Three-axis Inertial Measurement Unit

Implement three-axis inertial measurement unit (IMU)

• Library:

• Vehicle Dynamics Blockset / Sensors

• 

Description

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 Three-axis Accelerometer (Aerospace Blockset) and Three-axis Gyroscope (Aerospace Blockset).

Limitations

• Vibropendulous error, hysteresis affects, anisoelastic bias and anisoinertial bias are not accounted for in this block.

• This block is not intended to model the internal dynamics of different forms of the instrument.

Ports

Input

A_b — Actual accelerations

three-element vector

Actual accelerations in body-fixed axes, specified as a three-element vector, in selected units.

Data Types: double

w — Angular rates

three-element vector

Angular rates in body-fixed axes, specified as a three-element vector, in radians per second.

Data Types: double

w_dot — Angular accelerations

three-element vector

Angular accelerations in body-fixed axes, specified as a three-element vector, in radians per second squared.

Data Types: double

CG — Location of center of gravity

three-element vector

Location of the center of gravity, specified as a three-element vector, in selected units.

Data Types: double

g — Gravity

three-element vector

Gravity in body axis, specified as a three-element vector, in selected units.

Data Types: double

Output

A_meas — Measured accelerations

three-element vector

Measured accelerations from the accelerometer, specified as a three-element vector, in selected units.

Data Types: double

w_meas — Measured angular rates

three-element vector

Measured angular rates from the gyroscope, specified as a three-element vector, in radians per second.

Data Types: double

Parameters

Main

Units — Units

Metric (MKS) (default) | English

Input and output units, specified as:

Units	Acceleration	Length
Metric (MKS)	Meters per second squared	Meters
English (British Imperial)	Feet per second squared	Feet

Programmatic Use

Block Parameter: units

Type: character vector

Values: 'Metric (MKS)' | 'English'

Default: 'Metric (MKS)'

IMU location — IMU location

[0 0 0] (default) | three-element vector

The location of the IMU, which is also the accelerometer group location, from the vehicle center of gravity, along the vehicle-fixed axis. This measurement reference is the same for the center of gravity input. The units are in selected length units.

Programmatic Use

Block Parameter: imu

Type: character vector

Values: three-element vector

Default: '[0 0 0]'

Update rate — Update rate

0 (default) | real, double scalar

Update rate of the accelerometer and gyroscope, specified as a real, double scalar, in seconds. An update rate of 0 creates a continuous accelerometer and continuous gyroscope. If you select the Noise on parameter and the update rate is 0, the block updates the noise at a rate of 0.1.

Tip

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.

Programmatic Use

Block Parameter: a_Ts

Type: character vector

Values: real, double scalar

Default: '0'

Accelerometer

Second order dynamics for accelerometer — Second-order dynamics

on (default) | off

To apply second-order dynamics to acceleration readings, select this check box.

Programmatic Use

Block Parameter: dtype_a

Type: character vector

Values: 'on' | 'off'

Default: 'on'

Accelerometer natural frequency (rad/sec) — Accelerometer natural frequency

190 (default) | real, double scalar

Natural frequency of the accelerometer, specified as a real, double scalar, in radians per second.

Programmatic Use

Block Parameter: w_a

Type: character vector

Values: real, double scalar

Default: '190'

Dependencies

To enable this parameter, select Second order dynamics for accelerometer.

Accelerometer damping ratio — Accelerometer damping ratio

0.707 (default) | real, double scalar

Damping ratio of the accelerometer, specified as a real, double scalar, with no dimensions.

Programmatic Use

Block Parameter: z_a

Type: character vector

Values: real, double scalar

Default: '0.707'

Dependencies

To enable this parameter, select Second order dynamics for accelerometer.

Accelerometer scale factor and cross-coupling — Scale factor and cross coupling

[1 0 0; 0 1 0; 0 0 1] (default) | 3-by-3 matrix

Scale factor and cross-coupling, specified as a 3-by-3 matrix, to skew the accelerometer from body axes and to scale accelerations along body axes.

Programmatic Use

Block Parameter: a_sf_cc

Type: character vector

Values: 3-by-3 matrix

Default: '[1 0 0; 0 1 0; 0 0 1]'

Accelerometer measurement bias — Accelerometer measurement bias

[0 0 0] (default) | three-element vector

Long-term biases along the accelerometer axes, specified as a three-element vector, in selected acceleration units.

Programmatic Use

Block Parameter: a_bias

Type: character vector

Values: three-element vector

Default: '[0 0 0]'

Accelerometer upper and lower limits — Minimum and maximum values of acceleration

[-inf -inf -inf inf inf inf] (default) | six-element vector

Three minimum values and three maximum values of acceleration in each of accelerometer axes, specified as a six-element vector, in selected acceleration units.

Programmatic Use

Block Parameter: a_sat

Type: character vector

Values: six-element vector

Default: '[-inf -inf -inf inf inf inf]'

Gyroscope

Second-order dynamics for gyro — Gyroscope second-order dynamics

on (default) | off

To apply second-order dynamics to gyroscope readings, select this check box.

Programmatic Use

Block Parameter: dtype_g

Type: character vector

Values: 'on' | 'off'

Default: 'on'

Gyro natural frequency (rad/sec) — Gyroscope natural frequency

190 (default) | real, double scalar

Natural frequency of the gyroscope, specified as a real, double scalar, in radians per second.

Programmatic Use

Block Parameter: w_g

Type: character vector

Values: real, double scalar

Default: '190'

Dependencies

To enable this parameter, select Second-order dynamics for gyro.

Gyro damping ratio — Gyroscope damping ratio

0.707 (default) | real, double scalar

Damping ratio of the gyroscope, specified as a real, double scale, with no dimensions.

Programmatic Use

Block Parameter: z_g

Type: character vector

Values: real, double scalar

Default: '0.707'

Dependencies

To enable this parameter, select Second-order dynamics for gyro.

Gyro scale factors and cross-coupling — Gyroscope scale factors and cross-coupling

[1 0 0; 0 1 0; 0 0 1] (default) | 3-by-3 matrix

Gyroscope scale factors and cross-coupling, specified as a 3-by-3 matrix, to skew the gyroscope from body axes and to scale angular rates along body axes.

Programmatic Use

Block Parameter: g_sf_cc

Type: character vector

Values: 3-by-3 matrix

Default: '[1 0 0; 0 1 0; 0 0 1]'

Gyro measurement bias — Gyroscope measurement bias

[0 0 0] (default) | three-element vector

Long-term biases along the gyroscope axes, specified a three-element vector, in radians per second.

Programmatic Use

Block Parameter: g_bias

Type: character vector

Values: three-element vector

Default: '[0 0 0]'

G-sensitive bias — Maximum change in rates

[0 0 0] (default) | three-element vector

Maximum change in rates due to linear acceleration, specified as a three-element vector, in radians per second per g-unit.

Programmatic Use

Block Parameter: g_sens

Type: character vector

Values: three-element vector

Default: '[0 0 0]'

Gyro upper and lower limits — Minimum and maximum values of angular rates

[-inf -inf -inf inf inf inf] (default) | six-element vector

Three minimum values and three maximum values of angular rates in each of the gyroscope axes, specified as a six-element vector, in radians per second.

Programmatic Use

Block Parameter: g_sat

Type: character vector

Values: six-element vector

Default: '[-inf -inf -inf inf inf inf]'

Noise

Noise on — White noise

on (default) | off

To apply white noise to acceleration and gyroscope readings, select this check box.

Programmatic Use

Block Parameter: a_rand

Type: character vector

Values: 'on' | 'off'

Default: 'on'

Noise seeds — Noise seeds

[23093 23094 23095 23096 23097 23098] (default) | six-element vector

Scalar seeds for the Gaussian noise generator for each axis of the accelerometer and gyroscope, specified as a six-element vector.

Programmatic Use

Block Parameter: a_seeds

Type: character vector

Values: six-element vector

Default: '[23093 23094 23095 23096 23097 23098]'

Dependencies

To enable this parameter, select Noise on.

Noise power — Noise power

[0.001 0.001 0.001 0.0001 0.0001 0.0001] (default) | six-element vector

Height of the power spectral density (PSD) of the white noise for each axis of the accelerometer and gyroscope, specified as a six-element vector, in:

• (m/s²)/Hz for Metric (MKS)

• (ft/s²)/Hz for English

Programmatic Use

Block Parameter: a_pow

Type: character vector

Values: six-element vector

Default: '[0.001 0.001 0.001 0.0001 0.0001 0.0001]'

Dependencies

To enable this parameter, select Noise on.

Model Examples

Double Lane Change Reference Application

Simulate a full vehicle dynamics model undergoing a double lane change maneuver standard ISO 3888-2. Use for vehicle dynamics ride and handling analysis and chassis controls development, including yaw stability and lateral acceleration limits.

Open Example

References

[1] Rogers, R. M., Applied Mathematics in Integrated Navigation Systems, AIAA Education Series, 2000.

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using Simulink® Coder™.

Version History

Introduced in R2020a