Motor shaft fatigue diagnostic device

Abstract

To provide a motor shaft fatigue level diagnostic device that generates data for easily determining the deterioration of a motor shaft due to the long-term use.SOLUTION: A motor shaft fatigue level diagnostic device according to an embodiment acquires second time-series data of shear stress calculated on the basis of first time-series data of a torque value from a drive device that drives a motor, extracts the maximum shear stress for each period from the second time-series data, classifies the maximum shear stress for each period to multiple ranges, adds up the first number of times of extracting the maximum shear stress for each period for each of the multiple ranges, compares the second number of times of repetition of an S-N curve of a material forming the shaft of the motor with the first number of times for each of the multiple ranges, extracts a minimum value of a difference between the second number of times and the first number of times across all of the multiple ranges, and determines the fatigue level of the shaft on the basis of the minimum value.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] An embodiment of the present invention relates to a motor shaft fatigue level diagnosis device. [Background technology]

[0002] Motors used in rolling mills in steel plants and other equipment experience large load fluctuations during operation, which can result in shock loads being applied to the motor shaft via machinery such as mills. Such motors are often operated for 20 to 30 years, and shock loads are applied to the motor shaft over long periods of time. Therefore, if the number of repetitions exceeds the limit that the motor shaft can withstand, in the worst case scenario, the shaft may break.

[0003] To prevent such situations, motors are often required to have a load-bearing strength that exceeds their overload capacity when considering their specifications.However, in actual operation, it is often difficult to monitor and manage the load applied to the shaft and its frequency, so maintenance personnel conduct visual inspections on regular shutdowns to prevent sudden motor failures due to shaft load.

[0004] In light of this situation, it is necessary to easily and quantitatively diagnose the degree of fatigue of the motor shaft in order to prevent sudden motor failure. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-291842 Summary of the Invention [Problem to be solved by the invention]

[0006] Visual inspection of motor shafts is difficult to perform because it must be performed during periods when the factory is not in operation, and the sensitivity of visual inspection to detect deterioration can depend on the experience of the inspection technician.

[0007] Non-destructive testing other than visual inspection, such as ultrasonic testing, should preferably be performed by qualified personnel, and there is a problem that the testing time is long.

[0008] The present invention has been made to solve the above-mentioned problems, and aims to provide a motor shaft fatigue diagnosis device that generates data that can easily determine the deterioration of a motor shaft due to long-term use. [Means for solving the problem]

[0009] An embodiment of the present invention includes: obtaining second time series data of shear stress calculated based on first time series data of torque values ​​from a drive device that drives a motor that periodically outputs an instantaneous maximum value of torque; extracting a maximum shear stress for each period from the second time series data; classifying the maximum shear stress for each period into a plurality of ranges of maximum shear stress; accumulating a first number of times that the maximum shear stress for each period is extracted for each of the plurality of ranges; and comparing a second number of repetitions of a predetermined SN curve of a material that forms the shaft of the motor with the first number of times for each of the plurality of ranges; A ratio of the first number of times to the second number of times is calculated as a fatigue score; Over all of the above ranges The maximum value of the fatigue score is output. [Effects of the Invention]

[0010] According to the embodiment, a motor shaft fatigue level diagnosis device is provided that generates data that allows for a simple determination of the deterioration of a motor shaft due to long-term use. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a schematic block diagram illustrating a motor drive system to which a motor shaft fatigue level diagnosis device according to an embodiment is applied; [Figure 2] 4 is a schematic operational waveform diagram illustrating an example of an operation of the motor shaft fatigue level diagnosis device according to the embodiment; FIG. [Figure 3]Fig. 3(a) is an example of a histogram of shear stress generated by the motor shaft fatigue level diagnosis device according to the embodiment, and Fig. 3(b) is an enlarged view of part A in Fig. 3(a). [Figure 4] 10 is an example of time-series data of fatigue scores generated by a motor shaft fatigue level diagnosis device according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, embodiments will be described with reference to the drawings. The drawings are schematic or conceptual, and the relationship between the thickness and width of each part, the size ratio between parts, etc. are not necessarily the same as those in reality. Furthermore, even when the same part is shown, the dimensions and ratios may be different depending on the drawing. In the present specification and the drawings, elements similar to those described above with reference to the previous drawings are designated by the same reference numerals, and detailed descriptions thereof will be omitted as appropriate.

[0013] FIG. 1 is a schematic block diagram illustrating a motor drive system to which a motor shaft fatigue level diagnosis device according to an embodiment is applied. As shown in FIG. 1, a motor drive system 100 includes a motor shaft fatigue diagnosis device 10 and a drive device 20. The motor drive system 100 drives a motor 30. In the motor drive system 100, the motor 30 is driven according to a set speed pattern. In the following description, the motor 30 is assumed to be used for driving a rolling mill in a steel plant, etc., and a large torque is periodically generated by the biting and ejection of material, and the large torque is periodically applied to the motor shaft. The periodic torque applied to the motor shaft is assumed to be a pulse or impulse torque having a sufficiently short time width.

[0014] The motor shaft fatigue level diagnosis device 10 is, for example, a computer device having a programmable controller (PLC) function, and generates a speed command value according to a set program and outputs the speed command value to the drive device 20.

[0015] The drive device 20 is communicatively connected to the motor shaft fatigue level diagnosis device 10 via a control network 101. The drive device 20 generates a drive voltage and a drive current for driving the motor 30 in accordance with a speed command value supplied from the motor shaft fatigue level diagnosis device 10, and outputs them to the motor 30. The motor 30 operates in accordance with the drive voltage and drive current output by the drive device 20.

[0016] The drive device 20 generates a drive current command value based on the speed command value and controls the motor 30 so that a feedback value of the drive current output to the motor 30 follows the drive current command value. Since the drive current feedback value is proportional to the torque feedback value of the motor 30, the drive device 20 can also output a torque feedback value. Furthermore, the shear stress applied to the motor shaft of the motor 30 can be calculated using the polar section modulus of the shaft. In the following, the drive device 20 calculates the shear stress applied to the motor shaft based on the torque feedback value calculated by the drive device 20 and outputs it to the motor shaft fatigue diagnosis device 10. However, this is not limiting, and the motor shaft fatigue diagnosis device 10 may of course obtain a drive current feedback value from the drive device 20 and calculate the shear stress applied to the motor shaft based on the drive current feedback value.

[0017] The motor shaft fatigue level diagnosis device 10 receives data on the shear stress acting on the motor shaft from the drive device 20 via the control network 101, and extracts the maximum value from the shear stress values ​​in one cycle. The motor shaft fatigue level diagnosis device 10 extracts the maximum value of the shear stress in one cycle for each cycle, and generates a histogram.

[0018] The histogram of shear stress includes a maximum number of times that each shear stress is applied, which is preset based on the SN curve of the material that forms the motor shaft.The motor shaft fatigue diagnosis device 10 calculates a fatigue score based on the number of times the maximum value of the shear stress is extracted in one cycle.

[0019] For example, the motor shaft fatigue diagnosis device 10 extracts the number of shear stress applications that has the smallest difference from the maximum number set in the SN curve from the generated histogram, and calculates a fatigue score based on the maximum number and the extracted number of applications.

[0020] The motor shaft fatigue level diagnosis device 10 outputs the calculated fatigue level score at a preset timing and cycle. Preferably, the motor shaft fatigue level diagnosis device 10 has a preset fatigue level threshold value, and generates a predetermined alarm signal when the calculated fatigue level score reaches the threshold value. The alarm signal, for example, causes a predetermined alarm or warning to be output on the screen of an HMI terminal or the like communicatively connected to the motor shaft fatigue level diagnosis device 10 via a communication network.

[0021] The operation of the motor shaft fatigue level diagnosis device 10 according to the embodiment will be described in detail. FIG. 2 is an example of a schematic operational waveform diagram for explaining the operation of the motor shaft fatigue level diagnosis device according to the embodiment. Figure 2 shows three waveform diagrams of the operating parameters of the motor that drives the rollers of a steel rolling mill, synchronized at time t. The top graph in FIG. 2 shows data on the actual measured value of the speed of the motor 30, and indicates the change over time in the speed feedback value V [rpm] detected by a speed detector provided in the motor 30. The second diagram in FIG. 2 shows the change over time of the torque feedback value T [Nm] calculated by the drive device 20. The bottom diagram in FIG. 2 shows the time change of the signal output by the load relay provided in the screw down device of the rolling mill.

[0022] As shown in Figure 2, at time t1, the material is caught in the rollers of the rolling mill, and the load relay outputs an ON signal. At time t1, the speed feedback value V drops instantaneously as the material is caught. The torque feedback value T reaches its maximum value due to the impact of the material.

[0023] The roller then bites into the material and rolls it, discharging it at time t2. At time t2, the load relay turns off, the speed feedback value V rises instantaneously, and the torque feedback value T drops to a nearly constant value for driving the roller.

[0024] The period from time t1 to time t2 is the period during which the material is rolled, and corresponds to one rolling cycle. The same applies to the periods after time t(i), from time t(i) to time t(i+1) is one rolling cycle. As will be described later, in the motor shaft fatigue diagnosis device 10, there is one timing during which the shear stress reaches its maximum value per cycle, and the number of such times is used as a measure of the fatigue level of the motor shaft. Therefore, the length of the cycle does not need to be constant and may vary from cycle to cycle. In the above description, one cycle is defined as the period from when the load relay is turned on to when it is turned off, but it can also be defined as the period from when the load relay is turned on to when it is turned on again, as is the case normally. In the rolling process of material, the torque feedback value is low and the change in value is small during the period when the load relay is off. Therefore, by defining one cycle as the period from when the load relay is turned on to when it is turned off, the amount of time-series data to be collected can be reduced.

[0025] The drive device 20 calculates the shear stress τ [Pa] using the torque feedback value T [Nm], and outputs the time-series data of the calculated shear stress τ to the motor shaft fatigue level diagnosis device 10. The calculation formula (1) of the shear stress can be set, for example, as follows:

[0026] τ=T / Zp (1) Here, Zp[m 3] is the polar section modulus of the shaft of the motor 30, and can be calculated using the following conversion formula (2): d [mm] is the diameter of the shaft, and a design value or an actually measured value can be used. Zp=πd 3 / 16 (2)

[0027] The drive device 20 sequentially calculates the shear stress τ from the torque feedback value T using equations (1) and (2), and sequentially outputs the calculated shear stress τ data to the motor shaft fatigue level diagnosis device 10.

[0028] The motor shaft fatigue level diagnosis device 10 receives time series data of shear stress τ from the drive device 20. The motor shaft fatigue level diagnosis device 10 extracts the maximum value for each period from the time series data of shear stress τ received from the drive device 20.

[0029] In the example of Fig. 2, in the cycle from time t1 to time t2, the maximum value of the torque feedback value T is T1 at time t1. In addition, in the cycle from time t(i) to time t(i+1), the maximum value of the torque feedback value T is Ti at time t(i). Therefore, the maximum value of the shear stress τ for each cycle is data calculated from the maximum values ​​T1 and Ti of the torque feedback value T at times t1 and t(i).

[0030] The motor shaft fatigue diagnosis device 10 receives, for example, time series data of the output signal of a load relay from a screw down device. The motor shaft fatigue diagnosis device 10 can determine the start time and end time of one cycle of the shear stress τ from the time series data of the output signal of the load relay. The time series data of the shear stress τ and the time series data of the output signal of the load relay are time-synchronized. The motor shaft fatigue diagnosis device 10 determines the cycle of the time series data of the shear stress τ and searches for and extracts the maximum value of the shear stress τ for each determined cycle.

[0031] The motor shaft fatigue level diagnosis device 10 plots the extracted maximum value on a histogram every time it extracts the maximum value of shear stress τ for each cycle. Regarding the time-series data of shear stress, data other than the maximum value may be discarded after the maximum value is extracted or plotted on the histogram. Furthermore, the maximum value data may also be discarded after the fatigue level score, which will be described later, is calculated.

[0032] In the above description, the motor shaft fatigue diagnosis device 10 searches for and extracts the maximum value of shear stress for each cycle from the time-series data of shear stress. When the load on the motor 30 is a roller of a rolling mill, as shown in the specific example of FIG. 2, the time of impact of the material is often the maximum value of torque and therefore the maximum value of shear stress. In such a case, the maximum value of shear stress may simply be the data at the time when the output signal of the load relay is turned ON. By setting it in this way, the computational load on the motor shaft fatigue diagnosis device 10 can be reduced.

[0033] The generation of a histogram of maximum shear stress values ​​will now be described. Fig. 3(a) is an example of a histogram of shear stress generated by the motor shaft fatigue level diagnosis device according to the embodiment, and Fig. 3(b) is an enlarged view of part A in Fig. 3(a). As shown in Figure 3(a) and Figure 3(b), the maximum value of shear stress is shown on a logarithmic scale, with the vertical axis representing shear stress τ [Pa] and the horizontal axis representing the number of cycles. Figures 3(a) and 3(b) also show the SN curves of the material that makes up the motor shaft.

[0034] In the histogram, the range of maximum shear stress values ​​is set on the vertical axis, and the motor shaft fatigue diagnosis device 10 associates the extracted maximum shear stress value with a value in the range. Each time a maximum shear stress value is associated, the number of data points in the same range increases by one. In other words, the number of repetitions of impact increases by one.

[0035] The motor shaft fatigue diagnostic device 10 calculates the number of data points accumulated within each range of the maximum value of shear stress. n The motor shaft fatigue diagnosis device 10 acquires the number of repetitions (10) for each range of the maximum value of shear stress of the set SN curve. N The motor shaft fatigue diagnostic device 10 acquires 10 pieces of data for each range of the maximum value of shear stress (second number of times). n and 10 repetitions N The fatigue score for each range is calculated using the following formula (3), for example.

[0036] Fatigue score per range = 10 n / 10 N (3) In other words, the fatigue score is expressed as the ratio of the number of times the maximum shear stress was actually applied per cycle to the number of times on the SN curve.

[0037] The motor shaft fatigue level diagnosis device 10 periodically extracts the maximum value of the fatigue level score across the entire range from the fatigue level scores for each range. The extracted maximum value of the fatigue level score is output to the display of the motor shaft fatigue level diagnosis device 10 on each extraction date. The frequency at which the maximum value of the fatigue level score across the entire range is extracted can be set arbitrarily, and can be, for example, once a week, once every three months, etc.

[0038] FIG. 4 shows an example of time-series data of fatigue scores generated by the motor shaft fatigue level diagnosis device according to the embodiment. 4, the motor shaft fatigue level diagnosis device 10 outputs data on the change over time of the maximum value of the fatigue level score to a display. A threshold value for the maximum value of the fatigue level score may be set in the motor shaft fatigue level diagnosis device 10, and the motor shaft fatigue level diagnosis device 10 may output an alarm signal when the maximum value of the fatigue level score reaches the threshold value.

[0039] In the above, when setting the threshold, the SN curve is calculated 10 times.N As is well known, the SN curve is based on measurements under specified conditions, and is measured by applying a sinusoidal shear stress to the sample. On the other hand, as shown in Figure 2, the shear stress applied to the motor shaft is pulse-like or impulse-like and nonlinear, and does not necessarily match the conditions for obtaining the SN curve. In other words, the maximum number of repetitions based on the SN curve is 10. N is the number of times that shear stress is repeatedly applied to the motor shaft. n Therefore, when setting a threshold value, the value should be set with a sufficient margin and applied.

[0040] In the above description, the motor shaft fatigue level diagnosis device 10 may discard the time series data of shear stress after extracting the maximum value of shear stress for each cycle, but for example, the motor shaft fatigue level diagnosis device 10 may transmit the time series data to a host computer, etc. In this way, the shear stress data can be effectively utilized without increasing the storage capacity of the motor shaft fatigue level diagnosis device 10.

[0041] The effects of the motor shaft fatigue level diagnosis device 10 according to the embodiment will be described. The motor shaft fatigue diagnosis device 10 according to the embodiment acquires time-series data of shear stress from the drive device 20 at each cycle and extracts the maximum value of shear stress. The motor shaft fatigue diagnosis device 10 calculates the fatigue level of the motor shaft by accumulating the number of maximum shear stress data points, allowing for easy, long-term estimation of the deterioration status of the motor shaft with a small memory capacity. Furthermore, by calculating the shear stress on the drive device 20 side and extracting the maximum shear stress when the load relay is turned on, the load on the computing power of the motor shaft fatigue diagnosis device 10 can be reduced. Because the motor shaft fatigue diagnosis device 10 can be configured in this way without requiring increased computing power or memory capacity, it can be easily implemented in an existing PLC or the like.

[0042] The motor shaft fatigue diagnosis device 10 can set a threshold value for the fatigue score and generate and output an alarm signal when the fatigue score reaches the threshold value. Via an HMI terminal or the like that receives the alarm signal, a supervisor can reliably recognize the possibility that the motor shaft is deteriorating, and can schedule an inspection for the next scheduled downtime. Since there is no need to inspect the motor shaft on other downtime days, the inspection work can also be shortened.

[0043] In this way, it is possible to realize a motor shaft fatigue diagnostic device that generates data that allows for easy determination of motor shaft deterioration due to long-term use.

[0044] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as defined in the claims. [Explanation of symbols]

[0045] 10...motor shaft fatigue diagnostic device, 20...drive device, 30...motor, 100...motor drive system, 101...control network nine

Claims

1. second time-series data of shear stress calculated based on first time-series data of torque values ​​is acquired from a drive device that drives a motor that periodically outputs an instantaneous maximum value of torque; extracting a maximum shear stress for each period from the second time series data; classifying the maximum shear stress for each cycle into a plurality of ranges of maximum shear stress; accumulating a first number of times the maximum shear stress for each of the plurality of ranges is extracted for each of the cycles; comparing a second number of repetitions of an S-N curve of a material forming the shaft of the motor with the first number of repetitions for each of the plurality of ranges; calculating a fatigue score as a ratio of the first number of times to the second number of times; A motor shaft fatigue diagnostic device that outputs the maximum value of the fatigue score across all of the multiple ranges.

2. 2. The motor shaft fatigue diagnostic device according to claim 1, wherein after extracting the maximum shear stress for each cycle, data other than the maximum shear stress for the extracted cycle is discarded.

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