CN1082183C - Quartz resonance force/weighing sensor - Google Patents

Abstract

The invention belongs to the technical field of measuring instruments, including a quartz resonator for measuring force and a reference resonator for temperature compensation, and a parallelogram frame composed of four double-sided arcs with flexible hinges. The frame is also equipped with two There are two parallel pressure beams and support beams; the reference resonator is placed in the unstressed part of the frame, and the measurement quartz resonator is installed in the middle of the two parallel beams. The invention has the advantages of fewer components, fewer error links, simple assembly, good linearity, high stability, and small hysteresis; frequency output, easy for microprocessor processing; low power consumption, DC low-voltage power supply, and the like.

Description

Quartz Resonant Force/Load Cells

The invention belongs to the technical field of measuring instruments, and in particular relates to a structural design of a quartz resonant force/weighing sensor composed of an elastic body structure composed of a flexible hinge and a quartz resonator.

Force sensors are widely used, and the manufacturing technology is relatively mature. Common force sensors include resistance strain type, piezoelectric type, resonant type, etc., and the most mature and widely used one is the resistance strain type. In the field of electronic weighing instruments, the resistance strain type is the most widely used, and the resonance type has developed rapidly in recent years because of its good stability, digital output, and high resolution.

Resistance strain type includes metal strain gauge type and semiconductor strain type. Metal strain gauge is the force sensor with the longest application history. The resistance strain type is characterized by good dynamic characteristics, simple structure, and convenient use, so it has been widely used in weighing and force measurement. However, this kind of sensor needs to use adhesive to paste the strain gauge, so there are creep and hysteresis caused by the adhesive, and it is not suitable for mass production, and has disadvantages such as zero point and sensitivity drift. When it is connected with the microprocessor, it needs to perform A/D conversion on the output analog signal, which increases the cost and reduces the reliability and response speed of the sensor.

Resonant force sensors are mainly vibrating wire and quartz resonant. Its common feature is that the periodic quasi-digital signal output can be converted into a frequency digital signal that is easy for the microprocessor to receive and process through a simple digital circuit; it has high sensitivity, resolution and stability; anti-interference ability Strong, suitable for long-distance transmission. In this type of sensor, except for the quartz resonant type, other sensors are relatively complex, and have high requirements on the performance of manufacturing, assembly and materials.

The most common type of quartz resonant force/load sensor is the combined type, which uses a cylindrical shell and a metal diaphragm to fix the quartz resonator, and transmits the measured force to the quartz resonator. Its advantages are as mentioned above, and the cost is very low, but the main disadvantages are that there are many components, complicated assembly and low precision.

The object of the present invention is to provide a new structure of quartz resonant force/load sensor in order to overcome the deficiencies of the prior art. It uses the force-frequency effect that the resonant frequency of the quartz resonator is sensitive to force, fixes the quartz resonator through an elastic body and transmits the measured force to the quartz resonator, causing a corresponding change in the resonant frequency of the quartz resonator. By measuring the resonance The amount of change in frequency measures force or weight. It has few components, few error links, and simple assembly; good linearity, high stability, and small hysteresis; frequency output, and a digital signal suitable for microprocessor processing can be obtained through simple digital circuit processing; low power consumption, DC low-voltage power supply Etc.

The present invention proposes a quartz resonant type force/weighing sensor, comprising a measuring quartz resonator and a reference resonator as a temperature compensation and its circuit, characterized in that it also includes a parallelogram frame, the horizontal two sides of the frame are respectively There are two flexible hinges composed of double-sided arcs, the centers of the four flexible hinges form the four vertices of the frame, and the frame is also provided with two parallel pressure beams and support beams; the said reference resonator Placed in the frame without stress, the measuring quartz resonator is installed in the middle of the two parallel beams.

The support beam mentioned above is a cantilever beam, one end of which is flexibly or rigidly connected to the frame, and the other end is suspended in the air; the pressure beam can be a cantilever beam opposite to the support beam, and the measurement quartz resonator Installed in the middle of the two parallel beams and at the midpoint of the frame; the pressure beam can be fixed at both ends, one end is flexibly connected to the frame, and the other end is rigidly or flexibly connected to the frame; The pressure beam can also be divided into two parts that are not on the same horizontal line, and are connected as a whole by a vertical flexible hinge; the position of the vertical flexible hinge is at the midpoint of the parallelogram frame; A horizontal frame is formed, and the said supporting beam is arranged on the outside of the frame.

If a double cantilever beam is used without a vertical flexure hinge the stressed quartz resonator is mounted at the midpoint of the parallelogram.

The resonator circuit mentioned in the present invention can adopt a conventional known circuit, which will not be described in detail here.

Working principle of the present invention is described as follows in conjunction with Fig. 1:

In Fig. 1, flexible hinges 11, 12, 13, 14 constitute an elastic body frame 1, and the centers of these four flexible hinges are located at the midpoint O of the frame. The magnitude of the measured force is proportional, and the direction of the measured force on the sensor is guaranteed to remain unchanged. The support beam 4 is a cantilever beam EF, and the pressure beam 5 is composed of AB section and CD section. The two sections are connected by a flexible hinge 17 in the vertical direction at point O. The A end is a rigid connection, and the D end is a flexible connection. . The quartz resonator 2 for measurement is installed between the cantilever beam EF and the CD section of the pressure beam, and the reference resonator 3 used as temperature compensation is installed on the AB section of the pressure beam. The function of the flexible hinge 17 is to eliminate the influence of the lateral displacement of the frame on the output. When the frame produces a vertical deflection under the action of the measured force, B will produce a lateral displacement, which will cause a lateral displacement of the C end, thereby affecting the output of the sensor. When the measured force is large The impact is more pronounced. Flexible hinge 17 is rigid to vertical force and displacement, and is flexible to lateral force and displacement, therefore just guaranteed that the vertical force of B point and displacement can be transmitted to C point, and lateral force and displacements are isolated and cannot be passed to point C. The function of the flexible hinges 15 and 16 is to make the deflection of the beam CD and the beam EF proportional to the force, so as to ensure the linearity of the sensor.

Through the following design, this quartz resonant force/load sensor can only be sensitive to force P, but not sensitive to torque W. If it is considered that the flexible hinge 17 is disconnected at the center O, the vertical beams on the right side of the flexible hinges 12 and 13 will produce a downward deflection and a clockwise rotation angle of 2a under the action of the moment W shown in the figure, as shown in the figure Show. In this way, the cantilever beam AB must not only produce a downward displacement with the point A, but also produce a clockwise rotation angle of 2a. It is possible to make the point O under the combined action of these two movements by properly selecting the position of the point O. Any displacement, that is, the influence of the torque W cannot be transmitted to the CD beam through the O point, so the sensor is not sensitive to the torque. At this time, the O point is the rotation center of the elastic body under the W action. The same result remains when the direction of the torque is reversed from that shown in the figure. Therefore, when this sensor is used as a load cell to manufacture electronic weighing instruments, there will be no four-corner error. This is one of the biggest advantages of this sensor. After calculation, it can be obtained that when point O is at the center of the sensor, that is $l_{\mathrm{AB}}=\frac{1}{2}{\mathrm{<figure-callout\; id="12"\; label="l"\; filenames="C9810303000072.png"\; state="\{\{state\}\}">l</figure-callout>}}_{11,12}$ The torque has no effect on the output of the sensor, and the sensor is not sensitive to the torque.

The force transmitted by the elastic body to the quartz resonator is proportional to the measured force, and this proportional coefficient is related to the materials and geometric dimensions of the elastic body and flexible hinge. By changing the size of the elastomer and the size of the flexible hinge, the sensitivity and range of the sensor can be changed. For example, increasing the radius R of the flexible hinge or reducing the thickness t at the center of the flexible hinge will increase the sensitivity of the sensor and reduce the range of the sensor. On the contrary, reducing the radius R of the flexible hinge or increasing the thickness t at the center of the flexible hinge will reduce the sensor. Sensitivity and increase the range of the sensor.

The sensor uses the difference frequency of two identical quartz resonators as the output signal, the resonator 2 is under force and the resonator 3 is not under force, and the frequency obtained after the frequency difference between resonator 2 and 3 is used as the output signal, which can Reduce the frequency range of signal processing, and because the characteristics of resonators 2 and 3 are the same, the common mode variation of the two resonator frequencies caused by interference factors is offset after the difference frequency, so that the zero point of the sensor is almost free from external interference (especially is the effect of temperature change).

The temperature coefficient of the force sensitivity of the quartz resonator varies with the direction of the external force (the azimuth of the force). For an AT-cut quartz resonator, the temperature coefficient of force sensitivity is zero when the azimuth angle is around 40°. Of course, other cut-shaped quartz resonators can also be selected. To increase the measuring range, the quartz resonator can be trimmed.

The present invention is characterized by good linearity, small hysteresis and good repeatability; zero point and sensitivity are not affected by external disturbance (especially temperature); There is no four-corner error when manufacturing electronic weighing instruments; sensors with different ranges can be manufactured by adjusting the structural size of the elastic body. In addition, this kind of sensor uses frequency as the output quantity, which is suitable for computer (microprocessor) processing and does not require A/D conversion; the power consumption is very low, and it can be powered by DC low voltage.

Brief description of the drawings:

Fig. 1 is a schematic structural view of Embodiment 1 of the present invention;

Fig. 2 is a schematic structural diagram of Embodiment 2 of the present invention;

Fig. 3 is a schematic structural diagram of Embodiment 3 of the present invention;

FIG. 4 is a schematic structural view of Embodiment 4 of the present invention;

The present invention designs four kinds of quartz resonant force/load sensor embodiment structures, as shown in Fig. 1-Fig.

The structure of Embodiment 1 is shown in Figure 1, the flexible hinges 11, 12, 13, 14 in the figure constitute the elastic body frame 1, the centers of the four flexible hinges constitute the four vertices of the frame, the support beam 4 is a cantilever beam EF, and the compression Beam 5 is composed of section AB and section CD, and the two sections are connected by a vertical flexible hinge 17 located at the midpoint O of the frame. The A end is a rigid connection, and the D end is a flexible connection. The quartz resonator 2 for force measurement is installed between the cantilever beam EF and the CD section of the pressure beam, and the reference resonator 3 used as temperature compensation is installed on the AB section of the pressure beam. The elastomer frame material of this embodiment is 40CrNiMo, and other materials with better elasticity, such as 40Cr, 30CrMnSi, LY12 or LC4, can also be used. The resonators used in this embodiment are AT-cut 3.579 MHz and AT-cut 8.3 MHz. The geometric dimensions of the four flexible hinges are the same: R=4mm, t=1mm; l _11,12 =60mm, l _11,13 =60mm; the measuring range is 20Kq.

The structure of Embodiment 2 is shown in Figure 2, and its structure is more concise. The flexible hinges 11, 12, 13, 14 constitute the elastic body frame 1, and the supporting beam 4 is a cantilever beam, one end of which is rigidly connected with the frame, and the other end is suspended in the air; The beam 5 is a cantilever beam opposite to the supporting beam 4, and one end thereof is flexibly connected to the frame. The reference resonator 3 is placed at the end of the pressure beam 5, and the measurement quartz resonator 2 is installed between said two parallel beams. The geometric dimensions of the four flexible hinges are the same: R=8mm, t=2mm; l _11,12 =60mm, l _11,13 =50mm; the measuring range is 60Kq.

The structure of Embodiment 3 is shown in Figure 3. The difference in its structure is that the support beam 4 is a cantilever beam placed outside the frame, and one end of it is flexibly connected to the frame. There is no pressure beam in the frame, but a border of the frame is used. 5 as a pressure beam. The reference resonator 3 is placed in the middle of the frame 5, and the measurement quartz resonator 2 is installed on the supporting beam 4 so that the right end of the frame is pressed against the quartz resonator.

The structure of the fourth embodiment is shown in Fig. 4, the difference of the structure is that the left end of the pressure beam 5 is flexibly connected to the frame, and the right end is flexibly connected to the frame through two vertical flexible hinges.

Claims (5)

1. quartz resonance force/weighing sensor, comprise measuring quartz resonator and as the reference resonator and the circuit thereof of temperature compensation, it is characterized in that, also comprise a parallelogram lever, the horizontal both sides of this framework are respectively equipped with two flexible hinges of being made up of two-sided circular arc, the center of these four flexible hinges constitutes four summits of framework, and this framework also is provided with two parallel pressure beam and brace summers; Said reference resonator places the place that do not stress in the framework, and said measurement quartz resonator is installed in the middle of said two parallel girders.

2. sensor as claimed in claim 1 is characterized in that said brace summer is a semi-girder, and the one end is connected with the framework flexibility/stiffness, and the other end is unsettled; Said pressure beam is to become reverse semi-girder with said brace summer, and said measurement quartz resonator is installed in the middle of said two parallel girders and is positioned at the midpoint of said framework.

3. sensor as claimed in claim 1 is characterized in that said brace summer is a semi-girder, and the one end is connected with the framework flexibility/stiffness, and the other end is unsettled; Said pressure beam both-end is fixed, and an end and framework flexibly connect, and the other end is connected with the framework flexibility/stiffness.

4. sensor as claimed in claim 3 is characterized in that, said pressure beam is divided into not two parts on same horizontal line, is linked into an integrated entity by a vertical flexible hinge; Vertically the position of flexible hinge is in the midpoint of parallelogram lever.

5. sensor as claimed in claim 1 is characterized in that, said pressure beam is made of a horizontal frame of framework, and said brace summer is located at this frame outside.

Images