Inertial Sensing with Accelerometers and Gyroscopes€¦ · Accelerometer Model Ref: G. Zhang,...

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ECE 5900/6900 Fundamentals of Sensor Design Dr. Suketu Naik

ECE 5900/6900: Fundamentals of Sensor Design

Lecture 7Inertial Sensing with

Accelerometers and Gyroscopes

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Inertial Sensing

Q: What are we measuring?

A: Acceleration (accelerometers) and

Rate of Rotation or Angular Velocity (gyroscopes)

SI units: m/s2 (acceleration), rad/s (gyro)

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Inertial Sensing

Accelerometers

Analog Devices ADXL337

Gyroscopes

Texas Instruments TLV2772 STMicrelectronics LIS3DH

Ref: http://www.analog.com/media/en/news-marketing-collateral/product-selection-guide/MEMS_Inertial_Sensors_Selection_Tables.pdf

Analog Devices ADXRS646 MEMSIC VG800CA-200Bosch BMG160

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Applications of Accelerometer

Accelerometer can detect acceleration, displacement, tilt (angle of

orientation)

Smartphone: Up/Down, Sideways

Orientation

Ref: http://www.engadget.com/2012/05/22/the-engineer-guy-shows-how-a-smartphone-accelerometer-works/

Machine Vibration Measurement

for Condition Based Monitoring

Medical CPR Device:

measure the rate and depth

of chest compressions

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Applications of Gyroscope

Gyroscope can detect angular rate (angular velocity) or rate of

rotation

Automotive Safety and

controlMouse

Helicopter Inertial Measurement Unit (IMU)

Unmanned Aircraft System

(UAS)IMU

Ships Inertial Navigation

System (INS)

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Types of Magnetic Sensors

Accelerometers

Gyroscopes

Inertial Measurement Unit (IMU)

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Basics of Accelerometer

Measurements performed by Accelerometer

Types of accelerations: Linear acceleration (deceleration),

Vibration (periodic acceleration and deceleration), Shock

(instantaneous acceleration), Tilt (a slow change in position with

respect to gravity)

Measured in g-force: low-g sensing (< 20g, human motion), high-g

sensing (motion in machines, vehicles, airplanes, ships)

Force Change in capacitance Converted to voltage A/D

Microprocessor to correct/perform an action

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Accelerometer: Performance Parameters

Measurement/Linear Range: +/- g

Sensitivity:

Ratio of change in acceleration as input to the output signal

Measured as mV/g for analog output, and LSB/g for digital

output

Zero-g bias level: output level without any acceleration

Noise density: µg/ √(Hz)

Frequency Response or

Bandwidth

Ref: J. Wu, et. al., "A low-noise low-offset capacitive sensing amplifier for a 50-μg/√Hz monolithic CMOS MEMS accelerometer,"

IEEE Solid-State Circuits, vol.39, no.5, pp. 722- 730, May 2004,

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Accelerometer: Performance Parameters

Analog Devices ADXL337 Datasheet

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ADXL337 Schematic

Analog Devices ADXL337 Datasheet

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Evolution of Accelerometer

Analog Devices ADXL Series

Bosch Sensortec Series ASIC

MEMS

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Example of an Accelerometer System

Analog Devices IMU ADIS 16334

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Examples of MEMS Accelerometers

Ref: G. Zhang, “Design and Simulation of a CMOS-MEMS Accelerometer”,

M.S. Thesis, Carnegie Mellon University, May 2008

Ref: K. Sharma, et. al., “Design Optimization of

MEMS Comb Accelerometer”, ASEE Zone 1

Conference, Mar, 2009, West Point, NY

Ref:

http://www.princeton.edu/mae/people/faculty/soboyejo/re

search_group/research/mems/

Operational Principle

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Example of Triaxial MEMS Accelerometer [1/2]

Ref: Design and Analysis of MEMS Accelerometers by D. Serrano, IEEE Sensors 2013

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Example of Triaxial MEMS Accelerometer [2/2]

Ref: Design and Analysis of MEMS Accelerometers by D. Serrano, IEEE Sensors 2013

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Accelerometer Model

Ref: G. Zhang, “Design and Simulation of a CMOS-MEMS Accelerometer”, M.S. Thesis, Carnegie Mellon University, May 2008

Proof mass movement

changes due to the external

force

Movement is measured by

change in capacitance

between proof mass and

fixed electrodes

Common-mode output

signal for half-bridge or full-

bridge configuration

Higher sensitivity with lower

resonant frequency

Change in Voltage given

an acceleration

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Accelerometers

Gyroscopes


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Coriolis Effect

Coriolis effect in action on the atmosphere

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Coriolis Force

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GyroscopeMEMS Gyroscope principles

Proof mass and operational principle

Gyroscopes measure angular velocity or the rate of rotation

x

y

z

Coriolis Force

Gyro on rotating platform

= 2mΩz dr/dtmoving outward

=-2mΩz dr/dt moving inward

at

ar

Fc Fc

Ωz (constant)

Sense mode

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Gyroscope: Functional Operation

Capacitive sensing

Proof mass is driven by a periodic sinusoidal drive signal

On a rotating platform, Coriolis effect causes motion in the sense axis

Capacitance between the proof mass and sense plate(s) changes Sense electronics detect the Coriolis acceleration from the change in capacitance between the proof mass and the sense plate

The rate of rotation is derived from the Coriolis acceleration and the drive velocity

Digital output: Sense Electronics generate a pulse stream with frequency proportional to the acceleration Analog Output: Sense Electronics generate a voltage output proportional to the acceleration

Input AngularRate [deg/s]

Output Voltage(mV) Scale Factor

[mV/deg/s]

Comb Capacitor

Gyroscope TransferFunction

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Feb 22, 2011

Gyroscope: Performance Parameters

Zero-rate-output (ZRO)of gyroscope

Angular rate input range

Bandwidth (drive-mode) in which the gyroscope can produce a meaningful output (sense-mode)

Noise floorin the output ofgyroscope

Drive and sense electronics have an impact on the performance

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Gyroscope Model

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Examples of MEMS Gyroscope

Ref: C. Acar, et. al., “An Approach for Increasing Drive-Mode Bandwidth of MEMS Vibratory Gyroscopes”, Journal of MEMS, vol .14, no. 3, 2005

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Ref: S. Bhave, et. al., “An Integrated, Vertical-drive, In-plane-sense Microgyroscope”, 12th International Conference in Solid State

Sensors, Boston, June, 2003


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Ref: S. Alper, et. al., “A high-performance silicon-on-insulator MEMS gyroscope operating at atmospheric pressure”, Sensors and Actuators A, vol.

135, pp. 34-42, 2007


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Accelerometers

Gyroscopes


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IMUs provide motion, position, and navigational

sensing from a single device over more than 6 DOF

IMUs sense translational movement in three perpendicular axes

(surge, heave, sway) and rotational movement about three

perpendicular axes (roll, pitch, yaw)

Ref: http://www.instructables.com/id/9-Degrees-of-Freedom-IMU/

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Inertial Measurement Unit (IMU)IMU on PCBRef: ETH Zurich

GPS aided- altitude heading reference

system Ref: Moog

IMU: Gyroscopes are integrated with accelerometers,

magnetometers and GPS receivers

Silicon MEMS IMU by Silicon Sensing

9 Degrees of Freedom (DOF) IMU by

Sparkfun*

Ref: Magnetometers provide additional 3 DOF by compensating for change in magnetic field in Yaw (heading) measurement

https://sites.google.com/site/myimuestimationexperience/sensors/magnetometer

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IMU in UAV/UAS

Inertial Sensing with Accelerometers and Gyroscopes€¦ · Accelerometer Model Ref: G. Zhang,...

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