JP4195570B2 - Moving body speed sensor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a moving body speed sensor.
[0002]
[Prior art]
The magnetic sensor is a sensor that detects a magnetic flux density at a specific position, and a Hall element, a magnetoresistive element, a loop coil, an optical interferometer, or the like is used. Mobile magnetic sensors have been developed that use these magnetic sensors to detect the speed at which a moving body having a magnetic body passes through a certain section.
[0003]
As an application of the moving body magnetic sensor, for example, detection of a passing speed of an automobile traveling on a road can be cited. In other words, the mobile magnetic sensor is used to detect the speed of a traveling car for each vehicle, or to calculate the average speed of a number of passing vehicles within a certain time and observe the traffic flow. .
[0004]
In this specification, the moving body speed sensor is a sensor for observing traffic flow like the latter.
[0005]
FIG. 3 is a conceptual diagram of a conventional moving body speed sensor.
[0006]
In the figure, reference numeral 7 denotes a moving body having a magnetic body to be detected, for example, an automobile. Reference numerals 1 and 2 denote magnetic sensors that detect a change in magnetic flux density accompanying the passage of the moving body 7 and output signals V1 and V2 corresponding to the detected magnetic flux density. The road is separated by a predetermined distance L.
[0007]
Here, the traveling direction of the moving body 7 is taken as the X axis, the coordinate of one magnetic sensor 1 is set to X = 0, and the coordinate of the other magnetic sensor 2 is set to X = L. Signals from both the magnetic sensors 1 and 2 are processed by the signal processing unit 3.
[0008]
When the signals from the magnetic sensors 1 and 2 are input, the signal processing unit 3 calculates the moving speed v of the moving body 7 and outputs a signal V3 corresponding to the moving speed v.
[0009]
FIG. 4 is a flowchart of processing performed in the signal processing unit of the moving body speed sensor shown in FIG. 5A and 5B are diagrams showing temporal changes in the signals V1 and V2 of the magnetic sensor shown in FIG. 3, the horizontal axis indicates the time axis, and the vertical axis indicates the voltage axes of the signals V1 and V2, respectively. It is.
[0010]
When the magnetic sensors 1 and 2 are sensors that output signals V1 and V2 having voltages proportional to the magnetic flux densities B1 and B2 at the respective positions, the signals V1 and V2 from the magnetic sensors 1 and 2 are expressed by the following equation (9): It is expressed by the equation (10).
[0011]
[Equation 9]
V1 (t) = α ₁ B ₁ (t) + ΔV1
[0012]
[Expression 10]
V2 (t) = α ₂ B ₂ (t) + ΔV2
However, α ₁ and α ₂ are proportional coefficients, and ideally, it is assumed that the proportional coefficients α ₁ and α ₂ of the magnetic sensors ₁ and ₂ are equal (= α). ΔV1 and ΔV2 represent the noise widths of both magnetic sensors 1 and 2, and it is assumed that the noise widths ΔV1 and ΔV2 are also equal in the magnetic sensors 1 and 2 (= ΔV).
[0013]
Here, in order to simplify the description, the magnetic flux density at the position of the magnetic sensors 1 and 2 when the moving body 7 is sufficiently separated from the magnetic sensors 1 and 2 is assumed to be “0”.
[0014]
When the moving body 7 is sufficiently far from the magnetic sensors 1 and 2, the signals V1 and V2 of the magnetic sensors 1 and 2 are “0”. When the moving body 7 approaches the magnetic sensors 1 and 2, the magnetic flux density B1 of the magnetic sensor 1 arranged closer to the moving body 7 changes. As the magnetic flux density B1 changes, the signal V1 from the magnetic sensor 1 starts to change. When the moving body 7 further approaches the magnetic sensor 1, the magnetic flux density B2 at the position of the magnetic sensor 2 arranged farther from the moving body 7 changes. As the magnetic flux density B2 changes, the signal V2 from the magnetic sensor 2 starts to change. The time difference t between the signal changes of the signals V1 and V2 depends on the distance L between the magnetic sensors 1 and 2 and the speed v of the moving body, and is expressed by the following equation (11).
[0015]
[Expression 11]
t = L / v
Therefore, if the distance L between the magnetic sensors 1 and 2 is measured in advance and the time difference t can be measured, the speed v of the moving body 7 can be calculated by the following equation (12).
[0016]
[Expression 12]
v = L / t
In the conventional moving body speed sensor shown in FIG. 3, the signal processing unit 3 measures the time difference t as shown in FIG.
[0017]
A threshold value Vth is set in the signal processing unit 3 for the signals V1 and V2 from the magnetic sensors 1 and 2. The set level of the threshold value Vth is set to a level larger than the noise width ΔV of the signals V1 and V2 of the magnetic sensors 1 and 2.
[0018]
When the moving body 7 does not approach both the magnetic sensors 1 and 2, the values of the signals V1 and V2 are less than the threshold value Vth, respectively. Occurs, the moment comes when the values of the signals V1 and V2 of the magnetic sensors 1 and 2 exceed the threshold value Vth.
[0019]
The signal processing unit 3 determines whether or not the signal V1 exceeds the threshold value Vth (step S1a), stores the time when the signal V1 exceeds the threshold value Vth as t1 (step S2a), and the signal V2 is the threshold value Vth. (Step S3a), and the time when the signal V2 exceeds the threshold value Vth is stored as t2 (step S4a).
[0020]
The signal processing unit 3 calculates a time difference t = t 2 −t 1 between the time t1 and the time t2, and calculates the speed v of the moving body 7 by substituting the obtained result into Equation 12. A signal V3 corresponding to the obtained value is output to the outside (step S5a).
[0021]
The signal processing unit 3 assigns “0” to t, t1, and t2 to reset (step S6a), and determines whether the signal V1 is equal to or lower than the threshold value Vth and the signal V2 is equal to or lower than the threshold value Vth. (Step S7a) When both the signals V1 and V2 are the threshold value Vth, the process returns to step S1a and repeats the above steps S1a to S5a. When at least one of the signals V1 and V2 exceeds the threshold value Vth, the process returns to step S6a.
[0022]
The signal V3 from the signal processing unit 3 is input to the signal processing unit 4.
[0023]
The signal processing unit 4 calculates an average value of the signal V3 for a certain time and outputs a signal V4 corresponding to the obtained value.
[0024]
FIG. 6 is a flowchart of processing performed in the signal processing unit 4 of the moving body speed sensor shown in FIG.
[0025]
When the processing is started, the signal processing unit 4 determines whether or not the average time has been reached (step S1b), and outputs the signal V4 to the outside when it is determined that the average time has been reached (step S2b). ), The numerical data V3 to reset the value of the signal V3 “0” is substituted into buf, “0” is substituted into the numerical data N, and “0” is substituted into the numerical data of the signal V4 (step S3b).
[0026]
When it is determined that the average time has not been reached, the signal processing unit 4 determines whether or not the signal V3 is input (step S4b), and when it is determined that the signal V3 is input, the numerical data V3. Numeric data V3 in buf buf + V3 is substituted (step S5b), numeric data N + 1 is substituted for numeric data N (step S6b), and V4 = V3 buf / N is calculated, and it is determined again whether the average time has been reached (step S7b).
[0027]
When it is determined in step S4b that the signal V3 is not input, the signal processing unit 4 determines again whether the average time has been reached.
[0028]
[Problems to be solved by the invention]
In the case of the conventional example described above, when the fluctuation range Vp of the sensor output when the moving body 7 approaches the magnetic sensors 1 and 2 is sufficiently large with respect to the sensor noise width ΔV, the speed v of the moving body 7 is accurately determined. Although it can be calculated, the following shows that the speed calculation error increases when the noise width ΔV cannot be ignored with respect to the sensor output fluctuation width Vp.
[0029]
In order to simplify the explanation, the waveform of the magnetic flux density fluctuation when one moving body 7 passes the magnetic sensors 1 and 2 is approximated by a triangular wave. FIG. 7 shows how the signal V1 of the magnetic sensor 1 changes with time when the magnetic flux density fluctuation when passing through the moving body is approximated by a triangular wave.
[0030]
FIG. 7 is a diagram showing the signal V1 from the magnetic sensor 1 when the change in magnetic flux density when passing through the moving body is approximated by a triangular wave, with the horizontal axis indicating time and the vertical axis indicating the output of the magnetic sensor.
[0031]
The figure shows three waveforms La, Lb, and Lc. A waveform Lb indicates a true value of the signal V1 when a magnetic flux density change due to passage through a moving body is observed with a magnetic sensor having a noise width of “0”. On the other hand, the waveforms La and Lc represent the upper and lower limits when the magnetic flux density change of the waveform Lb is measured by a magnetic sensor having a finite noise width ΔV.
[0032]
It is assumed that the signal V1 changes in a triangular wave shape due to the passage of the moving body 7 and reaches the maximum value Vp after a time T from the rising edge. A threshold Vth is set for the signal V1 by the signal processing unit 3, and a time when the signal V1 (its true value) exceeds the threshold Vth is defined as t1. The signal V1 from the magnetic sensor 1 includes noise having a finite noise width ΔV.
[0033]
Here, it is assumed that the noise width ΔV is constant within the measurement time.
[0034]
Due to this noise width ΔV, an error Δt1 also occurs at time t1 when the signal V1 reaches the threshold value Vth. This error Δt1 is expressed by Equation 1.
[0035]
When the linearity of the magnetic sensor 2 and the noise width ΔV are equal to the linearity of the magnetic sensor 1 and the noise width ΔV, the detection error Δt2 at time t2 when the signal V2 of the magnetic sensor 2 exceeds the threshold value Vth is given by the following equation (2).
[0036]
From Equation 1 and Equation 2, the detection error of the time difference t (= t2−t1) is given by Equation 3.
[0037]
Here, in order to specifically give the maximum arrival time T of the signal V1, it is assumed that the change of the signal V1 when passing one moving body is a triangular wave with a period of 4T as shown in FIG. In this case, the time T is given by the length Lmag of the moving body as shown in Expression 13, and Expression 3 is expressed by Expression 14.
[0038]
[Formula 13]
T = (1 / v) · (Lmag / 4)
[0039]
[Expression 14]
Δt = (1 / v) · (LmagΔV / 2Vp)
The speed v of the moving body 7 is calculated from the time difference t according to the equation (12). Since the detection error Δt is included in the time difference t, the calculated speed v also includes the error Δv. That is, the relationship between the calculated speed v and the error Δv is expressed by Equation 15.
[0040]
[Expression 15]
v + Δv = L / (t + Δt)
From the equations (12) and (15), the calculated speed error | Δv | is expressed by the equation (16).
[0041]
[Expression 16]
| Δv | = LΔt / {t (t + Δt)}
Further, using the relationship of Formula 12, Formula 15 can be expressed by Formula 17 representing the speed error | Δv | / v.
[0042]
[Expression 17]
| Δv | / v = (Δt / t) / (1 + Δt / t)
Substituting Equation 12 and Equation 14 into Equation 17 and rearranging them yields Equation 18 and Equation 19.
[0043]
[Expression 18]
| Δv | / v = x / (1 + x)
However,
[0044]
[Equation 19]
x = LmagΔV / (2LVp)
FIG. 8 is a graph showing the parameter x dependency of the speed error in Equation 18, where the horizontal axis indicates x and the vertical axis indicates the relative speed error | v | / v.
[0045]
It can be seen from the figure that the relative velocity error is a function that increases monotonously with respect to x. Therefore, x needs to be sufficiently small to reduce the relative speed error.
[0046]
Here, taking a case where a vehicle traveling on a road is detected by two optical magnetic sensors as an example, a specific numerical value is substituted to find the value of x.
[0047]
Assuming that the distance L between the two magnetic sensors is 5 m, the total length of the vehicle is 4 m, and the magnetic sensor noise width ΔV is 1 μT, Expression 19 is expressed by Expression 20.
[0048]
[Expression 20]
x = 0.4 [μT] / Vp [μT]
For example, in order to achieve measurement with a relative speed error <10%, x <0.12 is required from FIG. By substituting Equation 20 into this condition and correcting it to the necessary condition of the magnetic sensor output change width Vp, Equation 21 is obtained.
[0049]
[Expression 21]
Vp> 3.3 [μT]
However, the magnetic flux density change width Vp due to the vehicle varies depending on the shape of the vehicle, the type and size of the load, the vehicle passing position, and the like, and may not satisfy Equation 21. In this case, the speed calculation error for one vehicle is 10% or more of the target, and there is a problem that an undesirable error is mixed in the average speed detection of the passing vehicle for a certain time.
[0050]
SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve the above-described problems and provide a moving body speed sensor with a small average speed calculation error of the moving body.
[0051]
[Means for Solving the Problems]
In order to achieve the above object, the invention described in claim 1 includes two magnetic sensors 1 and 2 arranged at a predetermined distance on a moving path of a moving body having a magnetic body, the magnetic sensor 1, Assuming that the linearity of 2 and the noise width are equal, the output changes to a triangular wave shape, and the noise width is constant within the measurement time, whether the signal V1 of the magnetic sensor 1 is greater than the threshold value Vth is compared. and, when the signal V1 is determined to be greater than the threshold value Vth stores the current time as t1, and stores the waveform of the signal V1 as numerical data V1 _ buf, whether the larger signal V2 threshold of the magnetic sensor 2 Vth or comparing, when the signal V2 is determined to be greater than the threshold value Vth stores the current time as t2, and store the waveform of the signal V2 as numerical data V2 _ buf, The time T from the rise to the waveform peak is obtained from the waveform data from one magnetic sensor, the noise width is ΔV, the waveform peak value Vp of the triangular wave, and the instant of time exceeding the threshold Vth of the signal V1 from the magnetic sensor 1 The expected measurement error Δt1 at t1 is obtained from Equation 1,
[Expression 1]
Δt1 = TΔV / 2Vp
The detection error Δt2 at time t2 when the signal V2 from the magnetic sensor 2 exceeds the threshold value Vth is expressed by equation (2).
[Expression 2]
Δt2 = TΔV / 2Vp
The detection error Δt of the time difference t between the time t1 and the time t2 is calculated from the equation (3).
[Equation 3]
Δt = Δt1 + Δt2
= TΔV / Vp
The velocity of the moving body is v, the error is Δv, and this detection error Δt is expressed by Equation 4
[Expression 4]
| Δv | / v = (Δt / t) / (1 + Δt / t)
By substituting into the above, it is determined whether or not the required speed accuracy can be obtained, and only when it is determined that the required speed accuracy is obtained, the above moving body is obtained from the time difference between the signals from both magnetic sensors. a first signal processing unit for calculating the speed, which the mobile speed signal outputted from the signal processing unit to a predetermined time-averaged, and a second signal processing unit for outputting the operation result to the outside It is.
[0052]
According to the second aspect of the present invention, there are two magnetic sensors 1 and 2 arranged at a predetermined distance on a moving path of a moving body having a magnetic body, and the linearity and noise width of the magnetic sensors 1 and 2 are Assuming that the output changes to a triangular wave shape and the noise width is constant within the measurement time, it is compared whether or not the signal V1 of the magnetic sensor 1 is greater than the threshold value Vth, and the signal V1 is equal to the threshold value Vth. when it is determined that the larger stores the current time as t1, and stores the waveform of the signal V1 as numerical data V1 _ buf, signal of the magnetic sensor 2 V2 compares whether greater than the threshold value Vth, the signal V2 when is it is determined that greater than the threshold value Vth stores the current time as t2, and store the waveform of the signal V2 as numerical data V2 _ buf, The time T from the rise to the waveform peak is obtained from the waveform data from one magnetic sensor, the noise width is ΔV, the waveform peak value Vp of the triangular wave, and the instant of time exceeding the threshold Vth of the signal V1 from the magnetic sensor 1 The expected measurement error Δt1 at t1 is obtained as a time derivative dV1 / dt | t = t1 at time t1 of the signal V1 from the magnetic sensor 1, and Equation 5
[Equation 5]
Δt1 = ΔV / 2 (dV1 / dt | t = t1 )
And the detection error Δt2 at time t2 when the signal V2 from the magnetic sensor 2 exceeds the threshold value Vth, and the time differential dV2 / dt | t = t2 at the time t2 of the signal V2 from the magnetic sensor 2 6 formulas
[Formula 6]
Δt2 = ΔV / 2 (dV2 / dt | t = t2 )
The detection error Δt of the time difference t between the time t1 and the time t2 is obtained by substituting
[Expression 7]
Δt = Δt1 + Δt2
= TΔV / Vp
The velocity of the moving body is v, the error is Δv, and this detection error Δt is expressed by Equation 8
[Equation 8]
| Δv | / v = (Δt / t) / (1 + Δt / t)
By substituting into the above, it is determined whether or not the required speed accuracy can be obtained, and only when it is determined that the required speed accuracy is obtained, the above moving body is obtained from the time difference between the signals from both magnetic sensors. And a second signal processing unit that averages the moving body velocity signal output from the signal processing unit for a certain period of time and outputs the calculation result to the outside. It is.
[0054]
According to the present invention, when it is determined that the desired speed accuracy is obtained by the first signal processing unit, the calculated speed signal is output to the second signal processing unit, and the desired expected speed accuracy cannot be obtained. When the determination is made, since the signal of the calculated speed is measured again without being output to the second signal processing unit, it is possible to obtain the moving body passing speed average value with the desired accuracy.
[0055]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
[0056]
FIG. 1 is a conceptual diagram showing an embodiment of a moving body speed sensor of the present invention. In addition, the same code | symbol was used for the member similar to the member shown in the prior art example.
[0057]
Reference numeral 7 denotes a moving body having a magnetic body to be detected. Reference numerals 1 and 2 denote magnetic sensors that detect a change in magnetic flux density accompanying the passage of the moving body 7 and output signals V1 and V2 corresponding to the detected magnetic flux density. is there. Both magnetic sensors 1 and 2 are arranged on the moving path of the moving body 7 by a predetermined distance L apart.
[0058]
Here, the traveling direction of the moving body 7 is taken as the x axis, the coordinate of one magnetic sensor 1 is x = 0, and the coordinate of the other magnetic sensor 2 is x = L. Signals V1 and V2 from both magnetic sensors 1 and 2 are processed by signal processors 4 and 5.
[0059]
The first signal processing unit 5 predicts a speed error from the waveforms of the signals V1 and V2 from the magnetic sensors 1 and 2, determines whether the required speed accuracy is obtained, and determines that the required speed accuracy is obtained. In this case, the moving body speed v is calculated from the time difference between the signals V 1 and V 2 from the magnetic sensors 1 and 2, and the calculation result V 5 is output to the second signal processing unit 4.
[0060]
Hereinafter, the operation of the first signal processing unit will be described with reference to FIGS. 2 and 5A and 5B.
[0061]
FIG. 2 is a flowchart of processing performed in the first signal processing unit used in the moving body speed sensor shown in FIG.
[0062]
When both the magnetic sensors 1 and 2 are sensors that output signals proportional to the magnetic flux densities B1 and B2 at the respective positions, the outputs V1 and V2 of both magnetic sensors are expressed by Equation 9 and Equation 10.
[0063]
However, α ₁ and α ₂ are proportional coefficients, and ideally, it is assumed that the proportional coefficients α ₁ and α ₂ of the magnetic sensors ₁ and ₂ are equal (= α). ΔV1 and ΔV2 represent the noise widths of both magnetic sensors 1 and 2, and it is assumed that the noise widths ΔV1 and ΔV2 are also equal in the magnetic sensors 1 and 2 (= ΔV).
[0064]
Here, in order to simplify the description, the magnetic flux density at the position of the magnetic sensors 1 and 2 when the moving body 7 is sufficiently separated from the magnetic sensors 1 and 2 is assumed to be “0”.
[0065]
When the moving body 7 approaches the magnetic sensors 1 and 2, the magnetic flux density B1 of the magnetic sensor 1 arranged closer to the moving body 7 changes, and the signal V1 starts to change. Further, when the moving body 7 approaches the magnetic sensors 1 and 2, the magnetic flux density B2 at the position of the magnetic sensor 2 arranged farther from the moving body 7 changes, and the signal V2 starts to change. The time difference t of the change of the signals V1 and V2 depends on the distance L between the magnetic sensors 1 and 2 and the moving speed v of the moving body 7, and is expressed by the following equation (11).
[0066]
Therefore, if the distance L between the magnetic sensors 1 and 2 is measured in advance and the time difference t can be measured, the velocity v of the moving body 7 can be calculated by the following equation (12).
[0067]
In the signal processor 5, the time difference t is measured as follows.
[0068]
For the signals V1 and V2 from both magnetic sensors 1 and 2, the signal processing unit 5 sets a threshold value Vth. The setting level of the threshold value Vth is set to a level larger than the noise width ΔV of the signals V1 and V2 from the magnetic sensors 1 and 2. When the moving body 7 does not approach both the magnetic sensors 1 and 2, the signals V1 and V2 are less than the threshold value Vth, respectively. However, when the moving body 7 approaches and the magnetic flux density changes, both magnetic fields A moment comes when the signals V1 and V2 from the sensors 1 and 2 exceed the threshold value Vth.
[0069]
The signal processing unit 5 compares whether or not the signal V1 is larger than the threshold value Vth (step S1). If it is determined that the signal V1 is larger than the threshold value Vth, the current time is stored as t1 (step S2). Waveform of numerical data V1 buf [n] is stored (step S3), whether or not the signal V2 is greater than the threshold value Vth is compared (step S4), and when it is determined that the signal V2 is greater than the threshold value Vth, the current time is stored as t2 ( Step S5), the waveform of the signal V2 is converted into numerical data V2. Stored as buf [n] (step S6).
[0070]
Here, the signal processing unit 5 is different from the conventional signal processing unit 3 shown in FIG. 3 in that the waveforms of the signals V1 and V2 near the times t1 and t2 are converted into time-series numerical data V1. buf [n], V2 It is a point to memorize | store simultaneously as buf [n].
[0071]
In the signal processor 5, these numerical data V1 buf [n], V2 Using the waveform data stored in buf [n], a predicted value of speed accuracy (predicted speed error) is calculated (step S7).
[0072]
Here, examples of a method for calculating the predicted speed error include the following methods.
[0073]
First, numerical data V1 The peak value Vp and the time T from the rise to the waveform peak value are obtained from the waveform data of buf [n]. Assuming that the rise of the signal V1 rises linearly from 0 to Vp during the time T, and assuming that the sensor noise width is ΔV, the expected measurement error Δt1 at the instant t1 exceeding the threshold Vth of the signal V1 is Given.
[0074]
When the linearity and noise width ΔV of the magnetic sensor 2 are equal to the linearity and noise width ΔV of the magnetic sensor 1, the detection error at time t2 at the moment when the signal V2 from the magnetic sensor 2 exceeds the threshold value Vth is considered in the same way. It is given by the formula.
[0075]
From Equation 1 and Equation 2, the detection error of the time difference t (= t2−t1) is given by Equation 3.
[0076]
By substituting this time difference Δt into Equation 17, an expected speed error | Δv | / v is obtained.
[0077]
Further, the following method can be cited as a method for calculating the expected speed error.
[0078]
A mechanism for obtaining the time differential dV1 / dt | _{t =} t1 of the signal V1 at time t1 is prepared, and the differential value of the signal V1 at time t1 is replaced with Vp / T in Formula 1, thereby obtaining Formula 5.
[0079]
Similarly, the differential value of the signal V2 at time t2 is replaced with Vp / T in equation (1) to obtain equation (6).
[0080]
Alternatively, Δt may be obtained by substituting these Δt1 and Δt2 into Equation 3, and Δt may be substituted into Equation 4 to obtain the predicted speed error (expected speed accuracy) | Δv | / v.
[0081]
Next, the signal processing unit 5 determines whether or not the predicted speed error | Δv | / v obtained as described above satisfies the required accuracy (step S8), and determines that the predicted speed accuracy satisfies the required speed accuracy. In this case, the time difference t2-t1 is set to time t1, L / t is set to V, and the calculated speed is output as V5 on the assumption that the expected speed error is reliable (step S9).
[0082]
The signal processing unit 5 resets “0” as times t, t1, and t2 (step S10), determines whether the signal V1 is equal to or lower than the threshold value Vth, and whether the signal V2 is equal to or lower than the threshold value Vth. , V2 is determined to be less than or equal to the threshold value Vth, the process returns to step S1.
[0083]
When the signal processing unit 5 determines that the predicted speed accuracy | Δv | / v does not satisfy the required accuracy (step S8), the value of the calculated speed is not output to the outside as unreliable. By doing so, the second signal processing unit 4 for calculating the time average of the calculated speed does not include a measurement result with a large error, and the speed accuracy required for the measurement system can be achieved.
[0084]
The signal processing unit 4 calculates an average value of the calculation speed signal V5 for a certain period of time, and outputs a signal V4 corresponding thereto. Since a measurement result having a large error is not input to the signal processing unit 4 in the signal processing unit 5, the signal V4 from the signal processing unit 4 satisfies the speed accuracy required for the moving body speed sensor.
[0085]
Since the signal processing in the signal processing unit 4 has already been described, a description thereof will be omitted.
[0086]
In the above, since the moving body passing speed average value is calculated by removing the moving body passing signal determined that the desired speed accuracy cannot be obtained by the first signal processing unit, the moving body passing speed average with the desired accuracy is calculated. A value can be obtained.
[0087]
【The invention's effect】
In short, according to the present invention, it is possible to provide a mobile body speed sensor with a small average speed calculation error of the mobile body.
[Brief description of the drawings]
FIG. 1 is a conceptual diagram showing an embodiment of a moving body speed sensor of the present invention.
FIG. 2 is a flowchart of processing performed in a first signal processing unit used in the moving body speed sensor shown in FIG. 1;
FIG. 3 is a conceptual diagram of a conventional moving body speed sensor.
4 is a flowchart of processing performed in a signal processing unit of the moving body speed sensor shown in FIG. 3;
5A and 5B are diagrams showing temporal changes in signals V1 and V2 of the magnetic sensor shown in FIG.
6 is a flowchart of processing performed in a signal processing unit 4 of the moving body speed sensor shown in FIG. 3;
FIG. 7 is a diagram illustrating a signal V1 from the magnetic sensor 1 when a change in magnetic flux density when passing through a moving body is approximated by a triangular wave.
FIG. 8 is a graph showing the dependence of the speed error of equation 18 on the parameter x.
[Explanation of symbols]
1, 2 Magnetic sensor 4 Second signal processing unit 5 First signal processing unit 7 Moving object

Claims (2)

Two magnetic sensors 1 and 2 arranged on a moving path of a moving body having a magnetic body separated by a predetermined distance, the linearity and noise width of the magnetic sensors 1 and 2 are equal, and the output changes to a triangular wave shape. Assuming that the noise width is constant within the measurement time, it is compared whether or not the signal V1 of the magnetic sensor 1 is greater than the threshold value Vth, and if it is determined that the signal V1 is greater than the threshold value Vth, the current time Is stored as t1, the waveform of the signal V1 is stored as numerical data V1_buf, and it is compared whether or not the signal V2 of the magnetic sensor 2 is greater than the threshold value Vth, and when it is determined that the signal V2 is greater than the threshold value Vth, The time is stored as t2, the waveform of the signal V2 is stored as numerical data V2_buf,
The time T from the rise to the waveform peak is obtained from the waveform data from one magnetic sensor, the noise width is ΔV, the waveform peak value Vp of the triangular wave, and the instant of time exceeding the threshold Vth of the signal V1 from the magnetic sensor 1 The expected measurement error Δt1 at t1 is obtained from Equation 1,
[Expression 1]
Δt1 = TΔV / 2Vp
The detection error Δt2 at time t2 when the signal V2 from the magnetic sensor 2 exceeds the threshold value Vth is expressed by the following equation (2).
Δt2 = TΔV / 2Vp
The detection error Δt of the time difference t between the time t1 and the time t2 is calculated from the equation (3).
Δt = Δt1 + Δt2
= TΔV / Vp
The velocity of the moving object is v, the error is Δv, and this detection error Δt is expressed by the following equation (4).
| Δv | / v = (Δt / t) / (1 + Δt / t)
By substituting into the above, it is determined whether or not the required speed accuracy can be obtained, and only when it is determined that the required speed accuracy is obtained, the above moving body is obtained from the time difference between the signals from both magnetic sensors. And a second signal processing unit that averages the moving body velocity signal output from the signal processing unit for a certain period of time and outputs the calculation result to the outside. A moving body speed sensor. Two magnetic sensors 1 and 2 arranged on a moving path of a moving body having a magnetic body separated by a predetermined distance, the linearity and noise width of the magnetic sensors 1 and 2 are equal, and the output changes to a triangular wave shape. Assuming that the noise width is constant within the measurement time, it is compared whether or not the signal V1 of the magnetic sensor 1 is greater than the threshold value Vth, and if it is determined that the signal V1 is greater than the threshold value Vth, the current time Is stored as t1, the waveform of the signal V1 is stored as numerical data V1_buf, and it is compared whether or not the signal V2 of the magnetic sensor 2 is greater than the threshold value Vth, and when it is determined that the signal V2 is greater than the threshold value Vth, The time is stored as t2, the waveform of the signal V2 is stored as numerical data V2_buf,
The time T from the rise to the waveform peak is obtained from the waveform data from one magnetic sensor, the noise width is ΔV, the waveform peak value Vp of the triangular wave, and the instant of time exceeding the threshold Vth of the signal V1 from the magnetic sensor 1 The expected measurement error Δt1 at t1 is obtained as a time derivative dV1 / dt | t = t1 of the signal V1 from the magnetic sensor 1 at time t1 , and Equation 5 is obtained.
Δt1 = ΔV / 2 (dV1 / dt | t = t1 )
And the detection error Δt2 at time t2 when the signal V2 from the magnetic sensor 2 exceeds the threshold value Vth, and the time differential dV2 / dt | t = t2 at the time t2 of the signal V2 from the magnetic sensor 2 6 formulas (6)
Δt2 = ΔV / 2 (dV2 / dt | t = t2 )
The detection error Δt of the time difference t between the time t1 and the time t2 is calculated by substituting
Δt = Δt1 + Δt2
= TΔV / Vp
The velocity of the moving object is v, the error is Δv, and this detection error Δt is expressed by the following equation (8).
| Δv | / v = (Δt / t) / (1 + Δt / t)
By substituting into the above, it is determined whether or not the required speed accuracy can be obtained, and only when it is determined that the required speed accuracy is obtained, the above moving body is obtained from the time difference between the signals from both magnetic sensors. And a second signal processing unit that averages the moving body velocity signal output from the signal processing unit for a certain period of time and outputs the calculation result to the outside. A moving body speed sensor.

Images