EP0485589A1 - Capteur de capacitance pour accelerometre a re-equilibrage de force - Google Patents

Capteur de capacitance pour accelerometre a re-equilibrage de force

Info

Publication number
EP0485589A1
EP0485589A1 EP91911942A EP91911942A EP0485589A1 EP 0485589 A1 EP0485589 A1 EP 0485589A1 EP 91911942 A EP91911942 A EP 91911942A EP 91911942 A EP91911942 A EP 91911942A EP 0485589 A1 EP0485589 A1 EP 0485589A1
Authority
EP
European Patent Office
Prior art keywords
paddle
coil
improvement
capacitor plate
accelerometer
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Withdrawn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
EP91911942A
Other languages
German (de)
English (en)
Inventor
Graeme A. Blake
Frederick V. Holdren
Brian L. Norling
Mitchell J. Novack
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.)
Sundstrand Data Control Inc
Original Assignee
Sundstrand Data Control Inc
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 Sundstrand Data Control Inc filed Critical Sundstrand Data Control Inc
Publication of EP0485589A1 publication Critical patent/EP0485589A1/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Withdrawn legal-status Critical Current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
    • G01P15/02—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

  • the present invention relates to force rebalance accelerometers in which an acceleration-sensitive movable element is maintained in a neutral position.
  • the accelerometer comprises three components, a reed, and upper and lower stators or magnetic circuits between which the reed is supported.
  • the reed includes a movable paddle that is suspended via flexures to an outer annular support ring, such that the paddle can pivot with respect to the support ring.
  • the paddle, flexures and support ring are commonly provided as a unitary structure composed of fused quartz.
  • Both upper and lower surfaces of the paddle include capacitor plates and force balancing coils.
  • Each force balancing coil is positioned on the paddle such that the central axis of the coil is normal to the top and bottom surfaces of the paddle, and parallel to the sensing axis of the accelerometer.
  • a plurality of mounting pads are formed at spaced apart positions around the upper and lower surfaces of the annular support ring. These mounting pads mate with inwardly facing surfaces of the upper and lower stators when the accelerometer is assembled.
  • Each stator is generally cylindrical, and has a bore provided in its inwardly- facing surface. Contained within the bore is a permanent magnet.
  • the bore and permanent magnet are configured such that an associated one of the force balancing coils mounted to the paddle- fits within the bore, with the permanent magnet being positioned within the cylindrical core of the coil. Current flowing through the coil therefore produces a magnetic field that interacts with the permanent magnet to produce a force on the paddle.
  • capacitor plates are also provided on the inwardly facing surfaces of the stators configured to form capacitors with the capacitor plates on the top and bottom surfaces of the paddle.
  • the accelerometer is affixed to an object whose acceleration is to be measured. Acceleration of the object along the sensing axis results in pendulous, rotational displacement of the paddle with respect to the support ring and the stators. The resulting differential capacitance change caused by this displacement is sensed by a feedback circuit. In response, the feedback circuit
  • the present invention provides a force rebalance accelerometer that has an increased servo force capacity relative to proof mass size.
  • the invention thereby increases g-range without increasing either the size or the power requirements for
  • An additional advantage of the invention is that it allows alignment of the center of mass of the proof mass and the force rebalance center without sacrificing servo force capacity or pick-off sensitivity.
  • the accelerometer has a reed that includes a support, a paddle, and a force balancing coil.
  • the paddle has a paddle_surface, and is suspended from the support
  • the coil is mounted on the paddle surface, such that the coil surrounds an area of the paddle surface.
  • the term eoil as used herein may include an associated structure for mounting the coil to the paddle.
  • the accelerometer also includes position detecting means for providing an indication of the relative position of the paddle with respect to the support.
  • the position detecting means includes a capacitor plate on the paddle. The improvement provided by the present invention lies in the fact that at least a portion of the capacitor plate is positioned in the area of the paddle surface surrounded by the coil.
  • the coil has an outer circumference a portion of which is coextensive with the outer circumference of the paddle, a second portion of the coil overhangs the flexure means, and the capacitor plate is positioned entirely within and substantially fills the surrounded area.
  • FIGURE 1 is a cross-sectional view of an accelerometer that includes the capacitor plate and coil positioned in accordance with the present invention
  • FIGURE 2 is a top plan view of the reed of the accelerometer of FIGURE 1;
  • FIGURE 3 is a cross-sectional view taken along the line 3-3 of FIGURE 2;
  • FIGURE 4 is a schematic view of a single coil accelerometer constructed in accordance with the present invention.
  • FIGURE 5 is a schematic view of a single coil accelerometer using a capacitor plate arrangement in accordance with the prior art
  • FIGURE 6 is a schematic view of a two coil accelerometer constructed in accordance with the present invention.
  • FIGURES 1-3 illustrate an accelerometer that includes an improved coil and capacitor plate geometry in accordance with a preferred embodiment of the present invention.
  • the accelerometer 10 measures acceleration along sensing axis
  • SA and includes stator 12, reed 14, ceramic plate 16 and electronics assembly 18, all mounted within an enclosure formed by mounting flange 20 and case 22.
  • Reed 14 is held between ceramic plate 16 and stator 12, and has coil 24 positioned on its upper surface. Stator 12 in turn bears against case 22 via positioning ring 26 and spring washer 28.
  • the stator comprises excitation ring 42, magnet 44 and pole piece 46.
  • the stator is shaped so that coil 24 occupies a comparatively narrow gap between pole piece 46 and excitation ring 42, to provide the force balancing function well known to those skilled in the art.
  • Ceramic plate 16 is held against the reed by inner shoulder 30 of mounting flange 20, and the mounting flange and case 22 are interconnected by welding or by any other suitable process.
  • Means (not shown) are provided for electrically interconnecting electronics assembly 18 with reed 14, and for providing connections between the electronics assembly and an electrical connector on the outer surface of mounting flange 20.
  • Reed 14 is shown in greater detail in FIGURES 2 and 3.
  • the reed has an overall disk-like shape, and includes annular support ring 32 and paddle 34 connected to one another via a pair of flexures 36 between which opening 40 is formed.
  • paddle 34 is separated from support ring 32 by circular gap 38.
  • a portion of the paddle is cut away, in the area indicated by reference numeral 48, to provide alignment between the center of mass of the proof mass and the force rebalance center, as described in greater detail below.
  • Three raised mounting pads 50-52 are located at approximately equally spaced positions around support ring 32, and three similar mounting " pads (not shown) are located immediately beneath mounting pads 50-52 on the lower surface of the support ring. When the accelerometer is assembled, the upper mounting pads 50-52 contact stator 12, while the lower mounting pads contact ceramic plate 16.
  • Paddle 34 is mounted via flexures 36 such that the paddle can pivot with respect to support ring 32 about hinge axis HA that passes through the midpoints of the flexures and that is horizontal and in the plane of the drawing in FIGURE 2.
  • Coil 24 is mounted on the upper surface of paddle 34. The outer edge of the coil is approximately coextensive with the outer edge of the paddle, except adjacent flexures 36 and cut away area 48.
  • a thin shim (not shown) is positioned between coil 24 and paddle 34, such that the coil is positioned a short distance above flexures 36, to avoid interference during paddle movement.
  • Capacitor plate 60 is positioned on paddle 34 entirely within the area of the paddle surface surrounded by coil 24, and forms a capacitor with the adjacent surface of pole piece 46, or with a second capacitor plate located on the pole piece surface. This capacitor forms a portion of a pick-off circuit that measures the capacitance between capacitor plate 60 and pole piece 46, or between capacitor plate 60 and the second capacitor plate, to thereby detect movement of the paddle from its null position. Capacitor plate 60 and the adjacent surface of pole piece 46 also provide squeeze film damping for the accelerometer.
  • the pick-off circuit may also include a second capacitor formed between plates (not -3-
  • a portion of support ring 32 adjacent to flexures 36 may be divided by slot 70 into inner ring 72 and outer ring 74.
  • Mounting pad 50 is positioned on outer ring 74 only, and the flexures are connected to inner ring 72.
  • flexures 36 are isolated from stress coupled into reed 14 via mounting pad 50.
  • the coil and capacitor plate may be electrically coupled to electronics module 18 via conductive strips (not shown) extending across flexures 36 and along each side of inner ring 72 to contacts on mounting pads 51 and 52. Corresponding conductors in ceramic plate 16 electrically connect these contacts to the electronics assembly.
  • FIGURE 4 illustrates an accelerometer constructed in accordance with the present invention
  • FIGURE 5 illustrates a prior art capacitor plate geometry.
  • the accelerometer shown in FIGURE 4 comprises paddle 80 connected to support 82 by flexure 84, such that the paddle can rotate with respect to the support.
  • the paddle has an upper surface 86 on which coil 88 is mounted.
  • Capacitor plate 90 is secured to surface 86 in the area of surface 86 surrounded by the coil.
  • the adjacent surface 92 of stator 94 forms a capacitor with plate 90.
  • FIGURE 5 schematically illustrates an accelerometer that utilizes a prior art arrangement of the type shown in U.S.P. 3,702,073.
  • This accelerometer includes paddle 100 mounted to support 102 by flexure 104, such that the paddle can rotate with respect to the support.
  • the paddle includes an upper surface 106 on which coil 108 and capacitor plate 110 are mounted.
  • the stator includes a portion 114 extending within coil 108, to provide the force rebalancing function.
  • a second capacitor plate 112 is mounted to the portion of the stator (not shown) opposite capacitor plate 110.
  • capacitor plates 110 and 112 have crescent shapes, and extend around the outside of coil 108, except adjacent to flexure 104.
  • the capaeitive pick-off system utilizes space on the paddle that is already used by the force rebalance system, i.e., by the coil.
  • the capacitor plates do not add any additional size to the accelerometer, or any additional weight to the paddle.
  • comparison of FIGURES 4 and 5 illustrates that for a given paddle size, the arrangement of the present invention permits use of a larger magnet and a larger coil, without losing capacitance or damping area. This feature permits an increase of the g-range of the accelerometer, without an increase in the accelerometer's overall size.
  • a further advantage of the invention is that the roughly circular damping areas provided by the capacitor plate and the adjacent pole piece surface provide greater damping per unit area than elongated narrow shapes such as an arc.
  • the present invention also provides another important advantage relating to force alignment.
  • the center of the acceleration force i.e., the center of mass of the proof mass
  • the center of rebalance force will lie along the symmetry axis of the magnet and coil, e.g., at centerline 62 shown in FIGURE 2.
  • the center of mass of the proof mass will typically not lie at centerline 62, but will be displaced away from the flexures relative to the centerline, i.e., in the downward direction shown in FIGURE 2.
  • the present invention provides a way of eliminating this misalignment without affecting the sensitivity of the pick-off system or the efficiency of the magnetic circuit.
  • a portion of the paddle indicated by reference numeral 48 has been removed, to shift the center of mass of the proof mass toward the flexures, such that it is positioned at centerline 62 and therefore coincides with the center of rebalance force.
  • This removal of paddle material can be accomplished without significant loss of capacitor plate area or damping area.
  • FIGURE 5 it may be seen that in a prior art accelerometer, removal of the outer lip of the paddle would have a significant effect on the amount of capacitor plate area that can be used for the pick-off function.
  • FIGURE 6 schematically illustrates a second preferred embodiment of the invention.
  • paddle 140 is suspended from support ring 142 by one or more flexures 144.
  • the flexures define a hinge axis HA about which paddle 140 can rotate with respect to support ring 142.
  • Hinge axis HA is normal to the plane of the drawing in FIGURE 2.
  • Paddle 140 includes parallel, opposed faces 150 and 160 to which coils 152 and 162, respectively, are mounted.
  • Capacitor plate 154 is positioned on that portion of surface 150 enclosed by coil 152, and capacitor plate 164 is positioned on that portion of surface 160 enclosed by coil 162.
  • the upper stator of the accelerometer illustrated in FIGURE 6 includes magnet 172 and pole piece 174.
  • the remaining components of the upper stator are conventional and are omitted for ease of illustration. However, such components function to provide a return path for magnetic flux lines passing from pole piece 174 through coil 152, and to provide support for support ring 142.
  • the lower stator comprises magnet 182 and pole piece 184.
  • the inner faces of pole pieces 174 and 184 form capacitors with capacitor plates 154 and 164, respectively.
  • the embodiment of FIGURE 6 includes all of the advantages discussed above in connection with the single coil embodiment.

Landscapes

  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • General Physics & Mathematics (AREA)
  • Pressure Sensors (AREA)

Abstract

Géométrie de plaque de condensateur améliorée pour un accéléromètre à ré-équilibrage de force. L'accéléromètre (10) comprend un relais (14) comportant un support (32, 82, 142), une plaquette (34, 80, 140) suspendue au support de manière à entrer en rotation par rapport à celui-ci, et une bobine d'équilibrage de force (24, 88, 152, 162). La bobine est montée sur une surface (86, 150, 160) de la plaquette de façon à entourer une région de cette surface. L'accéléromètre comprend aussi un circuit de détection de position qui fournit des indications quant à la position relative de la plaquette par rapport au support. Le circuit de détection de position comprend une plaque de condensateur (60, 90, 154, 164) située sur la plaquette. L'amélioration prévue par cette invention réside dans le fait qu'au moins une partie de la plaque de condensateur est située dans la région de la surface de la plaquette entourée par la bobine.
EP91911942A 1990-06-11 1991-05-20 Capteur de capacitance pour accelerometre a re-equilibrage de force Withdrawn EP0485589A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US53580390A 1990-06-11 1990-06-11
US535803 1990-06-11

Publications (1)

Publication Number Publication Date
EP0485589A1 true EP0485589A1 (fr) 1992-05-20

Family

ID=24135831

Family Applications (1)

Application Number Title Priority Date Filing Date
EP91911942A Withdrawn EP0485589A1 (fr) 1990-06-11 1991-05-20 Capteur de capacitance pour accelerometre a re-equilibrage de force

Country Status (3)

Country Link
EP (1) EP0485589A1 (fr)
IL (1) IL98346A0 (fr)
WO (1) WO1991019988A1 (fr)

Families Citing this family (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US7331229B2 (en) * 2004-12-09 2008-02-19 The Boeing Company Magnetic null accelerometer
US9016126B2 (en) * 2009-01-07 2015-04-28 Honeywell International Inc. MEMS accelerometer having a flux concentrator between parallel magnets
US9164117B2 (en) * 2012-10-19 2015-10-20 Honeywell International Inc. Stress reduction components for sensors
US10161956B2 (en) 2016-04-25 2018-12-25 Honeywell International Inc. Reducing bias in an accelerometer via a pole piece

Family Cites Families (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3513711A (en) * 1966-10-03 1970-05-26 Singer General Precision Subminiature single axis accelerometer
US3702073A (en) * 1969-02-28 1972-11-07 Sundstrand Data Control Accelerometer
US4932258A (en) * 1988-06-29 1990-06-12 Sundstrand Data Control, Inc. Stress compensated transducer
US4994184A (en) * 1990-06-04 1991-02-19 Infinitex Ultrafiltration device and process

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See references of WO9119988A1 *

Also Published As

Publication number Publication date
WO1991019988A1 (fr) 1991-12-26
IL98346A0 (en) 1992-07-15

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