Stabilizer For Elevatable Platform

Abstract

Apparatus in which a platform is supported by a scissors linkage on each side of the platform and upper and lower hydraulic rams are connected to each scissors linkage with means for supplying hydraulic fluid to the hydraulic rams to expand them to raise the linkage. Each lower ram is connected to an upper ram on the opposite linkage in such a way that the interconnected rams expand in unison and by equal amounts to maintain the platform level as it is being raised regardless of the loading on the platform.

Description

This invention relates to an elevator or a platform, and more particularly, the invention is an improvement in elevatable platforms of the type disclosed in U.S. Pat. No. 3,596,735. The apparatus is designed to provide a movable and elevatable scaffold for workmen who are, for example, making installations such as electrical wiring, heating duct and the like in ceiling structure. The basic apparatus includes a wheeled base which is preferably motorized, a scissors linkage on each side of the base and a platform supported on the scissors linkage. Hydraulic rams are connected to the scissors linkage in such a way that upon expansion of the hydraulic rams the scissors linkage extends to elevate the platform.

The problem to which the present invention is directed is the instability of the platform under conditions of unequal loading, that is, a heavier load on the side of one scissors linkage than on the other. Where there is a substantial load on one side of the platform, the hydraulic rams tend to raise the platform with a pronounced tilt to the platform which creates an unsafe condition for the workman. So critical is the problem that it is not unusual to find predominant signs mounted on the platform admonishing the workmen to be sure that their loads on the platform are distributed evenly.

In the apparatus of the patent, each linkage has upper and lower rams which are identical and which are mounted to the linkage in an identical fashion so that when hydraulic fluid is applied to the rams from a single source, the rams tend to expand uniformly to raise the platform. When the platform carries an unbalanced load, the rams connected to the linkage carrying the lighter side will tend to expand to a greater extent than the rams associated with the linkage on the heavier side, thereby creating the tilt in the platform.

Prior efforts to solve the problem have not been successful. For example, one attempt has been to employ a precision valve for distributing equal amounts of hydraulic fluid under equal pressures to the rams on both sides of the apparatus. The best of the valves, however, falls short of supplying absolutely identical amounts of fluid and hence do not provide a solution to the problem of platform tilt.

Interconnecting mechanical linkages restricting the platform to a level attitude at all elevated positions have not been successful, one objection being their adding to the cumbersomeness. weight and expense of the apparatus.

An objective of the present invention has been to provide a stabilizer for the platform to provide assurance of the maintenance of the platform in a horizontal attitude while it is being raised and while it is being used in its elevated position.

This objective of the invention is achieved by interconnecting each lower ram with the upper or slave ram on the opposite linkage in such a manner thaat the rams expand in unison and to the same extent. More specifically, each lower ram is a double acting piston in a cylinder with the primary supply being directed to one side of the piston. Hydraulic fluid on the other side of the piston is connected to the ram on the opposite linkage so that its expansion is a direct result of the displacement of hydraulic fluid from the cylinder of the lower ram to that of the upper ram when the lower ram is extended. Through this cross-connection of upper and lower rams, assurance is provided that regardless of the loading on the platform, there will be a uniform extension of all rams, thereby maintaining the platform at a level condition as it is elevated and while it is maintained at an elevated position.

It has been another objective of the invention to provide a system for replenishing hydraulic fluid in the interconnection between upper and lower rams. It is critically important that the volume of hydraulic fluid passing between each lower ram and its corresponding upper ram be maintained constant, for it is the constancy of the volumetric flow of hydraulic fluid which serves to maintain the level platform. Even the best of rams can be expected to leak to some extent, particularly under pressures of up to approximately 1,000 psi. To maintain the volume of fluid constant, the invention provides for a connection, from the main supply pump, to the interconnected rams through a pressure reducing valve and one-way check valves. The make up fluid is supplied at such a low pressure, e.g., 150 psi, in comparison with the operating pressure, e.g., 600-800 psi, that it has no unstabilizing effect on the system.

The several features and objectives of the invention will become more readily apparent from the following detailed description taken in conjunction with the accompanying drawings in which:

FIG. 1 is a side elevational view of an elevatable platform apparatus to which the invention is applied;

FIG. 2 is a front elevational view of the apparatus; and

FIG. 3 is a hydraulic circuit diagram illustrating the manner in which fluid is applied to the respective rams to maintain a level platform.

Referring to FIGS. 1 and 2, the elevating apparatus indicated at 10 includes a base 11, scissors linkage 12 and 13 mounted on each side of the base and a platform 14 mounted on the scissors. The base is preferably supported on a pair of rear wheels 16 and a pair of forward wheels 17. The rear wheels 16 are drivably connected to an electric motor (not shown), the operation of the electric motor being controlled from a control panel 18 mounted on the platform 14. The base also includes outrigger wheels 20 which are pivoted at 21 to the base and are connected to hydraulic rams 22 which are adapted to swing them from the operative position shown in FIGS. 1 and 2 to a raised position alongside the base. The outriggers 20 controlled from the panel 18 prevent the inadvertent tipping over of the vehicle when the platform is raised.

Each scissors linkage is formed by pivotally interconnected bars 24-29. Bars, 24, 25 are pivoted together at 30 to create a lower X-frame. Bars 26, 27 are pivoted together at 31 to form a central X-frame, and bars 28, 29 are pivoted together at 32 to form an upper X-frame. The upper ends of the lower X-frame are pivotally connected at 33 to the lower ends of the middle X-frame and the upper ends of the middle X-frame are pivotally connected at 34 to the lower ends of the upper X-frame to create a scissors or a lazy tong linkage at each side of the apparatus to which the platform is mounted.

At the lower ends of the scissors linkages, the bars 24 are pivoted at 40 to the base and the lower ends of the bars 25 are slidably mounted at 41 to the base by means of rollers secured to the lower ends of the bars 25. Similarly, at the upper ends of the linkages the upper ends of bars 29 are pivotally mounted at 43 to the platform 14 and the upper ends of the bars 28 are slidably mounted at 44 to the platform by means of rollers which are secured to the bars 28.

The platform is raised and lowered by the extension and contraction of the scissors linkages 12 and 13. Power for the operation of the linkages is derived from a pair of booster rams 47, a pair of lower secondary rams 48, 49 and a pair of upper secondary rams 50, 51. Each ram 48, 49 includes a cylinder 52 pivoted at 53 to the lower end portion of bar 24 and a rod 54 pivoted at 55 to the upper end portion of the bar 26. Similarly, each upper secondary ram 50, 51 has a cylinder 56 pivoted at its lower end 57 to the lower end portion of the bar 26 and has a rod 58 pivoted at its upper end 59 to the upper end portion of the bar 28.

Each booster ram 47 is pivotally mounted at 62 to the base and has an extendable rod 63 engageable with a socket 64 mounted on the bar 24. The booster ram 47 is only operative at the initial stage of the elevating of the platform or at the final stage of the lowering of the platform. When the platform is in a lower attitude with the rod 63 in engagement with the socket 64, the bars 24 are substantially at a horizontal attitude and the ram 47 is substantially at a vertical attitude, thereby providing the most favorable mechanical advantage for the application of the force of the ram to the bar 24 to pivot the bar with respect to its pivot axis 40 on the base 11.

When the platform is in the lower position referred to, the secondary rams have their most disadvantageous relationship with respect to the bars to which they are pivoted in that the rams lie almost parallel to the bars to which they are connected so that upon application of hydraulic pressure to extend the rams, only an extremely small component of force normal or perpendicular to the bars is applied to the bars by the rams. The utility can be seen, therefore, of the use of the booster rams to provide elevating force to the scissors linkage when the platform is in the lower position and the use of the secondary rams 48-51 to provide the greater and final extension of the scissors linkage after the booster rams have extended the scissors linkage to a condition wherein the angular relationship of the secondary rams to the linkage bars provides a more favorable force factor relationship.

A hydraulic pump 70 controllable at panel 18 is connected to all of the rams to supply the hydraulic fluid under pressures of up to 900 or 1,000 psi to extend the rams to cause the platform to raise. Lowering of the platform is effected by a metered withdrawal of the hydraulic fluid from the respective rams.

In the patented apparatus which has been generally described above, fluid was distributed to the rams from a single source via interconnected conduits. If the elevator platform 14 was heavily loaded to one side, as, for example, over the linkage 13, the secondary rams 48, 50 would, because of the reduced load on them, extend to a greater degree than the secondary rams 49, 51, causing the scissors linkage 12 to extend to a greater degree than the linkage 13, thereby causing the platform to tilt. To correct that situation, the invention employs the distribution system and ram configuration illustrated in FIG. 3. As shown in FIG. 3, a pump 70 is connected through a valve 71 operated by solenoids 72 to the rams 48 and 49. A line 75 connects the pump to the valve, a line 76 connects the valve to a common line 77 which is in turn connected to a lower port 78 in each cylinder 52.

Each ram 48, 49 is double acting and includes a piston 80 slidable within the cylinder 52 to which the rod 54 is connected. Each cylinder 52 has an upper port 81 connected to a common line 82. The upper port 81 of the ram 49 is cross-connected by a conduit 83 to the cylinder 56 of the ram 50 on the opposite linkage. Similarly, the upper port 81 of the ram 48 is cross-connected by a conduit 84 to the cylinder 56 of the ram 51 on the opposite linkage. One-way check valves 85 are located in the common conduit 82 to block flow of hydraulic fluid between the two upper ports 81.

Each upper ram 50, 51 is single acting and has a piston 86 to which the rod 58 is connected. The effective area of the piston 86 is the same as the effective area of the upper sides 88 of the piston 80 of the lower rams 48, 49. The effective area of the upper side 88 of the piston 80 is calculated by determining the area of the piston 80 and subtracting from it the area of the rod 54. The upper end of each ram 48, 49, the lower end of each ram 50, 51 and the conduits interconnecting them are filled with hydraulic fluid so that when the piston of the lower ram 48 moves, the displaced hydraulic fluid will cause the piston 86 of the ram 51 to move exactly the same distance. Similarly, when the piston 80 of the ram 49 moves, the displaced hydraulic fluid will cause the piston 86 of the ram 50 to move exactly the same amount. Therefore, if a greater load overlies the linkage 13, for example, the greater load will be felt equally by the upper ram 51 on the linkage 13 and the lower ram 48 on the linkage 12. Since the force of unequal loading of the platform is applied to rams on both linkages, the rams on both linkages will respond to that force to the same extent, thereby causing the platform supported by the linkages to maintain a horizontal attitude.

It is important to maintain the volumetric relationships of the fluids in the upper cylinders constant. Recognizing the probable loss of hydraulic fluid from each ram through leakage, the invention provides a system of supplying replenishing fluid to each of the upper rams. That replenishing fluid is supplied from the pump 70 via a replenishing circuit which includes a conduit 90 connected through a pressure reducing valve 91 connected to the common line 82 between the check valves 85. The check valves 85 permit the flow of fluid at 150 psi, for example, to the respective lines 83, 84 as the system demands, when the platform is in its lowermost position and the greater elevating pressure is not applied to the system.

While the invention has been described as involving two master rams on opposite linkages and at the lower portion of the elevator structure, the master rams being cross-connected to two upper slave rams, it should be understood that the invention admits of differing relationships provided that there is a cross-connection of master and slave rams. For example, master and slave rams on opposite linkages could be located at the lower end of the structure with a companion oppositely oriented master and slave combination at the upper portion of the apparatus. The illustrated embodiment is preferred, however, for the alternative configuration, while having the proper relationship for extending the linkages uniformly, creates a weight imbalance because the slave would normally be smaller than the master.

The invention also contemplates the use of a single master ram located on one linkage and a slave ram located on the opposite linkage. The single combination would again provide the uniform extension of the linkages, but for platforms elevated as high as contemplated by the present invention, the single ram system probably would place too much strain on the pins and other elements by which the rams are connected to the linkages, for a single combination of master and slave rams would be required to do twice the work as the double combination illustrated and described.

Claims

1. Elevator apparatus comprising,

a base,

a scissors linkage mounted on each side of said base,

a platform mounted on said scissors linkage,

upper and lower rams connected to each linkage to expand said linkages to raise said platform on application of hydraulic fluid to said rams,

means hydraulically connecting each lower ram to an upper ram on the opposite side of said linkage to drive said upper ram the same distance as

2. Elevator apparatus according to claim 1 in which said lower rams are double acting,

one end of each lower ram being hydraulically connected to the upper ram on the opposite side of said linkage to drive said upper ram with fluid

3. Elevator apparatus according to claim 2 in which each upper ram has an effective piston area identical to the piston area of said lower ram which

4. Elevator apparatus comprising,

a base,

a scissors linkage mounted on each side of said base,

a platform mounted on said scissors linkage,

upper and lower rams connected to each linkage,

each lower ram including a cylinder having a port at each end and a piston and rod slidable in said cylinder,

means hydraulically connecting the first of said ports to the upper ram on the opposite side of said linkage,

and means supplying hydraulic fluid under pressure to the second port of

5. Elevator apparatus as in claim 4 further comprising,

6. Elevator apparatus as in claim 5 in which said make up fluid is supplied at substantially lower pressure than said first mentioned fluid supplying

7. Elevator apparatus as in claim 4 in which said hydraulic fluid supplying means comprises,

a motor driven pump having an outlet,

conduits connecting said pump to said second ports,

a conduit interconnecting said first ports,

two one-way check valves in said conduit permitting flow from the center of said conduit toward said rams,

means including a pressure reducing valve connecting said pump to said conduit,

and conduits connected between check valves and rams respectively to said

8. Elevator apparatus comprising,

a base,

a scissors linkage mounted on each side of said base,

a platform mounted on said scissors linkage,

upper and lower rams connected to each linkage to expand said linkages to raise said platform on application of hydraulic fluid to said rams,

means connecting each lower ram to an upper ram on the opposite side of said linkage, said upper ram being slaved to its respective lower ram to expand said upper ram in unison with and to the same extent as said respective lower ram,

and means for supplying hydraulic fluid under pressure to said lower rams.

9. Elevator apparatus comprising,

a base,

a scissors linkage mounted on each side of said base,

a platform mounted on said scissors linkage,

upper and lower rams connected to each linkage to expand said linkages to raise said platform on application of hydraulic fluid to said rams,

means interconnecting said rams to provide one master ram on each linkage connected to a slave ram on the opposite linkage, the slave rams expanding in unison with and to the same extent as said master rams,

and means for supplying hydraulic fluid under pressure to said master rams.

10. Elevator apparatus comprising,

a base,

a scissors linkage mounted on each side of said base,

a platform mounted on said scissors linkage,

at least one master ram connected to one of said linkages and a slave ram connected to the opposite linkage,

means for supplying hydraulic fluid under pressure to the master ram,

means hydraulically interconnecting the master and slave rams to require the slave ram to extend in unison with and to the same extent as the master ram.