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AP_NavEKF: Modify method used to check for vibration errors 

This method checks for consistency between accelerometer readings and switches to the unit with the lowest vibration of the difference exceeds 0.3g
The threshold of 1.7 m/s/s corresponds to a maximum tilt error of 10 deg assuming one IMU is good, one is bad and the EKF is using the bad IMU.
This commit is contained in:
Paul Riseborough 2015-08-03 17:41:30 +10:00 committed by Randy Mackay
parent a7569e3a61
commit 12e884ba6b
2 changed files with 32 additions and 32 deletions
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57
libraries/AP_NavEKF/AP_NavEKF.cpp
View File

@ -2087,10 +2087,10 @@ void NavEKF::FuseVelPosNED()
} else {
IMU1_weighting = 0.5f;
}
// If either of the IMU's has experienced clipping within the last two filter time constants (approx 0.4 seconds) we apply a hard switch away from that sensor
// to the IMU with the lower
if (clipRateFilt1 > 0.1f || clipRateFilt2 > 0.1f) {
if (clipRateFilt1 > clipRateFilt2) {
// If the difference between IMU readings is greater than 1.7 m/s/s in length, then hard switch to the IMU with the lowest noise
// The maximum tilt error that can occur due to a 1.7 m/s/s error is 10 degrees
if (accelDiffLengthFilt > 1.7f) {
if (imuNoiseFiltState1 > imuNoiseFiltState2) {
IMU1_weighting = 0.0f;
} else {
IMU1_weighting = 1.0f;
@ -2241,20 +2241,16 @@ void NavEKF::FuseVelPosNED()
Kfusion[i+23] = Kfusion[i+4]; // IMU1 velNED
Kfusion[i+27] = Kfusion[i+4]; // IMU2 velNED
}
// Don't update Z accel bias values if we have clipping
// we achieve this by setting the corresponding Kalman gains to zero
if (clipRateFilt1 < 0.1f && clipRateFilt2 < 0.1f) {
// no clipping
// Don't update Z accel bias values for an acceleraometer we have hard switched away from
if ((IMU1_weighting >= 0.1f) && (IMU1_weighting <= 0.9f)) {
// both IMU's OK
Kfusion[22] = Kfusion[13];
} else if (clipRateFilt1 >0.1f && clipRateFilt2 > 0.1f) {
// both clipping;
Kfusion[22] = Kfusion[13] = 0.0f;
} else if (clipRateFilt1 > clipRateFilt2) {
// IMU1 clipping
} else if (IMU1_weighting < 0.1f) {
// IMU1 bad
Kfusion[22] = Kfusion[13];
Kfusion[13] = 0.0f;
} else {
// IMU2 clipping
// IMU2 bad
Kfusion[22] = 0.0f;
}
@ -4132,27 +4128,33 @@ void NavEKF::readIMUData()
if (ins.use_accel(0) && ins.use_accel(1)) {
// dual accel mode
// read IMU1 delta velocity data
readDeltaVelocity(0, dVelIMU1, dtDelVel1);
// apply a peak hold decaying envelope filter to the rate of increase if clip events on IMU1
// apply a peak hold 0.2 second time constant decaying envelope filter to the noise length on IMU1
float alpha = 1.0f - 5.0f*dtDelVel1;
clipRateFilt1 = max(float(ins.get_accel_clip_count(0) - lastClipCount1), alpha*clipRateFilt1);
lastClipCount1 = ins.get_accel_clip_count(0);
imuNoiseFiltState1 = max(ins.get_vibration_levels(0).length(), alpha*imuNoiseFiltState1);
// read IMU2 delta velocity data
readDeltaVelocity(1, dVelIMU2, dtDelVel2);
// apply a peak hold decaying envelope filter to the rate of increase if clip events on IMU2
// apply a peak hold 0.2 second time constant decaying envelope filter to the noise length on IMU2
alpha = 1.0f - 5.0f*dtDelVel2;
clipRateFilt2 = max(float(ins.get_accel_clip_count(1) - lastClipCount2), alpha*clipRateFilt2);
lastClipCount2 = ins.get_accel_clip_count(1);
imuNoiseFiltState2 = max(ins.get_vibration_levels(1).length(), alpha*imuNoiseFiltState2);
// Check the length of the vector difference between the two IMU's
float accelDiffLength = (ins.get_accel(0) - ins.get_accel(1)).length();
// apply a LPF filter to the length with a 1.0 second time constant
// the filtered output is used by the inertial strapdown calculation to determine if there is an accelerometer error
alpha = constrain_float(0.5f*(dtDelVel1 + dtDelVel2),0.0f,1.0f);
accelDiffLengthFilt = alpha * accelDiffLength + (1.0f - alpha) * accelDiffLengthFilt;
} else {
// single accel mode - one of the first two accelerometers are unhealthy
// read primary accelerometer into dVelIMU1 and copy to dVelIMU2
readDeltaVelocity(ins.get_primary_accel(), dVelIMU1, dtDelVel1);
// apply a peak hold decaying envelope filter to the rate of increase if clip events on IMU1
float alpha = 1.0f - 5.0f*dtDelVel1;
clipRateFilt1 = max(float(ins.get_accel_clip_count(0) - lastClipCount1), alpha*clipRateFilt1);
lastClipCount1 = ins.get_accel_clip_count(0);
clipRateFilt2 = clipRateFilt1;
dtDelVel2 = dtDelVel1;
dVelIMU2 = dVelIMU1;
}
@ -4728,9 +4730,8 @@ void NavEKF::InitialiseVariables()
yawRateFilt = 0.0f;
yawResetAngle = 0.0f;
yawResetAngleWaiting = false;
const AP_InertialSensor &ins = _ahrs->get_ins();
lastClipCount1 = ins.get_accel_clip_count(0);
lastClipCount2 = ins.get_accel_clip_count(1);
imuNoiseFiltState1 = 0.0f;
imuNoiseFiltState2 = 0.0f;
}
// return true if we should use the airspeed sensor

7
libraries/AP_NavEKF/AP_NavEKF.h
View File

@ -770,10 +770,9 @@ private:
float meaHgtAtTakeOff; // height measured at commencement of takeoff
// monitoring IMU quality
uint32_t lastClipCount1; // previous value of clip counter for IMU 1
uint32_t lastClipCount2; // previous value of clip counter for IMU 2
float clipRateFilt1; // filtered clip rate for IMU 1
float clipRateFilt2; // filtered clip rate for IMU 2
float imuNoiseFiltState1; // peak hold noise estimate for IMU 1
float imuNoiseFiltState2; // peak hold noise estimate for IMU 2
float accelDiffLengthFilt; // filtered length difference between IMU 1 and 2
// states held by optical flow fusion across time steps
// optical flow X,Y motion compensated rate measurements are fused across two time steps