Signal processing method, signal processing device, and program

Abstract

A signal processing method according to an embodiment of the present invention involves executing: a first process for acquiring a first sensor signal that is a sensor signal measured by a first sensor and that includes a component of a target signal and a component of ambient noise, and a second sensor signal that is a sensor signal measured by a second sensor and that includes a component of the target signal and a component of the ambient noise; a second process for generating a first processed signal obtained by removing, from the second sensor signal, the component of the target signal included in the second sensor signal; and a third process for generating, on the basis of the first processed signal, a second processed signal obtained by removing, from the first sensor signal, the component of the ambient noise included in the first sensor signal.

Description

Technical Field

[0001] The present disclosure relates to a signal processing method, a signal processing apparatus, and a program.

Background Art

[0002] In the field of signal processing, a process of removing components of environmental noise included in a measurement sensor signal from the measurement sensor signal measured by a measurement sensor is performed.

[0003] In the signal processing method described in Patent Document 1, a process of removing noise components from a plurality of measurement signals measured in a state where an information signal and a noise signal are mixed and extracting the information signal is performed (see Patent Document 1). Specifically, in this signal processing method, a plurality of measurement signals at different measurement locations are acquired, the correlation between the plurality of measurement signals is detected, the phase synchronization between the plurality of measurement signals is detected, and uncorrelated components with low correlation and non-phase synchronization components with low phase synchronization are removed from each of the plurality of measurement signals, and a plurality of estimated signals estimated as information signals are output.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in the conventional signal processing method, there are cases where components of environmental noise superimposed on the measurement sensor signal cannot be sufficiently removed.

[0006] For example, the signal processing method described in Patent Document 1 can remove uncorrelated components with low correlation between multiple measurement signals and non-phase-synchronous components with low phase synchronization as noise components, but it could not remove noise components with other characteristics. Specifically, in this signal processing method, it was difficult to effectively remove environmental noise components that have correlation and phase synchronization when they are superimposed on the measurement sensor signal. Furthermore, there is a need for the development of new technologies that can effectively remove environmental noise components superimposed on measurement sensor signals, regardless of whether the environmental noise is correlated or phase-synchronized.

[0007] This disclosure is made in view of the above circumstances and provides a signal processing method, a signal processing device, and a program that can effectively remove environmental noise components superimposed on a measurement sensor signal. [Means for solving the problem]

[0008] As an example configuration, the system performs the following: a first process to acquire a first sensor signal measured by a first sensor, which includes components of the target signal and environmental noise; a second sensor signal measured by a second sensor, which includes components of the target signal and environmental noise; a second process to generate a first processed signal from which the components of the target signal included in the second sensor signal have been removed; and a third process to generate a second processed signal from which the components of the environmental noise included in the first sensor signal have been removed based on the first processed signal. A signal processing method, wherein the second processing involves performing an averaging process on the second sensor signal to generate a template signal for the target signal, and then generating the first processed signal by removing the template signal from the signal portion corresponding to the component of the target signal included in the second sensor signal. This is a signal processing method. As an example configuration, the signal processing method comprises: a first process of acquiring a first sensor signal measured by a first sensor and including components of a target signal and environmental noise, and a second sensor signal measured by a second sensor and including components of the target signal and environmental noise; a second process of generating a first processed signal from which the components of the target signal included in the second sensor signal have been removed; and a third process of generating a second processed signal from which the components of the environmental noise included in the first sensor signal have been removed based on the first processed signal, wherein the first process acquires the first sensor signal and a first sensor signal group which is a group of sensor signals measured by each of a plurality of sensors including the second sensor but not the first sensor, and which include components of the target signal and environmental noise; and the second process generates the first processed signal by performing an averaging process on the first sensor signal group to generate a template signal of the target signal, and removing the template signal from the signal portion corresponding to the components of the target signal included in the second sensor signal. As an example configuration, the signal processing method includes: a first process of acquiring a plurality of sensor signals, each of which is measured by three or more sensors and includes components of a target signal and environmental noise; a second process of generating a first processed signal for each of these plurality of sensor signals, where each of the sensor signals is used as a first sensor signal, and the sensor signals other than the first sensor signals are used as second sensor signals, and the component of the target signal included in the second sensor signal is removed from the second sensor signal; and a third process of generating a second processed signal based on the first processed signal, where the component of the environmental noise included in the first sensor signal is removed from the first sensor signal. The second process is a signal processing method in which an averaging process is performed on a first sensor signal group, which is a group of sensor signals measured by two or more sensors, including the sensor that measured the second sensor signal but not the sensor that measured the first sensor signal, to generate a template signal of the target signal, and the first processed signal is generated by removing the template signal from the signal portion corresponding to the component of the target signal included in the second sensor signal.

[0009] As an example configuration, the system includes: a sensor signal acquisition unit that acquires a first sensor signal measured by a first sensor, which includes components of the target signal and environmental noise; a second sensor signal measured by a second sensor, which includes components of the target signal and environmental noise; a target signal removal unit that generates a first processed signal from which the components of the target signal included in the second sensor signal have been removed; and an environmental noise removal unit that generates a second processed signal from which the components of the environmental noise included in the first sensor signal have been removed based on the first processed signal. The target signal removal unit is a signal processing device that generates a template signal for the target signal by performing an averaging process on the second sensor signal, and generates the first processed signal by removing the template signal from the signal portion corresponding to the component of the target signal included in the second sensor signal. As an example configuration, the signal processing device comprises: a sensor signal acquisition unit that acquires a first sensor signal measured by a first sensor and including components of a target signal and environmental noise, and a second sensor signal measured by a second sensor and including components of the target signal and environmental noise; a target signal removal unit that generates a first processed signal from which the components of the target signal included in the second sensor signal have been removed; and an environmental noise removal unit that generates a second processed signal from which the components of the environmental noise included in the first sensor signal have been removed based on the first processed signal. The sensor signal acquisition unit acquires the first sensor signal and also acquires a first sensor signal group, which is a group of sensor signals measured by each of a plurality of sensors, including the second sensor but not the first sensor, and including components of the target signal and environmental noise. The target signal removal unit generates the first processed signal by performing an averaging process on the first sensor signal group to generate a template signal of the target signal and removing the template signal from the signal portion corresponding to the components of the target signal included in the second sensor signal. As an example configuration, the signal processing device includes: a sensor signal acquisition unit that acquires a plurality of sensor signals, each of three or more sensors, which include a component of the target signal and a component of environmental noise; a target signal removal unit that, for each of the plurality of sensor signals, uses each of the sensor signals as a first sensor signal and the sensor signals other than the first sensor signals as second sensor signals, and generates a first processed signal from which the component of the target signal included in the second sensor signal is removed; and an environmental signal removal unit that, based on the first processed signal, generates a second processed signal from which the component of the environmental noise included in the first sensor signal is removed. The target signal removal unit performs an averaging process on a first sensor signal group, which is a group of sensor signals measured by each of two or more sensors, including the sensor that measured the second sensor signal but not the sensor that measured the first sensor signal, to generate a template signal of the target signal, and generates the first processed signal by removing the template signal from the signal portion corresponding to the component of the target signal included in the second sensor signal.

[0010] As an example configuration, a computer is required to implement the following: a first function that acquires a first sensor signal measured by a first sensor, which includes components of the target signal and environmental noise; a second sensor signal measured by a second sensor, which includes components of the target signal and environmental noise; a second function that generates a first processed signal from which the components of the target signal included in the second sensor signal have been removed; and a third function that generates a second processed signal from which the components of the environmental noise included in the first sensor signal have been removed based on the first processed signal. A program wherein the second function generates a template signal of the target signal by performing an averaging process on the second sensor signal, and generates the first processed signal by removing the template signal from the signal portion corresponding to the component of the target signal included in the second sensor signal. It is a program. As an example configuration, a program for a computer to implement the following: a first function that acquires a first sensor signal measured by a first sensor and including components of a target signal and environmental noise, and a second sensor signal measured by a second sensor and including components of the target signal and environmental noise; a second function that generates a first processed signal from which the components of the target signal included in the second sensor signal have been removed; and a third function that generates a second processed signal from which the components of the environmental noise included in the first sensor signal have been removed based on the first processed signal, wherein the first function acquires the first sensor signal and also acquires a first sensor signal group which is a group of sensor signals measured by each of a plurality of sensors including the second sensor but not the first sensor, and which include components of the target signal and environmental noise; the second function performs an averaging process on the first sensor signal group to generate a template signal of the target signal, and generates the first processed signal by removing the template signal from the signal portion corresponding to the components of the target signal included in the second sensor signal. As an example configuration, a program for a computer to implement the following: a first function that acquires a plurality of sensor signals, each of three or more sensors, which include a component of the target signal and a component of environmental noise; a second function that, for each of these plurality of sensor signals, generates a first processed signal by treating each of the sensor signals as a first sensor signal and the other sensor signals as second sensor signals, and removing the component of the target signal contained in the second sensor signal from the second sensor signal; and a third function that generates a second processed signal based on the first processed signal by removing the component of the environmental noise contained in the first sensor signal from the first sensor signal. The second function is a program that performs an averaging process on a first sensor signal group, which is a group of sensor signals measured by each of two or more sensors, including the sensor that measured the second sensor signal but not the sensor that measured the first sensor signal, to generate a template signal of the target signal, and generates the first processed signal by removing the template signal from the signal portion corresponding to the component of the target signal contained in the second sensor signal. [Effects of the Invention]

[0011] According to the signal processing method, signal processing device, and program described herein, environmental noise components superimposed on the measurement sensor signal can be effectively removed. [Brief explanation of the drawing]

[0012] [Figure 1] This figure shows a schematic configuration example of a foreign object detection system according to an embodiment (first embodiment). [Figure 2] A diagram showing an example of the waveform of a measurement sensor signal (measurement sensor signal a1) according to an embodiment (the first embodiment). [Figure 3] A diagram showing an example of the waveform of a measurement sensor signal (measurement sensor signal a2) according to an embodiment (the first embodiment). [Figure 4] A diagram showing an example of the waveform of an environmental noise signal according to an embodiment (the first embodiment). [Figure 5] A diagram showing an example of the waveform of an environmental noise removal signal according to an embodiment (the first embodiment). [Figure 6] A diagram showing an example of the signal processing procedure performed by a foreign object detection device according to an embodiment (the first embodiment). [Figure 7] A diagram showing an example of a specific example of signal processing performed by a foreign object detection device according to an embodiment (the first embodiment). [Figure 8] A diagram showing an example of a template signal of a target signal according to an embodiment (the first embodiment). [Figure 9] A diagram showing an example of the signal processing procedure using the template signal of the target signal performed by a foreign object detection device according to an embodiment (the first embodiment). [Figure 10] A diagram showing an example of a specific example of signal processing using the template signal of the target signal performed by a foreign object detection device according to an embodiment (the first embodiment). [Figure 11] A diagram showing a schematic configuration example of a foreign object detection device and a sensor unit in a foreign object detection system according to an embodiment (the second embodiment). [Figure 12] A diagram showing an example of the signal processing procedure performed by a foreign object detection device according to an embodiment (the second embodiment). [Figure 13] A diagram showing an example of the signal processing procedure using the template signal of the target signal performed by a foreign object detection device according to an embodiment (the second embodiment). [Figure 14] A diagram showing an example of the signal processing procedure for a plurality of measurement sensor signals performed by a foreign object detection device according to an embodiment (the second embodiment). [Figure 15] This figure shows another example of the configuration of the sensor unit according to the embodiment (second embodiment). [Figure 16] This figure shows a schematic configuration example of the foreign object detection device and sensor unit in the foreign object detection system according to the third embodiment. [Figure 17] This figure shows an example of the signal processing procedure performed by the foreign object detection device according to the embodiment (third embodiment). [Figure 18] This figure shows a specific example of signal processing performed by the foreign object detection device according to the embodiment (third embodiment). [Modes for carrying out the invention]

[0013] This embodiment will now be described in detail with reference to the figures as appropriate.

[0014] (First Embodiment) [Foreign object detection system] Figure 1 is a diagram showing a schematic configuration example of a foreign object detection system 1 according to an embodiment (first embodiment). The foreign object detection system 1 comprises a foreign object detection device 11, a sensor unit 111, a line G1, a line G2, and a belt conveyor 211. Figure 1 also shows the object to be inspected 231 and the foreign matter 251 attached to the object to be inspected 231. Figure 1 also shows 232 other objects to be inspected. Figure 1 also shows the direction H1 in which the belt of the belt conveyor 211 moves. In this embodiment, the object placed on the belt conveyor 211 (in the example of Figure 1, the objects to be inspected 231 and 232) moves in direction H1.

[0015] The foreign object detection system 1 may also be called a signal processing system or the like. Furthermore, the functional part of the signal processing unit 32 of the foreign object detection device 11, or the device including the functional part of the signal processing unit 32 (the whole or a part of the foreign object detection device 11), may also be called a signal processing device or the like.

[0016] In this embodiment, the foreign object detection system 1 includes a belt conveyor 211, but in other configuration examples, the foreign object detection system 1 may be considered as not including a belt conveyor 211. Furthermore, in this embodiment, the foreign object detection system 1 does not include the objects to be inspected 231 and 232, but in other configuration examples, the foreign object detection system 1 may be considered to include the objects to be inspected 231 and 232.

[0017] <Sensor section> The sensor unit 111 is equipped with two measuring sensors A1 and A2. Here, each of the two measurement sensors A1 and A2 may be called a channel or the like. In this embodiment, each of the measurement sensors A1 and A2 is a magnetic sensor that outputs a signal (also called a measurement sensor signal for convenience of explanation) that represents the result of measuring magnetism (magnetic field).

[0018] In this embodiment, each measuring sensor A1 and A2 is located in a place where it is possible to measure the signal that is the target of measurement (for convenience of explanation, also referred to as the target signal). Here, the target signal is the signal that is to be measured. The measured sensor signal includes components of the target signal, sensor noise, and environmental noise. In this embodiment, the measured sensor signal is measured with these components mixed together.

[0019] Here, sensor noise is sensor-specific noise that originates from each sensor itself. In the example shown in Figure 1, sensor noise is generated in measurement sensor A1 due to the measurement sensor A1 itself. Similarly, sensor noise is generated in measurement sensor A2 due to the measurement sensor A2 itself.

[0020] In this embodiment, ambient noise is the component of the signal included in the measurement sensor signal that is not the component of the target signal or the component of sensor noise; in other words, it is the remaining component after removing the component of the target signal and the component of sensor noise.

[0021] Environmental noise is noise that arises from one or more environmental noise sources. Here, various sources of environmental noise can exist. Specifically, these could include electrical and electronic equipment, or the Earth's magnetic field. For example, the measurement sensor signal may contain components originating from electrical and electronic equipment (environmental noise components). Also, for example, the measurement sensor signal may contain components originating from the Earth's magnetic field (environmental noise components).

[0022] The source of environmental noise may be an environment caused by artificial devices, or it may be an environment caused by nature, such as the Earth, other than by devices. The number of sources of environmental noise may be one or multiple.

[0023] If the same source of ambient noise generates two or more ambient noise signals with different properties, it may be considered that there is a separate source of ambient noise for each type of ambient noise signal. For example, the same source of ambient noise may generate ambient noise signals of two or more different frequencies (assuming each frequency is constant). In this case, it may be assumed that there is a different source of ambient noise for each ambient noise signal of each frequency. Furthermore, there are no particular limitations on the number or types of environmental noise sources.

[0024] In the example shown in Figure 1, measurement sensors A1 and A2 are each installed near predetermined locations on the belt conveyor 211. Measurement sensor A1 and measurement sensor A2 are installed in different locations. Furthermore, various positions may be used for installing the respective measurement sensors A1 and A2.

[0025] In the example shown in Figure 1, the part containing the two measuring sensors A1 and A2 is shown as the sensor unit 111. However, for example, the two measuring sensors A1 and A2 may be combined into a single housing or the like, or the two measuring sensors A1 and A2 may be provided independently.

[0026] In this embodiment, the same sensor (for example, a sensor of the same type but different individual units) is used as measuring sensor A1 and measuring sensor A2. However, in other configuration examples, different sensors (for example, different types of sensors) may be used as measuring sensor A1 and measuring sensor A2.

[0027] Any sensor may be used as the respective measuring sensors A1 and A2. For example, not only magnetic sensors that measure magnetic signals (magnetic field signals), but also electric field sensors that measure electric field signals, current sensors that measure electric current, voltage sensors that measure voltage, sound sensors that measure sound, vibration sensors that measure vibration, temperature sensors that measure temperature, pressure sensors that measure pressure, light sensors that measure light, electromagnetic wave sensors that measure electromagnetic waves, etc. The electromagnetic wave sensor may be, for example, an infrared sensor that measures infrared rays, or a radio wave sensor that measures radio waves.

[0028] In this embodiment, the environmental noise component contained in the measurement sensor signal measured by measurement sensor A1 (also referred to as measurement sensor signal a1 for convenience of explanation) and the environmental noise component contained in the measurement sensor signal measured by measurement sensor A2 (also referred to as measurement sensor signal a2 for convenience of explanation) are shown to originate from the same source of environmental noise. In this embodiment, the process of measuring the sensor signals a1 and a2 using two measuring sensors A1 and A2 is performed simultaneously and in parallel during the same time period. Furthermore, the two sensor signals a1 and a2 have aligned time axes during that same time period.

[0029] In this embodiment, the measuring sensors A1 and A2 are shown as separate from the foreign object detection device 11. However, as another example of configuration, the measuring sensors A1 and A2 may be integrated into the foreign object detection device 11. The term "measurement" can also be used instead of "detection" or "measurement of measurement."

[0030] <Objects to be inspected and foreign objects> In this embodiment, the objects to be inspected 231 and 232 may be any object, for example, a predetermined product. Foreign object 251 is an object that affects the measurement sensor signals measured by the respective measurement sensors A1 and A2. In this embodiment, the foreign object 251 is, for example, a piece of metal. In other words, in this embodiment, if a foreign substance 251 is attached to the object to be inspected 231, a signal component caused by the foreign substance 251 is superimposed on the measurement sensor signals measured by the respective measurement sensors A1 and A2. In this embodiment, this signal component is used as the component of the target signal.

[0031] In the example in Figure 1, for the sake of simplicity, we show that the objects under inspection 231 and 232 are individual objects. However, in other examples, the objects under inspection 231 and 232 may be a collection (assembly) of multiple objects of the same or different types. Furthermore, in the example shown in Figure 1, for the sake of simplicity, we have shown a case where one foreign object 251 is attached to the object to be inspected 231. However, in other examples, multiple foreign objects may be attached to the same object to be inspected 231.

[0032] Thus, the foreign object detection device 11 may, for example, perform signal processing on signals (target signals) caused by foreign objects attached to the same type of object (object to be inspected), or it may perform signal processing on signals (target signals) caused by foreign objects attached to different types of objects (objects to be inspected) together.

[0033] <Target signal> In this embodiment, the component of the signal generated by the foreign matter 251 attached to the object 231 being inspected in the measurement sensor signal is the component of the target signal. In other words, in this embodiment, the signal generated by the foreign matter 251 attached to the object 231 being inspected is used as the target signal. In the example in Figure 1, since no foreign matter is attached to the object 232 being inspected, no target signal is generated for the object 232 being inspected, and therefore the target signal is not measured.

[0034] <Conveyor Belt> In the example shown in Figure 1, the objects to be inspected, 231 and 232, are placed at different locations on the conveyor belt 211. When the belt conveyor 211 is driven, each of the objects to be inspected, 231 and 232, is moved in direction H1 along the path of the belt conveyor 211. As a result, each of the objects being inspected, 231 and 232, gradually approaches the sensor unit 111 from a position far away from it, passes the closest point to the sensor unit 111, and then gradually moves away from it.

[0035] In this embodiment, the belt conveyor 211 is shown moving at a constant speed in a predetermined direction H1. However, in other configuration examples, the speed at which the belt conveyor 211 moves may be variable. In this case, for example, the foreign object detection device 11 may perform signal processing synchronized with the variable speed.

[0036] In the example shown in Figure 1, a portion of the belt conveyor 211 is depicted as a straight line for the sake of illustration; however, any shape (path) of the belt conveyor 211 may be used. For example, the conveyor belt 211 is not limited to a straight line; a circular (or elliptical, etc.) belt conveyor belt may be used. In this case, each object to be inspected, 231, 232, may be moved around two or more times, passing the position closest to the sensor unit 111 two or more times.

[0037] <connection> Line G1 connects the measurement sensor A1 and the foreign object detection device 11 in a way that enables communication. Line G2 connects the measurement sensor A2 and the foreign object detection device 11 in a way that enables communication. In this embodiment, lines G1 and G2 are wired lines, but in other configuration examples, lines G1 and G2 may be wireless lines.

[0038] For example, if the line G1 is a wireless line, the measuring sensor A1 and the foreign object detection device 11 each have wireless communication capabilities, and they use their respective wireless communication capabilities to perform one-way or bi-way communication from the measuring sensor A1 to the foreign object detection device 11. Similarly, if the line G2 is a wireless line, the measurement sensor A2 and the foreign object detection device 11 each have wireless communication capabilities, and they use their respective wireless communication capabilities to perform one-way or bi-way communication from the measurement sensor A2 to the foreign object detection device 11.

[0039] <Foreign object detection device> The foreign object detection device 11 may be a computer comprising, for example, a processor such as a CPU (Central Processing Unit) and a storage unit such as RAM (Random Access Memory) and ROM (Read Only Memory). In this case, the foreign object detection device 11 may perform various processes by having the processor execute a program stored in the storage unit. Furthermore, when the processor executes the program, the foreign object detection device 11 may use various parameters stored in the storage unit.

[0040] The foreign object detection device 11 includes a sensor signal acquisition unit 31, a signal processing unit 32, a foreign object determination unit 33, an input unit 34, an output unit 35, and a storage unit 36. The signal processing unit 32 includes a target signal removal unit 51 and an environmental noise removal unit 52.

[0041] The sensor signal acquisition unit 31 acquires the measurement sensor signal a1 measured by the measurement sensor A1. In this embodiment, the measurement sensor A1 outputs the measurement sensor signal a1 to the line G1, and the sensor signal acquisition unit 31 acquires the measurement sensor signal a1 by receiving the measurement sensor signal a1 via the line G1. Similarly, the sensor signal acquisition unit 31 acquires the measurement sensor signal a2 measured by the measurement sensor A2. In this embodiment, the measurement sensor A2 outputs the measurement sensor signal a2 to the line G2, and the sensor signal acquisition unit 31 acquires the measurement sensor signal a2 by receiving the measurement sensor signal a2 via the line G2.

[0042] Furthermore, if the line G1 is a wireless line, the sensor signal acquisition unit 31 acquires the measurement sensor signal a1 by receiving the measurement sensor signal a1 transmitted wirelessly from the measurement sensor A1. Similarly, if line G2 is a wireless line, the sensor signal acquisition unit 31 acquires the measurement sensor signal a2 by receiving the measurement sensor signal a2 transmitted wirelessly from the measurement sensor A2.

[0043] In this embodiment, the foreign object detection device 11 is shown to be equipped with a common sensor signal acquisition unit 31 for multiple measurement sensors A1 and A2. However, as an example of other configurations, each measurement sensor A1 and A2 may be equipped with a different sensor signal acquisition unit.

[0044] The signal processing unit 32 performs predetermined signal processing. In this embodiment, the signal processing unit 32 performs processing by the target signal removal unit 51 and processing by the environmental noise removal unit 52. The signal processing unit 32 may perform other processing.

[0045] The target signal removal unit 51 removes the target signal component contained in the measurement sensor signal a2 acquired by the sensor signal acquisition unit 31, and generates the resulting signal (which will also be called the environmental noise signal for convenience of explanation).

[0046] In this case, the target signal removal unit 51 may identify the component of the target signal included in the measurement sensor signal a2 by any method. For example, the target signal removal unit 51 may use digital filtering to remove components of the target signal. Any form of digital filtering may be used. For example, the target signal removal unit 51 may use one or more signal processing techniques such as principal component analysis, independent component analysis, or singular value decomposition to remove components of the target signal.

[0047] Furthermore, for example, when the target signal removal unit 51 removes components of the target signal, it may use processing such as averaging to generate a template signal for the target signal.

[0048] In this embodiment, the environmental noise signal does not contain components of the target signal, but contains components of environmental noise. Furthermore, in this embodiment, the environmental noise signal also contains components of sensor noise from the measurement sensor A2. In this embodiment, the ideal case is shown where the ambient noise signal does not contain any components of the target signal. However, in reality, for example, the ambient noise signal may contain components of the target signal to a degree that does not cause practical problems (i.e., some components of the target signal may remain after the components of the target signal have been removed).

[0049] The environmental noise removal unit 52 removes the environmental noise signal generated by the target signal removal unit 51 from the measurement sensor signal a1 acquired by the sensor signal acquisition unit 31, and generates the resulting signal (for convenience of explanation, also called the environmental noise-removed signal). As a result, the environmental noise-removed signal is a signal from which the components of the target signal have been extracted.

[0050] Here, when the environmental noise removal unit 52 removes the environmental noise signal from the measurement sensor signal a1, it may perform a process to adjust the level of one or both of the measurement sensor signal a1 and the environmental noise signal. In other words, the environmental noise removal unit 52 may perform the process of removing the environmental noise signal from the measurement sensor signal a1 after such adjustments.

[0051] In this embodiment, the environmental noise-removed signal does not contain environmental noise components but contains components of the target signal. In this embodiment, the ideal case is shown where the environmental noise reduction signal does not contain any components of the environmental noise signal. However, in reality, for example, the environmental noise reduction signal may contain components of the environmental noise signal to a degree that does not cause practical problems (i.e., some components of the environmental noise signal may remain after the removal of the components of the environmental noise signal).

[0052] Furthermore, in this embodiment, the environmental noise reduction signal may include the sensor noise component of measurement sensor A1 and the sensor noise component of measurement sensor A2. In this embodiment, the sensor noise components of measurement sensor A1 and measurement sensor A2 are considered to have little influence on the target signal and are therefore ignored. Alternatively, one or both of the sensor noise components of measurement sensor A1 and measurement sensor A2 may be removed by any method. In this case, the environmental noise-removed signal will not include one or both of the sensor noise components of measurement sensor A1 and measurement sensor A2. Such a method may be incorporated, for example, into the processing by the target signal removal unit 51, into the processing by the environmental noise removal unit 52, into both of these, or into another processing performed by the signal processing unit 32. Furthermore, the sensor noise component does not necessarily have to be completely removed; it may be reduced to a degree that does not cause practical problems.

[0053] In this embodiment, when the environmental noise reduction unit 52 subtracts the environmental noise signal from the measurement sensor signal a1, the time period during which the measurement sensor signal a1 was measured coincides with the time period during which the environmental noise signal (included in the measurement sensor signal a2) was measured. In other words, it is assumed that such a measurement sensor signal a1 and the environmental noise signal contain similar environmental noise components during the same time period. As a result, the environmental noise component is accurately removed from the measurement sensor signal a1.

[0054] The foreign object detection unit 33 determines the presence or absence of foreign object 251 based on the environmental noise reduction signal (in this embodiment, a signal considered to be the target signal) generated by the environmental noise reduction unit 52, and detects the presence of foreign object 251 if it is present. Here, any method may be used as the method for determining the presence or absence of foreign matter 251 by the foreign matter detection unit 33.

[0055] The input unit 34 is used to input information. For example, the input unit 34 has an operation unit that receives operations performed by a user (e.g., a person), and may input information corresponding to the content of the operation received by the operation unit. The operation unit may include one or more of the following: a key, a button, or a mouse. As another example, the input unit 34 may receive information output from other devices (devices other than the foreign object detection device 11).

[0056] The output unit 35 outputs information. For example, the output unit 35 may have a display screen, on which information may be displayed. This information is viewable by the user. As another example, the output unit 35 may have a speaker that outputs sound information (e.g., voice). This sound can be heard by the user. As another example, the output unit 35 may output information to other devices (devices other than the foreign object detection device 11).

[0057] The memory unit 36 ​​stores information. The storage unit 36 ​​may store, for example, a program (computer program) that defines the processing performed in the foreign object detection device 11. Furthermore, the storage unit 36 ​​may store, for example, the parameters used in the process.

[0058] Furthermore, the storage unit 36 ​​may store, for example, some or all of the measurement sensor signals a1, a2 acquired by the sensor signal acquisition unit 31, or signals generated by processing performed based on the measurement sensor signals a1, a2 (e.g., environmental noise signal, environmental noise removal signal). Furthermore, the memory unit 36 ​​may store, for example, information relating to the determination result by the foreign object detection unit 33.

[0059] [Examples of signal waveforms in signal processing] Referring to Figures 2 to 5, examples of signal waveforms in the signal processing performed in the foreign object detection device 11 are shown. In the graphs shown in Figures 2 through 5, the horizontal axis represents time, and the vertical axis represents level. Here, the level in question is, for example, the level of the measurement sensor signals a1 and a2 measured by measurement sensors A1 and A2, and specifically, the level of the voltage representing the measurement result. Note that the simulation results shown in Figures 2 to 5 are not necessarily exact waveforms, but are illustrative examples for illustrative purposes.

[0060] Figure 2 shows an example of the waveform of the measurement sensor signal (measurement sensor signal a1) according to the embodiment (first embodiment). The measurement sensor signal 2011 shown in Figure 2 is an example of the measurement sensor signal a1.

[0061] In the example in Figure 2, the measured sensor signal 2011 includes the portion where the component of the target signal appears (target signal 2021). In the example in Figure 2, for the sake of simplicity, only one target signal 2021 is indicated by a symbol, but portions with waveforms similar to the target signal 2021 appear periodically.

[0062] Here, the target signal 2021 (and portions of a similar waveform) does not necessarily have to have a periodic appearance characteristic; for example, it may have a random appearance characteristic. The measurement sensor signal 2011 includes the components of the target signal, the environmental noise component, and the sensor noise component of measurement sensor A1.

[0063] Figure 3 shows an example of the waveform of the measurement sensor signal (measurement sensor signal a2) according to the embodiment (first embodiment). The measurement sensor signal 2012 shown in Figure 3 is an example of the measurement sensor signal a2.

[0064] In the example shown in Figure 3, the measurement sensor signal 2012 includes the portion where the component of the target signal appears (target signal 2031). In the example shown in Figure 3, for the sake of simplicity, only one target signal 2031 is indicated by its code, but a portion of the waveform similar to that of the target signal 2031 appears periodically.

[0065] Here, the target signal 2031 (and portions with similar waveforms) does not necessarily have to have a periodic appearance characteristic; for example, it may have a random appearance characteristic. The measurement sensor signal 2011 includes the components of the target signal, the environmental noise component, and the sensor noise component of measurement sensor A2.

[0066] In this embodiment, the level of the target signal component in measurement sensor signal 2012 (measurement sensor signal a2) is assumed to be a (where a is an arbitrary value) times higher than the level of the target signal component in measurement sensor signal 2011 (measurement sensor signal a1). In the example in Figure 3, a is a value less than 1.

[0067] In this embodiment, the level of the environmental noise component in measurement sensor signal 2012 (measurement sensor signal a2) is assumed to be b (where b is an arbitrary value) times the level of the environmental noise component in measurement sensor signal 2011 (measurement sensor signal a1).

[0068] Figure 4 shows an example of the waveform of the environmental noise signal 2013 according to the embodiment (first embodiment). As shown in Figure 4, in the environmental noise signal 2013, the target signal 2031 (and portions with similar waveforms) included in the measurement sensor signal 2012 (measurement sensor signal a2) shown in Figure 3 has been removed.

[0069] Figure 5 shows an example of the waveform of the environmental noise reduction signal 2014 according to the embodiment (first embodiment). As shown in Figure 5, in the environmental noise-reduced signal 2014, the environmental noise component contained in the measurement sensor signal 2011 (measurement sensor signal a1) shown in Figure 2 has been removed.

[0070] In the examples shown in Figures 2 to 5, the target signal is generated periodically. For example, the belt conveyor 211 may be circular in shape, and the same object to be inspected 231 may pass over the sensor unit 111 multiple times at regular intervals. In such a configuration, the target signal is generated periodically, as shown in the examples in Figures 2 to 5.

[0071] As another example, a configuration may be used in which sensor units 111 and sensor units similar to sensor unit 111 are arranged at predetermined intervals along the path of the belt conveyor 211. In such a configuration, when the measurement sensor signals from the multiple sensor units arranged along the path of the belt conveyor 211 are viewed sequentially, the target signal is generated periodically, as shown in the examples in Figures 2 to 5.

[0072] For example, by combining the measurement sensor signals of multiple measurement sensors corresponding to each other (in this example, multiple measurement sensors corresponding to measurement sensor A1, or multiple measurement sensors corresponding to measurement sensor A2) in multiple sensor units arranged along the path of the belt conveyor 211, a signal is obtained in which the target signal is generated at predetermined intervals. As an example, if the interval (distance) between the multiple measurement sensors corresponding to each other is constant, a signal is obtained in which the target signal is generated periodically.

[0073] In the examples shown in Figures 2 to 5, the processing target is a measurement sensor signal that is generated periodically. However, other configurations may be used in which the processing target is a measurement sensor signal that is generated at any arbitrary timing. For example, the processing target may be a measurement sensor signal that is generated at random timings.

[0074] [An example of a signal processing procedure] Figure 6 shows an example of the signal processing procedure performed by the foreign object detection device 11 according to the embodiment (first embodiment).

[0075] (Step S1) In the foreign object detection device 11, the sensor signal acquisition unit 31 acquires the measurement sensor signal a1 and the measurement sensor signal a2. Then, the process moves on to step S2.

[0076] (Step S2) In the foreign object detection device 11, the target signal removal unit 51 removes the target signal component from the measurement sensor signal a2 to generate an environmental noise signal. Then, the process moves on to step S3.

[0077] (Step S3) In the foreign object detection device 11, the environmental noise removal unit 52 removes the environmental noise component from the measurement sensor signal a1 using the environmental noise signal. Then, the processing of this flow is completed.

[0078] [Specific examples of signal processing] Figure 7 shows an example of a specific signal processing method performed by the foreign object detection device 11 according to the embodiment (first embodiment).

[0079] (Process T1) The sensor signal acquisition unit 31 acquires the measurement sensor signal a1. The measured sensor signal a1 includes the component of the target signal, the component of environmental noise P1, and the component of sensor noise Q1. Here, environmental noise P1 represents environmental noise generated by one or more predetermined environmental noise sources. Furthermore, sensor noise Q1 represents the sensor noise of measurement sensor A1.

[0080] (Process T2) The sensor signal acquisition unit 31 acquires the measurement sensor signal a2. The measured sensor signal a2 includes the component of the target signal, the component of environmental noise P1, and the component of sensor noise Q2. In this embodiment, for the sake of simplicity, it is assumed that the environmental noise P1 affecting the measurement sensor signal a1 and the environmental noise P1 affecting the measurement sensor signal a2 are both environmental noises that originate from the same one or more environmental noise sources. Furthermore, sensor noise Q2 represents the sensor noise of measurement sensor A2.

[0081] (Process T3) The target signal removal unit 51 removes the target signal component from the measurement sensor signal a2 to generate an environmental noise signal.

[0082] (Process T4) The environmental noise reduction unit 52 removes the environmental noise component from the measurement sensor signal a1 using Adaptive Noise Cancelling (ANC) with the common component of the measurement sensor signal a1 and the environmental noise signal.

[0083] In this embodiment, ANC is used to remove environmental noise components from a signal that includes environmental noise. Note that ANC is one of the general environmental noise reduction techniques, and other general techniques may be used as environmental noise reduction techniques. Furthermore, in this embodiment, the common component is a component of environmental noise.

[0084] (Process T5) In the foreign object detection device 11, a signal from which environmental noise has been removed (environmental noise-removed signal) is obtained. The signal in question does not contain environmental noise components, but contains components of the target signal.

[0085] Furthermore, sensor noises Q1 and Q2 may be ignored, for example, because their impact on the target signal is small, or they may be removed during the process of generating the environmental noise reduction signal.

[0086] [Signal processing using a template signal of the target signal] As a concrete example of the signal processing in step S2 shown in Figure 6, signal processing using a template signal of the target signal is shown.

[0087] In this example, the target signal removal unit 51 generates a target signal template signal from the measurement sensor signal a2, and then removes the target signal template signal from the measurement sensor signal a2, thereby removing the target signal component from the measurement sensor signal a2 and generating an environmental noise signal.

[0088] In this example, as shown in Figure 3, the target signal 2031 is generated at multiple locations (points) in time in the measurement sensor signal a2. In the example in Figure 3, these multiple locations are positions that occur at a constant (or nearly constant) time interval.

[0089] The target signal removal unit 51 averages the signal portions (parts of the measurement sensor signal a2) of the target signal 2031 at multiple locations included in the measurement sensor signal a2. The target signal removal unit 51 acquires the signal resulting from this averaging as a template signal for the target signal.

[0090] In this case, the result of this averaging is that components of signals other than the target signal (in this example, the environmental noise component and the sensor noise component of measurement sensor A2) have been reduced. As a result, the template signal of the target signal ideally consists only of the target signal component. However, in other configuration examples, components of signals other than the target signal (in this example, environmental noise components and sensor noise components from measurement sensor A2) may remain to a degree that is practically effective. Furthermore, any number of times (2 or more) the averaging process is performed may be used.

[0091] Figure 8 shows an example of a template signal 2131 for the target signal according to the embodiment (first embodiment). In the graph shown in Figure 8, the horizontal axis represents time, and the vertical axis represents level (e.g., voltage). Here, the time on the horizontal axis of the graph shown in Figure 8 differs from the time shown in Figures 2 to 5 with respect to the template signal 2131 of the target signal, and represents the relative time relationship of the portion of the template signal 2131 of the target signal (and the periods before and after it).

[0092] Figure 8 shows a portion of the measurement sensor signal a2 that includes the target signal (for convenience of explanation, this is also referred to as the measurement sensor signal portion 2111), and the template signal 2131 of the target signal. In the example shown in Figure 8, the position (time) of the template signal 2131 of the target signal is aligned with the position (time) of the measurement sensor signal portion 2111 of the measurement sensor signal a2 on the horizontal axis of the graph. In other words, the target signal removal unit 51 arranges the generated target signal template signal to match the timing of the target signal (e.g., target signal 2031) in the measurement sensor signal to be applied (in this example, measurement sensor signal a2).

[0093] In the example shown in Figure 8, the target signal removal unit 51 temporally positions the generated target signal template signal so that the peak position of the generated target signal template signal matches the peak position of the target signal in the measurement sensor signal to which it is applied.

[0094] Here, the target signal removal unit 51 may adjust the level of the generated target signal template signal when arranging the generated target signal template signal to match the timing of the target signal in the measurement sensor signal to which it is applied.

[0095] In this example, the target signal in the measurement sensor signal has both a positive and a negative peak. Figure 8 shows the position of the positive peak (time t1) and the position of the negative peak (time t2) for the target signal of the measurement sensor signal portion 2111.

[0096] As an example, the target signal removal unit 51 may temporally position the generated target signal template signal so that the position of the positive peak in the generated target signal template signal matches the position (time t1) of the positive peak in the target signal of the measurement sensor signal portion 2111. As another example, the target signal removal unit 51 may temporally position the generated target signal template signal such that the position of the negative peak in the generated target signal template signal matches the position (time t2) of the negative peak in the target signal of the measurement sensor signal portion 2111.

[0097] Furthermore, as another example, the target signal removal unit 51 may temporally position the generated target signal template signal such that the positions of the positive and negative peaks of the generated target signal template signal are brought as close as possible (for example, as close as possible) to the positions of the positive peak (time t1) and negative peak (time t2) in the target signal of the measurement sensor signal portion 2111, using a predetermined method. Any method may be used as the predetermined method. For example, a method may be used to reduce (e.g., minimize) the error between the template signal of the generated target signal and the target signal of the measurement sensor signal portion 2111. This error may be, for example, the least squares error.

[0098] The target signal removal unit 51 uses the generated target signal template signal to remove the target signal component from one or more target signals (e.g., target signal 2031, etc.) in the measurement sensor signal to be applied (in this example, measurement sensor signal a2). In this example, the target signal removal unit 51 removes the target signal component by subtracting a time-aligned target signal template signal from each of the one or more target signals in the measurement sensor signal to be applied. As a result, the target signal removal unit 51 generates this resulting signal as an environmental noise signal.

[0099] Furthermore, one or more temporal positions (in the example in Figure 8, one or more peak positions) that serve as a reference for synchronizing each of the one or more target signals in the applicable measurement sensor signal with the template signal of the target signal may be called, for example, the trigger position or trigger time.

[0100] In this example, the environmental noise signal 2013 shown in Figure 4 is generated by subtracting the target signal template signal from each of the target signals at all points included in the measurement sensor signal 2012 shown in Figure 3. In other words, in the environmental noise signal 2013 shown in Figure 4, the components of the target signals at all points included in the measurement sensor signal 2012 shown in Figure 3 have been removed.

[0101] In the example shown in Figure 3, the multiple positions of the target signal included in the measurement sensor signal a2 are at positions with a fixed period (or approximately fixed period), but in other configuration examples, they may be at random positions. If the multiple positions of the target signal included in the measurement sensor signal a2 are at random positions, the target signal removal unit 51 may identify the position of each target signal by any method. This identification may be, for example, an estimated characteristic.

[0102] [An example of a signal processing procedure using a template signal for the target signal] Figure 9 shows an example of the signal processing procedure using a template signal of the target signal, performed by the foreign object detection device 11 according to the embodiment (first embodiment). The processing steps of the flow shown in Figure 9 are an example of the processing steps of step S2 shown in Figure 6.

[0103] (Step S11) In the foreign object detection device 11, the target signal removal unit 51 generates a template signal for the target signal by performing an averaging process on the measurement sensor signal a2. Then, the process moves on to step S12.

[0104] Here, the target signal removal unit 51 may store the generated target signal template signal in the storage unit 36. In this case, the target signal removal unit 51 can read out and use the target signal template signal stored in the storage unit 36 ​​at the necessary timing.

[0105] (Step S12) In the foreign object detection device 11, the target signal removal unit 51 generates an environmental noise signal from the measurement sensor signal a2 using a template signal of the target signal. Then, the processing of this flow is completed.

[0106] [Specific example of signal processing using a template signal for the target signal] Figure 10 shows an example of a specific example of signal processing using a template signal of the target signal performed by the foreign object detection device 11 according to the embodiment (first embodiment). Note that the content similar to the signal processing example shown in Figure 7 will be explained in a simplified manner.

[0107] (Process T11) The sensor signal acquisition unit 31 acquires the measurement sensor signal a1.

[0108] (Process T12) The sensor signal acquisition unit 31 acquires the measurement sensor signal a2.

[0109] (Process T13) The target signal removal unit 51 generates a template signal for the target signal from the measurement sensor signal a2 by averaging.

[0110] (Process T14) The target signal removal unit 51 removes the target signal component from the measurement sensor signal a2 by subtracting the target signal template signal from one or more points in the measurement sensor signal a2, while coordinating the timing, thereby generating an environmental noise signal.

[0111] (Process T15) The environmental noise reduction unit 52 removes the environmental noise component from the measurement sensor signal a1 using ANC, utilizing the common component between the measurement sensor signal a1 and the environmental noise signal.

[0112] (Process T16) In the foreign object detection device 11, a signal from which environmental noise has been removed (environmental noise-removed signal) is obtained. The signal in question does not contain environmental noise components, but contains components of the target signal.

[0113] Here, the timing of the measurement sensor signal a2 used to generate the template signal for the target signal may be different from the timing of the measurement sensor signal a1 from which the environmental noise component is to be removed (i.e., the measurement times may be different). Since averaging usually takes time, for example, a template signal of the target signal may be generated by first performing averaging of the measurement sensor signal a2 for about 10 minutes, and then the component of the target signal may be removed from the real-time measurement sensor signal a1 using the generated template signal of the target signal.

[0114] (Regarding the first embodiment) As described above, in the foreign object detection system 1 according to this embodiment, the foreign object detection device 11 can effectively remove the environmental noise component superimposed on the measurement sensor signal a1. In the foreign object detection system 1 according to this embodiment, the foreign object detection device 11 can remove environmental noise components included in the measurement sensor signal a1 without attenuating the components of the target signal.

[0115] In the foreign object detection system 1 according to this embodiment, for example, even if a reference sensor for measuring environmental noise is not installed, it is possible to remove the environmental noise component included in the measurement sensor signal a1. Thus, in the foreign object detection system 1 according to this embodiment, environmental noise can be removed even in environments where a reference sensor is not installed.

[0116] In the foreign object detection system 1 according to this embodiment, for example, when magnetic sensors are used as measurement sensors A1 and A2, the influence of the environmental magnetic field superimposed on the measurement sensor signal can be eliminated. In the foreign object detection system 1 according to this embodiment, for example, even when correlated and phase-synchronized environmental noise components are superimposed on the measurement sensor signal a1, the environmental noise components can be removed from the measurement sensor signal a1.

[0117] Furthermore, problems arose when, for example, each of the following two types of environmental noise reduction techniques was used. The first method for removing environmental noise involves installing reference sensors that acquire environmental noise. In this case, the reference sensors must not contain the target signal (the signal to be acquired). Also, in this case, it is necessary to install more reference sensors than the number of noise sources in the environment. Furthermore, since the reference sensor signal measured by the reference sensor is assumed not to contain the target signal, the reference sensor had to be installed in a location away from the measurement sensor. Even if the reference sensor signal contains components of the target signal, signal processing is still possible using the reference sensor signal, but the components of the target signal included in the environmental noise reduction signal will be attenuated.

[0118] The second environmental noise reduction method uses measurement sensor signals measured by multiple measurement sensors arranged in a grid, without installing a reference sensor. In this case, a certain number of measurement sensors are required.

[0119] In this embodiment, we have shown a case where the foreign object detection device 11 processes the measurement sensor signals a1 and a2 measured by measurement sensors A1 and A2 in real time. However, as an example of another configuration, a configuration may be used in which the measurement sensor signals a1 and a2 measured by measurement sensors A1 and A2 are first stored in the storage unit 36, and then the measurement sensor signals a1 and a2 stored in the storage unit 36 ​​are read out and processed.

[0120] Furthermore, although this embodiment shows a case where environmental noise removal processing (processing by the target signal removal unit 51 and processing by the environmental noise removal unit 52 in this embodiment) is performed on the measurement sensor signal a1, similar environmental noise removal processing may be performed on the measurement sensor signal a2 thereafter. In other words, environmental noise component removal processing may be performed on both of these measurement sensor signals a1 and a2, respectively. As a specific example, in the foreign object detection device 11, when two measurement sensor signals a1 and a2 are acquired, the process of removing the environmental noise component from one measurement sensor signal a1 may be performed first, and then the process of removing the environmental noise component from the other measurement sensor signal a2 may be performed.

[0121] In this embodiment, measurement sensor signal a1 and measurement sensor signal a2 have been described separately, but measurement sensor signal a1 and measurement sensor signal a2 may be interchanged when performing signal processing.

[0122] Furthermore, although this embodiment shows a case where a target signal caused by a foreign object 251 on an object to be inspected 231 being moved by a belt conveyor 211 is measured, a belt conveyor 211 is not necessarily required. Furthermore, the target signal does not necessarily have to be a signal originating from the foreign object 251 of the object being inspected 231; for example, a signal originating from any object may be used. For example, if the object to be inspected is located in a fixed position (or a nearly fixed position) and a periodic signal is generated by the object to be inspected, that signal may be used as the target signal.

[0123] (Second Embodiment) [Foreign object detection system] Figure 11 shows a schematic example of the configuration of the foreign object detection device 311 and sensor unit 411 in the foreign object detection system 301 according to the embodiment (second embodiment). In this embodiment, detailed explanations of the configuration and operation, which are the same as those in Figure 1 of the first embodiment, will be omitted.

[0124] In this embodiment, a sensor unit 411 is provided instead of the sensor unit 111 shown in Figure 1. Furthermore, in this embodiment, a foreign object detection device 311 is provided instead of the foreign object detection device 11 shown in Figure 1. In this embodiment, the belt conveyor 211, the objects to be inspected 231 and 232, and the foreign object 251 shown in Figure 1 are the same and are omitted from the illustration in Figure 11.

[0125] The foreign object detection system 301 according to this embodiment differs from the foreign object detection system 1 shown in Figure 1 in that it is equipped with three or more measuring sensors A1 to An (where n is an integer of 3 or more), and is otherwise similar.

[0126] <Sensor section> The sensor unit 411 is equipped with n measuring sensors A1 to An. Here, each of the n measurement sensors A1 to An may be called a channel or the like. In this embodiment, n measuring sensors A1 to An are arranged in a straight line. Furthermore, any arrangement of the n measuring sensors A1 to An may be used.

[0127] In this embodiment, the environmental noise components included in the measurement sensor signals (also referred to as measurement sensor signals a1 to an for convenience of explanation) measured by each measurement sensor A1 to An are shown to originate from the same source of environmental noise. In this embodiment, the process of measuring the sensor signals a1 to an using the measurement sensors A1 to An is performed simultaneously and in parallel during the same time period. Furthermore, the time axes of the sensor signals a1 to an are aligned during that same time period.

[0128] In this embodiment, the measurement sensors A1 to An are shown to be separate from the foreign object detection device 311. However, as another example of configuration, the measurement sensors A1 to An may be integrated with the foreign object detection device 311.

[0129] Multiple sensors (two or more sensors) may be referred to as a sensor group, and multiple sensor signals (two or more sensor signals) may be referred to as a sensor signal group. Multiple measurement sensors (in this embodiment, two or more measurement sensors from measurement sensors A1 to An) may be called a measurement sensor group, and multiple measurement sensor signals (in this embodiment, two or more measurement sensor signals from measurement sensor signals a1 to an) may be called a measurement sensor signal group, etc.

[0130] <connection> The communication line Gi (where i is an integer from 1 to n) connects the measurement sensor Ai and the foreign object detection device 311 in a way that enables communication.

[0131] <Foreign object detection device> The foreign object detection device 311 may be a computer, similar to the foreign object detection device 11 shown in Figure 1. The foreign object detection device 311 includes a sensor signal acquisition unit 331, a signal processing unit 332, a foreign object determination unit 333, an input unit 334, an output unit 335, and a storage unit 336. The signal processing unit 332 includes a target signal removal unit 351 and an environmental noise removal unit 352.

[0132] The sensor signal acquisition unit 331 acquires the measurement sensor signal ai measured by each of the n measurement sensors A1 to An, specifically the measurement sensor Ai. In this embodiment, the measurement sensor Ai outputs the measurement sensor signal ai to the line Gi, and the sensor signal acquisition unit 331 acquires the measurement sensor signal ai by receiving the measurement sensor signal ai via the line Gi.

[0133] In this embodiment, we have shown a case where a common sensor signal acquisition unit 331 is provided for multiple measurement sensors Ai in the foreign object detection device 311. However, as another example of configuration, a different sensor signal acquisition unit may be provided for each measurement sensor Ai.

[0134] The signal processing unit 332 performs predetermined signal processing. In this embodiment, the signal processing unit 332 performs processing by the target signal removal unit 351 and processing by the environmental noise removal unit 352.

[0135] The target signal removal unit 351 generates an environmental noise signal from two or more measurement sensor signals ai acquired by the sensor signal acquisition unit 331. Here, these two or more measurement sensor signals ai are measurement sensor signals other than the measurement sensor signal (for convenience of explanation, let's call it measurement sensor signal az (where z is any integer from 1 to n)) that is subject to removal of environmental noise components by the environmental noise removal unit 352.

[0136] In other words, the target signal removal unit 351 generates an environmental noise signal based on two or more measurement sensor signals ai other than the measurement sensor signal az. These two or more measurement sensor signals ai may be, for example, all of the two or more measurement sensor signals ai other than measurement sensor signal az, or they may be some of the two or more measurement sensor signals ai other than measurement sensor signal az.

[0137] As an example, the target signal removal unit 351 may generate a template signal of the target signal based on two or more measurement sensor signals ai other than the measurement sensor signal az. In this case, the target signal removal unit 351 may remove the component of the target signal contained in any of the two or more measurement sensor signals ai other than the measurement sensor signal az, based on the template signal of the target signal, and generate the resulting signal as an environmental noise signal.

[0138] As another example, the target signal removal unit 351 may, based on two or more measurement sensor signals ai other than the measurement sensor signal az, remove the component of the target signal contained in any of the two or more measurement sensor signals ai other than the measurement sensor signal az by any other arbitrary method, and generate the resulting signal as an environmental noise signal.

[0139] The environmental noise removal unit 352 removes the environmental noise signal generated by the target signal removal unit 351 from the measurement sensor signal az acquired by the sensor signal acquisition unit 331, and generates the resulting signal as the environmental noise-removed signal.

[0140] The foreign object detection unit 333, similar to the foreign object detection unit 33 shown in Figure 1, determines the presence or absence of foreign objects 251 based on the environmental noise reduction signal (a signal considered to be the target signal in this embodiment) generated by the environmental noise reduction unit 352.

[0141] The input unit 334, output unit 335, and storage unit 336 are, for example, the same as the input unit 34, output unit 35, and storage unit 36 ​​shown in Figure 1.

[0142] [An example of a signal processing procedure] Figure 12 shows an example of the signal processing procedure performed by the foreign object detection device 311 according to the embodiment (second embodiment). In this example, the measurement sensor signal az, which is the target of removal of environmental noise components by the environmental noise removal unit 352, is shown to be measurement sensor signal a1.

[0143] (Step S21) In the foreign object detection device 311, the sensor signal acquisition unit 331 acquires n measurement sensor signals a1 to an. Then, the process proceeds to step S22.

[0144] (Step S22) In the foreign object detection device 311, the target signal removal unit 351 generates an environmental noise signal based on the measurement sensor signals a2 to an. Then, the process moves on to step S23.

[0145] (Step S23) In the foreign object detection device 311, the environmental noise removal unit 352 removes the environmental noise component from the measurement sensor signal a1 using the environmental noise signal. Then, the processing of this flow is completed.

[0146] In this embodiment, the foreign object detection device 311 may generate two or more environmental noise signals in the process of step S22, and in the process of step S23, it may use the two or more generated environmental noise signals to remove the environmental noise component from the measurement sensor signal a1. As a specific example, the target signal removal unit 351 may generate environmental noise signals (two or more environmental noise signals obtained from each of the two or more measurement sensor signals) from each of two or more measurement sensor signals from among the measurement sensor signals a2 to an.

[0147] [An example of a signal processing procedure using a template signal for the target signal] The target signal removal unit 351 averages the signal portions of the target signal (parts of each measurement sensor signal ai) that are included in two or more measurement sensor signals ai other than the measurement sensor signal az from which the environmental noise component is to be removed by the environmental noise removal unit 352. The target signal removal unit 351 acquires this averaging result signal as a template signal for the target signal. This example demonstrates a case where the environmental noise component is reduced by such averaging. In other words, this example shows a case where the waveforms of environmental noise contained in two or more measurement sensor signals ai are different, and are reduced when averaged.

[0148] Figure 13 shows an example of the procedure for signal processing using a template signal of the target signal, performed by the foreign object detection device 311 according to the embodiment (second embodiment). The processing steps of the flow shown in Figure 13 are an example of the processing steps of step S22 shown in Figure 12.

[0149] (Step S31) In the foreign object detection device 311, the target signal removal unit 351 generates a template signal for the target signal by performing an averaging process on the measurement sensor signals a2 to an. Then, the process proceeds to step S32.

[0150] Here, the target signal removal unit 351 may store the generated target signal template signal in the storage unit 336. In this case, the target signal removal unit 351 can read out and use the target signal template signal stored in the storage unit 336 at the necessary timing.

[0151] (Step S32) In the foreign object detection device 311, the target signal removal unit 351 generates an environmental noise signal from one or more of the measurement sensor signals a2 to an using a template signal of the target signal. Then, the processing of this flow is completed.

[0152] [An example of a signal processing procedure for signals from multiple measurement sensors] Figure 14 is a diagram showing an example of the signal processing procedure for multiple measurement sensor signals a1 to an performed by the foreign object detection device 311 according to the embodiment (second embodiment).

[0153] (Step S41) In the foreign object detection device 311, the sensor signal acquisition unit 331 acquires n measurement sensor signals a1 to an. Then, the process proceeds to step S42.

[0154] (Step S42) In the foreign object detection device 311, the signal processing unit 332 sets the variable k (in this example, k is an integer greater than or equal to 1) to 1. Then, the process proceeds to step S43.

[0155] (Step S43) In the foreign object detection device 311, the signal processing unit 332 performs environmental noise removal processing (in this example, processing by the target signal removal unit 351 and processing by the environmental noise removal unit 352) on the measurement sensor signal ak using the target signal removal unit 351 and the environmental noise removal unit 352. In other words, the signal processing unit 332 performs processing to remove the environmental noise component from the measurement sensor signal ak. Then, the process moves on to step S44.

[0156] (Step S44) In the foreign object detection device 311, the signal processing unit 332 increases the variable k by 1. Then, the process moves on to step S45.

[0157] (Step S45) In the foreign object detection device 311, the signal processing unit 332 determines whether the variable k is greater than n. If the signal processing unit 332 determines that the variable k is greater than n (step S45: YES) based on this determination, it terminates the processing of this flow. On the other hand, if the signal processing unit 332 determines that the variable k is less than or equal to n (step S45: NO) as a result of this determination, it proceeds to the process in step S43. In this way, the signal processing unit 332 repeats the process in step S43 until the environmental noise removal process (in this embodiment, the process by the target signal removal unit 351 and the process by the environmental noise removal unit 352) for all measurement sensor signals a1 to an is completed.

[0158] Through this process, the foreign object detection device 311 can remove environmental noise components from each of the n measurement sensor signals a1 to an based on other measurement sensor signals (measurement sensor signals other than measurement sensor signal a1 to an).

[0159] In the example shown in Figure 14, signal processing (environmental noise reduction processing) for multiple measurement sensor signals a1 to an is performed sequentially for these multiple measurement sensor signals a1 to an. However, such signal processing (environmental noise reduction processing) may also be performed in parallel in time for multiple measurement sensor signals a1 to an, for example.

[0160] Furthermore, while Figure 14 shows an example where environmental noise reduction processing is performed on all n measurement sensor signals a1 to an, another configuration example is where environmental noise reduction processing is performed on only some (any two or more) of the n measurement sensor signals a1 to an.

[0161] [Other configuration examples for the sensor unit] Figure 15 shows another example of the configuration of the sensor unit according to the embodiment (second embodiment). The sensor unit 431 is an example of a sensor unit having a grid-shaped sensor (multi-channel sensor). For the sake of explanation, Figure 15 shows the XY Cartesian coordinate system, which is a two-dimensional Cartesian coordinate system. Alternatively, it may be called an array or matrix instead of a grid.

[0162] The sensor unit 431 is equipped with (x × y) sensors A11 to Axy, where x is an integer greater than or equal to 2, and y is an integer greater than or equal to 2. Each of the (x × y) sensors A11 to Axy corresponds to a different channel.

[0163] The (x × y) sensors A11 to Axy are arranged in a sequence of x sensors parallel to the X-axis at a first predetermined interval, and y sensors are arranged in a sequence of y sensors parallel to the Y-axis at a second predetermined interval. The first predetermined interval is not particularly limited and may be, for example, equal intervals. The second predetermined interval is not particularly limited and may be, for example, equal intervals. Furthermore, the first predetermined interval and the second predetermined interval may be the same, for example.

[0164] In the example shown in Figure 11, a linear sensor unit 411 is used, but as another example of configuration, a grid-shaped sensor unit 431 may be used, as shown in Figure 15.

[0165] Furthermore, in the grid-shaped sensor section 431, if we consider the case where x is 1 and y is multiple, or where x is multiple and y is 1, the sensor section becomes line-shaped. Furthermore, as another example of a configuration, a sensor unit having multiple sensors arranged in various configurations other than a line or grid may be used.

[0166] (Regarding the second embodiment) As described above, in the foreign object detection system 301 according to this embodiment, the foreign object detection device 311 can effectively remove environmental noise components superimposed on the measurement sensor signals a1 to an. In the foreign object detection device 311 according to this embodiment, for example, the accuracy of the environmental noise signal can be improved by generating an environmental noise signal using two or more measurement sensor signals, thereby improving the accuracy of generating a signal from which the environmental noise signal has been removed (environmental noise-removed signal).

[0167] As a specific example, in the foreign object detection device 311 according to this embodiment, for one measurement sensor signal ai, an environmental noise signal (two or more environmental noise signals) may be generated by removing the target signal component from each of two or more other measurement sensor signals. In this case, the foreign object detection device 311 according to this embodiment can, for example, use multiple (two or more) environmental noise signals when removing the environmental noise component from one measurement sensor signal ai, thereby improving the accuracy of generating a signal from which the environmental noise signal has been removed (environmental noise-removed signal).

[0168] In the foreign object detection device 311 according to this embodiment, it is possible to obtain an environmental noise signal using other measurement sensor signals (for example, a number of other measurement sensor signals) for each measurement sensor signal a1 to an, thereby effectively removing the environmental noise component.

[0169] For example, even if there is only one type of environmental noise, the accuracy of removing the environmental noise component will be higher if there are many signals used in the environmental noise removal process (in this embodiment, multiple measurement sensor signals). Furthermore, even when there are two or more types of environmental noise, the accuracy of removing environmental noise components is higher when there are many signals used in the environmental noise removal process (in this embodiment, multiple measurement sensor signals).

[0170] (Third embodiment) [Foreign object detection system] Figure 16 shows a schematic example of the configuration of the foreign object detection device 511 and sensor units 611 and 631 in the foreign object detection system 501 according to the embodiment (third embodiment). In this embodiment, detailed explanations of the configuration and operation, which are the same as those in Figure 11 of the second embodiment, will be omitted.

[0171] In this embodiment, the foreign object detection system 501 is provided with a sensor unit 611 having a plurality of u (where u is an integer of 2 or more) measuring sensors A1 to Au, and a sensor unit 631 having r (where r is an integer of 1 or more) reference sensors C1 to Cr. Furthermore, in this embodiment, a foreign object detection device 511 is provided instead of the foreign object detection device 311 shown in Figure 11. In this embodiment, the belt conveyor 211, the objects to be inspected 231 and 232, and the foreign object 251 shown in Figure 1 are the same and are omitted from the illustration in Figure 16.

[0172] The foreign object detection system 501 according to this embodiment differs from the foreign object detection system 301 shown in Figure 11 in that it is equipped with two or more measuring sensors A1 to Au and reference sensors C1 to Cr, and is otherwise similar.

[0173] <Sensor part of the measuring sensor> The sensor unit 611 is equipped with u measuring sensors A1 to Au. Here, each of the u measurement sensors A1 to Au may be called a channel or the like. In this embodiment, u measuring sensors A1 to Au are arranged in a straight line. Furthermore, any arrangement of the u measuring sensors A1 to Au may be used.

[0174] In the example shown in Figure 16, for illustrative purposes, three or more measurement sensors A1 to Au are shown, but the number of measurement sensors A1 to Au may be two (u=2).

[0175] In this embodiment, the measurement sensors A1 to Au are shown as separate from the foreign object detection device 511. However, as another example of a configuration, the measurement sensors A1 to Au may be integrated into the foreign object detection device 511.

[0176] Furthermore, multiple measurement sensors (in this embodiment, two or more measurement sensors when there are multiple measurement sensors A1 to Au) may be called a group of measurement sensors, and multiple measurement sensor signals (in this embodiment, two or more measurement sensor signals when there are multiple measurement sensor signals a1 to au) may be called a group of measurement sensor signals, etc.

[0177] <Sensor part of the reference sensor> The sensor unit 631 is equipped with r reference sensors C1 to Cr. Here, each of the r reference sensors C1 to Cr may be called a channel or the like. In this embodiment, r reference sensors C1 to Cr are arranged in a straight line. Furthermore, any arrangement of the r reference sensors C1 to Cr may be used.

[0178] In this embodiment, each of the reference sensors C1 to Cr is installed at a location (place) where environmental noise is measured without including the target signal. Therefore, in this embodiment, the signals measured by each of the reference sensors C1 to Cr (also referred to as reference sensor signals c1 to cr for convenience of explanation) do not contain components of the target signal, but contain components of environmental noise. Furthermore, each of the reference sensor signals c1 to cr includes the sensor noise component of the respective reference sensor C1 to Cr.

[0179] In the example shown in Figure 16, three or more reference sensors C1 to Cr are shown for illustrative purposes, but the number of reference sensors C1 to Cr may be two (r=2). Furthermore, in this embodiment, for the sake of explanation, a case in which multiple reference sensors C1 to Cr are provided is shown, but as an example of another configuration, the number of reference sensors C1 to Cr may be 1 (r=1). In other words, the foreign object detection system 501 may be configured to have only one reference sensor C1.

[0180] In this embodiment, for the sake of explanation, the case in which the foreign object detection system 501 is equipped with one reference sensor C1 will also be described together. Although the foreign object detection system 1 is equipped with multiple reference sensors C1 to Cr, if only one reference sensor C1 is used, the same processing is performed as when the foreign object detection system 501 is equipped with one reference sensor C1.

[0181] Here, if the accuracy of removing environmental noise components is affected by the number of reference sensors C1 to Cr relative to the number of environmental noise sources, the number of reference sensors C1 to Cr may be set so as to ensure the required accuracy. For example, the number of reference sensors C1 to Cr may be the same as or greater than the number of environmental noise sources.

[0182] In this embodiment, the environmental noise components included in the reference sensor signals c1 to cr, measured by each of the reference sensors C1 to Cr, are shown to originate from the same environmental noise source as the environmental noise components included in the measured sensor signals a1 to au.

[0183] For example, the measurement sensors A1 to Au may be installed near the source of the target signal (in this embodiment, near the path of the belt conveyor 211 that moves the object to be inspected 231), and the respective reference sensors C1 to Cr may be installed at a location so far away from the source that the target signal is not significantly measured.

[0184] In this embodiment, the process of measuring the respective measurement sensor signals a1 to au using the respective measurement sensors A1 to Au, and the process of measuring the respective reference sensor signals c1 to cr using the respective reference sensors C1 to Cr, are performed simultaneously and in parallel within the same time period. Furthermore, the time axes of the measurement sensor signals a1 to au and the reference sensor signals c1 to cr are aligned within that same time period.

[0185] In this embodiment, the reference sensors C1 to Cr are shown as separate from the foreign object detection device 511. However, as an example of another configuration, some or all of the reference sensors C1 to Cr may be integrated into the foreign object detection device 511.

[0186] Furthermore, multiple reference sensors (in this embodiment, two or more reference sensors when there are multiple reference sensors C1 to Cr) may be called a group of reference sensors, and multiple reference sensor signals (in this embodiment, two or more reference sensor signals when there are multiple reference sensor signals c1 to cr) may be called a group of reference sensor signals.

[0187] <connection> The line Gi (where i is an integer from 1 to u) connects the measurement sensor Ai and the foreign object detection device 511 in a way that enables communication.

[0188] The line Fj (where j is an integer from 1 to r) connects the reference sensor Cj and the foreign object detection device 511 in a way that enables communication. In this embodiment, each line Fj is a wired line, but in other configuration examples, each line Fj may be a wireless line.

[0189] For example, if the line Fj is a wireless line, the reference sensor Cj and the foreign object detection device 511 each have wireless communication capabilities, and they use their respective wireless communication capabilities to perform one-way or bi-way communication from the reference sensor Cj to the foreign object detection device 511.

[0190] <Foreign object detection device> The foreign object detection device 511 may be a computer, similar to the foreign object detection device 11 shown in Figure 1. The foreign object detection device 511 includes a sensor signal acquisition unit 531, a signal processing unit 532, a foreign object determination unit 533, an input unit 534, an output unit 535, and a storage unit 536. The sensor signal acquisition unit 531 includes a measurement sensor signal acquisition unit 551 and a reference sensor signal acquisition unit 552. The signal processing unit 532 includes a target signal removal unit 571 and an environmental noise removal unit 572.

[0191] The measurement sensor signal acquisition unit 551 acquires the measurement sensor signal ai measured by each of the u measurement sensors A1 to Au, namely the measurement sensor Ai. In this embodiment, the measurement sensor Ai outputs the measurement sensor signal ai to the line Gi, and the measurement sensor signal acquisition unit 551 acquires the measurement sensor signal ai by receiving the measurement sensor signal ai via the line Gi.

[0192] In this embodiment, the foreign object detection device 511 is shown to be equipped with a common measurement sensor signal acquisition unit 551 for multiple measurement sensors Ai. However, as an example of other configurations, each measurement sensor Ai may be equipped with a different sensor signal acquisition unit.

[0193] The reference sensor signal acquisition unit 552 acquires the reference sensor signal cj measured by each of the r reference sensors C1 to Cr, specifically the reference sensor signal cj measured by each of the reference sensors Cj. In this embodiment, the reference sensor Cj outputs the reference sensor signal cj to the line Fj, and the reference sensor signal acquisition unit 552 acquires the reference sensor signal cj by receiving the reference sensor signal cj via the line Fj.

[0194] Furthermore, if the line Fj is a wireless line, the reference sensor signal acquisition unit 552 acquires the reference sensor signal cj by receiving the reference sensor signal cj transmitted wirelessly from the reference sensor Cj.

[0195] In this embodiment, the foreign object detection device 511 is shown to be equipped with a common reference sensor signal acquisition unit 552 for multiple reference sensors Cj. However, as an example of other configurations, each reference sensor Cj may be equipped with a different reference sensor signal acquisition unit.

[0196] In this embodiment, the sensor signal acquisition unit 531 is shown to have separate sensor signal acquisition units (measurement sensor signal acquisition unit 551 and reference sensor signal acquisition unit 552) for the measurement sensors A1 to Au and the reference sensors C1 to Cr. However, as another example of configuration, a common sensor signal acquisition unit may be provided for these.

[0197] The signal processing unit 532 performs predetermined signal processing. In this embodiment, the signal processing unit 532 performs processing by the target signal removal unit 571 and processing by the environmental noise removal unit 572.

[0198] The target signal removal unit 571 generates an environmental noise signal from one or more measurement sensor signals ai acquired by the measurement sensor signal acquisition unit 551. Here, one or more measurement sensor signals ai are measurement sensor signals other than the measurement sensor signal (for convenience of explanation, let's call it measurement sensor signal az (where z is any integer from 1 to u)) that are subject to environmental noise signal removal by the environmental noise removal unit 572.

[0199] In other words, the target signal removal unit 571 generates an environmental noise signal based on one or more measurement sensor signals ai other than the measurement sensor signal az. Such one or more measurement sensor signals ai may be, for example, all of the one or more measurement sensor signals ai other than measurement sensor signal az, or it may be a part of the one or more measurement sensor signals ai other than measurement sensor signal az.

[0200] As an example, the target signal removal unit 571 may generate a template signal of the target signal based on one or more measurement sensor signals ai other than the measurement sensor signal az. Then, based on the template signal of the target signal, the target signal removal unit 571 may remove the component of the target signal contained in one or more measurement sensor signals ai other than the measurement sensor signal az, and generate the resulting signal as an environmental noise signal.

[0201] As another example, the target signal removal unit 571 may, based on one or more measurement sensor signals ai other than the measurement sensor signal az, remove the component of the target signal contained in one or more of the measurement sensor signals ai other than the measurement sensor signal az by any other arbitrary method, and generate the resulting signal as an environmental noise signal.

[0202] The environmental noise removal unit 572 removes the environmental noise component from the measurement sensor signal az, based on the measurement sensor signal az acquired by the measurement sensor signal acquisition unit 551, the environmental noise signal generated by the target signal removal unit 571, and one or more reference sensor signals cj acquired by the reference sensor signal acquisition unit 552, and generates the resulting signal as an environmental noise-removed signal.

[0203] Here, one or more such reference sensor signals cj may be, for example, all of the plurality of reference sensor signals c1 to cr, or may be a part of the plurality of reference sensor signals c1 to cr.

[0204] Similar to the foreign object determination unit 533 shown in FIG. 1, the foreign object determination unit 533 determines the presence or absence of the foreign object 251 based on the environmental noise removal signal (a signal regarded as the target signal in this embodiment) generated by the environmental noise removal unit 572.

[0205] Each of the input unit 534, the output unit 535, and the storage unit 536 is, for example, the same as each of the input unit 34, the output unit 35, and the storage unit 36 shown in FIG. 1.

[0206] [An example of the signal processing procedure] FIG. 17 is a diagram showing an example of the signal processing procedure performed by the foreign object detection device 511 according to the embodiment (the third embodiment). This example shows the case where the measurement sensor signal az to be subjected to the removal of the environmental noise component by the environmental noise removal unit 572 is the measurement sensor signal a1.

[0207] (Step S51) [[ID=le=23]]In the foreign object detection device 511, the measurement sensor signal acquisition unit 551 acquires u measurement sensor signals a1 to au. Then, the process proceeds to the process of step S52.

[0208] (Step S52) In the foreign object detection device 511, the reference sensor signal acquisition unit 552 acquires r reference sensor signals c1 to cr. Then, the process proceeds to the process of step S53.

[0209] (Step S53) In the foreign object detection device 511, the target signal removal unit 571 generates an environmental noise signal based on the measurement sensor signals a2 to au. Then, the process moves on to step S54.

[0210] (Step S54) In the foreign object detection device 511, the environmental noise removal unit 572 removes the environmental noise component from the measurement sensor signal a1 using the environmental noise signal and the reference sensor signals c1 to cr. Then, the processing of this flow is completed.

[0211] [Specific examples of signal processing] Figure 18 shows an example of a specific signal processing method performed by the foreign object detection device 511 according to the embodiment (third embodiment). In this example, we show the case where the measurement sensor signal az, which is the target of removal of environmental noise components by the environmental noise removal unit 572, is the measurement sensor signal a1. Furthermore, this example demonstrates a case where an environmental noise signal is generated using the measurement sensor signal a2. Furthermore, this example shows the case where the reference sensor signal c1 is used in the processing by the environmental noise reduction unit 572.

[0212] (Process T21) The measurement sensor signal acquisition unit 551 acquires the measurement sensor signal a1. The measured sensor signal a1 includes the component of the target signal, the component of environmental noise P1, and the component of sensor noise Q1. Here, environmental noise P1 represents environmental noise generated by one or more predetermined environmental noise sources. Furthermore, sensor noise Q1 represents the sensor noise of measurement sensor A1.

[0213] (Processing T22) The measurement sensor signal acquisition unit 551 acquires the measurement sensor signal a2. The measured sensor signal a2 includes the component of the target signal, the component of environmental noise P1, and the component of sensor noise Q2. Here, in the present embodiment, for the sake of simplicity of explanation, it is assumed that the environmental noise P1 that affects the measurement sensor signal a1 and the environmental noise P1 that affects the measurement sensor signal a2 are environmental noises generated from the same environmental noise source. Also, the sensor noise Q2 represents the sensor noise of the measurement sensor A2.

[0214] (Processing T23) The reference sensor signal acquisition unit 552 acquires the reference sensor signal c1. The reference sensor signal c1 includes the component of the environmental noise P1 and the component of the sensor noise Q3. Here, in the present embodiment, for the sake of simplicity of explanation, it is assumed that the environmental noise P1 measured by the reference sensor signal c1 and the environmental noise P1 that affects the measurement sensor signals a1 to a2 are environmental noises generated from the same environmental noise source. Also, the sensor noise Q3 represents the sensor noise of the reference sensor C1.

[0215] In the present embodiment, it is assumed that the level of the component of the environmental noise included in the reference sensor signal c1 is c (c is an arbitrary value) times the level of the component of the environmental noise included in the measurement sensor signal a1.

[0216] (Processing T24) The target signal removal unit 571 removes the component of the target signal from the measurement sensor signal a2 and generates an environmental noise signal.

[0217] (Processing T25) The environmental noise removal unit 572 uses the common component among the measurement sensor signal a1, the environmental noise signal, and the reference sensor signal c1 to remove the component of the environmental noise from the measurement sensor signal a1 by ANC. Here, as the ANC, for example, a general technique may be used. Also, in the present embodiment, the common component is the component of the environmental noise.

[0218] (Processing T26) In the foreign object detection device 511, a signal from which environmental noise has been removed (environmental noise-removed signal) is obtained.

[0219] In this embodiment, the environmental noise-removed signal does not contain environmental noise components but contains components of the target signal. In this embodiment, the ideal case is shown where the environmental noise reduction signal does not contain any components of the environmental noise signal. However, in reality, for example, the environmental noise reduction signal may contain components of the environmental noise signal to a degree that does not cause practical problems (i.e., some components of the environmental noise signal may remain after the removal of the components of the environmental noise signal).

[0220] Furthermore, in this embodiment, the environmental noise reduction signal may include the sensor noise component of measurement sensor A1, the sensor noise component of measurement sensor A2, and the sensor noise component of reference sensor C1. In this embodiment, the sensor noise components of measurement sensor A1, measurement sensor A2, and reference sensor C1 are considered to have little influence on the target signal and are therefore ignored. Alternatively, one or more of the sensor noise components of measurement sensor A1, measurement sensor A2, and reference sensor C1 may be removed by any method. In this case, the environmental noise-removed signal will not contain one or more of the sensor noise components of measurement sensor A1, measurement sensor A2, and reference sensor C1. Such a method may be incorporated, for example, into the processing by the target signal removal unit 571, into the processing by the environmental noise removal unit 572, into both of these, or into another processing performed by the signal processing unit 532.

[0221] In this embodiment, when the environmental noise removal unit 572 subtracts the environmental noise component from the measurement sensor signal a1, the time period during which the measurement sensor signal a1 was measured, the time period during which the environmental noise signal (included in the measurement sensor signal a2) was measured, and the time period during which the reference sensor signal c1 was measured coincide. In other words, it is assumed that the measurement sensor signal a1, the environmental noise signal, and the reference sensor signal c1 all contain similar environmental noise components during the same time period. As a result, the environmental noise component is accurately removed from the measurement sensor signal a1.

[0222] In this example, we have shown a case where an environmental noise signal is generated based on one measurement sensor signal a2 in processes T22 and T24. However, as an example of other configurations, a process may be performed to generate an environmental noise signal using two or more measurement sensor signals ai. Furthermore, in this example, we showed the case where one reference sensor signal c1 is used to remove the environmental noise component from the measurement sensor signal a1 in processes T23 and T25. However, as another example of a configuration, processing may be performed using two or more reference sensor signals cj when removing the environmental noise component from the measurement sensor signal a1.

[0223] In the examples in Figures 17 and 18, environmental noise reduction processing (in this embodiment, processing by the target signal reduction unit 571 and processing by the environmental noise reduction unit 572) is shown for one measurement sensor signal a1. However, as an example of other configurations, environmental noise reduction processing may be performed for all or some (any two or more) of the multiple measurement sensor signals a1 to an.

[0224] (Regarding the third embodiment) As described above, in the foreign object detection system 501 according to this embodiment, the foreign object detection device 511 can effectively remove the environmental noise component superimposed on the measurement sensor signal a1. In the foreign object detection device 511 according to this embodiment, for example, by performing environmental noise removal processing using the reference sensor signals c1 to cr together with the measurement sensor signals a1 to au, the accuracy of generating a signal from which the environmental noise component has been removed (environmental noise-removed signal) can be improved.

[0225] Furthermore, in the foreign object detection device 511 according to this embodiment, in a configuration in which reference sensors C1 to Cr are used, it is also possible to utilize measurement sensor signals a1 to au. In other words, in the foreign object detection device 511 according to this embodiment, for example, in an environment where a small number of reference sensors are installed, it is possible to accurately remove environmental noise components by using the measurement sensor signal to reinforce a small number of reference sensors.

[0226] For example, even if there is only one type of environmental noise, the accuracy of removing the environmental noise component will be higher if there are multiple signals used to remove the environmental noise (in this embodiment, the measurement sensor signal and the reference sensor signal).

[0227] For example, if there is only one type of environmental noise, one reference sensor is often sufficient. However, in ANC, accuracy is improved when there are more sensors than there are environmental noise sources. In other words, when there are multiple types of noise sources, the environmental noise components included in each sensor signal (measurement sensor signal or reference sensor signal) may differ in degree from each type of environmental noise source. For this reason, the foreign object detection device 511 according to this embodiment is effective.

[0228] (Fourth Embodiment) [Foreign object detection system] In this embodiment, the foreign object detection system 501 shown in Figure 16 will be described with reference. In this embodiment, if the reference sensor signal cj measured by one or more reference sensors Cj contains a component of the target signal, the reference sensor signal cj is treated as a measured sensor signal and signal processing is performed by the signal processing unit 532.

[0229] In this case, the reference sensor signal cj does not inherently contain the components of the target signal. However, in this embodiment, if the reference sensor signal cj contains the components of the target signal as a result of the measurement, the foreign object detection device 511 treats the reference sensor signal cj as a measurement sensor signal and uses it to perform environmental noise removal processing.

[0230] Here, for example, the signal processing unit 532 may determine whether or not the component of the target signal is included in each reference sensor signal cj. Any method may be used for such determination. For example, the signal processing unit 532 may, if it determines that a reference sensor signal cj containing the components of the target signal has been generated, even though the reference sensor signal cj normally does not contain the components of the target signal, treat that reference sensor signal cj as the measurement sensor signal and use it.

[0231] For example, in a foreign object detection system comprising one measuring sensor, one reference sensor, and a foreign object detection device, the foreign object detection device may, if the reference sensor signal measured by the reference sensor contains a component of the target signal, treat the reference sensor signal as the measuring sensor signal and use it to perform environmental noise reduction processing based on the measuring sensor signal measured by the measuring sensor and the reference sensor signal.

[0232] (Regarding the fourth embodiment) As described above, in the foreign object detection system 501 according to this embodiment, even if the reference sensor signal cj measured by the reference sensor Cj in the foreign object detection device 511 unintentionally contains components of the target signal (for example, if the original reference fails), the reference sensor signal cj can be used to effectively remove the environmental noise components superimposed on the measured sensor signal.

[0233] In the foreign object detection system 501 according to this embodiment, the original reference sensor signal is used together with the environmental noise signal generated from the measurement sensor signal ai (a signal that is essentially like a reference sensor signal) in the environmental noise removal process. This effectively increases the number of environmental noise signals and enhances the effectiveness of removing environmental noise components.

[0234] Thus, in the foreign object detection system 501 according to this embodiment, even if, for example, the components of the target signal are superimposed on the measurement results from the installed reference sensor Cj, it is possible to reduce the components of environmental noise.

[0235] <Example Configuration> As an example configuration, the signal processing method includes: a first process of acquiring a first sensor signal measured by a first sensor, which includes components of the target signal and environmental noise; a second sensor signal measured by a second sensor, which includes components of the target signal and environmental noise; a second process of generating a first processed signal from which the components of the target signal contained in the second sensor signal have been removed; and a third process of generating a second processed signal from which the components of the environmental noise contained in the first sensor signal have been removed based on the first processed signal.

[0236] In the example in Figure 1, measurement sensor A1 is an example of a first sensor, and measurement sensor signal a1 is an example of a first sensor signal. In the example in Figure 1, measurement sensor A2 is an example of a second sensor, and measurement sensor signal a2 is an example of a second sensor signal. In the examples in Figure 6, Figure 7, and Figure 10, the processes in step S1, T1, T2, and T11, T12 are examples of the first process; the processes in step S2, T3, and T13, T14 are examples of the second process; and the processes in step S3, T4, T5, and T15, T16 are examples of the third process. In these examples, the ambient noise signal is an example of the first processed signal, and the ambient noise removal signal is an example of the second processed signal. In these examples, the first sensor and the second sensor are sensors (measuring sensors) provided to measure the target signal, respectively.

[0237] In the example in Figure 16, measurement sensor A1 may be an example of a first sensor, and measurement sensor signal a1 may be an example of a first sensor signal. In the example in Figure 16, reference sensor C1 may be an example of a second sensor, and reference sensor signal c1, which includes components of the target signal and environmental noise, may be an example of a second sensor signal. In this example, the ambient noise signal is an example of the first processed signal, and the ambient noise removal signal is an example of the second processed signal. In this example, the first sensor is a sensor (measuring sensor) provided to measure the target signal. In this example, the second sensor is a sensor (reference sensor) provided to measure environmental noise, and as a result of the measurement, a second sensor signal is obtained that includes components of the target signal and components of environmental noise.

[0238] As an example configuration, in a signal processing method, the first process acquires a first sensor signal and a first sensor signal group, which is a group of sensor signals measured by each of a plurality of sensors, including a second sensor but not the first sensor, and which includes components of the target signal and environmental noise. The second process generates a first processed signal based on the first sensor signal group.

[0239] In the example in Figure 11, measurement sensor A1 is an example of a first sensor, and measurement sensor signal a1 is an example of a first sensor signal. In the example in Figure 11, multiple measurement sensors A2 to An, including measurement sensor A2, are an example of multiple sensors including a second sensor, and measurement sensor signals a2 to an are examples of sensor signals measured by each of the multiple sensors including the second sensor. In the example in Figure 12, the process in step S21 is an example of the first process, the process in step S22 is an example of the second process, and the process in step S23 is an example of the third process. In this example, the ambient noise signal is an example of the first processed signal, and the ambient noise removal signal is an example of the second processed signal.

[0240] As an example configuration, in a signal processing method, the second process generates a first processed signal from which the component of the target signal contained in the second sensor signal has been removed from the second sensor signal, and also generates a third processed signal from which the component of the target signal contained in the sensor signals other than the second sensor signal that are included in the first sensor signal group has been removed, and the third process generates a second processed signal based on the first processed signal and the third processed signal.

[0241] In the example shown in Figure 12, in step S22, environmental noise signals (two or more environmental noise signals in total) may be generated from each of two or more measurement sensor signals. In this case, an environmental noise signal generated from one measurement sensor signal is an example of a first processing signal, and an environmental noise signal generated from another measurement sensor signal is an example of a third processing signal.

[0242] As an example configuration, the signal processing method further performs a fourth process, which generates a fourth processed signal from which the component of the target signal contained in the sensor signal has been removed, based on one or more sensor signals other than the second sensor signal; and a fifth process, which generates a fifth processed signal from which the component of environmental noise contained in the second sensor signal has been removed, based on the fourth processed signal.

[0243] In the example shown in Figure 14, the process in step S41 is an example of the first process. In the example shown in Figure 14, the processing in step S43 is an example of the second and third processing when the target for removing environmental noise components is the first sensor signal (e.g., measurement sensor signal a1). In the example shown in Figure 14, the processing in step S43 is an example of the fourth and fifth processes when the target for removing environmental noise components is the second sensor signal (e.g., the measurement sensor signal a2). In this example, the environmental noise signal and the environmental noise removal signal are examples of the first and second processing signals, respectively, when the target for removing environmental noise components is the first sensor signal (e.g., measurement sensor signal a1). In this example, the environmental noise signal and the environmental noise removal signal are examples of the fourth and fifth processing signals, respectively, when the target for removing environmental noise components is the second sensor signal (e.g., measurement sensor signal a2). In the example shown in Figure 14, environmental noise reduction processing is performed on each of the multiple measurement sensor signals a1 to an.

[0244] As an example configuration, in a signal processing method, each of the sensor signals, including the first sensor signal and the second sensor signal, is designated as a target sensor signal, and for each target sensor signal, an environmental noise signal for removal is generated based on some or all of the other sensor signals, thereby removing the environmental noise component from the target sensor signal.

[0245] In the example in Figure 14, each of the multiple measurement sensor signals a1 to an is designated as the target sensor signal in order. In the example shown in Figure 14, the process in step S43 is performed for each target sensor signal. In the process in step S43, for example, for each target sensor signal (measurement sensor signal ak), an environmental noise signal for removal is generated based on some or all of the other sensor signals, and the environmental noise component is removed from the target sensor signal.

[0246] As an example configuration, in a signal processing method, the second process generates a template signal of the target signal by performing an averaging process on the second sensor signal, and generates the first processed signal by removing the template signal from the signal portion corresponding to the component of the target signal contained in the second sensor signal.

[0247] In the examples in Figures 8 to 10, the target signal template signal 2131 shown in Figure 8 is an example of a target signal template signal. Also, in the example in Figure 3, the target signal 2031 (and a similar waveform portion) included in the measurement sensor signal 2012 (measurement sensor signal a2) is an example of a signal portion corresponding to the component of the target signal included in the second sensor signal.

[0248] As an example configuration, in a signal processing method, the second process generates a template signal of the target signal by performing an averaging process on the first sensor signal group, and generates the first processed signal by removing the template signal from the signal portion corresponding to the component of the target signal included in the second sensor signal.

[0249] In the example shown in Figure 13, a template signal for the target signal is generated based on multiple measurement sensor signals a2 to an.

[0250] As an example configuration, in a signal processing method, the first process further acquires a first reference sensor signal measured by a first reference sensor, which includes environmental noise components and does not include components of the target signal, and the third process generates a second processed signal based on the first processed signal and the first reference sensor signal, from which the environmental noise components included in the first sensor signal have been removed.

[0251] In the examples shown in Figures 16 to 18, reference sensor C1 is an example of a first reference sensor, and reference sensor signal c1 is an example of a first reference sensor signal. Note that two or more of the multiple reference sensors C1 to Cr and reference sensor signals c1 to Cr may be used. In the examples in Figure 17 and Figure 18, steps S51 to S52 and processes T21 to T23 are examples of the first process, steps S53 and T24 are examples of the second process, and steps S54 and T25 and T26 are examples of the third process. In these examples, the ambient noise signal is an example of the first processed signal, and the ambient noise removal signal is an example of the second processed signal.

[0252] As an example configuration, in the signal processing method, the second process uses digital filtering. As an example configuration, in a signal processing method, the second process uses one or more of the following: principal component analysis, independent component analysis, or singular value decomposition. As an example configuration, in a signal processing method, the sensor signal is a magnetic signal.

[0253] It is possible to provide a device that has the function of performing predetermined signal processing (foreign object detection devices 11, 311, and 511 in the examples of Figures 1, 11, and 16). As an example configuration, the signal processing device (foreign object detection devices 11, 311, and 511 in the examples of Figures 1, 11, and 16) includes a sensor signal acquisition unit (sensor signal acquisition units 31, 331, and 531 in the examples of Figures 1, 11, and 16) that acquires a first sensor signal measured by a first sensor, which includes components of the target signal and environmental noise, and a second sensor signal measured by a second sensor, which includes components of the target signal and environmental noise; a target signal removal unit (target signal removal units 51, 351, and 571 in the examples of Figures 1, 11, and 16) that generates a first processed signal from which the components of the target signal contained in the second sensor signal have been removed; and an environmental noise removal unit (environmental noise removal units 52, 352, and 572 in the examples of Figures 1, 11, and 16) that generates a second processed signal from which the components of the environmental noise contained in the first sensor signal have been removed based on the first processed signal.

[0254] It is possible to provide a program (computer program) that has the function of performing predetermined signal processing. As an example configuration, the program is a program that causes a computer (in the examples in Figures 1, 11, and 16, the computers that make up the foreign object detection devices 11, 311, and 511) to implement the following functions: a first function that acquires a first sensor signal measured by a first sensor, which includes components of the target signal and environmental noise; a second sensor signal measured by a second sensor, which includes components of the target signal and environmental noise; a second function that generates a first processed signal from which the components of the target signal included in the second sensor signal have been removed; and a third function that generates a second processed signal from which the components of the environmental noise included in the first sensor signal have been removed based on the first processed signal.

[0255] Furthermore, a program to implement the function of any component in any of the foreign object detection devices 11, 311, 511, etc., described above, may be recorded on a computer-readable recording medium, and the program may be loaded into a computer system and executed. Here, "computer system" includes hardware such as operating systems and peripheral devices. Furthermore, "computer-readable recording medium" refers to portable media such as flexible disks, magneto-optical disks, ROMs, CD (Compact Disc)-ROMs (Read Only Memory), and storage devices such as hard disks built into computer systems. In addition, "computer-readable recording medium" also includes volatile memory inside a computer system that retains a program for a certain period of time, such as volatile memory inside a computer system that acts as a server or client when a program is transmitted via a network such as the Internet or a communication line such as a telephone line. Such volatile memory may be, for example, RAM (Random Access Memory). The recording medium may be, for example, a non-temporary recording medium.

[0256] Furthermore, the above program may be transmitted from a computer system that stores the program in a memory device or the like to another computer system via a transmission medium or by transmission waves within the transmission medium. Here, the "transmission medium" used to transmit the program refers to a medium that has the function of transmitting information, such as a network like the Internet or a communication line like a telephone line. Furthermore, the above program may be intended to implement only a portion of the functions described above. Moreover, the above program may be a so-called differential file, capable of implementing the aforementioned functions in combination with programs already recorded in the computer system. A differential file may also be called a differential program.

[0257] Furthermore, the functions of any component in any of the foreign object detection devices 11, 311, 511, etc., described above may be implemented by a processor. For example, each process in the embodiment may be implemented by a processor that operates based on information such as a program, and a computer-readable recording medium that stores information such as a program. Here, the processor may be implemented by having the functions of each part implemented by separate hardware, or by having the functions of each part implemented by integrated hardware. For example, the processor includes hardware, and the hardware may include at least one of a circuit that processes digital signals and a circuit that processes analog signals. For example, the processor may be configured using one or more circuit devices or one or both of one or more circuit elements mounted on a circuit board. An IC (Integrated Circuit) may be used as the circuit device, and a resistor or capacitor may be used as the circuit element.

[0258] Here, the processor may be, for example, a CPU. However, the processor is not limited to a CPU; various types of processors may be used, such as a GPU (Graphics Processing Unit) or a DSP (Digital Signal Processor). The processor may also be, for example, a hardware circuit using an ASIC (Application Specific Integrated Circuit). Furthermore, the processor may be composed of, for example, multiple CPUs, or multiple hardware circuits using ASICs. The processor may also be composed of, for example, a combination of multiple CPUs and multiple hardware circuits using ASICs. The processor may also include, for example, one or more amplifier circuits or filter circuits that process analog signals.

[0259] While embodiments of this invention have been described in detail above with reference to the drawings, the specific configuration is not limited to these embodiments and includes designs and the like that do not depart from the spirit of this invention. [Explanation of Symbols]

[0260] 1, 301, 501 Foreign Object Detection System 11, 311, 511 Foreign object detection device 31, 331, 531 Sensor signal acquisition unit 32, 332, 532 Signal Processing Unit 33, 333, 533 Foreign object detection section 34, 334, 534 Input section 35, 335, 535 Output section 36, 336, 536 storage section 51, 351, 571 Target signal removal section 52, 352, 572 Environmental noise reduction section 111, 411, 431, 611, 631 Sensor section 211 Belt conveyor 231, 232 Items to be inspected 251 Foreign matter 2011, 2012 Measurement sensor signals 2013 Environmental Noise Signals 2014 Environmental Noise Reduction Signal 2021, 2031, 2041 target signal 2111 Measurement sensor signal portion 2131 Target signal template signal A1~An, Au, A11~Axy measurement sensors G1~Gn, Gu, F1~Fr Network H1 direction

Claims

1. A first process for acquiring a first sensor signal measured by a first sensor, which includes components of the target signal and environmental noise, and a second sensor signal measured by a second sensor, which includes components of the target signal and environmental noise. A second process that generates a first processed signal from the second sensor signal, in which the component of the target signal contained in the second sensor signal is removed, A third process that generates a second processed signal from the first sensor signal based on the first processed signal, from which the environmental noise component contained in the first sensor signal has been removed. A signal processing method that performs the following: The second process described above is: The second sensor signal is subjected to an averaging process to generate a template signal for the target signal. The first processing signal is generated by removing the template signal from the signal portion corresponding to the component of the target signal included in the second sensor signal. Signal processing method.

2. The first process further acquires a first reference sensor signal measured by the first reference sensor, which includes the environmental noise component but does not include the target signal component. The third process generates a second processed signal from the first sensor signal, based on the first processed signal and the first reference sensor signal, from which the environmental noise component included in the first sensor signal has been removed. The signal processing method according to claim 1.

3. The second process uses digital filtering. The signal processing method according to claim 1 or claim 2.

4. The second process uses one or more of the following methods: principal component analysis, independent component analysis, or singular value decomposition. The signal processing method according to any one of claims 1 to 3.

5. The aforementioned sensor signal is a magnetic signal. The signal processing method according to any one of claims 1 to 4.

6. A first process for acquiring a first sensor signal measured by a first sensor, which includes components of the target signal and environmental noise, and a second sensor signal measured by a second sensor, which includes components of the target signal and environmental noise. A second process that generates a first processed signal from the second sensor signal, in which the component of the target signal contained in the second sensor signal is removed, A third process that generates a second processed signal from the first sensor signal based on the first processed signal, from which the environmental noise component contained in the first sensor signal has been removed. A signal processing method that performs the following: The first process acquires the first sensor signal and also acquires a first sensor signal group which is a group of sensor signals that include the components of the target signal and the components of the environmental noise, measured by each of a plurality of sensors that do not include the first sensor but include the second sensor, and includes the components of the target signal and the environmental noise. The second process described above is: The first sensor signal group is subjected to an averaging process to generate a template signal for the target signal. The first processing signal is generated by removing the template signal from the signal portion corresponding to the component of the target signal included in the second sensor signal. Signal processing method.

7. The second process generates a first processed signal from which the component of the target signal contained in the second sensor signal has been removed, and generates a third processed signal from which the component of the target signal contained in the sensor signals other than the second sensor signal included in the group of first sensor signals has been removed. The third process generates the second process signal based on the first process signal and the third process signal. The signal processing method according to claim 6.

8. moreover, A fourth process that generates a fourth processed signal from which the component of the target signal contained in the sensor signal is removed, based on one or more sensor signals other than the second sensor signal, A fifth process that generates a fifth processed signal from the second sensor signal, in which the environmental noise component contained in the second sensor signal is removed, based on the fourth processed signal. Execute The signal processing method according to claim 6 or claim 7.

9. A first process for acquiring a plurality of sensor signals, each of three or more sensors, which include a component of the target signal and a component of environmental noise, For each of these multiple sensor signals, a second process is performed to generate a first processed signal from which the component of the target signal contained in the second sensor signal is removed, with each of the sensor signals being treated as a first sensor signal and the other sensor signals being treated as second sensor signals. A third process that generates a second processed signal from the first sensor signal based on the first processed signal, from which the environmental noise component contained in the first sensor signal has been removed. A signal processing method that performs the following: The second process described above is: A template signal for the target signal is generated by performing an averaging process on the first sensor signal group, which is a group of sensor signals measured by two or more sensors, including the sensor that measured the second sensor signal but not the sensor that measured the first sensor signal. The first processing signal is generated by removing the template signal from the signal portion corresponding to the component of the target signal included in the second sensor signal. Signal processing method.

10. The first process further acquires a first reference sensor signal measured by the first reference sensor, which includes the environmental noise component but does not include the target signal component. The third process generates a second processed signal from the first sensor signal, based on the first processed signal and the first reference sensor signal, from which the environmental noise component included in the first sensor signal has been removed. The signal processing method according to any one of claims 6 to 9.

11. The second process uses digital filtering. The signal processing method according to any one of claims 6 to 10.

12. The second process uses one or more of the following methods: principal component analysis, independent component analysis, or singular value decomposition. The signal processing method according to any one of claims 6 to 11.

13. The aforementioned sensor signal is a magnetic signal. The signal processing method according to any one of claims 6 to 12.

14. A sensor signal acquisition unit acquires a first sensor signal measured by a first sensor, which includes components of the target signal and environmental noise, and a second sensor signal measured by a second sensor, which includes components of the target signal and environmental noise. A target signal removal unit generates a first processed signal from which the component of the target signal contained in the second sensor signal has been removed, An environmental noise removal unit generates a second processed signal from the first sensor signal based on the first processed signal, from which the environmental noise component contained in the first sensor signal has been removed. Equipped with, The aforementioned target signal removal unit is: The second sensor signal is subjected to an averaging process to generate a template signal for the target signal. The first processing signal is generated by removing the template signal from the signal portion corresponding to the component of the target signal included in the second sensor signal. Signal processing device.

15. A sensor signal acquisition unit acquires a first sensor signal measured by a first sensor, which includes components of the target signal and environmental noise, and a second sensor signal measured by a second sensor, which includes components of the target signal and environmental noise. A target signal removal unit generates a first processed signal from which the component of the target signal contained in the second sensor signal has been removed, An environmental noise removal unit generates a second processed signal from the first sensor signal based on the first processed signal, from which the environmental noise component contained in the first sensor signal has been removed. Equipped with, The sensor signal acquisition unit acquires the first sensor signal and also acquires a first sensor signal group which is a group of sensor signals that include the components of the target signal and the components of the environmental noise, and which are measured by each of a plurality of sensors that do not include the first sensor but include the second sensor. The aforementioned target signal removal unit is: The first sensor signal group is subjected to an averaging process to generate a template signal for the target signal. The first processing signal is generated by removing the template signal from the signal portion corresponding to the component of the target signal included in the second sensor signal. Signal processing device.

16. A sensor signal acquisition unit that acquires a plurality of sensor signals, each of three or more sensors, which include a component of the target signal and a component of environmental noise, A target signal removal unit generates a first processed signal from each of these multiple sensor signals, with each of the sensor signals being treated as a first sensor signal and the other sensor signals being treated as second sensor signals, and the component of the target signal contained in the second sensor signal being removed from the second sensor signal. An environmental signal removal unit generates a second processed signal from the first sensor signal, in which the environmental noise component contained in the first sensor signal is removed, based on the first processed signal. Equipped with, The aforementioned target signal removal unit is: A template signal for the target signal is generated by performing an averaging process on the first sensor signal group, which is a group of sensor signals measured by two or more sensors, including the sensor that measured the second sensor signal but not the sensor that measured the first sensor signal. The first processing signal is generated by removing the template signal from the signal portion corresponding to the component of the target signal included in the second sensor signal. Signal processing device.

17. A first function that acquires a first sensor signal measured by a first sensor, which includes components of the target signal and environmental noise, and a second sensor signal measured by a second sensor, which includes components of the target signal and environmental noise. A second function generates a first processed signal from which the component of the target signal contained in the second sensor signal has been removed, A third function that generates a second processed signal from the first sensor signal based on the first processed signal, in which the environmental noise component contained in the first sensor signal has been removed. A program to make a computer realize this, The second function described above is: The second sensor signal is subjected to an averaging process to generate a template signal for the target signal. The first processing signal is generated by removing the template signal from the signal portion corresponding to the component of the target signal included in the second sensor signal. program.

18. A first function that acquires a first sensor signal measured by a first sensor, which includes components of the target signal and environmental noise, and a second sensor signal measured by a second sensor, which includes components of the target signal and environmental noise. A second function generates a first processed signal from which the component of the target signal contained in the second sensor signal has been removed, A third function that generates a second processed signal from the first sensor signal based on the first processed signal, in which the environmental noise component contained in the first sensor signal has been removed. A program to make a computer realize this, The first function acquires the first sensor signal and also acquires a group of first sensor signals, which is a group of sensor signals measured by each of a plurality of sensors, including the second sensor but not the first sensor, and which include the components of the target signal and the environmental noise. The second function described above is: The first sensor signal group is subjected to an averaging process to generate a template signal for the target signal. The first processing signal is generated by removing the template signal from the signal portion corresponding to the component of the target signal included in the second sensor signal. program.

19. A first function for acquiring a plurality of sensor signals, each of three or more sensors, which include a component of the target signal and a component of environmental noise, A second function that, for each of these multiple sensor signals, generates a first processed signal from which the component of the target signal contained in the second sensor signal is removed, with each of the sensor signals being treated as a first sensor signal and the sensor signals other than the first sensor signal being treated as second sensor signals. A third function that generates a second processed signal from the first sensor signal based on the first processed signal, in which the environmental noise component contained in the first sensor signal has been removed. A program to make a computer realize this, The second function described above is: A template signal for the target signal is generated by performing an averaging process on the first sensor signal group, which is a group of sensor signals measured by two or more sensors, including the sensor that measured the second sensor signal but not the sensor that measured the first sensor signal. The first processing signal is generated by removing the template signal from the signal portion corresponding to the component of the target signal included in the second sensor signal. program.

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