EP1216949A2 - Traction elevator with back-pack car arrangement - Google Patents

Abstract

The lift cabin moves along guide rails (3) through a counterweight (5) driven by a drive (7) comprising a motor (8), drive pulley (9) for the support cables (6), and brake (10). The axial length of the drive is greater than its diameter and the motor and drive pulley are arranged coaxial with each other. The supporting steel wire cables have a nominal diameter of about 8 mm or less and the diameter of the drive pulley is about 32 cm. The axial length of the drive pulley can be sufficient to house at least five support cables axially side by side.

Description

The invention relates to a traction sheave elevator with an elevator car, which can be moved along guide rails, with a counterweight also guided on rails, with in Cross section round suspension elements on which the elevator car and the counterweight is attached without a pulley in a backpack design are, and with at least one engine, one Traction sheave for the suspension means and a brake formed Drive that is in the upper area of the elevator shaft between the Shaft wall and the space that the elevator car in its top position needed, and / or in a vertical extension this area is arranged, the axis of the Traction sheave approximately horizontally and at the same time parallel to the neighboring one Shaft wall and / or to the adjacent cabin wall is oriented.

Such a traction sheave elevator is from the Japanese utility model publication JP 4-50 297 known. The advantage this arrangement is that a separate machine room for the drive of this elevator is not required. Furthermore, the Backpack construction advantageous because it is inexpensive as it with relatively few parts and even without deflection disks. Furthermore, an arrangement of the traction sheave on a horizontal lying parallel to the adjacent shaft wall Axle a convenient loop and guide for the suspension elements.

In this known arrangement, however, the disadvantage is relative large space requirement of the entire drive in this previously known solution is caused by the fact that the axis of the Drive motor arranged at right angles to the axis of the traction sheave is, so that a corresponding reversing gear is required is.

It was therefore already claimed in EP 0 631 967 A2, in particular 16, a backpack-type traction sheave elevator proposed, where the axis of the traction sheave and the motor perpendicular to the neighboring shaft wall and to the neighboring one Cabin wall are arranged and the entire drive unit so is designed to be flat in the space between Shaft wall and cabin or vertical continuation of this area fits. However, these are more complex under the elevator car Way provided pulleys and without pulleys a relatively large shaft head height would be required.

There is therefore the task of a traction sheave elevator to create the type mentioned, in which the advantages of a rucksack-less elevator without a pulley stay where the entire drive is inside the elevator shaft can be arranged and where the shaft head height be low above the uppermost position of the elevator car can.

To solve this apparently contradicting task is the characterized at the beginning characterized that the axial length of the drive is greater than its diameter and that the motor and the traction sheave are coaxial with each other are arranged. In this way there is a relative slim long drive unit, its diameter planes across or arranged at right angles to the adjacent shaft wall are, but because of their relatively small diameter has a correspondingly small space requirement and in particular also claimed a relatively low height. Also at This drive therefore needs an arrangement in the shaft head there only a small height, so that the shaft head height in the desired can advantageously be kept low. In addition, common parts and construction units from Backpack-style lifts including the usual suspension devices Find use.

WO 99/43589 is also used for an elevator of a different type Deflection rollers under the elevator car have been a relatively long time Drive engine known in the upper area of the shaft, however it is not a backpack-style elevator and above all, special ropes are used as suspension elements, namely flat ropes or straps are required to ensure adequate Traction is transmitted and still the traction sheave can be carried out with a relatively small diameter.

Because of the simple drive and its space-saving arrangement is advantageously possible that the suspension means Steel wire ropes with a nominal diameter of about 8 mm or are less. This allows a correspondingly small diameter the traction sheave and still use more common Wire ropes as a suspension element, so that the usual known Calculation methods can be applied. This also bears contribute to an overall inexpensive, space-saving traction sheave elevator ready to provide.

The diameter of the traction sheave can be about 36 cm or 32 cm or less. The torque requirement is correspondingly low on the one hand and the space requirement on the other.

The axial length of the drive can be at least twice as large in particular about 2 1/2 times to 3 times or more than the diameter of the traction sheave. Accordingly slim the entire drive fails and is correspondingly low Space required between the cabin and the shaft wall or if necessary in a vertical continuation range of this distance between Cabin and shaft wall.

The traction sheave can be directly on the output of the motor arranged and the drive is designed in particular gearless his. Because the torque requirement of the traction sheave by the aforementioned Measures can be kept low, a transmission can be saved.

The axial length of the drive pulley can be chosen so that they have space for at least five, in particular six suspension elements or has hoisting ropes axially next to each other. This allows for small Traction sheave diameter the transmission correspondingly higher Load capacities, so that despite the small suspension means in diameter the elevator car enables a satisfactory payload.

The slim design of the drive, which is kept small in diameter allows different attachments within the Elevator shaft.

For example, to fasten the drive in the elevator shaft two parallel and at least in some areas one clear distance between the carrier provided and the drive can be the one located between the carriers Bridge the gap or space in the assembled position. This results in good statics for the mounting of the drive and a simple introduction of the forces emanating from it into the Shaft walls, since the ends of the girders end up in the shaft walls recessed or in the case of a recess in the ceiling of the shaft can be supported on these walls. Instead of in wall openings to intervene, the straps can also be attached to consoles be anchored to the shaft walls. Thus it results in any case by the two parallel beams and the a compact drive attached to these two supports itself stable, rigid and simple construction, which is also a easy assembly allowed.

The two spaced carriers can thus by the respective drive attached to each other to form a structural unit be connected before or after the assembly is formed.

Those used to hold the drive in the elevator shaft Carriers can be roughly horizontal and parallel to the drive immediately adjacent shaft wall mounted in the elevator shaft be and attachment points or feet of the drive can be on the top or on the bottom or - with profiled Beams - essentially horizontal in cross-section oriented flanges or legs of these beams in Use position be fixed. In particular an attachment on the top of the straps or also on the top of Flanges or thighs provide great security because the Force application based on pressure.

A further embodiment of the invention can consist in that the feet or attachment points of the drive with at least a plate or several cross struts are connected in turn in particular detachable on the carriers, consoles or the like are attached. This will result in greater stiffening this construction unit from the drive and its Attachment achieved.

As additional stiffening of the beams that receive the drive can be provided on these attacking cross-connections. This is especially the case with relatively large elevator shafts with appropriately long straps to support the bracing and improve load capacity.

A simplification of assembly and possible disassembly can can be achieved if at least one of the two carriers Can be moved parallel to itself and therefore the distance between the two carriers can be enlarged such that the Drive for assembly or disassembly between the carriers is movable through. A drive mounted on the carrier can then either be pulled up over the straps from below or be drained between them. Conversely, it can also a drive hanging from under the brackets from above drained between the initially moved carriers and then assembled or when disassembling between the beams be pulled up.

The diameter of the traction sheave can already be used for the above explained dimensional ratios equal to or less than theirs axial dimension and in particular about half of the axial length of the traction sheave. This way offers the traction sheave has enough space for several side by side Suspension means, especially those in their training and Flexibility of particularly cheap round wire ropes with relative small diameter or cross section.

Another convenient way to attach the drive can be that the drive with its attachment points directly or through one or more consoles on the shaft wall adjacent to the drive, in particular by means of anchors engaging approximately horizontally in this shaft wall is attached. This allows running through the shaft Carriers are avoided.

But it is also possible that the drive on or under one Carrier is attached and an additional support on the Shaft wall and / or on at least one or two guide rails is provided to prevent tipping. To this Way can also be the attachment or suspension of the drive inside the shaft and preferably in the space between space-saving yet effective between the cabin and the shaft wall shape.

Overall, therefore, the drive can be used directly or indirectly attached to the shaft wall (s), what towards the solution of the Japanese utility model publication 4-50997 has the advantage that the guide rails for the elevator car or the counterweights are not additionally loaded become. But it is also possible that the drive on one at the upper ends of the elevator car guide rails and / or the counterweight, in particular by means of carriers and / or a plate is arranged, if for example carrier, Consoles or wall fastenings inside the shaft should be avoided.

For an even distribution of the occurring Forces, it is useful if the traction sheave is approximately in the Middle between the guide rails or their extensions is arranged. This allows a largely symmetrical rope arrangement with correspondingly uniform force distribution. It can also be avoided that the traction sheave elevator and especially those from the engine, brake and traction sheave existing drive unit possibly in niches or openings a boundary wall must intervene, that is, such Niches or openings or other weakening of the shaft wall can be avoided.

It is for the leanest possible design of the drive useful if the ratio of the traction sheave diameter to the rope diameter less than 40, in particular about 25 to 35, preferably about 30. This embodiment of the invention makes itself in the interest of a drive as lean as possible to use the knowledge that modern ropes with small radii of curvature can be operated.

Especially when combining one or more of the above Features and measures result in a traction sheave elevator with a drive in the uppermost part of the elevator shaft, which only requires a small head height there and yet, due to its slim shape, well between Cabin and shaft wall or in the continuation of such Gap can be accommodated so that the elevator car also in the upper area up to the ceiling of the shaft can be moved. At the same time comes the advantageous Backpack construction for use that requires few parts and is structurally simple and yet also has a high load-bearing capacity allowed.

Fig. 1

eine Seitenansicht eines erfindungsgemäßen Treibscheibenaufzugs in Rucksack-Bauweise, wobei der Aufzugsschacht im Längsschnitt und der Antrieb in Stirnansicht dargestellt sind, wobei der Antrieb einen relativ kleinen Durchmesser in Relation zu seiner axialen Länge hat und im oberen Bereich des Schachts in einem Raum angeordnet ist, dessen Breite etwas kleiner als der lichte Abstand zwischen der Schachtwand und der dieser unmittelbar benachbarten Kabinenwand ist,

Fig. 2

einen Querschnitt des Aufzugsschachts mit Draufsicht der Kabine und ihres Antriebs,

Fig. 3

in vergrößerter und schaubildlicher Darstellung die Befestigung des Antriebs an zwei parallelen horizontalen Trägern, die innerhalb des Schachts in dessen oberen Bereich parallel zu der Kabinenwand und der benachbarten Schachtwand anbringbar sind,

Fig. 4

eine abgewandelte Ausführungsform der Befestigung des Antriebs an zwei parallelen Trägern, wobei die Befestigungsstellen des Antriebs an einander zugewandten Flanschen der Träger angreifen,

Fig. 5

eine der Fig. 4 etwa entsprechende Darstellung einer weiter abgewandelten Ausführungsform der Befestigung des Antriebs an zwei parallelen Trägern sowie

Fig. 6

eine Befestigung des Antriebs an einer Konsole, die an der parallel zur Kabinenwand benachbarten Schachtwand teils an deren vertikalen Bereich, teils an einer Wandaussparung verankert ist.

Exemplary embodiments of the invention are described in more detail below with reference to the drawing. It shows in a partially schematic representation:

Fig. 1

a side view of a traction sheave elevator according to the invention in backpack design, the elevator shaft being shown in longitudinal section and the drive in front view, the drive having a relatively small diameter in relation to its axial length and being arranged in the upper region of the shaft in a room whose Width is slightly smaller than the clear distance between the shaft wall and the cabin wall immediately adjacent to it,

Fig. 2

a cross section of the elevator shaft with a top view of the car and its drive,

Fig. 3

in an enlarged and diagrammatic representation, the fastening of the drive to two parallel horizontal supports, which can be attached inside the shaft in its upper area parallel to the cabin wall and the adjacent shaft wall,

Fig. 4

a modified embodiment of the attachment of the drive to two parallel supports, the attachment points of the drive attacking mutually facing flanges of the supports,

Fig. 5

one of FIG. 4 approximately corresponding representation of a further modified embodiment of the attachment of the drive to two parallel supports and

Fig. 6

an attachment of the drive to a console, which is anchored on the shaft wall adjacent to the cabin wall, partly at its vertical area, partly at a wall recess.

A traction sheave elevator designated as a whole or also abbreviated to "elevator 1", has an elevator car 2 which along for the sake of simplicity in Fig. 1, in Fig. 2, however, indicated guide rails 3 in an elevator shaft 4 can be moved up and down. It recognizes one also in Fig. 1 a counterweight 5, which like the elevator car 2 is guided in a known manner on rails and to the Elevator car 2 performs an opposite movement.

The elevator car 2 and the counterweight 5 hang on suspension elements 6, preferably wire ropes, which are round in cross section, and are free of deflection pulleys and in a backpack design.
For the movement of the elevator car 2, an overall designated 7 drive is provided, which is formed from a motor 8, a traction sheave 9 for the suspension means 6 and a brake 10 and especially in FIGS. 3 to 6 also with regard to various fastening options within the Elevator shaft 4 is shown.

1, this drive 7 is located in the upper area the elevator shaft 4 between the shaft wall 4a and the room, which the elevator car 2 needs in its uppermost position or in a vertical extension of this area. One recognises 1 clearly shows that this drive 7 in its lateral expansion to the clear distance between the shaft wall 4a and this immediately adjacent cabin wall 2a limited and of course compared to these walls can also keep a safe distance. So can a relatively low shaft head above the top position of the elevator car are sufficient, the elevator car 2 in Fig. 1 has not yet reached its top position.

The central axis of the traction sheave 9 and thus also of the motor 8 is roughly horizontal and parallel to the neighboring one Shaft wall and also to the adjacent cabin wall 2a oriented. So that the drive 7 fits into this space, 2 to 6 it is relatively slim and its axial length is greater than its diameter. Furthermore are the motor 8, the traction sheave 9 and also in the exemplary embodiment the brake 10 coaxial to one another or one behind the other arranged. For example, Fig. 3 illustrates that the axial length of the drive 7 larger than the largest diameter this drive is 7.

The suspension means suitably designed as steel wire ropes 6 can have a nominal diameter of about 8 mm or less have, so that there is also a relatively small diameter Traction sheave 9 of, for example, about 36 cm or 32 cm or more less realizes what the overall lean training of the entire drive 7 benefits.

The axial length of the drive 7 is more in the exemplary embodiment than twice as large, especially about two and a half times to about three times or even several times larger than the one already mentioned, relatively small diameter of the traction sheave 9. This leads to an elongated slim shape of the drive 7 with accordingly small outer diameter that works well in this way the clear space between the shaft wall 4a and the adjacent adjacent cabin wall 2a fits and a relative small dimension of this distance or space allowed.

The exemplary embodiments according to FIGS. 2 to 6 also show that the traction sheave 9 directly on the output of the motor 8 is arranged, the entire drive 7 is gearless overall can be trained. So it's a simple, relatively light and therefore less prone to failure Drive 7.

The axial length of the traction sheave 9 is in the embodiment chosen so that they have space for several suspension elements or hoisting ropes 6 has axially side by side. For example, it can be five or six or possibly more such suspension means 6 next to each other record, so that correspondingly large loads be made possible. But here is the diameter of the traction sheave 9 only about the same or even smaller than their axial Dimension and can be, for example, about half the axial Length of the traction sheave 9. This is useful because in sufficient space in the axial direction to accommodate the drive 7 and its traction sheave 9 is present during this space is limited in the transverse direction in that the distance between the cabin 2 and the shaft wall 4a as small as possible should be.

Especially in FIGS. 3 to 6 there are different options shown how the drive 7 directly or indirectly on the or the shaft walls, be they those transverse to the shaft wall 4a extending shaft walls 8a or also on the shaft wall 4a itself can be attached:

3 to 5 can be used to fasten the drive 7 in the elevator shaft 4 two parallel and at least partially a clear distance between the carrier 11 different cross sections can be provided. The drive 7 bridges the one located between these carriers 11 Distance or space in the mounted position and thereby contributes to stiffen this arrangement. You can do this Beam 11 below the shaft ceiling 12 through the shaft 4 run through or directly at the bottom of the Manhole cover 12 attached or even in whole or in part be sunk. Can in a manner not shown the ends of the beams come to rest on the shaft walls 4b or intervene in these shaft walls 4b in order to prevent them the forces absorbed are preferably introduced into these shaft walls 4b. 3 to 5 illustrate that the two are spaced apart Carrier 11, be it U-profiles according to FIG. 3 or 4 and 5, or other profiles, by the drive 7 each attached to them to one another Construction unit can be connected before assembly or formed only after assembly in the shaft 4 becomes.

Fig. 3 shows an arrangement in which the for holding the Drive 7 serving carrier 11 approximately horizontally and parallel to the shaft wall 4a directly adjacent to the drive 7 in the elevator shaft 4 can be mounted, the attachment points or feet 13 of the drive 7 on the top this carrier 11 attack, so that the statics to a pressure load leads at this point. In this case they run Beam 11 at a distance below the shaft cover 12.

4 and 5 show solutions in which the attachment points or feet 13 of the drive 7 in cross section essentially horizontally oriented lower flanges 11a of these Carriers 11 are fastened, the drive 7 according to FIG. 4 hanging down while in Fig. 5 in on such Flanges 11a standing position is shown.

In contrast, it would also be possible that the drive 7 immediately on the underside of the carrier 11 or its flanges 11a is screwed on.

In Fig. 5 it is also indicated that the feet or Fastening points 13 of the drive 7 connected to a plate 14 can be, in turn, in particular releasably to the Carriers 11 or attached to a console or the like is. This is useful if the distance between the Carrier 11 too large for the width of the attachment point 13 the drive 7. In addition, such an additional plate 14 increase the rigidity and stability of the entire arrangement and the two carriers 11 even better with each other connect.

In Fig. 3 it is indicated that the additional stiffening the drive 7 receiving carrier 11 engaging them Cross connections 15 can be provided, which is especially the case relatively long straps 11 is expedient by the drive 7 and the movable cabin 2 are loaded dynamically.

Fig. 6 shows an arrangement in which the drive 7 with its attachment points 13 via a console 16 on the Drive adjacent shaft wall 4a is attached. Doing the shaft wall 4a in this area a recess 17, so that the console 16 partly in this recess 17 with vertical Screws 18, partly on the inside of the shaft wall 4a horizontal screws 19 or other fasteners can be anchored. The recess 17 thus enables one very stable attachment of the console 16 and thus also the drive 7 to be realized on the shaft wall. The drive 7 is accessible from the outside of the shaft 4 because of the recess 17 is continuous. If necessary, it is also sufficient a niche as a recess 17.

In a manner not shown, the drive 7 could also be fixed on or under only one support 11 in such a way as shown in the figures by means of two carriers and is described in addition, and there could be additional support on the shaft wall 4a and / or 4b and / or at least one or both guide rails 3 for securing be provided against tipping.

Finally, the drive 7 could also be shown in FIG Way on one at the upper ends of the guide rails 3 of the elevator car 2 and / or the counterweight 5 for Example can be arranged by means of carriers and / or a plate.

Especially in Fig. 2 you can clearly see that in the illustrated Embodiment the traction sheave 9 approximately in the middle between the guide rails 3 or their extensions is arranged. The run accordingly symmetrically Rope strands and correspondingly even can occur Powers are distributed. At the same time, this arrangement leads to the fact that the entire drive 7, ie the motor 8, the traction sheave 9 and the brake 10 within the shaft cross section Find space and no openings or niches in the shaft walls 4b must be provided.

The ratio of the diameter of the traction sheave 9 to the diameter the round suspension element 6, so the ropes can be in the interest a small diameter traction sheave less than 40, for example about 25 to 35, preferably about Be 30. This also allows the use of relative heavily dimensioned suspension elements or ropes 6, even if the Diameter of the traction sheave 9 is small and, as already mentioned, Is 32 cm or even less. So this contributes a space-saving arrangement that accommodates the Drive 7 within the shaft 4 allows.

The traction sheave elevator 1 with an elevator car 2 running along of guide rails 3 is movable, with one also Counterweight 5 guided on rails and with a cross-section round suspension elements 6 or hoisting ropes is in backpack design executed, that is, the elevator car 2 and the counterweight 5 hang on the suspension elements, which in turn are attached to a traction sheave 9 one formed from motor 8, traction sheave 9 and brake 10 Drive 7 is arranged. This drive 7 is in upper area of the elevator shaft 4 between the immediate adjacent shaft wall 4a and the cabin 2 respectively between the shaft wall 4a and the space that the elevator car 2 needed in its uppermost position or in a vertical Extension of this area arranged. The axis of the traction sheave 9 runs approximately horizontally and simultaneously in parallel to the adjacent shaft wall 4a and to the adjacent cabin wall 2a. The axial length of the drive 7 is greater than its diameter and the motor 8 and the traction sheave 9 are arranged coaxially to each other, so that an angular gear between motor 8 and traction sheave 9 can be avoided.

Claims (19)

Traction sheave elevator (1) with an elevator car (2) which can be moved along guide rails (3), with a counterweight (5) also guided on rails, with suspension elements (6) which are round in cross section and on which the elevator car (2) and the like Counterweight (5) are attached without a pulley in a backpack design, and with a drive (7) formed at least from a motor (8), a traction sheave (9) for the suspension means (6) and a brake (10), which is in the upper area the elevator shaft (4) is arranged between the shaft wall (4a) and the space which the elevator car (2) needs in its uppermost position and / or in a vertical extension of this area, the axis of the traction sheave (9) being approximately horizontal and is simultaneously oriented parallel to the adjacent shaft wall (4a) and / or to the adjacent cabin wall (2a), characterized in that the axial length of the drive (7) is greater than its diameter and that the motor (8) and the traction shear ibe (9) are arranged coaxially to each other. Traction sheave elevator according to claim 1, characterized in that the support means (6) are steel wire ropes with a nominal diameter of approximately 8 mm or less. Traction sheave elevator according to claim 1 or 2, characterized in that the diameter of the traction sheave (9) is approximately 36 cm or 32 cm or less. Traction sheave elevator according to one of claims 1 to 3, characterized in that the axial length of the drive (7) is at least twice as large, in particular approximately 2 1/2 to 3 times or more than the diameter of the traction sheave (9). Traction sheave elevator according to one of claims 1 to 4, characterized in that the traction sheave (9) is arranged directly on the output of the motor (8) and the drive (7) is in particular gearless. Traction sheave elevator according to one of Claims 1 to 5, characterized in that the axial length of the traction sheave (9) is selected such that it has space for at least five, in particular six, suspension means or hoisting ropes (6) axially next to one another. Traction sheave elevator according to one of claims 1 to 6, characterized in that the diameter of the traction sheave (9) is equal to or smaller than its axial dimension and is in particular approximately half the axial length of the traction sheave (9). Traction sheave elevator according to one of claims 1 to 7, characterized in that the drive (7) is fastened directly or indirectly to the shaft wall or walls (4a, 4b). Traction sheave elevator according to one of claims 1 to 8, characterized in that for the fastening of the drive (7) in the elevator shaft (4) there are two parallel and at least in some areas a clear distance between the supports (11) and the drive (7) bridged distance or space between the carriers (11) in the assembled position. Traction sheave elevator according to one of Claims 1 to 9, characterized in that the two spaced-apart supports (11) are connected to one another by means of the drive (7) attached to them to form a constructional unit. Traction sheave elevator according to one of claims 1 to 10, characterized in that the supports (11) used to hold the drive (7) are mounted approximately horizontally and parallel to the shaft wall (4a) directly adjacent to the drive (7) in the elevator shaft (4) are and that attachment points or feet (13) of the drive (7) on the top or on the bottom or - in the case of profiled beams - are attached to flanges (11a) or legs of these beams (11) which are essentially horizontal in cross-section in the use position. Traction sheave elevator according to one of claims 1 to 11, characterized in that the feet or fastening points (13) of the drive (7) are connected to at least one plate (14) or in particular a plurality of cross struts, which in turn in particular are detachably attached to the carriers (11), Consoles or the like are attached. Traction sheave elevator according to one of Claims 1 to 12, characterized in that cross-connections (15) which engage the drive (7) and which act on it are provided as additional stiffening. Traction sheave elevator according to one of Claims 1 to 13, characterized in that at least one of the two carriers (11) can be displaced parallel to itself and the distance between the two carriers (11) can thus be increased in such a way that the drive (7) during assembly or disassembly between the carriers (11) is movable. Traction sheave elevator according to one of claims 1 to 14, characterized in that the drive (7) with its fastening points (13) directly or via one or more brackets (16) on the shaft wall (4a) adjacent to the drive, in particular by means of approximately horizontally in this shaft wall engaging anchors is attached. Traction sheave elevator according to one of the preceding claims, characterized in that the drive (7) is fastened on or under a support (11) and an additional support on the shaft wall (4a, 4b) and / or on at least one or two guide rails (3) is provided to prevent tipping. Traction sheave elevator according to one of the preceding claims, characterized in that the drive (7) on one of the upper ends of the guide rails (3) of the elevator car (2) and / or the counterweight (5), in particular by means of carriers (11) and / or one Plate (14) is arranged. Traction sheave elevator according to one of claims 1 to 17, characterized in that the traction sheave (9) is arranged approximately in the middle between the guide rails (3) or their extensions. Traction sheave elevator according to one of the preceding claims, characterized in that the ratio of the traction sheave diameter to the rope diameter is less than 40, in particular approximately 25 to 35, preferably approximately 30.

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