GB2388582A

GB2388582A - A folding stabiliser leg.

Info

Publication number: GB2388582A
Application number: GB0210884A
Authority: GB
Inventors: Frank Roger Bowden
Original assignee: Nifty Lift Ltd
Current assignee: Nifty Lift Ltd
Priority date: 2002-05-13
Filing date: 2002-05-13
Publication date: 2003-11-19
Anticipated expiration: 2022-05-13
Also published as: GB2388582B; GB0210884D0

Abstract

A stabiliser leg comprises a first, primary leg, member 20, a second, secondary leg, member 22, a ram 32, a leg support structure 28 and a control rod 42. The secondary leg member 22 can be extended or retracted with respect to the first leg member 20 e.g. By a lost motion mechanism. The first member 20 and the second member 22 are connected at a first pivot 24 and are extended by the ram 32 attached to the first member 20. The ram 32 and first member are attached to the leg support structure 28 and so is one end of the control rod 42 with the lost motion mechanism. The rod 42 and lost motion mechanism are for controlling the deployment of the second member 22. The second member 22 has a hook formation 36 that engages the ram pivot point 34 when fully extended to lock it. The leg may have a seperate foot at the ground engaging end of the second member 22. A micro switch 38 is used to sense when the leg is fully extended. The leg is used to support an access platform during deployment.

Description

STABILISER LEG

The present invention relates to a stabiliser leg and in particular, but not exclusively, to a stabiliser leg for a mobile access platform.

5 Mobile access platforms are used for example in shopping centres and on building sites to allow workers to work conveniently at heights of between typically 10 and 30 metres above the ground. Most mobile access platforms include an operator cage mounted on the end of a hydraulically actuated boom, which is in turn mounted on a movable platform.

There are two main groups of mobile access platform in common use. The first group I O comprises self-stabilisingplatfoTms, which generallyhave a very heavy base with negligible suspension travel. The chassis provides the necessary stability without the need for external stabilisers. The chassis may be self-propelled, allowing the platform to be driven while the operator cage is erected.

The second group comprises platforms that require external stabiliser legs (also called "jack 15 legs") to provide the necessary stability. This latter type includes trailer-type platforms, whi ch are generally much lighter than self-propelled platforms and are normally towed into position either by another vehicle or by hand, and truck-mounted platforms. This second group also includes hybrid type of mobile access platform, which is self-propelled so that it can be driven to the position where access is required, but which also has stabiliser legs 2O that are deployed during use. This type cannot be driven while the platoon is in use.

The present invention is concerned particularly with the second group of mobile access platforms, which need stabiliser legs to provide the necessary stability when the boom is erected. When the stabiliser legs are deployed, they lift the chassis and wheels of the mobile access 25 platform clear of the ground so that all the weight is carried by the legs. The stabiliser legs on most existing mobile access platforms provide a clearance beneath the wheels of typically about 20cm. This is the maximum clearance that can normally be achieved with conventional legs, since the dimensions of those legs are limited by the fact that when the :. L.::.', (. it'd, I' '.: (. Lt:

legs are stowed upright, the overall height of the mobile access platform has to be less than about 2 metres, to allow access through doorways. A ground clearance of 20cm is satisfactory if the surface of the ground is relatively smooth and flat, but if the ground is rough or sloping it may be insufficient, making it impossible to achieve a stable and 5 horizontal base for the platform. There is a need therefore for a stabiliser leg that provides greater penetration. i.e. that provides a greater clearance between the ground and the wheels and chassis of the mobile access platform.

The limited dimensions ofthe existing stabiliser legs also limits the maximum width ofthe platform base when the legs are deployed, typically to a maximum of about 4 metros. This 10 in turn limits the permissible range of movement of the operator cage, without causing the platform to tip over.

For safety, mostmobile access platforms include sensors for detecting any danger oftipping over. These sensors typically include microswitches that are connected to the feet and are tripped if the force exerted against the ground by any foot falls to less than 400N. An alarm ] S signal is then generated, indicating that the boom is nearing the limit of its safe operation.

The figure of 400N is selected somewhat arbitrarily and is intended to prevent the safety system being easily overridden by a negligent operator' for example by interfering with the microswitches and artificially propping up one of the stabiliser feet. However, this requirement for a force of at least 400N acting on each foot again limits the range of 20 operation of the boom and the performance of the platform.

It is an object ofthe present invention to provide a mobile access platform that mitigates at least some of the aforesaid disadvantages.

According to the present invention there is provided a stabiliser leg including a primary stabiliser and a secondary stabiliser that is attached to the primary stabiliser by a first pivot 25 joint, the secondary stabiliser being pivotable relative to the primary stabiliser between a fully extended condition and a retracted condition in which the overall length of the leg is less than the length of the fully extended leg.

By using a two-part leg, it is possible to increase the overall extended length of the leg without increasing its stowed dimensions. This allows the platform to have a larger base I, l. A., . I,, ( '. ' 1..

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width, increasing its stability and allowing a longer boom to be used. The longer legs also provide increased penetration, allowing the platform to be used on rough ground and steeper slopes.

The primary and secondary stabilisers may include complementary locking formations that 5 engage one another when the leg is in a fully extended condition.

The primary stabilisermay include a second pivot joint formountingthe leg on a leg support structure and an actuator for causing rotation of the primary stabiliser about the second pivot joint. The actuator may be connected to the primary stabiliser by means of a third pivot joint. The secondary stabiliser may include a hook formation that engages the third 10 pivot joint when the leg is in a fully extended condition.

The secondary stabiliser may include a control element that controls movement of the secondary stabiliser according to the movement of the primary stabiliser. The control element may include a connecting rod having a proximal end for connection to an anchor point on a leg support structure and a distal end that is connected to the secondary stabiliser.

15 The control element may include a lost motion mechanism at the proximal end of the connecting rod that is constructed and arranged to allow limited relative movement between the connecting rod and the anchor point.

(he lost motion mechanism may include a resilient member that is constructed and arranged to exert a force on the connecting rod according to the relative displacement between the 20 connecting rod and the anchor point. The resilient member is advantageously constructed and arranged to exert a force on the connecting rod that is sufficient to move the secondary stabiliser towards an extended position when the primary stabiliser is in a fully extended position, but which is insufficient to move the secondary stabiliser to a fully extended position. This ensures that when the leg is being deployed, the secondary stabiliser is 25 extended' but it is not locked into position until the foot engages the ground. The resilient biassing of the connecting rod also serves to transfer the majority of the legs weight to the chassis of the platform, thereby increasing its stability.

The stabiliser leg may include sensing means for sensing when the leg is in a fillly extended position. The sensing means may be located adjacent the first pivot joint, for sensing the (,... I,I,, À.À. À -

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relative positions of the primary and secondary stabilisers. By detecting that the leg is fully extended, the stability of the platform can be confinned.

When the leg is fillly extended, the longitudinal axes ofthe primary and secondary stabilisers may be displaced from an aligned condition by an angle in the range 10 to 80 , preferably 5 20 to 60 , and more preferably approximately 40 . By off-setting the secondary, stabiliser, the penetration of the leg can be increased, allowing the platform to be used on rougher or more steeply sloping ground.

The secondary stabiliser may be interchangeable, allowing it to be adapted to different circumstances. O A foot member may be attached to a distal end of the secondary stabiliser.

According to a second aspect of the invention there is provided a mobile access platform including a chassis, a boom member mounted on the chassis and an operator cage attached to the boom, the chassis including a plurality of stabiliser legs as claimed in any one of the preceding claims.

15 Advantageously, the mobile access platform has an overall height of no more than 2 metros with the stabiliser legs in a stowed condition, and a 'base width with the legs fully extended of at least 4.5 metres, preferably 5 metres, and more preferably approximately 5 metros. 2 Advantageously. the mobile access platform has an overall height of no more than 2 metres with the stabiliser legs in a stowed condition, and a ground clearance with the legs fully 20 extended on flat,]eve] ground of at least 30cm, preferably at least 40cm, and more preferably at least 50cm.

An embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure is a side view of a prior art mobile access platform having four stabiliser legs,

25 shown in a deployed condition; Figure 2 is an end view of the prior art mobile access platform, showing the stabiliser legs

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Figure 3 is an end view of the chassis of a mobile access platform having stabiliser legs according to the present invention, shown in a deployed condition; Figure 4 is an isometric view of the chassis, showing the stabiliser legs in a deployed condition; S Figure 5 is a schematic side view of a stabiliser leg in a stowed condition; and Figure 6 is a schematic side view of the stabiliser leg in a deployed condition.

Figures I and 2 show the basic components of a prior art mobile access platform. The

platform includes a chassis 2 having a pair of running wheels 4 and a towing bar 6 with a trolley wheel 8. A hydraulically operated boom I O is mounted on the chassis 2 and an 10 operator cage 12 Is attached to the end of the boom. Four hydraulically operated stabiliser legs 14 are mounted by means of pivot joints 16 on the chassis. The stabiliser legs 14 may be deployed as shown in Figures I and 2 to lift the chassis and wheels clear of the ground, or they may be pivoted to an upright position, for transportation or storage of the platform.

An example of a stabiliser leg according to the present invention will now be described with 1: reference to figures 3 to 6. Figures 3 and 4 show the chassis of a mobile access platform having four stabiliser legs 18. The boom and its associated operating mechanism and the operator cage are conventional and have been omitted from the drawings for clarity.

One ofthe stabiliser legs 18 is shown schematically in Figures 5 and 6. The leg is hinged and includes a primary stabiliser 20 that forms the upper part of the leg and a secondary 20 stabiliser 72 that forms the lower part of the leg and is connected to the primary stabiliser 20 by means of a first pivot pin 24 provided in a knee joint 26 at the distal end of the primary stabiliser 20. The primary stabiliser 20 comprises a Ushaped steel section and the secondary stabiliser comprises a steel box section. A foot 27 is provided at the distal end of the secondary stabiliser. As shown in figures 3 and 4, the foot 27 optionally comprises 25 a foot plate that is pivotably mounted on the distal end of the secondary stabiliser 22.

The primary stabiliser 20 is attached to a leg support structure 28 by means of a second pivot pin 30 that extends through the lower part of the support structure 28. The support structure 28 is welded to the chassis. A hydraulic ram 32 is attached to a pivot pin 33 in the I ';.:,,5\ It, ,,. . ...

upper past of the support structure 28, the distal end of the ram 32 being attached to the distal end of the primary stabiliser 20 by means of a third pivot pin 34 that extends through the upper part of the knee joint 26.

The secondary stabiliser 22 is attached to the distal end of the primary stabiliser 20 by means 5 of the first pivot pin 24, which extends through the lower part of the knee j oint 26. The first pivot pin 24 is offset slightly below the longitudinal axis of the primary stabiliser 20, allowing the primary and secondary stabilisers to be stowed with their longitudinal axes -

approximately parallel to one another, as shown in Figure 3.

The secondary stabiliser 22 includes an outer portion that extends outwards beyond the first 10 pivot pin 24 and an inner portion that extends inwards from the first pivot pin. A hook formation 36 is provided in the upper part of the inner portion, which engages the third pivot pin 34 when the leg is fully extended. A microswitch 38 is provided adjacent the hook formation, which is tripped when the hook formation locks against the third pivot pin 34.

The microswitch 3 8 is connected to an alanr system (not shown), which generates an alarm 15 when the boom is extended, if any of the legs is not locked in the fully extended condition.

A fourth pivot pin 40 extends through the lower part of the inner portion of the secondary stabiliser 22. This fourth pivot pin 40 is connected to the distal arid of a connecting rod 42 that extends inwards towards the leg support structure 2g and which serves, in use. to control movement of the secondary stabiliser 22.

20 The proximal end of the connecting rod 42 is connected by means of a sliding link mechanism to an anchor point 44 that is mounted on the support structure 28. Ewo i compression springs 46,48 are mounted on the connecting rod 42, one on each side of the anchor point 44, each spring being compressed between the anchor point 44 and a respective stop member 50.52 mounted on the connecting rod. Thus, the first spring 46 is 25 mounted between the anchor point 44 and a first stop member 50 at the proximal end of the rod, and the second spring 48 is mounted between the anchor point 44 and a second stop member 52 mounted on the connecting rod on the opposite side of the anchor point. The degree of compression of each of these two springs depends on the relative positions of the connecting rod and the anchor point as the rod slides through the anchor point, the , ,,, À,

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j compression of those springs tending to bias the rod towards a position in which the anchor point 44 is located equidistant between the two stop members 50,52 When the stabiliser leg is in a stowed position as shown in Figure 5 with the hydraulic ram in a contracted condition, the second spring 48 is compressed more than the first spring 46.

5 The connecting rod 42 is therefore in a state of compression and exerts an outward force on the fourth pivot pin 34, which clamps the secondary stabiliser 22 against the primary stabiliser 20. This prevents the secondary stabiliser from swinging outwards, for example during transportation.

To deploy the stabiliser leg. the hydraulic ram 32 is extended, causing the primary stabiliser 10 20 to rotate about the second pivot pin 30 (in a clockwise direction as shown in the drawings) to the position shown in Figure 6. As the primary stabiliser 20 rotates, the connecting rod 42 slides outwards through the anchor point, increasing the compression of the first spring 46 and decreasing the compression of the second spring 48. The connecting rod 42 therefore changes from a state of compression to a state of tension and acts on the secondary stabiliser 22 through the fourth pivot pin 34, pulling it outwards towards the extended position shown in Figure 6.

The relative strengths of the first and second springs are selected so that when the primary stabiliser 20 is fully extended, the tensile force exerted by the connecting rod 42 on the second stabiliser 22 is not quite sufficient to lock the hook formation 36 in engagement with 2() the second pivot pin 34. Therefore' if the foot 27 is suspended above the ground (for example because the ground is uneven or sloping), the microswitch 38 will not be tripped and the alarm system will be activated and will generate an alarm signal if any attempt is made to raise the platform. Further, if the primary stabiliser 20 is not substantially fully extended, the microswitch cannot be tripped by lifting the foot, since the connecting rod 42 25 limits the movement of the secondary stabiliser 22 and prevents it being lifted sufficiently to trip the switch, unless the primary stabiliser 20 is substantially, fully extended.

If the foot 27 is pressed against the ground, the hook formation 36 will be locked against the third pivot pin 34 and the microswitch 3 8 will be tripped, thereby deactivating the alarm.

The alarm system therefore provides a warning only if the platform is not properly stabilised 30 or if it starts to tip during use. However, it is not necessary for each foot to exert a large ,, < \, '.. .

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1' force against the ground, and because most of the weight of the second stabiliser 22 is transferred through the connecting rod to the chassis, this increases the effective weight of the chassis and improves its stability.

To stow the leg, the hydraulic ram 32 is actuated in the contracting direction, thereby causing the primary stabiliser 20 to rotate (in the anti-clockwise direction as shown in the drawings) back to the upright position shown in Figure 3. As the primary stabiliser rotates, the connecting rod 42 slides through the anchor point 44, thereby increasing the compression of the second spring 48, decreasing the compression of the first spring 46 and placing the connecting rod in a state of compression. The connecting rod then exerts an 10 outwards force on the fourth pivot pin 34, causing the secondary stabiliser 22 to rotate back to the stowed position showed in Figure 5.

Various modifications of the stabiliser leg are of course possible. For example, instead of using two compression springs, two tension springs can be used, or the two springs can be replaced by a single spring that acts both in compression and tension.

1 S It will be noted that when the stabiliser leg is in a fully extended condition, the primary and secondary stabilizers 20.22 are not fully aligned, the axes of those stahilisers being offset from an aligned position by an angle of approximately 400. This increases the penetration ofthe stabiliser leg, thereby providing an increased ground clearance. Also, because the leg is hinged, its extended length is far greater than its stowed length, which increases the width 20 of the platform base. Thus, we have found that in a mobile access platform having an overall height of less than 2 metres with the stabiliser legs in the stowed position, it is possible using the stabiliser legs of the present invention to achieve a ground clearance of SO-I OOcm and an overall base width of potentially 5.5 metros. This compares to a ground clearance of approximately 20cm and a base width of 4 metres for a conventional mobile 25 axis platform having straight, rigid stabiliser legs of similar stovred dimensions.

Because the microswitches for the alarm system are fully enclosed within the knee joints, they cannot be tampered with, which increases the safety of the mobile access platform.

Further, because it is then no longer necessary for each leg to exert a force of at least 400N against the ground, this also improves the stability and performance of the platform.

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The secondary stabilizers 22 may be interchangeable with other stabilisers having a larger or smaller dimensions, to provide an increased or reduced ground clearance and/or an increased or reduced base width. An increased base width may be required when, for example, lifting heavy loads or using the boom at maximum extension, and a reduced base 5 width may be required when operating in restricted spaces. An increased penetration may be required when operating on steep slopes, to provide the ground clearance needed for a horizontal platform. Each ofthe stabiliserlegs can tee controlled individually, to ensure that the platform is stable and horizontal when used on uneven ground.

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Claims

JO CLAIMS

1. A stabiliser leg including a primary stabiliser and a secondary stabiliser that is 5 attached to the primary stabiliser by a first pivot j oint, the secondary stabiliser being pivotable relative to the primary stabiliser between a fully extended condition and a retracted condition in which the overall length of the leg is less than the length of the fully extended leg 2. A stabiliser leg according to claim I, in which the primary and secondary stabilisers 10 include complementary locking formations that engage one another when the leg is in a fully extended condition.

3. A stabiliser leg according to claim 1 or claim 2, in which the primary stabiliser includes a second pivot joint for mounting the leg on a leg support structure and an actuator for causing rotation of the primary stabiliser about the second pivot joint.

15 4 A stabiliser leg according to claim 3, in which the actuator is connected to the primary stabiliser by means of a third pivot joint.

5. A stabiliser leg according to claim 4, in which secondary stabiliser includes a hook formation that engages the third pivot joint when the let, is in a fully extended condition. 90 6. A stabiliser leg according to any one ofthe preceding claims, in which the secondary stabiliser includes a control element that controls movement of the secondary stabiliser according to the movement of the primary stabiliser.

7. A stabiliser leg according to claim 6, in which the control element includes a connecting rod having a proximal end for connection to an anchor point on a leg 25 support structure and a distal end that is connected to the secondary stabiliser.

8. A stabiliser leg according to claim 7, in which the control element includes a lost motion mechanism at the proximal end of the connecting rod that is constructed and .,i,.,, . À. .., (,..

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arranged to allow limited relative movement between the connecting rod and the anchor point.

9. A stabiliser leg according to claim 8, in which the lost motion mechanism includes a resilient rnernber that is constructed and arranged to exert a force on the I connecting rod according to the relative displacement between the connecting rod and the anchor point.

10. A stabiliser leg according to claim 9, in which the resilient member is constructed and arranged to exert a force on the connecting rod that is sufficient to move the secondary stabiliser towards an extended position when the primary stabiliser is in 1 O a fully extended position, but which is insufficient to move the secondary stabiliser to a fully extended position 11. A stabiliser leg according to any one of the preceding claims, including sensing means for sensing when the leg is in a fully extended position.

12. A stabiliserlegaccordingto claim 11, in whichthe sensing means is located adjacent 15 the first pivot joint, for sensing the relative positions of the primary and secondary stabiliser 13. A stabiliser leg according to any one of the preceding claims wherein when the leg is fully extended, the longitudinal axes of the primary and secondary stabilisers are displaced from an aligned condition by an angle in the range 10 to 80 , preferably 20 20 to 60 ' and more preferably approximately 40 .

14. A stabiliser leg according to any one of the preceding claims, i n which the secondary stabiliser is interchangeable.

I S. A stabiliser leg according to any one of the preceding claims, including a foot member attached to a distal end of the secondary stabiliser.

25 16. A stabiliser leg substantially as described herein with reference tot and as illustrated by, the accompanying drawings.

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17. A mobile access platform including a chassis, a boom member mounted on the chassis and an operator cage attached to the boom, the chassis including a plurality of stabiliser legs as claimed in any one of the preceding claims.

18. A mobile access platform according, to claim 1 7, having an overall height of no more than 2 metres with the stabiliser legs in a stowed condition, and a base width with the legs fully extended of at least 4.5 metros, preferably S metres, and more preferably approximately 5.5 metres.

19. A mobile access platform according to claim 17 or claim 1 8, having an overall height of no more than 2 metres with the stabiliser legs in a stowed condition, and a ground 10 clearance with the legs fully extended on flat, level ground of at least 30cm, preferably at least 40cm, and more preferably at least 50cm.

20. A mobile access platform substantially as described herein with reference to, and as illustrated by, the accompanying drawings.

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