Sensor and method for detecting vibrations of an object using a fiber Bragg grating

Abstract

The invention relates to a sensor for detecting vibrations of an object (12), comprising an optical waveguide (1) having a fiber Bragg grating (13), and comprising a sensor structure element (15) to which the optical waveguide (1) is fastened at two fastening points (10). The sensor structure element (15) comprises two holding sections (2) designed to fix the sensor structure element (15) to a surface of the object (12) in a vibration-damped, in particular vibration-decoupled, manner. The sensor structure element (15) comprises a detection section (3) designed to be in contact with the object (12) for coupling in vibrations. The invention further relates to a robot joint (12) having such a sensor, the holding sections (2) and the detection section (3) being fixed to a surface, in particular an outer contour, of the robot joint (12), in particular each via an adhesive connection.Furthermore, the invention relates to methods for detecting vibrations of an object.

Description

[0001] The invention relates to a sensor for detecting vibrations of an object using an optical waveguide that has a fiber Bragg grating. The invention further relates to a robot joint with such a sensor. Furthermore, the invention relates to a method for detecting vibrations of an object, wherein light is coupled into an optical waveguide that has a fiber Bragg grating, and light reflected by the fiber Bragg grating is detected and evaluated. Background of the invention

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[0003] Industrial robots are increasingly being used as a more efficient and safer alternative to manual tasks in various industrial applications, such as automated manufacturing and aerospace (see [1-4]. Robot joints, which serve to assist adjacent limbs in various movements, are important moving components of industrial robots. Since most industrial robots are typically used in production lines to increase work efficiency, a failure of a robot joint due to adverse working conditions, overloads, and unexpected events could lead to expensive unplanned downtime and significant economic losses (see [5]. Therefore, it is necessary to develop condition monitoring (CM) systems for robot joints.

[0004] In condition monitoring systems, the vibration signal is one of the typical signals that can reflect the fault characteristics of robot joints. It can be detected by various types of sensors, such as fiber optic sensors [6], piezoelectric accelerometers [7], and microelectromechanical systems (MEMS) [8]. Among the various available sensors, fiber Bragg grating (FBG) sensors, a type of fiber optic sensor, are more suitable for CM applications in robot joints. This is because FBG sensors are lightweight, small, flexible, embeddable, multiplexed, highly sensitive, corrosion-resistant, and easy to connect into a sensor network. In particular, FBG sensors have the advantage of being insensitive to electromagnetic interference [9-11].

[0005] To meet the sensitivity and operating frequency range requirements of vibration sensors in various engineering fields, an increasing number of FBG vibration sensors have been developed to measure acceleration caused by vibration. Based on the measurement principle and monitoring architecture, these FBG vibration sensors are mainly divided into three categories: FBG vibration sensors based on beam structure (FBGVSBS), FBG vibration sensors based on the transverse property of optical fiber (FBGVSTPOF), and FBG vibration sensors based on elastomer structure (FBGVSES)

[12] .

[0006] The FBG vibration sensor, based on a cantilever structure, is the most classic and popular sensor due to the simple structure and high stability of the cantilever beam. Two types of encapsulation methods, full encapsulation and two-point encapsulation, have a significant impact on the measurement performance of this type of FBG vibration sensor. Some research results based on the two encapsulation methods are presented below: In the fully encapsulated FBG vibration sensor, the Bragg wavelength changes with the axial strain of the bonded part when a mass block mounted on the cantilever beam vibrates; the Bragg wavelength shift can then be converted into acceleration information through the principle of wavelength modulation. Liu et al.

[13] presented a new sensor based on dual cantilever beams and a short FBG. Tiwari et al.

[14] designed a highly sensitive sensor based on a curved cantilever beam to measure low-frequency vibrations. To simultaneously measure strain, vibration, and temperature, Yao et al.

[15] proposed a multiparameter sensor based on two FBGs and a trapezoidal beam. Udos et al.

[16] hybridized the magnetic damper with the cantilever beam for resonance suppression to extend the operating frequency band of the FBG vibration sensor. Xiong et al.

[17] combined a crossbeam type elastomer with five FBGs for triaxial vibration measurements.

[0007] In a two-point encapsulation FBG vibration sensor, the optical fiber is subjected to the axial inertial force when the sensor is affected by the vibration, resulting in axial tension or compression of the FBG. With the two-point encapsulation, the chirp effect of the FBG can be effectively avoided. Ramos and Romero

[18] fixed an FBG between the frame and the cantilever beam. Parida et al.

[19] improved the measurement performance of the FBG vibration sensor by replacing the T-shaped beam with double L-shaped beams and fixing two FBGs between the substrate and the double L-shaped beams. A Y-beam-based FBG vibration sensor, in which an FBG was fixed between two mass blocks, was proposed by Luo et al.

[20] . Zhao et al.

[21] reported a temperature-compensated FBG vibration sensor in which two FBGs are mounted on a mass block connected to a composite beam.Jia et al.

[22] developed a two-dimensional vibration sensor using two FBGs mounted on a sensor system. For measuring low-frequency vibrations, Fan et al.

[23] proposed an FBG vibration sensor based on a diaphragm-like cantilever, and Li et al.

[24] presented a highly sensitive FBG vibration sensor using a cantilever connected to two FBGs, a bearing, and two springs.

[0008] Considering the sensitivity of the stretched FBG to the transverse force, some researchers have developed a series of FBG vibration sensors based on the transverse property of the optical fiber for low-frequency vibrations (i.e., below 150 Hz) and low- and medium-frequency vibrations (i.e., from 150 Hz to 500 Hz). For the measurement of low-frequency vibrations, Ni et al.

[25] used an FBG with a biconical taper as the sensing element and utilized a power detection method to convert the acceleration into the change in the power of the light reflected from the FBG. Zhang et al.

[26] designed a microfiber-based FBG sensor by applying a special chemical etching process to integrate a microbeam and the mass block into an optical fiber. Li et al.

[27] used the optical fiber as an elastomer to fix the mass block directly in the center of two FBGs.For measuring vibrations at low and medium frequencies, Li et al.

[28] proposed a membrane-type FBG vibration sensor by arranging two optical fibers on either side of a membrane and connecting their centers to the mass block. Furthermore, Li et al. [29, 30] exploited the transverse property of a fixedly suspended optical fiber and developed two different types of FBG vibration sensors for one- and two-dimensional vibration measurement, respectively.

[0009] FBG vibration sensors based on a beam structure and the transverse property of the optical fiber cannot be used for measuring mid- and high-frequency vibrations due to their low resonance frequencies. To overcome this problem, the FBG vibration sensor based on an elastomer structure was developed by using a special elastomer to increase the resonance frequency of the sensor. However, the measurement performance of this type of FBG vibration sensor is significantly affected by the material and structure of the elastomer. Li et al.

[0010]

[25] proposed an FBG vibration sensor based on an elastic diaphragm structure that can restrict the movement of the mass block in non-vibration directions. An FBG vibration sensor based on an elastic tube structure, in which a steel tube is fixed on the mass block and a threaded tube, was designed by Wang et al.

[26] . Gutiérrez et al.

[27] reported an FBG vibration sensor based on an elastic shell structure using a hollow cylinder with a hexagonal lattice as the elastomer. Liu et al.

[28] presented an FBG vibration sensor based on an elastic cylinder structure, in which the FBG is embedded in an inertial cylinder mass sandwiched between two diaphragms. Xu et al.

[29] presented an FBG vibration sensor based on a pendulum structure for simultaneous measurement of inclination and acceleration. For two-dimensional vibration measurement, Song et al.

[30] proposed an FBG vibration sensor based on an orthogonal bending hinge structure.

[0011] The aforementioned FBG vibration sensors are designed for measuring and amplifying acceleration signals induced by vibrations. Their basic information is listed in Table 1. The maximum sensitivity is 2430 pm / g, the maximum operating frequency is 1200 Hz, and the maximum resonant frequency is 3806 Hz. These FBG vibration sensors are highly sensitive to vibrations, while their operating frequency bands and resonant frequencies are relatively low, so they cannot be used to measure high-frequency vibrations. Most FBG vibration sensors cannot ensure a high resonant frequency and a wide operating frequency band while maintaining high sensitivity. This is mainly due to limitations in the measurement principle and material properties.

[0012] Since the working principle of the FBG sensor is based on the shift of the Bragg wavelength due to strain and temperature changes, some researchers have bonded FBG sensors directly to the measuring object to monitor dynamic strain changes caused by vibrations (so-called "bare" sensors). Khmelnitsky et al.

[37] experimentally investigated the feasibility of using FBG sensors for bearing failure prediction. Using two FBG sensors in the stator, Sousa et al.

[38] measured the strain change caused by the dynamic eccentricity of an induction motor. With the aim of using strain measurement based on FBG sensors to detect bearing faults and estimate the extent of damage, Alian et al.

[39] tested two sensor installation methods, each aimed at reducing or eliminating the influence of the distance between the sensors and the outer ring.to analyze the feasibility of installing the sensors without modifying the bearing housing. Medvedovsky et al.

[40] mounted a bare FBG sensor on the side of the bearing housing to detect faulty bearings by strain measurement.

[0013] For the fault diagnosis of gear drives, Bachar et al.

[41] proposed a new diagnostic method by bonding a bare FBG sensor as close as possible to the gear. Furthermore, FBG sensors alone are also used for vibration measurement in various areas besides rotating machinery by detecting dynamic strain changes [42-45].

[0014] The bare FBG sensor offers the possibility of measuring vibration in robot joints. However, the dynamic strain changes induced by vibrations are typically so weak that it is difficult to extract useful vibration information from weak strain signals, resulting in low fault diagnosis accuracy. Disclosure of the invention

[0015] As explained above, the majority of known sensors for detecting vibrations are based on the principle of inducing a displacement of a test mass, which leads to a shift in the Bragg wavelength. Due to the test mass, these sensors have a low resonance frequency, so high-frequency vibrations cannot be detected (see Table 1). Furthermore, due to the test mass, such sensors are generally unsuitable for monitoring objects where space is limited, such as robot joints. Against this background, the task arises of enabling the detection of high-frequency vibrations, such as the vibrations of a robot joint, for condition monitoring with improved sensitivity.

[0016] To achieve this object, a sensor for detecting vibrations of an object is proposed according to patent claim 1. The sensor according to the invention for detecting vibrations of an object comprises an optical waveguide having a fiber Bragg grating, and a sensor structure element to which the optical waveguide is fastened at two fastening points, wherein the sensor structure element comprises two holding sections which are configured to fix the sensor structure element to a surface of the object in a vibration-damped, in particular vibration-decoupled, manner, and wherein the sensor structure element comprises a detection section which is configured to be in contact with the object for coupling in vibrations.

[0017] The sensor according to the invention comprises a sensor structure element which can be designed without a dedicated test mass, i.e. without a mass block. A change in the Bragg wavelength of the fiber Bragg grating is not caused by an oscillating test mass, but rather by vibrations of the object which are directly picked up on the object by the detection section of the sensor structure element. The vibrations cause dynamic bending of the sensor structure element. This bending compresses or stretches the fiber Bragg grating of the optical waveguide attached to the two attachment points. Consequently, a shift in the Bragg wavelength can be observed in the light reflected by the fiber Bragg grating. Due to the omission of a test mass, the sensor according to the invention can be designed to be comparatively compact and have a high resonant frequency.This allows even high-frequency vibrations to be monitored on objects that offer limited space for corresponding sensors. By tapping the vibrations directly on the object being monitored with the detection section, increased sensitivity can be achieved.

[0018] Preferably, the optical waveguide of the sensor is attached to the sensor structure element exclusively at the two aforementioned attachment points. As a result, the remaining regions or sections of the sensor structure element can move and / or deform relative to the optical waveguide. Such deformation of the sensor structure element as a result of an oscillation or vibration coupled by the detection section can lead to an expansion or compression of the fiber Bragg grating in the axial direction of the optical waveguide. The optical waveguide is preferably attached to the sensor structure element via an adhesive connection, for example, with an adhesive that cures upon exposure to UV light. In this way, a particularly durable attachment can be achieved.

[0019] According to an advantageous embodiment of the invention, the two holding sections each comprise a vibration-damping element, which preferably comprises an elastomer. The vibration-damping elements allow the holding sections of the sensor structure element to be fixed to the object in a vibration-damped manner. The vibrations of the object can therefore be coupled into the sensor structure element essentially, in particular exclusively, via the detection section. Any interference that may result from the coupling of vibrations through the holding sections can be effectively reduced, in particular avoided.

[0020] According to an advantageous embodiment of the invention, the sensor structure element has a transmission section arranged between the two fastening points for transmitting the vibrations to the optical waveguide, which extends parallel to the optical waveguide, with the detection section extending perpendicular to the transmission section. Vibrations coupled into the detection section can be transmitted to the optical waveguide by means of the transmission section, for example by bending the transmission section and thereby causing an axial expansion or compression of the optical waveguide, in particular of the fiber Bragg grating of the optical waveguide. In this way, the optical waveguide can be arranged at a distance from the object, but vibrations of the object can nevertheless be tapped directly and transformed into a compression or expansion of the fiber Bragg grating without the use of a test mass.The transmission section is preferably plate-shaped. The optical waveguide, in particular the region of the optical waveguide that features the fiber Bragg grating, can rest against a surface of the transmission section. Due to the perpendicular orientation of the detection section relative to the transmission section, vibrations in the direction of the main extension direction of the detection section can be efficiently converted into bends in the transmission section. The detection section is preferably plate-shaped.

[0021] According to an advantageous embodiment of the invention, the sensor structure element, in particular the transmission section of the sensor structure element, has a groove in a region between the two fastening points, in which the optical waveguide is arranged. The groove is preferably arranged on a surface of the sensor structure element facing away from the detection section. Preferably, the groove is not provided continuously in the transmission section in the axial direction of the optical waveguide, but only in a partial region, in particular in a central partial region which is arranged at the same location in the axial direction of the optical waveguide as the detection section, only on the opposite surface of the sensor structure element. The groove is preferably dimensioned such that movement of the optical waveguide arranged in the groove out of the groove is prevented.The groove can also be used to specify a position for arranging the optical waveguide on the sensor structure element during manufacturing. Furthermore, arranging the optical waveguide in the groove ensures that bending of the transmission section in the optical waveguide only results in compression and / or expansion in the axial direction of the optical waveguide, in particular of the fiber Bragg grating.

[0022] According to an advantageous embodiment of the invention, the sensor structural element comprises two flexible sections, each arranged between one of the two holding sections and the detection section. The flexible sections enable an increase in the deflection of the structural element in the region of the detection section and / or transmission section, thereby enabling greater sensor sensitivity.

[0023] According to a particularly advantageous embodiment of the invention, the bendable sections are designed as flat regions with at least one continuous recess. A continuous recess in this context is understood to mean a continuous opening from one surface of the sensor structure element to the respective opposite surface. Due to the continuous recess, a bendable section with a substantially O-shaped base area can result. Alternatively, it can be provided that at least two such continuous recesses are present in the bendable section, resulting in a base area of ​​the bendable section in the shape of an 8 (written out: eight).

[0024] According to an advantageous embodiment of the invention, the fastening points are each arranged between the detection section and one of the bendable sections. This allows for greater bending of the sensor structure element in those areas not located between the two fastening points.

[0025] According to an alternative, advantageous embodiment, the fastening points are each arranged in one of the bendable sections. Such an arrangement also facilitates bending of the sensor structure element in the area between the two fastening points. Preferably, the fastening points are each arranged in a center of symmetry of the base area of ​​the bendable sections. If the bendable sections each have a base area in the shape of a figure eight, the fastening points can, for example, be arranged at the intersection point of the figure eight.

[0026] According to an advantageous embodiment of the invention, the sensor has a resonant frequency greater than 5,000 Hz, for example, 10,000 Hz, and an operating range from 50 Hz to just below the resonant frequency, i.e., for example, an operating range Hz from 50 Hz to 9,000 Hz. Compared to the prior art sensors listed in Table 1, a higher resonant frequency can thus be achieved with the sensor according to the invention. This makes it possible to extend the operating range of the sensor according to the invention into a higher frequency range than with prior art sensors.

[0027] According to an advantageous embodiment of the invention, the sensor has a thickness in the range of 0.5 to 2 mm, in particular a thickness of 1 mm. The sensor preferably has a length in the range of 25 mm to 30 mm, preferably in the range of 27 mm to 28 mm. The width of the sensor is preferably in the range of 4 mm to 6 mm, for example 5 mm.

[0028] The sensor structure element of the sensor can be designed as a one-piece element.

[0029] A further subject matter of the invention is a robot joint with a sensor as described above, wherein the holding sections and the detection section are fixed to a surface, in particular an outer contour, of the robot joint, in particular each via an adhesive connection.

[0030] With the robot joint according to the invention, the same technical effects and advantages can be achieved as have already been described in connection with the sensor according to the invention.

[0031] According to an advantageous embodiment of the invention, the robot joint has a curved contour that is in contact with the detection section, wherein the detection section has a detection section contour that is adapted to the curved contour of the robot joint. Such a configuration enables a particularly effective coupling and thus a high sensitivity.

[0032] Alternatively or in addition to the advantageous embodiment of the robot joint described above, the advantageous features and embodiments disclosed in connection with the sensor according to the invention can also be used, alone or in combination, in the robot joint.

[0033] The invention further relates to a method for detecting vibrations of an object, wherein light is coupled into an optical waveguide having a fiber Bragg grating, and light reflected by the fiber Bragg grating is detected and evaluated, wherein the optical waveguide is fastened to a sensor structure element at two fastening points, wherein the sensor structure element comprises two holding sections, via which the sensor structure element is fixed to a surface of the object, in particular in a vibration-decoupled manner, wherein the sensor structure element comprises a detection section which is in contact with the object for coupling in vibrations.

[0034] The method according to the invention can achieve the same technical effects and advantages as have already been described in connection with the sensor according to the invention.

[0035] According to an advantageous embodiment of the method, light is coupled into a reference optical waveguide having a reference fiber Bragg grating, and light reflected by the reference fiber Bragg grating is detected and evaluated. The reference optical waveguide is attached to a reference sensor structure element at two points. The reference sensor structure element comprises two holding sections, via which the reference sensor structure element is fixed to a surface of the object, in particular in a vibration-decoupled manner. The reference sensor structure element comprises a detection section that is in contact with the object for coupling in heat. The reference sensor structure element with reference optical waveguide and reference fiber Bragg grating can compensate for temperature influences during the measurement.Such temperature compensation is advisable because the Bragg wavelength depends not only on vibrations but also on temperature. In this context, it is advantageous if the detection section of the reference sensor structure element is coupled to the object using a thermally conductive material, such as thermally conductive silicone.

[0036] Further details and advantages of the invention will be explained below with reference to the exemplary embodiment illustrated in the drawings. Fig. 1 shows a first embodiment of a sensor according to the invention in a schematic, perspective view; Fig. 2 a perspective detailed view of the holding section of the sensor structure element according to Fig. 1 from a view from below; Fig.3 a perspective detailed view of the detection section of the sensor structure element according to Fig. 1; Fig. 4 a perspective detailed view of the transmission section of the sensor structure element according to Fig. 1; Fig. 5 the sensor according to Fig. 1 in a lateral sectional view along the longitudinal axis; Fig. 6 a second embodiment of a sensor according to the invention in a schematic, perspective view: and Fig. 7 the sensor according to Fig. 6 in a lateral sectional view along the longitudinal axis.

[0037] In the Fig.Figure 1 shows a first exemplary embodiment of a sensor according to the invention for detecting vibrations of an object in a schematic, perspective view. The sensor comprises a sensor structure element 15, which in particular has a substantially flat design and extends along a longitudinal axis L, which here runs in a Y-direction. An optical fiber 1 is attached to the sensor structure element 15. The attachment is designed such that the optical fiber is attached to the structural element 15 exclusively at two attachment points 10. In the present exemplary embodiment, these attachment points 10 are designed as adhesive points that have an adhesive that has been cured by irradiation with UV light. In a region between these attachment points 10, the optical fiber 1 comprises a fiber Bragg grating 13, which can also be abbreviated to FBG.

[0038] At the two opposite ends of the sensor structure element 15 in the Y direction, i.e., along the longitudinal axis L, the sensor structure element 15 has one of a total of two holding sections 2. The holding sections 2 are configured to fix the sensor structure element 15 to a surface of the object to be monitored in a vibration-damped, in particular vibration-decoupled manner. Fig. 2 shows a perspective view of such a holding section 2 from a viewing direction towards the Fig. 1 hidden underside.

[0039] In an area between the two holding sections 2, in the present embodiment in the middle between the two holding sections 2, the sensor structure element 15 comprises a detection section 3, which is designed to be in contact with the respective object to be monitored in order to couple in vibrations. This detection section is described in detail in Fig.3 and is designed as a substantially plate-shaped element. In the illustration according to Fig. 1, the detection section 3 is located on the non-visible underside of the sensor structure element 15 and is connected to a transmission section 4 of the sensor structure element 15.

[0040] This transmission section 4 is designed to bend due to the vibrations picked up by the detection section 3 and to cause an expansion or compression of the optical waveguide 1, in particular of the fiber Bragg grating 13 of the optical waveguide 1. The transmission section 4 extends parallel to the optical waveguide 1, i.e., parallel to the longitudinal axis L. Fig.4 shows a view of the transmission section 4 without the optical waveguide 1 arranged thereon. It can be seen that the transmission section 4 comprises a groove 9 running in the direction of the longitudinal axis L. This groove 9 does not extend over the entire length of the transmission section 4 along the longitudinal axis L. As in Fig. 1, the optical waveguide 1 is arranged in the groove 9; in particular, the fiber Bragg grating 13 of the optical waveguide 1 is arranged in the groove 9. The groove 9 can prevent undesired slipping of the optical waveguide 1 perpendicular to the longitudinal axis L in the plane of the transmission section 4. Furthermore, the arrangement of the optical waveguide 1 in the groove 9 ensures that the fiber Bragg grating 13 is stretched or compressed by the vibrations in the force direction F exclusively in the axial direction, i.e., along the longitudinal axis L.

[0041] The representation in Fig. 5 shows the sensor according to Fig. 1 in a lateral sectional view along the longitudinal axis L, wherein the sensor is attached to an object 12 to be monitored. This object can be, for example, a robot joint. The sensor can detect vibrations of the object 12, in particular in a force direction F. This force direction is arranged perpendicular to the longitudinal axis L of the sensor structure element 15 and parallel to that of the plate-shaped detection section 3. To ensure that vibrations are coupled into the sensor structure element 15 exclusively via the detection section 3 and not via the holding sections 2, the holding sections 2 each have a vibration damping element 11, which can, for example, comprise an elastomer. The vibration damping elements 11 can each be connected to the object 12 via adhesive bonds.

[0042] How to continue in Fig. 1 and Fig.5, the sensor structure element 15 comprises two flexible sections 5, each of which is arranged between one of the two holding sections 2 and the detection section 3. In the present exemplary embodiment, the flexible sections 5 are designed as essentially flat regions with two continuous recesses 14. This results in two flexible sections 5, each of which has a base area in the shape of the figure eight. The flexible sections are each connected to the holding sections 2 via a narrow connecting section 8. Further narrow connecting sections 6 are formed in the transition to the transmission section 4 arranged in the center of the sensor structure element 15. A corresponding connecting section 7 is provided in the present exemplary embodiment as part of the flexible section 5 and connects the two O-shaped regions that form the flexible section 5.

[0043] The representation in Fig. Figure 6 shows a second embodiment of a sensor according to the invention for detecting vibrations of an object in a schematic, perspective view. The second embodiment essentially corresponds to the first embodiment, so that the explanations regarding Fig. 1 to 5. In contrast to the first embodiment, in the second embodiment, the fastening points 10, at which the optical waveguide 1 is fixed to the sensor structure element, are arranged within the flexible section 5. Here, the fastening points are each provided in a connecting section 7, which is part of the flexible region.

[0044] The Fig. 7 shows the sensor according to the second embodiment in a lateral sectional view along the longitudinal axis L.

[0045] According to a modification of the embodiments shown above, the robot joint 12 comprises a curved contour that is in contact with the detection section 3. According to this modification, the detection section 3 has a detection section contour that is adapted to the curved contour of the robot joint 12.

[0046] With the sensors described above according to the exemplary embodiments, a method for detecting vibrations of an object can be carried out, wherein light is coupled into an optical waveguide 1 having a fiber Bragg grating 13, and light reflected by the fiber Bragg grating 13 is detected and evaluated, wherein the optical waveguide 1 is fastened to a sensor structure element 15 at two fastening points 10, wherein the sensor structure element 15 comprises two holding sections 2, via which the sensor structure element 15 is fixed to a surface of the object 12, in particular in a vibration-decoupled manner, wherein the sensor structure element 15 comprises a detection section 3 which is in contact with the object 12 for coupling in vibrations. Optionally, a reference sensor can be provided which is of identical construction.To compensate for temperature influences, light is coupled into a reference optical waveguide 1 of the reference sensor, which has a reference fiber Bragg grating 13. Light reflected by the reference fiber Bragg grating 13 is detected and evaluated, wherein the reference optical waveguide 1 is attached to a reference sensor structure element 15 at two points, wherein the reference sensor structure element 15 comprises two holding sections 2, via which the reference sensor structure element 15 is fixed to a surface of the object 12, in particular in a vibration-decoupled manner, wherein the reference sensor structure element 15 comprises a detection section 3, which is in contact with the object 12 for coupling in heat. Table 1: reference category Resonance frequency (Hz) Operating frequency range (Hz) Sensitivity (pm / g)

[13] FBGVSBS 41 4-30 77.6-108

[14] FBGVSBS - 5-100 88

[15] FBGVSBS - - 7.69

[16] FBGVSBS 70 20-100 -

[17] FBGVSBS 980 (x) / 960 (y) / 640 (z) 20-600 (x and y) / 10-400 (z) 9.7 (x) / 10.13 (y) / 7.45 (z)

[18] FBGVSBS 227.3 10-210 339

[19] FBGVSBS 86 5-50 406.7

[20] FBGVSBS 700 50-400 57.4

[21] FBGVSBS 247 40-140 234.5

[22] FBGVSBS 505 (x) / 177 (y) 60-150 (x) / 30-150 (y) 125.85 (x) / 82.32 (y)

[23] FBGVSBS 90 5-60 485.75

[24] FBGVSBS 111 (theoretical value) 0.5-40 575.8

[31] FBGVSTPOF 20 - 4.85 nw / g

[32] FBGVSTPOF 34.4 0.5-100 -

[33] FBGVSTPOF 34 0-22 2362

[34] FBGVSTPOF 300 10-150 31.25

[35] FBGVSTPOF 50 12-250 193.6

[36] FBGVSTPOF 1074 (x) / 194.6 (y) 10-150 (x) / 10-800 (y) 21.5 (x) / 52.7 (y)

[25] FBGVSES 600 10-200 20.189

[26] FBGVSES 3806 0-1200 4.01

[27] FBGVSES 708 0-236 19.65

[28] FBGVSES 441 5-300 152

[29] FBGVSES 32 0-20 2430

[30] FBGVSES 1275 (x) / 1482 (y) 20-800 (x and y) 41.2 (x) / 34.5 (y) List of reference symbols 1 optical fiber 2 holding section 3 Detection section 4 Transmission section 5 flexible section 6 connecting section 7 connecting section 8 connecting section 9 grooves 10 attachment point 11 Vibration damping element 12 Object / Robot Joint 13 Fiber Bragg Gratings 15 Sensor structure element F Direction of force of vibrations X, Y, Z spatial direction QUOTES CONTAINED IN THE DESCRIPTION

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[0002]

Claims

[1] Sensor for detecting vibrations of an object (12), with an optical waveguide (1) having a fiber Bragg grating (13), characterized by a sensor structure element (15) to which the optical fiber (1) is attached at two attachment points (10), wherein the sensor structure element (15) comprises two holding sections (2) which are designed to fix the sensor structure element (15) to a surface of the object (12) in a vibration-damped, in particular vibration-decoupled, manner, and wherein the sensor structure element (15) comprises a detection section (3) which is designed to be in contact with the object (12) for coupling in vibrations. [2] Sensor according to claim 1, characterized by that the two holding sections (2) each comprise a vibration damping element (11), which preferably comprises an elastomer. [3] Sensor according to one of the preceding claims, characterized bythat the sensor structure element (15) has a transmission section (4) arranged between the two fastening points (10) for transmitting the vibrations to the optical waveguide (1), which transmission section extends parallel to the optical waveguide (1), wherein the detection section (3) extends perpendicular to the transmission section (4). [4] Sensor according to one of the preceding claims, characterized by that the sensor structure element (15), in particular the transmission section (4) of the sensor structure element (15), has a groove (9) in a region between the two fastening points (10), in which the optical waveguide (1) is arranged. [5] Sensor according to one of the preceding claims, characterized by that the sensor structure element (15) has two bendable sections (5), each of which is arranged between one of the two holding sections (2) and the detection section (3). [6] Sensor according to claim 5, characterized bythat the bendable sections (5) are designed as flat areas with at least one continuous recess (14). [7] Sensor after one of the sprays 5 or 6, characterized by that the fastening points (10) are each arranged between the detection section (3) and one of the bendable sections (5) or that the fastening points (10) are each arranged in one of the bendable sections (5). [8] Robot joint (12) with a sensor according to one of the preceding claims, wherein the holding sections (2) and the detection section (3) are fixed to a surface, in particular an outer contour, of the robot joint (12), in particular each via an adhesive connection. [9] Robot joint (12) according to claim 8, characterized bythat the robot joint (12) has a curved contour which is in contact with the detection section (3), wherein the detection section (3) has a detection section contour which is adapted to the curved contour of the robot joint (12). [10] Method for detecting vibrations of an object (12), wherein light is coupled into an optical waveguide (1) having a fiber Bragg grating (13), and light reflected by the fiber Bragg grating (13) is detected and evaluated, wherein the optical waveguide (1) is attached to a sensor structure element (125) at two attachment points (10), wherein the sensor structure element (15) comprises two holding sections (2), via which the sensor structure element (15) is fixed to a surface of the object (12), in particular in a vibration-decoupled manner, wherein the sensor structure element (15) comprises a detection section (3) which is in contact with the object (12) for coupling vibrations.

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