EP0412106A1 - Accelerometre - Google Patents

Accelerometre

Info

Publication number
EP0412106A1
EP0412106A1 EP19890905445 EP89905445A EP0412106A1 EP 0412106 A1 EP0412106 A1 EP 0412106A1 EP 19890905445 EP19890905445 EP 19890905445 EP 89905445 A EP89905445 A EP 89905445A EP 0412106 A1 EP0412106 A1 EP 0412106A1
Authority
EP
European Patent Office
Prior art keywords
filaments
transducer
inertial mass
support
filament
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.)
Withdrawn
Application number
EP19890905445
Other languages
German (de)
English (en)
Inventor
Dennis John Miles
Sidney George Smith
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
UK Secretary of State for Defence
Original Assignee
UK Secretary of State for Defence
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by UK Secretary of State for Defence filed Critical UK Secretary of State for Defence
Publication of EP0412106A1 publication Critical patent/EP0412106A1/fr
Withdrawn legal-status Critical Current

Links

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
    • G01P15/18—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration in two or more dimensions
    • 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
    • G01P15/0802—Details
    • 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
    • G01P15/097—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 vibratory elements
    • 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
    • G01P15/12—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 alteration of electrical resistance
    • G01P15/122—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 alteration of electrical resistance by metal resistance strain gauges, e.g. wire resistance strain gauges

Definitions

  • This invention relates to transducers and, in particular, to miniature transducers adapted for use as accelerometers for applications in vehicle navigation and guidance.
  • One type of miniature accelerometer known for this purpose is made from silicon and comprises a tension-sensitive filament formed as a double-ended tuning fork and supported within a framework which functions as an inertial mass.
  • this device has the limitation of being sensitive to acceleration along one axis only.
  • the output from the transducer is sensitive to temperature fluctuations and therefore requires some form of compensation.
  • Two objects of the present invention are, firstly, to provide a transducer capable of measuring accelerations along two or three axes and secondly, to configure a plurality of tension-sensing elements so that common mode effects (such as temperature-dependent output fluctuations) are virtually eliminated and therefore little or no form of temperature compensation is necessary.
  • the present invention therefore consists of a transducer comprising a central support, an annular inertial mass co-planar with the central support and connected thereto by at least two filaments, whereby movement of the central support relative to the inertial mass causes a corresponding extension of one filament and compression of the other, and sensing means incorporated in said two filaments for detecting said extension and compression.
  • the transducer may be of unitary construction and made from any elastic material, for example silicon. Conventional photolithography and etching techniques may be used to form the desired configuration if a silicon wafer or the like is used as a starting material.
  • the filaments it is preferable, though not essential, for the filaments to have similar dimensions.
  • a transducer in accordance with the invention which is configured to have two filaments diametrically opposed on either side of the central support may be used as a single-axis accelerometer. Accelerations along an axis which connects the two filaments will result in a stretching of one filament and a compression in the other owing to the effect of the inertial mass.
  • the sensing means incorporated in each of the two filaments may be arranged to give a differential output indicative of the magnitude of the applied acceleration.
  • a transducer in accordance with the invention may be made sensitive to components of acceleration along two orthogonal axes by arranging three or more filaments, each incorporating sensing means, around a central support.
  • An embodiment comprising four equally-spaced filaments is preferred due to the inherently high common mode rejection of this configuration. This embodiment will be described in detail hereinafter. It may be desirable to limit the relative rotation of the central support and inertial mass or their relative movement along an axis perpendicular to their common plane, particularly in the case where only two filaments are provided. In such a case, one or more filamentary tie-bars linking the support with the inertial mass but not incorporating sensing means may be distributed around said support.
  • a transducer in accordance with the invention may include a plurality of tension-sensitive filaments which are configured so that the transducer is sensitive to components of accelerations along three orthogonal axes. Such a configuration will be described in greater detail hereinafter.
  • the sensing means may comprise semi-conductor strain-gauges implanted in the filaments. An accurately adjusted amount of impurity can give the desired characteristics. A variation in tension in the filaments gives rise to a change in strain-gauge resistance which can be measured by a Wheatstone bridge. This type of sensor may be used with either a single or multi-axis transducer configuration. In an alternative embodiment the filaments are caused to vibrate transversely.
  • Each filament has a natural frequency of vibration whose value is a function of the dimensions of the filament, the tension applied to it, and the elastic modulus and density of the material from which it is constructed. Any variation in tension in the filament will cause a corresponding change in frequency. Measurement of this frequency change can then be used to determine the magnitude of any acceleration to which the transducer has been subjected.
  • This embodiment requires the provision of means for initiating and sustaining the vibrations of the filaments. This may be achieved, for example, by exploiting the piezo-electric effect or the thermo-mechanical properties of the transducer material. If silicon has been chosen then it is possible to sputter a piezo-electric layer of zinc oxide or barium titanate onto the filaments.
  • thermo-mechanical drive mechanism This technique is known in the field of electro-acoustics.
  • the thermal expansion of a silicon transducer (which has an inherently high thermal conductivity) can be used as a thermo-mechanical drive mechanism.
  • This technique has hitherto been applied successfully to diaphragm pressure sensors.
  • a heating resistor is embedded in each filament by ion implantation and an alternating current at the natural frequency of vibration of each filament is passed through each resistor.
  • the resulting cyclic temperature changes cause the filaments to expand and contract which results in a mechanical driving force. Vibrations of the filaments may be detected by a piezo-electric layer deposited onto each filament and connected to a frequency measuring circuit.
  • the thermally induced expansion and contraction may induce strains in a second implanted resistor.
  • this resistor is constant-current driven, then a measurable voltage at the frequency of vibration will develop across it.
  • Either type of drive or sensing means, piezo-electric or resistive may be used with either a single axis or multi-axis transducer configuration.
  • the vibrating filaments may be arranged to vibrate in a plane perpendicular to the plane of the support and inertial mass or they may be double-ended tuning forks whose tines are arranged to vibrate in anti-phase with one another and in the plane of the support and inertial mass.
  • the transducer may have deep but narrow filaments arranged to vibrate in the plane of the support.
  • a transducer comprising a central support and annular inertial mass requires attachment to an accelerating body at one mounting point only (on the central support).
  • a transducer having an outer support and a central inertial mass would require multiple mounting points and if, for example, thermal expansion were to occur at one point and not another, a differential strain between filaments would be produced which would be seen as an erroneous acceleration. This disadvantage is not inherent in the present invention.
  • Figure 1 is a plan view of a first embodiment of the invention
  • Figure 2 is a cross-section along the line II-II shown in Figure 1;
  • Figure 3 is a plan view of a second embodiment;
  • Figure 4 is a plan view of a third embodiment;
  • Figure 5 is a cross-section along a line V-V of Figure 4;
  • Figure 6 is a circuit diagram of a transducer thermal drive and measurement circuit suitable for use with any of the above embodiments.
  • a transducer for measuring components of acceleration along two orthogonal axes comprises a support 1 connected to an inertial mass 2 by four equally-spaced filaments 3, 4 ,5 and 6.
  • the support, mass and filaments are etched from a silicon slice of thickness approximately 0.4 mm, the outer diameter of the transducer being approximately 10 mm and the filaments having dimensions of typically 1 mm ⁇ 50 ⁇ m ⁇ 50 ⁇ m.
  • the central support of the transducer is attached to a vehicle, for example, whose accelerations are to be monitored. If, for example, the host vehicle were to be accelerated along the x axis, then owing to the presence of the inertial mass the filament 6 would be tensioned and filament 4 compressed.
  • f 6 f 0 (1 + kma x ) 1 ⁇ 2
  • f 6 is the frequency of vibration of filament 6 when subjected to an acceleration a x exerted in the x direction
  • m is the mass of the inertial mass
  • f 0 is the frequency of vibration of the filaments under zero acceleration
  • k is a known constant which is related to the dimensions of the filament and its elasticity.
  • kma x is small under most circumstances as the breaking strains would normally be reached before a 10% change in frequency takes place.
  • f 6 f 0 (1 + 1 ⁇ 2 kma x )
  • f 4 f 0 (1 - 1 ⁇ 2 kma x ) if the filaments 4 and 6 have equal dimensions.
  • filaments 4 and 6 have different dimensions so that their frequencies of vibration under zero acceleration are not equal, then the effect of this will be, broadly, to generate a non-zero a x value under zero acceleration conditions. This can be simply allowed for and may indeed be beneficial in certain applications in preventing frequency lock.
  • All four filaments are forced to vibrate transversely and in a plane perpendicular to that of the support by a drive resistor R D which is one of a pair of heating resistors implanted into each of the four filaments (see Fig 1). This frequency of vibration is monitored by the second of the resistor pair, a sense resistor R S for each of the four filaments.
  • R D and R S By connecting R D and R S to a suitable drive and measurement circuit, accelerations in two axes may be detected and measured.
  • Each filament requires connection to a separate circuit.
  • a second embodiment of the invention is shown in Figure 3.
  • a support 1, inertial mass 2 and four filaments 7, 8, 9 and 10 are made as before from a single silicon slice having a thickness of typically 0.4 mm and a diameter of 10 mm.
  • the filaments 7-10 are configured as double-ended tuning forks and have the same thickness as the inertial mass in order to restrict vertical movement thereof.
  • the tines of each of the filaments are forced to vibrate In anti-phase with one another and in the plane of the support 1 by electrically driven resistors (not shown) implanted in each filament.
  • Sense resistors implanted in the filaments enable any change in the natural frequency of vibration brought about by accelerations applied along the x or y axes to be detected.
  • a third embodiment is shown in Figures 4 and 5. It permits sensitivity to accelerations in three orthogonal axes.
  • This embodiment is similar in construction to the first embodiment having a central support 11, an annular inertial mass 12 and four filaments p, q, r and s but incorporating two extra filaments m and n.
  • the filament m includes an implanted drive and sense resistor pair (not shown), which, in conjunction with the resistors (not shown) implanted in the filament p enables meaaurement of accelerations in the z direction.
  • the filaments p and q and their associated resistors also permit measurement of acceleration in the x direction and filaments r and s plus their associated resistor pairs (not shown) permit measurement of acceleration in the y direction.
  • a transducer may be composed of a mixture of plate-like filaments and tuning forks.
  • Fig 6 shows an oscillator circuit 13 for sustaining and detecting oscillation of filament 4
  • the sense resistor R S is supplied with a constant current (of about 5 mA) from a power supply Vs via a transistor 14.
  • the drive resistor R D is supplied with an alternating drive voltage and a DC bias from the output of an operational amplifier 15.
  • Two more operational amplifiers 16 and 17 amplify the alternating sense voltage of approximately 5 mV peak to peak developed across the sense resistor R S and apply It to an input of the operational amplifier 15.
  • Two diodes 18 and 19 limit the output signal appearing on line 20 to 4 volts.
  • the alternating drive voltage (of 4V peak to peak) supplied to the drive resistor R D causes thermal expansion and contraction of the filament 4. In turn, this mechanical distortion of the filament induces strains in the sense resistor R S causing its resistance to vary sinusoidally.
  • a DC bias of 2V is applied in order that the voltage applied to the resistor swings from 0 to +4V so that only one heating pulse is generated in each cycle ie the sense voltage developed across the sense resistor R S oscillates at the same frequency as the drive voltage.
  • the oscillator circuit 13 has a quality factor Q of approximately 2000 and runs at, typically, 60 kHz.
  • a transducer embodied as shown in any of Figures 1 to 5 has an x axis and a y axis sensitivity of approximately 20 Hz/g (where g is the acceleration due to gravity) over an active range of ⁇ 100 g.
  • the embodiment of Figure 5 has a higher sensitivity along its z axis of about 100 Hz/g.
  • the sensivitity of any of the embodiments may be enhanced by employing the known technique of frequency multiplication using, for example, a phase-locked-loop.
  • a transducer in accordance with the invention is not restricted solely to operation In conjunction with the closed loop circuit of Fig 6. Those skilled in the electronics art will be aware of possible commonplace alternative choices of components and their values which will still achieve the desired results. Furthermore, any of the transducers described herein will function satisfactorily with an open-loop circuit.
  • the transducer may be used for navigation and guidance of vehicles although it is not limited to this application.
  • a three-axis transducer or alternatively a two-axis transducer together with a single axis transducer may be strapped to the vehicle and provide output signals relating to accelerations thereof in three orthogonal directions. Such information may be processed by the vehicle's navigation and guidance computer along with additional navigational data in order to guide the vehicle on some chosen trajectory.
  • the simplicity of the transducer's construction enables a robust and low-cost navigation and guidance system to be realised.
  • the transducer as an accelerometer, it will be appreciated that it may alternatively be used as a pressure or force sensor.

Landscapes

  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Gyroscopes (AREA)

Abstract

Un transducteur destiné au mesurage de l'accélération est réalisé dans une tranche de silicium et comprend quatre filaments (3, 4, 5 et 6) qui assurent l'interconnexion d'un support central (1) avec une masse inerte (2). Les filaments vibrent dans un plan commun, leurs fréquences de résonance étant déterminées par n'importe quelles forces externes qui leur sont appliquées. Les vibrations sont constantes et détectées au moyen de deux résistances thermiques (RS, RD) implantées dans chaque filament. Le transducteur décrit est configuré comme un accéléromètre à deux axes s'utilisant dans des systèmes de navigation et de guidage de véhicule. Des moyens piézoélectriques permettant de soutenir et de détecter les vibrations des filaments peuvent être utilisés à la place des résistances thermiques (RS et RD).
EP19890905445 1988-04-25 1989-04-25 Accelerometre Withdrawn EP0412106A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB8809755 1988-04-25
GB8809755A GB8809755D0 (en) 1988-04-25 1988-04-25 Accelerometer

Publications (1)

Publication Number Publication Date
EP0412106A1 true EP0412106A1 (fr) 1991-02-13

Family

ID=10635805

Family Applications (1)

Application Number Title Priority Date Filing Date
EP19890905445 Withdrawn EP0412106A1 (fr) 1988-04-25 1989-04-25 Accelerometre

Country Status (4)

Country Link
EP (1) EP0412106A1 (fr)
JP (1) JPH03503932A (fr)
GB (2) GB8809755D0 (fr)
WO (1) WO1989010567A1 (fr)

Families Citing this family (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH02129513A (ja) * 1988-11-09 1990-05-17 Aisin Seiki Co Ltd 二軸回転検出装置
FR2656929B1 (fr) * 1990-01-11 1994-05-13 Etat Francais Delegue Armement Accelerometre differentiel a resonateurs piezoelectriques.
US5165289A (en) * 1990-07-10 1992-11-24 Johnson Service Company Resonant mechanical sensor
US5233874A (en) * 1991-08-19 1993-08-10 General Motors Corporation Active microaccelerometer
US5355712A (en) * 1991-09-13 1994-10-18 Lucas Novasensor Method and apparatus for thermally actuated self testing of silicon structures
JP3311633B2 (ja) * 1997-04-04 2002-08-05 日本碍子株式会社 センサユニット
DE19812773C2 (de) * 1998-03-24 2002-11-14 Conti Temic Microelectronic Mikrosensor mit einer Resonatorstruktur
DE69932516T2 (de) 1999-09-10 2007-02-15 Stmicroelectronics S.R.L., Agrate Brianza Integrierter Halbleiter-Inertialsensor mit Mikroantrieb zur Kalibration
GB2505875A (en) * 2012-09-04 2014-03-19 Cambridge Entpr Ltd Dual and triple axis inertial sensors and methods of inertial sensing
US10168194B2 (en) 2015-12-24 2019-01-01 Analog Devices, Inc. Method and apparatus for driving a multi-oscillator system

Family Cites Families (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE1243895B (de) * 1961-07-14 1967-07-06 Litton Industries Inc Elektromechanischer Messumformer zur Messung einer Kraft, insbesondere zur Verwendung als Beschleunigungsmesser
US3303452A (en) * 1964-05-12 1967-02-07 Textron Electronics Inc Piezoresistive device
GB2174500B (en) * 1985-05-04 1988-02-10 Stc Plc Accelerometer

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See references of WO8910567A1 *

Also Published As

Publication number Publication date
GB2238874A (en) 1991-06-12
GB8809755D0 (en) 1988-06-02
JPH03503932A (ja) 1991-08-29
WO1989010567A1 (fr) 1989-11-02
GB9023236D0 (en) 1991-02-27
GB2238874B (en) 1992-02-12

Similar Documents

Publication Publication Date Title
US4381672A (en) Vibrating beam rotation sensor
US5767405A (en) Comb-drive micromechanical tuning fork gyroscope with piezoelectric readout
US4654663A (en) Angular rate sensor system
US7481112B2 (en) Silicon inertial sensors formed using MEMS
US4744249A (en) Vibrating accelerometer-multisensor
US5905202A (en) Tunneling rotation sensor
USRE42916E1 (en) Single bar type vibrating element angular rate sensor system
JP3151927B2 (ja) 加速度センサ
US5285686A (en) Coliolis rate sensor using tunnel-effect displacement sensor
US11913808B2 (en) Inertial sensor and method of inertial sensing with tuneable mode coupling strength
GB2158579A (en) Angular rate sensor system
EP0601120B1 (fr) Detecteur de rotation
US6453744B2 (en) Low radiation capture cross-section electrode material for prompt radiation environments
EP0917652B1 (fr) Detecteur d'effet tunnel avec reequilibrage de force lineaire
EP0412106A1 (fr) Accelerometre
JPH063455B2 (ja) 振動ジャイロ
US5315874A (en) Monolithic quartz resonator accelerometer
KR100254114B1 (ko) 2축 동시 측정용 압전 회전 센서 및 그 측정 회로
US5461918A (en) Vibrating beam accelerometer
WO1989010568A1 (fr) Transducteur
US6895819B1 (en) Acceleration sensor
JPH06300776A (ja) 回転加速度計
US6796176B2 (en) Inertial sensor with an integrated temperature probe
SE457189B (sv) Foerfarande och anordning foer att avkaenna rotationshastighet och acceleration hos en kropp
KR100277425B1 (ko) 박막 이동파 회전 센서의 전극 구조물 및 그 센서

Legal Events

Date Code Title Description
PUAI Public reference made under article 153(3) epc to a published international application that has entered the european phase

Free format text: ORIGINAL CODE: 0009012

17P Request for examination filed

Effective date: 19901018

AK Designated contracting states

Kind code of ref document: A1

Designated state(s): AT BE CH DE FR GB IT LI LU NL SE

17Q First examination report despatched

Effective date: 19910813

STAA Information on the status of an ep patent application or granted ep patent

Free format text: STATUS: THE APPLICATION IS DEEMED TO BE WITHDRAWN

18D Application deemed to be withdrawn

Effective date: 19911224