RU2281515C1 - Resonator sensor - Google Patents

Abstract

FIELD: technology for measuring mechanical parameters.

SUBSTANCE: sensor contains base made of material with low acoustic fading, in which through slits are made with forming of sensitive element with pendulum support in form of rod or rod resonator, ends of which are connected to base on one side and to sensitive element on other side. Sensitive element is freely positioned in recesses of lids, which are positioned on both sides of base are connected to it along perimeter. Measuring axis of indicator is positioned in plane of its base, which is achieved due to symmetric positioning of resonator relatively to pendulum support, connected to base by resilient joint, ratio of yielding of which in direction of measuring axis and in orthogonal direction is significantly greater than 1. for increasing aforementioned ratio, torsion is additionally provided, connecting sensitive element to base, in a particular case, torsion may be in Z-shaped form.

EFFECT: simplified manufacturing technology due to changing direction of measuring axis, thus making it possible to have planetary structure of sensor.

2 cl, 3 dwg

Description

The invention relates to the field of measurement of mechanical parameters.

A known sensor (see US patent No. 5165279, class G 01 P 15/10, 06/06/1989 published 11/24/92), which is the closest in technical essence to the claimed device and is taken as a prototype. The sensor is made of a flat base with the formation of a sensitive element in it, connected to it through the elastic hinges of the suspension and the resonator, freely placed in its slot. The resonator is electrically and mechanically connected with an electromechanical converter, providing excitation of mechanical vibrations and their inverse transformation into an electrical signal. In addition, the base is closed on both sides by covers, which are fastened around its perimeter and have recesses for the free movement of the sensing element.

The disadvantage of the prototype is a more complex manufacturing technology, requiring double-sided deep etching of the flat workpiece with the formation of thin jumpers with high accuracy. This leads to a greater technological spread and low yield of finished products.

The technical result of the proposed sensor is to simplify manufacturing technology by changing the direction of the measuring axis from a position almost perpendicular to the plane of the workpiece, in a position that coincides with it.

The technical result is achieved by the fact that the sensor is resonant, containing a base in which through slots are made with the formation of a sensitive element, its suspension in the form of a rod and a rod resonator, some ends of which are connected to the base, and the other ends are connected to the sensitive element freely placed in the recesses covers that are located on both sides of the base and connected to it along the perimeter, one end of the suspension rod through an elastic hinge is connected to the base to move the sensitive element ententa in the direction of the measuring axis, and the other end of the suspension rod is connected to the sensing element, the rod resonator is electrically and mechanically connected to the electromechanical transducer.

What is new is that the rod resonator is located asymmetrically with respect to the suspension, the rigidity of the elastic hinge of which is minimal in the direction of the measuring axis located in the plane of the base and maximum in the direction of the perpendicular plane of the base, at least one more guide is formed through the through slots in the base a torsion bar, one end of which is connected to the base and the other end to the sensor to allow the sensor to move in the direction of measurement axis, parallel to the plane of the base, and providing maximum rigidity in the direction perpendicular to the plane of the base. The guide torsion bars have a Z-shape, in the places of bending of which and at the points of connection with the sensing element and the base, elastic hinges are made.

Figure 1 shows the resonator sensor without covers.

Figure 2 shows one of two identical covers.

Figure 3 shows the kinematic diagram of the sensor.

The device (Fig. 1) contains a sensing element 1 connected through a suspension 2 and its hinge 3 to the base 4, in addition, the sensitive element 1 is connected to the base 4 by means of a rod resonator 5, made, for example, in the form of a two-branch tuning fork and one or two torsion bars 6, 8 of a Z-shape having section weakening in the form of a reduction in the width of the rods at the places of bending of the torsion bar and its attachment to the sensing element 1 and base 4, forming elastic joints 7, 9. The small width of the elastic joints 3, 7, 9 compared with them then thickness equal to the thickness of the base and, accordingly, the thickness of the plate of the workpiece, allows you to obtain greater flexibility in the direction of the measuring axis in comparison with other directions.

The resonator sensor operates as follows. When the force F is applied to the sensor 1 (see FIG. 3), a force F _res arises in the rod plane 5 in an arbitrary direction in the rod resonator 5 _. causing a change in its resonant frequency in accordance with the expression (1):

where ƒ ₀ is the initial value of the resonant frequency at F _res = 0;

B is a constant coefficient equal to the reciprocal of the critical force of the resonator (longitudinal compressive force at which the rod loses stability)

where l, b, h is the length, width and thickness of the resonator rods (bending vibrations of the resonator rods occur in a plane that coincides with its width);

E, ρ - modulus of elasticity and density of the rods of the resonator.

The relationship between the longitudinal force acting on the resonator and the force applied to the sensitive element is determined from the equilibrium condition of the system depicted in figure 3:

1) The sum of the moments of all the forces acting in the system must be equal to 0;

2) The sum of all the forces acting in the system must be equal to 0.

From the analysis of the system of figure 3 follows:

where F _res - the longitudinal force acting on the resonator;

F _nor - component of the force F, perpendicular to the line connecting the point of application of force F with the axis of rotation of the hinge;

α is the angle between the force vector F and the line AB connecting the point of application of force with the axis of rotation of the suspension in an elastic hinge;

M _r.Sh - reactive moment of the elastic hinge;

l _under - distance from point A of application of force F to the axis of rotation of the elastic joint;

h is the distance between the axis of the elastic hinge 3 and the connection point of the resonator 5 with the base 4.

From the expression (4), the dependence of the force acting on the rod resonator on the external force F is determined

The reactive moment of the elastic joint M _r.s. depends on the moment F · l _under · sinα, causing its deformation. With a rational design of the sensor, the contribution of M _r.s. should be significantly less than the total moment that causes the appearance of a longitudinal force in the resonator. In a first approximation, the dependence of M _r.s. on F · l _under · sinα can be taken as linear:

where K <1 is a constant coefficient.

Then the expression for the longitudinal force acting on the resonator will take the form:

In the case when inertial forces act on the sensor element 1, their resultant vector is applied to the center of mass of the sensor, and the measuring axis is directed perpendicular to the line connecting the axis of rotation of the elastic joint and the center of mass through which the measuring axis passes. The expression for the longitudinal force acting on the resonator will be:

where m is the mass of the sensing element;

a · cosβ is the projection of the acceleration vector a on the measuring axis;

β is the angle between the acceleration vector and the measuring axis.

The conversion function (conversion characteristic) of the sensor in question is determined by expressions (1), (6) or (7) taking into account (2), (3).

Under the action of component forces perpendicular to the plane of the sensor, longitudinal forces do not arise in the cavity, but the cavity bends, its resonant frequency changes very slightly.

To increase the stiffness (reduce compliance) in the directions perpendicular to the flat part of the sensor, torsion bars 6, (8) are used, connecting the sensitive element 1 to the base 4. The shape, dimensions of the torsion bar and the joints with the sensitive element and base are selected from the condition of ensuring minimum compliance sensitive element 1 in the direction perpendicular to the plane of the sensor, and maximum compliance along the measuring axis. One of the possible versions of such a torsion bar is a three-arm torsion bar 6, 9 of a Z-shape, equipped with four elastic hinges located at the joints of three arms with the sensing element 1 and base 4. To protect the elastic hinges from damage under extreme loads, determined by operating conditions and outside the range of measured values, covers are installed on both sides of the sensor, connected to its base 4 around the perimeter. In the lids on the inner side in the area of the location of the moving elements of the sensor (sensing element 1, suspension 2, torsion bars 6, 8), recesses are made to ensure the free movement of these elements. Under extreme loads (for example, shocks) in the direction perpendicular to the plane of the sensor, the covers act as limiters of movements of the sensor elements, thereby limiting mechanical stresses in them at a level not exceeding the limit values. The conversion of the frequency of the mechanical resonance of the resonator 5 to the frequency of the electrical signals is performed using an electromechanical transducer interacting with the resonator and the electric signal amplifier with positive feedback, in the circuit of which an electromechanical transducer is included. Electromechanical transducers can be performed using various physical phenomena: piezoelectric properties of materials (piezoelectric transducers); interaction of electric charges (electrostatic converters); interaction of conductors with electric current with a magnetic field (magnetoelectric converters). In the manufacture of sensors using microelectronic technology, it is possible to perform miniature with a core width of less than 50 microns. For this case, electromechanical transducers of the magnetoelectric and electrostatic type are most preferred.

Claims (2)

1. The resonant sensor, containing a base in which through the slots are made with the formation of the sensing element, its suspension in the form of a rod and a rod resonator, one ends of which are connected to the base, and the other ends are connected to the sensitive element, freely placed in the recesses of the covers, which are located on both sides of the base and connected to it along the perimeter, one end of the suspension rod through an elastic hinge is connected to the base to move the sensing element in the direction of the measuring axis, and the angular end of the suspension rod is connected to the sensing element, the rod resonator is electrically and mechanically connected to the electromechanical transducer, characterized in that the rod resonator, made in the form of a two-branch tuning fork, is located asymmetrically relative to the suspension, the rigidity of the elastic joint of which is minimal in the direction of the measuring axis located in the plane of the base, and maximum in the direction perpendicular to the plane of the base, additionally due to through slots in the base of the sample call, at least one guide torsion bar having one end connected to the base and the other end - with a sensing element in order to move the sensor in the direction of the measuring axis parallel to the plane of the base and ensure maximum rigidity in the direction perpendicular to the base plane. 2. The device according to claim 1, characterized in that the guide torsion bar has a Z-shape, in the places of bending of which and at the points of connection with the sensing element and the base, elastic hinges are made.

Images