Implement three-axis inertial measurement unit (IMU)

GNC/Navigation

The Three-Axis Inertial Measurement Unit block implements an inertial measurement unit (IMU) containing a three-axis accelerometer and a three-axis gyroscope.

For a description of the equations and application of errors, see the Three-Axis Accelerometer block and the Three-Axis Gyroscope block reference pages.

**Units**Specifies the input and output units:

Units Acceleration Length `Metric (MKS)`

Meters per second squared Meters `English`

Feet per second squared Feet **IMU location**The location of the IMU, which is also the accelerometer group location, is measured from the zero datum (typically the nose) to aft, to the right of the vertical centerline and above the horizontal centerline. This measurement reference is the same for the center of gravity input. The units are in selected length units.

**Update rate (sec)**Specify the update rate of the accelerometer and gyroscope. An update rate of 0 will create a continuous accelerometer and continuous gyroscope. If noise is selected and the update rate is 0, then the noise will be updated at the rate of 0.1. The units of update rate are seconds.

If you:

Update this parameter value to 0 (continuous)

Configure a fixed-step solver for the model

you must also select the

**Automatically handle rate transition for data transfer**check box in the**Solver**pane. This check box enables the software to handle rate transitions correctly.**Second order dynamics for accelerometer**Select to apply second-order dynamics to acceleration readings.

**Accelerometer natural frequency (rad/sec)**The natural frequency of the accelerometer. The units of natural frequency are radians per second.

**Accelerometer damping ratio**The damping ratio of the accelerometer. A dimensionless parameter.

**Accelerometer scale factors and cross-coupling**The 3-by-3 matrix used to skew the accelerometer from body-axis and to scale accelerations along body-axis.

**Accelerometer measurement bias**The three-element vector containing long-term biases along the accelerometer axes. The units are in selected acceleration units.

**Accelerometer lower and upper output limits**The six-element vector containing three minimum values and three maximum values of acceleration in each of the accelerometer axes. The units are in selected acceleration units.

**Gyro second order dynamics**Select to apply second-order dynamics to gyroscope readings.

**Gyro natural frequency (rad/sec)**The natural frequency of the gyroscope. The units of natural frequency are radians per second.

**Gyro damping ratio**The damping ratio of the gyroscope. A dimensionless parameter.

**Gyro scale factors and cross-coupling**The 3-by-3 matrix used to skew the gyroscope from body axes and to scale angular rates along body axes.

**Gyro measurement bias**The three-element vector containing long-term biases along the gyroscope axes. The units are in radians per second.

**G-sensitive bias**The three-element vector contains the maximum change in rates due to linear acceleration. The units are in radians per second per g-unit.

**Gyro lower and upper output limits**The six-element vector containing three minimum values and three maximum values of angular rates in each of the gyroscope axes. The units are in radians per second.

**Noise on**Select to apply white noise to acceleration and gyroscope readings.

**Noise seeds**The scalar seeds for the Gaussian noise generator for each axis of the accelerometer and gyroscope.

**Noise power**The height of the PSD of the white noise for each axis of the accelerometer and gyroscope.

Input | Dimension Type | Description |
---|---|---|

First | Three-element vector | Contains the actual accelerations in body-fixed axes, in selected units. |

Second | Three-element vector | Contains the angular rates in body-fixed axes, in radians per second. |

Third | Three-element vector | Contains the angular accelerations in body-fixed axes, in radians per second squared. |

Fourth | Three-element vector | Contains the location of the center of gravity, in selected units. |

Fifth | Three-element vector | Contains the gravity in body axis, in selected units. |

Output | Dimension Type | Description |
---|---|---|

First | Three-element vector | Contains the measured accelerations from the accelerometer, in selected units. |

Second | Three-element vector | Contains the measured angular rates from the gyroscope, in radians per second. |

Vibropendulous error, hysteresis affects, anisoelastic bias and anisoinertial bias are not accounted for in this block. Additionally, this block is not intended to model the internal dynamics of different forms of the instrument.

See `asbhl20`

for
an example of this block.

Rogers, R. M., *Applied Mathematics in Integrated
Navigation Systems*, AIAA Education Series, 2000.