PORTABLE LIFT WITH LADDER

Technical Field

The oresent invention relates to portable, exten¬ sible lifts having a work platform at the top, and, more particularly, to such a lift in which there is access to the platform.

Background Art

Various portable units with adjustable-height work platforms are in use in construction and maintenance jobs. For maximum utility, these units should be stable for safety in use and yet should be adapted to be easily moved about on a job site and from one job site to another. It is also preferred that they be compact enough to be wheeled through doorways. Although lift units of the type described can be used to raise a worker and/or materials to the desired work- inq height, it is also preferred that there be easy and safe ladder access to the work platform. Various ladder arrangements have been used, but such have not provided a sturdy, compact ladder sloped throughout its length when the work platform is in raised position. Also, there has been a need for a compact extensible mast and extensible ladder arrangement in which maximum platform height with a fenced platform can be achieved for passage through a doorway when the mast and ladder are retracted. It is important that such needs be filled while at the same time providing ade¬ quate outrigger stability in a convenient-to-use manner and without sacrificing mobility when the unit is to be moved on the work site.

Disclosure of the Invention

The present invention provides an improved port¬ able lift meeting the above-discussed needs and requirements.

OMPI

In accordance with the invention, a multistage, extensible mast on a wheeled base has means for extending and retracting the mast to raise and lower a fenced platform at its upper end. To gain access to the platform when raised, a multi-sectioned, sloped ladder is provided which extends and retracts with the mast. The ladder has its upper section fixed in sloped position on the top stage of the mast, whereas the rest of the sections are swing-mounted at their lower ends and have a slide interfit at their upper ends with the adjoining ladder section. When the ladder is extended, the sections thereof partly overlap and are held in parallel sloped position by tightening screw clamps.

The fence for the platform can be swung downwardly to lower the height of the lift accordingly when there is an overhead clearance problem when the lift is being moved by wheeling it along. The wheels include casters on outrigger arms that may be extended in reach or retracted. When retracted, the outrigger arms prevent the mast from being extended. The outrigger arms also have screw jacks to lift the casters form ground engagement. To free the outriggers of load when they are to be extended or retracted, a cam leg is provided which will lift the casters above the ground level when the cam leg is swung into ground engagement. Wheels are provided on the base opposite the outriggers and these can be deactivated by anti-roll ^' lates which can be swung on the wheel axle to a position beneath the wheels.

Various means can be used to extend and retract the mast. For purposes of example, a cable-reeving system is used with the cable being wound on a hand winch mounted on the lower stage of the mast.

Brief Description of the Drawings

Fig. 1 is a side elevational view of a lift according to the present invention, shown in the lowered position in full lines and the raised position in phantom;

Fig. 2 is a top perspective view of the base assembly, partly broken away, with one of the outrigger arms extended and the other retracted;

OMPI

Fig. 3 is a detail perspective view of the plat¬ form and fence assembly;

Fig. 4 is a schematic elevational view showing the cable reeving; Fig. 5 is a detail perspective view showing the interconnection between the top portion of the intermediate ladder section and the bottom portion of the top ladder section; and

Fig. 6 is a detail perspective view of an anti- roll device for the rear wheels.

Best Mode for Carrying Out the Invention

Referring to the drawings, it is seen that the lift made according to the invention has a mobile base assembly 20 on which are mounted, front and back, a tele¬ scopic, multistage tower 22 and an extensible ladder 24. The tower 22 has a winch 25 at the front and a fenced plat¬ form 26 at the top thereof, and the base assembly 20 has a rectangular frame 27 with a cross-member 27a near the front, on which the tower 22 is fixed. A pair of outriggers 28 are at the front of the base assembly 20.

For purposes of example, the tower 22 has been illustrated as having a three-stage mast comprising a sta¬ tionary bottom mast section 30 rigidly mounted on the cross- member 27a, an intermediate mast section 31 slidably mounted on the bottom section 30, and a top mast section 32 in turn slidingly mounted on the intermediate section 31. Addition¬ al like intermediate mast sections can be provided if addi¬ tional stages are desired for the tower 22. The sections 30-32 of the tower 22 are preferably constructed and roll-mounted relative to one another in front-to-back relationship in the same manner as the sec¬ tions of the multistage mast shown in my prior United States Patent No. 4,015,686. It is also preferred to use the same type of cable-reeving system shown in that patent for ex¬ tending and retracting the mast by operation of the winch 25 mounted on the front of the bottom mast section 30 and to provide the automatic safety system of the patent for lock¬ ing the mast sections together in case of cable failure.

The reeving for the cable 29 wound on the winch 25 is illustrated schematically in Fig. 4. A series of four sheaves 33a, b, c and d are provided over which the cable 29 passes consecutively from the winch 25 to an anchor connec- tion near the upper end of the top mast section 32. Sheave 33a is mounted at the top of the bottom mast section 30 and sheaves 33b,33c are mounted at the bottom and top, respec¬ tively, of the intermediate mast section 31. Sheave 33d is in turn mounted at the bottom of the top mast section 32. When the tower 22 is in its lowered, fully retracted posi¬ tion, the maximum amount of cable 29 is unwound from the winch 25. When the cable is then wound on the winch, the top mast section 32 will normally raise first, until a stop near the bottom of the top section 32 engages a stop near the top of the intermediate mast section 35. The intermedi¬ ate section 35 then raises until a stop near its lower end engages a stop near the upper end of the bottom mast section 30. These stops are not shown in the drawing but are iden¬ tical to those shown in my aforesaid prior patent. If the automatic safety system in such patent is not used, the sheaves 33d can be eliminated and the cable 29 dead-ended on the top mast section 32 near the bottom thereof rather than as previously indicated.

The ladder 24 has a respective section for each of the tower sections 30-32, namely, a bottom ladder section 34 pivotally mounted at its lower end on the rear of the base frame 27, an intermediate ladder section 35 pivotally con¬ nected at the bottom to the rear of a pair of braces 38 at the bottom of the intermediate mast section 31, and a top ladder section 36 connected at the bottom to the rear of a pair of rearwardly extending braces 40 at the bottom of the top mast section 32. The top ladder section 36 is also con¬ nected at the top to the top mast section 32 by way of angle brackets connected to a lateral cross-member 42 fixed to the top mast section a short distance beneath the platform assembly 26. Hence the top ladder section 36 is fixed in a rearwardly sloped position relative to the top mast section 32, whereas the other two ladder sections 34,35 are free to

pivot fore and aft relative to their respective mast sec¬ tions 30,31. The reason for this pivotal movement will be explained later.

The side rails of the ladder sections 34-36 are preferably laterally facing channels so that the side rails 35a and 36a of the intermediate and top ladder sections 35- 36 comprise tracks for respective rollers 45-46. Rollers 45 have their axles 45a mounted on the forward leg of a respec¬ tive forwardly projecting, S-shaped bracket 47 fixed at the rear to the upper end of the corresponding side rail 35a of the intermediate ladder section 35. Similarly, rollers 46 have their axles mounted on the forward leg of a respective forwardly projecting, S-shaped bracket 48 mounted at the rear to the upper end of the corresponding side rail 35a of the bottom ladder section 34. Passing through holes in the channel legs of the side rails 35a,36a and a threaded hole 51 in the center webs of the S-shaped brackets 47,48 are respective clamping bolts 49,50, each having a turning handle as its head. Each bolt 49,50 has a threaded portion screwed through the respective hole 51. The purpose of the bolts 49,50 is to bear, when tightened, against the opposed back faces of the ladder side rails to thereby stiffen the ladder 24 when the tower 22 is extended to the desired height. At the lower end of the side rails 36a of the top ladder section 36, stops 52 are provided to limit the down¬ ward travel of the rollers 45 in these side rails as the top ladder section moves upwardly with the top mast section as the tower, is raised. The stops 52 are located so that as the top mast section 32 reaches the limit of its upward travel relative to the intermediate mast section 31, the rollers 45 engage the stops 52, whereby lifting of the intermediate ladder section 35 by the top ladder section 36 commences at the same moment as upward movement of the intermediate mast section 31. This arrangement makes it unnecessary for the braces 38 at the bottom of the inter¬ mediate ladder section 35 to be adapted to take any signifi¬ cant portion of the vertical loads on the ladder.

It will be noted that as the rollers 45 move down¬ wardly in the side rails 36a responsive to upward movement of the top mast section 32 and the ladder section 36 as a unit, the slope of the intermediate ladder section 35 gradu- ally becomes steeper until it preferably reaches substan¬ tially the same slope as the top ladder section. This change in slope is permitted by way of the pivotal connec¬ tion between the bottom of the intermediate ladder section 35 and the rear end of the intermediate braces 38. It will be appreciated that the lengths of these braces 38 and the shorter top braces 40 are made such that the top and inter¬ mediate ladder sections will overlap in substantially paral¬ lel relation when the top mast section 32 is fully extended. Similarly, the pivotal connection of the lower end of the bottom ladder section 34 to the base frame 27 permits this section to likewise assume a steeper slope as the rollers 46 at its upper end travel down the side rails 35a responsive to upward travel of the intermediate ladder section 35 with the intermediate mast section 31 during the raising thereof. Hence, when the tower 22 and the ladder 24 are both fully extended, the three ladder sections 34-36 will be in over¬ lapping, substantially parallel, sloped relationship. The ladder 24 then can be made stiffened by tightening bolts 49,50. The base frame 27 has a pair of U-shaped retaining brackets 54 diagonally bridging its front corner portions to receive elongated outrigger sleeves 56 of square cross-sec¬ tion which are swing-mounted on the top of the cross-member 27a by vertical bolts 57. Tubular outrigger arms 58 are slidably mounted in these sleeves 56 and have screw jacks 60 mounted at their outer ends with ground-engaging pads 61 at their lower end and crank handles 62 at their upper end. Adjacent these jacks 60 are casters 64 which support the forward end of the base assembly 20 when moving the lift is desired. These casters 64 are complemented by a pair of wheels 66 on a cross-axle 67 at the rear of the base frame 27. Pivoted locking hooks 68 are provided on the central bridge portion of the retaining brackets 54 to keep the out-

o?v:?r

rigger sleeves 56 in outwardly swung, diverging position when the hooks 68 are dropped into a generally horizontal position. Spring-loaded locking pins 70 are preferably provided on the outrigger sleeves 56 to interfit with re- spective holes 71 in the outrigger arms 58 when they are in their extended and retracted positions. It will be noted that when the tower 22 is in the lowered position and the outrigger arms 58 are fully retracted, they project inwardly of the base frame 27 above the cross-member 27a to a posi- tion directly over the braces 35,36 on the lower ends of the top mast section. This arrangement prevents the sections of the tower 22 from extending until the outrigger arms 58 have been shifted to reach forwardly into their maximum support¬ ing position. When the outrigger arms 58 are in their retracted position, the base assembly 20 will normally be supported at the front by the casters 64 and at the rear by the wheels 66.

A cam leg 72 is pivotally mounted between a pair of forwardly projecting fork arms 73 at the front of the base frame 27 to raise the casters 64 out of ground engage¬ ment when the cam leg is rocked downwardly into ground engagement and while the lift is being rolled forwardly on the casters 64 and rear wheels 66. This takes the load from the outrigger arms so that they can be more easily pulled forwardly through the sleeves to clear the bottom mast sec¬ tion 30 and so that the sleeves can then be swung outwardly on the pivot bolts 56 until they engage the outer extents of the retaining brackets 54. The sleeves are then locked by the hooks 68 in diverging position, and the outrigger arms are locked in forwardly extended diverging position by the locking pins 70 on the sleeves 56. Following this, the handles 62 on the jackscrews 60 are turned to lower the pads 61 into ground engagement and take the load off the cam leg 72 while the caster wheels remain raised off the ground. The cam leg 72 is then swung upwardly into inactive position. It is referred that the lift of the invention be capable of being wheeled through a doorway when the tower is in lowered, retracted position. However, since the platform

OMPI

26 should preferably have a fence 74 when occupied, and height ^" of the lift preferably should not be sacrificed for the fence, there is a need to have an arrangement for con¬ veniently lowering the fence when it is desired to move the lift through a doorway. Hence the fence 74 is hinged at 76 along its bottom front edge to the front of the platform 26 so that the fence can swing downwardly in the rearward direction until the front frame portions of the fence engage the top of the platform. To make this possible, the back of the fence is clear of framework except for the upper fence rail. To hold the fence 74 in upright position, a pair of spring-loaded slide bolts 78 are provided at the rear of the platform which move laterally outward to fit into keeper holes 80 presented by downwardly extending ears near the lower rear corners of the fence frame.

Directing attention to Fig. 6, it is seen that the rear wheels 66 are each preferably provided with an anti¬ skid device 84 pivotally mounted on the axle 67. The device 84 is generally U-shaped, providing cheek plates 84a, 84b on opposite sides of the wheel and a central web 84c on which is mounted an anti-skid pad 85. When the device 84 is in inactive position, the web 84c is above the wheel. To activate the device 84, it is swung down rearwardly into ground engagement, and then the lift unit is rolled rear- wardly, thereby causing the respective wheel 66 to move into an inactive position over the inner face of the web 84c and the anti-skid pad 85 to rest flat against the ground surface. Those skilled in the art could make many modifica¬ tions to the preferred embodiment described and shown with- out departing from the general concept of this invention. Therefore, this invention should not be limited unless it is necessary to do so because of the teachings of the prior art or the fair reading of the appended claims.