Position measuring device and method for operating a position measuring device

Abstract

The present invention relates to a position measuring device and a method for operating a position measuring device. The position measuring device has: • a graduation carrier on which a measuring graduation is arranged, • at least one position sensor by means of which a position-related measuring signal can be generated by scanning the measuring graduation, • a processing unit by means of which the position-related measuring signal can be processed into a position signal, and • an interface unit for communicating with a slave electronics via at least one data transmission channel, wherein the position measuring device includes a monitoring unit to which at least one operating condition of the position measuring device can be supplied, and the monitoring unit includes an evaluation unit which determines the component failure rate of at least one component to be monitored based on at least one operating condition, and thereby determines the current operating failure rate of the position measuring device. The present invention further relates to a method for operating such a position measuring device.

Description

Field of the Invention

[0001] The present invention relates to a position measuring device and a method for operating a position measuring device. Background Art

[0002] Position measuring devices are employed in machines and facilities of automation technology, for example in machine tools or production robots. The position measuring device is used to measure the position or position change of a movable part. Thus, a rotary encoder or an angle measuring device measures a rotational movement, for example the rotational movement of a rotating shaft. And a length measuring device measures the linear movement of machine parts that are movably arranged relative to each other.

[0003] Machines and facilities require a high degree of reliability from them. Reliability means on the one hand malfunction-free operation (availability), and on the other hand functional safety, that is, the ability to reliably identify occurring functional disorders.

[0004] EP 2273238 A2 describes a possibility of determining the remaining service life of a position measuring device. For this purpose, for the determination of the remaining service life, operating variables that influence the service life are included in a weighted manner. However, for this a large database that is often unavailable is required. The reason for this is precisely the high quality of the measuring device, because only a small number of failed devices can be examined thereby. Often the exact circumstances that have led to the failure are also unknown or can no longer be determined, which further complicates the analysis of the cause of the failure. In addition, measuring devices are often replaced before they fail (preventive maintenance).

[0005] Measures for increasing functional safety are used to identify occurring malfunctioning of the measuring device, such that dangerous situations caused by defects of the measuring device are avoided as far as possible. In other words, occurring defects must neither allow the operating personnel staying in the danger zone of the machine or facility to be put in danger, nor allow material losses to occur.

[0006] The residual probability (that is, despite all provided fault detection measures there are still undetected defects) is described by the so-called PFH value ("Probability of a dangerous undetected Failure per Hour"). In a position measuring device, the PFH value is usually determined by the manufacturer with the aid of a system FMEDA. Here, it is based on the application conditions of typical application profiles of this device. As long as the position measuring device operates within the scope of these application conditions, the PFH value is guaranteed. Possible deviations in the actual use of the position measuring device from these application conditions are not considered. SUMMARY OF THE INVENTION

[0007] It is an object of the present invention to provide a position measuring device having improved data on the failure probability.

[0008] This object is achieved by a position measuring device disclosed in the present application.

[0009] A position measuring device is proposed, which has:

[0010] · A division carrier on which a measurement division is arranged,

[0011] · At least one position sensor by which, by scanning the measurement division, a position-related measurement signal can be generated,

[0012] · A processing unit by which the position-related measurement signal can be processed into a position signal, and

[0013] · An interface unit for communicating via at least one data transmission channel with a following electronics, wherein the position measuring device includes a monitoring unit to which at least one operating condition of the position measuring device can be supplied, and the monitoring unit includes an evaluation unit which determines the component failure rate of at least one component to be monitored based on at least one operating condition and thereby determines the current operating failure rate of the position measuring device.

[0014] Furthermore, it is an object of the present invention to describe a method which enables improved data on the failure probability of a position measuring device.

[0015] This object is achieved by a method for operating a position measuring device disclosed in the present application.

[0016] For this purpose, a method for operating a position measuring device is proposed, which position measuring device includes:

[0017] · A division carrier on which a measurement division is arranged,

[0018] · At least one position sensor by which, by scanning the measurement division, a position-related measurement signal is generated,

[0019] · A processing unit by which the position-related measurement signal is processed into a position signal, and

[0020] · An interface unit for communicating via at least one data transmission channel with a following electronics,

[0021] The position measuring device further includes a monitoring unit to which at least one operating condition of the position measuring device is fed, and the monitoring unit includes an evaluation unit which determines the component failure rate of at least one component to be monitored based on at least one operating condition, and thereby determines the current operating failure rate of the position measuring device. Description of the Drawings

[0022] Other advantageous features of the invention result from the disclosure of the present application and from the description of advantageous embodiments based on the drawings.

[0023] Wherein:

[0024] Figure 1 A block diagram of a position measuring device according to the invention is shown,

[0025] Figure 2 A block diagram of a further embodiment of a position measuring device according to the invention is shown,

[0026] Figure 3 A block diagram of a further embodiment of a position measuring device according to the invention is shown, and

[0027] Figure 4 A block diagram of a further embodiment of a position measuring device according to the invention is shown. Detailed Description of the Invention

[0028] Figure 1 A block diagram of a position measuring device 10 according to the invention is shown. For measuring, processing and outputting position-related signals, the position measuring device 10 includes a graduation carrier 12 with a measuring graduation 14, at least one position sensor 20, a processing unit 30 and an interface unit 40.

[0029] The position sensor 20 is configured appropriately to scan the measuring graduation 14 on the graduation carrier 12. The graduation carrier 12 and the position sensor 20 are arranged in a known manner so as to be movable relative to each other in the measuring direction, for example in such a way that they are connected to movable parts of a machine tool, the relative position of which relative to each other is to be determined. The position sensor 20 and the measuring graduation 14 are configured according to the physical scanning principle used, which is employed in position measurement.

[0030] Whether the position measuring device is a length measuring device or (as in Figure 1The angle measuring device (rotary encoder) shown in [figures] is not critical for the present application. Thus, the indexing carrier 12 can be a straightedge with measuring graduations 14 arranged in the scale direction for measuring linear motion, or it can be a circular disk with measuring graduations 14 arranged radially around the disk rotation center D for measuring rotational motion (e.g., of a shaft).

[0031] A position-dependent position signal PS is generated by scanning the measuring graduations 14, and the position signal PS is fed to the processing unit 30. The position signal PS can include analog or digitally encoded signals. The processing unit 30 processes the position signal PS into a digital position value P and outputs the digital position value P to the interface unit 40. The processing, such as signal correction, digitization, etc., can be completed without further discussion in the present invention. In addition to the position value P, other position-dependent variables, such as speed, acceleration, or jerk (Ruck), can also be determined in the processing unit 30 if necessary.

[0032] The interface unit 40 is used to transmit data (e.g., the position value P) via the data transmission channel 45 to the slave electronics 100. In addition, it can be arranged that the slave electronics 100 transmit instructions and data to the interface unit 40, enabling communication between the slave electronics 100 and the interface unit 40 (and thus the position measuring device 10). Thus, the slave electronics 100 can request data (e.g., the current position value P) of the position measuring device 10 by means of a data request instruction. For data transmission between the slave electronics 100 and the position measuring device 10, a serial interface is preferably used.

[0033] In the position measuring device 10, at least one integrated circuit (IC) is provided. In this embodiment, the integrated circuit 50 includes the circuits of the processing unit 30 and the interface unit 40. The integrated circuit 50 can be an application-specific integrated circuit (ASIC) or a programmable integrated circuit (e.g., FPGA). As shown by the dashed line, the integrated circuit 50 can also include the position sensor 20 in addition. This is particularly advantageous in the case of the optical scanning principle, since in the present invention the position sensor includes a photodetector, which can be manufactured on a semiconductor chip using known manufacturing methods. Integrated circuits that include not only optical components but also analog and digital circuit parts are also known under the name "Opto-ASIC".

[0034] Each functional component of the position measuring device 10 has a component failure rate, which describes the failure probability of the component. The component failure rate is usually specified in FIT (Failure In Time (failures per unit time)), where: 1 FIT = 1 x 10 -9 / h. The component failure rate is a variable quantity that varies according to critical operating conditions. Critical operating conditions are those operating conditions that have a significant impact on the component failure rate. In this example, the integrated circuit 50 is assigned a component failure rate AR_K1.

[0035] According to the present invention, the position measuring device 10 includes a monitoring unit 60. The monitoring unit 60 is suitably constructed to determine at least one component failure rate (determine the failure rate of system components to be monitored according to at least one operating condition) according to the operating conditions of the position measuring device 10 and to determine therefrom the operating failure rate AR_B of the position measuring device 10. In this example, the component failure rate AR_K1 of the integrated circuit 50 is observed.

[0036] The monitoring unit 60 can be a separate integrated circuit, for example a microcontroller, a programmable component (FPGA) or an application-specific integrated circuit (ASIC). However, the monitoring unit 60 can also (as depicted by the dotted line) be integrated as a circuit module in the integrated circuit 50, such that an integrated circuit 50' is formed.

[0037] The operating conditions that have an impact on the component failure rate and thus on the operating failure rate AR_B can be divided into external operating conditions and internal operating conditions. The external operating conditions are detected or ascertained outside the position measuring device 10 and can be conveyed to the monitoring unit 60 via the interface unit 40, for example by the slave electronics 100.

[0038] An example of an external operating condition is time information. Based on the time information including the date and optionally the clock, the age of the position measuring device 10 can be determined, and therefrom the age-induced share of the operating failure rate AR_B can be determined. This share can have a slightly higher value at the start of the service life of the position measuring device 10, which then decreases to a low level and only increases again towards the end of the service life (bathtub curve).

[0039] Another example of an external operating condition is the operating altitude above sea level. This operating altitude affects the so-called "soft-error-rate" of the integrated circuit, because cosmic radiation increases with increasing altitude. This means that the position measuring device 10 is exposed to high-energy particle radiation, which in particular increases the component failure rate AR_K1 of the integrated circuit 50, which in turn has an adverse effect on the operating failure rate AR_B. If the position measuring device 10 operates in the environment of a machine (for example in a medical radiation device), a similar effect can occur, in which there is high-energy ionizing radiation.

[0040] The internal operating conditions are the operating conditions detected by the position measuring device 10 itself. The following operating conditions are considered as internal operating conditions: The operating conditions act directly on the components of the position measuring device 10 and are thus advantageously determined at the location where they occur (or appear). For the detection, sensors can be arranged within the housing of the position measuring device 10. An example of an internal operating condition is temperature. Temperature has a particularly large influence on the failure rate of integrated circuits.

[0041] In the first embodiment, a temperature sensor 70 is provided in the position measuring device 10. The temperature sensor 70 is arranged together with the integrated circuit 50 within the housing of the position measuring device 10, for example, on a printed circuit board. With the temperature sensor 70, the ambient temperature Ta of the components (especially the integrated circuit 50) arranged in the position measuring device 10 can thus be measured.

[0042] In addition to the temperature sensor 70, other sensors 72, 74 can be provided for determining other internal operating conditions. For example, the other sensors 72, 74 can include acceleration sensors, vibration sensors, structure-borne sound sensors, humidity sensors, current sensors, voltage sensors, and time sensors (operating hour meters). The position sensor 20 (optionally in combination with the processing unit 30) can also be considered as a sensor for determining internal operating conditions, since the position or position changes (speed, acceleration) can also have an impact on the operating failure rate AR_B. The measured values of the other sensors 72, 74 are also fed to the evaluation unit 62 and can be considered for determining the component failure rate AR_K1 of the components and thus for determining the operating failure rate AR_B.

[0043] To connect the sensors 20, 70, 72, 74 to the monitoring unit 60, suitable interfaces are provided. Depending on whether analog sensors or digital sensors are involved, an A / D converter or a digital data interface can be used to feed digital measured values of the operating conditions to be detected to the evaluation unit 62 for further processing.

[0044] In practice, the operating failure rate AR_B is mostly determined by the component failure rates of a few components of the position measuring device 10. This is the case on the one hand if the components have a relatively high component failure rate and thus make a significant contribution to the operating failure rate AR_B, and on the other hand if the component failure rates of the components have a high fluctuation under the influence of changing operating conditions. Such components are referred to below as components to be monitored. When determining the operating failure rate AR_B, components with a relatively low component failure rate and / or components whose component failure rates are as constant as possible when the operating conditions change can be ignored if necessary, or the contribution of these parts to the operating failure rate AR_B can be assumed to be constant.

[0045] In this embodiment, the integrated circuit 50 is the component to be monitored. The integrated circuit 50 has a component failure rate AR_K1.

[0046] Determining the operating failure rate AR_B in the evaluation unit 62 requires the following steps:

[0047] · Determine critical operating conditions

[0048] · Determine the component failure rate AR_K1 of at least one component to be monitored

[0049] · Based on the component failure rate AR_Kn, determine the operating failure rate AR_B of the position measuring device 10

[0050] The operating condition to be observed in this example is the barrier layer temperature of the semiconductor chip of the integrated circuit 50.

[0051] The starting point for determining the component failure rate AR_K1 is the reference failure rate AR_R1 of the integrated circuit 50. The reference failure rate AR_R1 of the integrated circuit 50 is determined by wafer technology (structural width, manufacturing process, etc.) and reference conditions (in this case, the reference temperature of the barrier layer of the semiconductor chip). The reference failure rate AR_R1 is manufacturer data of the integrated circuit 50. Since this manufacturer data is as independent as possible from the internal circuit of the integrated circuit 50 and is therefore applicable to all integrated circuits manufactured using the same wafer technology, a secure database is based on this reference failure rate AR_R1. Analysis of the cause of failure of the failed device is therefore no longer necessary. The reference failure rate AR_R1 is stored in the storage unit 64, and the storage unit 64 is arranged in the monitoring unit 60. The deviation from the reference temperature causes a change in the component failure rate AR_K1 of the integrated circuit 50, and this change is determined by the Arrhenius law. In the case of a known power consumption of the integrated component 50, the barrier layer temperature of the semiconductor chip of the integrated circuit 50 can be determined based on the ambient temperature Ta and the thermal resistance of the housing of the integrated circuit 50, and the ambient temperature Ta can be measured using the temperature sensor 70.

[0052] The ambient temperature Ta is fed to an evaluation unit 62, which is arranged in the monitoring unit 60. The evaluation unit 62 determines the component failure rate AR_K1 of the integrated circuit 50 based on the ambient temperature Ta and thereby determines the operating failure rate AR_B of the position measuring device 10. For this purpose, a table with the component failure rate AR_K1 of the integrated circuit 50 related to the ambient temperature Ta can be stored in the storage unit 64. Alternatively, the component failure rate AR_K1 of the integrated circuit 50 can also be determined by calculation. For this purpose, the Arrhenius law can be applied in the case of this temperature, and suitable alternative calculation rules can be used to determine the influence of other operating conditions.

[0053] As already mentioned above, external operating conditions can also flow into the determination of the operating failure rate AR_B. In Figure 1 the example, the operating altitude HM is fed to the position measuring device 10 by the slave electronics 100, which indicates the altitude above sea level at which the position measuring device 10 operates. The operating altitude HM is forwarded by the interface unit 40 to the monitoring unit 60. In the monitoring unit 60, the evaluation unit 62 determines (again, for example, from a table in the storage unit 64) the soft error rate SER resulting from the operating altitude HM. The soft error rate SER can also be stated in FIT and is included in the determination of the component failure rate AR_K1.

[0054] Based on the component failure rate AR_K1 (and, if necessary, other component failure rates), the evaluation unit 62 can then determine the operating failure rate AR_B of the position measuring device 10. In the simplest case, the individual component failure rates can be added. In particular, when it comes to the component failure rates of electronic devices, the operating failure rate AR_B can be determined by Markov analysis (Markow-Analyse).

[0055] The operating altitude HM may already have been transmitted to the position measuring device 10 by the manufacturer and stored there. This is particularly meaningful if the location of use and thus the operating altitude HM were already known when ordering the position measuring device 10. Here, it is advantageous for the value of the operating altitude HM to be stored in a write-protected manner so that only authorized professionals can change this value.

[0056] Advantageously, the value of the operating altitude HM is readable (ruecklesbar), that is, this value can be transmitted to the slave electronics 100 via the interface unit 40. In this way, the correctness of this value can be checked in the slave electronics 100.

[0057] In addition to the operating altitude HM, other external operating conditions can be fed to the position measuring device 10 and taken into account when determining the operating failure rate AR_B, such as time information T (date and, if necessary, clock).

[0058] The operating failure rate AR_B of the position measuring device 10 can be used by the applicant to determine the overall failure rate of a machine or installation in which the position measuring device 10 is integrated. Based on the overall failure rate, the availability of the machine or installation can be evaluated. Furthermore, based on the operating failure rate AR_B in combination with the results of FMEDA (or a similar method for analyzing operating safety), the so-called PFH value of the position measuring device 10 can be determined, which reflects the functional safety of the position measuring device 10. From this, a measure for the functional safety of the entire machine or installation can be derived.

[0059] The operating failure rate AR_B can be determined continuously or can be started by a corresponding instruction of the slave electronics 100. The result is then transmitted via the interface unit 40 and the data transmission channel 45 to the slave electronics 100.

[0060] To make it easier for the operator of a machine or installation in which the position measuring device 10 is integrated to analyze the failure rate of said machine or installation, it is advantageous to provide start and stop instructions from the side of the slave electronics 100, which start or stop the continuous determination of the operating failure rate AR_B, and the evaluation unit 62 is suitably configured to determine the maximum operating failure rate AR_B in the time interval determined by the start and stop instructions. In this way, it can be checked whether the machine or installation reaches the necessary measures for availability and functional safety at any time during the operating cycle to be monitored. When the overall failure rate exceeds or falls below a pre-given value, corresponding measures can then be taken to optimize the operation of the machine or installation with respect to operating speed and functional safety.

[0061] Figure 2 Another embodiment of the position measuring device 10 according to the invention is shown. Components that have already been described in connection with the previous embodiments have the same reference numerals. This example shows an improved possibility of determining the temperature of the barrier layer of a semiconductor chip of an integrated circuit 50. Since this temperature has an essential influence on the component failure rate AR_K1, this temperature can be determined more precisely thereby.

[0062] In this embodiment, in addition to the ambient temperature Ta determined by the temperature sensor 70, the current power consumption of the integrated circuit 50 is also taken into account. Together with the known thermal resistance of the housing of the integrated circuit 50, the exact change in the barrier layer temperature of the semiconductor chip can then be calculated. In combination with the ambient temperature Ta, the current barrier layer temperature of the integrated circuit 50 can then be calculated.

[0063] To determine the power consumption of the integrated circuit 50, a current sensor (implemented, for example, as a measuring resistor R1) is now provided. The measuring resistor R1 is connected between the ground potential GND of the current supply of the position measuring device 10 and the ground terminal of the integrated circuit 50 in this example. The voltage drop across the measuring resistor R1 is fed as a sensor value to the evaluation unit 62 again. Based on the voltage drop and the value of the measuring resistor R1, the operating current I1 of the integrated circuit 50 can now be calculated in the evaluation unit 62. The current power consumption of the integrated circuit 50 is obtained from the operating current I1 of the integrated circuit 50 and the known supply voltage VDD. The temperature increase of the semiconductor chip is finally calculated using the current power consumption in combination with the thermal resistance of the housing. By adding the ambient temperature Ta, the current barrier layer temperature of the semiconductor chip is then obtained. In other configurations of this method, the fluctuations in the supply voltage VDD can also be included in the calculation by measuring the current value of the supply voltage in the evaluation unit 62. For this purpose, the measuring line between the supply voltage VDD and the A / D converter can be provided in the evaluation unit 62 (not shown). This measuring line can be regarded as a voltage sensor in the sense of the present invention.

[0064] The evaluation unit 62 determines the component failure rate AR_K1 of the integrated component 50 from the current barrier layer temperature of the semiconductor chip of the integrated component 50 (again by calculation or from a table), and thereby determines the operating failure rate AR_B of the position measuring device 10.

[0065] The monitoring unit 60 itself also has a component failure rate AR_K2, which may affect the operating failure rate AR_B of the position measuring device 10. Therefore, the monitoring unit 60 itself can be a component to be monitored. In particular, when the monitoring unit 60 is implemented as an integrated component, the component failure rate AR_K2 can be determined analogously to the component failure rate AR_K1 of the integrated component 50, that is, based on the ambient temperature Ta and, if necessary, based on the operating current I2 (which can be determined by means of the current sensor R2) and the supply voltage VDD. The monitoring unit 60 is therefore advantageously configured to determine its own component failure rate AR_K2 according to the critical operating conditions (in this embodiment form, the ambient temperature Ta and, if necessary, the operating current I2 in combination with the supply voltage VDD), and to include this component failure rate AR_K2 in the determination of the operating failure rate AR_B of the position measuring device 10.

[0066] In summary, this means that firstly the ambient temperature Ta, the operating current I1 of the integrated module 50 and, if applicable, the supply voltage VDD of the integrated module 50 are determined as relevant operating conditions. Subsequently, the current component failure rate AR_K1 of the integrated module 50 is determined.

[0067] If the monitoring unit 60 is also taken into account, the operating current I2 and, if applicable, the supply voltage VDD of the monitoring unit 60 are additionally measured and the component failure rate AR_K2 is determined.

[0068] From the component failure rates AR_K1 and AR_K2, the current operating failure rate AR_B is finally determined.

[0069] Figure 3 A further exemplary embodiment of a position measuring device 10 according to the invention is shown. Components which have already been described in connection with the previous exemplary embodiments have the same reference numerals. This example shows an alternative possibility of determining the barrier temperature of a semiconductor chip of an integrated circuit 50 .

[0070] In the present invention, an on-chip temperature sensor 78 is now integrated on the semiconductor chip of the integrated circuit 50. In this way, the barrier temperature of the semiconductor chip can be measured directly, which is therefore more accurate than an indirect determination via a bypass measurement of the ambient temperature, the operating current and the supply voltage. In addition, the measurement becomes independent of the actual mechanical structure, in particular the embodiment of the housing of the integrated circuit 50 (material, size, etc.).

[0071] The measurement signal of the on-chip temperature sensor 78 is supplied to the evaluation unit 62 in the monitoring unit 60 in order to determine the component failure rate AR_K1.

[0072] In this exemplary embodiment, other operating conditions can naturally also be detected or included in the determination of the component failure rate AR_K1 .

[0073] Figure 4 The block diagram shows a further embodiment of a position measuring device 10 according to the present invention. The functional blocks which have already been described in connection with the previous exemplary embodiments also have the same reference numerals in the present invention.

[0074] During the period in the previous embodiment where the functional safety of the position measuring device 10 was only evaluated in the slave electronic device 100, the monitoring unit 60 is now trained to determine a measure in the form of a safety-specific failure rate AR_S of the position measuring device 10. For this purpose, safety data SD of the position measuring device 10 is stored in the storage unit 64. The safety data SD is detected by the manufacturer in the context of FMEDA (or a similar method for checking the functional safety of a device). These safety data include not only information on measures for improving the functional safety of individual components (such as the integrated circuit 50), but also information on measures for improving functional safety through the interaction of different components. For example, the latter involves monitoring functions for internal signals (such as clock pulse signals) and generating redundancy through parallel signal and measurement paths.

[0075] The safety-specific failure rate AR_S determined from the operating failure rate AR_B corresponds to the PFH value known from safety technology for the position measuring device 10 and is also stated in FIT (Failure In Time) units, where: 1 FIT = 1 x 10 -9 / h, which in this case means that a dangerous undetected failure can occur every billion hours. This safety-specific failure rate AR_S is also transmissible via the interface unit 40 to the slave electronic device 100. In addition to availability, this enables the operator of the machine or facility in which the position measuring device 10 is operating to easily determine the current measure of functional safety for the operating situation without the need for other information about the position measuring device 10 in this regard.

[0076] It goes without saying that, depending on Figure 1 and Figure 2 the described embodiment, the determination of the safety-specific failure rate AR_S can also be extended.

[0077] The invention is not limited to the described embodiments. Rather, those skilled in the art can develop alternative embodiments without departing from the scope of protection defined by the claims.

Claims

1. A position measuring device, comprising: · A dividing carrier (12) on which a measuring graduation (14) is arranged, · At least one position sensor (20) by means of which a position-related measurement signal (PS) can be generated by scanning the measuring graduation (14), · A processing unit (30) by means of which the position-related measurement signal (PS) can be processed into a position signal (P), and · An interface unit (40) for communicating with a slave electronic device (100) via at least one data transmission channel (45), wherein the position measuring device (10) includes a monitoring unit (60) to which at least one operating condition (Ta, I1, I2, VDD, HM) of the position measuring device can be fed, and the monitoring unit (60) includes an evaluation unit (62) which determines the component failure rate of at least one component to be monitored based on the at least one operating condition (Ta, I1, I2, VDD, HM), and thereby determines the current operating failure rate of the position measuring device.

2. The position measuring device according to claim 1, wherein safety data (SD) can be stored in a storage unit (64) of the monitoring unit (60), and in the evaluation unit (62), a safety-specific failure rate (AR_S) can be determined from the operating failure rate (AR_B) by means of the safety data (SD), and the safety-specific failure rate (AR_S) is a measure of the functional safety of the position measuring device (10).

3. The position measuring device according to claim 1, wherein the position measuring device includes at least one sensor (70, 72, 74, 78, R1, R2), and the measured values of the sensor (70, 72, 74, 78, R1, R2) can be fed to the monitoring unit (60) as operating conditions, and / or at least one operating condition can be fed to the monitoring unit (60) by the slave electronic device (100) via the interface unit (40).

4. The position measuring device according to any one of claims 1-3 above, wherein at least one component to be monitored is an integrated component.

5. The position measuring device according to claim 4, wherein in the evaluation unit (62), the component failure rate (AR_K1) of the integrated component (50, 60) can be determined based on the blocking layer temperature of the semiconductor chip, and the blocking layer temperature can be measured by means of an on-chip temperature sensor (78) integrated on the semiconductor chip.

6. The position measuring device according to claim 4, wherein In the evaluation unit (62), the component failure rate (AR_K1) of the integrated component (50, 60) can be determined based on the barrier layer temperature of the semiconductor chip. The barrier layer temperature is determined by the ambient temperature (Ta), the power consumption of the integrated component (50, 60), and the thermal resistance of the housing of the integrated component (50, 60). The ambient temperature (Ta) can be measured by means of a temperature sensor (70), and the power consumption can be calculated from the supply voltage (VDD) and the operating current (I1) of the integrated component (50, 60). And in order to measure the operating current (I1), a current sensor (R1) is provided.

7. The position measuring device according to claim 6, wherein, the supply voltage (VDD) of the integrated component (50, 60) can also be measured by the evaluation unit (62).

8. A method for operating a position measuring device, the position measuring device comprising: · An indexing carrier (12) on which a measuring index (14) is arranged, · At least one position sensor (20) by means of which a position-related measurement signal (PS) is generated by scanning the measuring index (14), · A processing unit (30) by means of which the position-related measurement signal (PS) is processed into a position signal (P), and · An interface unit (40) for communicating with a slave electronic device (100) via at least one data transmission channel (45), wherein the position measuring device (10) comprises a monitoring unit (60) to which at least one operating condition (Ta, I1, I2, VDD, HM) of the position measuring device is fed, and the monitoring unit (60) comprises an evaluation unit (62) which determines the component failure rate of at least one component to be monitored based on the at least one operating condition (Ta, I1, I2, VDD, HM), and thereby determines the current operating failure rate of the position measuring device.

9. The method according to claim 8, wherein, safety data (SD) is stored in the storage unit (64) of the monitoring unit (60), and in the evaluation unit (62), by means of the safety data (SD), a safety-specific failure rate (AR_S) is determined from the operating failure rate (AR_B), and the safety-specific failure rate (AR_S) is a measure of the functional safety of the position measuring device (10).

10. The method according to claim 8, wherein, The position measuring device includes at least one sensor (70, 72, 74, 78, R1, R2), and the measured values of the sensors (70, 72, 74, 78, R1, R2) are fed to the monitoring unit (60) as operating conditions, and / or at least one operating condition is fed to the monitoring unit (60) by the servo electronics (100) via the interface unit (40).

11. The method according to any one of claims 8 to 10, wherein, at least one component to be monitored is an integrated component (50, 60), and in the evaluation unit (62), the component failure rate (AR_K1) of the integrated component (50, 60) is determined based on the barrier layer temperature of the semiconductor chip, the barrier layer temperature is measured by means of an on-chip temperature sensor (78), and the on-chip temperature sensor (78) is integrated on the semiconductor chip.

12. The method according to any one of claims 8 to 10, wherein, at least one component to be monitored is an integrated component (50, 60), and in the evaluation unit (62), the component failure rate (AR_K1) of the integrated component (50, 60) is determined based on the barrier layer temperature of the semiconductor chip, the barrier layer temperature is determined by the ambient temperature (Ta), the power consumption of the integrated component (50, 60), and the thermal resistance of the housing of the integrated component (50, 60), and the ambient temperature (Ta) is measured by means of a temperature sensor (70), and the power consumption is calculated from the supply voltage (VDD) and the operating current (I1) of the integrated component (50, 60), and the operating current (I1) is measured by means of a current sensor (R1).

13. The method according to claim 12, wherein, the supply voltage (VDD) of the integrated component (50, 60) is also measured by the evaluation unit (62).

14. The method according to any one of claims 8 to 10, wherein, the continuous determination of the operating failure rate (AR_B) is started or stopped by the servo electronics by start and stop commands.

15. The method according to claim 14, wherein, the evaluation unit (62) determines the maximum operating failure rate in the time interval determined by the start command and the stop command.

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