Applications: Angular Rate Sensors CSE 495/595: Intro to Micro- and Nano- Embedded Systems Prof. Darrin Hanna

Applications:Angular Rate Sensors

CSE 495/595: Intro to Micro- and Nano- Embedded Systems

Prof. Darrin Hanna

Angular Rate Sensors

Angular Rate Sensors – Good Ole Gyroscopes

• large angular momentum that is proportional to the heavy mass of the flywheel• substantial size• high rate of spin

• Won’t work in MEMS


• Coriolis Effect• deflection of a moving object in a rotating frame of reference

• Coriolis acceleration

• a = 2Ω x v

• V is the velocity of the particle in the rotating system• ω is the angular velocity vector of the rotating system

• magnitude equal to the rotation rate• points in the direction of the axis of rotation.

• Multiply by the mass of the object to produce the Coriolis force.



• Coriolis acceleration is perpendicular both to the direction of the velocity of the moving mass and to the rotation axis

• if the velocity is zero, the Coriolis acceleration is zero • if the velocity is parallel to the rotation axis, the Coriolis acceleration is zero • if the velocity is perpendicularly inward to the axis, the acceleration will follow the direction of rotation (i.e., be perpendicular to the rotation axis and the particle velocity) • if the velocity is following the rotation, the acceleration will be (perpendicularly) outward from the axis


• Two tines of the fork normally vibrate in opposite directions in the plane of the fork

• flexural mode• Rotating it: Coriolis acceleration subjects the tips to a displacement perpendicular to the primary mode of oscillation, forcing each tip to describe an elliptical path.

• excites a secondary vibration torsionalmode around the stem with energy transferred from the primary flexural vibration of the tines.



• Main specifications of an angular-rate sensor• full-scale range (expressed in º/s or º/hr)• scale factor or sensitivity [V/(º/s)]• noise, °/(s ∙ (Hz)1/2) • bandwidth (Hz)• resolution (º/s)• dynamic range (dB)

• dynamic range and resolution are a function of noise and bandwidth.

• Short- and long-term drift of the output, known as bias drift (º/s) or (º/hr)• withstand shocks of at least 1,000G.


• Primary and secondary mode resonance

Delphi Delco Electronic Systems




• Ring shell is anchored at its center to the substrate• deforms as it vibrates through a full cycle from a circle to an ellipse, back to a circle, then to an ellipse rotated at right angles to the first ellipse, then back to the original circle



• Points on the shell that remain stationary are called nodes • Points that undergo maximal deflection are called antinodes.• The nodes and antinodes form a vibration pattern—or standing-wave pattern—around the ring• The pattern is characteristic of the resonance mode



• Because of symmetry, a ring shell possesses two frequency-degenerate resonant modes with their vibration patterns offset by 45º with respect to each other.

• The nodes of the first mode coincide with the antinodes of the second mode.



• The external control electronics excite only one of the two modes—the primary mode. • Under rotation, the Coriolis effect excites the second resonance mode, and energy transfer occurs between the two modes. • The deflection amplitude builds up at the antinodes of the second mode—also, the nodes of the first mode.



• The overall vibration becomes a linear combination of the two modes with a new set of nodes and antinodes forming a vibration pattern rotated with respect to the pattern of the primary mode.



• Open-loop configuration• deflection amplitude at the nodes and antinodes is a measure of the angular rate of rotation. • the angular shift of the vibration pattern is another measure.

• Closed-loop configuration• electrostatic actuation by a feedback voltage applied to the excitation electrodes • nulls the secondary mode and maintains a stationary vibration pattern• Angular rate is directly proportional to this feedback voltage.



• 32 electrodes positioned around the suspended ring shell• of this eight electrodes positioned at 45º intervals—at the nodes and antinodes—capacitively sense the deformation of the ring shell

• A phased-locked loop (PLL) drives the ring into resonance through the electrostatic drive electrodes

• maintains a lock on the frequency



• Preprocessed CMOS control circuitry• Electroplated nickel ring shell

• 15 to 50 µm thick• Packaging completed in vacuum

• minimize air damping of the resonant ring • provide a large quality factor



• Specifications over the temperature range of –40° to +125ºC• resolution of 0.5º/s • bandwidth of 25 Hz

• limited by noise in the electronic circuitry• nonlinearity in a rate range of ±100 º/s is less than 0.2º/s• sensor survives the standard automotive shock test

• a drop from a height of one meter



Documents

Applications: Angular Rate Sensors CSE 495/595: Intro to Micro- and Nano- Embedded Systems Prof. Darrin Hanna