JP5370397B2 - Motor speed monitoring device - Google Patents

Abstract

The present invention generates, by shaping the waveform of a pseudo AC voltage that is made by pulse modulation and that is to be supplied to an AC motor, a shaped signal that has the ON/OFF thereof switched with the same cycle as the switching of the pseudo AC voltage between plus and minus, and derives the rotational speed of the AC motor on the basis of the shaped signal. Abnormality is evaluated on the basis of the derived rotational speed, and when abnormality is evaluated as having occurred, a control signal for stopping or decelerating the AC motor is outputted.

Description

  The present invention relates to a motor rotation speed measuring device and a motor rotation speed monitoring device in an AC motor.

  AC motors used in industrial machines are designed with the expectation of power from three-phase AC, and have the property of obtaining a rotational speed proportional to the input frequency. Therefore, in order to accelerate / decelerate an AC motor or perform speed control, a method of smoothly controlling an arbitrary motor speed by a frequency changing device such as an inverter is employed in many devices.

  On the other hand, in an industrial machine, an apparatus or a function capable of monitoring an abnormal operation in which a motor rotates at an unexpected speed due to a failure or the like and quickly stopping the motor is important.

  Assuming that the motor is equipped with a speed detector such as an encoder or sensor on the motor shaft as a device to prevent it from operating at a speed exceeding the expected speed due to human error or failure of the control device. A general method is to physically obtain the difference between the rotational speed and the actual rotational speed. In the following Patent Document 1, a technique for outputting a rotation state of a motor including a stopped state to an abnormality detection means from a rotation speed sensor provided in the motor is disclosed.

JP 2010-288390 A

As described above, if a motor is equipped with a speed detector, the detection result can be fed back to the motor control unit to detect abnormal rotation due to a failure. If this is to be added to a motor that is not equipped with a motor, it must conventionally be physically attached by modification. However, depending on the environment, the speed detector may not be installed due to location restrictions, and even if it can be installed, there is a demerit that the apparatus becomes larger.

  On the other hand, the technology for estimating the rotational speed of the motor from the waveform of the electric power supplied to the motor is adopted in technology such as sensorless vector control of the inverter, but the method using the current detector does not meet the purpose of downsizing. In addition, noise is erroneously detected as a high-speed signal by voltage control based on PWM modulation used for simplification of the system, which is not suitable for speed detection.

  It is an object of the present invention to provide a motor speed measuring device and a motor speed monitoring device that can measure and monitor the rotational speed of an AC motor without physically adding a sensor or the like to the motor rotation shaft.

  In order to achieve the above object, in the motor speed measuring device and motor speed monitoring device according to the present invention, the motor speed is derived and the motor is stopped or decelerated by the following means or processing.

  A motor speed measuring device according to the present invention is a motor speed measuring device used in parallel connected to a power line of an AC motor, and from the AC voltage supplied to the AC motor through the power line, the motor speed measuring device It has speed deriving means for deriving the rotation speed, and the speed deriving means derives the rotation speed of the AC motor by measuring a required time between zero cross positions from the waveform of the AC voltage. .

  By adopting such a configuration, the rotational speed of the motor can be obtained only by acquiring the AC voltage supplied to the AC motor without installing a speed detector on the rotating shaft of the motor.

  The AC voltage may be a pseudo AC voltage by pulse modulation.

  The control of the AC motor often uses a pseudo AC voltage by pulse modulation, and the present invention can be applied even to a motor that performs voltage control using the pulse modulation.

  A motor speed monitoring apparatus according to the present invention is a motor speed monitoring apparatus that is used in parallel connected to a power line of an AC motor, and from the AC voltage supplied to the AC motor through the power line, A speed deriving means for deriving the rotational speed, and a control for determining whether or not the rotational speed derived by the speed deriving means is abnormal, and for stopping or decelerating the rotation of the AC motor when it is determined as abnormal Motor control means for outputting a signal, the alternating voltage is a pseudo alternating voltage by pulse modulation, and the speed deriving means adds / minus the pseudo alternating voltage by shaping the waveform of the pseudo alternating voltage. Waveform shaping means for generating a shaped signal that switches on / off at the same cycle as the switching of the waveform, and based on the shaped signal output from the waveform shaping means. Is characterized by deriving the rotational speed of the AC motor are.

  By adopting such a configuration, it is possible to detect the rotational speed of the motor and detect an abnormality in the speed simply by acquiring the alternating voltage supplied to the alternating current motor without installing a speed detector on the rotational shaft of the motor. In this case, an instruction for stopping or decelerating can be output to the outside.

  The waveform shaping means in the present invention includes first extraction means for extracting only a positive component signal from the waveform of the pseudo AC voltage, and second extraction means for extracting only a negative component signal from the waveform of the pseudo AC voltage. And a shaping signal generating means for generating and outputting the shaping signal from the output signal of the first extracting means and the output signal of the second extracting means.

  In addition, the first extraction unit includes a first comparator that compares the pseudo AC voltage with a positive threshold voltage, and the second extraction unit calculates the pseudo AC voltage and the negative threshold voltage. The shaping signal generating means can be constituted by a flip-flop to which the output signal of the first comparator and the output signal of the second comparator are input.

  Thus, the waveform shaping means in the present invention can shape the AC voltage waveform for deriving the rotational speed of the motor with only at least three semiconductor elements, so that the entire apparatus can be miniaturized. Because there is no need to select a sensor for each motor current consumption capacity, and even if you want to detect the speed without changing the existing machine, you can change only the electric circuit. It has the advantage of being able to. In addition, by comparing the waveform of the pseudo alternating voltage with the threshold voltage, there is an advantage that the waveform can be reliably shaped without being affected by power supply noise.

  In the motor speed monitoring apparatus according to the present invention, the combination of the logic of the three signals of the output signal of the first extraction unit, the output signal of the second extraction unit, and the shaping signal is a possible combination. It is also preferable to have a failure diagnosing unit that determines whether the waveform shaping unit is out of order when the combination is not possible.

  As a result, when the signal output from the first extraction means, the signal output from the second extraction means, and the three signals of the shaping signal are not logically matched, that is, when a failure occurs in the apparatus, this is detected. It becomes possible to do. When a failure is detected, the user may be notified, or the motor may be stopped for the reason that the unmonitored state is entered.

  Similarly, in the motor speed monitoring apparatus according to the present invention, a test signal having a predetermined waveform is input to the first extraction means and the second extraction means, and the logic of the shaping signal output from the shaping signal generation means. Second failure diagnosis means for determining whether or not the waveform shaping means is in failure when the waveform shaping means is not corresponding to the waveform of the test signal. It is also preferable to have.

  By inputting a test signal and comparing it with the output result, it is possible to confirm whether a predetermined operation is being performed correctly. In the failure detection by the logical consistency check, if the circuit is stopped in the correct logic state, the failure cannot be detected, but there is an advantage that the failure detection can be surely performed as compared with this.

  The control signal output from the motor control means in the present invention is a signal output to a circuit breaker that interrupts the supply of the AC voltage to the AC motor or a controller that supplies the AC voltage to the AC motor. May be.

  When the motor is stopped immediately, for example, the circuit breaker may receive a control signal and stop power supply to the motor. When the motor is decelerated, the motor controller, for example, a control circuit of the inverter device may receive the control signal and decelerate the motor until the speed reaches an allowable range.

  By outputting a control signal to the circuit breaker or motor controller, it is possible to stop the motor reliably by opening the circuit breaker, or to give an alarm to the user and decelerate and continue operation. Is possible. This has the advantage of not only monitoring controller failures but also monitoring user abnormal operations. Of course, if the rotation speed does not decrease even if the control signal for deceleration is output to the controller, it is determined that there is a failure and the control signal for stopping is output to the circuit breaker. You may use together.

  ADVANTAGE OF THE INVENTION According to this invention, the motor speed measuring apparatus and motor speed monitoring apparatus which can monitor the rotational speed of an AC motor can be provided, without adding a sensor etc. to a motor rotating shaft physically.

It is a figure which shows the waveform which remove | eliminated the modulation component of the time-axis direction from the input waveform by which PWM modulation was carried out, and the said waveform. It is a figure which shows the structure of the speed detection part based on 1st-3rd embodiment. 3 is a circuit diagram showing a pulse width detection unit 201. FIG. FIG. 6 is a diagram illustrating a waveform of a signal processed by a pulse width detection unit 201. It is a figure showing the whole motor speed monitoring device composition concerning a 1st embodiment. It is a figure which shows the modification of the motor speed monitoring apparatus based on 1st Embodiment. It is a figure which shows the whole structure of the motor speed monitoring apparatus based on 2nd Embodiment. It is a figure which shows the whole structure of the motor speed monitoring apparatus based on 3rd Embodiment. It is an operation | movement flowchart of the abnormality detection part 502 based on 1st Embodiment. It is a logical table based on 4th Embodiment. It is a circuit diagram added to the pulse width detection part 201 based on 5th Embodiment. It is a figure showing the diagnostic pulse based on 5th Embodiment. It is a figure which shows the structure of the speed detection parts 601 and 701 based on 4th, 5th embodiment. It is a figure which shows the structure of the signal consistency confirmation part 204 based on 4th Embodiment.

  In the present invention, the AC frequency is measured from the voltage waveform input to the motor, and the speed of the motor is derived. However, the electric power used by industrial motors is a circuit that is overwhelmingly higher than the operation of electronic control circuits, such as 200V and 400V. Furthermore, in the pseudo sine wave generated from the PWM circuit by the inverter, the waveform distortion Since the rate is high, an advanced noise removal technique is required to completely restore the sine wave before modulation without malfunctioning the electronic circuit. In the following, an embodiment of the invention for satisfying the above requirements and obtaining a frequency accurately will be described.

(First embodiment)
First, the outline of the speed deriving means in the present embodiment will be described with reference to FIG. A speed detector 501 serving as a speed deriving unit is installed in parallel with the motor 505, and acquires a three-phase power input to the motor. Although the power supply has three phases, since only the phases are different and the frequencies are the same, it is sufficient to acquire at least one arbitrary phase.

  As shown in FIG. 1A, the waveform of the AC voltage input to the motor 505 (at the same time as the speed detection unit 501) is a signal that is modulated by changing the duty ratio of the pulse wave and reproducing a sine wave by PWM. is there. A signal that artificially represents the waveform of an AC voltage by pulse modulation (PWM or PAM) is called a “pseudo AC voltage”. Hereinafter, a configuration for acquiring (restoring) the input frequency from the waveform of such a pseudo AC voltage will be described.

  FIG. 2 is a diagram illustrating the configuration of the speed detection unit 501 in the configuration illustrated in FIG. 5A. The speed detection unit 501 includes a pulse width detection unit 201, a pulse width measurement unit 202, and a rotation speed determination unit 203. The pulse width detection unit 201 is a waveform shaping unit of the present invention, and generates a shaped signal that is turned on / off at the same cycle as the plus / minus switching of the pseudo AC voltage by shaping the waveform of the pseudo AC voltage. Have a role. When the waveform shown in FIG. 1A passes through the pulse width detector 201, a shaped signal having the waveform shown in FIG. 1B is obtained. The pulse width measuring unit 202 measures the width of one cycle of the waveform shown in FIG. 1B, and converts the reciprocal thereof as an input frequency to the motor. The rotational speed determination unit 203 determines the rotational speed of the motor from the acquired input frequency to the motor.

FIG. 3 is a diagram illustrating a circuit configuration of the pulse width detection unit 201. The pulse width detection unit 201 includes a comparator 101 as a first extraction unit, a comparator 102 as a second extraction unit, and an RS flip-flop 103 as a shaping signal generation unit. The power supply 104 input to the motor is stepped down and then input to the comparator 101 and the comparator 102. The comparator 101 has a reference voltage (threshold voltage) Vref1 larger than 0V and lower than the maximum voltage of the pulse wave, and the comparator 102 has a reference voltage (threshold voltage) smaller than 0V and higher than the maximum voltage of the pulse wave. ) Vref2 is applied. The operation of this circuit will be described with reference to FIGS. 4 (a) to 4 (d).

  The power supply 104 input to the pulse width detector 201 has the waveform shown in FIG. As for the comparator 101, when the input 104 is higher than the reference voltage Vref1, the output logic becomes positive. Here, when the pulse oscillates to the positive side (phase 1 in FIG. 4A), the input 104 becomes higher than the reference voltage Vref1, so that the output waveform when the waveform in FIG. Is as shown in FIG.

  On the other hand, the comparator 102 is connected in reverse polarity to the comparator 101, and the output logic becomes true when the reference voltage Vref 2 is higher than the input 104. In other words, when the pulse oscillates to the positive side (phase 1 in FIG. 4A), the reference voltage Vref2 is always lower than the input 104, so the output logic is false.

  When the pulse oscillates to the negative side (phase 2 in FIG. 4A), the output logic of the comparator 101 is false because the input 104 is always lower than the reference voltage Vref1. On the other hand, for the comparator 102, since the reference voltage Vref2 is higher than the input 104 and the output logic becomes true, the output waveform when the waveform of FIG. 4A is input to the comparator 102 is as shown in FIG. become. As a result, the comparators 101 and 102 can reliably extract only the positive and negative components of the input waveform.

  The RS flip-flop 103 has an S input, an R input, and a Q output. The RS flip-flop has a feature that the logic of the S input is held in the Q output, and the held logic is reset when the R input becomes true. When the output of the above-described comparator 101 (FIG. 4B) is given to the S input of the flip-flop 103, and the output of the comparator 102 (FIG. 4C) is given to the R input, the waveform of the Q output 106 is shown. Is as shown in FIG. This is the shaped signal obtained by removing the pulse width modulation component from the input waveform to the motor, which is the purpose of the pulse width detector 201.

  Next, the pulse width measurement unit 202 measures the width of one cycle of the acquired shaped signal waveform (FIG. 4D), and determines the reciprocal thereof as the input frequency to the motor. For the measurement of the pulse width, for example, a zero-cross circuit is used to measure the cycle of the timing when the applied voltage becomes zero. As a result of the measurement, for example, when one waveform period is 5 milliseconds, the input frequency to the motor is 200 Hz which is the reciprocal thereof.

  After determining the input frequency, the rotation speed determination unit 203 derives the motor synchronization speed and the rotation speed based on the measured frequency. In the case of a synchronous motor, the rotational speed of the motor coincides with the synchronous speed calculated from the input frequency.

For example, when the input frequency for the 8-pole synchronous motor is 200 Hz, the number of rotations can be determined as (2 × 200 ÷ 8) × 60 = 3000 rotations / minute by the above formula. In the case of an induction motor, since the input frequency and the synchronization speed do not match, the rotation speed of the motor is obtained by subtracting the amount corresponding to the slip from the synchronization speed calculated above. For example, in the above example, when the slip is 0.1, the rotation speed can be set to 3000− (3000 × 0.1) = 2700 rotations / minute. By performing the above processing, the speed detection unit 501 can derive the number of rotations of the motor.

  Next, the operation of the abnormality detection unit 502 illustrated in FIG. 5A will be described with reference to FIG. The flowchart in FIG. 8 shows the operation of the abnormality detection unit 502. First, when the operation is started, step S801 for deriving the rotational speed of the motor is executed from the speed detector 501.

  Subsequently, based on the derived speed, step S802 for confirming whether the rotational speed is within the allowable range is executed. If the rotational speed deviates from the allowable range, the process proceeds to step S805 in which a control signal is output to the motor control unit 503, which is the motor control unit of the present invention. If the rotational speed is within the allowable range, the rotational speed stored in the previous process is referred to, and the process proceeds to step S803 to calculate the increment of the rotational speed (if the process is the first time, stored in the previous process) The rotation speed is 0). Subsequently, the process proceeds to step S804 in which it is confirmed whether the increment of the rotation speed (motor acceleration) is within the allowable range. If the acceleration deviates from the allowable range, the process proceeds to step S805 in which a control signal is output to the motor control unit 503. If the acceleration is within the allowable range, the process returns to step S801 after transitioning to step S806 in which the derived rotation speed is temporarily stored.

  Therefore, it is possible to monitor the current motor speed and acceleration by repeatedly executing this processing. When either the speed or the acceleration deviates from the allowable range, a control signal is output to the motor control unit 503. Can do.

  When step S805 is executed, the abnormality detection unit 502 issues a control signal to the motor control unit 503. In the first embodiment, the motor control unit 503 is connected to an inverter device 506 that is a motor controller and an electromagnetic contactor 504 (breaker) installed on a circuit of the motor 505. And motor control part 503 will open electromagnetic contactor 504, if a control signal is received. Thereby, since the power supply of the motor 505 is cut off, the rotation of the motor 505 is stopped.

  According to the present embodiment, it is possible to obtain the rotation speed of the motor without using a speed detector by acquiring the voltage waveform input to the AC motor, shaping the waveform, and deriving the rotation speed of the motor. it can. Further, the use of a semiconductor element for deriving the speed eliminates the disadvantage of the conventional apparatus, that is, the size of the apparatus.

  In addition to shutting off the power using the magnetic contactor 504, there is an advantage that the motor can be surely stopped, and by monitoring the rotational speed or acceleration, not only the failure of the inverter device but also the allowable It is possible to detect a user's operation mistake such as giving an instruction to exceed the speed or performing a rapid acceleration operation exceeding the allowable range. Instead of using the magnetic contactor 504, as shown in FIG. 5b, a blocking circuit 507 may be installed in the inverter device to block the control signal.

(Second Embodiment)
The configuration in the second embodiment will be described with reference to FIG. Similar to the first embodiment, the speed detection unit 601, the abnormality detection unit 602, and the motor control unit 603 are installed in parallel with the motor 605, and the operation thereof is the same as that of the first embodiment.

In the second embodiment, the motor control unit 603 is connected to an electromagnetic contactor 604 installed on a circuit connecting the power source 600 and the inverter device 606. When the motor control unit 603 receives the control signal, the motor control unit 603 opens the electromagnetic contactor 604. Thereby, since the power supply of the inverter apparatus 606 is interrupted | blocked, rotation of the motor 605 stops similarly to 1st Embodiment.

  In the second embodiment as well, the rotational speed or acceleration of the motor can be monitored without using a speed detector, as in the first embodiment, but input to the inverter device 606 using the electromagnetic contactor 504. By shutting off the power supply, not only the motor but also the inverter device can be stopped simultaneously. When a plurality of motors are driven by a single inverter device, this method is effective because failure of the inverter device may affect other motors.

(Third embodiment)
The configuration in the third embodiment will be described with reference to FIG. The speed detection unit 701, the abnormality detection unit 702, and the motor control unit 703 are installed in parallel with the motor 705 as in the first embodiment, but may be arranged outside the inverter device 706, May be arranged. The operation is the same as in the first embodiment.

  In the third embodiment, the motor control unit 703 is connected to a control circuit 704 included in the inverter device 706. Upon receiving the control signal, the motor control unit 603 outputs a signal indicating that an abnormality has occurred to the control circuit 704. As a result, the inverter device 706 reduces the rotation speed until the motor 705 is urgently stopped or no abnormal signal is detected. The countermeasure for temporarily lowering the rotation speed is effective when an abnormal operation of the user is assumed rather than a failure of the inverter device. In this case, an alarm may be issued to the user.

  In the third embodiment as well, the rotational speed or acceleration of the motor can be monitored without using a speed detector, as in the first embodiment, but the inverter device 706 is not turned off. By outputting the control signal, it is possible to adjust the speed of the motor instead of forcibly stopping the power supply. For example, if an overspeed occurs due to a user's operation mistake, the alarm is issued and the vehicle is decelerated so that it is below the predetermined speed, or the acceleration operation is not accepted while the speed is exceeded. Such an effect can be expected.

(Fourth embodiment)
The fourth embodiment will be described with reference to FIG. In the fourth embodiment, a self-diagnosis function is realized by adding a signal consistency confirmation unit 204 (failure diagnosis unit) to the pulse width detection unit 201. Specifically, in the flip-flop 103 in FIG. 3, there are an S input to which an output signal from the first extraction unit is input, an R input to which an output signal from the second extraction unit is input, and a shaping signal. When the state of Q output is acquired and a combination that is not logically possible is acquired, the speed detection units 501, 601, and 701 determine that an abnormality has occurred in itself.

  FIG. 9 is a diagram showing the logic states of the S input, R input, and Q output and the result of abnormality determination. In the following, each case that is determined to be normal or abnormal will be described.

  When the S input is false and the R input is false, the Q output is indefinite due to the characteristics of the flip-flop, and therefore is determined to be normal regardless of the contents of the Q output (cases 901 and 902).

  If the S input is false and the R input is true, the Q output is always false. Therefore, if the Q output is false, it is normal (case 903), and if it is true, it is determined that the flip-flop is faulty. (Case 904).

  If the S input is true and the R input is false, the Q output is always true. Therefore, if the Q output is true, it is normal (case 905), and if it is false, it is determined that the flip-flop is faulty. (Case 906).

  Since the outputs from the comparators 101 and 102 are not true at the same time, if the S input is true and the R input is true, it is determined that the comparator is faulty (cases 907 and 908).

  FIG. 13 is a circuit configuration example of the signal consistency check unit 204 using the logic circuit corresponding to FIG. In the diagnosis result 305, true is output when it is determined to be abnormal, and false is output when it is normal. When it is determined as abnormal, the pulse width detection unit 201 does not input the measurement result to the pulse width measurement unit 202 and stops the monitoring operation by locking out the apparatus. At the same time, the user may be notified that an abnormality has occurred in the monitoring device.

  The logic check according to the present embodiment may be performed continuously or at regular intervals. In order to acquire the state of each input / output, it is desirable to use a photocoupler or the like for insulation.

  In the fourth embodiment, unintended operations of the comparators 101 and 102 and the flip-flop 103 can be prevented by performing a logic check. Thereby, when any element deteriorates and breaks down, this can be detected promptly, and a user can be notified. If a failure of the pulse width detection unit 201 is detected, for example, the monitoring function may be stopped, or the motor itself may be stopped or decelerated. This has the advantage that the motor can be prevented from operating in a state where speed monitoring is not functioning correctly.

(Fifth embodiment)
The fifth embodiment will be described with reference to FIG. In the fifth embodiment, a dynamic test function is realized by adding a test signal input unit 205a to the input of the pulse width detection unit 201 and a test signal detection unit 205b to the output. In the present embodiment, the test signal input units 205a and 205b correspond to the second failure diagnosis unit of the present invention. FIG. 10 is a circuit diagram in which a test signal input unit 205a is added to the input part of the pulse width detection unit 201 shown in FIG.

  The test signal input unit 205a includes a test input signal line 1 (107a), a test input signal line 2 (107b), and photocouplers 108 and 109. The operation when a dynamic test is performed during motor drive monitoring will be described below with reference to FIGS.

  When a signal is input to the test input signal line 1 (107a), the input to the pulse width detector 201 is clamped to Vcc by the effect of the photocoupler regardless of the input waveform supplied to the motor. When a signal is input to the test input signal line 2 (107b), the input to the pulse width detector 201 is similarly clamped to Vss regardless of the input waveform supplied to the motor.

  Therefore, as shown in the timing charts of FIGS. 11A and 11B, when pulse signals are applied to the two test input lines, the waveforms input to the comparators 101 and 102 are as shown in FIG. It becomes like this. The shaded portion is a portion depending on the input waveform actually supplied to the motor.

  Further, the output of the flip-flop 103 is as shown in FIG. For this reason, if the waveform as illustrated is input from the test signal input unit 205a, the output result of the flip-flop 103 is acquired by the test signal detection unit 205b, and the waveform as illustrated cannot be acquired, the device is out of order. It can be judged.

  Further, the test signal detection unit 205b may be arranged so as to be connected to the pulse width measurement unit 202 or the rotation speed determination unit 203. When connected to the pulse width measuring unit 202, it is understood that the apparatus is normal if a frequency that matches the input test signal can be measured. Similarly, when connected to the rotational speed determination unit 203, it can be understood that the apparatus is normal if the expected rotational speed is derived for the input test signal.

  In the fifth embodiment, dynamic failure diagnosis of the comparators 101 and 102 and the flip-flop 103 included in the motor speed monitoring device can be performed by clamping the input waveform with the test signal. Whereas the fourth embodiment checks only the logic of the input / output signals, this embodiment checks the operation of the apparatus by actually inputting the test signal. In the case where a failure occurs and the operation stops while maintaining the logic of the case 901, this cannot be detected in the fourth embodiment, but can be detected in this embodiment. As described above, the fifth embodiment has an advantage that, in addition to the fourth embodiment, it is possible to cope with a case where the apparatus itself for detecting an abnormality fails.

  As described above, in the present invention, attention is paid to the fact that, among the complicated signal changes in PWM modulation, only the part where the waveform change leading to the motor rotation is zero-crossed. Of the PWM waveform, the period during which only the positive side is output is the waveform for the same motor magnetic pole, and in order to move to the next magnetic pole, it is necessary to get over the magnetic pole, so the voltage is applied in the reverse direction. .

  In addition, since the motor is a coil, the zero cross position can be ordered in a relatively simple manner by combining with a low-pass filter that eliminates high-speed changes that the motor cannot respond to, such as the basic frequency for PWM modulation and spiked noise. It is possible to sample at a later time.

  After detecting the zero-cross position, the main frequency that the output energy gives to the motor rotation can be measured by measuring the time required between the zero-cross positions using general techniques. Thus, accurate speed detection by an independent circuit becomes possible.

  Note that the above description of the series of embodiments is merely an example for explaining the present invention, and the present invention should not be construed as being limited to the above embodiments. For example, in the third embodiment, when the motor control unit 703 outputs a signal indicating abnormality to the inverter device 706 but the motor rotation speed does not decrease, the electromagnetic contactor disposed on the power line is opened. Then, a plurality of embodiments may be combined such that the motor 705 is stopped.

  In the abnormality detection units 502, 602, and 702, only the speed may be monitored, or both the speed and acceleration may be monitored. The failure determination according to the fourth embodiment may be performed by a microcomputer in addition to the exemplified logic circuit.

  In the fourth and fifth embodiments, when the failure of the apparatus is determined, the monitoring operation is stopped and a control signal is output to the motor control units 503, 603, and 703 to operate the motor. It may be stopped. As a result, it is possible to cope with not allowing motor operation in a state where the monitoring is not operating.

101, 102 Comparator 103 RS flip-flop 104 Input power supply line 106 Output power supply line 107a Test signal line 1
107b Test signal line 2
108, 109, 301 Photocoupler 201 Pulse width detection unit 202 Pulse width measurement unit 203 Rotational speed determination unit 302 NOT gate 303 AND gate 304 OR gate 500, 600, 700 Power supply unit 501, 601, 701 Speed detection unit 502, 602 702 Abnormality detection unit 503, 603, 703 Motor control unit 504 Magnetic contactor 505, 605, 705 AC motor 506, 606, 706 Inverter device 507 Shut-off circuit 704 Inverter control circuit

Claims (6)

A motor speed monitoring device used in parallel connected to a power line of an AC motor,
Speed deriving means for deriving the rotational speed of the AC motor from the AC voltage supplied to the AC motor through the power line;
Determining whether or not the rotational speed derived by the speed deriving means is abnormal, and motor control means for outputting a control signal for stopping or decelerating the rotation of the AC motor when it is determined as abnormal. Have
The alternating voltage is a pseudo alternating voltage by pulse modulation,
The speed deriving unit includes a waveform shaping unit that generates a shaping signal that is turned on / off at the same cycle as the plus / minus switching of the pseudo AC voltage by shaping the waveform of the pseudo AC voltage. A motor speed monitoring apparatus, wherein the rotational speed of the AC motor is derived based on a shaping signal output from the shaping means. The waveform shaping means includes
First extraction means for extracting only a positive component signal from the waveform of the pseudo alternating voltage;
Second extraction means for extracting only a negative component signal from the waveform of the pseudo alternating voltage;
From the output signal of the first extraction means and the output signal of the second extraction means, the shaping signal generation means for generating and outputting the shaping signal;
The motor speed monitoring device according to claim 1 , comprising: The first extraction means includes a first comparator that compares the pseudo alternating voltage with a positive threshold voltage,
The second extraction means includes a second comparator that compares the pseudo AC voltage and a negative threshold voltage,
The motor speed monitor according to claim 2 , wherein the shaping signal generation unit is configured by a flip-flop to which an output signal of the first comparator and an output signal of the second comparator are input. apparatus. It is determined whether or not the logical combination of the three signals of the output signal of the first extraction means, the output signal of the second extraction means, and the shaping signal is a possible combination. The motor speed monitoring device according to claim 2 , further comprising a failure diagnosis unit that determines that the waveform shaping unit is out of order. A test signal having a predetermined waveform is input to the first extraction unit and the second extraction unit, and the logic of the shaping signal output from the shaping signal generation unit corresponds to the waveform of the test signal. whether it determined, and further comprising a second failure diagnosis means for determining that the waveform shaping means when do not correspond to the waveform of the test signal has failed, from the claims 2 motor speed monitoring device according to any one of 4. The control signal output from the motor control means is output to a circuit breaker that cuts off supply of AC voltage to the AC motor or a controller that supplies AC voltage to the AC motor. The motor speed monitoring apparatus according to any one of claims 1 to 5 .

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