JPS6231863Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a tuning fork vibrator for load measurement that is easy to manufacture industrially and has excellent accuracy and reliability.

Tuning fork vibrators have accurate and stable natural frequencies, so they are used in an extremely wide range of applications, and in some cases, they are also used to measure loads.

Figure 1 shows a conventional example of a tuning fork vibrator, in which two vibrating pieces 1a, 1 are symmetrical about the central axis and parallel to the axis.
b. First and second U-shaped coupling parts 2a and 2b that connect these ends together, support parts 3a and 3b that support these vibrating parts at both ends, and the whole connected to a fixed part or a force transmission part. It is composed of mounting parts 4a and 4b. First and second piezoelectric elements 5a and 5b are attached to both sides of the second coupling part 2b, respectively, and by connecting to a separately provided amplifier 6, the first piezoelectric element 5a can be used for pickup,
The second piezoelectric element 5b is used for excitation.

In the configuration of such a conventional tuning fork vibrator,
By appropriately selecting the gain and frequency characteristics of the amplifier 6, the vibrating pieces 1a and 1b oscillate at the fundamental frequency of the symmetric mode as shown in Fig. 2, and when a load F is applied in the axial direction, the frequency changes. Since this changes, the load F can be determined by detecting this frequency.

In order to accurately measure the load F, the Q of the vibrator must be
It is necessary that the vibration frequency is high and the vibration frequency is stable, that there is little leakage of vibration energy to the outside, and that undesirable external vibrations do not affect the oscillation frequency of the vibrating pieces 1a and 1b. for that purpose,
The vibrating pieces 1a and 1b must be made correctly and symmetrically, and the generated vibration modes must be symmetrical with no phase difference.

However, the vibration pieces 1a, 1b and the coupling part 2
It is extremely difficult to obtain strict symmetry in a normal vibrator in which a and 2b are made into an integral structure by machining or the like. For example, vibrating piece 1
Dimensions of a and 1b are length 15mm, width 3mm, thickness 0.2mm
When designing, thickness symmetry or consistency, which has a particularly large effect on vibration characteristics, is reduced to 1%.
If you try to keep it within ±1μm (±0.001mm)
It became necessary to flatten an area of 15 mm x 3 mm with an accuracy of , which is nearly impossible when considering actual machining accuracy. Even after repeating troublesome special precision machining many times, it is difficult to match the characteristics of the vibrating pieces 1a and 1b. If there is a slight difference between 1a and 1b, the vibration mode will be asymmetrical even though the vibrator vibrates at a single frequency, and the improvement in characteristics will be minimal even though the manufacturing cost of the vibrator is high, making it impractical.

The purpose of this invention is to eliminate the above-mentioned drawbacks, to allow slight machining errors in the long plate-shaped vibrating piece, to make it extremely easy to make adjustments to match the vibration characteristics of the two, and to prevent the effects of atmospheric pressure and temperature. The object of the present invention is to provide a tuning fork vibrator for measuring load which can reduce
A tuning fork vibrator consisting of a long plate-shaped vibrating piece and two connecting parts that connect both ends of the vibrating piece, and configured so that the natural frequency changes according to the load applied in the axial direction. The vibrator is characterized in that a balance weight whose mass can be adjusted is formed approximately at the center of each of the elongated plate-shaped vibrating pieces.

The present invention will be explained in detail based on the embodiment shown in FIG. Note that the same reference numerals as in FIG. 1 indicate the same members.

The structure of the vibrator according to the present invention is basically the same as the conventional example shown in FIG.
The difference is that balance weights 7a and 7b, each of which is a bulge integral with the vibrating pieces 1a and 1b, are provided approximately at the center of 1b. The only condition for the shape of the balance weights 7a and 7b is that the length in the load axis direction is as short as possible, and in addition to the cylindrical shape shown in the figure, any other shape such as a prismatic shape or a spherical shape may be used. It may be constructed by projecting only on either the outside or inside side, or by bonding another member. balance weight 7
a, 7b at the center of the vibrating pieces 1a, 1b, although the natural frequency decreases, as is clear from the fundamental vibration mode diagram in FIG.
Since the central portion of 1b corresponds to the antinode of vibration, it does not have any adverse effect on the stability of vibration.

In such a tuning fork vibrator shown in FIG.
Measure the individual natural frequencies of the vibrating pieces 1a and 1b individually, and reduce the required amount of the balance weight 7a or 7b on the lower frequency side to match the higher frequency, or observe the vibration mode and find the desired one. Either of the balance weights 7a, 7 is adjusted so that the symmetry of
It can be adjusted by removing b. By doing this, the vibration characteristics of the vibrating pieces 1a and 1b are made uniform, enabling accurate symmetrical mode vibration with no phase difference, increasing the Q value of the vibrator, and almost eliminating leakage of vibration energy to the outside. Can be done. In addition, by faithfully transmitting only the load F to the vibrating section and changing its frequency without being affected by external vibrations, extremely accurate load measurement can be performed.

Furthermore, when the vibrating pieces 1a and 1b vibrate, the air in their vicinity is forced to vibrate at the same time.
The result is similar to the apparent increase in the mass of the vibrating pieces 1a and 1b, and changes in air density due to changes in atmospheric pressure and temperature affect the vibration frequency. The frequency of the tuning fork vibrator taking into account the influence of this nearby air is given by the following equation (1).

ω={k/(m+2M+Cρ)} ^1/2 …(1) In addition, ω is the vibration angular frequency, k is the effective spring coefficient of the vibrating piece, m is the mass of the vibrating piece, M is the mass of the balance weight, and Cρ is the proximity Equivalent added mass due to air,
C is a constant depending on the shape of the vibrating element, and ρ is the air density.

The size of the equivalent additional mass Cρ due to the nearby air is:
In the case of a tuning fork vibrator for load measurement, the mass of the vibrating piece m is
It is 0.3% or less. How the frequency ω changes when the air density ρ changes is given by the following equation (2) by differentiating equation (1) with respect to ρ and rearranging it.

dω/ω=-(1/2) ・{Cρ/(m+2M+Cρ)}・(dρ/ρ)
...(2) Here, balance weights 7a and 7b of mass M
Let's consider the influence and effectiveness of adding this to the vibrating pieces 1a and 1b of mass m using equations (1) and (2). For example, if the masses M and m are equal, the frequency ω is calculated from equation (1) before adding the balance weights 7a and 7b.
Although it decreases to 1/3 ^1/2 , that is, 58%, this degree of decrease in the frequency ω does not cause any disadvantage in load measurement. On the other hand, the rate of change of the frequency ω based on the change in the air density ρ is 1/3 of the value before the addition using equation (2).
It can be seen that the load measurement accuracy is greatly improved.

As explained above, according to the tuning fork vibrator for load measurement according to the present invention, the Q value of the vibrator is high, and adjustment at the time of manufacture using a balance weight for vibration in a symmetric mode is extremely easy. This enables highly accurate load measurements that are less affected by changes in air density due to changes in air temperature and air temperature.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of a conventional tuning fork vibrator, FIG. 2 is an explanatory view of its operating state, and FIG. 3 is a perspective view of an embodiment of the tuning fork vibrator for measuring load according to the present invention. Symbols 1a and 1b are vibrating pieces, 2a and 2b are coupling parts, 5a and 5b are piezoelectric elements, 6 is an amplifier, 7a,
7b is a balance weight.

Claims (1)

[Claims for Utility Model Registration] 1. Consisting of two long plate-shaped vibrating pieces installed symmetrically and parallel to the central axis, and two connecting parts that connect their respective ends to each other, In the tuning fork vibrator configured so that the natural frequency changes according to the load applied in the direction, a balance weight whose mass can be adjusted is formed approximately at the center of each of the long plate-shaped vibrating pieces. A tuning fork vibrator for load measurement featuring: 2. The tuning fork vibrator for load measurement according to claim 1, wherein the balance weight is shaved off as necessary to adjust the symmetry of vibration.