Push actuator

This telescopic tube is formed of a first and of a second continuous bands wound in a spiral and in a helix, respectively, with the turns of each band lying flat against each other in the retracted position of the tube. The turns of the respective bands are normal to one another. To extend the tube, the turns of the first band are spaced from each other, and the turns of the second band are inserted between the spaced turns of the first band, so as to act as spacers for the latter turns. A mechanism is described to cause extension and retraction of the tube which is mainly used as a push actuator.

FIELD OF THE INVENTION 
The present invention relates to telescopic tubes, more particularly to be 
used as push actuators. 
BACKGROUND OF THE INVENTION 
Telescopic, single-acting hydraulic cylinders can be considered as push 
actuators. There is a practical limit in increasing the number of 
telescopic sections of such a hydraulic cylinder for the same to be 
confined within a minimum longitudinal extent when in retracted position. 
Therefore, such actuators, depending on the required stroke, occupy quite 
an important minimum length, when retracted. When used as a lifting 
device, for instance when several such cylinders are used to lift a floor 
section of a theatre scene, it is necessary to make important excavations 
in the ground to house such cylinders at their lower end portion. 
It has been found that in certain locations, the water level in the ground 
does not permit such excavations. Therefore, there is a need for such 
particular theatre applications and also for some other applications where 
the available room is limited, to provide a push actuator which takes a 
minimum of length when retracted relative to its extension stroke. 
OBJECTS OF THE INVENTION 
The general object of the present invention is to provide a telescopic 
tube, which, for a given extension stroke, occupies minimum length when in 
retracted position. 
Another object of the present invention is to provide a telescopic tube 
used as a push actuator which is of simple mechanical construction and 
which can exert a very high pushing force. 
Another object of the present invention resides in the provision of a push 
actuator more particularly to be used as a lifting device or jack for 
lifting and lowering heavy loads. 
SUMMARY OF THE INVENTION 
The telescopic tube of the invention comprises a first annular band wound 
in helical form about a central axis with its turns transversely normal to 
said central axis and capable of taking a retracted stacked position, with 
its turns resting flat against one another, and an extended position with 
its turns spaced from one another in the direction of said central axis, a 
second band wound on itself, with its turns transversely parallel to said 
central axis, and capable of taking a retracted spiral position with its 
turns nested one within another and an extended position with its turns 
forming a helix around said central axis and generally equally, radially 
spaced therefrom to form a tube, said first and second bands, when in 
retracted position, in respective locations so as to clear each other, 
spacer means to successively space the turns of said first band, driving 
means to cause relative rotation of said first band of said spacer means 
about said central axis, and guide means to insert the turns of the second 
band between the spaced turns of the first band, with the edges of the 
turns of the second band bearing against the turns of the first band, the 
second band thus forming a spacer for the latter turns of the last band. 
Said spacer means preferably include a support means forming a helix about 
said central axis, engageable between two successive turns of said first 
band and bearing against one of said turns. Preferably, the second band 
has an unstressed radius of curvature about equal to that of the extended 
tube. This causes easy insertion of the second band between the turns of 
the first band. 
In one embodiment of the invention, said driving means include a power 
driven rotor rotatable about said central axis on a base, and surrounding 
the retracted first band. Said support means is fixed to the inside of 
said rotor and the retracted portion of said second band is carried by 
said rotor on the outside thereof. Said guide means is carried on the 
outside of said rotor. Locating means is carried by the turns of the first 
band and is engageable by the turns of the second band to locate the 
latter turns transversely of the turns of the first band. 
In a second embodiment, both bands and the support means are arranged on 
the outside of the power-driven rotor.

In the drawings, like reference numerals indicate like elements throughout. 
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIG. 1 shows two lifting jacks in accordance with the invention, generally 
indicated at 10, fixed to the ground 12 at their lower end and to a 
platform 14 at their upper end, the jacks 10 raising and lowering the 
platform 14. The platform 14 can be a section of a theatre scene, in which 
case there would be provided several jacks 10 to lift the same in 
synchronism. 
Referring to FIG. 2, each jack 10 of the first embodiment comprises an 
annular base 16 anchored to the ground 12, by means of L-shaped ground 
anchors 18 and nuts 20, or any other suitable anchoring means. 
A rotor 22, in the form of a cylindrical body with a lower radially- 
outwardly-extending flange 24, is rotatable on the base 16 by means of 
roller bearings 26 engaging annular V-shaped grooves made in the base 16 
and lower flange 24. Thus, the rotor 22 is rotatable about the central 
axis of the base 16 and rotor 22. The peripheral edge of the lower flange 
24 forms gear teeth 28 all around, in meshing engagement with a driving 
gear 30 (see FIG. 3) driven in rotation in both directions by a suitable 
motor, such as a reversible hydraulic motor, not shown. 
A first continuous annular band 32, which will hereinafter be called the 
horizontal band for the particular application shown, is wound in an helix 
and is of such an external diameter as to fit within the rotor 22 and the 
base 16. The turns of this horizontal annular band can be successively 
lifted to provide a space therebetween. The lower end of the horizontal 
band 32 simply rests on the floor or ground G, while its upper leading end 
34 is secured underneath the platform 14 by means, not shown. 
A second band 36, hereinafter called the vertical band for the particular 
application described, is wound in spiral form, said band being 
continuous, and when in stacked condition, located within an annular 
storage box 38, disposed on the outside of rotor 22 and rotatably 
supported with respect to said rotor by means of three equally-angularly 
spaced L-shaped brackets 40 (see FIGS. 2 and 3) fixed to the outside of 
rotor 22 by bolts 42 and provided at their outer end with an idle roller 
44 rotatably supporting the storage box 38. Brackets 40 could be fixed to 
floor G or to base 16. 
As shown in FIG. 2, it is clear that the coil formed by vertical band 36 
has a minimum diameter which is greater than the external diameter of the 
horizontal band 32, so as to clear the horizontal band when the latter is 
practically fully stacked, or when it is being extended. The radially 
outer end of the vertical band 36 need not be secured to the storage box 
38. The radially inner leading end of the vertical band 36 extends through 
a rectangular opening 46 of rotor 22, inwardly of this rotor, and is 
tapered widthwise, as shown at 48 in FIG. 2, to be secured to the 
underside of the platform 40 by suitable means, such as a 
cross-sectionally I-shaped member 50. Leading end 48 fits between the 
radially inner flanges of member 50, the latter being longitudinally 
tapered as the leading end 48 and being directly secured underneath the 
platform 14. Therefore, the platform is maintained in level condition 
despite the fact that the vertical band 36 extends upwardly along a helix, 
as shown. 
The rotor 22 is provided along its internal surface with a series of 
equally-spaced idle rollers 52, each mounted on a horizontal shaft 54, 
secured to the rotor by means of a nut 56. The idle rollers 52 are 
generally equally spaced for a full circle around the inside of the rotor 
22 and arranged in a helix in accordance with the desired pitch of the 
assembly of the horizontal band 32 and vertical band 36. As shown in FIG. 
2, the leading roller 52A is longitudinally aligned with the elongated 
opening 46, itself inclined in accordance with the above-noted pitch. The 
trailing roller 52B is vertically above and spaced from the leading roller 
52A. 
It will be understood that when the rotor 22 is rotated in accordance with 
arrows 58, shown in FIG. 1, in a direction to elevate platform 14, the 
idle rollers 52 will roll under the radially outer margin of the turns of 
the horizontal band 32 (see FIGS. 2 and 4), so as to space the same from 
the underlying adjacent turn. At the same time, the vertical band 36 
enters opening 46 and is guided radially inwardly by the inner flat faces 
of the rollers 52 to be inserted between two adjacent turns of the 
horizontal band 32. As the horizontal band 32 is being elevated by 
rotation of the rotor, and consequently of the rollers 52, along an helix 
concentric with the central axis of the rotor, the vertical band is 
gradually inserted between the adjacent turns of the horizontal band, so 
as to gradually build up a kind of tube or column. As shown in FIG. 2, 
insertion of the vertical band is facilitated, since the weight of the 
horizontal band at the point of insertion causes the latter to form a gap 
60. 
Means are provided to properly locate the vertical band between adjacent 
turns of the horizontal band. These means are more clearly shown in FIGS. 
4 and 5. At the same time, these means allow flat stacking of the 
horizontal band in retracted position (see FIG. 2). These locating means 
include a plurality of studs 62 press-fitted within certain ones of a 
series of equally-spaced corresponding through-bores 64 made through the 
horizontal band 32, these through-bores 64 being at an equal distance from 
the outer peripheral edge of the horizontal band 32. As shown in FIG. 5, 
some of the studs 62 are upwardly directed, while the others are 
downwardly directed; this to locate both the top and bottom edges of the 
vertical band 36, this band abutting against said studs. 
Some of the through-bores 64 are left without any studs, so as to receive 
the studs of the next adjacent turn of the horizontal band when the same 
is in retracted position, the protruding portion of the studs 62 not being 
any longer than the thickness of the horizontal band. 
In this manner, flat stacking of the horizontal band is obtained to store 
the same in a minimum of height. As shown in FIG. 4, the assembly of two 
adjacent turns of the horizontal band 32, with a turn of the vertical band 
36 inserted therebetween, forms a substantially I-shaped cross-section. 
The resulting assembly is very strong and can support a very large load, 
and yet it is very stable transversely of the central axis. Depending on 
the length of the two bands 32 and 36, the push actuator of the invention 
can have a very long stroke compared to its length when the two bands are 
in retracted position. 
Preferably, the vertical band is pre-rolled to possess when unstressed, a 
radius of curvature about equal to that of the assembled tube. This 
facilitates proper insertion of the vertical band between the turns of the 
horizontal band. 
Magazine or box 38 is free to rotate about the tube axis to permit vertical 
band insertion and removal despite the resulting variation of the internal 
diameter of the coil formed by the vertical band in the box 38. 
The second and preferred embodiment of the invention is illustrated in 
FIGS. 6 and 7. Also, FIG. 8 shows the preferred arrangement of the 
locating means for locating the vertical band transversely and centrally 
of the horizontal band. The locating means, shown in FIG. 8, are designed 
to replace the locating pins 62 inserted in holes 64 of the horizontal 
band 32, as illustrated in FIG. 5. The improved locating means simply 
consist of an upper and a lower continuous groove 70 made in the opposite 
main faces of the horizontal band 72. The grooves are disposed centrally 
of the width of the horizontal band 72 and are coaxial and co-extensive 
therewith. Thus, the grooves 70 serve to receive the longitudinal edges of 
the vertical band 74 to properly locate and retain the latter transversely 
of the horizontal band 72. 
This modified arrangement can be used with the apparatus of FIGS. 1 to 4 as 
well as the apparatus shown in FIGS. 6 and 7. The telescopic tube shown in 
FIGS. 6 and 7 includes a base 76, of cylindrical shape, fixed to a ground 
plate 78. A rotor 80 is rotatably supported on the cylindrical base 76 
through a ball bearing arrangement 82. The rotor 80 includes a cylindrical 
wall 84 press-fitted to an end disc 86. 
The rotor 80 is power driven by a motor, not shown through a sprocket chain 
88, trained on a sprocket gear 90, the shaft 92 of which is fixed to the 
underside of disc 86. Sprocket chain 88 issues through openings 94 made in 
cylindrical base 76. The several turns of the horizontal band 72 are 
stacked, when the band is in retracted position, on a flange 96 radially 
outwardly protruding from and secured to the base 76. Thus, the horizontal 
band 72 is coiled on the outside of the rotor 80. 
A plurality of rollers 98 are mounted on the rotor 80 near the upper edge 
thereof on the outside of said rotor about radially-directed and 
downwardly-directed axes defined by retaining bolts 100. The rollers 98 
are frusto-conical in shape so as to support a turn of the horizontal band 
72 in transversely-horizontal position normal to the central axis of the 
rotor 80. Each roller 98 has a tapered flange 102 to engage the inner 
longitudinal edge of the horizontal band 72 and center this band with 
respect to the rotor. 
The rollers 98 are arranged in a helix through a full turn around the 
rotor, with the leading lower roller indicated at 98A and the trailing 
higher roller at 98 B with respect to the rotation of the rotor when the 
column or tube is being elevated. 
The vertical band 74 is wound in a coil, indicated at 104, which is housed 
in an annular magazine or box 106 freely rotatably mounted on support 
wheels 107, 108 and 109 carried by upright arms 110 fixed at their lower 
end to the flange 96 outwardly of the horizontal band 72. The annular 
magazine 106 is of a minimum diameter greater than that of the horizontal 
band 72, so that the latter may freely extend through the magazine 106. 
The magazine is mounted for free rotation about the central axis of the 
tube or column. The vertical band 74 is pre-rolled or pre-formed to have a 
radius of curvature, when in unstressed condition, about equal to the 
diameter of the tube or column once the latter is assembled. The outermost 
turn of the coil 104 is led upwardly from the magazine and guided to move 
radially inwardly along a helix to be inserted between two adjacent turns 
of the horizontal band 72, the vertical band being guided by a guiding 
roller 112 (see FIG. 7), which is rotatably carried by a bracket 114 
secured to the rotor 80. The roller 112 is rotatable about an axis 116, 
which is parallel to the central axis of the rotor 80, and the roller is 
applied against the outside face of the vertical band 74 to press the same 
for insertion between two adjacent turns of the horizontal band 72. 
A rod 118 is also secured to the rotor 80 and extends radially outwardly 
therefrom to be applied against the top of the coil 104 at a position just 
before the outermost turn of the coil starts to move upwardly. This rod 
118 serves to return the turns of the vertical band 74 in proper stacked 
position within the magazine 106 when the column is retracted. The guide 
roller 112 positively moves the vertical band 74 into engagement with the 
grooves 70 of the adjacent turns of the horizontal band 72. 
The topmost end of the column may be defined by a pusher plate 120, which 
is fixed to the uppermost turn of the vertical band 74, the latter being 
tapered so that the plate 120 be normal to the central axis of the column 
or tube.