JP2001147233A - Speed detecting mechanism - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a speed detecting mechanism by which a precise speed can be detected on the basis of the detected displacement and the detected acceleration of an object to be measured. SOLUTION: This speed detecting mechanism is provided with a displacement sensor 1 which detects the displacement of an object to be measured. The speed detecting mechanism is provided with an accelerometer 2 which detects the acceleration of the object. The speed detecting mechanism is provided with a filter Fa and a filter Fb. The filters Fa, Fb are constituted in such a way that the transmission characteristic of a function of [integral characteristic]×[filter Fa]+[differential characteristic]×[filter Fb] becomes nearly a constant in a frequency band required for calculating a speed (where filter Fa=differential characteristic and filter Fb=integral characteristic). The speed detecting mechanism is constituted so as to calculate the speed of the object, in such a way that a value which is obtained by passing the detected displacement through the filter Fa is added to a value which is obtained by passing the detected acceleration through the filter Fb.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mechanism for determining the speed of an object to be measured without directly detecting it.

[0002]

2. Description of the Related Art As a method of determining the speed of an object to be measured without directly detecting it, a method of detecting the displacement of the object to be measured and differentiating the same, or detecting the acceleration of the object to be measured and integrating it is performed. There is a way to ask.

[0003]

[Problems to be solved by the invention]
In the method of calculating velocity by differentiating displacement, it is theoretically impossible to create ideal differential characteristics due to causality, and it is necessary to use a pseudo-differential method, so accurate velocity can not be obtained There was a problem. Further, since the differential characteristic has a high gain in a high frequency region as shown by the hatched portion in FIG. 2, there is a problem that noise of the displacement signal is excited.

On the other hand, in the method of calculating the velocity by integrating the acceleration, the output of the acceleration sensor has a slight offset because the integration characteristic has a high gain in the low frequency region as shown by the hatched portion in FIG. However, there is a problem that the offset is integrated and the calculated speed shifts to either plus or minus. Usually, a high-pass filter is inserted to solve this problem,
Accurate speed cannot be obtained because of the extra filter.

The present invention has been made in view of the above technical problems, and has as its object to provide a speed detecting mechanism capable of detecting an accurate speed based on the detected displacement and acceleration of the measured object.

[0006]

According to a first aspect of the present invention, there is provided a displacement sensor for detecting a displacement of an object to be measured, an acceleration sensor for detecting an acceleration of the object to be measured, a first filter and a second filter. And the transfer function of {integral characteristic} × {first filter} + {differential characteristic} × {second filter} is substantially constant in a frequency band required for speed calculation. A first filter and a second filter (however, the first filter１the differential characteristic, the second filter
Filter), the speed of the object to be measured is calculated by adding the value obtained by passing the detected displacement through the first filter and the value obtained by passing the detected acceleration through the second filter. This is a speed detection mechanism characterized by being configured.

A second invention comprises a displacement sensor for detecting a displacement of an object to be measured, an acceleration sensor for detecting an acceleration of the object to be measured, a first filter and a second filter. Characteristics} × {Transfer characteristics of displacement sensor and its amplifier} ×
{First filter} + {differential characteristic} × {transfer characteristic of acceleration sensor and its amplifier} × {transfer characteristic of second filter} such that the transfer characteristic becomes substantially constant in a frequency band required for speed calculation. The first filter and the second filter are configured (however, the first filter ≠ the differential characteristic, the second filter
Filter), the speed of the object to be measured is calculated by adding the value obtained by passing the detected displacement through the first filter and the value obtained by passing the detected acceleration through the second filter. This is a speed detection mechanism characterized by being configured.

In a third aspect based on the first or second aspect, the substantially constant is characterized in that a variation width of the transfer characteristic is 3 dB or less.

According to a fourth aspect of the present invention, in the first to third aspects, the shape of the first filter is as _follows : F _a = K ₁ s / (s + ω ₁ ) where K ₁ : constant gain ω ₁ : break point and frequency, the shape of the second _{filter, F b = K 2 / (} s + ω 2) where, K _2: constants gain omega _2: is characterized in that it has a corner frequency.

In a fifth aspect based on the first to third aspects, the shape of the first filter is represented by: F _a = K ₃ s / {(s + ω ₃ ) (s + ω ₄ )}, where K _{3 is a} constant. Gains ω ₃ , ω ₄ : breakpoint frequency, and the form of the second filter is _Fb = K ₄ (s + ω ₇ ) / {(s + ω ₅ ) (s + ω ₆ )}, where K ₄ : constant gain ω ₅ , Ω ₆ , ω ₇ : corner frequency.

In a sixth aspect based on the first to third aspects, the shape of the first filter is expressed as _follows : F _a = K ₅ s (s + ω ₁₁ ) / {(s + ω ₈ ) (s + ω ₉ ) (s + ω
₁₀ )} where K ₅ : constant gain ω ₈ , ω ₉ , ω ₁₀ , ω ₁₁ : corner frequency, and the form of the second filter is F _b = K ₆ s (s + ω ₁₅ ) / {(s + ω ₁₂ ) (s + ω ₁₃ ) (s + ω
₁₄ )}, where K ₆ : constant gain ω ₁₂ , ω ₁₃ , ω ₁₄ , ω ₁₅ : breakpoint frequency.

[0012]

According to the first to sixth aspects of the present invention, the speed is calculated by adding the detected displacement that has passed through the first filter and the detected acceleration that has passed through the second filter. The function is {integral characteristic} × {first filter} + {differential characteristic} × {second filter} or {integral characteristic} × {transfer characteristic of displacement sensor and its amplifier} ×
{First filter} + {Differential characteristic} × {Transfer characteristic of acceleration sensor and its amplifier} × {Transfer characteristic of {Second filter} becomes substantially constant in a frequency band required for speed calculation. By configuring the first filter and the second filter, the first filter can have a differential characteristic in a low frequency region, and the second filter can have an integral characteristic in a high frequency region.

[0013] This makes it possible to calculate the speed by utilizing the advantages of both the method of obtaining the speed by differentiating the displacement and the method of obtaining the speed by integrating the acceleration. The accuracy can be calculated based on the displacement signal and the acceleration signal. Speed can be calculated well.

In particular, when the first and second filters are configured according to the fourth aspect of the present invention, if the corner frequency is set small, the first
, The high frequency gain of the filter becomes small, and the problem of noise in the displacement signal can be avoided. Also, if the break point frequency is set to be large, the low frequency gain of the second filter becomes small,
The problem of the offset of the acceleration signal can be avoided.

Further, when the first and second filters are of second order according to the fifth invention, the first filter is in the form of a band-pass filter as shown in FIG. 9 to further reduce the problem of noise in the displacement signal. Can be avoided.

Further, when the first and second filters are constituted by the third order according to the sixth aspect of the present invention, the respective filters are arranged as shown in FIG.
1. As shown in FIG. 12, a band-pass filter is formed, and both the problem of the noise of the displacement signal and the problem of the offset of the acceleration signal can be avoided.

[0017]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a block diagram showing the configuration of a speed detecting mechanism according to the present invention. The speed detecting mechanism detects a displacement sensor 1 for detecting a displacement of an object to be measured and an acceleration of the object to be measured. It comprises an acceleration sensor 2 and a speed calculation unit 3 which calculates the speed of the object to be measured based on those output signals and outputs it to another calculation unit or the like.

The velocity computation unit 3 includes a first filter F _a displacement signal is input, a second filter F _b the acceleration signal is input, the filters F _a and the filter F _b
, And a constant gain C that multiplies the output of the addition point by a predetermined number and outputs the result.

The filters F _a and F _b are configured as described below.

As pointed out in the prior art, the method of calculating the velocity by differentiating the displacement has the problem that the noise of the displacement signal is excited because the gain of the differential characteristic is high in the high frequency region as shown by the hatched portion in FIG. There is. In the method of calculating the speed by integrating the acceleration, since the gain of the integration characteristic is high in the low frequency region as shown by the hatched portion in FIG. 3, the offset of the acceleration signal is integrated and the speed signal is shifted. Problem.

However, the method of calculating the speed by differentiating the displacement has a problem in the high frequency region, but can calculate the speed in the low frequency region without any problem. Further, the method of calculating the speed by integrating the acceleration has a problem in the low frequency region, but has no problem in the high frequency region.

Therefore, in the speed detecting mechanism according to the present invention,
Focusing on the fact that the two speed calculation methods have such contradictory properties, the speed is calculated using only the good points of both methods. For this purpose, the filter Fa has _a characteristic that only the low-frequency region shown in FIG. 4 has a differential characteristic and the other is substantially zero, and the filter _Fb has an integral characteristic only in the high-frequency region shown in FIG. The filters F _a and F _b may be configured so that

[0024] However, FIG. 4, the filter having the characteristic of FIG. 5 can not make theoretically, in practice, the filter F _a is to always have a differential characteristic in the low frequency region, the filter F _b is always in a high frequency region Filters F _a , F _b are provided so as to have integral characteristics, and to approach the characteristics of FIGS. 4 and 5 as much as possible.
Is configured.

In order to provide the filter F _a and the filter F _b with such characteristics, a function {integral characteristic} × {transfer characteristic of the displacement sensor and its amplifier} × {filter _Fa } + {differential characteristic} × {Transfer characteristics of acceleration sensor and its amplifier} × {Filter F _b } ························································· (A) In consideration of the above, it is sufficient that the order of the numerator does not exceed the order of the denominator. However, the filter F _a are not differential characteristic in the frequency band throughout which is necessary in the speed signal calculation, the filter F _b shall not integration characteristic in the frequency band throughout which is necessary in the speed signal calculation. That is, F _a ≠ k ₁ s and F _b ≠ k ₂ / s, where k ₁ , k ₂ : arbitrary coefficient s: differential operator, (F _a , F _b ) = (0, 1 / s), (s, 0), (s /
2, 1/2 s) and the like are not included.

The reason why the transfer characteristic is set to the "substantially" constant under the above condition is that there is no practical problem even if there is a fluctuation of about 3 dB (depending on the purpose of use). However, ideally, it should be a constant.

When the filters F _a and F _b are configured so that the transfer characteristic of the function A becomes (substantially) constant, the sum of the path A and the path B in the block diagram shown in FIG. 6 becomes (substantially) constant. , The output signal of the block diagram is (approximately) a constant multiple of the actual speed, but the portion surrounded by the broken line in the diagram corresponds to the speed calculation unit 3. Therefore, if the filters F _a and F _b are configured in this way, , The output signal of the speed calculation unit 3 is also (substantially) a constant multiple of the actual speed.

Although the function A considers "the transfer characteristic of the displacement sensor and its amplifier" and "the transfer characteristic of the acceleration sensor and its amplifier", if they can be ignored, the function A is a simplified function of the function A. , {Integral characteristic} × {filter F _b } + {differential characteristic} × {filter F _b }... (A ′) such that the transfer characteristic becomes substantially constant in a frequency band required for speed signal calculation. May be configured with filters F _a and F _b .

The filters F _a and F _b are specifically configured as described below.

For example, let us consider a case where the shape of the filter Fa is _a first-order filter, and F _a = K ₁ s / (s + ω ₁ ) where K ₁ : constant gain ω ₁ : corner frequency. Then, the shape of the filter F _{b is, F b = K 2 / (} s + ω 2) where, K _2: constants Gain omega _2: determined uniquely and break frequency. At this time, if the gain C is 1 and the "transfer characteristics of the displacement sensor and its amplifier" and the "transfer characteristics of the acceleration sensor and its amplifier" can be ignored, the function A becomes a function A '.

Then, when the above F _a and F _b are substituted into the function A ′, 1 / s × K ₁ s / (s + ω ₁ ) + s × K ₂ / (s + ω ₂ ) = {K ₂
s ² + (K ₂ ω ₁ + K ₁ ) s + K ₁ ω ₂ } / {s ² + (ω ₁ + ω ₂ ) s
+ Ω ₁ ω ₂ }, but in order to make the output signal of the speed calculation unit 3 coincide with the actual speed, it is necessary to make this transfer characteristic a constant (here, 1).

In order to make the transfer characteristic a constant, it is necessary that K ₁ = ω ₁ from the zero-order term of the numerator on the right-hand side, and K ₂ = ω ₂ / ω ₁ from the first-order term. Therefore, it is necessary that K ₂ = ω ₂ / ω ₁ = 1 in consideration of the second-order terms.

[0033] Finally, the condition that ω ₁ = ω ₂ is guided, ideal filter F _a in the state, each filter F _{b is, F a = ωs / (s} + ω) F b = 1 / (s + ω) where, ω: Turn frequency.

FIGS. 7 and 8 show examples of Bode diagrams when the filters F _a and F _b are configured as described above. Thus, the filter F _a is a differential characteristic only low frequencies, the filter F _b it can be seen that a integral characteristic only high-frequency region.

Therefore, when the displacement signal has a lot of noise, the filter F _a can be set by setting the corner frequency ω to a small value.
In the case where the gain in the high-frequency region becomes small, the problem of the noise of the displacement signal can be avoided, and the noise of the displacement signal is not so much a problem, and the offset of the acceleration signal becomes a problem, it can be set large value of the frequency ω low-frequency gain of the filter F _b to reduce the influence of small becomes offset.

Here, the transfer characteristic of the function A 'is a constant
The corner frequency ω ₁, Ω_TwoIs the filter F
_a, F_b, But the transfer characteristic of the function A 'is practical
The frequency can be changed within a range that does not cause any problem.
ω₁, Ω_TwoAre different to the extent that the function A 'is substantially constant.
Is also good.

When the order of the filters F _a and F _b is the second order, the shape of the filter F _a is expressed as follows: F _a = K ₃ s / {(s + ω ₃ ) (s + ω ₄ )} where K ₃ : constant gain ω _3, ω _4: When break frequency, the shape of the filter F _{b is, F b = K 4 (s} + ω 7) / {(s + ω 5) (s + ω 6)} However, K _4: constants gain omega ₅ , Ω ₆ , ω ₇ : corner frequency Then, if these F _a and F _b are substituted into the function A or A ′, the relations established among the constant gains K ₃ , K ₄ , and ω _{3 to} ω ₇ having the transfer characteristics of the function A or A ′ as constants. An expression is obtained.

FIGS. 9 and 10 show examples of Bode diagrams in the case where the filters F _a and F _b are of the second order.

According to this, when the filters F _a and F _b are configured in the second order, the filter F
_a has a differential characteristic in the low frequency region, the filter F _b is seen to have an integral characteristic in the high frequency region. In particular, since the filter _Fa takes the form of _a band-pass filter and approaches the ideal form shown in FIG. 4, the problem of noise in the displacement signal can be further avoided.

Further, a case where the order of the filters F _a and F _b is set to 3 will be described. In this case, the filter F _a
For example, F _a = K ₅ s (s + ω ₁₁ ) / {(s + ω ₈ ) (s + ω ₉ ) (s +
omega _10)} where, K _5: constant gain _{ω 8, ω 9, ω 10} , ω 11: When break frequency, the shape of the filter F _{b is, F b = K 6 s (} s + ω 15) / {(s + ω ₁₂ ) (s + ω ₁₃ ) (s + ω
₁₄ )} where K ₆ : constant gain ω ₁₂ , ω ₁₃ , ω ₁₄ , ω ₁₅ : corner frequency. Then, if these F _a and F _b are substituted into the function A and the function A ′ when the characteristics of the sensor and the amplifier can be ignored, the constant gains K ₅ and K ₆ that make the transfer characteristics of the function A or A ′ constant, A relational expression that is established between the corner frequencies ω _{8 to} ω ₁₅ is obtained.

FIGS. 11 and 12 show examples of Bode diagrams in the case where filters F _a and F _b are of the third order.

As shown in FIGS. 11 and 12, the filter Fa has _a differential characteristic only in the low-frequency region and the filter _Fb has an integral characteristic only in the high-frequency region when the filter is of the third order.
In particular, in the case of a third-order configuration, each filter takes the form of a band-pass filter, which approaches the ideal shape shown in FIGS. 4 and 5, which causes both the problem of noise in the displacement signal and the problem of offset in the acceleration signal. Can be avoided.

The filter F _a, the detailed description is omitted for the case where the further higher F _b, the filter F _a, increasing the order of F _b the filter F _a high-frequency region and a low-frequency filter F _b In the region, the inclination further increases and approaches the ideal characteristics shown in FIGS. 4 and 5, and the problem of the noise of the displacement signal and the problem of the offset of the acceleration signal can be avoided more efficiently. However, if the order of the filter is high, the design of the filter will be complicated accordingly, so the displacement signal,
It is preferable to determine the optimum order after confirming the offset level and the like of the acceleration signal.

Next, an example in which this speed detecting mechanism is applied to the detection of the piston rod speed of a vibration test machine will be described.

FIG. 13 shows a schematic configuration of a vibration test machine using an electrohydraulic servo mechanism. This vibration test machine is for vibrating a test object with an arbitrary waveform. When a test object (not shown) is mounted between the mounting jigs 4 and 5, and the hydraulic cylinder 6 is driven to expand and contract. The device under test is vibrated vertically. In the figure, 7 is a voltage-current converter, 8 is a servo valve, 9 is a hydraulic source, and these constitute an electro-hydraulic servo mechanism.

The displacement of the cylinder rod 10 of the hydraulic cylinder 6 is detected by the displacement sensor 1, and the displacement is controlled based on the difference between the detected displacement and the target displacement (here, P
ID control) is performed.

In order to detect the speed of the cylinder rod 10 without using a speed sensor in the vibration tester having such a configuration, as shown in FIG.
The acceleration sensor 2 for detecting the acceleration of the above and the speed calculation unit 3 described above are added. Since the speed calculation unit 3 includes a filter, a gain, and the like as described later, the speed calculation unit 3 can be configured by an analog circuit using an operational amplifier or the like.
Further, a digital processing may be performed by a control device or a personal computer.

Hereinafter, a specific setting method of the filters F _a and F _b and the gain C of the speed calculation unit 3 will be described.

The piston rod speed is changed from DC to 100 [Hz].
Assuming that it is necessary to obtain in the band up to, first, "transfer characteristic of displacement sensor 1 + amplifier" and "transfer characteristic of acceleration sensor 2 + amplifier" are confirmed. These operations mainly check the frequency characteristics of the sensor and the filter characteristics of the amplifier.

Here, if the frequency characteristics of the displacement sensor 1 and the acceleration sensor 2 are flat up to several k [Hz], and the filter of the amplifier is also about 1 k [Hz], the "displacement sensor" in the frequency band required for speed signal calculation is obtained. The “1 + amplifier transfer characteristic” and the “acceleration sensor 2 + amplifier transfer characteristic” can be regarded as gain 1 and phase zero.

Therefore, the filter F _a and the filter F _b are a function A ′ obtained by simplifying the function A, {integral characteristic} × {filter _Fa } + {differential characteristic} × {filter F
_b } may be configured to be substantially constant in a frequency band required for speed signal calculation. Here, the order of the filters F _a and F _b is set to 1, and the shape of the filter F _a is _expressed as _follows : F _a = K ₁ s / (s + ω ₁ ) where K ₁ : constant gain ω ₁ : corner frequency forms of _{b, F b = K 2 / (} s + ω 2) where, K _2: constants gain omega _2: determined uniquely and break frequency.

At this time, the filter F_a, F_bCorner frequency ω
₁, Ω_TwoIs set between DC and 100 [kHz].
Become. Specifically, the noise level of the displacement signal and the acceleration signal
Adjust while checking the offset level of the
Is high, the corner frequency is ω ₁To a higher
When the level is high, the corner frequency ω_TwoSet smaller
You. Where ω₁, Ω_TwoIs 1 [rad / s] = 1 / 2π
Set to [Hz].

The filter F_a, F_bAt the addition point after passing
It is necessary to make the unit equal to the gain.
Signal is output at 0.1 [V / mm] and the acceleration signal is 0.5 [V / mm].
(cm / s ^Two)], And their units are 1 [V / (m / s)]
If aligned to₁, K_TwoIs K₁= 10 ÷ 1000 = 0.01 K_Two= 2 ÷ 100 = 0.02.

Since the filters F _a and F _b are not completely differentiating and integrating, respectively, the unit at the addition point after passing through the filters F _a and F _b is strictly 1 [V / (m / s)]. However, the unit obtained by adding the signal after passing through the filter F _a and the signal after passing through the filter F _b is always 1 [V / (m / s)].

Finally, a method of setting the gain C will be described. To set the gain C, it is sufficient to consider how to output a speed signal. That is, 1 [V / (m /
s)], if it is desired to output the voltage as it is, the gain C may be set to 1 and the signal may be passed. If the unit is to be changed, the gain C may be adjusted accordingly. Here, the gain C is set to 1 to output the speed signal as 1 [mV / (m / s)].
000.

Therefore, the speed calculation unit 3 eventually becomes as shown in FIG. Thus, the speed calculation unit 3
With this configuration, the speed of the piston rod 10 can be accurately calculated based on the output signal of the displacement sensor 1 and the output signal of the acceleration sensor 2 regardless of the high frequency region or the low frequency region. In order to further improve the detection accuracy, the filters F _a and F _b may be configured to have a higher order as described above.

Although the example in which the speed detecting mechanism according to the present invention is used for detecting the piston rod speed of the vibration testing machine has been described above, this example is merely an example of a configuration to which the speed detecting mechanism according to the present invention can be applied. And the application range of the speed detection mechanism according to the present invention is not limited to this.

[Brief description of the drawings]

FIG. 1 is a block diagram of a speed detection mechanism according to the present invention.

FIG. 2 is a Bode diagram showing differential characteristics.

FIG. 3 is a Bode diagram showing integration characteristics.

FIG. 4 is _a Bode diagram of an ideal filter Fa.

FIG. 5 is a Bode diagram of an ideal filter F _b.

FIG. 6 is a block diagram for explaining a method of setting filters F _a and F _b .

FIG. 7 is an example of a Bode diagram of _a filter F _a (first order).

FIG. 8 is an example of a Bode diagram of a filter F _b (first order).

FIG. 9 is an example of a Bode diagram of _a filter F _a (second order).

FIG. 10 is an example of a Bode diagram of a filter F _b (second order).

FIG. 11 is an example of a Bode diagram of _a filter F _a (3rd order).

FIG. 12 is an example of a Bode diagram of a filter F _b (third order).

FIG. 13 is a schematic configuration diagram of a vibration test machine.

FIG. 14 is a schematic configuration diagram of a vibration tester provided with a speed detection mechanism according to the present invention.

FIG. 15 is a specific configuration of the speed calculation unit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Displacement sensor 2 Acceleration sensor 3 Speed calculation unit 4, 5 Jig for mounting DUT 6 Hydraulic cylinder 7 Voltage-current converter 8 Servo valve 9 Hydraulic source 10 Piston rod

Claims (6)

[Claims] 1. A displacement sensor for detecting a displacement of an object to be measured, an acceleration sensor for detecting an acceleration of the object to be measured, a first filter and a second filter, and a function: {integral characteristic} × The first filter and the second filter are configured such that the transfer characteristic of {first filter} + {differential characteristic} × {second filter} becomes substantially constant in a frequency band required for speed calculation. (However, the first filter ≠ differential characteristic, the second filter ≠ integral characteristic), the one where the detected displacement is passed through the first filter and the one where the detected acceleration is passed through the second filter are A speed detection mechanism characterized in that the speed of an object to be measured is calculated by adding the speed. 2. A displacement sensor for detecting a displacement of an object to be measured, an acceleration sensor for detecting an acceleration of the object to be measured, a first filter and a second filter, and a function {integral characteristic} × {Transfer characteristics of displacement sensor and its amplifier} ×
{First filter} + {differential characteristic} × {transfer characteristic of acceleration sensor and its amplifier} × {transfer characteristic of second filter} such that the transfer characteristic becomes substantially constant in a frequency band required for speed calculation. The first filter and the second filter are configured (however, the first filter ≠ the differential characteristic, the second filter
(1) The speed of the object to be measured is calculated by adding the value obtained by passing the detected displacement through the first filter and the value obtained by passing the detected acceleration through the second filter. A speed detection mechanism, characterized in that it is configured. 3. The substantially constant means that a variation width of the transfer characteristic is 3d.
The speed detection mechanism according to claim 1 or 2, wherein the speed is equal to or less than B. 4. The form of the first filter is F _a = K ₁ s / (s + ω ₁ ), where K _{1 is a} constant gain and ω _{1 is a} corner frequency. The form of the second filter is F _b = K ₂ / (s + ω ₂ ) where K ₂ : constant gain ω ₂ : corner frequency. 4. The speed detecting mechanism according to claim 1, wherein: 5. The shape of the first filter is as _follows : F _a = K ₃ s / {(s + ω ₃ ) (s + ω ₄ )} where K ₃ : constant gain ω ₃ , ω ₄ : corner frequency The form of the second filter is _Fb = K ₄ (s + ω ₇ ) / {(s + ω ₅ ) (s + ω ₆ )} where K ₄ : constant gains ω ₅ , ω ₆ , ω ₇ : break point frequency The speed detecting mechanism according to any one of claims 1 to 3, wherein 6. The shape of the first filter is expressed as _follows : F _a = K ₅ s (s + ω ₁₁ ) / {(s + ω ₈ ) (s + ω ₉ ) (s +
ω ₁₀ )} where K ₅ : constant gain ω ₈ , ω ₉ , ω ₁₀ , ω ₁₁ : corner frequency, and the form of the second filter is F _b = K ₆ s (s + ω ₁₅ ) / {( s + ω ₁₂ ) (s + ω ₁₃ ) (s + ω
₁₄ )}, wherein K ₆ : constant gain ω ₁₂ , ω ₁₃ , ω ₁₄ , ω ₁₅ : breakpoint frequency The speed detection mechanism according to claim 1, wherein: