Leakage inspection method and leakage inspection device

Abstract

Provided are a leakage inspection method and a leakage inspection device which are capable of automatically inspecting air leakage in a plurality of objects to be inspected. The leakage inspection method for inspecting air leakage in an object to be inspected that has an internal space decompressed to a predetermined vacuum level and hermetically sealed includes: a moving step for moving, to a predetermined measurement position, an optical measurement unit which projects excitation light from the outside of the internal space to a pressure-sensitive paint, provided in the internal space and having a light emission intensity that changes with the oxygen concentration in the internal space, and detects light from the pressure-sensitive paint to which the light is projected; a light projection step for projecting the excitation light to the pressure-sensitive paint; a search step for finding a detection position at which the light from the pressure-sensitive paint is brightest; a measurement step for measuring the attenuation rate of the light emission intensity at the detection position; and a determination step for determining the presence or absence of air leakage in the object to be inspected on the basis of the attenuation rate.

Description

Leak inspection method and leak inspection device

[0001] The present invention relates to a leak inspection method and a leak inspection device.

[0002] An optical oxygen concentration measurement method is known in which a light-emitting layer that emits light upon receiving excitation light and an absorption dye layer whose light absorption spectrum changes depending on the degree of binding with oxygen molecules that change according to the oxygen concentration are used in combination, and the light intensity of output light that changes based on the fact that when incident light for causing the light-emitting layer to emit light or light emitted from the light-emitting layer passes through the absorption dye layer, a part of it is absorbed is detected to measure the oxygen concentration (Patent Document 1).

[0003] A coating film thickness measurement system is also known that includes a transport device that transports a measurement object having a coating film in one direction, a movement amount detection device that detects the movement amount of the measurement object by the transport device, a thermal film thickness measurement head that irradiates the coating film with a laser and detects the amount of heat from the laser-irradiated coating film, a robot having a manipulator on which the film thickness measurement head is mounted and that moves the film thickness measurement head, and a control unit that controls the manipulator. The control unit controls the manipulator so that during at least the measurement operation of the film thickness measurement head, the separation distance between the film thickness measurement head and the measurement object does not change according to the movement amount of the measurement object detected by the movement amount detection device, and makes the film thickness measurement head follow the measurement object.

[0004] Japanese Unexamined Patent Application Publication No. 2004-28650, Japanese Unexamined Patent Application Publication No. 2022-114936

[0005] The present invention provides a leak inspection method and a leak inspection device that can automatically inspect the air leaks of a plurality of inspection objects.

[0006] To solve the aforementioned problems, the leak inspection method described in claim 1 is a leak inspection method for inspecting an air leak in an object to be inspected having an internal space that is depressurized to a predetermined degree of vacuum and airtightly sealed, comprising: a moving step of moving an optical measuring unit to a predetermined measuring position, which projects excitation light from outside the internal space onto a pressure-sensitive paint provided in the internal space whose luminescence intensity changes with changes in the oxygen concentration in the internal space, and detects the light from the pressure-sensitive paint onto which the light has been projected; a light projection step of projecting the excitation light onto the pressure-sensitive paint; a search step of finding a detection position where the light from the pressure-sensitive paint is brightest; a measurement step of measuring the decay rate of the luminescence intensity at the detection position; and a determination step of determining whether or not there is an air leak in the object to be inspected based on the decay rate.

[0007] The invention described in claim 2 is characterized in that, in the leak inspection method described in claim 1, the entire surface of the pressure-sensitive paint is scanned with the projected excitation light, and the light emitted from the pressure-sensitive paint by the scanned excitation light is detected in each region divided by a predetermined mesh to find the detection position in which the light from the pressure-sensitive paint is brightest.

[0008] The invention described in claim 3 is characterized in that, in the leak inspection method described in claim 2, the excitation light is selected to have an oscillation wavelength that results in the strongest emission intensity of the pressure-sensitive paint.

[0009] The invention described in claim 4 is characterized in that, in the leak inspection method described in claim 3, the excitation light is positioned in close proximity to the surface of the pressure-sensitive paint.

[0010] The invention described in claim 5 is characterized in that, in the leak inspection method described in claim 1, the measurement step involves measuring the decay rate of the luminescence intensity under ambient light.

[0011] The invention described in claim 6 is a leak inspection method according to any one of claims 1 to 6, characterized in that, after the measurement of the decay rate of the luminescence intensity at the measurement position of one of the objects to be inspected is completed, the optical measuring unit is moved to a predetermined measurement position for the measurement position of the next object to be inspected, based on the information of the measurement order.

[0012] To solve the aforementioned problems, the leak inspection device described in claim 7 is a leak inspection device for inspecting an air leak in an object to be inspected having an internal space that is depressurized to a predetermined degree of vacuum and airtightly sealed, comprising: an optical measuring means that projects excitation light from outside the internal space onto a pressure-sensitive paint provided in the internal space whose luminescence intensity changes with changes in the oxygen concentration in the internal space, and detects the light from the pressure-sensitive paint onto which the light has been projected; a moving means that moves the optical measuring means to a predetermined measurement position; a search means that finds a detection position where the light from the pressure-sensitive paint is brightest; a measuring means that measures the decay rate of the luminescence intensity at the detection position; and a determination means that determines whether or not there is an air leak in the object to be inspected based on the decay rate.

[0013] The invention described in claim 8 is characterized in that, in the leak inspection apparatus described in claim 7, the moving means is movable in three axes, X, Y, and Z, relative to the object to be inspected.

[0014] According to the invention described in claim 1, it is possible to automatically inspect for air leaks in multiple objects to be inspected.

[0015] According to the invention described in claim 2, the reliability of the measurement can be improved.

[0016] According to the invention described in claim 3, the reliability of the measurement can be improved.

[0017] According to the invention described in claim 4, the reliability of the measurement can be improved.

[0018] According to the invention described in claim 5, the reliability of the measurement can be improved.

[0019] According to the invention described in claim 6, the reliability of the measurement can be improved.

[0020] According to the invention described in claim 7, air leaks in multiple objects to be inspected can be automatically inspected.

[0021] According to the invention described in claim 8, air leaks in multiple objects to be inspected can be automatically inspected based on the measurement order.

[0022] According to the invention described in claim 9, inspection can be performed at measurement positions that are in close proximity to multiple objects to be inspected.

[0023] This is a block diagram showing the functional configuration of the leak inspection device according to this embodiment. This is a schematic diagram illustrating an example of the leak inspection device according to this embodiment. This is a diagram showing an example of the configuration of the optical measurement unit. This is a flowchart diagram illustrating the flow of leak inspection according to this embodiment. This is a schematic diagram explaining the preparation of the object to be inspected. This is a diagram conceptually illustrating the attenuation of luminescence intensity. This is a diagram showing an example of the measurement results of luminescence lifetime under vacuum and atmospheric pressure. This is a diagram showing an example of the measurement results of the attenuation rate of luminescence intensity under vacuum with varying ambient brightness. This is a diagram showing an example of the results of measuring the attenuation rate of luminescence intensity by sequentially moving the optical measurement unit to the inspection position of the object to be inspected. This is a schematic cross-sectional diagram showing the configuration of a water meter as an example of an object to be inspected.

[0024] Next, the present invention will be described in more detail below with reference to the drawings, including embodiments and specific examples. However, the present invention is not limited to these embodiments and specific examples. Furthermore, in the following description using the drawings, it should be noted that the drawings are schematic, and the ratios of the dimensions, etc., may differ from those of reality. For ease of understanding, illustrations of components other than those necessary for the explanation have been omitted as appropriate.

[0025] The leak inspection method according to this embodiment is a leak inspection method for inspecting air leaks in an object under inspection having an internal space that is depressurized to a predetermined degree of vacuum and airtightly sealed. The leak inspection method includes a moving step of moving an optical measuring unit to a predetermined measurement position, which projects excitation light from outside the internal space onto a pressure-sensitive paint whose luminescence intensity changes with changes in the oxygen concentration inside the internal space and detects the light from the pressure-sensitive paint onto which the light has been projected; a light projection step of projecting excitation light onto the pressure-sensitive paint; a search step of finding a detection position where the light from the pressure-sensitive paint is brightest; a measurement step of measuring the decay rate of the luminescence intensity at the detection position; and a determination step of determining whether or not there is an air leak in the object under inspection based on the decay rate.

[0026] The leak inspection device 1 for implementing the leak inspection method according to this embodiment includes an optical measuring unit 10 that projects excitation light from outside the internal space onto a pressure-sensitive paint P whose luminescence intensity changes with changes in the oxygen concentration inside the internal space and detects the light from the pressure-sensitive paint P onto which the light has been projected, and a moving device 20 that moves the optical measuring unit 10 to a predetermined measurement position. The leak inspection device 1 also includes a search unit 30 that finds the detection position where the light from the pressure-sensitive paint P is brightest, a measurement unit 40 that measures the decay rate of the luminescence intensity of the light received by the optical measuring unit 10, and a determination unit 50 that determines whether or not there is an air leak in the object under inspection based on the decay rate.

[0027] First, the leak inspection device 1 and a water meter 100 as an example of an object to be inspected, which implement the leak inspection method according to this embodiment, will be described with reference to the drawings. Figure 1 is a block diagram showing the functional configuration of the leak inspection device 1 according to this embodiment, Figure 2 is a schematic diagram showing an example of an example of the leak inspection device 1 according to this embodiment, Figure 3 is a diagram showing an example of the configuration of the optical measuring unit 10, and Figure 10 is a schematic cross-sectional view showing the configuration of a water meter 100 as an example of an object to be inspected.

[0028] (Water Meter) As an example of an object to be inspected, the water meter 100 has a lower case 110 with an inlet 111 and an outlet 112 formed at both ends, as shown in Figure 10, and an inner case 120 is housed inside the lower case 110. The inner case 120 is provided with a plurality of inlet nozzles 121 and outlet nozzles 122, and an impeller support member 123 is erected at the center of the inner bottom of the inner case 120. An impeller 124 having a magnet M1 on the upper part of its shaft is rotatably supported on the impeller support member 123.

[0029] An indicator unit 130 is provided above the impeller 124 via a gasket G1. The indicator unit 130 consists of a register box 131, a lower base plate 132, an upper base plate 133, a magnetic gear 134 with a magnet M2 attached, a gear train 135, a pointer (not shown), a numeral wheel 136, and a glass plate 137 attached via an O-ring S1. The magnet M2 of the magnetic gear 134 and the magnet M1 of the impeller 124 face each other across the bottom wall of the register box 131 and are magnetically coupled. The indicator unit 130 configured in this way is depressurized to a predetermined degree of vacuum and airtightly sealed. In this embodiment, the leak inspection device 1 uses an indicator unit 130 that has been sealed by vacuuming with a pressure-sensitive paint P applied to the upper base plate 133 as the object to be inspected for leak inspection.

[0030] (Overall Configuration of Leak Inspection Device) The leak inspection device 1 for implementing the leak inspection method according to this embodiment includes, as shown in Figure 1, an optical measuring unit 10, a moving device 20, a search unit 30, a measuring unit 40, a determination unit 50, and a control unit 60. The optical measuring unit 10 projects excitation light from outside the internal space onto a pressure-sensitive paint P provided in the internal space, whose emission intensity changes with changes in the oxygen concentration in the internal space, and detects the light from the pressure-sensitive paint P onto which the light has been projected. The moving device 20 moves the optical measuring unit 10 to a predetermined measurement position. The search unit 30 finds the detection position where the light from the pressure-sensitive paint P is brightest. The measuring unit 40 measures the decay rate of the emission intensity of the light received by the optical measuring unit 10. The determination unit 50 determines whether or not there is an air leak in the object under inspection based on the decay rate. The control unit 60 is a so-called computer and has a CPU (Central Processing Unit), ROM (Read Only Memory), RAM (Random Access Memory), storage unit 61, and input / output unit 62, and controls the operation and processing of the optical measurement unit 10, moving device 20, search unit 30, measurement unit 40, and determination unit 50.

[0031] (Optical Measurement Unit) The optical measurement unit 10 consists of an excitation light source 11, a drive unit 12 that controls the emission of light from the excitation light source 11, a focusing optical system 13 that guides the light beam emitted from the excitation light source 11 to the pressure-sensitive paint P, a photodetector 14 that receives light from the pressure-sensitive paint P, and a trans-impedance amplifier (TIA) 15.

[0032] The excitation light source 11 can emit a predetermined amount of light onto the pressure-sensitive paint P. In this embodiment, for example, it is a direct-modulated laser (DML) with an emission wavelength of 400 nm to 700 nm, and is emitted in a pulsed manner by the drive unit 12. The emission intensity of the excitation light source 11 can be the same as the light intensity emitted by the pressure-sensitive paint P when pressure is applied, and the decay rate of the emission intensity of the pressure-sensitive paint P does not depend on the emission intensity of the excitation light source 11.

[0033] As shown in Figure 3, the focusing optical system 13 includes a collimator lens 101 that converts the light emitted from the excitation light source 11 into a parallel beam, and a focusing lens 102 that focuses the parallel beam CL from the collimator lens 101 onto the pressure-sensitive paint P. It is desirable that the collimator lens 101 adjusts the light emitted from the excitation light source 11 to an appropriate beam diameter so that it can be incident within the effective diameter of the focusing lens 102. The focusing lens 102 has the function of focusing light so that the beam is focused onto the irradiated position of the pressure-sensitive paint P. Specifically, it is positioned so that it is incident onto the irradiated position of the pressure-sensitive paint P near the portion where the diameter of the beam is smallest (beam waist).

[0034] The photodetector 14 uses a photodiode as a light-receiving element. When light is incident on the photodiode, an electric charge is generated in the photodiode through photoelectric conversion. The amount of charge generated depends on the amount of light incident on the photodiode. The charge generated in the photodiode is converted into a voltage signal by a trans-impedance amplifier (TIA) 15.

[0035] (Moving Device) As shown in Figure 2A, the moving device 20 is a three-axis robot consisting of a base 21, a gantry frame 22, a holding part 23, and a rod 24 housed in the holding part 23 so as to be able to move back and forth. It moves the optical measuring unit 10, which is fixed to the tip of the rod 24, to a predetermined measuring position. The base 21 is a fixed part and is equipped with a rail part 211 that guides the gantry frame 22 in the horizontal direction (X-axis direction). The gantry frame 22 is formed in a gantry shape so as to straddle the object to be measured and is movable in the horizontal direction (X-axis direction) along the rail part 211 of the base 21. The holding part 23 is movable in the horizontal direction (Y-axis direction) perpendicular to the X-axis along the rail part 221 of the gantry frame 22. The rod 24 is housed in the holding part 23 so as to be able to move back and forth in the vertical direction (Z-axis direction) perpendicular to the direction of movement of the holding part 23 (Y-axis direction). The optical measuring unit 10 described above is attached to the tip of the rod 24. With the configuration described above, the optical measuring unit 10 attached to the tip of the rod 24 is able to move relative to the object being inspected in the three orthogonal axes of X, Y, and Z.

[0036] (Search Unit) As shown in Figure 2B, the search unit 30 scans the laser light emitted from the optical measurement unit 10 (excitation light source 11) and irradiates the pressure-sensitive paint P, and the light emitted from the pressure-sensitive paint P due to this laser light irradiation is detected by the optical measurement unit 10 (photodetector 14). In this case, the laser light is irradiated onto the entire surface of the pressure-sensitive paint P while the optical measurement unit 10 is moved by the moving device 20 with the X-axis direction as the main scanning direction and the Y-axis direction as the sub-scanning direction. The light emitted from the pressure-sensitive paint P excited by the laser light irradiation is received by the photodetector 14. The light received by the photodetector 14 is acquired as a histogram representing the brightness distribution of pixels for each pixel that is set in advance corresponding to the entire surface of the pressure-sensitive paint P, and the pixel position with the highest brightness is found based on the histogram. The pixel position found in this way is set as the detection position when the optical measurement unit 10 detects light from the pressure-sensitive paint P.

[0037] (Measurement Unit) The measurement unit 40 is equipped with an oscilloscope 41 and reads out the voltage signal converted by the TIA 15 to measure the decay rate of the light emission intensity received by the photodetector 14. Specifically, the oscilloscope 41 reads out the voltage signal converted by the TIA 15 and obtains the time waveform of the light emission intensity from the light emission intensity information from the photodetector 14. The measurement unit 40 performs signal processing on the digitized time waveform information of the light emission intensity from the oscilloscope 41 to calculate the decay rate of the light emission intensity received by the photodetector 14.

[0038] (Determination Unit) The determination unit 50 determines that there is an air leak if the decay rate of the luminescence intensity calculated by the measurement unit 40 exceeds a predetermined threshold Th. Here, it is known that the decay rate of the luminescence intensity detected from the time waveform information of the luminescence intensity depends on the number of collisions with oxygen. The relationship between the luminescence lifetime τ and the luminescence intensity I(t) at a certain time t is given by equation (1): I(t) = I0 × exp(-t / τ) (1) I ０ I(τ) is expressed as the emission intensity (maximum value) when the excitation light disappears, and when t = τ, the emission intensity I(τ) is given by I(τ) = (1 / e)I ０ ~0.37I ０ As a result, the luminescence intensity reaches its maximum value (I ０ The time it takes for the amount of air to decrease to 37% (attenuation rate) is measured to determine whether or not there is an air leak.

[0039] (Leak Inspection Method) Figure 4 is a flowchart illustrating the flow of the leak inspection according to this embodiment, Figure 5 is a schematic diagram explaining the preparation of the object to be inspected, and Figure 6 is a diagram conceptually illustrating the attenuation of light emission intensity. The leak inspection method according to this embodiment includes a moving step of moving an optical measuring unit 10, which projects excitation light onto a pressure-sensitive paint P inside the object to be inspected and detects the light from the pressure-sensitive paint P, to a predetermined measurement position; a light projection step of projecting excitation light onto the pressure-sensitive paint P; a search step of finding a detection position where the light from the pressure-sensitive paint P is brightest; a measurement step of measuring the attenuation rate of light emission intensity at the detection position; and a determination step of determining whether or not there is an air leak in the object to be inspected based on the attenuation rate.

[0040] (Preparation of the Specimen) In the present embodiment, as an example of an internal space that is depressurized to a predetermined vacuum level and hermetically sealed, the indicating unit 130 of the water meter 100 is used as the specimen for the air leak inspection. First, the pressure-sensitive paint P is inserted into the internal space that serves as the specimen. Examples of the pressure-sensitive paint P include platinum-porphyrin complexes such as PtTFPP and PtOEPP, palladium-porphyrin complexes such as PdTFPP, ruthenium complexes, and polycyclic aromatic hydrocarbons such as pyrene.

[0041] In the present embodiment, as the pressure-sensitive paint P, a ruthenium complex that is less expensive than the platinum-porphyrin complex, for example, Ru(dpp) ３ and other ruthenium-diphenylphosphine complexes are applied on a white plate and used. By applying the pressure-sensitive paint P on the white plate, the reflection of the excitation light source can be improved. The size of the pressure-sensitive paint P to be applied is preferably 10 mm or more in diameter. The pressure-sensitive paint P is a paint whose emission intensity and emission lifetime change according to the oxygen partial pressure, and the emission intensity gradually decays when it is quenched. It is known that the decay rate of the emission intensity depends on the number of collisions with oxygen, and by evaluating the decay rate of the emission intensity, the amount of oxygen partial pressure, that is, the depressurized state can be determined.

[0042] Next, as schematically shown in FIG. 5, the indicating unit 130 is connected to a vacuum pump and evacuated to depressurize the inside of the indicating unit 130 to a predetermined vacuum level. At this time, it is desirable to connect a pressure gauge to confirm the depressurized state of the indicating unit 130. In this way, the prepared indicating units 130 are arranged side by side on the table of the leak inspection device 1 in a predetermined number.

[0043] (Moving Step) Drive the moving device 20 to move the optical measurement unit 10 toward one of the instruction units 130 placed on the table of the leak inspection device 1 (S101). The moving device 20 moves the gantry frame 22 horizontally (in the X-axis direction) along the rail portion of the base 21, and the holding portion 23 moves horizontally (in the Y-axis direction) perpendicular to the X-axis along the rail portion of the gantry frame 22 and is positioned above the instruction unit 130. Then, the rod 24 extends in the vertical direction (Z-axis direction) perpendicular to the moving direction (Y-axis direction) of the holding portion 23, and the optical measurement unit 10 stops in a posture facing one of the instruction units 130 that is the inspection object.

[0044] (Light Projection Step) Then, cause the excitation light source 11 to emit light and irradiate the pressure-sensitive paint P in the instruction unit 130 depressurized to a predetermined vacuum degree with light (S102). In the present embodiment, the excitation light source 11 is a directly modulated laser (DML (Direct Modulated Laser)) having an emission wavelength of 400 nm to 700 nm and emits light in a pulsed manner by the drive unit 12.

[0045] (Search Step) With the excitation light source 11 emitting light, move the optical measurement unit 10 with the moving device 20 while irradiating the entire surface of the pressure-sensitive paint P with light, with the X-axis direction as the main scanning direction and the Y-axis direction as the sub-scanning direction. The light emitted from the pressure-sensitive paint P is received by the photodetector 14. The light received by the photodetector 14 is acquired as a histogram representing the brightness distribution of each pixel preset corresponding to the entire surface of the pressure-sensitive paint P, and the brightest pixel position is searched based on the histogram (S103). The brightest pixel position found here is set as the detection position.

[0046] (Measurement Step) Cause the excitation light source 11 to emit light at the detection position searched in step S103, irradiate the pressure-sensitive paint P with light, and receive the light emitted from the pressure-sensitive paint P with the photodetector 14 (S104). The photodetector 14 generates charges in proportion to the amount of received light. The charges generated by the photodetector 14 are amplified by the TIA 15 and then converted into a digital signal by an A / D converter (not shown) and output to the measurement unit 40 as a voltage signal (S105).

[0047] In the measurement unit 40, the voltage signal converted by the TIA 15 is read out by the oscilloscope 41, and the decay rate of the light emission intensity received by the photodetector 14 is measured (S106). Specifically, the oscilloscope 41 reads out the voltage converted by the TIA 15, and obtains the time waveform of the light emission intensity from the light emission intensity information from the photodetector 14. The measurement unit 40 performs high-frequency component removal processing and smoothing processing using a Fourier filter on the time waveform information of the light emission intensity converted into a digital signal from the oscilloscope 41, and calculates the decay rate of the light emission intensity received by the photodetector 14. That is, I ０ If we define the emission intensity (maximum value) when the excitation light disappears, then the emission intensity I is the maximum value (I ０ The time it takes for the value to decrease to 37% is calculated as the decay rate.

[0048] (Determination Step) Figure 6 conceptually illustrates the attenuation of luminescence intensity. As shown in Figure 6, the luminescence of the pressure-sensitive paint P is emitted while it is being irradiated with excitation light from the excitation light source 11, and then attenuates when the irradiation of excitation light stops. This attenuation rate changes according to the oxygen partial pressure inside the indicator unit 130, with the attenuation rate being faster the higher the oxygen partial pressure and slower in a vacuum. In this embodiment, when the luminescence intensity I reaches its maximum value (I ０ The time it takes for the pressure to decrease to 37% is calculated as the decay rate, and if it is greater than a predetermined threshold Th, it is determined that there is a constant oxygen partial pressure, that is, that an air leak is occurring and it is not a vacuum (S107; Yes).

[0049] If an air leak is detected in step S107, this fact is recorded (S108). If no air leak is detected in step 107 (S107; No), the process returns to step S101, and an air leak test is performed on the next instruction unit 130.

[0050] An air leak test was performed on the indicator unit 130 of the water meter 100 using the leak testing device 1 shown in Figure 2.

[0051] "Example 1" A ruthenium complex was applied as a pressure-sensitive paint P to the upper base plate 133 of the indicator unit 130, and the time it took for the luminescence intensity to decrease to 37% of its maximum value was measured as the decay rate of luminescence intensity in a vacuum state (under vacuum) and in an open valve state (under atmospheric pressure). As shown in Figure 7, there was a difference in the decay rate of luminescence intensity between under vacuum and under atmospheric pressure. The decay rate of luminescence intensity was 3.36 μs under vacuum, while it was 1.33 μs under atmospheric pressure. Thus, the decay rate of luminescence intensity is greater when the internal space of the indicator unit 130 is under atmospheric pressure compared to under vacuum, and by measuring the change in luminescence lifetime due to oxygen quenching, it is possible to accurately and quickly determine whether or not there is an air leak in the indicator unit 130.

[0052] "Example 2" A ruthenium complex was applied as a pressure-sensitive paint P to the upper base plate 133 of the indicator unit 130, and the decay rate of the luminescence intensity under vacuum conditions was measured while varying the ambient brightness.

[0053] Figure 8 shows the results of measuring the decay rate of luminescence intensity under vacuum, while varying the ambient brightness to 0 lx (lux), 15 lx (lux), 125 lx (lux), and 660 lx (lux), and keeping the luminescence intensity of the excitation light source 11 constant. As shown in Figure 8, when the ambient brightness was varied to 0 lx (lux), 15 lx (lux), 125 lx (lux), and 660 lx (lux), the decay rates of luminescence intensity were 0.933 μs, 1.071 μs, 1.663 μs, and 0.233 μs, respectively, confirming that the decay rate of luminescence intensity can be measured even when the brightness of the inspection environment changes.

[0054] "Example 3" A ruthenium complex was applied as a pressure-sensitive paint P to the upper base plate 133 of the indicator unit 130, and four indicator units 130 (units-1, -2, -3, -4) were arranged in different positions on the table of the leak inspection device 1 while under vacuum. Then, the moving device 20 was driven to move the optical measuring unit 10 sequentially to the inspection position of the indicator unit 130 and the decay rate of the luminescence intensity was measured.

[0055] As shown in Figure 9, the decay rates of luminescence intensity in units 1, 2, 3, and 4 were 1.18 μs, 1.10 μs, 1.05 μs, and 0.98 μs, respectively, confirming that the difference in the decay rate of luminescence intensity depending on the measurement position (inspection position) was extremely small.

[0056] Thus, when the internal space of the indicator unit 130 is under atmospheric pressure, the rate of decay of the luminescence intensity is greater than in a vacuum. By measuring the change in luminescence lifetime due to oxygen quenching, it becomes possible to determine whether or not there is an air leak in the indicator unit 130. Furthermore, it was confirmed that the rate of decay of the luminescence intensity can be measured even when the brightness of the inspection environment changes. With the indicator units 130 lined up at different positions on the table of the leak inspection device 1, the optical measuring unit 10 is moved sequentially to the inspection position of the indicator units 130 to measure the rate of decay of the luminescence intensity, thereby enabling automatic inspection of air leaks in multiple indicator units 130. In other words, measurement is possible even in bright ambient environments, and for example, air leaks in the indicator units 130 can be automatically inspected at the production site of a water meter 100.

[0057] Although embodiments of the present invention have been described in detail above, the present invention is not limited to the above embodiments, and various modifications can be made within the scope of the gist of the present invention as described in the claims. For example, as the pressure-sensitive coating P, platinum-porphyrin complexes such as PtTFPP and PtOEPP, which have a longer luminescence lifetime due to oxygen quenching compared to ruthenium complexes, may be used.

[0058] 1... Leak inspection device 10... Optical measurement unit, 11... Excitation light source, 12... Drive unit, 13... Focusing optical system, 14... Photodetector, 15... Transimpedance amplifier (TIA) 20... Moving device, 21... Base, 22... Gantry frame, 23... Holding unit, 24... Rod 30... Search unit 40... Measurement unit, 41... Oscilloscope 50... Judgment unit 100... Water meter 130... Indication unit, 131... Register box, 132... Lower base plate, 133... Upper base plate P... Pressure-sensitive paint

Claims

1. A leak inspection method for inspecting an object under inspection having an internal space that is depressurized to a predetermined degree of vacuum and airtightly sealed, comprising: a moving step of moving an optical measuring unit to a predetermined measurement position, which projects excitation light from outside the internal space onto a pressure-sensitive paint provided in the internal space whose luminescence intensity changes with changes in the oxygen concentration in the internal space, and detects the light from the pressure-sensitive paint onto which the light has been projected; a light projection step of projecting the excitation light onto the pressure-sensitive paint; a search step of finding a detection position where the light from the pressure-sensitive paint is brightest; a measurement step of measuring the decay rate of the luminescence intensity at the detection position; and a determination step of determining whether or not there is an air leak in the object under inspection based on the decay rate.

2. The leak inspection method according to claim 1, characterized in that the entire surface of the pressure-sensitive paint is scanned with the projected excitation light, and the light emitted from the pressure-sensitive paint by the scanned excitation light is detected in each region divided by a predetermined mesh to find the detection position in which the light from the pressure-sensitive paint is brightest.

3. The leakage inspection method according to claim 2, characterized in that the excitation light is selected to have an oscillation wavelength that produces the strongest emission intensity of the pressure-sensitive paint.

4. The leak inspection method according to claim 3, characterized in that the excitation light is positioned in close proximity to the surface of the pressure-sensitive paint.

5. The leak inspection method according to claim 1, characterized in that the measurement step involves measuring the rate of decay of the luminescence intensity under ambient light.

6. The leak inspection method according to any one of claims 1 to 5, characterized in that, after the measurement of the decay rate of the luminescence intensity at the measurement position of one of the objects to be inspected is completed, the optical measuring unit is moved to a predetermined measurement position for the next object to be inspected based on the information of the measurement order.

7. A leak inspection device for inspecting air leaks in an object under inspection having an internal space that is depressurized to a predetermined degree of vacuum and airtightly sealed, comprising: an optical measuring means that projects excitation light from outside the internal space onto a pressure-sensitive paint provided in the internal space whose luminescence intensity changes with changes in the oxygen concentration in the internal space, and detects the light from the pressure-sensitive paint onto which the light has been projected; a moving means that moves the optical measuring means to a predetermined measurement position; a search means that finds a detection position where the light from the pressure-sensitive paint is brightest; a measuring means that measures the decay rate of the luminescence intensity at the detection position; and a determination means that determines whether or not there is an air leak in the object under inspection based on the decay rate.

8. The leak inspection apparatus according to claim 7, characterized in that the moving means is movable in three axes, X, Y, and Z, relative to the object to be inspected.

Images