Abstract:
A load balancing hoist constructed to combine the power module and the travel module of the hoist into a single unit to substantially reduce the cost and the length of the hoist without effecting its operation and application.

Description:
FIELD OF THE INVENTION 
   The present invention relates to a load balancer and more particularly to a pneumatically operated load balancing hoist. 
   DESCRIPTION OF THE PRIOR ART 
   Fluid operated hoists which include means for balancing the load while the load is being raised, lowered, or moved from one position to another have been in use for a number of years. Such hoists are in common use for supporting loads such as workpieces or tools that have to be positioned relative to a work operation where the loads are too heavy to be conveniently manipulated by hand at all or for any extended period of time. 
   An early example of such a load balancing hoist can be found in U.S. Pat. No. 2,500,879 to C. D. P. Smallpiece. That patent illustrates a pneumatically operated hoist in which balancing is achieved by moving a piston within a housing to move a pulley through a piston rod to raise and lower a hoisting cable. A manually operated control valve regulates the pressure applied to the piston to achieve the balancing effect for the hoist as the workload is manipulated. 
   U.S. Pat. Nos. 3,669,411 and 3,675,899 both issued to McKendrick disclose balancers similar in construction to the Smallpiece patent. These patents are directed to the control circuit for controlling operation of the balancer. 
   SUMMARY OF THE INVENTION 
   The present invention provides a load balancing hoist that is substantially less costly to produce than load balancing hoist of the prior art. Such prior art hoists are commonly constructed as shown in  FIG. 1  accompanying this description and include a power module having as a part thereof a pneumatically actuated piston and piston rod assembly which moves a moveable pulley in a travel module toward and away from a fixed pulley to raise and lower the cable carrying a load. The distance the travel module is permitted to move determines the length that the cable can be extended from the hoist. 
   As will be apparent as the description of the balancing hoist of the present invention proceeds the power module and the travel module of prior art devices has been combined into a single unit. The piston rod of the prior art construction has been eliminated and the result is a compact load balancing hoist that is less costly to produce than those of the prior art without sacrifice to its operation or application. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A preferred embodiment of the improved load balancing hoist of the present invention is illustrated in the following drawings in which; 
       FIG. 1  is a longitudinal cross sectional view illustrating a load balancing hoist constructed in the manner shown in the prior art; 
       FIG. 2  is a longitudinal cross sectional view of a load balancing hoist of the present invention; 
       FIG. 3  is a transverse cross sectional view of the hoist shown in  FIG. 2  taken substantially at line  3 - 3  of  FIG. 2 ; and 
       FIG. 4  is a transverse cross sectional view similar to  FIG. 3  but taken substantially along line  4 - 4  of  FIG. 2 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  illustrates a load balancing hoist constructed in accordance with the prior art. The hoist  10  shown in  FIG. 1  is constructed substantially like the hoist shown in U.S. Pat. No. 3,669,411. A cable  12  extends from the hoist  10  to support a load (not shown) at the end of the cable  12 . 
   The hoist  10  includes a housing  14  having one end closed by a front end cap  16  and the other end closed by a rear cap  17  to define a cylindrical chamber  18 . A dual piston assembly  20  is supported for movement axially within the chamber  18  and is comprised of a pressure piston  22  and a support piston  24  axially spaced and connected to each other by a tie rod  26  so as to be movable in the chamber  18  as a unit. A pulley  28  is rotatably mounted to the support piston  24  and a pulley  30  is rotatably fixed to the housing  14  within the chamber  18  such that movement of the piston assembly  20  causes the pulley  28  to move toward and away from the pulley  30 . 
   One end of the cable  12  is anchored to the housing  14  within the chamber  18  and extends over the pulleys  28  and  30  and from the housing  18  through an opening  32  so that movement of the pulley  28  toward and away from the pulley  30  within the chamber  18  causes the cable  12  to extend from and to retract into the housing  14  through the opening  32 . 
   A fluid pressure chamber  34  is formed in one end of the chamber  18  and fluid under pressure is directed into and exhausted from the pressure chamber  34  to cause the pressure piston  22  to move in the chamber  18  causing the pulley  28  to move toward and away from the pulley  30  to extend, retract, and balance the load carried by the cable  12 . 
   The piston assembly  20  and the portion of the chamber  18  utilized by the piston assembly  20  as the hoist  10  is being used is considered to be the “power module” of the hoist  10  while the pulley  28  and the portion of the chamber  18  occupied by the pulley  28  as it is moving through the chamber  18  is considered to be the “travel module” of the hoist. 
   What has been described to now is conventional in the prior art and forms no part of the present invention. A hoist will now be described which is a considerable improvement over the prior art. The hoist of the present invention, which will become much more apparent as the description proceeds, combines the power module and the travel module into a single unit thus resulting in a less costly hoist requiring less chamber length to achieve the same length of travel for the cable than in prior art devices and requiring less parts and being much simpler in construction and less costly to produce than prior art hoists. 
   As can best be seen in  FIGS. 2-4  the hoist  110  of the present invention includes a substantially cylindrical housing  112  closed at each end by end caps  114  and  116  to from a substantially cylindrical chamber  118 . The caps  114  and  116  are provided with chain link connectors  120  and  122  respectively which are adapted to be mounted to a rail or the like (not shown) to support the hoist  110  in the workplace. 
   A piston  124  is axially slidably mounted within the chamber  118  and is provided with spaced seal rings  126  and  128  to seal the chamber from fluid communication across the piston  124 . The piston  124  is provided with removed portion  130  on the side of the piston  124  facing the end cap  116  and a pulley  132  is rotatably mounted within the portion  130  of the piston  124  so that the piston  124  and the pulley  132  travel together in the chamber  118 . 
   A second pulley  134  is mounted in a removed portion  136  of the end cap  116  to be fixed to the end cap  116  but to rotate about an axis parallel to and substantially aligned with the axis of rotation of the pulley  132 . One end  138  of a cable  140  is anchored to the end cap  116  within the housing  112 . The cable  140  extends over the pulleys  132  and  136  and exteriorly of the hoist  110  through the end cap  116 . A seal  141  is provided in the end cap  116  to prevent a pressure leak where the cable  140  extends though the end cap  116 . 
   As the piston  124  moves axially in the chamber  118  toward and away from the pulley  134  the cable  140  is extended and retracted from the housing  112 . As can best be seen in  FIGS. 3 and 4  the pulleys  132  and  134  are constructed to permit several turns of the cable  140  to be carried by the pulleys  132  and  134  and the length of cable which can be extended from the hoist is determined by the number of turns of the cable  140  provided by the pulleys  132 ,  134 . 
   The end cap  116  is provided with a connector  142  that provides communication (not shown) through the end cap  116  to the chamber  118  between the piston  124  and the end cap  116 . The connector  142  is connected to a source  144  of fluid pressure, preferably pneumatic pressure, though a valve  146 . The valve  146  is constructed to selectively provide pressure from the source  144  or to exhaust as shown at  147 . 
   The end cap  114  is provided with a connector  148  that provides communication through a passage  150  in the end cap  114  to the chamber  118  between the piston  124  and the end cap  114 . The connector  148  is connected to a source  152  of fluid pressure, preferably pneumatic pressure, though a valve  154 . The valve  154  is constructed to selectively provide pressure from the source  152  or to exhaust as shown at  156 . 
   It should be apparent that selectively operating the valves  146  and  154  the piston  124  can be moved axially within the chamber  118  to extend and retract the cable  140  and to maintain the load (not shown) on the end of the cable  140  in the desired position. Regulating the pressure against each side of the piston  124  can act to balance the load so that even a heavy load can be moved by hand with minimum effort. 
   Also it should be apparent that other controls than those illustrated can be utilized to achieve the desired manipulation of the load in the load balancing hoist of the present invention. The controls are not a part of the present invention. Although pneumatic pressure has been disclosed as the force used to move and to balance the piston  124 , other forms of fluid pressure such as hydraulic pressure could be used as well. 
   The construction of the present invention provides a load balancing hoist that has combined the power module and the travel module found in prior art constructions into a single unit. This is accomplished by mounting one of the pulleys that carries the cable to a position within the end cap and the other pulley within and to the piston. This substantially reduces the necessary length of the hoist and substantially reduces the cost of manufacturing a hoist of this type by reducing the number of necessary parts. 
   It should also be apparent that although a preferred embodiment of the load balancing hoist of the present invention has been disclosed changes and modifications can be mad to the disclosed embodiment without departing from the spirit of the invention or the scope of the appended claims.