Elevator assemblies generally include a support platform that vertically ascends or descends by means of a lift mechanism. Conventionally the lift mechanisms used in such assemblies include cables and pulleys, or chains and sprockets. Such lifting mechanisms are relatively cumbersome.

It is known to locate piston rod and cylinder assemblies of per se known design on each side of a beam, platform or flexible link in order to raise or lower it. Such piston rod and cylinder assemblies are controlled via a hydraulic valve system, a flow divider or a dual pump.

The piston rod and cylinder assemblies may be controlled in sequence. In such arrangements, the piston rod of one assembly is extended so that oil is forced out of the corresponding cylinder into the cylinder of the other assembly causing the piston rod of the other assembly to extend. In this way a pair of piston rod and cylinder assemblies may be controlled to extend or retract the piston rods equal distances. Such arrangements preferably operate in both directions to ensure each piston rod and cylinder assembly controls the movement of the other, and to ensure that the assemblies operate in unison when they are used to raise an uneven load.

The lifting height, to which the support platform of an elevator assembly employing two piston rod and cylinder assemblies may be raised, is dependent on the overall length of each assembly when its piston rod is

extended. If a greater lifting height is required, a relatively longer cylinder and a relatively longer piston rod may be employed. This increases the overall size of the lifting mechanism.

According to an aspect of the invention there is provided an elevator assembly comprising a support platform attached to first and second legs, and a control means, the first leg including primary and secondary length adjustable members, which members are secured together and arranged so that they are axially offset and extend in substantially opposite directions ; the second leg including second primary and secondary length adjustable members, which members are secured together and arranged so that they are axially offset and extend in substantially opposite directions; the first primary length adjustable member being operably connected to both the control means and the second secondary length adjustable member, and the second primary length adjustable member being operably connected to both the control means and the first secondary length adjustable member such that, on operation of the control means, the primary length adjustable members extend or retract causing the secondary length adjustable members to extend or retract respectively, to raise or lower the support platform.

Because the primary and second length adjustable members of each leg are offset and extendable in opposite directions, they may be aligned such that the retracted length of each leg is minimised. The retracted length will be equal to the length of either the primary or the secondary member, whichever is longer. The lifting mechanism of the elevator assembly may therefore be formed in a relatively compact manner, offering a greater lifting height with smaller retracted length than would otherwise be possible.

In preferred embodiments of the invention, each of the primary and secondary length adjustable members is a piston rod and cylinder assembly.

Such embodiments provide advantages over previously known assemblies that employ a single piston rod and cylinder assembly on each side of the support platform. This is because they permit greater lifting height of the elevator assembly without having to increase the length of the cylinders.

Other advantageous features of the invention are defined in dependent Claims 4 to 17.

According to another aspect of the invention there is provided an elevator assembly comprising a support platform attached to first and second legs, and a control means, the first leg including primary and secondary length adjustable members, which members are secured together and arranged so that they extend in substantially opposite directions; the second leg including second primary and secondary length adjustable members, which members are secured together and arranged so that they extend in substantially opposite directions; the first primary length adjustable member being operably connected to both the control means and the second secondary length adjustable member, and the second primary length adjustable member being operably connected to both the control means and the first secondary length adjustable member such that, on operation of the control means, the primary length adjustable members extend or retract causing the secondary length adjustable members to extend or retract respectively, to raise or lower the support platform.

Embodiments of the invention will now be described, by way of non- limiting examples, with reference to the accompanying drawings in which:

Figures 1 and 2 are partial schematic illustrations of an elevator assembly according to an embodiment of the invention; Figure 3 is partial schematic illustration of an elevator assembly according to another embodiment of the invention; Figures 4 and 5 show a free motion device for use in the elevator assemblies of Figures 1-3; Figures 6 and 7 show other free motion devices for use in the elevator assemblies of Figures 1-3; and Figures 8-10 shows make-up systems for use in the elevator assemblies of Figures 1-3.

An elevator 10 according to an embodiment of the invention is shown in Figure 1.

The elevator assembly 10 includes a substantially planar support platform 12 attached to first and second, generally parallel and spaced apart legs 14, 16.

The first leg 14 is formed from first primary and secondary piston rod and cylinder assemblies 20,22 having primary and secondary cylinders 24,26 and piston rods 28,30 respectively. The first primary and secondary cylinders 24,26 are secured together in an axially offset manner so that the first primary and secondary piston rods 28,30 are extendable in opposite directions.

The second leg 16 is formed from second primary and secondary piston rod and cylinder assemblies 32,34 having primary and secondary cylinder 36,38 and piston rods 40,42 respectively. The second primary and secondary cylinders 36,38 are secured together in an axially offset manner so that the

second primary and secondary piston rods 40,42 are extendable in opposite directions.

In the embodiment shown in Figure 1, the free ends 28a, 40a of the primary piston rods 28,40 are secured to the support platform 12, while the free ends 30a, 42a of the secondary piston rods 32,42 are secured relative to a support surface 44.

Each of the primary cylinders 24,36 is filled with a substantially incompressible fluid 46 such as, for example, oil. A first primary piston and seal assembly 48 is secured to the first primary piston rod 28 and is housed within the fluid 46 contained within the first primary cylinder 24.

A second primary piston and seal assembly 50 is secured to the second primary piston rod 40 and is housed within fluid 46 contained within the second primary cylinder 36.

The primary piston and seal assemblies 48,50 slidably engage an inner surface of the respective cylinder 24,36 in a sealed manner. This means that fluid 46 from the annulus A1, A2 surrounding the primary piston rod 28,40 housed in the respective primary cylinder 24,36 cannot communicate with the bore B1, B2 on the other side of the respective primary piston and seal assembly 48, 50.

In a similar manner, a first secondary piston and seal assembly 52 is secured to the first secondary piston rod 30 and is housed within the first secondary cylinder 26. The annulus Cl surrounding the first secondary piston rod 30 is filled with the same, substantially incompressible fluid 46 as the primary cylinders 24,36.

A second secondary piston and seal assembly 54 is secured to the second secondary piston rod 42 and is housed within the second secondary cylinder 38. The annulus C2 surrounding the second secondary piston rod 42 is filled with the same, substantially incompressible fluid 46 as the primary cylinders 24,36.

While the annulus C1, C2 of each of the secondary cylinders 26, 38 is filled with fluid 46, bores D1, D2 of the secondary cylinders 26, 38 are not.

Each of the secondary piston and seal assemblies 52,54 slidably engages an inner surface of a respective secondary cylinder 26, 38 in a sealed manner such that fluid 46 from the annulus C1, C2 of each of the secondary cylinders 26, 38 cannot communicate with the respective bore D1, D2.

A pump 18 is connected to the annulus end 24a, 36a of each of the primary cylinders 24,36, as shown in Figure 2.

A first connecting pipe 56 is connected between the bore end 24b of the first primary cylinder 24 and the annulus end 38a of the second secondary cylinder 38.

Similarly a second connecting pipe 58 is connected between the bore end 36b of the second primary cylinder 36 and the annulus end 26a of the first secondary cylinder 26.

The first and second connecting pipes 56,58 are filled with fluid 46. The first primary cylinder 24 is therefore in fluid communication with the second secondary cylinder 38, and the second primary cylinder 36 is in fluid communication with the first secondary cylinder 26.

In use, articles that require lifting by the elevator assembly 10 are mounted on a support surface 60 (Figure 1) of the support platform 12. A load 62 is therefore applied to the support platform 12, which in turn means that first and second load components 64,66 are applied to the first and second legs 14,16 respectively.

The first and second load components 64,66 will be equal in size if the load 62 is applied to the support platform 12 midway between the first and second legs 14,16. The load components will otherwise differ in size.

On operation of the pump 18 to raise the support platform 12, fluid pressure on the first side al, a2 (Figure 2) of each of the primary piston and seal assemblies 48,50 is increased. The increase in fluid pressure causes the fluid 46 to exert a force on the primary piston and seal assemblies 48, 50 to retract the primary piston rods 28, 40.

A proportion of the first load component 64 resists retraction of the first primary piston rod 28 and, by means of the fluid communication between the first primary cylinder 24 and the second secondary cylinder 38, a proportion of the second load component 66 also resists retraction of the first primary piston rod 28.

Similarly, a proportion of the second load component 66 resists retraction of the second primary piston rod 40 and, by means of the fluid communication between the second primary cylinder 36 and the first secondary cylinder 26, a proportion of the first load component 64 also resists retraction of the second primary piston rod 40.

A proportion of the first and second load components 64,66 is therefore applied to each of the first and second legs. By virtue of the crossed fluid

communication between the primary and secondary cylinders of the two legs 14,16, this in turn means that the first and second load components 64, 66 are distributed equally between the two legs 14,16 regardless of whether the components 64,66 are themselves equal.

When the fluid pressure increase is large enough so that the force applied to the first side al, a2 of each of the primary piston and seal assemblies 48,50 is sufficient to overcome the resistance to retraction of the respective primary piston rods 28,40, the primary piston rods 28,40 extend.

On retraction of the first primary piston rod 28, fluid 46 is forced out of the bore end 24b of the first primary cylinder 24 and, via the first connecting pipe 56, into the annulus end 38a of the second secondary cylinder 38. This increases the fluid pressure on the first side cl of the second secondary piston and seal assembly 54 such that the fluid 46 exerts a force on the second secondary piston and seal assembly 54 to retract the second secondary rod 42.

On retraction of the second primary piston rod 40, fluid 46 is forced out of the bore end 36b of the second primary cylinder 36 and, via the second connecting pipe 58, into the annulus end 26a of the first secondary cylinder 26. This increases the fluid pressure on the first side c2 of the first secondary piston and seal assembly 52 such that the fluid 46 exerts a force on the first secondary piston and seal assembly 52 to retract the first secondary piston rod 30.

In view of the fact that the same pump 18 is connected to the annulus ends 24a, 36a of the primary cylinders 24,36, the fluid pressure on the first sides al, a2 of the primary piston and seal assemblies 48,50 is increased equally

such that an equal force is applied to each of the primary piston and seal assemblies 48,50.

The length and diameter of each cylinder 24,26, 36,38 is preferably chosen such that, at a given fluid pressure, the piston rods 28, 30,40, 42 each retract by the same amount. This is achieved by ensuring that the volume of fluid, per unit length, displaced from the bore end 24b, 36b of each primary cylinder 24,26 is equal to the annulus volume, per unit length, of the annulus end 26a, 38a of the respective secondary cylinder 26,38.

Consequently, the support platform 12 is raised an equal distance by each leg 14,16 so that it can maintain its angular orientation.

In other embodiments, the lengths and diameters of the cylinders may vary, as long as the total extension of one leg 14 is the same as the total extension of the other legl6.

The pump 18 may be controlled automatically or manually to obtain a fluid pressure increase on the first sides al, a2 of the primary piston and seal assemblies 48,50 that is required to produce a particular retraction of the first and second legs 14,16.

The pressure of the fluid 46 on the first sides al, a2 of the primary piston and seal assemblies 48, 50 prevents extension of the primary piston rods 28, 40, and therefore the secondary piston rods 30,42.

On reduction of the fluid pressure, the primary piston rods 28,40 extend, thereby causing the secondary piston rods 30,42 to extend such that the platform is lowered.

The distribution of the first and second load components, together with the relative volumes of the primary and secondary cylinders and the equal force being applied to the primary piston and seal assemblies 48,50, ensures that the total extension of each leg is equal. Consequently, the support platform 12 is lowered an equal distance by each leg 14,16 so that it can maintain the same angular orientation.

While the embodiment shown in Figures 1 and 2 provides for vertical movement of the support platform 12 below a support surface 44, it is envisaged that the support platform 12 may be mounted on legs 14,16 to provide vertical movement of the support platform 12 above the support surface 44, as shown in Figure 3.

It is also envisaged that the support platform 12 may be secured to extendable"leg-type"members 14,16 to facilitate sideways movement of the support platform 12 in response to pulling and pushing actions of the leg-type members 14,16.

To compensate for situations where the support platform 12 is being lowered towards the ground, and the ground is sloped, the free ends 28a, 40a of each primary piston rod 28,40 may be secured to the support platform 12 by means of a lost motion device. This enables the support platform 12 to be lowered to lie flat on the ground.

Examples of such lost motion devices are shown in Figures 4-7.

In Figures 4a and 4b, the lost motion device comprises shoes 70 having inner recesses 72 in which the free ends 28a, 40a of the primary piston rods 28,40 are received.

On downward movement of the primary piston rods 28,40 towards the ground, lower surfaces 74 of the shoes 70 are brought into contact with the ground and thereby bring the support platform 12 into contact with the ground.

The openings to the recesses 72 include inwardly extending flanges 76 that engage outwardly extending flanges 78 provided on the free ends 28a, 40a of the primary piston rods 28,40. This means that the shoes 70 effectively hang from the free ends 28a, 40a of the primary piston rods 28,40 until the lower surfaces 74 of the shoes 70 contact the ground.

If the ground is flat, extension of the primary piston rods 28,40 is stopped when the lower surfaces 74 of the shoes 70 contact the ground. If however the ground is not flat such that the lower surface 74 of the shoe 70 on the first primary piston rod 28 contacts the ground first, the primary piston rods 28,40 will continue to extend until the lower surface 74 of the shoe 70 on the second primary piston rod 40 also contacts the ground. This continued movement brings the other side of the support platform 12 into contact with the ground such that support platform lies flat on the ground, as shown in Figure 5.

The recess 72 in which the free end 28a of the first primary piston rod 28 is received allows the free end 28a to move downwards therein, and thereby provides for free motion of the first primary piston rod 28 as the primary piston rods 28,40 continue to extend (see Figure 4b). The amount of free motion allowed by the shoe 70 is determined by the size of the recess 72 provided therein.

On retraction of the primary piston rods 28, 40, the shoe 70 provided on the primary piston rod 28 remains in contact with the ground until the

outwardly extending flanges 78 on the first primary piston rod 28 are brought into contact with the inwardly extended flanges 76 provided at the opening of the recess 72.

Figures 6-7 show other examples of lost motion devices.

In Figures 6a and 6b, the lost motion device comprises a shoe 80 having an axially extending slot 82 formed in a sidewall 84 thereof. In use, projections 86 provided on the free ends 28a, 40a (not shown) of the primary piston rods 28,40 (not shown) engage within the slot 82 of a respective shoe 80. In such arrangements, the length of the slot 82 determines the amount of free motion of the primary piston rods 28, 40 (see Figure 6b).

In Figures 7a and 7b, the lost motion device comprises a chain 85. In use, the support platform 12 is connected to the free ends 28a, 40a (only one of which is shown) of the primary piston rods 28,40 by means of chains 85. In this arrangement, the length of each chain 85 determines the amount of free motion of the primary piston rods 28, 40 (see Figure 7b).

To ensure that the level of fluid 46 provided in the cylinders 24,26, 36,38 is maintained at required levels, and does not alter through wear of the piston and seal assemblies 48, 50,52, 54, the cylinders 24,26, 36, 38 may include make-up systems.

For example, in a situation where the piston and seal assembly 48 secured to the first primary piston rod 28 is worn, it allows fluid 46 to leak around it.

This means that on extension of the first primary piston rod 28, the fluid 46 pushed out of the annulus end 24a of the cylinder 24 is not sufficient to extend the second secondary piston rod 42 by the same amount.

To overcome this problem, the piston and seal assembly 54 provided on the second secondary piston rod 42 may be provided with a make-up system to make-up the missing fluid, and ensure that the cylinders 24,26, 36,38 continue to operate synchronously.

Examples of several make-up system arrangements are shown in Figures 8- 10.

In Figure 8, the make-up system includes two holes 90,92 formed in the piston and seal assembly 54. The holes 90,92 are provided on opposite sides of the seal 94 provided by the piston and seal assembly 54, and allow fluid 46 to leak from one side of the seal 94 to the other. The holes 90,92 differ in size, the first hole 90 being relatively larger than the second hole 92.

In Figure 9, the make-up system includes a bypass neck 93 formed in the wall of the second secondary cylinder 38. The bypass neck allows fluid 46 to leak from one side of the seal 94 provided by the piston and seal assembly 54 to the other.

In Figure 10, the make-up system includes a taper 95 formed in the wall of the second secondary cylinder 38. The tapered wall allows fluid 46 to leak from one side of the seal 94 formed by the piston and seal assembly 54 to the other side of the seal 94.

While each of these make-up systems is described with reference to the second secondary piston rod 42, it is envisaged that such make-up systems may be provided in association with each piston and seal assembly 48, 50, 52, 54.

As well as permitting fluid to leak from one side of the seal 94 to the other, and make-up the fluid in the cylinders 24,26, 36,38, the make-up systems may facilitate the initial bleeding of the system to pass fluid 46 into the closed areas of the cylinders 24,26, 36, 38.