JP2012240068A - Preventive maintenance device for motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a preventive maintenance device for a motor that avoids erroneous diagnosis due to varied rotational speed or a change in rolling load and prevents unexpected failure giving an influence on the operation of entire rolling plant beforehand.SOLUTION: The preventive maintenance device for a motor collects measurement data of a specific physical quantity (radially axial change, thrustward axial change) showing the status of motor axis, measurement data of rotational speed of the motor and drive output current data input from a motor-driving device as evaluation data. The collected evaluation data are matched with an evaluation model, and abnormality concerning the motor is monitored based on the degree of agreement between the evaluation data and evaluation model. The evaluation model may use a formula approximated by a quadratic or higher-order function in a relation between the rotational speed and drive output current during rolling and the physical quantity showing the status of motor axis when the motor is normal.

Description

  The present invention relates to a preventive maintenance apparatus for an electric motor, and more particularly to a preventive maintenance apparatus suitable for use in predictive diagnosis of a large electric motor used in a steel plant rolling plant.

  One of the equipment that makes up the rolling mill of an ironworks is an electric motor. Since a rolling plant has many load fluctuations, a variable speed electric motor is used as an electric motor for the rolling plant. In this electric motor, frequent acceleration / deceleration control is performed, and a sudden failure may be caused by a mechanical shock or an electrical overload applied at that time. In particular, the impact from the machine side connected to the electric motor is large at the timing of biting the rolling material, and the bearing base of the electric motor may receive an abnormal force and suddenly break down. The failure of the electric motor affects the entire rolling plant, and if it is a serious failure, the operation of the rolling plant may be stopped. In particular, when a sudden failure occurs in a remote rolling plant, it takes time to repair and repair, and a lot of resources are used. For this reason, in the operation of a rolling plant, it is necessary to prevent the failure of the electric motor by monitoring whether or not abnormality has occurred in the electric motor. In other words, preventive maintenance of the electric motor is required.

  As a conventional preventive maintenance method for an electric motor, for example, a method disclosed in Japanese Patent Laid-Open No. 10-285546 is known. According to the conventional method disclosed in this publication, a normal time function equation that approximates the relationship between the rotation speed (the number of rotations per predetermined time) and the vibration value at the start of use of the electric motor, and when the electric motor is continuously used. In-use function equations that approximate the relationship between the rotational speed and the vibration value are obtained by the least square method. Then, the in-use function equation is divided by the normal function equation, and when the result of the division exceeds a preset threshold, it is determined that an abnormality has occurred in the motor.

Japanese Patent Laid-Open No. 10-285546

  However, in an electric motor of a rolling plant, even if the motor rotates at the same rotational speed, the vibration value may change when the rolling load changes. This rolling load varies depending on factors such as the material, width, length, and temperature of the rolled material. In the above-described conventional method, these load elements are not taken into consideration, and the threshold value for determining whether the load is normal or abnormal is determined only by the rotation speed. For this reason, in the above-described conventional method, depending on the relationship between the rotational speed and the rolling load, a misdiagnosis in which it is determined to be abnormal despite being normal, or that it is normal despite being abnormal. There was a risk that a misdiagnosis would be performed.

  The present invention has been made in view of the problems as described above, and can avoid misdiagnosis due to fluctuations in rotational speed and changes in rolling load, and thus sudden failures that affect the operation of the entire rolling plant. It is an object of the present invention to provide a preventive maintenance device for an electric motor that can prevent the occurrence of the problem.

  The preventive maintenance device for an electric motor according to the present invention collects measurement data of the rotation speed of the electric motor together with measurement data of a specific physical quantity representing the state of the shaft of the electric motor, and is further input from the electric motor drive device as information expressing the rolling load. Collect drive output current data. During actual rolling, a necessary current is allowed to flow from the electric motor driving device in accordance with the rolling load, so that the drive output current can be used as information representative of the rolling load. Note that the rolling load varies depending on factors such as the material, width, length, and temperature of the rolled material, but it is not possible to grasp the relationship between the state of the motor shaft and the rotational speed for each of these load elements. difficult. In that respect, if it is a drive output current, it is possible to represent the rolling load by itself, so it is easy to grasp the relationship with the state of the shaft of the motor and the relationship with the rotational speed.

  The preventive maintenance apparatus for an electric motor according to the present invention collects the above-mentioned data as evaluation data during operation of the electric motor. Then, the collected evaluation data is collated with the evaluation model, and the degree of coincidence between the evaluation data and the evaluation model is determined. The evaluation model models the relationship between the specific physical quantity and the rotational speed and drive output current during rolling when the motor is normal. For example, an equation approximated by a higher-order function of the second or higher order is used. Can be used. The preventive maintenance device for an electric motor of the present invention monitors an abnormality related to the electric motor based on the degree of coincidence between the evaluation data and the evaluation model.

  The specific physical quantity representing the state of the motor shaft is the radial displacement or axial displacement of the motor that can be measured by an axial displacement sensor, or the axial direction of the motor that can be measured by an axial load sensor. It is preferable to use this axial load. In addition, as the evaluation data collected during operation of the motor, it is preferable to collect data at the biting timing of the rolled material.

  As a specific method for monitoring the abnormality related to the motor, it is preferable to detect that the degree of coincidence between the evaluation data and the evaluation model is lower than a predetermined determination value as an abnormality related to the motor. In addition, counting the number of times that the degree of coincidence has decreased below a predetermined determination value (number of abnormalities) for every fixed period and recording the change over time in the number of abnormalities is also a preferred method of abnormality monitoring.

  According to the present invention, on the basis of an evaluation model that models the relationship between the rotational speed and drive output current during normal rolling and the specific physical quantity, the rotational speed and drive output current collected during operation of the motor and the specific physical quantity It is determined whether the relationship is a normal motor relationship. Thus, in addition to the rotational speed, the drive output current representing the rolling load is used as information for abnormality diagnosis, so that misdiagnosis due to fluctuations in the rotational speed and changes in the rolling load can be avoided. Therefore, according to the present invention, the motor is stopped for a long time with respect to the abnormality related to the motor, specifically, the malfunction of the motor itself, the malfunction of the machine driven by the motor, the malfunction of the bearing base or the deterioration of the aging. A highly reliable determination can be made without any problem. As a result, it is possible to know in advance the signs of failure of the electric motor and related machinery and other equipment, and to properly perform maintenance according to the symptoms, so that sudden failures that affect the operation of the entire rolling plant can be prevented. Preventing is achieved.

It is a block diagram which shows the structure of the system with which the preventive maintenance apparatus of the electric motor of Embodiment 1-4 of this invention is applied. It is a block diagram which shows the structure of the preventive maintenance apparatus of Embodiment 1 of this invention. It is a graph which shows the evaluation model by Embodiment 1 of this invention. It is a graph which shows the evaluation model by Embodiment 1 of this invention. It is a graph which shows the evaluation model by Embodiment 1 of this invention. It is a graph which shows the evaluation model by Embodiment 1 of this invention. It is a flowchart which shows the method of preparation of the evaluation model by Embodiment 1 of this invention. It is a flowchart which shows the method of the abnormality determination by Embodiment 1 of this invention. It is a graph which shows the method of abnormality determination by Embodiment 1 of this invention. It is a graph which shows the method of abnormality determination by Embodiment 1 of this invention. It is a block diagram which shows the structure of the preventive maintenance apparatus of Embodiment 2 of this invention. It is a graph which shows the evaluation model by Embodiment 2 of this invention. It is a graph which shows the evaluation model by Embodiment 2 of this invention. It is a graph which shows the method of abnormality determination by Embodiment 2 of this invention. It is a graph which shows the method of abnormality determination by Embodiment 4 of this invention.

Embodiment 1 FIG.
Embodiment 1 of the present invention will be described below with reference to FIGS. 1 to 10.

  FIG. 1 is a block diagram showing a configuration of a system to which the preventive maintenance device for an electric motor according to the present embodiment is applied. In this system, the electric motor 1 and the electric motor driving device 2 are arranged at remote locations, and are connected to the network 7 via the remote IO boards 3 and 4, respectively. The operation signal output by the electric motor drive device 2 is output to the network 7 via the remote IO board 3 and is input to the electric motor 1 from the network 7 via the remote IO board 4. The rotation of the electric motor 1 is controlled by an operation signal transmitted from the electric motor driving device 2. The electric motor 1 is provided with an axial displacement sensor 5 for measuring the axial displacement in the radial direction and the axial displacement in the thrust direction, and a rotational speed sensor 6 for measuring the rotational speed (the number of rotations per predetermined time). ing.

  The motor preventive maintenance device 8 of the present embodiment is connected to a network 7. The operation signal output from the electric motor drive device 2 includes a drive output current that is an operation amount of the electric motor 1. The motor preventive maintenance device 8 collects data of the drive output current of the motor 1 from the remote IO board 3 via the network 7 and stores it. The motor preventive maintenance device 8 collects and stores the measurement data of the shaft displacement sensor 5 and the rotation speed sensor 6 from the remote IO board 4 via the network 7. The drive output current data capture timing by the motor preventive maintenance device 8 and the capture timing of each measurement data are synchronized.

  FIG. 2 is a block diagram showing the configuration of the motor preventive maintenance device 8 of the present embodiment. As described above, the motor preventive maintenance device 8 collects measurement data of rotational speed, radial direction axial displacement, and thrust direction axial displacement, and data of drive output current. Both the radial direction axial displacement and the thrust direction axial displacement are physical quantities representing the state of the shaft of the electric motor 1. The drive output current is captured as information representing a load (rolling load) acting on the electric motor 1 during rolling. The motor preventive maintenance device 8 collates these collected data with the evaluation model, and outputs an alarm based on the collation result. Two types of evaluation models, evaluation model A and evaluation model B, are prepared. Hereinafter, the contents of the evaluation models A and B and the creation method thereof will be described.

  The evaluation model A models the relationship between the rotational speed and drive output current during rolling and the axial displacement in the radial direction when the electric motor 1 is normal, and is expressed by an approximate function equation as described later. . FIG. 3 is a graph showing an example of the relationship between the rotational speed and radial axial displacement when the drive output current is constant in the evaluation model A. FIG. 4 is a graph showing an example of the relationship between the drive output current and the radial axial displacement in the evaluation model A when the rotation speed is constant. As can be seen from these figures, the radial axial displacement during rolling varies depending on the rotational speed and the drive output current.

  The evaluation model B models the relationship between the rotational speed during rolling and the drive output current and the axial displacement in the thrust direction when the electric motor 1 is normal, and is expressed by an approximate function equation as described later. . FIG. 5 is a graph showing an example of the relationship between the rotational speed and the axial displacement in the thrust direction when the drive output current is constant in the evaluation model B. FIG. 6 is a graph showing an example of the relationship between the drive output current and the axial displacement in the thrust direction when the rotation speed is constant in the evaluation model B. As can be seen from these figures, the axial displacement in the thrust direction during rolling varies depending on the rotational speed and the drive output current.

  FIG. 7 is a flowchart showing a method of creating each evaluation model according to the present embodiment. This flowchart includes two steps, STP1 and STP2. In STP1, which is the first step, data of drive output current, rotational speed, radial direction axial displacement, and thrust direction axial displacement are collected for a certain period during normal rolling. The more data you collect, the better. Then, in STP2, evaluation models A and B are created based on the collected data. Each evaluation model A, B is expressed by an expression approximated by a higher-order function of the second or higher order as shown below.

The following approximate function expression represents the evaluation model A. In this equation, z ₁ is the axial displacement in the thrust direction, x is the drive output current, and y is the rotational speed. A ₀ , a ₁ ,... A _n , b ₀ , b ₁ ,... B _n are coefficients determined by the least square method using the collected data.

The following approximate function expression represents the evaluation model B. In this equation, z ₂ is the radial axial displacement, x is the drive output current, and y is the rotational speed. _{Then, c 0, c 1, ...} c n, d 0, d 1, ... d n are coefficients determined by least square method using the collected data.

  The motor preventive maintenance device 8 performs the abnormality determination described below using the evaluation models A and B created as described above. FIG. 8 is a flowchart showing a method of abnormality determination performed by the motor preventive maintenance device 8 in the present embodiment. This flowchart includes six steps from STP11 to STP16. In STP 11, the current drive output current, rotational speed, radial axial displacement, and thrust axial displacement data are collected by the motor preventive maintenance device 8. In STP 12, a threshold value for radial axial displacement is set using evaluation model A based on the current drive output current and rotational speed. In STP13, a threshold value for thrust direction axial displacement is set using evaluation model B based on the current drive output current and rotational speed.

  In FIG. 9, a part of the curved surface drawn by the approximate function formula of the evaluation model A is drawn. The closer the coordinate specified by the collected data is from the curved surface of the evaluation model A, the lower the degree of coincidence between the current state of the electric motor 1 and the evaluation model A. The threshold value set in STP 12 is used as a determination value for determining whether or not the degree of coincidence between the current state of the electric motor 1 specified by the collected data and the evaluation model A is within an allowable range. In FIG. 9, the threshold value is located on a curved surface (threshold curved surface shown in the figure) provided at a certain distance from the curved surface of the evaluation model A. In STP14, whether the current radial axial displacement exceeds the threshold set in the evaluation model A, that is, whether the degree of coincidence between the current state of the electric motor 1 and the evaluation model A is lower than the determination value. Is determined. When the current radial axial displacement exceeds the threshold value, that is, when the coordinates specified by the collected data are located outside the threshold curved surface as indicated by black dots in FIG. It is detected as some abnormality related to. In that case, an alarm is issued in STP16.

  As a result of the determination of STP14, if the current radial axial displacement does not exceed the threshold value, that is, as indicated by white points in FIG. 9, the coordinates specified by the collected data are located inside the threshold curved surface. In that case, the determination of STP15 is made. In STP15, whether or not the current axial displacement in the thrust direction exceeds the threshold set in the evaluation model B, that is, whether or not the degree of coincidence between the current state of the electric motor 1 and the evaluation model B is lower than the determination value. Is determined. In FIG. 10, a part of the curved surface drawn by the approximate function formula of the evaluation model B is drawn. In FIG. 10, the threshold set in STP 13 is located on a curved surface (threshold curved surface shown in the figure) provided at a certain distance from the curved surface of evaluation model B. The threshold value is used as a determination value for determining whether or not the degree of coincidence between the current state of the electric motor 1 specified by the collected data and the evaluation model B is within an allowable range. When the current axial displacement in the thrust direction exceeds the threshold value, that is, as shown by the black dots in FIG. 10, when the coordinates specified by the collected data are located outside the threshold curved surface, the electric motor 1 It is detected as some abnormality related to. In that case, an alarm is issued in STP16.

  On the other hand, when the current axial displacement in the thrust direction does not exceed the threshold value, that is, when the coordinates specified by the collected data are located inside the threshold curved surface, as indicated by white points in FIG. It is determined that the electric motor 1 and the equipment related to the rotation state of the electric motor 1 are normal. Therefore, in this case, no alarm is issued, and the process returns to the STP 11 to start collecting data.

  As described above, in the present embodiment, the rotation speed of the electric motor 1, the drive output current representing the rolling load, the radial axial displacement representing the state of the shaft of the electric motor 1, and the thrust axial displacement are included in three types of data. Based on this, an abnormality is monitored. According to this, it is possible to avoid erroneous diagnosis due to fluctuations in rotational speed and changes in rolling load, so that signs of failure of the electric motor 1 can be known earlier and more accurately than in the conventional method.

  Further, according to the present embodiment, it is possible to detect an abnormality on the machine side connected to the electric motor 1 as well as a failure of the electric motor 1 itself. For example, in the case where the motor 1 and the machine are connected using a universal coupling, when a problem occurs in the conformity of the joint portion between the universal coupling and the shaft of the motor 1, the lubrication of the bearing on the machine side is insufficient. When this occurs, an excessive force may be applied to the shaft of the electric motor 1 to cause a sudden failure. However, according to the present embodiment, by comparing the measurement data of the axial displacement in the thrust direction with the evaluation model B, it is possible to detect an abnormality on the machine side and perform appropriate inspection and maintenance. As a result, sudden failure of the electric motor 1 can be prevented in advance.

  Further, in a large electric motor such as the electric motor 1 of the present embodiment, a slide bearing is used for the bearing. This bearing is lubricated with lubricating oil supplied from a bearing oil supply device. Then, when the electric motor 1 is started, the electric motor 1 is rotated by lifting the shaft of the electric motor 1 with the oil pressure of the lubricating oil. However, a phenomenon of insufficient hydraulic pressure may occur due to clogged piping or deterioration of the pump over time, and the shaft of the electric motor 1 may not be lifted to the target float amount. In that case, friction may occur between the bearing metal of the radial bearing and the shaft of the electric motor 1, and the metal may burn out. However, according to the present embodiment, it is possible to monitor the float amount of the jacking pump by collating the measurement data of the radial axial displacement with the evaluation model A, and to prevent an accident caused by a defective bearing oil supply device. Can be prevented.

Embodiment 2. FIG.
Hereinafter, Embodiment 2 of the present invention will be described with reference to FIGS. 11 to 14.

  The preventive maintenance device for an electric motor according to the present embodiment is applied to the system having the configuration shown in FIG. 1 as in the first embodiment. However, in the present embodiment, since the displacement of the shaft of the electric motor 1 in the thrust direction is regulated by the end plate, the physical quantity representing the state of the shaft of the electric motor 1 is a thrust direction axial load instead of the thrust direction axial displacement. Is used. For this reason, the electric motor 1 of the present embodiment is provided with a load sensor for measuring the thrust direction axial load instead of the axis displacement sensor for measuring the thrust direction axial displacement. Regarding the radial direction, as in the first embodiment, an axial displacement sensor for measuring the radial axial displacement is provided.

  FIG. 11 is a block diagram showing a configuration of the motor preventive maintenance device 8 of the present embodiment. The motor preventive maintenance device 8 of the present embodiment collects each measurement data of rotational speed, radial direction axial displacement and thrust direction axial load and data of drive output current. The motor preventive maintenance device 8 collates these collected data with the evaluation model, and outputs an alarm based on the collation result. In the present embodiment, two types of evaluation models are prepared: the evaluation model A described above and the evaluation model C described below.

  The evaluation model C is a model of the relationship between the rotational speed and drive output current during rolling and the axial load in the thrust direction when the electric motor 1 is normal. It is expressed by a high-order function equation. FIG. 12 is a graph showing an example of the relationship between the rotational speed and the axial load in the thrust direction when the drive output current is constant in the evaluation model C. FIG. 13 is a graph showing an example of the relationship between the drive output current and the axial load in the thrust direction when the rotation speed is constant in the evaluation model C. As can be seen from these figures, the axial load in the thrust direction during rolling varies depending on the rotational speed and the drive output current. The creation method of the evaluation model C is the same as the creation method of the evaluation models A and B, and an approximate function formula of the evaluation model C is created based on the actual data at the time of rolling when the electric motor 1 is normal.

  The motor preventive maintenance device 8 of the present embodiment performs an abnormality determination using the evaluation models A and C. In the present embodiment, the threshold value of the thrust axial load is set using the evaluation model C based on the current drive output current and the rotational speed. In FIG. 14, a part of the curved surface drawn by the approximate function expression of the evaluation model C is drawn. In FIG. 14, the threshold is located on a curved surface (threshold curved surface shown in the figure) provided at a certain distance from the curved surface of the evaluation model C. The threshold value is used as a determination value for determining whether or not the degree of coincidence between the current state of the electric motor 1 specified by the collected data and the evaluation model C is within an allowable range. When the current axial load in the thrust direction exceeds the threshold value, that is, as shown by the black dots in FIG. 14, when the coordinates specified by the collected data are located outside the threshold curved surface, Detected as some kind of abnormality. In that case, an alarm is issued from the motor preventive maintenance device 8. On the other hand, if the current axial load in the thrust direction does not exceed the threshold value, that is, as indicated by white points in FIG. 14, the coordinates specified by the collected data are located inside the threshold curved surface, It is determined that the electric motor 1 and the equipment related to the rotation state of the electric motor 1 are normal.

Embodiment 3 FIG.
The third embodiment of the present invention will be described below.

  The preventive maintenance device for an electric motor according to the present embodiment is applied to the system having the configuration shown in FIG. 1 as in the first and second embodiments. The feature of this embodiment is that data for abnormality determination is not always collected, but is collected only at a specific timing. Many rolling mill plants operate for 24 hours except for regular inspections. Therefore, in order to monitor the abnormality, it is necessary to continuously collect data during operation for 24 hours. However, if data is collected in units of 5 or 10 years, the amount of data becomes quite large, and analysis takes time and cost. On the other hand, there is a high probability that the failure of the electric motor is caused by a mechanical impact or an electrical overload applied to the electric motor at the timing of rolling the rolled material.

  Therefore, in the present embodiment, data is collected only at the timing of rolling material biting, and the abnormality of the electric motor is monitored. According to this, data can be used effectively, and the cost and time required for analysis can be reduced.

Embodiment 4 FIG.
The fourth embodiment of the present invention will be described below with reference to FIG.

  The motor preventive maintenance device of the present embodiment is applied to the system having the configuration shown in FIG. 1 as in the first, second, and third embodiments. In the present embodiment, the motor preventive maintenance apparatus collects data at a fixed monitoring cycle, and collates the collected data with the evaluation model each time. Specifically, the measurement data of the radial direction axial displacement, the thrust direction axial displacement, or the thrust direction axial load, which are specific physical quantities representing the state of the electric motor, and the threshold value obtained from the evaluation model are compared. Then, the number of times that the measurement data of the specific physical quantity exceeds the threshold value, that is, the number of times that the degree of coincidence falls below the determination value (abnormal number of times) is counted for each predetermined period, and the temporal change of the abnormal number is recorded.

  FIG. 15 shows several examples of changes in the number of abnormalities over time. If the number of abnormalities increases in one direction as in case 1, it can be determined that the machine has failed, the motor bearing oil supply device has failed, or the motor itself has deteriorated. If the number of abnormalities is large as in the case 2, but is kept almost constant, it can be determined that the state of the electric motor and related equipment is stable. If the absolute number of abnormal times is not very large as in case 3, but the rate of increase is rapid, it can be determined that some sudden failure has occurred.

  According to the present embodiment, the recorded data of the time-dependent change in the number of abnormalities is displayed on the display of the motor preventive maintenance device so that it can be easily seen by human eyes. According to this, since the increase / decrease in the number of abnormalities can be monitored over a long period of time, there is an effect that the deterioration of the motor over time can be predicted. In the case of a computer, an alarm is not output unless the number of abnormalities exceeds a certain threshold, but when data is visualized as in this embodiment, the tendency of abnormalities in a range that does not reach the threshold is visually observed. It is possible to monitor immediately, and it is possible to take preventive measures immediately for abnormalities relating to the motor.

Others.
The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention. For example, as the specific physical quantity representing the state of the motor shaft, only one of radial axial displacement, thrust axial displacement, and thrust axial load may be used. Alternatively, the vibration of the shaft of the motor may be measured, and the measured value may be used as a specific physical quantity that represents the state of the shaft of the motor.

DESCRIPTION OF SYMBOLS 1 ... Electric motor 2 ... Electric motor drive device 3, 4 ... Remote IO board 5 ... Axial displacement sensor 6 ... Rotational speed sensor 7 ... Network 8 ... Electric motor preventive maintenance device

Claims (7)

A preventive maintenance device for a motor of a rolling plant whose rotation is controlled by a drive output current input from an electric motor drive device,
Data collection means for collecting measurement data of a specific physical quantity representing the state of the shaft of the electric motor, measurement data of the rotational speed of the electric motor, and data of the drive output current;
Evaluation model storage means for storing an evaluation model modeling the relationship between the rotation speed, the drive output current and the specific physical quantity during normal rolling;
An anomaly monitoring means for collating the data collected by the data collecting means with the evaluation model, and monitoring an abnormality related to the electric motor based on the degree of coincidence;
A preventive maintenance device for an electric motor comprising:   2. The preventive maintenance apparatus for an electric motor according to claim 1, wherein the data collection unit collects radial axial displacement measurement data of the electric motor obtained by an axial displacement sensor as measurement data of the specific physical quantity. .   2. The preventive maintenance apparatus for an electric motor according to claim 1, wherein the data collection unit collects axial displacement measurement data obtained by an axial displacement sensor as the measurement data of the specific physical quantity. .   2. The preventive maintenance apparatus for an electric motor according to claim 1, wherein the data collection unit collects axial load measurement data obtained by an axial load sensor as the measurement data of the specific physical quantity. 3. .   5. The preventive maintenance apparatus for an electric motor according to claim 1, wherein the data collection unit collects data at a biting timing of the rolled material.   6. The preventive maintenance of an electric motor according to any one of claims 1 to 5, wherein the abnormality monitoring unit detects that the degree of coincidence is lower than a predetermined determination value as an abnormality relating to the electric motor. apparatus.   6. The abnormality monitoring unit according to any one of claims 1 to 5, wherein the abnormality monitoring unit counts the number of times that the degree of coincidence is lower than a predetermined determination value for every predetermined period, and records a change with time of the number. The preventive maintenance device for an electric motor according to Item.

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