JP6006901B1 - metal detector - Google Patents

Abstract

An object of the present invention is to reduce the occurrence of erroneous detection due to sudden external factors at a low cost with a simple configuration in a metal detector equipped with a magnetic bias type metal sensor. A transfer unit for transferring an object to be inspected, a magnetic bias type metal sensor having a permanent magnet attached to a sensor coil, an amplifying means for amplifying a detection signal from the metal sensor, and predetermined control. A white noise waveform signal in a metal detector 1A that includes a control unit 2A having a control unit that performs detection and detects and detects a metal foreign object in the inspection object 50 that moves on the conveyance unit 3 with the metal sensor 10A. A white noise excitation power supply 15 that outputs an excitation current is provided, and the sensor coil 10A is pre-excited with an excitation current having a strength corresponding to the magnetic noise caused by the installation site environment assumed to be a cause of erroneous detection. Thus, the detection signal due to magnetic noise that has entered from the outside is reduced to a level at which it is not detected as a metallic foreign object. [Selection] Figure 2

Description

  The present invention relates to a metal detector for detecting a metallic foreign object of a magnetic substance mixed in a product or the like, and in particular, it is possible to reduce the occurrence frequency of false detection due to magnetic noise caused by an installation environment or sudden external factors. It relates to a metal detector.

  As a technique for detecting magnetic metal foreign matter mixed in products such as foods and pharmaceuticals, a metal detector that detects a metal foreign matter with a core sensor in which a conductive wire is wound around an E-type core of a ferromagnetic material is known. For example, when a magnetic bias type metal sensor 10A in which a permanent magnet (bias magnet) 14 and a core sensor 11 are combined as shown in FIG. When the magnetic foreign material 100 passes through the magnetic material structure, the magnetic material is magnetized and the static magnetic field structure composed of the upper and lower sensors fluctuates due to the magnetic field, and each sensor changes its variation. Therefore, a compact metal detector can be realized at a low cost with a simple configuration.

  That is, when the metal foreign object 100 is mixed in the inspection object, the metal foreign object 100 is magnetized by the permanent magnet 14 while moving in front of the metal sensors 10A and 10A at the same speed as the inspection object together with the conveyor belt 30. Therefore, the static magnetic field structure by the metal sensor 10A, 10A in which the magnetic body and the magnetic field by the magnetic substance face each other is instantaneously changed, and the change is detected by the core sensor 11 as a foreign substance signal.

  However, when the object to be inspected is covered with an electrically conductive packaging container or packaging bag such as aluminum foil, an eddy current magnetic field is generated while generating an eddy current in the packaging part according to the passing speed in the magnetic field. Therefore, there is a problem that it causes a false detection. In addition, the magnetic bias type metal sensor has a characteristic in which the permanent magnet 14 is in close contact with the side surface of the E type core sensor 11 and has a characteristic of sensitively detecting magnetic noise in the vicinity of the sensor. It also has the disadvantage of high frequency of occurrence.

  In response to such a problem, the inventors of the present application disclosed in Japanese Patent No. 5779273 that the detection magnetic field generated by the sensor coil so as to overlap the magnetic field of the bias magnet is at the same level as the assumed eddy current magnetic field. Has proposed a metal sensor that can cancel an eddy current generated in an aluminum packaged product by using a magnetic field having an antiphase with a frequency of 1 or an alternating magnetic field with a predetermined strength and a predetermined magnification.

  However, in facilities that inspect metal foreign objects such as food production factories, flashing of glow starter type fluorescent lights, starting and stopping of water supply and drainage pumps, ON / OFF operations of inverters and solenoid valves for air conditioning, electromagnetic contactors, vacuum cleaners, Magnetic noise due to the installation environment with multiple frequencies and multiple magnetic strengths is frequently generated due to the start / stop of the filling machine, stirrer and various control motors. Although it is considered as one of the main causes of the erroneous detection that occurs, the erroneous detection cannot be sufficiently reduced even by using the technique described above.

  On the other hand, Japanese Patent Laid-Open No. 2008-218729 discloses a detection area of a metal sensor by providing an inner wall projecting duct and an outer wall projecting duct at an opening of a magnetic shield box that covers a metal sensor of a metal detector. A technology has been proposed that attempts to reduce the frequency of false detections by creating a situation that is difficult to enter.

  However, even with this technique, it is impossible to completely shut out external noise as long as there is an opening in the shield box, and the provision of such a shield box complicates and increases the size of device manufacturing. As a result, the cost increases.

  Furthermore, in addition to the magnetic noise caused by the installation environment described above, in addition to the eddy current magnetic field generated in the inspection object itself of the aluminum packaging and high concentration electrolyte solution, what causes the false detection in the metal detector, Since there are many external factors that are difficult to predict, such as external lightning, it is extremely difficult to deal with most of these external factors with one noise countermeasure.

Japanese Patent No. 5779273 JP 2008-218729 A

  The present invention is intended to solve the above-described problems, and a metal detector including at least one magnetic bias type metal sensor is a sudden occurrence in which a plurality of frequencies and a plurality of magnetic strengths are mixed. An object of the present invention is to reduce a false detection signal generated by magnetic noise due to an external factor at a low cost with a simple configuration.

  Therefore, the present invention performs a predetermined control with a conveying means for conveying an object to be inspected, a magnetic bias type metal sensor having a permanent magnet attached to a sensor coil, and an amplifying means for amplifying a detection signal from the metal sensor. A white noise excitation power supply means for outputting an excitation current based on a white noise waveform signal in a metal detector for detecting a metal foreign object in an object to be inspected moving on a conveying means by the metal sensor. The sensor coil has entered from the outside by pre-exciting the sensor coil with the excitation current having a strength corresponding to the magnetic noise caused by the installation site environment that is assumed to be a cause of erroneous detection. The detection signal due to magnetic noise is reduced to a level at which it is not detected as a metal foreign object.

  In this way, by exciting the sensor coil with the excitation current based on the white noise waveform signal with the intensity set according to the magnetic noise that is expected to occur in the installation environment of the metal detector, in the wide frequency range. The sensor will operate stably, and the detection signal due to the predetermined magnetic noise (magnetic noise caused by the installation environment) assumed to occupy most of the causes of erroneous detection is suppressed to a level at which no erroneous detection occurs. Therefore, it is possible to effectively reduce the occurrence of false detection due to magnetic noise without increasing the size and cost of the apparatus.

  Further, in this metal detector, if the input intensity of the excitation current from the white noise excitation power supply means to the sensor coil is 100 to 700 mVp-p, the detection accuracy of the metal foreign object is not lowered. Therefore, it is possible to cope with various types of magnetic noise including magnetic noise derived from various devices and apparatuses using a commercial power source.

  In this case, if the excitation current input intensity is set so as to form a voltage waveform having a level equivalent to one third of the waveform of the detection signal before the expected reduction of magnetic noise, it is practical. Therefore, the occurrence of false detection can be significantly reduced while ensuring the correct detection accuracy.

  Further, in the above-described metal detector, the detection signal from the sensor coil is used to determine the presence or absence of metal foreign objects and / or display the waveform with the white noise waveform signal component removed. If it is characterized by the fact that the foreign signal becomes clear by removing the white noise component in the amplification process of the detection signal, it is high while enhancing the resistance to the surrounding magnetic field by excitation with white noise. The detection accuracy can be ensured.

  Furthermore, in the above-described metal detector, the metal sensor is of a magnetic bias type in which the conveyance path of the object to be inspected by the conveyance means is opposed to the upper side and the upper side is a magnetic bias type in which a permanent magnet is attached to the sensor coil. If the lower side is not provided with a permanent magnet, the magnetic fine powder existing in the vicinity of the lower sensor is solidified by the magnetic attraction force of the permanent magnet while being transported ( The erroneous detection peculiar to the magnetic bias type metal sensor due to the movement of the sensor surface in a state of being attached to the conveyor belt) does not occur.

  According to the present invention, a detection signal due to magnetic noise is corrected to a state where no erroneous detection occurs by exciting a sensor coil with a white noise excitation power source corresponding to an assumed magnetic noise. It is possible to reduce the occurrence of false detection due to the low cost with a simple configuration.

(A) is a top view of the metal sensor which is 1st Embodiment in this invention, (B) is the longitudinal cross-sectional view expanded by the AA of (A). It is a front view of the metal detector which has arrange | positioned the metal sensor of FIG. It is a front view which shows the application example of the metal detector of FIG. It is a functional block diagram of the metal detector of FIG. It is a longitudinal cross-sectional simulation figure which shows the state of the magnetic field by the metal sensor of the metal detector of FIG. FIG. 5 is a drawing-substituting photograph showing an oscilloscope waveform of a detection signal by a metal detector in the functional block diagram of FIG. The waveform at TP_1 when a metallic foreign object is detected in the state, and the lower part is a waveform at OUT_1 amplified by removing the white noise component from the middle part waveform. In the functional block diagram of the metal detector of FIG. 4, when the magnetic bias sensor coil is not excited with white noise and excessive magnetic noise is generated in the vicinity of the sensor, the oscilloscope waveform substitute photograph is shown above. The waveform at TP_1 is shown below, and the waveform at OUT_1 is amplified by removing the white noise component. FIG. 5 is a drawing-substituting photograph showing an oscilloscope waveform of a detection signal when an excessive magnetic noise is generated near the sensor while exciting the magnetic bias sensor coil with white noise in the metal detector of the functional block diagram of FIG. Is the waveform at TP_1, and the bottom is the waveform at OUT_1 amplified by removing the white noise component. It is a longitudinal cross-sectional simulation figure which shows the state of the magnetic field by a magnetic bias type metal sensor for both the upper and lower sensors.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. White noise (white noise) is a noise having the same intensity at all frequencies, and is a wave that oscillates up and down irregularly. In the present invention, white noise includes pink noise. Shall be included.

  FIG. 1A is a plan view of a metal sensor 10A disposed in a metal detector 1A according to an embodiment of the present invention, and FIG. 1B shows a cross-sectional view along the line AA. The metal sensor 10A includes a sensor coil 11 in which a conductive wire 13 is wound around a core 12 having an E-shaped cross section formed by stacking thin electromagnetic steel plates into a bar shape, and a magnetic field attached to a side surface of the sensor coil 11. Is a magnetic bias type sensor including a permanent magnet 14 that magnetizes a metal foreign object, but changes caused by the metal foreign object passing through a magnetic field (static magnetic field) formed by the permanent magnet 14. Is detected by the sensor coil 11.

  FIG. 2 shows a metal detector 1A including the metal sensor 10A of FIG. This metal detector 1A is arranged on the lower surface side of the conveyor belt 30 in the middle of a conveyance path by the conveyance unit 3 and a conveyance unit having a conveyor belt 30 that operates in an endless loop orbit by driving a motor 4. A detection unit (not shown) having the metal sensor 10A and a control unit 2A having a microcomputer 20A for executing various controls including determination of contamination of metal foreign matter. After the detection by the sensor 7, the microcomputer 20 </ b> A is configured to determine whether there is a metal foreign object based on a signal detected when passing over the metal sensor 10 </ b> A.

  The metal detector 1A according to the present embodiment includes a white noise excitation power supply 15 (see FIG. 4) that outputs an excitation current based on a predetermined white noise waveform signal. When the sensor coil 11 is excited in advance, the sensor stably operates in a wide frequency range, and a detection signal due to magnetic noise caused by an installation environment that suddenly enters from the outside and causes false detection is detected by a metal foreign object. This is a characteristic part in the present invention.

  That is, the magnetic bias type metal sensor 10 </ b> A has a characteristic capable of detecting a metal foreign object without exciting the sensor coil 11, but the permanent magnet 14 is closely attached to the sensor coil 11. As described above, there is a problem that the sensor coil 11 sensitively detects magnetic noise suddenly generated from devices / equipment arranged in the surrounding area and easily causes erroneous detection.

  In response to this problem, the inventors of the present invention are resistant to magnetic noise that adversely affects the magnetic field structure of the static magnetic field by exciting the sensor coil 11 in advance with a white noise waveform signal of a predetermined level and moving it in the stable region of the sensor. As a result, it has been found that the occurrence frequency of erroneous detection can be remarkably reduced, and thus the configuration as described above has been adopted.

  As the input intensity of the excitation current by the white noise excitation power supply 15, the result of the experiment carried out by the inventors of the present application mainly focuses on the one derived from a device using a commercial power supply without reducing the detection accuracy of metal foreign matter. In order to deal with most of the magnetic noise, it has been found effective to set in the range of 100 to 700 mVp-p. In addition to this, it is preferable that the input intensity can be adjusted within the range according to the type and level of magnetic noise assumed at the installation site.

  Specifically, with respect to magnetic noise that is expected to occur frequently in the environment where the metal detector 1A is installed, a waveform having the same level as one third of the detected waveform before reduction is formed and detected. By adjusting the input intensity of the excitation current so that the waveform is smaller than the detection waveform before reduction due to the metallic foreign object assumed as the target, the occurrence of false detection is remarkable while ensuring practical detection accuracy. It will be possible to reduce it.

  Further, with respect to the detection signal from the sensor coil 11, in the amplification process or the like, the white noise waveform signal component is removed by a predetermined white noise removing means, and the presence / absence of metal foreign matter is detected and / or the waveform is displayed. Recommended. In other words, by removing the white noise component from the detection signal, the metal foreign object signal appears clearly and a high-accuracy determination is possible. Therefore, even if the tolerance to magnetic noise is enhanced by excitation with white noise, the detection accuracy This is because it is difficult to cause a decrease in the temperature.

  FIG. 3 shows a metal detector 1B as an application example of the above-described metal detector 1A, and FIG. 4 shows a functional block diagram thereof. The metal detector 1B has the same basic configuration and function as the metal detector 1A, but the metal sensors 10A and 10B sandwich the conveyance path of the inspection object 50 in the conveyance unit 3 from above and below. The magnetic bias type metal sensor 10A is disposed opposite to each other, and the upper side is provided with a permanent magnet 14 on the sensor coil 11, and the lower side is the metal sensor 10B including only the sensor coil 11 provided with no permanent magnet. It is a feature.

  Referring to the functional block diagram of FIG. 4, this metal detector 1B is configured so that the metal sensors 10A and 10B arranged vertically opposite to each other are excited by the white noise excitation power supply 15 and the detection signals from them are transmitted to the control unit 2B. Amplification is performed by a plurality of amplifiers arranged inside, and input to the microcomputer 20B via a low-pass filter, thereby determining the presence or absence of metallic foreign matter.

  FIG. 5 shows a simulation analysis of the magnetic field structure by the pair of metal sensors 10A and 10B in the above-described metal detector 1B. The interval between the metal sensors 10A and 10B arranged opposite to each other is set to 80 mm, but the magnetic lines of force of the permanent magnet 14 attached to the upper metal sensor 10A have an influence on the lower metal sensor 10B. It turns out that it is in the state which can detect the metal foreign material which passes a part.

  And by providing the permanent magnet 14 only on the upper side of the metal sensors 10A and 10B, it is possible to reduce the occurrence of erroneous detection due to external vibration. Further, since the permanent magnets 14 are arranged so as to be lifted up to the height, the magnetic fine powder existing in the vicinity of the lower sensor is attracted to the sensor by the magnetic attraction force and is attached to the conveyor belt 30 while being hardened. The false detection peculiar to the magnetic bias type sensor due to the movement of the surface does not occur.

  Next, the present invention will be described in more detail with reference to an embodiment using an actual metal detector. The metal detector used has the same configuration and function as the metal detector 1B described in FIGS. 3 and 4, and the distance between the upper and lower metal sensors is 80 mm, the belt conveyance speed is 40 m / min, and the amplification is performed. The rate was 1000 times to 20,000 times. Further, TSG-109C manufactured by Tamagawa Electronics Co., Ltd. was used as a white noise excitation power source, and excitation was performed with an output intensity of 500 mVp-p (-6 dB).

  The upper part of FIG. 6 shows the waveform of the white noise excitation power supply voltage TP_0 applied to the magnetic bias sensor coil. It is a waveform at OUT_1 amplified by removing components. Thus, it can be seen that the detection signal of the metallic foreign object is clarified by removing the white noise component from the detection signal of the sensor coil excited by the white noise.

  FIG. 7 shows a waveform when the upper metal sensor (magnetic bias sensor) is amplified without being excited, and magnetic noise due to ON / OFF operation of the glow lamp type fluorescent lamp in the state is given in the vicinity of the sensor. The upper side is the output waveform of the first-stage amplifier, and the lower side is the waveform of the output (detection signal). In this case, it can be seen that the lower output is greatly affected by the magnetic noise (determination of the presence of foreign matter in this signal).

  FIG. 8 shows a waveform when the upper metal sensor is excited by white noise to be amplified, and magnetic noise due to ON / OFF operation of the glow lamp type fluorescent lamp is applied a plurality of times in the same manner as described above. . In this case, even if magnetic noise intrudes, the influence is suppressed to a relatively small level and the output on the lower side is stable. It can be seen that the resistance to sudden magnetic noise is enhanced by white noise excitation (this signal Then, it is determined that there is no foreign object.

  From the above, by using the metal detector 1B having the simple configuration as described above, the occurrence of erroneous detection due to the magnetic noise derived from a fluorescent lamp, which is considered to occupy a large number of causes of erroneous detection, is effectively achieved. It was found that it can be avoided. In addition, the metal detector 1B according to the present embodiment adjusts the output intensity of the white noise excitation power source appropriately according to the assumed magnetic noise mode, so that most of the magnetic noise that can cause false detection. The same effect can be expected for.

  Therefore, according to the present invention, it is possible to effectively reduce the occurrence of erroneous detection due to various causes while ensuring high detection accuracy without incurring an increase in the size of the apparatus or an increase in cost. In the configuration of the above-described embodiment, it has been experimentally found that there is an effect of reducing the eddy current generated in the aluminum packaging material, and it is extremely effective in reducing the occurrence of false detection caused by the eddy current. It is.

  As described above, the present invention makes it possible to reduce the occurrence of erroneous detection due to sudden external factors at a low cost with a simple configuration for a metal detector equipped with a magnetic bias type metal sensor. .

  1A, 1B metal detector, 2A, 2B control unit, 3 transport unit, 10A, 10B metal sensor, 11 sensor coil, 12 core, 13 conductor, 14 permanent magnet, 15 white noise excitation power supply, 20A, 20B microcomputer, 50 covered Inspection object, 100 metal foreign matter

Claims (5)

  Conveying means for conveying an object to be inspected, a magnetic bias type metal sensor having a permanent magnet attached to a sensor coil, an amplifying means for amplifying a detection signal from the metal sensor, and a control means for performing predetermined control The metal detector for detecting and notifying the metal foreign object in the object to be inspected moving on the conveying means by the metal sensor comprises a white noise excitation power supply means for outputting an excitation current based on a white noise waveform signal. By pre-exciting the sensor coil with the excitation current having a strength corresponding to the magnetic noise caused by the installation site environment that is supposed to cause false detection, the magnetic noise that has entered from the outside A metal detector characterized in that the detection signal is reduced to a level at which it is not detected as a metal foreign object.   2. The metal detector according to claim 1, wherein an input intensity of the excitation current from the white noise excitation power supply unit to the sensor coil is 100 to 700 mVp-p.   The said input intensity is set so that the voltage waveform to 1/3 equivalent level waveform by the detection signal before the reduction | decrease of the said magnetic noise to be assumed may be formed. Metal detector.   The detection signal from the sensor coil is configured such that the presence or absence of the metal foreign object and / or the waveform display are performed in a state where the component of the white noise waveform signal is removed. Item 4. The metal detector according to item 1, 2 or 3.   The metal sensor is disposed so as to sandwich the conveyance path of the inspection object by the conveyance means from above and below, the upper side is a magnetic bias type in which a permanent magnet is attached to the sensor coil, and the lower side is the above-described The metal detector according to claim 1, 2, 3, or 4, wherein a permanent magnet is not attached.