JP4173255B2 - Air leak test device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an air leak test apparatus.
[0002]
[Prior art]
A general differential pressure type air leak test apparatus called a balanced type will be briefly described. A master side and a work side branch air passage are connected to a common air passage extending from a test pressure source. A master container is connected to the master side branch air passage, and a work is connected to the work side branch air passage. The master container has the same shape, volume and material as the workpiece, and no leakage has been confirmed.
After applying a test pressure from the test pressure source to the two branch air passages, the branch air passages are shut off to form an independent closed system. Thereafter, the differential pressure between the two closed branch air passages is monitored to detect a workpiece leak.
[0003]
By the way, a predetermined time is waited until the branch air passage is closed after the application of the test pressure is started. This is to wait for the workpiece to reach the test pressure and to avoid a large initial pressure fluctuation. That is, when a test pressure is applied to the branch air passage, the temperature once rises due to compression, and then settles to the ambient temperature due to heat dissipation. The amount of heat radiation is greatest at the initial stage of applying test pressure.If the branch air passage is closed at this stage, the pressure drop due to heat radiation is too large, and there is a slight difference in heat radiation characteristics between the master container and the workpiece. This is because a differential pressure is generated.
[0004]
When the predetermined waiting time has elapsed as described above, the heat dissipation continues even after the branch air passage is closed, and the pressures of the two branch air passages in the closed state are reduced. The pressure drop in the two branch air passages due to this heat radiation is equal to each other because the master container has the same heat radiation characteristic of the workpiece and the same volume. Therefore, the differential pressure is not affected by the pressure drop due to the heat radiation, and the pressure drop corresponding to the leakage of the workpiece can be reliably detected.
[0005]
However, if the master container has the same shape, material, and volume as the workpiece as described above, many types of master containers are required in the production line for many types and small quantities, which increases equipment costs and management costs. .
Therefore, recently, an unbalanced type apparatus has been developed in which a master container having a predetermined shape, volume and material is used without changing the master container even if the workpieces are different. In this apparatus as well, the test pressure is applied to the two branch air passages, and when the predetermined waiting time elapses, the branch air passage is closed and the differential pressure is detected. The master container has a heat dissipation characteristic different from that of the work. Therefore, even if there is no leakage in the work, a differential pressure due to the difference in the heat dissipation characteristic is detected.
Therefore, the heat dissipation compensation value data is stored for each type of the workpiece, and the differential pressure corresponding to the workpiece leakage is obtained by subtracting the heat dissipation compensation value from the detected differential pressure.
[0006]
[Problems to be solved by the invention]
In the non-equilibrium type device in which the heat dissipation characteristics between the master container and the workpiece are different as described above, the heat dissipation characteristics change according to changes in the environment such as the temperature. It was.
In the above-described apparatus, if a relatively long time is waited after the branch air passage is closed, heat radiation is lost, and the differential pressure changes linearly corresponding to leakage. For this reason, it is conceivable to detect leakage based on the linearly changing differential pressure without performing the heat dissipation compensation. However, in that case, the test time for each workpiece becomes longer, and the productivity is lowered.
Therefore, accurate heat dissipation compensation has been required without increasing the test time.
[0007]
The above discussion can also be applied to a simple air leak test apparatus that is not a differential pressure type. In this apparatus, a test pressure source is connected to the upstream end of the air passage, and a workpiece is connected to the downstream end. After applying the test pressure, the air passage is closed, and leakage of the workpiece is detected based on a change in the pressure of the closed air passage. Even in this device, in order to eliminate the effect of pressure fluctuation due to heat radiation, the air passage is closed after the test pressure is applied until the heat radiation has settled, or after the air passage is closed, the pressure is linearly changed and the pressure is changed. The test time was long because leaks were detected. If the test time is to be shortened, the heat dissipation compensation data is used in the same manner as described above, and it becomes impossible to cope with environmental changes.
[0008]
[Means for Solving the Problems]
According to a first aspect of the present invention, in an air leak test apparatus, a test pressure source, a common air passage connected to the test pressure source, a master side branch air passage and a work side branch branched from the common air passage An air passage, first closing means for closing the branch air passages in communication with each other, second closing means for closing the branch air passages in an independent state, and branch air closed in the communication state A pressure sensor for detecting the pressure of the passage, a differential pressure sensor for detecting a differential pressure of the branch air passage closed in the independent state, and a control means,
The control means applies the test pressure from the test pressure source to the master side and work side branch air passages via the common air passage, and then drives the first closing means to connect the branch air passage. Immediately after closing, the heat radiation compensation value is calculated based on the change in the pressure detected by the pressure sensor, and then the second closing means is driven to close the branch air passage in an independent state. A workpiece leakage is detected based on a value obtained by subtracting the heat dissipation compensation value from a differential pressure detected by the differential pressure sensor.
[0009]
According to a second aspect of the present invention, in the air leak test apparatus, a test pressure source, a common air passage connected to the test pressure source, a master side branch air passage branched from the common air passage, and a work side branch An air passage, closing means for closing the branch air passages in an independent state, a pressure sensor for detecting the pressure of the work side branch air passage closed in the independent state, and two branches closed in an independent state A differential pressure sensor for detecting the differential pressure in the air passage, and a control means;
The control means applies the test pressure from the test pressure source to the branch air passage on the master side and the work side via the common air passage, and then drives the closing means to make the two branch air passages independent. Immediately after closing, the heat dissipation compensation value is calculated based on the change in the pressure detected by the pressure sensor, and then the differential pressure between the branch air passages is detected by the differential pressure sensor in the closed state. Based on a value obtained by subtracting the heat dissipation compensation value from the differential pressure, workpiece leakage is detected.
[0011]
Preferably, after the calculation of the heat dissipation compensation value, the control means opens the closing means once to connect the two branch air passages and then closes the closing means again, and then detects leakage based on the detected differential pressure and the heat dissipation compensation value. It is characterized by performing.
Preferably, the control means obtains, as master data, a time change curve of the detected pressure detected by the pressure sensor at the predetermined time in a state in which a work having no leakage is connected to the work side branch air passage, and then the inspection is performed. The time change curve of the pressure detected by the pressure sensor obtained at the predetermined time with the target work connected to the work side branch air passage is compared with the master data, and the curve of the master data is used as the time axis. The pressure change curve is specified by overlapping the detected pressure change curve by moving the detected pressure change curve, and the heat radiation compensation value is calculated based on the specified pressure change curve.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a first embodiment of the present invention will be described with reference to FIGS. The air leak test apparatus shown in FIG. 1 includes a compressed air source 1, a common air passage 2 having an upstream end connected to the compressed air source 1, a master side branch air passage 3 branched from the common air passage 2, and a workpiece side. And a branch air passage 4.
[0014]
In the common air passage 2, a pressure adjusting means 5 and an electromagnetically driven normally closed two-way valve 6 (hereinafter referred to as a pressurizing valve) are provided in order from the upstream side. The pressure adjusting means 5 has a pressure adjusting valve 5a and a pressure sensor 5b provided downstream thereof. The pressure control valve 5a is controlled so that the pressure sensor 5b has a predetermined test pressure. Therefore, the compressed air source 1 and the pressure adjusting means 5 constitute a test pressure source. The pressure adjusting means 5 may be a pressure reducing valve (regulator). The pressurizing valve 6 constitutes a first closing means in the claims.
[0015]
The master side branch air passage 3 is provided with a pneumatically driven two-way valve 7 that is normally open (hereinafter referred to as a shutoff valve), and a master container 8 is connected to the downstream end thereof. This shut-off valve 7 constitutes the second closing means in the claims in cooperation with the pressurizing valve 6. The master container 8 is made of a predetermined shape, volume, and material, and is different from a workpiece W described later. In addition, the master container 8 is devised so that the heat radiation after compression is completed in a short time by reducing the volume and attaching the heat radiation fins. The master container itself may be omitted and the downstream end of the master side branch air passage 3 may be closed.
[0016]
The work side branch air passage 4 is provided with a pneumatically driven normally open two-way valve 9 (hereinafter referred to as an exhaust valve). A work W to be inspected is connected to the downstream end of the branch air passage 4.
[0017]
The air leak test apparatus according to the present embodiment further includes a pressure sensor 11, a differential pressure sensor 12, and a control means 10. The pressure sensor 11 is connected to the upstream side of the shutoff valve 7 in the master side branch air passage 3. Further, the two input ports 12 a and 12 b of the differential pressure sensor 12 are respectively connected to the upstream side and the downstream side of the shutoff valve 7 in the master side branch air passage 3.
One input port 12 a of the pressure sensor 11 and the differential pressure sensor 12 may be connected to the work side branch air passage 4.
[0018]
The control means 10 controls the pressurizing valve 6, the shutoff valve 7, and the exhaust valve 9. Furthermore, the control means receives the detection signals from the pressure sensor 11 and the differential pressure sensor 12, and controls the display 13, the pass lamp 14, and the fail lamp 15.
[0019]
The operation of the apparatus having the above configuration will be described with reference to the time chart of FIG. First, the exhaust valve 9 is turned on and closed, and then the pressurization valve 6 is turned on to open it, thereby applying the test pressure from the pressure adjusting means 5 to the branch air passages 3 and 4. In this embodiment, since the process of connecting the work W to the work side branch air passage 4 is started at the same time as the exhaust valve 9 is closed, the closing operation of the pressurizing valve 6 is delayed for several seconds. When the connection process of the workpiece W is completed, the time from the closing operation of the exhaust valve 9 to the opening operation of the pressurizing valve 6 is short.
[0020]
The opening time of the pressurizing valve 6 corresponds to the minimum time required for the work W to be filled with air of the test pressure, and varies depending on the volume of the work W, but here is several seconds. This opening time is shorter than the waiting time from the start of applying the test pressure in the conventional apparatus to the closing of the branch air passage. This is to obtain data on relatively large pressure fluctuations due to heat dissipation as will be described later.
[0021]
When the pressurizing valve 6 is opened, since the air in the downstream side, that is, the master container 8, the work W, and the branch air passages 3 and 4 changes from the atmospheric pressure to the test pressure, the temperature rises due to the compression heat.
A predetermined time from the time when the pressurizing valve 6 is closed (or when a short time has passed) is defined as a first measurement time ΔTa. In the first measurement time ΔTa, data for heat radiation compensation is obtained based on the detected pressure from the pressure sensor 11. Details will be described below.
[0022]
When the pressurizing valve 6 is closed, the downstream side becomes a closed system. In this closed system, the branch air passages 3 and 4 are in communication. As shown in FIG. 3, the pressure in the closed system decreases along an exponential curve H as the internal temperature decreases due to heat dissipation. When there is no leakage in the workpiece W, this curve H coincides with the change in pressure detected by the pressure sensor 11. When the workpiece W is scratched and leaks, a linear pressure drop corresponding to the leak occurs (see the straight line M). Therefore, the detected pressure decreases by drawing a curve D in FIG. 3 including the pressure drop due to heat radiation and the pressure drop due to leakage.
[0023]
As is clear from the straight line H in FIG. 3, the pressure drop due to heat radiation is greatest immediately after the pressurizing valve 6 is closed, and settles with time. In the first measurement time Ta, the pressure drop caused by heat dissipation is much larger than the pressure drop caused by leakage (for example, 100: 1). For this reason, the detected pressure almost represents a pressure drop caused by heat dissipation. As a result, the heat radiation characteristic can be known from the change in the detected pressure. The control means 10 calculates heat radiation compensation data based on the detection output change data (curve D data) and the stored master data.
[0024]
The master data is obtained as follows. A work without leakage is connected to the branch air passage 4 in advance, and time change data of the detected pressure at the first measurement time ΔTa is obtained by the same operation as described above, and this is used as master data. The method of changing the detected pressure (in other words, the shape of the change curve of the detected pressure when the detected pressure is on the vertical axis and the time is on the horizontal axis) depends on the work material's material, surface area, shape, etc. Therefore, this change data is used as master data. As long as the workpiece W is not changed even if the ambient temperature is different, the pressure change curve of the above master data does not change. By simply moving this pressure change curve in the time axis direction, it matches the pressure change curve due to heat dissipation at different ambient temperatures. Should do.
In the actual leak test, the change data of the detected pressure is compared with the master data, and the master data curve is moved along the time axis, and the overlapping range with the detected pressure change curve varies depending on the ambient temperature during the test. It is specified as a curve of pressure change caused by heat dissipation. Based on the specified pressure change curve (pressure change data), a pressure change due to heat dissipation expected in a second measurement time ΔTb described later is calculated, and the data is stored as heat dissipation compensation data.
The first measurement time ΔTa for obtaining the heat radiation compensation data, in the conventional device is a time corresponding to the prior leak detection latency, never Hence time setting of the first measurement time ΔTa is prolonged.
[0025]
The control means 10 turns on the shut-off valve 7 and closes it when a predetermined time (longer than the first measurement time ΔTa but may be the same) has elapsed since the pressurization valve 6 was closed. Thereby, the downstream side and the upstream side of the master side branch passage 3 are blocked. Since the upstream side of the master side branch passage 3 is in communication with the workpiece side branch passage 4, the closed system downstream of the master side branch passage 3 and the closed system including the workpiece side branch passage 4 become a closed system independent of each other. .
[0026]
The heat release continues even after two independent closed systems are obtained by the closing operation of the shutoff valve 7, and the pressure drop due to the heat release continues in the work side branch air passage 4. In the present embodiment, the heat radiation in the master side branch air passage 3 is already substantially stabilized before the closing operation of the shut-off valve 7 and is in a stable state. It does not appear.
[0027]
When the shut-off valve 7 is closed, the degree of pressure fluctuation (decrease) due to the heat radiation is almost the same level as the pressure fluctuation (decrease) due to leakage. A predetermined time from the closing time is defined as a second measurement time ΔTb, and the detected differential pressure of the differential pressure sensor 7 is monitored. As shown in FIG. 4, the detected differential pressure D ′ is obtained by adding a differential pressure M ′ generated by leakage of the workpiece W and a differential pressure H ′ generated by heat dissipation of the workpiece W. Therefore, the differential pressure M ′ due to leakage can be obtained by subtracting the differential pressure H ′ due to heat radiation from the detected differential pressure D ′. Here, as the data of the differential pressure H ′, the data of the heat radiation compensation value obtained at the first measurement time ΔTa is used. Since this heat dissipation compensation value represents a heat dissipation characteristic that takes into account the influence of the environment such as ambient temperature during the test, an accurate differential pressure due to leakage can be detected.
[0028]
In the present embodiment, the heat radiation compensation data is a set of heat radiation compensation values for each predetermined sampling period in the second measurement time ΔTb, and the elapsed time is obtained by reading the detected pressure in this sampling period and subtracting the heat radiation compensation value. It is possible to calculate a change in the differential pressure due to leakage corresponding to. By calculating a linear line from this differential pressure change data, a differential pressure corresponding to an accurate leak can be calculated. From this differential pressure data, an atmospheric pressure equivalent leakage amount in a unit time or a predetermined time is calculated and displayed on the display 13. Further, this atmospheric pressure equivalent leakage amount is compared with a threshold value, and if it is lower than the threshold value, the pass lamp 14 is turned on, and if it is more than the threshold value, the fail lamp 15 is turned on.
When the detection of the differential pressure due to leakage is completed, the shutoff valve 7 is opened and the exhaust valve 9 is opened to end the test.
[0029]
The differential pressure due to leakage may be detected by detecting the differential pressure when a predetermined time has elapsed from the closing time of the shutoff valve 7 and subtracting the heat dissipation compensation value. In this case, the heat dissipation compensation data only includes a single heat dissipation compensation value.
[0030]
The calculation of the heat dissipation compensation data need not be performed for each leak test, and may be performed once for a plurality of tests. Alternatively, the heat dissipation compensation data may be directly calculated based on the detected pressure change at the first measurement time without storing the heat dissipation compensation master data in advance.
[0031]
Next, a second embodiment of the present invention will be described with reference to FIG. In this embodiment, the work side branch air passage 4 is additionally provided with an air pressure driven normally open two-way valve 17 (shutoff valve). In this case, the shut-off valve 17 is closed and the downstream side is shut off from the upstream side of the master side branch air passage 3. The input port 12 a of the differential pressure sensor 12 is connected to the downstream side of the shutoff valve 17. In this embodiment, the pressurizing valve 6 constitutes a first closing means, and the shutoff valves 7 and 17 constitute a second closing means. The shut-off valve 17 is driven in synchronization with the master-side shut-off valve 7. Since other operations are the same as those in the first embodiment, description thereof is omitted.
[0032]
Next, a third embodiment of the present invention will be described. This third embodiment is the same as the second embodiment except that the pressure sensor 11 is connected not to the upstream side of the shutoff valve 17 but to the branch air passage 4 on the downstream side as indicated by the imaginary line in FIG. The configuration is the same. In this case, as shown in the time chart of FIG. 6, the first measurement time ΔTa is started after the closing time of the shutoff valves 7 and 17 or slightly delayed, and then the second measurement time ΔTb is set. The closing timing of the pressurizing valve 6 may be the same as the closing time of the shutoff valves 7 and 17 or may be delayed.
[0033]
Next, a fourth embodiment of the present invention will be described. The fourth embodiment is the same in configuration as the second embodiment except that the pressure sensor 11 is omitted in FIG. Further, the control of the valves 6, 7, 9, and 17 is the same as that in the third embodiment (see FIG. 6). However, in the fourth embodiment, instead of the pressure sensor 11, the pressure drop in the work side branch air passage 4 due to heat radiation is detected by the differential pressure sensor 12, and the heat radiation compensation data is calculated from the differential pressure data.
[0034]
In the third and fourth embodiments, a two-position three-way valve may be used instead of the pressurizing valve 6 and the exhaust valve 9. In this case, test pressure is applied to the branch air passages 3 and 4 at the communication position, and the branch air passages 3 and 4 are opened to the atmosphere at the open position.
[0035]
In the third and fourth embodiments, as shown in FIG. 7, the shutoff valves 7 and 17 are temporarily opened between the first measurement time ΔTa and the second measurement time ΔTb, and the branch air circuits 3 and 4 are set to the same pressure. May be. Thereby, the differential pressure detection by the differential pressure sensor 12 in the second measurement time ΔTb can be performed more accurately.
[0036]
Next, a fifth embodiment of the present invention will be described with reference to FIG. This embodiment relates to a simple air leak test apparatus rather than a differential pressure type. In this apparatus, a test pressure source including the compressed air source 1 and the pressure adjusting means 5 is connected to the upstream end of the air passage 2A, and a work W is connected to the downstream end. A pressurizing valve 6 (closing means), a pressure sensor 11 (pressure detecting means), and an exhaust valve 9 are connected to the air passage 2A in order from the upstream side.
[0037]
In the above apparatus, by applying the test pressure to the air passage 2A and the workpiece W on the downstream side of the pressurization valve 6 by opening the pressurization valve 6 for a necessary minimum time, the pressurization valve 6 is closed, and the A change in pressure detected by the pressure sensor 11 is read in one measurement time. Then, heat radiation compensation data is calculated from the pressure change data or from the pressure change data and master data. Then, by subtracting the heat dissipation compensation data from the change in pressure detected by the pressure sensor 11 in the subsequent second measurement time, a pressure drop due to leakage of the workpiece W is calculated, and leakage is detected from this calculated value.
[0038]
【The invention's effect】
As described above, according to the first aspect of the present invention, the workpiece leakage can be detected in a short time by subtracting the heat radiation compensation value from the detected differential pressure value. In addition, by calculating the heat dissipation compensation value based on a relatively large pressure fluctuation due to heat dissipation immediately after closing, an accurate heat dissipation compensation value can be obtained, and thus leakage of the workpiece can be accurately detected. Further, since the pressure fluctuation due to heat radiation is detected in a state where the two branch air passages on the master side and the work side are in communication and closed, the subsequent differential pressure sensor detects a differential pressure change from substantially zero differential pressure. And more accurate leak detection is possible.
According to the second aspect of the present invention, the same effect as that of the first aspect can be obtained except that differential pressure detection is started from zero differential pressure.
According to the third aspect of the present invention, since the two branch air passages are once communicated before the differential pressure is detected and then made independent from each other again, the differential pressure detection can be started from the differential pressure zero by the differential pressure sensor, high accuracy of leak detection is Ru possible der.
[Brief description of the drawings]
FIG. 1 is a circuit diagram of an air leak test apparatus according to a first embodiment of the present invention.
FIG. 2 is a time chart of valve control executed by the apparatus.
FIG. 3 is a diagram illustrating a state of a decrease in detected pressure, a pressure decrease due to heat dissipation, and a pressure decrease due to leakage after the pressurization valve is closed.
FIG. 4 is a diagram showing changes in detected differential pressure due to shut-off valve closing, changes in differential pressure due to heat dissipation, and changes in differential pressure due to leakage.
FIG. 5 is a circuit diagram of an air leak test apparatus according to a second embodiment of the present invention.
FIG. 6 is a time chart of valve control executed by an air leak test apparatus according to a third embodiment of the present invention.
FIG. 7 is a time chart of valve control executed when the third and fourth embodiments of the present invention are slightly changed.
FIG. 8 is a circuit diagram of an air leak test apparatus according to a fifth embodiment of the present invention.
[Explanation of symbols]
2 Common air passage 2A Air passage 3 Master side branch air passage 4 Work side branch air passage 6 Pressurizing valve (closing means, first closing means)
7 Shut-off valve (second closing means)
10 control means 11 pressure sensor (pressure detection means)
12 Differential pressure sensor (pressure detection means)

Claims (4)

A test pressure source, a common air passage connected to the test pressure source, a master side branch air passage and a work side branch air passage branched from the common air passage, and the branch air passages in communication with each other in a first closing means for closing the second closing means for closing these branch air passage in a state independent of each other, a differential pressure sensor for detecting the differential pressure of the branch air passage which is closed by the independent state, the difference A pressure sensor that is separate from the pressure sensor and that detects the pressure of the branch air passage that is closed in the communication state, and a control means,
The control means applies the test pressure from the test pressure source to the master side and work side branch air passages via the common air passage, and then drives the first closing means to connect the branch air passage. And the heat dissipation compensation value is calculated based on the change in the pressure detected by the pressure sensor in a predetermined time immediately after the closing, and then the second closing means is driven to close the branch air passage in an independent state. An air leak test apparatus for detecting a leak of a workpiece based on a value obtained by subtracting the heat dissipation compensation value from a differential pressure detected by the differential pressure sensor immediately after closing. A test pressure source, a common air passage connected to the test pressure source, a master side branch air passage and a work side branch air passage branched from the common air passage, and the branch air passages being independent from each other. and closure means for closing, a differential pressure sensor for detecting the differential pressure of two branch air passage which is closed by the independent state, closed working side branch air above independent state without a separate body from the differential pressure sensor A pressure sensor for detecting the pressure in the passage, and a control means;
The control means applies the test pressure from the test pressure source to the branch air passage on the master side and the work side via the common air passage, and then drives the closing means to make the two branch air passages independent. The heat radiation compensation value is calculated based on the change in the pressure detected by the pressure sensor in a predetermined time immediately after the closing, and then the differential pressure between the branch air passages is detected by the differential pressure sensor in the closed state. An air leak test apparatus for detecting a work leakage based on a value obtained by subtracting the heat radiation compensation value from the detected differential pressure. After the calculation of the heat dissipation compensation value, the control means opens the closing means once to connect the two branch air passages, then closes the closing means again, and then performs leak detection based on the detected differential pressure and the heat dissipation compensation value. The air leak test apparatus according to claim 2 . The control means obtains, as master data, a time change curve of the detected pressure detected by the pressure sensor at the predetermined time in a state where a leak-free workpiece is connected to the workpiece-side branch air passage, and then the workpiece to be inspected. Is compared to the master data, and the curve of the master data is moved along the time axis. The pressure change curve is specified by overlapping the detected pressure change curve, and a heat radiation compensation value is calculated based on the specified pressure change curve. The air leak test apparatus according to any one of the above.

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