Back to results
US 10,241,128 B2Granted
Accelerometer control
AssigneeAtlantic Inertial Systems Limited
InventorsAlan Richard Malvern, Kiran Harish
Life of this patent
Estimating the term…
Abstract
A closed loop method of controlling a capacitive accelerometer uses two servo loops. A Vcrit servo loop uses an output signal (S2) modulated by a sine wave signal (S1). The Vcrit control signal adjusts the magnitude of the PWM drive signals applied to the fixed capacitor electrodes of the accelerometer, thereby optimising open loop gain.
Claims15
A closed loop method of controlling a capacitive accelerometer comprising a proof mass moveable relative to first and second fixed capacitor electrodes, the method comprising:
- applying in-phase and anti-phase pulse width modulation (PWM) drive signals to the first and second fixed capacitor electrodes with an adjustable mark/space ratio;
- operating in closed loop so that mechanical inertial forces are balanced by electrostatic forces to maintain an operating point of the proof mass at a null position;
- detecting an output signal from the accelerometer representing a displacement of the proof mass from the null position to provide a error signal;
- using the error signal so as to vary the mark/space ratio of the PWM drive signals so that the output signal from the accelerometer is proportional to an acceleration;
- adding a sine wave modulation at a frequency f to the output signal from the proof mass before providing the error signal;
- further detecting a phase shift resulting from the sine wave modulation at the frequency f so as to recognise a critical drive signal magnitude Vcrit representing the null position;
- and
- providing a Vcrit control signal so as to adjust a magnitude of the PWM drive signals applied to the first and second fixed capacitor electrodes, or applying a separate, adjustable drive signal to at least one further fixed capacitor electrode, to lock to the Vcrit and thereby optimise open loop gain.
5 more elements
An accelerometer closed loop control system comprising:
- a capacitive accelerometer comprising a proof mass moveable relative to first and second fixed capacitor electrodes;
- a pulse width modulation (PWM) generator arranged to apply in-phase and anti-phase PWM drive signals to the first and second fixed capacitor electrodes with an adjustable mark/space ratio;
- a PWM servo operating in closed loop so that mechanical inertial forces are balanced by electrostatic forces to maintain an operating point of the proof mass at a null position;
- an output signal detector arranged to detect an output signal from the accelerometer representing a displacement of the proof mass from the null position to provide an error signal, wherein the PWM servo uses the error signal to vary the mark/space ratio of the PWM drive signals so that the output signal from the accelerometer is proportional to an acceleration;
- a modulator arranged to add a sine wave modulation at a frequency f to the output signal before providing the error signal to the PWM servo;
- and
- a Vcrit servo arranged to:
- (i) detect a phase shift resulting from the sine wave modulation at the frequency f so as to recognise a critical drive signal magnitude Vcrit representing the null position;
- and
- (ii) provide a Vcrit control signal to adjust a magnitude of the PWM drive signals applied to the first and second fixed capacitor electrodes, or to apply a separate drive signal to a further fixed capacitor electrode, to lock to the Vcrit and thereby optimise open loop gain.
7 more elements
Dependencies are inferred from the claim text.