Displacement measurement system

Abstract

When measuring displacement using the amplitude level of standing waves on a transmission line, the amplitude level of the standing waves follows a curve, and the slope differs depending on the location on the transmission line, resulting in different detection accuracy depending on the location. [Solution] A displacement measurement system characterized by comprising: a first coupler that receives a first signal and moves in a predetermined direction; a second coupler that extends in the predetermined direction and receives the signal by electromagnetic field coupling with the first coupler; a first phase difference detection unit that detects the phase difference between the signal transmitted to one end of the second coupler and the signal transmitted to the other end of the second coupler in the signal received by the second coupler; and a calculation unit that calculates the position based on the phase difference information output from the first phase difference detection unit.

Description

Technical Field

[0001] The present invention relates to a displacement measurement system that measures the displacement of a detector moving along a transmission line. Background Art

[0002] In recent years, systems for measuring the displacement of a detector that moves in a non-contact manner along a transmission line have been researched and developed. For example, Prior Art Document 1 proposes a system that generates a standing wave on a transmission line, acquires the amplitude level and phase of the standing wave with a detector, and measures the displacement of the detector on the transmission line. Prior Art Documents Patent Documents

[0003] Patent Document 1 IEEE Sensors Journal, Volume 23, No.16, 15 August 2023, P.18609-18623 "A Wide-Range Transmission Line-Based Linear Displacement Sensor" Summary of the Invention Problems to be Solved by the Invention

[0004] However, in the displacement measurement system described in Non-Patent Document 1, the amplitude level of the standing wave on the transmission line varies depending on the position. When a graph with position on the horizontal axis and amplitude level on the vertical axis is drawn, the graph forms a curve, and the slope of the curve varies depending on the position along the transmission line. In particular, near the peak of the curve, that is, at positions where the amplitude level is large, the slope is gentle and there is little change in the amplitude level. Accordingly, there is a problem that detection accuracy becomes coarse. In view of the above problems, an object of the present invention is to provide a displacement measurement system that can maintain constant detection accuracy regardless of the position of the detector on the transmission line. Means for Solving the Problems

[0005] One aspect of the present invention is a first coupler to which a first signal is input and which moves in a predetermined direction, The device is characterized by having a second coupler that extends in the predetermined direction and receives signals by electromagnetic field coupling with a first coupler, a first phase difference detection unit that detects the phase difference between a signal transmitted to one end of the second coupler and a signal transmitted to the other end of the second coupler in the signal received by the second coupler, and a calculation unit that calculates a position based on the phase difference information output from the first phase difference detection unit. [Effects of the Invention]

[0006] According to the present invention, it is possible to provide a system that can maintain a constant detection accuracy regardless of the position of the detector on the transmission line. [Brief explanation of the drawing]

[0007] [Figure 1] Configuration of the displacement measurement system according to Embodiment 1 [Figure 2] Configuration of the phase difference detection unit according to Embodiment 1 [Figure 3] Graph showing the relationship between displacement and phase difference of the transmission line coupler according to Embodiment 1 [Figure 4] Configuration of the displacement measurement system according to Embodiment 2 [Figure 5] First graph relating to the relationship between displacement and phase difference of the transmission line coupler according to Embodiment 2 [Figure 6] Second graph relating to the relationship between displacement and phase difference of the transmission line coupler according to Embodiment 2. [Figure 7] Configuration of the displacement measurement system according to Embodiment 3 [Modes for carrying out the invention]

[0008] Embodiments of the present invention will be described below with reference to the drawings.

[0009] [Embodiment 1] Figure 1 shows the configuration of the displacement measurement system according to this embodiment. The displacement measurement system 100 consists of a first AC signal source 101, a first coupler 102, a first transmission line coupler 103, a first cable 104, a second cable 105, a first phase difference detection unit 106, a first counting unit 107, and a displacement calculation unit 108.

[0010] The first coupler 102 and the first transmission line coupler 103 are both on a straight line, and the first coupler 102 is shorter than the first transmission line coupler 103. The first coupler 102 is not terminated at both ends of the transmission line, but it may be a transmission line coupler with matched termination. The first transmission line coupler 103 extends in a predetermined direction, and the first coupler 102 moves in the direction of the extension of the first transmission line coupler 103 while maintaining a constant distance from the first transmission line coupler 103. The first coupler 102 and the first transmission line coupler 103 are coupled using an electromagnetic field, and the signal input to the first coupler 102 is received by the first transmission line coupler 103 via electromagnetic field coupling. The first transmission line coupler 103 is, for example, a transmission line on a printed circuit board with signal wiring and GND arranged on it.

[0011] Both ends of the first transmission line coupler 103 are connected to the first phase difference detection unit 106 via the first cable 104 and the second cable 105, respectively. The lengths of the first cable 104 and the second cable 105 can be arbitrary, but for the sake of simplicity in this explanation, they are assumed to be of equal length to avoid phase differences caused by delays within the cables.

[0012] The impedances of the first transmission line coupler 103, the first cable 104, and the second cable 105 are matched. Of the two ends of the first transmission line coupler 103, the end connected to the first cable 104 is referred to as the first end, and the other end connected to the second cable 105 is referred to as the second end.

[0013] A first phase difference detection unit 106 detects the phase difference between a signal received by a first transmission line coupler 103 and input from a first cable 104 and a signal input from a second cable 105, and outputs the detected phase difference. A specific configuration of the phase difference detection unit will be described with reference to Figure 2.

[0014] When the phase difference output from the first phase difference detection unit 106 is 180 degrees or more, or -180 degrees or less, a counting unit 107 counts the number of such occurrences and changes the stored counter value. It may be configured such that 1 is added to count up when the phase difference becomes 180 degrees or more, and 1 is subtracted to count down when the phase difference becomes -180 degrees or less. Alternatively, it may be configured such that 1 is added to increment a first count when the phase difference becomes 180 degrees or more, 1 is added to increment a second count when the phase difference becomes -180 degrees or less, and calculation is performed using the first count and the second count.

[0015] Furthermore, counting up or counting down may be performed when the phase difference becomes 180 degrees or more, or -180 degrees or less relative to the phase difference (initial phase difference) at the initial position where the first coupler 102 is initially located. In this case, the initial phase difference may be any value.

[0016] Note that at least one of the first phase difference detection unit 106 and the counting unit 107 includes a storage unit that stores the phase difference at the initial position where the first coupler 102 is initially located.

[0017] A displacement calculation unit 108 calculates a position from the information on the phase difference detected by the phase difference detection unit and the counter value output from the counting unit.

[0018] The displacement measurement system 100 of the present embodiment aims to measure the movement amount of the first coupler 102 as displacement.

[0019] Displacement measurement based on phase difference detection will be described.

[0020] First, the first AC signal source 101 inputs a sine wave signal of an arbitrary frequency to the first coupler 102. Let the sine wave signal be S0, and it is represented as follows. S0=A0sinωt Equation (1) A0 is the amplitude of S0, and ω is the angular frequency of the sinusoidal signal.

[0021] When the first coupler 102 is in its initial position, the amount of phase change of the signal generated by propagation to the phase difference detection unit 106 via the first cable 104 and the second cable 105 is denoted as φ.

[0022] Let f be the frequency of the signal from the first AC signal source 101, and v be the maximum propagation speed at which the signal propagates through the first transmission line coupler 103.

[0023] Let S1 be the signal propagated to the first phase difference detection unit 106 via the first cable 104, and S2 be the signal propagated to the first phase difference detection unit 106 via the second cable 105. Furthermore, when L is the total length of the first transmission line coupler 103, x0 is the distance between the first coupler 102 and the first end of the first transmission line coupler 103 at the initial position, and x is the amount of movement of the first coupler 102, S1 and S2 are expressed as follows.

[0024]

number

[0025]

number

[0026] A1 is the amplitude when the sinusoidal signal is propagated to the first transmission line coupler 103. Also, let θ1 be the phase of S1 and θ2 be the phase of S2.

[0027] Figure 2 shows an example of the configuration of the phase difference detection unit according to this embodiment. The first phase difference detection unit 106 consists of a 90-degree phase shifter 201, multipliers 202 and 203, low-pass filters 204 and 205, and a polar coordinate transformation unit 206. The 90-degree phase shifter 201, multipliers 202 and 203, and low-pass filters 204 and 205 are collectively referred to as the quadrature demodulation unit.

[0028] The result of multiplying S1 and S2 by multiplier 202 is shown below.

[0029]

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[0030] Here, from equations 2 and 3

[0031]

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[0032]

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[0033] It can be expressed as follows. Here, from equation 5, of equation 4

[0034]

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[0035] It was found that the signal contains a second harmonic component, which is removed by the low-pass filter 204. Therefore, the signal S3 input to the polar coordinate transformation unit 206 is expressed as follows.

[0036]

number

[0037] The signal S4 obtained by phase-shifting S1 by 90 degrees using the phase shifter 201 is expressed as follows:

[0038]

number

[0039] The result of multiplying S2 and S4 by multiplier 202 is shown below.

[0040]

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[0041] Here, from equation 5 to equation 9

[0042]

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[0043] It was found that the signal contains a second harmonic component, which is removed by the low-pass filter 204. Therefore, the signal S5 input to the polar coordinate transformation unit 206 is expressed as follows.

[0044]

number

[0045] The polar coordinate transformation unit 206 transforms the Cartesian coordinates obtained by equations 7 and 10 into polar coordinates and outputs the phase difference shown in equation 6.

[0046] Furthermore, as can be seen from equations 1 to 10, the configuration shown in Figure 2 allows the first phase difference detection unit 106 to output phase difference information.

[0047] Furthermore, focusing on the right-hand side of Equation 6, x0, L, ω, and v are known values. Therefore, it can be seen that the change in phase difference θ1-θ2 has a unique relationship with the displacement x. Thus, it can be seen that the displacement x can be calculated from the phase difference.

[0048] Figure 3 shows the relationship between the amount of movement x of the first coupler 102 relative to its initial position and the phase difference Δθ = θ1 - θ2 according to this embodiment. The signal frequency f of the first AC signal source 101 is set to 10.2 GHz, and the phase difference Δθ = 0 deg. at the initial position x = 0 mm. Although there are multiple amounts of movement x that show the same phase difference, the amount of movement of the first coupler 102 can be calculated by using the output value of the counting unit 107. For example, Figure 3 shows that the amount of movement x = 10 mm when a phase difference Δθ = 90 deg. is detected and the output of the counting unit 107 is 1.

[0049] More specifically, the displacement calculation unit 111 calculates that the phase difference is at least 180 degrees based on the initial position x=0mm where the phase difference Δθ=0deg and the output of the counting unit 107 being 1. This is obtained from 180 degrees × counter value - initial phase difference. Furthermore, if a phase difference Δθ=90deg. is detected, 90 degrees is added to the calculated 180 degrees to calculate that the actual phase difference is 270 degrees. Based on this 270-degree phase difference, the displacement is calculated using equation 6.

[0050] In this embodiment, the phase difference Δθ = 0 degrees at the initial position x = 0 mm is assumed, but the phase difference at the initial position can be any value. This is because the phase difference can be calculated using the formula: 180 degrees × counter value - initial phase difference.

[0051] Alternatively, the first coupler 102 and the first transmission line coupler 103 may simultaneously measure the displacement and generate a data signal. In this case, a low-pass filter or a high-pass filter should be used to separate the two frequencies, matching the frequency of the signal from the first sinusoidal signal source 101 and the frequency of the data signal.

[0052] [Embodiment 2] Figure 4 shows a displacement measurement system according to this embodiment, in which a second sinusoidal signal source 301 is added, which inputs a signal of a different frequency from the first sinusoidal signal source 101 of Embodiment 1 to the first coupler 102. Furthermore, it shows a configuration that adds a first bandpass filter 302, a second bandpass filter 303, and a second phase difference detection unit 306. Only the differences from Embodiment 1 will be explained.

[0053] Let f be the frequency of the first sine wave signal input from the first sine wave signal source 101, and let f' be the signal frequency of the second sine wave signal input from the second sine wave signal source 301. As in Embodiment 1, each signal is input to the first coupler 102 and propagated to the first transmission line coupler 103 via electromagnetic field coupling.

[0054] The signal propagating through the first transmission line coupler has two frequency components. The signal input to the first phase difference detection unit 106 has only the frequency component f due to the first bandpass filter 302. Therefore, the phase difference detected by the first phase difference detection unit 106 is only the phase difference Δθ in the signal with the frequency component f. Similarly, the phase difference detected by the second phase difference detection unit 306 is only the phase difference Δθ' in the signal with the frequency component f'.

[0055] Signal propagation via electromagnetic field coupling is difficult at low frequencies because the coupling capacitance impedance becomes large, and the amplitude of the signal input to the first transmission line coupler via the first coupler 102 becomes small. Since smaller signal amplitudes have lower immunity to external noise, it is preferable to use high-frequency bands such as the GHz band. However, as shown in Embodiment 1, the higher the frequency, the shorter the rotation period of the phase difference relative to the movement of the first coupler becomes, making a counting unit essential.

[0056] In this embodiment, a displacement measurement system is presented that reduces the rotation period relative to the amount of movement by a combination of two phase differences Δθ and Δθ', and does not require a counting unit.

[0057] Figure 5 shows the relationship between the amount of movement x relative to the initial position of the first coupler 102 according to this embodiment, and the phase differences Δθ and Δθ'. The signal frequency f of the first AC signal source 101 is set to 10.2 GHz, and the phase difference Δθ = 0 degrees at the initial position x = 0 mm. The signal frequency f' of the second AC signal source 301 is set to 11.2 GHz, and the phase difference Δθ' = 0 degrees at the initial position x = 0 mm.

[0058] Figure 6 shows the displacement x of the first coupler 102 relative to its initial position and the difference in phase differences Δθ″ = Δθ - Δθ´. From Figure 6, it can be confirmed that Δθ″ is an eigenvalue for the displacement x from -38 mm to 38 mm. In other words, there is no need to count the number of rotations of the phase difference, and a counting unit is unnecessary. Therefore, it can be seen that the first phase difference detection unit and the second phase difference detection unit can be directly connected to the displacement calculation unit to calculate the displacement and determine the position of the first coupler 102.

[0059] [Embodiment 3] Figure 7 shows the configuration of the displacement measurement system according to this embodiment, which includes a second sinusoidal signal source 401 having a signal of a different frequency than the first sinusoidal signal source 101 of Embodiment 1, amplifiers 402 and 403, and multipliers 404 and 405. Only the differences from Embodiment 1 will be explained.

[0060] As described in Embodiment 2, the signal input from the first sinusoidal signal source 101 is preferably a high frequency such as the GHz band. In Embodiment 2, the frequency of the signal input from the first coupler was increased, and the rotation period of the phase difference used for displacement measurement was reduced. In this embodiment, frequency conversion is performed by multiplying the signal propagating through the first transmission line coupler and the sinusoidal signal input from the second sinusoidal signal source 401 using multipliers 404 and 405. When the frequency of the signal input from the first sinusoidal signal source 101 is f and the frequency of the signal input from the second sinusoidal signal source 401 is f', the frequency of the signal input to the first phase difference detection unit 106 becomes f''=|ff'|. As the signal is down-converted, the rotation period of the phase difference detected by the first phase difference detection unit 106 is reduced, and as shown in Figure 6 of Embodiment 2, an eigenvalue of the phase difference can be assigned to each amount of movement of the first coupler 102, eliminating the need for a counting unit. [Explanation of symbols]

[0061] 100 Displacement Measurement System 101 First AC signal source 102 The first coupler 103 First transmission line coupler 104 First Cable 105 Second cable 106 First phase difference detection unit 107 Counting Section 108 Displacement Calculation Unit

Claims

1. A first coupler receives a first signal and moves in a predetermined direction, A second coupler extends in the predetermined direction and receives signals through electromagnetic field coupling with the first coupler, A first phase difference detection unit detects the phase difference between the signal transmitted to one end of the second coupler and the signal transmitted to the other end of the second coupler in the signal received by the second coupler. A displacement measurement system characterized by having a calculation unit that calculates a position based on phase difference information output from the first phase difference detection unit.

2. The displacement measuring system according to claim 1, further comprising a counting unit that changes the value of a counter each time the phase difference exceeds 180 degrees.

3. The displacement measuring system according to claim 2, characterized in that the calculation unit calculates the position of the second coupler relative to the first coupler based on the phase difference and the value of the counter output from the counting unit.

4. The first phase difference detection unit is, The displacement measurement system according to claim 1, characterized in that it outputs a phase difference by orthogonally demodulating the signal transmitted to one end of the second coupler and the signal transmitted to the other end, and converting them to polar coordinates.

5. The second coupler moves toward one end of the first coupler, The displacement measurement system according to claim 2, characterized in that the counting unit subtracts 1 from the value of the counter when the phase difference becomes -180 degrees.

6. The displacement measuring system according to claim 2, characterized in that when the second coupler moves toward one end of the first coupler and the phase difference becomes 180 degrees, the counting unit increments the value of the counter by 1.

7. The displacement measuring system according to any one of claims 1 to 6, characterized in that a second signal having a frequency different from the frequency of the first signal is further input to the first coupler.

8. The displacement measurement system according to any one of claims 1 to 6, characterized in that the signal transmitted to both ends of the second coupler is down-converted using a second signal having a frequency different from that of the first signal.

9. The displacement measuring system according to claim 1, characterized in that the second coupler is made of a circuit board.

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