Method for operating a linear bearing with a position sensor and an acceleration sensor

Abstract

The invention relates to a method for operating a linear bearing, wherein a linear bearing is provided, the linear bearing comprising a guide rail extending along a longitudinal axis, on which a guide carriage is movably mounted in the direction of the longitudinal axis, the guide rail being provided with a scale comprising a plurality of markings distributed along the longitudinal axis and fixedly arranged on the guide rail, a position sensor (31) and a separately designed acceleration sensor (32) being attached to the guide carriage, a digital data output interface (34) being arranged on the guide carriage, the data transmission of which is synchronous with a predetermined output time clock (50), the acceleration sensor (32) indicating the output of a new digital acceleration measurement value (51) by means of an interrupt signal (54),wherein the digital acceleration measurement value (51) is temporarily stored (55), wherein the stored acceleration measurement value (57) is output on the digital data output interface (34) according to the output time clock (50) until the acceleration sensor (32) indicates the presence of a new acceleration measurement value (51) by means of the interrupt signal (54).

Description

[0001] The invention relates to a method for operating a linear bearing with a position sensor and an acceleration sensor.

[0002] From DE 10 2009 033 137 B4, a linear bearing with a guide carriage, which is movably guided along a guide rail along a longitudinal axis, is known. The guide carriage includes an acceleration sensor with which the acceleration along the longitudinal axis can be measured.

[0003] From DE 10 2017 204 871 A1, a linear bearing is known whose guide carriage is equipped with a position sensor. The position sensor scans a scale on the guide rail to measure the position of the guide carriage relative to the guide rail. This position sensor operates absolutely, so that a position measurement can be obtained after the system is switched on without having to move the guide carriage. However, the present invention can also be used for an incrementally operating position sensor, in which the guide carriage must first be moved to a reference position after switching on in order to obtain an absolute position measurement.

[0004] The position measurement can be transmitted digitally to a control device, for which, for example, the DRIVE-CLiQ bus or comparable bus systems can be used. The corresponding digital data transmission occurs synchronously according to a predefined time grid. This time grid is based on a constant, very short cycle time, enabling highly dynamic servo control using the position measurements.

[0005] The datasheet "DMA456 - Digital, triaxial acceleration sensor" from Bosch Sensortec GmbH describes an acceleration sensor capable of measuring accelerations along three mutually orthogonal axes and digitally outputting the corresponding measurement. This is achieved using the SPI or I2C digital buses, which are designed for multiple participants accessing the bus asynchronously. Consequently, the precise timing of the next measurement is not guaranteed. The data receiver is notified of a new measurement via an interrupt signal. The maximum output rate of the measurement data is generally insufficient to output a new measurement at every clock cycle of the DRIVE-CLiQ bus described above.

[0006] From DE 10 2022 120 830 A1, a sensor unit for detecting a distance and a method for operating the sensor unit are known. In particular, a linear displacement sensor is provided.

[0007] From EP 3 851 806 A1, a sensor arrangement and a method for operating the sensor arrangement are known. The sensor arrangement comprises a position measurement system with an optical sensor and an accelerometer.

[0008] According to the invention, a linear bearing is to be equipped with a position sensor and an acceleration sensor, wherein the corresponding measurement data are output jointly and synchronously at a predetermined time interval via a data output interface, the acceleration sensor outputting its acceleration measurements asynchronously. The data output is to be configured such that the second time derivative of the position measurements is essentially identical to the acceleration vector component of the acceleration sensor associated with the longitudinal axis. It should be noted that the acceleration sensor can measure significantly higher-frequency acceleration fluctuations than is possible by the time derivative of the position measurements. This is relevant, for example, in the evaluation of machine vibrations.

[0009] According to the inventive method for operating a linear bearing, a linear bearing is provided, wherein the linear bearing comprises a guide rail extending along a longitudinal axis, on which a guide carriage, preferably by means of a plurality of rolling elements, is movably mounted in the direction of the longitudinal axis, wherein the guide rail is provided with a scale which comprises a plurality of markings which are fixedly arranged along the longitudinal axis, wherein a position sensor and a separately designed acceleration sensor are attached to the guide carriage, wherein a digital data output interface is arranged on the guide carriage, the data transmission of which takes place synchronously to a predetermined output time clock, wherein the acceleration sensor indicates the output of a new digital acceleration measurement value by means of an interrupt signal.wherein the digital acceleration measurement is temporarily stored, wherein the stored acceleration measurement is output on the digital data output interface according to the output time clock until the acceleration sensor indicates the presence of a new acceleration measurement by means of the interrupt signal.

[0010] Preferably, the guide carriage comprises several rows, for example four rows, of rolling elements, which most preferably circulate endlessly within the guide carriage. The position sensor is preferably designed such that the markings influence the corresponding sensor signal in such a way that the position of the guide carriage relative to the guide rail can be determined from said sensor signal. The data output interface is preferably designed for use with a cable.

[0011] The dependent claims specify advantageous further developments and improvements of the invention.

[0012] The acceleration measurement can be a vector comprising several separate vector components, each represented by a numerical value that represents the acceleration with respect to a specific axis. This vector preferably comprises exactly three vector components. The axes are preferably pairwise orthogonal to each other, with one axis most preferably being parallel to the longitudinal axis.

[0013] It can be provided that the position sensor is evaluated so frequently that a new position measurement is output in each individual period of the output clock. For this purpose, it is conceivable, on the one hand, that the evaluation of the position sensor is performed synchronously with the output clock. On the other hand, it is also conceivable that the position sensor is evaluated more frequently than would be required by the output clock. Preferably, it is intended that the corresponding evaluation frequency is an integer multiple of the clock frequency underlying the output clock.

[0014] It can be provided that the position sensor is arranged at such a distance from the guide rail that no frictional forces acting in the direction of the longitudinal axis act between the guide rail and the position sensor. Consequently, the acceleration measurements from the accelerometer contain high-frequency components that can be used for damage detection and which are not included in the second time derivative of the position measurements. It should be noted that the commonly used scales with permanent magnetic markings do not permit such a distance. Only the inductively detectable markings known from EP 1 164 358 B1 allow such a distance. Theoretically, such a distance can also be achieved with optically detectable markings. However, optical systems are susceptible to contamination, which is why they have not proven suitable for linear bearings.

[0015] It may be possible to determine, using the acceleration measurements transmitted via the data output interface, whether the linear bearing has reached the end of its service life. This determination can be carried out, for example, in accordance with EP 3 546 778 B1. The corresponding procedure is easier to implement on a control device because it has significantly more computing power available than the linear bearing itself.

[0016] It may be possible to determine the end of the linear bearing's service life using only the vector components of the acceleration measurement that are directed perpendicular to the longitudinal axis. These acceleration components are caused solely by vibrations of the linear bearing and not by the desired movement of the linear bearing and the associated external forces.

[0017] It may be possible to use the acceleration measurements transmitted via the data output interface to determine whether the guide carriage or a component rigidly connected to it has collided with an obstacle. In the event of a collision, an exceptionally high acceleration occurs along the longitudinal axis, which is easily detected automatically. To prevent damage resulting from the collision, a response to the corresponding acceleration signal must be triggered within a very short time, for example, by de-energizing the relevant electric motor. It is conceivable to implement collision detection using the position measurement. However, the necessary calculation of the second derivative of time causes a time delay that is greater than the delay expected when using the acceleration measurement directly.Currently, collision monitoring is typically implemented by monitoring the current at the electric motor. This results in a much greater time delay than that described in the invention.

[0018] It may be possible to use only the vector component of the acceleration measurement, directed along the longitudinal axis, for the aforementioned collision detection. The highest accelerations occur along the longitudinal axis during a collision, making it particularly easy to detect and allowing for rapid time delays.

[0019] It can be provided that the position sensor and the acceleration sensor are arranged in a common measuring head that is separate from the guide carriage, wherein the measuring head is attached to an end face of the guide carriage pointing in the direction of the longitudinal axis, and wherein the data output interface is located on the measuring head. The measuring head thus forms a single assembly that can be mounted as a whole on the guide carriage and is usable on various types of guide carriages.

[0020] It is possible for the accelerometer to be a MEMS sensor equipped with a temperature sensor, whereby both the acceleration and position measurements are compensated for measurement errors caused by temperature changes using the corresponding temperature reading before being transmitted via the data output interface. This allows the temperature sensor, which is typically already present on a MEMS sensor, to also be used for temperature compensation of the position sensor, thus improving its accuracy.

[0021] It is understood that the features mentioned above and those to be explained below can be used not only in the combinations specified, but also in other combinations or on their own, without leaving the scope of the present invention.

[0022] The invention is explained in more detail below with reference to the accompanying drawings. They show: Fig. 1 a rough schematic representation of a linear bearing according to the invention, which is connected to a control device; and Fig. 2 a signal flow diagram which describes the method according to the invention.

[0023] Fig. Figure 1 shows a schematic representation of a linear bearing 10 according to the invention, which is connected to a control device 60 via a measurement data line 56. The linear bearing 10 comprises a guide rail 20 extending along a longitudinal axis 11. The guide rail 20 can, for example, be designed according to DE 10 2006 003 915 B4. Accordingly, the guide rail 20 comprises a base body made of bearing steel, which extends along the longitudinal axis with a constant cross-sectional shape. The cross-sectional shape forms, for example, four raceways for spherical or cylindrical rolling elements, wherein the base body is hardened at least in the area of ​​the raceways. A separate dimensioning element 21 in the form of a metal strip with a plurality of openings is attached to the base body. At least some of the openings form markings 22, which are arranged distributed along the longitudinal axis 11.At least a part of the markings 22 is preferably arranged uniformly distributed along the longitudinal axis 11, so that incremental position measurement is made possible.

[0024] The markings 22 can be detected by means of a position sensor 31, which is designed, for example, according to EP 1 164 358 B1. The corresponding position sensor 31 comprises at least one transmitting coil which is supplied with an alternating current. The resulting alternating magnetic field induces an electrical voltage in at least one receiver coil of the position sensor, the voltage forming a sensor signal. The markings 22 influence the inductive coupling between the at least one transmitting coil and the at least one receiver coil, such that this coupling depends on the position of the guide carriage 12 relative to the guide rail 20. However, it is also conceivable to use permanent magnetic or optical markings 22, with the position sensor 31 being designed accordingly.

[0025] The position sensor 31 is housed in a separate measuring head 30, which is attached to the front face of the guide carriage 12. A corresponding guide carriage 12 is known, for example, from EP 2 952 761 B1. This guide carriage comprises four rows of spherical rolling elements that circulate endlessly within the guide carriage 12 and roll on the raceways of the guide rail 20, so that the guide carriage 12 is movably guided on the guide rail 20 in the direction of the longitudinal axis 11.

[0026] The measuring head 30 mentioned above can, for example, be designed according to DE 10 2008 022 312 B4. A separate acceleration sensor 32 is integrated into the measuring head 30, which can, for example, be designed according to the datasheet "DMA456 - Digital, triaxial acceleration sensor" from Bosch Sensortec GmbH. This is an acceleration sensor designed as a micromechanical system (MEMS) that outputs its acceleration measurements as digital numerical values, for example via the I2C or SPI bus system. Each acceleration measurement contains three vector components, with the corresponding numerical values ​​of the acceleration each assigned to one axis. These axes are arranged orthogonally to each other in pairs. The acceleration sensor 32 is preferably mounted on the guide carriage 12 such that one of the axes is parallel to the longitudinal axis 11.

[0027] The accelerometer 32 includes a temperature sensor 33. Within the accelerometer 32, the corresponding temperature measurements are used to perform temperature compensation of the acceleration measurements. The aforementioned temperature measurements (No. 53 in Fig. 2) are also output digitally via the aforementioned bus system.

[0028] The measuring head 30 includes a data output interface 34, which can, for example, be implemented according to the DRIVE-CLiQ standard. Reference is made, for example, to the document "DQ100 Application Guide, Version 2.1" of Siemens AG. It is understood that other data output interfaces 34 can also be used. Within the scope of the invention, it is essential that the data output interface 34 is based on a data transmission that occurs synchronously. That is, the measured values ​​are output according to a fixed time grid with a constant cycle time. This time grid can be preset by the user and does not change during operation. The aforementioned time grid does not have to be implemented in a physical sense. It is at least conceivable that the data packets containing the measured values ​​are provided with a timestamp indicating the time at which the measured value is valid. The timestamps are selected according to the time grid.The corresponding data transmission is preferably digital. The aforementioned DRIVE-CLiQ standard is optimized to enable highly dynamic servo control using the transmitted measured values. The time grid is therefore based on a very short cycle time. The acceleration sensor described above is typically not capable of outputting new acceleration measurements at such a rapid pace.

[0029] The measurement data line 56, which leads to the control device 60, is connected to the data output interface 34. The control device 60 can include a module for lifetime determination 61 and / or a module for collision detection 62. The acceleration measurements (No. 51 in) can be recorded in both modules 61 and 62. Fig. 2) of the accelerometer 32 can be used to good effect.

[0030] Fig.Figure 2 shows a signal flow diagram describing the method according to the invention. The accelerometer 32 does not output its measured values ​​according to a fixed, predetermined time interval, but rather according to a time interval that is subject to fluctuations. Therefore, the availability of a new measured value is indicated by an interrupt signal 54. Upon receiving this interrupt, an acceleration measurement 51 and an associated temperature measurement 53 are output via an asynchronous bus system, for example, via an SPI or an I2C bus.

[0031] The temperature measurement 53 can be used to also perform temperature compensation in the position sensor 31, thus improving the accuracy of the determined position measurement 52.

[0032] The data evaluation in the position sensor 31 preferably takes place synchronously with the constant output clock 50 or according to a clock that is an integer multiple of the output clock 50. Accordingly, it would be possible to output the position measurements 52 directly to the data output interface 34. However, it is advantageous to briefly buffer the position measurements 52 in the memory 55 so that the stored acceleration measurement 57 and the stored position measurement 58 are output simultaneously to the data output interface 34 according to the output clock 50.

[0033] In contrast, the memory 55 is required for the acceleration measurements 51 because the acceleration sensor 32 typically outputs new measurements less frequently than required by the output clock 50. The memory 55 operates like an asynchronous FIFO (https: / / en.wikipedia.org / wiki / FIFO_(computing_and_electronics)#Synchronicity). When an interrupt signal 54 is present, a new acceleration measurement 51 is stored. The stored acceleration measurement 57 is output at each clock cycle of the output clock 50. Preferably, the temperature measurement 53 and the stored temperature measurement 58 are handled analogously. Reference sign 10 linear roller bearings 11 Longitudinal axis 12 guide cars 20 guide rail 21. Embodiment of measure 22 Marking 30 measuring head 31 Position sensor 32 Accelerometer 33 Temperature sensor 34 Data output interface 50 output time interval 51 Acceleration measurement 52 Position measurement value 53 Temperature reading 54 Interrupt signal 55 storage 56 Measurement data line 57 stored acceleration measurement values 58 stored position measurement values 60 Control device 61 Determining service life 62 Collision detection

Claims

[1] Method for operating a linear bearing (10), wherein a linear bearing (10) is provided, the linear bearing (10) comprising a guide rail (20) extending along a longitudinal axis (11), on which a guide carriage (12) is movably mounted in the direction of the longitudinal axis (11), preferably by means of a plurality of rolling elements, wherein the guide rail (20) is provided with a dimensioning element (21) comprising a plurality of markings (22) distributed along the longitudinal axis (11) and fixedly arranged on the guide rail (20), wherein a position sensor (31) and a separately designed acceleration sensor (32) are attached to the guide carriage (12), wherein a digital data output interface (34) is arranged on the guide carriage (12), the data transmission of which is synchronous with a predetermined output time clock (50),wherein the accelerometer (32) indicates the output of a new digital acceleration measurement (51) by means of an interrupt signal (54), wherein the digital acceleration measurement (51) is temporarily stored (55), wherein the stored acceleration measurement (57) is output on the digital data output interface (34) according to the output clock (50) until the accelerometer (32) indicates the presence of a new acceleration measurement (51) by means of the interrupt signal (54). [2] Method according to claim 1, wherein the acceleration measurement value (51) is a vector comprising several separate vector components, each of which is formed by a numerical value, each of which represents the acceleration with respect to an associated axis. [3] Method according to one of the preceding claims, wherein the position sensor (31) is evaluated so frequently that a new position measurement value (52) is output in each individual period of the output time act (50). [4] Method according to one of the preceding claims, wherein the position sensor (31) is arranged at a distance from the guide rail (20) such that no frictional forces directed in the direction of the longitudinal axis (11) act between the guide rail (20) and the position sensor (31). [5] Method according to one of the preceding claims, wherein using the acceleration measurement values ​​(51) transmitted via the data output interface (34) it is determined whether the linear bearing (10) has reached the end of its service life. [6] Method according to claim 5, insofar as it refers back to claim 2, wherein for the said determination of the end of the service life of the linear bearing (10) only the vector components of the acceleration measurement value (51) are used which are directed transversely to the longitudinal axis (11). [7] Method according to one of the preceding claims, wherein using the acceleration measurement values ​​(51) transmitted via the data output interface (34) it is determined whether the guide carriage (12) or a component rigidly connected thereto has collided with an obstacle. [8] Method according to claim 7, insofar as it refers back to claim 2, wherein for the said determination of a collision only the vector component of the acceleration measurement value (51) is used which is directed in the direction of the longitudinal axis (11). [9] Method according to one of the preceding claims, wherein the position sensor (31) and the acceleration sensor (32) are arranged in a common measuring head (30) which is formed separately from the guide carriage (12), wherein the measuring head (30) is attached to an end face of the guide carriage (12) pointing in the direction of the longitudinal axis (11), wherein the data output interface (34) is arranged on the measuring head (30). [10] Method according to one of the preceding claims wherein the acceleration sensor (32) is a MEMS sensor equipped with a temperature sensor (33), wherein the corresponding temperature measurement (53) is used to compensate both the acceleration measurement (51) and the position measurement with respect to measurement errors caused by temperature changes before they are transmitted via the data output interface (34).

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