RU2297965C2 - Elevator belt (versions) and elevation system - Google Patents

Abstract

FIELD: load-bearing parts, in particular, belts used in elevation systems.

SUBSTANCE: elevator belt has group of cords placed within enclosure. Enclosure is equipped with channels spaced apart from one another along belt length. Each of said channels has group of parts inclined at a skew angle to belt longitudinal axis. According to first version of embodiment, channels are spaced from one another so that adjacent channels are arranged at opposite sides relative to certain longitudinal coordinate on belt. According to second version of embodiment, transition portions between parts inclined at a skew angle are arranged at points with different longitudinal coordinates on belt. Elevation system comprises cabin, pulley and group of belts.

EFFECT: reduced noise and vibration of elevation system.

22 cl, 7 dwg

Description

The present invention generally relates to load-bearing elements used in lifting systems. In particular, the present invention relates to a belt device (hereinafter referred to as the "belt") of an elevator (elevator) having a special arrangement of grooves.

State of the art

Lifting systems, such as elevators, usually include a cabin and a counterweight that move inside the elevator shaft, transporting passengers or cargo, for example, to various floors inside the building. A load bearing member, such as a rope or belt, typically moves along a pulley block and carries the weight of the cab and counterweight. In lifting systems, load-bearing elements of various types are used.

One of the varieties of load-bearing elements is a steel belt in a shell. A typical configuration includes a plurality of steel cords (cords or cores) elongated along the entire length of the belt. A sheath (coating) is applied over the cords, forming the outer part of the belt. In some cases, grooves on at least one side of the belt remain on the surface of the shell during molding the sheath. Sometimes, during the molding process, distortions and heterogeneities of the arrangement of steel cords relative to the outer surface of the shell along the belt occur.

For example, FIG. 7 illustrates both of these phenomena. It can be seen that the distance between the outer surface of the sheath 200 and the cords 210 varies along the belt. As can be understood from this example, the cords 210 are located inside the shell as if they formed a sequence of sections of the cord of the same length in accordance with the interval between the grooves. For clarity of the picture, in the image in Fig. 7, the geometric relationships in the arrangement of the cord are exaggerated relative to those usually existing in reality. Actual deviations or changes in the position of the cords relative to the outer surfaces of the sheath are often indistinguishable by the eye.

With the conventional sheathing technology and the method used to maintain the cords during sheathing, it is not possible to avoid such distortions in the geometry or configuration of the cords relative to the outer surface of the sheath along the length of the belt.

Despite the practical usefulness of such a configuration, it requires improvement. One of the problems associated with such belts is that when the belt moves in the lifting system, the configuration of the grooves and the position of the cord in the shell when interacting with other system components, such as pulleys, contributes to the appearance of unwanted noise, vibration, or both together. For example, when the belt moves at a constant speed, the contact of the grooves with the pulleys at a constant frequency creates an annoying audible sound. It is believed that repeated changes in the position of the cord relative to the outer surfaces of the sheath also contribute to this noise.

An alternative design is required to minimize or eliminate vibration or annoying sound when operating the lifting system. The present invention is dedicated to solving this problem.

Disclosure of invention

In General terms, the present invention is a belt device (belt) for use in lifting systems. The elevator belt, designed to carry the load from the elevator car and to place around the pulley to drive the elevator car with at least partial coverage, contains a group of cords placed mainly parallel to the longitudinal axis of the belt. On top of the cords is a shell having a group of grooves, the configuration and location of which are selected so as to minimize the occurrence of annoying audible noise during operation of the lift.

In one embodiment of the belt according to the invention, there is a group of grooves on the sheath on at least the contact surface of the pulley. Each groove has a group of parts inclined at an oblique (indirect) angle relative to the axis of the belt. The grooves are spaced from each other so that adjacent grooves are on opposite sides with respect to some longitudinal coordinate on the belt.

In one embodiment, adjacent grooves are on opposite sides of an imaginary line running across the axis of the belt. With this mutual arrangement of the grooves, any overlapping of any parts of the grooves with adjacent grooves is excluded. Maintaining this mutual arrangement between the grooves reduces the energy that generates noise due to collisions between the grooves and the pulley when the belt bypasses part of the pulley during operation of the lifting system.

The longitudinal arrangement of the grooves may be such that the intervals between adjacent grooves vary along the length of the belt. Due to the various intervals between adjacent grooves, the frequency of interaction of the grooves with other components of the system ceases to be constant, which was the main reason for the presence of unwanted noise or vibration during operation of the elevator.

In a belt designed in accordance with the present invention, spacing between the grooves, the angular orientation of the groove segments in accordance with the invention, or a combination of both can be specified.

Thus, in an alternative embodiment of the invention, the belt includes a group of grooves on at least one surface of the shell. Each groove has a group of parts placed at an oblique angle with respect to the longitudinal axis of the belt. Each groove has a transition section between adjacent parts. Each groove has a group of such transitional sections, and each transitional section has a different arrangement along the belt (located at different longitudinal coordinates on the belt).

In one embodiment, the location of the transition sections with different longitudinal coordinates is achieved by using different oblique angles for different parts of the grooves. The location of the transition sections in places with different longitudinal coordinates along the belt reduces the noise-causing collisions between the belt and pulleys in the lifting system.

In preferred embodiments of the invention, each groove is elongated over the entire width of the belt, defined in a direction generally perpendicular to the longitudinal axis of the belt between opposing side edges on the belt.

Each part of each groove may be located relative to each part of each adjacent groove on the opposite side of the longitudinal coordinate. Each part of each groove may be inclined at the same oblique angle, or at least a first part of the groove inclined at the first oblique angle and at least a second part inclined at the second oblique angle. In another embodiment, each groove includes a first part extending in the longitudinal direction at a first oblique angle, a second part adjacent to the first, extending in the opposite longitudinal direction at the first oblique angle, a third part adjacent to the second part extending in the opposite longitudinal direction from the second parts at a second oblique angle, and a fourth part adjacent to the third part extending in the opposite longitudinal direction from the third part at the second oblique angle. At least two transitional sections between adjacent parts have positions with different longitudinal coordinates on the belt. Each groove has a curved transitional section between adjacent parts.

The invention also provides a lifting system comprising a cab mounted to move in a predetermined vertical direction, at least one pulley and a group of belts arranged with at least partial coverage of the pulley and the ability to move around the pulley as the cab moves in a given direction moreover, each belt has a group of cords located mainly parallel to the longitudinal axis of the belt, and a shell located around the cords and having a group of grooves on at least one turn Nost shell. Each groove has a group of parts located at an oblique angle to the axis of the belt, and at least one transition section between adjacent parts, and the transition sections on the first of the belts have different longitudinal coordinates than the transition sections on the second of the belts.

In preferred embodiments of the invention, the parts of the grooves on the first belt and on the second belt have different values of said oblique angle. Each groove on the first belt includes a first part extending longitudinally at a first oblique angle, a second part adjacent to the first part extending in the opposite longitudinal direction at a first oblique angle, and each groove on the second belt includes a third part extending in the opposite longitudinal direction the direction from the second part at the second oblique angle, and the fourth part adjacent to the third part, passing in the opposite longitudinal direction from the third part at the second oblique angle.

Various features and advantages of this invention will be apparent to those skilled in the art from the above detailed description of preferred embodiments with the accompanying drawings.

Brief Description of the Drawings

Figure 1 schematically shows part of an exemplary belt device developed in accordance with the present invention.

Figure 2 shows a section along the lines 2-2 in figure 1.

Figure 3 presents a two-dimensional schematic illustration of the location of the grooves for the embodiment of figure 1, showing the selected geometric features.

Figure 4 presents an enlarged image of the highlighted part in figure 1, which schematically illustrates the configuration of the cross-section of the grooves selected for example.

5 is a schematic illustration of an alternative arrangement of grooves.

6 schematically illustrates a method of manufacturing a belt, the design of which corresponds to an embodiment of the present invention.

7 schematically shows the geometry of the position of the cord relative to the outer surfaces on the belt shell, typical of known structures.

The implementation of the invention

Figures 1 and 2 are a schematic illustration of a belt 20 designed for use in a lifting system. Several cords 22 are oriented approximately parallel to the longitudinal axis of the belt 20. In one example, the cords 22 are made of strands (twists) of steel wire.

Sheath or coating 24 covers cords 22. In a preferred embodiment, sheath 24 comprises a polyurethane-based material. Such materials of various grades are commercially available and are used in well-known constructions of hoist belts. Using the present description, one skilled in the art will easily select the appropriate material for the sheath, in accordance with the requirements of a particular application.

The shell determines the external length L, width W and thickness t of the belt 20. In one example, the width W of the belt is 60 mm, the thickness t is 3 mm, and the length L is determined by the parameters of the particular system where the belt will be used. In the same example, cords 22 have a diameter of 1.65 mm. In this example, twenty-four cords are used. In a preferred embodiment, the cords 24 extend over the entire length L of the belt.

The sheath 24 has a plurality of grooves (grooves) 30, 32, 34, 36, 38, 40, and 42 with at least one side of the sheath 24. In an illustrative example, the grooves extend across the belt across its entire width.

Grooves result from certain operations used in forming the belt 20, many of which are well known. As can be clearly seen in FIG. 2, the grooves extend (deepened) between the outer surface of the sheath 24 and the surface of the cords 22 facing the same outer surface of the sheath.

As shown in FIGS. 1 and 3, in this embodiment, used as an example, there are grooves having a substantially W-shape. Each groove includes several parts that are inclined at an oblique (indirect) angle relative to the longitudinal axis (center line) 48 of the belt. If a groove 34 is used as an example, then the first part 50 (grooves) extends at an oblique angle A in the first longitudinal direction. The second part 52 extends in the opposite longitudinal direction with an inclination also at an angle A. The third part 54 extends in the same direction as the first part 50, but is inclined at the second oblique angle B. The fourth part 56 extends in the opposite longitudinal direction with an inclination at the second angle B.

In one embodiment, angle A is approximately 50 °. In the same example, angle B is approximately 53.5 °. The use of different oblique inclination angles for different parts of the grooves makes it possible to optimally select the places of the transitional section between the inclined parts.

The groove 34 in FIG. 3, for example, has a first transition section 60, a second transition section 62, and a third transition section 64. In each transition section, two parts of the grooves inclined at an oblique angle are connected. Since the first oblique angle A is different from the second oblique angle B, the longitudinal coordinate of the transition section 60 is different from the longitudinal coordinate of the transition section 64. The term "longitudinal coordinate" as used in this description refers to the position on the belt along its length (i.e., in direction parallel to axis 48).

For example, the distance between the line 70, which runs across the belt axis 48 across the entire width of the belt, and the transition section 60 is different from the distance between the line 70 and the transition section 64. In this example, the transition section 60 is closer to the line 70 than the transition section 64, since angle A is less than angle B. Line 70 is for explanatory purposes only and does not correspond to any actual line on the belt.

Placing the transition sections at points with different longitudinal coordinates significantly changes the phase of the two halves of the grooves. If the transition sections are not in phase, then the contact energy of the transition sections with the pulleys is extinguished. Therefore, the configuration of the invention reduces vibration and noise in the lifting system.

As shown in the presented example, the transition sections represent essentially peaks located along the grooves. In this example, each transition section has a curved shape. Due to the curvilinearity of the transition sections between the groove parts of the grooves diverging in opposite directions, vibration and noise-causing collision energy are reduced when the grooves come into contact with the pulley in the lifting system.

As can be seen in figure 3, in the above example, the parts 50, 52, 54 and 56 retain linearity over most of their length. The linear parts are oriented at a given oblique angle or angles, depending on the desired groove configuration. The present invention is not limited to a belt with grooves with strictly straight parts. In an exemplary belt design, where the parts are at least partially curved, it is desirable that the tangent lines corresponding to these curved parts are directed at predetermined oblique angles to the axis of the belt.

In the example of FIG. 3, the distance 72 between adjacent grooves (i.e., between grooves 32 and grooves 34, between grooves 34 and grooves 36, and between grooves 36 and grooves 38, respectively) is selected so that no overlap occurs with any parts of any adjacent grooves. If we assume that line 70 marks the longitudinal coordinate on the belt 20, then the grooves 36 and 38 are on the opposite sides of the line 70. Accordingly, there is no overlap between any part of the grooves 36 and any part of the grooves 38. Due to the fact that the entire groove 36 is longitudinally spaced with all the grooves 38, vibration and noise-causing collision energy are reduced when the grooves are in contact with the pulley during operation of the lifting system.

In a preferred embodiment, the interval 72 between the grooves prevents overlapping adjacent grooves along the entire length of the belt. In some cases, the interval 72 may be maintained along the entire length of the belt. In other examples, the interval 72 varies from grooves to groove in a predetermined manner, as will be described below.

In addition to differences in the longitudinal coordinates of the locations of the transition sections and the absence of any longitudinal overlapping of adjacent grooves, the belt made in accordance with the present invention may differ in other features, which reduce vibration and noise. Figure 4, for example, shows an example configuration of grooves where a rounded edge or fillet 74 is present at the junction of the grooves with the outer surface of the sheath 24. Using such a rounded edge 74 reduces vibration and noise-causing collision energy when the grooves and the pulley surface come into contact in a lifting system. In this example, fillets 74 have a radius of curvature in the range of about 0.05 to 0.15 mm.

In the example of FIG. 4, the side walls 76 of the grooves 38 extend from the outer surface of the sheath 24 to the bottom 78 of the grooves, which is directly adjacent to the surface of the cords 22. The intersections between the side walls 76 and the bottom 78 in this example include rounded surfaces having same radius of curvature as edges 74.

In one embodiment, for the edges 74 and transition sections between the side walls and the bottom 78, the same radius of curvature of 0.1 mm is used. The configuration in one embodiment is characterized in that the side walls 76 are located at an angle C to each other of approximately 30 °. In the embodiment used, the height of the grooves is 0.7 mm and the width S of the grooves is 0.7 mm.

The groove configuration in some exemplary embodiments is determined by the shape of the cord support used in the belt manufacturing process. Specialists in this field who have become acquainted with this description will be able to choose among the materials used for the manufacture of shells for hoist belts, and determine the requirements for technological equipment or other equipment for forming grooves to ensure the required groove profile in accordance with a specific application.

Figure 5 shows another, used as an example, belt 20, developed in accordance with the present invention. In this example, each groove has only two parts 80 and 82, diverging in opposite longitudinal directions, but at the same oblique angle A. Parts 80 and 82 are connected at a single point 84 of the transition section. In this example, both parts 80 and 82 diverge at the same angles A, and the transition section 84 is aligned with the center line 85, which coincides with the longitudinal axis of the belt. Of course, other configurations are possible within the scope of the present invention.

In this example, the interval 86 between adjacent grooves is selected so that adjacent grooves are located on opposite sides relative to some longitudinal coordinate on the belt 20. For example, line 88 marks a longitudinal coordinate defining a position across the longitudinal axis 85 of the belt. In an exemplary embodiment, such a line can be drawn between each group of adjacent grooves, and there will be no longitudinal overlap between these grooves, since each groove will be located on the opposite side of this line. The location of the grooves in such a way as to avoid longitudinal overlapping reduces the energy associated with collisions when the grooves touch the surface of the pulley in the lifting system.

One embodiment, for example, shown in FIG. 5, is used for a belt with a width W of approximately 30 mm, while a belt with a configuration corresponding to that shown in FIG. 3 has a width of approximately 60 mm. The choice of belt width depends, in part, on the expected rated loads of the lifting system in which the belt will be used.

6 schematically shows an example of a method for manufacturing a belt for a lift in accordance with the present invention. Shown as an example in FIG. 3, a belt 90 60 mm wide is cut in half along the longitudinal axis of the belt on a cutting machine 92. Two belts 94 and 96 are obtained, having the configuration shown for the example in FIG. 5. This approach to the manufacture of belts for the hoist allows you to use the same technological equipment for the manufacture of belts, for example, 60 mm wide and 30 mm wide.

An exemplary lifting system comprising belts designed in accordance with the present invention utilizes several parallel working belts moving simultaneously along pulleys. Several belts in this example have groove portions inclined at an oblique angle, the angles of inclination being different for at least two belts. The advantage of different tilt angles is that the longitudinal coordinates of the transition sections on one belt are different from their location on the other belt. The use of such a longitudinal arrangement allows the phase to be shifted for at least two belts having different oblique inclination angles. Due to the misphasing of the transition sections, the energy associated with the contacts of the transition sections with the pulleys of one belt is effectively compensated by the energy associated with the same contacts between the pulleys and another belt.

In one example, for each belt, parts of the grooves are inclined at different oblique angles than other belts. In another example, the belts use the same oblique angle, however, the belts in the system are arranged relative to each other so that the transitional sections of the grooves of one belt have different longitudinal coordinates compared to the transitional sections of the grooves of at least one other belt.

Additional means for reducing vibration and noise of the belt, corresponding to some exemplary embodiments of the present invention, include spacing the grooves at different distances so that different intervals are between different grooves. For example, as shown in FIG. 2, the first interval 144 separates the groove 30 from the adjacent groove 32. A different interval 146 separates the groove 32 from the neighboring groove 34. Similarly, at least some of the intervals 148, 150, 152 and 154 differ in size.

It is not necessary that all the intervals shown are different, however, it is desirable that the belt length has at least several intervals that are different from each other. In practice, a periodically repeating pattern with varying intervals will usually be observed along the entire length of the belt 20. Depending on the specific design features of the belt and the equipment used for molding and applying the sheath 24, the pattern at different intervals will be repeated at different intervals. In a preferred embodiment, the gap at which the pattern is repeated should be as large as the processing equipment allows. In one example, a pattern is selected with a sequence of different intervals, repeating approximately every fifty grooves or every two meters of belt length. Within each two-meter segment, the intervals between adjacent grooves are defined as changing and non-periodic.

In one embodiment, the intervals between the grooves are selected to be 13.35, 12.7, and 11.8 mm. Such intervals are preferably used in a non-periodic, non-repeating sequence on a portion of the belt including approximately fifty grooves. In one exemplary embodiment, the pattern determined by the processing equipment used to make the belt is repeated after every 47th groove. In another embodiment, intervals of 11, 2, 12.1 and 12.7 mm are used. A person skilled in the art, having read the present description, will be able to choose suitable intervals for the location of the grooves to achieve the desired level of smoothness and noise, in accordance with the specific requirements of the application.

In one example, modeling is used to determine the magnitude of the intervals and pattern. The effect of the grooves is characterized by a complex oscillation approximating the energy of the input disturbance. The complex oscillation in this example is determined by taking measurements on a working belt and obtaining a suitable function that describes the behavior of the investigated belt. This input function is used for each cord (i.e. each belt segment between adjacent grooves). The summation of these functions is made taking into account the relative phases of the cords. Total energy is the sum of all contributions from individual cords. Thus, the phasing of the cords (i.e., the distance between the grooves) determines the overall amplitude. To assess the overall relative level of energy generated by the belt, an analysis based on the fast Fourier transform is used.

Due to the change in the intervals between adjacent grooves, the noise caused by the contact of the belt with other components of the lifting system during its operation, for example, by pulleys, is distributed over a wider frequency range. Thus, it is possible to avoid noise at a constant frequency, thereby eliminating the likelihood of an audible annoying sound.

In addition to changing the interval between the grooves, in the device proposed in the invention, it is possible to change the length of the "segments" of the cord, which is associated with some features of the manufacturing technology (not necessarily included in the invention). In the belt structure developed in accordance with the present invention, sequences of cord segments may be used along which the distance between the cord and the outer surfaces of the sheath changes. The ends of such “segments” of the cord coincide with the position of the grooves. When changing the intervals between the grooves, the length of the segments also changes and, as a result, the pattern in the geometry of the position of the cords relative to the outer surfaces of the shell changes. In some examples of the use of the invention, the length of the cord segments varies along the length of the belt.

Since the cord segments extending between adjacent grooves are of different lengths, there is no periodic, repetitive arrangement of the cords relative to the outer surfaces of the sheath. By changing the length of the cord segments (i.e., by changing the intervals between similar distortions in the cord position relative to the outer surfaces of the sheath), the addition to noise or vibration due to the geometry of the cord can be reduced or eliminated. By eliminating periodicity in cord geometry, the present invention provides a significant advantage in reducing vibration and noise during operation of the lifting system.

The above description, in fact, is an illustration and does not limit the invention. One skilled in the art can suggest changes and modifications to the disclosed examples, which will not necessarily deviate from the gist of the present invention. The scope of the present invention should be determined only on the basis of the following formula.

Claims (22)

1. The belt of the elevator, designed to carry the load from the elevator car and to place around the pulley to drive the elevator car with at least partial coverage, containing a group of cords placed mainly parallel to the longitudinal axis of the belt with the possibility of bearing the load from the elevator car, and the shell located on top of the cords and having a group of grooves at least on the contact surface with the pulley, characterized in that each groove has a group of parts located at an oblique angle relative to odolnoy axis of the belt, and wherein the grooves are spaced from adjacent grooves located on opposite sides of a longitudinal position on the belt. 2. The belt according to claim 1, characterized in that each groove is elongated along the entire width of the belt, determined in the direction mainly perpendicular to the longitudinal axis of the belt, between opposite side edges on the belt. 3. The belt according to claim 1, characterized in that the longitudinal coordinate is on a line transverse to the longitudinal axis of the belt. 4. The belt according to claim 1, characterized in that each part of each groove is located relative to each part of each adjacent groove on the opposite side of the longitudinal coordinate. 5. The belt according to claim 1, characterized in that each part of each groove is inclined at the same oblique angle. 6. The belt according to claim 1, characterized in that there is at least a first part of the groove, inclined at a first oblique angle, and at least a second part, inclined at a second oblique angle. 7. The belt according to claim 6, characterized in that each groove has a transition section between adjacent parts and at least two transition sections have positions with different longitudinal coordinates on the belt. 8. The belt according to claim 6, characterized in that each groove includes a first part extending in the longitudinal direction at a first oblique angle, a second part adjacent to the first, passing in the opposite longitudinal direction at a first oblique angle, a third part adjacent to the second a part extending in the opposite longitudinal direction from the second part at a second oblique angle, and a fourth part adjacent to the third part extending in the opposite longitudinal direction from the third part at the second oblique angle. 9. The belt according to claim 8, characterized in that between each of the adjacent parts there is a transition section, each of which is in a position with a longitudinal coordinate different from the longitudinal coordinate of the position of the other transition sections. 10. The belt according to claim 1, characterized in that each groove has a curved transitional section between adjacent parts. 11. A hoist belt comprising a group of cords arranged substantially parallel to the longitudinal axis of the belt and a sheath located over the cords and having a group of grooves on at least one sheath surface, characterized in that each groove has a group of parts located at an oblique angle with respect to the longitudinal axis of the belt, with transitional sections between adjacent parts, each groove has a group of transitional sections located at different longitudinal coordinates on the belt. 12. The belt according to claim 11, characterized in that there is at least a first part of the groove, inclined at a first oblique angle, and at least a second part, inclined at a second oblique angle. 13. The belt according to item 12, wherein each groove includes a first part extending in the longitudinal direction at a first oblique angle, a second part adjacent to the first, passing in the opposite longitudinal direction at a first oblique angle, a third part adjacent to the second a part extending in the opposite longitudinal direction from the second part at a second oblique angle, and a fourth part adjacent to the third part extending in the opposite longitudinal direction from the third part at the second oblique angle. 14. The belt according to claim 11, characterized in that the transition sections are made curved. 15. The belt according to claim 11, characterized in that each groove is elongated along the entire width of the belt, which is determined in the direction mainly perpendicular to the longitudinal axis of the belt, between opposite side edges on the belt. 16. The belt according to claim 11, characterized in that the grooves are spaced with the location of adjacent grooves on opposite sides relative to some longitudinal coordinate on the belt. 17. A lifting system comprising a cab mounted to move in a predetermined vertical direction, at least one pulley and a group of belts located with at least partial coverage of the pulley and the ability to move around the pulley as the cab moves in a given direction, each belt has a group of cords located mainly parallel to the longitudinal axis of the belt, and a shell located around the cords and having a group of grooves on at least one surface of the shell, characterized in that each avka has a group of parts arranged at an oblique angle to the axis of the belt, and at least one transition portion between the adjacent portions, wherein the transition portions of the belts at the first longitudinal position have other than a second transition sections of the belts. 18. The system according to 17, characterized in that the parts of the grooves on the first belt and on the second belt have different values of the specified oblique angle. 19. The system according to p. 18, characterized in that each groove on the first belt includes a first part extending in the longitudinal direction at the first oblique angle, a second part adjacent to the first part, passing in the opposite longitudinal direction at the first oblique angle, and each the groove in the second belt includes a third part extending in the opposite longitudinal direction from the second part at a second oblique angle, and a fourth part adjacent to the third part extending in the opposite longitudinal direction from the third part under the second oblique angle. 20. The system according to 17, characterized in that the transition sections on at least one of the belts are made curved. 21. The system according to 17, characterized in that the grooves on at least one of the belts are spaced with the location of adjacent grooves on opposite sides relative to some longitudinal coordinate between adjacent grooves. 22. The belt according to item 21, wherein each part of each of the grooves is located on the opposite side of a longitudinal coordinate relative to each part of each adjacent groove.

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