The present invention relates to an abnormality determination device.
There is known a device that determines abnormality of an industrial apparatus such as a machine tool. For example, PTL 1 describes a device that calculates, by a machine learning method, a degree of divergence between data acquired when an industrial apparatus normally operates, and data acquired from an industrial apparatus that is a target of diagnosis, and determines abnormality, based on the obtained degree of divergence.
[PTL 1] Japanese Patent No. 6451662
Referring to
According to one mode of the present disclosure, an abnormality determination device that determines abnormality of a machine includes a normal data storage unit configured to correlate and store normal data that is data relating to a state of the machine at a time when the machine normally operates, and an environmental temperature of the machine at a time when the normal data is acquired; a diagnosis data storage unit configured to correlate and store diagnosis data that is data relating to the state of the machine at a time of diagnosing the machine, and the environmental temperature of the machine at a time when the diagnosis data is acquired; a compensation value deriving unit configured to calculate a predetermined feature at each of the environmental temperatures in regard to the normal data stored in the normal data storage unit, and derive a statistical quantity obtained from the calculated feature at each of the environmental temperatures, as a compensation value at each of the environmental temperatures; a compensation value interpolation unit configured to calculate, by interpolation, the compensation value in regard to the environmental temperature at a time when the diagnosis data is acquired, by using the compensation values in regard to at least two environmental temperatures with respect to which the normal data is included in the normal data storage unit; a normal data compensation unit configured to compensate the feature of the normal data by using the compensation value at each of the environmental temperatures; a learning unit configured to construct a learning model by performing learning by using the feature of the compensated normal data as training data at a normal time; a diagnosis data compensation unit configured to compensate the feature of the diagnosis data by using the compensation value calculated by the compensation value interpolation unit; and a machine abnormality determination unit configured to determine whether the diagnosis data is normal, based on a degree of divergence between the feature of the compensated diagnosis data and the learning model.
As described above, according to the present embodiment, exact diagnosis can be performed by calculating a compensation value from normal data in accordance with an environmental temperature, and compensating data relating to a state of a machine.
From a detailed description of typical embodiments of the present invention illustrated in the accompanying drawings, the objects, features and advantageous effects of the present invention, and other objects, features and advantageous effects of the invention, will be clearer.
Next, embodiments of the present disclosure will be described with reference to the accompanying drawings. In the drawings to be referred to, similar structural parts or functional parts are denoted by the same reference numerals. These drawings use different scales as appropriate to facilitate understanding. The mode illustrated in each drawing is one example for carrying out the present invention, and the present invention is not limited to the modes illustrated in the drawings.
Besides, the abnormality determination device 10 includes a machine learning device 24. The machine learning device 24 includes a learning unit 242 that constructs a learning model by performing learning by using the feature of the state data compensated by the normal data compensation unit 103 as training data at a normal time; a learning model storage unit 241 that stores the learning model constructed by the learning unit 242; and a machine abnormality determination unit 243 that determines whether the diagnosis data is normal, based on a degree of divergence between the diagnosis data compensated by the diagnosis data compensation unit 106 and the learning model.
The machine 50 includes a machine tool, an industrial robot, and other various machines. As the state data of the machine 50, various data representative of physical states of the machine 50 is included. Here, by way of example, a case is described in which the machine 50 is a machine tool, and the state data is a torque command (torque control) waveform for an electric motor that drives an axis of the machine tool.
In the abnormality determination device 10, the normal data compensation unit 103 compensates the state data in accordance with a predetermined rule by using a compensation value of the state data at each of temperatures. The predetermined rule is, for example, an arithmetic operation of dividing the feature of the state data that is a compensation target by the compensation value in regard to each of environmental temperatures. Thereby, when the state data that is the compensation target is the state data at the normal time, a feature after compensation becomes approximately 1, regardless of the environmental temperature, and a comparison in diagnosis can easily be executed.
The compensation value used in the compensation in the normal data compensation unit 103 is a predetermined statistical quantity calculated by the compensation value deriving unit 105 with respect to the feature calculated from the waveforms of the state data at the normal time at each environmental temperature. The compensation value deriving unit 105 extracts state data at a specific environmental temperature from a state data group that is stored in the normal data storage unit 113 by being correlated with environmental temperature data. A predetermined statistical quantity calculated with respect to the feature of the extracted state data waveform is set as the compensation value at the environmental temperature. As the feature of the waveform, a P2P (Peak to Peak) is used. Note that a maximum value or a minimum value may be used as the feature of the waveform. In the present embodiment, although it is assumed that an average value is used as the predetermined statistical quantity, a median, a mode or the like may be used, or two or more features may be used. By executing a similar operation, if state data at a corresponding environmental temperature exists in the normal data storage unit 113, the compensation value at this environmental temperature can be derived.
By the above-described configuration, the state data at the normal time of the machine 50 can be obtained in regard to each of environmental temperatures. However, in general, the environmental temperature of the machine does not greatly change, and it is difficult to acquire in advance the state data at the normal time in regard to all environmental temperatures, and to accumulate the state data in the normal data storage unit 113. Accordingly, there arises such a problem that a compensation value is not obtained for the environmental temperature with respect to which the state data could not be obtained in advance. As regards this point, the abnormality determination device 10 according to the present embodiment is configured to acquire, in regard to an environmental temperature with respect to which a compensation value has not been obtained, the compensation value by an interpolation operation, based on compensation values at environmental temperatures with respect to which state data have been obtained. In the abnormality determination device 10, the compensation value interpolation unit 104 executes this function.
An interpolation operation of a compensation value by the compensation value interpolation unit 104 is described. By way of example, as illustrated in
As another example of the interpolation calculation, as illustrated in
The diagnosis data compensation unit 106 calculates, by using the compensation value interpolation unit 104, a compensation value at an environmental temperature corresponding to the diagnosis data stored in the diagnosis data storage unit 114. Then, the diagnosis data compensation unit 106 compensates the diagnosis data by using a similar method to the method in the normal data compensation unit 103.
Next, learning by the machine learning device 24 is described. The machine learning device 24 includes a learning model storage unit 241, a learning unit 242, and a machine abnormality determination unit 243. The learning unit 242 executes machine learning by using the feature of the compensated normal state data waveform calculated by the normal data compensation unit 103, and constructs a learning model. The constructed learning model is stored in the learning model storage unit 241, and is used for abnormality determination by the machine abnormality determination unit 243.
In the present embodiment, the machine learning device 24 executes abnormality determination by an MT method (Mahalanobis Taguchi method). Using the feature of the normal data compensated by the normal data compensation unit 103, the learning unit 242 provides a mathematical model below, by which the machine abnormality determination unit 243 executes abnormality determination, based on the degree of divergence from the normal data.
[Math. 1]
d=√{square root over ((x−μ)TΣ−1(x−μ))} (1)
wherein d is a Mahalanobis distance representative of a degree of divergence of the diagnosis data from the normal data; x is a vector in which features of diagnosis data waveforms compensated by the diagnosis data compensation unit 106 are arranged; μ is a vector in which average values of features of normal state data waveforms compensated by the normal data compensation unit 103 are arranged; and Σ is a variance-covariance matrix of features of normal state data waveforms compensation by the normal data compensation unit 103.
The learning unit 242 provides the mathematical model (learning model) expressed by the above equation (1) to the machine abnormality determination unit 243. The machine abnormality determination unit 243 calculates the degree of divergence from the normal data as the Mahalanobis distance d by the above equation (1) in regard to the feature x of the diagnosis data waveform compensated by the diagnosis data compensation unit 106. Then, when the Mahalanobis distance d calculated by equation (1) is greater than a preset threshold, the machine abnormality determination unit 243 determines that the diagnosis data is abnormal. The threshold used here may be set, for example, based on an experimental value or an empirical value. Such a configuration may be adopted that a user can set the threshold for the abnormality determination device 10.
Hereinafter, embodiments of the abnormality determination device 10 are described. It is assumed that the learning model is already constructed by the learning unit 242.
Next, by the above-described interpolation operation, the compensation value interpolation unit 104 calculates a compensation value in regard to the environmental temperature at the time when the diagnosis data is obtained (step S103). Furthermore, at this time, the diagnosis data compensation unit 106 compensates the diagnosis data by using the compensation value relating to the diagnosis data, which is acquired by the interpolation operation of the compensation value interpolation unit 104 (step S103). Next, the machine abnormality determination unit 243 calls the learning model (i.e. the above equation (1)) already constructed by the learning unit 242 (step S104). Subsequently, the machine abnormality determination unit 243 calculates the degree of divergence of the diagnosis data from the learning model, and determines normality/abnormality of the diagnosis data by comparing the degree of divergence with a predetermined threshold (step S105).
When the acquisition of additional data is necessary (S201: YES), the abnormality determination device 10 acquires additional state data (additional data) for learning from the machine 50 (step S202). A compensation value corresponding to the additional data is derived by the compensation value deriving unit 105 (step S203). Known compensation values necessary for the update of the compensation values (the update of the relational expression) are taken in (step S204). Then, update is executed to add the compensation value corresponding to the additional data to the known compensation values that are taken in. A set of the thus updated compensation values is prepared (step S205).
The process returns to step S201, and when the acquisition of further additional data is unnecessary (S201: NO), the diagnosis process by the above-described steps S101 to S105 is executed. In the diagnosis process of steps S101 to S105, the compensation value prepared in step S205 is applied (step S205, S102).
Then, update of the compensation values is executed to add the compensation value corresponding to the additional data to the known compensation values that are taken in. A set of the thus updated compensation values is prepared (step S305). The learning unit 242 calls the trained learning model (step S306). The learning unit 242 executes re-learning by adding the additional data to the already acquired state data, and reconstructs the learning model (update of the learning model) (step S307). The process returns to step S301, and whether the acquisition of additional data is necessary is determined once again (step S301).
When the acquisition of additional data is unnecessary (S301: NO), the diagnosis process by the above-described steps S101 to S105 is executed. In the diagnosis process of steps S101 to S105, the new compensation value and new learning model updated in steps S305 and S307 are applied (step S305, S307, S102, S104).
The diagnosis process illustrated in
As described above, according to the present embodiment, exact diagnosis can be executed by calculating the compensation value from the normal data in accordance with the environmental temperature, and compensating the state data. In addition, by calculating, by interpolation, a compensation value at an unknown environmental temperature from known compensation values, compensation becomes possible in regard to the environmental temperature at which normal data could not be acquired in advance.
The present invention has been described above by using typical embodiments. It can be understood, however, that a person skilled in the art can make changes, various other modifications, omissions and additions to the above-described embodiments, without departing from the scope of the present invention.
In the above embodiments, the example was described in which the torque command waveform is used as the data relating to the state of the machine, but this is merely an example. As the data indicative of the state of the machine, use can be made of various data, such as data of various sensors, various data (velocity, acceleration, and the like) relating to the input and output of the electric motor, and the like.
In the above embodiments, the example was described in which the MT method is used as the machine learning, but methods other than the MT method may be used as methods for evaluating the degree of divergence of the diagnosis data from the normal data. For example, when both the data at normal time and the data at abnormal time are sufficiently acquired as the data relating to the state of the machine, a learning model may be constructed by applying supervised learning in the machine learning device, and the abnormality determination may be executed by using the learning model.
In the above embodiments, the abnormality determination device 10 is configured to acquire the state data from the machine 50. Instead of this configuration, the abnormality determination device may be configured to acquire the state data from the input device such as a keyboard, or from an external computer.
The functional blocks of the abnormality determination device 10 illustrated in
A program for executing the diagnosis process (
Number | Date | Country | Kind |
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2020-046633 | Mar 2020 | JP | national |
This is the U.S. National Phase application of PCT/JP2021/009903, filed Mar. 11, 2021, which claims priority to Japanese Patent Application No. 2020-046633, filed Mar. 17, 2020, the disclosures of these applications being incorporated herein by reference in their entireties for all purposes.
Filing Document | Filing Date | Country | Kind |
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PCT/JP2021/009903 | 3/11/2021 | WO |