JPH07107495B2 - Vibration measuring device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vibration measurement for facilitating the attachment / detachment of an accelerometer to / from an object to be measured, which is used for measuring the vibration characteristics of products successively sent from the manufacturing line. Regarding the device.

2. Description of the Related Art Accelerometers are used to measure vibration, in which a piezoelectric element is placed on the bottom plate of a case, and a weight is fixed on the piezoelectric element. It is mounted on a target and the acceleration due to vibration is taken out as an electric signal of the voltage change of the piezoelectric element via the weight.

Therefore, there are other terms such as vibration pickup, vibration sensor, accelerometer, vibration detector, and acceleration sensor for the acceleration pickup.

However, as an example of that is described, it is actually Kaisho 58.
-141837 gazette "vibration detection device" or Japanese Utility Model Sho 58-77
There is an acceleration sensor type knock sensor in Japanese Patent No. 436, the former describes a simple vibration detecting device and its improvement as a conventional example, and the latter describes a model of a conventional compression type acceleration sensor and its improvement. Is listed.

Although there are various types of acceleration pickups as described above, when actually using this pickup, it is necessary to make various examinations regarding the attachment to the object to be detected in terms of measurement range and ease of attachment. .

In order to accurately transmit the vibration acceleration of the object to be detected to the pickup as it is, it is necessary to integrate the pickup and the object to be detected, and there is a method of screwing with a bolt for the strongest integration.

In Fig. 5, the horizontal axis shows the frequency and the vertical axis shows the relative sensitivity, and the relationship between them is shown. (A) is the case of the screw fastening described above, and the relative sensitivity dB is smooth up to a frequency of about 10 KHz. There is no change, but if it exceeds 10 KHz, the relationship between the two will be disturbed.

As can be seen, the screwing can be measured in a wide frequency range, but its mounting is extremely complicated.

Next, there is mounting with a magnet, which is easier to study than screwing, but as shown in (b), the smoothness of relative sensitivity has already been lost near 10 KHz. .

Furthermore, as a simplest mounting method, a method of holding down the accelerometer by hand is examined. However, as shown in (c), it is difficult for even a skilled measurer to keep the relative sensitivity constant, and the wobbling fluctuation occurs. To be

By the way, for an object to be detected that rotates at high speed, such as an engine motor, the vibration measurement range is at least 10 KHz
is necessary.

Therefore, if you are measuring only one object to be detected, you will use the above-mentioned mounting by screwing,
In order to continuously measure a large number of objects to be detected with one accelerometer, it is not possible to use screwing.

Therefore, in the case of continuous measurement, the measurement is performed on the sound closely related to the vibration, and conventionally, only the measurement of the vibration having a relatively low frequency is carried out by the expert's careful manual pressing. In this case, at the same time, apply a small amount of lubricating oil or silicone oil between the lower surface of the pickup and the object to be detected, thereby substantially increasing the contact area between the two and increasing the elastic coefficient of the contact part, and eventually It was also attempted to make it better.

Problems to be Solved by the Invention The method of pressing the pickup by hand is the simplest method of attaching and detaching the pickup as in the case of the stationary type, but has an advantage that the elastic coefficient of the contact portion can be increased by the pressing. However, even if the vibration has a low frequency, it is unavoidable that the pressing force and the pressing direction become unstable because the pressing force is manually applied. As a result, as shown in FIG. 5 (c), the vibration is generated. There has been a problem as a means for accurately detecting vibration, because the frequency characteristic of the measurement system fluctuates and the difference also occurs depending on the person making the measurement.

Means for Solving the Problems The present invention is intended to solve the above problems and provide a vibration measuring device that is easy to mount and remove, and that can always apply a pressing force of a fixed direction and magnitude. To do.

First, in order to satisfy the condition of easy mounting and dismounting, it is necessary to leave the accelerometer and the object to be detected in a non-sticking state. Only the pressing force corresponding to the weight of the pickup is applied to the contact layer. Therefore, next, it is conceivable that a weight having a weight corresponding to the insufficient force is placed on the upper portion of the pickup. However, this increases the elastic coefficient of the contact layer and increases the degree of integration between the pickup and the object to be detected, but on the other hand, the mass of this vibration system increases by the mass of the weight. Normally, due to the effect of this increase in mass, the resonance angular frequency ω of the contact layer is rather
Will decrease.

That is, when attaching the pickup to the detection target,
Since the contact layer itself is also a spring, the vibration system is composed of the spring and the mass of the pickup, and the actual vibration measurement range depends on the resonance angular frequency (also called contact resonance frequency) ω of this vibration system. Be restricted.

Now, to examine this contact resonance angular frequency ω, this is (K / M) ^1/2 [where,
K is the spring constant of the contact layer, M is the pickup mass], and K increases when a weight is added, but M also increases, and in the normal case, the contact resonance angular frequency ω decreases.

Now, focusing on the high frequency region beyond the resonance frequency in the vibration system with one degree of freedom, the state is a vibration insulation state in which almost no vibration is transmitted to the mass. Then, if an elastic body is interposed between the additional weight and the pickup directly without placing it on the pickup, a vibration system of the additional weight and the elastic body is further added to the upper part of the pickup, and the total weight is 2 degrees. Vibration system is configured, and if the resonance frequency of the vibration system above it is made sufficiently smaller than the resonance frequency of the lower pickup and the contact layer, in the region that is sufficiently higher than the resonance frequency above it. , The pressing force based on the additional weight acts on the pickup, but the additional weight and the pickup are in a vibration insulation state, and the mass of the additional weight is different from that of the lower vibration system composed of the pickup and the contact layer. It will be irrelevant.

That is, as shown in FIG. 2, the displacement of the object to be detected is Ub, the masses of the pickup and the weight are M ₁ and M ₂ , respectively, and the displacements are U ₁ and U ₂ . The spring constant and damping ratio of the contact layer are K ₁ and C ₁ , and the spring constant and damping ratio of the elastic body are K ₂ and C _{2 respectively.}
In the calculation, assuming that the damping ratio C is 0, Ub is Ub = A ₀ sinωt (1) The equation of motion is −K ₁ (U ₁ −Ub) −K ₂ (U ₁ −U ₂ ) = M ₁ becomes ₁ and _{(2) -K 2 (U 2} -U 1) = M 2 2 (3). By rearranging the equations (2) and (3) and substituting them into the equation (1) and setting them as f ₀ = K ₁ A ₀ , M _{1 1} + (K ₁ + K ₂ ) U ₁ −K ₂ U ₂ = f ₀ sin ωt (4) M _{2 2} + K ₂ U−K ₂ U ₁ = 0 (5)

Here, the solution of equations of motion (4) and (5) is represented by the sum of the solution of free vibration and the solution of strong vibration when the right side of (4) is 0, and the term of free vibration is , It becomes 0 after a sufficient time has elapsed, so consider only a stationary solution.

Substituting the solution into equations (4) and (5) as U ₁ = Asinωt (6) U ₂ = Bsinωt (7), and obtaining A and B, Here, ωn ₁ = (K ₁ / M ₁ ) ^1/2 ωn ₂ = (K ₂ / M ₂ ) ^1/2 , and f ₀ = K ₁ A ₀ , A / A ₀ and B / A ₀ When asked, Becomes

If the spring constant ratio is k and the mass ratio is m, Than FIGS. 3 and 4 show the results obtained by substituting the expressions (12), (13) and (14) into (10) and graphing the transfer characteristics. FIG. 3 shows the case where the mass ratio m is changed, and FIG. 4 shows the case where the spring constant ratio k is changed. (Ω / ωn ₂ ) =
It is calculated as 1. In this case, the usable frequency range is a flat band of ω / ωn ₂ ω / ωn ₁ , and m is large,
It can be seen that the smaller k is, the wider the flat transfer characteristic portion is.

That is, as the mass of the additional weight is larger than the mass of the pickup, the elastic coefficient of the contact layer (proportional to the spring constant)
Is larger than the elastic coefficient of the elastic body, the flatter transfer characteristic portion expands.

The present invention was created based on the results of the above-described examination, and an acceleration pickup is slidably and detected in a cylindrical holder having an opening at least one end facing the surface to be detected. The contact surface with the target surface is held so as to project outward from the opening, and the pressing means for pressing the contact surface of the acceleration pickup against the detection target surface is combined with the other end of the acceleration pickup via an elastic body. As a weight, the ratio of the elastic coefficient of the elastic body of the pressing means and the mass of the weight is calculated from the ratio of the elastic coefficient of the contact layer between the acceleration pickup contact surface and the surface to be detected and the mass of the acceleration pickup. It is also characterized by being a small one.

In the above-mentioned operation, at the time of measurement, the acceleration pickup of the vibration measuring device is brought into contact with the surface to be detected, and the tubular holder is lightly held by hand to prevent the entire body from falling sideways. Take out. In that case, looking at the elastic coefficient of the contact layer, if the part to be detected that is in contact with the pickup is deformed during vibration, the vibration itself cannot be measured, and the pickup itself is made of a material and shape that does not easily deform. However, the elastic modulus of the contact layer formed by both surfaces of the contact surface of the acceleration pickup and the contact surface of the detection target surface is large to some extent, although it is affected by the unevenness of the surface. The elastic coefficient is further increased by the weight added by the pressing means. On the other hand, the mass of this additional weight is separated from the vibration system of the pickup by an elastic body having a relatively small elastic coefficient, and is completely irrelevant to the resonance frequency of the system. The smaller the ratio of the mass of the weight to the ratio of the mass of the acceleration pickup to the elastic coefficient of the contact layer between the contact surface of the acceleration pickup and the surface to be detected, the larger the flat transfer characteristic range is. You can As a result, a vibration measuring device having desired vibration characteristics can be obtained by appropriately selecting one or both of the elastic coefficient of the elastic body of the pressing means and the mass of the weight according to the vibration measuring range.

The specifications of the above elastic body and additional weight should be determined experimentally by selecting the value estimated by calculation according to the vibration measurement range or by mounting this vibration measuring device on a vibration tester. Become.

When the test object vibrates at an extremely low frequency, the pickup, the elastic body, and the additional weight vibrate integrally with the test object. Next, when the vibration frequency increases slightly, the elastic body deforms, but its displacement is displaced from that of the pickup that displaces integrally with the object under test, and eventually the displacement of the additional weight and the pickup. There is a phase shift between and. When the frequency of vibration further rises and the phase shift becomes large and reaches 90 degrees, the system consisting of the elastic body and the additional weight becomes in a resonance state. When the frequency of vibration further rises, the vertical movement speed of the pickup becomes faster than the expansion / contraction speed of the elastic body, and the vertical movement of the pickup, that is, vibration is not transmitted to the additional weight, resulting in a vibration insulation state.

Therefore, in the frequency range higher than this, the additional weight only has the role of pressing the pickup against the object under test,
The vibration system is separated from the pickup, and the range from this frequency to the resonance frequency of the pickup itself is the measurement range of this vibration measuring device.

Below, the output of the pickup is measured for vibrations within that range.

In addition, the above is movably inserted into the cylindrical holder to prevent the sideways falling, and the holder is held by hand, but the same may be held by an appropriate support. Further, the same holds true even if the holder acceleration pickup of the vibration measuring device, the elastic body of the pressing means and the weight are lifted up and lowered onto the surface to be detected by an appropriate vertical movement mechanism such as an air cylinder. is there.

Example Hereinafter, the prime mover flowing on the line is stopped at a predetermined position,
An example of the present invention will be described by taking as an example the case where the vibration characteristic is measured by the vibration measuring device of the present invention at that position.

In FIG. 1, reference numeral 1 is an acceleration pickup having a small diameter portion on the upper side, and the outer peripheral surface of the small diameter portion is inserted and fixed to the inner peripheral portion of an elastic body 2 made of silicon rubber in an inverted cup shape. The outer peripheral surface of the elastic body 2 is inserted and fixed in an inverted cup-shaped weight 3, and the top of the weight 3 is connected to a piston shaft 5 of an air cylinder (not shown). These are arranged at the vibration measurement positions on the above line. The outer peripheral surface of the weight 3 is inserted into a holder 4 having an inverted cup shape and having a through hole for the piston shaft 5 at the top, and is vertically movable. Also, the holder 4
A small-diameter through hole is vertically formed in the side wall of the, and silicon oil is injected into the inside thereof. At the time of measurement, at the stop position of the prime mover that is sequentially fed, a vertical space is provided between the prime mover and the measurement location of the prime mover, and the holder 4 is held by a fixed frame (not shown). The lower surface of the pickup 1 is pushed down onto the measurement location of the prime mover via the weight 3 and the elastic body 2, and is separated from the measurement location of the prime mover. In this case, the measured prime mover is sent to its stop position while the piston shaft 5 is raised, and the piston shaft 5 is lowered by a manual command in that state, and the pickup 1 is pushed down to the measurement location of the prime mover. At this time, the holder 4
The oil droplets, which have come out from the lower part of the through hole and are spherical between the lower surface of the pickup 1 and the side surface, spread between the measurement point and the lower surface of the pickup 1 and are pressed in a state where an oil film is formed. The pressing force at this time is the sum of the weight of the weight 3, the weight of the pickup 1 and the pressing force of the piston 5.
As described above, if the pressing force of the piston 5 is excessively large, the spring constant of the contact portion becomes large, but the apparent mass becomes large, and the peak at resonance becomes large in terms of frequency characteristics. As the skirt expands and the flat part becomes smaller,
The pressing force is adjusted appropriately.

With the above, preparation for measurement is completed, and the prime mover is driven in this state to measure the output of the pickup 1. The measurement range is between the lower limit determined by the vibration system including the elastic body 2 and the weight 3 as described above and the upper limit determined by the pickup 1 and the contact portion affected by the pressing force of the weight 3 and the piston 5. Based on the output of the pickup 1 of 1, the vibration characteristics of the prime mover are evaluated.

In addition, although the case where the holder 4 is fixed to the fixed frame is illustrated in the above embodiment, it may be held by hand as described above, and the weight 3 is not coupled to the piston shaft 5 and is manually operated. It may be lifted by.

FIG. 5 (d) (vi) In the vibration measuring device according to the present invention,
FIG. 4 is a frequency characteristic diagram when a pickup having a weight of about 45 g, a weight of 340 g, and two layers of commercially available hard and soft sponges as elastic bodies are combined into a thickness of about 16 mm and a diameter of about 24 mm. The spring constant of the elastic body is sufficiently small with respect to the contact portion, and extremely good flat characteristics are obtained. In addition, even in the case of other elastic data,
Good flat characteristics were obtained in all cases. At the same time, we also examined the finishing state of the contact surface of the acceleration pickup, the surface to be detected, the surface of the contact part, the influence of the pressing force, etc. There is no big difference if it is statically smooth, and the resonance frequency can be raised by increasing the pressing force,
It has been confirmed that the skirt becomes wider as a result, and as a result the flat part does not become so large.

EFFECTS OF THE INVENTION As described above, the present invention has a structure in which a vibration system is further added to the upper part of the acceleration pickup, and the resonance frequency thereof is reduced, and it is sufficient to mount the vibration pickup system on the object to be detected. Vibration measurement can be performed based on frequency characteristics, and highly efficient and accurate and simple measurement can be performed on a large number of objects to be measured.

[Brief description of drawings]

FIG. 1 is a front view with a partial cross section showing an embodiment of the present invention, FIG. 2 is a model diagram showing the principle of the vibration system of the present invention, and FIGS. 3 to 5 are transfer characteristics and spring constant ratios, respectively. Mass ratio,
FIG. 9 is a frequency characteristic diagram showing a relationship with a mounting method of a pickup. 1: Accelerometer 2: Elastic body of pressing means 3: Weight of pressing means

Claims (1)

[Claims] 1. An accelerometer is slidable in a cylindrical holder having at least one end facing an object surface to be detected, and an abutment surface with the object surface to be detected is outwardly directed to the opening portion. An elastic coefficient of the elastic body of the pressing means, which is held so as to be able to project freely, is a weight for combining the contact surface of the acceleration pickup against the surface to be detected with the other end of the acceleration pickup via an elastic body. And the mass of the weight are smaller than the ratio of the elastic modulus of the contact layer between the acceleration pickup contact surface and the surface to be detected and the mass of the acceleration pickup. measuring device