TECHNICAL FIELD
[0001] The present invention relates to a condition diagnosis method, a condition diagnosis
device, and a program.
10 BACKGROUND ART
[0002] Conventionally, when diagnosing the condition of materials, methods such as
physical property analysis (for example, apparent viscosity), chemical component analysis
(for example, deterioration degree), and structural analysis using a microscope are used. Such
methods generally require complicated operations. Moreover, it is difficult to perform the
15 above-described methods non-destructively on the target, and in many cases, the target to be
diagnosed is discarded.
[0003] On the other hand, there is a method of performing impedance analysis using an AC
power source. Impedance analysis can be used to make it possible to derive the electrical
properties of the material.
20 [0004] For example, Patent Literature 1 discloses a method of using blood as a target to be
analyzed and measuring the dielectric constant of the blood while changing the frequency to
measure damage to blood cells. Further, Patent Literature 2 discloses a method of evaluating
changes in the composition of an extraction solvent based on frequency characteristics of
relative dielectric constant and relative dielectric loss factor.
25
CITATION LIST
PATENT LITERATURE
[0005] Patent Literature 1: JP-A-2008-215901
Patent Literature 2: JP-A-H7-239316
30
SUMMARY OF INVENTION
TECHNICAL PROBLEM
[0006] Materials used in actual devices include, for example, lubricants. Understanding the
2
condition of the lubricant is extremely useful in preventing damage or the like to devices that
use the lubricant. On the other hand, it is difficult to observe the target such as a lubricant by
taking the target out of the device in a non-destructive manner.
[0007] In view of the above problems, an object of the present invention is to provide a
5 method for easily diagnosing the condition of a lubricant without destroying the target to be
diagnosed.
SOLUTION TO PROBLEM
[0008] In order to solve the above problems, the present invention has the following
10 configuration. In other words, there is provided a condition diagnosis method including: a
measurement step of measuring relative dielectric constant of a lubricant by applying a
voltage to the lubricant while changing a frequency from an AC power source; a derivation
step of deriving parameters indicating electrical properties of the lubricant by applying the
relative dielectric constant measured in the measurement step to a theoretical formula; and a
15 diagnosis step of diagnosing a condition of the lubricant using the parameters.
[0009] Moreover, another aspect of the present invention has the following structure. In
other words, there is provided a condition diagnosis device including: a measurement unit for
measuring relative dielectric constant of a lubricant by applying a voltage to the lubricant
while changing a frequency from an AC power source; a derivation unit for deriving
20 parameters indicating electrical properties of the lubricant by applying the relative dielectric
constant measured in the measurement unit to a theoretical formula; and a diagnosis unit for
diagnosing a condition of the lubricant using the parameters.
[0010] Moreover, another aspect of the present invention has the following structure. In
other words, there is provided a program for causing a computer to execute a measurement
25 step of measuring relative dielectric constant of a lubricant by applying a voltage to the
lubricant while changing a frequency from an AC power source, a derivation step of deriving
parameters indicating electrical properties of the lubricant by applying the relative dielectric
constant measured in the measurement step to a theoretical formula, and a diagnosis step of
diagnosing a condition of the lubricant using the parameters.
30
ADVANTAGEOUS EFFECTS OF INVENTION
[0011] According to the present invention, it is possible to easily diagnose the condition of a
lubricant without destroying the target to be diagnosed.
3
BRIEF DESCRIPTION OF DRAWINGS
[0012] Fig. 1 is a conceptual diagram showing a configuration of a lubricant which is a
target to be diagnosed and an AC power source according to the present invention.
5 Fig. 2 is a diagram for explaining an equivalent circuit composed of a lubricant
which is a target to be diagnosed and an AC power source according to the present invention.
Fig. 3 is a schematic configuration diagram showing an example of a device
configuration according to the present invention.
Figs. 4A and 4B are diagrams for explaining a relationship between frequency, and
10 relative dielectric constant and relative dielectric loss factor.
Figs. 5A and 5B are diagrams for explaining derivation of parameters by fitting to a
theoretical formula (Debye type).
Figs. 6A and 6B are diagrams for explaining derivation of parameters by fitting to a
theoretical formula (Cole-Cole type).
15 Figs. 7A and 7B are diagrams for explaining derivation of parameters by fitting to a
theoretical formula (Cole-Cole improved type).
Fig. 8 is a flowchart of condition diagnosis processing according to one embodiment
of the present invention.
Figs. 9A and 9B are diagrams for explaining a relationship between a condition of
20 the lubricant and parameters.
Fig. 10 is a diagram for explaining a relationship between a condition of the lubricant
and parameters.
Fig. 11 is a diagram for explaining a relationship between a thickener and relaxation
strength.
25 Figs. 12A and 12B are diagrams for explaining a roll state of the thickener.
Figs. 13A and 13B are diagrams for explaining a relationship between frequency and
parameters according to a fiber state of thickener.
Fig. 14 is a diagram for explaining a relationship between frequency and parameters
according to a fiber state of thickener.
30 Figs. 15A and 15B are diagrams for explaining a relationship between deterioration
of base oil and relative dielectric constant.
Figs. 16A and 16B are diagrams for explaining a relationship between deterioration
of base oil and relative dielectric loss factor.
4
Figs. 17A and 17B are diagrams for explaining a relationship between deterioration
of grease and parameters.
Figs. 18A and 18B are diagrams for explaining a relationship between a water
content in grease and parameters.
5 Fig. 19 is a diagram for explaining a relationship between a water content in grease
and average dielectric constant.
Fig. 20 is a diagram for explaining a relationship between an iron powder amount in
grease and relative dielectric loss factor.
10 DESCRIPTION OF EMBODIMENTS
[0013] Hereinafter, embodiments of the present invention will be described below with
reference to the drawings. In addition, the embodiment described below is one embodiment
for describing the present invention, and is not intended to be construed as limiting the present
invention. Not all configurations are essential configurations for solving the problems of the
15 present invention. Moreover, in each drawing, the same component is indicated by the same
reference number to indicate the correspondence relationship.
[0014] [Target to be diagnosed]
In the present embodiment, a lubricant used for lubricating components will be
described as an example of a target to be diagnosed. The lubricant used here is grease having
20 a characteristic of causing dielectric relaxation. More specifically, lithium 12-hydroxystearate
grease and the like can be targeted. Grease generally is composed of a base oil, a thickener,
and additives. Although the details will be described later, the values of the parameters
indicating the electrical properties will fluctuate depending on the configuration or condition
of the grease.
25 [0015] In the present embodiment, assuming that the grease is in a bulk state, parameters
indicating electrical properties corresponding to the internal condition are derived, and the
condition of the grease is diagnosed using the parameters. Fig. 1 is a conceptual diagram
showing the configuration of a lubricant (here, grease) and an AC power source when
evaluating (measuring) the electrical properties of the lubricant according to the present
30 embodiment. Electric power is supplied from an AC power source 10 to grease 12 filled
between electrodes 11. In addition, the distance between the electrodes 11 here may be
configured on the order of mm, for example.
[0016]
5
Fig. 2 is a diagram showing an electrically equivalent electric circuit around the
grease 12 shown in Fig. 1. An electric circuit E has a configuration in which a capacitor C
composed of the grease 12 and a resistance R caused by peripheral elements are connected in
parallel. In addition, the impedance of the electric circuit E is indicated by Z. Here, the AC
5 voltage V applied to the electric circuit E, the current I flowing through the electric circuit E,
and the complex impedance Z of the entire electric circuit E are expressed by the following
Equations (1) to (3).
V = |V|e x p(jωt) ... (1)
I = |I|e x p(jωt - jθ) ... (2)
10 Z = V/I = |V/I|e x p(jθ) = |Z|e x p(jθ) ... (3)
j: Imaginary number
ω: Angular frequency of voltage
t: Time
θ: Phase angle (phase shift between voltage and current)
15 [0017] [Device configuration]
Fig. 3 is a schematic configuration diagram showing an example of the overall
configuration of a system to which the condition diagnosis method according to the present
embodiment can be applied. Fig. 3 shows a condition diagnosis device 30 using the condition
diagnosis method according to the present embodiment, a measurement device 31, and
20 material inclusions 32 including the grease 12 which is a target to be diagnosed. Note that the
configuration shown in Fig. 1 is an example, and a different configuration may be used
depending on the target to be diagnosed and the like.
[0018] The measurement device 31 includes the AC power source 10 shown in Fig. 1, and
applies power to the grease 12 contained in the material inclusions 32 during diagnosis.
25 [0019] The condition diagnosis device 30 instructs the measurement device 31 to use the AC
voltage V of the angular frequency ω of the AC power source 10 as the input value of the
power to be applied to the grease 12, and acquires the impedance |Z| (|Z| indicates the absolute
value of Z) of the grease 12 and the phase angle θ from the measurement device 31 as
corresponding outputs (measurement values). Then, the condition diagnosis device 30 uses
30 these values to derive parameters indicating the electrical properties of the grease 12, and then
performs diagnosis. Details of parameter types and derivation methods will be described later.
[0020] The condition diagnosis device 30 may be realized by, for example, an information
processing device including a control device, a storage device, and an output device (not
6
shown). The control device may be composed of a central processing unit (CPU), a micro
processing unit (MPU), a digital single processor (DSP), a dedicated circuit, or the like. The
storage device is composed of volatile and non-volatile storage media such as a hard disk
drive (HDD), a read only memory (ROM), and a random access memory (RAM), and it is
5 possible to input and output various information to and from the storage device according to
the instruction from the control device. The output device is composed of a speaker, a light, a
display device such as a liquid crystal display, or the like, and notifies the operator according
to the instruction from the control device. The output method by the output device is not
particularly limited. In addition, the output device may be a network interface having a
10 communication function, and may perform an output operation by transmitting data to an
external device (not shown) via a network (not shown).
[0021] Further, the forms of the condition diagnosis device 30 and the measurement device
31 are not particularly limited. For example, the condition diagnosis device 30 and the
measurement device 31 may be connected by wire or wirelessly. Alternatively, the condition
15 diagnosis device 30 and the measurement device 31 may be integrated. Alternatively, the user
may be in charge of data input/output between the condition diagnosis device 30 and the
measurement device 31.
[0022] [Relative dielectric constant and relative dielectric loss factor]
Figs. 4A and 4B are diagrams for explaining the tendency of changes in relative
20 dielectric constant and relative dielectric loss factor according to changes in frequency. Here,
as described above, the lithium 12-hydroxystearate grease will be described as an example of
the grease 12. Using the configuration shown in Fig. 3, the dielectric relaxation phenomenon
is confirmed by sweeping the frequency and measuring the relative dielectric constant εr' and
the relative dielectric loss factor εr'' of the grease 12.
25 [0023] In Fig. 4A, the horizontal axis indicates the frequency [Hz], and the vertical axis
indicates the relative dielectric constant εr'. Fig. 4A shows experimental values obtained from
the grease 12. As shown in Fig. 4A, the relative dielectric constant εr' tends to decrease
(monotonically decrease) as the frequency increases.
[0024] In Fig. 4B, the horizontal axis indicates the frequency [Hz], and the vertical axis
30 indicates the relative dielectric loss factor εr''. Fig. 4B shows experimental values obtained
from the grease 12. As shown in Fig. 4B, the relative dielectric loss factor εr'' once decreases
as the frequency increases, then tends to increase and then decrease again.