Technique for measuring the wear of a ball screw drive

Abstract

Measuring device (100) for measuring the wear of a ball screw drive (10), wherein the measuring device (100) comprises: a magnetic sensor unit (120) that can be arranged on or near the ball screw drive (10) and is configured to generate an alternating magnetic field (22) that interacts with a spindle nut (12) of the ball screw drive (10) and to detect a change in the alternating magnetic field (22) caused by deformation of the spindle nut (12) of the ball screw drive (10); and an evaluation unit (140) which is designed to infer the wear of the ball screw drive (10) on the basis of the detected change in the alternating magnetic field (22).

Description

Technical area

[0001] The present invention relates to ball screws. In particular, the present invention relates to a technique for measuring the wear of a ball screw. State of the art

[0002] Ball screws are used to move axes, for example, on a machine tool. A ball screw is a helical gear with balls inserted between the spindle (or screw) and the spindle nut (screw nut). An example of this type of ball screw is described in DE 10 2013 225 467 B4.

[0003] Ball screws are used to convert rotary motion into linear motion (or translational motion) or vice versa. The advantage of ball screws compared to conventional screw drives is that they exhibit significantly lower friction and wear. They are durable and the preferred drive in many applications.

[0004] Furthermore, various approaches for measuring wear in ball screws are known from the prior art. For example, in DE 10 2013 225 467 B4, the condition of the ball screw is monitored using strain gauges. For this purpose, a recess is provided in the spindle nut that extends right up to the ball raceway, so that the spindle nut has a thin wall thickness in the area of ​​the bottom of the recess. The thin-walled bottom is deformed by the passing balls. This deformation is detected by the strain gauges. With increasing wear, the ball diameter decreases, so that the deformation caused by the balls also decreases. Thus, the bottom deformation detected by the strain gauges is a measure of the wear of the ball screw.

[0005] Furthermore, DE 10 2007 038 890 B4 discloses a method for determining the service life or remaining service life of a machine component driven by a motor (e.g., a threaded spindle of a ball screw). The method is based on the integration of a sensor device in the motor, which continuously reads motor parameters during operation and, on the basis of this, a statement can be made about the actual load on the machine component during operation and thus about the service life or remaining service life of the machine component.

[0006] DE 10 2005 015 465 B4 also discloses a method and device for categorizing rolling bearing damage based on structure-borne sound vibrations. The structure-borne sound vibrations are recorded using a static magnetic field.

[0007] Furthermore, DE 10 2014 102 108 B3 discloses a technique in which wear and tear on a ball screw are determined using a magnetic element and the collection of chips or metal particles on the magnetic element. The remaining service life is determined based on the data obtained.

[0008] Furthermore, a technique is known from DE 10 2019 118 639 A1 in which the wear of a spindle drive is determined by measuring the distance between the spindle nut and the spindle.

[0009] Furthermore, the integration of complex sensors in a spindle of a ball screw is known for measuring, for example, the load / load change, temperature / temperature change, vibrations, etc. in the ball screw in order to make statements about the condition or wear of the ball screw.

[0010] The object of the present invention is to provide a technology for measuring the wear condition of a ball screw that is simple to implement, retrofittable, reliable, and insensitive to external influences. Furthermore, the object of the present invention is to reliably predict the future wear condition of a ball screw. Brief outline

[0011] To achieve at least the above-mentioned objects, according to a first aspect of the invention, a measuring device for measuring the wear of a ball screw is provided, wherein the measuring device comprises: a magnetic sensor unit that can be arranged on or in the immediate vicinity of the ball screw, which is designed to generate an alternating magnetic field that interacts with the spindle nut of the ball screw, and to detect a change in the alternating magnetic field caused by deformation of a spindle nut of the ball screw; and an evaluation unit that is designed to infer wear of the ball screw on the basis of the detected change in the alternating magnetic field.

[0012] The magnetic sensor unit can comprise at least one excitation coil designed to generate the alternating magnetic field. The generated alternating magnetic field can be a low-frequency alternating field (for example, in the frequency range of 10 to 500 Hz). The generated alternating magnetic field is also referred to below as the "excitation field." The at least one excitation coil can be arranged on or near the ball screw drive in such a way that the excitation field extends into the spindle nut of the ball screw drive. The alternating magnetic field can thus enter into (magnetic) interaction with the spindle nut. According to one variant, the at least one excitation coil can be arranged on one of the axial end faces or on the radial outer surface of the spindle nut.

[0013] Since the spindle nut of the ball screw drive is usually ferromagnetic, the interaction of the ferromagnetic spindle nut with the excitation field leads to a change or deformation of the magnetic field lines of the excitation field in the (immediate) vicinity of the spindle nut. This change or deformation of the magnetic field lines leads to a measurable change in the magnetic flux density of the alternating magnetic field (excitation field).

[0014] The degree (or strength) of the deformation of the magnetic field lines and thus the degree (or strength) of the change in the magnetic flux density depends on the condition (internal stress or deformation) of the spindle nut, which interacts with the excitation field. The internal stress or deformation of the spindle nut, in turn, depends on the preload and thus on the wear of the ball screw. A certain preload is generally desired. This is because the higher the preload, the greater the rigidity of the ball screw. This is required in various applications. Wear on a ball screw primarily manifests itself in the loss of preload, which leads to positioning inaccuracies and a decrease in rigidity.

[0015] The preload of the ball screw can be adjusted by an offset in the raceway pitch in the spindle nut or by a split spindle nut or double nut (2-point support). The preload can also be adjusted by selecting the size of the balls used (4-point support). The reason for wear is the same for all variants: decreasing ball size. This will be examined using the last variant as an example. The larger the balls used in the ball screw (i.e., the larger the ball diameter), the greater the preload of the ball screw and the greater the internal stress or deformation of the spindle nut. The balls wear with increasing operating time, which is manifested by the fact that the diameter of the balls becomes successively smaller with increasing operating time.A smaller ball diameter results in a smaller preload of the ball screw and thus in less internal stress or deformation of the spindle nut. This change in the condition of the spindle nut (i.e., less internal stress or deformation) has a direct impact on the magnetic interaction of the spindle nut with the magnetic excitation field. Thus, measuring the magnetic flux density of the excitation field or the change in the magnetic flux density of the excitation field in the immediate vicinity of the spindle nut is a direct measure of the wear / degree of wear of the balls and thus of the ball screw.

[0016] To detect (measure) the change in the alternating magnetic field caused by the spindle nut, the magnetic sensor unit can comprise at least one detector coil that can be arranged on or near the ball screw drive. For example, the at least one detector coil can be arranged on one of the axial end faces or on the radial outer surface of the spindle nut. Furthermore, the at least one detector coil can be arranged in the immediate vicinity of the excitation coil, so that the alternating magnetic field generated by the excitation coil and modified by interaction with the spindle nut can induce a voltage in the at least one detector coil.The at least one detector coil can thus be arranged with respect to the at least one excitation coil (and the spindle nut) in such a way that the alternating magnetic field generated by the at least one excitation coil and modified by the spindle nut through magnetic interaction induces a voltage in the at least one detector coil.

[0017] Thus, the change in the alternating magnetic field generated by interaction with the spindle nut can be detected by reading the at least one induced voltage signal generated by the alternating magnetic field in the at least one detector coil. The at least one read-out induced voltage signal is proportional to the magnetic flux density in the at least one detector coil. The magnetic flux density in the detector coil is determined by the interaction of the external alternating magnetic field with the spindle nut. As described above, the spindle nut can deform the external alternating magnetic field to varying degrees depending on its internal stress or deformation, which is determined by the size of the sphere, and thus cause a varying degree of change in the magnetic flux density in the at least one detector coil.The at least one read-out induction voltage signal is thus a direct measure of the internal stress or deformation of the spindle nut and thus a direct measure of the wear of the balls or the ball screw drive.

[0018] According to one variant, the magnetic sensor unit can comprise at least two detector coils peripherally surrounding the at least one excitation coil. The advantage of this arrangement is that multiple induced voltage signals can be detected and read out simultaneously. Thus, measurement errors can be more easily detected and eliminated, thereby improving measurement sensitivity.

[0019] In order to further determine the degree of wear of the balls or the ball screw, the evaluation unit can further be designed to determine a degree of wear of the ball screw or the balls of the ball screw. The degree of wear can be determined from a comparison of one or more read-out induction voltage signals with a reference signal. The reference signal can preferably be an induction voltage signal that was obtained after installation but before commissioning of the ball screw in a machine tool. The reference signal can thus have been obtained at a time when the ball screw does not yet show any appreciable wear and therefore has the desired ball size and preload. The degree of wear (i.e. the severity of the wear) of the ball screw can be determined from the comparison of the induction voltage signals.

[0020] The evaluation unit can also be configured to perform a wear classification based on the determined degree of wear. In other words, the measurement result(s) can be classified into predefined wear categories depending on the determined degree of wear. Classification into different wear categories (starting, for example, with the category "no wear" through "medium wear" to "high wear") enables a machine tool user to determine early on whether the ball screw can continue to be used or whether maintenance is necessary.

[0021] Furthermore, the evaluation unit can be configured to make a prediction about future wear based on the detected wear / degree of wear. This makes it possible to make a statement about the remaining service life of the ball screw or future maintenance times.

[0022] According to a second aspect of the invention, a ball screw assembly is provided, the ball screw assembly comprising: a screw and a screw nut; balls that roll along raceways between the screw and the screw nut upon translation of the screw nut relative to the screw; and the measuring device described above.

[0023] The magnetic sensor unit of the measuring device can be arranged (directly) on or near the ball screw drive. According to one implementation, the magnetic sensor unit can be arranged (directly) on the spindle nut or at a predetermined distance from the spindle nut. According to one variant, the magnetic sensor unit can be positioned directly on the radial outer surface of the spindle nut. According to an alternative variant, the magnetic sensor unit can be positioned in a milled recess on the outer surface of the spindle nut. The direct positioning of the magnetic sensor unit on the spindle nut or in a milled recess of the spindle nut described here has the advantage that the generated magnetic field interacts directly with the clamped spindle nut and thus the effect of the change in the alternating magnetic field (or its flux density) due to interaction with the spindle nut can be better detected.This means that the magnetic sensor unit is sufficiently sensitive even to the smallest changes in the spindle nut.

[0024] Alternatively, the magnetic sensor unit can also be mounted outside the spindle nut, for example, in a tool table. In such a case, the distance to the spindle nut should preferably not be too great to achieve the necessary sensitivity, so that even slight deformations of the spindle nut remain detectable.

[0025] According to a third aspect of the invention, a method for measuring the wear of a ball screw is provided, wherein a measuring device is provided for measuring the wear, which measuring device comprises at least one magnetic sensor unit arranged on or near the ball screw. The method comprises the following steps: generating, with the aid of the magnetic sensor unit, an alternating magnetic field such that the alternating magnetic field interacts with a spindle nut of the ball screw; detecting, with the aid of the magnetic sensor unit, a change in the alternating magnetic field caused by the interaction with the spindle nut, wherein the change in the alternating magnetic field depends on a deformation of the spindle nut; and determining wear of the ball screw based on the detected change in the alternating magnetic field.

[0026] The provided measuring device can be a measuring device with at least one excitation coil and at least one detector coil, as described above. In particular, the alternating magnetic field can be generated using the at least one excitation coil of the magnetic sensor unit. Furthermore, the change in the alternating magnetic field can be detected using the at least one detector coil of the magnetic sensor unit. For this purpose, the at least one detector coil can be arranged with respect to the at least one excitation coil (and the spindle nut) such that the alternating magnetic field changed by interaction with the spindle nut penetrates the at least one detector coil and induces a voltage (voltage signal) there. The at least one induced voltage is proportional to the magnetic flux or the magnetic flux density generated by the changed alternating magnetic field in the at least one detector coil.As already explained above, the alternating magnetic field and thus the magnetic flux or the magnetic flux density in the at least one detector coil changes proportionally to the deformation or internal stress of the spindle nut. The at least one induced voltage signal is thus a direct measure of the deformation or internal stress of the spindle nut and thus also a direct measure of the wear / degree of wear of the ball screw (or its balls). The step of detecting the change in the alternating magnetic field can thus be based on reading the at least one voltage signal induced in the at least one detector coil of the measuring device.

[0027] A wear value proportional to the signal amplitude and / or signal shape of the induction voltage signal can be assigned to the at least one read induction voltage signal. This allows the wear of the ball screw to be determined or quantified. This evaluation of the at least one read induction voltage signal can be performed by an evaluation unit of the measuring device, as already described above. Optionally, the evaluation unit can determine the degree of wear of the ball screw, for example, by comparing a determined wear value with a reference value. The reference value can be a reference voltage signal that is determined or measured before the ball screw is put into operation.

[0028] Optionally, the evaluation unit can also carry out a wear classification in which the determined wear or degree of wear is classified into predefined wear categories, as described above in connection with the measuring device.

[0029] The described measurement procedure can be repeated (at specified intervals) to detect wear on the ball screw. The measured values ​​can also be used to predict future wear and thus the service life of the ball screw.

[0030] In particular, at least one idle measurement can be performed before installing the ball screw in a machine tool. The at least one idle measurement (or offset measurement) serves to determine the influence of the preloaded ball screw without wear and without load on the recorded measurement signals. In particular, this offset measurement can be used as a reference for subsequent measurements in order to determine the degree of wear as accurately as possible.

[0031] In addition to or as an alternative to the no-load measurement described above, a measurement can also be performed after a ball screw has been installed in a machine tool, either without load or with a defined load, to detect any assembly errors. Subsequently (i.e., after the machine tool has been put into regular operation), further measurements can be performed at specified intervals to measure and predict wear on the ball screw. Short description of the drawings

[0032] Further details and advantages of the invention will be described further with reference to embodiments illustrated in the figures. They show: Fig. 1 is a schematic representation of a measuring device according to the present invention; Fig. 2 a schematic representation of a magnetic sensor unit as used in the measuring device according to Fig. 1 is used; Fig. 3a to 3c show representations of the measuring principle of the measuring device according to the present invention; Fig. 4a, Fig. 4b shows the assembly of at least a part of the measuring device according to the present invention; and Fig. 5 a flow chart showing a measuring method according to the invention for measuring the wear of a ball screw drive. Detailed description

[0033] In connection with the Fig. 1 describes a measuring device 100 for measuring the wear of a ball screw 10. The ball screw 10 is shown schematically in the Fig. 3a-3c and comprises a spindle 16, a spindle nut 12, and balls 14 arranged between the spindle 16 and the spindle nut 12. The balls 14 are arranged in raceways between the spindle 16 and the spindle nut 12 and run along these raceways when the spindle nut 12 moves longitudinally (i.e., translationally) relative to the rotating spindle 16.

[0034] The measuring device 100 (see Fig. 1) comprises a magnetic sensor unit 120. This is designed to generate an alternating magnetic field 22, the magnetic field lines of which extend into the spindle nut 12 (see Fig. 3a-3c). The magnetic sensor unit 120 is further configured to detect (measure) a change in the alternating magnetic field 22 caused by the spindle nut 12 of the ball screw 10. Furthermore, the measuring device 100 comprises an evaluation unit 140 configured to infer the wear of the ball screw 10 based on the detected change in the alternating magnetic field 22. For this purpose, the evaluation unit 140 is in communication with the magnetic sensor unit 120 in order to receive and evaluate the measurement data of the magnetic sensor unit 120 indicating the change in the alternating magnetic field 22, i.e., to derive a wear or wear value from the measured changes in the alternating magnetic field 22. The communication between the magnetic sensor unit 120 and the evaluation unit 140 can be wireless or wired and is in Fig. 1 is only schematically indicated by line 130. It is understood that with wireless and / or wired communication, the acquired measurement data (voltage signals) can still be processed and digitized in the magnetic sensor unit 120 to enable rapid communication (using a standard protocol).

[0035] To generate the alternating magnetic field 22 (hereinafter also referred to as excitation field 22), the magnetic sensor unit 120 comprises at least one excitation coil 122 (see also Fig. 2). The at least one excitation coil 122 is designed to generate the alternating magnetic field 22. The generated excitation field 22 can be an alternating field in the low-frequency range, in particular in the frequency range from 10 to 1000 Hz, preferably in the range from 100 to 500 Hz. It is understood that the generation of alternating magnetic fields 22 in other frequency ranges is conceivable without significantly affecting the measuring principle described here.

[0036] Furthermore, the magnetic sensor unit 120 comprises at least one detector coil 124 (see also Fig. 2). The at least one detector coil 124 is designed to detect changes in the alternating magnetic field 22. For this purpose, the at least one detector coil 124 is brought into proximity with the excitation coil 122 and the spindle nut 12, so that the alternating magnetic field 22, altered by the interaction of the excitation field 22 with the spindle nut 12, penetrates the at least one detector coil 124 and induces at least one voltage proportional to the magnetic flux density of the altered alternating magnetic field 22.

[0037] From the at least one read voltage signal, the evaluation unit 140 can calculate (derive) a wear value for the ball screw drive 10. This can be done with the aid of a computing module 142 integrated into the evaluation unit 140. Furthermore, the evaluation unit 140 can be configured to calculate a degree of wear (severity of wear) of the ball screw drive 10 by comparing the calculated wear or wear value with a reference value. This can be done with the aid of a comparison module 144 integrated into the evaluation unit 140. Furthermore, the evaluation unit 140 can be configured to perform a wear classification based on the calculated wear or degree of wear. This can be done with the aid of a classification module 146 integrated into the evaluation unit 140.Furthermore, the evaluation unit 140 can be configured to predict future wear development based on previous measurements and calculated wear values. This can be done with the aid of a prediction module 148 integrated into the evaluation unit 140. The modules 142-148 described here can be standalone software and / or hardware modules that have the necessary software routines as well as memory and computing capacity to perform the described functions. Alternatively, it is also conceivable that the modules 142-148 are part of a higher-level computing module.

[0038] In connection with the Fig. 2 shows a concrete implementation of the magnetic sensor unit 120. The magnetic sensor unit 120 according to the implementation in the Fig. 2 comprises an excitation coil 122 and four detector coils 124. The excitation coil 122 is arranged centrally with respect to the four detector coils 124. In contrast, the four detector coils 124 are arranged equidistant from one another and at equal radial distances from the excitation coil 122 around the excitation coil 122. It is understood that this arrangement is merely exemplary, and that different implementations are conceivable. For example, it is conceivable that the magnetic sensor unit 120, instead of four detector coils 124, has only two, three, or more than four detector coils 124 arranged in a symmetrical arrangement around the excitation coil 122. It is only important that the distance of each detector coil 124 from the excitation coil 122 is selected such that the excitation field 22 or the modified excitation field 22 passes through the respective detector coil 124 due to the interaction with the spindle nut 12.The use of a large number of detector coils 124 increases the measurement accuracy, since measurement fluctuations and measurement errors due to the device can be more easily detected and eliminated.

[0039] The measuring principle is used in conjunction with the Fig. 3a to 3c. The Fig. 3a to 3c show, by way of example, a section of the spindle nut 12, the spindle 16 and a ball 14 arranged therebetween. The excitation coil 122 and the at least one detector coil 124 of the magnetic sensor unit 120 are also indicated schematically (in the Fig. 3a-3c, only one detector coil 124 is shown for clarity. The excitation coil 122 generates the excitation field 22 (alternating magnetic field 22), which extends into the spindle nut 12 and is deformed or changed by the ferromagnetic spindle nut 12. The magnetic flux or magnetic flux density generated by the excitation field 22 in the at least one detector coil 124 is proportional to the degree of deformation or change of the excitation field 22 by the spindle nut 12. The degree of deformation or change of the excitation field 22, in turn, depends on the strength of the deformation or internal stress of the spindle nut 12. In Fig. 3a, the spindle nut 12 is not deformed or strained and the excitation field 22 exhibits a slight deformation / change of its field lines in the vicinity of the spindle nut 12 due to the interaction of the excitation field 22 with the ferromagnetic material of the spindle nut 12. In Fig. 3b, the (not worn) ball 14 exerts a considerable tension on the spindle nut 12 due to its large diameter. The spindle nut 12 is locally stressed or deformed, whereby the excitation field 22 is also significantly deformed or changed in the vicinity of the spindle nut 12. In Fig. 3c, the ball 14 is already worn and has a smaller diameter than in Fig. 3b has a smaller diameter. Accordingly, the ball 14 exerts a smaller force than the non-worn ball 14 in Fig. 3b exerts less stress on the spindle nut 12. Accordingly, the spindle nut 12 is in Fig. 3b is less strongly locally strained or deformed, as a result of which the excitation field 22 is also less strongly deformed or changed in the vicinity of the spindle nut 12. The change in the excitation field 22 described here due to the deformation of the spindle nut 12 leads to a change in the magnetic flux density in the at least one detector coil 124 and thus to a change in the induced voltage. The induced voltage of the at least one detector coil 124 or the induced voltage signal read from the at least one detector coil 124 is thus a measure of the degree of strain in the spindle nut 12 and thus also a measure of the size or wear of the balls 14. The degree of wear of the ball screw 10 or its balls 14 can thus be determined from the read induced voltage signal.

[0040] In connection with the Fig. 4a and Fig. 4b, the arrangement of the measuring device 100, in particular the magnetic sensor unit 120, is further described. As already explained above, the measuring device 100, in particular the magnetic sensor unit 120, is arranged on or near the ball screw 10. According to one variant, the magnetic sensor unit 120 is arranged (directly) on the outer surface of the spindle nut 12 (see Fig. 4a). According to an alternative variant, which is Fig. 4b, the magnetic sensor unit 120 can also be arranged in a recess 12a on the spindle nut 12. The advantage of this arrangement is that the magnetic sensor unit 120 rests flat on the spindle nut 12 and the deformation or tension of the spindle nut 12 generated by the balls 14 can be measured even better. In both variants, the magnetic sensor unit 120 is arranged near the flange 12b (only a few centimeters away from it), since this is where the strongest deformation forces act on the spindle nut 12. According to a further alternative variant, the magnetic sensor unit can also be arranged radially around the spindle nut. However, this requires flexible sensors and / or an arrangement and evaluation adapted for each spindle nut size.

[0041] According to another variant (in the Fig. 4a and Fig. 4b), it is also conceivable for the magnetic sensor unit 120 to be arranged near the spindle nut 12 (for example, in a specially provided recess in a bearing table of the machine tool). It is only essential that the excitation field 22 generated by the magnetic sensor unit 120 extends into the spindle nut 12 in order to be able to detect the deformation of the spindle nut 12.

[0042] In connection with the Fig. 5, a method for measuring the wear of a ball screw 10 will now be further described (hereinafter also referred to as a wear measurement method). The method is carried out using the above-described measuring device 100, which comprises at least the above-described magnetic sensor unit 120 and evaluation unit 140. The magnetic sensor unit 120 is arranged on or near the ball screw 10, in particular on the spindle nut 12, as described in connection with the Fig. 4a and Fig.4b.

[0043] The method comprises step S10 of generating an alternating magnetic field 22 such that the alternating magnetic field 22 interacts with the spindle nut 12 of the ball screw 10. More precisely, the generated alternating field 22 (or excitation field 22) extends into the spindle nut 12 and is deformed by the spindle nut 12 to varying degrees depending on its degree of tension.

[0044] The method further comprises step S12 of detecting a change in the alternating magnetic field 22 caused by the interaction with the spindle nut 12. Step S12 can be performed using at least one of the above-described detector coils 124. The at least one detector coil 124 can be arranged with respect to the excitation coil 122 (and the spindle nut 12) such that it detects the change in the alternating magnetic field 22 and outputs an induced voltage proportional thereto as a measurement signal, as already described above in connection with the measuring device 100.

[0045] The method further comprises step S14 of determining the wear of the ball screw drive based on the detected change in the alternating magnetic field 22. Step S14 can be carried out with the aid of the evaluation unit 124 described above. For this purpose, the evaluation unit 124 reads the at least one induction voltage signal generated by the at least one detector coil 124 (this is proportional to the degree of tension of the spindle nut 12 and thus a measure of the size or wear of the balls 14) and calculates a wear or wear value of the balls 14 from the at least one read induction voltage signal. To determine the wear, for example, the amplitude or other signal variables (such as the signal shape and / or the time-dependent signal development) of the at least one detected voltage signal can be analyzed in order to calculate a wear value therefrom.For example, the at least one detected induced voltage signal can be a time-dependent voltage signal. Using a fast Fourier transformation (FFT), the detected time-dependent voltage signals can then be transformed into the frequency domain and subjected to subsequent frequency analysis. This can identify frequency ranges that allow conclusions to be drawn about either incorrect installation and / or wear of the ball screw drive.

[0046] Step S14 of determining the wear may further comprise determining the degree of wear (severity of wear) of the ball screw 10 by comparing the detected at least one induced voltage signal indicating wear with a reference signal. The reference signal may be an induced voltage signal detected at a time when the ball screw 10 did not yet exhibit any significant wear (e.g., before installation and / or commissioning of the ball screw).

[0047] The method may further comprise classifying the degree of wear into different wear classes. For example, a classification into at least four different classes is conceivable, with a first class indicating no wear, a second class indicating low wear, a third class indicating moderate wear, and a fourth class indicating high wear.

[0048] The wear measurement method described here can be repeated at specified intervals to detect the wear development of the ball screw 10. In particular, a prediction of the future wear of the ball screw 10 can be made from the development of the wear measurements. In particular, a time can be predicted at which maintenance of the ball screw 10 is to be expected. In particular, the wear on the ball screw caused by the previous process(es) can be derived from the wear development and thus allocated to the process costs. This allows a more precise and transparent calculation of wear, particularly in the context of machine leasing, for example.

[0049] The wear measurement technology described here is simple in implementation, can be retrofitted to any ball screw, and is also space-saving in its design. A further advantage of the technology described here is that it is inexpensive, the sensor unit of the measuring device can be easily replaced, and the measuring device as a whole is robust and resistant to external influences. The magnetic measuring device described here can detect even the slightest deformations of the magnetic excitation field, thus allowing precise statements to be made about the wear / degree of wear of a ball screw.

Claims

[1] Measuring device (100) for measuring the wear of a ball screw (10), the measuring device (100) comprising: a magnetic sensor unit (120) which can be arranged on or near the ball screw drive (10) and which is designed to generate an alternating magnetic field (22) which interacts with a spindle nut (12) of the ball screw drive (10) and to detect a change in the alternating magnetic field (22) caused by deformation of the spindle nut (12) of the ball screw drive (10); and an evaluation unit (140) which is designed to draw conclusions about the wear of the ball screw drive (10) on the basis of the detected change in the alternating magnetic field (22). [2] Measuring device (100) according to claim 1, wherein the magnetic sensor unit (120) comprises at least one excitation coil (122) which can be arranged on or in the vicinity of the ball screw drive (10) and which is designed to generate the alternating magnetic field (22). [3] Measuring device (100) according to one of the preceding claims, wherein the magnetic sensor unit (120) comprises at least one detector coil (124) which can be arranged on or in the vicinity of the ball screw drive (10) and which is designed to detect the change in the alternating magnetic field (22) caused by the spindle nut (12). [4] Measuring device (100) according to claim 3, wherein the change in the alternating magnetic field (22) is detected by reading at least one induction voltage signal from the at least one detector coil (124) which is proportional to the magnetic flux density in the at least one detector coil (124) which is generated by interaction of the alternating magnetic field (22) with the spindle nut (12) in the detector coil (124). [5] Measuring device (100) according to claim 4, wherein the magnetic flux density in the at least one detector coil (124) or the at least one induced voltage signal read from the at least one detector coil (124) depends on the internal stress or deformation of the spindle nut (12) interacting with the alternating magnetic field (22) and is thus a measure of the wear and / or an indicator of incorrect assembly of the ball screw drive (10) or the balls (14) of the ball screw drive (10). [6] Measuring device (100) according to claim 4 or 5, wherein the evaluation unit (140) is designed to determine a degree of wear of the ball screw drive (10) or of the balls (14) of the ball screw drive (10) on the basis of the at least one read-out induction voltage signal. [7] Measuring device (100) according to claim 6, wherein the degree of wear is determined by comparing one or more read-out induction voltage signals with a reference signal. [8] Measuring device (100) according to one of the preceding claims, wherein the evaluation unit (140) is further designed to carry out a wear classification on the basis of the detected wear or degree of wear. [9] Measuring device (100) according to one of the preceding claims, wherein the evaluation unit (140) is further designed to make a prediction about the future wear on the basis of the detected wear or degree of wear. [10] Ball screw assembly comprising: a spindle (16) and a spindle nut (12); Balls (14) which roll along grooves between the spindle (16) and the spindle nut (12) when the spindle nut (12) is translated relative to the spindle (16); and the measuring device (100) according to one of claims 1 to 9. [11] Ball screw assembly according to claim 10, wherein the magnetic sensor unit (120) of the measuring device (100) is arranged on the spindle nut (12) or at a predetermined distance from the spindle nut (12). [12] Ball screw assembly according to claim 11, wherein the magnetic sensor unit (120) is positioned on the radial outer surface of the spindle nut (12). [13] Ball screw assembly according to claim 11, wherein the magnetic sensor unit (120) is positioned in a milled recess (12a) of the spindle nut (12). [14] Ball screw assembly according to claim 11, wherein the magnetic sensor unit (120) is positioned radially around the spindle nut (12). [15] Method for measuring the wear of a ball screw (10), wherein a measuring device (100) is provided for measuring the wear, which comprises at least one magnetic sensor unit (120) which is arranged on or in the vicinity of the ball screw (10), the method comprising the following steps: Generating (S10), with the aid of the magnetic sensor unit (120), an alternating magnetic field (22) such that the alternating magnetic field (22) interacts with a spindle nut (12) of the ball screw drive (10); Detecting (S12), with the aid of the magnetic sensor unit (120), a change in the alternating magnetic field (22) caused by the interaction with the spindle nut (12), wherein the change in the alternating magnetic field (22) depends on a deformation of the spindle nut (12); and Determining (S14) the wear of the ball screw (10) on the basis of the detected change in the alternating magnetic field (22). [16] Method according to claim 15, wherein the alternating magnetic field (22) is generated by means of at least one excitation coil (122) of the magnetic sensor unit (120), wherein the change in the alternating magnetic field (22) is detected by means of at least one detector coil (124) of the magnetic sensor unit (120). [17] Method according to claim 15 or 16, wherein the step (S12) of detecting the change in the alternating magnetic field (22) is based on reading out at least one induction voltage signal in at least one detector coil (124) of the measuring device (100), which is proportional to the magnetic flux density in the at least one detector coil (124) of the measuring device (100) generated by the changed alternating magnetic field (22) in the at least one detector coil (124). [18] Method according to claim 17, wherein the wear of the ball screw drive (10) is determined by assigning a wear value to the at least one read-out induction voltage signal, which is proportional to the signal amplitude and / or signal shape. [19] Method according to one of claims 15-18, wherein the step of determining (S14) the wear comprises at least one of the following sub-steps: Determining a degree of wear of the ball screw (10) by comparing a determined wear value with a reference value; Carry out a wear classification based on the determined wear or degree of wear. [20] Method according to one of claims 15-19, wherein the measuring method is repeated at predetermined time intervals in order to detect the wear development. [21] Method according to any one of claims 15-20, further comprising making a prediction of the future wear development based on previous wear measurements.

Images