JPH028750A - Acceleration sensor and manufacture thereof - Google Patents

Abstract

PURPOSE: To form a highly precise acceleration sensor by constituting a torsional rod fixed on one side and including a mass system in a mechanical spring and providing an electric contact element at the free end thereof. CONSTITUTION: The sensor 10 has a common substrate 11 and in the substrate 11, a tubular torsional rod 12 is fixed only to one side thereof. Contact bars 13-20 arranged around the torsional rod 12 on a circular course have substantially same length as the torsional rod 12 and eight contact bars are distributed on a circle of 360 deg.C, for example. Direction of acceleration vector for oscillating the torsional rod 12 upon application of an acceleration is shown by an arrow and the oscillation matches the acceleration. When the oscillation of torsional rod exceeds a level dependent on the dimensions and material of contact bars 13-20, free end thereof touches one or two contact bar to short-circuit electric contacts thus indicating the acting direction of acceleration precisely.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention comprises a mass capable of oscillation on one plane, provided with a first electrical contact element, and a second plurality of electrical contact elements on said plane. surrounding said mass, a first electrical contact element comes into contact depending on the direction of the acceleration to be measured on said plane when one or more of the second electrical contact elements exceeds a predetermined acceleration limit value; The present invention relates to an acceleration sensor that measures acceleration in a plurality of coordinate directions.

An acceleration sensor of the above type is disclosed in German Patent Publication No. 21
No. 22 471.

The invention further relates to a method for manufacturing an acceleration sensor of the type mentioned above.

Acceleration sensors with various configurations are known.

Known acceleration sensors generally operate using a spring-mass system, where the applied acceleration causes the mass to swing, and this amplitude is converted into an analog electrical signal.

Furthermore, acceleration sensors are known which have a binary measurement characteristic, which only indicates whether a certain acceleration limit value has been exceeded. In addition, it is known on the one hand to connect analog sensors to electronic switching means, in particular to comparators, and to detect in this way when limit values are exceeded. On the other hand, however, acceleration sensors are also known which, based on their design, are already designed in the measuring system to generate a specific logic signal only when a predetermined limit value of the acceleration is exceeded.

In the detection device known from DE 21 22 471 mentioned at the outset, a metal ball is arranged on a disc-shaped electrically conductive base. The base has a hole in the center, the diameter of the hole is smaller than the diameter of the sphere. A magnet is located below the hole. When at rest, the ball lies within the mouth of the hole and is further fixed in this rest position by a magnet. Above the sphere is a rotationally symmetrical crown of contact elements distributed along the truncated conical surface. When at rest, these contact elements are spaced apart from the sphere. When a ball swings from a resting position due to acceleration, it becomes a ball.

The frictional connection between the magnets is broken and the sphere lies sideways on the conductive base.
Rolls in the direction of acceleration or deceleration. After following a certain path, the surface of the sphere abuts one of the contact elements. Since the ball itself is made of electrically conductive material, it then closes an electrical circuit between the contact element and the base, and depending on which contact element it touches, the direction of the ball's trajectory and thus the direction of its acceleration can be detected.

However, the disadvantage of the known detection device is that the ball is not guided in its path from its rest position fixed by a magnet to the contact position, and if the ball is subjected to another force on its path, this force will cause a displacement. Obstacles cannot be eliminated because the middle ball is not restricted by any holding force, which has a significant effect on the ball's path of movement. Furthermore, the resting position of the sphere is relatively unstable, and the known detection device can only eventually configure two mounting positions, the electrically conductive base being located on a horizontal plane.

The well-known sensor from European Patent Publication No. 251 048 uses a pendulum formed by an optical fiber and a mass, in which the light rays emitted from the optical fiber are directed onto a surface and the point of impact is determined at a predetermined point. It is monitored whether it lies in a circular plane (isotropic measurement) or in an ellipsoidal plane (anisotropic measurement).

Furthermore, acceleration sensors with a mechanical spring-mass system are known, in which the mass is mechanically coupled to the surroundings over the entire path of the movable sensing element, so that the mass moves from a rest position to a deflection position. Mechanically guided along the route. However, in this type of well-known sensor, the direction of deflection of the detection element is determined by design.

Therefore, it has already been proposed to use two or three sensors to measure acceleration in multiple coordinate directions.
There, the mass of the spring-mass system can swing each time in one coordinate direction. In this well-known acceleration/vector sensor, the analog electrical signals generated in this manner are vector-added using electronic switching means, allowing display and evaluation in terms of quantity and direction.

Acceleration sensors for one-dimensional or multidimensional measurements are used in a wide variety of applications. Binary acceleration sensors are primarily useful for detecting extreme situations, for example in passenger safety systems of motor vehicles, ie for releasing airbags or belt tensioners. It is also known to use such binary acceleration sensors for monitoring mechanical equipment, for example to detect when the machine or equipment has fallen into an unacceptable self-resonance.

In many of the above-mentioned types of applications, it is necessary to monitor whether a certain acceleration limit value is exceeded in a given acceleration direction or in which direction an acceleration exceeding a given limit value appears. In this case, there is generally a desire to realize acceleration sensors with as small a size as possible using as few simple components as possible in order to enable reliable and trouble-free measurements even under difficult space conditions.

According to German Patent Publication No. 35 20 383,
Crash indicators used in car collisions are also known. This known indicator also uses a spherical contact element, with the contact element being disposed in the center of an outer raised ball crown. When acceleration or deceleration is applied, the ball rolls outward and upward in the direction of the acceleration and deceleration. The spherical crown has a number of annularly arranged contact paths, which are subdivided into sectors so that the path of movement of the ball can be measured in terms of quantity and direction.

However, this known crash indicator also has the disadvantages already mentioned above for the known detection device from German Patent Application Box 21 22 471.

Secondly, methods of manufacturing acceleration sensors are also known in which the actual measuring system is not assembled from discrete mechanical elements, but rather is formed by a chemical process.

U S -Z - I E E E 'Transact
1ons ona! ectron devices
, vol, ED-26, No. 12゜1979 12
It is known to form an acceleration sensor from a silicon substrate by an etching method.

However, this known method only allows the acceleration sensor to be manufactured using silicon technology. However, silicon has extremely high rigidity as a ceramic material, so the response behavior must be designed appropriately.

In addition, due to the rigidity of this ceramic material, there is a risk that the sensor element will fall into vibrations.

Therefore, the present invention provides an acceleration sensor of the type mentioned at the beginning, which has extremely high operational reliability, is small in size, can be used in any mounting position, and can be easily manufactured. The purpose is to show the method of manufacturing the same.

This purpose is achieved in the acceleration sensor mentioned at the outset by making the mass part of a mechanical spring-mass system, which system is constructed as a torsion rod fixed on one side, with a first electrical contact at its free end. This is achieved by providing elements.

The underlying objective of the invention is thus easily achieved, which is that by using a mechanical spring-mass system, the movable mass is constantly guided and the movable sensor element is reliably guided throughout its range of motion. This is because it is guaranteed. When using a torsion bar according to the invention, this is achieved by constantly mechanically connecting the swinging free end of the torsion bar to a plate on which the torsion bar is fixed. The acceleration sensor according to the invention can furthermore be used in any mounting position since the torsion bar arrangement works regardless of whether the torsion bar is vertical, horizontal or oriented in any direction with respect to the center of the earth.

Although it is normally preferred for the second electrical contact element to be disposed about the first contact element in a circular path, in a preferred embodiment of the invention the second electrical contact element is arranged in an elliptical shape. The first contact element may be disposed on the track around the first contact element.

The advantage of this measure is that the weighting of the acceleration limits can be set freely depending on the direction of acceleration in the plane, when different paths have to be bridged in different directions to connect the electrical contact elements to each other. can already be done within the sensor itself.

It is self-evident that the shape of the elliptical track in the above context is to be understood as merely an example, since any other non-circular track can of course also be used instead of the elliptical track.

In a particularly preferred practical embodiment of the acceleration sensor according to the invention, the spring-mass system is constructed as a torsion rod fixed on one side, the free end of which is provided with a first electrical contact element.

The advantage of this measure is that the construction is extremely simple, with the torsion rod acting as the only moving element, which can be torsionally adjusted by dimensioning, shaping and material selection as desired in the particular application. The bending stiffness of the rod can be adjusted over a wide range, especially on a microscopic scale.

In one development of the above embodiment, the torsion rod is made of a material with high internal friction, in particular a synthetic resin, and is provided at least at its free end with an annular metallization.

The advantage of this measure is that, as a result of the high internal friction of the materials used, the self-resonance of the torsion rod is largely suppressed.

An advantage of annular metallization is that, despite the use of electrically nonconductive materials for the torsion rods, full-surface contact can be achieved with simple technical manufacturing steps.

In an embodiment of the invention, the torsion bar is configured as a cylindrical body.

This measure once again has the advantage that the response behavior is isotropic, since the cylindrical torsion bar fixed on one side acts with uniform stiffness in all deflection directions.

In that alternative, the torsion bar is configured as a cylinder with an elliptical cross section.

A certain anisotropy of the response behavior can also be achieved by this measure, and here again the elliptical cross section is one example of a number of non-cylindrical needle geometries.

In a particularly preferred embodiment of the invention, the second electrical contact element is constructed as a rigid bar, which together with the torsion bar is arranged on a common substrate.

The advantage of this measure is again that it is very simple to manufacture and that, due to its simplicity, a very simple structure is obtained which is particularly resistant to disturbances, and in extreme cases even a monolithic structure.

In another embodiment of the acceleration sensor described above, the bar is made of a metal material.

The advantage of this measure is that the contact of the torsion rod with the bar can be detected without additional contact elements, wiring, etc. on the bar by optionally drawing off the voltage from the bar.

In a further embodiment of the invention, the second electrical contact element is arranged as a conductor track on the inner surface of the tube surrounding the torsion rod.

An advantage of this measure is that the second electrical contact element is provided, which has a rigid structure on its inner surface that withstands particularly well the applied accelerations. The advantage of attaching the conductor track to the inner surface of the tube is that, by providing a very narrow conductor track, very fine grading can be achieved and the angular resolution when measuring the acceleration vector is particularly high.

In a further embodiment of the invention, the first electrical contact element contacts one of the second electrical contact elements, so that the electrical evaluation device Generate a signal.

The advantage of this measure is that, by means of suitable conversion processes, a digital signal can be directly prepared which can be further processed, for example in a customary data processing unit installed on the board of a motor vehicle.

In one development of this variant, the electrical evaluation device forms an intermediate value as a signal when two or more second adjacent electrical contact elements are touched.

The advantage of this measure is that the resolution of the angular accuracy can be increased by simple means.

Particularly preferred within the framework of the invention are ultra-compact acceleration sensors in which the length of the torsion rod 12 is 200 to 1000 times, in particular 500 times, the thickness and the thickness is 1 to 10 μm, preferably 5 μm. .

In an acceleration sensor of the above type, the object underlying the invention is also achieved by a manufacturing method in which the torsion rod, rigid bar or tube and the substrate are manufactured by Lithographic Electroplating (LIGA).

For details on the LIGA method, please refer to the Karlsruhe Nuclear Research Center's KfK Report Magnet 3995 r.
...Manufacture of microstructures".

The advantage of this measure is that the above-mentioned structures can be shaped with high precision, but at the same time almost arbitrarily, and can be manufactured, in particular on a microscopic scale, from a large number of possible raw materials, in particular metals, plastics or ceramics. Since there are many possible shapes, specific characteristics can be given in advance.
The response behavior of acceleration sensors produced in this way can be varied almost arbitrarily depending on the requirements of the individual case.

Further advantages will become apparent from the following description and the accompanying drawings.

The features mentioned above and those further explained below can of course be applied not only in the respective combinations mentioned, but also in other combinations or alone, without departing from the scope of the invention.

Embodiments of the invention are shown in the drawings and will be explained in detail below.

In FIG. 1, reference numeral 10 denotes the entire acceleration sensor that can be used for vector measurement of acceleration on a plane formed by Cartesian coordinates x+Y.

This acceleration sensor 10 has a common substrate 11 in which a cylindrical torsion rod 12 is fixed on one side only. A contact bar 13 arranged around the torsion bar 12 on a circular track
~20 is approximately the same length as the torsion rod 12, and is 360″
For example, eight contact bars can be distributed over the circumference of the contact bar. However, it is of course also possible to arrange fewer or more contact bars around the torsion bar 12, depending on the use case and the desired resolution.

The arrow 21 indicates the direction in which the torsion rod 12 is swung due to the acceleration acting thereon, and the acceleration vector is also directed in this direction. The extent to which the free end of the torsion rod 12 swings corresponds to the amount of acceleration. When the amount of acceleration grating exceeds a value that depends on the dimensions and material selection of the torsion rod 12 and the contact bars 13-20, the torsion rod 12 contacts one or two of the contact bars 13-20 with its free end. The more you do it, the more you can swing it. torsion rod 1
2 is arranged so that contact with one or two of the contact bars 13-20 closes the electrical contacts, this condition can be selectively detected.

Of course, contact bars 13-20 are preferably constructed to be more rigid than elastic torsion bar 12 so that they do not deform themselves when subjected to acceleration.

As can be seen from the top view of the arrangement shown in FIG. 2, the torsion rod 12 is preferably made of synthetic resin and can be provided with a metallization 28 on its circumferential surface. The contact bars 13-20, on the other hand, are preferably made of a metallic material, as indicated for the contact bar 15, so that the metallization 28 is in contact with one or two of the metal contact bars 13-20. Closing of electrical contacts can be easily detected.

For this reason, the metallization 28 is connected to the first connection terminal 30 of the acceleration sensor 10, while the contact bars 13 to 2
are the connection terminals 31 to 38 as seen in detail in FIG.
It is tied to

FIG. 2 further shows an example in which an acceleration is applied diagonally downward to the right on the torsion rod 12, and the amount of this acceleration is such that the torsion rod 12 is brought into a position where it just contacts the contact bar 15. It's so big that you can shake it. Therefore, in this case, contact between the connecting terminals 30 and 35 can be detected.

In the modified acceleration sensor 10a shown in FIG. 3, the torsion rod 12a is not of cylindrical design but rather is constructed as a cylinder with an elliptical cross section. In the arrangement shown in FIG. 3, this means, for example, that the upward acceleration has to exceed only a small limit to make contact with the contact bar 20a; torsion rod 12
a is shown as having swung; on the other hand, in the case of swaying to the right or left in FIG. 3, a significantly higher acceleration limit must be overcome before contact is reached. The reason for this is as follows. In other words, when one side of a torsion rod with an elliptical cross section is fixed, the runout depends on its surface moment of inertia, as is known, and in the case of a torsion rod with an elliptical cross section, this moment depends on the two principal axes. It depends on the cube of the length.

Another variant of an acceleration sensor with anisotropic measurement properties is shown in FIG.

In this variant, the cylindrical torsion rod 12b is again located in the center of a tube 40 of oval cross-section, and the conductor track 41 is provided on the inner surface of the tube.

In this case, when the torsion rod 12b is subjected to an acceleration directed diagonally to the right as shown in FIG. 4, the contact position 12b is reached after a certain angle-dependent deflection, as can be read directly from FIG. be done.

Until now, we have only explained cylindrical or oval shapes, but
Of course, this should be understood as just an example, and in order to weight the acceleration value in one direction relative to the acceleration value in another direction,
It is of course possible to choose other shapes both with respect to the cross section of the torsion rod 12 and also with respect to the arrangement of the surrounding electrical contacts.

The evaluation device 50, which is shown very schematically in FIG. 5, has an input terminal 51 and an output terminal 52. A voltage source 53 connected to one of the input terminals 51 can be connected, for example, to a connecting terminal 30 arranged as shown in FIG. In this case, the metallization 28 of the torsion bar 12 passes a positive voltage, which in turn passes through the contact bar 13
~20 appears on one or two of the connecting terminals 31-38, depending on which one of them came into contact with the torsion rod 12.

A signal appears at the output terminal 52 when there is contact between the torsion rod 12 and the contact bars 13-20, i.e. when one of the predetermined acceleration limits is exceeded; For example, in BCD encoding, a bit pattern appears that is a measure of α, the angle at which the torsion rod 12 swings in accordance with the direction of action of the acceleration.

Finally, in the truth table shown in Fig. 6, the connection terminal 31...
・The status is filled out.

The −th row of the truth table in FIG.
The state where there is a negative logic signal is described. This includes the torsion rod 12 to which a positive voltage is applied and the contact bars 13 to 20.
This means that no contact will occur between them. Therefore, the torsion bar 12 either does not swing at all or swings in an unmeasurable direction.

If a positive logic signal appears at the connection terminal 31, this means that the deflection angle with respect to the y-axis is 0° in the angle definition of FIG. Next, the angle becomes slightly larger to 22.5°.
, a contact occurs between the two adjacent contact bars, bars 19 and 20, and a positive logic signal appears at the connection terminals 31, 32.

This state continues as the angle α increases, that is, first a positive logic signal appears only at the connection terminal 32, then at the connection terminal 3.
Only 4 appears, etc. Thus 45” 67.5°
It is possible to detect angles such as 90". This concerns the case where only eight contact bars 13 to 20 are arranged around the torsion rod 12. FIG. 4
As suggested in Section 1, if the number of contacts increases appropriately, the resolution of angle measurement can naturally be improved accordingly.

Acceleration sensors of the above type can advantageously be manufactured by lithography-electroplating (LIGA) or alternatively by silicon etching techniques. The additional installation of a seismic mass at the free end of the torsion rod reduces the response speed and increases the tendency for self-resonance, but this allows the torsion rod to be extremely small in size and eliminates the need for this. The application of the LlGA method provides great freedom in the choice of materials, allowing the desired structure to be manufactured from metals, synthetic resins or ceramics.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing one embodiment of an acceleration sensor according to the present invention. FIG. 2 is a plan view of the acceleration sensor shown in FIG. 1 with wiring according to the present invention added. FIG. 3 is a diagram showing another embodiment of the acceleration sensor similarly to FIG. 2; FIG. 4 is a diagram similar to FIG. 2 showing an acceleration sensor according to yet another embodiment. FIG. 5 is a schematic block diagram of an evaluation device used in accordance with the present invention. FIG. 6 is a truth table for evaluating the measurement signal of the acceleration sensor shown in FIG. 2. a・・・・・・・・・・・・・・・Direction b・・・・・・
・・・・・・・・・Acceleration 12・・・・・・・・・・
...Torsion bar 13-20...Rigidity bar procedure amendment (voluntary)

Claims (1)

[Scope of Claims] 1) having a mass capable of oscillating on one plane (x/y), providing a first electrical contact element on this mass,
y) surrounding said mass by a second plurality of electrical contact elements on said plane (x/y) when one or more of the second electrical contact elements exceeds a predetermined acceleration limit; a plurality of coordinate directions (
x, y), wherein said mass is part of a mechanical spring-mass system, said system being configured as a torsion bar (12) fixed on one side;
An acceleration sensor characterized in that a first electrical contact element is provided at its free end. 2) Acceleration sensor according to claim 1, characterized in that the second electrical contact element is arranged around the first contact element on a non-circular, in particular elliptical path. 3) In the acceleration sensor according to claim 1 or 2, the torsion rod (12) is made of a material with high internal friction, in particular a synthetic resin, and has an annular metallization (28) at least at its free end.
). 4) The acceleration sensor according to claim 1, wherein the torsion rod (12) is configured as a cylindrical body. 5) Acceleration sensor according to one or more of claims 1 to 3, characterized in that the torsion rod (12) is constructed as a cylinder with a non-circular, in particular elliptical, cross section. 6) In the acceleration sensor according to any one or more of claims 1 to 5, the second electrical contact element is configured as a rigid bar (13 to 2O), which is connected together with the torsion bar (12) in a common An acceleration sensor characterized in that it is disposed on a substrate (11). 7) In the acceleration sensor according to claim 6, the bar (1
An acceleration sensor characterized in that 3 to 20) are made of a metal material. 8) An acceleration sensor according to any one or more of claims 1 to 5, in which the second electrical contact element is provided with a conductor track (41) on the inner surface of the tube (40) surrounding the torsion rod (12).
). 9) In the acceleration sensor according to any one or more of claims 1 to 8, since the first electrical contact element contacts one of the second electrical contact elements, the electrical evaluation device ( 50) is an acceleration sensor characterized in that it generates an electric signal corresponding to a deflection angle (α) of a spring/mass system. 10) Acceleration sensor according to claim 9, characterized in that the electrical evaluation device (50) forms an intermediate value as a signal when it contacts two or more second adjacent electrical contact elements. sensor. 11) In the acceleration sensor according to any one or more of claims 1 to 10, the length of the torsion rod (12) is 200 to 1000 times, preferably 500 times, the thickness; 10 μm), preferably 5 μm. 12) A method for manufacturing an acceleration sensor (10) according to any one or more of claims 6 to 11, comprising: a torsion rod (12), a substrate (11) and a rigid bar (13-20).
Alternatively, the tube (40) is formed by lithography/electroplating (L
IGA).