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WO1991015774A1 - Accelerometre - Google Patents

Accelerometre Download PDF

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Publication number
WO1991015774A1
WO1991015774A1 PCT/GB1991/000436 GB9100436W WO9115774A1 WO 1991015774 A1 WO1991015774 A1 WO 1991015774A1 GB 9100436 W GB9100436 W GB 9100436W WO 9115774 A1 WO9115774 A1 WO 9115774A1
Authority
WO
WIPO (PCT)
Prior art keywords
accelerometer
movement
light
acceleration
main body
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.)
Ceased
Application number
PCT/GB1991/000436
Other languages
English (en)
Inventor
Michael Andrew Kellett
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.)
Individual
Original Assignee
Individual
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 Individual filed Critical Individual
Publication of WO1991015774A1 publication Critical patent/WO1991015774A1/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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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
    • G01P15/13—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 measuring the force required to restore a proofmass subjected to inertial forces to a null position
    • G01P15/132—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 measuring the force required to restore a proofmass subjected to inertial forces to a null position with electromagnetic counterbalancing means

Definitions

  • This invention relates to accelerometers and to systems utilising such accelerometers, and more particularly to servo accelerometers
  • Accelerometers are known and can conveniently be regarded as basically incorporating an element/object that is mounted with respect to a support/main body in such manner that the object/element is displaceable in single direction relative to the main body, that is the element/object has a single degree of displacement freedom together with means to apply force in either direction of the single degree of freedom.
  • Servo accelerometers have been utilised for a variety of applications in situations in which it is required to measure the acceleration direction and/or magnitude of the • acceleration.
  • the operational set-up or application of such accelerometers has been such as to ensure that during the measurement procedures associated with the detection and or measurement of the acceleration giving rise to a particular deflection of the element/object it is conventionally required that the deflection of the object/element should be counterbalanced by being should be restrained by the restoring force to a location close to its initial rest positionreturned to its initial rest position and maintained in such position.
  • an accelerometer comprising a main body, acceleration responsive means mounted from the main body in such manner as to be movable on application to the accelerometer of acceleration along a single axis or about a single axis, sensor means for sensing the magnitude and sense of any such movement of the acceleration responsive means relative to the main body and for providing output characteristic of the such movement; means for producing from ther sensor output digital signals; means for deriving from the digital signals control signals which are utilisable to oprate means for applying force to the responsive means to counteract said movement; and means for producing output signals characteristic of the applied forces.
  • Figure 1 is a schematic representation of an accelerometer incorporating the concepts of the present invention
  • Figure 2 is a perspective view illustrating the main components of a practical embodiment of the accelerometer shown in Figure 1;
  • Figure 3 is a block diagram indicating in general terms a control circuit for controlling the accelerometer of Figures 1 and 2.
  • a servo accelerometer Before considering in detail the accelerometers of the invention it is convenient to recount some of the major features of a servo accelerometer.
  • the general principle upon which a servo accelerometer operates is to mount an object/element in such manner that it is constrained to move along one direction only, i.e., the element/object is constrained to a single degree of freedom of movement which is the sensitive axis of the accelerometer.
  • the element/object In general, if an imposed acceleration is applied to the body of the accelerometer, along its working axis, the element/object will move relative to the body of the accelerometer. A measuring/control system senses this relative displacement and as mentioned produces a force that acts upon the element/object in such direction as to reduce the relative displacement arising from the acceleration. If this restoring force is just sufficient to prevent substantial further relative movement of the element/object and the body of the accelerometer , the magnitude of the restoring force is the product of the mass of the element/object and the imposed acceleration. Since the mass is readily known the value of the imposed acceleration value may be obtained.
  • an element/object is a beam 1 (represented in the Figure 1 by a single line) which is hinged or otherwise mounted by hinges 1A with respect to an accelerometer main body 2 (represented in the Figure 1 by a cross in a circle) for displacement along the direction indicated by the double ended arrow AB.
  • the beam will, depending upon the sense of the imposed acceleration forces causing the beam to be moved relative to the main body 2 either in the sense A to B or alternatively in the sense B to A.
  • the support of the beam 1 is such that any displacements are restricted to the direction A to B or B to A.
  • the sensitive axis of the accelerometer is along the line AB.
  • the displacement of the beam from a rest position along a direction extending perpendicular to the line AB and passing through the pivot/hinge axis is small compared with its length any errors -introduced into the measuring/control system as a result of the degree of freedom being rotational rather than purely linear will also be small .
  • the arrangements for producing the restoring forces include a motor assembly 3 comprising a magnet unit 4 including a core 5 mounted to the accelerometer body 2 and an associated coil 6 carried by the beam 1 and dimensioned as to be freely axially displaceable with respect to the core 5.
  • the instantaneous position of the beam 1 with respect to the main boy is sensed by a photoelectric detection assembly 7 including a light emitter/transmitter 8, a light detector 9 for receiving light emitted by the emitter/transmitter 8 and a variable attenuation light transmission arrangement 10 producing a controlled variation of the amount of light that can pass from the emitter/transmitter 8 to the detector 9 in relation to the instantaneous displacement of the beam.
  • a photoelectric detection assembly 7 including a light emitter/transmitter 8, a light detector 9 for receiving light emitted by the emitter/transmitter 8 and a variable attenuation light transmission arrangement 10 producing a controlled variation of the amount of light that can pass from the emitter/transmitter 8 to the detector 9 in relation to the instantaneous displacement of the beam.
  • the arrangement 10 is shown in the form of vane.
  • the light emitter/transmitter 8 includes an infra-red emitting diode and the detector 9 a light sensitive diode.
  • the vane 10 which is carried by the beam 1 extends generally at right angles to the longitudinal direction of the beam, and is so formed that it is able variably to attenuate the intensity of light passing therethrough according to its instantaneous location between the transmitter/emitter 8 and detector 9.
  • the attenuation is arranged progressively to increase along its length in a direction transverse to the length of the beam 1.
  • the attenuation effect is in one sense i.e, increasing
  • the vane moves in the reverse direction the attenuation effect is in the opposite sense i.e. decreasing.
  • the sense and extent of the attenuation change are indicative of the magnitude and direction of beam displacement relative to the main body as a result of imposed acceleration forces.
  • a particular embodiment of a vane 10 includes a length of clear plastics strip of such thickness as to maintain lengthwise stiffness.
  • the variable light attenuation capability is produced by photographically forming a pattern of dots on the strip, the dots pattern having a progressively varying density of distribution such that the light attenuation is a function of the density of distribution of the dots on the vane 10.
  • the current in its collector will be correspondingly varied.
  • the difference between the resulting voltage at the collector and a reference voltage (a practical value for the reference voltage being 2.5 Volts) which is characteristic of the mechanical centre position of the beam.
  • the mechanical centre position can conveniently be regarded as that position where one wishes the beam to be in the absense of imposed acceleration, and is usually midway between the end stops 11. In practice, also it is the place where the coil/magnet unit 4 is designed to provide linear response.
  • the angle of the beam 1 is exactly 90 degrees of arc to the intended axis of the whole assembly.
  • This output signal is utilised to produce a voltage that is applied to the coil 6.
  • the energisation of the coil 6 produces a force which interacts with the core 5 such as to move the beam in such direction and of such magnitude as to return the beam 1 to balance the effect of the imposed acceleration, and constraining the beam to its mechanical centre.
  • Figure 2 schematically illustrates a practical embodiment of the accelerometer of the invention.
  • the control circuit of Figure 3 includes a microprocessor 12 which is utilised operationally to inter-relate a number of factors as will now be considered. Since the output from the light responsive detector 9 is of a relatively low magnitude it is amplified by amplifier 13, the degree of amplification effected will be as found necessary to produce an adequate signal on an output line 14. Since the output signal from the detector 9 is analogue it is converted to digital form by an analogue to digital converter 15 which is shown as being incorporated in the microprocessor. In practice, the analogue signal is converted, into an eight bit digital form.
  • the microprocessor 12 On receipt of the eight bit digital signal which is characteristic of beam deflection and the direction of the deflection the microprocessor 12 operates using a simple form of control algorithm for the purposes of beam deflection control by simply being arranged to respond to 5 beam displacement and to produce as output a corresponding correcting current i.e., the control system is arranged to adjust, in response to beam displacement only, the drive i.e., current flow, to a driver circuit 17 for the beam position control coil 6 in such sense and direction as to Q produce the requisite magnetic field in the coil 6 that reacts with the core 5 in such sense and of such magnitude as to return the beam towards its undeflected position.
  • the control system is arranged to adjust, in response to beam displacement only, the drive i.e., current flow, to a driver circuit 17 for the beam position control coil 6 in such sense and direction as to Q produce the requisite magnetic field in the coil 6 that reacts with the core 5 in such sense and of such magnitude as to return the beam towards its undeflected position.
  • the microprocessor 12 is arranged to not only produce a succession of voltage pulses for application drive circuit 5 to the coil 6 but also incorporates facilities for adjusting the pulse width (as indicated at 18) by generating a series of pulses of constant frequency and variable width.
  • the coil driver 19 converts these voltage pulses to current pulses in the coil 6.
  • the 0 microprocessor 12 generates pulses in either direction, thereby to adjust the magnitude of the pulses and thus the restoring current for successive pulses by suitable variation of the pulse width of the digital signals.
  • the repetition rate of the pulses is arranged to be sufficiently fast compared with the mechanical time constants of the beam so that for practical purposes the force applied to the beam by the coil 6 can be considered to be continuous and of magnitude proportional to the pulse width, the variation of which the microprocessor 12 uses to control the force applied to the beam 1 by variation of pulse width.
  • Kl and K2 are constants of the system and would be determined by suitable calibration of the accelerometer of the invention; 'd' the beam displacement relative to the main body 2; 'v' the velocity and 'I 1 the current.
  • the control system of the present invention is digital in character the linear function represented by the equation involves a succession of measurements and calculations
  • the microprocessor 12 makes a beam position measurement at the start of a time interval T and a calculation is effected according to the equation to determine the appropriate pulse width and to ensure that the pulse is delivered to the driver circuit 17 in time for the pulse to be completed by at the end of the timing interval T.
  • the end of the pulse is set by the end time of the timing interval T and the time of the start of the pulse within the timing interval T is set according to the result of the measurement and calculation.
  • the pulse width could be substituted for the term I in the equation.
  • the maximum drive force from the coil will be of the order of that able to apply 2g acceleration to the beam.
  • the provision of more power for the purposes of control of beam position will be found to be inefficient or expensive in relation to the capability of the remainder of the system.
  • the approximate linear range of the coil/core system can be arranged to be of the order of + or - 1mm., for a beam of length 20mm., from the hinge 1A.
  • the use of wider linear coil displacements have been found to involve disproporationate expense in the production of the accelerometer and its associated control system.
  • the time 'T' is essentially controlled by the cost of the control system.
  • An eight bit convertor arranged so that the limit stop to limit stop displacement of the beam 1 is about 3mm in total and gives a change in the converter count of 200. It is important to ensure that the convertor is still functioning within the limits of its operational range when the beam is located at either of its end stops 11. This is ensured by allowing the convertor to have a counting range of 200 from limit stop to limit stop. This results, " in practice, in a count of +- 66 for +- 1mm of beam motion.
  • the time interval 'T' is set to 2ms, this being a value possible with a conveniently available eight bit microprocessor type.
  • the resolution of current control is one part in 767 with the components used in a practical realisation of the invention such as shown in Figures 2 and 3.
  • the quantisation of both displacement detector 9 and the coil driver 17 as well as the discrete time sampling of the control system can, . in conjunction with suitably selected control constants, even to the extent of deliberately introducing beam disturbing components into the control algorithm, ensure that the beam can never move to an in-balance condition but is caused always to oscillate at a small (a few counts) amplitude all of the time and in so doing avoid problems that can arise from beam movement time lags arising from, for example, mechanical inertias of the system.
  • the frequency of oscillation is set at about 50Hz. With this arrangement the beam is effectively held in balance on average over several sampling periods.
  • the amplitude of beam oscillation is not so great as to cause errors due to non-linearity the ultimate accuracy of the control system is determined by the ratio of the sampling time to the reading time.
  • a particular problem arising with the detection of the beam as illustrated in the embodiment of Figure 2 is that if an output of 2.5 Volts is obtained at mechanical centre position at room temperature then the beam position for 2.5 volts at the extremes of operating temperature might be several millimetres from the mechanical centre arising from temperature changes in the characteristics of the optical system.
  • temperature sensing arrangements are utilised for enabling a self calibration function which serves to adjust the current in the ⁇ hotoemitter 8 ir. order to reduce the effects of teraperature change.
  • This calibration can be under the control of the microprocessor or under separate control.
  • control system incorporates temperature sensing arrangements 16 which are intended to initiate compensation for temperature drift of the optical beam position sensor, the vane 10, and the emitter detector combination. Compensation is effected by driving the beam to each of its beam deflection limit stops i.e., towards B and towards A and measuring the voltage output from the detector at each limit stop. The control system is arranged to adjust the current to the emitter 8 so that the output of the phototransistor 9 will be 2.5 Volts with the beam at the mechanical centre.
  • the compensation can be initiated when external parameters/factors change i.e., temperature change detected by the microprocessor 1; when the accelerometer is part of a larger system with temperature compension such other systems can create the demand for the compensation or at specified time intervals.
  • the temperature calibration i.e., the variation of temperature sensitivity with temperature changes can be measured and stored in the manner disclosed in our copending British Patent Application ELECTRONIC CONTROLLER UNIT No 8823409.1
  • the optical system could take alternative forms for example, the vane can be replaced by a shutter arrangement using parallel light between emitter and detector.

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  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • General Physics & Mathematics (AREA)
  • Control Of Position Or Direction (AREA)

Abstract

Accéléromètre comprenant un corps principal (2), des moyens réagissant à l'accélération (1) montés à partir du corps principal de façon à de déplacer en un seul sens (A-B) ou autour d'un seul axe lorsqu'on applique une accélération à l'accéléromètre, des moyens de détection (8, 9, 10) servant à détecter l'intensité et le sens de chacun des mouvements des moyens réagissant à l'accélération par rapport au corps principal et à produire une sortie caractéristique dudit mouvement; des moyens servant à produire des signaux numériques (12, 15) à partir de la sortie du détecteur; des moyens (12, 18) de calcul de signaux de commande à partir des signaux numériques, s'utilisant pour actionner des moyens (5, 6) d'application d'une force aux moyens de réaction (1) pour contrer ledit mouvement et des moyens de production de signaux de sortie caractéristiques des forces appliquées.
PCT/GB1991/000436 1990-04-03 1991-03-22 Accelerometre Ceased WO1991015774A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB9007483.2 1990-04-03
GB909007483A GB9007483D0 (en) 1990-04-03 1990-04-03 Servo accelerometer and control systems therefor

Publications (1)

Publication Number Publication Date
WO1991015774A1 true WO1991015774A1 (fr) 1991-10-17

Family

ID=10673785

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/GB1991/000436 Ceased WO1991015774A1 (fr) 1990-04-03 1991-03-22 Accelerometre

Country Status (4)

Country Link
EP (1) EP0523101A1 (fr)
AU (1) AU7577591A (fr)
GB (2) GB9007483D0 (fr)
WO (1) WO1991015774A1 (fr)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0553877A1 (fr) * 1992-01-31 1993-08-04 Canon Kabushiki Kaisha Accéléromètre et accéléromètre angulaire

Citations (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3610354A (en) * 1968-01-25 1971-10-05 Stamicarbon Balance
US3664196A (en) * 1968-03-04 1972-05-23 Gravimetrics Accelerometer
US3897690A (en) * 1973-01-15 1975-08-05 Systron Donner Corp Miniature inertial grade high shock and vibration capability accelerometer and method with axis alignment and stability features
GB2052047A (en) * 1979-03-20 1981-01-21 Secr Defence Accelerometer
DE3315958A1 (de) * 1982-07-01 1984-01-05 Jenoptik Jena Gmbh, Ddr 6900 Jena Anordnung zur bestimmung der winkelgeschwindigkeit und beschleunigung
GB2163847A (en) * 1984-08-31 1986-03-05 Northrop Corp Compensation of gain temperature coefficient in an optical pick-off for an accelerometer
US4649748A (en) * 1984-03-30 1987-03-17 Kabushikikaisha Tokyo Keiki Accelerometer
US4856333A (en) * 1986-12-27 1989-08-15 Jeco Company Limited Servo type accelerometer
EP0338688A1 (fr) * 1988-04-01 1989-10-25 Hitachi, Ltd. Accéléromètre
WO1990001169A1 (fr) * 1988-07-26 1990-02-08 Szekely Levente Dispositif de mesure et d'enregistrement de donnees relatives a l'acceleration

Family Cites Families (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1469764A (en) * 1973-06-30 1977-04-06 Ferranti Ltd Accelerometers
US4315434A (en) * 1980-05-21 1982-02-16 The United States Of America As Represented By The Secretary Of The Army Pulse width modulation (PWM) with jewel pivot accelerometer
GB2127637B (en) * 1982-08-26 1985-12-11 British Aerospace Improvements in or relating to pulse rebalanced servomechanisms
IL75470A0 (en) * 1984-06-20 1985-10-31 Sundstrand Data Control Digital output instrument
US4922756A (en) * 1988-06-20 1990-05-08 Triton Technologies, Inc. Micro-machined accelerometer

Patent Citations (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3610354A (en) * 1968-01-25 1971-10-05 Stamicarbon Balance
US3664196A (en) * 1968-03-04 1972-05-23 Gravimetrics Accelerometer
US3897690A (en) * 1973-01-15 1975-08-05 Systron Donner Corp Miniature inertial grade high shock and vibration capability accelerometer and method with axis alignment and stability features
GB2052047A (en) * 1979-03-20 1981-01-21 Secr Defence Accelerometer
DE3315958A1 (de) * 1982-07-01 1984-01-05 Jenoptik Jena Gmbh, Ddr 6900 Jena Anordnung zur bestimmung der winkelgeschwindigkeit und beschleunigung
US4649748A (en) * 1984-03-30 1987-03-17 Kabushikikaisha Tokyo Keiki Accelerometer
GB2163847A (en) * 1984-08-31 1986-03-05 Northrop Corp Compensation of gain temperature coefficient in an optical pick-off for an accelerometer
US4856333A (en) * 1986-12-27 1989-08-15 Jeco Company Limited Servo type accelerometer
EP0338688A1 (fr) * 1988-04-01 1989-10-25 Hitachi, Ltd. Accéléromètre
WO1990001169A1 (fr) * 1988-07-26 1990-02-08 Szekely Levente Dispositif de mesure et d'enregistrement de donnees relatives a l'acceleration

Non-Patent Citations (6)

* Cited by examiner, † Cited by third party
Title
Derwent's abstract No. 124 360 J/47, SU 901 915, publ. week 8247 *
Derwent's abstract, No. 85- 66 853/11, SU 1 107 063, publ. week 8511 *
Derwent's abstract, No. 90- 65 523/09, SU 1 478 128, publ. week 9009 *
Patent Abstracts of Japan, Vol 10, No 101, P447, abstract of JP 60-233565, publ 1985-11-20 *
Patent Abstracts of Japan, Vol 11, No 248, P604, abstract of JP 62- 55563, publ 1987-03-11 *
Patent Abstracts of Japan, Vol 11, No 84, P556, abstract of JP 61-239164, publ 1986-10-24 *

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0553877A1 (fr) * 1992-01-31 1993-08-04 Canon Kabushiki Kaisha Accéléromètre et accéléromètre angulaire
US5336983A (en) * 1992-01-31 1994-08-09 Canon Kabushiki Kaisha Accelerometer and angular accelerometer

Also Published As

Publication number Publication date
GB2243451A (en) 1991-10-30
EP0523101A1 (fr) 1993-01-20
AU7577591A (en) 1991-10-30
GB9007483D0 (en) 1990-05-30
GB9106345D0 (en) 1991-05-08
GB2243451B (en) 1994-11-16

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