Bae Systems, Inc.

Atlantic Inertial Systems, Inc.

British Aerospace Public Limited Company

Silicon Sensing Systems Limited

Sumitomo Precision Products

Atlantic Inertial Systems UK

Christopher Paul Fell

Kevin Townsend

Ian David Hopkin

Ian Michael Sturland

Rebecka Eley

Colin H J Fox

Stewart McWilliam

Alan R Malvern

Andrew Kazer

Timothy Robert Mason

Michael Terence Durston

Osamu Torayashiki

Ryuta Araki

Koji Nakamura

Tracey Hawke

Tsuyoshi Takemoto

Colin Hnery John Fox

Colin Henry John Fox

Rebecca Eley

Toru Kitamura

Hiroshi Kawasaki

Andrew Kazar

Michael Durston

Alan Richard Malvern

Stewart Mcwilliam

A method for forming a MEMS structure for an inertial sensor from fused silica includes: depositing a conductive layer on one or more selected regions of a first surface of a fused silica substrate, and illuminating areas of the fused silica substrate with laser radiation in a pattern defining features of the MEMS structure for an inertial sensor. A masking layer is deposited at least on the one or more selected regions of the first surface of the fused silica substrate where the conductive layer has been deposited, such that the illuminated areas of the fused silica substrate remain exposed. A first etch of the exposed areas of the fused silica substrate is performed so as to selectively etch the pattern defining features of the MEMS structure for an inertial sensor.

Fabrication of MEMS structures from fused silica for inertial sensors

A capacitive accelerometer includes a proof mass, first and second fixed capacitive electrodes, and a DC biasing element arranged to apply a DC voltage (V) to the proof mass based on a threshold acceleration value. A first closed loop circuit is arranged to detect a signal resulting from displacement of the proof mass and control the pulse width modulation signal generator to apply the first and second drive signals V, Vwith a variable mark:space ratio. A second closed loop circuit keeps the mark:space ratio constant and to change the magnitude, V, of the DC voltage applied to the proof mass by the DC biasing element so as to provide a net electrostatic restoring force on the proof mass for balancing the inertial force of the applied acceleration and maintaining the proof mass at a null position, when the applied acceleration is greater than a threshold acceleration value.

Methods for closed loop operation of capacitive accelerometers

A method for closed loop operation of a capacitive accelerometer includes applying a first drive signal Vto a first fixed capacitive electrode and a second drive signal Vto a second fixed capacitive electrode the first and second drive signals each having a periodic waveform varying in amplitude between zero and a maximum value Vand sensing a displacement of the proof mass and applying pulse width modulation to the first and second drive signals with a constant frequency fand a variable mark/space ratio. The method also includes applying a voltage offset V/2 to the proof mass and applying the pulse width modulation such that the first and second drive signals have a waveform that varies so that when either one of the first and second drive signals is at Vor zero the other drive voltage is at V/2.

A vibrating structure angular rate sensor comprises a MEMS structure includes a mount, a plurality of supporting structures fixed to the mount, and a vibrating planar ring structure flexibly supported by the plurality of supporting structures to move elastically relative to the mount. At least one primary drive transducer is arranged to cause the ring structure to oscillate in a primary mode at the resonant frequency of the primary mode. At least one primary pick-off transducer arranged to detect oscillation of the ring structure in the primary mode. At least three secondary pick-off transducers are arranged to detect oscillation of the ring structure in a secondary mode induced by Coriolis force when an angular rate is applied around an axis substantially perpendicular to the ring structure. At least one secondary drive transducer is arranged to null the induced oscillation in the secondary mode.

Noise performance for vibrating structure gyroscopes

A sensor comprises a substrateand a sensor elementanchored to the substratethe substrateand sensor elementbeing of dissimilar materials and having different coefficients of thermal expansion, the sensor elementand substrateeach having a generally planar face arranged substantially parallel to one another, the sensor further comprising a spacerthe spacerbeing located so as to space at least part of the sensor elementfrom at least part of the substratewherein the spaceris of considerably smaller area than the area of the smaller of face of the substrateand that of the sensor element

Strain decoupled sensor

A sensor comprises a substrate () and a sensor element () anchored to the substrate (), the substrate () and sensor element () being of dissimilar materials and having different coefficients of thermal expansion, the sensor element () and substrate () each having a generally planar face arranged substantially parallel to one another, the sensor further comprising a spacer (), the spacer () being located so as to space at least part of the sensor element () from at least part of the substrate (), wherein the spacer () is of considerably smaller area than the area of the smaller of face of the substrate () and that of the sensor element ().

A silicon MEMS gyroscope is described having a ring or hoop-shaped resonator. The resonator is formed by a Deep Reactive Ion Fitch technique and is formed with slots extending around the circumference of the resonator on either side of the neutral axis of the resonator. The slots improve the Quality Factor Q of the gyroscope without affecting the resonant frequency of the resonator.

Sensor

An angular velocity sensor is described with improved ageing and hysteresis properties. The sensor may be of a ring type driven by a driver circuit, the sensor further comprising primary and secondary portions having corresponding signal pickoffs. The gain of the primary pickoff signal and the capacitance of the primary portions of the sensor are controlled relative to the gain of the secondary pickoff and the capacitance of the secondary portions of the sensor. Control electronics is provided that enables matching of the relative signals from the respective channels. In this way, temperature hysteresis and ageing effects of materials used in forming the sensor are overcome.

Angular rate sensor with improved aging properties

An exemplary vibrating structure gyroscope includes a ring structure, an external frame and a flexible support including a pair of symmetrical compliant legs arranged to retain the ring structure within the external frame. A metal track is provided on an upper surface of the ring structure, the compliant legs and the external frame, over an insulating surface oxide layer. Each flexible support is arranged to carry a metal track associated with a single drive or pick-off transducer. The metal track is repeated for eight circuits, one circuit for each transducer. Each circuit of metal track associated with a transducer begins at a first bond-pad on the external frame, runs along a first compliant leg, across an eighth segment of the ring structure and back along the other compliant leg to a second bond-pad on the external frame.

Vibrating structure gyroscopes

An angular velocity sensor or gyroscope has a ring and a primary drive transducer arranged to cause the ring to oscillate in a primary mode substantially at the resonant frequency of the primary mode of the ring. A primary control loop receives primary pick-off signals from the primary pick-off transducer and provides primary drive signals to the primary drive transducer so as to maintain resonant oscillation of the ring. The primary control loop includes a demodulator arranged to determine the amplitude of the fundamental frequency of the primary pick-off signals and a demodulator arranged to determine the amplitude of the second harmonic frequency of the primary pick-off signals and a drive signal generator arranged to produce the primary drive signals with an amplitude that is dependent on a ratio of the amplitude of the second harmonic frequency of the primary pick-off signal over the amplitude of the fundamental frequency of the primary pick-off signal as derived by a divider.

Angular velocity sensors

A gyroscope structureincludes ring structuresupported from a central hubby eight compliant support legstoPrimary drive transducersandand secondary drive transducersandare all located around and in spaced relationship with the external periphery of the ring structureto create capacitive gaps and primary pick-off transducersandand secondary pick-off transducersandare all located around and in spaced relationship with the internal periphery of the ring structureto create capacitive gaps. The gyroscope structureincludes sixteen capacitor platestoin spaced relationship to the ring structureto create capacitive gaps. Two groups of capacitive platestoandtoare all located around the internal periphery of the ring structureand two groups of capacitor platestoandtoare all located around the external periphery of the ring structureEach capacitor platetois arranged to generate a predetermined electrostatic force, which acts upon the ring structureto locally adjust the stiffness of the ring structure The positioning of the transducerstoand capacitor platestoreduces the effect of variation a capacitive gap with ring structuredue to temperature change, thereby improving the scalefactor of the gyroscope structure.

Vibrating structure gyroscope

A vibrator, which is formed in a silicon waferby means of MEMS technique, has eight beam portions (beams)supported at a central portionand extending in the radial direction while mutually keeping the same angle and has a ring portionconnected to the eight beam portions. Outside the ring portion, eight electrodestofor electrostatic actuation, capacitance detection, or the like are spaced uniformly with a gapcreated between the ring portionand the electrodesto. Inside the ring portion, sixteen electrodesfor frequency adjustment are spaced uniformly with a gapcreated between the ring portionand the electrodes

Angular velocity sensor with vibrator having ring portion and electrodes positioned inside and outside the ring portion

A method for reducing bias error in a Vibrating Structure Gyroscope having a vibrating structure, a primary drive for putting the vibrating structure into carrier mode resonance, a primary pick-off device for sensing carrier mode motion, a secondary pick-off for sensing response mode vibration of the vibrating structure in response to applied rotation rate, a secondary drive for applying a force to control the response mode motion, closed loop primary control loops for maintaining a fixed amplitude of motion at the primary pick-off device, for maintaining the drive frequency at the resonance maximum, and secondary control loops for maintaining a null at the secondary pick-off device. In the method the ratio SFover SFis measured from the secondary control loop to provide a direct measurement of Sin (&#x3c6;+&#x3c6;), according to the relationship SF=SF&#xd7;Sin (&#x3c6;+) where SFis the quadrature scalefactor SFis the in-phase scalefactor, &#x3c6;is the phase error in the secondary drive and &#x3c6;is the phase error in the primary pick-off device. The total phase error &#x3c6;is obtained directly from the measured Sin (&#x3c6;+&#x3c6;) according to the relationship; &#x3c6;=&#x3c6;+&#x3c6;and phase corrections applied to the secondary drive and/or primary pick-off device to reduce the phase error &#x3c6;, and hence the quadrature bias error, to enhance the performance of the gyroscope.

Method for reducing bias error in a vibrating structure gyroscope

Apparatus for measuring variation in scalefactor from a predetermined value for a vibrating structure gyroscope has a vibrating structure (R), fixed primary and fixed secondary drives () for putting and maintaining the vibrating structure (R) in vibrating resonance, fixed primary and fixed secondary pick offs () for detecting vibration of the vibrating structure (R), with the drives and pick offs () being located radially around the vibrating structure (R), quadrature component and real component loop systems (), automatic gain control and phase locked loop systems (), a sin/cos pick off resolver () for receiving signals from the primary and secondary pick offs () and for outputting signals to the quadrature component and real component loop systems () and to the automatic gain control and phase locked loop systems (), a sin/cos drive resolver () for receiving output signals from the quadrature component and real component loop systems () and from the automatic gain control and phase locked loop systems () and for feeding control signals to the primary and secondary drives (), and an angular displacement control () for feeding angular displacement control signals to the sin/cos drive and pick off resolvers () to control uniform displacement of the resolved carrier and response mode drives and pick offs axes angularly around the vibrating structure (R), with respect to a central axis of the vibrating structure, at a known rate.

Method and apparatus for measuring scalefactor variation in a vibrating structure gyroscope

A two axis gyroscope including a substantially planar vibratory resonator () having a substantially ring or hoop-like structure with inner and other peripheries extending around a common axis, carrier mode drive () for causing the resonator () to vibrate in a cosn&#x3b8; vibration mode, carrier mode pick-off () for sensing movement of the resonator () in response to the carrier mode drive (), X-axis response mode pick-off () for detecting movement of the resonator in response to rotation about the X-axis, X-axis response mode drive () for nulling said motion, y-axis response mode pick-off () for detecting movement of the resonator in response to rotation about the y-axis, y-axis response mode drive () for nulling said motion, and a support () for flexibly supporting the resonator () and for allowing the resonator to vibrate relative to the support () in response to the carrier mode drive () and to applied rotation, wherein the support () comprises only L legs, where, when L is even:=2, andwhere, when L is odd:where K is an integer, L&#x3e;2 and N is the carrier mode order.

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Plymouth, United Kingdom

Christopher Paul Fell