AC motor monitoring device

Abstract

To enable, with no need of external trigger provided, measurement for detecting an abnormality in a motor to be started when the motor is operating in a desired operation mode.SOLUTION: An AC motor monitoring device includes: a storage unit that stores a trigger range; a calculation unit that calculates at least one of current amplitude and frequency of an alternating current that drives an AC motor; and a measuring unit that starts measuring parameters for detecting an abnormality in the AC motor when at least one of the current amplitude and frequency calculated by the calculation unit falls within the trigger range.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present invention relates to a monitoring device for an AC motor. [Background technology]

[0002] In a servo system, a servo driver generally controls a servo motor in accordance with commands from a controller such as a PLC, etc. Techniques for detecting abnormalities in such servo motors have been proposed (see, for example, Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-204155 [Patent Document 2] Japanese Patent Publication No. 2020-035187 Summary of the Invention [Problem to be solved by the invention]

[0004] A servo motor switches its rotation direction, rotation speed, and torque (hereinafter, the combination of rotation direction, rotation speed, and torque is also referred to as an "operation mode") according to servo control. In such a servo motor, the fluctuation range of the current value caused by switching the operation mode may be larger than the fluctuation range of the current value caused by an abnormality in the servo motor. Therefore, even if an attempt is made to detect an abnormality in the servo motor by fluctuations in the current value of the servo motor, the fluctuations in the current value caused by the abnormality in the servo motor may be buried in the fluctuations in the current value caused by switching the operation mode, which may reduce the detection accuracy of the abnormality in the servo motor.

[0005] In order to prevent a decrease in detection accuracy due to switching of the operation mode, it is preferable to perform abnormality detection in a specific operation mode. Therefore, for example, it is conceivable to input an external trigger to the servo driver in a specific operation mode to start abnormality detection. However, in order to adopt such a configuration, it is necessary to provide an input terminal for the external trigger to the servo driver and to set a programmable controller to execute processing in response to the external trigger. This has been a major obstacle to adopting a configuration using an external trigger, as it requires modifying the program of a logic controller (PLC), etc. This issue is not limited to servo motors, but can also occur in AC motors, including servo motors and induction motors.

[0006] One aspect of the disclosed technology aims to provide a monitoring device for an AC motor that can start measurements to detect abnormalities in the AC motor when the AC motor is operating in a desired operating mode, without providing an external trigger. [Means for solving the problem]

[0007] One aspect of the disclosed technology is exemplified by the following AC motor monitoring device, which includes a storage unit that stores a trigger range, a calculation unit that calculates at least one of a current amplitude and a frequency of an AC current that drives the AC motor, and a measurement unit that starts measuring parameters for detecting an abnormality in the AC motor when at least one of the current amplitude and the frequency calculated by the calculation unit falls within the trigger range.

[0008] The current amplitude of the AC current that drives the AC motor is related to the torque of the AC motor, and the frequency of the AC current that drives the AC motor is related to the rotation speed of the AC motor. Therefore, when the current amplitude and the frequency fall within the trigger range, the measurement by the measurement unit is started. This allows the measurement by the measurement unit to be started when the AC motor is operating in a desired operation mode. In other words, according to this AC motor monitoring device, it is possible to start measurement for detecting an abnormality in the AC motor when the AC motor is operating in a desired operation mode, without providing an external trigger.

[0009] The AC motor monitoring device may further include the following feature: the calculation unit calculates both the current amplitude and the frequency, generates a histogram indicating the frequency of occurrence of pairs of the current amplitude and the frequency calculated at the same time, and stores the generated histogram in the storage unit. The AC motor monitoring device further includes a setting unit that sets the trigger range based on the histogram. By including these features, the AC motor monitoring device can reduce the storage capacity of the storage unit required for storing the frequency and the current amplitude.

[0010] The monitoring device for an AC motor may further include the following feature: the setting unit outputs the histogram to a display unit, and sets a specified range of the output histogram as the trigger range. By including this feature, the monitoring device for an AC motor can set a user-desired range of the AC motor as the trigger range.

[0011] The monitoring device for an AC motor may further include the following feature: the calculation unit generates the histogram by excluding pairs in which at least one of the current amplitude and the frequency is equal to or less than a threshold value indicating a stop of the AC motor. By including this feature, the monitoring device for an AC motor can prevent the measurement unit from starting measurement when the AC motor is stopped.

[0012] The AC motor monitoring device may further include the following feature: the calculation unit further calculates a rate of change of the frequency of the AC current, and the setting unit sets, in the histogram, a region where the rate of change is within a predetermined range that indicates steady operation of the AC motor, as the trigger range. By including such a feature, the AC motor monitoring device can more accurately measure parameters that are preferably measured when the AC motor is operating steadily.

[0013] The AC motor monitoring device may further include the following feature: A notification unit may be provided that notifies an abnormality in the AC motor when the parameter exceeds a threshold value indicating an abnormality in the AC motor. By including such a feature, the AC motor monitoring device can notify an abnormality in the AC motor.

[0014] In the monitoring device for an AC motor, the parameters may include a harmonic content of the AC current. [Effects of the Invention]

[0015] According to the disclosed technique, it is possible to start measurement for detecting an abnormality in an AC motor when the AC motor is operating in a desired operation mode, without providing an external trigger. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a diagram schematically illustrating an example of the configuration of a servo system according to an embodiment. [Figure 2] FIG. 2 is a diagram showing a schematic configuration of the motor. [Figure 3] FIG. 3 is a diagram showing a schematic configuration of a functional section of the servo driver. [Figure 4] FIG. 4 is a diagram schematically showing the current value supplied to the motor. [Figure 5] FIG. 5 is a diagram schematically showing the harmonic content measured by the monitoring device when the motor is operating normally. [Figure 6] FIG. 6 is a diagram schematically showing the harmonic content measured by the monitoring device when an abnormality occurs in the motor. [Figure 7] FIG. 7 is a diagram showing a schematic configuration of the functional units of the monitoring device. [Figure 8] FIG. 8 is a diagram schematically showing the current amplitude calculated by the calculation unit. [Figure 9] FIG. 9 is a diagram schematically illustrating the frequency calculated by the calculation unit. [Figure 10] FIG. 10 is a diagram schematically showing the current amplitude and frequency calculated by the calculation unit. [Figure 11] FIG. 11 is a diagram illustrating time-series data of current amplitude calculated by the calculation unit. [Figure 12] FIG. 12 is a diagram illustrating time-series data of frequencies calculated by the calculation unit. [Figure 13] FIG. 13 is a diagram illustrating an example of a histogram generated by the calculation unit. [Figure 14] FIG. 14 is a diagram schematically showing an area set as a trigger on a histogram. [Figure 15] FIG. 15 is a flowchart showing an example of a processing flow of a process for setting the ranges of current amplitude and frequency by the setting unit. [Figure 16] FIG. 16 is a diagram illustrating an example of a processing flow of a process for detecting an abnormality in a motor by a monitoring device. [Figure 17] FIG. 17 is a diagram illustrating another example of a processing flow of a process for detecting an abnormality in a motor by a monitoring device. [Figure 18] FIG. 18 is a diagram schematically showing an area set as a trigger on a three-dimensional histogram in the first modified example. DETAILED DESCRIPTION OF THE INVENTION

[0017] <Embodiment> Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, identical or corresponding parts are designated by the same reference numerals, and their description will not be repeated. In this disclosure, an industrial system is shown as one exemplary embodiment of a servo system. However, the use of the servo system according to the present invention is not particularly limited.

[0018] <Embodiment> FIG. 1 is a diagram schematically illustrating an example configuration of a servo system 100 according to an embodiment. The servo system 100 includes a PLC 1, a servo driver 2, and a monitoring device 9. The servo driver 2 is arranged to drive and control a servo motor 3. An output shaft 32 of the servo motor 3 is connected to a screw shaft 52 by a coupling 51. A precision stage 53 is arranged on the screw shaft 52. The precision stage 53 is displaced on the screw shaft 52 by being driven by the servo motor (hereinafter referred to as "motor") 3.

[0019] Stoppers (not shown) are provided at both ends of the driving range of precision stage 53 along screw shaft 52. The impact when precision stage 53 comes into contact with the stoppers is reduced as much as possible by torque control of motor 3. Workpiece 8 is placed on precision stage 53. Thus, in the servo system 100 illustrated in FIG. 1, one drive shaft driven by motor 3 is provided, but two or more drive shafts may be provided.

[0020] The PLC 1 outputs a command signal to the servo driver 2. The PLC 1 functions as, for example, a monitoring device for the servo driver 2 by executing processing in accordance with a program prepared in advance.

[0021] The servo driver 2 receives a command signal from the PLC 1. Servo driver 2 receives a feedback signal from motor 3. Servo driver 2 is formed with a servo system that performs feedback control using a position controller, a speed controller, a current controller, etc., and these signals are used to servo-control and drive motor 3.

[0022] The motor 3 includes a motor main body 30 and an encoder 31. The motor 3 is, for example, an AC servo motor. The motor 3 is supplied with a driving current from the servo driver 2 via a power line 40. The encoder 31 detects the displacement of the output shaft 32 of the motor main body 30. Examples of the displacement of the output shaft 32 detected by the encoder 31 include the direction of rotation, amount of rotation, and rotation speed of the output shaft 32. The encoder 31 outputs a feedback signal indicating the detected displacement to the servo driver 2 via an encoder cable 41. A monitoring device 9 that monitors the motor 3 is provided on the power line 40. The "driving current" is an example of an AC current.

[0023] Next, a description will be given of the functional configuration of the encoder 31. Fig. 2 is a diagram showing a schematic configuration of the motor 3. The encoder 31 provided in the motor 3 includes a signal generating unit 311, a communication unit 312, and a storage unit 313.

[0024] The signal generating unit 311 detects the operation of the motor main body 30 of the motor 3 driven by the servo driver 2, and generates a feedback signal indicating the detected operation. The feedback signal is output to the communication unit 312. The feedback signal includes, for example, information about the rotational position (angle) of the rotational shaft of the motor main body 30, information about the rotational speed of the rotational shaft, information about the rotational direction of the rotational shaft, etc. The signal generating unit 311 can be configured, for example, as a known incremental type or absolute type.

[0025] The communication unit 312 is an interface for communicating with the servo driver 2. In this embodiment, the communication unit 312 sends a feedback signal to the servo driver 2 via the encoder cable 41. In this embodiment, serial communication is used to transmit the feedback signal and the detection signal from the communication unit 312. This makes it possible to reduce the number of signal lines included in the cable. For serial communication via the encoder cable 41, known communication standards such as Recommended Standards 232 (RS-232C), RS-422, or RS-485 can be used.

[0026] The storage unit 313 is a storage unit that stores data related to servo control of the motor 3. The storage unit 313 is, for example, an Electrically Erasable Programmable Read Only Memory (EEPROM). The motor 3 is an example of an "AC motor."

[0027] The motor 3 is driven by servo control by the servo driver 2. FIG. 3 is a diagram showing a schematic configuration of the functional units of the servo driver 2. The servo driver 2 can be regarded as a computer having an arithmetic unit, a storage device, etc. The functional units shown in FIG. 6 are realized by the execution of a predetermined program, etc. in the servo driver 2. The servo driver 2 has a communication unit 21 and a servo control unit 22, but may have other functional units.

[0028] The communication unit 21 is a functional unit that controls communication with the outside via the communication cable 11. For example, the communication unit 21 functions as an interface for communication with the PLC 1. Furthermore, the communication unit 21 also functions as an interface for communication with the encoder 31 via the encoder cable 41.

[0029] The servo control unit 22 is a functional unit for servo-controlling the motor 3 based on commands from the PLC 1, and specifically, is a functional unit that performs feedback control using a position controller, a speed controller, a current controller, etc. Note that for the position controller, speed controller, current controller, etc., control parameters such as speed gain are appropriately set so that servo control of the motor 3, which is the control target, is performed appropriately. The servo control unit 22 switches the operating mode of the motor 3 according to, for example, the workpiece 8 placed on the precision stage 53.

[0030] The monitoring device 9 monitors the motor 3, which is driven by servo control using the servo driver 2, to detect abnormalities in the motor 3. Parameters used for abnormality detection include the harmonic content of the current supplied to the motor 3, the average current value, and the effective current value. In this embodiment, the monitoring device 9 detects abnormalities in the motor 3 using the harmonic content of the current supplied to the motor 3.

[0031] FIG. 4 is a diagram showing a schematic diagram of the current value supplied to the motor 3. FIG. 4 illustrates an example in which the operation modes of "Operation A," "Operation B," "Operation C," and "Stop" are switched by servo control by the servo driver 2. Referring to FIG. 4, it can be seen that the current value supplied to the motor 3 fluctuates greatly each time the operation mode is switched. Here, it is assumed that during "Operation B," a workpiece 8 is placed on the precision stage 53, and the workpiece 8 is transported by driving the motor 3. It is also assumed that the user of the servo system 100 wants to detect an abnormality in the motor 3 when transporting the workpiece 8.

[0032] FIG. 5 is a diagram schematically showing the harmonic content measured by the monitoring device 9 when the motor 3 is operating normally. FIG. 6 is a diagram schematically showing the harmonic content measured by the monitoring device 9 when an abnormality occurs in the motor 3. FIG. 6 illustrates an example in which an abnormality occurs in the motor 3 during operation B. FIG. 6 also illustrates a threshold value set to detect an abnormality in the motor 3 during "operation B." Here, the threshold value is set lower than the harmonic content during "operation A."

[0033] It can be seen from Fig. 6 that the occurrence of an abnormality has caused the harmonic content rate to exceed the threshold value in operation B. However, in the example of Fig. 6, the occurrence of an abnormality in operation B causes the difference between the harmonic content rate in operation A and the harmonic content rate in operation B to be larger than the fluctuation in the harmonic content rate.

[0034] In such a case, if an attempt is made to detect an abnormality by setting a uniform threshold as shown in Fig. 6, an abnormality occurring in operation B may be detected, while an abnormality may be erroneously detected as occurring in operation A even though no abnormality has occurred. Therefore, in order to prevent such erroneous detection from occurring, the present embodiment employs the following configuration of the monitoring device 9.

[0035] Fig. 7 is a diagram showing a schematic configuration of the functional units of the monitoring device 9. The monitoring device 9 can be regarded as a computer having an arithmetic unit, a storage device, etc. The functional units shown in Fig. 7 are realized by the execution of predetermined programs, etc. in the monitoring device 9. The monitoring device 9 has a calculation unit 91, a setting unit 92, a measurement unit 93, a notification unit 94, and a storage unit 95, but may have functional units other than these.

[0036] The calculation unit 91 is a functional unit that calculates the current amplitude and frequency of the drive current supplied to the motor 3. The frequency can be calculated, for example, from the current waveform. The calculation unit 91 can, for example, detect zero crossing points of the current waveform and calculate the frequency based on the time until the next zero crossing point. The current amplitude and frequency calculated by the calculation unit 91 are used, for example, as triggers for the measurement unit 93 to start measurement. The current amplitude of the drive current is used as a trigger for the motor 3 to start measurement. The torque of the motor 3 is related to the torque of the drive current, and the frequency of the drive current is related to the number of rotations of the motor 3.

[0037] Furthermore, the calculation unit 91 calculates the frequency of occurrence of the current amplitude and frequency of the drive current supplied to the motor 3 at the same time. FIGS. 8 to 10 are diagrams that schematically explain how the calculation unit 91 calculates the frequency of occurrence of pairs of current amplitude and frequency. FIG. 8 is a diagram that schematically shows the current amplitude calculated by the calculation unit 91. The vertical axis of FIG. 8 indicates the current amplitude, and the horizontal axis indicates time. FIG. 9 is a diagram that schematically shows the frequency calculated by the calculation unit 91. The vertical axis of FIG. 9 indicates the frequency, and the horizontal axis indicates time. In FIGS. 8 and 9, the current amplitude and frequency calculated at the same time are associated with circled numbers. For example, the current amplitude exemplified by the circled "3" in FIG. 8 and the frequency exemplified by the circled "3" in FIG. 9 are calculated at the same time.

[0038] FIG. 10 is a diagram schematically illustrating the current amplitude and frequency calculated by the calculation unit 91. In FIG. 10, the vertical axis represents the current amplitude, and the horizontal axis represents the frequency. In FIG. 10, pairs of current amplitude and frequency calculated at the same time are plotted on a graph. By plotting pairs of current amplitude and frequency in a space where one axis represents the current amplitude and the other axis represents the frequency, it is possible to understand which pairs of current amplitude and frequency appear frequently.

[0039] Based on the above explanation, the calculation by the calculation unit 91 of the frequency of occurrence of pairs of current amplitude and frequency calculated at the same time will be further explained. The calculation unit 91 calculates the current amplitude and frequency of the drive current during a predetermined learning period. The calculation by the calculation unit 91 of the current amplitude and frequency is performed for each operation mode of the motor 3 switched by the servo driver 2.

[0040] Fig. 11 is a diagram illustrating time series data of current amplitude calculated by the calculation unit 91. In Fig. 11, the vertical axis represents current amplitude (A) and the horizontal axis represents time (seconds). Fig. 12 is a diagram illustrating time series data of frequency calculated by the calculation unit 91. In Fig. 12, the vertical axis represents frequency (Hz) and the horizontal axis represents time (seconds).

[0041] The calculation unit 91 calculates the occurrence frequency of each pair of current amplitude and frequency calculated at the same time based on the calculated time series data of the current amplitude and the time series data of the frequency. The calculation unit 91 may store the occurrence frequencies of all calculated pairs of current amplitude and frequency in the storage unit 95. Note that if the occurrence frequencies of all calculated pairs of current amplitude and frequency are stored in the storage unit 95, the amount of data stored in the storage unit 95 will increase. For this reason, a storage unit 95 with a large storage capacity will be employed, or the data will be transferred to a higher-level device. Therefore, in order to reduce the amount of data stored in the storage unit 95, the calculation unit 91 generates a two-dimensional histogram of the collected data indicating the occurrence frequencies of the pairs.

[0042] FIG. 13 is a diagram illustrating a histogram 241 generated by the calculation unit 91. In FIG. 13, the vertical axis represents frequency, and the horizontal axis represents current amplitude. In the histogram 241, the current amplitude and frequency are divided at predetermined intervals to define a plurality of regions. Each of the determined regions includes a pair of current amplitude and frequency. The shade of color in each determined region indicates the frequency of occurrence of the pair of current amplitude and frequency associated with that region, with a darker color indicating a higher frequency of occurrence. By storing the frequency of occurrence of pairs of current amplitude and frequency as such a histogram 241 in the storage unit 95, the storage capacity used to store the frequency of occurrence of pairs of current amplitude and frequency can be reduced to a size obtained by multiplying the number of predetermined intervals of current amplitude by the number of predetermined intervals of frequency.

[0043] Here, the calculation unit 91 may, for example, exclude from the histogram 241 a pair of current amplitude and frequency where at least one of the calculated current amplitude and frequency is equal to or less than a predetermined value indicating the stop of the motor 3. In other words, the calculation unit 91 may exclude from the histogram 241 a pair of current amplitude and frequency where at least one of the calculated current amplitude and frequency is equal to or less than a predetermined value indicating the stop of the motor 3. The histogram 241 may be generated by excluding pairs of current amplitude and frequency, at least one of which is equal to or less than a predetermined value indicating that the motor 3 has stopped.

[0044] The setting unit 92 sets a trigger for starting measurement by the measurement unit 93. The setting unit 92 may set, for example, an area in the histogram 241 that satisfies predetermined trigger setting conditions as the trigger. Examples of the trigger setting conditions include current amplitude and frequency that appear at a frequency of 5% or more of the total number of data in the histogram 241. Examples of an area in the histogram 241 that satisfies such trigger setting conditions include area R1 in FIG. 13. By setting a trigger according to such trigger setting conditions, the operating state of the motor 3 that appears most frequently can be used as the trigger.

[0045] Furthermore, for example, the trigger setting condition may be that the frequency is the highest in the region in the histogram 241 where the occurrence frequency is equal to or greater than a predetermined value. In the example of Fig. 13, an example of a region that satisfies such a trigger setting condition is region R1 in Fig. 13. By setting a trigger with such a trigger setting condition, a high occurrence frequency and a high rotation frequency of the motor 3 can be used as the trigger.

[0046] The trigger setting condition may also be the region in histogram 241 where the current amplitude is the largest among regions where the frequency of occurrence is equal to or greater than a predetermined value. An example of a region in histogram 241 that satisfies such a trigger setting condition is region R2 in Fig. 13. By setting a trigger under such trigger setting condition, a high frequency of occurrence and a large torque of motor 3 can be used as the trigger.

[0047] The setting unit 92 may display the histogram 241 on a display or the like, and allow the user to specify the region to be set as a trigger. Since the frequency and current amplitude vary depending on the operation mode of the motor 3, for example, if it is desired to detect an abnormality in the motor 3 during "operation B" (see FIG. 4), the region corresponding to "operation B" may be specified on the histogram 241.

[0048] Then, the setting unit 92 stores the set trigger in the memory unit 95. FIG. 14 is a diagram schematically showing an area set as a trigger on the histogram 241. The vertical axis of FIG. 14 represents frequency, and the horizontal axis represents current amplitude. FIG. 14 illustrates an example of an area R3 set as a trigger. Area R3 is a rectangle with a frequency range of A1 or more and A2 or less, and a current amplitude range of B1 or more and B2 or less. When area R3 is set as a trigger, the measurement unit 93, which will be described later, starts measurement when the frequency calculated by the calculation unit 91 is A1 or more and A2 or less, and the current amplitude calculated by the calculation unit 91 is B1 or more and B2 or less.

[0049] The measurement unit 93 performs measurement for detecting an abnormality in the motor 3 when the current amplitude and frequency calculated by the calculation unit 91 fall within a region set as a trigger by the setting unit 92. The measurement unit 93 measures, for example, the harmonic content rate contained in the current waveform supplied to the motor 3. The measurement unit 93 obtains the fundamental wave and n-th order harmonics (n is an integer equal to or greater than 2) of the current waveform supplied to the motor 3, for example, by performing a fast Fourier transform (FFT) on the current waveform supplied to the motor 3. The measurement unit 93 then measures the harmonic content rate by calculating the ratio of second-order and higher harmonics to the fundamental wave.

[0050] The notification unit 94 notifies of an abnormality when the harmonic content measured by the measurement unit 93 exceeds a threshold value stored in the storage unit 95. Methods for notifying of an abnormality include outputting an alarm sound, outputting a warning message on a display, and sending a notification by email.

[0051] The storage unit 95 is, for example, an EEPROM. The storage unit 95 stores a set trigger and a threshold value used by the notification unit 94. The storage unit 95 may also store a measurement time during which the measurement unit 93 performs measurement. The monitoring device 9 is an example of a "monitoring device."

[0052] 15 is a flowchart showing an example of a processing flow of a process for setting the ranges of current amplitude and frequency by the setting unit 92. Hereinafter, an example of a processing flow of a process for setting the ranges of current amplitude and frequency by the setting unit 92 will be described with reference to FIG.

[0053] At T1, the PLC 1, the servo driver 2, and the motor 3 are connected to construct the servo system 100. Then, the servo control unit 22 of the servo driver 2 starts driving the motor 3 in a predetermined operation mode (for example, operation A in FIG. 4) in response to a command signal from the PLC 1.

[0054] At T2, the calculation unit 91 of the monitoring device 9 calculates the current amplitude and frequency of the drive current supplied to the motor 3. The calculation unit 91 continues to calculate the current amplitude and frequency of the drive current supplied to the motor 3 for a predetermined time. Furthermore, the calculation unit 91 calculates the occurrence frequency of pairs of current amplitude and frequency calculated at the same time.

[0055] At T3, the servo control unit 22 of the servo driver 2 switches the operation mode of the motor 3. For example, if the servo control unit 22 is driving the motor 3 in operation mode "operation A," it can switch to operation mode "operation B" and drive the motor 3. If recording of the current amplitude and frequency of the drive current supplied to the motor 3 for all operation modes of the motor 3 is completed ("YES" at T4), the process proceeds to T5. If recording of the current amplitude and frequency of the drive current supplied to the motor 3 for all operation modes of the motor 3 is not completed ("NO" at T4), the process proceeds to T2.

[0056] At T5, the setting unit 92 of the monitoring device 9 sets a trigger. The setting unit 92 may calculate a histogram 241 based on the current amplitude and frequency calculated by the calculation unit 91 at T2, and set a region in the histogram 241 that satisfies a predetermined trigger setting condition as a trigger. Alternatively, the setting unit 92 may display the histogram 241 on a display or the like, and allow a user to specify a region to be set as a trigger.

[0057] Fig. 16 is a diagram showing an example of a processing flow of processing by the monitoring device 9 to detect an abnormality in the motor 3. Fig. 16 illustrates a case in which measurement by the measuring unit 93 continues while the current amplitude and frequency calculated by the calculation unit 91 are within a region set as a trigger. Hereinafter, an example of a processing flow of processing by the monitoring device 9 to detect an abnormality in the motor 3 will be described with reference to Fig. 16.

[0058] In T11, the calculation unit 91 calculates the current amplitude and frequency of the drive current supplied to the motor 3. If the calculated current amplitude and frequency fall within the region set as the trigger at T5 in FIG. 15 ("YES" at T12), for example, the process proceeds to T13. If the calculated current amplitude and frequency do not fall within the region set as the trigger at T5 in FIG. 15 ("NO" at T12), for example, the process proceeds to T11.

[0059] In T13, the measurement unit 93 measures the harmonic content rate contained in the current waveform of the current supplied to the motor 3. If the measured harmonic content rate exceeds the threshold value stored in the memory unit 95 ("YES" in T14), the process proceeds to T15. If the measured harmonic content rate is equal to or less than the threshold value stored in the memory unit 95 ("NO" in T14), the process proceeds to T11.

[0060] At T15, the notification unit 94 notifies that an abnormality has occurred in the motor 3.

[0061] Fig. 17 is a diagram showing another example of the processing flow of the process by the monitoring device 9 to detect an abnormality in the motor 3. Fig. 17 describes the processing flow when measurement by the measurement unit 93 continues for a certain period of time. Hereinafter, with reference to Fig. 17, another example of the processing flow of the process by the monitoring device 9 to detect an abnormality in the motor 3 will be described. Note that the same processes as in Fig. 16 are assigned the same reference numerals, and their description will be omitted.

[0062] In T14a, if the harmonic content measured in T13 exceeds the threshold value stored in the memory unit 95 ("YES" in T14a), the process proceeds to T15. If the harmonic content measured in T13 is equal to or less than the threshold value stored in the memory unit 95 ("NO" in T14a), the process proceeds to T16.

[0063] In T16, the measuring unit 93 determines whether the measurement time for measuring the harmonic content rate has passed the measurement time stored in the memory unit 95. If the measurement time has passed ("YES" in T16), the process proceeds to T11. If the measurement time has not passed ("NO" in T16), the process proceeds to T13.

[0064] <Effects of the embodiment> In this embodiment, a trigger region is set based on the pre-calculated current amplitude and frequency of the drive current supplied to the motor 3. The current amplitude of the drive current is related to the torque of the motor 3, and the frequency of the drive current is related to the rotation speed of the motor 3. Therefore, in this embodiment, by setting a trigger based on such current amplitude and frequency, it is possible to perform measurement for abnormality detection on the motor 3 in a desired operating mode without inputting a trigger from outside to start measurement for abnormality detection.

[0065] In this embodiment, the frequency and current amplitude calculated by the calculation unit 91 are stored in the storage unit 95 as a histogram 241. By performing such processing, in this embodiment, it is possible to reduce the storage capacity of the storage unit 95 required for storing the frequency and current amplitude.

[0066] In addition, in this embodiment, the setting unit 92 can display the histogram 241 on a display or the like, and allow the user to specify an area to be set as a trigger. By providing such a feature, this embodiment allows the user to set a desired area as a trigger.

[0067] In this embodiment, the calculation unit 91 can generate the histogram 241 by excluding pairs of current amplitude and frequency where at least one of the calculated current amplitude and frequency is equal to or less than a predetermined value that indicates the stop of the motor 3. In this embodiment, by generating the histogram 241 in this manner, it is possible to prevent the measurement unit 93 from performing measurement when the motor 3 is stopped.

[0068] <First Modification> In the embodiment described above, a trigger for starting measurement by the measuring unit 93 is set based on a pair of current amplitude and frequency. In the first modified example, a trigger for starting measurement by the measuring unit 93 is set based on the rate of change of frequency in addition to the current amplitude and frequency.

[0069] In the first modification, the calculation unit 91 may generate a three-dimensional histogram in which the current amplitude, frequency, and frequency change rate are arranged on three orthogonal axes, instead of the histogram 241. Fig. 18 is a diagram schematically showing a region set as a trigger on the three-dimensional histogram in the first modification. Even when a three-dimensional histogram including three parameters is generated as in the first modification, the trigger region can be set based on the histogram.

[0070] If the parameter for setting a trigger includes the rate of change of frequency, it is preferable to select a region where the rate of change of frequency is close to 0 as the region that will become the trigger. For example, the rate of change of frequency being close to 0 means that the rate of change of frequency is within a predetermined range from 0 that indicates no fluctuation in the rotation speed of the motor 3. By specifying a region in the three-dimensional histogram where the rate of change of frequency is close to 0 as the trigger, it is possible to set the condition for the trigger as being that the motor 3 is operating in a steady state (operating at a substantially constant speed).

[0071] By starting measurement by the measurement unit 93 based on the trigger set in this way, it is possible to more accurately measure parameters that are preferably measured when the motor 3 is operating steadily. For example, a parameter that is preferably measured when the motor 3 is operating steadily can be the harmonic content calculated by FFT. In other words, by using the steady state operation of the motor 3 as a trigger, it is possible to more accurately measure the harmonic content.

[0072] <Other variations> In the above-described embodiment, the motor 3 is a servo motor, but the motor 3 is not limited to a servo motor. The motor 3 may be, for example, an induction motor.

[0073] In the embodiment described above, a trigger is set to cause the measuring unit 93 to start measurement based on both the current amplitude and frequency of the drive current supplied to the motor 3, but a trigger may also be set to cause the measuring unit 93 to start measurement based on at least one of the current amplitude and frequency of the drive current.

[0074] In the embodiment described above, the monitoring device 9 is provided separately from the servo driver 2, but the monitoring device 9 may be built into the servo driver 2.

[0075] The embodiments and modifications disclosed above can be combined with each other.

[0076] <Appendix 1> a memory unit (95) for storing the trigger range; a calculation unit (91) that calculates at least one of a current amplitude and a frequency of an AC current that drives an AC motor (3); a measurement unit (93) that starts measuring a parameter for detecting an abnormality in the AC motor (3) when at least one of the current amplitude and the frequency calculated by the calculation unit (91) falls within the trigger range. AC motor monitoring device (9). [Explanation of symbols]

[0077] 1. PLC 2. Servo driver 3. Motor 8. Work 9...Monitoring device 21. Communications Department 22 Servo control unit 91··Calculation section 92 Settings section 93··Measurement section 94...Notification Department 95...Storage section 30··Motor body 31 Encoder 241··Histogram 311 Signal generation unit 312··Communications Department 313...Storage section 32 Output shaft 41 Encoder cable 51 Coupling 52··Screw shaft 53 Precision Stage 100··Servo System

Claims

1. a storage unit that stores the trigger range; a calculation unit that calculates at least one of a current amplitude and a frequency of an AC current that drives an AC motor; a measurement unit that starts measuring a parameter for detecting an abnormality in the AC motor when at least one of the current amplitude and the frequency calculated by the calculation unit falls within the trigger range, the calculation unit calculates both the current amplitude and the frequency, generates a histogram indicating an appearance frequency of pairs of the current amplitude and the frequency calculated at the same time, and stores the generated histogram in the storage unit; The AC motor monitoring device further includes a setting unit that sets the trigger range based on the histogram. AC motor monitoring device.

2. the setting unit outputs the histogram to a display unit, and sets a specified range of the output histogram as the trigger range.

2. The AC motor monitoring device according to claim 1.

3. the calculation unit generates the histogram by excluding the pairs in which at least one of the current amplitude and the frequency is equal to or less than a threshold value indicating a stop of the AC motor.

3. The monitoring device for an AC motor according to claim 1 or 2.

4. The calculation unit further calculates a rate of change of the frequency of the AC current, the setting unit sets, as the trigger range, a region in the histogram where the rate of change is within a predetermined range that indicates steady operation of the AC motor. The monitoring device for an AC motor according to any one of claims 1 to 3.

5. the parameters include a harmonic content of the AC current; The monitoring device for an AC motor according to any one of claims 1 to 4.

6. When the parameter exceeds a threshold value indicating an abnormality of the AC motor, A notification unit is further provided to notify the user of the abnormality. The monitoring device for an AC motor according to any one of claims 1 to 5.

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