JP5195685B2 - Rotational speed sensor and rotational speed monitoring device - Google Patents

Description

  The present invention relates to a rotational speed sensor and a rotational speed monitoring device capable of detecting the rotational state of an electric motor driven by electric power supplied from a power converter such as an inverter or a servo amplifier and realizing an excellent safety function. About.

  In recent years, power converters that drive motors at variable speeds such as inverters and servo amplifiers are becoming popular due to the need for energy saving. On the other hand, accidents such as elevators and revolving doors have become a social problem, and abnormal operation of electrical and mechanical equipment can have a significant impact on the human body. Therefore, it is particularly safe to monitor equipment abnormalities and ensure safety and reliability when abnormalities are detected. The function to stop the equipment is important.

  For an electric motor, it is necessary to detect and decelerate and stop safely by detecting that the operating range is deviated from the condition of the safety function. As this detection method, a method of monitoring the rotational speed using a rotational speed sensor is generally employed.

  However, when the rotation speed of the electric motor is monitored by the rotation speed sensor, it is necessary to consider the failure of the rotation speed sensor to be used. That is, the output signal does not change because the output signal of the rotation speed sensor does not change because the motor is stopped or the speed is limited, or because of the failure of the rotation speed sensor or the abnormality of the signal transmission line that transmits the output signal Must be accurately determined.

  As a technique for detecting a failure in the rotational speed sensor, for example, in the rotational speed sensor described in Patent Document 1, the sensor failure is detected from the pulse pattern of the output signal and the change of the pulse pattern using sensor outputs of three or more systems. Yes.

  Further, in the rotational speed sensor described in Patent Document 2, an analog value is used for the sensor output, and the failure of the sensor is detected based on the magnitude of the peak value of the output signal. In addition, if the sensor output has a voltage value different from that of the power supply or GND during normal operation, and the output terminal is fixed at the potential of the power supply or GND, the sensor output terminal or signal transmission line short-circuit failure This is a technique for detecting an open failure.

JP 2000-184774 A JP 2006-266727 A

  However, in the above conventional technique, in order to detect a failure of the rotational speed sensor, multiple use of the rotational speed sensor, redundancy by increasing the number of output terminals of the rotational speed sensor, or analogization of the rotational speed sensor is performed. There is a need. For this reason, there is a problem that the apparatus becomes complicated and the cost of the apparatus increases due to an increase in the number of parts.

  The present invention has been made in view of the above-described circumstances, and a rotation speed sensor and a rotation speed capable of detecting an abnormality of a rotation speed sensor and a signal transmission line for transmitting an output signal of the rotation speed sensor with a simple structure. An object of the present invention is to provide a monitoring device.

  In order to achieve the above object, the rotational speed sensor according to the present invention is provided with a small hole concentrically associated with each phase of the rotational speed signal on the rotating disk, and the rotational position is determined by the light passing through the small hole. And a rotation speed sensor having a rotation detection means for generating and outputting a rotation speed signal capable of detecting the rotation speed, the rotating disk having small holes corresponding to rotation speed signals of two or more phases, The rotation speed signal has a small hole for a redundant signal that can be uniquely determined by a predetermined logical relationship with respect to the rotation speed signal, and the rotation detecting means outputs a failure monitoring signal generated by light passing through the small hole for the redundant signal. It is characterized by outputting.

  Preferably, a signal corresponding to the exclusive OR of the rotational speed signals of the respective phases is used as the redundant signal. Thereby, a redundant signal can be generated with a simple configuration.

  In the present invention, for example, for an A / B phase incremental rotation speed sensor, a failure monitoring signal output means is provided separately from the rotation detection means for outputting a rotation speed signal (A phase, B phase). The failure monitoring signal output means outputs a signal (A ^ B phase output signal) corresponding to EXOR (exclusive OR) of the A phase signal and the B phase signal. The self-diagnosis unit inside the rotation speed sensor and the external failure monitoring unit indicate that there is no failure in the failure detection target range when the logical relationship between the rotation speed signal (A phase and B phase) and the failure monitoring signal match. judge. The target range for failure detection varies depending on the position of the monitoring function. The included range is the target range.

  Further, in the rotational speed sensor according to the present invention, the rotating disk has a reference section including a reference position of rotation in part, and the rotation detecting unit fails the exclusive OR of the rotational speed signals in a range other than the reference section. A monitoring signal is output, and an inverted signal of an exclusive OR of the rotation speed signal is output as a failure monitoring signal in the reference section.

  The rotation detecting means outputs an inverted signal of the exclusive OR of the rotation speed signal as a failure monitoring signal in a range other than the reference interval, and outputs the exclusive OR of the rotation speed signal in the reference interval as a failure monitoring signal. May be output as

  The rotational speed monitoring device according to the present invention inputs a rotational speed signal and a failure monitoring signal sent from a rotational speed sensor via a signal transmission line, and the inputted rotational speed signal and failure monitoring signal. And a failure monitoring means for determining a reference section from the transition process (state transition) of the rotation speed signal and the failure monitoring signal. And

  Preferably, the width of the reference section is set to N-1 / 4 (N is an integer) times the width of the section corresponding to the repetition period of the rotation speed signal.

  In the present invention, for example, with respect to an A / B / Z phase type incremental rotation speed sensor, the Z phase rotation detection means is provided with a function as an output means of a failure monitoring signal. The Z phase rotation detection means outputs a signal (A ^ B ^ Z phase output signal) corresponding to EXOR (exclusive OR) of the A phase signal, the B phase signal, and the Z phase signal. The failure monitoring unit or self-diagnosis unit determines that there is no failure in the target range when the rotational speed signals (A phase, B phase, Z phase) match, and there is a failure when the logical relationship does not match. Is determined.

  According to the present invention, failure of the rotational speed sensor and the signal transmission line can be reliably detected, and the apparatus cost can be reduced by reducing the number of signal transmission lines. In particular, a redundant signal small hole is provided using the Z phase indicating the reference position of the rotating disk, and the redundant signal is identified by identifying the reference section including the reference position from the transition process of the rotation speed signal and the failure monitoring signal. It is possible to suppress an increase in the number of light emitting and light receiving elements for production.

  The rotational speed sensor according to the present invention further includes speed determining means for determining whether the rotational speed is high or low, and the speed determining means determines that the rotational speed is lower than a predetermined value and is self- When the diagnostic means determines that there is no failure, a low rotational speed signal indicating that the low rotational speed state is present is output.

  Preferably, by using an alternating current signal having a cycle longer than a predetermined value for determining whether or not the low rotational state is used as the low rotational speed signal, it is possible to accurately detect a short circuit or a touch of the signal. .

  According to the present invention, it is possible to reliably detect a failure in the rotational speed sensor and the signal transmission line even in a low rotational speed state such as a stopped state.

  According to the present invention, a small hole for a redundant signal is provided in the rotating disk, and this signal is used to determine whether the logical relationship with the rotating speed signal is normal. Can be detected.

  In particular, by identifying the reference section of the rotating disk from the transition process of the rotational speed signal and the failure monitoring signal, and by inverting the logic of the redundant signal outside the reference section and the reference section, the light emitting unit for generating the redundant signal and the light receiving It is possible to detect failures with high accuracy by suppressing an increase in the number of elements and the number of signal transmission lines.

  Furthermore, by using an AC signal with a period longer than the set value for determining whether or not the engine is in a low rotation state as a low rotation speed signal that is output when the low rotation state of the motor is detected, a short circuit of the signal, an incompatibility, etc. Can be surely distinguished from each other and the low rotation state can be transmitted.

It is a functional block diagram of the monitoring apparatus of the rotational speed by the 1st Embodiment of this invention. It is a block diagram of the rotational speed detection part 4 of FIG. It is a circuit block diagram by one Example of the failure monitoring part 8 of FIG. It is a state transition diagram of the structure by the other Example of the failure monitoring part 8 of FIG. It is an operation | movement waveform diagram when there is no failure in 1st Embodiment. It is an operation | movement waveform diagram in case there exists a failure in 1st Embodiment. It is a functional block diagram of the monitoring apparatus of the rotational speed by the 2nd Embodiment of this invention. It is a circuit block diagram of the rotational speed sensor 16 of FIG. It is a functional block diagram of the monitoring apparatus of the rotational speed by the 3rd Embodiment of this invention. FIG. 10 is an operation waveform diagram of the rotation speed monitoring device of FIG. 9. It is an example of arrangement | positioning of the small hole of the rotating disk 85 of FIG. It is explanatory drawing of the state transition of the self-diagnosis part 7 and the failure monitoring part 8 of FIG. It is an operation | movement waveform diagram when passing a reference | standard area without a failure in 3rd Embodiment. It is an operation | movement waveform diagram when there is no failure in the 3rd Embodiment and it reverses in the base area vicinity. It is an operation | movement waveform diagram when a failure generate | occur | produces in 3rd Embodiment. (Part 1) It is an operation | movement waveform diagram when a failure generate | occur | produces in 3rd Embodiment. (Part 2) It is an operation | movement waveform diagram when a failure generate | occur | produces in 3rd Embodiment. (Part 3) It is an operation | movement waveform diagram when a failure generate | occur | produces in 3rd Embodiment. (Part 4) It is an operation | movement waveform diagram when a failure generate | occur | produces in 3rd Embodiment. (Part 5) It is a functional block diagram of the monitoring apparatus of the rotational speed by the 4th Embodiment of this invention. It is explanatory drawing of the state transition of the self-diagnosis part 7 and the failure monitoring part 8 of FIG. 21 is a circuit configuration example according to the first embodiment of the comparison unit 6 of FIG. 20. 21 is a circuit configuration example according to the second embodiment of the comparison unit 6 of FIG. 20. FIG. 21 is a circuit configuration example according to Example 3 of the comparison unit 6 of FIG. 20. FIG. 21 is a circuit configuration example according to a fourth embodiment of the comparison unit 6 of FIG. 20. It is an operation | movement waveform diagram when there is no failure in 4th Embodiment. It is an operation | movement waveform diagram in case there exists a failure in 4th Embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a functional block diagram of a rotational speed monitoring device (hereinafter simply referred to as “monitoring device”) according to the first embodiment.

  In FIG. 1, a monitoring device 1 includes a rotation speed sensor (Encoder) 16 that detects the rotation speed of an electric motor, a signal transmission line (Cable) 17 that transmits a rotation speed signal output from the rotation speed sensor 16 and a monitoring signal, and It comprises an abnormality detection unit (PowerAMP) 18 that detects and outputs an abnormality based on a monitoring signal. In FIG. 1, M indicates a reference potential and Vcc indicates a power source.

  The rotation speed sensor 16 includes a rotation speed detector 4 that detects the rotation speed of the motor and outputs a rotation speed signal corresponding to the rotation position of the motor. The rotational speed detection unit 4 includes a light emitting unit 84, a rotating disk 85, and a light receiving unit 86, and a rotational position of an electric motor connected to each pair of transistors 31 to 36 constituting an output circuit of the light receiving unit 86. Outputs rotation speed signals (A, B) and failure monitoring signals (A ^ B) according to (rotary disk position).

  Here, the rotation speed signals (A, B) mean the output signals of the A phase and B phase output from the rotation speed detector 4, and the failure monitoring signal (A ^ B) is the A phase, B phase. It means an exclusive OR (EXOR) output signal of phase output signals.

  The failure monitoring unit 8 detects a failure in the rotation speed sensor 16 or the signal transmission line 17 from the logical relationship between the rotation speed signal (A, B) transmitted through the signal transmission line 17 and the failure monitoring signal (A ^ B). When it is determined that there is no failure, a no fault signal (non Fault) is output.

  FIG. 2 shows a configuration of the rotation speed detection unit 4 of FIG. The light emitted from the light emitting unit 84 reaches the light receiving unit 86 through a small hole (hole) 85 a disposed in the rotating disk 85. The rotating disk 85 is provided with a light emitting unit 84 so that a two-phase rotational speed signal (A, B) and a failure monitoring signal (A ^ B) corresponding to these rotational speed signals (A, B) are output. A small hole for passing the irradiation light is provided. When light passes through the small hole 85a and the light receiving unit 86 detects this light, the 'H' level is output, and when light does not pass and the light receiving unit 86 does not detect light, the 'L' level is output. Output. In FIG. 2, the small holes of each phase are arranged on the straight line from the outer periphery of the rotating disk 85 to the center of rotation so that the relationship between the signal (A, B) and the corresponding signal (A ^ B) is obtained. . The light receiving unit 86 is a transistor of the output circuit as a rotational speed signal (A, B) or a failure monitoring signal (A ^ B) based on the light detection result of the light receiving unit 86 of A phase, B phase, and A ^ B phase. 'H' and 'L' are output through 31-36.

  Since the light emitting elements corresponding to the respective phases of the light emitting section 84 are also arranged on a straight line from the rotation center of the rotary disk 85, the light receiving section 86 always outputs the A phase, the B phase, and the A ^ B phase at an arbitrary light receiving timing. Light can be received with correct logic.

  FIG. 3 shows a circuit configuration example of the failure monitoring unit 8 of FIG. In this figure, an EXOR circuit 81 calculates an exclusive OR of the A phase and the B phase of the rotation speed signal. The EXNOR circuit 82 compares the failure monitoring signal (A ^ B) with the output of the EXOR circuit 81, and outputs “H” if they match, and outputs “L” if they do not match. . Since the failure monitoring signal (A ^ B) is configured to output a signal corresponding to the exclusive OR of the A phase and B phase of the rotation speed signal by the above configuration, the failure monitoring unit 8 When this logical relationship matches, it can be determined that there is no failure.

  From the above, it is possible to monitor the failure of the rotation speed sensor 16 and the signal transmission line 17 by using the output of the EXNOR circuit 82 as a non-failure signal.

  Next, FIG. 5 shows an example of an operation waveform when there is no failure, and FIG. 6 shows an example of an operation waveform when there is a failure. 5 and 6, EXOR 81 indicates the output waveform of the EXOR circuit 81.

  In FIG. 5, the failure monitoring signal (A ^ B) and EXOR 81 have the same waveform shape. The failure monitoring unit 8 determines that the rotation speed signal (A, B) and the failure monitoring signal (A ^ B) are in a normal operation because the logical relationship is the same, and the failure monitoring signal (non Fault ) Is output as “H”.

  FIG. 6 is an operation waveform assuming a case where the A-phase output of the rotation speed signal is fixed to “H” due to a failure of the rotation speed sensor. In the latter half of the operation waveform, phase A fails, and the failure monitoring signal (A ^ B) and EXOR 81 have different waveform shapes. The failure monitoring unit 8 determines that there is a failure because the logical relationship between the rotation speed signals (A, B) and the failure monitoring signal (A ^ B) does not match, and outputs “L” as a non-failure signal (non Fault). To do.

  FIG. 4 is another circuit configuration example of the failure monitoring unit 8 of FIG. In FIG. 4, circles indicate states corresponding to combinations of rotational speed signals (A, B) and failure monitoring signals (A ^ B), solid arrows connecting the circles indicate state transitions during forward rotation, and broken arrows indicate states during reverse rotation. Dotted arrows toward the state transition and the fault state (Fault) indicate the state transition at the time of failure, respectively. When there is no failure in the rotation speed sensor 16, state transition is performed according to a solid line arrow or a broken line arrow by a combination of the rotation speed signal (A, B) and the failure monitoring signal (A ^ B). When a combination of signals other than the state transitions indicated by the solid line arrows and the broken line arrows occurs, it is determined that the logical relationship between the rotation speed signals (A, B) and the failure monitoring signal (A ^ B) does not match. The fault monitoring unit 8 outputs “L” as a no-fault signal (non Fault) when transitioning to a fault state (Fault), and outputs a non-fault signal (non Fault) when not in the fault state (Fault). ) Is output as “H”.

  As described above, the failure monitoring unit 8 can detect a failure in the rotation speed sensor 16 and the signal transmission line 17 by detecting that the combination of input signals and the switching pattern do not logically match. Since the operation waveforms are the same as those shown in FIGS.

Next, a second embodiment of the present invention will be described with reference to FIGS.
FIG. 7 is a functional block diagram of the monitoring device 1 according to the second embodiment. The difference from FIG. 1 is that a self-diagnosis unit 7 is added to the rotation speed sensor 16 and a non-fault signal (non Fault) is output based on the self-diagnosis result. The abnormality detection unit 18 transmits the signal via a signal transmission line 17. That is, an AND circuit 9 for calculating a logical product of the failure-free signal (non Fault) and the failure-free signal (non Fault) output from the failure monitoring unit 8 is added.

  Note that the OptOK signal output from the light emitting unit 84 of the rotation speed detecting unit 4 to the self-diagnosis unit 7 shown in FIGS. 7 and 8 is a signal indicating that the light emitting unit 84 has no failure. Further, Flg (non Fault (1), (2)) in FIG. 8 is a signal indicating that there is no failure in the light receiving unit. In addition, about the same element as 1st Embodiment, the same code | symbol is attached | subjected and description is abbreviate | omitted.

  The self-diagnosis unit 7 outputs a no failure signal (non Fault) when it is determined that there is no failure in the rotation speed sensor 16 from the logical relationship between the rotation speed signals (A, B) and the failure monitoring signal (A ^ B). To do. The self-diagnostic unit 7 compares the logical relationship between the rotation speed signals (A, B) and the failure monitoring signal (A ^ B) according to the failure detection principle described in FIGS. Diagnose.

  When the self-diagnosis unit 7 determines that the rotation speed sensor 16 has no failure, the self-diagnosis unit 7 outputs ‘H’ as a non-failure signal (non Fault), and outputs ‘L’ when it determines that there is a failure. Thereby, regardless of the presence or absence of the failure monitoring unit 8, the self-diagnosis unit 7 can individually detect the failure of the rotation speed sensor 16.

  The AND circuit 9 on the abnormality detection unit 18 side is only when both the no failure signal (non Fault) output from the self-diagnosis unit 7 and the no failure signal (non Fault) output from the failure monitoring unit 8 are 'H'. 'H' level is output. On the abnormality detection unit 18 side, the occurrence location of the failure can be investigated by comparing the outputs of the self-diagnosis unit 7, the failure monitoring unit 8, and the AND circuit 9. For example, if the output of the self-diagnosis unit 7 is ‘H’ and the output of the failure monitoring unit 8 is ‘L’, it can be determined that the signal transmission line 17 has failed.

FIG. 8 is a circuit configuration example in which a failure diagnosis unit 20 of the light emitting unit and a failure diagnosis unit 40 of the light receiving unit output are added to the failure diagnosis circuit described in FIG. In FIG. 8, the phase A is mainly described, but the other phases have the same circuit configuration. In FIG. 8, the light emitting unit 84 includes impedance elements 11 and 13 and light emitting elements 12 and 14, one end of the impedance elements 11 and 13 is connected to the power source Vcc, and the other end is on the anode side of the light emitting elements 12 and 14. It is connected. The cathode sides of the light emitting elements 12 and 14 are connected to a reference potential (ground) M.
In order to prevent an overcurrent of the signal output unit of the rotation speed sensor 16, impedance elements 37 to 39 are inserted in series in the A-phase, B-phase, and Z-phase signal lines outside the light receiving unit 3, respectively. Yes. The impedance elements 37 to 39 may be provided in any of the rotational speed sensor 16, the signal transmission line 17, and the abnormality detection unit 18, and a plurality of combinations may be used.

  In FIG. 8, EXOR 81 and EXNOR 82 diagnose a failure in the same manner as in FIG. When it is determined that there is no failure, 'H' is output to the output (Flg (non fault (1)). When it is determined that there is a failure, 'L' is output to the output (Flg (non fault (1)). Is output.

  The failure diagnosis unit 20 of the light emitting unit 84 is a circuit that detects a failure of the light emitting unit 84. The failure diagnosis unit 20 of the light emitting unit 84 compares the reference voltage generated by the impedance elements 21 to 23 with the anode side terminal voltages of the light emitting elements 12 and 14 using the comparators 24 to 27. When the terminal voltage is within a normal range, the failure diagnosis unit 20 outputs an 'H' level as a signal (OptOK) indicating that there is no failure in the light emitting unit 84 from the AND circuits 28 and 29. On the other hand, when the terminal voltage is out of the normal range, 'L' level is output as a signal (OptOK) indicating that the light emitting unit 84 has no failure.

  In the failure diagnosis unit 40 that monitors the output signal of the light receiving unit 86, the voltage at the output terminal of the light receiving unit 86 is determined by the voltage drop of the transistors 31 to 36 (internal resistance in the case of MOSFET) and the voltage dividing ratio of the impedance elements 37 to 39. A failure of the light receiving unit 86 is detected by determining whether or not it is equal to the terminal voltage.

  The fault diagnosis unit 40 compares the “H” level reference voltage generated by the impedance elements 41 to 43 with the output voltage of the rotation speed signal (A, B, A ^ B) by the comparators 46 and 47, and outputs the output voltage. AND circuit 50 outputs an “H” level when is within the normal range. In addition, the reference voltage of “L” level generated by the impedance elements 43 to 45 and the output voltage of the rotation speed signals (A, B, A ^ B) are compared by the comparators 48 and 49, and the output voltage is in a normal range. AND circuit 51 outputs the “H” level when it is within the range. The outputs of the AND circuit 50 and the AND circuit 51 are input to the OR circuit 52. The OR circuit 52 outputs the “H” level when either one of the AND circuits 50 and 51 is the “H” level.

  Further, the delay circuit is configured by connecting the diode 53, the capacitor 54, and the impedance element 55 as shown in FIG. The output of the OR circuit 52 and the signal that has passed through the delay circuit are respectively input to the OR circuit 56, and the rise time (L → H) and fall time (H → H) of the rotation speed signal (A, B, A ^ B). It is determined whether or not (L) is completed within a period determined by the time constant of the capacitor 54 and the impedance element 55. When the rise time and fall time change of the rotation speed signal (A, B, A ^ B) is completed within the set period, the output of the fault diagnosis unit 40 of the light receiving unit output (Flg (non fault (2)) ) Maintains the “H” level and the rise time and fall time of the rotation speed signal are not completed within the set period or the output voltage of the rotation speed signal (A, B, A ^ B) is within the reference voltage range. When deviating, the output (Flg (non fault (2))) of the fault diagnosis unit 40 of the light receiving unit output becomes 'L' level.

  The AND circuit 59 outputs a failure-free signal of each failure diagnosis unit, that is, an output from the AND circuit 58 (OptOK), a Flg (non fault (1)) output from the EXNOR circuit 82, and an AND circuit 57. When all of Flg (non fault (2))) are “H”, “H” is output as a non-fault signal (non fault) of the self-diagnosis unit 7.

  As described above, a failure of a plurality of types of rotation speed sensors 16 can be detected by implementing this failure diagnosis method together with other failure diagnosis methods. Further, by comparing the failure-free signals (OptOK, Flg (non fault (1)), Flg (non fault (2)), etc.) of the respective failure diagnosis units, the location where the failure has occurred can be investigated. The operation waveforms are the same as those shown in FIGS.

  Note that the present invention is not limited to the failure diagnosis method described with reference to FIG. 3. For example, instead of the EXOR circuit 81 and the EXNOR circuit 82, the failure diagnosis method using the state transition realized by the program described with reference to FIG. Thus, the same effect may be achieved.

Next, a third embodiment of the present invention will be described.
FIG. 9 is a functional block diagram of the monitoring device 1 according to the third embodiment. The difference from FIG. 7 is that a non-failure signal (non Fault) output from the self-diagnosis unit 7 is not sent via the signal transmission line 17 but is logically ANDed with the signals (A, B, A ^ B). Thus, the signal is sent to the abnormality detection unit 18. As a result, the AND circuit 9 that takes the logical product of the failure-free signal (non Fault) detected by the self-diagnosis unit 7 and the failure monitoring unit 8 is deleted on the abnormality detection unit 18 side.

  In FIG. 9, the operation of the rotational speed sensor 16 is basically the same as that of the second embodiment. The basic operation of the abnormality detection unit 18 is the same as that of the first embodiment.

  In this embodiment, the signal (A ^ B ^ Z) is another signal defined by a logic different from the failure monitoring signal (A ^ B) defined in the first and second embodiments. This is a failure monitoring signal.

  In FIG. 9, AND circuits 97 to 99 are configured so that the rotation speed signals (A, B) and the failure monitoring signals (A ^ B, Enable output of A ^ B ^ Z). When the non-failure signal (non Fault) of the self-diagnosis unit 7 is “L”, the AND circuits 97 to 99 cause the rotation speed signals (A, B) and the failure monitoring signals (A ^ B, A ^ B). ^ Z) is set to the “L” level to notify the abnormality detection unit 18 that the rotation speed sensor 16 is malfunctioning.

  FIG. 10 is an operation waveform assuming a case where the A-phase output of the rotation speed signal is fixed to “H” due to a failure of the rotation speed sensor. In this figure, Fault Diagnosis 7 represents the output waveform of the self-diagnosis unit 7.

  In the first half of the operation waveform of FIG. 10, the failure monitoring signal (A ^ B) and EXOR 81 have the same waveform shape. The self-diagnosis unit 7 determines that the rotation speed sensor 16 is operating normally because the logical relationship between the rotation speed signals (A, B) and the failure monitoring signal (A ^ B) is the same. The diagnosis unit 7 outputs “H” as a failure-free signal (Fault Diagnosis 7). Since the failure diagnosis signal (Fault Diagnosis 7) of the self-diagnosis unit 7 is “H”, the AND circuits 97 to 99 are the rotation speed signals (A, B) and the failure monitoring signals (A ^ B, A ^ B ^ Z). Is output as is.

  In the latter half of the operation waveform of FIG. 10, the phase A has failed, and the failure monitoring signal (A ^ B) and EXOR 81 have different waveform shapes. The self-diagnosis unit 7 determines that the rotation speed sensor 16 has failed because the logical relationship between the rotation speed signals (A, B) and the failure monitoring signal (A ^ B) does not match. 'L' is output as a no failure signal (Fault Diagnosis 7). Since the failure diagnosis signal (Fault Diagnosis 7) of the self-diagnosis unit 7 is ‘L’, the AND circuits 97 to 99 output ‘L’.

  Thus, the failure-free signal (non Fault) on the rotational speed sensor 16 side can be transmitted to the abnormality detection unit 18 without using a dedicated signal transmission line for transmitting the failure-free signal (non Fault).

  Here, a failure monitoring signal (A ^ B ^ Z) having a logic different from that of the failure monitoring signal (A ^ B) defined in the first and second embodiments will be described.

  FIG. 11 is an example of the arrangement of small holes in the rotating disk 85, and FIG. As the failure monitoring signal, an exclusive OR of the rotation speed signal (A, B) and the signal (Z) indicating the reference position is used.

  In FIG. 11, one position during one rotation is set as a reference section of the rotation position, a small hole for light passage is provided in this reference section, and light emitted from the light emitting unit 84 passes through the small hole in this reference section. Sometimes Z = 'H'. In other sections, Z = 'L' is defined, and a small hole for passing light is provided according to the logic of A ^ B ^ Z. In other words, in the sections other than the reference section, Z = 'L', corresponding to the small holes of the A phase and B phase, and small on the concentric circle with the small holes of the reference section so that the logic of A ^ B ^ Z is established. A hole is provided.

  FIG. 12 is a state transition diagram when this reference section is set to 3/4 cycles of the rotational speed signal (A, B). Description of the same parts as those in FIG. 4 is omitted. In FIG. 12, the right half surface (Y part) shows the state transition in the reference section of the rotational position, and the left half surface (X part) shows the state transition in the part other than the reference section of the rotational position. In the selection of the reference section in FIG. 11, one state (A = 'H in FIG. 12) is shown when transitioning from the reference section to the outside of the reference section or from the outside of the reference section to the reference section in FIG. ', B =' H ', A ^ B ^ Z =' L ').

  Also in FIG. 12, when there is no failure in the rotation speed sensor 16, the state transition is performed according to the solid line arrow or the broken line arrow by the combination of the rotation speed signal (A, B) and the failure monitoring signal (A ^ B ^ Z). .

  Thereby, the self-diagnosis unit 7 and the failure monitoring unit 8 can detect the failure of the rotation speed sensor 16 and the signal transmission line 17 depending on whether or not the state is changed to the failure state (Fault). In addition to the failure detection function, the self-diagnosis unit 7 and the failure monitoring unit 8 using the failure detection principle shown in FIGS. 11 and 12 extract a signal (Z-phase signal) indicating the reference position in the reference section. be able to.

  FIG. 13 shows an operation waveform when passing through the reference section, and FIG. 14 shows an operation waveform when the rotation direction is reversed in the vicinity of the reference section. In FIG. 13, when the state (A, B, A ^ B ^ Z) = (H, H, L) changes to (L, H, L), a signal (Flg (Z )) Is set to the “H” level. Thereafter, when the state (L, L, H) is entered, the 'H' level is output as the Z-phase signal output. Thereafter, when the state (H, H, L) is transferred via the state (H, L, L), Flg (Z) is set to the 'L' level. The reverse rotation operation is the same except that the state (L, H, L) and the state (H, L, L) in the state transition are switched.

  In FIG. 14, the intrusion into the reference section, that is, the state (H, H, L) is changed to (L, H, L) and Flg (Z) becomes the “H” level, but the state (L , L, H), the Z-phase signal output is maintained at the “L” level. Thereafter, when returning to the state (H, H, L), Flg (Z) returns to the 'L' level. The same applies when the rotation direction is reversed from the reverse rotation operation. Intrusion into the reference section (from state (H, H, L) to (H, L, L)) is detected and Flg (Z) becomes 'H' level, but state (L, L, H) Since the state returns to the state (H, H, L) before shifting to, the Z-phase signal output is maintained at the “L” level.

  The principle of failure detection outside the reference section is the same as in FIG. Therefore, failure detection operation waveforms from states other than the states (H, H, L) are the same as those in FIG. Here, description of operations other than the reference section is omitted, and operations from a state (H, H, L) indicating entry into the reference section will be described.

  15 to 19 show operation waveforms when a failure occurs in the rotation speed sensor 16 and the signal transmission line 17. In addition, when the A ^ B ^ Z phase is fixed to the 'H' level due to a failure, it is clear that the state (H, H, L) cannot be changed. Therefore, since it can be determined that there is a failure based on the same principle as in FIG.

  FIG. 15 shows an example of operation waveforms when the A ^ B ^ Z phase is fixed to the ‘L’ level due to a ground fault or the like. When the A phase becomes 'L' level from the state (H, H, L), Flg (Z) becomes 'H' level, but even if the B phase signal becomes 'L' level after that, A ^ B ^ Z The phase does not go to 'H' level. Due to this state transition abnormality, the self-diagnosis unit 7 and the failure monitoring unit 8 determine that a failure has occurred in any phase.

  FIG. 16 shows an example of an operation waveform when the A phase is fixed to the “H” level by stacking (a stuck-at fault fixed to the “L” level or the “H” level) or the like. Even if the A ^ B ^ Z phase is set to the “H” level from the state (H, H, L), the A phase does not become the “L” level. It is determined that a failure has occurred in any of the phases due to the abnormal state transition.

  FIG. 17 is an example of an operation waveform when the A phase is fixed to the “L” level due to a ground fault or the like. When the A phase becomes 'L' level from the state (H, H, L), Flg (Z) becomes 'H' level, but after that, even if the A ^ B ^ Z phase signal becomes 'H' level, B The phase does not go to 'L' level. It is determined that a failure has occurred in any of the phases due to the abnormal state transition.

  FIG. 18 is an example of an operation waveform when the B phase is fixed to the “H” level by stack-at or the like. From the state (H, H, L), the A phase becomes ‘L’ level and the A ^ B ^ Z phase signal becomes ‘H’ level. Thereafter, even if the A ^ B ^ Z phase signal becomes ‘L’ level, the B phase does not become ‘L’ level. It is determined that a failure has occurred in any of the phases due to the abnormal state transition.

  FIG. 19 is an example of an operation waveform when the B phase is fixed to the “L” level due to a ground fault or the like. From the state (H, H, L), the A phase becomes ‘L’ level and the A ^ B ^ Z phase signal becomes ‘H’ level. Thereafter, even if the A ^ B ^ Z phase signal becomes ‘L’ level, the B phase does not become ‘H’ level. It is determined that a failure has occurred in any of the phases due to the abnormal state transition.

  In any of the cases of FIGS. 15 to 19, it can be detected that a failure has occurred within a quarter of the rotation speed signal (A, B) after the failure has occurred.

  In addition, when the reference section is set to 7/4, 11/4,... Of the rotation speed signal (A, B), the state transition of the right half (Y part) in FIG. It is possible to detect a failure based on the same principle just as.

  The same effect can be obtained by using a logic inversion signal of the A ^ B ^ Z phase (-A ^ B ^ Z phase) instead of the A ^ B ^ Z phase as a failure monitoring signal. In addition, the same effect can be obtained by using a logical inversion signal (-Z phase) of the Z phase instead of the Z phase in the setting of the A ^ B ^ Z phase.

  In addition, in the rotating disk 85 of the present embodiment, three types of small holes are provided, one for each phase, but the arrangement is not limited to one type of small holes for each phase. Two types of small hole arrangements in which the logic is inverted with respect to one phase may be used, and six types and three pairs of small hole arrangements may be used in total for the three phases. The failure probability can be reduced.

Next, a fourth embodiment of the present invention will be described.
FIG. 20 is a functional block diagram of the monitoring device 1 according to the fourth embodiment. The main difference from the configuration of FIG. 9 is that an oscillator 5 and a rotation speed comparison unit 6 are added to the rotation speed sensor 16 side, and a low rotation speed signal generation unit 10 is added to the abnormality detection unit 18 side. . This low rotation speed signal is a signal indicating that the electric motor is in a low rotation state or a stopped state. The elements denoted by reference numerals 91 to 95 are EXOR circuits, and the StopOK signal is a signal indicating a low rotational speed and no failure. The same elements as those in FIG.

  In FIG. 20, the basic operations of the rotation speed sensor 16 and the abnormality detection unit 18 are the same as those in the third embodiment. Hereinafter, the difference from the third embodiment will be mainly described.

The rotation speed comparison unit 6 compares the rotation speed of the motor from the rotation speed signals (A, B) input within a fixed period obtained from the output signal of the oscillator 5. When the comparison unit 6 determines that the rotation speed is lower than the set value, the comparison unit 6 outputs an alternating-current signal generated from the output signal of the oscillator 5 to the output (StopSig) of the comparison unit 6. On the other hand, when it is determined that the rotation speed is higher than the set value, the output of the comparison unit 6 (StopSig) is output at the “L” level. The EXOR circuits 91 and 92 output an exclusive OR of the output (StopSig) of the comparison unit 6 and the rotation speed signal (A, B). The output signals are input to AND circuits 97 and 98, respectively, and the self-diagnosis unit 7 has no failure signal (non Fault).
And the logical product of

  Thus, the rotation speed sensor uses the outputs (A / StopSig, B / StopSig) of the EXOR circuits 91 and 92 as the rotation speed signal only when the non-failure signal (non Fault) of the self-diagnosis unit 7 is “H”. Output. This signal and a signal (A ^ B ^ Z) logically ANDed with a non-fault signal (non Fault) by the AND circuit 99 are input to the abnormality detection unit 18 via the signal transmission line 17.

  If the low rotation speed signal generation unit 10 detects that the rotation speed signals (A / StopSig, B / StopSig) input to the abnormality detection unit 18 are logically inverted at the same time, the low rotation speed signal generation unit 10 determines that the motor is at a low rotation speed. To do. When it is determined that the rotation speed is low, a 'H' level is output as a low rotation speed signal (StopSig ').

  The EXOR circuits 94 and 95 exclusively use the low rotational speed signal (StopSig ′) generated by the low rotational speed signal generation unit 10 and the rotational speed signal (A / StopSig, B / StopSig) input to the abnormality detection unit 18. Output logical sum. By using the outputs of the EXOR circuits 94 and 95 as the rotation speed signal, a conventional A-phase / B-phase rotation speed signal can be obtained.

  The AND circuit 9 is in a low rotation speed state and indicates a failure-free state when both a failure-free signal (non Fault) and a low rotation speed signal (StopSig ') output from the failure monitoring unit 8 are' H '. 'H' is output as a signal (StopOK).

  FIG. 21 is an operation explanatory diagram of the self-diagnosis unit 7 and the failure monitoring unit 8 in the present embodiment. Hereinafter, the difference from FIG. 12 will be mainly described. In FIG. 21, a dashed line arrow indicates a state transition when an AC signal is output to the output (StopSig) of the comparison unit 6.

  Also in FIG. 21, when there is no failure in the rotation speed sensor, the combination of the rotation speed signal (A / StopSig, B / StopSig) and the failure monitoring signal (A ^ B ^ Z) is changed to a solid line arrow, a broken line arrow, or a one-point broken line arrow. Follow the state transition. From this, the self-diagnosis unit 7 and the failure monitoring unit 8 can detect the failure of the rotation speed sensor 16 and the signal transmission line 17 depending on whether or not the state is changed to the fault state (Fault). In addition to the failure detection function, the self-diagnosis unit 7 and the failure monitoring unit 8 can extract a signal indicating a reference section (Z-phase signal) in the same manner as in the third embodiment.

  FIG. 22 to FIG. 25 show configuration circuit examples of the rotational speed comparison unit 6 shown in FIG. 20, FIG. 26 shows an example of operation waveforms when there is no failure, and FIG. 27 shows an example of operation waveforms when there is a failure. .

  In FIG. 22, edge detection circuits 61 and 62 and an OR circuit 63 detect the rising and falling edges of the output signal of the oscillator 5 and generate a clock signal (Clk) that determines the detection timing of the rotational speed. The EXOR circuit 64 outputs an exclusive OR of the rotation speed signals (A, B). This exclusive OR output (A ^ B) is a signal that is inverted when any one of the rotation speed signals (A, B) changes.

  The count circuits 65 and 66 determine whether a rising edge or a falling edge exists in the exclusive OR output (A ^ B ^ Z) during one cycle of the clock signal (Clk). If there is a rising edge during one cycle, the output (Judge Up) of the count circuit 65 outputs the “H” level. When there is a falling edge during one period, the output (Judge Dn) of the count circuit 66 outputs the “H” level. The output signal of the AND circuit 67 outputs “H” level when both the rising edge and the falling edge exist during one cycle of the clock signal (Clk), and at least one of the rising edge and the falling edge is output. When one of them does not exist, 'L' level is output. The inverted output of the D-FF 68 to which the output of the AND circuit 67 is connected outputs an “L” level when both the rising edge and the falling edge exist during one cycle of the clock, and the rising edge and the falling edge are output. When at least one of the edges does not exist, 'H' level is output. The inverted output of the D-FF 68 is used as a signal (Flg (stop)) indicating that the rotation speed is equal to or lower than the set value.

  The AND circuits 69 and 71 and the T-FF 70 divide the output signal (Timer) of the oscillator 5 by 2 when the signal (Flg (stop)) indicating that the rotational speed is equal to or lower than the set value is at the “H” level. An AC signal with a fixed period is output. The output of the AND circuit 71 is used as an output signal (StopSig) of the rotation speed comparison unit 6.

  A signal having a frequency lower than the cycle of the output signal (Timer) of the oscillator 5 is used as a source signal of the low rotational speed signal (Stop signal) (StopSig). As a result, when the rotation speed signal (A, B) is applied to the signal line of the low rotation speed signal (stop signal) (StopSig) due to a failure (ground fault, contact, electromagnetic induction, etc.) of the signal transmission line 17 However, it is possible to confirm that the low rotational speed signal generation unit 10 is not a normal low rotational speed signal (stop signal) (StopSig) by determining the frequency of the AC signal. Accordingly, the output of the low rotation speed signal (stop signal) (StopSig) can be stopped before the low rotation speed signal (stop signal) (StopOK) on the abnormality detection unit 18 side is output.

  In the first half period of the operation waveform of FIG. 26, both the outputs (Judge Up, Judge Dn) of the count circuits 65 and 66 are at the “H” level at the timing of the clock signal (Clk). A signal (Flg (stop)) indicating that there is a low rotation speed signal (stop signal) (StopSig) outputs an “L” level.

  In the low rotation speed state continuation period (Stop (Low Speed)) in the latter half of the operation waveform of FIG. 26, one or both of the outputs (Judge Up, Judge Dn) of the count circuits 65 and 66 are at the timing of the clock signal (Clk). Since it is at the L level, the signal (Flg (stop)) indicating that the rotation speed is equal to or lower than the set value outputs the “H” level, and the output (StopSig) of the rotation speed comparison unit 6 is the clock signal (Clk). ) Is output.

The first half period of the operation waveform in FIG. 27 is the same as that in FIG.
In the failure detection period (Fault) in the latter half of the operation waveform in FIG. 27, the signal (Flg (stop)) indicating that the rotational speed is equal to or lower than the set value is output at the “H” level by the same operation as in FIG. The output (StopSig) of the rotation speed comparison unit 6 outputs an AC signal obtained by dividing the clock signal (Timer). When there is no failure, the low rotational speed signal (stop signal) (StopSig), which is the output of the AND circuit 71, outputs an alternating current signal having a constant cycle by the same operation as in FIG. On the other hand, in the fault period (Fault) of FIG. 27, the rotation speed signals (A / StopSig, B / StopSig) and the fault monitoring signal (A ^ B ^ Z) on the signal transmission line are all at the “H” level. . In this case, the no-failure signal (non Fault) output from the failure monitoring unit 8 becomes “L”, and the low rotation speed signal (stop signal) (StopOK) also outputs the “L” level. In other failure modes, the failure can be detected by the same operation. When the self-diagnosis unit 7 detects a failure, the AND circuit 97, 98, 99 causes the rotation speed signal (A / StopSig, B / StopSig) and the failure monitoring signal (A ^ B, A ^ B ^ Z). Stop the output of. By stopping the signal output by the AND circuits 97, 98, and 99, the failure monitoring unit 8 can be notified that there is a failure.

  In FIG. 23, a failure monitoring signal (A ^ B, A ^ B ^ Z) is used instead of the output of the EXOR circuit 64. The failure monitoring signals (A ^ B, A ^ B ^ Z) are designed in advance so that a signal corresponding to the exclusive OR of the A phase and B phase of the rotation speed signal is output. Therefore, when there is no failure in the rotation speed sensor, the same operation as that in FIG. 22 is performed. If there is a failure in the rotation speed sensor, the failure is detected by the self-diagnosis unit 7, and the rotation speed signal (A / StopSig, B / StopSig) and the failure monitoring signal (A ^) are detected by the AND circuits 97, 98, 99. By stopping the output of B, A ^ B ^ Z), the transmission of the low rotation speed signal (stop signal) (StopSig) can be stopped.

  In FIG. 24, the output of the EXOR circuit 64, which is the exclusive OR of the rotation speed signals (A, B), is input to the edge detection circuits 61, 62. By connecting the outputs of the edge detection circuits 61 and 62 to the input of the OR circuit 63, a clock signal (Clk) that determines the detection timing of the rotational speed is generated.

  The count circuits 65 and 66 determine whether a rising edge or a falling edge is present in the output (Timer) of the oscillator 5 during one cycle of the clock signal (Clk). The AND circuit 67 and the D-FF 68 output “H” level when both the rising edge and the falling edge exist during one clock cycle, and at least one of the rising edge and the falling edge exists. If not, 'L' level is output. The output of the D-FF 68 is used as a signal (Flg (stop)) indicating that the rotation speed is equal to or less than the set value.

  The AND circuits 69 and 71 and the T-FF 70 have a constant period obtained by dividing the output signal of the oscillator 5 by 2 when the signal (Flg (stop)) indicating that the rotational speed is equal to or lower than the set value is at the “H” level. The AC signal is output. The output of the AND circuit 71 is used as an output signal (StopSig) of the rotation speed comparison unit 6.

  In FIG. 25, an oscillator 5 that outputs a signal having a constant pulse width synchronized with the rotation speed signal is prepared. The rotation speed comparison unit 6 compares the output pulse width of the oscillator 5 with the pulse width of the rotation speed signal, and determines whether the rotation speed is equal to or less than a set value. The method for generating the clock signal (Clk) that determines the detection timing of the rotational speed is the same as that in the second embodiment, and thus the description thereof is omitted. The oscillator 5 includes a charging circuit including a capacitor 72 and a constant current source 73, a determination circuit including a constant voltage source 74 and a comparator 75, and a discharging circuit including an OR circuit 76 and a constant current source 77. The comparator 75 compares the voltage of the capacitor 72 with the constant voltage source 74 and outputs “H” level when the voltage of the capacitor 72 is higher, and outputs “L” level when the voltage of the capacitor 72 is lower. To do. The constant current source 77 discharges the capacitor 72 and resets the oscillator 5 when the output of the OR circuit 63 is at the “H” level and when the output of the comparator 75 is at the “H” level. When the output of the OR circuit 63 is at the “L” level, the oscillator 5 outputs a signal having a constant pulse width set by the capacitance of the capacitor 72 and the constant current source 73. The RS-FF 78 holds whether or not the output of the comparator 75 has become the “H” level from the input of the clock signal (Clk) to the input of the next clock signal (Clk). The output of the RS-FF 78 outputs the “H” level when the pulse width of the clock signal (Clk) is wider than the output signal of the oscillator 5, and outputs the “L” level when it is narrow. The D-FF 68 holds the output of the RS-FF 78 at the timing when the clock signal (Clk) is input. The output of the D-FF 68 is used as a signal (Flg (stop)) indicating that the rotation speed is equal to or less than the set value.

  The signal generator 79 and the AND circuit 71 output an AC signal having a preset constant frequency when the signal (Flg (stop)) indicating that the rotational speed is equal to or lower than the set value is at the “H” level. The output of the AND circuit 71 is used as the output (StopSig) of the rotation speed comparison unit 6.

  As described above, according to the present embodiment, it is possible to detect a low rotational speed state (including a stopped state) of the electric motor. Further, even in a low rotational speed state such as a stopped state, a failure in the rotational speed sensor and the signal transmission line can be reliably detected.

1 Rotational speed monitoring device 4 Rotational speed detection unit (rotation detection means)
5 Oscillator 6 Comparison part (speed judgment means)
7, 20, 40 Fault diagnosis unit (self-diagnosis means)
8 Failure monitoring unit (failure monitoring means)
9, 28, 29, 50, 51, 57 to 59, 67, 69, 71, 97 to 99 AND circuit 10 Low rotation speed signal generator 11, 13, 21 to 23, 37 to 39, 41 to 45, 55 Impedance element 12, 14 Light-emitting element 16 Rotational speed sensor 17 Signal transmission line 18 Abnormality detection unit 24-27, 46-49, 75 Comparator 53 Diode 54, 72 Capacitor 56, 63, 76 OR circuit 61, 62 Edge detection circuit 64 , 81, 91, 92, 94, 95 EXOR circuit 65, 66 Count circuit 73, 77 Constant current source 74 Constant voltage source 79 Signal generator 82 EXNOR circuit 84 Light emitting part 85 Rotating disk 86 Light receiving part

Claims (11)

A rotation speed sensor having a rotation detection means for generating and outputting a rotation speed signal capable of detecting a rotation position and a rotation speed by a concentric circular hole formed in the rotating disk, and passing through the small hole,
The rotating disk has small holes corresponding to rotation speed signals of two or more phases, and has a small hole for redundant signals that can be uniquely determined by a predetermined logical relationship with respect to the rotation speed signal of each phase, The rotation speed sensor outputs a failure monitoring signal generated by the light passing through the small hole for the redundant signal.   The rotational speed sensor according to claim 1, wherein the redundant signal is a signal corresponding to an exclusive OR of rotational speed signals of respective phases.   3. The rotational speed sensor according to claim 1, wherein the rotary disk has a reference section including a reference position of rotation in a part thereof, and the rotation detecting means is configured to detect the rotational speed signal in a range other than the reference section. An exclusive OR is output as the failure monitoring signal, and an inversion signal of an exclusive OR of the rotation speed signal is output as the failure monitoring signal in the reference interval.   3. The rotational speed sensor according to claim 1, wherein the rotary disk has a reference section including a reference position of rotation in a part thereof, and the rotation detecting means is configured to detect the rotational speed signal in a range other than the reference section. An inversion signal of exclusive OR is output as the failure monitoring signal, and an exclusive OR of the rotation speed signals is output as the failure monitoring signal in the reference section.   5. The rotational speed sensor according to claim 3, wherein the width of the reference section is set to N-1 / 4 (N is an integer) times the width of the section corresponding to the repetition period of the rotational speed signal. Rotational speed sensor.   6. The rotational speed sensor according to claim 1, further comprising self-diagnosis means for determining the presence or absence of a failure based on a logical relationship between the rotational speed signal and the failure monitoring signal. Rotational speed sensor.   7. The rotational speed sensor according to claim 6, wherein the self-diagnosis unit permits the output of the rotational speed signal only when it is determined that there is no failure.   The rotational speed sensor according to claim 6 or 7, further comprising speed determining means for determining whether the rotational speed is high or low, wherein the speed determining means determines that the rotational speed is lower than a predetermined value. A rotation speed sensor that outputs a low rotation speed signal indicating a low rotation speed state when the self-diagnosis means determines that there is no failure.   The rotational speed sensor according to claim 8, wherein an alternating current signal having a cycle longer than the predetermined value for determining whether or not the low rotational speed state is used as the low rotational speed signal.   An apparatus for monitoring the rotational speed of an electric motor using the rotational speed sensor according to any one of claims 1 to 9, wherein the rotational speed sent from the rotational speed sensor via a signal transmission line. And a failure monitoring means for inputting a signal and the failure monitoring signal, and determining that there is no failure when the input rotational speed signal and the failure monitoring signal are in the predetermined logical relationship. Rotation speed monitoring device. An apparatus for monitoring the rotational speed of an electric motor using the rotational speed sensor according to claim 3 or 4,
The rotational speed signal and the failure monitoring signal sent from the rotational speed sensor via a signal transmission line are input, and the input rotational speed signal and the failure monitoring signal are in the predetermined logical relationship. A rotation speed monitoring device comprising failure monitoring means for determining that there is no failure in some cases and identifying the reference section from a transition process between the rotation speed signal and the failure monitoring signal.