Advanced elevator installation and elevator improvement methods

Abstract

The invention relates to an elevator installation comprising: - a shaft (10') having an upper end (14'); - at least one drive pulley (20') installed in said upper end (14') and having an axis of rotation (22'); - at least one flat belt (26') defining a succession of segments and having two opposite faces (48', 49'), said belt (26') being mounted astride said drive pulley (20') extending from one side to an end (40') anchored in said upper end (14') to form a loop (38'); - a car (24') comprising at least one free pulley (34', 36') for being suspended from said loop (38').The two opposite faces (48', 49') have grooves that engage with at least one drive pulley (20') and at least one idler pulley (34', 36'), while all the mean planes of the belt segments of the loop (38') extend parallel to the axis of rotation (22') of the drive pulley. Figure to be published with the abbreviation: Fig. 4.

Description

Title of the invention: Improved elevator installation and method for improving elevators

[0001] The present invention relates to an improved elevator installation and to a method of improving conventional elevators aimed at implementing said installation.

[0002] The elevators thus targeted by the improvement method comprise a vertical shaft extending between a lower end and an upper end, and they have the particularity of being devoid of a technical room in which the drive machines are usually installed.

[0003] They usually also include two drive pulleys spaced apart and mounted coaxially on the same drive shaft. The drive shaft extends horizontally in the upper end of the sheath.

[0004] They also comprise at least two flat, flexible linear traction elements. These linear elements comprise a plurality of parallel steel cables regularly spaced from each other across the width of the linear element, and embedded in a matrix of a polymer material.

[0005] These linear elements have a face on which longitudinal grooves are formed and they are mounted respectively astride the two drive pulleys so that the grooved faces engage with the drive pulleys.

[0006] The two drive pulleys have parallel circular ribs regularly spaced from each other forming grooves, which ribs extend into the longitudinal grooves.

[0007] The linear elements then extend parallel to each other, from one side of the drive pulleys to an end anchored in the upper end of the sheath, at a distance from the drive pulleys, to form at least two initial loops inside the sheath. They then extend on the other side towards the lower end, forming at least two second hairpin loops from which a counterweight is suspended.

[0008] And the elevators comprise a car equipped with at least two free-spinning pulleys mounted coaxially on an axis parallel to the drive shaft of the two drive pulleys. The at least two free-spinning pulleys have an axis of rotation parallel to the drive shaft of the two drive pulleys.

[0009] The cabin is then suspended from said at least two loops by the two free pulleys so that it can be moved between the two ends of the shaft, while the flexible elements of the loops are respectively twisted 180° between the drive pulleys and the free pulleys so that the grooved faces of the Two linear elements also engage with the free pulleys, which also feature circular ribs. These circular ribs prevent the flexible loop elements from shifting laterally.

[0010] When the cabin is located at the lower end of the shaft, the twist spacing of the linear elements is relatively large, and the tensions in the steel cables of each linear element are approximately equal. Conversely, as the cabin moves upward toward the upper end of the shaft, the twist spacing decreases, and tension differentials appear between the edge steel cables of the linear elements and the middle steel cables. In other words, the edge cables are subjected to greater stress, and the steel wires that compose them tend to break.

[0011] Thus, one problem that arises and that the present invention aims to solve is to provide an elevator installation in which the service life of the flexible linear traction elements is improved. Therefore, the object of the invention also aims at improving existing elevators to increase the service life of the linear elements.

[0012] In order to solve this problem and according to a first object, an elevator installation is proposed comprising:

[0013] - a sheath having an upper end and an opposite lower end;

[0014] - at least one drive pulley installed in said upper end and having an axis of rotation that is approximately horizontal;

[0015] - at least one flat belt defining longitudinally, a succession of belt segments and having two opposite faces, said belt being mounted astride said drive pulley, extending on one side to an end anchored in said upper end of said sheath at a distance from said drive pulley to form a loop in said sheath, and extending on the other side towards said lower end to join a counterweight; and,

[0016] - a cabin comprising at least one free pulley having an axis of rotation substantially parallel to said axis of rotation of said at least one drive pulley, said cabin being suspended from said loop by said at least one free pulley in order to be able to drive said cabin in motion between the two ends of said sheath, each of the belt segments of said loop defining a mean plane.

[0017] Said two opposite faces of said belt have longitudinal grooves coming into contact respectively in said at least one driving pulley and in said at least one free pulley, while all the average planes of said belt segments of said loop extend substantially parallel to said axis of rotation of said driving pulley.

[0018] Thus, a feature of the invention lies in the implementation of a belt having longitudinal grooves on its two opposite faces so as to be able to be extended in an S shape from the end anchored in the upper end of the sheath to the counterweight.

[0019] In this way, one side of the belt engages with the drive pulley, while the other side engages with the free pulley of the untwisted cabin.

[0020] Indeed, when all the mean planes of the belt segments remain substantially parallel to the axis of rotation of the drive pulley between the lower and upper ends during the movement of the cabin, then the belt does not twist between the drive pulley and the idler pulley. This is true even when the segments are sufficiently short, for example less than ten centimeters.

[0021] Consequently, the tensions exerted in all the steel cables of the belt are substantially equal, regardless of their transverse position in the belt between the two opposite edges. As a result, the belts have a longer service life than those used according to the prior art.

[0022] Also, said at least one drive pulley and said at least one idler pulley each comprise a plurality of grooves. In other words, the drive pulley and the idler pulley have parallel circular ribs regularly spaced from one another. They are spaced at a distance equal to the distance separating the grooves on the two opposite faces of the belt. In other words, their pitches are identical. In this way, the ribs extend inside the grooves so as to increase the contact area between the pulleys and the belt and, moreover, to guide the belt laterally over the pulleys.

[0023] According to a particularly advantageous embodiment of the invention, said cabin comprises two free pulleys having two substantially parallel axes of rotation, spaced apart from each other. The two axes of rotation are preferably located at two lateral walls opposite the cabin. In this way, the suspension forces are divided between two parts of the cabin for increased safety.

[0024] Preferably, the cabin comprises a base and three walls erected on the base, with the two free-swinging pulleys mounted on the base. Thus, the cabin has two opposing walls and a back wall extending opposite the cabin door. The two free-swinging pulleys extend below the base, directly below the two opposing walls, while the belt loops under the cabin. In this way, the cabin rests within the loop of the belt. Therefore, the cabin would remain suspended from the belt if either of the two free-swinging pulleys failed.

[0025] According to a particularly advantageous embodiment of the invention, one of said faces of said belt has parallel and contiguous ribs of trapezoidal cross-section to form V-shaped grooves. Preferably, the face of the The belt with the V-shaped grooves is the one that engages with the drive pulley. Conversely, the drive pulley has circular ribs with a triangular cross-section to fit precisely into the V-grooves. This increases the contact area between the drive pulley and the belt, preventing slippage between them.

[0026] Furthermore, the other face of said belt has parallel and contiguous ribs with a semicircular cross-section to form grooves with rounded sides. Preferably, the face of the belt with these grooves is the one that engages with the free pulleys of the cab. This prevents lateral displacement of the belt relative to the free pulley.

[0027] According to a particularly advantageous embodiment of the invention, the installation comprises two coaxial drive pulleys spaced apart and two flat belts respectively mounted astride said two drive pulleys forming two loops, while said cabin comprises at least two coaxial free pulleys spaced apart so as to be able to be suspended from said two loops respectively by said two free pulleys.

[0028] Thanks to the two drive pulleys spaced apart and the two flat belts forming two loops, the cabin is entirely suspended from the belt and its vertical orientation remains constant during its movement. Friction between the cabin and its vertical guides is thus reduced.

[0029] In certain situations, where the cabin is large, the installation advantageously includes two additional flat belts mounted respectively astride the two drive pulleys, forming two further loops. In other words, the installation includes four belts to support the load.

[0030] Preferably, said belt also has an opposite end anchored between said loop and the extension of said belt on the other side of said loop to form a hairpin loop adapted to receive said counterweight in suspension. The counterweight is then equipped with at least one free counterweight pulley, which has circular ribs of triangular cross-section, identical to those of the drive pulley, as will be explained in more detail later in the description. The advantages of such a configuration will also be explained.

[0031] Furthermore, said flat belt comprises a plurality of steel cables extending parallel to and at a distance from one another, said plurality of steel cables being embedded in a matrix of a polymer material. For example, the polymer material is an elastomer. Polyurethane is an elastomer perfectly suited for forming the matrix of the belt.

[0032] Preferably, the plurality of steel cables extends in the belt near the face that applies to the free pulleys of the cabin.

[0033] Also, steel cables are formed from a plurality of stranded steel wires.

[0034] According to a second object, the invention proposes a method for improving a vertical transport device comprising the following steps:

[0035] - an elevator is provided comprising:

[0036] - a sheath having an upper end and an opposite lower end;

[0037] - at least one drive pulley installed in said upper end and having an axis of rotation that is approximately horizontal;

[0038] - at least one flat, flexible linear traction element having a grooved face longitudinally, said element being mounted astride said drive pulley extending on one side to an end anchored in said upper end of said sheath at a distance from said drive pulley to form a loop in said sheath and extending on the other side towards said lower end to join a counterweight;

[0039] - a cabin comprising at least one free pulley having an axis of rotation substantially parallel to said axis of rotation of said at least one drive pulley, said cabin being suspended from said loop by said at least one free pulley in order to be able to drive said cabin in motion between the two ends of said sheath, said flat flexible linear traction element being twisted 180° between said at least one drive pulley and said at least one free pulley so that said grooved face engages in said at least one drive pulley and in said at least one free pulley.

[0040] A flat belt is provided, defining longitudinally a succession of belt segments and having two opposite faces longitudinally ribbed.

[0041] And, said belt is substituted for said linear element so that said two opposite faces of said belt come into contact respectively in said at least one driving pulley and in said at least one free pulley, while all the mean planes of said belt segments of said loop extend substantially parallel to said axis of rotation of said driving pulley.

[0042] In this way, in accordance with the method described above, the defective linear elements of existing devices are replaced by belts according to the invention which have much longer service lives.

[0043] Other features and advantages of the invention will become apparent from the following description of particular embodiments of the invention, given by way of example but not limitation, with reference to the accompanying drawings in which:

[0044] [Fig.1] is a partial schematic view of a lift according to the prior art in vertical section;

[0045] [Fig.2A] and [Fig.2B] are schematic detail views of an element illustrated in [Fig.1] from two different angles offset from each other by 90°;

[0046] [Fig.3] is a schematic cross-sectional view of an element of the invention; and,

[0047] [Fig.4] is a partial schematic view of an elevator installation conforming to the invention including the element shown in [Fig.3].

[0048] Figure 1 partially illustrates an elevator in accordance with the prior art. It shows an elevator shaft 10 defining a vertical internal conduit 12. More specifically, Figure 1 shows an upper end 14 thereof. The shaft 10 has two lateral shaft walls 16, 18 extending vertically opposite each other.

[0049] Also, a drive pulley 20 is installed in the inner conduit 12 at the upper end 14 of the duct 10 near one 16 of the two side walls. The drive pulley 20 has a drive shaft 22 which extends in a substantially horizontal direction and parallel to the duct wall 16. In other words, the axis of rotation of the drive pulley 20 extends horizontally.

[0050] In addition, [Fig.1] shows a cabin 24 suspended in the inner conduit 12 of the duct 10 from a flat flexible linear traction element 26.

[0051] The cabin has two cabin side walls 28, 30 erected opposite each other on a base 32.

[0052] The cabin 24 is equipped with two lateral free pulleys 34, 36 mounted under the base 32, respectively in line with the cabin side walls 28, 30.

[0053] The flat flexible linear traction element 26 is mounted astride the drive pulley 20 and extends in the sheath by forming a loop 38 to a first end 40 anchored in the upper end of the sheath 10 at the drive pulley 20 and near the other 18 of the two side walls 16, 18.

[0054] On the other side of the drive pulley 20, the flat flexible linear traction element 26 extends along the sheath wall 16, towards a lower end of the sheath 10, opposite the upper end 14. It thus joins a counterweight 42 and then returns, forming a hairpin loop 45, under the drive pulley 20 to a second end 44 anchored in the upper end 14 of the sheath.

[0055] The counterweight 42 is suspended from the hairpin loop 45 by means of a free counterweight pulley 46.

[0056] As for the cabin 24, it is suspended in the loop 38 of the flat flexible linear traction element 26 by means of the two lateral free pulleys 34, 36. In other words, the cabin 24 rests in the bottom of the loop 38.

[0057] Also, the drive pulley 20 has regularly spaced parallel circular ribs forming grooves between them. These parallel circular ribs have a substantially triangular cross-section. They are not shown in the drawings.

[0058] As for the flat flexible linear traction element 26, it has a first ribbed face 48, opposite a second face 49, the first face 48 coming into contact with the drive pulley 20.

[0059] The first face 48 has parallel and contiguous longitudinal ribs of trapezoidal cross-section to form V-shaped grooves. The longitudinal ribs are regularly spaced at a distance equal to that which extends between the circular ribs of the drive pulley 20.

[0060] Consequently, when the linear element 26 engages with the drive pulley 20, the circular ribs of the drive pulley 20 extend into the V-grooves of the linear element 26. In this way, the rotational movement of the drive pulley 20 causes the linear element 26 to move linearly without slippage. Therefore, the movement of the drive pulley 20 induces the vertical movement of the cabin 24.

[0061] The two lateral free pulleys 34, 36 of the cabin 24 also have circular ribs similar to those of the drive pulley 20. And in addition, the two lateral free pulleys 34, 36 respectively have two free pulley rotation axes 50, 52, which extend substantially parallel to the drive shaft 22 of the drive pulley 20.

[0062] Consequently, the flat flexible linear traction element 26, between the drive pulley 20 and the lateral free pulley 34, is twisted 180° into a twist 54, so that the first face 48, which has ribs, engages with the lateral free pulleys 34, 36.

[0063] The twist 54 is schematically shown in detail in front view in [Fig. 2A] and in side view in [Fig. 2B]. In [Fig. 2B], only the second face 49 is visible, while in [Fig. 2A], both faces 48 and 49 are visible. The twist 54 has a segment of length SI, the mean plane of which it defines extends substantially perpendicularly to the mean plane defined by another segment located outside the twist 54. The mean plane of the segment of length SI is also substantially perpendicular to the drive shaft 22.

[0064] Also, [Fig. 2A] and [Fig. 2B] schematically show first peripheral steel cables 56 extending longitudinally along the edges of the linear element 26 and at least a second central cable 58 extending equidistant from said edges. The steel cables here are made of twisted steel wires.

[0065] Only five steel cables extending parallel to each other at regular intervals are shown in [Fig. 2A] and [Fig. 2B] for illustrative purposes. The number of steel cables may be greater, and they are further embedded in a matrix of polymer material so that they are not visible from the outside.

[0066] In addition, the longitudinal striations are not represented on the first face 58.

[0067] Figures 2A and 2B highlight the problem posed by the twist 54 of the linear element 26. Indeed, it is clear that the second central cable 58 located in the core of the linear element 26 does not undergo any additional elongation due to the twist. However, with regard to the first peripheral steel cables 56, it is clear that additional longitudinal stresses are exerted on them. Consequently, over time and with the raising and lowering of the cabin, the voltage differentials in the steel cables between the peripheral cables 56 and the central cables 58 cause at least partial breakage of the wires in the peripheral cables 56.

[0068] Also, in accordance with the invention, it is proposed to replace the flat flexible linear traction element 26 with a flat belt 26', a cross-section of which is shown in [Fig. 3]. The flat belt 26' has the same reference numeral as the flexible linear element, marked with a prime sign: "'", because it has the same function.

[0069] It thus presents a first face 48' opposed to a second face 49'. Also, the first face 48' has contiguous ribs of trapezoidal cross-section 60. They extend longitudinally over the first face 48' and they are regularly spaced from each other to form V-shaped striations 62. They are, for example, spaced from each other by a distance of between 3 mm and 4 mm.

[0070] The belt 26' shown in [Fig. 3] is made of a relatively rigid elastomeric polymer material. Embedded within it are twelve steel cables Cl, C2, ..., C12. These steel cables extend parallel to each other by the same distance, for example, between 4 mm and 5 mm. They are overmolded so as to extend close to the second face 49' and to define contiguous parallel ribs 64 with a semicircular cross-section. In turn, the contiguous parallel ribs 64 define, among themselves, grooves with rounded flanks 66.

[0071] Thus, the steel cables Cl, C2.. ..C12 extend into the half-thickness of the belt 26' located towards the second face 49', while the additional half-thickness comprising the trapezoidal cross-section ribs 60 consists solely of polymer material. Furthermore, the bottom of the rounded-sided grooves 66 extends substantially below the center of the steel cables.

[0072] In this way, the second face 49', which is applied to the drive pulley, will have a larger contact surface with the pulley. As for the second face 49', it is more rigid thanks to the steel cables Cl, C2.. ..C12. However, the role of this second face 49' is limited to lateral guidance, as will be explained below.

[0073] Also, according to another embodiment, the belt 26' is replaced by two belts of a smaller width and each equipped with six cables.

[0074] Furthermore, the width of the belts, and consequently the number of cables for each belt, is adapted according to the maximum load of the cabin. Naturally, the width of the pulleys is adapted accordingly.

[0075] Thus, in accordance with the invention, the object of [Fig. 1] is improved by means of the belt 26' in particular. To do this, the cabin 24 and the counterpoint 42 are removed, and then the linear element 26 is removed.

[0076] Then the belt 26' is installed in its place, then the cabin 24 and the counterweight 26 as illustrated in [Fig.4].

[0077] Before installing the belt 26', it is checked that the drive pulley 20 has circular ribs of triangular section coinciding with the V-grooves 62. Thus, it is checked whether the circular ribs are spaced the same distance apart as that which separates the V-grooves 62, and whether the height of the ribs corresponds to the depth of the V-grooves 62.

[0078] If not, a drive pulley 20' with the correct characteristics is installed so that it can cooperate perfectly with the belt 26'. Similarly, the counterweight pulley 46 is replaced with another counterweight pulley 46', having the same characteristics as the drive pulley 20' in order to accommodate the belt 26'.

[0079] In addition, before installing the belt 26', pulleys 34', 36', having circular ribs adapted to cooperate with the grooves with rounded flanks 66, are substituted for the free pulleys 34, 36.

[0080] The belt 26' is thus installed in place of the linear element 26 so that it engages with the drive pulley 20'. In other words, it is installed so that the first face 48' is pressed against the drive pulley 20', then it is extended to the free pulleys 34', 36' under the cabin 24' without twisting, so that the second face 49' of the belt 26' is pressed against the free pulleys 34', 36'.

[0081] It will then be observed that the cables embedded in the flat belt 26' extend between the circular ribs of the second phase 49'. In this way, the flat belt 26' is perfectly guided laterally on the free pulleys 34', 36'.

[0082] In other words, all the belt segments 26', in particular between the drive pulley 20' and the free pulleys 34', 36', whatever their length, define average planes substantially parallel to the drive shaft 22'.

[0083] In this way, the movement of the cabin 24' induced by the rotation of the drive pulley 20' and the translational drive of the belt 26', between the lower end and the upper end 14' of the sheath 10', is carried out with a substantially equivalent tension in all the steel cables of the belt 26', from one edge to the other of the flat belt 26'.

[0084] Fig. 1 and Fig. 4 illustrate a single linear element 26 and a single belt 26', and therefore a single drive pulley 20, 20', two single free pulleys 34, 36; 34', 36', and a single counterweight pulley 46, 46'.

[0085] Preferably, the installation comprises two coaxial drive pulleys spaced apart and at least two flat belts mounted respectively astride the two drive pulleys, forming at least two parallel loops. As for the cabin, it comprises two pairs of free pulleys, the free pulleys of each pair being coaxial and spaced apart so as to be able to be suspended from said at least two loops respectively by said at least two pairs of free pulleys.

[0086] Although the cabin is connected to the shaft by guide elements, the implementation of two flat belts allows for better stability of the cabin during these vertical movements.

[0087] Also, the cabin 24' is equipped with two vertical guide rails on the outer faces of the two cabin side walls 28' and 30', along the median lines of the walls. The two belts extend along the cabin side walls on either side of the vertical guide rails, equidistant from them. In this way, the cabin's suspension point, located midway between the belts, and the cabin's vertical guide axis are substantially aligned with each other. Therefore, the cabin's vertical guide rails remain aligned with the guide ribs installed in the shaft.

[0088] When the cabin is designed to accommodate a larger load, four belts are installed, two on each side of the guide rails. In other words, an even number of belts are installed to support the cabin and ensure its stability.

Claims

Demands

1. Elevator installation comprising: - a shaft (10') having an upper end (14') and an opposite lower end; - at least one drive pulley (20') installed in said upper end (14') and having a substantially horizontal axis of rotation (22'); - at least one flat belt (26') defining longitudinally, a succession of belt segments and having two opposite faces (48', 49'), said belt (26') being mounted astride said drive pulley (20') extending on one side to an end (40') anchored in said upper end (14') of said shaft at a distance from said drive pulley to form a loop (38') in said shaft (10') and extending on the other side towards said lower end to join a counterweight (42');- a cabin (24') comprising at least one free pulley (34', 36') having an axis of rotation (50', 52') substantially parallel to said axis of rotation (22') of said at least one drive pulley, said cabin (14') being suspended from said loop (38') by said at least one free pulley in order to be able to drive said cabin in motion between the two ends of said sheath (10'), each of the belt segments of said loop defining a mean plane; characterized in that said two opposite faces (48', 49') of said belt (26') have longitudinal grooves coming into contact respectively with said at least one drive pulley (20') and with said at least one free pulley (34', 36'), while all the mean planes of said belt segments of said loop (38') extend substantially parallel to said axis of rotation (22') of said drive pulley.;

2. Elevator installation according to claim 1, characterized in that said at least one drive pulley (20') and said at least one free pulley (34', 36') each comprise a plurality of grooves.

3. Elevator installation according to claim 1 or 2, characterized in that said cabin (14') comprises two free pulleys (34', 36') having two axes of rotation substantially parallel and at a distance from each other.

4. Elevator installation according to claim 3, characterized in that said cabin (24') comprises a base (32') and three walls (28', 30') erected on said base, said two free pulleys (34', 36') being mounted on said base.

5. Elevator installation according to any one of claims 1 to 4, characterized in that one (48') of said faces of said belt (26') has parallel and contiguous ribs of trapezoidal cross-section (60) to form V-grooves (62).

6. Elevator installation according to any one of claims 1 to 5, characterized in that the other (49') of said faces of said belt (26') has parallel and contiguous ribs of semicircular cross-section (66) to form grooves with rounded flanks.

7. Elevator installation according to any one of claims 1 to 6, characterized in that it comprises two coaxial drive pulleys spaced apart and two flat belts respectively mounted astride said two drive pulleys forming two loops, while said cabin comprises at least two coaxial free pulleys spaced apart so as to be able to be suspended from said two loops respectively by said two free pulleys.

8. Elevator installation according to claim 7, characterized in that it further comprises two other flat belts mounted respectively astride said two drive pulleys forming two other loops.

9. Elevator installation according to any one of claims 1 to 8, characterized in that said belt (26') has an opposite end (44') anchored between said loop (38') and the extension of said belt on the other side of said loop to form a hairpin loop (45') adapted to receive said counterweight (42) in suspension.

10. Elevator installation according to any one of claims 1 to 9, characterized in that said flat belt (26') comprises a plurality of steel cables (Cl..., Cl2) extending parallel and at a distance from each other, said plurality of steel cables being embedded in a matrix of a polymer material.

11. A method for improving a vertical transport apparatus comprising the following steps: - an elevator is provided comprising: - a sheath (10) having an upper end (14) and an opposite lower end; - at least one drive pulley (20) installed in said upper end (14) and having a substantially horizontal axis of rotation (22); - at least one flat flexible linear traction element (26) having a longitudinally ribbed face (48), said element being mounted astride said drive pulley (20) extending on one side to an end (40) anchored in said upper end of said sheath at a distance from said drive pulley (20) to form a loop (38) in said sheath and extending on the other side towards said lower end to join a counterweight (42); - a cabin (24) comprising at least one free pulley (34, 36) having an axis of rotation (50, 52) substantially parallel to said axis of rotation (22) of said at least one drive pulley, said cabin being suspended from said loop (38) by said at least one free pulley (34, 36) in order to be able to drive said cabin (24) in motion between the two ends of said sheath, said flat flexible linear traction element (26) being twisted by 180° between said at least one drive pulley (20) and said at least one free pulley (34, 36) so that said grooved face (48) engages in said at least one drive pulley and in said at least one free pulley; - a flat belt (26') is provided, defining longitudinally a succession of belt segments and having two opposite faces longitudinally ribbed (48', 49'); and, - said belt (26') is substituted for said linear element (26) so that said two opposite faces (48', 49') of said belt engage respectively in said at least one drive pulley (20') and in said at least one free pulley (34', 36'), while all the mean planes of said belt segments of said loop (38') extend substantially parallel to said axis of rotation (22') of said drive pulley.

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