DE102021200478A1 - Device and method for determining longitudinal elongation of a belt - Google Patents

Abstract

The invention relates to a device (2) and a method for determining the longitudinal elongation of a belt (4). The device (2) has the belt (4) with a predetermined longitudinal stiffness, a drive device (6), a transmission device and an evaluation unit (14). Two ferromagnetic marking parts (20, 22) arranged at a predetermined distance from one another are embedded in the belt (2). The transmission device is designed to generate an alternating reference field which is changed by each of the two marking parts (20, 22) when the respective marking part (20, 22) is moved through the alternating reference field (26) as the belt (4) rotates. The change in the reference alternating field (26) resulting from the corresponding interaction between the respective marking part (20, 22) and the reference alternating field (26) can be detected by the transmission device. Based on this, the evaluation unit (14) is designed to determine a longitudinal elongation of the belt (4).

Description

The invention relates to a device and a method for determining the longitudinal elongation of a belt.

Methods and devices that have a belt and a drive device for the belt are known in principle from the prior art. In this case, the drive device has a plurality of pulleys, for example two. The belt is designed to be annular in a circumferential direction and wraps around the belt pulleys at least partially. In addition, the belt can be driven in the circumferential direction by the drive device. A belt is preferably a drive belt for transmitting tensile forces. A belt is often subjected to pretension, useful forces, centrifugal forces and/or bending.

The service life of a belt is at least partly determined by the elongation of the belt, in particular the elongation in the circumferential direction. The rate at which the belt moves and/or the power required to drive the belt can provide information about the stress on the belt. However, based on this load, only a rough estimate can be made of an actually locally occurring elongation of the belt. An exact determination based on the aforementioned load is not possible.

Strain gauges are known from the prior art. However, the use of a strain gauge requires an electrical measuring circuit which is to be coupled to the strain gauge in order to evaluate a strain detected by the strain gauge or to provide a corresponding evaluation signal. Therefore, in order to use a strain gauge for a belt, it is also necessary to attach the aforementioned evaluation circuit to the belt. In particular, if the belt is exposed to a high temperature during use, which is influenced, for example, by friction of the belt on a deflection pulley and/or by a high ambient temperature, a robust evaluation circuit can only be produced with a great deal of technical effort and corresponding costs high temperatures ensures a reliable measurement of the strain using the strain gauge.

the DE102018215478A1 discloses a system for determining an elongation of a belt. The system has the belt, a drive device, a transmitter and an evaluation unit. Embedded in the belt are two ferromagnetic marker members spaced apart from each other by a predetermined distance. The transmitter is designed to generate an alternating reference field, which is changed by each of the two marking parts when the respective marking part is moved through the alternating reference field as the belt rotates. The change in the alternating reference field resulting from the corresponding interaction between the respective marking part and the alternating reference field can be detected by the transmitter. The evaluation unit is designed to determine a longitudinal elongation of the belt based on the reference distance between the ferromagnetic marking parts, the belt speed, the first detection time and the second detection time. A particular disadvantage here is that only one measurement can be carried out per revolution of the belt. The accuracy of the measurement can be adversely affected by this circumstance. The invention is therefore based on the object of providing a device and a method with which a reliable and robust detection of an elongation of a belt - even during operation - can be guaranteed, which compared to known systems has a higher measuring accuracy and measuring frequency, as well as a provides additional redundancy.

The object is achieved by a device having the features of claim 1. Further advantageous developments are disclosed in the dependent claims. Claim 14 discloses a method for determining a longitudinal elongation of a belt.

A device according to the invention for determining a longitudinal elongation of a belt is therefore provided. The device has a belt with a predetermined longitudinal rigidity, a drive device, a transmission device and an evaluation unit. The drive device has a plurality of pulleys. The evaluation unit can be combined with the transmission device. The belt has a base material, a reinforcement, a first ferromagnetic marking part and a second ferromagnetic marking part. The base material can be formed, for example, at least partially from rubber material or polyurethane material. Preferably, the base material is rubber material. The belt is formed annularly in a circumferential direction of the belt. In addition, the belt wraps around the pulleys at least partially. The belt can be driven in the circumferential direction from the drive direction. The reinforcement of the belt is designed as a continuous cord wound helically in the circumferential direction and embedded in the base material of the belt. The first marking part and the second marking part are each embedded in the base material and/or attached to the base material. The transmission device is designed to generate a first electromagnetic alternating field, which is referred to as the reference alternating field. The first ferromagnetic marking part is designed to change the alternating reference field into a first alternating reaction field when the alternating reference field acts on the first ferromagnetic marking part. The second ferromagnetic marking part is designed to change the alternating reference field into a second alternating reaction field when the alternating reference field acts on the second ferromagnetic marking part. The second marker part is arranged circumferentially behind the first marker part by a predetermined reference distance in a no-load state of the belt. The reference distance changes to a measurement distance when the belt stretches as a result of power transmission, for example. The transmission device is arranged without contact with the belt in such a way that the first marking part and the second marking part can be guided past the transmission device one after the other and through the alternating reference field by means of the belt, which results in the alternating reference field acting on the first marking part and the second marking part one after the other . The transmission device is also designed to detect the first alternating reaction field and an associated, first detection time when the first marking part is moved past the transmission device. In addition, the transmission device is designed to detect the second alternating reaction field and the associated second detection time when the second marking part is moved past the transmission device. The device is configured to determine a belt circumferential speed of the belt based on the first alternating reaction field and the second alternating reaction field. The evaluation unit is configured to determine a longitudinal elongation of the belt based on the reference distance, the belt speed, the first detection time and the second detection time. Because the device has at least two sensors in connection with an evaluation unit, these can be adjusted as part of a calibration device at a distance from one another running in the circumferential direction of the belt and, in the unloaded state of the belt, congruent with the reference distance of the first ferromagnetic marking part and the second ferromagnetic marking part be arranged, each of the sensors being designed to generate the reference alternating field. At the time of a maximum change in the alternating reference field, both the first and the second sensor are designed to detect a first detection time through the first alternating reaction field of the first marking part. Likewise, both the first sensor and the second sensor are designed to detect a second detection time at the time of a maximum change in the reference alternating field by the second alternating reaction field of the second marking part. The device is configured both to determine a belt speed of the belt in the circumferential direction based on the running time of the first or second alternating reaction field via the distance between the sensors, and also to determine a longitudinal stretching of the belt due to the deviation of the measuring distance from the reference distance from a determined change in running time of the second compared to the to determine the first alternating reaction field. Using the longitudinal stiffness and the determined longitudinal elongation of the belt, the operating force of the belt can be determined. The device offers the advantage that, by means of two sensors and an evaluation unit, longitudinal elongation of the belt can be closed with a higher measurement accuracy, independent of the belt length, and additional redundancy. The sensors can also be designated and/or designed as a transmission unit. In addition, the belt of the device is particularly robust in relation to high temperatures and/or other mechanical, external influences.

An alternating reference field can be generated by means of the sensors, through which the belt can be moved, driven by the drive device, so that the first marking part and the second marking part of the belt are moved through the alternating reference field one after the other. Each of the two marking parts can be designed for coupling into the respective alternating reference field. This makes it possible for the alternating reference field to be changed into the first alternating reaction field when the first marking part is moved through the alternating reference field and thereby acts on the alternating reference field. The same applies to the second marking part, in that the alternating reference field changes into the second alternating reaction field when the second marking part is guided through the alternating reference field and thereby acts on the alternating reference field. At this point it should be pointed out that the reference alternating field, the first alternating reaction field and the second alternating reaction field do not exist simultaneously on one sensor. Rather, only one of the aforementioned alternating fields can exist on a sensor at any given time.

A first detection time is detected by the sensors when the first alternating reaction field is detected. This occurs when the first marking part is moved past the sensors designed to generate the alternating reference field that is. However, as a result of the first marking part being moved past, the first marking part is coupled into the alternating reference field, which leads to a change in the alternating reference field into the first alternating reaction field. This change occurs at the first detection time detected by the sensors. The same applies to the second marking part or the second detection time. At least in the unloaded state of the belt, the second marking part is arranged at the predetermined reference distance in the circumferential direction behind the first marking part. If the belt is driven in the circumferential direction by means of the drive device, the first marking part first moves through the first alternating reference field of sensor A and then the second marking part moves through the same alternating reference field of sensor A. When the second marking part is guided past sensor A, coupling takes place of the second marking part into the alternating reference field, which leads to the change of the alternating reference field into the second alternating reaction field. The sensor A is designed to detect this second alternating reaction field and the associated second detection time. The first marking part then moves through the second alternating reference field of sensor B and then the second marking part through the same alternating reference field of sensor B. When the second marking part is moved past sensor B, the second marking part is coupled into the alternating reference field, which leads to the Changing the reference alternating field leads to the second alternating reaction field. The sensor B is designed to detect this second alternating reaction field and the associated second detection time. The sensors A and B can be adjusted as part of a calibration device at a distance from one another in the circumferential direction of the belt, so that when the belt is not under load they are arranged congruently with the reference distance of the first ferromagnetic marking part and the second ferromagnetic marking part. The calibration process can be carried out both when the belt drive is at a standstill and during operation, as long as no power is being transmitted through the belt. In this way, the original reference distance between the ferromagnetic marking parts can be traced using the distance between sensors A and B, even during operation. A change in the distance between the ferromagnetic marking parts can already be noticed when sensor B identifies the first marking part at a time offset from the identification of the second marking part on sensor A.

As previously explained, each of the two ferromagnetic marking parts causes a change in the alternating reference field. However, the change does not necessarily take place uniformly over the entire frequency band of the alternating reference field. Rather, it is possible for each of the two ferromagnetic marking parts to be designed to change a predetermined frequency range, so that the resulting change in the alternating reference field is characteristic and/or representative of the respective marking part. Each marking part therefore preferably causes an associated change in the alternating reference field, so that the interaction of the alternating reference field with the respective marking part produces a corresponding alternating reaction field, namely the first alternating reaction field or the second alternating reaction field. However, the respective alternating reaction field exists at least only for a short time when the respective marking part is passed through the alternating reference field.

Each acquisition time can also be referred to as an acquisition time. Each detection time preferably represents the point in time of the maximum change in the respective reference alternating field by the respective marking part. Both sensor A and sensor B each record a first detection time at the time of a maximum change in the alternating reference field due to the first alternating reaction field of the first marking part, and a second detection time at the time of a maximum change in the alternating reference field due to the second alternating reaction field of the second marking part. If the first or the second marking part is moved through the alternating reference field, the greatest change in the alternating reference field is often present, for example, when the respective marking part is arranged in the middle of the alternating reference field. The movement of the respective marking part to the central arrangement or the movement out of this central arrangement leads to a decrease in the change in the reference alternating field. In order to be able to determine the detection times as precisely as possible, it is preferably provided that the respective detection time represents the point in time of the maximum change in the reference alternating field by the marking part.

Periods of time can be determined from the detection times of sensor A or sensor B, and conclusions can be drawn about the relative elongation of the belt from the periods of time, the belt speed and the reference distance. For this purpose, the evaluation unit is preferably configured accordingly. The sensors and the evaluation unit can be formed by a common unit, which can also be referred to as a sensor evaluation unit.

Furthermore, the device is configured to determine the operating force of the belt using the longitudinal stiffness and the determined longitudinal elongation of the belt. The longitudinal stiffness of the belt can be stored in the evaluation unit as a material constant. The longitudinal stiffness can be determined individually for each belt specification and dimension, for example by means of a tensile test, in which an elongation is assigned to the applied force.

The determined longitudinal stiffness of the belt can be multiplied by the relative elongation of the belt to determine the operating force of the belt.

In principle, it is possible for the first and second marking parts to be of the same design. However, the two marking parts can also be designed differently.

In addition, the device is configured to determine the belt speed of the belt in the circumferential direction based on the distance between sensors A and B and a transit time difference between the first alternating reaction field at sensor A and sensor B or the second alternating reaction field at sensor A and sensor B. For this purpose, the sensors can be in the form of magnetoresistive sensors and/or have the function of a magnetoresistive sensor.

When the belt is driven at a certain belt speed in the circumferential direction and the belt is in an unloaded state, the second marker part is located a predetermined reference distance behind the first marker part in the circumferential direction. However, if the belt is not in the unloaded state but, for example, in a loaded state in which a tensile force is acting on the belt, in particular on a tension strand of the belt, the distance between the second marking part and the first marking part increases in the circumferential direction . As a result, at the same belt speed, the gap between the second detection time at sensor A and the first detection time at sensor A or the second detection time at sensor B and the first detection time at sensor B increases as the belt moves from the no-load condition to the previously explained load condition changes. The result is that from the second detection time at sensor A and the first detection time at sensor A or the second detection time at sensor B and the first detection time at sensor B, the belt speed and the reference distance on the elongation of the belt in the circumferential direction, also known as longitudinal elongation of the belt can be closed. The evaluation unit is therefore configured to determine a longitudinal elongation of the belt based on the reference distance, the belt speed, the first detection time and the second detection time.

In order to determine the elongation of the belt, no mechanical intervention in the belt is required during operation of the belt. Rather, the longitudinal expansion of the belt can be detected without contact during operation of the belt. In addition, the first marking part and the second marking part, which are each embedded in the base material of the belt, offer the advantage that the longitudinal elongation of the belt can be determined particularly precisely and/or robustly with respect to temperature influences even when the belt is at high temperature. Because the first and second marking parts are embedded in the base material, the determination of the longitudinal expansion of the belt is also particularly robust with regard to possible mechanical influences that can affect the belt.

The elongation is preferably a relative elongation. The longitudinal elongation of the belt can thus be a relative elongation of the belt in the longitudinal direction.

A further advantageous embodiment of the device is characterized in that the sensors, in particular as part of a sensor evaluation unit, are aligned in a contact-free manner on a strand of the belt. The strand can be formed by a tension strand of the belt. Since the sensors or the sensor evaluation unit are arranged without contact with the strand, in particular the tight strand, of the belt, the belt can be moved past the sensors without friction. There is therefore no wear and tear on the belt and/or the sensors when using the sensors and/or the evaluation unit to determine the lengthwise extension of the belt.

A further advantageous embodiment of the device is characterized in that the sensors, in particular as part of the sensor evaluation unit, are arranged at a distance of between 1 mm and 50 cm from the strand of the belt. This is preferably a tight strand of the belt. The predetermined distance can ensure that the sensors have no direct mechanical contact with the belt. In this way, the longitudinal stretching of the belt can be carried out during operation without any negative mechanical influence on the belt. Furthermore, by having the predetermined distance between 1 mm and 50 cm, it can be ensured that electromagnetic disturbances Influences have at most a negligible influence on the detection of the first and/or second alternating reaction field. It is thus possible to detect the first or second alternating reaction field in a way that is very robust to disturbance variables.

A further advantageous embodiment of the device is characterized in that the sensors are in the form of inductive or capacitive sensors.
In a further advantageous embodiment, the sensors are designed as eddy current sensors.
Due to the basic suitability of different sensor types, a sensor technology that optimally meets the requirements of the respective application can be selected in an advantageous manner.

A further advantageous embodiment of the device is characterized in that the reference distance is smaller than the smallest strand length of the belt. The second marker part is located behind the first marker part by the reference distance in the circumferential direction of the belt when the belt is in an unloaded state. The smallest strand length of the belt preferably relates to the smallest of the at least one strand length of the at least one tension strand of the belt. However, it is also possible for the device to be designed in such a way that the reference distance is less than a strand length of any desired tension strand of the belt. Thus, the reference distance is determined in such a way that when the belt rotates, there is at least one point in time at which both the first marking part and the second marking part are arranged in the same tight strand. Due to the tensile load, the distance between the two marking parts can be greater than the reference distance. However, this is usually only the case in a single-digit percentage range. It can therefore also be assumed that, even with a tensile load, the requirement is met that both marking parts are arranged at the same time in the same tension strand at least at one point in time during the circulation of the belt. The two marking parts can be moved one after the other through the alternating reference field of the sensors, which enables the previously explained determination of the longitudinal expansion of the belt. The longitudinal stretching of the belt determined represents the longitudinal stretching of the belt in the tight strand. This is particularly interesting and/or representative. This is because the greatest load and/or the greatest tensile load on the belt often takes place in the tight strand. This load or the longitudinal elongation of the belt recorded there can therefore be advantageously used for further evaluation and/or for further predictions about the state of the belt. However, there are other cases where the state of elongation of a slack side of the belt is of interest. In this case it can be provided that the reference distance between the marking parts is smaller than a strand length of a slack strand. The device can then be used, for example, to determine the longitudinal expansion of the slack side, in particular on the basis of a pretensioning of the belt. This can also be of interest in practice.

A further advantageous embodiment of the device is characterized in that the reference distance is at most 90%, at most 80%, at most 70%, at most 60% or at most 50% of a strand length of the belt. This is preferably the shortest strand length and/or the strand length of the tightened strand, in particular the shortest tightened strand. Limiting the reference distance makes it particularly easy to ensure that the two marking parts are arranged simultaneously in the corresponding strand with the strand length as the belt rotates, in order to ensure the detection of the first and second alternating reaction field on the corresponding strand.

A further advantageous embodiment of the device is characterized in that each marking part is designed to be passive, in particular purely passive. Each of the two marking parts can thus be designed as a passive, ferromagnetic marking part. The passive configuration of the respective marking part is sufficient for changing the alternating reference field of the sensors, since the ferromagnetic material of the respective marking part can cause an induction-based change in the alternating field due to the arrangement in the alternating reference field. Neither of the two marking parts is therefore coupled to other electronic components. Rather, it is preferably provided that each of the two marking parts is completely embedded in the base material of the belt, so that each of the two marking parts is completely encased by the base material. This can ensure that each of the two marking parts is arranged without contact with the reinforcement of the belt and/or other possible components of the belt. This in turn offers the advantage that even with a greater load on the belt, there is no friction effect between the reinforcement of the belt and one of the two marking parts. It can thus be effectively ensured that no friction and/or wear of the belt is caused by the embedding of the marking parts in the base material of the belt. The belt is therefore particularly robust.

A further advantageous embodiment of the device is characterized in that each marking part is a rod-shaped marking part or is designed as a foil-shaped marking part. In addition, it is preferably provided that each marking part extends at its greatest extent transversely to the circumferential direction of the belt. For example, the longitudinal axis of each rod-shaped marking part can be arranged transversely to the circumferential direction. In the case of a marking part in the form of a film, there is also the possibility that the film has a greatest extent in a direction which is arranged transversely to the circumferential direction. In addition, it is preferably provided that each marking part extends from one side wall to the opposite side wall of the strap. Each sidewall may be located on a corresponding side flank of the belt. Thus, each marking part can extend at least substantially completely in the transverse direction from one side wall to the opposite side wall. However, it is also possible that an extension length of each marking part is between 95% and 70% of the distance between the two side walls. It can thus be effectively ensured that each marking part is offset inwards by at least a small distance from the respective outer side. As a result, an electromagnetic influence on the marking parts can be prevented and/or insulation of the marking parts by the base material can be ensured particularly effectively. Each marking part can have a diameter and/or a thickness of 5 μm to 0.5 mm, for example. This has a negligible effect on the stiffness of the belt.

An advantageous embodiment of the device is characterized in that each marking part is prefabricated. A correspondingly prefabricated marking part can thus be particularly easily embedded in the base material of the belt during manufacture of the belt.

A further advantageous embodiment of the device is characterized in that each marking part is designed as a printed marking part. In this case, the marking part can be formed by a printed, ferromagnetic metal marking part. However, it is also possible for the marking part to be formed from a material mixture of ferromagnetic material and another printable material. During the manufacture of the belt, each marking part can be printed at a designated point in order to then completely embed the respective marking part in the rubber material. As a result, a particularly simple and at the same time precise embedding of the respective marking part in the rubber material is possible.

A further advantageous embodiment of the device is characterized in that each marking part is designed in one piece. This allows each marking part to be completely embedded in the belt surrounded by the base material. Due to the base material, each marking part can thus be arranged separately from the other possible components in the belt and/or be electrically insulated from the rest of the belt. The two marking parts can be arranged separately due to their one-piece design, specifically preferably at the reference distance from one another.

A further advantageous embodiment of the device is characterized in that the first marking part and the second marking part are connected to one another at least indirectly. Connecting webs can extend between the first and the second marking part, for example in the circumferential direction. These connecting webs enable the first and second marking parts to have a mechanically fixed connection to one another. The connecting webs are preferably designed to be electrically insulating. The first and second marking parts as well as the connecting webs can be arranged in the form of a rectangular frame. As a result, the reference distance between the two marking parts in the circumferential direction can be guaranteed in a particularly reliable manner. Thus, the corresponding frame with the first and second marking part and the connecting webs can be embedded in the base material in order to then vulcanize the base material, for example. The reference distance can be maintained by the connecting webs. The reference distance between the first and second marking parts when the belt is in the unloaded state can therefore be ensured in a particularly reliable manner. The connecting webs can be designed to be electrically insulating or electrically conductive. Even with an electrically conductive design of the connecting webs, it was found in practice that each of the two marking parts causes a recognizable, associated change in the reference magnetic field, which leads to the first and second alternating reaction field. It is therefore also possible for the first and second marking part and the two connecting webs to be designed as a connected and/or one-piece frame.

A further advantageous embodiment of the device is characterized in that the evaluation unit is configured to determine a remaining service life of the belt based on a history of determined longitudinal elongations of the belt compared to predetermined limit values. The evaluation unit can be designed in this way, chronologically behind to determine several longitudinal strains. The determination can take place at fixed intervals. However, it is also possible for the determination to be triggered by the detection of the second alternating reaction field. The detected longitudinal expansions can be stored by the evaluation unit. Based on these determined longitudinal strains, the evaluation unit can therefore be configured to determine the remaining service life of the belt. A correspondingly determined remaining service life can be used to plan the maintenance intervals and/or the replacement of the belt in advance.

1. a) Kalibrierung der Sensoren in der Übertragungsvorrichtung auf einen Abstand in Umfangsrichtung des Riemens, wobei die Sensoren in dem Abstand im unbelasteten Zustand des Riemens deckungsgleich mit dem Referenzabstand des ersten ferromagnetischen Markierungsteils und des zweiten ferromagnetischen Markierungsteil angeordnet werden. Mit anderen Worten gesagt können die Sensoren in ihrem Abstand zueinander in Umfangsrichtung des Riemens verstellt werden, sodass im kalibrierten Zustand der Abstand der Sensoren dem Referenzabstand der ferromagnetischen Markierungen im unbelasteten Zustand entspricht. Der Kalibrierungsvorgang kann sowohl bei stillstehendem Riementrieb als auch während des Betriebes erfolgen, solange keine Leistung durch den Riemen übertragen wird.
2. b) Detektion einer ersten Erfassungszeit des ersten Sensors zum Zeitpunkt einer maximalen Veränderung des Referenzwechselfelds durch das erste Reaktionswechselfeld des ersten Markierungsteils. Mit anderen Worten gesagt erfasst der erste Sensor zu dem Zeitpunkt des Durchgangs des ersten Markierungsteils ein verändertes Reaktionswechselfeld, welches als erste Erfassungszeit des ersten Sensors definiert ist.
3. c) Detektion einer ersten Erfassungszeit des zweiten Sensors zum Zeitpunkt einer maximalen Veränderung des Referenzwechselfelds durch das erste Reaktionswechselfeld des ersten Markierungsteils. Mit anderen Worten gesagt erfasst der zweite Sensor zu dem Zeitpunkt des Durchgangs des ersten Markierungsteils ein verändertes Reaktionswechselfeld, welches als erste Erfassungszeit des zweiten Sensors definiert ist.
4. d) Detektion einer zweiten Erfassungszeit des ersten Sensors zum Zeitpunkt einer maximalen Veränderung des Referenzwechselfelds durch das zweite Reaktionswechselfeld des zweiten Markierungsteils. Mit anderen Worten gesagt erfasst der erste Sensor zu dem Zeitpunkt des Durchgangs des zweiten Markierungsteils ein verändertes Reaktionswechselfeld, welches als zweite Erfassungszeit des ersten Sensors definiert ist.
5. e) Detektion einer zweiten Erfassungszeit des zweiten Sensors zum Zeitpunkt einer maximalen Veränderung des Referenzwechselfelds durch das zweite Reaktionswechselfeld des zweiten Markierungsteils. Mit anderen Worten gesagt erfasst der zweite Sensor zu dem Zeitpunkt des Durchgangs des zweiten Markierungsteils ein verändertes Reaktionswechselfeld, welches als zweite Erfassungszeit des zweiten Sensors definiert ist.
6. f) Ermittlung der Riemengeschwindigkeit des Riemens in Umfangsrichtung basierend auf einer Laufzeit des ersten oder zweiten Reaktionswechselfelds über den Abstand der Sensoren. Mit anderen Worten gesagt wird durch Messung der Laufzeit eines der beiden Markierungsteile über die bekannte Strecke zwischen dem ersten Sensor und dem zweiten Sensor die Geschwindigkeit des Riemens ermittelt.
7. g) Ermittlung einer Längsdehnung des Riemens durch Erfassung der Abweichung des Messabstandes vom Referenzabstand aus einer ermittelten Laufzeitveränderung des zweiten gegenüber des ersten Reaktionswechselfeldes über den Abstand der Sensoren. Mit anderen Worten gesagt wird eine Längung des Riemens über einen historischen Abgleich der Laufzeit zwischen dem zweiten Markierungselement und dem ersten Markierungselement an einem der Sensoren ermittelt.
8. h) Ermittlung der Betriebskraft des Riemens unter Verwendung der Längssteifigkeit und der ermittelten Längsdehnung des Riemens. Mit anderen Worten gesagt kann durch Kenntnis der Längssteifigkeit des Riemens mit Multiplikation der ermittelten relativen Längsdehnung die Zugkraft im Riementrum ermittelt werden.

A method for determining a longitudinal elongation of a belt is also provided. The belt has a predetermined longitudinal rigidity, a drive device, a transmission device and an evaluation unit. The drive device has a plurality of pulleys. The evaluation unit can be combined with the transmission device. The belt has a base material, a reinforcement, a first ferromagnetic marking part and a second ferromagnetic marking part. The base material can be formed, for example, at least partially from rubber material or polyurethane material. Preferably, the base material is rubber material. The belt runs in a ring shape in a circumferential direction of the belt. In addition, the belt wraps around the pulleys at least partially. The belt is driven in the circumferential direction by the driving direction. The reinforcement of the belt is designed as a continuous cord wound helically in the circumferential direction and embedded in the base material of the belt. The first marker part and the second marker part are each embedded in the base material and/or attached to the base material. The transmission device generates a first and a second electromagnetic alternating field, each of which is referred to as a reference alternating field. The first ferromagnetic marking part changes the alternating reference fields into a first alternating reaction field when the alternating reference field acts on the first ferromagnetic marking part. The second ferromagnetic marking part changes the alternating reference field into a second alternating reaction field when the alternating reference field acts on the second ferromagnetic marking part. The second marker part is arranged circumferentially behind the first marker part by a predetermined reference distance in a no-load state of the belt. The transmission device is arranged without contact with the belt in such a way that the first marking part and the second marking part are guided one after the other past the transmission device by means of the belt and through the alternating reference field, which results in the alternating reference field acting on the first marking part and the second marking part in succession . The transmission device also detects a first alternating reaction field and an associated first detection time formed when the first marking part is moved past the transmission device. In addition, the transmission device detects a second alternating reaction field and an associated second detection time when the second marking part is moved past the transmission device. The device determines a belt speed of the belt in the circumferential direction based on the first alternating reaction field or the second alternating reaction field. The evaluation unit determines an elongation of the belt based on the reference distance, the belt speed, the first detection time and the second detection time. The process is characterized by the following process steps:

1. a) Calibration of the sensors in the transmission device at a distance in the circumferential direction of the belt, the sensors being arranged at the distance in the unloaded state of the belt congruent with the reference distance of the first ferromagnetic marking part and the second ferromagnetic marking part. In other words, the distance between the sensors can be adjusted in the circumferential direction of the belt, so that in the calibrated state the distance between the sensors corresponds to the reference distance of the ferromagnetic markings in the unloaded state. The calibration process can be carried out both when the belt drive is at a standstill and during operation, as long as no power is being transmitted through the belt.
2. b) Detection of a first detection time of the first sensor at the time of a maximum change in the reference alternating field by the first alternating reaction field of the first marking part. In other words, at the point in time at which the first marking part passes through, the first sensor detects a changed alternating reaction field, which is defined as the first detection time of the first sensor.
3. c) Detection of a first detection time of the second sensor at the time of a maximum change in the reference alternating field by the first alternating reaction field of the first marking part. In other words, at the point in time at which the first marking part passes through, the second sensor detects a changed alternating reaction field, which is defined as the first detection time of the second sensor.
4. d) Detection of a second detection time of the first sensor at the time of a maximum change in the reference alternating field by the second alternating reaction field of the second marking part. In other words, at the point in time at which the second marking part passes through, the first sensor detects a changed alternating reaction field, which is defined as the second detection time of the first sensor.
5. e) Detection of a second detection time of the second sensor at the time of a maximum change in the reference alternating field by the second alternating reaction field of the second marking part. In other words, at the point in time at which the second marking part passes through, the second sensor detects a changed alternating reaction field, which is defined as the second detection time of the second sensor.
6. f) determining the belt speed of the belt in the circumferential direction based on a running time of the first or second alternating reaction field over the distance between the sensors. In other words, the speed of the belt is determined by measuring the running time of one of the two marking parts over the known distance between the first sensor and the second sensor.
7. g) Determination of a longitudinal elongation of the belt by detecting the deviation of the measurement distance from the reference distance from a determined runtime change of the second versus the first alternating reaction field over the distance of the sensors. In other words, an elongation of the belt is determined via a historical comparison of the running time between the second marking element and the first marking element on one of the sensors.
8. h) Determination of the operating force of the belt using the longitudinal stiffness and the determined longitudinal elongation of the belt. In other words, by knowing the longitudinal stiffness of the belt by multiplying the determined relative longitudinal expansion, the tensile force in the belt strand can be determined.

It has proven to be particularly advantageous that the method according to the invention enables the longitudinal elongation of the belt to be measured as a representative of the force with a high degree of measurement accuracy and a redundant recording of measured values.

• 1 zeigt eine vorteilhafte Ausgestaltung der Vorrichtung in einer schematischen Ansicht.
• 2 zeigt eine beispielhafte Ausgestaltung eines zeitlichen Verlaufs einer mittleren Feldstärke zu den Zeitpunkten T1A, T2A, T1 B und T2B.

Further features, advantages and possible applications of the present invention result from the following description of the exemplary embodiments and the figures. All features described and/or illustrated form the subject matter of the invention on their own and in any combination, also independently of their composition in the individual claims or their back-references. In the figures, the same reference symbols continue to stand for the same or similar objects.

• 1 shows an advantageous embodiment of the device in a schematic view.
• 2 FIG. 12 shows an exemplary embodiment of an average field strength over time at times T1A, T2A, T1B and T2B.

In the 1 an advantageous embodiment of the device 2 is shown schematically. The device 2 has a belt 4 and a drive device 6 with two pulleys 8, 10, for example. One of the two pulleys 8, 10 can be coupled as a driving pulley to a motor of the drive device. The belt 4 is annular in the circumferential direction U and loops around each of the two pulleys 8, 10 partially. The belt 4 can therefore be driven by the drive device 6 with the two pulleys 8, 10, so that the belt 4 rotates in the circumferential direction U.

The belt 4 has a base material and at least one reinforcement. Purely by way of example, it is assumed below that the belt 4 has a reinforcement. The base material can be formed, for example, partially or fully from rubber material or partially or fully from polyurethane material. However, other materials for the base material can also be provided. The base material 16 is preferably designed to be electrically insulating. The reinforcement is embedded in the base material as a continuous cord wound helically in the circumferential direction U. The reinforcement serves to transmit forces in the circumferential direction U of the belt 4. The reinforcement can be formed, for example, from a metallic wire or from a plastic filament strand, such as a plastic fiber strand made of polyamide. The individual windings of the cord forming the reinforcement in the transverse direction of the belt 4 can be distributed relative to one another. Each of the windings extends in the circumferential direction U.

The belt 4 also has a first ferromagnetic marking part 20 and a second ferromagnetic marking part 22 . The first ferromagnetic marking part 20 is also referred to as the first marking part 20 for short. The second ferromagnetic marking part 22 is also referred to as the second marking part 22 for short. The first marking part 20 and the second marking part 22 are embedded in the base material of the belt 4, respectively. The two marking parts 20, 22 can be embedded in the base material above the reinforcement. In principle, however, it is also possible for the two marking parts 20, 22 to be embedded in the base material below the reinforcement. In addition, there is the possibility that the two marking parts 20 , 22 are arranged on an outside 44 of the belt 4 . The outside 44 can be the so-called back of the belt 4, for example.

Each of the two ferromagnetic marking parts 20, 22 can be formed entirely or at least partially from ferromagnetic material and/or substance. For example, iron, nickel or cobalt are substances with ferromagnetic properties. In practice, however, alloys with ferromagnetic properties are often used. Corresponding alloys can be, for example, ALNiCo, SmCo or NiFeCo alloys. Each of the two marking parts 20, 22 can therefore be, for example, a ferromagnetic metal marking part or a ferromagnetic alloy metal marking part.

In an unloaded state of the belt 4, ie when no tensile force acts on the belt 4 in the circumferential direction, the second marking part 22 is arranged at a predetermined reference distance R in the circumferential direction U behind the first marking part 20. This is preferably the average distance between the two marking parts 20, 22 in the unloaded state of the belt 4.

It is preferably provided that each of the two marking parts 20, 22 is designed as a rod-shaped marking part 20, 22. Each of the two marking parts 20, 22 can thus extend in the transverse direction from a first side wall of the belt 4 to an opposite side wall of the belt 4. However, it is preferably provided that each of the two marking parts 20, 22 is shorter than the distance in the transverse direction between the two side walls. This ensures that each of the two marking parts 20, 22 is completely embedded in the base material of the belt 4.

In addition, it is preferably provided that the second marking part 22 is arranged parallel to the first marking part 20 . As a result, a constant reference distance R between the two marking parts 20, 22 can be guaranteed. However, the reference distance R between the two marking parts 20, 22 is preferably present only in the unloaded state of the belt. When the belt 4 is in operation, tensile forces act on the belt 4 in the circumferential direction U, which causes the belt 4 to stretch in the circumferential direction U. As a result, the distance between the first marking part 20 and the second marking part 22 increases to a measurement distance M, which is greater than the reference distance R. The quotient of the measurement distance M and the reference distance R is representative of the longitudinal elongation of the belt. This is because the longitudinal stretching of the belt is a relative stretching of the belt 4. The longitudinal stretching of the belt is preferably determined by the ratio of the measuring distance M to the reference distance R. In particular, if the first and second marking parts 20, 22 are embedded in the base material of the belt 4, the two marking parts 20, 22 can only be detected indirectly.

The device shown in 1 , therefore has two sensors, sensor A 12 and sensor B 13, and an evaluation unit 14. Sensor A 12, sensor B 13 and the evaluation unit 14 can be combined and/or assigned to a common device 50. The device 50 can thus have and/or form sensor A 12 and sensor B as well as the evaluation unit 14 .

Sensor A 12 and sensor B 13 are spaced a predetermined distance A from the belt 4 . For example, sensor A 12 and sensor B 13 can be arranged at a distance A between 1 mm and 50 cm from a tight strand 52 of belt 4 . In this case, sensor A 12 and sensor B can face the back or the outside 44 of the belt 4 . The aforementioned, predetermined distance A ensures in a particularly simple manner that sensor A 12 and sensor B 13 are arranged without contact on strand 32, in particular tension strand 52, of belt 4.

Furthermore, sensor A 12 and sensor B 13 are arranged at an adjustable distance S apart from one another. The adjustment of the distance S enables the device 2 to be calibrated by setting the distance S to the reference distance R between the first and second marking parts 20,22. Calibration has taken place as soon as sensor A 12 senses the second acquisition time T2A, while transmitter B 13 simultaneously senses the first acquisition time T1B. By locking sensor A 12 and/or sensor B 13, the distance S is unchangeable and represents the reference distance R as the basis for calculating the strain during the dynamic change of the distance M of the first and second marking parts 20, 22. The calibration can be carried out both when the belt 4 is stationary and when it is dynamically operated, as long as no power is transmitted through the belt. Sensor A 12 and sensor B 13 are configured to generate a first and second alternating electromagnetic field, referred to as the alternating reference field 26 . The alternating reference field 26 is in 1 indicated schematically by magnetic field lines. The alternating reference field 26 penetrates the belt 4 . The belt 4 is driven by the drive device 6 . This ensures that the first marking part 20 and the second marking part 22 are moved one after the other in the circumferential direction U through the alternating reference field 26 .

The first ferromagnetic marking part 20 is designed to change the alternating reference field 26 into the first alternating reaction field when the alternating reference field 26 acts on the first ferromagnetic marking part 20, or vice versa. The interaction between the alternating reference field 26 and the first marking part 20 results from the alternating reference field 26 in the first alternating reaction field. This shows a change compared to the original alternating reference field 26 . The same applies to the second ferromagnetic marking part 22, which is designed to change the alternating reference field 26 into the second alternating reaction field when the alternating reference field 26 acts on the second ferromagnetic marking part 22, or vice versa.

As previously explained, the first marking part 20 and the second marking part 22 are guided past sensor A 12 and sensor B 13 in succession, so that first the first marking part 20 causes the first alternating reaction field through interaction with the alternating reference field 26 . Sensor A 12 is designed to detect the first alternating reaction field and an associated first detection time T1A when the first marking part 20 is guided past sensor A 12 . This also applies to sensor B 13 and the associated signal of the first detection time T1B. The second marking part 22 is formed by the interaction with the reference alternating field 26 to form the second alternating reaction field when the second marking part 22 is moved past sensor A 12 or sensor B 13 . Sensor A 12 is designed to detect an associated second detection time T2A. This also applies to sensor B 13 and the associated signal of the second detection time T2B. In the 2 the average field strength H of the alternating field in the area between the belt 4, sensor A 12 and sensor B 13 is shown schematically as an example. If a belt area without one of the two marking parts is moved through the alternating reference field 26, there is at least essentially no change in the average field strength H. If, on the other hand, the first marking part 20 is guided through the alternating reference field 26 with the belt 4, the mean field strength H in the region 28 changes, which is referred to as the first change in the field strength H, which is representative of the first detection time T1A at sensor A. After the first marking part 20 has passed sensor A 12, the average field strength H at least essentially resumes the previous value, while the first marking part 20 reaches sensor B 13 and is guided through its alternating reference field 26 again, which leads to a further change of field strength H in area 29, which is representative of the first acquisition time T1B at sensor B.

$$T1B-T1A=T2B-T2A$$

The second ferromagnetic marking part 22 is designed to change the alternating reference field 26 into the second alternating reaction field when the alternating reference field 26 acts on the second marking part 22, or vice versa. The interaction between the alternating reference field 26 and the second marking part 22 results from the alternating reference field 26 in the second alternating reaction field. This shows a change compared to the alternating reference field 26 . A corresponding change in area 30 in the 2 therefore also shows the corresponding change in mean field strength H, which is representative of the second detection time T2A at sensor A. This is caused by the movement of the second marking part 22 through the alternating reference field 26 . After the second marking part 22 has passed sensor A 12, the mean field strength H at least essentially resumes the previous value, while the second marking part 22 reaches sensor B 13 and is again passed through its alternating reference field 26, which leads to a further change of the field strength H in the region 31, which is representative of the second acquisition time T2B at sensor B. The belt 4 is driven by the drive device 6 at a belt speed in the circumferential direction U. With a constant belt speed of belt 4 assumed as an example, the time interval between the second detection time at sensor A T2A and the first detection time at sensor A T1A or the second detection time at sensor B T2B and the first detection time at sensor B T1B increases if the tensile forces acting on the belt 4 in the circumferential direction U increase. This is because the measuring distance M between the second marking part 22 and the first marking part 20 is increased by the increase in the tensile forces. Corresponding to the increased measurement distance M, the time interval between the second acquisition time at sensor B T2B and second acquisition time at sensor A T2A or first acquisition time at sensor B T1B and first acquisition time at sensor A T1A. The use of two sensors results in a redundant time measurement according to the following formulas: $$T2A-T1A=T2B-T1B$$

$$T1B-T1A=T2B-T2A$$

The device 2 is also configured to determine the belt speed of the belt 4 in the circumferential direction U based on the first alternating reaction field or the second alternating reaction field. For this purpose, sensor A 12 and sensor B 13 can be designed as a magnetoresistive sensor or have one. Thus, sensor A 12 and sensor B 13 of the device 2 are designed to determine the belt speed of the belt 4 in the circumferential direction U based on the first alternating reaction field or the second alternating reaction field. The speed is calculated according to the following formula stored in the evaluation unit 14 . The calculation is listed as an example based on the signal determination at sensor A 12. The redundant measurement described above using the second marking part 22 in conjunction with sensor A 12 and sensor B 13 also applies here. $$v=\frac{S}{T1B-T1A}$$

Sensor A 12 and sensor B 13 are coupled to the evaluation unit 14, in particular via a signal line. As a result, the measured variables recorded by sensor A 12 and sensor B 13 are available to the evaluation unit. The evaluation unit 14 is configured to determine a longitudinal elongation of the belt 4 based on the reference distance R, the belt speed, the second detection time T2A at sensor A 12 and the first detection time T1A at sensor A 12 or the second detection time T2B at sensor B 13 and the first To determine detection time T1 B at sensor B 13. The following formula can be stored in the evaluation unit 14 for this purpose. The evaluation unit 14 can be designed to evaluate the formula. The redundant measurement at sensor B 13 described above also applies here. $$L\ddot{a}nGs\mathrm{i.e}eHn\mathrm{and}nG=\frac{RiemenGescHwin\mathrm{i.e}iGkeit\ast \left(T2A-T1A\right)}{R}-1$$

Furthermore, using the longitudinal stiffness of the belt, the operating force of the belt can be determined. The longitudinal stiffness of the belt can be stored in the evaluation unit as a material constant. The longitudinal stiffness can be determined individually for each belt specification and dimension, for example by means of a tensile test, in which an elongation is assigned to the applied force.

The determined longitudinal stiffness of the belt can be multiplied by the relative elongation of the belt according to the following formula to determine the operating force of the belt: $$f=L\ddot{a}nGssteifiGkeit\ast L\ddot{a}nGs\mathrm{i.e}eHn\mathrm{and}nG=EA\ast e$$

As is exemplified from the 1 can be seen, it is preferably provided that sensor A 12 and sensor B 13 face the tightening strand 52 . In addition, it is preferably provided that the reference distance R between the second marking part 22 and the first marking part 20 is smaller than the strand length B of the tension strand 52. It is preferably provided that the reference distance R is a maximum of 70% or a maximum of 50% of the strand length W of the tightening strand 52.

Additionally, it should be noted that "comprising" does not exclude other elements or steps, and "a" or "an" does not exclude a plurality. Furthermore, it should be pointed out that features that have been described with reference to one of the above exemplary embodiments can also be used in combination with other features of other exemplary embodiments described above. Any reference signs in the claims should not be construed as limiting.

Reference List

A

Distance

H

mean field strength

M

measuring distance

R

reference distance

S

Distance of sensor A and sensor B

T1A

first detection time at sensor A

T1B

first acquisition time at sensor B

T2A

second acquisition time at sensor A

T2B

second acquisition time at sensor B

u

circumferential direction

W

span length

2

contraption

4

belt

6

drive device

8th

pulley

10

pulley

12

Sensor A

13

Sensor B

14

evaluation unit

20

first marking part

22

second marking part

26

Alternating reference field indicates the first change in field strength

28

Sensor A shows the first change in field strength

29

Sensor B shows a second change in field strength

30

Sensor A second change in field strength

31

Sensor B

32

drum

44

outside

50

sensor evaluation unit

52

tightening strand

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• DE 102018215478 A1 [0005]

Claims (14)

Device for determining a longitudinal elongation of a belt (4), comprising: a belt (4) with a predetermined longitudinal stiffness, a drive device (6) with a plurality of belt pulleys (8, 10), a transmission device, and an evaluation unit (14), the belt ( 4) has a base material, a reinforcement, a first ferromagnetic marking part (20) and a second ferromagnetic marking part (22), wherein the belt (4) is designed to run annularly in a circumferential direction (U), the belt (4) having the pulleys (8, 10) at least partially wraps around and can be driven by the drive device (6) in the circumferential direction (U), the transmission device being designed to generate a first alternating electromagnetic field which is referred to as the alternating reference field (26), the first ferromagnetic marking part ( 20) is designed to change the alternating reference field (26) into a first alternating reaction field if the alternating reference field (26) acts on the first ferromagnetic marking part (20), the second ferromagnetic marking part (22) being designed to change the alternating reference field (26) into a second alternating reaction field when the alternating reference field (26) acts on the second ferromagnetic marking part (22) acts, the second marking part (22) being arranged at a predetermined reference distance (R) in an unloaded state of the belt (4) in the circumferential direction (U) behind the first marking part (20), the reference distance (R) changing in the loaded state of the belt (4) is changed to a measuring distance (M), the transmission device being arranged without contact with the belt (4) in such a way that the first and second marking parts (20, 22) can be guided past the transmission device one after the other by means of the belt (4). and can be passed through the alternating reference field (26), resulting in the alternating reference field (26) acting in succession r results in the first and second marking part (20, 22), the transmission device being designed to detect the first alternating reaction field and an associated first detection time (T1) when the first marking part (20) is guided past the transmission device, the transmission device for Detection of the second alternating reaction field and the associated second detection time (T2) is formed when the second marking part (22) is guided past the transmission device, the device (2) is configured, a belt speed of the belt (2) in the circumferential direction (U) based on to determine the first and the second alternating reaction field, and wherein the evaluation unit (14) is configured to determine a longitudinal elongation of the belt (2) based on the reference distance (R), the belt speed, the first detection time (T1) and the second detection time (T2 ) to determine, characterized in that the transmission Vo The device has at least two sensors (12, 13) in connection with an evaluation unit (14), the sensors (12, 13) being part of a calibration device and being adjustable relative to one another at a distance (S) in the circumferential direction (U) of the belt (2). are arranged in the transmission device and in the unloaded state of the belt (2) are arranged congruently with the reference distance (R) of the first ferromagnetic marking part (20) and the second ferromagnetic marking part (22), each of the sensors (12, 13) for generating of the alternating reference field (26), a first detection time (T1A) being detectable by the first sensor (12) at the time of a maximum change in the alternating reference field (26) by the first alternating reaction field of the first marking part (20), the second sensor (13) at the time of a maximum change in the reference alternating field (26) by the first alternating reaction field of the first marker a first detection time (T1 B) can be detected by the first sensor (12) at the time of a maximum change in the reference alternating field (26) due to the second alternating reaction field of the second marking part (22). , wherein a second detection time (T2B) can be detected by the second sensor (13) at the time of a maximum change in the reference alternating field (26) by the second alternating reaction field of the second marking part (22), the device (2) being configured to detect a belt speed of the To determine the belt (2) in the circumferential direction (U) based on a running time of the first or second alternating reaction field via the distance (S) of the sensors (12, 13), the device (2) being configured to determine a longitudinal stretching of the belt (4) by the deviation of the measurement distance (M) from the reference distance (R) from a determined change in the transit time of the second compared to the first reaction change to determine elfeldes, wherein the device (2) is configured, using the longitudinal stiffness and determined Longitudinal stretching of the belt (4) to determine the operating force of the belt. Device (2) after claim 1 , characterized in that the sensors (12,13) are aligned without contact on a strand (32) of the belt (4). Device (2) according to the preceding claim, characterized in that the sensors (12, 13) are arranged at a distance (A) of between 1 mm and 50 cm from the strand (32) of the belt (4). Device (2) according to one of the preceding claims, characterized in that the sensors (12, 13) are in the form of inductive or capacitive sensors. Device (2) according to one of Claims 1 until 3 , characterized in that the sensors (12,13) are designed as eddy current sensors. Device (2) according to one of the preceding claims, characterized in that the reference distance (R) is smaller than the smallest strand length (W) of the belt (4). Device (2) according to one of the preceding claims, characterized in that the reference distance (R) is at most 90% of the span length (W). Device (2) according to one of the preceding claims, characterized in that each marking part (20, 22) is passive. Device (2) according to one of the preceding claims, characterized in that each marking part (20, 22) is designed as a rod-shaped and/or foil-shaped marking part (20, 22), with each marking part (20, 22) having its greatest extent extends transversely to the circumferential direction (U). Device (2) according to one of the preceding claims, characterized in that each marking part (20, 22) is prefabricated or is designed as a printed marking part (20, 22). Device (2) according to one of the preceding claims, characterized in that each marking part (20, 22) is constructed in one piece. Device (2) according to one of the preceding claims , characterized in that the first and second marking part (20, 22) are designed to be connected to one another at least indirectly. Device (2) according to one of the preceding claims, characterized in that the evaluation unit (14) is configured to determine a remaining service life of the belt (4) based on a history of determined longitudinal elongations of the belt (4) compared to predetermined limit values. Method for determining a longitudinal elongation of a belt (4), comprising: a belt (4) with a predetermined longitudinal stiffness, a drive device (6) with a plurality of belt pulleys (8, 10), a transmission device, and an evaluation unit (14), the belt ( 4) has a base material, a reinforcement, a first ferromagnetic marking part (20) and a second ferromagnetic marking part (22), the belt (4) running around in a ring shape in a circumferential direction (U), the belt (4) having the belt pulleys (8 , 10) at least partially wraps around and is driven by the drive device (6) in the circumferential direction (U), the transmission device generating a first and a second electromagnetic alternating field, each of which is referred to as a reference alternating field (26), the first ferromagnetic marking part (20 ) The alternating reference fields (26) changed into a first alternating reaction field when the alternating reference field (26) on the first e acts on the ferromagnetic marking part (20), the second ferromagnetic marking part (22) changing the alternating reference fields (26) into a second alternating reaction field when the alternating reference field (26) acts on the second ferromagnetic marking part (22), the second marking part (22) is arranged at a predetermined reference distance (R) in an unloaded state of the belt (4) behind the first marking part (20) in the circumferential direction (U), the reference distance (R) in the loaded state of the belt (4) being reduced to a measuring distance (M ) is changed, the transmission device being arranged without contact with the belt (4) in such a way that the first and second marking parts (20, 22) are guided past the transmission device one after the other by means of the belt (4) and are guided through the alternating reference field (26). What in an action of the reference alternating field (26) successively on the first and second marking part (20, 22) resu lted, wherein the transmission device detects a first alternating reaction field and an associated first detection time (T1A, T1B) when the first marking part (20) is moved past the transmission device, wherein the transmission device detects a second alternating reaction field and an associated second detection time (T2A, T2B) when the second marking part (22) is guided past the transmission device, with the device (2) determining a belt speed of the belt (2) in the circumferential direction (U) based on the first or the second alternating reaction field, and with the evaluation unit (14) measuring a longitudinal expansion of the belt (2) based on the reference distance (R), the belt speed, the first detection time (T1A, T1B) and the second detection time (T2A, T2B), characterized by the following method steps: a) Calibration of the sensors (12,13) in the transmission device to a distance (S) in the circumferential direction (U) of the belt s (2), the sensors (12,13) being arranged at the distance (S) in the unloaded state of the belt (2) congruently with the reference distance (R) of the first ferromagnetic marking part (20) and the second ferromagnetic marking part (22). b) detection of a first detection time (T1A) of the first sensor (12) at the time of a maximum change in the reference alternating field (26) by the first alternating reaction field of the first marking part (20) c) detection of a first detection time (T1 B) of the second sensor ( 13) at the time of a maximum change in the reference alternating field (26) by the first alternating reaction field of the first marking part (20) d) detection of a second detection time (T2A) of the first sensor (12) at the time of a maximum change in the reference alternating field (26) by the second alternating reaction field of the second marking part (22) e) detection of a second detection time (T2B) of the second sensor (13) at the time of a max Immal change in the reference alternating field (26) by the second alternating reaction field of the second marking part (22) f) Determination of the belt speed of the belt (2) in the circumferential direction (U) based on a running time of the first or second alternating reaction field over the distance (S) of the sensors ( 12, 13) g) Determination of a longitudinal elongation of the belt (4) by detecting the deviation of the measuring distance (M) from the reference distance (R) from a determined change in the transit time of the second versus the first alternating reaction field over the distance (S) of the sensors (12, 13 ) h) Determination of the operating force of the belt using the longitudinal stiffness and the determined longitudinal elongation of the belt (4)

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