GB2268467A

GB2268467A - Lift.

Info

Publication number: GB2268467A
Application number: GB9314046A
Authority: GB
Inventors: Frederick George Wilson
Original assignee: Individual
Current assignee: Individual
Priority date: 1992-07-07
Filing date: 1993-07-07
Publication date: 1994-01-12
Also published as: GB9314046D0

Abstract

A lift comprises a frame having a plurality of substantially vertical columns 12 and a substantially horizontal load platform 14 guided for vertical movement by the columns. A hydraulically operated system of pulleys 16 is mounted on the frame for raising and lowering the platform. Preferably the hydraulic cylinders (20 A,B) are operated as master and slave. The lift can be used for vehicles or a loading bay. For the latter use, the lift may be tiltable and/or extensible to allow lining up with a vehicle to be loaded/unloaded (e.g. by means of rams 37, 38). <IMAGE>

Description

A LIFT This invention relates to a lift, particularly of the type which is used for vehicle maintenance or installed on warehouse floors. The invention is not, however, limited to these applications.

There are many. constructions of lift known for these purposes; for example, the scissor lift which uses beams built in the form of an "x" with hydraulic rams to raise the platform, and the kind having lifting screws or hydraulic rams at each corner of the platform.

A disadvantage of these is that excavation of the floor is required to accommodate the working parts of the lift underneath the load platform. Thus they cannot be readily moved to another location.

An object of the present invention is to provide a construction of lift which is simple, can be manufactured at low cost, and may be made as a portable unit or located by a small number of bolts to the floor.

According to the present invention a lift comprises a frame having a plurality of substantially vertical columns, a substantially horizontal load platform guided for vertical movement by the columns, and a hydraulically operated system of pulleys mounted on the frame for raising and lowering the platform.

Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a side view of a first embodiment of the invention; Figure 2 is a perspective view of the embodiment of figure 1; Figure 3 shows the hydraulically operated pulley system of figure 1; Figure 4 is a horizontal cross section of the embodiment of figure 1; Figure 5 is a perspective view of a second embodiment of the invention; Figure 6 shows the hydraulically operated pulley system of figure 5; Figure 7 is a plan view of a hydraulic mechanism for positioning the lift of figures 1 to 4 or figures 5 and 6; and Figure 8 shows and alternative positioning mechanism.

Referring first to figures 1 to 4, the lift comprises a floorstanding steel frame 10 having a square base 11 and four s.ubstantially vertical columns 12 upstanding from the four corners of the base. The two columns on the left of the frame 10 as seen in figure 1 are referred to herein as the front columns, and the other two columns as the rear columns. The front and rear columns 12 on opposite sides of the frame 10 are connected at their top ends by bridging members 13. Further bridging members, not shown, may connect the tops of the front columns and the tops of the rear columns.

A substantially horizontal load platform 14 located within the frame 10 is guided for vertical movement by the columns 12. As seen in figure 4, each column 12 is in the form of a hollow, internally greased guide which slidably accommodates a respective ear or lug 15 welded to a respective corner of the platform 14.

The platform 14 is raised and lowered in the frame 10 by two similar hydraulically operated systems of pulleys 16 arranged on opposite sides of the frame respectively. Each pulley system comprises two fixed pulleys 17 and 18 mounted in respective pulley boxes 19 atop the front and rear columns 12. A hydraulic ram 20A and 20B is mounted upright on the frame 10 alongside the front column 12. Each ram 20 has its cylinder 21 fixed to the base 11 and its piston rod 22 carries a further movable pulley 23.

A first rope or chain 24 has one end fixed to the top of the frame 10 above the movable pulley 23 and it extends down and around the pulley 23, up and over the fixed front pulley 17, and down to the near corner of the platform 14 where it is connected to the lug 15 at the lifting point 15A. A second rope or chain 25 likewise has one end fixed to the top of the frame 10 above the pulley 23 and it extends down and around the pulley 23, up and over the pulley 17, across to the rear fixed pulley 18, and down to the far corner of the platform 14 where it is connected to the corresponding lug 15.

Both rams 20A and 20B are double acting and are designed to pull using the annular side of the ram to provide the pulling power. The ram 20A is a master and the ram 20B is a slave. Thus, hydraulic pressure to operate the lift is applied to the annular side of the master ram 20A through a pipe 26 and the full bore side of the master ram 20A is connected to the annular side of the slave ram 20B through a pipe 27. A valve 28 in the pipe 26 is normally open, and a valve 29 connected across the pipes 26 and 27 is normally closed.

When hydraulic pressure is applied to the annular -side of the master ram 20A through the pipe 26 the piston rod 22 is retracted into the cylinder 21.

This pulls down the pulley 23, which in turn draws the chains or ropes 24 and 25 over the pulley 17. This raises the two corners of the platform 14 to which such chains are attached by an equal amount.

As the piston of the master fram 20A moves down in the cylinder 21 it forces oil in the full bore side of the master ram into the annular side of the slave ram 20B through the pipe 27. Thus the slave ram 20B retracts its piston rod 22 at the same time as the master ram 20A does, and raises the two corners of the platform 14 on its side of the frame 10 at the same time as the other side is raised by the master ram 20A.

When the hydraulic pressure in the pipe 26 is released, the weight of the platform 14 pulls both piston rods 22 upwards. Oil moves back from the annular side of the slave ram 20B to the full bore side of the master ram 20A. The raising and lowering of the platform 14 is controlled by a push button solenoid valve 30 which in one position connects the pipe 26 to hydraulic pressure to force oil into the annular side of the master ram 20A to raise the platform 14, and in another position releases oil from the annular side of the master ram 20A to lower the platform.

The bores of the two rams 20A and 20B are sized so that the area of the full bore side of the master ram 20A is the same as the area of the annular side of the slave ram 20B, after deducting the area of the slave ram piston rod. Thus any movement of the piston rod in the master ram 20A is exactly duplicated in magnitude and direction by a movement of the piston rod in the slave ram 20B. This ensures that, in the absence of oil leakage past the piston seal or from the cylinders, the platform 14 remains level during its raising and lowering.

In order to permit realignment of the platform 14 to compensate for such leakage, the normally open valve 28 and the normally closed valve 29 are provided.

The valve 28 is a shut-off valve, and first of all this is closed to prevent oil entering the ram 20A from the pipe 27. Next the valve 29, which is a needle valve, is opened slightly. Now, by operating the solenoid valve 30 either oil is added to the ram 20B or released from it, as appropriate to level the front edge of the platform 14. When the front edge is level the valves 28 and 29 are returned to their normal positions. Any front to rear adjustment of the platform is by adjustment of the chains 25, for which purpose adjusters (not shown) are provided in the chains 25 adjacent each rear corner of the platform 14.

Figures 5 and 6 illustrate a second embodiment of the invention. The same reference numerals have been used for the same or equivalent parts. The difference is in the arrangement of the pulley systems. In this case the rams 20A and 20B are arranged horizontally in the bridging members 13 and their piston rods 22 are connected directly to the ends of the chains 24 and 25, omitting the pulley 23. This requires a greater degree of movement of the pistons for a given movement of the platform compared to the previous embodiment, and therefore requires longer rams. However, the bridging members 13 have sufficient length for these. The single fixed pulley 17 has in this embodiment been replaced by two pulleys 17A and 17B.

Figure 1 shows the typical use environment of the lifts described above. The front of the frame 10 is placed right up next to a loading dock 31 for transfer of loads to and from a truck 32 which has backed up next to the rear of the frame 10. By appropriate control of the solenoid valve 30 the platform 14 may be brought to the level of the loading dock 31 or either the bottom deck 33 or top deck 34 of the truck.

Since it is difficult to place a long vehicle directly in line with a loading bay or lift, the front of the frame is mounted to a pivot 35 (figure 7) for movement about a substantially vertical axis, and a double acting hydraulic ram 36 connects the frame 10 to the loading dock 31 on one side of the pivot. Opening or closing the ram 36 causes the frame 10 to rotate in a small arc so that the frame can be positioned relative to a vehicle.

Alternatively, as shown in figure 8, two double acting hydraulic rams 37 and 38 are pivoted at one end to the base 11 on opposite sides of the frame 10 respectively. The other ends of the rams are pivoted to external points 39, the rams 37 and 38 making a small angle with the sides of the frame. By appropriately actuating the rams 37 and 38 the frame may be rotated and/or translated to position it relative to a vehicle, as indicated by the arrows 40 and 41. The points 39 to which the rams are connected may be fixed to the floor on which the frame is standing. Alternatively, the entire frame may stand in a shallow tray 42 with the points 39 being fixed to the sides 43 of the tray.

Then, gross movements of the frame (for example from one loading bay to another) may be achieved by moving the entire tray, while fine positioning at a particular loading bay may be achieved by the use of rams 37 and 38.

Naturally, appropriate bearings are provided under the base 11 and, where the tray 42 is used, under the tray, to reduce friction during movement of the frame and/or tray.

Claims

CLAIMS:

1. A lift comprising a frame having a plurality of substantially vertical columns, a substantially horizontal load platform guided for vertical movement by the columns, and a hydraulically operated system of pulleys mounted on the frame for raising and lowering the platform.

2. A lift as claimed in Claim 1, wherein there are two systems of pulleys acting on the platform each operated by a respective hydraulic ram, and wherein one hydraulic ram is a master and the other is a slave.

3: A lift as claimedin Claim 2, wherein external hydraulic pressure to operate the lift is applied to the annular side of the master ram, wherein the full bore side of the master ram is connected to the annular side of the slave ram, and wherein the cross-sectional area of the full bore side of the master ram is equal to the cross-sectional area of the annular side of the slave ram less the cross-sectional area of the slave ram piston rod.

4. A lift as claimed in Claim 1, 2 or 3, wherein the frame is freestanding and pivoted for movement about a substantially vertical axis, the lifting having a further hydraulic ram connecting the frame to a fixed external point such that by actuation of the further ram the frame may be rotated about the said axis to position it relative to a vehicle.

5. A lift as claimed in Claims 1, 2 or 3, wherein the frame is freestanding and wherein two hydraulic rams connect opposite sides of the frame to respective external points such that by actuation of the further rams the frame may be rotated and/or translated to position it relative to a vehicle.

6. A lift substantially as described herein with reference to the accompanying drawings.