Patent Description:
A rail used in a railroad and the like is deformed as a vehicle runs, and a positional deviation of the rail is caused. When the positional deviation of the rail is unattended, a vehicle derailment may occur. Therefore, there is proposed a technique for providing an apparatus which detects the positional deviation of the rail in an inspection vehicle (a railway vehicle for inspecting a state of a route and an overhead wire).

For example, in Paragraph <NUM> of PTL <NUM>, there is described "Therefore, in a rail position detection unit <NUM> according to the embodiment (that is, a two-dimensional laser displacement meter), as illustrated in Fig. <NUM>(a), a distance from the rail position detection unit <NUM> to a rail R, and a distance from the rail position detection unit <NUM> to a vehicle wheel <NUM> are measured at the same time to detect a position (hereinafter, simply referred to as "position of the rail") in a vehicle axial direction of the rail with respect to the vehicle wheel <NUM>".

In addition, in Abstract of PTL <NUM>, there is described "According to an embodiment, the present technique is to provide a test device for testing perfectness of a material in a test target. The test device includes an electrical conductor and a detection device. In a typical inspection device, the electrical conductor generally extends in a linear direction, and a current generally flows in a direction traversing a longitudinal axis of the test target. The path of the current flowing in the electrical conductor affects a magnetic field around the test target, and generates an overcurrent indirectly. In addition, the test device includes a detection device which is disposed at a position away from the electrical conductor, and detects a magnetic field generated according to the current flowing through the electrical conductor.

PTL <NUM> describes a magnetic field that is used to induce eddy currents on both ends of a sensor coil, such that an induction signal is generated on both ends of the sensor coil. As mechanical displacement of the sensor coil is caused by the eddy currents acting on the sensor coil, the mechanical displacement of the sensor coil is used to generate a direct current voltage signal.

PTL <NUM> discloses a rail displacement detection system comprising a primary coil and two secondary coils which are arranged on a truck of a measuring car. When the primary coil is excited by an AC, the secondary coil are magnetically coupled by magnetic lines of force. Since both secondary coils are differentially connected, the output becomes zero when the rail is located at the central position between both coils. When the rail is displaced in the horizontal direction, the detected signal corresponding to the amount of the displacement is outputted.

However, in the technique of PTL <NUM>, if foreign matters such as snow, ice, weeds, and fallen leaves are attached to a rail, a laser beam is reflected on these foreign matters, and thus a position of the rail is erroneously detected.

In addition, in the technique of PTL <NUM>, a magnetic field generated by an overcurrent is detected. However, a magnitude of the overcurrent is reversely proportional to a square of a distance between a test device and a test target (rail). Therefore, an error generated by vibration of an inspection vehicle becomes large, and a positional deviation of the rail is hardly detected with accuracy.

The invention has been made in view of the problems, and an object thereof is to provide a rail inspection system which can detect the positional deviation of the rail with accuracy. Solution to Problem.

In order to solve the problems, a rail inspection system of the invention as defined in claim <NUM> is provided.

According to the rail inspection system of the invention, it is possible to detect a positional deviation of a rail with accuracy.

<FIG> is a perspective view partially broken away of a rail inspection system <NUM> in a first embodiment of the invention.

The rail inspection system <NUM> in <FIG> includes a detection device <NUM>, a processing device <NUM>, and a cable <NUM> which connects the detection device <NUM> and the processing device <NUM>. The rail inspection system <NUM> is mounted in an inspection vehicle (not illustrated). The detection device <NUM> is provided at a position facing a railroad rail <NUM> (rail) which is an inspection target. The processing device <NUM> is provided in a cabin of the inspection vehicle. Herein, a layout direction of the railroad rail <NUM> is set to a "front and rear direction", a direction horizontally perpendicular to the layout direction is set to a "left and right direction", and a direction vertically perpendicular to the layout direction is set to an "upper and lower direction".

The detection device <NUM> includes a chassis <NUM> which is formed in a hollow cuboid shape, and a rectangular flange <NUM> (attaching tool) which is fixed to the upper surface of the chassis <NUM>. Through holes 25a are formed at four corners of the flange <NUM>. In addition, screw holes are formed at positions facing these through holes 25a in a dolly (not illustrated) of the inspection vehicle. Bolts (not illustrated) pass through the through holes 25a and the screw holes, and are fastened, so that the detection device <NUM> is fixed at a predetermined position of the dolly. When the railroad rail <NUM> is laid at a predetermined reference position, and the detection device <NUM> is fixed to the predetermined position, a center line CR of the railroad rail <NUM> and a center line CS of the detection device <NUM> coincide as in the drawing. Therefore, the flange <NUM> serves as a tool to adjust the center line CR of the detection device <NUM> to a predetermined position.

The chassis <NUM> is a non-magnetic material such as glass epoxy. In the bottom surface of the chassis <NUM>, a sensor unit <NUM> (first sensor unit) of a substantially cuboid shape and an amplification/filter unit <NUM> are fixed. In the center in the sensor unit <NUM>, a receiver coil <NUM> (first receiver coil) cylindrically winding a coated wire is disposed, and an oscillation coil 5A (first oscillation coil) and an oscillation coil 5B (second oscillation coil) formed similarly to the receiver coil <NUM> are disposed at an equal interval in the left and right direction of the receiver coil <NUM>. In the oscillation coils 5A and 5B, AC voltage of a predetermined oscillation frequency f is applied from the processing device <NUM> through the cable <NUM>. Thus, the oscillation coils 5A and 5B generate AC magnetic fields peripherally. In addition, an induced voltage is generated in the receiver coil <NUM> in proportion to a differentiated value of an interlinking magnetic flux.

The amplification/filter unit <NUM> amplifies the induced voltage of the receiver coil <NUM>, and performs filtering, and supplies the result to the processing device <NUM>. The processing device <NUM> detects a magnitude of a positional deviation of the railroad rail <NUM> based on the supplied detection signal. Herein, the positional deviation is a value corresponding to a displacement L (see <FIG>) of the center line CR of the railroad rail <NUM> and the center line CS of the detection device <NUM>. An inner space <NUM> of the chassis <NUM> is filled with resin (not illustrated). With this configuration, even when vibration and impact are added to the detection device <NUM>, deviation is not caused in the sensor unit <NUM> and the like.

Next, a principle of the position detection in this embodiment will be described with reference to <FIG>.

<FIG> illustrates a layout of the oscillation coils 5A and 5B and the receiver coil <NUM> when the center line CR of the railroad rail <NUM> and the center line CS of the detection device <NUM> (see <FIG>) are matched.

As illustrated in the drawing, the center line CS of the detection device <NUM> is also a center line of the receiver coil <NUM>. A distance in the upper and lower direction between the oscillation coils 5A and 5B and the receiver coil <NUM> and the railroad rail <NUM> is called a sensor gap d (distance). AC voltage having a reverse phase is applied to the oscillation coils 5A and 5B to generate reverse magnetic fields from the oscillation coils 5A and 5B. More specifically, the oscillation coils 5A and 5B are connected in series, and the AC voltage is applied to the series circuit.

Magnetic fluxes ΦA and ΦB respectively generated by the oscillation coils 5A and 5B are propagated through the railroad rail <NUM> and the air. Both magnetic fields cancel each other in the receiver coil <NUM>, the interlinking magnetic flux in the receiver coil <NUM> becomes almost zero, and the induced voltage of the receiver coil <NUM> also becomes almost zero.

In addition, <FIG> illustrates a layout of the oscillation coils 5A and 5B and the receiver coil <NUM> when the center line CR of the railroad rail <NUM> and the center line CS of the detection device <NUM> (see <FIG>) are not matched.

The magnetic field generated by the oscillation coil 5A is propagated through the air with low magnetic permeability in a longer distance than the railroad rail <NUM> with high magnetic permeability. Therefore, the magnetic flux ΦB (amplitude) generated by the oscillation coil 5B becomes relatively stronger than that magnetic flux ΦA (amplitude) generated by the oscillation coil 5A. In the receiver coil <NUM>, a non-zero interlinking magnetic flux is generated, and a non-zero induced voltage is generated. Therefore, the induced voltage is measured and output as the detection signal, so that the displacement L between the center line CR of the railroad rail <NUM> and the center line CS of the detection device <NUM> can be measured. When a left edge position EL of the railroad rail <NUM> is located between the oscillation coil 5A and the receiver coil <NUM> (the illustrated state), or a right edge position ER of the railroad rail <NUM> is located between the oscillation coil 5B and the receiver coil <NUM>, a peak amplitude of the detection signal appears.

Next, <FIG> illustrates levels of the detection signals output from the receiver coil <NUM> in accordance with various sensor gaps d. In <FIG>, the horizontal axis represents the displacement L, and the vertical axis represents the level of the detection signal. Further, when the phase of the AC voltage applied to the oscillation coils 5A and 5B and the phase of the detection signal are matched, the value of the detection signal is set to be positive. When the both phases are reverse, the value of the detection signal is set to be negative. Further, characteristics P20, P25, P30, P35, and P40 in the drawing are characteristics when these sensor gaps d are <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>.

These characteristics P20 to P40 all are maximized at a displacement L<NUM> (first displacement), and minimized at a displacement L<NUM> (second displacement). Considering the amplitude of the induced voltage, it means that a first maximum value appears at the displacement L<NUM>, and a second maximum value of which the phase is reversed against the first maximum value appears at the displacement L<NUM>. In addition, characteristics P20 to P40 are almost linear near the displacement L = <NUM>, and the displacement L is almost proportional to the detection signal.

<FIG> is a block diagram illustrating an entire configuration of the rail inspection system <NUM> according to the embodiment.

As described above, the rail inspection system <NUM> includes the detection device <NUM> and the processing device <NUM>.

In addition, the detection device <NUM> includes the sensor unit <NUM> and the amplification/filter unit <NUM>, and the sensor unit <NUM> includes the oscillation coils 5A and 5B and the receiver coil <NUM>. In addition, the processing device <NUM> includes an amplifying unit <NUM> (AC voltage source), a digital-analog converting unit <NUM> (AC voltage source), an oscillating unit <NUM> (AC voltage source), a wave detecting unit <NUM>, an analog-digital converting unit <NUM>, a memory unit <NUM>, a data communication unit <NUM>, a power source <NUM>, and an evaluation device <NUM> (displacement detection unit).

The oscillating unit <NUM> outputs a sinusoidal digital oscillation signal of the predetermined oscillation frequency f (for example, <NUM>). The digital-analog converting unit <NUM> converts the digital oscillation signal output by the oscillating unit <NUM> into analog AC voltage. The amplifying unit <NUM> amplifies the AC voltage and applies the AC voltage to the oscillation coils 5A and 5B. The oscillation coils 5A and 5B generate the reverse magnetic fields of which the phases are reversed.

In addition, the amplification/filter unit <NUM> in the detection device <NUM> amplifies and filters the detection signal supplied from the receiver coil <NUM>, and transmits the signal to the wave detecting unit <NUM> of the processing device <NUM>. Further, the "filtering" is a low-pass filtering (LPF) in which frequency components equal to or more than the oscillation frequency f are mainly removed. In addition, the wave detecting unit <NUM> performs a full-wave rectification on the detection signal supplied from the amplification/filter unit <NUM> using a reference signal from the oscillating unit <NUM>, and supplies the signal to the analog-digital converting unit <NUM>. The analog-digital converting unit <NUM> converts the analog signal received from the wave detecting unit <NUM> into a digital signal. The digital signal output from the analog-digital converting unit <NUM> is stored in the memory unit <NUM> as data, and output from the data communication unit <NUM> to the evaluation device <NUM>. The power source <NUM> supplies power to the respective configurations in the rail inspection system <NUM>.

Next, the evaluation device <NUM> will be described. The evaluation device <NUM> is a computer device which executes an inspection process program to specify the positional deviation of the railroad rail <NUM> based on the inspection data which is received from the detection device <NUM> or the components <NUM> to <NUM>. Further, the "inspection data" in the embodiment is assumed to correspond to data of all stages from the receiver coil of the detection device <NUM> to a data input unit <NUM> of the evaluation device <NUM>. The evaluation device <NUM> includes the data input unit <NUM>, a control unit <NUM>, a data processing unit <NUM>, an output processing unit <NUM>, an operation input unit <NUM>, a display unit <NUM>, and a storage unit <NUM>.

The data input unit <NUM> receives the output signal (inspection data) of the data communication unit <NUM>.

The control unit <NUM> includes a central processing unit (CPU), a random access memory (RAM), and a read only memory (ROM), and controls process such as data transfer and calculation. The data processing unit <NUM> performs inspection based on the output signal (inspection data) (to be described in detail later). Information such as the inspection result is appropriately stored in the storage unit <NUM>.

The display unit <NUM> is a liquid crystal display (LCD), a cathode ray tube (CRT) display, or the like, for displaying the inspection result. The output processing unit <NUM> causes the display unit <NUM> to display the inspection result. At that time, the output processing unit <NUM> performs a process of displaying the result in a format easy to visually understand using an appropriate graph or table format. The operation input unit <NUM> is an information input unit such as a keyboard and a mouse. The storage unit <NUM> stores data processed by the data processing unit <NUM>. Further, the data processing unit <NUM> and the output processing unit <NUM> are realized by loading a program and data stored in the storage unit <NUM> to the control unit <NUM> and performing the calculation process.

<FIG> is a flowchart of the inspection process program which is executed by the data processing unit <NUM> of the evaluation device <NUM>.

First, the data processing unit <NUM> acquires the inspection data from the storage unit <NUM> (step S1).

Next, the data processing unit <NUM> repeatedly performs the following steps S3 to S5 for every predetermined duration (for example, about <NUM> to <NUM>) (step S2 to S6).

The data processing unit <NUM> performs determination on the inspection data of a predetermined duration whether there is a detection signal deviated from a reference range (step S3). When there is no deviated signal, it is determined as normal (step S4). When there is a deviated signal, it is determined as abnormal (step S5).

When the processes of step S2 to S6 are performed on all the inspection data, the data processing unit <NUM> displays an inspection result in the display unit <NUM> (step S7).

As described above, according to the rail inspection system (<NUM>) of the embodiment, when the displacement (L) is the first displacement (L<NUM>), the first maximum value appears in the induced voltage. When the displacement (L) is the second displacement (L<NUM>), the second maximum value of which the phase is reversed against the first maximum value appears in the induced voltage. Therefore, the displacement (L), that is, the positional deviation of the rail, can be detected with accuracy.

In addition, the attaching tool (<NUM>) is provided to attach the chassis (<NUM>) to the bottom surface of the vehicle such that the chassis (<NUM>) for storing the first sensor unit (<NUM>) and the first sensor unit (<NUM>) are disposed at predetermined positions of the bottom surface of the vehicle, so that the first sensor unit (<NUM>) can be mounted at an accurate position.

In addition, the AC voltage source (<NUM>, <NUM>, <NUM>) applies the AC voltage to generate a reverse magnetic field with respect to the first oscillation coil (5A) and the second oscillation coil (5B). Therefore, the induced voltage generated in the receiver coil (<NUM>) can be set to almost zero at the reference position.

Next, a rail inspection system according to a second embodiment of the invention will be described.

<FIG> is a block diagram illustrating an entire configuration of a rail inspection system 1a according to the embodiment. In addition, <FIG> is a top view partially broken away illustrating a detection device 2a according to the embodiment. Further, in <FIG> and <FIG>, the portions corresponding to the respective portions of <FIG> will have the same symbol, and the description thereof may be omitted.

In <FIG>, the rail inspection system 1a includes a processing device 3a and a plurality of detection devices 2a, and is mounted in the inspection vehicle (not illustrated) similarly to the first embodiment. However, in <FIG>, the inner configuration of the plurality of detection devices 2a are surrounded by one frame. Each detection device 2a has an outer appearance similar to that of the detection device <NUM> of the first embodiment (see <FIG>). The plurality of detection devices 2a include sensor units <NUM>-<NUM> to <NUM>-N of N channels (N is a plural number). Each of the sensor units <NUM>-<NUM> to <NUM>-N is configured similarly to the sensor unit <NUM> of the first embodiment (see <FIG>).

As illustrated in <FIG>, in one detection device 2a, the sensor units <NUM>-<NUM> (first sensor unit) and <NUM>-<NUM> (second sensor unit) of two channels are disposed along the front and rear direction. Therefore, if two detection devices 2a are mounted in the inspection vehicle, the number (N) of channels becomes "<NUM>". The sensor units <NUM>-<NUM> and <NUM>-<NUM> include receiver coils <NUM>-<NUM> (first receiver coil) and <NUM>-<NUM> (second receiver coil) disposed at each center in the left and right direction, oscillation coils 5A-<NUM> (first oscillation coil) and 5A-<NUM> (third oscillation coil) disposed on left sides thereof, and oscillation coils 5B-<NUM> (second oscillation coil) and 5B-<NUM> (fourth oscillation coil) disposed on right sides of the receiver coils <NUM>-<NUM> and <NUM>-<NUM>.

In addition, a gap L<NUM> between the coils (for example, the oscillation coils 5B-<NUM> and 5B-<NUM>) which are adjacent in the front and rear direction is set to be larger than a diameter L<NUM> of each coil. The reason is to prevent crosstalk between the sensor units <NUM>-<NUM> and <NUM>-<NUM>. In <FIG>, the oscillation coils 5A-<NUM> and 5B-<NUM> which face obliquely generate the same phase of magnetic field. The oscillation coils 5A-<NUM> and 5B-<NUM> generate a reverse magnetic field of which the phase is reversed against that of the oscillation coils 5A-<NUM> and 5B-<NUM>. For example, as illustrated in the drawing, the oscillation coils 5A-<NUM> and 5B-<NUM> generate a downward magnetic field at timing when the oscillation coils 5A-<NUM> and 5B-<NUM> generate an upward magnetic field. The detection signal output from the receiver coils <NUM>-<NUM> and <NUM>-<NUM> becomes ideally a signal which has the same amplitude and the reverse phase.

Returning to <FIG>, N amplifying units <NUM>-<NUM> to <NUM>-N (AC voltage source) provided in the processing device 3a, amplify the analog AC voltage output from the digital-analog converting unit <NUM>, and apply the AC voltage to the oscillation coils 5A and 5B of the corresponding sensor units <NUM>-<NUM> to <NUM>-N. In addition, N amplification/filter units <NUM>-<NUM> to <NUM>-N amplify and filter the detection signal supplied from the corresponding receiver coil <NUM>, and then transmit the signal to corresponding wave detecting units <NUM>-<NUM> to <NUM>-N in the processing device 3a.

In addition, the wave detecting units <NUM>-<NUM> to <NUM>-N perform the full-wave rectification on the detection signal of N channels supplied from the amplification/filter units <NUM>-<NUM> to <NUM>-N using the reference signal from the oscillating unit <NUM>, and supply the signal to the analog-digital converting unit <NUM>. The analog-digital converting unit <NUM> converts the analog signals of N channels into digital signals. The digital signal output from the analog-digital converting unit <NUM> is stored in the memory unit <NUM> as data, and output from the data communication unit <NUM> to the evaluation device <NUM>.

The configuration of the evaluation device <NUM> is also similar to that of the first embodiment (see <FIG>), but the operation of the data processing unit <NUM> in the embodiment is slightly different from that of the first embodiment. In other words, the data processing unit <NUM> of the embodiment obtains a difference between the detection signals (for example, the detection signals output from the receiver coils <NUM>-<NUM> and <NUM>-<NUM> in <FIG>) output from the same detection device 2a, and determines whether there is an abnormality considering the calculation result as the detection signal in the detection device 2a (step S3 of <FIG>).

As described above, according to the embodiment, the amplitude of the detection signal can be made about two times the amplitude of the detection signal in the first embodiment, and an S/N ratio can be made higher than that of the first embodiment. Therefore, it is possible to determine whether there is an abnormality with further accuracy. In addition, assume a case that a noise source is near the detection device 2a, and the magnetic flux generated by the noise source is interlinked to the receiver coils <NUM>-<NUM> and <NUM>-<NUM>. In this case, the magnetic fluxes interlinked to the receiver coils <NUM>-<NUM> and <NUM>-<NUM> become almost the same level and the same phase. Therefore, if a difference of the detection signals of both magnetic fields is obtained, the noise component contained in the detection signals can be removed. In this way, the rail inspection system 1a of the embodiment is advantageous compared to the first embodiment in that the S/N ratio can be made high, and the noise component can be removed.

Next, a rail inspection system according to a third embodiment of the invention will be described.

The entire configuration of the rail inspection system of the third embodiment is similar to that of the second embodiment (<FIG>). However, a detection device 2b illustrated in <FIG> is applied to the embodiment instead of the detection device 2a of the second embodiment. Further, <FIG> is a side view partially broken away illustrating the detection device 2b. The portions corresponding to those of <FIG> will have the same symbols, and the description thereof may be omitted.

In <FIG>, the detection device 2b includes the chassis <NUM> and the flange <NUM>, which are similar to those of the detection device <NUM> of the first embodiment (see <FIG>).

In the detection device 2b of the embodiment, the sensor units <NUM>-<NUM> to <NUM>-<NUM> of three channels are disposed along the front and rear direction. These sensor units <NUM>-<NUM> to <NUM>-<NUM> are each configured similarly to the sensor unit <NUM> of the first embodiment. However, the sensor units <NUM>-<NUM>, <NUM>-<NUM>, and <NUM>-<NUM> are attached to different positions in the chassis <NUM> such that sensor gaps d<NUM>, d<NUM>, and d<NUM> (distance) become different with respect to the railroad rail <NUM>.

Further, the reason for such a configuration will be described with reference to <FIG>. As illustrated in <FIG>, characteristics P20 to P40 of the detection signal are different according to the sensor gap d. Therefore, if the sensor gap d is unknown even though the value of the detection signal is detected, the displacement L is not possible to be specified. In addition, in <FIG>, the detection signal is less changed with respect to the change of the displacement L as the sensor gap d is increased.

In <FIG>, the detection device 2b is mounted in the inspection vehicle (not illustrated) such that the sensor gaps d<NUM>, d<NUM>, and d<NUM> in a stop state each become a predetermined reference value. However, when vertical vibration occurs in the inspection vehicle, the sensor gaps d<NUM>, d<NUM>, and d<NUM> are deviated from the reference value. In the embodiment, the sensor units <NUM>-<NUM> to <NUM>-<NUM> of three channels output the detection signals. Then, the data processing unit <NUM> (see <FIG>) calculates estimated values of the sensor gaps d<NUM>, d<NUM>, and d<NUM> based on the phenomenon "the detection signal is less changed with respect to the change of the displacement L as the sensor gap d is increased", and calculates the displacement L (see <FIG>) based on the phenomenon and the detection signals of three channels.

As described above, according to the embodiment, the displacement L is calculated while compensating variations of the sensor gaps d<NUM>, d<NUM>, and d<NUM> based on the vibration. Therefore, the variation of the detection signal caused by the vertical vibration of the detection device 2b can be compensated, so that the displacement L can be measured with still more accuracy.

The invention is not limited to the above embodiments, and various modifications can be made within the scope of the appended claims.

Claim 1:
A rail inspection system (<NUM>, 1a), comprising:
a first sensor unit (<NUM>) which is disposed to face a rail (<NUM>) for a vehicle, and includes at least one receiver coil (<NUM>, <NUM>-<NUM>) and at least one oscillation coil (5A, 5B) which are arranged in an arrangement direction intersecting with a layout direction of the rail (<NUM>);
wherein the layout direction is a front and rear direction of the rail (<NUM>) and the arrangement direction is a direction perpendicular to the layout direction;
an AC voltage source;
and
a displacement detection unit (<NUM>, 2a, 2b) which is configured to detect a displacement between the rail (<NUM>) and the first sensor unit (<NUM>) based on an induced voltage of the receiver coil (<NUM>, <NUM>-<NUM>),
characterized in that
the first sensor unit (<NUM>) includes a first oscillation coil (5A-<NUM>), a first receiver coil (<NUM>-<NUM>), and a second oscillation coil (5B-<NUM>) which are arranged along the arrangement direction, and
the AC voltage source is configured to apply the AC voltage to the first oscillation coil (5A-<NUM>) and the second oscillation coil (5B-<NUM>) having a reverse phase, such that reverse magnetic fields are generated from the first oscillation coil (5A-<NUM>) and the second oscillation coil (5B-<NUM>),
wherein the first oscillation coil (5A-<NUM>) and the second oscillation coil (5B-<NUM>) are connected in series and the AC voltage source is configured to apply the AC voltage to a series circuit comprising the first oscillation coil (5A-<NUM>) and the second oscillation coil (5B-<NUM>), and
wherein the first oscillation coil (5A-<NUM>) and the second oscillation coil (5B-<NUM>) are disposed at an equal interval in a left and right direction of the receiver coil (<NUM>), such that, when the displacement is a first displacement, to generate a detection signal, in which a voltage with a first maximum value is induced, and when the displacement is a second displacement, to generate a detection signal in which a second maximum value of which a phase is reversed against the first maximum value is induced.