WO2013104890A1 - Improvements in accelerometers - Google Patents

Improvements in accelerometers Download PDF

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Publication number
WO2013104890A1
WO2013104890A1 PCT/GB2013/000012 GB2013000012W WO2013104890A1 WO 2013104890 A1 WO2013104890 A1 WO 2013104890A1 GB 2013000012 W GB2013000012 W GB 2013000012W WO 2013104890 A1 WO2013104890 A1 WO 2013104890A1
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WO
WIPO (PCT)
Prior art keywords
accelerometer
beams
deflection
proof mass
actuator
Prior art date
Application number
PCT/GB2013/000012
Other languages
French (fr)
Inventor
David George
Edward Davies
Malcolm ENGLISH
Karl Werner
Andrew Holmes
Original Assignee
The 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 The Secretary Of State For Defence filed Critical The Secretary Of State For Defence
Priority to US14/371,225 priority Critical patent/US9470527B2/en
Priority to CN201380013993.XA priority patent/CN104169724B/en
Priority to JP2014551670A priority patent/JP6082028B2/en
Priority to EP13703854.3A priority patent/EP2802882A1/en
Publication of WO2013104890A1 publication Critical patent/WO2013104890A1/en
Priority to HK15104167.2A priority patent/HK1203628A1/en

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01C—MEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY
    • G01C19/00—Gyroscopes; Turn-sensitive devices using vibrating masses; Turn-sensitive devices without moving masses; Measuring angular rate using gyroscopic effects
    • G01C19/56—Turn-sensitive devices using vibrating masses, e.g. vibratory angular rate sensors based on Coriolis forces
    • G01C19/5642—Turn-sensitive devices using vibrating masses, e.g. vibratory angular rate sensors based on Coriolis forces using vibrating bars or beams
    • 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
    • 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
    • G01P15/093—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 photoelectric pick-up
    • 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
    • G01P15/125—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 capacitive pick-up
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01C—MEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY
    • G01C19/00—Gyroscopes; Turn-sensitive devices using vibrating masses; Turn-sensitive devices without moving masses; Measuring angular rate using gyroscopic effects
    • G01C19/56—Turn-sensitive devices using vibrating masses, e.g. vibratory angular rate sensors based on Coriolis forces
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01C—MEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY
    • G01C19/00—Gyroscopes; Turn-sensitive devices using vibrating masses; Turn-sensitive devices without moving masses; Measuring angular rate using gyroscopic effects
    • G01C19/56—Turn-sensitive devices using vibrating masses, e.g. vibratory angular rate sensors based on Coriolis forces
    • G01C19/5607—Turn-sensitive devices using vibrating masses, e.g. vibratory angular rate sensors based on Coriolis forces using vibrating tuning forks
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01C—MEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY
    • G01C19/00—Gyroscopes; Turn-sensitive devices using vibrating masses; Turn-sensitive devices without moving masses; Measuring angular rate using gyroscopic effects
    • G01C19/56—Turn-sensitive devices using vibrating masses, e.g. vibratory angular rate sensors based on Coriolis forces
    • G01C19/5642—Turn-sensitive devices using vibrating masses, e.g. vibratory angular rate sensors based on Coriolis forces using vibrating bars or beams
    • G01C19/5649—Signal processing
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01C—MEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY
    • G01C19/00—Gyroscopes; Turn-sensitive devices using vibrating masses; Turn-sensitive devices without moving masses; Measuring angular rate using gyroscopic effects
    • G01C19/56—Turn-sensitive devices using vibrating masses, e.g. vibratory angular rate sensors based on Coriolis forces
    • G01C19/5719—Turn-sensitive devices using vibrating masses, e.g. vibratory angular rate sensors based on Coriolis forces using planar vibrating masses driven in a translation vibration along an axis
    • 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
    • G01P2015/0805—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 being provided with a particular type of spring-mass-system for defining the displacement of a seismic mass due to an external acceleration
    • G01P2015/0808—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 being provided with a particular type of spring-mass-system for defining the displacement of a seismic mass due to an external acceleration for defining in-plane movement of the mass, i.e. movement of the mass in the plane of the substrate
    • G01P2015/0811—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 being provided with a particular type of spring-mass-system for defining the displacement of a seismic mass due to an external acceleration for defining in-plane movement of the mass, i.e. movement of the mass in the plane of the substrate for one single degree of freedom of movement of the mass
    • G01P2015/0814—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 being provided with a particular type of spring-mass-system for defining the displacement of a seismic mass due to an external acceleration for defining in-plane movement of the mass, i.e. movement of the mass in the plane of the substrate for one single degree of freedom of movement of the mass for translational movement of the mass, e.g. shuttle type

Definitions

  • This invention relates to accelerometers and the like.
  • An accelerometer typically employs a damped proof mass on a spring. Under the influence of external accelerations a proof mass deflects from its neutral position. This deflection is measured and from it the acceleration is calculated. Commonly, the capacitance between a set of fixed electrodes and a set of electrodes attached to the proof mass is measured. This method is simple, reliable, and inexpensive.
  • Modern accelerometers are often small micro electro-mechanical systems (MEMS), and consist of little more than a cantilever beam with a proof mass (also known as seismic mass). Damping results from the residual gas sealed in the device.
  • MEMS micro electro-mechanical systems
  • a common way to make such devices is to etch the components from a single silicon block. As the proof mass moves, the displacement between this proof: mass and the base of the cantilever beam on which it is suspended is measured.
  • MEMS accelerometers are often used as components in many modern devices.
  • Solid state accelerometers are found in many current smart phones, for example, so that the phone software can detect its orientation and rotate the display accordingly.
  • the invention provides for an accelerometer comprising a proof mass within a. fixed substrate wherein the proof mass is connected to the substrate by one or more V-beams, acceleration of the substrate being determined by measuring deflection of the V-beam or beams. Such an arrangement leads to an amplification of the deflection thereby heightening the device sensitivity to acceleration.
  • the v beam deflects, either by bowing or bending in the middle and this deflection is picked up by a detector. Since geometrically, the deflection of the V-beam is greater than the movement of the proof mass, there is built in to the accelerometer an amplification rendering it more sensitive.
  • Detection might be via detecting variations in capacitance or by electro optical detection.
  • the detection method is optical, it is possible to put an optically reflective coating at the apex of the V beam to enhance sensitivity, such as gold or another suitably reflective metal.
  • This forms one mirror of a Fabry Perot interferometer which can be used to measure the deflection.
  • the Fabry Perot cavity may be formed by reflection from the V-beam mirror and the end of the optical fibre interrogating the device.
  • the V-beam need not be articulated.
  • a straight or bowed beam can be used as long as it deflects in the proper direction in a predictable manner.
  • the Fabry-Perot cavity may be formed between the opposing sidewalls of two adjacent silicon blocks.
  • Silicon is optically transmissive at optical wavelengths beyond 1 .13 pm, so by choosing an appropriate wavelength in the infrared region, 1 .55 pm for example, the cavity can be illuminated by light entering through one of the blocks. Unwanted additional reflections from the outer sidewalls of the blocks can be avoided by making the blocks wedge-shaped rather than rectangular.
  • Illumination could be delivered via a single mode optical fibre, although multimode fibres could also be used.
  • the light output from the cavity may be collected by the same optical fibre (reflection mode), or by a second optical fibre on the opposite side of the cavity (transmission mode).
  • the optical fibre(s) may be lensed so as to collimate the light. Collimation produces a higher finesse cavity while also ensuring maximum coupling of light into the output optical fibre for sensing. If the mirror blocks are wedge-shaped, the input fibre should be mounted obliquely so that an axial ray emerging from the fibre is refracted to lie along the axis of the cavity on entering the first block.
  • the Fabry-Perot cavity may alternatively be formed between the mirror on the V-beam and the end facet of the optical fibre.
  • the mirror surfaces may be coated with a thin metal layer to achieve higher reflectivity and hence cavity finesse. Highly reflective thin film coatings or distributed Bragg reflectors may also be used. Additionally, the input an output fibre end facets may be anti-reflection coated to avoid unwanted reflections from these surfaces. It should be noted that while the device described here is an optical accelerometer, the method of mechanical amplification described could also be used to increase the sensitivity and/or bandwidth of an accelerometer employing electrical readout.
  • two V-beams are used. These deflect in opposing directions. This doubles the change in cavity length for a given mass displacement and thereby further enhancing the sensitivity of the device, by allowing measurement between two points of maximum deflection of the separated beams.
  • the fact that the separation between the two beams can be used conveniently mitigates effects such as transverse movement of the system leading to erroneous measurement, so the two beam system promotes heightened accuracy as well as heightened amplification.
  • the Fabry Perot cavity is formed between two reflective surfaces on the V-beams.
  • each face of the proof mass could be fixed with V-beams.
  • the beams could also provide the restoring force for the proof mass if of appropriate elasticity.
  • the device has all the advantages of MEMS devices (including qualities such as being compact, manufacturable, precise). In addition, being optically addressed it has all the advantages of optical over electrical systems (including suitable for harsh environments, no electromagnetic interference, high bandwidth, no connecting conductors hence may be deployed in sensitive environment)
  • Amplification of the proof mass motion allows the resonant frequency, and hence the measurement bandwidth, of the accelerometer to be increased while retaining the same sensitivity. Alternatively, it, allows the sensitivity to be increased for a given bandwidth. Most generally, it allows the bandwidth-sensitivity product to be increased
  • the device may be used in any circumstances where accelerometers are applied. Consequently there are a huge number of commercial opportunities. These could be for navigation and guidance systems, dynamics testing of materials and structures / systems. It is particularly suited to microsystems, for instance MEMS accelerpmeters for airbag deployment, inertial sensors, virtual reality / entertainment systems (eg Nintendo WiiTM) and mobile telecommunications. It lends itself to miniaturisation and high performance where optical systems are favoured over electrical systems eg Harsh Environments (High EMI, explosives etc) or for high fidelity, high bandwidth applications.
  • MEMS accelerpmeters for airbag deployment, inertial sensors, virtual reality / entertainment systems (eg Nintendo WiiTM) and mobile telecommunications. It lends itself to miniaturisation and high performance where optical systems are favoured over electrical systems eg Harsh Environments (High EMI, explosives etc) or for high fidelity, high bandwidth applications.
  • Figure 1 shows a plan of an accelerometer according a first embodiment of the invention.
  • Figure 2 shows a plan of an accelerometer according a second embodiment of the invention
  • Figure 3 shows a plan of an accelerometer according a third embodiment of the invention
  • a proof mass (10) is etched into a silicon Block (12) so that it is able to move within a silicon cavity. This is achieved through photo-lithography and Reactive Ion Etching (RIE) and wet etching of silicon on insulator wafers to produce the cavity.
  • RIE Reactive Ion Etching
  • a single V beam ( 14) is located between the proof mass (10) and the edge of the block (12) and is affixed to the wall of the block.
  • the device is assembled using UV cured epoxy and active alignment techniques.
  • the proof mass is in contact with the walls of the block through springs (15) which limit the motion to one direction and provide a restoring force. .
  • the movement of the proof mass causes deflection of the V-beam, resulting in an amplified deflection at its centre in a direction orthogonal to the proof mass motion.
  • a silicon mirror is mounted at the centre of the V-beam such that a Fabry-Perot cavity is formed between this mirror and a fixed mirror.
  • a thin Gold coating or other reflective layer(16) may alternatively be provided on the beam to act as a mirror, using sputter coating / evaporation of thin film coating technology.
  • An optical analyser (18) can detect movement of the beam. The amplified motion is detected by means of interrogation by one or two optical fibres.
  • the device may be fabricated in silicon using standard Micro-Electro-Mechanical-Systems (MEMS) processing.
  • MEMS Micro-Electro-Mechanical-Systems
  • two V-beams are used in such a way that the amplified motion in each is in opposing direction to that in the other. This enables a further x2 amplification of the proof mass motion since the two beams deflect in opposing and equal directions.
  • the Fabry-Perot cavity is formed between mirrors (16, 16') mounted on the. two V-beams (14, 14').
  • the design with two V-beams provides better performance in terms of cross-axis sensitivity because an applied acceleration along the same axis as the mirror motion should have the same effect on both V-beams, resulting in no change in the cavity length.
  • a second V-beam (24) is attached to the middle of the first V-beam (14) and to the wall of the substrate. This gives a multiplicative amplification as when the first V-beam deflects the second reamplifies this deflection.
  • a third V-beam (34) js attached to the middle of the second V-beam (24) and to the wall of the substrate, thus providing further . multiplicative amplifications caused by the cumulative effect of the deflection of the first V- beam (14, the second V-beam (24 and the third V-beam (34).
  • the magnitude, of the deflection of the V-beam or V-beams determines the magnitude of a force generated by an actuator that opposes the , movement of the proof mass.
  • the actuator may, for example, be an electrostatic actuator . or a thermal actuator. This occurs within a closed loop mode of operation such that the deflections of the V-beam or V-beams continuously determine the magnitude of the force required to prevent the accelerometer from operating in a hon-linear mode.
  • acceleration can thus additionally be ascertained by measuring the magnitude of the force applied by the actuator.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Radar, Positioning & Navigation (AREA)
  • Remote Sensing (AREA)
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Abstract

The invention provides for an accelerometer comprising a proof mass within a fixed substrate wherein the proof mass is connected to the substrate by one or more v-beams. Acceleration is determined by measuring the deflection of the v-beam or beams.

Description

Improvements in Accelerometers
This invention relates to accelerometers and the like.
An accelerometer typically employs a damped proof mass on a spring. Under the influence of external accelerations a proof mass deflects from its neutral position. This deflection is measured and from it the acceleration is calculated. Commonly, the capacitance between a set of fixed electrodes and a set of electrodes attached to the proof mass is measured. This method is simple, reliable, and inexpensive.
Modern accelerometers are often small micro electro-mechanical systems (MEMS), and consist of little more than a cantilever beam with a proof mass (also known as seismic mass). Damping results from the residual gas sealed in the device. A common way to make such devices is to etch the components from a single silicon block. As the proof mass moves, the displacement between this proof: mass and the base of the cantilever beam on which it is suspended is measured.
Because they are inexpensive and small, MEMS accelerometers are often used as components in many modern devices. Solid state accelerometers are found in many current smart phones, for example, so that the phone software can detect its orientation and rotate the display accordingly.
The sensitivity of such devices is limited however, and it would be advantageous to create a MEMS type device with an increased sensitivity. Accordingly the invention provides for an accelerometer comprising a proof mass within a. fixed substrate wherein the proof mass is connected to the substrate by one or more V-beams, acceleration of the substrate being determined by measuring deflection of the V-beam or beams. Such an arrangement leads to an amplification of the deflection thereby heightening the device sensitivity to acceleration.
As the proof mass moves with respect to the fixed substrate, the v beam deflects, either by bowing or bending in the middle and this deflection is picked up by a detector. Since geometrically, the deflection of the V-beam is greater than the movement of the proof mass, there is built in to the accelerometer an amplification rendering it more sensitive.
Detection might be via detecting variations in capacitance or by electro optical detection. Where the detection method is optical, it is possible to put an optically reflective coating at the apex of the V beam to enhance sensitivity, such as gold or another suitably reflective metal. This forms one mirror of a Fabry Perot interferometer which can be used to measure the deflection. If one v beam is used, the Fabry Perot cavity may be formed by reflection from the V-beam mirror and the end of the optical fibre interrogating the device. The V-beam need not be articulated. A straight or bowed beam can be used as long as it deflects in the proper direction in a predictable manner. The Fabry-Perot cavity may be formed between the opposing sidewalls of two adjacent silicon blocks. Silicon is optically transmissive at optical wavelengths beyond 1 .13 pm, so by choosing an appropriate wavelength in the infrared region, 1 .55 pm for example, the cavity can be illuminated by light entering through one of the blocks. Unwanted additional reflections from the outer sidewalls of the blocks can be avoided by making the blocks wedge-shaped rather than rectangular.
Illumination could be delivered via a single mode optical fibre, although multimode fibres could also be used. The light output from the cavity may be collected by the same optical fibre (reflection mode), or by a second optical fibre on the opposite side of the cavity (transmission mode). The optical fibre(s) may be lensed so as to collimate the light. Collimation produces a higher finesse cavity while also ensuring maximum coupling of light into the output optical fibre for sensing. If the mirror blocks are wedge-shaped, the input fibre should be mounted obliquely so that an axial ray emerging from the fibre is refracted to lie along the axis of the cavity on entering the first block.
-
For the design with a single V-beam, the Fabry-Perot cavity may alternatively be formed between the mirror on the V-beam and the end facet of the optical fibre.
For all variants of the accelerometer, the mirror surfaces may be coated with a thin metal layer to achieve higher reflectivity and hence cavity finesse. Highly reflective thin film coatings or distributed Bragg reflectors may also be used. Additionally, the input an output fibre end facets may be anti-reflection coated to avoid unwanted reflections from these surfaces. It should be noted that while the device described here is an optical accelerometer, the method of mechanical amplification described could also be used to increase the sensitivity and/or bandwidth of an accelerometer employing electrical readout.
In one embodiment two V-beams are used. These deflect in opposing directions. This doubles the change in cavity length for a given mass displacement and thereby further enhancing the sensitivity of the device, by allowing measurement between two points of maximum deflection of the separated beams. In this embodiment, the fact that the separation between the two beams can be used conveniently mitigates effects such as transverse movement of the system leading to erroneous measurement, so the two beam system promotes heightened accuracy as well as heightened amplification. In this case the Fabry Perot cavity is formed between two reflective surfaces on the V-beams.
Although the description has focused on measuring accelerations in one. direction, each face of the proof mass could be fixed with V-beams. The beams could also provide the restoring force for the proof mass if of appropriate elasticity.
The device has all the advantages of MEMS devices (including qualities such as being compact, manufacturable, precise). In addition, being optically addressed it has all the advantages of optical over electrical systems (including suitable for harsh environments, no electromagnetic interference, high bandwidth, no connecting conductors hence may be deployed in sensitive environment)
Amplification of the proof mass motion allows the resonant frequency, and hence the measurement bandwidth, of the accelerometer to be increased while retaining the same sensitivity. Alternatively, it, allows the sensitivity to be increased for a given bandwidth. Most generally, it allows the bandwidth-sensitivity product to be increased
The device may be used in any circumstances where accelerometers are applied. Consequently there are a huge number of commercial opportunities. These could be for navigation and guidance systems, dynamics testing of materials and structures / systems. It is particularly suited to microsystems, for instance MEMS accelerpmeters for airbag deployment, inertial sensors, virtual reality / entertainment systems (eg Nintendo Wii™) and mobile telecommunications. It lends itself to miniaturisation and high performance where optical systems are favoured over electrical systems eg Harsh Environments (High EMI, explosives etc) or for high fidelity, high bandwidth applications.
The invention will now be described with reference to the following figures:
Figure 1 shows a plan of an accelerometer according a first embodiment of the invention. Figure 2 shows a plan of an accelerometer according a second embodiment of the invention
Figure 3 shows a plan of an accelerometer according a third embodiment of the invention
In figure 1 , a proof mass (10) is etched into a silicon Block (12) so that it is able to move within a silicon cavity. This is achieved through photo-lithography and Reactive Ion Etching (RIE) and wet etching of silicon on insulator wafers to produce the cavity. A single V beam ( 14) is located between the proof mass (10) and the edge of the block (12) and is affixed to the wall of the block. The device is assembled using UV cured epoxy and active alignment techniques. The proof mass is in contact with the walls of the block through springs (15) which limit the motion to one direction and provide a restoring force. .
The movement of the proof mass causes deflection of the V-beam, resulting in an amplified deflection at its centre in a direction orthogonal to the proof mass motion. A silicon mirror is mounted at the centre of the V-beam such that a Fabry-Perot cavity is formed between this mirror and a fixed mirror.
A thin Gold coating or other reflective layer(16) may alternatively be provided on the beam to act as a mirror, using sputter coating / evaporation of thin film coating technology. An optical analyser (18) can detect movement of the beam. The amplified motion is detected by means of interrogation by one or two optical fibres. The device may be fabricated in silicon using standard Micro-Electro-Mechanical-Systems (MEMS) processing.
In an second embodiment figure 2, two V-beams are used in such a way that the amplified motion in each is in opposing direction to that in the other. This enables a further x2 amplification of the proof mass motion since the two beams deflect in opposing and equal directions. In this case the Fabry-Perot cavity is formed between mirrors (16, 16') mounted on the. two V-beams (14, 14').
Compared to the single V-beam design, the design with two V-beams provides better performance in terms of cross-axis sensitivity because an applied acceleration along the same axis as the mirror motion should have the same effect on both V-beams, resulting in no change in the cavity length.
In figure 3, a second V-beam (24) is attached to the middle of the first V-beam (14) and to the wall of the substrate. This gives a multiplicative amplification as when the first V-beam deflects the second reamplifies this deflection. A third V-beam (34) js attached to the middle of the second V-beam (24) and to the wall of the substrate, thus providing further . multiplicative amplifications caused by the cumulative effect of the deflection of the first V- beam (14, the second V-beam (24 and the third V-beam (34). Indeed, it is possible to have a 'cascade' of V-beams (4) all located between a wall of the substrate and the apex of a previous V-beam. Although this adds complexities to the manufacture in both the interrogation and etching processes and may reduce robustness, in highly specialised applications, the engineering challenges required could be justified by the benefits gained. In a further embodiment of this invention, the magnitude, of the deflection of the V-beam or V-beams determines the magnitude of a force generated by an actuator that opposes the , movement of the proof mass. The actuator may, for example, be an electrostatic actuator . or a thermal actuator. This occurs within a closed loop mode of operation such that the deflections of the V-beam or V-beams continuously determine the magnitude of the force required to prevent the accelerometer from operating in a hon-linear mode. The
acceleration can thus additionally be ascertained by measuring the magnitude of the force applied by the actuator.

Claims

Claims
1 . An accelerometer comprising a proof mass within a fixed substrate wherein the proof mass is connected to the substrate by one or more V-beams, and acceleration is determined by measuring the deflection of the V-beam or beams.
2. An accelerometer as claimed in Claim 1 in which the deflection of the V-beam or beams is measured at the point of maximum deflection of the V-beam or beams.
3. An accelerometer as claimed in Claim 1. or Claim 2 in which the deflection is measured by measuring variations in capacitance due to the deflection of the V- beam or beams.
4. An accelerometer as claimed in Claim 1 or Claim 2 in which the deflection is measured by optical means.
5. An accelerometer as -claimed in claim 4 in which the optical means is a fibre optical cable and the end of the fibre optical cable and one V-beam form a Fabry-Perot cavity,
6. An accelerometer as claimed in any of claims 1 to 4 comprising two beams located on the same side of the proof mass wherein the two V-beams deflect in opposite directions to each other.
7 An accelerometer as claimed in claim 6 in which a Fabry-Perot cavity is formed between the two opposing V-beams.
8. An accelerometer as claimed in any preceding claim in which the V-beam or beams comprises a section coated with a reflectivity enhancing layer.
9. An accelerometer as claimed in claim 8 in which the reflectivity enhancing layer comprises gold.
10. An accelerometer according to any preceding claim in which a further V-beam depends from the V-beam and is connected to the substrate.
1.1 . An accelerometer according to any previous claim in which the proof mass and substrate are formed out of Silicon.
12. An accelerometer according to any previous claim in which the deflection of the V- beam or V-beams determines the magnitude of a .force opposing the movement of the proof mass that is generated by an actuator.
13. An accelerometer according to Claim 12 in which the actuator is an electrostatic actuator.
14. An accelerometer according to Claim 12 in which the actuator is a thermal actuator.
15. An accelerometer substantially as described herein with reference to the accompanying drawings.
PCT/GB2013/000012 2012-01-13 2013-01-11 Improvements in accelerometers WO2013104890A1 (en)

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US14/371,225 US9470527B2 (en) 2012-01-13 2013-01-11 Accelerometers
CN201380013993.XA CN104169724B (en) 2012-01-13 2013-01-11 The accelerometer improved
JP2014551670A JP6082028B2 (en) 2012-01-13 2013-01-11 Improvements in accelerometers
EP13703854.3A EP2802882A1 (en) 2012-01-13 2013-01-11 Improvements in accelerometers
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Families Citing this family (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2498520A (en) * 2012-01-13 2013-07-24 Secr Defence Accelerometer
DE102015217430A1 (en) * 2015-09-11 2017-03-16 Siemens Aktiengesellschaft Fiber optic acceleration sensor
CN111337701B (en) * 2020-03-20 2023-08-04 南京智慧基础设施技术研究院有限公司 Sensing device for acceleration detection
CN114034300A (en) * 2021-11-09 2022-02-11 中国电子科技集团公司信息科学研究院 Optical accelerometer and inertial navigation system

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1245960A2 (en) * 2001-02-26 2002-10-02 Sagem S.A. Vibrating beam accelerometer
US20040237648A1 (en) * 2003-06-02 2004-12-02 Jones Richard Todd Optical accelerometer or displacement device using a flexure system

Family Cites Families (23)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE69509312T2 (en) * 1994-06-29 1999-11-04 New Sd, Inc. Accelerometer and process for its manufacture
GB9416683D0 (en) * 1994-08-18 1994-10-19 British Tech Group Accelerometer
US6046840A (en) * 1995-06-19 2000-04-04 Reflectivity, Inc. Double substrate reflective spatial light modulator with self-limiting micro-mechanical elements
US6183097B1 (en) 1999-01-12 2001-02-06 Cornell Research Foundation Inc. Motion amplification based sensors
US6401536B1 (en) * 2000-02-11 2002-06-11 Motorola, Inc. Acceleration sensor and method of manufacture
US6805008B2 (en) * 2000-06-21 2004-10-19 Input/Output, Inc. Accelerometer with folded beams
US6662658B2 (en) * 2001-01-17 2003-12-16 Honeywell International, Inc. Whiffletree accelerometer
US7428054B2 (en) * 2002-10-15 2008-09-23 University Of Maryland Micro-optical sensor system for pressure, acceleration, and pressure gradient measurements
US7137299B2 (en) * 2005-04-21 2006-11-21 Northrop Grumman Corporation Fiber optic accelerometer
US7583390B2 (en) * 2006-03-02 2009-09-01 Symphony Acoustics, Inc. Accelerometer comprising an optically resonant cavity
CN101443629B (en) * 2006-03-10 2015-12-02 大陆-特韦斯贸易合伙股份公司及两合公司 There is the speed probe of articulated beam
CN101131354A (en) * 2006-08-23 2008-02-27 中国科学院微电子研究所 Micro-cantilever sensor with triangular structure and manufacturing method thereof
CA2569159C (en) * 2006-11-28 2015-01-13 Nanometrics Inc. Inertial sensor
US20080289429A1 (en) * 2007-05-22 2008-11-27 Zhou Tiansheng Fiber optic mems seismic sensor with mass supported by hinged beams
WO2008156018A1 (en) * 2007-06-18 2008-12-24 Alps Electric Co., Ltd. Capacitance type acceleration sensor
US7661313B2 (en) * 2007-11-05 2010-02-16 The United States Of America As Represented By The Secretary Of The Navy Acceleration strain transducer
CN101271124B (en) * 2008-05-16 2010-09-29 中国科学院上海微系统与信息技术研究所 L-beam piezoresistance type micro-accelerometer and production method thereof
JP5431076B2 (en) * 2009-09-03 2014-03-05 日本発條株式会社 Slide structure for vehicle seat
JP2011153836A (en) * 2010-01-26 2011-08-11 Seiko Epson Corp Acceleration sensor, and accelerometer
CN101858929B (en) * 2010-05-21 2012-09-05 中国科学院上海微系统与信息技术研究所 Capacitive micro-acceleration sensor with symmetrically combined elastic beam structure and production method thereof
US8904867B2 (en) * 2010-11-04 2014-12-09 Qualcomm Mems Technologies, Inc. Display-integrated optical accelerometer
CN102128953B (en) * 2010-12-10 2012-10-17 中国科学院上海微系统与信息技术研究所 Capacitive micro-acceleration sensor with symmetrically inclined folded beam structure
GB2498520A (en) * 2012-01-13 2013-07-24 Secr Defence Accelerometer

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1245960A2 (en) * 2001-02-26 2002-10-02 Sagem S.A. Vibrating beam accelerometer
US20040237648A1 (en) * 2003-06-02 2004-12-02 Jones Richard Todd Optical accelerometer or displacement device using a flexure system

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CN104169724A (en) 2014-11-26
CN104169724B (en) 2016-12-07
JP2015503759A (en) 2015-02-02
JP6082028B2 (en) 2017-02-15
US9470527B2 (en) 2016-10-18
GB201200521D0 (en) 2012-02-29
HK1203628A1 (en) 2015-10-30
EP2802882A1 (en) 2014-11-19
US20140352432A1 (en) 2014-12-04
GB2498454B (en) 2016-06-22
GB2498454A (en) 2013-07-17
GB2498520A (en) 2013-07-24
GB201300511D0 (en) 2013-02-27

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