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Arrow Brasil Rodrigo Rodrigues Field Application Engineer Rodrigo.rodrigues@arrowbrasil.com.br F:+55 11 3613-9331 Date: 30/01/2014 TM 2
State-of-the-art review Introduction How a Gyro Works Performance and Applications Fusion with Other Sensors FXAS2100 Enablement Conclusions and Questions TM 3
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3 DOF: A single particle movement in just the three dimensions;no rotation 3-axis accelerometer 6 DOF: Motion of a rigid body in three-dimensional space, namely the ability to move forward/backward, up/down, left/right combined with rotation about three perpendicular axes. Movement along each of the three axes is independent of each other and independent of the rotation about any of these axes 3-axis accelerometer plus 3-axis magnetometer OR 3-axis accelerometer plus 3-axis gyroscope TM 5
9 DOF: Incorporation of motion sensors for relative linear and rotational acceleration and a magnetometer for absolute direction 3-axis accelerometer plus 3-axis magnetometer plus 3-axis gyroscope 10 DOF: 3-axis accelerometer plus 3-axis magnetometer plus 3-axis gyroscope plus either a pressure or temperature sensor Dead Reckoning The process of estimating one's current position based upon a previously determined position and advancing that position based upon known or estimated speeds over elapsed time, and course A disadvantage of dead reckoning is that since new positions are calculated solely from previous positions, the errors of the process are cumulative, so the error in the position fix grows with time TM 6
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An accelerometer sense straight line motion (linear motion) Measured in m/s 2 or g A Gyro senses rotation angular rate Measured in deg/s Earth rotation: 0.004 o /s TM 8
Input angular rate ( ) Coriolis Force A fictional force on a moving object when observed on a rotating frame. The Coriolis force scales with the angular velocity of the frame. Angular rate ( ), drive motion (V d ) and Coriolis force (Fc) are always located on there axes orthogonal to each other. Fc 2 m Vr Drive Motion Coriolis Force This is where the confusion might begin. We called XY gyro with the sensing direction is in Z- axis while Z gyro with sensing direction in XY direction. Coriolis Force Input Rotation Drive Velocity Y (V d ) F 2 m c V d TM Z ( ) 9 X (Fc) Coriolis force causes spiral motion in Hurricanes
Three types of Gyros: Spinning Mass (Gimbal) -tilting produces precession Impractical in MEMS Optical measure time differences in laser paths Very expensive, but also the best performance Vibrating based on Coriolis effect The most common TM 10
Four main components: Proof mass Elastic springs Drive (actuation) system Sensing method Proof mass is put into oscillation (x-axis) Sensitive to angular rotation in the z-axis Induced Coriolis acceleration (y- axis) TM 11
DAU Drive actuation unit, DMU Drive measurement unit Goal is to maintain an oscillation with large and constant amplitude to provide enough Coriolis force for sensing the angular rate Comb drive is natural choice for DAU and DMU - Capable of large travel range with linear force A high Q system is preferred (vacuum package) - Close looped and positive feedback system with amplitude control (AGC) to enable oscillation - Two port differential drive (push/pull) often used - Travel amplitude is magnified by Q-factor (4000 20,000) times at resonance TM 12
SMU sense measurement unit, FFU force feedback unit Goal is to convert Coriolis force into sense displacement, into a different capacitance change - Sense displacement is also an oscillatory motion! - Coriolis force will mix (amplitude-modulate) the angular rate (low frequency) with drive velocity (high frequency carrier) - Demodulation is require to extract the angular rate information from Capacitive sensing similar to accelerometer in terms of MEMS structure - Gap closing parallel plate electrodes TM 13
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Governed by noise Drifting over time/temperature TM 15
Operating range (Full scale range) Bias (Zero rate output ZRO) or Offset Angle Random Walk (white noise) Bias Instability ( o /hr) (1/f, flicker noise) Rate Random Walk (1/f 2 noise) TCO Scale factor (sensitivity) Accuracy (trim error, scale factor stability) Linearity Cross-axis TCS Noise, resolution Turn on time Linear/angular vibration/acoustic sensitivity Shock resistance (1/g, 1/gxg) TM 16
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Segway Scooter Uses five MEMS gyroscopes for tilt and rotation detection. TM 20
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Accelerometer + Magnetometer Fused Data Accelerometer plus magnetometer can provide device orientation and magnetic heading. A magnetometer can also be used as a virtual gyro in certain situations (magnetically clean and stable environment). Major weakness of this sensor pair is its sensitivity to linear acceleration, which leads to errors in both orientation and heading. Accelerometer + Gyroscopes Fused Data Accelerometer can help stabilize the drift in the gyroscope output data Rotation and linear acceleration can be separated Major weakness of this pair is the lack of an absolute heading reference Accelerometer + Gyroscope + Magnetometer Fused Data This combination of sensors can overcome the inherent limitations of each of the previous sensor pairings as their error sources (deficiencies) complement each other. Accelerometer + Gyroscope + Magnetometer + Pressure Fused Data This combination of sensors further improves on the previous pair with the addition of elevation. This is essential for use within buildings to sense the floor you are on. The pressure sensor can also be used to enable weather prediction. TM 23
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Sensor Adapter Board for Demonstration FXCL950000 tools for Sensor Hub and gyro applications 9-Axis DIP for Prototyping Xtrinsic ISF Gyro Adapters available TM 25
High Demo of key functionality ODR, FS, HPF, Sample Time, Data logger TM 26
Q&A Rodrigo Rodrigues Field Application Engineer Rodrigo.rodrigues@arrowbrasil.com.br F:+55 11 3613-9331 Date: 30/01/2014 TM 27
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