JPH03108628A - Vibration beam pressure sensor - Google Patents

Abstract

PURPOSE: To improve measurement accuracy by fixing a drive means and a frequency detection means relative to each other, connecting them on a substrate on the same side of a vibration beam in one piece, and providing a shaft in the longitudinal direction that is nearly vertical to the shaft in the longitudinal direction of the vibration beam at the drive means. CONSTITUTION: When a tongue 23 between bellows 15 and 16 is moved due to the deviation or move of the bellows, a pivotal shaft lever part 30 is subjected to pivotal shaft move around a pivot 27 by the tongue 23. The move gives a change in the tension and compression force of a vibration beam 42, and the resonance frequency of vibration is changed. The change in the resonance frequency is proportional to the difference of pressure at pressure entrances 20 and 21, and hence the bellows 15 and 16. Since one pressure entrance is connected to atmosphere or vacuum, the difference of the pressures is measured. Also, isolation parts 43 and 44 have masses 43A and 44A that are extended vertically to the beam 42 and have separation springs 43B and 43C and 44B and 44C each. The separation materials retain the beam 42 in a nonconnected state with the placement part of the edge part, thus decreasing energy loss that causes the quality of the beam 42 to deteriorate.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a digital output pressure sensor that uses a vibrating beam as a sensing element.

Conventionally, various sensors using vibrating beams have been developed. Typically, some type of digital pulse is used to indicate the force or pressure exerted on the beam.

Certain sensors utilize piezoelectric sensing technology, such as US Pat. No. 3,470,400 and US Pat. No. 3,479,536. A type of pivoted beam restrained in its path of movement is disclosed in US Pat. No. 3,649,857.

Another patent related to vibrating beams, also of photographic interest, is No. 5,664,257. Vibrating beam volume fjk sensing techniques are illustrated in US Pat. Nos. 3,187,579 and 5,762,223. In both of these patents, the sensing capacitor plate is on the opposite side of the member from the drive coil.

A piezoelectric beam that traps for mass acceleration at the end of the beam or laterally bends for the impact of a small flow rate is disclosed in U.S. Pat. No. 3,304.
No. 773. An accelerometer using a vibrating beam with capacitive sensing means is shown in US Pat. No. 3,505,866.

U.S. Patent No. 4149 issued April 17, 1979
No. 422 has a thin wire that is held under a spring load to create a pretensilane and whose natural frequency changes with pressure loading. A vibrating wire type pressure cassette is disclosed. The lever used to load the vibrating wire is mounted on the cross-sectional curvature joint for relative freedom of pivot movement.

The sensing means is such that the current from the oscillator flows through the wire;
This current reacts with the magnetic field from the permanent magnet to move the wire. This creates an opposing EMF (electromotive force) and positive feedback in the oscillating circuit for current generation sustains the vibration of the ear. Thus, the sensor disclosed in US Pat. No. 4,149,422 does not utilize capacitive sensing technology.

The present invention relates to a pressure sensor, and more particularly to a pressure sensor that applies a load and shape to the natural frequency of a vibrating beam. The frequency is sensed and an output is provided in the form of a digital pulse that allows direct digital measurement or a pressure reading to be measured.

The beam is loaded, as shown, by a pivotally mounted lever that helps isolate the beam from unnecessary stress while loading the beam.

Excitation of the beam is performed from a coil driven by an imager, and the sensing means is a capacitor. In this way, there is little interaction between the excitation and sensing signals, which can improve accuracy.

In the particular embodiment shown, the excitation coil and the take-off capacitor plate are integrally coupled to each other and mounted on the same side of the vibrating beam, thereby facilitating mounting and shielding of these combinations and the drive coil. , the resonance of the spatial arrangement between the sensing capacitor and the vibrating beam can be better controlled, and having the components of the sensing circuit that can be mounted on the extraction member has little detrimental effect on the volume effect.

Hereinafter, a concrete example of the present invention will be explained with reference to the drawings. The general arrangement of the senna according to the invention is shown in Figures M1 and 2. The senna assembly is indicated at 10, and the outer frame 11 has a substrate for mounting various parts. The base of the frame, designated 12, is a flat plate and the frame has upright walls 13,14. The outer surface of the outer frame 11 is coated with silicone rubber, preferably about 157 mm (0.062 inches) thick, to dampen external vibrations.

The wall 13 has an opening and mounting means for mounting the bellows 15,16.

The bellows 16 has a collar 17 at its end. The collar & main are small ring-shaped, and the ring is clamped 23
A partially fits into the inside of the clamp 23A, and is held in a recess in the clamp 23A. Clamp 23A is slidingly attached to and slides along a tongue 23, indicated generally at 24, which forms part of the pivoting and loading lever member.

The tongue 23 extends between the bells 15 and 16. The bellows 15 is connected to the tongue 23 because it has an end ring 17A that is partially fitted into a recess in the tongue 23. The bells 15 and 16 are capable of absorbing loads from pressure that would cause the bells to expand in the axial direction.
3. The tongue 23 has a dovetail end for sliding with the clamp 25A.

The bellows is of a common design used as a sensor and is usually placed in the K, stationary or equilibrium position as shown. The first pressure port 20 is connected to the bellows 15 and the second pressure port 21 is connected to the bellows 16. The bellows.

Of course, when pressure is applied, it tends to expand along the axis, and the inner end in contact with the tongue 23 and clamp 23A stretches.

In this way, the pressure difference displaces the position of the tongue 23.

The clamp 23A slides along the tongue 23 and is adjusted transverse to the direction of movement of the bellows, so that movement of the bellows 16 around the hinge, such as the pivot shown at 27, will be displaced in relation to the movement of 15. This movement of clamp 25A along tongue 26 allows adjustment of the force from one bellows or the other so that when equal pressure is applied to bellows 15 and 16, the resultant force (
moment) is zero.

The lever assembly 24 is attached to the frame 1 as shown in the plan view.
1 has a mounting block 25 in contact with one substrate wall 12 and is connected to the block 25 through a pivot such as.

The pivot has a substantially reduced cross-sectional thickness and connects block 25 and section 30 along the pivot axis. The lever assembly thus has a lever part 30 that pivots with the mounting part 25. The lever portion 60 is connected to the base plate 12 of the frame.
Since it is not in contact with the other parts, it pivots when there is a pressure difference. A suitable spacer is placed below block 25 to separate lever portion 30 from substrate 12.

The lever portion 60 pivots about a hinge or pivot portion 270 that provides little resistance to pivoting but is capable of twisting the lever portion 30 about an axis parallel to the plane of pivoting. The resistance (stiffness) is strong. This resistance is also effective against acceleration in the direction along the pivot axis. The lever part is connected to the tongue 23 by a coupling part 31.

The load beam, designated 35, is a single block of magnetic material, preferably Ni-8pan C, alloy 902. manufactured by International Nickel Company. is made from. The load beam 35 includes a central vibrating beam portion 42
, and the portion 42 has first and second
It is arranged between and integrally with the isolated parts 43 and 44 of.

The isolation part 43 is located on the opposite side from the joint part with the vibration beam part.
At its outer end, as indicated at 6, it is attached to a support handle 37 forming part of the block 25. The outer end of standoff portion 43 may be mounted separately from substrate 12 of the housing. The connection to the support 37 is a fixed connection, soldered or brass-fitted. The outer end of the isolation portion 43 is
Alternatively, it may be bolted or fixed with a suitable cap screw.

The outer end of the isolation part 44 is located at the end opposite the load beam 35 and includes a support part 41 from which the pivot lever part 30 also projects.
is attached as shown at 40.

The means for attaching it may be any suitable method.

The sensor assembly is one that is accelerationally balanced on at least two axes, with little or no response to acceleration in the rYJ or rXJ axes as shown in FIG.
Not possible. This is because the sum of the torque moments on the sensor side of the pivot shaft is the same as the sum of the torque moments on the bellows side. Senna is not balanced on the rZJ axis (see Figure 7), so the resistance of the pivot axis (stay 7 failure)
The strength of is effectively subtracting acceleration effects from the force delivered along this axis.

If necessary, it is also possible to balance the torque moments around this axis. Within permissible limits, each senna assembly has a somewhat different torque moment. The effect of these tolerances related to acceleration is that by placing a small amount of material, such as solder, at a location near pivot 270 to equalize the torque moments about the axis, as shown at 27A in FIG. minimized by

The vibration beam portion 42 is connected to the 5&C1 support members 37 and 41 in this manner.
It is supported by standoff parts 43, 44 and K in between.

The beam portion 42 is then subjected to the force exerted by the movement of the pivot lever portion 3o. Isolation part 43
and 44 form a pair of thin bands (straps) (
, is deformed in its central part.

Therefore, when the tongue 26 between the bellows 5 and 16 moves due to deflection or movement of the bellows, the pivot 27
The tongue 23 pivots the pivot lever portion 30 around the pivot lever portion 30 . This movement changes the tension, compressive stress or load on the vibrating beam section 42. A change in the load on the vibrating beam section 42 changes the resonant frequency of vibration.

The change in resonance frequency is caused by pressure populations 20 and 21. It is therefore proportional to the difference in pressure between bellows 15 and 16.

One pressure inlet is open to atmosphere or vacuum, so that each pressure value is measured. Furthermore, one of the bellows can be omitted.

The pressure signal generated by the bellows 15.1B is transmitted via the pivot lever part 30 to one end (free end) of the vibrating beam part 42 by its link action, so that the several-axis lever part 30 has sufficient mechanical rigidity. All you have to do is have .

The beam is driven or excited into resonance by using a coil excited by an AC signal controlled at a resonant frequency. Furthermore, while at rest, the beam is in equilibrium, neither in compression nor in tension. That is,
There is no creep or loosening of the support structure or beams, contributing to stability.

The beam may be operated at low stresses, preferably within the durability limits of the beam material.

Isolation sections 43 and 44 have masses 45 A, 44 A, and 45 extending perpendicular to beam section 42, and each have an isolated isolating spring 45 B, 45 C, and 4
It has 4B and 44C. These isolation members keep the vibrating beam portion 42 uncoupled from the end mounting portions, thereby reducing energy losses that reduce the rQJ of the beam. , 1pigo eaves, chi & 2yo mjj (
rddji), vibration beam part 42 and masses 43A and 4
It should be noted that it is utilized at the junction between 4A.

In the design of the beam section 42 and the isolation sections 46 and 44, the beam section 7) must be able to sweep the wide range of frequencies used.
42, the natural frequency is easily driven by 5,
It is important that it does not have any components. If the other element has a natural frequency of 5 such that it can be driven by the beam section 42, the beam section 42 is particularly suitable if its natural frequency is equal to or a multiple of the beam frequency (e.g.
1, 2.3 and 4 times) will excite such elements in the system.

When this occurs, the effectiveness of the isolation member decreases, reducing the rQJ of the beam and changing its frequency. This results in a discontinuity in the straightness and smoothness of the beam for a given stress. In addition, it can be seen that the central beam is easily driven at its resonant frequency and twice the resonant frequency. This is because for each half cycle of the beam, a tensile force is applied to one end of the vibrating beam section 42. During its operation, the beam deflects in its rest plane to its opposite side.

As a matter of fact, it is not possible to make the isolation member vibrate at such low frequencies that it cannot be driven by the vibrating beam. This is because the body of the vagina must be long (and thin). Therefore, the overall size of the senna must be thick (and the device must be made As mentioned above, it is possible for the vibrating beam section to drive the isolation spring with secondary, tertiary or harmonic waves.

And also, in practice, it is not possible to drive these isolation springs to high frequencies and not to have them maintain the necessary low frequency isolation. In this way,
It will be appreciated that the frequency of the isolation spring must be selected to have a "window" such that it does not interfere with the vibrating beam section 42 over the stressed frequency range.

That is, when stress is applied to the vibrating beam portion 42, its natural frequency and twice this frequency are the same as those of the separation spring 43B.
and 43C and -44B and 44C must not match the resonant frequencies. The widest "window" is one in which the fundamental isolation spring perturbation number of each of these four springs is greater than the highest frequency of the vibrating beam section corresponding to the maximum stress (and It is set to be lower than twice the natural frequency of 42.

A specific example of the beam portion 42 is that the beam portion 42 is generally small (approximately 0.
025 tone (0,001 inch), about 0.25 at most
within the throat (o, oio inches), approximately o, 12 rrn
It has a beam portion with a thickness of (0,004 inches).

The beam portion is generally small (approximately 2.54 mm (0.10 inch), at most approximately 12.7 mm (O, SO inch), and has a length of approximately 635 orders (0,250 inch). and having a width of approximately at least about 0,20 inches and at most about 0,100 inches, and about 0,042 inches (1.07++n). There is.

The nuisance thermal frequency in the unstressed state is proportional to the thickness of the beam and inversely proportional to the square of the beam length;
When using materials such as pan C, approximately 14.5
It is KHz. Ni-5pan C is a composition that exhibits excellent spring properties and has a temperature coefficient of substantially zep over a wide temperature range. Other natural frequencies could also be used.

The change in frequency is determined by the stress in the beam generated by the force on the lever assembly 24.

- By way of example, this stress is - created by a bellows of about 12.7% inch diameter at - atmospheric pressure, about i,
13 KSI (2.5 bond). Vibration beam part 4
The stress in 2 is adjusted by changing the width without changing the frequency of the unstressed state of the beam section.

- As an example, the stress is approximately 7 using Ni-5pan C.
03.7h/lri (10,000psi)
adjusted to.

This stress is ideal as it is very low compared to the permissible strength of Ni-5pan C, making the resulting hysteresis error very low. In addition, there is no long-term change in frequency. As a result, the frequency variation of the vibrating beam section 42 is about 2300 Hz, which is also about 16 of the maximum scale frequency when the beam is placed in either compression or tension.
%. Thus, for example, a change from zero atmosphere to one atmosphere will result in a resonant frequency change from 14.5 KHz to 16.8 KH3.

As mentioned above, the frequency for the isolation spring is 16
．． The vibration beam portion 42
It is adjusted in the same way as for. In fact, the frequency of the 5-separation spring is good from 22 KHz to 24 KHz (
It was found to work. Spring 43B and 430
and 44B and 440 are about 8m (0,
It has a thickness K of about 0.012 inches for a length of 315 inches.

The separation masses (43A and 44A) are adjusted to produce a separation system frequency of 2600 Hz. And this frequency provides an excellent isolation system for the frequency ratio of the vibrating beam section and therefore also a very low transmissibility.

The mechanical structure of the coil and take-out portion is shown in FIGS. 1-4. K as shown, ceramic mounting block 5
0 is mounted on the disk member 51. The disk member is metal and is attached to the block 50 in a conventional manner. As necessary.

Blocks may be pinned to disks.

The disk member 51 is located in the recess 5 of the base plate of the frame body (see FIG. 2).
2, and the block 5o protrudes into the frame. The disc can be rotated within the recess 52 and assumes the desired position. The disks are then soldered and pressed so that they are held precisely in rotational position during use. The block 5o is made of a non-magnetic and non-conductive material, such as alumina or ceramic material.

5, the block 50 has a protrusion 53 having a surface 53A that is close to and parallel to the plane of the vibrating beam 42. Block 53 fits between each end of separation portions 43 and 44. The pro-73 has a cylindrical recess pfr54 extending inward from a surface 57 opposite to the surface 53A (see FIG. 3).

A mandrel 55 is mounted in this recess and secured to block 53 by conductive epoxy or solder. The mandrel 55 is preferably made of magnetic stainless steel, and is preferably a material with high "mu" (μ), that is, high magnetic permeability.

The mandrel has a disc-shaped end 56 and between the face 57 of the block 53 and the disc 56 is a coil indicated at 58. This is a single coil with the appropriate number of turns to generate the magnetic force necessary to drive the beam.

A block 53 adjacent to and facing the vibrating beam portion 42
On the surface 53A, a conductive strip 61 forming a capacitor plate is placed over the ceramic material and sintered. Capacitor plate 61 is shown in FIG. Other electrical components are mounted directly to the surface of the ceramic block 500, and nine different components are connected to capacitor plates mounted on strips of conductive material. For such parts.

This is discussed later in this specification.

A block 530 surface 57 proximate to the coil 58 and opposite the block 530 with respect to the capacitor plate 61 absorbs current from the coil 58 so as not to affect the capacitance sensed between the vibrating beam section 42 and the capacitor plate 61. May be metallized to shield interference.

By rotating the disc 51, the spacing between the capacitor plate and the vibrating beam section 42 is adjusted during assembly. Block 5o and plate or disk 51 are attached after beam 35 is placed. The space between plate 61 and vibrating beam section 42 is approximately 0.15 inches (0.005 inches).

The vibrating portion 42 of the beam forms the other electrode of the variable capacitor formed in combination with the plate 61, and this portion is grounded. Block 50 may be formed into a circuit that is powered through bottle 50A and connection port 50B, if desired.

A modified configuration is shown in FIGS. 6 and 7. Beam 35. The attachment means for the lever assembly 24 (particularly the pivot shaft portion 30) and the bellows are substantially the same. Mounting block 25 has been modified to mount a modified drive and extraction sensor assembly 74 .

The shaft 75 is mounted in an opening provided in the block 25, as shown in FIG. 6, and a screw 76 adjusts the length of the shaft 75 with respect to the vibrating beam portion 42. On the other hand, the shaft 75 is connected to a disk 79, and the disk 79 has a rod 78 extending on the outside so as to support the coil. Disk 79 is connected to one end of shaft 75 in a conventional manner with epoxy or other adhesive material.

A coil 82 is wound around the mandrel 78 between the inner surface of the disk 79 and the surface 83 of a ceramic disc-shaped pickup 840. A coil core 78 extends a desired distance into a recess in the ceramic disc 84, and this mandrel 78 is secured to the ceramic take-off body so that the coil core 78 is wound on the coil core and then the two are connected together. Support in place.

The ceramic disk 84 has a conductive surface, shown shaded in FIG. 8, to allow the circuit or its components to be mounted close to the beam. The components attached to disk 84 preferably include a capacitor plate 85 and a thick film capacitor 88 with appropriate connecting pieces 86 and corresponding to plate 61. The connecting piece 86 is connected to a thick film hybrid resistor 87, while the thick film capacitor 8B is electrically connected to the connecting piece 86 by cementing.

Appropriate contacts 87A and 88A connect capacitor 88 and resistor 8.
Connected to the other end of 7. As can be seen, the hybrid capacitor 88 and resistor 87 are mounted close to the capacitor plate 85 and protrude from the ceramic disc member, so that the vibrating beam portion 42 is sandwiched between these two components. There is. The vibrating beam portion 42 is located close to and generally parallel to the capacitor plate 85.

In operation, in both versions of the invention, the beam is caused to vibrate by energizing the associated coil. A magnetic flux is generated which deflects the vibrating beam section 42 to either side in a direction perpendicular to its longitudinal plane. The mandrel 55 or 78 extends a considerable length through the ceramic block 53 or 84 and the magnetic field couples with the beam portion 42. The capacitance change of the capacitor is sensed and the drive circuit is actually controlled to cause the vibrating beam to resonate and provide a frequency output.

The change in pressure difference is caused by the lever part 30 around the pivot axis 27.
This induces a movement of the tongue 23 which causes it to rotate, thereby changing the compressive or tensile load on the vibrating beam section 42 and changing the resonant frequency of the beam. This change is sensed by a change in the frequency of the signal from the capacitor formed between the vibrating beam section 42 and either plate 61 or 85, depending on the sensor placed proximate to this beam section.

This signal change represents the difference in pressure with respect to the frequency of the reference pressure. Preferably, the beam is driven at its fundamental frequency, but the capacitor pick-o
ff ) allows the extraction capacitor to be repositioned to be sensitive to desired harmonics of the fundamental frequency or other desired frequencies.

FIG. 9 is a simple diagram of a circuit for extracting the frequency output signal from the vibrating beam of the present invention. This circuit can take several different implementations. In FIG. 9, the vibrating beam portion 42 is connected to the separating member 43 and 4 as described above.
It is illustrated as being supported between 4. A capacitor pickup electrode indicated at 61 (also 85) is spaced from the vibrating beam section 42 and forms a variable capacitor.

The circuit of FIG. 9 has applied voltage terminals 90. It has a ground terminal 91 and an output terminal 92. A power source (not shown) with an applied voltage V0 is connected to the applied voltage terminal 90.

A resistor 96 and a coil 58 (
or 82) is connected.

When direct current flows through resistor 93 and coil 58, a steady magnetic field is created from mandrel or magnetic core 54 (or 75). coil 58
The stationary magnetic field created by the direct current flowing through the magnet may be replaced by a permanent magnet if necessary.

A bias resistor 88 is also connected between the terminal 90 and the extraction electrode 61 (in FIG. 7, it is mounted on a ceramic disk). Bias resistor 88 applies a DC bias to connection point 95 where resistor 88 and electrode 61 are connected. As a result, the voltage developed across the variable capacitor formed by the vibrating beam portion 42 and the extraction electrode 61 is a function of the direct current and the frequency of vibration of the vibrating beam portion 42 .

The signal derived from node 95 is applied to amplifier 97 through filter capacitor 87 (FIG. 7). The amplified output of the amplifier 97 is sent to the output terminal 9 as an output signal of the circuit.
2. The output of the amplifier 97 is connected to a contact α point 94 between the resistor 96 and the drive coil 58 through a feedback capacitor 98 .

When the circuit is activated, the magnetic field from coil 58 displaces beam portion 42. The capacitor capacitance between beam section 42 and plate 61 provides an input order effect that is fed through bias resistor 88 and capacitor 87 to amplifier 97 . The output of amplifier 97 changes the feedback signal applied to capacitor 98, which in turn affects the current through coil 58.

The change in current through the coil 58 changes the magnetic field through the S-beam section 42 and the vibrating beam section 42 is again displaced. The vibrating beam section 42 is thus excited to its natural frequency and the output of the amplifier 97 varies at this vibration frequency. Each component is selected to allow appropriate phase adjustment to produce oscillation in the desired frequency range.

The circuit of FIG. 9 thus provides a time-varying output signal such that the frequency of the output signal is a function of the vibration frequency of beam section 42. This output signal can be converted to a digital or analog signal. The output signal provides an indication of the tensile or compressive force on the beam section 42 varying its frequency.

It is also a function of the pressure to be sensed.

The actual circuit components for the amplifier 97 and other components for converting the signal at the output terminal 92 into a digital or analog signal can be mounted as shown schematically in FIG. Alternatively, if desired, all components may be mounted on block 50, as shown in FIG.

If low frequency vibrations from external sources (such as aircraft vibrations when the Senna is used in an aircraft) cause low frequency oscillations in the output signal, then use a suitable filter. Such undesired oscillations can be eliminated.

[Brief explanation of drawings]

FIG. 1 is a plan view of a pressure sensor having a sensing means according to the present invention, FIG. 2 is a front view taken from line 2-2 in FIG. 1, and FIG.
The figure is a partial sectional view taken along line 5-3 in figure 2, figure 4 is a front view taken from line 4-4 in figure 3, and figure 5 is a partial cross-sectional view taken along line 5-3 in figure 1.
6 is a partial top plan view of a modification of the present invention, and FIG. 7 is a partial cross-sectional view taken along the line 7-5 in FIG. 7 is a side view taken along line 7, FIG. 8 is a front view taken from line 8--8 of FIG. 7, and FIG. 9 is a schematic diagram of the driving and sensing circuit used in the sensor of the present invention. 10... Pressure sensor, 12... Frame, 15.
16... Peroz. 20.21... Pressure inlet, 23... Tank, 27... Pivot, 42... Vibration beam, 58... Coil, 61... Electrode.

Claims (2)

[Claims] (1) an actuator comprising a base body, a vibrating beam having a longitudinal axis, means for mounting one end of the vibrating beam in relation to the base body, and a lever member pivotably mounted on the base body; a first end of the actuator operatively coupled to an end of the vibrating beam opposite the attachment of the vibrating beam to the substrate; , means for supplying a pressure signal to a second end of the actuator such that the actuator varies the force exerted by the actuator on the vibrating beam; and a drive for causing the vibrating beam to vibrate at its natural frequency. and a frequency detecting means for detecting the frequency of vibration of the vibrating beam, wherein the driving means and the frequency detecting means are fixed relative to each other and on the same side of the vibrating beam. a vibrating beam pressure sensor, the driving means having a longitudinal axis substantially perpendicular to the longitudinal axis of the vibrating beam; (2) The vibrating beam type pressure sensor according to claim 1, wherein the frequency detecting means is a capacitor plate arranged in a plane substantially parallel to a side surface of the vibrating beam.