0024]    As can be seen by  FIG. 2 , the dough trough  42  is pivotable to provide a dumping action for the dough trough. Referring particularly to  FIGS. 3 and 4 , each support column  16  and  18  includes a track  52  having a vertical component  54  and a horizontal component  56 . A wheel  58  or other suitable follower on each side of the dough trough  42  is received in each track  52  at the lower end of the track. The wheels  58  of the dough trough  42  ride along each component  54  and  56  of the track  52 , the horizontal component  56  causing the dough trough to pivot forward in the direction of arrow  55  as the trough carriage assembly  38  is raised (see  FIG. 2 ). The radius  60  of the track  52  is selected to provide a smooth transition of the dough trough  42  from its upright, vertical position to its dumping position. In some embodiments, an actuator, such as a pneumatic cylinder, is used to pivot the dough trough  42  forward relative to the trough carriage assembly  38  into the dumping position illustrated by  FIG. 2  and to retract the dough trough back to its upright, vertical position shown by  FIGS. 3 and 4 . 
         [0025]    Referring to  FIG. 5 , first column  16  including drive assembly  48  is shown in isolation. Because drive assemblies  48  and  50  include the same components, only drive assembly  48  will be described in detail. 
         [0026]    A threaded screw  62  (e.g., a 2″-3 RH ACME screw) is clamped at a top  64  of the threaded screw to the first support column  16  by a clamp assembly  66 . In this embodiment, the threaded screw  62  is clamped to a top  68  of the first support column  16 , however, the threaded screw  62  could be clamped to another wall that spans the channel  44 , below the top  68 . 
         [0027]    The threaded screw  62  extends vertically along a height of the first support column  16  and is located within the channel  44  of the first support column. Threaded screw  62  is clamped by the clamp assembly  66  so that it does not rotate and such that an end  69  opposite the clamped end  64  hangs freely above the bottom  24 , which enables some lateral movement of the threaded screw. As an alternative embodiment, the end  69  may be supported above the bottom  24  by a flexible, resilient bar of material such as a plastic or rubber rod extending upwardly from the bottom  24 . 
         [0028]    As described below, the drive assembly  48  moves vertically along the threaded screw  62  by rotating a driving nut relative to the threaded screw. A housing  72  of the drive assembly  48  is used to house various components of the drive assembly and is also a load bearing component of the drive assembly connecting the drive assembly to the trough carriage assembly  38 . Sewn bellows  67  are provided for covering the threaded screw  62  as the drive assembly descends for inhibiting contaminants from collecting on the threaded screw. 
         [0029]    A flexible cable carrier, represented by line  71 , carries flexible cables from a control panel enclosure  70  ( FIG. 1 ) to the drive assembly  48  for use in powering and controlling the drive assembly. The flexible cable carrier  71  and flexible cables move along with the drive assembly  48  along the height of the first column  16 . 
         [0030]    An adjustment assembly, generally referred to as element  74 , is provided for guiding the drive assembly  48  within the channel  44  of the first column  16 . The adjustment assembly  74  includes a pair of track members  76  and  78  located on opposite sides of the drive assembly  48 . The track members  76  and  78  are V-shaped in cross-section and are engaged by upper rollers  80  and  82  and lower rollers  84  and  86  of the drive assembly  48 , each of the rollers having a track engaging surface  87  (e.g., V-shaped; see  FIG. 7 ) corresponding to the shape of the track members. 
         [0031]      FIG. 6  shows the drive assembly  48  in isolation. The drive assembly  48  utilizes an offset drive system where the axial drive component is applied at a location offset vertically from the driving nut. Drive assembly  48  includes an upper connecting plate  88  and a lower connecting plate  90 . The connecting plates  88  and  90  are connected to a load bearing plate  92  that forms a sidewall of the housing  72  to which the trough carriage assembly  38  is connected. 
         [0032]    Mounted on the upper connecting plate  88  is a motor assembly  94  (e.g., a four HP drive gear motor). The motor assembly  94  is connected to a driving gear  96  for rotating the driving gear. The driving gear  96  rotates a driven gear  98 , which is rigidly connected to a driven bushing  100  such that the driven bushing rotates with the driven gear. The driven bushing  100  is, in turn, rigidly connected to a driving nut  102 , which is internally threaded and mates with the threads of the threaded screw  62 . 
         [0033]    Referring also to  FIG. 7 , the threaded screw  62  extends through the driving nut  102 , driven bushing  100 , driven gear  98  and the upper and lower connecting plates  88  and  90 . The driven bushing  100  also extends from the driving nut  102 , to which it is connected, through the driven bushing  100 , driven gear  98  and the upper and lower connecting plates  88  and  90 . Upper and lower radial load bearings  104  and  106  are provided above and below the driven gear  98  for offsetting or inhibiting any radial load from being transferred from the driving gear to the driving nut  102  through the driven bushing  100 . This way, any load placed on the driving nut  102  is axial only due to the weight of the load being conveyed up the trough hoist assembly  10 . This axial load arrangement can minimize binding between the driving nut  102  and the threaded screw  62  during use. The axial load acting on the driving system is offset or inhibited by thrust bearings  108  (e.g., needle roller thrust bearings). The driven gear  98  can be locked to the driving bushing  100  using a threaded set collar and retaining snap ring thereby preventing play therebetween. 
         [0034]      FIG. 8  shows the connection between the driving nut  102  and the driven bushing  100 . The driven bushing  100  has internal threads only to a certain depth and the driving nut  102  has a flange with external threads which are engaged with the internal threads of the driven bushing. Pins  103  are press fit into drilled holes  105  to ensure that the driven bushing  100  and the driving nut  102  are interlocked and thereby preventing any cross rotation between them. The pins  103  are backed into the holes  105  by a set screw  107  to prevent the pins from backing out of the holes. 
         [0035]    Referring back to  FIGS. 6 and 7 , the drive assembly  48  further includes a nut wear detection system, generally referred to as element  110 , that is used to detect excessive wear on the driving nut  102 . The nut wear detection system  110  includes an internally threaded back-up nut  112  that is threaded onto the threaded screw  62 . The back-up nut  112  is also connected to the driving nut  102  by pins  114  such that the back-up nut  112  rotates with the driving nut and moves vertically with the driving nut to maintain a gap  116  (e.g., about ⅓ inch) therebetween. The pins  114  are press fit into recesses  118  in the driving nut  102  and are located within recesses  120  associated with the back-up nut  112 . The recesses  118  and  120  of the driving nut  102  and the back-up nut  112  are sized to allow some vertical movement between the driving nut and the back-up nut. In other words, seating surfaces  122  and  124  of the recesses  118  and  120  are spaced-apart a distance that is greater than a length of the pins  114 . In some embodiments, the seating surfaces  122  and  124  are spaced apart such that a gap of about one inch is provided below the pins  114 . 
         [0036]    A detector  126 , such as a proximity sensor (e.g., a photoelectric sensor), is connected to the lower connecting plate  88  by a bracket  128 . The bracket  128  is sized to position the detector  126  adjacent a lower edge  130  of the back-up nut  112  such that the detector detects the presence of the back-up nut during normal operation. 
         [0037]    Because the driving nut  102  supports the weight of the drive assembly  48 , when excessive wear on the driving nut occurs, the driving nut along with the housing  72  and the detector  126  drop down toward the back-up nut  112 . The distance of the drop is sufficient to cause the detector  126  to no longer detect the presence of the back-up nut  112  as the detector drops below the lower edge  130 . 
         [0038]    Referring now to  FIG. 9 , the detector  126  provides an excessive wear indication to a controller  132 . The controller  132  is also connected to the first and second drive assemblies  48  and  50  for controlling operation and synchronization of the drive assemblies such that the drive assemblies ascend and descend along their respective threaded screws  62  together. In response to the excessive wear indication, the controller  132  can reverse the motor assemblies  94  of each of the first and second drive assemblies  48  and  50  to lower the trough carriage assembly  38  to its fully lowered, resting position. In some embodiments, the controller  132  may prevent further lifting of the trough carriage assembly  38  until the driving nut  102  is replaced and the detector  126  detects the presence of the back-up nut  112 . A user input  134  is provided for user control of the trough hoist assembly  10 , such as ON/OFF, speed and direction of travel controls. 
         [0039]    A position sensor  135  is provided for determining vertical position of the first and second drive assemblies  48  and  50 . Any suitable position sensor may be used (e.g., a string potentiometer) and the sensor  135  provides a signal to the controller  132  indicative of position of the respective drive assembly  48 ,  50 . The controller  132  uses this position information to synchronize movement of the drive assemblies  48  and  50  to ensure they are at substantially the same elevation. 
         [0040]    The driving and back-up nuts  102  and  112  can be formed of any suitable material such as AMPCO®  18  bronze. In some embodiments, the driving nuts  102  are turned at a maximum speed of 346 RPM using the motor assemblies  94  and controller  132 . The lead of the threaded screws  62  can be ⅓ inch which provides a maximum linear speed of 117 in/min for the drive assemblies  48  and  50  in the direction of travel. 
         [0041]      FIGS. 10-12  show the clamp assembly  66  used to clamp the top ends of the threaded screws  62  to their respective first and second support column. The clamp assembly  66  includes a top clamp plate  136 , a fork plate  138 , a top mount  140  and thrust bearings  142 . An upper end  144  of the threaded screw  62  extends upwardly through the top mount  140  and an opening  146  in the top clamp plate  136 . The upper end  144  of the threaded screw  62  has a square cut portion  146  that is received in a correspondingly-shaped opening  148  in the fork plate  138  located between the top clamp plate  136  and the top mount  140 . The fork plate  138  includes a pair of prongs  150  and  152  that are spaced apart from each other to receive a mount spacer  154  therebetween to prevent rotation of the fork plate and the threaded screw  62 . The clamp assembly  66  is received within an opening  156  in the top  68  of the support column (see  FIG. 12 ). The mount spacers  154  are bolted to the top  68  of the support columns. 
         [0042]    The clamp assembly  66  prevents rotation of the threaded screw  62  as the drive assembly  48  moves up and down along the height of the threaded screw while mounting the threaded screw above the bottom of the respective column such that the opposite end of the screw hangs freely above the floor. The clamp assembly  66  does allow some side-to-side movement of the threaded screw  62  which can inhibit binding of the drive assembly  48  as it moves along the threaded screw. 
         [0043]    It is to be clearly understood that the above description is intended by way of illustration and example only and is not intended to be taken by way of limitation, and that changes and modifications are possible. Accordingly, other embodiments are contemplated and modifications and changes could be made without departing from the scope of this application.
A trough hoist apparatus that raises, dumps and lowers dough troughs includes a column assembly comprising a first column and a second column spaced laterally from the first column. A first externally threaded screw is mounted within the first column such that the first threaded screw extends vertically along a height of the first column. A second externally threaded screw is mounted within the second column such that the second threaded screw extends vertically along a height of the second column. A first drive assembly includes a first internally threaded drive nut internally receiving the first threaded screw. The first drive assembly is configured to rotate the first drive nut relative to the first threaded screw to move the first drive assembly vertically along the first threaded screw. A second drive assembly includes a second internally threaded drive nut internally receiving the second threaded screw. The second drive assembly is configured to rotate the second drive nut relative to the second threaded screw to move the second drive assembly vertically along the second threaded screw. A trough carriage assembly is located between the first column and the second column. The trough carriage assembly is mounted to the first drive assembly and the second drive assembly for vertical movement therewith. The trough carriage is configured to receive a dough trough.