Load displacement apparatus

A load displacement apparatus to displace a mobile platform along a structure includes a worm screw mounted on the platform for rotation about its axis that meshes with a plurality of support blocks mounted on the structure. The support blocks are spaced apart from one another along the structure to be successively engaged by the worm screw. Each support block includes a plurality of bearing balls freely movably supported and retained therein to selectively and movably engage the worm screw over at least an arc segment thereof such that the worm screw is always in meshing engagement with at least one of the support blocks. A scaffolding system incorporating the apparatus is also described.

FIELD OF THE INVENTION

The present invention relates to load displacement systems and is more particularly concerned with a load displacement apparatus and the components used in the displacement mechanism thereof for longitudinal displacement of a load along a structure as in scaffoldings or the like, there being vertical, inclined or horizontal.

BACKGROUND OF THE INVENTION

It is well known in the art to use different lifting mechanisms in scaffoldings. Known scaffolding systems, and other types of load displacement systems, include a work platform or the like that is displaceable along a tower or the like.

Some towers support a plurality of work platforms, each carrying its own lifting mechanism. Furthermore, when the uppermost work platform needs to go back down, all platforms underneath obviously need to go down first, which is relatively expensive and inefficient. Most of the lifting mechanisms offer relatively slow platform displacement speeds in the order of a few (about 2 to 5) feet per minutes (about 0.6 to 1.5 meters per minute) which is really time consuming when the platform needs to be raised at and lowered from a few hundred feet high. Furthermore, the lifting mechanisms usually need additional safety mechanisms to prevent any possible free fall of the platforms. Lifting mechanisms using rollers meshing with a worm screw are subject to surface wear at the contacting interface there between and are limited to their loading capacity by the roller shafts and their support bearings. Furthermore, they suffer drawbacks from the tedious alignment of the rollers required in assembly. Also, in the event of shaft rupture, the platform risks to simply fall down until a safety mechanism is activated, thereby providing a braking shock and possible injuries or other types of subsequent failures.

Load displacement mechanisms that use balls into conventional ball screw systems as load carriers are typically expensive to manufacture and in maintenance. Accordingly, the balls of the ball screw circulate inside a loop that circles around at least one complete turn (360°) of the screw thread in a cycle fashion; which is relatively complex in manufacturing.

Other bearing systems, as disclosed by Sievert in U.S. Statutory Invention Registration No. H1384 published on Dec. 6, 1994, has a continuous bearing with the load bearing balls undergoing extensive shear loads instead of compressive loads, which would not be acceptable in case of failure. Furthermore, the bearing of Sievert is made to work in reciprocating displacement with the bearing balls never circling along the entire ball receptacle loop, which would be prevented by the balls jamming therein (because of a tendency of a ball to start rolling over or under a preceding ball—zig-zag phenomenon), and with the exposed balls being prevented from falling off by a race of the outer bail (moving part). Additionally, each ball of Sievert's bearing would not be capable of sustaining on its own without any damage a charge weighing many tons as would be the case in most load displacement systems.

Accordingly, there is a need for an improved load displacement apparatus with a simple configuration and improved components used therefor.

SUMMARY OF THE INVENTION

It is therefore a general object of the present invention to provide an improved load displacement apparatus with a simple configuration and/or improved components used therefor.

The innovative features of the load displacement apparatus of the present invention allows for the apparatus to have different functions that enable the apparatus to be usable in a wide variety of applications. Amongst these features is the fact that the apparatus is what is called a ‘fail-safe’ apparatus to ensure that all users will never be endangered upon failure of the apparatus, and prevent any free fall or the like displacements. Also, the present apparatus can be used for vertical, inclined, and even horizontal displacements of charges with rectilinear or curved trajectories. In some embodiments, all components, including gear trains, brakes and controls, are located inside the main screw of the displacement mechanism. The apparatus can also prevent the free downward acceleration of the mobile screw upon uncontrolled free rotation thereof simply because of the small pitch angle of the screw thread interacting with the inherent frictional forces occurring within the bearing blocs or blocks (it is noted that all words ‘bloc’ and ‘blocs’ appearing hereinafter have the intended meaning of ‘block’ and ‘blocks’, respectively). Furthermore, in order to allow the apparatus to function with a multi-ton load charge acting on a single bearing ball, extensive research work, analysis, calculations and tests (up to different destruction tests) were performed, including different aspects such as components geometry, alloy compositions, thermal treatments, and the like. Therefore, one skilled in the art would realize that it would not as simple as assembling different parts coming from different apparatuses together to get the present load displacement apparatus although some features may seem obvious after the fact, but aren't in reality.

An advantage of the present invention is that the load displacement apparatus has ball bearing blocs, mounted on a structure, that are successively engaged by a screw device and that can support the latter over only an angular (arc) segment thereof that typically varies between about ten and about sixty-five degrees, although the actual could be really small in the case only one of the bearing balls would momentarily supports the screw device by itself.

Another advantage of the present invention is that the load displacement apparatus could never end up in a free fall; if a bearing ball gets broken, the entire weight of the mobile platform would be supported directly by the support bloc that would even prevent any free fall rotation of the screw. Furthermore, with a pitch angle less than about three degrees (3°), frictional forces would prevent vertical free fall acceleration of the screw, even with lubricated bearing balls.

A further advantage of the present invention is that the load displacement unit allows certain misalignment of the screw device on its axis relative to the fixed structure, such that the bearing balls supporting the screw are allowed to be radially displaced (relative to the radial direction of the screw) within an arcuate recess of the screw and/or a width of the loop channel allowing this transverse displacement of the balls therein. The load displacement unit further allows for small variations of the distance between successive supporting bearing blocs with the screw having a slightly larger pitch for either or both end threads.

A further advantage of the present invention is that the load displacement apparatus (lifting mechanism) has a speed range from about 1 to about 300 feet per minute (about 0.3 to about 100 meters per minute).

Still another advantage of the present invention is that the load displacement apparatus can be programmable to stop at different predetermined locations along the tower.

Another advantage of the present invention is that the load displacement apparatus is easily adaptable to existing load displacement or scaffolding systems because of compactness, existing platforms and along existing towers or simple beams having support blocs attached thereto.

Still a further advantage of the present invention is that the lifting mechanism is about 85% efficient when non-lubricated and about 95% when lubricated.

According to an aspect of the present invention, there is provided a load displacement apparatus for displacing a mobile component along an elongate fixed structure, said apparatus comprises: a worm screw mountable on the mobile component for rotation about a screw axis, said worm screw defining an arc segment thereof and having at least one thread helically extending therearound about the screw axis, said thread defining a thread angle; a plurality of support blocks mountable on the fixed structure, said plurality of support blocks being spaced apart from one another along the fixed structure to be successively in meshing engagement with said worm screw for movably supporting the mobile component along the fixed structure; each of said plurality of support blocks including a plurality of bearing balls freely movably mounted thereon, said plurality of bearing balls selectively and movably engage said worm screw, said plurality of bearing balls being located within a closed-loop ball path channel formed into a respective one of said plurality of said support blocks, said closed-loop ball path channel having a contacting path portion where said plurality of bearing balls selectively and movably engaging said worm screw, said contacting path portion having a depth larger than a radius of said plurality of bearing balls, said contacting path portion being curved about the screw axis so as to span over and in register with said arc segment; and said curved contacting path portion lying in a plane oriented with a contacting angle similar to the thread angle, each of said plurality of support blocks allowing each said plurality of bearing balls, when being in meshing engagement with said worm screw, to be spaced from an adjacent one of said plurality of bearing balls; whereby said worm screw being always in meshing engagement with at least one of said plurality of support blocks.

In one embodiment, each said bearing ball successively and movably engaging said worm screw over said arc segment thereof when entering said contacting portion of said closed-loop ball channel.

Typically, a width of at least said contacting portion of said closed-loop ball channel has a width adapted to allow displacement of said bearing balls located therein in a direction generally perpendicular to a direction of displacement along said contacting portion.

Typically, a bottom wall of said closed-loop ball path channel is profiled.

Conveniently, the contacting portion of said bottom wall is raised relative to the remaining portion thereof so as to allow only said bearing balls located over said contacting portion to be successively in meshing engagement with said worm screw.

Conveniently, the contacting portion of said bottom wall is spaced from the remaining portion thereof by an upward slope section and a downward slope section located therebetween, said contacting portion with said upward and downward slope sections forming a front section of said closed-loop ball path channel.

Conveniently, at least a top portion of the bearing balls located only within said front section of said closed-loop ball path channel are exposed to selectively contact said worm screw.

In one embodiment, each said support bloc includes a lower section and an upper section, said closed-loop ball path channel being formed at least partially within said lower section, said upper section having said channel opening formed therein.

Typically, the upper section extends laterally beyond said lower section for protection of said plurality of bearing balls against weather conditions.

Conveniently, the upper section is shaped so as to follow a shaped thread of said worm screw.

In one embodiment, the apparatus further includes an actuator mechanism connecting to said worm screw for selectively actuating rotation thereof.

In one embodiment, the worm screw is a hollow screw, said actuator mechanism mounting inside said hollow screw for selective actuation thereof.

Conveniently, the worm screw has a thread with a first pitch at a first end thereof, a last pitch at a second end thereof and at least one intermediate pitch therebetween, at least one of said first and last pitches being larger than the at least one intermediate pitch.

Typically, the worm screw has a thread with a thread angle being equal or less than three (3) degrees.

In one embodiment, the worm screw includes at least one thread helically extending therearound, said thread having an arcuate recess extending inwardly into and circumferentially all along a contacting surface of said thread for alignment of said balls selectively meshing therewith.

Conveniently, the arcuate recess tapers wide at least one helical end of said thread for self alignment of said at least one bearing ball at meshing engagement thereof with said worm screw.

In one embodiment, the apparatus further includes a safety mechanism connected to said worm screw to prevent locking and unlocking of rotation thereof as long as said mobile component is either anchored to or released from the structure.

In one embodiment, the arc segment of said worm extends over a range between about ten (10) degrees and about sixty-five (65) degrees.

Conveniently, the closed-loop ball channel has ball retaining wall protrusion to prevent said bearing balls from being spaced from a bottom wall of said closed-loop ball path channel.

Typically, the ball retaining wall protrusion is a top wall of said closed-loop ball path channel in a remaining portion other than the contacting portion thereof.

According to another aspect of the present invention, there is provided a scaffolding system comprising a mobile platform, an elongate tower and a load displacement apparatus as described hereinabove connected to the platform and the tower for selective displacement of the platform along the tower, wherein the platform and the tower form the mobile component and the fixed structure respectively.

In one embodiment, the tower includes a pair of substantially parallel elongate beams, said plurality of support blocs interconnecting said beams to one another.

In one embodiment, the tower has a peripheral wall with a longitudinal slit extending therealong and defining an open cross section of said tower, said worm screw being located inside said open cross section.

Typically, the platform is located outside the tower, said platform including a link structure connecting to said worm screw, said link structure extending through said longitudinal slit.

Conveniently, the system further includes at least one work platform located outside of the tower and releasably attaching thereto, said at least one work platform being releasably anchorable to the mobile platform for displacement thereof along the tower.

Typically, the mobile platform is releasably anchorable to the tower at selective positions therealong.

Conveniently, the link structure includes a safety mechanism connected thereto to prevent locking and unlocking of rotation of said worm screw as long as said mobile platform is either anchored to or released from the tower.

In one embodiment, the plurality of support blocs are arranged in a magazine movably connected to the tower to convey said support blocs along the tower in a preceding relationship relative to the worm screw.

In one embodiment, the plurality of support blocs are arranged in groups, all said support blocs of each said group simultaneously selectively being in meshing engagement with said worm screw.

Conveniently, all said support blocs of each said group simultaneously selectively being in meshing engagement with said worm screw over a 360-degree section of a thread thereof.

Other objects and advantages of the present invention will become apparent from a careful reading of the detailed description provided herein, with appropriate reference to the accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to the annexed drawings the preferred embodiments of the present invention will be herein described for indicative purpose and by no means as of limitation.

Referring toFIG. 1, there is schematically shown an embodiment of a load displacement apparatus or system10in accordance with the present invention. Although it is obvious to one having ordinary skill in the art that the load displacement apparatus10could be used in many different configurations in different technical areas, only the configuration of a lifting mechanism18of a scaffolding system12will be described in further details hereinbelow.

Referring more specifically toFIGS. 1 and 2, the scaffolding system12includes a generally vertically oriented tower14or post that supports a platform16movable there along. Typically, the tower14is rectangular in cross-section but could also be of any polygonal shape or circular shape without departing from the scope of the present invention. Typically, a mobile component20of a lifting mechanism18mounted on the platform16meshes with a corresponding fixed component22connected to the tower14.

As seen more specifically inFIG. 3, the mobile component20of the lifting mechanism18is typically a worm screw24mounted on the platform16via conventional roller bearings25or the like for free rotation about its generally vertical axis26. The worm screw24is meshable with a plurality of support blocs or blocks28(it is noted that all words ‘bloc’ and ‘blocs’ appearing hereinafter have the intended meaning of ‘block’ and ‘blocks’, respectively) that form the fixed component22of the lifting mechanism18. The support blocs28are typically equally spaced from one another along a side wall30of the tower14such that at least one, preferably two, support bloc28is fully engaged by a thread23of the worm screw24at any given longitudinal position of the platform16along the tower14. The tower14could also include a plurality of vertical beams15linked together via the support blocs28, as shown inFIGS. 3 and 9.

The platform16supporting the mobile component20of the lifting mechanism18is movably guided along the tower14using a guiding mechanism, typically side rollers31, conventional in the art, or the like rollably connecting to the tower14.

As shown inFIGS. 3 to 8, in order to significantly reduce the friction between the worm screw24and the support blocs28, the latter includes a bearing32, formed of at least one support or bearing ball34movably or rollably mounted on the support bloc28, that extends over a contacting angular or arc segment33of the thread23of the worm screw24along which it is in contact therewith to support the weight of the entire platform16including any equipment, material or workers standing thereon during its up and down displacements along the tower14.

As shown inFIGS. 3 to 8, the bearing32typically includes a plurality of support balls34rolling within a lower open loop channel36at least partially, typically entirely, formed within a lower section38of the support bloc28and defining a closed-loop ball path channel. Preferably, the balls34have their top portion exposed along a front section40of the lower loop channel36. When outside of the front section40, the balls34are typically fully covered by an upper open loop channel42(seeFIGS. 5 and 7) formed within an upper section44of the support bloc28. Typically, the lower loop front section40extends over at least a contacting portion46of the lower loop channel36which corresponds to the angular segment33in which the balls34′ contact the worm screw24and support the platform16. Obviously, the balls34′ of the bearing32typically lie within a plane oriented with a contacting angle similar to the pitch angle47of the thread23of the worm screw24it meshes with as seen inFIG. 8. Although the pitch angle47could be selected to any value, it is preferably three degrees (3°) or less, at which angle the frictional forces inside the bearing32are sufficient to prevent an accelerated free rolling fall of the screw in case of inadvertent failure of all other safety mechanisms.

The closed-loop path channel followed by the balls34could also lie in a generally vertical plane, for substantially horizontal displacement of the worm screw in relation therewith, without departing from the scope of the present invention. In such a case, each bloc28would typically include a second bearing for engaging the opposite side of the thread23during displacement of the worm screw24in the reverse direction. Alternatively, a second series of blocs28could be used to engage the opposite side of the thread23. Accordingly, the displacement trajectory of the mobile component20could also be inclined, and any trajectory could be either rectilinear or curved such that, for example, the load displacement apparatus10of the present invention could well be used to displace a load in a vertical trajectory that gradually changes to a horizontal one.

In order to prevent the balls34,34′ to come out from the channel36, as more specifically illustrated inFIGS. 13 to 14, the channel36typically has a depth D larger than the radius R of the balls34,34′ (at least in the contacting portion46thereof) and a transverse (as seen in a crass-sectional plane of the channel) channel opening49smaller than a diameter 2R of the balls34,34′.

Accordingly, the channel opening49is defined by a ball retaining wall protrusions49′ (at least on one side of the channel but preferably on symmetrically on both sides thereof) that further prevent the balls34,34′ from being spaced from the bottom wall48of the channel36. The ball retaining wall protrusions49′ contribute to prevent any zig-zag phenomenon that would cause wear and ultimately jamming of the bearing32. As shown inFIG. 5, the ball retaining wall protrusions49′ are provided at the remaining portion of the channel36(other than the front section40) by the top wall42′ of the upper open loop channel42formed within the upper section44.

As detailed inFIGS. 7 and 8, the bottom wall48of the lower loop channel36is typically profiled at least over a portion of the front section40, that includes the contacting portion46(seeFIGS. 4 and 6) in which the balls34′ contact the worm screw24, to ensure that each ball34successively gets into contact with the worm screw24, one at a time after being pushed by the following balls34ramping up the upward slope40u, without contacting adjacent balls34once in contact with the screw24(due to a pulling effect caused by the contact therewith). Accordingly, just before contacting the thread23of the worm screw24, a ball34engages an upward slope40uof the bottom wall48along the angular segment33at a location adjacent the beginning of the contacting portion46to be slightly raised and displaced away from the following ball34. The bottom wall48has a following downward slope40dalong the angular segment33at a location adjacent the end of the contacting portion46to allow the balls34′ to disengage from the thread23of the worm screw24and smoothly follow a return portion of the lower loop channel36by pushing on the preceding balls34. Accordingly the balls34are typically spaced enough from the contacting surface of the thread23to be able to travel generally radially relative therefrom at both ends of the front section40spanning over and in register with the angular segment33. Typically, the contacting portion46circumferentially extends or spans over about ten and about twenty-five degrees) (10°-25°, although it could be a singular point (in the case of only one ball34′ contacting the screw thread23) or even extend beyond 25°. Similarly, both the upward and the downward slopes40u,40d(or vice versa depending on the direction of displacement of the screw23relative to the blocs28) typically circumferentially extend over about ten and about twenty degrees (10°-20°. These above angle values are provided as examples only and could vary without departing from the scope of the present invention.

As shown inFIGS. 4 and 8, the balls34′ typically engage an arcuate recess50extending inwardly and circumferentially all along the contacting surface52of the thread23of the worm screw24to ensure proper alignment of the worm screw24with the support blocs28.

In case of hazard occurring at the bearing32level (such as the collapse or destruction thereof), the supporting bloc28itself would support the load of the platform16and prevent the latter from falling down at incontrollable speeds because of the screw thread23directly engaging the support blocs28.

As shown inFIGS. 1 and 2, an actuator54for rotating the worm screw24is also mounted on the platform16generally adjacent the worm screw24. Typically, the actuator54is connected to the worm screw24via a reducer gearbox56or the like, the latter forming an actuator mechanism with the actuator54. As it would be obvious to one skilled in the art, the actuator54could be any conventional actuator such as an electric motor, a stepper motor, a generator vector motor (acting as a motor in one direction and as a generator in the other), a hydraulic motor, a pneumatic motor, an internal combustion engine, a steam engine or the like. Depending of the actuator54considered (such as pneumatic motor or steam engine), one can have a submersible platform if required, for underwater activities such as for port installations, boatyards, shipyards, drilling platforms, large swimming pools and the like or in toxic gaseous environment working conditions.

Obviously, when used in a scaffolding system12, the actuator54could only actuate the worm screw24in one direction to raise the platform16since the gravity can be used to lower the platform16. In such a case, the lifting mechanism18obviously includes a brake mechanism58to control the rotational speed of the worm screw24, especially during the downward displacement thereof. The brake mechanism58can include a plurality of parallel braking systems using conventional drum brakes, disc brakes, a safety gear (pawl or grige gear) or the like or even frictionless resistive magnetic brakes that could eventually recuperate the braking energy to recharge a battery, or magnets with non-nuclear low molecular magnetic fields (neodium magnets) or using the molecular resistance of high density antistock transmission oils or the like. The brake mechanism58could possibly be embedded within the gearbox56if preferred.

On the other hand, the actuator54could be a double action actuator or the gearbox56could include a switching mechanism (not shown) to reverse the rotation of the worm screw24.

Alternatively, as shown inFIG. 9, the actuator54′, the gearbox56′ and the brake mechanism58′ could be entirely or at least partially located inside the hollow worm screw24′. In such a case, the gearbox56′ could be a planetary-type reducer gearbox.

Furthermore, in a situation with at least two scaffolding systems12assembled side-by-side, the adjacent platforms16mounted on adjacent towers14could have retractable couplings (not shown) such as telescopic splines connectable to one another to enable an operator to either control all platforms16with only the lifting mechanism18of one of the towers14or to synchronize the actuation of all lifting mechanisms18of all the towers14.

As described hereinabove, the mobile component20of the lifting mechanism18is typically mounted on the platform16. Now referring more specifically toFIGS. 10 and 11, the mobile component120of the lifting mechanism118is alternatively connected to or mounted on a service platform116. Furthermore, instead of being located outside of the tower114, the lifting mechanism118is substantially located inside the limits of the generally open cross section of the tower114such that the peripheral wall of the open tower114includes at least one longitudinal slit115extending there along, shown in the front thereof. Such an open tower114could also have an H-shaped cross section (not shown) without departing from the scope of the present invention. The fixed component122of the lifting mechanism118is typically connected to an internal surface of the tower114. A link structure117extending through the tower slit115connects the lifting mechanism118to the service platform116located outside the tower114. When relatively long towers114are used, a plurality of tower anchors113secure the tower114to an adjacent building structure111at generally regularly spaced intervals. Typically, the tower anchors113connect to the tower114on a side generally opposite to the longitudinal slit115.

In such a scaffolding system112, the work platforms116areleasably attached to the tower114at same levels or not are typically located on either side of the tower114adjacent the building structure111to balance the overall load supported on both sides of the tower114, as shown inFIG. 11. The service platform116is used first to successively displace the different work platforms116areleasably anchored thereto up to their respective desired location along the tower114and release them when the work platform116aare properly secured to the tower114, and second to carry material and workers from/to the ground to/from the different work platforms116aor between work platforms116a. For example, the service platform116could also carry a manual or remotely operable lifting or handling arm160mounted thereon to lift and displace the material between the service platform116and the different work platforms116a. The handling arm160can also serve to handle tower longitudinal sections for self-erection of the tower114.

Typically, the service platform116needs to be anchored to the tower114to enable the anchoring of the work platform to the tower114. A safety mechanism162prevents the operator from blocking and unblocking the rotation of the worm screw124unless the service platform116is either anchored to the tower114, at any selective position there along, with platform anchors164being in full engagement configuration or released therefrom with the platform anchors164being in full released configuration.

The safety mechanism162includes a retractable shear pin166mounted on the link structure117and releasably engageable into one of a plurality of bore holes168integral with the worm screw124and circumferentially spaced from one another about the axis126thereof.

The link structure117supporting the mobile component120of the lifting mechanism118is movably guided along the tower114using a guiding mechanism, typically side rollers131, conventional in the art, or the like rollably connecting to the tower114.

Although shown with similar side rollers131a, the work platforms116adon't really need these side rollers131asince they are selectively carried by the service platform116when displaced along the tower114while not being supported thereby or anchored thereto.

When no side rollers131aare used to guide the work platforms116aalong the tower114, the shape of the work platforms116aaround the tower114typically at least partially follows or embraces the cross-sectional projections of the tower114such as corner posts170or the like to prevent the work platforms116afrom separating from the tower114and falling down in case of inadvertent disengagement of the anchor connecting the two together. In such an undesirable situation, the work platform116awould slightly tilt relative to the tower114and remain hooked thereto until emergency actions are taken.

To increase the load capability of the support blocks28could include at least one additional bearing32(not shown) that would lie in a substantially parallel path relative to the other over a substantially similar angular segment33. Accordingly, one of the lower loop channels36would fully enclose the other one.

Alternatively, the bearing32could includes only one ball34rotatably mounted on a shaft (or two coaxial shafts) generally perpendicular to the thread23of the worm screw24. Furthermore, the ball34could be a roller rotatably mounted on a shaft extending there through with an arcuate contacting surface to prevent wear thereof during rolling engagement with the thread23of the worm screw24.

As illustrated inFIGS. 12 and 13, each support bloc28could include a bearing cover80, or extended upper section, to protect the bearing32or balls34from the different weather conditions. The bearing cover is either permanent and spaced from the balls34to allow the thread23of the worm screw24to pass there between when in meshing engagement with the balls34, or movable (not shown) between a bearing covering position when the support bloc28is not in meshing engagement with the worm screw24and an open configuration away from the bearing when the support bloc28is in meshing engagement with the worm screw24. The cover80is typically shaped to get around or partially follow a shaped thread82that protrudes radially, outwardly and upwardly from the worm screw body84. Such a cover80generally extends laterally (circumferentially and radially) beyond the support bloc28to fully protect the bearing32therein.

For heavy duty lifting mechanism18, the support blocs28could be arranged in groups (not shown) of preferably three blocs28typically simultaneously engaging a same 360-degree section thread23of the worm screw24. Each bloc group would typically cover an overall segment large enough (such as about 240 degrees with the three blocs28spaced about 120 degrees from each other) not only to ensure the engagement of the worm screw24with the group of support blocs28but also to further ensure longitudinal guiding of platform16relative to the tower14and forming the guiding mechanism instead of the side rollers31. The bloc groups are obviously spaced from one another, typically equally, such that at least one group is in good engagement with a same 360-degree section thread23of the worm screw24at any location along the tower14.

Although not illustrated in the Figures, a plurality of support blocs28could also be arranged in a loop tray or magazine of support blocs28movably connected to the tower14that would be conveyed along the tower14in parallel to the worm screw24by always preceding the latter (in either up and down directions). The support blocs28would slidably engage and disengage successive bloc receptacles spaced apart from one another along the tower14. The fine alignment of the support blocs28with the thread23of the worm screw24could be ensure by the balls34′ engaging the arcuate recess50extending inwardly and all along the contacting surface52of the thread23, or the like alignment mechanism. Such an arcuate recess50allows the balls34′ to have a slight radial misalignment relative to the screw thread23and allow the proper realignment thereof. As highlighted inFIG. 14, the width W of at least the contacting portion46, and preferably the front section40, of the channel36is slightly larger than the diameter 2R of the balls34′ to allow transverse displacement of the balls34′ located therein in a direction (represented by the ball34′ shown in the two extreme positions in solid and dashed lines) generally perpendicular to a direction of displacement along the channel36. It is noted that the small transverse displacement is small enough to prevent the above-mentioned zig-zag phenomenon that could lead to wearing and/or jamming of the bearing32.

In order to be stronger in reducing some weak points of the apparatus10that could cause breaking of the support bloc28, the latter is preferably made out of a single piece, as schematically exemplified inFIG. 13ain which all the balls34,34′ are kept captive into the entire loop channel36. The ball access to the channel is a rear bore hole60with a threaded counter bore62closed by a corresponding screw plug64or the like which could locally act as the channel bottom wall48′.

As partially shown by numeral reference50′ inFIG. 4, both helical ends23′ of the thread23of the worm screw24taper wide, radially, circumferentially and/or axially, to ensure a smooth and gradual meshing engagement of the bearings32of the different support blocs28that may not be perfectly aligned. In doing so, the balls34′ will self align because of the arcuate widen recess50′ of the contacting surface52of the worm screw24. To account for small variations of the distance between successive support blocs28, the screw24typically has at least one, preferably both end threads with an end pitch P2(seeFIG. 1) slightly larger than the nominal intermediate pitch P1, typically by about 1/16thof an inch over 24 inches (about 1.5 mm over 60 cm), namely about 0.14 degree as an example.

Although the present load displacement apparatus has been described with a certain degree of particularity, it is to be understood that the disclosure has been made by way of example only and that the present invention is not limited to the features of the embodiments described and illustrated herein, but includes all variations and modifications within the scope and spirit of the invention as hereinafter claimed.