Abstract:
A pneumatically operated hoist system including a load support is disclosed, wherein the system is capable of sensing an overload and preventing the raising of the load support.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     This application claims the benefit of provisional patent application No. 60/702,535, filed Jul. 26, 2005. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates to lifting systems and more particularly to a system which will prevent the system to attempt to lift the load should the load exceed a predetermined amount.  
       BACKGROUND OF THE INVENTION  
       [0003]     Many industrial applications utilize air operated hoist systems to enable loads to be lifted. Air hoists are equipped with air motors which are sized to provide a specific maximum lifting capacity (i.e., ¼ Ton, ½ Ton, 1 Ton, etc.). The hoist controls typically control the vertical movement of the lifting mechanism. When in a lifting mode, the hoist will have the capability to lift up a predetermined rated lift capacity.  
         [0004]     Many applications require a tool or lifting device, suspended from the hoist to engage the load. These devices are called “End-Effectors” or “Below the Hook Tooling”. It is very common for the end-effector tooling and load to weigh less than the rated lifting capacity of the air hoist. Therefore, excess capacity remains for the hoist to lift a greater load. This can create an unsafe environment in many industrial applications.  
         [0005]     Examples of safety related issues may be: 1. Attempting to lift heavier objects than the rated capacity of the end-effector tool, which may be less than the hoist. The hoist could continue to lift and the tool be placed in an unsafe condition. A further problem may occur wherein the hoist applies a maximum lift force against a load to be lifted, where the load is too heavy for the hoist to lift. Upon removing the load from the hoist, the hoist may continue to supply the maximum lift force, causing the end-effector tool to abruptly lift upward with the maximum lift force, possibly damaging equipment, tooling, or placing the operator in an unsafe situation.  
         [0006]     2. The tool and/or load contacting an obstacle such as an adjacent shelf or a machine component. The hoist may have the lifting capacity to continue an upward movement possibly damaging equipment, tooling, or placing the operator in an unsafe situation.  
         [0007]     It is an object of the present invention to produce a pneumatically operated hoist system which is capable of sensing an overload and preventing any further flow of the supply of pressure operating fluid.  
       SUMMARY OF THE INVENTION  
       [0008]     The above object of the invention may typically be achieved by a pneumatic overload protection circuit comprising: a source of pressure fluid; pressure fluid actuated hoist including a load handling device; conduit means providing pressure fluid communication between the source of pressure fluid and the hoist; and a sensor for sensing the load imposed on the load handling device to control the flow of pressure fluid through the conduit means between the source of pressure fluid and the hoist.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]     The above object as well as other objects and advantages of the invention will become readily apparent to those skilled in the art from reading the following detailed description of a preferred embodiment of the invention in the light of the accompanying drawings in which:  
         [0010]      FIG. 1  is an enlarged fragmentary perspective view of a lifting hoist incorporating a pressure fluid overload circuit embodying the features of the present invention;  
         [0011]      FIG. 2  is a side view of the hoist illustrated in  FIG. 1 ; and  
         [0012]      FIG. 3  is a schematic illustration of the operative control circuit of the invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0013]     The following detailed description and appended drawings describe and illustrate various exemplary embodiments of the invention. The description and drawings serve to enable one skilled in the art to make and use the invention, and are not intended to limit the scope of the invention in any manner.  
         [0014]      FIGS. 1 and 2  show a lifting hoist  10  in accordance with an embodiment of the invention. The hoist  10  is typically attached to a crane that can be used to rotate the hoist  10  about a longitudinal axis, and can also move the hoist  10  in a horizontal direction. The hoist  10  includes an end-effector tooling  12  for supporting a load to be lifted. The end-effector tooling  12  may be mounted on a bracket  14  which is rotatably mounted to a backing plate  16 . The end-effector tooling  12  and the associated bracket  14  are guided through different pivotal positions by an operating ring  18  which may be grasped by an operator to facilitate rotation of the end-effector tooling  12 . The position of the bracket  14  may be fixed by a locking pin and handle  20 .  
         [0015]     A pneumatic device including two airbags  22  is disposed between an upper hoist load hook guide plate  24  and a spaced apart lower hoist hook mounting plate  26 . In a preferred embodiment, the airbags  22  have a 1¼″ diameter. Threaded fastening means  28  are employed to connect the upper ends of the airbags  22  to the upper hoist load hook guide plate  24  which in turn is secured to the backing plate  16 . The lower ends of the airbags  22  are fastened to the plate  26  by threaded fasteners  30  which also provide a communication between a source of fluid pressure and the airbags  22  through a regulator  32 . The airbags  22  are employed to vary the amount of energy required to move the plates  24  and  26  toward one another by order to vary the energy required to compress the airbags  22 . The airbags  22  may be manually adjusted to control an amount of fluid pounds per square inch (p.s.i.) to be maintained in the airbags  22 . The amount of fluid p.s.i. maintained in the airbags  22  will determine the lifting capacity of the hoist  10 .  
         [0016]     An eye bolt  36  extends through apertures formed in the hoist load hook guide plate  24  and the hoist hook mounting plate  26 . The eye bolt  36  receives the attachment means  38  which is attached to a raising/lowering device  40 . The threaded end of the eye bolt  36  is adapted to extend through an aperture in the plate  26  and receives a nut  42  attached thereto. The nut  42  contacts a lower surface of the hoist hook mounting plate  26  and limits downward movement of the hoist hook mounting plate  26 .  
         [0017]     A limit switch assembly  44  is mounted on the backing plate  16  and includes a pivotally mounted arm that is biased to contact the hoist hook mounting plate  26 . Normally the pivotally mounted arm of the limit switch assembly is in contact with the lower surface of the hoist hook mounting plate  26 .  
         [0018]     The limit switch  44  is connected to a pilot valve  46  shown in  FIG. 3 . The pilot valve  46  permits the passage of pressure fluid therethrough while the pivotal arm of the limit switch  44  is in a first position. If the arm is moved into a second position by upward movement of the mounting plate  26 , the limit switch  44  causes the pilot valve  46  to move into a second position to prevent the flow of pressure fluid therethrough. The pilot valve  46  is in fluid communication with a control valve  48 , which in turn, is in fluid communication with the raising/lowering device  40  and is in pneumatic communication with a control panel  50 . The control panel  50  may be manually operated to send an appropriate signal to raise and lower the raising/lowering device  40 . If the pilot valve  46  is positioned to permit the flow of fluid therethrough, a fluid pilot signal flows to the control valve  48  permitting the flow of fluid to the raising/lowering device  40 , thereby allowing the raising/lowering device  40  to move upwardly. Pressure fluid may be allowed to flow to atmosphere from the raising/lowering device  40  thereby causing the raising/lowering device  40  to move downwardly. However, if the pilot valve  46  is positioned to prevent the flow of pressure fluid therethrough, the fluid pilot signal does not flow to the control valve  48  and is caused to move into a second position. While in the second position, the control valve  48  prevents the flow of pressure fluid to the raising/lowering device  40 , thereby preventing the raising/lowering device  40  moving upwardly. However, pressure fluid is permitted to flow from the raising/lowering device  40  to atmosphere, thereby allowing the raising/lowering device  40  to move downwardly.  
         [0019]     The hoist load hook guide plate  24 , the load support bracket  14 , and the limit switch assembly  44  are mounted on the backing plate  16  which is slidably mounted on a pair of spaced apart vertically extending guide rails  60 . The backing plate  16  may be adjusted to any desired position between the upper and lower position. The raising/lowering device  40  may be used to adjust the position of the backing plate  16  in accordance with the operation of the control panel  50 .  
         [0020]      FIG. 3  shows a schematic illustration of the circuit for controlling the operation of the apparatus illustrated and described in  FIGS. 1 and 2 . In operation, pressure fluid is supplied from a pressure fluid source  62 . Satisfactory results have been obtained by producing dry clean air at  90  p.s.i. Pressure fluid is supplied from the source  62  to the pilot valve  46 . Pressure fluid is permitted to flow through the pilot valve  46  to the control valve  48 , thereby causing the valve to be positioned in a first position. In the first position, the control valve  48  permits the flow of pressure fluid from the main pressure fluid source  62  through the control valve  48  to the raising/lowering device  40 . Pressure fluids may also be permitted to flow from the raising/lowering device  40  to atmosphere. Accordingly, the raising/lowering device  40  is permitted to move upwardly and downwardly respectively. In the second position of the pilot valve  46  as discussed above, the flow of fluid through the pilot valve  46  is prevented, thereby causing the control valve  48  to move to a second position. In the second position, the flow of pressure fluid from the pressure fluid source  60  through the control valve  48  to the raising/lowering device  40  is prevented. Accordingly, upward movement of the hoist  10  is prevented. However, pressure fluid is permitted to flow from the raising/lowering device  40  to atmosphere permitting downward movement.  
         [0021]     The pressure regulator  32 , manually controls the amount of pressure to be maintained in the airbags  22 . Once a desired pressure is achieved in the airbags  22 , the regulator  32  prevents the flow of fluid therethrough. If it is desired to reduce the pressure in the airbags  22 , the regulator  32  can be manually operated to permit the flow of pressure fluid to exit the airbags  22  to atmosphere.  
         [0022]     In use, the crane is manually adjusted to position the hoist  10  in a desired location. The regulator  32  is manually adjusted to inflate the airbags  22  to a predetermined setting that includes the weight of the end-effector tooling  12  and the prescribed load weight to be lifted, plus 10%, for example, thereafter, the control panel  50  is manually adjusted by the operator to raise and lower the raising/lowering device  40 .  
         [0023]     To facilitate a raising of the raising/lowering device  40 , an appropriate signal from the control panel  50  causes the pressure fluid source  62  to supply pressure fluid through the pilot valve  46  and the control valve  48  to the raising/lowering device  40 , thereby causing the raising/lowering device  40  to move upwardly. The upward movement of the raising/lowering device  40  causes the eye bolt  36  and the hoist hook mounting plate  24  to move upwardly. The hoist hook mounting plate  24  applies a force against the airbags  22 . If the force applied to the airbags  22  by the hoist hook mounting plate  24  is less than or equal to the force created by the pressure fluid in the airbags  22 , the hoist load hook guide plate  24  is caused to move upwardly with the raising/lowering device  40 . Since the hoist load hook guide plate  24  is mounted to the backing plate  16 , the backing plate  16  will be caused to move upwardly along with the raising/lowering device  40 . The limit switch assembly  44 , the bracket  14 , and the end-effector tooling  12  also move upwardly along with the raising/lowering device  40 , until the signal from the control panel is terminated or the raising/lowering device  40  reaches a maximum allowed height.  
         [0024]     If the force applied to the airbags  22  by the hoist hook mounting plate  26  exceeds the force created by the pressure maintained in the airbags  22 , the airbags  22  will collapse. The collapsing of the bags  22  causes the hoist hook mounting plate  26  to move upwardly and to thereby lose contact with the arm of the limit switch  44 , which forces the pivotal arm of the switch  44  and the pilot valve  46  into a second position, wherein the flow of pressure fluid through the pilot valve  46  is prevented. The control valve  48  is thereby caused to move into a second position, wherein the flow of pressure fluid from the source  62  to the raising/lowering device  40  is prevented, and raising of the raising/lowering device  40  is prevented.  
         [0025]     To facilitate a lowering of the raising/lowering device  40 , an appropriate signal from the control panel  50  causes the raising/lowering device  40  to supply pressure fluid to the atmosphere, thereby causing the raising/lowering device  40  to move downwardly. The downward movement of the raising/lowering device  40  causes the eye bolt  36  and the hoist hook mounting plate  26  to move downwardly and apply a force against the airbags  22 . If the force applied to the airbags  22  by the hoist hook mounting plate  20  is less than or equal to the pressure in the airbags  22 , the hoist load hook guide plate  24  is caused to move downwardly with the raising/lowering device  40 . Since the hoist load hook guide plate  24  is mounted to the backing plate  16 , the backing plate  16  is also caused to move downwardly along with the raising/lowering device  40 . The limit switch assembly  44 , the bracket  14 , and the end-effector tooling  12  move downwardly along with the raising/lowering device  40  until the signal from the control panel  50  is terminated or the raising/lowering device  40  reaches a minimum allowed height.  
         [0026]     If the pressure on the airbags  22  by the hoist hook mounting plate  26  exceeds the pressure created by the pressure fluid in the airbags  22 , the airbags  22  will collapse. The collapsing of the airbags  22  causes the hoist hook mounting plate  26  to move upwardly and to thereby lose contact with the plate contact of the limit switch  44 . The loss of the contact of the plate contact of the limit switch  44  with the hoist hook mounting plate  26  causes to pilot valve  46  to move into the second position, wherein the flow of pressure fluid through the pilot valve  46  is prevented. The control valve  48  is thereby caused to move into the second position, wherein the flow of pressure fluid to the raising/lowering device  40  from the main pressure fluid source  62  is prevented. However, pressure fluid flowing from the raising/lowering device  40  is permitted to escape into atmosphere, thereby allowing the raising/lowering  40  device to move downwardly.  
         [0027]     The lifting capacity of the hoist  10  is controlled by the amount of fluid maintained in the airbags  22 . If an overload condition occurs, the raising of the raising/lowering device  40  is prevented, while the lowering of the raising/lowering device  40  is permitted. When the overload condition has been removed, the hoist  10  reverts to normal operation.  
         [0028]     From the foregoing description, one ordinarily skilled in the art can easily ascertain the essential characteristics of this invention and, without departing from the spirit and scope thereof, can make various changes and modifications to the invention to adapt it to various usages and conditions.