Three-axis Inertial Measurement Unit
Libraries:
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).
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.
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
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' |
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]' |
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 scalar, 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 as 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 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.
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
See Also
Three-axis Gyroscope (Aerospace Blockset) | Three-axis Accelerometer (Aerospace Blockset)
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