Measurement methods, measuring devices, and procedures

Abstract

The present invention relates to a method for measuring the state of an apparatus that uses a lubricant to lubricate parts. An alternating current voltage is applied to a circuit composed of parts lubricated by the aforementioned lubricant. The impedance and phase angle of the aforementioned circuit are measured when the aforementioned alternating current voltage is applied. Based on the aforementioned impedance and the aforementioned phase angle, the oil film thickness and metal contact ratio between the aforementioned parts are derived. The oil film thickness and metal contact ratio between the aforementioned parts are derived using the following formula, which is defined by the probability density function of the surface roughness between the aforementioned parts in the contact area between the aforementioned parts, and the electrostatic capacitance of the aforementioned contact area is calculated.

Description

Measurement methods, measuring devices, and procedures This invention relates to a measurement method, a measurement device, and a program. Previously, in rolling devices such as bearing assemblies, it was common to use lubricants (e.g., lubricating oil or grease) to lubricate their rotation. On the other hand, for rotating parts such as bearing assemblies, the following actions are performed: by periodically performing condition diagnostics, damage or wear can be detected in advance, and failures of rotating parts can be prevented. In rolling devices using lubricants, it is desirable to accurately detect the internal condition in order to diagnose their operational status. For example, Patent Document 1 discloses a method in which, assuming the electrostatic capacitance of the oil film on a contact surface with surface roughness is equal to the electrostatic capacitance of a smooth surface, the thickness of the oil film on the non-metallic contact surfaces is set to be the same using an average oil film thickness, and the electrostatic capacitance of the contact surfaces is calculated. [Prior Art Documents] [Patent Documents] [Patent Document 1] Japanese Patent Application Publication No. 2019-211317 [The problem that the invention aims to solve] However, since electrostatic capacitance is inversely proportional to oil film thickness, the actual influence of the thin film portion increases, and the electrostatic capacitance may be larger compared to the case where the average oil film thickness is assumed to be the same. In the method of Patent Document 1, since the electrostatic capacitance is calculated using the average oil film thickness, the accuracy of the calculated electrostatic capacitance decreases when the oil film thickness at the contact surface deviates from the average oil film thickness. In particular, since the surface roughness of the contact surface also affects the oil film thickness, it is assumed that the accuracy of the calculated electrostatic capacitance will decrease as a result. In view of the above-mentioned problems, the purpose of this application is to provide a measurement method for detecting oil film thickness and metal-to-metal contact ratio between parts within a device with higher accuracy than previous methods. [Technical Means for Solving the Problems] To address the aforementioned issues, the invention of this application comprises the following: a measurement method characterized by measuring the state of a device for lubricating parts using a lubricant, applying an alternating voltage to a circuit composed of parts lubricated by the lubricant, measuring the impedance and phase angle of the circuit when the alternating voltage is applied, and deriving the oil film thickness and metal contact ratio between the parts based on the impedance and phase angle. The oil film thickness and metal contact ratio between the parts are derived using the following formula, which defines the surface roughness of the parts in the contact area according to a probability density function and calculates the electrostatic capacitance of the contact area. Furthermore, another aspect of the invention in this application has the following configuration: a measuring device characterized in that it measures the state of a device for lubricating parts using a lubricant, and includes: an acquisition mechanism that applies an alternating voltage to a circuit composed of parts lubricated by the aforementioned lubricant, and acquires the impedance and phase angle of the aforementioned circuit when the aforementioned alternating voltage is applied; and a derivation mechanism that, based on the aforementioned impedance and the aforementioned phase angle, derives the oil film thickness and metal contact ratio between the aforementioned parts; and the oil film thickness and metal contact ratio between the aforementioned parts are derived using the following formula, which is defined by the probability density function of the surface roughness of the aforementioned parts in the contact area between the aforementioned parts, and calculates the electrostatic capacitance of the aforementioned contact area. Furthermore, another aspect of the invention in this application has the following configuration: a program that enables a computer to function as: an acquisition mechanism that applies an AC voltage to a circuit composed of parts lubricated by a lubricant, and acquires the impedance and phase angle of the circuit when the AC voltage is applied; and a derivation mechanism that, based on the aforementioned impedance and phase angle, derives the oil film thickness and metal contact ratio between the aforementioned parts; and the oil film thickness and metal contact ratio between the aforementioned parts are derived using a formula that calculates the electrostatic capacitance of the contact area by defining the surface roughness between the aforementioned parts in the contact area according to a probability density function. [Effects of the Invention] According to the invention of this application, it is possible to detect the oil film thickness and the metal contact ratio between parts in the device with higher accuracy than previous methods. The following description, with reference to figures, illustrates the embodiments used to implement the invention of this application. Furthermore, the embodiments described below are merely illustrative of one embodiment of the invention and are not intended to limit the scope of the invention. Also, not all configurations described in each embodiment are necessarily necessary to solve the problems of the invention of this application. In each drawing, the same reference numerals are used to indicate the correspondence of the same constituent elements. <First Embodiment> Hereinafter, a first embodiment of the present invention will be described. Furthermore, the measurement method of the present invention is applicable to devices in which a metal surface with a certain roughness is lubricated on one side and in rolling contact or sliding on the other. Examples of such devices include rolling bearings, gears, sliding bearings, cams, traction mechanisms, and CVTs (Continuously Variable Transmissions). Specific examples of applicability will be described later, but the invention is not limited thereto; the present invention is applicable to all devices having the characteristics described above. For example, types of rolling bearings to which the diagnostic method of the present invention is applicable include deep groove ball bearings, angular contact ball bearings, tapered roller bearings, cylindrical roller bearings, and self-aligning roller bearings. [Solid Model] Figures 1 and 2 will be used to explain the contact states between the constituent parts of the device to which the diagnostic method of this embodiment is applied. Figure 1 shows a solid model of a circular contact. Figure 2 shows a solid model of an elliptical contact. Since the basic concepts are the same, Figure 1 will be used here for explanation. Figure 1 is a diagram showing a solid model of a ball and a disc rolling in contact within the device. The top of the figure shows the view viewed along the x-axis, and the right side shows the view viewed along the y-axis. Furthermore, for the sake of simplicity, an example is shown here where one of the contacting parts (the ball) has a curved shape and the other (the disc) has a planar shape. However, it is also possible for both parts to have curved shapes and be in contact. In such a configuration, the solid model shown in Figure 2 becomes a more approximate model. The h-axis represents the direction of oil film thickness, and the x-axis and y-axis represent directions orthogonal to the direction of oil film thickness. Furthermore, the variables shown in Figure 1 are as described below. S 1: Hertzian contact area (Hertzian contact region) c: Radius of the Hertzian contact circle (=√(S)) 1 / π)) α: Oil film breakage rate (metal contact ratio) (0≦α<1) r b The radius αS of the sphere 1: Actual contact area (oil film breakage area) h: Oil film thickness (both in the x-axis and y-axis directions) 1: Oil film thickness h within the Hertzian contact area 2: Maximum oil film thickness around the contact area In the Hertzian contact region, the ratio of the contacting area to the non-contacting area is α:(1-α). Furthermore, in the ideal state where the sphere and disc are not in contact, α=0. In this case, h>0 when y=0. Similarly, h>0 when x=0. In the upper part of Figure 1, the oil film thickness h is expressed, for example, by the following formula: h = 0 (-αS 1 / 2≦y≦αS 1 / 2) h=h 1(-c≦y<-αS 1 / 2, or αS 1 / 2<y≦c) h=h 1+√(r b 2 -c 2)-√(r b 2 -y 2 ) (-r b ≦y<-c, or c<y≦r b …(1) Similarly, in the right-hand diagram shown in Figure 1, the oil film thickness h is expressed by the following formula: h = 0 (-αS 1 / 2≦x≦αS 1 / 2) h=h 1(-c≦x<-αS 1 / 2, or αS 1 / 2<x≦c) h=h 1+√(r b 2 -c 2 )-√(r b 2 -x 2 ) (-r b ≦x<-c, or c<x≦r b …(2) Furthermore, the variables in Figure 2 are as follows: a': radius of the Hertzian contact ellipse along the y-axis; b': radius of the Hertzian contact ellipse along the x-axis; r x ▔ The radius r of the ellipse of the sphere along the x-axis. y ▔ The elliptic radius h of the sphere along the y-axis. 2: The thickness h of the maximum oil film thickness around the contact area, located in the middle. 3: Maximum oil film thickness around the contact area Furthermore, when using the solid model in Figure 2, since the sphere is elliptical, a portion of the formulas need to be replaced accordingly. That is, without further explanation, when using the model in Figure 2, only the formulas for elliptical shapes need to be applied. Therefore, other formulas can be used corresponding to the structure of the envisioned solid model or the bearing device of the object. Also, while a two-dimensional formula was given above as an example, a three-dimensional formula can also be used. [Equivalent Circuit] Figure 3 shows the physical model shown in Figure 1 using an electrically equivalent circuit (equivalent circuit). Furthermore, the same configuration is used in the physical model of Figure 2. The equivalent circuit E1 includes a resistor R. 1. Capacitor C 1. and capacitor C 2. Resistance R 1 is equivalent to the fracture region (=αS) 1) Resistance of the capacitor C. 1 is equivalent to a capacitor formed by an oil film in the Hertzian contact region, denoted as electrostatic capacitance C. 1. Capacitor C 2 is equivalent to the periphery of the Hertz contact region (Figure 1 -r) b ≦y<-c and c<y≦r b -r b ≦x<-c and c<x≦r b The capacitor formed by the oil film is designated as the electrostatic capacitance C. 2. Hertzian contact region (=S) 1) Form the resistor R in the equivalent circuit E1 of Figure 3. 1 and capacitor C The parallel circuit of 1. Furthermore, the capacitor C in the equivalent circuit E1 of Figure 3 is formed around the Hertz contact region. The circuit of 2. Furthermore, by connecting these parallel circuits in parallel, an equivalent circuit E1 is formed. At this time, it is assumed that the area around the Hertz contact region (Figure 1, -r) is... b ≦y<-c and c<y≦r b -r b ≦x<-c and c<x≦r b It is filled with lubricant. The impedance of the equivalent circuit E1 is represented by Z. Here, the AC voltage V applied to the equivalent circuit E1, the current I flowing in the equivalent circuit E1, and the complex impedance Z of the equivalent circuit E1 as a whole are represented by the following equations (3) to (5). V=|V|exp(jωt) …(3) I=|I|exp(j(ωt-θ)) …(4) Z=V / I=|V / I|exp(jθ)=|Z|exp(jθ) …(5) j: imaginary number ω: angular frequency of AC voltage t: time θ: phase angle (phase shift between voltage and current) [Overview of the Impedance Method] First, before explaining the diagnostic method of this embodiment, a brief explanation of the previous impedance method, which is used as a comparison object, will be given. The impedance method used in Patent Document 1, etc., is also based on the above-mentioned physical model and equivalent circuit. In the previous impedance method, the oil film thickness h and the metal contact ratio α were calculated based on the complex impedance (Z, θ) obtained by applying the load voltage to the object being measured. The oil film thickness h and the metal contact ratio α can be calculated using the following formula. In the following formula, the contact area S is used as the oil film thickness. 1. Average oil film thickness. [Number 1] [Number 2] R 10 Resistance value when stationary (i.e., α=1); Phase angle |Z|; Impedance of the entire equivalent circuit under dynamic contact conditions. ▔ Average oil film thickness c; radius of contact area r b : Radius of the sphere W(): Lambert W function exp(): Exponential function π: Pi ε: Dielectric constant of the oil film (lubricant) ω: Angular frequency of the AC voltage Figure 4 is a semi-logarithmic graph showing the results of the previous impedance method measurement and the actual roughness after the test, obtained by analytical analysis using the well-known μEHL (Elasto-Hydrodynamic Lubrication) method, for a two-cylinder test conducted using the apparatus described later in Figure 8. The test conditions, measurement conditions, and analytical conditions are as follows. (Test Conditions) Lubricant viscosity (ISO viscosity classification): VG320; Surface pressure: 2.25 GPa; Pull-in speed: 0.785 m / s; Sliding speed: 0 m / s; Temperature: 50–100 °C; Combined roughness (σ): 40, 120, 260 nm. (Impedance Measurement Conditions) Applied voltage: 0.5 V; AC frequency: 1 MHz. (Analysis Conditions) Input roughness: 2.9 × 1.6 mm (Δx ≒ 1.6 μm); Sieve size: 512 × 512 (Δx ≒ 3 μm); Calculation range: -2.5a–1.5a, -1.75b–1.75b. In Figure 4, the horizontal axis represents temperature T [°C], and the vertical axis represents oil film thickness h [nm]. Furthermore, as a comparative example, the results calculated using the well-known Hamrock & Dowson film thickness formula (hereinafter, the HD formula) are represented by solid lines. As mentioned above, three surface roughnesses (σ = 40, 120, and 260 [nm]) were used in the experiment. The surface roughness used here is the combined roughness of the contact surfaces. First, looking at the previous impedance method measurement results, there is a tendency for the measured values ​​to decrease compared to the calculation results of the HD formula as the temperature increases. This phenomenon is more pronounced with rougher surfaces. Furthermore, the higher the temperature, the more the previous impedance method measurement results deviate from the HD formula calculation results. Next, the effect of surface roughness will be investigated. Here, the oil film thickness h will be calculated using the formula derived from HD. H-D Let the ratio of roughness σ to Λ(=h) be Λ(=h) H-D / σ). Figure 5 shows the results calculated in Figure 4 from another perspective. In Figure 5, the horizontal axis represents Λ, and the vertical axis represents the oil film thickness h calculated by the previous impedance method and the calculated oil film thickness h. H-D The ratio. According to Figure 5, within the range of 3≦Λ, the same calculated result is obtained under any roughness, therefore the influence of roughness is small. The oil film thickness h and h calculated by the previous impedance method are... H-D The ratio becomes approximately 1. However, as Λ decreases, the effect of roughness increases. That is, the ratio increases with the calculated oil film thickness h. H-D In comparison, the calculated film thickness h is smaller (h / h) H-D (Become smaller). Therefore, this invention focuses on the roughness of the contact area. In particular, considering the case where the roughness has a significant impact when the value of Λ is below a certain value, as shown in FIG5, a method for improving the previous impedance method is proposed. [Roughness Treatment] First, for the contact area S in the previous impedance method... The roughness treatment of 1 will be explained. Figure 6 is a schematic diagram of the contact area around which the surface roughness in the previous impedance method is described. As shown in Figure 1, in the contact area S1, two components (here, a ball and a disc) are in contact, and their periphery is filled with lubricant. Figure 6(a) shows the actual mixed lubrication state. Here, for the sake of simplicity, a composite roughness is used, with the surface of the ball being rough and the surface of the disc being smooth. Compared to the state in Figure 6(a), Figure 6(b) shows the geometric model used in the previous impedance method. In the previous impedance method, the measurement was performed by treating the state in Figure 6(a) as equivalent to the geometric model shown in Figure 6(b). That is, the contact area S was used. The average oil film thickness h is the average oil film thickness h. ▔ . The electrostatic capacitance C corresponding to the model in Figure 6(a) a It can be calculated using the following formula. [Number 3] The electrostatic capacitance C corresponding to the geometric model in Figure 6(b) b It can be calculated using the following formula. [Number 4] Actual C a With C b The values ​​are different, becoming C a >C b Furthermore, in the previous impedance method, the oil film thickness h was calculated using the following equations (10) and (11). 1 and average oil film thickness h ▔ . [Number 5] [Number 6] In C a >C b In the case of using C a Replace C b And calculate h At time 1, the calculated oil film thickness will naturally differ. Therefore, C will vary due to the influence of roughness. a With C b The greater the deviation from the given value, the lower the accuracy of the calculated oil film thickness. Therefore, in this embodiment, the surface roughness around the contact area is considered by means of the processing described below. Figure 7 is a schematic diagram illustrating the surface roughness around the contact area in the impedance method of the present invention. As shown in Figure 1, in the contact area S In step 1, two components (here, a ball and a disc) are in contact, and their periphery is filled with lubricant. Figure 7(a) shows the actual mixed lubrication state. Here, for the sake of simplicity, composite roughness is used, with the surface of the ball being rough and the disc being smooth for illustration. In contrast to the state in Figure 6(a), in this embodiment, it is assumed that the surface roughness has a conventional distribution, and the formula taking into account the surface roughness is defined. That is, the probability density of the interval between the two surfaces under the assumption of a Gaussian distribution is calculated by the following formula. [Number 7] Figure 7(b) shows the relationship between film thickness and probability of occurrence under the assumption that the surface roughness follows a conventional distribution. In Figure 7(b), the vertical axis represents film thickness h, and the horizontal axis represents probability of occurrence. Furthermore, α, as illustrated in Figure 1, corresponds to the oil film breakage rate. Here, the surface roughness, i.e., the oil film thickness distribution, is represented by the inverse function of the following cumulative distribution function. [Number 8] F: Cumulative probability distribution (0~1) The region where the oil film exists is the region where h > 0. In this region, by setting ε / h as the area portion, the electrostatic capacitance C of the contact surface can be... 1. The following formula (14) is used to calculate the result. [Number 9] Here, it is not easy to process the above equation (14) unchanged. Therefore, in this embodiment, by approximating and transforming the above equation as described below, a certain accuracy in measuring the oil film thickness μ is achieved, and the computational load is suppressed. Equation (15) represents the approximation achieved by Taylor expansion. Furthermore, Equation (16) is C after transforming Equation (14) based on Equation (15). An approximation of 1. [Number 10] [Number 11] [Number 12] [Number 13] At this point, through the following formula (19), formula (18) becomes the following formula (20). [Number 14] [Number 15] Therefore, in this embodiment, equations (17) and (20) are used to determine the contact area S. 1. Oil film thickness μ. Furthermore, as described above, in this embodiment, the contact is defined as a smooth surface and a rough surface, and the standard deviation of the surface roughness of the rough surface, i.e., the root mean square roughness R, is... ｑ Used as σ. In the case where both surfaces in contact are rough, it can be understood as the contact between a rough surface with a combined roughness and a smooth surface. In this case, the roughness of each of the two rough surfaces is set as σ. 1, σ In case 2, the surface roughness of the composite surface can be calculated using the following formula. [Number 16] Furthermore, as mentioned above, the line roughness R is given as an example. ｑ For example, but surface roughness S ｑ The same approach can also be applied. Furthermore, in this embodiment, the probability density function is defined based on the assumption that the surface roughness follows a Gaussian distribution. However, it is not limited to this; as long as the distribution of surface roughness can be defined, it can also be defined based on a distribution other than Gaussian, and such a distribution is applicable. In the case of a distribution other than Gaussian, the electrostatic capacitance C can be calculated using the following equation (22). 1. [Number 17] Furthermore, the surface roughness distribution described above can be approximated. Also, the use of formula (17), formula (20), or formula (22) can be switched depending on the configuration of the rolling device being diagnosed. That is, since the allowable accuracy or processing load will differ depending on the configuration of the rolling device or the purpose of the diagnosis, the above formulas can be used differently. [Applicable Examples] The following describes applicable examples of the diagnostic method using this embodiment. [Device Configuration] Figure 8 is a schematic configuration diagram showing an example of the overall configuration of the diagnostic method applicable to this embodiment. Figure 8(a) is a view of the rolling device 800 along the y-axis direction, showing a schematic of the interior of the connecting portion 810 constituting the rolling device 800. Figure 8(b) is a view of the rolling device 800 along the z-axis direction, which is orthogonal to the y-axis direction. In Figure 8, the rolling device 800, which is the object of diagnosis, the LCR tester 830, and the diagnostic device 840 for performing the diagnosis are provided. Furthermore, the configuration shown in Figure 8 is an example, and different configurations can be used depending on the configuration of the rolling device 800, etc. The rolling device 800 includes a rotating shaft 822, which is composed of two cylindrical shafts with insulating joints at a portion. A bearing section 820 is provided on the rotating shaft 822, which is composed of a plurality of rolling bearings 821. In the example of Figure 8, three rolling bearings 821 (here, ball bearings) are arranged in a rolling manner on the rotating shaft 822. A load is applied to the bearing section 820 from a certain direction. The rotating shaft 822 is inserted into the connecting part 810, and rotates internally in conjunction with each other. Although not shown in Figure 8, a drive motor, which serves as the power source for the rotating shaft 822, is connected to one or both of the two cylinders. In the example of Figure 8(a), the right cylinder rotates counterclockwise, and the left cylinder rotates clockwise. In the part where the rotating shaft 822 is inserted, a seal 816 is provided to prevent leakage of the lubricant 813 filled in the connecting part 810 or the intrusion of dust. Within the connecting portion 810, a contact member 811 located at the front end of the rotating shaft 822 makes contact at position A. A thermocouple 812 is installed within the connecting portion 810 to measure the ambient temperature at position A. The chamber 815 is filled with lubricant 813 to reduce friction in the contact area at position A. The lubrication method is not particularly limited; for example, grease lubrication or oil lubrication may be used. The type of lubricant is also not particularly limited. Furthermore, a heater 814 is provided to adjust the temperature within the chamber 815. The rotating shaft 822 is connected to the LCR tester 830 via a rotary connector (not shown). Furthermore, the configuration of the rotary connector is not particularly limited. The LCR tester 830 is also electrically connected to the contact member 811, functioning as a source of AC power for the contact member 811. The diagnostic device 840 operates as a testing device capable of performing the testing method of this embodiment. During diagnosis, the diagnostic device 840 receives the angular frequency ω of the AC power supply and the AC voltage V as inputs to the LCR meter 830, and obtains the impedance |Z| (where |Z| represents the absolute value of Z) and phase angle θ of the rolling device 800 from the LCR meter 830 as its output. The diagnostic device 840 then uses these values ​​to diagnose the rolling device 800. The diagnostic device 840 can be implemented, for example, using an information processing device comprising a control device, a memory device, and an output device (not shown). The control device can be composed of a CPU (Central Processing Unit), an MPU (Micro Processing Unit), a DSP (Digital Single Processor), or dedicated circuitry. The memory device is composed of volatile and non-volatile memory media such as HDD (Hard Disk Drive), ROM (Read Only Memory), or RAM (Random Access Memory), and can perform various information input and output via instructions from the control device. The output device is composed of a speaker, a lamp, or a display device such as an LCD, and provides notification to the operator via instructions from the control device. The notification method performed by the output device is not particularly limited; for example, it can be an auditory notification via sound or a visual notification via screen output. Furthermore, the output device can be a network interface with communication capabilities, or it can perform a notification action by sending data to an external device (not shown) via a network (not shown). The notification content here is not limited to notification when an abnormality is detected, for example, in the case of abnormality diagnosis based on detection results, it can also include notification that the scrolling device 800 is normal. [Processing Flow] Figure 9 is a flowchart of the diagnostic processing of this embodiment. This processing is executed using a diagnostic device 840. For example, the program for implementing the processing of this embodiment can be read from a memory device (not shown) and executed by a control device (not shown) included in the diagnostic device 840. In S901, the diagnostic device 840 controls the rolling device 800 to apply a load in a predetermined direction. In this example, it controls the application of a load to the bearing portion 820 in the direction indicated by the arrow in Figure 8. Furthermore, the load application can be controlled by a device other than the diagnostic device 840. At this time, the phase and impedance under static contact conditions are measured. In S902, the diagnostic device 840 initiates the rotation of the rotating shaft 822 via a motor (not shown). Furthermore, the motor can be controlled by a device other than the diagnostic device 840. In S903, the diagnostic device 840 controls the LCR tester 830 to apply an AC voltage V with angular frequency ω to the rolling device 800 using the AC power supply (not shown) provided by the LCR tester 830. In this way, an AC voltage V with angular frequency ω is applied to the rolling device 800. In S904, the diagnostic device 840 obtains the impedance |Z| and phase angle θ from the LCR tester 830 as the output for the input of S903. That is, the LCR tester 830 outputs the impedance |Z| and phase angle θ as the detection results of the rolling device 800 for the input, namely the AC voltage V and the angular frequency ω of the AC voltage, to the diagnostic device 840. In S905, the diagnostic device 840 derives the oil film thickness h and the breakage rate α by applying the impedance |Z| and phase angle θ obtained in S904 and the angular frequency ω of the AC voltage used in S903 to the above formulas. In S906, the diagnostic device 840 uses the oil film thickness h and breakage rate α derived from S905 to diagnose the lubrication status of the rolling device 800. Furthermore, the diagnostic method here can, for example, set threshold values ​​for the oil film thickness h or breakage rate α, and the lubrication status can be determined by comparing the values ​​with these threshold values. Then, the process ends. [Measurement Results] Hereinafter, the measurement results obtained by the measurement method of this embodiment will be explained using Figures 10 to 12. Figure 10 is a semi-logarithmic graph showing the measurement results of the test conducted using the measurement method of this embodiment and the calculated results of the HD formula. The test conditions are assumed to be the same as those explained using Figures 4 and 5. In Figure 10, the horizontal axis represents the temperature T [°C], and the vertical axis represents the oil film thickness h. Similar to Figure 4, here, three examples of composite roughness σ are used (σ = 40, 120, 260 [nm]). Referring to Figure 10, for synthetic roughnesses of σ=40 and σ=120, values ​​approximately equivalent to the calculated oil film thickness obtained using the HD formula can be derived at any temperature. Furthermore, for a synthetic roughness of σ=260, a value higher than the calculated oil film thickness is derived, but it converges to a value of approximately 300 nm, becoming a value similar to σ. This is considered to be because, in the presence of roughness, the oil film thickness is not less than the roughness due to contact with protrusions caused by surface roughness. Therefore, the measurement results of this embodiment are considered appropriate. Figure 12 shows the calculated results of Figure 10 from other perspectives, corresponding to Figure 5. Here, Figure 11 shows a diagram that matches the scale (vertical axis) of the graph in Figure 5 and Figure 12. In Figure 12, the horizontal axis represents Λ, and the vertical axis represents the oil film thickness h calculated using the measurement method of this embodiment and the calculated oil film thickness h. H-DThe ratio. Referring to Figure 11 (and Figure 5) of the previous method and Figure 12 of this method, in the previous method, in the region where Λ is small (Λ<3), the calculated oil film thickness is smaller. This is believed to be due to the failure to consider the increase in electrostatic capacitance of the contact surface caused by roughness. On the other hand, in the method of this embodiment, a value similar to the calculated oil film thickness can be calculated in a wider region than the previous method (more specifically, using 1<Λ<3). Furthermore, as shown in Figure 12, in the region where Λ < 1, h / h H-D The value is greater than 1. It is assumed that due to the influence of roughness, the oil film thickness (i.e., the distance between the two surfaces) will not decrease further, consistent with the calculation result using a smooth surface, i.e., h. H-D The thickness of the oil film is greater than the actual thickness. Therefore, the measurement results of this embodiment are considered appropriate. Based on this embodiment, an apparatus with higher precision than previous methods can be used to detect the oil film thickness and the metal-to-metal contact ratio between parts. <Other Embodiments> Furthermore, in the invention of this application, the following processing can also be achieved: using a network or memory medium, a program or application program for implementing the functions of one or more of the above embodiments is supplied to a system or device, and one or more processors in the computer of the system or device read out and execute the program. Alternatively, it can be implemented by a circuit that performs more than one function (e.g., ASIC (Application Specific Integrated Circuit) or FPGA (Field-Programmable Gate Array)). As described above, the present invention is not limited to the embodiments described above. Any combination of the various components of the embodiments, or any modifications or applications made by those skilled in the art based on the description in the specification and well-known technologies, are also considered implementations of the present invention and are included within the scope of protection. As described above, this specification discloses the following: (1) A measurement method characterized by measuring the state of an apparatus for lubricating parts using a lubricant, applying an alternating voltage to a circuit composed of parts lubricated by the aforementioned lubricant, measuring the impedance and phase angle of the aforementioned circuit when the aforementioned alternating voltage is applied, and deriving the oil film thickness and metal contact ratio between the aforementioned parts based on the aforementioned impedance and the aforementioned phase angle. The oil film thickness and metal contact ratio between the aforementioned parts are derived using the following formula, which is defined by the probability density function of the surface roughness of the aforementioned parts in the contact area between the aforementioned parts, and calculates the electrostatic capacitance of the aforementioned contact area. According to this configuration, the oil film thickness and metal contact ratio between parts can be detected with higher accuracy than previous methods. (2) The measurement method as in (1), wherein the electrostatic capacitance C of the aforementioned contact area is used to derive the capacitance C. The previously calculated formula is as follows: [Number 18] Based on this configuration, the electrostatic capacitance of the contact area can be calculated with good accuracy based on the roughness distribution of the contact area. (3) The measurement method as in (1), wherein the aforementioned calculation formula is a calculation formula that defines the surface roughness between the aforementioned parts according to the Gaussian distribution. Based on this configuration, the Gaussian distribution accuracy can be used as the roughness distribution of the contact area, and the electrostatic capacitance of the contact area can be calculated well. (4) The measurement method as in (3), wherein the electrostatic capacitance C of the aforementioned contact area is used to derive the capacitance C. The previously calculated formula is as follows: [Number 19] . Based on this configuration, a Gaussian distribution can be used as the roughness distribution of the contact area, and the electrostatic capacitance of the contact area can be calculated with good accuracy. As in the measurement method of (4), the formula used to derive the aforementioned oil film thickness μ is: [Number 20] [Number 21] . Based on this configuration, a Gaussian distribution can be used as the roughness distribution of the contact area, and the electrostatic capacitance of the contact area can be calculated with good accuracy. (6) The measurement method of any one of (1) to (5) further uses the aforementioned oil film thickness and the aforementioned metal contact ratio to diagnose the condition of the aforementioned device. According to this configuration, the diagnosis of the device using oil film thickness and metal contact ratio can be achieved with higher accuracy than before. (7) A measuring device, characterized in that it measures the state of a device that lubricates parts using a lubricant, and comprises: an acquisition mechanism that applies an alternating voltage to a circuit composed of parts lubricated by the lubricant, and acquires the impedance and phase angle of the circuit when the alternating voltage is applied; and a derivation mechanism that derives the oil film thickness and metal contact ratio between the parts based on the impedance and the phase angle; wherein the oil film thickness and metal contact ratio between the parts are derived using a formula that calculates the electrostatic capacitance of the contact area by defining the surface roughness of the parts in the contact area according to a probability density function. According to this configuration, the oil film thickness and metal contact ratio between parts of a device can be detected with higher accuracy than previous methods. (8) A program that enables a computer to function as: an acquisition mechanism that applies an alternating voltage to a circuit composed of lubricated parts and acquires the impedance and phase angle of the circuit when the alternating voltage is applied; and a derivation mechanism that, based on the impedance and phase angle, derives the oil film thickness and metal contact ratio between the parts; and the oil film thickness and metal contact ratio between the parts are derived using a formula that calculates the electrostatic capacitance of the contact area by defining the surface roughness of the parts in the contact area according to a probability density function. According to this configuration, the oil film thickness and metal contact ratio between parts can be detected with higher accuracy than previous methods. The various embodiments have been described above with reference to the accompanying drawings. However, this invention is not limited to the examples described. Those skilled in the art will readily conceive of various modifications or alterations within the scope of the claims, and these will also fall within the technical scope of this invention. Furthermore, the constituent elements of the above embodiments can be combined arbitrarily without departing from the intent of the invention. The various embodiments have been described above; however, the present invention is not limited to the examples described herein. Those skilled in the art will obviously conceive of various modifications or alterations within the scope of the claims, and these should also fall within the technical scope of the present invention. Furthermore, the constituent elements of the above embodiments can be combined arbitrarily without departing from the intent of the invention. Furthermore, this application is based on Japanese patent application filed on March 14, 2022 (Invention Patent Application 2022-039415), the contents of which are incorporated herein by reference. 800: Rolling device; 810: Connecting part; 811: Contact member; 812: Thermocoupler; 813: Lubricant; 814: Heater; 815: Chamber; 816: Seal; 820: Bearing part; 821: Rolling bearing; 822: Rotating shaft; 830: LCR meter; 840: Diagnostic device; A: Position a': Hertzian contact ellipse radius in the y-axis direction; b': Hertzian contact ellipse radius in the x-axis direction; C 1,C 2: Capacitor / Static Capacitance c: Radius of the contact area E 1: Equivalent circuit h: Oil film thickness / Film thickness h: Average oil film thickness h 1: Oil film thickness h within the Hertzian contact area 2: Maximum oil film thickness h around the contact area 3: Maximum oil film thickness h around the contact area H-D Calculate the oil film thickness R 1: Resistance r b The radius r of the sphere x The radius r of the ellipse of the sphere along the x-axis. y The radius S of the ellipse of the sphere along the y-axis 1: Hertzian contact area (Hertzian contact region) T: Temperature x, y, z: Axis Z: Complex impedance |Z|: Overall impedance of the equivalent circuit under dynamic contact conditions α: Oil film rupture rate (metal-to-metal contact ratio) αS 1: Actual contact area (oil film breakage area) θ: Phase angle μ: Oil film thickness (in contact area) Λ: Calculated oil film thickness to roughness σ: Roughness / Composite roughness Figure 1 is a diagram showing a physical model of the bearing device of the present invention. Figure 2 is a diagram showing a physical model of the bearing device of the present invention. Figure 3 is a circuit diagram illustrating the equivalent circuit around the contact area of ​​the present invention. Figure 4 is a diagram illustrating the analytical results of a previous method. Figure 5 is a diagram illustrating the analytical results of a previous method. Figures 6(a) and (b) are conceptual diagrams illustrating the state around the contact area of ​​the present invention. Figures 7(a) and (b) are conceptual diagrams illustrating the contact distribution of the contact area of ​​the present invention. Figures 8(a) and (b) are schematic diagrams showing an example of the configuration of a diagnostic device applicable to one embodiment of the present invention. Figure 9 is a flowchart illustrating the diagnostic process of one embodiment of the present invention. Figure 10 is a diagram illustrating the analytical results of the diagnostic method of the present invention. Figure 11 is a diagram illustrating the analytical results of the diagnostic method of the present invention. Figure 12 is a diagram illustrating the analytical results of the diagnostic method of the present invention. h: Oil film thickness / film thickness α: Oil film breakage rate (metal contact ratio) μ: (oil film thickness in the contact area)

Claims

1. A measurement method for measuring the state of a device that lubricates parts using a lubricant, applying an alternating voltage to a circuit composed of parts lubricated by the lubricant, measuring the impedance and phase angle of the circuit when the alternating voltage is applied, and deriving the oil film thickness and metal contact ratio between the parts based on the impedance and phase angle. The oil film thickness and metal contact ratio between the parts are derived using the following formula, which defines the surface roughness of the parts in the contact area between the parts according to a probability density function, and calculates the electrostatic capacitance of the contact area. The formula for deriving the electrostatic capacitance C1 of the contact area is: [Number 1] S1: Hertzian contact area (Hertzian contact region) α: Oil film breakage rate (metal contact ratio) (0≦α<1) ε: Dielectric constant of the oil film (lubricant) h(F): Oil film thickness distribution F: Cumulative distribution probability (0~1).

2. The measurement method as described in claim 1, wherein the aforementioned calculation formula is a calculation formula that defines the surface roughness between the aforementioned parts according to the Gaussian distribution.

3. As in the measurement method of claim 2, the electrostatic capacitance C1 of the aforementioned contact area is calculated as follows: [Number 2] S1: Hertzian contact area (Hertzian contact region) α: Oil film breakage rate (metal contact ratio) (0≦α<1) ε: Dielectric constant of oil film (lubricant) F: Cumulative distribution probability (0~1) μ: Oil film thickness σ: Surface roughness.

4. The method of determination as requested in item 3, wherein the formula for deriving the aforementioned oil film thickness μ is: [Number 3] h1: oil film thickness.

5. The measurement method of any one of claims 1 to 4, which further uses the aforementioned oil film thickness and the aforementioned metal contact ratio to diagnose the condition of the aforementioned device.

6. A measuring apparatus for measuring the state of an apparatus for lubricating parts using a lubricant by means of any one of claims 1 to 5, comprising: an acquisition mechanism that applies an alternating voltage to a circuit composed of parts lubricated by the lubricant and acquires the impedance and phase angle of the circuit when the alternating voltage is applied; and a derivation mechanism that derives the oil film thickness and metal contact ratio between the parts based on the impedance and the phase angle; wherein the oil film thickness and metal contact ratio between the parts are derived using the following formula, which is defined by the surface roughness of the parts in the contact area between the parts according to a probability density function, and the electrostatic capacitance of the contact area is calculated. The formula for deriving the electrostatic capacitance C1 of the contact area is: [Number 1] S1: Hertzian contact area (Hertzian contact region) α: Oil film breakage rate (metal contact ratio) (0 ≦ α < 1) ε: Dielectric constant of oil film (lubricant) h(F): Oil film thickness distribution F: Cumulative distribution probability (0~1).

7. A program for determining the state of an apparatus for lubricating parts using a lubricant by means of any one of claims 1 to 5, and enabling a computer to function as: an acquisition mechanism that applies an alternating voltage to a circuit composed of parts lubricated by the lubricant and acquires the impedance and phase angle of the circuit when the alternating voltage is applied; and a derivation mechanism that derives the oil film thickness and metal contact ratio between the parts based on the impedance and the phase angle; and the oil film thickness and metal contact ratio between the parts are derived using a formula that defines the surface roughness of the parts in the contact area between the parts according to a probability density function, calculates the electrostatic capacitance of the contact area, and the formula for deriving the electrostatic capacitance C1 of the contact area is: [Number 1] S1: Hertzian contact area (Hertzian contact region) α: Oil film breakage rate (metal contact ratio) (0 ≦ α < 1) ε: Dielectric constant of oil film (lubricant) h(F): Oil film thickness distribution F: Cumulative distribution probability (0~1).

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