JP5431792B2 - Foreign object detection method - Google Patents

Description

  The present invention relates to a foreign matter detection method and a foreign matter detection system, for example, to a technique for detecting a foreign matter contained in a measurement object using a high frequency signal such as a microwave.

  In a production line for sheets, films, etc., foreign matters such as metal pieces may adhere to or mix in products due to equipment, ambient environment, production process, or the like. Therefore, attempts have been made to prevent the outflow of defective products and improve quality control by providing a clean room in the production line or inspecting for the presence of foreign matter by installing an inspection device.

  For the detection of foreign matter, a measurement technique using a high-frequency signal such as a microwave may be used. As an example of such a measurement technique, a reflection method for measuring a reflected wave of a measurement object, a resonator method using a resonator, and the like are known (for example, Patent Documents 1 to 3 below).

JP-A-10-185839 JP 63-45547 A JP 62-124449 A

  When trying to detect foreign matter such as metal particles contained in a measurement object such as a sheet or film by the reflection method, the size of the detectable foreign matter (in other words, detection sensitivity) is the wavelength of the high-frequency signal used for measurement. Depends on. For example, the reflection method is said to be able to detect foreign matters having a size of about 1/360 of the wavelength (for example, about 100 μm at 9 GHz). On the other hand, in the resonator method, for example, a sample is inserted into the resonator, and the resonance frequency and the Q value (an index representing the sharpness of resonance) are measured. In the resonator method, the detection sensitivity tends to be higher than that in the reflection method. However, for example, when trying to measure the resonance frequency or the Q value itself, signal processing such as numerical analysis may be complicated.

  Accordingly, one of the objects of the present invention is to improve the detection sensitivity of foreign matters contained in a measurement object. Another object of the present invention is to facilitate detection processing.

  In addition, the present invention is not limited to the above-described object, and other effects of the present invention can be achieved by the functions and effects derived from the respective configurations shown in the embodiments for carrying out the invention which will be described later. It can be positioned as one of

  One aspect of the foreign matter detection method of the present invention includes a process of inputting a signal having a frequency different from the resonance frequency of the cavity resonator to the cavity resonator, and a change in the signal output through the cavity resonator. And detecting a foreign substance contained in a sheet-like measurement object located in the cavity resonator.

  Here, the cavity resonator has a slit-shaped through-hole through which the sheet-shaped measurement object can pass through the cavity resonator, and the sheet-shaped measurement object is in the detection process, You may make it convey so that the inside of the said cavity resonator may pass continuously through the said penetration part.

  Further, the frequency different from the resonance frequency may be a frequency corresponding to an inflection point of a frequency versus transmittance characteristic of a signal that has passed through the cavity resonator.

  Furthermore, the measurement object may have a constant cross-sectional shape.

  The signal input to the cavity resonator is a mixed signal of a plurality of signals having a frequency different from the resonance frequency and different from each other, and the change in the signal is detected for each of the plurality of signal components. It is good as it is.

  Furthermore, after passing through the first cavity resonator, the sheet-like measurement object passes through the second cavity resonator having the same resonance frequency as the resonance frequency of the first cavity resonator. The first cavity resonator receives a first signal having a frequency different from the resonance frequency, and the second cavity resonator has a frequency different from the resonance frequency. A second signal having a frequency different from that of the first signal is input, and the change in the signal is performed for each signal that has passed through the first and second cavity resonators. It may be detected.

  In addition, the sheet-like measurement object passes through the first cavity resonator and then has a second resonance frequency that is different from the first resonance frequency of the first cavity resonator. A signal having a frequency different from the first and second resonance frequencies is commonly input to the first and second cavity resonators, and The change in the signal may be detected for each signal that has passed through the first and second cavity resonators.

  Further, the sheet-like measurement object is conveyed so that the through portions of adjacent cavity resonators sequentially pass through a plurality of cavity resonators arranged non-parallel to each other on the measurement object conveyance path. It may be that.

  In addition, a frequency component that is determined according to the conveyance speed of the measurement object and changes over a long time compared with the time required for the foreign matter to pass through the cavity resonator passes through the cavity resonator. The frequency of the signal input to the cavity resonator may be controlled so as to be separated from the output signal and to minimize the fluctuation of the separated frequency component signal.

  ADVANTAGE OF THE INVENTION According to this invention, the detection sensitivity of the foreign material contained in a measuring object can be improved. In addition, the detection process can be facilitated.

It is a mimetic diagram showing an example of a foreign substance detection system concerning one embodiment. It is a perspective view which shows typically the external appearance of the sensing unit illustrated in FIG. It is a schematic diagram explaining the foreign material detection principle using a cavity. It is a graph which illustrates the relationship between the size of a foreign material, and the change of a resonance state. It is a frequency-transmittance characteristic diagram explaining the change of the resonance state by a foreign material. It is a figure which shows the time series data which are an example of the detection result by the system illustrated in FIG. It is a figure which shows the time series data which are an example of the detection result by the system illustrated in FIG. It is a figure which shows the time series data which are an example of the detection result by the system illustrated in FIG. 2 is a graph illustrating the relationship between the foreign substance equivalent size and the S / N ratio in order to explain the detection sensitivity of the system illustrated in FIG. 1. (A)-(c) is a figure explaining an example of the signal processing with respect to the detection result (time series data) by the system illustrated in FIG. (A)-(c) is a figure explaining an example of the signal processing with respect to the detection result (time series data) by the system illustrated in FIG. It is a figure explaining complementation of detection sensitivity distribution by the system illustrated in FIG. FIG. 6 is a schematic plan view illustrating a modification of the system illustrated in FIG. 1. FIG. 6 is a schematic plan view illustrating a modification of the system illustrated in FIG. 1. FIG. 6 is a schematic plan view illustrating a modification of the system illustrated in FIG. 1.

  Embodiments of the present invention will be described below with reference to the drawings. However, the embodiment described below is merely an example, and there is no intention to exclude various modifications and technical applications that are not explicitly described below. In other words, the present invention can be implemented with various modifications (combining the embodiments, etc.) without departing from the spirit of the present invention. In the following description of the drawings, the same or similar parts are denoted by the same or similar reference numerals. The drawings are schematic and do not necessarily match actual dimensions and ratios. In some cases, the dimensional relationships and ratios may be different between the drawings.

(System configuration example)
FIG. 1 is a schematic diagram illustrating an example of a foreign object detection system according to an embodiment. The foreign object detection system shown in FIG. 1 exemplarily includes a sensing unit 10 including a cavity (cavity resonator) 11, a network analyzer 20, and a personal computer (PC) 30 as an example of an information processing apparatus. The system can also include, for example, a transfer device 40, a movable stage 50, a take-up motor controller 60, and the like.

  The cavity 11 exemplarily has a structure in which both ends of a waveguide having a rectangular cross-sectional shape are closed with a conductive plate 123 having a hole at the center as an input / output opening for a high frequency signal such as a microwave. It is a square cavity resonator. The cavity 11 introduces (inputs) a high-frequency signal such as a microwave through a hole opened in the central portion of the plate 123, so that a resonance wave such as a TE mode or a TM mode is generated at a specific frequency (resonance frequency). Designed to occur. The cavity 11 may be a standardized size such as WRJ-9 or WRJ-10, or a unique size. A plate 123 having a hole in the center is calibrated by a conductive plate having a certain thickness larger than the cross-sectional shape of the waveguide, preferably a metal plate, and a coaxial waveguide described later with the flange portion 111 of the cavity 11. It is fixed in a state of being sandwiched between the tube converter 12.

  As the high-frequency signal, for example, a microwave signal in the range of several GHz to several tens GHz can be used. The high-frequency signal can be input from an input opening (not shown) provided at one end in the longitudinal direction (X-axis direction in FIG. 1) of the cavity 11 and is output at the other end. A high-frequency signal that has passed through the cavity 11 can be derived (output) from a section (not shown). The introduction of the high-frequency signal into the cavity 11 and the derivation from the cavity 11 can be performed, for example, by using the coaxial waveguide converters 12 provided at both ends in the longitudinal direction of the cavity 11.

  Each of the coaxial waveguide converters 12 performs transmission path conversion between a signal transmission line such as a coaxial cable and the waveguide transmission path. Illustratively, the coaxial waveguide converter 12 is provided with a connector 121 to which a coaxial cable 80 capable of transmitting a high-frequency signal such as a microwave can be connected. Are connected to the network analyzer 20 at one end.

  The connection between the cavity 11 and each coaxial waveguide converter 12 is, for example, as shown in FIG. 2 which is a schematic perspective view of the sensing unit 10 and flange portions 111 provided at both ends in the longitudinal direction of the cavity 11. The flange portion 122 provided in the coaxial waveguide converter 12 can be joined to each other with a plate 123 having a hole in the center portion. The joining can be performed by, for example, a screw.

  As a non-limiting example, in FIG. 2, the size of the cavity 11 is 10 mm (width) × 20 mm (height) × 80 (length) mm, and the sizes of the flange portions 111 and 122 are 10 mm (thickness) ×. 42 (width) mm × 42 mm (length), and the size of the coaxial waveguide converter 12 excluding the flange portion 122 is expressed as about 10 mm (width) × 20 mm (height) × 40 mm (length). . Further, the plate 123 having a hole in the center is a copper plate, has the same area on the surface in contact with the flange 122, has a thickness of 1 mm, and the size of the hole in the center is 4 mm to 7 mm.

  As illustrated in FIG. 1 and FIG. 2, slit-like penetrating portions 110 (hereinafter simply referred to as “slits 110”) are provided on opposite side surfaces of the cavity 11 except for the longitudinal ends. Yes.

  The slit 110 has a size that allows a sheet-like measurement object 70 such as a film to be introduced into the cavity 11 and pass therethrough. For example, if the measurement object 70 is a belt-like sheet or film, the width is 50 to 60 mm, and the film thickness is about several tens of μm to several hundreds of μ, as illustrated in FIG. It can be set to about 70 mm × 1 mm.

  When the measurement object 70 is a continuous belt-like sheet or film (sheet-like continuous body) having a predetermined length, the measurement object 70 passes through the cavity 11 continuously in one direction through the slit 110. The measuring object 70 can be moved to the position. By the movement, it is possible to continuously change the measurement target region by the cavity 11 of the measurement target 70.

  The measurement object 70 can be moved by the transport device 40, for example. For example, the transport device 40 can transport the measurement object 70 continuously through the slit 110 using a winding mechanism such as a roller that is rotationally driven by a winding motor. At that time, the transport device 40 applies tension within a range that does not damage the film 70 so that the measurement object 70 (at least the measurement target region) passing through the cavity 11 does not bend or wrinkle. Can do. The transport direction can be reversed at an appropriate timing by appropriately reversing the rotation direction of the take-up motor, for example. The transport direction can be controlled by giving a predetermined control signal from the PC 30 to the transport device 40, for example.

  The relative positional relationship between the conveyance path of the measurement object 70 and the slit 110 can be adjusted by controlling one or both of the position of the conveyance device 40 (roller) and the position of the cavity 11. For example, in FIG. 1, the adjustment is made possible by providing the sensing unit 10 on the movable stage 50 that can move in at least one of the X, Y, and Z directions. The movable stage 50 can be driven (moved) by, for example, the movable stage drive mechanism 51. The movable stage drive mechanism 51 can be controlled by the PC 30, for example. The movable range of the movable stage 50 can be about ± 20 cm for each axis, for example.

  The speed at which the measurement object 70 passes through the cavity 11, in other words, the conveyance speed of the measurement object 70 can be adjusted by controlling the winding speed (number of rotations) of the winding motor in the conveyance device 40, for example. It is. The winding speed (conveying speed) can be adjusted in the range of 0 to 100 m per minute, for example, and can be set by the winding motor controller 60, for example.

  The take-up motor controller 60 receives a speed setting value corresponding to an operation by a user such as a system maintainer, and controls the rotation speed of the take-up motor according to the set value. The speed setting value can also be given from the PC 30 by connecting the winding motor controller 60 and the PC 30 so that they can communicate with each other. Further, the speed control function by the winding motor controller 60 may be provided in the PC 30 as an alternative or in addition. In this case, the speed control can be performed from the PC 30.

  The network analyzer 20 is an example of a measuring apparatus that can measure the electrical characteristics of a high-frequency circuit. A high-frequency signal is input to the circuit or element, and the reflection or passage state (for example, amplitude or phase) from the circuit or element is measured. By doing so, it is possible to measure the electrical characteristics of circuits and elements. In this example, the network analyzer 20 includes, for example, a signal source (oscillator) (not shown), and one (input side) coaxial waveguide converter 12 (input) through one coaxial cable 80 (input cable 80a). A high frequency signal can be input to the side converter 12a).

  It is not always necessary to input a high frequency signal using a signal source built in the network analyzer 20. It is also possible to input a high frequency signal using an individual signal source. The signal source may be a multiple signal source that generates a mixed signal obtained by multiplexing (mixing) a plurality of different frequency signals. The multiple signal source can be configured to mix the output signals of a plurality of signal sources by, for example, a mixer. Thereby, the high frequency signal of 1 or several frequency can be input in the cavity 11 through the input side converter 12a.

  On the other hand, the network analyzer 20 converts a high-frequency signal output through the cavity 11 from, for example, the other (output side) coaxial waveguide converter 12 (output side converter 12b) to the other coaxial cable 80. (Output cable 80b) can be received. The reception and measurement of the high-frequency signal output through the cavity 11 does not necessarily have to be performed using the network analyzer 20. Other measurement devices such as a spectrum analyzer and a power meter may receive and measure. As described above, when a high-frequency signal having a plurality of frequencies is used, the signal that has passed through the cavity 11 is separated into a signal of each frequency component by a signal separation means such as a filter and received by one or a plurality of measuring instruments. it can.

  In other words, in the foreign object detection system of this example, the network analyzer 20 is not an essential component. The network analyzer 20 may be used for either or both of the input of the high-frequency signal to the cavity 11 and the reception (measurement) of the high-frequency signal that has passed through the cavity 11, or alternatively or additionally, a spectrum analyzer or power Other measuring devices such as a meter may be used. However, hereinafter, as a non-limiting example, a case where the network analyzer 20 is used to receive a high frequency signal and receive (measure) an output high frequency signal will be described.

  The frequency of the high-frequency signal input into the cavity 11 through the input cable 80a is directly determined by the operation of the network analyzer 20 or the PC 30 that is communicably connected to the network analyzer 20 and the oscillation frequency and / or mixed wave number of the signal source. Or it can change suitably by controlling indirectly (remotely). For connection between the network analyzer 20 and the PC 30, a communication (network) interface such as a USB (Universal Serial Bus) connection or a LAN (Local Area Network) can be used.

  As described above, the network analyzer 20 inputs a high-frequency signal to the cavity 11 and receives a high-frequency signal output through the cavity 11, thereby converting the input / output signal of the cavity 11 into the time domain and / or the frequency. The time series data and / or frequency data (hereinafter may be collectively referred to as “analysis data”) as analysis results can be provided to the PC 30.

  The PC 30 is a computer that can comprehensively control the operation (measurement) of the system of this example, and includes, for example, a display 31, a PC main body 32, and input devices such as a keyboard 33 and a mouse 34. The main body 32 is connected to, for example, a CPU (not shown), a storage device (such as a memory or a hard disk drive (HDD)), and external devices (for example, the network analyzer 20, the take-up motor controller 60, and the movable stage drive mechanism 51) (communication). ) An interface or the like is provided, and each is connected by an internal bus so that they can communicate with each other.

  The storage device of the PC main body 32 can store software used to perform the operation (measurement) of the system of this example, the analysis data, and the like. The CPU performs overall control of signal processing such as foreign object detection processing and numerical analysis by reading out (developing) software and data from the storage device to a memory as a work area as necessary. be able to.

  The software includes numerical analysis software such as MATLAB (registered trademark), which is an abbreviation of “Matrix Laboratory”, and the PC 30 (CPU) uses numerical values such as MATLAB for analysis data obtained by the network analyzer 20. Arithmetic processing using analysis software can be performed. The analysis data obtained by the network analyzer 20 may be provided to the PC 30 as communication data between the PC 30 and the network analyzer 20, or provided to the PC 30 as data recorded on a recording medium such as a USB memory. Also good.

  In addition, the PC 30 (CPU) appropriately records analysis data and calculation processing results on a recording medium such as an internal and / or external HDD, and performs data reading, processing, editing, and the like as necessary, It can be appropriately output (presented to the user) to a display 31 or a printer (printing apparatus) (not shown) which is an example of the device.

(Foreign matter detection processing)
Hereinafter, the foreign object detection processing by the above-described system will be described in detail.

  As illustrated in FIG. 3, a foreign substance, for example, on the XY plane (hereinafter referred to as “detection reference plane”) 112 including a node of a resonance wave generated in the cavity 11 when a high frequency signal is input to the cavity 11. If a conductive substance such as metal particles is present, the electric field strength at that position on the detection reference surface 112 is lowered and becomes constant (for example, the potential becomes zero). Therefore, the electric field intensity distribution on the detection reference surface 112 changes between the case (1) where the conductive substance 71 does not exist and the case (2) where the conductive substance 71 exists, and the resonance state (resonance frequency and Q value) in the cavity 11 Change.

As illustrated in FIG. 4, the change (rate) tends to increase in proportion to the size of a foreign object (one side d when converted to a cubic volume). The vertical axis in FIG. 4 represents the change (rate) [%] as | ω−ω ₀ | / ω ₀ (where ω represents an arbitrary frequency and ω ₀ represents a resonance frequency).

  Therefore, the measurement object 70 is positioned on the detection reference plane 112 in the cavity 11, and the conveyance path of the measurement object 70 is set so that different regions of the measurement object 70 pass through the cavity 11 sequentially. In this case, it is possible to detect that a conductive substance 71 such as metal particles is mixed as a foreign substance in the measurement object 70 passing through the cavity 11 by the change in the resonance state.

Here, the change in the resonance state can be detected as a change in the resonance frequency, for example, as illustrated in FIG. However, the curve 300 represents an example of the frequency versus transmission (transmission) rate characteristic of the high-frequency signal output through the cavity 11 when no foreign substance is present, and the curve 200 is the frequency versus passage when the foreign substance is present. An example of (transmission) rate characteristics is shown. As can be understood by comparing these characteristics 300 and 200, when a foreign substance is present, the resonance frequency (f ₀ ), that is, the frequency at which the transmittance reaches a peak, is represented by f ₀ ′ ( <F ₀ ) and shift to the low frequency side.

The change in the resonance frequency is a specific frequency in the reference characteristic 300 (which can be regarded as the resonance characteristic of the cavity 11), for example, a frequency slightly away from the resonance frequency f ₀ (in FIG. 5, as an example, on the low frequency side). Come to focus on distant frequency) f _1, the change in the resonant frequency f _0, the change in transmittance of the frequency f ₁ of the signal (amplitude intensity), for example changes indicated by the arrow 400 in FIG. 5 (FIG. 5 Will appear as a decrease).

Accordingly, the frequency of the high-frequency signal input from the network analyzer 20 to the cavity 11 is fixed to a frequency f ₁ different from the resonance frequency f _{0 of} the cavity 11, and the transmittance (amplitude) of the frequency f ₁ component output from the cavity 11. ) Periodically (that is, in the time domain) with the network analyzer 20 (for example, sampling), it is possible to detect a change in the resonance frequency equivalently. In this case, the time change of the transmittance when the measurement object 70 continuously passes through the cavity 11 can be obtained as the time-series data described above.

That is, the network analyzer 20 of this example functions as an example of an input device that inputs a signal having a frequency f ₁ different from the resonance frequency f ₀ of the cavity 11 to the cavity 11, and cooperates with the PC 30 to provide the cavity 11. It functions as an example of a detection device that detects a foreign substance contained in the measurement object 70 located in the cavity 11 based on a change in a signal output through the inside. Note that these functions may be realized in different devices.

According to the detection method described above, a change in the resonance frequency f ₀ can be detected more easily than when monitoring in the frequency domain. As shown in a modification example to be described later, when a plurality of different resonance frequencies are used, it is difficult to specify which resonance frequency is changed in the frequency domain. It can be said that monitoring is more advantageous. In other words, as long as data representing the temporal change of the transmittance can be obtained, the function as the detection device does not necessarily have to be realized using the network analyzer 20 as described above. For example, a cheaper measuring device such as a spectrum analyzer or a power meter may be used.

The frequency f ₁ has a transmittance change 400 larger between the frequency vs. transmittance characteristic 300 in the absence of foreign matter and the frequency vs. transmittance characteristic 200 in the presence of foreign matter compared to other frequencies. It is preferable to set the frequency, for example, a frequency corresponding to the inflection point of the characteristic 300 or the vicinity thereof. As a non-limiting example, the frequency is 8.278 GHz with respect to the resonance frequency of 8.27911 GHz. If the frequency is set to such a frequency, the foreign substance detection sensitivity can be improved as compared with the case where the frequency is set to another frequency. However, since the amount of resonance frequency tends to increase as the foreign matter increases, the output may decrease. In order to cope with this, the frequency f ₁ can be set to a frequency further away from the resonance frequency.

  Note that if the cross-sectional shape of the measuring object 70 in the width direction (X-axis direction) is not constant in the length direction (Y-axis direction), an error may occur in the detection result, so that the cross-sectional shape of the detection object 70 is long. The direction is preferably as constant as possible. However, it may not be constant as long as it is within an allowable detection error range.

FIG. 6 shows an example of time-series data obtained when the frequency f ₁ of the high-frequency signal input to the cavity 11 is constant at 7.39843 GHz. However, the conveyance speed of the measuring object 70 is 9 mm per second. As an example of the foreign matter, conductive (metal) fine particle samples a to h shown in the following Table 1 can be used, and a sample e is used as a representative example.
As a sample of the measuring object 70, for example, a film sample having a width of 8 mm × a length of 280 mm × a thickness of 16 μm or 18 μm can be used, and the conductive fine particle sample was fixed to the film sample with an adhesive or the like.

  In this example, the standard deviation of the amplitude (signal level) in the range indicated by the arrow 600 in FIG. 6 is set as the noise level, and the amplitude (signal level) in the range indicated by the arrow 700 in FIG. The amplitude at the time of detection is set. FIG. 6 illustrates that the amplitude (signal change) exceeding the noise level appears at different timings, and that the presence of a foreign object could be detected at these two locations. In FIG. 6, the detection time of the amplitude exceeding the noise level corresponds to the time required for the foreign object to pass through the cavity 11, for example, the time required to pass through the cavity 11 (width 10 cm) at about 9 mm per second. It corresponds to.

Other detection result examples are shown in FIGS. 7 and 8, respectively. 7 and 8 both show examples of detection results when a polyethylene sheet having a width of 50 mm is used as the measurement object 70, and FIG. 7 uses a conductive fine particle sample having a diameter of 150 μm and a length of 2 mm as a foreign object. FIG. 8 exemplifies a case where a conductive fine particle sample having a diameter of 150 μm × length of 0.3 mm (= 300 μm) is used as the foreign matter. Note that the frequency f ₁ of the input high-frequency signal is set to a constant 8.27634 GHz in any case.

  In either case of FIG. 7 and FIG. 8, the timing at which the signal level (amplitude) exceeding the noise level is obtained can be identified. Therefore, it can be detected that the measurement object 70 (measurement target region) located in the cavity 11 contains the conductive fine particle sample as a foreign substance at the timing.

(Detection sensitivity)
About the detection sensitivity in the above-mentioned detection method, it can represent with the graph shown, for example in FIG. The horizontal axis of the graph represents the foreign substance equivalent size (length of one side when the volume of the foreign substance is converted to the volume of a cube), and the vertical axis represents S / S when the noise level (standard deviation) described above is 1. It represents the N ratio. Symbol ◇ represents the sample value when the frequency of the input high-frequency signal is 7.39843 GHz, symbol □ represents the same frequency of 8.27847 GHz, and symbol Δ represents the sampled frequency when the frequency is 9.37321 GHz.

  From FIG. 9, it can be seen that up to S / N ratio = about 3, it is possible to detect a foreign substance having a foreign substance equivalent size of about 50 μm without performing special processing on the obtained time-series data. Therefore, the detection sensitivity can be improved to the order of several tens of μm in the foreign substance equivalent size. For example, in the production line of the measurement object 70, the presence or absence of minute foreign objects can be reliably and continuously detected on the conveyance path of the measurement object 70. It is possible to detect easily.

  If the obtained time-series data is subjected to signal processing such as filtering or wavelet transform, the S / N ratio can be improved, and a foreign object with a smaller size can be detected. In this example, since the foreign substance passes through the cavity 11 having a specific resonance frequency, the signal waveform to be detected can be uniquely determined, and as a result, signal processing can be facilitated. As an example of filtering, for example, a signal waveform when a foreign object is detected is measured and recorded in advance as time-series data, and a correlation calculation process using the signal waveform as reference data is performed. Such signal processing can be performed by, for example, the PC 30 (CPU).

  10 and 11 show examples of improving the S / N ratio when filtering or wavelet transform is used, respectively. The wavelet transform uses a “coif 1” wavelet filter defined by MATLAB. FIG. 10 shows an example of time-series data when the foreign object equivalent size is 73 μm, and FIG. 11 shows an example of time-series data when the foreign object equivalent size is 156 μm. (Raw data), (b) shows time-series data subjected to filtering, and (c) shows time-series data subjected to wavelet transform. From these FIG. 10 and FIG. 11, it can be seen that the S / N ratio can be improved to about 3 times or more by using filtering or wavelet transform.

(Modification 1)
In the example described above, the frequency of the high-frequency signal input to the cavity 11 is one type. For this reason, a region where detection sensitivity is low or absent (hereinafter, sometimes referred to as “dead zone”) in the width direction (X-axis direction) of the above-described detection reference plane 112 (see FIG. 3). May occur (that is, the sensitivity distribution in the X-axis direction is uneven).

  For example, as shown schematically in FIG. 12, the detection sensitivity in the X-axis direction on the detection reference surface 112 tends to be lower as the position is closer to the position corresponding to the node of the resonance wave, and corresponds to the antinode of the resonance wave. The position closer to the position tends to be higher. Therefore, if there is only one type of frequency of the signal input to the cavity 11, the position corresponding to the node of the resonance wave and the vicinity thereof tend to be a dead zone.

Therefore, in the first modification, as illustrated in FIG. 12, two types (or more) of f ₁₁ and f ₁₂ (f ₁₁ ≠ f ₁₂ ) are used as the frequency of the resonance wave generated in the cavity 11. Use frequency. This makes it possible to compensate at any frequency f ₁₁ or the frequency f ₁₂ or f ₁₁ the deadband different other caused by f _12. Theoretically, as the frequency type is increased, the dead zone in the X-axis direction of the detection reference surface 112 can be reduced to reduce the unevenness of the sensitivity distribution. In other words, even if the sensitivity distribution is uneven, it can be easily dealt with by superimposing a plurality of resonance waves (waves having a relatively simple shape).

  When using a plurality of frequencies in this way, all the frequencies may be input to the same cavity 11 or individually input to the plurality of cavities 11 arranged so that the same measurement object 70 passes continuously. May be.

  In the former case, the timing for inputting the signal of each frequency to the cavity 11 may be the same timing or different timing. To achieve the same timing, for example, a mixed signal obtained by mixing signals of a plurality of types of frequencies in the network analyzer 20 functioning as an example of an input device is used as an input high-frequency signal. In this case, each frequency component included in the output signal of the cavity 11 is separated by, for example, the network analyzer 20 that functions as an example of a detection device, and a signal change (amplitude time change) is observed (detected) for each separated frequency component. Is possible. On the other hand, in order to make the timing different, the time required for the specific region of the measurement object 70 to pass through the same cavity 11 is time-divided, and the frequency of the input high-frequency signal is changed in each time-division slot. Is given as an example.

  On the other hand, in the latter case, that is, when a plurality of cavities 11 are used, the resonance frequencies of some or all of the cavities 11 may be the same or different. For convenience, the resonance frequency may be the same if the shape of the cavity 11 is the same, and the resonance frequency may be different if the shape of the cavity 11 is different. As an example, the case of using two cavities 11 is shown in FIGS.

13 uses two cavities 11 having the same shape and the same resonance frequency (f ₀ ), and FIG. 14 uses two cavities 11 having different shapes and different resonance frequencies (f ₀₁ , f ₀₂ ). Each case is illustrated.

  In any case, the first and second cavities 11 are respectively installed on the conveyance path of the measurement object 70, and the measurement object 70 sequentially passes through each cavity 11 sequentially through the respective slits 110. Is set to

Therefore, in the case of FIG. 13, the measurement object 70, after passing through the first cavity 11, the second cavity 11 having the same resonance frequency f ₀ and having the resonance frequency f ₀ of the first cavity 11 Will pass. On the other hand, in the case of FIG. 14, the measurement object 70 passes through the first cavity 11 and then has a second resonance frequency f ₀₂ that is different from the resonance frequency f ₀₁ of the first cavity 11. It passes through the cavity 11.

In the case of FIG. 13, the network analyzer 20 has a frequency different from the resonance frequency f ₀ of each cavity 11 and different from each other (f ₁₁ and f ₁₂ : f ₀ ≠ f ₁₁ ≠ f ₁₂ ). High frequency signals (first and second signals) are individually input to the individual cavities 11. On the other hand, in the case of FIG. 14, for example, the network analyzer 20 inputs a high-frequency signal having a frequency (f) different from the resonance frequencies f ₀₁ and f ₀₂ of each cavity 11 to each cavity 11 in common.

  In any case, the measurement object 70 sequentially passes through the plurality of cavities 11 and receives electric fields generated by resonance waves having different frequencies at different timings. Accordingly, the dead band of each other frequency can be compensated for at different timings on the detection reference plane 112, and sensitivity unevenness in the width direction (X-axis direction) of the cavity 11 (slit 110), that is, the width direction of the measurement object 70 is reduced. can do.

(Modification 2)
When a plurality of cavities 11 are used, the plan view arrangement of each cavity 11 with respect to the conveyance direction of the measurement object 70 is parallel to the X axis as illustrated in FIGS. 13 and 14 (perpendicular to the conveyance direction of the measurement object 70). For example, as shown in FIG. 15, the arrangement is not parallel to the X axis, in other words, the slits 110 of the adjacent cavities 11 are not parallel to each other on the conveyance path of the measurement object 70. It is good also as arrangement.

  According to the non-parallel arrangement illustrated in FIG. 15, the required time (transport distance) from when the measurement object 70 passes through the first cavity 11 at the front stage to the second cavity 11 at the rear stage. Can be varied depending on the position or region of the measurement object 70 in the width direction (X-axis direction).

  Therefore, if the foreign object detection process using the frequency common to each cavity 11 is performed a plurality of times, for example, in the PC 30, based on the difference in the required time, the position in the width direction of the measurement object 70 in which the signal change is detected or It becomes easy to specify the area. The relationship between the difference in the required time and the position in the width direction of the measuring object 70 can be stored in advance in the PC 30 as map data, for example.

  In the second modification as well, as described in the first modification, a plurality of different frequencies may be used in each cavity 11 for the purpose of reducing the detection sensitivity dead zone.

(Modification 3)
The resonance frequency of the cavity 11 may change due to a change in measurement environment such as a change in ambient temperature. If the resonance frequency of the cavity 11 changes, the above-described foreign object detection accuracy may be reduced. Changes in the measurement environment, such as changes in ambient temperature, are considered to occur over a longer time than the time required for foreign matter to pass through the cavity 11. Note that the time required for the foreign substance to pass through the cavity 11 is determined based on the length of the cavity 11 in the width direction (Y-axis direction) and the conveyance speed of the measurement object 70.

  Therefore, for example, the network analyzer 20 or the PC 30 separates and detects, from the output signal of the cavity 11, the frequency component that changes over a long time compared to the time required for the foreign object to pass through the cavity 11, and detects the frequency component. The frequency of the high-frequency signal input to the cavity 11 is controlled so that the signal fluctuation is minimized. Thereby, even if a change occurs in the measurement environment such as a temperature change and the resonance frequency of the cavity 11 changes, the frequency of the input high-frequency signal can be corrected following the change. Therefore, it is possible to suppress a decrease in detection accuracy.

(Other)
In the above-described embodiment, the foreign object is detected while the measurement object 70 is conveyed by the conveyance device 40 and passed (moved) through the cavity 11, but the measurement object 70 is not moved. In some cases, foreign matter detection is possible. For example, an output signal waveform when the measurement object 70 does not contain foreign matter is recorded as known data in advance, and the data and the actual output signal waveform when the input high-frequency signal is input to the cavity 11 are recorded. In comparison, it is also possible to detect foreign matter contained in the measurement object 70 that has not moved.

10 Sensing unit 11 Cavity (cavity resonator)
12 Coaxial waveguide converter 12a Input side converter 12b Output side converter 20 Network analyzer 30 Personal computer (PC)
31 Display 32 Main body 33 Keyboard 34 Mouse 40 Transport device 50 Movable stage 51 Movable stage drive mechanism 60 Winding motor controller 70 Measurement object 71 Conductive material 80 Coaxial cable 80a Input cable 80b Output cable 110 Penetration (slit)
111 Flange 112 Detection Reference Surface 121 Connector 122 Flange 123 Plate

Claims (6)

A process of inputting a signal having a frequency different from the resonant frequency of the cavity into the cavity;
A process for detecting a foreign substance contained in a sheet-like measurement object located in the cavity resonator based on a change in a signal output through the cavity resonator; and
Have
The cavity resonator has a slit-shaped through portion through which the sheet-like measurement object can pass through the cavity resonator,
The sheet-like measurement object is conveyed so as to continuously pass through the cavity through the penetration part in the detection process,
The frequency different from the resonance frequency is a frequency corresponding to an inflection point of a frequency-transmittance characteristic of a signal that has passed through the cavity resonator,
The measurement object has a constant cross-sectional shape,
The signal input to the cavity resonator is a mixed signal of a plurality of signals having different frequencies, which are different from the resonance frequency and complement each other in regions where detection sensitivity is poor .
The foreign object detection method , wherein the signal change is detected for each of the plurality of signal components.   The plurality of signals having different frequencies are a plurality of resonance waves that are superimposed so that a position corresponding to the antinode of another resonance wave or a vicinity thereof is located at or near a position corresponding to any node of the resonance waves. The foreign matter detection method according to claim 1, comprising: A process of inputting a signal having a frequency different from the resonant frequency of the cavity into the cavity;
A process for detecting a foreign substance contained in a sheet-like measurement object located in the cavity resonator based on a change in a signal output through the cavity resonator; and
Have
The cavity resonator has a slit-shaped through portion through which the sheet-like measurement object can pass through the cavity resonator,
The sheet-like measurement object is conveyed so as to continuously pass through the cavity through the penetration part in the detection process,
After passing through the first cavity resonator, the sheet-like object to be measured passes through the second cavity resonator having the same resonance frequency as that of the first cavity resonator. Conveyed,
A first signal having a frequency different from the resonance frequency is input to the first cavity resonator, and a frequency different from the resonance frequency is input to the second cavity resonator. A second signal having a frequency different from the frequency of the first signal is input; and
The signal changes are detected the first and second cavity resonator for each signal that has passed through each foreign object detection method. A process of inputting a signal having a frequency different from the resonant frequency of the cavity into the cavity;
A process for detecting a foreign substance contained in a sheet-like measurement object located in the cavity resonator based on a change in a signal output through the cavity resonator; and
Have
The cavity resonator has a slit-shaped through portion through which the sheet-like measurement object can pass through the cavity resonator,
The sheet-like measurement object is conveyed so as to continuously pass through the cavity through the penetration part in the detection process,
After the sheet-like object to be measured passes through the first cavity resonator, the second cavity resonance has a second resonance frequency different from the first resonance frequency of the first cavity resonator. Transported to pass through the vessel,
A signal having a frequency different from the first and second resonance frequencies is commonly input to the first and second cavity resonators, and
The signal changes are detected the first and second cavity for each signal that has passed through each foreign object detection method. A process of inputting a signal having a frequency different from the resonant frequency of the cavity into the cavity;
A process for detecting a foreign substance contained in a sheet-like measurement object located in the cavity resonator based on a change in a signal output through the cavity resonator; and
Have
The cavity resonator has a slit-shaped through portion through which the sheet-like measurement object can pass through the cavity resonator,
The sheet-like measurement object is conveyed so as to continuously pass through the cavity through the penetration part in the detection process,
The sheet-like measurement object is conveyed so that the through portions of adjacent cavity resonators sequentially pass through a plurality of cavity resonators arranged non-parallel to each other on the measurement object conveyance path . Foreign object detection method. A process of inputting a signal having a frequency different from the resonant frequency of the cavity into the cavity;
A process for detecting a foreign substance contained in a sheet-like measurement object located in the cavity resonator based on a change in a signal output through the cavity resonator; and
Have
The cavity resonator has a slit-shaped through portion through which the sheet-like measurement object can pass through the cavity resonator,
The sheet-like measurement object is conveyed so as to continuously pass through the cavity through the penetration part in the detection process,
The frequency component, which is determined according to the conveyance speed of the measurement object and changes over a long time compared with the time required for the foreign object to pass through the cavity resonator, is separated from the signal output from the cavity resonator. And
The way variations of the separated frequency component signal becomes minimum, the frequency of the signal input to the cavity resonator is controlled, foreign object detection method.