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 Wont work in MEMS

Angular Rate Sensors Coriolis Effect deflection of a moving object in a rotating frame of reference Coriolis acceleration a = 2 x v V is the velocity of the particle in the rotating system 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. Angular Rate Sensors Angular Rate Sensors 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

Angular Rate Sensors 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 torsional mode around the stem with energy transferred from the primary flexural vibration of the tines. Angular Rate Sensors Angular Rate Sensors Main specifications of an angular-rate sensor

full-scale range (expressed in /s or /hr) scale factor or sensitivity [V/(/s)] noise, /(s (Hz)1/2) bandwidth (Hz) resolution (/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

(/s) or (/hr) withstand shocks of at least 1,000G. Angular Rate Sensors Delphi Delco Electronic Systems Primary and secondary mode resonance Angular Rate Sensors

Delphi Delco Electronic Systems Angular Rate Sensors 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

Angular Rate Sensors Delphi Delco Electronic Systems 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 patternor standingwave patternaround the ring The pattern is characteristic of the resonance mode Angular Rate Sensors

Delphi Delco Electronic Systems Because of symmetry, a ring shell possesses two frequencydegenerate resonant modes with their vibration patterns offset by 45 with respect to each other. The nodes of the first mode coincide with the antinodes of the second mode. Angular Rate Sensors

Delphi Delco Electronic Systems 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 modealso, the nodes of the first mode. Angular Rate Sensors

Delphi Delco Electronic Systems 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. Angular Rate Sensors Delphi Delco Electronic Systems

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. Angular Rate Sensors Delphi Delco Electronic Systems 32 electrodes positioned around the suspended ring shell of this eight electrodes positioned at 45 intervalsat the nodes and antinodescapacitively 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 Angular Rate Sensors Delphi Delco Electronic Systems Preprocessed CMOS control circuitry Electroplated nickel ring shell

15 to 50 m thick Packaging completed in vacuum minimize air damping of the resonant ring provide a large quality factor Angular Rate Sensors Delphi Delco Electronic Systems Specifications over the temperature range of 40 to +125C

resolution of 0.5/s bandwidth of 25 Hz limited by noise in the electronic circuitry nonlinearity in a rate range of 100 /s is less than 0.2/s sensor survives the standard automotive shock test a drop from a height of one meter Angular Rate Sensors