Abstract:
A breakdown hoist has a secondary stage that permits continuous operation. The breakdown hoist may be run with the secondary stage disabled. In some embodiments a primary and secondary stage can discharge lumber simultaneously onto two conveyors. Providing two conveyors can increase surge capacity.

Description:
TECHNICAL FIELD 
   The invention relates to hoists for breaking down packages of objects such as lumber. The invention has application in sawmills and other operations in which packages or lumber or other elongated objects are handled. 
   BACKGROUND 
   Lumber is typically handled in packages. Each package comprises a number of tiers of boards. Some of the tiers may be spaced apart from corresponding adjacent tiers by sticks which extend crosswise to the boards. 
   A continuous breakdown hoist is used to separate boards from packages of lumber. For example, such a hoist may be used to break a package of lumber into a stream of individual boards that may be fed into a planer in a planer mill. Examples of continuous breakdown hoists are described in:
         Jacobsen U.S. Pat. No. 4,640,655   Johnson U.S. Pat. No. 4,838,748 and CA 1318334,   Ritola U.S. Pat. No. 5,249,915 and CA 2089436,   Newnes U.S. Pat. No. 5,879,129 and CA 2230464, and   Hellstrom SE 7501507.3.
 
Other hoists are described in: SE161631; U.S. Pat. No. 5,795,126; CA2121401; SU906358; SE7405427; U.S. Pat. No. 1,676,957 and U.S. Pat. No. 1,549,149.
       

   The continuous breakdown hoists described above each have a hoist capable of lifting a package of lumber to a discharge location and a secondary hoist, set of accumulator arms, or the like, that can support a package of lumber (or partial package of lumber) while another package of lumber is loaded onto the hoist. This permits a substantially continuous discharge of boards to downstream equipment such as a planer. 
   The present inventors have determined that the continuous breakdown hoists described above suffer to at least some degree from some or all of the following disadvantages:
         The secondary hoist must be located in the feed path that delivers lumber to a planer or other device. There is no way to bypass use of the secondary hoist. Therefore, the secondary hoist must be used for all packages, whether it is truly needed or not.   The secondary hoists are complex mechanically, and subject to mechanical failure. Since they cannot be bypassed, failure of a secondary hoist can cause an entire plant to be shut down at great expense.   Debris such as sticks and snow spilling from lumber packages can interfere with the operation of the continuous breakdown hoist mechanisms.   Some of the designs cannot be retrofitted to an existing conventional tilt hoist.   Designs that provide arms that are located underneath the package, impose further constraints that impair the overall functionality of the machine—i.e. such designs typically provide slots for the arms to extend and index through. Such slots make the machine prone to jamming as a result of debris entering the slots.   In designs that have bottom arms that support a package, the need to lower and retract the bottom arms before raising the main hoist to spill can increase the over-all cycle time.       

   To maintain the most profitable operation, it is generally desirable to run a planer mill or other lumber-processing operation at its maximum throughput. The rate at which a planer mill can receive lumber typically depends upon the width and length of the lumber being processed. This rate is often limited by the power available at the cutting heads. Therefore, wider material is typically processed at a reduced linear rate while narrower material can be processed at an increased rate. The capacity of a planer mill may also be limited by a rate at which downstream equipment can receive and handle individual boards. Therefore, the rate at which short wide material can be processed may be constrained by the rate at which the material can be processed by a breakdown hoist. By contrast, the rate at which long wide material can be processed may be constrained by the rate at which that material can be processed by a planer. 
   The performance required of a breakdown hoist can be reduced by providing surge capacity between the hoist and a planer or other downstream machine. However, increasing the surge capacity takes up space and can cost more to install and operate. 
   There remains a need for reliable and cost-effective continuous breakdown hoists. 
   SUMMARY OF THE INVENTION 
   This invention has a number of aspects that may be combined or applied individually. 
   One aspect of the invention provides a breakdown hoist for breaking down packages comprising multiple tiers of lumber. The breakdown hoist comprises a main frame having a top edge and a face, a main lift arranged to lift packages along the face of the main frame, an extension frame and a secondary hoist. The extension frame has a face and is moveable between an extended position wherein the face of the extension frame extends past the top edge of the main frame and a retracted position wherein lumber can spill over the top edge of the main frame. The secondary hoist has a lifting support that is extendable to receive and support a package lifted by the main hoist and retractable. The secondary hoist is adapted to lift a package to a secondary top edge above the top edge of the main frame. 
   Further aspects of the invention and features of specific embodiments of the invention are described below. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings illustrate non-limiting embodiments of the invention. 
       FIG. 1  is a schematic diagram showing major components of a planer mill in which apparatus according to the invention could be applied. 
       FIGS. 2A and 2B  are partially schematic diagrams illustrating a continuous breakdown hoist according to an embodiment of the invention. In  FIG. 2A  the breakdown hoist is configured to bypass a secondary hoist. If  FIG. 2B  the breakdown hoist is configured to use the secondary hoist. 
       FIGS. 3A through 3H  illustrate steps in the operation of the breakdown hoist of  FIGS. 2A and 2B . 
       FIGS. 4A and 4B  are partially schematic diagrams illustrating a continuous breakdown hoist according to another embodiment of the invention. 
       FIGS. 5A to 5I  illustrate steps in the operation of the breakdown hoist of  FIGS. 4A and 4B . 
       FIGS. 6A to 6E  illustrate steps in the operation of a breakdown hoist according to another embodiment. 
       FIG. 7  illustrates a control system for the breakdown hoist of  FIGS. 2A and 2B . 
   

   LIST OF REFERENCE CHARACTERS 
   
     
       
             
             
             
           
         
             
                 
                 
             
           
           
             
                 
               L 
               piece of lumber 
             
             
                 
               P 
               package of lumber 
             
             
                 
               10 
               planer mill 
             
             
                 
               12 
               breakdown hoist (FIG. 1) 
             
             
                 
               14 
               planer 
             
             
                 
               16 
               conveyor 
             
             
                 
               16A 
               lower conveyor 
             
             
                 
               16B 
               upper conveyor 
             
             
                 
               20 
               breakdown hoist (FIGS. 2A to 3H) 
             
             
                 
               22 
               tilting frame 
             
             
                 
               22A 
               face 
             
             
                 
               22B 
               top edge 
             
             
                 
               23 
               pivot for frame 22 
             
             
                 
               24 
               actuator for tilting frame 22 
             
             
                 
               25 
               main lifting arms 
             
             
                 
               27 
               conveyor 
             
             
                 
               30 
               secondary lifting arms 
             
             
                 
               32 
               track for secondary lifting arms 
             
             
                 
               33 
               arrow 
             
             
                 
               34 
               arrow 
             
             
                 
               35 
               arrow 
             
             
                 
               40 
               extension frame 
             
             
                 
               40A 
               face 
             
             
                 
               40B 
               top edge 
             
             
                 
               42 
               carriage 
             
             
                 
               43 
               actuator 
             
             
                 
               44 
               pivot for extension frame 
             
             
                 
               50 
               movable conveyor section 
             
             
                 
               50A 
               end of lower conveyor 
             
             
                 
               50B 
               end of upper conveyor 
             
             
                 
               52 
               pivot 
             
             
                 
               54 
               actuator for movable conveyor section 
             
             
                 
               60 
               breakdown hoist (FIG. 6A) 
             
             
                 
               72 
               secondary frame 
             
             
                 
               72A 
               face 
             
             
                 
               72B 
               top edge 
             
             
                 
               72C 
               bottom edge 
             
             
                 
               73 
               gap 
             
             
                 
               80 
               controller 
             
             
                 
               82A to 82F 
               actuators 
             
             
                 
                 
             
           
        
       
     
   
   DESCRIPTION 
   Throughout the following description, specific details are set forth in order to provide a more thorough understanding of the invention. However, the invention may be practiced without these particulars. In other instances, well known elements have not been shown or described in detail to avoid unnecessarily obscuring the invention. Accordingly, the specification and drawings are to be regarded in an illustrative, rather than a restrictive, sense. 
     FIG. 1  shows schematically the overall arrangement of a planer mill  10 . Packages P of lumber are broken down into individual pieces L of lumber by a breakdown hoist  12 . Individual pieces L of lumber are carried from breakdown hoist  12  to a planer  14  by an infeed conveyor  16 . Ideally, breakdown hoist  12  can break down packages P at a rate sufficient to keep planer  14  operating continuously. There should be no interruption in the operation of breakdown hoist  12  that is long enough to cause planer  14  to be required to wait for a next piece of lumber to plane. 
   Infeed conveyor  16  can hold enough lumber for planer  14  to run for a short time. The length of time that planer  14  can run on the lumber on infeed conveyor  16  depends upon the length of infeed conveyor  16  and the dimensions of the lumber. This is illustrated by the following example. Suppose that planer  14  is capable of planing 2×12 lumber at 2000 ft/min, and 2×4 lumber at 3000 ft/min, with a maximum piece rate of 140 pcs/min (due to limitations in the downstream equipment), while processing boards having lengths between 8 ft and 20 ft. In this example, 20 ft long 2×12 boards would be processed at a rate of (2000/20)=100 pcs/min whereas 2×12 boards 14 ft long or shorter would be processed at 140 pcs/min. The maximum piece rate of 140 pcs/min constrains the 2×4 production in all cases. 
   At 140 pcs/min, the consumption rate of the material coming off of breakdown hoist  12  is approximately 140 ft/min (140 pcs/min×1 ft/pc) for the 2×12 s, and 46 ft/min for the 2×4 s. Therefore, if the length of infeed conveyor  16  upstream from planer  14  is 46 ft then infeed conveyor  16  can contain 1 minute of capacity for 2×4 boards, and only 20 seconds of capacity for short 2×12 boards. 
     FIGS. 2A and 2B  show a breakdown hoist  20  according to an embodiment of the invention. Breakdown hoist  20  comprises a tilting frame  22  and main lifting arms  25 . Frame  22  is pivoted at pivot  23  so that it can be moved between an upright configuration for receiving packages of lumber and a tilted configuration, as shown, for discharging lumber from packages onto infeed conveyor  16 . In the illustrated embodiment, a linear actuator  24 , such as a hydraulic cylinder is connected to move frame  22  between its upright and tilted positions. 
   Packages P of lumber L are supported from below by main lifting arms  25 . Main lifting arms  25  can be moved along frame  22  to slide packages of lumber L along a face  22 A of frame  22 . When a tier of lumber reaches top edge  22 B of frame  22  the tier of lumber can slide over top edge  22 B onto infeed conveyor  16 . 
   Main lifting arms  25  may be lifted until they are at least even with top edge  22 B so that all of the lumber being carried on main lifting arms  25  can be delivered onto infeed conveyor  16 . 
   Breakdown hoist  20  has a set of secondary lifting arms  30  that are movable along a track  32  as indicated by arrows  33 . Track  32  extends substantially parallel to face  22 A. Secondary lifting arms  30  are retractable and extendable as indicated by arrow  34 . Secondary lifting arms  30  are optionally pivotable as indicated by arrow  35 . Making secondary hoist arms  30  pivotable can reduce the overall height of breakdown hoist  20  so that breakdown hoist  20  can be installed in a shorter building than would otherwise be required. 
   An extension frame  40  is movable between a position wherein a face  40 A of extension frame  40  extends face  22 A (see  FIG. 2B ) and a position wherein extension frame  40  is out of the way (see  FIG. 2A ). In the illustrated embodiment, extension frame  40  is mounted pivotally on a carriage  42 . Carriage  42  is movable toward or away from top edge  22 B of frame  22  by means of a suitable actuator. With carriage  42  positioned toward top edge  22 B of frame  22  extension frame  40  can be pivoted into a position wherein face  40 A forms an extension of face  22 A as shown in  FIG. 2B . An actuator  43  is provided to pivot extension frame  40  about a pivot  44  carried on carriage  42 . 
   When extension frame  40  is in position to extend frame  22 , as shown in  FIG. 2B , lumber can spill over top edge  40 B of extension frame  40 . As described below, secondary lifting arms  30  can support one package of lumber (or a portion thereof) while spilling the lumber over the tope edge  40 B of extension frame  40  while frame  22  is tilted into its upright position to receive a new package of lumber on main lifting arms  25 . 
   The end of conveyor  16  adjacent to breakdown hoist  20  is movable between a lowered position (see  FIG. 2A ) in which it is positioned to receive lumber spilling over tope edge  22 B of frame  22  and an upper position (see  FIG. 2B ) in which it is positioned to receive lumber spilling over top edge  40 B of extension frame  40 . In the illustrated embodiment, a section  50  of conveyor  16  is pivoted at a pivot  52  so that it can be raised or lowered by an actuator  54 . 
   Breakdown hoist  20  can be operated in the configuration shown in  FIG. 2A  without using secondary lifting arms  30 , if desired. In this mode, breakdown hoist  20  ceases discharging lumber while main lifting arms  25  are reloaded with lumber. 
     FIGS. 3A to 3H  show stages in the operation of breakdown hoist  20  when configured as shown in  FIG. 2B  to use secondary lifting arms  30 . In  FIG. 3A , packages P are supported on main hoist arms  25  and lumber is being spilled over top edge  40 B of extension frame  40  onto conveyor  16 . After each tier of lumber has been spilled onto conveyor  16 , main hoist arms  25  are raised sufficiently to allow the next tier of lumber to spill over top edge  40 B. Also in  FIG. 3A , secondary lifting arms  30  are being retracted and more packages P are brought into a loading position adjacent breakdown hoist  20  on conveyor  27 . 
   In  FIG. 3B , main lifting arms  25  are controlled so that lumber continues to spill onto conveyor  16  while secondary lifting arms  30  are lowered along track  32 . 
   In  FIG. 3C , main lifting arms  25  are controlled so that lumber continues to spill onto conveyor  16  while secondary lifting arms  30  are being rotated into a position where they are ready for use, parallel to the tiers of packages P. 
   In  FIG. 3D , main lifting arms  25  have lifted package P to a hand-off position in which the lower surface of package P is above secondary lifting arms  30 . Secondary lifting arms  30  can be extended so that they lie below package P. 
   In  FIG. 3E , secondary lifting arms  30  have been fully extended and are supporting package P. As each tier of lumber spills over edge  40 B, secondary lifting arms  30  lift package P farther up to allow the next tier of lumber to spill over top edge  40 B. Frame  22  is being pivoted toward its upright position and main lifting arms  25  are being lowered to receive one or more packages of lumber from conveyor  27 . 
   In  FIG. 3F , secondary lifting arms  30  are controlled so that lumber continues to spill onto conveyor  16 . Frame  22  has reached its loading position, main lifting arms  25  have been lowered and conveyor  27  is being operated to load packages P onto main lifting arms  25 . 
   In  FIG. 3G , frame  22  has been moved to its tilted position, main lifting arms  25  are beginning to lift the newly-loaded packages P and more packages P are being brought into position for loading on conveyor  27 . 
   In  FIG. 3H  the last tier of lumber has been discharged from secondary lifting arms  30  and secondary lifting arms  30  are being pivoted out of the way. Main lifting arms  25  complete lifting packages P to allow the top tier of lumber from packages P to be discharged over top edge  40 B. 
     FIGS. 4A and 4B  show a breakdown hoist  60  according to another embodiment. Hoist  60  differs from hoist  20  in the outfeed arrangement. Otherwise, breakdown hoist  60  can be the same as breakdown hoist  20 . The same reference numerals are used to indicate certain parts of breakdown hoist  60  that are similar to or the same as corresponding parts of the breakdown hoist  20  described above. 
   Breakdown hoist  60  feeds two conveyors  16 A and  16 B. Conveyor  16 A has an end  50 A positioned to receive lumber that spills over top edge  22 A of frame  22 . Conveyor  16 B has an end  50 B positioned to receive lumber that spills over top edge  40 B of extension frame  40 . This design provides increased surge capacity without requiring a commensurate increase in building area. In some embodiments, breakdown hoist  60  may be configured to allow lumber to be discharged simultaneously onto both of conveyors  16 A and  16 B during certain phases of operation. 
     FIGS. 5A to 5H  illustrate a mode of operation of breakdown hoist  60 . In  FIG. 5A , extension frame  40  is being moved to its retracted position, secondary arms  30  have been pivoted and are being retracted, and main lifting arms  25  are lifting packages of lumber so that a tier of lumber can spill over top edge  22 B onto lower conveyor  16 A. Conveyor  27  is being operated to bring more packages of lumber into position for loading onto breakdown hoist  60 . 
   In  FIG. 5B , main lifting arms  25  are controlled so that lumber continues to spill onto lower conveyor  16 A while secondary lifting arms  30  are lowered along track  32 . Extension frame  40  is in its retracted position. 
   In  FIG. 5C , main lifting arms  25  are controlled so that lumber continues to spill onto lower conveyor  16 A while secondary lifting arms  30  are being rotated into a position where they are ready for use, parallel to the tiers of packages P. 
   In  FIG. 5D , extension frame  40  has been rotated into position and main lifting arms  25  have been raised so that lumber from the packages P now spills over top edge  40 B of extension frame  40  onto upper conveyor  16 B. Main lifting arms  25  are controlled so that lumber continues to spill onto upper conveyor  16 B. 
   In  FIG. 5E  main lifting arms  25  have lifted package P to a hand-off position in which the lower surface of package P is above secondary lifting arms  30 . Secondary lifting arms  30  can be extended so that they lie below package P. 
   In  FIG. 5F , secondary lifting arms  30  have been fully extended and are supporting package P. As each tier of lumber spills over edge  40 B, onto upper conveyor  16 B, secondary lifting arms  30  lift package P farther up to allow the next tier of lumber to spill over top edge  40 B. Frame  22  is being pivoted toward its upright position and main lifting arms  25  are being lowered to receive one or more packages of lumber from conveyor  27 . 
   In  FIG. 5G , secondary lifting arms  30  are controlled so that lumber continues to spill onto upper conveyor  16 B. Frame  22  has reached its loading position, main lifting arms  25  have been lowered and conveyor  27  is being operated to load packages P onto main lifting arms  25 . 
   In  FIG. 5H , frame  22  has been moved to its tilted position, main lifting arms  25  are beginning to lift the newly-loaded packages P, and more packages P are being brought into position for loading on conveyor  27 . 
   In  FIG. 5I , the last tier of lumber has been discharged from secondary lifting arms  30  and secondary lifting arms  30  are being pivoted out of the way while extension frame  40  is being retracted. Main lifting arms  25  complete lifting packages P to allow the top tier of lumber from packages P to be discharged over edge  22 B onto lower conveyor  16 A. 
   It can be appreciated that hoist  60  could be operated to deliver lumber only to top conveyor  16 B or only to bottom conveyor  16 A. 
     FIGS. 6A to 6E  show schematically a breakdown hoist  70  according to another embodiment which is similar to breakdown hoist  60  except that it has a secondary frame  72  having a face  72 A capable of supporting lumber while extension frame  40  is retracted. Secondary frame  72  has a top edge  72 B. Lumber can spill over top edge  72 B onto top conveyor  16 B. Secondary frame  72  is spaced above tilting frame  22  such that there is a gap  73  between the lowermost edge  72 C of secondary frame  72  and top edge  22 B of frame  22 . 
   As shown in  FIG. 6A , when extended, extension frame  40  bridges gap  73 . This permits packages P to be lifted to a level at which top tiers of the package can spill over top edge  72 B. Main lifting arms  25  can lift packages P to at least a hand-off location at which secondary arms  30  can be extended to support the package from below. Secondary arms  30  can then be operated to lift the package P so that the tiers of lumber spill tier-by-tier over top edge  72 B. 
   In  FIG. 6A , two packages P of lumber have been loaded onto main lifting arms  25  and frame  22  has been tilted into its operating position. In  FIG. 6B , main lifting arms  25  have lifted the packages of lumber to the hand-off position. Secondary lifting arms  30  are retracted but are ready to be extended to support packages P. 
   In  FIG. 6C , secondary lifting arms  30  are extended and supporting packages P. Packages P have been lifted so that the top tier is ready to spill over top edge  72 B onto upper conveyor  16 B. Main lifting arms  25  are being lowered to receive one or more packages of lumber from conveyor  27 . 
   In  FIG. 6D , frame  22  has been tilted to receive two new packages P while secondary lifting arms continue to discharge tiers of lumber from the previously-loaded packages P onto upper conveyor  16 B. The previously-loaded packages P have passed extension frame  40  and extension frame  40  has been retracted. 
   In  FIG. 6E , frame  22  has been tilted into its operating position and main lifting arms  25  have been raised to start spilling lumber from the newly-loaded packages P over top edge  22 B onto lower conveyor  16 A. Secondary lifting arms continue to be operated to discharge tiers of lumber from the previously-loaded packages P onto upper conveyor  16 B. The next packages are indexing into position on conveyor  27 . 
   The operation of apparatus according to any of the embodiments described herein may be controlled by a suitably programmed controller, such as a PLC, computer, or other data processor that controls the operation of actuators that operate the apparatus.  FIG. 7  shows schematically a control system that may be incorporated into a breakdown hoist  20  of the type shown in  FIG. 2A . Similar control systems may be provided for breakdown hoists according to other embodiments. 
   The control system has a controller  80  that receives inputs from sensors in breakdown hoist  20 . Software  81  controls actuators that operate apparatus  20  in a desired mode of operation in response to the sensor inputs. In addition to the actuators  24 ,  43  and  54  which are expressly mentioned above,  FIG. 7  shows an actuator  82 A for raising and lowering main lift  25 , an actuator  82 B for moving secondary arms  30  up or down along track  32 , an actuator  82 C for extending and retracting secondary arms  30 , an actuator  82 D for pivoting secondary arms  30 , an actuator  82 E for operating package feed conveyor  27 , and an actuator  82 F for moving carriage  42 . The sensor signals may include position and/or velocity signals from some or all of the actuators that operate breakdown hoist  20 . 
   Where a component (e.g. a software module, processor, assembly, device, circuit, etc.) is referred to above, unless otherwise indicated, reference to that component (including a reference to a “means”) should be interpreted as including as equivalents of that component any component which performs the function of the described component (i.e., that is functionally equivalent), including components which are not structurally equivalent to the disclosed structure which performs the function in the illustrated exemplary embodiments of the invention. 
   As will be apparent to those skilled in the art in the light of the foregoing disclosure, many alterations and modifications are possible in the practice of this invention without departing from the spirit or scope thereof. For example:
         Any suitable actuators may be used to implement a breakdown hoist. The actuators may, for example, comprise pneumatic or hydraulic cylinders, electrically driven linear actuators, electric, hydraulic or pneumatic motors, or the like. The actuators may be connected directly to an actuated component or may be connected to the component by way of a suitable linkage, transmission or the like.
 
Accordingly, the scope of the invention is to be construed in accordance with the substance defined by the following claims.