JPS6210371B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a holder for a pressure-sensitive diaphragm when the quartz crystal diaphragm is used as a pressure-sensitive oscillation element for detecting stress.

In recent years, sensors for detecting stress, temperature, etc. have shown remarkable progress in both quality and quantity, particularly in the field of industrial measurement, such as expanding the range of measurement targets and improving accuracy.

However, in many conventional products, mechanical and physical quantities such as stress and temperature are processed analogously in the process of converting them into electrical signals, and therefore many complex correction methods are required to achieve high accuracy. had to be used.

On the other hand, crystal diaphragms have long been widely used in wireless communications and timekeeping as a vibrating body that provides stable frequencies, and by processing frequency as a digital quantity, it is easy to perform high-precision measurements. be able to.

On the other hand, a crystal diaphragm that vibrates at a stable frequency,
The vibration frequency can be varied by applying external stress parallel to the plate surface. Since so-called digital stress detection sensors that digitally process frequencies using this stress-frequency characteristic have been put into practical use, transmission lines,
High-precision force sensors that have very small errors due to changes in amplifier characteristics, fluctuations in power supply voltage, etc. have attracted attention.

However, when applying a quartz diaphragm as a force sensor, such as a quartz crystal pressure-sensitive transducer, despite its excellent performance, a stress transmission mechanism for applying external stress to the diaphragm and its holding means are required. This difficulty has hindered the practical application of the pressure-sensitive transducer.

The main reason for this is that the crystal used in pressure-sensitive elements is an anisotropic and brittle material, so the coefficient of linear thermal expansion of the crystal diaphragm differs depending on the direction, and the stress transmission mechanism using metal materials This was because it was not easy to join with the metal, errors occurred due to differences in linear thermal expansion coefficients, and the workability of drilling, grinding, etc. was poor, and plastic deformation was impossible.

The present invention solves the above problems and holds a quartz diaphragm with a holder manufactured by cutting out a quartz crystal, and the direction of the holder is aligned with the direction of the pressure-sensitive axis of the diaphragm. Furthermore, the coefficient of linear thermal expansion of the holder in the thickness direction is made equal to that of the metal material of the holder mounting portion.

A detailed explanation will be given below with reference to the drawings.

Figure 1 shows the relationship between the crystal axis of a quartz crystal and the cutting angle of a pressure-sensitive diaphragm cut out from it. direction, and the other side (side B) perpendicular to this is cut in a direction rotated by an angle θ around the X axis. Here, 2 is the electrode provided on the front and back of the pressure-sensitive diaphragm, F,
F′ indicates the external stress (in this case, for example, in the compressive direction) to be measured by the force sensor.

That is, when external forces F and F' are applied to the pressure-sensitive diaphragm constructed in this way, the vibration frequency changes in accordance with the magnitude of the external forces F and F'.

FIG. 2 shows an example of a pressure-sensitive transducer that uses two pressure-sensitive diaphragms to operate differentially, where 3 and 4 are pressure-sensitive diaphragms, and 5 is a holding stand. In this case, the pressure-sensitive diaphragms 3 and 4 are bonded and fixed to the holding table 5 by appropriate means at the parts C and D to which the stresses F and F' shown in FIG. In FIG. 2, only the upper pressure-sensitive diaphragm 3 is shown).

The holding stand 5 has one end 5A fixed to the outside, and the other end 5A.
When an external force F _p is applied to B, the holding table 5 receives the external force F _p
As a result, the free end 5B is bent downward, albeit very slightly, so that the upper pressure-sensitive diaphragm 3 shown in the drawing is bent in the extending direction as shown by the arrow E, and the lower pressure-sensitive diaphragm 4
A stress is applied in the compressive direction as shown by arrow G, and the vibration frequencies change in opposite directions. That is, the holding table 5 holds the pressure-sensitive diaphragm and acts as a stress transmission mechanism, and the pressure-sensitive diaphragms 3 and 4 operate differentially, and the vibration frequencies change in opposite directions in the positive and negative directions, respectively. , by taking the difference frequency between the two frequencies, a signal output proportional to the external stress can be obtained, and it acts as a highly sensitive pressure-sensitive transducer.

FIG. 3 shows a principle explanatory diagram when the pressure-sensitive transducer shown in FIG. 2 is used as a pressure difference measuring device, where 6 is a pressure-sensitive co-transducer, 7,
9 is a frame to which the pressure sensitive transducer ₆ and the bellows 7 _, 8 are mounted.

In this case, if the bellows 7 and 8 are of exactly the same shape, the pressure sensitive transducer 6 has the bellows 7 and 8.
Stress corresponding to the pressure difference (P _A - P _B ) applied through 8 acts, and stress in each direction of expansion and compression is transmitted to the pressure-sensitive diaphragms 3 and 4, and the stress in the positive and negative directions of each vibration frequency is transmitted to the pressure-sensitive diaphragms 3 and 4. It appears as a change in

Here, the stress applied to the pressure sensitive transducer 6 is extremely small because it is a pressure difference.
To detect this, it is necessary that the pressure-sensitive diaphragms 3 and 4 operate stably. Conventionally, various materials have been used for the holding base 5 of the pressure-sensitive transducer, but the coefficient of thermal expansion of these materials does not match that of the pressure-sensitive diaphragm in the operating temperature range, and therefore It was inevitable that slight changes would cause errors and extremely unstable operation.

In the present invention, we have clarified that the unstable operation of conventional pressure-sensitive transducers is due to the difference in thermal expansion between the pressure-sensitive diaphragm and the holder as described above, and we have solved this drawback. In order to solve this problem, the coefficient of thermal expansion of the holder of the pressure-sensitive transducer is kept the same as that of the pressure-sensitive diaphragm within the operating temperature range. This can be achieved by cutting out the holder from a quartz crystal in the same way as the pressure-sensitive diaphragm and by making the cutting angle appropriate.

In other words, as is clear from Figs. 1 and 2, (1) the A side direction of the pressure-sensitive diaphragm to which external stress is applied, and the direction in which the holder holds the pressure-sensitive diaphragm (H direction in Fig. 2); (2) As shown in FIG. 3, the coefficient of thermal expansion in the thickness direction of the fixed end of the holder, that is, the end of the holder held by the frame 9, is the same as that of the iron material, etc. that constitutes the frame 9. is equal to the linear thermal expansion coefficient of

It is necessary. Therefore, as shown in Figure 4,
The above condition (1) is satisfied by setting the extrusion direction of the holding base 5 so that the direction in which the pressure-sensitive diaphragm is held (the above-mentioned H direction) is the X-axis direction of the crystal, similar to the pressure-sensitive diaphragm. be done.

Next, condition (2) will be explained. When the rotation angle θ' around the X-axis in Fig. 4 is changed,
The coefficient of linear thermal expansion in the thickness direction of the cut out holding base is expressed by the following equation.

α _t = 13.71−6.23 sin ² θ′ (×10 ^-6 /℃) ...(1) In other words, from the above formula, the linear thermal expansion coefficient in the thickness direction of the holding table is 7.48 when θ′ = 0° It can be seen that it can vary within a range of 13.7 (×10 ^-6 /°C in both cases) when θ′ = 90°.

On the other hand, the linear thermal expansion coefficients of the metal materials that make up the frame are iron: 11.7×10 ^-6 /°C and nickel: 12.8×10 ^-6 /°C, and their alloys are also in the same range. Therefore, the rotation angle θ' of the X-axis that makes the coefficient of linear thermal expansion in the thickness direction of the holder match that of the above-mentioned iron is 34°36'. This rotation angle is the linear thermal expansion coefficient on the Y' axis, which is the thickness direction of the holding table. Therefore, the third
As shown in the illustrated embodiment, when the frame is made of iron and is tightened, the rotation angle is such that the linear thermal expansion coefficients of both members match in the tightening direction of the holder. Even for materials other than iron, by varying the rotation angle θ' when cutting out the holder using equation (1), the linear thermal expansion coefficient of the holder can be adjusted within the range of 7.48 to 13.7×10 ^-6 /°C. can be matched to the coefficient of the tightening member.

On the other hand, the holding direction (or pressure-sensitive direction) of the pressure-sensitive diaphragm
The coefficient of linear thermal expansion in the X-axis direction is constant regardless of the rotation angle θ'.

Next, the aspect of thermal strain caused by the coefficient of linear thermal expansion of a quartz crystal will be specifically explained using numerical examples.

Each linear expansion coefficient α in the three axial directions of the quartz crystal
is as follows.

α ₁₁ = α ₂₂ = 13.71×10 ^-6 /℃ α ₃₃ = 7.48×10 ^-9 /℃ Here, α ₁₁ is the coefficient of linear expansion in each direction of the X axis, α ₂₂ is the Y axis, and α ₃₃ is the coefficient of linear expansion in each direction of the Z axis. shows.

If the longitudinal direction of the holding table is set not as the X-axis but in the Z-axis direction, the difference in linear thermal expansion coefficients in the X- and Z-axis directions is 6.23×10 ^-6 /°C. If the distance between the mounting part of the pressure-sensitive diaphragm on the holder is 10 mm and a temperature change of 100°C occurs, the difference in thermal expansion between the mounting part of the holder and the pressure-sensitive diaphragm is 6.23×10 ^-6 × 10 (mm) x 100 (℃) = 6.23 x 10 ^-3 mm In other words, it becomes a large value of 6.23 μm, which is the limit value of 4 μm calculated from the fracture limit value of 400 μST (×10 ^-6 ) in the X-axis direction of the crystal. If the pressure-sensitive diaphragm is exceeded, it may destroy the pressure-sensitive diaphragm. Therefore, when the holding table is made of quartz and is cut out from a quartz crystal, it is necessary to set the crystal axis direction and the cutting angle correctly.

In addition, in the above explanation, the holding stand is one that differentially operates two pressure-sensitive diaphragms, but the present invention is not necessarily limited to this, and the holding stand is one that differentially operates two pressure-sensitive diaphragms. It can also be applied to tables.

As detailed above, the pressure-sensitive diaphragm holding stand is
The mounting direction of the pressure-sensitive diaphragm should be the X-axis direction of the quartz crystal, and the rotation angle around the X-axis should be selected to match the linear thermal expansion coefficient of the metal material that makes up the frame to which the holder is attached. By making them equal, it is possible to obtain a pressure sensitive transducer with high sensitivity and stable operation without the risk of measurement errors due to temperature changes.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram showing the relationship between the crystal axis of the quartz crystal and the cutout angle of the pressure-sensitive diaphragm, Figure 2 is a perspective view showing the external shape of the pressure-sensitive transducer, and Figure 3 is the pressure-sensitive transformer. FIG. 4 is an explanatory diagram showing a state in which the diucer is used in a pressure difference measuring device, and FIG. 4 is an explanatory diagram showing the relationship between the cutting angle and the crystal axis of the holding stand cut out from the quartz crystal according to the present invention. 3, 4...pressure-sensitive diaphragm, 5...holding stand, 9...
Frame for mounting the holding stand.

Claims (1)

[Claims] 1 Holds a pressure-sensitive diaphragm whose plate surface is cut out in the X-axis direction of the quartz crystal body and changes the vibration frequency in accordance with the external force when an external force is applied in the X-axis direction, and also In the holding stand that acts as a transmission mechanism to the pressure-sensitive diaphragm, the holding stand is cut out from the quartz crystal, and when cutting out, the direction in which the holding stand holds the pressure-sensitive diaphragm is aligned with the X axis of the quartz crystal. The cut-out surface of the quartz crystal that will serve as the pressure-sensitive diaphragm holding surface is adjusted so that the linear thermal expansion coefficient in the thickness direction is equal to the linear thermal expansion coefficient of the external mounting mechanism that fixes the holding base. A pressure-sensitive diaphragm holding stand characterized by having a selected rotation angle around the X-axis.