IMU Alignment, How to find where X-axis is oriented when IMU is not fixed in place?

[SK.4]

Hi,

I am working on ASM330LHH IMU module. And I want to understand process or steps to get IMU alignment and calibration information.

I have following queries

1. IMU is kept in board which can be placed in any orientation. Now, I do not know whether the X-axis of car is aligned with X-axis of IMU and same for other axes. Is there any method or process that we need to follow ? Or we have to make sure IMU orientation before using it.
2. What is difference between IMU alignment and IMU calibration

Regards,

Sagar

[Eleon BORLINI]

Hi @SK.4​ , the ASM330LHH axis orientation depends on the direction of the mounted device on the application board. You can understand the initial device orientation by reading the axis value and calculating the g vector direction from its x, y and z components: so, you basically have to make sure IMU orientation before using it. The IMU calibration procedure, especially the one implemented in the ST MEMS libraries (such as the MotionAC accelerometer calibration and the MotionGC gyroscope calibration in the X-CUBE-MEMS1 function pack) includes the device offset cancellation to avoid error propagation during the data integration in time of the acceleration and the angular velocity (to get the device position in space). Without an absolute reference (such as the magnetometer that gives the device position related to the magnetic field direction of the Earth), you have to refer all the data to the device initial, calibrated, position. Regards