Abstract:
Devices and methods to relieve lift chains from being maintained under constant, or nearly constant, tension are provided.

Description:
TECHNICAL FIELD 
       [0001]    The field of the present disclosure relates to accessories for lift truck masts. 
       SUMMARY 
       [0002]    The present inventors have recognized that lift chains on certain lift truck masts are typically under constant, or nearly constant, tension. For example, when the mast is not fully lowered with an attachment resting on the ground the lift chains are under constant tension. For some lift trucks in certain applications, such as empty container handling, the lift chains rarely, if ever, are relieved from being tensioned. Some lift truck lift chains therefore carry a relatively large proportion of the rated load for a lift truck, even when not lifting a load, because of the construction, kinematics, dimensions, and weight of attachments secured to the mast. 
         [0003]    The present inventors have also recognized that maintaining lift chains under constant, or nearly constant, tension inhibits effective lubrication of such chains. The present inventors have also recognized that maintaining lift chains under constant, or nearly constant, tension typically reduces lift chain life. 
         [0004]    To address the above, and other problems, the present inventors created devices and methods to relieve lift chains from being maintained under constant, or nearly constant, tension. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]      FIG. 1  illustrates a rear right-hand side isometric view of a mast hanger embodiment. 
           [0006]      FIG. 1A  illustrates a rear right-hand side isometric view of another mast hanger embodiment. 
           [0007]      FIG. 1B  illustrates a rear right-hand side isometric view of another mast hanger embodiment. 
           [0008]      FIG. 2  illustrates a front left-hand side isometric view of the mast hanger of  FIG. 1  on a lift truck mast. 
           [0009]      FIG. 3  illustrates a left-hand side cut away view of the mast hanger of  FIG. 1  on a lift truck mast. 
           [0010]      FIG. 4  illustrates a rear left-hand side isometric view of another mast hanger embodiment at a non-mast receiving position. 
           [0011]      FIG. 5  illustrates a rear left-hand side isometric view of the mast hanger embodiment of  FIG. 4  at a mast receiving position. 
           [0012]      FIG. 6  illustrates a flow chart of an exemplary method of relieving tension from lift chains. 
           [0013]      FIG. 7  illustrates a flow chart of another exemplary method of relieving tension from lift chains. 
           [0014]      FIG. 8  illustrates an exemplary schematic of a mast hanger system interface. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]    A device for facilitating lift chain tension relief is illustrated in  FIGS. 1-3 . A mast-hanger  10  includes a first support  15  and a second support  20  that are connected by an optional spacer  25 . Each of the first support  15  and the second support  20  include a mast receiving formation  30 , an attachment receiving formation  35 , and an optional mast attachment  40 . In the embodiment illustrated in  FIG. 1 , the mast receiving formation  30  comprises a raised portion  31  and a lip  32  that forms a pocket  33 . The attachment receiving portion  35  comprises a sloped shelf  36 . The mast attachment  40  comprises a hook-shape. Preferably, each of the first support  15  and the second support  20  are integrally formed with a mast receiving formation  30 , an attachment receiving formation  35 , and a mast attachment  40 , for example, by casting, forging, cutting, or stamping using ductile iron, steel, or other suitable material. Optionally, the first support  15  and the second support  20  may be formed by providing an elongate bar and securing one or more of a mast receiving formation  30 , an attachment receiving formation  35 , and a mast attachment  40  to each elongate bar by welding, bolting or other suitable attachment. 
         [0016]    In other embodiments, a mast hanger  10 A includes only a mast receiving formation  30 A ( FIG. 1A ). In other embodiments, a mast hanger  10 B includes only an attachment receiving formation  35   b  ( FIG. 1  B). 
         [0017]    The optional spacer  25  is preferably secured to each of the first support  15  and the second support  20  via bolts, welds, or other suitable attachment. The spacer  25  may be constructed from a relatively lightweight material such as sheet metal or a rigid plastic. 
         [0018]      FIG. 2  illustrates the mast-hanger  10  of  FIG. 1  installed on a two stage mast  45  of a lift truck  50  (partially illustrated) where the second stage is removed for clarity. Optionally, the mast may include more than two stages and the mast hanger  10  may include one or more mast receiving formations, such as mast receiving formation  30 . The mast-hanger  10  hangs on a cross member  55  of the two stage mast  45  via the mast attachments  40 . Optionally, for a mast with more than two stages, multiple mast-hangers, such as mast hanger  10  or mast hanger  100 , may be provided, preferably with one mast-hanger on a fixed stage and one or more mast hangers on one or more moveable stages. A lip  26  ( FIG. 1 ) of the optional spacer  25  facilitates maintaining the first support  15  and the second support  20  in contact with cross members  55  and  60  by engaging a back-side of the cross member  55 . Optionally, the mast-hanger  10  may be bolted, welded, or otherwise suitably secured in place. In some embodiments where the first support  15  and the second support  20  are secured in place, one or both of the optional spacer  25  and mast attachment  40  may be omitted. In other embodiments, the optional spacer  25  may be omitted even if the mast-hanger  10  is not bolted, welded or otherwise fastened to the two stage mast  45 . 
         [0019]      FIG. 3  illustrates the mast-hanger  10  of  FIG. 1  supporting the second stage  65  of the two stage mast  45  and an attachment  70 . By the nature of their design, construction, kinematics, dimensions, weight, or other relevant characteristic, some attachments do not permit a lift truck operator to fully lower the attachment to the ground, thus removing some or all of the tension in the lift chains. For example, attachments designed to handle empty cargo containers typically cannot be set on the ground and thus do not permit a lift truck operator to fully lower such attachments. 
         [0020]    Pocket  33  is shaped and sized to receive the second stage  65  of the two stage mast and thus transfer some or all of the weight of the second stage  65  from the lift chains to the cross member  55 . Sloped shelf  36  is shaped and sized to receive the attachment  70  and thus transfer some or all of the weight of the attachment  70  from the lift chains to the cross member  55 . In the illustrated embodiment, the attachment  70  includes an integrated carriage. However, some carriages are not integrated with an attachment, and in certain embodiments the sloped shelf  36 , or another suitable portion of a mast-hanger, is preferably shaped and sized to receive such a non-integrated carriage, a non-integrated attachment, or both. An attachment receiving portion is therefore a portion of a mast-hanger that is (1) sized and shaped to receive an integrated carriage and attachment, (2) sized and shaped to receive a non-integrated carriage, (3) sized and shaped to receive a non-integrated attachment, or (4) sized and shaped to receive a non-integrated carriage and a non-integrated attachment. Preferably, the two stage mast  45  is oriented in a substantially vertical position to facilitate transferring some or all of the weight of the second stage  65  and of the attachment  70  to the cross member  55 . Optionally, the mast receiving formation  30 , the attachment receiving formation  35 , or both, may be shaped, sized and located such that the two stage mast  45  may be substantially vertical without some or all of the weight of one or both of the second stage  65  and the attachment  70  creating stress, and thus tension, on the lift chains. 
         [0021]    When a mast-hanger, such as mast-hanger  10 , is used with a lift truck equipped with an attachment that does not permit the operator to fully lower the attachment to the ground, such mast-hanger provides a location at which the mast, the carriage, the attachment, or any combination thereof, including all three, may be placed to remove all, substantially all, or a portion of the tension from the lift chains. When all, substantially all, or a portion of the tension is removed from the lift chains, such lift chains may have an extended life compared to lift chains of an equivalent lift truck equipped with the same attachment, but without a mast-hanger. For example, lift chain life may be extended because the relaxed tension may permit lubrication oil to flow into the links better than if such tension were not removed from the lift chains. As another example, lift chain life may be extended because relaxing or removing tensions from such lift chains reduces internal stresses within such lift chains. 
         [0022]    Another device for facilitating lift chain tension relief is illustrated in  FIGS. 4 and 5 . Details of the lift truck  150  and mast  145  are omitted for clarity Likewise, no attachment is illustrated on the mast  145 . The mast-hanger  100  includes two supports comprising a first beam  115  and a second beam  120  that are supported by a first stage  146  of a multi-stage mast  145 . In the illustrated example, the multi-stage mast  145  is a two-stage mast, however more than two stages may be included, or the mast may not be a multi-stage mast and only one stage may be included. Beams  115  and  120  are supported by beam supports  125  and  130 , respectively, such that beams  115  and  120  are moveable with respect to the first stage of the multi-stage mast  145 . In the illustrated example, beams  115  and  120  slide with respect to beam supports  125  and  130 , however beams  115  and  120  may rotate or pivot with respect to beam supports  125  and  130 , or may otherwise be suitably configured for movement with respect to the first stage  146  of the multi-stage mast  145 . 
         [0023]    Beams  115  and  120  may be manually moveable, or may be moveable via an automated device, such as hydraulic extension cylinders  135 , an electric linear actuator, an electric motor, or other suitable motive source. Two supports are illustrated, but some embodiments include only one support and other embodiments include three or four supports. 
         [0024]    Mast hanger  100  optionally includes one or more signal devices, such as lights  805  and  815  ( FIG. 8 ). A signal device may be mounted on a portion of a lift truck such as an operator compartment, or other suitable location where the signal device may be readily viewed by the lift truck operator. In other embodiments, the signal device may include a hand-held electronic device that wirelessly communicates with a mast hanger and provides operational information regarding the mast hanger via a screen, such as by displaying printed information or graphic information. 
         [0025]    The signal device communicates with the mast hanger, such as mast hanger  100 , and is configured to provide information regarding the operational status of the mast hanger to someone viewing the signal device. In the embodiment illustrated in  FIGS. 4 and 5 , the mast hanger  100  is associated with one or more position sensors, such as optical sensors, an encoder associated with the motive source, one or more Hall-effect sensors and one or more magnets, or other suitable position sensor for providing a signal indicative of the position of the beams  115  and  120 . One signal indicates that the beams  115  and  120  are in a fully retracted, or non-mast receiving, position (illustrated in  FIG. 4 ) where the beams  115  and  120  do not interfere with lowering the second stage  155  of the mast  145 . Another signal indicates that the beams  115  and  120  are in a fully extended, or mast receiving, position (illustrated in  FIG. 5 ) where the beams  115  and  120  inhibit lowering the second stage  155  of the mast  145 . 
         [0026]    Additional sensors that detect the position of the mast  145 , an attachment connected to the mast, or both, optionally communicate with the signal device. By knowing the position of the mast  145 , an attachment, or both, the signal device may indicate to the operator when a mast hanger receives the mast  145 , an attachment, or both and provide a signal to inform the operator that the mast  145  should not be lowered any further. Optionally, an indication that a mast hanger receives the mast  145 , an attachment, or both may be communicated to a processor on-board a lift truck and the processor may inhibit or prevent the operator from further lowering the mast  145 , an attachment, or both. Inhibiting or preventing further lowering of the mast  145 , an attachment, or both once received by a mast hanger may prevent the lift chains from becoming excessively slack which may cause the lift chains to become damaged or move out of alignment, or may cause unwanted stress from a sudden impact on the chains when the mast  145 , an attachment, or both are lifted from the mast hanger. 
         [0027]    Optionally, a strain gauge or other suitable weight bearing determination device may be associated with the beams  115  and  120  to provide an additional signal that the beams  115  and  120  are bearing at least a portion of the weight of the second stage  155  of the mast  145  and of any attachment and load connected to the mast  145 . When an optional weight bearing determination device is included, an illuminated light or other suitable indicator that indicates that the beams  115  and  120  are at the fully extended position may only be illuminated if the beams  115  and  120  are at the fully extended position and are bearing weight, or there may be one indicator, such as an illuminated light, that indicates that the beams  115  and  120  are at the fully extended position and another indicator, such as an illuminated light, that indicates that the beams  115  and  120  are bearing weight. 
         [0028]    Optionally, a shock absorber, such as an impact pad, damper or other suitable device for absorbing some of the shock resulting from contacting the mast  145 , an attachment, or both with the beams  115  and  120  may be included. For example, a shock absorber  122  ( FIG. 4 ) may be provided on a top surface of beams  115  and  120 . Shock absorber  122  may be a pad of resilient material, such as natural rubber, soft plastic, or other suitable material, that is affixed to the beams  115  and  120 ; or shock absorber  122  may include dampening devices such as springs, resilient absorbers or other suitable devices interposed between a contact plate and the beam  115  or  120  Likewise, a shock absorber  122 , or other suitable device, may be located on the top side of pocket  33 , sloped shelf  36 , or both ( FIG. 1 ). 
         [0029]      FIG. 6  illustrates a flowchart for a method of facilitating lift chain tension relief. At step  600 , a lift truck operator raises a second stage of a multi-stage mast and an attachment above the position of a mast-hanger to an initial position. For example, an initial position may be any position above pockets  33  ( FIG. 1 ) or the beams  115  and  120  ( FIG. 4 ), but is preferably a position that is 5 cm to 25 cm above the pockets  33  or the beams  115  and  120 . Optional step  605  involves moving the mast-hanger into a mast receiving position. Step  605  is optional for mast-hangers that may be maintained in a mast receiving position such as mast-hanger  10 , for example. At step  610 , the lift truck operator lowers at least the second stage of a multi-stage mast and optionally an attachment onto the mast hanger. At step  615 , the lift truck operator continues to apply a lower command to the mast to relieve at least some of the tension from the lift chains as the weight of the attachment and at least the second stage of the multi-stage mast are transferred to the first stage of the multi-stage mast via the mast-hanger. In other words, the attachment does not contact the ground at step  615 . 
         [0030]    With reference to  FIGS. 7 and 8 , an exemplary process for operating a mast hanger that includes beams  115  and  120  is described. With the engine of a lift truck running, an operator activates the park brake at step  700 . The operator then manipulates key switch  800  to the “on” position to activate the mast hanger system at step  705 . A processor associated with the mast hanger system detects the activation of the park brake, and switches blue light  805  on at step  710  to indicate that the mast hanger system is active. If the processor does not detect that the park brake has been activated, the mast hanger system may prompt the operator to activate the park brake, for example, by flashing blue light  805 . Preferably, any time there is an error with operation of the mast hanger system detected by the processor, the blue light  805  is flashed. The processor activates a park brake lock at step  715  to prevent disengagement of the park brake while the mast hanger system is active. 
         [0031]    At step  720  the operator moves an attachment connected to the mast  145  into an initial position, for example, the operator may move a spreader for moving cargo containers to a position that is in the range of 5 cm to 25 cm above the beams  115  and  120 , and preferably approximately 12 cm, and at step  725  the processor detects when the attachment is in an initial position by receiving input from a proximity switch or other suitable sensor positioned and configured to send a signal when the attachment is in the initial position. Optionally, the processor may cause the attachment to move into an initial position and may receive information from a proximity switch or other suitable sensor associated with the mast  145  to indicate when the attachment is in the initial position in response to receiving a signal, for example from a move to position switch (not illustrated) manipulated by the operator, from the extend switch  810 , or from another suitable signal source. 
         [0032]    At step  730  the processor activates a lowering interrupt function that inhibits or prevents the operator from lowering the attachment, and enables the extend switch  810 . At step  735  the operator activates the extend switch  810  and the processor activates an automated device to extend the beams  115  and  120  to their extended positions. Optionally, the processor may automatically activate a lowering interrupt function and cause the beams  115  and  120  to extend in response to receiving a signal that the attachment is in an initial position above the beams  115  and  120 , in response to receiving a signal from the extend switch  810 , or in response to another suitable signal. 
         [0033]    At step  740 , the processor determines whether the beams  115  and  120  are at the retracted position, for example, via signals sent from a proximity switch, Hall effect sensor, or other suitable sensor, and if not, activates a reduced lowering speed function that limits the speed at which an attachment may be lowered. At step  745 , the processor determines whether the beams  115  and  120  are at their extended positions, for example, via signals sent from a proximity switch, Hall effect sensor, or other suitable sensor, and if so, disables the extend switch  810  and deactivates the lowering interrupt function. At step  750 , the operator lowers the attachment until the attachment, the mast  145 , or both, contact the beams  115  and  120 . Optionally, the processor may automatically activate a reduced lowering speed, deactivate the lowering interrupt function, and lower the attachment until the attachment, the mast  145 , or both, contact the beams  115  and  120  in response to determining that the beams  115  and  120  are at their extended positions, or in response to another suitable signal. 
         [0034]    Contact of the attachment, the mast  145 , or both, with the beams  115  and  120  is detected at step  755 , for example, via signals sent from a proximity switch, strain gauge, or other suitable sensor, and the processor activates the lowering interrupt function and an indicator, such as green light  815 , to indicate to the operator that the attachment, the mast  145 , or both are in position on the beams  115  and  120 . The processor also deactivates the retract switch  820 . 
         [0035]    To disengage the mast hanger system, the operator lifts the attachment, the mast  145 , or both from the beams  115  and  120  at step  760 . At step  765 , the processor detects that the attachment, the mast  145 , or both are no longer supported by the beams  115  and  120 , for example, via signals sent from a proximity switch, strain gauge, or other suitable sensor, and enables the retract switch  820 . The processor also disables the lowering interrupt function and turns the green light  815  off, thus indicating to the operator that the attachment, the mast  145 , or both are no longer supported by the beams  115  and  120 . The operator manipulates the retract switch  820  at step  770  and the beams  115  and  120  are moved to their retracted positions. Optionally, the processor may lift the attachment, the mast  145 , or both from the beams  115  and  120 , detect that the attachment, the mast  145 , or both are no longer supported by the beams  115  and  120 , disable the lowering interrupt function, turn the green light  815  off, and move the beams  115  and  120  to their retracted positions in response to receiving a signal from the retract switch  820 , or from another suitable signal source. 
         [0036]    At step  775 , the processor detects whether the beams  115  and  120  are at their extended positions, for example, via signals sent from a proximity switch, hall effect sensor, or other suitable sensor, and if not, enables the extend switch  810  and the lowering interrupt function. At step  780 , the processor detects whether the beams  115  and  120  are at their retracted positions, for example, via signals sent from a proximity switch, hall effect sensor, or other suitable sensor, and if so, deactivates the reduced lowering speed function, deactivates the lowering interrupt function, enables the extend switch  810 , preferably only if the attachment, the mast  145 , or both are in an initial position above the beams  115  and  120 , and disables the retract switch  820 . 
         [0037]    The operator deactivates the mast hanger system at step  785  by manipulating the key switch  800  to the off position. At step  790 , the processor deactivates the blue light  805  to indicate to the operator that the mast hanger system is deactivated and deactivates the park brake lock. 
         [0038]    While the above has been described as a series of steps, the aggregation and order of the described operations is not important, and various operations may be combined or omitted.