Abstract:
A gas cylinder lifting system is useful for loading and unloading heavy tanks of gases onto and off of a welding power supply running gear. The gas cylinder lifting system comprises one or more sliders that are constrained for vertical reciprocation on a frame mounted to the running gear. The slider includes a pan for supporting a gas cylinder. A crank lever is pivotally mounted to the frame by a pivot pin, and a linkage is pivotally connected between the crank lever and the slider. The linkage has a crook in it. Pivoting the crank lever to a first angular position lowers a slider and places the linkage crook remote from the pivot pin. Rotating the crank lever to a second angular position raises the slider and places the linkage crook adjacent the pivot pin. The crank lever and linkage cooperate to place the gas cylinder lifting system in an over-center self-locked condition when the crank lever is in its second angular position. A spring-loaded latch may be installed on the frame that positively maintains the crank lever at its second angular position but that is manually operable to enable the crank lever to rotate to its first angular position.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention pertains to lifting devices and more particularly to apparatus for raising heavy objects a short distance above a horizontal surface. 
     2. Description of the Prior Art 
     It is a common practice in the arc welding industry to mount a welding power supply to a running gear. The running gear enables the welding power supply to be transported with ease to different jobs in an area. The running gears are normally steerable, which aids in maneuvering them to the desired locations. 
     It is further well known to carry one or more large cylinders of inert arc-shielding gases on the running gears. The gas cylinders are very heavy, often weighing as much as 180 pounds. The gas inside the cylinders is under very high pressure, as, for example, 2,000 pounds per square inch. At the top of the cylinder is a valve, which is protected by a removable cover. The gas cylinders are normally supported on a sturdy horizontal pan on the back end of the running gear. The pan is located a few inches above the floor. In that manner, the welding power supply and the gas cylinders are transportable together by the running gear. 
     It has long been a major problem to load the gas cylinders onto and unload them from the running gear pan. Overhead cranes are rarely available at the cylinder storage area. Consequently, the usual loading and unloading method has been to manually lift the cylinders. A person hugs a cylinder, wrapping his arms around it, and lifts it by using his back and/or legs. Another prior solution has been to tip the cylinder away from the running gear pan such that the cylinder bottom surface is in contact with the edge of the pan. The cylinder is then tilted to the upright position, partially supported on the pan, and the cylinder is slid fully onto the pan. 
     Both prior solutions are far from satisfactory. Direct lifting has the potential for causing serious injury to the person. Tilting the cylinder presents the risk of the cylinder slipping and striking a fixed structure with the valve cover or the valve itself. Damage to the valve creates a danger because of the high gas pressure inside the cylinder. 
     In a few situations, it may be possible to tip the running gear such that the edge of the pan is on or close to the floor, and then tip and slide the cylinder up onto the pan. However, that solution is impractical for the great majority of cases. 
     Thus, a need exists for a way to safely load gas cylinders onto and unload them from welding power supply running gears. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, a gas cylinder lifting system is provided that lifts and lowers heavy objects in a safe and easy manner. This is accomplished by apparatus that includes a self-locking slider-crank mechanism. 
     The slider-crank mechanism comprises a slider that is constrained to reciprocate vertically within a frame. The slider includes a pan that can support a heavy object. A crank lever is rotatably connected to the frame. A linkage is pivotally connected between the crank lever and the slider. By manually rotating the crank lever, the slider undergoes vertical linear movement. Thus, oscillating the crank lever causes the slider to raise and lower along the frame. 
     The gas cylinder lifting system is designed such that when the crank lever is at a first angular position the slider pan is close to a horizontal surface. A heavy object can then be moved from the horizontal surface onto the slider pan. The crank lever is rotated to a second angular position, thereby raising the slider and object to a raised location above the horizontal surface. 
     It is a feature of the present invention that the gas cylinder lifting system is in an over-center self-locking condition when the crank lever is in its second angular position and the slider and object are at their raised location. The over-center self-locking condition is achieved by forming the linkage with two legs that join each other at an angle. When the crank lever is in its second angular position, the junction of the linkage legs is adjacent the pivotal connection between the crank lever and the frame, with the linkage junction and the connection between the linkage and the crank lever lying on opposite sides of the connection between the crank lever and the frame. In that situation, the weight of the object does not cause the slider to lower or the crank lever to rotate. On the contrary, the weight of the object actually serves to more firmly hold the crank lever in its second angular position and thus maintain the slider and object at their raised location. Only by intentionally rotating the crank lever back toward its first angular position can the slider be lowered from its raised location. 
     According to another aspect of the invention, a stop is employed that positively maintains the slider and object at their raised location. The stop comprises a spring-loaded latch installed on the top of the frame and in the path of the crank lever. As the crank lever is rotated toward its second angular position, an end of the crank lever contacts the latch and cams it out of the crank lever path. When the crank lever is at its second angular position, it has passed out of contact with the latch. The spring then pivots the latch back into the path of the crank lever. Reverse rotation of the crank lever toward its first angular position is positively prevented by the latch until a person intentionally pivots the latch out of the crank lever path. 
     The method and apparatus of the invention, using a slider-crank mechanism, thus enables heavy objects to be raised and lowered with minimum effort applied to the crank lever. The invention includes a self-locking feature that keeps the slider and object at a raised location without maintaining any manual force on the crank lever. 
     Other advantages, benefits, and features of the present invention will become apparent to those skilled in the art upon reading the detailed description of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a typical welding power supply and running gear that advantageously include the gas cylinder lifting system of the present invention. 
     FIG. 2 is a side view of the gas cylinder lifting system of the present invention. 
     FIG. 3 is a partially broken front view of the gas cylinder lifting system of the present invention. 
     FIG. 4 is a partially broken top view on an enlarged scale of the gas cylinder lifting system of the present invention. 
     FIG. 5 is a partial front view of a modified gas cylinder lifting system that includes a positive stop. 
     FIG. 6 is a view taken along line 6--6 of FIG. 5. 
     FIG. 7 is a cross sectional view on an enlarged scale taken along line 7--7 of FIG. 6. 
     FIG. 8 is a view similar to FIG. 5, but showing the crank lever in contact with the stop. 
     FIG. 9 is a view similar to FIG. 8, but showing the stop in position to positively maintain the crank lever at its second angular position. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Although the disclosure hereof is detailed and exact to enable those skilled in the art to practice the invention, the physical embodiments herein disclosed merely exemplify the invention, which may be embodied in other specific structure. The scope of the invention is defined in the claims appended hereto. 
     Referring to FIG. 1, a running gear 1 for a welding power supply 3 is illustrated. The particular running gear 1 and welding power supply 3 shown are merely representative of a wide variety of such equipment that is currently in widespread use. The welding power supply can be of any size and shape that suits the particular welding system with which it is used. Similarly, the running gear is designed to fit a particular welding power system. The running gear enables the heavy welding power supply to be transported between job sites with ease. Typically, the running gear comprises a front steering unit 5 that is attached to one end of the welding power supply and a fixed-wheel back unit 7 that is attached to the other end of the welding power supply. 
     In accordance with the present invention, the back unit 7 of the running gear 1 includes a gas cylinder lifting system 11 that enables heavy gas cylinders 9 to be easily loaded and unloaded from the running gear. Looking also at the FIGS. 2-4, the running gear back unit comprises a pair of spaced beams 12 that are mounted to and extend horizontally from the welding power supply 3. The beams 12 include shims 19 that support an axle 21. Rotatably supported on the axle 21 are wheels 23 that cooperate with the running gear front unit 5 to roll the welding power supply along a floor 25. 
     By way of example, and as best shown in FIGS. 3 and 4, the gas cylinder lifting system 11 comprises two slider-crank mechanisms 33, 33A mounted to a vertical frame 17. However, it will be understood that the gas cylinder lifting system may consist of only a single slider-crank mechanism 33, if desired. The vertical frame 17 has a pair of vertical outside guide channels 51 and a bottom end that is secured to the beams 12 of the running gear back unit 7. Each outside guide channel 51 has an inside leg 49 that is fabricated with a pair of vertically spaced slots 50. The vertical frame also has a center channel 57 with side legs 55. Each side leg 55 of the center channel 57 has two slots 52 that correspond to the slots 50 in the outside guide channels. To provide support for the upper end of the vertical frame 17, a tie bar 27 extends between and is attached to, as by screws 31, a top horizontal angle 3 of the vertical frame and the welding power supply 3. 
     The two slider-crank mechanisms 33, 33A have identical components, but those components are arranged symmetrically about a central vertical plane 34 passing through the welding power supply 3 and the vertical frame 17. Looking first at the slider-crank mechanism 33, it comprises a slider 36 that is constrained for vertical reciprocation within the vertical frame 17. In turn, the slider 36 comprises a horizontal pan 35 and a vertically extending plate 37. Preferably, gussets 39 are used to help support the pan 35 on the vertical plate 37. The pan 35, vertical plate 37, and gussets 39 may be lined with a liner 40 of synthetic material. 
     In the illustrated construction, the middle legs 41 of two strong support bars 43 are welded or otherwise secured to the vertical plate 37 of the slider 36. Assembled to end legs 45 of the support bars 43, as by screws and nuts 44, are pairs of bushings 46 and 48. The bushings 46 are captured and ride within the corresponding slots 50 in the side leg 49 of the outside guide channel 51. The slider bushings 48 are captured and ride within corresponding slots 52 in the side leg 55 of the center channel 57. The bushings and slots cooperate to prevent horizontal motion of the slider in directions parallel to the central plane 34, that is, motion to the left and right with respect to FIG. 2. Horizontal motion of the slider 36 in directions perpendicular to the central plane, i.e., to the left and right with respect to FIG. 3, is prevented by washers 58 associated with the screws and nuts 44 and the bushings 46 and 48. In that manner, the slider is constrained against all horizontal movement relative to the vertical frame 17. On the other hand, the slider is free for vertical translation along the outside and center guide channels. In the construction illustrated, the slider-crank mechanism 33A includes a slider 36A that is constrained to the vertical frame in the same manner and using the same components as the slider 36. 
     The slider-crank mechanism 33 further includes a linkage 61 and a crank lever 63. The linkage 61 has a first leg 65 that preferably is substantially longer than a second leg 67. The first and second linkage legs 65 and 67, respectively, make an obtuse angle relative to each other to form a crook 69. The free end of the linkage first leg is pivotally connected to the vertical plate 37 of the slider 36 by a slider pin 71. 
     The crank lever 63 has a relatively long handle 73 and a relatively short leg 75. The handle 73 and the short leg 75 make an obtuse angle relative to each other. The crank lever is rotatably connected to the vertical frame 17 by a pivot pin 77 that is located at the junction of the crank lever handle and the short leg. The pivot pin 77 is supported and restrained within a vertical plate 78 that depends from the angle 32 and by leg 83 of the angle 32. The pivot pin 77 and the slider pin 71 define a generally vertical plane 72. The free end of the crank lever short leg is pivotally connected to the free end of the linkage second leg 67 by a hinge pin 80. 
     In FIG. 3, the slider-crank mechanism 33 is shown such that the slider 36 is in a lowered location at which the slider pan 35 is on the ground 25. The crank lever 63 is then at a corresponding first angular position whereat its handle 73 is approximately vertical above the pivot pin 77. In that situation, the hinge pin 80 lies between the plane 72 and central plane 34, and the hinge pin lies between the pivot pin and the slider pin 71. The crook 69 of the linkage 61 also lies between the pivot pin and the slider pin. Also, the centerline 79 of the crank lever short leg 75 is approximately coplanar with the centerline 81 of the second leg 67 of the linkage 61. 
     To actuate the slider-crank mechanism 33 and raise the slider 36 to the raised location of the slider 36A of FIG. 3, the crank lever 63 is manually rotated about the pivot pin 77 in a counterclockwise direction with respect to FIG. 3. That action rotates and raises the hinge pin 80 and thus raises the entire linkage 61 and the slider 36. The slider raises approximately the same amount as the vertical distance traveled by the hinge pin. Rotation of the crank lever continues through an angle that is somewhat less than the obtuse angle between the crank lever handle 73 and the short leg 75 until the crank lever short leg is vertical above the pivot pin. At that point, the slider has raised a maximum amount from its lowered location. The pivot pin is then between the hinge pin and the slider pin, the crook 69 of the linkage 61 is approximately horizontally aligned with the pivot pin, and the hinge pin lies close to the plane 72. A slight further counterclockwise rotation of the crank lever rotates the hinge pin 80 to the opposite side of the plane 72 as the central plane 34 and causes the linkage crook 69 to approach and finally contact the pivot pin 77. The crank lever handle 73 is approximately vertical and below the pivot pin 77. No further counterclockwise crank lever rotation is then possible, and the slider-crank mechanism is in an over-center self-locked condition. That situation is shown by the slider-crank mechanism 33A of FIG. 3. 
     When the slider-crank mechanism 33A is in the over-center self-locked condition, a vertically downward force on the slider 36A merely serves to more securely lock the slider-crank mechanism 33A in place. The only way the slider 36A can be lowered is by deliberately rotating the crank lever 63A counterclockwise with respect to FIG. 3. 
     In operation, a welder rotates the crank lever associated with the desired slider-crank mechanism, such as crank lever 63, to the position approximately as shown on the left side of FIG. 3 until the pan 35 of the slider 36 rests on the floor 25. The welder can then easily tilt and roll a gas cylinder 9 onto the pan. A chain or strap 10 (FIGS. 1 and 2) is connected. Then the welder rotates the crank lever counterclockwise with respect to FIG. 3 to raise the slider 36 and the gas cylinder. The large mechanical advantage provided by the crank lever enables even the heaviest gas cylinders to be raised with modest manual effort. The crank lever is rotated until it reaches its over-center locked condition. At that point, the slider and gas cylinder are safely in the raised location, such as is shown on the right side of FIG. 3. The welder can then transport the running gear 1 and gas cylinder together to a job site. 
     Further in accordance with the present invention, a stop can be incorporated into the gas cylinder lifting system that positively maintains a slider and object at their raised location. Turning to FIGS. 5-7, a stop 85 is composed of a latch 87 and a compression spring 89. The latch 87 is formed with a first flat section 91 and a second flat section 93. The first and second sections 91 and 93, respectively, join each other along a junction 96 at an obtuse angle of approximately 135 degrees. 
     In the preferred embodiment, the interior of the first section 91 of the latch 87 is punched to create a strip 95. The strip 95 is bent at a right angle to the plane of the first section. The junction of the strip 95 with the latch first section 91 is close to the junction 96 of the latch first section with the second section 93. There is a notch or hole 97 near the free end of the strip 95. The latch further includes a pair of legs 103 that join to the first section and extend in the direction of the strip. 
     A hole 105 is punched in the bar 27 that joins the top end of the vertical frame 17 to the welding power supply 3. The hole 105 is large enough to accept the strip 95 of the latch 87. Two small slits 107 are also punched in the bar 27. The slits 107 are sized and located relative to the hole 105 to accept the legs 103 of the latch 87 when the latch strip is inserted through the hole 105. 
     One end of the wire of the spring 89 is bent into a diametrical section 104. The spring 89 is placed over the latch strip 95 and is compressed against the underside 109 of the bar 27. The spring is turned such that the diametrical section 104 enters the notch 97 in the latch strip 95. Upon releasing the spring, it is captured between the underside 109 of the bar 27 and the strip notch 97. The spring thus acts to hold the latch 87 in a normal condition whereat the latch first section 91 lies against the top surface 110 of the bar 27. However, by manually depressing the latch second section against the force of the spring, the latch can pivot about the junction 96. 
     When the stop 85 is incorporated into the gas cylinder lifting system, a modified crank lever 114 is required. The crank lever 114 has a handle 73&#39; and a short leg 75&#39; that are substantially identical to the handle 73 and short leg 75 of the crank lever 63 previously described in conjunction with FIGS. 2-4. Further, the crank lever 114 is rotationally connected to the frame 17 with a pivot pin 77&#39; in the same manner as the connection using the pivot pin 77 of FIGS. 2-4. However, the crank lever 114 includes a handle extension 111 on the opposite side of the pivot pin 77&#39; as the handle 73&#39;. The handle extension 111 has a free end 112. 
     FIG. 5 shows the crank lever 114 at a first angular position whereat the slider, not shown in FIG. 5, is at a corresponding lowered location. To translate the slider and any object on it to a raised location, the crank lever 114 is manually rotated in a counterclockwise direction with respect to FIG. 5, thereby raising the slider, FIG. 8. As the crank lever nears its second angular position, the free end 112 of the handle extension 111 contacts the underside 115 of the first section 91 of the latch 87. Continued rotation of the crank lever causes the handle extension end 112 to cam against and pivot the latch in a clockwise direction about the junction 96 out of the path of the handle extension. When the crank lever ultimately reaches its second angular position, FIG. 9, the handle free end 112 has passed the free end 113 of the latch first section 91, and the spring 89 snaps the latch back to its normal condition of FIG. 5. In that situation, the crank lever 114 is locked against rotation back toward its first angular position. As a consequence, the slider and any object on it are positively maintained in their raised location. 
     To lower the slider, a person manually depresses the second section 93 of the latch 87 to pivot the free end 113 of the latch first section 91 above the free end 112 of the handle extension 111. The crank lever 114 is then free to rotate clockwise with respect to FIG. 9 and thereby lower the slider. In some situations, the over-center self-locking feature of the gas cylinder lifting system previously described may be eliminated, and the stop 85 may be used as the exclusive mechanism for maintaining the slider and object at their raised location. 
     In summary, the results and advantages of welding power supply running gears 1 can now be more fully realized. The gas cylinder lifting system 11 of the present invention enables welders to load heavy gas cylinders 9 onto and to unload them from a running gear with ease. This desirable result comes from using the combined features of the slider, linkage, and crank lever. The slider provides a reciprocable support for a gas cylinder. The crank lever enables the slider to be actuated with ease. Selectively rotating the crank lever causes raising and lowering of the slider and of a gas cylinder supported on the slider. The gas cylinder lifting system is designed with an over-center self-locking feature that positively prevents unintentional lowering of the slider and gas cylinder. A stop can be incorporated into the gas cylinder lifting system that cooperates with the crank lever to positively prevent lowering of the slider from its raised location. 
     It will also be recognized that in addition to the superior performance of the gas cylinder lifting system 11, its construction is of very modest cost. Consequently, owners and users of welding equipment can incorporate the invention into welding power supplies 3 and running gears 1 for only small capital outlays. 
     Thus, it is apparent that there has been provided, in accordance with the invention, a gas cylinder lifting system that fully satisfies the aims and advantages set forth above. While the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations as fall within the spirit and broad scope of the appended claims.