Patent Publication Number: US-7213796-B2

Title: Linear actuator with releasably interlocking bands

Description:
FIELD OF THE INVENTION 
   The present invention relates to a linear actuator, and more particularly to a linear actuator with releasably interlocking bands that form a retractable telescopic column. 
   BACKGROUND OF THE INVENTION 
   U.S. Pat. No. 4,875,660 issued in 1989 to the inventors Pierre GAGNON and Pierre LAFOREST (the inventor of the present invention), hereafter the “Gagnon patent” which is hereby incorporated to the present specification by way of reference, shows a push actuator to be used as a pushing device, for example instead of a hydraulic cylinder. The push actuator of the Gagnon patent has the advantage of requiring less space than conventional hydraulic cylinders when in a contracted position, due to the fact that no concentric column portions have to be stored within each other. Also, it can support very heavy loads, since it forms a cylindrical column when in an extracted position, without any concentric portions as with a hydraulic cylinder, and this vertical structure has a high vertical rigidity in compression. Very important world-wide commercial success of the push actuator of the Gagnon patent has proven it to be a very advantageous alternative to conventional hydraulic cylinders. 
   The Gagnon push actuator generally works as follows. A hollow cylindrical rotor is rotatably carried over a base fixed to the ground. A motor selectively activates the rotor. A first horizontal band is vertically stacked in a helix and rests on the ground, while a second vertical band is horizontally stacked in a spiral, the latter located in an annular magazine located co-axially around the rotor. The upper end of each band is fixedly attached to a load-bearing platform. When the rotor is rotated, each turn of the vertical band is guided and installed in helical configuration between two vertically successive turns of the horizontal band, to thus gradually form a vertical telescopic column. The load of the platform supported by the push actuator is induced through the vertical and horizontal band turns which rest on each other, and then to idle rollers provided on the rotor which support the horizontal band. 
   One problem associated to the push actuator of the Gagnon patent is that the horizontal and vertical bands simply rest on each other without being interlocked in any way. This is not problematic when a load is applied on the push actuator platform both axially and in compression, since the push actuator has a very important vertical load-bearing capacity. However, the structural integrity of the column is likely to be compromised if a force is exerted on the column perpendicularly to its central axis. Indeed, in such a case, the two intertwined bands of the column may accidentally disengage themselves from one another, which would lead to the column collapsing. To circumvent this problem, the push actuator of the Gagnon patent is usually used together with guiding devices, such as scissor-type linkages, that prevent lateral movement of the load carried by the push actuator. Indeed, the scissor-type linkages will only allow the load being carried to be moved in the direction of the axis of the push actuator. Also, it can be seen that the vertical column of the Gagnon push actuator may not be submitted to any type of tension force, since once again the two intertwined bands would disengage themselves from each other and the column would collapse. 
   SUMMARY OF THE INVENTION 
   The present invention relates to a linear actuator comprising:
     an elongated first band wound in helical form about a central axis and capable of taking a retracted position and an extended position with its turns spaced from one another in the direction of said central axis;   first fastening means carried by said first band and longitudinally disposed therealong;   an elongated second substantially flat band wound on itself, with its turns substantially transversely parallel to said central axis, and capable of taking a retracted, spiral position with its turns nested within one another and an extended position with its turns forming a helix around said central axis and generally equally radially spaced therefrom to form a telescopic column, said first and second bands, when in retracted position, in respective locations so as to clear each other;   second fastening means carried by said second band and longitudinally disposed therealong, said second fastening means capable of cooperating with said first fastening means to releasably interlock said first and second bands;   spacer means to successively space the turns of said first band;   drive means to cause relative rotation on one hand of said first and second bands and on the other hand of said spacer means about said central axis;   guide means to guide the turns of said second band towards the turns of said first band to releasably interlock said first and second fastening means; and   retaining means retaining said first and second fastening means in interlocked fashion in said telescopic column.   

   In one embodiment, each said two consecutive turns of said second band that form said retractable telescopic column partly overlap to form an overlapping section, with a portion of said first band being wound in a helix adjacent to said overlapping section and with said first and second fastening means engaging each other at said overlapping section to releasably link said each two consecutive turns of said second band that form said retractable telescopic column. 
   In one embodiment, said first fastening means comprise longitudinally spaced-apart teeth protruding from said first band, and said second fastening means comprise openings longitudinally disposed along said second band and positioned in said each two consecutive turns of said second band that form said retractable telescopic column so as to register in said overlapping section by pairs, with at least some of said pairs of openings being engaged by corresponding said teeth. 
   In one embodiment said retaining member and said guiding member are a roller mounted to said rotor. 
   In one embodiment, said second band is preformed in an inclined configuration so that each turn defines a slightly conical shape. 
   In one embodiment, said linear actuator further comprises a first anti-rotation member attached to either one of said structural and first bands and engaging a second anti-rotation member attached to said frame, wherein said structural and first bands are prevented from rotating. 
   In one embodiment, said teeth are also first anti-rotation members that cooperate with second anti-rotation members provided on said frame in spaced-apart fashion around said central axis, with at least one of said teeth engaging a corresponding space defined between two said second anti-rotation members at all times, wherein said structural and first bands are prevented from rotating while they are moved between their extended and retracted positions. 
   In one embodiment, said drive means includes a power driven rotor rotatably mounted to a first frame portion, said rotor carrying said guide means, said retaining means and said spacer means, said linear actuator also comprising a second band magazine movable relative to said rotor and said frame and carrying the portion of said second band which is in said retracted, spiral position with its turns nested within one another, said first and second elongated bands having a first end located near said first frame portion and a second end attached to a second frame portion. 
   In one embodiment, said spacer means includes a support member having a helical configuration, carried by said rotor and engaged by a portion of said first band. 
   In one embodiment, said support member is a helical groove. 
   In one alternate embodiment, said linear actuator further comprises:
     a first frame portion carrying said spacer means, said guide means, said retaining means and a second band magazine movable relative to said first frame portion and carrying the portion of said second band which is in said retracted, spiral position with its turns nested within one another; and   a second frame portion, with said drive means including a power driven rotor fixedly attached to a first end of said first and second bands and rotatably carried by said second frame portion.   

   In one embodiment, said spacer means includes a support member having a helical configuration, carried by said first frame portion and engaged by a portion of said first band. 
   In one embodiment said support member is a helical groove made in said first frame portion. 
   The present invention also relates to an elongated linear actuator having opposite first and second ends and an intermediate portion between said first and second ends, said linear actuator further defining a central axis extending between said first and second ends and comprising:
     a frame comprising a first frame portion at said first end and a second frame portion at said second end movable relative to said first frame portion between retracted and extracted positions, with said second frame portion being closer to said first frame portion in said retracted position than in said extracted position;   a rotor member rotatably carried by said first frame portion and rotatable about said central axis;   drive means, capable of selectively rotating said rotor member relative to said first frame portion;   a first elongated band wound according to a helical pattern about said central axis, having a first end portion adjacent to said linear actuator first end and a second end portion attached to said second frame portion, and comprising longitudinally disposed releasable fasteners;   a second elongated substantially flat band substantially parallel to said central axis and wound about said central axis in a helical configuration between said intermediate portion and said second end and in a spiral configuration between said intermediate portion and said first end, said second band having a first end portion adjacent to said linear actuator first end and a second end portion attached to said second frame portion;   a support member carried by said rotor in a helical pattern about said central axis, with part of said first band movably engaging said support member and allowing rotation of said rotor member relative to said first band;   a guiding member at said linear actuator intermediate portion and carried by said rotor member, said guiding member guiding said second band in a transition between its said spiral and helical configurations, said guiding member guiding each turn of said second band substantially edgewisely adjacent to the preceding turn of said second band between said intermediate portion and said second end when said rotor member is rotated in a first direction around said central axis, with said fasteners of said first band engaging and releasably linking each two consecutive turns of said second band between said intermediate portion and said second end thus forming a retractable telescopic column composed of the releasably interconnected first and second bands between said intermediate portion and said second end, with said first and said second bands each being independently stackable between said intermediate portion and said first end; and   a retaining member retaining said first and second bands in their releasably interconnected relationship between said intermediate portion and said second end.   

   The present invention further relates to a linear actuator having a central axis and comprising:
     a frame including spaced-apart and distinct first and second frame portions;   an elongated fastening band comprising a first portion of variable length stacked in a helical configuration and a second portion of variable length also having a helical configuration, said fastening band further comprising longitudinally disposed first releasable fastening means and having a first end located near said first frame portion and a second end attached to said second frame portion;   an elongated substantially flat structural band having its turns generally parallel to said central axis and comprising a first portion of variable length stacked in a spiral pattern separately from said fastening band and having a first end located near said first frame portion, a second portion of variable length having a helical configuration and having a second end attached to said second frame portion, and second releasable fastening means that can cooperate with said first fastening means to releasably interlock said structural and fastening bands;   a support member carried by said first frame portion and forming a helical pattern about said central axis, with part of said fastening band movably engaging said support member whilst allowing relative rotation of said support member relative to said fastening band;   a guiding and retaining member mounted to first frame portion; and   drive means to cause relative rotation on one hand of said fastening and horizontal bands and on the other hand of said support member about said central axis; wherein upon relative rotation on one hand of said fastening and structural bands and on the other hand of said support member in a first direction, a retractable telescopic column is formed with the second portions of said fastening and structural bands, by said fastening band being lifted and its turns being spaced through its engagement on said support member, and by each turn of said structural band being guided by said guiding and retaining member into an edgewisely adjacent configuration with respect to the preceding turn of said vertical band to form a substantially continuous cylindrical wall of said column, with said first and second fastening means engaging each other to releasably link each two successive turns of the second portion of said structural band with a corresponding turn of said fastening band, and with said guiding and retaining member retaining said first and second fastening means in their engagement at said each two successive turns of the upper portion of said structural band;
 
and wherein upon rotation of said rotor in the direction opposite said first direction, said retractable telescopic column is retracted.
   

   In one embodiment, each said two consecutive turns of said structural band that form said retractable telescopic column partly overlap to form an overlapping section, with a portion of said fastening band being wound in a helix adjacent to said overlapping section and with said first and second fastening means engaging each other at said overlapping section to releasably link said each two consecutive turns of said structural band that form said retractable telescopic column. 
   In one embodiment, said first fastening means comprise longitudinally spaced-apart teeth protruding from said fastening band, and said second fastening means comprise spaced-apart openings longitudinally disposed along said structural band and positioned in said each two consecutive turns of said structural band that form said retractable telescopic column so as to register in said overlapping section by pairs, with at least some of said pairs of openings being each engaged by a corresponding said tooth. 
   In one embodiment, said guiding and retaining member is a punctual abutment member mounted to said rotor that prevents disengagement of said teeth of said fastening band from the turn of said structural band forming said telescopic column nearest said structural band first portion, with the other turns of said structural band forming said telescopic column being securely engaged by said teeth of said fastening band as long as said turn of said structural band forming said telescopic column nearest said structural band first portion remains engaged by said teeth. 
   In one embodiment, said guiding and retaining member is a roller. 
   In one embodiment, said linear actuator further comprises an additional guiding member mounted to said rotor for guiding said second band towards the telescopic column. 
   In one embodiment, said linear actuator further comprises a first anti-rotation member attached to either one of said structural and fastening bands and engaging a second anti-rotation member attached to said frame, wherein said structural and fastening bands are prevented from rotating. 
   In one embodiment, said teeth are also first anti-rotation members that cooperate with second anti-rotation members provided on said frame in spaced-apart fashion around said central axis, with at least one of said teeth engaging a corresponding space defined between two said second anti-rotation members at all times, whereby said structural and fastening bands are prevented from rotating. 
   In one embodiment, said structural band is preformed in an inclined configuration so that each turn defines a slightly conical shape. 
   In one embodiment, said drive means includes a power driven rotor rotatably mounted to said first frame portion and carrying said guiding and retaining member and said support member, said linear actuator also comprising a structural band magazine movable relative to said rotor and said frame and carrying said structural band first portion. 
   In one alternate embodiment, said first frame portion carries said guiding and retaining member and a structural band magazine movable relative to said first frame portion and carrying said structural band first portion, with said second frame portion carrying said drive means that includes a power driven rotor fixedly attached to said first end of said fastening and structural bands and rotatably carried by said second frame portion. 

   
     DESCRIPTION OF THE DRAWINGS 
     In the annexed drawings: 
       FIG. 1  is a perspective view of a linear actuator according to the present invention in its retracted condition, with the top portion of the drive shaft being partly removed to show the engagement of the drive shaft with the rotor geared flange; 
       FIG. 2  is a partial perspective view of the linear actuator of  FIG. 1 , at a different angle, with the peripheral wall, the second band, the rotor, the hub, the ring of idle wheels, the wheel ring, the wheel support plate, the corner posts and the drive shaft casing being partly broken to more clearly show the inner parts of the linear actuator; 
       FIG. 3  is a view similar to  FIG. 2 , but with the linear actuator being in its extracted condition; 
       FIG. 4  is a cross-sectional view of the linear actuator taken along line IV—IV of  FIG. 1 ; 
       FIG. 5  is a cross-sectional view similar to  FIG. 4 , but with the linear actuator being in its extracted condition; 
       FIG. 6  is a partial perspective view of the linear actuator of  FIG. 1 , with the peripheral wall, the ring of idle wheels and its support plate, the top load-bearing platform and the second band being removed, with the first band partly shown, with the rotor being removed except for its geared flange portion, and with the central hub being partly broken, for showing particularly the second band guides and the first band opening in the rotor flange; 
       FIG. 7  is a cross-sectional top plan view taken along line VII—VII of  FIG. 4  with the rotor being removed; 
       FIG. 8  is an enlarged, partial perspective view of a portion of the intertwined bands forming the retractable telescopic column; 
       FIG. 9  is a partial perspective view of a linear actuator according to another embodiment of the invention; and 
       FIG. 9A  is a cross-sectional view of the linear actuator of  FIG. 9A . 
   

   DETAILED DESCRIPTION OF THE EMBODIMENTS 
     FIGS. 1–8  show a linear actuator  10  according to one embodiment of the present invention, for use in exerting pushing and/or pulling actions on outer elements. One example of an application of the linear actuator  10  of the present invention, to which it is not limited, is for use as a vertical pushing member similarly to the push actuator described in the Gagnon patent discussed in the Background of the Invention section. Other alternate uses of the linear actuator will be described later on. 
   Linear actuator  10  defines opposite first and second ends  10   a ,  10   b  and an intermediate portion between first and second ends  10   a ,  10   b  wherein its first and second bands are being releasably linked or interconnected to each other, as described hereinafter. Linear actuator  10  further defines a central axis  11  extending between first and second ends  10   a ,  10   b  and comprises a frame  13  including a base  12  formed of a bottom, ground-resting plate  14  and an upstanding cylindrical hub  16  carried by bottom plate  14 . The linear actuator also comprises a rotor  18  rotatably carried by base  12  over bottom plate  14  and around hub  16 . Rotor  18  includes a radially outwardly extending peripheral flange  20  which is provided with gear teeth on its outer periphery. Geared flange  20  is operatively coupled to a threaded drive shaft  22  which is intended to be operatively coupled to a suitable power source  25  (schematically shown in  FIG. 1 ) such as a motor or the like. A drive shaft casing  24  is provided over shaft  22 . 
   Linear actuator  10  also comprises a first elongated fastening band  26  wound in helical configuration about the actuator central axis  11  and capable of taking a retracted stacked position, and an extended position with its turns spaced from one another in the direction of the central axis  11 . First band  26  is more particularly stacked between the linear actuator intermediate portion and the linear actuator first end  10   a , with the stack of turns of the first band  26  resting on base  12  around rotor  18  and frame hub  16 . The helical first band  26  has a first end near the actuator first end  10   a  which may be attached thereto, and extends through an opening  28  in the geared flange  20  of rotor  18  (see  FIGS. 6 and 7 ) upwardly into a helical groove  30  made in the outer periphery of rotor  18  above its geared flange  20 . First band  26  further extends upwardly beyond rotor  18 , and it has a second end attached to the lower surface of a load-bearing platform  32 . The elongated first band  26  is generally flat and comprises a number of longitudinally disposed releasable fasteners in the form of longitudinally spaced-apart teeth  34  protruding from its outer edge. When it engages helical groove  30 , first band  26  is entirely embedded therein except for teeth  34  that protrude outside of groove  30 , and first band  26  can freely slide within groove  30 . 
   Linear actuator  10  also comprises a second elongated flat structural band  36  which is vertically disposed and wound on itself, with its turns transversely parallel to the actuator central axis  11 . Second band  36  is capable of taking a retracted spiral position with its turns nested within one another, and an extended position with its turns forming a helix around the actuator central axis  11  and generally equally radially spaced therefrom to form a retractable telescopic column having a substantially cylindrical wall. More particularly, second band  36  has a first end located within a second band magazine  38  which is slidably carried by rotor  18 . The first end of second band  36  may be attached to second band magazine  38 . The portion of second band  36  which is located between the intermediate portion of linear actuator  10  and its first end  10   a  is stored in magazine  38 , distinctly of first band  26 , with its turns nested within one another. Second band  36  is guided between magazine  38  and the telescopic column being formed by a spring-loaded pivotable guide arm  37  (see  FIGS. 6 and 7 ) pivotally mounted to a guide support block  41  attached to the radially extending flange  20  of rotor  18  at the linear actuator intermediate portion, and by a retaining member in the form of a retaining roller  39  upstanding from and rollably attached to guide support block  41  at the linear actuator intermediate portion. Retaining roller  39  is formed with upper and lower peripheral grooves  39   a ,  39   b  that allow the protruding teeth  34  of first band  26  to slide therein, as detailed hereinafter. The second end of second band  36  is attached to the lower surface of load-bearing platform  32 . The portion of second band  36  forming the telescopic column is located between the intermediate portion and the second end  10   b  of linear actuator  10 . Second band  36  comprises a number of longitudinally disposed spaced-apart lower and upper openings  40 ,  42  made spacedly adjacent to each edge of the elongated second band  36 . 
   To form a retractable telescopic vertical column, rotor  18  is rotated in a first direction by means drive shaft  22 . Upon this rotation being imparted to rotor  18 , first and second bands  26 ,  36  will both be guided to gradually form the column as described hereinafter. 
   As rotor  18  rotates in its first direction, the helical groove  30  made in the outer periphery of rotor  18  above geared flange  20  will guide first band  26  upwardly, with first band  26  slidingly engaging helical groove  30  in the intermediate portion of linear actuator  10 . This will result in first band  26  being raised vertically along the actuator central axis  11 , although without any rotation being imparted to first band  26 , while the turns of first band  26  are gradually and successively spaced from one another. 
   Simultaneously, second band  36  will be engaged by guide arm  37  and by retaining roller  39 , which rotate integrally with rotor  18 , in the intermediate portion of actuator  10 , to successively guide each turn of second band  36  located within second band magazine  38  radially inwardly. Each turn of second band  36  will thus be guided so that its upper edge portion is applied against and overlaps the lower edge portion of the preceding turn of second band  36 . Furthermore, the overlapping section of each two consecutive turns of second band  36  forming the column will further be interconnected through the instrumentality of one turn of first band  26 . More particularly, each turn of second band  36  forming the telescopic column will have its upper openings  42  registering with the lower openings  40  of the preceding turn of second band  36  in the overlapping section, and each pair of registering lower and upper openings  40 ,  42  is engaged by a corresponding tooth  34  of first band  26 . The first band  26  is suitably spaced to allow this releasable interconnection between first and second bands  26 ,  36  by setting the appropriate pitch in the helical groove  30  formed in rotor  18 . 
   Also, retaining roller  39  will ensure by its position that the turns of second band  36  are applied and maintained against the turns of first band  26  with first band teeth  34  engaging the registering pairs of second band openings  40 ,  42 . Indeed, retaining roller  39  is located very near first band  26 , being spaced therefrom approximately of the thickness of second band  36  or very slightly more, with the teeth  34  of first band  26  sliding through the peripheral grooves  39   a ,  39   b  of retaining roller  39  to allow retaining roller  39  to engage second band  36  all along its width, including beyond the two rows of teeth  34  that project near retaining roller  39 . Since second band  36  extends between retaining roller  39  and first band  26 , second band  36  will be positively guided against first band  26  and first band teeth  34  will be forced into second band openings  40 ,  42  when rotor  18  rotates. Furthermore, the portion of second band  36  forming the telescopic column will be prevented by retaining roller  39  from accidental release from first band  26  to prevent the column from collapsing. Indeed, by maintaining a generally punctual pressure, relative to the entire length of second band  36 , against second band  36  with retaining roller  39  at the lowermost portion of the telescopic column being formed to ensure that second band  36  remain engaged by the teeth  34  of first band  26 , second band  36  will be prevented from disengagement from teeth  34  of first band  26  throughout the telescopic column being formed. Thus, retaining roller  39  is a punctual abutment member that prevents second band  36  from gradually unwinding and resulting in the telescopic column collapsing. It is understood that retaining roller  39  could be replaced by any suitable retaining member which prevents second band  36  from disengagement from teeth  34 , including other punctual abutment members such as a low-friction block punctually forcing second band to be engaged by teeth  34  by being positioned close to first band  26 , or other retaining members such as hooks or the like elements provided on each tooth  34 . 
   In summary, retaining roller  39  acts as a guiding and retaining member that thus has more than one purpose: it guides each turn of second band  36  being incorporated into the telescopic column into a proper alignment for engagement with first band  26  and with the preceding turn of second band  36 , it ensures that teeth  34  of first band  26  engage the second band openings  40 ,  42 , and it also retains second band  36  to prevent the telescopic column from collapsing. 
   Guide arm  37  has the purpose of generally guiding second band  36  between second band magazine  38  and the telescopic column being formed, but linear actuator  10  could theoretically be used without guide arm  37  since retaining roller  39  also plays the role of a guiding member in linear actuator  10  since it guides each turn of second band  36  to position it properly against first band  26  and against the preceding turn of second band  36  when the telescopic column is being formed. The purpose of guide arm  37  is mostly to help guide second band  36  when there are sudden changes of the speed of rotation of rotor  18 . In such situations, the inertia of the second band magazine, possibly loaded with one or more turns of second band  36 , may carry second band magazine  38  in rotation at a faster or slower speed than necessary relative to the telescopic column, and it is then desirable to have spring-loaded guide arm  37  dampen the movement of second band  36  and help calibrate the speed of rotation of magazine  38  in addition to the natural intrinsic elasticity of second band  36 . 
   Second band  36  will consequently form the substantially cylindrical structural wall of the telescopic column being formed, while first band  26  will act to releasably interconnect each two consecutive turns forming the column to prevent. Each turn of second band  36  forming the column will be raised as the column is formed, although these turns of second band  36  forming the column are not imparted with any rotation whatsoever. Consequently, the telescopic column being formed does not rotate as it is raised as explained hereinabove. 
   The load of the telescopic column formed by the interconnected first and second bands  26 ,  36  is supported by the engagement of first band  26  within the helical groove  30  formed in rotor  18 . In other words, the entire load pushed or pulled by load-bearing platform  32  is transmitted through bands  26 ,  36  to the portion of first band  26  which engages groove  30 , and is supported by the latter. 
   For retracting the telescopic column, rotor  18  is rotated in the opposite direction by means of power source  25  acting on drive shaft  22 . By doing so, the lowermost turn of second band  36  which forms the column is disassembled from the column and is guided by retaining roller  39  and guide arm  37  radially outwardly back into the second band magazine  38 . Simultaneously, the first band  26  is gradually lowered through helical groove  30  into its ground-resting stacked position. 
   Second band  36  is stored in magazine  38  which is slidable relative to rotor  18  on which it is mounted, to allow rotation of magazine  38  relative to rotor  18  during extraction or retraction of the telescopic column. Indeed, since the portion of second band  36  which forms the telescopic column does not rotate, magazine  38  rotates relative to rotor  18  to allow the second band  36  to remain properly positioned relative to the telescopic column. This rotation of magazine  38  will be imparted by the intrinsic elastic bending resistance of the second band  36  itself when rotor  18  is rotated and as second band  36  is fed into or from the telescopic column. It is noted that second band magazine  38  will not remain stationary in rotation relative to base  12  even though the portion of vertical band  36  which forms the vertical column will remain stationary in rotation. Indeed, since the diameter of one turn of second band  36  is greater in second band magazine  38  than in the telescopic column, absolute rotation of second band magazine  38  together with the portion of second band  36  stored therein relative to base  12  will occur as a result to compensate this diameter difference. 
   It is noted that the portion of second band  36  forming the telescopic column will have its turns slightly inclined, i.e. defining a slight conical shape, due to their overlapping relationship. Indeed, each turn abuts directly against first band  26  at its edge closest to the actuator first end  10   a , while it is spaced from first band  26  by the underlying edge portion of the adjacent turn it overlaps at its edge closest to the actuator second end  10   b . Consequently, in one embodiment, second band  36  is preformed with a slight inclination corresponding to the inclination it will have when forming the telescopic column to reduce stresses in second band  36 . Generally, it is understood that in the present specification, the shape of the telescopic column may be referred to as being cylindrical or substantially cylindrical, and that this cylindrical or substantially cylindrical shape will include an inclination of each turn of the second band due to overlapping sections in the telescopic column. Also, it is understood that second band  36  will be said to have its turns parallel or substantially parallel to the central axis  11  of linear actuator  10 , and that this parallel or substantially parallel relationship is considered to include the fact that the turns of second band  36  may in fact be slightly inclined or conical as described hereinabove. 
   The engagement of the first band teeth  34  within registering top and bottom edge openings  42 ,  40  of the consecutive turns of second band  36  allows the load from two consecutive turns of second band  36  to be transmitted from one to the other through first band  26 . In addition to allowing such a load transfer, first band teeth  34  also allow a secure interconnection between each two consecutive turns of second band  36 , which helps to prevent the telescopic column from collapsing if a force having a radial vectorial component is applied against the telescopic column. Indeed, with prior art push actuator devices wherein the turns of the vertical band simply rest on the turns of the horizontal band, such transversely applied forces may accidentally disengage the vertical turns from their underlying horizontal turns, resulting in the column collapsing. However, with the first band teeth  34  of the present invention engaging the corresponding pairs of registering top and bottom openings  42 ,  40  in successive partly overlapping turns of the second band  36 , relative axial movement of successive turns of the second band  36  is prevented, which results in each turn of the second band  36  forming the telescopic column being interlocked with the top and bottom adjacent turns of the second band  36  to prevent accidental unwinding of the turns of the second band  36  from the column, and which consequently prevents the column from collapsing. Since the lowermost turn of second band  36  forming the telescopic column is prevented from unwinding due to its abutment against retaining roller  39 , the entire portion of second band  36  forming the telescopic column will remain structurally stable and the telescopic column will be able to axially transfer important loads. 
   The first band teeth  34  engaging the second band openings  40 ,  42  also allow the column of the present invention to be used without the load-bearing platform  32  actually being attached to a fixed outside element, such as a load being lifted. Indeed, with the prior art push actuator, if the load-bearing platform was not attached to an outside element, power-rotating the rotor resulted in the horizontal and vertical bands also undesirably rotating, with the consequence that the load-bearing platform would also rotate. With the linear actuator of the present invention, however, the first band teeth  34  that protrude beyond the substantially cylindrical outer wall surface of the telescopic column formed of successive helical turns of the second band  36 , are used as first anti-rotation members that cooperate with second complementary anti-rotation members provided on the fixed linear actuator frame  13 . Indeed, as the column is extracted or retracted, teeth  34  slide within spaces defined between idle wheels  44  that are rotatably mounted to shafts  46  supported by a support ring  48  attached to a wheel support plate  50  fixedly carried spacedly over base  12  by means of posts  52 . These idle wheels  44 , that form the second anti-rotation members, prevent teeth  34  from rotating in one direction or another due to the tangential abutment of teeth  34  against a corresponding wheel  44 , while allowing teeth  34  to freely move in the direction of the actuator central axis  11 . This is allowed due to the fact that teeth  34  are all aligned in the direction of central axis  11  with corresponding openings between idle wheels  44 . It is understood that as the telescopic column is extracted or retracted, the consecutive turns of first band  26  will gradually be lifted to or lowered from the telescopic column and some teeth  34  of first band  26  will engage spaces between idle wheels  44  at all times. Consequently, even if load-bearing platform  32  is not attached to an outside element, the telescopic column will be prevented from rotation. 
   A peripheral wall  54  is installed about the lower portion of the linear actuator, between base plate  14  and wheel support plate  50 . In one embodiment, the whole area within peripheral wall  54  is filled with lubricant such as oil to ensure low-friction sliding engagements of the different elements that slide against one another in linear actuator  10 . 
   In one embodiment of the invention, linear actuator  10  is used not only as a pushing or lifting device, but may also be used as a pulling device. Indeed, due to the integral interconnection of the successive turns of second band  36  that form the column resulting from the releasable engagement of fastening teeth  34  that engage top and bottom openings  42 ,  40  in overlapping sections of the second band  36 , linear actuator  10  may be used to pull a load attached to load-bearing platform  32  towards base  12 . 
   Furthermore, linear actuator  10  could be used with its central axis  11  being horizontal or inclined. Thus, generally, linear actuator may be used to push or pull a load along its central axis, with the axis being horizontal, vertical or inclined. This versatility in the orientation of the linear actuator central axis  11  is brought about by the interlock between the consecutive turns of second band  36  by means of the first band  26  which is provided with fasteners in the form of teeth  34  that engage the registering top and bottom openings  42 ,  40  in the overlapping sections of second band  36 . Indeed, this interlock allows a load, including the telescopic column&#39;s own weight, to be moved along the actuator central axis notwithstanding its orientation with this load not resulting in the telescopic column collapsing due to the fact that the consecutive turns of the second band  36  forming the telescopic column are attached to one another. 
   Generally, the base  12  and the platform  32  can be said to both be part of the push actuator frame  13 , with the first frame portion (base  12 ) being movable relative to the second base portion (platform  32 ) as the telescopic column formed of first and second bands  26 ,  36  is extracted and retracted. 
   It is understood that the helical groove  30  in rotor  18  will form a portion of a helix. In one embodiment, it will preferably form at least one full turn of a helix. Also, alternate support members could be used to support the first band  26  and consequently support the load of the linear actuator  10 , including for example a series of spaced-apart or adjacent rollers forming at least a portion of a helix, or a series of balls supported on a track forming at least a portion of a helix. 
   Also, it could be envisioned to alternately have the second structural band supported by a suitable support member, the sole purpose of the first fastening band then being to releasably fasten the consecutive turns of the second band that form the telescopic column. In a linear actuator where the second structural band is supported directly by the support member, the entire load to be displaced or supported by the telescopic column would be transferred to the linear actuator rotor through the lowermost second band turn forming the telescopic column. 
   Consequently, the support member carried by rotor  18  will form at least a portion of a helix for supporting part of either the first band  26  or the second band  36  and will successively space the turns of the band thus supported, to allow an axially oriented load applied on linear actuator  10  to be transmitted from the band it supports directly to rotor  18  while allowing a rotation of rotor  18  relative to this supported band. 
   Although the embodiment of the invention shown in the drawings includes a second band  36  located outwardly of the rotor  18  in the second band magazine  38 , it is envisioned in an alternate embodiment that the second band be provided inside a hollow rotor within a second band magazine also located inside the rotor, and with the first band extending through a helical groove made on the inner surface of the hollow rotor. The second band would then be wound on itself in a spiral pattern within the rotor, with the spiral turns having a lesser diameter than that of the telescopic column being formed. 
   The second band could also be configured differently. In the embodiment shown in the drawings, second band  36  will preferably be preformed with in an inclined configuration to conform to the position it will take in the telescopic column, as in indicated hereinbelow, but it could for example instead be formed for example of two flat sections joined at an intermediate cross-sectionally elbowed section linking the two flat sections. Generally, it can be said that the second band is substantially flat, but it is understood that it may in fact include cross-sectionally elbowed portions, reinforcement ribs, or other such relief. 
   It is envisioned to use alternate fastening means to releasably fasten the first and second bands  26 ,  36  to each other in the telescopic column. Generally, it is understood that the first band comprises first fastening means that cooperate with second fastening means provided on the second band to releasably link or interlock the first and second bands. For example, the second band could be provided with fasteners such as teeth while the first band would be provided with openings to be engaged by the second band teeth. Alternately, other types of fasteners could be used altogether, such as hook-type fasteners (the first fastening means) provided on the first band that would attach themselves to the upper edge (the second fastening means) of the second band. It is also envisioned that each two consecutive turns of the second band forming the column not include any overlapping sections but rather be positioned in close proximity without overlap, with the first band still linking the consecutive turns of the second band forming the column. Generally, it can be said that the consecutive turns of the second band forming the column are positioned into successive adjacent helical configuration, with this adjacent configuration including overlap or not, and including direct contact or proximity without direct contact. 
   Another alternate embodiment of the invention is shown in  FIGS. 9 and 9A , where the linear actuator  100  is similar to the linear actuator  10  of the first embodiment, except as noted hereinbelow. 
   Linear actuator  100  comprises opposite first and second frame portions  102 ,  104  for attachment to respective outside elements (not shown) to be pulled towards one another or drawn apart by means of linear actuator  100 . First frame portion  102  comprises a base  105  to which is fixedly mounted a hub  106 , and an intermediate plate  108  is attached spacedly to first frame portion by means of a few posts  110 . An optional outer peripheral wall  109  is provided to form a lubricant enclosure which may be filled with lubricant. No anti-rotation devices, such as the idle wheels as in the first embodiment, are provided in this alternate embodiment. The telescopic column is formed by releasably interconnected first and second bands  112 ,  114  similar to the ones of the first embodiment. 
   According to the alternate embodiment of the invention shown in  FIGS. 9 and 9A , there is no rotor member carried by the first frame portion. Instead, the first toothed band  112  engages a support member in the form of a helical groove  116  made directly into the outer surface of the first frame hub  106 . The first extremity of second band  114  is stored in a second band magazine  118  movably carried by hub  106 , and second band  114  is guided towards the telescopic column being formed by means of a retaining roller  102  and by an optional spring-loaded guide arm  122 , both also carried by hub  106 . The first extremity of first band  112  is stored above base plate  105 , with first band  112  extending through an opening  120  made in a peripheral flange  123  integrally radially projecting from hub  106 . 
   The respective second extremities of the first and second bands  112 ,  114  are fixed underneath a rotor platform  124  which replaces the load-bearing platform of the first embodiment, and which is toothed to be coupled to the drive shaft  128  of a motor  126  by means of a chain  130 . Motor  126  is fixedly attached to second frame portion  104 , and rotor  124  is rotatably mounted to second frame portion  104 . 
   According to this alternate embodiment of the invention, the telescopic column will be extracted or retracted upon the motor  126  rotating the rotor  124 . Indeed, rotating rotor  124  in a first direction to extract the telescopic column will cause simultaneous rotation of both the first and second bands  112 ,  114  in this first direction since they are integrally attached to the rotor  124 . This will result in relative rotation of first band  112  and hub  106  permitted by the sliding engagement of first band  112  within helical groove  116 . This relative rotation of first band  112  and hub  106  will cause the consecutive turns of first band  112  stored atop base plate  105  to be spaced apart and to be gradually carried towards the second frame portion  104 . 
   Simultaneously, the rotation of second band  114  will cause the consecutive turns of second band  114  to engage the guide arm  122  and the guiding and retaining roller  120  to be guided towards corresponding spaced-apart turns of the first band  112 , about the upper portion of hub  106 , where the second band holes  132  will engage the protruding first band teeth  134 . Thus, in a similar manner than in the first embodiment of the invention shown in  FIGS. 1-8 , each two consecutive helical turns of second band  114  will be releasably interconnected by one helical turn of the first band  112 , to gradually form a telescopic column. The second band  114  will form the outer peripheral wall of the telescopic column, having a substantially cylindrical wall, and the first band  112  will link each two consecutive turns of the second band  114 . 
   Consequently, it can be seen that the support members or helical grooves  30 ,  116  that allow the consecutive turns of the first bands  26 ,  112  to be spaced represent spacer means for the first bands  26 ,  112 . These spacer means could have any other suitable alternative configuration, including for example spaced-apart rollers arranged in a helical configuration, or a multiple ball helical track. Generally, the telescopic column will be formed if relative rotation of the spacer means or support member relative to the first and second bands is imparted within the linear actuator. Thus, the drive means can engage any suitable component of the linear actuator  10 ,  100 , including a rotor  18  carrying the spacer means such as in the first embodiment of the linear actuator  10 , a rotor  124  attached to the second extremity of the first and second bands as in the alternate embodiment of the linear actuator  100 , the first or second bands themselves, or any other component capable of imparting a relative rotation on one hand of the first and second bands, and on the other hand of the spacer means that will space the consecutive turns of the first band. It is understood that the drive means of linear actuators  10 ,  100  has been shown as including a drive shaft coupled to the geared flange of the rotor and operatively linked to a power source such as a motor, but it is understood that this drive means could include any suitable alternate drive means such as, although not limited to, a motor being directly linked to the linear actuator rotor, a powered rotor engaging the first band teeth, or any suitable drive means by which relative rotation on one hand of the first and second bands and on the other hand of the spacer means or support member is achieved. 
   Any further modification, which does not deviate from the scope of the present invention, is considered to be included therein, as will be obvious for someone skilled in the art of the present invention in view of the appended claims.