Abstract:
A hoist limiting system ( 15 ) comprising a frame ( 16 ), a hoist drum ( 17 ) supported by the frame and rotatable about a hoist axis (x-x), a hoist driver ( 19 ) supported by the frame and configured to rotate the hoist drum in opposite upward ( 30 ) and downward ( 31 ) directions about the hoist axis, a hoist line ( 18 ) in engagement with the hoist drum such that the hoist line winds in the upward or downward direction in response to rotation of the hoist drum, at least one gear ( 20 ) mechanically coupling the hoist driver and hoist drum and configured to rotate about a gear axis (x-x), the gear having a face ( 21 ) that rotates about the gear axis in a upward or downward direction in response to rotation of the hoist drum, a first proximity limit switch ( 26 ) supported by the frame adjacent the rotating face such that the rotating face moves relative to the proximity switch and a second proximity limit switch ( 28 ) supported by the frame adjacent the rotating face such that the rotating face moves relative to the second proximity switch, the first and second proximity switches configured to sense the presence or absence of the face and communicating with a controller ( 29 ), the first and second proximity switches, the control unit, and the hoist driver configured to prevent the hoist drum from rotating in the upward direction as a function of signals from the first and the second proximity switches and configured and arranged to prevent the hoist drum from rotating in the downward direction as a function of the signals from the first and the second proximity switches.

Description:
TECHNICAL FIELD 
   The present invention relates generally to the field of winches or hoists and, more particular, to a hoist having a system for setting and imposing an upper and lower limit of travel. 
   BACKGROUND ART 
   Because of safety issues associated with moving heavy objects, hoisting equipment often includes safety features that limit how high or how low the loading line can travel. The desire is to limit how high the load can travel so that, for example, it is not damaged or hit by the load or the load is not moved too far in one direction. Similarly, it is often desirable to limit how low the hoist can travel. Several methods or devices are known in the prior art for achieving such hoisting limits. 
   U.S. Pat. No. 7,097,155 teaches a hoist that includes a device for signaling when a preset minimum number of cable windings are left on the winding drum. The device uses an optical sensor to count the number of revolutions of the drum and the direction of rotation. An alarm is activated when only the preset minimum number of winding layers remain on the drum. Because this system requires an optical sensor that keys off of windings on a drum, it does not have application across a broad number of hoists. 
   U.S. Pat. No. 6,966,544 also keys off of windings on the drum of a hoist, but with a proximity limit switch. A first proximity limit switch is mounted on the frame adjacent to the hoist drum and it senses the presence or the absence of the hoist rope around the drum. When it senses the presence of the hoist rope around the drum at that point, it signals a control to prevent the hoist motor from further rotating the hoist drum in the wind-on direction, thereby preventing further lifting of the load. A second proximity limit switch is positioned adjacent a second point along the drum, and it signals the control to prevent the hoist motor from further rotating the hoist drum in the wind-off direction when it senses the absence of the hoist rope, thereby preventing further lowering of the load. However, this type of configuration is difficult to adjust depending on the desired limits and also requires a winding drum. 
   Paddle type or block operated limit switches utilize a mechanical actuator on the hoist that activates a switch when the hoist lifting block makes physical contact with the hoist. However, this type of switch is not usually considered adjustable. 
   A geared limit switch is one that is typically driven by the same shaft that drives the sprocket on a chain hoist or drum on a wire rope hoist. A geared limit switch operates by counting the number of revolutions of the hoist drum, and when a threshold is met a cam or gear actuates a micro-switch and power is cut. Typically there are a pair of micro-switches, one for up or one for down. However, while a geared limit switch can be fitted with different gear ratios to accommodate various lift ranges, the adjustment becomes more sensitive as the gear ratio becomes numerically higher. 
   The screw type limit switch has a fine thread shaft with a pair of nuts which travel along its length. A micro switch near each end of the threaded shaft provides the limits. While the nuts are adjusted to provide the settings, this device is limited by the length of the threaded shaft. 
   Thus, it would be beneficial to provide a limiting device for a hoist or winch that has set points that are easily adjustable and can be used with hoists having non-winding drums or sprockets. 
   DISCLOSURE OF THE INVENTION 
   With parenthetical reference to the corresponding parts, portions or surfaces of the disclosed embodiment, merely for the purposes of illustration and not by way of limitation, the present invention provides an improved hoist apparatus ( 15 ) comprising a frame ( 16 ), a hoist drum ( 17 ) supported by the frame and rotatable about a hoist axis (x-x), a hoist driver ( 19 ) supported by the frame and configured to rotate the hoist drum in opposite upward ( 30 ) and downward ( 31 ) directions about the hoist axis, a hoist line ( 18 ) in engagement with the hoist drum such that the hoist line winds in the upward or downward direction in response to rotation of the hoist drum, at least one gear ( 20 ) mechanically coupling the hoist driver and hoist drum and configured to rotate about a gear axis (x-x), the gear having a face ( 21 ) that rotates about the gear axis in a upward or downward direction in response to rotation of the hoist drum, a first proximity limit switch ( 26 ) supported by the frame adjacent the rotating face such that the rotating face moves relative to the proximity switch and a second proximity limit switch ( 28 ) supported by the frame adjacent the rotating face such that the rotating face moves relative to the second proximity switch, the first and second proximity switches configured to sense the presence or absence of the face and communicating with a controller ( 29 ), the first and second proximity switches, the control unit, and the hoist driver configured to prevent the hoist drum from rotating in the upward direction as a function of signals from the first and the second proximity switches and configured and arranged to prevent the hoist drum from rotating in the downward direction as a function of the signals from the first and the second proximity switches. 
   The rotating face may comprise a positive area ( 35 - 38 ) and a negative area ( 22 - 25 ) that rotate about the gear axis in the upward or downward direction in response to rotation of the hoist driver, the first and second proximity switches supported by the frame adjacent the rotating face such that the rotating positive and negative areas move relative to the proximity switch such that the switches sense the presence of the face when adjacent the positive area and sense the absence of the face when adjacent the negative area. The negative area may comprise multiple notches in the face. The positive and the negative areas may be positioned and aligned relative to the proximity switches such that the proximity switches provide a first sequence of signals with rotation of the face in the upward direction and the proximity switches provide a second and different sequence of signals with rotation of the face in the downward direction. 
   The hoist line may be selected from a group consisting of wire, chain and rope. The controller may be configured and adapted to set an upper limit for rotation of the hoist drum and to set a lower limit for rotation of the hoist drum. The controller may comprise a user interface ( 39 ) for adjustably setting an upper limit and a lower limit of rotation for the hoist drum. The driver may comprise a motor and a brake ( 34 ). The hoist drum may be a sprocket. 
   Accordingly, the general object of the present invention is to provide a hoist in which an upper limit of travel and a lower limit of travel may be set. 
   Another object is to provide a hoist in which the upper and lower limits are entirely adjustable. 
   Another object is to provide a hoist having limits triggered by rotation in the gear train. 
   Another object is to provide a hoist in which the upper and lower limits may be set electronically. 
   Another object is to provide a hoist which limits the upper and lower vertical travel of the loads using slots or bosses in a rotating component of the hoists gear train. 
   Another object is to provide a hoist having limit switches that are independent of the hoist&#39;s available lift. 
   These and other objects and advantages will become apparent from the foregoing and ongoing written specification, the drawings, and the appended claims. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a cross sectional view of the preferred embodiment&#39;s orientation of the hoist drum, gear and proximity switches. 
       FIG. 2  is a partial vertical sectional view of the preferred embodiment hoist. 
       FIG. 3  is an illustration of the relative orientation of the gear end face and proximity switches shown in  FIG. 1  at a first rotational position. 
       FIG. 4  is an illustration of the relative orientation of the gear end face and proximity switches shown in  FIG. 1  at a second rotational position. 
       FIG. 5  is an illustration of the relative orientation of the gear end face and proximity switches shown in  FIG. 1  at a third rotational location. 
       FIG. 6  is an illustration of the relative orientation of the gear end face and proximity switches shown in  FIG. 1  at a fourth rotational position. 
       FIG. 7  is a schematic of the electronics of the hoist shown in  FIG. 1 . 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   At the outset, it should be clearly understood that like reference numerals are intended to identify the same structural elements, portions or surfaces, consistently throughout the several drawing figures, as such elements, portions or surfaces may be further described or explained by the entire written specification, of which this detailed description is an integral part. Unless otherwise indicated, the drawings are intended to be read (e.g., cross-hatching, arrangement of parts, proportion, degree, etc.) together with the specification, and are to be considered a portion of the entire written description of this invention. As used in the following description, the terms “horizontal”, “vertical”, “left”, “right”, “up” and “down”, as well as adjectival and adverbial derivatives thereof (e.g., “horizontally”, “rightwardly”, “upwardly”, etc.), simply refer to the orientation of the illustrated structure as the particular drawing figure faces the reader. Similarly, the terms “inwardly” and “outwardly” generally refer to the orientation of a surface relative to its axis of elongation, or axis of rotation, as appropriate. 
   Referring now to the drawings and, more particularly to  FIG. 2  thereof, this invention provides an improved hoist limiting system, of which the presently preferred embodiment is generally indicated at  15 . Hoist  15  generally includes a conventional frame or housing  16 , load bearing chain  18  extending over a drum or sprocket  17 , a motor  19  for selectively rotating drum  17 , a gear train between motor  19  and drum  17 , and an AC motor brake  34 . 
   Motor  19  is a conventional motor having one or more speeds. As shown in  FIG. 7 , a standard contactor control between power supply  48  and motor  19  is used to power and control the direction of motor  19 . Up contactor and coil  46  powers motor  19  in upward direction  30 , and down contactor and coil  47  powers motor  19  in downward direction  31 . Any time there is a cut in power to motor  19 , brake  34  automatically sets. 
   Chain  18  extends over drum  17  such that it moves, with rotation of drum  17  counterclockwise or clockwise about axis x-x, in an upward  30  or downward direction  31 . In this embodiment, a chain  18  and sprocket  17  is employed, but it is contemplated that other load bearing lines may be employed, such as wire or rope, and that other types of drums may be used, such as a conventional drum around which the wire of a winch is wound-on or wound-off. Thus, the use of the term drum herein is meant to encompass and include sprockets as well as conventional rope drums. 
   Hoist  15  also includes a conventional forged gear train between drum  17  and motor  19 . The gear train couples hoist motor  19  to hoist drum  17  and transfers the torque and speed of the hoist motor  19  output to a torque and speed that is utilized to drive hoist drum  17  and raise or lower chain  18 . The output shaft of the gear train is coupled to hoist drum  17  to selectively rotate hoist drum  17  at the output torque and speed of the gear train. While a forged gear arrangement is shown, it is contemplated that other gear arrangements and ratios may be employed. For example, a billet gear arrangement may be used as an alternative. 
   Sprocket gear  20  in the gear train is connected to drum  17  and rotates with rotation of motor  19  and drum  17  in either the upward or downward direction. As shown, sprocket gear  20  rotates about axis x-x, as does drum or sprocket  17 . As shown in  FIG. 1 , gear  20  has a rightwardly facing end surface  21  which rotates with drum  17  in either the upward or downward direction. Frame  16 , hoist drum  17 , hoist chain  18 , motor brake  34 , hoist motor  19  and sprocket gear  20  are generally know components in a hoist. 
   However, hoist  15  includes a unique limiting system. The preferred embodiment of the system includes two proximity switches  26  and  28  supported by frame  16  such that their sensing ends are adjacent to the rightwardly facing and rotating surface  21  of gear  20 , as shown in  FIG. 1 . As shown in  FIG. 7 , proximity switches  26  and  28  each communicate with a controler  29 , which is a component part of the hoist&#39;s control circuit shown in  FIG. 7 , and includes a user interface  39  with set buttons  44  and  45 . 
   Proximity switches  26  and  28  are conventional and known proximity limit switches which are the type that is capable of sensing the presence or absence of an object or surface within one to two millimeters of its sensing end without touching the surface. The E57-08GU02-C model proximity limit switch manufactured by Cutler-Hammer may be used in the preferred embodiment. 
   As shown in  FIG. 1 , proximity switches  26  and  28  are mounted on frame  16  with a mounting bracket  40  in close proximity to face  21  of gear  20 . Switches  26  and  28  are each positioned adjacent face  21  at the same radius  42  from axis x-x. Thus, they each sense the same annular portion  41  of face  21  as it rotates about axis x-x. They are also positioned so that they are not at right angles to each other. In the preferred embodiment, they are 109 degrees apart relative to axis x-x. 
   Proximity switches  26  and  28  provide one of two signals to control  29 . They either provide an “on” signal, which indicates that they are sensing the presence of an object, or they provide an “off” signal, which indicates that they are sensing the absence of an object. Sequences of pairs of signals are recorded by control  29 . When the signal from either switch changes from “on” to “off”, or vice versa, a new count is recorded. 
   Face  21  in turn includes an annular portion  41  that rotates, generally at the same radius  42  from axis x-x as switches  26  and  28 , by and adjacent to switches  26  and  28 . Portion  41  has an alternating series of positive areas  35 - 38  and negative areas  22 - 25 . Annular portion  41  of face  21  and switches  26  and  28  are configured and orientated such that when each of positive areas  35 - 38  rotate by adjacent switches  26  and  28 , respectively, switches  26  and  28  register an “on” signal. Annular portion  41  of face  21  and switches  26  and  28  are also configured and orientated such that when each of negative areas  22 - 25  rotate by switches  26  and  28 , respectively, switches  26  and  28  register an “off” signal. In the preferred embodiment, face  21  is generally a planar rightwardly-facing annular surface spaced within 2 mm from the sensing ends of switches  26  and  28  and having four elongated slots  22 - 25  oriented about axis x-x at right angles to each other. The center of slots  22 - 25  are a distance  42  from axis x-x. Slots  22 - 25  form the negative area of face  21  and surfaces  35 - 38  between slots  22 - 25  provide the positive area. 
   As shown in  FIGS. 3-6 , the orientation of switches  26  and  28 , and the relative orientation of slots  22 - 25 , will result in proximity switches  26  and  28  sending a sequence of signals to control  29  as gear  20  rotates about axis x-x. As shown, the rotation of face  21  in a clockwise direction  31  correlates to drum  17  moving in a downward direction and the load bearing end of chain  18  moving away from drum  17  and hoist  15 . Alternatively, the rotation of face  21  in a counterclockwise direction  30  correlates to drum  17  moving in an upward direction and the load bearing end of chain  18  moving up or towards drum  17  and hoist  15 . Because slots  22 - 25  are orientated at right angles relative to each other, and because proximity switches  26  and  28  are not at right angles, proximity switches  26  and  28  send a different sequence of signals to control unit  29  depending on whether face  21  is moving in an upward  30  or downward  31  direction. As shown, slots  22 - 25  are not perfectly circular but have an elongated shape. Thus, the middle of the notch is formed by opposed parallel surfaces and the ends are semicircular with a radius the same or larger than the radius of the ends of switches  26  and  28 . Slots  22 - 25  are thus longer than the diameter of the sensing ends of proximity switches  26  and  28 . 
     FIGS. 3-6  show the generation of a sequence of signals from switches  26  and  28  when face  21  rotates in the counterclockwise or upward direction  30 .  FIG. 3  shows a first signal count of “on-on”, with switch  26  registering an “on” signal as it senses the presence of positive surface  38  and switch  28  registering an “on” signal as it senses the presence of positive surface  37 . As shown in  FIG. 4 , when face  21  moves in a counterclockwise direction and the leading edge of slot  22  passes in front of switch  26 , proximity switch  26  will change its signal from “on” to “off” as it senses the absence of a surface. However, at the time that proximity switch  26  sends an “off” signal, proximity switch  28  will still be sending an “on” signal because proximity switches  26  and  28  are more than 90 degrees apart, while slots  22  and  25  are only 90 degrees apart. Thus, the next count in the sequence is “off-on”. With continued rotation, as shown in  FIG. 5 , the next count in the upward direction is “off-off”. Because slot  22  is elongated and longer than the diameter of the sensing end of proximity switch  26 , switch  26  is still indicating an “off” while switch  28  changes to an “off” signal as it senses the absence of a surface with the leading edge of slot  25  passing by proximity switch  28 . As shown in  FIG. 6 , with continued rotation in a counterclockwise direction, proximity switch  26  changes to “on” with its sensing of the presence of surface  35 , while proximity switch  28  continues to sense the absence of any surface as it is aligned with the trailing end of slot  25 . Thus, the sequence of signals when drum  17  is rotating in an upward direction  30  as shown in  FIGS. 3-6  is as follows: 
   
     
       
             
           
             
             
             
           
         
             
                 
             
             
               Raising Sequence 
             
           
        
         
             
                 
               26 
               28 
             
             
                 
                 
             
             
                 
               On 
               On 
             
             
                 
               Off 
               On 
             
             
                 
               Off 
               Off 
             
             
                 
               On 
               Off 
             
             
                 
                 
             
           
        
       
     
   
   If drum  17  and face  21  are moving in the downward or clockwise direction  31 , the sequence will differ. Using  FIG. 3  as a starting point but rotating in the opposite direction, the first signal is “on-on”. However, in the clockwise direction proximity switch  26  will still be sensing the presence of surface  38  when proximity switch first senses the absence of surface  37  as the leading edge of slot  24  passes by proximity switch  28 . This will result in an “on-“off” signal. As the trailing edge of slot  24  approaches passing over proximity switch  28 , resulting in an continued “off” signal, the leading edge of slot  25  will pass by proximity switch  26 , resulting in proximity switch  26  registering the absence of surface  38 . This will result in an “off”-“off” count. Next, as slot  24  passes by proximity switch  28  such that proximity switch  28  begins to register the presence of surface  36 , proximity switch  26  will be aligned with the trailing end of slot  25 , and therefore still registering an “off” signal. Thus, at this point the sequence changes with an “off”-“on” count. The sequence indicating that drum  17  and chain  18  are moving in the downward direction  31  is shown in the following chart. 
   
     
       
             
           
             
             
             
           
         
             
                 
             
             
               Lowering Sequence 
             
           
        
         
             
                 
               26 
               28 
             
             
                 
                 
             
             
                 
               On 
               On 
             
             
                 
               On 
               Off 
             
             
                 
               Off 
               Off 
             
             
                 
               Off 
               On 
             
             
                 
                 
             
           
        
       
     
   
   Thus, because the sequence of signals over four counts will differ depending on whether the drum is moving in the upward or downward direction, system  15  is able to determine which way drum  17  and chain  18  are moving. 
   In addition, the preferred embodiment provides a check of location when the hoist is turned off and then turned back on. For example, if hoist  15  is shut-off at in “on-on” condition, control  29  will check to assure that the hoist is in that same condition when it is turned back on. However, some account for play in the gears is provided. If the reading when the hoist is turned back on has changed to “on-off”, the control knows that the drum has rotated one count down, and if control  29  registers “off-on”, the system has rotated one count up. However, if control  29  registers “off-off”, it is not able to determine whether the gears have rotated two counts up or down, and thus the hoist is immediately shut-off until re-calibrated as described below. 
   Control  29  includes a user interface  39  which allows for the hoist&#39;s upper and lower limit to be easily adjusted without reference to the total travel of the hoist or requiring mechanical adjustment of the switches. As shown in  FIG. 7 , user interface  39  includes an up-set button  44  and a down-set button  45 . User interface  39  also includes a conventional panel or remote pad for the user to control movement of the hoist up or down. Because control  29  counts sequences of signals, the upper and lower limit can be set by running the hoist between the desired upper and lower limit and using the system to count and store the number of sequence changes between those upper and lower limits, thereby calibrating the travel limits and setting a reference sequence and count for the permitted travel of chain  18 . Thus, to set the upper and lower limits, the user pushes both up-set button  44  and down-set button  45  simultaneously. This sends a signal to control  29  to both zero and temporarily inactivate the sequence counter. The hoist is then operated so that the load bearing end of chain  18 , which typically comprises a hook, is at the desired upper or lower limit. Assuming that the hook is moved to the desired upper limit, the user then pushes the up-set button  44 . This activates the sequence counter of control  29 . The user then moves the hook to the desired lower position and pushes the down-set limit button  45 . Control  29  counts and records the sequence of signals between the operator&#39;s activation of the up-set button  44  and the down-set button  45  and stores this range. 
   The operator then operates the hoist and throughout that operation control  29  keeps track of the direction and count of signals from switches  26  and  28 . If control  29  receives an aggregate upward count of signals that is greater than the selected limit when motor  19  is moving in the upward direction, control  29  sends a signal to open the hoist&#39;s contactor coil  46 , thereby disconnecting power from the motor, setting brake  34  and stopping the hoist from moving beyond the preset limit. Similarly, if control  29  receives an aggregate downward count of signals when motor  19  is moving in the downward direction that would bring the hook below the lower limit, control  29  sends a signal to open contactor coil  47 , thereby disconnecting power from the motor and setting brake  34 . Thus, the system allows for a new method of setting an upper and lower limit on the travel which is independent of the hoist&#39;s available lift and is easily and greatly adjustable within a wide range. 
   The present invention contemplates that many changes and modifications may be made. Therefore, while the presently preferred form of the hoist has been shown and described, and certain modifications discussed, persons skilled in this art will readily appreciate that various additional changes and modifications may be made without departing from the spirit of the invention, as defined and differentiated by the following claims.