GB2336436A - Piezoelectric acceleration sensor with negative feedback for damping - Google Patents
Piezoelectric acceleration sensor with negative feedback for damping Download PDFInfo
- Publication number
- GB2336436A GB2336436A GB9908661A GB9908661A GB2336436A GB 2336436 A GB2336436 A GB 2336436A GB 9908661 A GB9908661 A GB 9908661A GB 9908661 A GB9908661 A GB 9908661A GB 2336436 A GB2336436 A GB 2336436A
- Authority
- GB
- United Kingdom
- Prior art keywords
- piezoelectric
- acceleration sensor
- strip
- negative feedback
- piezoelectric strip
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
- 230000001133 acceleration Effects 0.000 title claims abstract description 47
- 238000013016 damping Methods 0.000 title claims abstract description 13
- 238000005452 bending Methods 0.000 claims abstract description 12
- 239000011248 coating agent Substances 0.000 claims description 3
- 238000000576 coating method Methods 0.000 claims description 3
- 230000002452 interceptive effect Effects 0.000 description 5
- 238000013461 design Methods 0.000 description 4
- 239000004575 stone Substances 0.000 description 3
- 230000005540 biological transmission Effects 0.000 description 2
- 238000011161 development Methods 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 238000011156 evaluation Methods 0.000 description 2
- 238000013459 approach Methods 0.000 description 1
- 239000000919 ceramic Substances 0.000 description 1
- 238000010276 construction Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 230000005672 electromagnetic field Effects 0.000 description 1
- 230000005686 electrostatic field Effects 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 230000010287 polarization Effects 0.000 description 1
- 108090000623 proteins and genes Proteins 0.000 description 1
- 230000035945 sensitivity Effects 0.000 description 1
- 230000003068 static effect Effects 0.000 description 1
- 238000012546 transfer Methods 0.000 description 1
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01P—MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT
- G01P15/00—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration
- G01P15/02—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses
- G01P15/08—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values
- G01P15/09—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values by piezoelectric pick-up
- G01P15/0922—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values by piezoelectric pick-up of the bending or flexing mode type
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01P—MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT
- G01P1/00—Details of instruments
- G01P1/003—Details of instruments used for damping
Landscapes
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Air Bags (AREA)
- Pressure Sensors (AREA)
- Electrophonic Musical Instruments (AREA)
- Measurement Of Mechanical Vibrations Or Ultrasonic Waves (AREA)
- Measuring Fluid Pressure (AREA)
- Force Measurement Appropriate To Specific Purposes (AREA)
Abstract
A piezoelectric acceleration sensor 10 for a safety trigger switch for airbag systems in a motor vehicle, has a piezoelectric strip 1 which is mounted on one side, flexes as a function of acceleration forces acting on it and generates a corresponding piezoelectric voltage that can be picked off via contacts on both sides. Negative feedback means 3, 4, exerts a damping force on the piezoelectric strip 1, the said damping force being directed oppositely to the acceleration-induced bending movement.
Description
1 Piezoelectric acceleration sensor 2336436 The invention relates to a
piezoelectric acceleration sensor having a piezoelectric strip, which flexes as a function of acceleration forces acting on it and generates a corresponding piezoelectric voltage on both sides.
DE 44 19 843 AI discloses a piezoelectric acceleration sensor of this type. This sensor in that document has a piezoelectric component comprising piezoelectric plate parts of opposite piezoelectric polarization which lie one on the other. The two surfaces of the piezoelectric component are provided with conductive electrodes which are electrically connected to the inputs of an electronic evaluation unit.
DE 44 40 078 AI describes a piezoelectric acceleration sensor comprising two beam-like bending elements made of piezoelectric ceramic which are provided with outer electrodes and are clamped centrally such that they project from a clamping device on the left and right, so that the two free ends of the bending elements are deflected under the action of accelerations. The piezoelectric voltage induced as a result of this can be evaluated by a connected electronic evaluation unit for determining the acceleration.
With a micromechanical design, in particular, conventional piezoelectric acceleration sensors of the abovementiohed type also respond to very brief interfering acceleration impulses, for example, wheli the said sensors are used in motor vehicles, as a result of hammer blows or stone blows acting in proximity to the sensor. This is undesirable in certain cases; for ex," in the case of driving an airbag, triggering of the latter should not be caused by such momentary interfering acceleration impulses.
The present invention web to provide a piezoelectric acceleration sensor which is insensitive to momentary ierfering acceleration impulses even with a micromechanical design.
According to the presed invention there is provided a piezoelectric acceleration sensor having a piezoelectric strip, which flexes as a function of acceleration forces acting on it and gene a corresponding piezoelectric voltage on both sides, including negative feedback means, which exert a damping force on the piezoelectric strip, the said damping force being directed oppositely to the acceleration- 2 induced bending movement.
This acceleration sensor has negative feedback means, which exert a damping force on the piezoelectric strip, the said damping force being directed oppositely to the acceleration-induced bending movement. What is achieved in this way is that the sensor can be configured to be very small, in particular with a micromechanical design, in which the acceleration-sensitive piezoelectric strip has a very low mass. This low mass leads to a very high transmission frequency of the piezoelectric strip, which thus also responds, in principle, to high-frequency accelerative effects, such as those from hammer or stone blows. However, the sensitivity of the acceleration sensor to such momentary interfering effects is reduced by the negative feedback means. Consequently, the piezoelectric acceleration sensor can be designed to respond bidirectionally and in a frequency-selective manner and be used e.g. for a safety trigger switch in airbag systems of motor vehicles, which trigger switch is not supposed to switch as a result of momentary impacts, such as hammer or stone blows initiated in proximity, rather only in the case of genuine, marked vehicle decelerations, such as occur when there is the risk of an accident.
In a development of the piezoelectric acceleration sensor, the negative feedback means comprise two spaced-apart plate electrodes, between which the piezoelectric strip is situated and to which negative feedback charge is applied as a function of the bending movement of the piezoelectric strip in such a way that the resultant damping of movement increases as the speed of bending movement rises. A simple design of negative feedback means which are effective and frequency-selective, that is to say damp momentary acceleration impulses to a greater extent, is realized as a result of this.
In a further preferred development of the piezoelectric acceleration sensor, the plate electrodes are connected to the contacts of the piezoelectric strip via a high-pass filter and diodes. In this way, the piezoelectric signal is used directly for the generation of the negative feedback force by the plate electrodes. The diodes ensure the correct driving polarity, while the high-pass filter ensures that only the momentary interfering acceleration impulses are damped.
In a preferred embodiment of the sensor electromagnetic negative feedback means are provided.
3 An advantageous embodiment of the invention is illustrated in the drawings and is described below. In the figures:
Figure 1 shows a block diagram of a piezoelectric acceleration sensor in a quiescent position, Figure 2 shows a block diagram corresponding to Figure 1, but with the piezoelectric acceleration sensor in a deflected state. The heart of the piezoelectric acceleration sensor 10 illustrated in Figures 1 and 2 is a piezoelectric strip 1, which is constructed from two halves la, 1b lying one on the other, is situated between two lateral plate electrodes 3 and 4 and is held on one side in a mechanical bearing 2. Whereas the piezoelectric strip 1 in Figure 1 is in its non-deflected, central quiescent position, Figure 2 shows how the piezoelectric strip 1 flexes on account of the forces of inertia when an acceleration occurs in the direction of the arrow 11. A charge transfer between opposite outer electrodes la, lb of the piezoelectric strip 1 is then produced in a manner corresponding to the amplitude of the deflection of the said piezoelectric strip, with the result that a corresponding electric voltage is built up between the said electrodes. This piezoelectric voltage is picked off via terminal contacts and amplified by means of a differential amplifier 9, and then represents the output signal of the piezoelectric acceleration sensor 10 as a measure of the acceleration to which the said sensor is subjected.
The outer electrodes la, 1b of the piezoelectric strip 1 are earthed via resistors 8, with the result that charge balancing takes place between them after a characteristic time. At the same time, the two outer electrodes la, lb of the piezoelectric strip 1 are connected to the.input of a high-pass filter 7, via two diodes 6 connected in parallel, in such a way that the said filter only has applied to it a positive voltage signal originating from a ive one of the two outer electrodes la, lb of the piezoelectric strip 1. This high-pass filtered signal is fed to an amplifier 5 in order to be amplified, the output of which amplifier is connected to the plate electrodes 3 and 4. Consequently, the plate electrodes 3 and 4 are charged positively in the event of a deflection of the piezoelectric strip 1. In the case of the deflection of the piezoelectric strip 1 as illustrated in Figure 2, this leads, due to identical polarity, to the piezoelectric strip 1 being repelled by the right-hand plate electrode 3, which the strip 1 approaches, and, due to different polarity, to the piezoelectric strip 1 being 4 attracted by the left-hand plate electrode 4.
Consequently, the piezoelectric strip 1 is subjected to a force which counteracts its deflection, and negative feedback is produced. This negative feedback is frequency-selective on account of the high-pass filter 7. A rapid deflection of the piezoelectric strip 1 with respect to the characteristic filter thne of the high-pass filter 7 is counteracted to a significant extent, whereas, by contrast, a slow deflection remains largely uninfluenced.
The acceleration sensor shown is suitable e.g. as a safety trigger switch for an airbag system of a motor vehicle. Such a switch serves to prevent spurious triggering of an airbag as a result of momentary mechanical interfering impulses, for example from hammer blows, but, on the other hand, to enable triggering of the airbag in the event of severe vehicle decelerations due to an accident. The sensor shown fulfils these requirements even when it is produced with a very small construction using micromechanical technology, since the correspondingly high transmission frequency on account of the very low mass of the piezoelectric strip 1 is counteracted by the highpass-filtered electrostatic negative feedback damping.
It goes without saying that, in addition to the example shown, further realizations of the piezoelectric acceleration sensor according to the invention are possible, for example one in which a deflection of the piezoelectric strip is counteracted with negative feedback by an electromagnetic field rather than an electrostatic field. To that end, the piezoelectric strip, which is once again accommodated in a mechanical bearing on one side, is additionally provided with a magnetic coating. Two correspondingly arranged electromagnets are used instead of the two lateral plate electrodes 3 and 4 of the embodiment illustrated in the figures. In order to counteract a deflection of the piezoelectric strip, current is applied to the said electromagnets via a voltage-current convertor, which, analogously to the embodiment illustrated in the figures, receives its input voltage signal, in a manner corresponding to the deflection of the piezoelectric strip, from the outer electrodes of the piezoelectric strip via a respective one of two diodes and a highpass filter connected downstream. This voltage-current convertor consequently replaces the amplifier 5 in the embodiment illustrated. Depending on the current intensity, these two electromagnets generate a larger or smaller magnetic field with which the magnetic coating on the piezoelectric strip interacts, a force that counteracts deflection of the piezoelectric strip thereby being engendered. As in the embodiment illustrated in the figures, the negative feedback is likewise effected in a frequency- selective manner.
The above-described embodiments of the piezoelectric acceleration sensor can, if required, be simplified by modification such that the piezoelectric strip is not exposed to a time-varying electric or magnetic field effecting negative feedback in accordance with the deflection of the said piezoelectric strip, but rather merely to a static electric or magnetic field originating from electrodes or electromagnets. Diodes, high-pass filter and amplifier or voltage-current convertor are then omitted in the case of such a piezoelectric acceleration sensor, with the result that it can be produced at correspondingly lower cost. In the case of such embodiments of the piezoelectric acceleration sensor, rapid and slow deflections of the piezoelectric strip are damped to approximately the same extent.
The invention can be applied both to a piezoelectric acceleration sensor having a piezoelectric strip mounted on one side, as illustrated in the embodiment, and to a piezoelectric acceleration sensor having a centrally mounted strip, as is disclosed in DE 44 40 078 A l cited in the introduction.
I p 1 6
Claims (5)
1. A piezoelectric acceleration sensor having a piezoelectric strip, which flexes as a function of acceleration forces acting on it and generates a corresponding piezoelectric voltage on both sides, including negative feedback means, which exert a damping force on the piezoelectric strip, the said damping force being directed oppositely to the acceleration-induced bending movement.
2. A piezoelectric acceleration sensor according to Claim 1, wherein the negative feedback means comprise two spaced-apart plate electrodes, between which the piezoelectric strip is situated and to which negative feedback charge is applied as a function of the bending movement of the piezoelectric strip in such a way that the resultant damping of movement increases as the speed of bending movement rises.
3. A piezoelectric acceleration sensor according to Claim 2, wherein the plate electrodes are connected to contacts of the piezoelectric strip via a high-pass filter and diodes.
4. A piezoelectric acceleration sensor according to Claim 1, wherein the piezoelectric strip is provided with a magnetic coating and the negative feedback means are formed by two spaced-apart electromagnets, between which the piezoelectric strip is situated and which are driven with negative feedback as a function of the bending movement of the piezoelectric strip in such a way that the resultant damping of movement increases as the speed of bending movement rises.
5. A piezoelectric acceleration sensor substantially as described herein with reference to and as illustrated in the accompanying drawings.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US168946A US3128347A (en) | 1962-08-10 | 1962-01-26 | Arrangements for automatically identifying calling numbers in telephone systems |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE19816802A DE19816802C2 (en) | 1998-04-16 | 1998-04-16 | Piezoelectric acceleration sensor |
Publications (3)
| Publication Number | Publication Date |
|---|---|
| GB9908661D0 GB9908661D0 (en) | 1999-06-09 |
| GB2336436A true GB2336436A (en) | 1999-10-20 |
| GB2336436B GB2336436B (en) | 2000-03-22 |
Family
ID=7864673
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB9908661A Expired - Fee Related GB2336436B (en) | 1962-08-10 | 1999-04-15 | Piezoelectric acceleration sensor |
Country Status (5)
| Country | Link |
|---|---|
| JP (1) | JPH11352145A (en) |
| DE (1) | DE19816802C2 (en) |
| FR (1) | FR2777657B1 (en) |
| GB (1) | GB2336436B (en) |
| IT (1) | IT1307556B1 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2454466A (en) * | 2007-11-08 | 2009-05-13 | Haldex Brake Products Ltd | Vehicle odometer system |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE10131284A1 (en) * | 2001-06-28 | 2003-01-09 | Krupp Berco Bautechnik Gmbh | Device for converting measurement signals, which are triggered by impact processes of a hydraulic impact unit in a piezo sensor, into digital signals |
| JP2007263916A (en) * | 2006-03-30 | 2007-10-11 | National Institute Of Advanced Industrial & Technology | Active accelerometer |
| CN107402099B (en) * | 2017-09-12 | 2024-04-23 | 沈阳振科仪表有限公司 | Impact transmitter |
Citations (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4197478A (en) * | 1979-01-25 | 1980-04-08 | Southwest Research Institute | Electronically tunable resonant accelerometer |
Family Cites Families (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4399700A (en) * | 1981-07-14 | 1983-08-23 | Sundstrand Data Control, Inc. | Force transducer flexure with conductors on surfaces in the neutral bending plane |
| US4473768A (en) * | 1983-09-30 | 1984-09-25 | Teledyne Industries, Inc. | Piezoelectric force-balance accelerometer system |
| GB2158243B (en) * | 1984-05-05 | 1986-10-22 | Ferranti Plc | Accelerometer system |
| DE4419843A1 (en) * | 1994-06-07 | 1995-12-14 | Bosch Gmbh Robert | Piezoelectric force or acceleration sensors e.g. for releasing airbag in motor vehicle |
| DE4440078A1 (en) * | 1994-11-10 | 1996-05-15 | Telefunken Microelectron | Piezoelectric accelerometer |
| US5596144A (en) * | 1995-08-04 | 1997-01-21 | Delco Electronics Corporation | Piezoresistive force rebalance accelerometer |
-
1998
- 1998-04-16 DE DE19816802A patent/DE19816802C2/en not_active Expired - Fee Related
-
1999
- 1999-04-14 IT IT1999RM000223 patent/IT1307556B1/en active
- 1999-04-15 GB GB9908661A patent/GB2336436B/en not_active Expired - Fee Related
- 1999-04-15 JP JP11143788A patent/JPH11352145A/en active Pending
- 1999-04-16 FR FR9904785A patent/FR2777657B1/en not_active Expired - Fee Related
Patent Citations (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4197478A (en) * | 1979-01-25 | 1980-04-08 | Southwest Research Institute | Electronically tunable resonant accelerometer |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2454466A (en) * | 2007-11-08 | 2009-05-13 | Haldex Brake Products Ltd | Vehicle odometer system |
Also Published As
| Publication number | Publication date |
|---|---|
| IT1307556B1 (en) | 2001-11-14 |
| ITRM990223A1 (en) | 2000-10-14 |
| FR2777657A1 (en) | 1999-10-22 |
| DE19816802C2 (en) | 2000-08-31 |
| GB9908661D0 (en) | 1999-06-09 |
| GB2336436B (en) | 2000-03-22 |
| JPH11352145A (en) | 1999-12-24 |
| FR2777657B1 (en) | 2000-10-13 |
| DE19816802A1 (en) | 1999-10-28 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PCNP | Patent ceased through non-payment of renewal fee |
Effective date: 20030415 |