Method for monitoring a preloaded rotary table bearing

Abstract

Method for monitoring a preloaded rotary table bearing (1) during operation of the rotary table bearing (1) comprising an inner bearing ring (2), an outer bearing ring (3), and at least one series of rolling elements (4.n) which roll on raceways (5.1, 5.2 - 5.6) provided by the bearing rings (2, 3), wherein one of the bearing rings (2) is set in rotation by a drive arrangement (6) and wherein the rotational speed of the bearing ring (2) driven by the drive arrangement (6) is detected and controlled by a control unit (7), characterized in that - the elastic deformations of the bearing ring (2, 3) along or across the axis of rotation DA of the rotary table bearing (1) are detected by at least one sensor (8.n) connected to a bearing ring (2; 3), - at least the sensors (8.n) which detect the deformation of the respective bearing ring (2; 3) are glued to the outer and / or end faces (11; 12) of the respective bearing ring (2; 3), - by means of at least one sensor (8.n) the detected elastic deformation is transmitted to the control unit (7), which is equipped with an evaluation arrangement (9), - values ​​are recorded by a temperature sensor (10) and fed to the evaluation arrangement (9), - in the evaluation arrangement (9) the detected physical deformations are verified on the basis of the values ​​recorded by the temperature sensor (10), - in case of impermissible deviations of the detected deformation from a target value, the applied rotational speed of the driven bearing ring (2; 3) is changed by means of the evaluation arrangement (9).

Description

Field of the invention

[0001] The present invention relates to a method for monitoring a preloaded rotary table bearing during operation thereof, comprising an inner bearing ring, an outer bearing ring, at least one row of rolling elements rolling on raceways provided by the bearing rings, a drive arrangement which sets one of the bearing rings in rotation and, with a control and regulating unit, detects and regulates the rotational speed of the bearing ring driven by the drive arrangement. Background of the invention

[0002] Machine tools used for material removal are typically equipped with a rotary table mounted to rotate about a vertical axis, on which a workpiece or the workpiece to be machined is clamped. The rotary table is mounted to rotate relative to the processing machine via a rotary table bearing and coupled to a drive. Known rotary table bearings or rotary table assemblies used to support such rotary tables, for example, which can rotate about a vertical axis, are typically equipped with a multi-row axial-radial bearing. One such arrangement is known from WO 2013 / 034 341 A1, in which one row of cylindrical rollers forms the radial row and two rows of cylindrical rollers form the axial rows of the rotary table bearing. The three cylindrical rollers of this rotary table bearing roll on raceways provided by the two bearing rings.

[0003] Such rotary table bearings are generally preloaded in order to meet the rigidity requirements for use in machine tools by eliminating bearing clearance. This elimination of bearing clearance, which increases the precision of workpieces manufactured on such arrangements, has the disadvantage, however, that in a rotary table bearing, the bearing friction causes the outer bearing ring to heat up more than the inner bearing ring due to the design. This means that in rotary table bearings whose bearing rings are made of the same material, the outer bearing ring expands more than the inner bearing ring and leads to a loss of the radial preload introduced at the assembly temperature of 20°C or room temperature. This loss of radial preload means that the alignment of a rotary table orThe transfer of a workpiece clamped on it to a machining tool becomes inaccurate and the manufacturing quality of the workpieces produced with it deteriorates. This applies not only to conventional applications, i.e., when the rotary table bearing is used for simple milling or turning operations, but especially when rotary table bearings are used in multi-process machines, which expand the range of applications of the preloaded rotary table bearings used by changing the temperature gradient during the various processes.

[0004] To counteract this problem, it was proposed to construct the outer bearing ring from a material with a lower coefficient of thermal expansion than the inner bearing ring. Besides the fact that rotary table bearings made of different materials are very complex, such bearings can only solve the problem within a very narrow temperature range.

[0005] Attempts were also made to measure temperatures in at least one of the bearing rings and use the measured temperatures to draw conclusions about the preload still present in the rotary table bearing. However, such approaches are very inaccurate because, firstly, temperature changes in bearing rings occur very slowly, and, secondly, mere temperature measurements can easily be influenced by external factors that could distort the measurement results, such as very high ambient temperatures.

[0006] An example of a device in which, in particular, a temperature sensor is used as a sensor on a bearing arrangement of a machine tool table is WO 2008 / 025335 A2. This describes a device for monitoring an operating variable using a sensor, which also has a transmitter unit with a receiver and a power supply unit. Active cooling is mentioned as a control variable for actively influencing an operating variable.

[0007] DE 10 2012 001 903 A1 discloses a bearing arrangement for a machine tool spindle, comprising a housing and a spindle for receiving a tool. The spindle is supported in the housing via two bearings. Between these bearings is an adjustment unit, which can be subjected to a preload force. The preload force is determined by a force measuring unit and transmitted to a control module. The adjustment unit is connected to an actuator-sensor unit. The actuator-sensor unit has a module base body with a piezo actuator. By activating the piezo actuator, the control module can trigger an adjustment of the preload between the two bearings. Furthermore, the control module can also trigger a change in the spindle speed.

[0008] DE 27 46 937 A1 discloses a device for measuring forces on a rolling bearing. The outer and / or inner ring of the bearing is equipped with at least two strain gauges arranged at different locations on the bearing. The resistance changes of the respective strain gauges are to be recorded individually. Subtraction is to determine signal values ​​proportional to the external forces acting on the rolling bearing.

[0009] DE 11 2008 001 321 T5 discloses a bearing device comprising a spacer arranged between races of axially arranged rolling bearing units. The bearing device comprises a deformation detector and a deformation-inducing element that deforms under an axial deformation occurring in the spacer. The deformation-inducing element is arranged in an axially aligned region of the spacer.

[0010] JP 2021 - 15 117 A discloses a device for data acquisition to detect anomalies. For this purpose, data is to be collected at a specific sampling rate. This is to be implemented until a predetermined threshold of a defined input variable is exceeded. The data is then to be collected more frequently, and anomalies are to be determined from the rate of change of the input variable. Object of the invention

[0011] Therefore, the object of the invention is to provide a method for monitoring a preloaded rotary table bearing, wherein the respective preload can be determined simply and precisely. Description of the invention

[0012] This object is achieved by a method for monitoring a preloaded rotary table bearing as specified in claim 1. Advantageous embodiments and further developments of the invention can be found in the respective dependent claims.

[0013] The invention is based on a preloaded rotary table bearing which is provided with an inner bearing ring, with an outer bearing ring, with at least one row of rolling elements which roll on raceways provided by the bearing rings, with a drive arrangement which sets one of the bearing rings in rotation, and with a control and regulating unit for detecting and regulating the speed of the bearing ring driven by the drive arrangement. According to the invention, at least one sensor connected to a bearing ring detects elastic deformations of this bearing ring along or across the axis of rotation DA of the rotary table bearing. At least the sensors which detect the deformation of the respective bearing ring are adhesively bonded to the outer surface and / or end surfaces of the respective bearing ring. The detection of the deformation orThe extent of the deformation is of crucial importance for the preloaded rotary table bearing system because, unaffected by other variables, the degree of pre-formation of a bearing ring allows clear statements to be made about the actual preload changes that the operation of the rotary table bearing actually causes. Therefore, the deformation in the respective bearing ring detected by the sensor or sensors is transmitted to the control and regulation unit, which is equipped with an evaluation device. Values ​​are recorded by a temperature sensor and fed to the evaluation device. In the evaluation device, the physical deformations detected are verified based on the values ​​recorded by the temperature sensor. Additional temperature sensors have the advantage that they make it very easy to verify the plausibility of a detected deformation and can rule out the possibility that the determined deformation has purely mechanical causes.The applied speed of the driven bearing ring is changed if the deformation detected in an evaluation system, which is or can be part of the control and regulation system, deviates from a setpoint. The evaluation system, which provides a setpoint range for the respective rotary table bearing, is of crucial importance. If the deformation determined by the sensors is close to the limits of the setpoint range, this is a reliable indication that the preload in the rotary table bearing is almost nonexistent, and a recommended course of action, including a speed change, is required.

[0014] According to an advantageous embodiment of the invention, it can be provided that at least one sensor which detects deformations in the respective bearing ring is a resistance sensor.

[0015] The advantage of this design is that resistance sensors in the form of strain gauges provide a cost-effective and established technology for reliably and accurately detecting tensile deformations.

[0016] According to a further preferred development of the invention, it can also be provided that the sensors of a bearing ring equipped with more than one sensor are mounted symmetrically on this bearing ring with respect to the rotational axis DA of the rotary table bearing. This is very advantageous because the various sensors not only achieve good resolution, but also allow conclusions to be drawn about misalignments of the rotary table bearing by comparing deformation values ​​from different sensors, and these value differences can be used to eliminate them.

[0017] In a likewise preferred embodiment of the invention, it can also be provided that pockets are provided in the bearing rings, and that at least the sensors that detect deformations in a bearing ring are arranged in pockets. Apart from the fact that the sensors are particularly protected from external influences by locating the sensors in pockets, the depth of the pockets allows the distance to the rolling elements to be shortened, which, due to the resulting short distance to the rolling elements, helps to detect deformations in the bearing rings close to the rolling elements. Short description of the drawings

[0018] The invention will be explained in more detail below with the aid of drawings, without limiting the general inventive concept. The drawings are merely schematic in nature and serve solely to facilitate understanding of the invention. They show: Fig. 1 a first embodiment of a rotary table bearing; Fig. 2 a second embodiment of a rotary table bearing; Fig. 3 a third embodiment of a rotary table bearing, Fig. 4 a fourth embodiment of a rotary table bearing; Fig. 5 a top view of a rotary table bearing. Detailed description of the drawings

[0019] The same elements are provided with the same reference numerals. Furthermore, the different features of the various embodiments can be freely combined within the bounds of technical feasibility.

[0020] The Fig. Figure 1 shows a rotary table bearing 1 with an inner bearing ring 2 and an outer bearing ring 3, with rolling elements 4.1, 4.2, 4.3 arranged in three rows, which roll on raceways 5.1, 5.2 - 5.6 provided by the bearing rings 2, 3. Relative to the rotational axis DA of the rotary table bearing 1, the rows of rolling elements 4.1 and 4.3 each form an axial support, while the row of rolling elements 4.2 provides the radial support. As is usual with a preloaded rotary table bearing 1, the outer bearing ring 3 and the inner bearing ring 2 are preloaded relative to one another, i.e., the outer bearing ring 3 is preloaded on the inner bearing ring 2. This preload inevitably also preloads the corresponding axial and radial bearings, so that the resulting elimination of bearing play on rotary tables equipped with preloaded rotary table bearings allows high-precision workpieces to be manufactured, for example by applying mechanical removal processes.

[0021] Furthermore, Fig. 1 schematically shows that the inner bearing ring 2 can be set in rotation by a drive arrangement 6. Consequently, the outer bearing ring 3 forms the stationary bearing ring, which is connected, for example, to a frame of a processing machine (not shown). The respective bearing ring 2 can be rotated by a drive arrangement 6. Fig. 1 only schematically shown drive arrangement 6 desired speed of the inner bearing ring 2 is regulated and monitored by a control and regulating device 7.

[0022] As already explained, due to bearing friction, the outer bearing ring 3 heats up more than the inner bearing ring 2. This is due to the fact that the inner bearing ring 2 has a larger volume than the outer bearing ring 3 and can therefore dissipate the heat generated by bearing friction much more effectively. This difference in heat dissipation results in the outer bearing ring 3 expanding more than the inner bearing ring 2. As a result, the preload present at room temperature, for example, is eliminated with increasing operation of the rotary table bearing 1.

[0023] In order to accommodate these changes in the preload of the rotary table bearing 1, in the embodiment according to Fig. 1, the outer bearing ring 3 is provided with a circumferential pocket 13, which is introduced into one of the end faces 12 of the outer bearing ring 3. In this pocket 13, as Fig. 3 shows, three sensors 8.1 are arranged, each of these sensors 8.1 filling an angular range of slightly less than 120° of the circumferential pocket 13. Each of these sensors 8.1 is designed as a resistance sensor in the form of a strain gauge. If, during operation, the outer bearing ring 3 heats up more than the inner bearing ring 2, the outer bearing ring 3 and with it the circumferential pocket 13 increase in circumference. This increase in circumference inevitably leads to an elongation of the sensor 8.1 or strain gauge, since the sensor 8.1 is firmly connected to the pocket 13 by gluing. As the sensor 8.1 or strain gauge elongates, the electrical resistance of the wires running in the sensor 8.1 increases compared to the non-elongated sensor 8.1 or strain gauge. Consequently, the degree of increase in electrical resistance can be adjusted to a value applied to the sensor 8.1 orThe electrical current applied to the strain gauge can be used as a dimensional standard for circumferential enlargement and as a measure of the decrease in the preload running transversely to the axis of rotation DA of the rotary table bearing. It is irrelevant whether the circumferential enlargement or the increase in diameter in the outer bearing ring 3 is used to assess the preload, because the diameter D is defined as a recess in the direction transverse to the axis of rotation DA and the circumference U of the rotary table bearing 1 or its two bearing rings 2, 3 is determined using the known relationship. U=D*π are in direct relationship.

[0024] In order to determine the extent of the loss of preload in the rotary table bearing, the three sensors 8.1 are connected to an evaluation device 9. This evaluation device 9, which in the present embodiment is part of the control and regulation device 7, compares the resulting increase in circumference or diameter in the outer bearing ring 3 with a stored target value range, which, for the preloaded rotary table bearing used, spans a value range within which a preload can still be expected for the rotary table bearing.If it turns out that, taking into account the increasing circumference or diameter and the preloaded rotary table bearing 1 used, this has lost at least part of its preload, this can lead to the speed of the inner bearing ring 2 of the driving drive arrangement 6 being either reduced or even set to zero entirely by means of the control and regulating unit 7 for subsequent process steps to be carried out on the rotary table, because a speed reduction has the effect of reducing friction and reducing the heat input into the rotary table bearing 1 and at the same time restoring any preload that has been lost or reduced in the meantime.

[0025] Of course, this operating principle can also be reversed. If an increase in circumference or diameter is relatively small or does not reach a preferred target value range, this situation can be exploited to increase the heat input into the rotary table bearing 1 or shift it into the target value range by increasing the speed of the inner bearing ring 2.

[0026] As the embodiment according to Fig. 1 shows, in addition to the three sensors 8.1 ( Fig. 5) A temperature sensor 10 is also arranged in the pocket 13 of the outer bearing ring 3 and, like the sensors 8.1, is electrically connected to the evaluation system 9. This temperature sensor 10 is not used to make statements about the degree of the outer bearing ring 3 based on the measured temperatures, but rather to verify the plausibility of the values ​​recorded by the sensors 8.1.

[0027] The embodiment according to Fig. 2 differs from the embodiment according to Fig. 1 in that the rotary table bearing 1 according to Fig. 2, not the inner but the outer bearing ring 3 is rotated by a drive arrangement 6, which is also only shown schematically here. In order to easily detect the respective degrees of preload loss in the rotary table bearing 1, a pocket 13 is provided in the inner bearing ring 2, which accommodates the sensor(s) 8.2. These sensors 8.2 are also strain gauges in this exemplary embodiment. In contrast to the sensors 8.1 or strain gauges, the resistance wires in the sensors 8.2 or strain gauges run straight in the direction of the axis of rotation DA of the rotary table bearing 1. This means that the resulting resistance value can be used directly, i.e. without extensive conversion, to determine the preload of the rotary table bearing 1.

[0028] For the sake of completeness, it should be noted that in the case of a rotating outer bearing ring 3, the attachment of the sensor to the inner bearing ring 2 is not mandatory. Thus, in the case of a rotating outer bearing ring 3, a sensor can also be installed in this ring according to Fig. 1 may be provided if the contacting of the sensors 8.1, 10 is ensured, for example, via sliding contacts and the associated additional effort.

[0029] The embodiment according to Fig. 3 is based on the embodiment according to Fig. 1 and therefore has a driven inner bearing ring 2 like this. In contrast to the embodiment according to Fig. 1 are in accordance with Fig. 3, the sensors 8.1, 10 are not mounted in elaborately manufactured, countersunk pockets 13 of the outer bearing ring 3, but are attached directly to one of the two end faces 11 of the outer bearing ring 2 by adhesive bonding. With the reference symbol 8.1', which designates a sensor 8.1 corresponding to Fig. 1 or Fig. 3 is the subject of Fig. 3 indicates that in the case of non-interfering attachments and modifications, the radially outer surface 12 of the outer bearing ring 2 can also be provided with sensors 8.1, 13.

[0030] In the embodiment according to Fig. 4 is in accordance with the design according to Fig. 2, the outer bearing ring 3 is driven by a drive arrangement 6. In order to minimize the effort required for contacting the sensors 8.2, 10, the sensors 8.2, 10 are attached directly to the stationary inner bearing ring 3, i.e., without providing pockets 13 for accommodating the sensors 8.2, 10.

[0031] As already mentioned in connection with Fig. 1 and in connection with Fig. 5, three sensors 8.1 are provided on the outer bearing ring 3 to record the loss or change of preload in the rotary table bearing 1. If a rotary table bearing 1 according to the embodiments according to Fig. 2 and Fig. 4 to any sensor 8.1, 10 in the outer bearing ring 3, it is advantageous to provide a plurality of sensors 8.2 on the inner bearing ring 2 and to position them symmetrically on the inner bearing ring 2. Such a positioning of sensors 8.2 on the inner bearing ring 3 is in Fig. 5 is illustrated by the dashed sensors 8.2.

[0032] Due to the equidistant spacing of the sensors 8.1, 8.2 in the circumferential direction of the rotary table bearing 1, statements can also be made about a possible misalignment of the rotary table bearing 1 by comparing the various measured values ​​by comparing the measured values ​​of the various sensors 8.1 or 8.2 and using deviations, for example, as an indication of a misalignment of the corresponding bearing ring.

[0033] The invention is not limited to the embodiments illustrated in the figures. The above description is therefore not to be considered restrictive, but rather explanatory. The following claims are to be understood in such a way that a stated feature is present in at least one embodiment of the invention. This does not exclude the presence of further features. Where the claims and the above description define 'first' and 'second' features, this designation serves to distinguish between two similar features without establishing a priority. List of reference symbols 1 rotary table bearing 2 inner bearing ring 3 outer bearing ring 4. n rolling elements 5. n careers 6 Drive arrangement 7 Control and regulation unit 8. n sensors evaluation arrangement 9 Evaluation arrangement 10 Temperature sensor 11 Shell surface 12 Frontal surface 13 bag DA rotation axis

Claims

[1] Method for monitoring a preloaded rotary table bearing (1) during operation of the rotary table bearing (1) comprising an inner bearing ring (2), an outer bearing ring (3), and at least one row of rolling elements (4.n) rolling on raceways (5.1, 5.2 - 5.6) provided by the bearing rings (2, 3), wherein one of the bearing rings (2) is set in rotation by a drive arrangement (6) and wherein the speed of the bearing ring (2) driven by the drive arrangement (6) is detected and regulated by a control and regulating unit (7), characterized by , that - the elastic deformations of a bearing ring (2; 3) along or across the rotational axis DA of the rotary table bearing (1) are detected by at least one sensor (8.n) connected to the bearing ring (2; 3), - at least the sensors (8.n) which detect the deformation of the respective bearing ring (2; 3) are glued to the outer and / or end surfaces (11; 12) of the respective bearing ring (2; 3), - by means of the at least one sensor (8.n) the detected elastic deformation is transferred to the control and regulation unit (7), which is provided with an evaluation arrangement (9), - values ​​are recorded by a temperature sensor (10) and fed to the evaluation device (9), - in the evaluation device (9) the detected physical deformations are verified on the basis of the values ​​recorded by the temperature sensor (10), - in the event of inadmissible deviations of the detected deformation from a target value, the applied speed of the driven bearing ring (2; 3) is changed by means of the evaluation arrangement (9). [2] Method according to claim 1, characterized by that the speed of the respective driven bearing ring (2; 3) is reduced if the measured physical deformation of the respective bearing ring (2; 3) is greater than a preferred value stored in the evaluation arrangement (9). [3] Method according to claim 2, characterized bythat the speed change also includes zero speed.

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