JP4948145B2 - Gas detector - Google Patents

Description

  The present invention relates to a gas detection device for detecting a gas filled in an inspection object, and more particularly to a gas detection device capable of efficiently detecting a filling gas in an inspection object in a non-contact and remote manner.

  In recent years, in order to maintain the freshness of various foods such as raw meat, ham and sausage for a long period of time, gas-filled packaging filled with gas such as carbon dioxide and nitrogen gas has been performed. In such gas-filled packaging, the gas concentration in the package (pack) affects the quality. For this reason, conventionally, a gas in a package is collected by a syringe and the concentration of the gas is inspected, or a gas concentration is detected in a decompressed chamber to inspect a gas leak in the package. ing. However, in the former case, since it is a destructive inspection, all products cannot be inspected, and even if there is even one rejected product, it is discarded in lot units. In addition, because of the destructive inspection, the product to be inspected has no commercial value. In the latter case, although it is an inspection of all products, it does not inspect the packing gas concentration, but inspects the gas leakage of the package.

By the way, as a conventional gas detection device, there is one that utilizes a light absorption phenomenon of a molecule that detects a gas concentration by irradiating a gas with light (for example, infrared rays) and measuring the amount of light energy absorbed by the gas molecules ( For example, see Patent Documents 1 and 2). And it is possible to use this gas detection apparatus for the filling gas test | inspection of a gas filling packaging.
Japanese Patent Laid-Open No. 5-52745 JP-A-7-167784

However, in conventional gas detection devices that use molecular absorption phenomenon, a method of collecting and measuring a gas sample is generally used. There has never been anything that directly irradiates an object with light and can remotely inspect the gas.
The present invention has been made paying attention to the above problems, and an object of the present invention is to provide a gas detection device that can easily and efficiently detect a filling gas of a test object filled with a gas without contact.

For this reason, the invention of claim 1 is a gas detection device for detecting the filling gas of an inspection object filled with gas, and a laser light source for emitting light, and reflected light of the emitted light from the inspection object And a light receiving means for receiving light and intermittently a drive current having a waveform shape that supplies a current value equal to or greater than the light emission threshold current of the laser light source at the beginning of the waveform, with the waveform head gradually increasing in waveform to the laser light source. And a control means for controlling the light emission of the laser light source so that the wavelength of the emitted light of the laser light source falls within a wavelength range including only one specific absorption wavelength of the filling gas, and a light receiving output of the light receiving means. Determination means for detecting the presence or absence of the filling gas by detecting the presence or absence of absorption of light energy at the specific absorption wavelength, and detecting the temperature of the laser light source and setting the laser light source to a constant temperature according to the detected temperature System A laser light source temperature control means for, characterized by being configured with a light receiving unit temperature control means for controlling the light receiving means at a constant temperature in accordance with detected and the detected temperature the temperature of the light receiving means.

In such a configuration, the control means intermittently applies a drive current having a waveform shape that supplies a current value equal to or greater than the emission threshold current of the laser light source at the beginning of the waveform, with the waveform head gradually increasing and the waveform head gradually increasing. The laser light source is controlled to emit light so that the wavelength of the light emitted from the laser light source falls within a wavelength range including only one specific absorption wavelength of the filling gas filled in the test object. The laser light source is a light receiving means that emits light in the above-mentioned wavelength range while maintaining a constant temperature by the laser light source temperature control means, and the reflected light from the inspection object of the emitted light is controlled to a constant temperature by the light receiving means temperature control means. Receive light. The determination means determines the presence or absence of the filling gas by detecting the presence or absence of absorption of light energy at the specific absorption wavelength based on the light reception output of the light reception means. If there is an output reduction portion due to the absorption of light energy in the received light output, the filling gas is present.

According to a second aspect of the present invention, when the light energy is absorbed, the determination means calculates a ratio of the light reception output value reduced by the absorption to the original light reception output value without the absorption as an absorption rate, and the absorption The concentration of the filling gas may be obtained based on the rate.
With this configuration, the concentration of the filling gas filled in the inspection object can be known.

According to a third aspect of the present invention, the inspection object may include an optical scanning unit that scans the emitted light of the laser light source.
With such a configuration, the presence or absence of the filling gas of the inspection object can be detected two-dimensionally (planar).

According to a fourth aspect of the present invention, the concentration distribution of the filling gas in the inspection object may be obtained. In this case, as described in claim 5 , the density distribution may be visualized and displayed on the display means.

According to a sixth aspect of the present invention, it is preferable that the inspection object is a food packaging body in gas-filled packaging, and the food packaging body being conveyed by the conveying means can be irradiated with the emitted light of the laser light source.
With such a configuration, all products can be inspected easily and efficiently without contact with the filling gas in the food packaging body of the gas-filled packaging.

According to the gas detection device of the present invention, the filling gas inspection of the inspection object filled with the gas can be performed easily and efficiently without contact. Accordingly, non-destructive inspection of all products and the like in gas-filled packaging is possible, so that product waste can be eliminated and product safety can be improved. In addition, for the light emission control of the laser light source, a drive current having a waveform shape that supplies a current value equal to or higher than the light emission threshold current of the laser light source at the beginning of the waveform with the waveform head gradually increasing and the waveform head gradually increasing is absorbed. To obtain the reference value of the received light output (the point where the received light output is zero) when calculating the ratio of the received light output value reduced by the absorption with respect to the original received light output value with no absorption as the absorption rate. There is an advantage that a reference signal is not required and only one control current signal is required.
Further, if the configuration in which the filling gas concentration distribution is visualized and displayed, there is an advantage that the leakage state of the filling gas can be easily known. Furthermore, by scanning the emitted light, the emitted light can be reliably irradiated even if the position of the inspection object is shifted when the inspection object is being conveyed by the conveying means, and the inspection is performed without the filling gas inspection. It is possible to prevent an error that an object passes through and improve the reliability of inspection.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a configuration diagram showing an embodiment of a gas detection device according to the present invention.
In FIG. 1, the gas detection apparatus of this embodiment includes a laser light source 1, an optical scanning system 2, a light receiving element 3, a signal processing unit 4, a laser control unit 5, a scanning mirror control unit 6, and a light receiving element. A control unit 7, a data processing unit 8, and a display unit 9 are provided.
The laser light source 1 is a light source that emits light, and is, for example, an infrared semiconductor laser diode. The laser light source 1 is configured to be temperature-controllable by a Peltier element (not shown).

The optical scanning system 2 scans the emitted light (infrared rays) of the laser light source 1, and is, for example, a transport means for transporting an inspection object 21 such as a food package of gas-filled packaging, as shown in FIG. It is provided on a support base 23 installed so as to straddle the belt conveyor 22. As shown in FIG. 3, the optical scanning system 2 includes a perforated mirror 2A having a hole at the center, and a scanning mirror 2B composed of, for example, a semiconductor galvanometer mirror as a swingable optical scanning means as indicated by an arrow in the figure. A reflecting mirror 2C, a concave mirror 2D, a condenser lens 2E, and a band-pass filter 2F for cutting noise contained in the reflected light. The optical scanning system 2 having such a configuration guides, for example, infrared rays from the laser light source 1 through a collimating lens (not shown) to the scanning mirror 2B through the holes in the perforated mirror 2A, and scans the infrared rays by swinging the scanning mirror 2B. Then, the scanning light is converted into parallel light through the reflecting mirror 2C and the concave mirror 2D, and the inspection object 21 on the belt conveyor 22 is irradiated with the infrared rays substantially vertically, and the reflected light is collected by the perforated mirror 2A. 2E and the band pass filter 2F are guided to the light receiving element 3.
Note that the reflection mirror 2C and the concave mirror 2D may be omitted, and the inspection light 21 may be directly irradiated with the scanning light from the scanning mirror 2B.

  The light receiving element 3 is a light receiving means for receiving the infrared reflected light of the laser light source 1 and uses, for example, a photodiode. Similar to the laser light source 1, the light receiving element 3 is configured to be temperature-controllable by a Peltier element (not shown). The signal processing unit 4 amplifies the light reception output of the light receiving element 3 to cut noise, and includes an amplifier and a filter.

The laser control unit 5 sets the wavelength of the emitted light of the laser light source 1 to a wavelength range including only one specific absorption wavelength of a measurement target filling gas (for example, CO ₂ , N _2, etc.) filled in the inspection object 21. This controls the light emission of the laser light source 1 and functions as a control means. Specifically, since the laser light source 1 has a characteristic that the wavelength of the emitted light changes in proportion to the temperature and the supply current, in this embodiment, the Peltier element is controlled based on the laser light source temperature detected by the temperature sensor 10. Then, the control current supplied to the laser light source 1 is varied while the laser light source 1 is kept at a constant temperature. The variable range of the control current is regulated so that the wavelength range of infrared rays emitted from the laser light source 1 is a wavelength range including only one specific absorption wavelength of the filling gas. Here, the temperature sensor 10, the laser controller 5, and the Peltier element constitute a laser light source temperature control means.

The scanning mirror controller 6 supplies an alternating drive signal to the scanning mirror 2B to control the scanning angle of the scanning mirror 2B.
The light receiving element control unit 7 controls the Peltier element based on the light receiving element temperature detected by the temperature sensor 11 to keep the light receiving element 3 at a constant temperature and keep the sensitivity of the light receiving element 3 constant. Here, the temperature sensor 11, the light receiving element control unit 7, and the Peltier element constitute a light receiving means temperature control means.

  The data processing unit 8 determines the presence or absence of the filling gas by detecting the presence or absence of absorption of light energy at one specific absorption wavelength of the filling gas based on the light reception output of the light receiving element 3, and functions as a determination unit. Prepare. Specifically, the received light output is sampled at a predetermined interval, and if there is an output decrease portion, it is determined that light energy is absorbed by the filling gas, and it is determined that the filling gas is present. In addition, when light energy is absorbed, the ratio of the light reception output value reduced by the absorption to the original light reception output value without absorption is calculated as an absorption rate, and the absorption rate and gas concentration stored in the database in advance are calculated. From the relationship, the concentration value corresponding to the calculated absorption rate is searched to obtain the concentration of the filling gas. Further, the scanning region is divided into pixels based on the control current signal of the laser control unit 5, the drive signal of the scanning mirror control unit 6, and the moving speed of the inspection object 21, and the obtained density is changed from the position of the scanning mirror 2B to each pixel position. The concentration distribution is obtained in association with the data, and the obtained concentration distribution data is transmitted to the display unit 9 as display means. The display unit 9 visualizes the input concentration distribution data and displays the visualized data.

Here, the creation of the density distribution data described above will be briefly described with reference to FIG.
Assuming that the frequency of the drive signal of the scanning mirror 2B is f _G and the frequency of the control current signal of the laser light source 1 is f _LD , the inspection object 21 moving on the belt conveyor 22 as shown in FIG. ) Is the number of pixels in the scanning direction when
Number of pixels = f _G / (2 × f _LD )
It is.
And the size of one pixel is as follows. When the scanning width of the laser beam is L in the scanning direction,
X = L / number of pixels, and in the direction perpendicular to the scanning direction, if the speed of the belt conveyor 22 is V,
Y = V / (2 × f _G )
It becomes.
In FIG. 4A, black circles indicate laser light irradiation points, and squares indicate one pixel.
Then, as shown in FIG. 4B, the laser beam is scanned on the inspection object 21 in, for example, a zigzag pattern, and the density distribution data is visualized with the scanning from end to end of the inspection object 21 as one line. Visualize as in (C). At this time, the size in the direction perpendicular to the scanning direction of the pixel when represented by one line is visualized as a rectangular shape in FIG. Further, as shown in FIG. 4C, the visualization data of each line is combined to create two-dimensional visualization data and displayed on the display unit 9.

Next, the filling gas detection operation by the data processing unit 8 according to the present embodiment will be described with reference to the time chart of FIG. 5 and the flowchart of FIG.
First, the filling gas detection principle of this embodiment will be described with reference to the time chart of FIG.
The laser control unit 5 intermittently supplies the laser light source 1 with a control current signal having a substantially rectangular shape as shown in FIG. That is, the first and last control current values of the waveform are set so that the wavelength range includes only one specific absorption wavelength of the filling gas, and the control current is controlled to continuously increase within the control current range. Since the laser light source 1 does not emit light up to a certain current value and emits light at the current value (light emission threshold current) or more, it supplies the current above the light emission threshold current at the beginning of the waveform to emit light. Is continuously increased. As a result, the laser light source 1 intermittently blinks in accordance with the control current signal to emit infrared rays, and the infrared light emission output value at the time of lighting continuously increases as shown in FIG. 5B. At this time, the wavelength of the emitted infrared rays changes according to the control current value as shown in FIG. 5C, and this change width is a wavelength range including only one specific absorption wavelength of the filling gas. Further, the light reception output also increases as shown in FIG. 5D in proportion to the light emission output of FIG. When the filling gas exists in the inspection object 21, absorption of infrared light energy occurs due to the absorption phenomenon when the infrared wavelength matches the absorption wavelength of the filling gas, and the light reception output decreases as shown in FIG. Thus, it can be seen that a filling gas is present.

Next, the operation of the data processing unit 8 will be described based on the flowchart of FIG.
In step 1 (indicated by S1 in the figure, the same shall apply hereinafter), it is determined whether or not the reference position of the scanning mirror 2B has been detected based on the drive signal of the scanning mirror control unit 6. If detected, the process proceeds to step 2.
In step 2, it is determined whether or not the reference position of the control current signal has been detected based on the control current signal of the laser controller 5. Here, after detecting the reference position of the scanning mirror 2B in step 1, if the rising of the first waveform of the control current signal in FIG. 5A is detected, it is determined that the reference position of the control current signal is detected, and the process proceeds to step 3. .
In step 3, the pixel position is specified. Specifically, for example, a number such as “1” is given.
In step 4, the received light output of one waveform in FIG. 5D is read at a predetermined sampling interval with one waveform of the control current signal as one pixel.
In step 5, the received light output is read until the received light output is inputted for one pixel.

In step 6, it is determined whether or not there is a filling gas. If there is a decrease in the received light output for one pixel, it is determined that light energy has been absorbed and it is determined that there is a filling gas. move on.
In step 7, the gas concentration is detected. The ratio (a / b) of the light reception output value a (see FIG. 5 (d)) reduced by the absorption to the original light reception output value b (see FIG. 5 (d)) having no absorption is calculated as an absorption rate. Based on the relationship between the absorption rate stored in advance and the concentration value of the filling gas, a concentration value corresponding to the calculated absorption rate (a / b) is searched for as the filling gas concentration of the first pixel.
In step 8, it is determined whether or not the measurement is finished, and the operations in steps 3 to 7 are repeated until the measurement is finished, and the gas concentration of each pixel is measured. When the inspection object 21 passes the position of the optical scanning system 2 and the measurement of the preset number of lines is completed, it is determined that the measurement is completed, and the process proceeds to Step 9.
In step 9, the detection result (density distribution data) is output to the display unit 9. As a result, the display unit 9 visualizes the input concentration distribution data to create and display two-dimensional visualization data.

  As shown in FIG. 5A, it is necessary to calculate the absorption rate (a / b) that the initial current value of the waveform of the control current signal is not less than the light emission threshold current value of the laser light source 1. This is to obtain a standard value of the received light output (a point at which the received light output is zero).

  According to such a configuration, it is possible to easily and efficiently perform a filling gas inspection in a package such as a gas filling package without contact. Accordingly, non-destructive inspection of all products in gas-filled packaging can be performed directly, and the waste of the products can be eliminated, and the safety of the products can be improved. Further, since the filling gas concentration distribution is visualized and displayed, the leakage state of the filling gas can be easily known. Further, since the laser beam is scanned, the laser beam can be reliably irradiated even if the position of the inspection object 21 on the belt conveyor 22 is shifted, so that the inspection object 21 passes without a filling gas inspection. Can be prevented, and the reliability of inspection can be improved.

Next, a second embodiment of the present invention will be described.
The second embodiment is an example in which one point of the inspection object 21 is irradiated without scanning with laser light. In this case, the laser beam may be irradiated directly onto the inspection object 21 via the perforated mirror 2A, and therefore the scanning mirror control unit 6 from the scanning mirror 2B to the concave mirror 2D of the optical scanning system 2 is not necessary.
Next, the data processing operation of the second embodiment will be described based on the flowchart of FIG.
In step 11, as in step 2 of FIG. 6, it is determined whether or not the reference position of the control current signal has been detected based on the control current signal of the laser control unit 5.
In step 12, the received light output of one waveform in FIG. 5D is read at a predetermined sampling interval in the same manner as in step 4 in FIG.

In step 13, it is determined whether or not the sampling is completed for the light reception output data of one waveform in FIG. 5 (d).
In step 14, it is determined whether or not there is a filling gas. If there is a decrease in the light reception output, it is determined that the light energy has been absorbed and it is determined that there is a filling gas, and the process proceeds to step 15.
In step 15, the absorption rate (a / b) is calculated in the same manner as in step 7 of FIG. 6, and the concentration of the filling gas is searched from the relationship between the absorption rate stored in advance in the database and the concentration value of the filling gas.
In step 16, the detection result is output to the display unit 9. Thereby, what is necessary is just to make it display on a display part 9, such as gas concentration, a pass, and a failure.

In 1st and 2nd embodiment, it was set as the structure which displays a detection result on the display part 9, However, It is not restricted to this, For example, an alarm device is provided and there is no filling gas based on a detection result, or an inadequate rejected product In such a case, a configuration may be considered in which an alarm is generated and notified, a detection result is written in a tag attached to each inspection object 21, or data is registered in a central management device that centrally manages the inspection object. It is done.
Needless to say, the gas detection device of the present invention is not limited to the detection of a filling gas in a package of a gas-filled packaging, and can be applied to the detection of a filling gas in any container.

  In the above embodiment, the inspection object 21 is described as having the same shape and the same filling gas space thickness. However, for example, in the case of inspecting an inspection object in which only the gas is filled in the container, When the shape is indefinite and the height is different, the absorption rate of the gas varies depending on the height of the test object as a function of the concentration and the optical path length in the gas. For example, as shown by the broken line in FIG. A distance measuring sensor 12 may be provided for detecting the height of the object 21, and the density value obtained from the absorption rate may be corrected based on the detection value of the distance measuring sensor 12.

In the present invention , the control current signal of the laser control unit 5 for controlling the light emission of the laser light source 1 is a waveform signal as shown in FIG. 5A. However, as a reference example, a rectangular wave pulse signal will be described. . In this case, as shown in FIG. 8A, a rectangular wave pulse signal having a control current value (crest value) in which the wavelength of the laser light emitted from the laser light source 1 is the same wavelength as one specific absorption wavelength of the filling gas is used. . Then, when the filling gas is present, absorption of infrared light energy occurs due to the light absorption phenomenon, and the received light output value is lowered as shown in FIG. 8B, indicating that the filling gas is present. However, when a rectangular wave pulse signal is used, a control current value of a wavelength at which no light absorption phenomenon occurs in order to obtain an original received light output value b without absorption necessary for calculating the absorption rate (a / b). Pulse signal (reference signal) is required separately. On the other hand, if the control current signal waveform of the present invention as shown in FIG. 5A is used, there is an advantage that a reference signal is unnecessary and only one control current signal is required. Note that one pulse in FIG. 8A corresponds to one pulse in FIG. 5A, and when the density distribution data is visualized, one pulse corresponds to one pixel.

The block diagram of 1st Embodiment of the gas detection apparatus of this invention The figure which shows the irradiation form of the laser beam to the test object of embodiment same as the above Configuration diagram of optical scanning system of embodiment same as above Explanatory drawing of density distribution data visualization processing of the same embodiment Explanatory drawing of the gas detection principle of the same embodiment Flowchart explaining the data processing operation of the embodiment The flowchart explaining the data processing operation of 2nd Embodiment of this invention. The figure which shows the reference example of the control current signal for laser light source control

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Laser light source 2 Optical scanning system 2B Scanning mirror 3 Light receiving element 5 Laser control part 6 Scanning mirror control part 8 Data processing part 9 Display part 21 Inspection object 22 Belt conveyor

Claims (6)

A gas detection device for detecting the filling gas of an inspection object filled with gas,
A laser light source that emits light;
A light receiving means for receiving reflected light from the inspection object of the emitted light;
The laser light source is intermittently supplied with a drive current having a substantially rectangular shape and having a waveform shape that gradually increases the waveform head and supplies a current value equal to or greater than the light emission threshold current of the laser light source at the beginning of the waveform. Control means for controlling the emission of the laser light source so that the wavelength of the light emitted from the light source falls within a wavelength range including only one specific absorption wavelength of the filling gas;
Determining means for detecting the presence or absence of the filling gas by detecting the presence or absence of absorption of light energy at the specific absorption wavelength based on the light reception output of the light receiving means;
Laser light source temperature control means for detecting the temperature of the laser light source and controlling the laser light source at a constant temperature according to the detected temperature;
A light receiving means temperature control means for detecting the temperature of the light receiving means and controlling the light receiving means at a constant temperature according to the detected temperature;
A gas detection device comprising:   When the light energy is absorbed, the determination means calculates a ratio of the light reception output value reduced by the absorption to the original light reception output value without the absorption as an absorption rate, and the filling gas is based on the absorption rate. The gas detection device according to claim 1, wherein the concentration is determined. Gas detector according to claim 1 or 2 has a structure provided with the optical scanning means for scanning the light emitted the laser light source with respect to the inspection object. The gas detection device according to claim 3 , wherein a concentration distribution of the filling gas in the inspection object is obtained. The gas detection apparatus according to claim 4 , wherein the concentration distribution is visualized and displayed on a display unit. The inspection object is a food package of a gas filling and packaging, in the any one of claims 1 to 5 and capable of emitting structure emitted light of the laser light source to the food package being conveyed by the conveying means The gas detection apparatus as described.

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