METHOD AND DEVICE FOR MONITORING THE TRACK SIGNALS OF A POSITION CHANGE SENSOR

Abstract

In a method and device for monitoring the track signals of a position change sensor, a resource-optimized diagnosis of errors of track signals of a position change sensor is performed.

Claims

1-12. (canceled)

13. A method for monitoring track signals of a position change sensor, comprising: cyclically sampling the track signals of the position change sensor using a chronological sequence; and evaluating sampling values obtained in the sampling step; wherein the sequence includes time periods, each time period including more than four sampling times set apart temporally from each other at regular intervals, and each time period corresponding to a respective temporal spacing.

14. The method according to claim 13, wherein the method is performed with the aid of an encoder signal diagnostic device.

15. The method according to claim 13, wherein the sequence includes a succession of sampling times.

16. The method according to claim 13, wherein each time period is uniquely corresponds to a respective spacing.

17. The method according to claim 13, wherein the temporal spacing corresponding to a first one of the time periods is less than the temporal spacing corresponding to a second one of the time periods occurring later within the sequence.

18. The method according to claim 17, wherein the temporal spacing corresponding to a time period of the sequence directly following a preceding time period of the sequence is twice as large as the temporal spacing correspinding to the preceding time period.

19. The method according to claim 13, wherein the spacing corresponding to a temporally-first time period of the sequence corresponds to a fifth of a period length of a maximum permissible frequency of output signals of the position change sensor or less, and/or the spacing corresponding to a temporally-last time period of the sequence corresponds to a fifth of a period length of a limiting signal frequency or less.

20. The method according to claim 13, further comprising further evaluating the track signals based on digital signal parameters and combining the result of the evaluating and the further evaluating to completely diagnose for errors the track signals up to a maximum signal frequency.

21. The method according to claim 20, wherein the digital signal parameters include trailing and/or leading switching edges.

22. The method according to claim 13, wherein the sequence is generated in advance and/or during production or initial operation, and are stored in a lookup table unit.

23. A device for diagnosing errors of track signals of a position change sensor and/or of an incremental encoder, comprising: a first evaluation unit; a further evaluation unit; and a logic operations unit; wherein the first evaluation unit is adapted to evaluate the track signals based on digital signal parameters; wherein the first evaluation unit is adapted to compute, and to make available at a first output of the first evaluation unit, a status information item, a speed information item, a position information item, a direction of movement information item, an acceleration information item, and/or a feedback information item from the digital signal parameters; wherein the first evaluation unit is adapted to generate an error signal at a further output of the first evaluation unit in response to detection of an error condition of the digital signal parameters; wherein the further evaluation unit is adapted to evaluate the track signals based on analog signal parameters; wherein the further evaluation unit is adapted to generate an error signal at an output of the further evaluation unit in response to departure from a valid range of the analog signal parameters; wherein the logic operations unit is adapted to generate, by performing a logic operation, a resulting error signal at an output of the logic operations unit as a function of a computed status information item, a state of the error signal of the first evaluation unit, and a state of the error signal of the further evaluation unit; and wherein logic operations unit is adapted to transmit the resulting error signal to a first output of the device.

24. The device according to claim 23, wherein the digital signal parameters include trailing and/or leading switching edges and/or the analog signal parameters include voltage levels and/or current levels.

25. The device according to claim 23, wherein the resulting error signal indicates whether the track signals of the position change sensor are erroneous

26. The device according to claim 23, wherein the first evaluation unit is adapted to transmit the status information item to a further output of the device.

27. The device according to claim 23, wherein the first evaluation unit includes a Schmitt trigger unit, a quadrature decoder, an edge counter, a status information computation unit, and a comparator unit; wherein the Schmitt trigger unit is adapted to convert the track signals of the position change sensor to square-wave signals; wherein the quadrature decoder is adapted to generate a direction-dependent edge count value from the square-wave signals; wherein the edge counter is adapted to generate a direction-independent edge count value from the square-wave signals; the status information computation unit is adapted to compute a status information item from the direction-dependent edge count value and to make the status information item available at a first output of the first evaluation unit; and wherein the comparator unit is adapted to check, within a measuring cycle, a magnitude of change in the direction-dependent edge count value and a change in the direction-independent edge count value for equality and to set, in the event of inequality, an error signal at a further output of the first evaluation unit.

28. The device according to claim 23, wherein the further evaluation unit includes a timing generator unit, a lookup table unit, an analog-to-digital converter unit, and a trigonometric unit; wherein the timing generator unit is adapted to generate synchronization signals cyclically in variable intervals, as a function of data from a lookup table unit; wherein the analog-to-digital converter unit is adapted to convert a current analog level of the track signals of the position change sensor to corresponding digital pairs of values (U.sub.A, U.sub.B) as a function of the synchronization signal; and wherein the trigonometric unit is adapted to check the digital pairs of values of the track signals for validity, using the equation:
U.sub.A.sup.2+U.sub.B.sup.2=(.Math..sub.A*sin(2*f*t)).sup.2+(.Math..sub.B*cos(2*f*t)).sup.2=R.sup.2, and, upon departure from a defined tolerance range of values, to set an error signal at an output of the further evaluation unit.

29. The device according to claim 23, wherein the logic operations unit includes a switch element and a logic unit; wherein the switch element is adapted to transmit or not transmit an error signal of the first evaluation unit to an output as a function of the status information item of the first evaluation unit; and the logic unit is adapted to set an error signal at an output of the logic operations unit, as soon as the error signal of the first evaluation unit transmitted by the switch element and/or the error signal of the further evaluation unit is applied.

30. The device according to claim 23, further comprising a frequency converter and a position change sensor; wherein the evaluation units and the logic operations unit are integrated in the frequency converter; wherein the position change sensor includes an analog output stage; and wherein, on an output side, the first evaluation unit is connected to a regulating portion of signal electronics of the frequency converter.

31. The device according to claim 30, wherein the evaluation units and the logic operations unit are integrated in the position change sensor; wherein, on an input side, the evaluation units are connectable to an analog output stage of the position change sensor; wherein the analog output stage of the position change sensor is adapted to generate and/or condition analog track signals; wherein, on an output side, the first evaluation unit and/or the logic operations unit are connectable to a converter to a serial communications interface; wherein the position change sensor is connectable to a frequency converter via a serial communications interface; and wherein, via the serial communications interface, at least the track signals and/or the status information item of the output of the first evaluation unit and the resulting error signal of the output of the logic operations unit are transmittable by a further converter to the regulating portion of the signal electronics of the frequency converter.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0059] FIG. 1 schematically illustrates an encoder signal diagnostic device.

[0060] FIG. 2 schematically illustrates an encoder signal diagnostic device.

[0061] FIG. 3 schematically illustrates the generation of measuring times for an evaluation unit.

[0062] FIG. 4 schematically illustrates an implementation of an encoder signal diagnostic device.

[0063] FIG. 5 schematically illustrates an implementation of an encoder signal diagnostic device.

DETAILED DESCRIPTION

[0064] An encoder signal diagnostic device 1 is schematically illustrated in FIG. 1.

[0065] An exemplary implementation of the encoder signal diagnostic device 1 according to an example embodiment of the present invention, including a first evaluation unit 2, a further evaluation unit 3 and a logic operations unit 4, is illustrated in FIG. 2.

[0066] The generation of the measuring times for the further evaluation unit 3 in accordance with an example embodiment of the present invention is described in FIG. 3.

[0067] An example of an implementation of an encoder signal diagnostic device 1 according to an example embodiment of the present invention, in which the encoder signal diagnostic device 1 is constructed so as to be integrated in a frequency converter 5 of an electric power drive system, is schematically illustrated in FIG. 4.

[0068] A further example of an implementation of an encoder signal diagnostic device 1 according to an example embodiment of the present invention, in which the encoder signal diagnostic device 1 is constructed so as to be integrated in a position change sensor 6, is schematically illustrated in FIG. 5.

[0069] As illustrated in FIG. 1, the input signal of encoder signal diagnostic device 1 typically includes two signal tracks. In this context, the two signal tracks include a first signal track A and a second signal track B, second signal track B being 90 out of phase with respect to first signal track A. The two track signals form the input signals for both first evaluation unit 2 and further evaluation unit 3. From these track signals, first evaluation unit 2 computes, on the basis of digital signal parameters, at least one status information item, typically, a speed information item and/or a position information item and/or a direction of movement information item and/or an acceleration information item and/or a feedback information item, and makes this status information item available at a first output of first evaluation unit 2. In addition, first evaluation unit 2 checks the digital signal parameters for plausibility and, in response to the detection of an error, sets an error signal at a further output of first evaluation unit 2. A further evaluation unit 3 evaluates the track signals of position change sensor 6 on the basis of analog signal parameters and, in response to the detection of an error, for example, due to departure from a range of validity of the track signal level, generates an error signal at the output of further evaluation unit 3. The error signals at both the output of first evaluation unit 2 and the output of further evaluation unit 3 are dynamic and are only applied for the duration of an occurring and detected error. In light of the status information item generated in first evaluation unit 2, logical operations unit 4 decides how the error signals of first evaluation unit 2 and of further evaluation unit 3 are logically combined with each other and generates, from this, a resulting error signal at its output. For example, both the status information item of first evaluation unit 2 and the resulting error signal of logic operations unit 4 are transmitted to the outputs of encoder signal diagnostic device 1. In this context, the resulting error signal indicates if the track signals of position change sensor 6 are erroneous.

[0070] An exemplary implementation of first evaluation unit 2, further evaluation unit 3 and logic operations unit 4 is illustrated in FIG. 2. In the first evaluation unit 2, the two track signals of position change sensor 6 are initially converted to square-wave signals by Schmitt trigger unit 21. These square-wave signals are supplied to both a quadrature decoder 22 and an edge counter 23. If the square-wave signal of signal track A leads signal track B in time, then a movement in one direction is taking place. If signal track A trails signal track B in time, then a movement in the opposite direction is taking place. Quadrature decoder 22 detects this direction of movement and, at each switching edge, adds or subtracts a numerical value, typically, a 1, to or from a first counter as a function of the detected, current direction of movement. At each switching edge of the square-wave signal of track A and/or of the square-wave signal of track B, edge counter 23 adds a value to a further counter independently of the direction of movement. Status information computation unit 24 computes a status information item from the movement-direction-dependent, first counter of quadrature decoder 22. Within a measuring cycle T.sub.CYCLE, comparator unit 25 compares the magnitude of the change in the count of quadrature decoder 22 to the change in the count of edge counter 23. If the two changed values are unequal, then an error signal is generated at the output of comparator 25. Due to the differing computation methods in quadrature decoder 22 and edge counter 23, an inequality of the two changed values is always produced, if the direction of movement reverses inside of a measuring cycle T.sub.CYCLE and/or an error in the generation of a track signal in position change sensor 6 and/or an error in the transmission and/or processing of the track signals has occurred. In order to ensure that only the errors are detected, and not the permitted reversal of the direction of movement, the error signal of first evaluation unit 2 is only evaluated, if the status-information item lies above a certain limiting frequency f.sub.G. Based on the inertia of the actuator, whose movement is reflected by track signals A and B, this limiting frequency ensures that no change in the direction of movement can have occurred within a measuring cycle T.sub.CYCLE.

[0071] In further evaluation unit 3, track signal levels A and B are converted to synchronized pairs of values (U.sub.A, U.sub.B) by an analog-to-digital converter unit 31. The measuring times of the analog-to-digital conversion are specified by a timing generator unit 32, the measuring times being calculated as a function of numerical values from a lookup table unit 33. In this context, by storing different measuring times, lookup table unit 33 provides the flexibility of adapting further evaluation unit 3 to the specific needs of an application. In trigonometric unit 34, synchronized pairs of values (U.sub.A, U.sub.B) are evaluated via the Pythagorean trigonometric identity, using the relationship:

U.sub.A.sup.2+U.sub.B.sup.2=(.Math..sub.A*sin(2*f*t)).sup.2+(.Math..sub.B*cos(2*f*t)).sup.2=R.sup.2,

[0072] If calculated value R.sup.2 exits a predefined, typically constant range, then an error signal is generated at the output of trigonometric unit 34, the error signal also being transmitted to the output of further evaluation unit 3. In this connection, this predefined range may be adapted application-specifically and is typically specified by the manufacturer of position change sensor 6. Logic operations unit 4 combines the error signal of first evaluation unit 2 and the error signal of further evaluation unit 3. In this context, the error signal of first evaluation unit 2 is gated out via switch element 41, if the status information item is less than limiting frequency f.sub.G and therefore does not always supply a valid error signal (see further above). Logic unit 42 sets an error signal at the output, if an error signal is applied to either the output of switch element 41 or to the output of further evaluation unit 3. Thus, below a limiting frequency f.sub.G, only the error signal of further evaluation unit 3, and above limiting frequency f.sub.G, the error signals of both first evaluation unit 2 and further evaluation unit 3, are used for generating a resulting error signal.

[0073] Thus, as illustrated in FIG. 2, the output signal of position change sensor 6 is monitored, on one hand, with regard to deviation from a permissible value of the sum of the squares of the two track signals, and, on the other hand, for counter errors in accordance with the described function of first evaluation unit 2. In this context, the monitoring for deviation is only carried out at the times, which are specified according to lookup table unit 33, which means that gap-free, continuous monitoring is not present. However, since the monitoring for counter errors according to the described function of first evaluation unit 2 is also carried out simultaneously to this monitoring, sufficiently high reliability may be ensured. In particular, all relevant types of errors are covered.

[0074] The generation of measuring times according to example embodiments of the present invention, which are stored in lookup table unit 33 of further evaluation unit 3, and which are provided by timing generator unit 32 for synchronous analog-to-digital conversion of track signals A and B by analog-to-digital converter unit 31, is illustrated in FIG. 3. In this context, measuring interval T.sub.1 is selected so that a track signal having a limiting frequency f.sub.G is sampled so often, that a number N, typically, a number of N 5, of measuring times sufficient for the needed diagnostic coverage is attained within a track signal period. In order to attain continuous sampling, a first set of measuring times is generated over entire measuring cycle T.sub.CYCLE, using this measuring interval T.sub.1. Simultaneously, a second set of measuring times is generated, by selecting a second measuring interval T.sub.2 having half the length of measuring interval T.sub.1 and adding a number K, typically, a quantity of 9, measuring times at the beginning of measuring cycle T.sub.CYCLE. Each additional set of measuring times includes, in turn, of a number K of measuring times, which are added at the start of measuring cycle T.sub.CYCLE; measuring interval T.sub.N always corresponding to half the length of preceding measuring interval t.sub.N-1. The generation of further sets of measuring points is continued until at least a number N of measuring times lie within a track signal period of a track signal having a maximum frequency f.sub.MAX. The number K of measuring times of a set of measuring times must be selected in such a manner, that over the entire frequency range to be covered by the specific set of measuring times, the respective measuring interval is at least 75% or at least 270 of the track signal period. The final set of measuring times T.sub.M is yielded ultimately from the sum of all of the individual sets of measuring times; simultaneous measuring times being combined to form a common measuring time.

[0075] Thus, according to example embodiments of the present invention, the analog output signal of position change sensor 6 is sampled cyclically according to a sequence of sampling times. The sequence is finite and may also be referred to as a one-dimensional pattern. Therefore, according to this specified pattern, the sampling times are positioned temporally one after another.

[0076] As illustrated in FIG. 3, the pattern is used in a cyclically repeated manner. In this context, the temporal length of the pattern is T.sub.CYCLE, which means that the pattern is used so as to be repeated with this period duration.

[0077] The pattern includes a plurality of directly consecutive time periods, in which, in each instance, a plurality of sampling times are positioned so as to be temporally set apart from each other at regular intervals. However, the spacing is different in each time period, that is, variable. In the first time period, a very short spacing is implemented, in the second time period, a greater spacing, etc. In this context, each time period subsequent to a time period has a greater spacing.

[0078] Referring to FIG. 3, the composition of the pattern as a sum of base patterns is explained in more detail. The first base pattern includes a regular spacing of sampling times having a time interval T.sub.1. In this case, the spacing is selected in such a manner, that at the maximum permissible frequency, that is, frequency f.sub.MAX=1/T.sub.MAX, a period of the output signal is sampled five times. Thus, T.sub.MAX=5*T.sub.1.

[0079] Further base patterns are generated on the basis of the first base pattern. In this context, the spacing of a subsequent base pattern is calculated as a function of the spacing of the respective, preceding base pattern according to the formula T.sub.N=2*T.sub.N-1.

[0080] The number of base patterns generated results from a technically sensible reduction in the scanning times in comparison with the scanning at the highest possible frequency.

[0081] In the present case, 5 base patterns are generated.

[0082] The first base pattern having spacing T.sub.1 extends over eight periods.

[0083] The second base pattern has a greater spacing, namely, T.sub.2=2*T.sub.1, and extends over eight periods.

[0084] The third base pattern has a greater spacing, namely, T.sub.3=2*T.sub.2, and extends over eight periods.

[0085] The fourth base pattern has a greater spacing, namely, T.sub.4=2*T.sub.3, and extends over eight periods.

[0086] The fifth base pattern has a greater spacing, namely, T.sub.5=2*T.sub.4, and extends temporally over time T.sub.CYCLE.

[0087] This yields a lower limiting frequency f.sub.G=1/T.sub.G, where T.sub.G=5*T.sub.5, characterized in that an output signal having frequency f.sub.G is continuously scanned five times per period.

[0088] The base patterns generated are summed or superimposed. In this context, simultaneous sampling times of different base patterns are combined to form one sampling time in the sum of the base patterns.

[0089] Thus, the sum or superpositioning of the base patterns results in the pattern, which has, in the first time period, eight scanning times temporally set apart regularly from each other by T.sub.1; has, in the following time period, four scanning times temporally set apart regularly from each other by T.sub.2; has, in the time period following that, four scanning times temporally set apart regularly from each other by 13; has, in the time period following that, four scanning times temporally set apart regularly from each other by T.sub.4; and has, in the time period following that, scanning times temporally spaced apart regularly from each other by T.sub.5.

[0090] In this manner, it is ensured that at least once per T.sub.CYCLE, a period of the output signal is sampled at least five times, as long as its frequency is in the permissible range between f.sub.G and f.sub.MAX. The periods of output signals having a frequency lower than f.sub.G are always sampled at least five times over a plurality of T.sub.CYCLE's.

[0091] An advantage of this is that computing time may be reduced, since sampling at the highest possible frequency is not carried out over the entire interval T.sub.CYCLE. However, gap-free, continuous monitoring, thus, diagnosis as well, would not be able to be ensured, if the sampling represented in FIG. 3 were used; but this gap in monitoring is reduced by digital monitoring carried out simultaneously.

[0092] A first exemplary implementation of an encoder signal diagnostic device 1 according to an example embodiment of the present invention, which is integrated in a frequency converter 5 of an electric power drive system, is illustrated in FIG. 4. In this context, the external position change sensor 6 connected to frequency converter 5 in an electrically conductive manner is typically mounted to the shaft of an electric motor M; position change sensor 6 converting the angular motion to track signals A and B via a mechanical adapter 61 and with the aid of an analog signal recorder 62; for their part, the track signals being 90 out of phase and constituting the input track signals for encoder signal diagnostic device 1. The output signals of encoder signal diagnostic device 1, the status information item of first evaluation unit 2 and the resulting error signal of logic operations unit 4, are supplied to the regulating portion of signal electronics 51 of frequency converter 5. Regulating portion 51 uses the status information item for regulating and controlling electric motor M, and the resulting error signal is used as information as to whether the status information item is valid and may be used for regulation. In the event of an invalid status information item, the driving of electric motor M is immediately interrupted, so that a dangerous movement, which may cause damage to the system and/or cause injury to persons, does not take place. Consequently, only with a valid status information item, is it possible to set electric motor M into motion application-specifically via power electronics 52.

[0093] A second exemplary implementation of an encoder signal diagnostic device 1 according to an example embodiment of the present invention, which is constructed so as to be integrated in a position change sensor 6, is illustrated in FIG. 5. In contrast to FIG. 4, in this case, the signal input of encoder signal diagnostic device 1 is connected directly to analog signal recorder 62 of position change sensor 6 in an electrically conductive manner. The output signals of encoder signal diagnostic device 1 are adapted to the protocol of a serial communications interface via a converter (63); the serial communications interface being connected to both position change sensor 6 and frequency converter 5. Using a further converter 63 in frequency converter 5, both the status information item and the resulting error signal of encoder signal diagnostic device 1 are provided cyclically to the regulating portion of control electronics 51 of frequency converter 5 in digitized form. In this manner, errors in the transmission between position change sensor 6 and frequency converter 5 may additionally be reduced.

[0094] Thus, example embodiments of the present invention relate to resource-optimized diagnosis of errors of track signals of a position change sensor. This object is achieved by carrying out the diagnostic evaluation in a manner adapted to a maximum occurring track signal frequency, using both digital signal parameters and analog signal parameters; by suitably combining the two types of signal parameters, the number of measuring times needed being able to be reduced in such a manner, that consequently, costs, in particular, component and/or manufacturing costs, may be reduced.

[0095] The following list of reference characters is included in the description and clarifies further features hereof.

LIST OF REFERENCE CHARACTERS

[0096] 1 encoder signal diagnostic device [0097] 2 first evaluation unit; digital signal parameter evaluation [0098] 21 Schmitt trigger unit [0099] 22 quadrature decoder [0100] 23 edge counter [0101] 24 status information computation unit [0102] 25 comparator unit [0103] 3 further evaluation unit; analog signal parameter evaluation [0104] 31 analog-to-digital converter unit [0105] 32 timing generator unit [0106] 33 lookup table unit [0107] 34 trigonometric unit [0108] 4 logic operations unit [0109] 41 switch element [0110] 42 logic unit [0111] 5 frequency converter [0112] 51 regulating portion of the signal electronics [0113] 52 power electronics for operating an electric motor [0114] 6 position change sensor [0115] 61 mechanical adapter [0116] 62 analog signal recorder [0117] 63 converter to the protocol of a serial communications interface [0118] M electric motor [0119] f signal frequency [0120] f.sub.G limiting signal frequency [0121] f.sub.MAX maximum signal frequency [0122] t time [0123] T.sub.1 first test interval [0124] T.sub.n nth or current test interval [0125] T.sub.n-1 preceding test interval [0126] T.sub.M sum of the measuring times [0127] T.sub.CYCLE measuring cycle [0128] N number of measuring times needed per signal period for sufficient diagnostic coverage [0129] K number of measuring times needed for a set of measuring times [0130] U.sub.A signal level of track signal A [0131] U.sub.B signal level of the track signal B 90 out of phase with respect to track signal A [0132] .Math..sub.A amplitude of track signal A [0133] .Math..sub.B amplitude of track signal B