IMU Alignment with Mounting Structures Using CMM and Inclinometers
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Solution Overview
Problem
Existing calibration methods for inertial measurement units (IMUs) are insufficient for precise aerospace applications, where high accuracy in aligning IMU sensing axes with mounting structures is required.
Innovation Solution
The use of systems and methods that calibrate angular relationships between IMU sensing axes and mounting fixtures using advanced equipment such as coordinate measuring machines (CMM), inclinometers, and rate tables, determining rotation matrices to achieve precise alignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If existing calibration methods are used, then the calibration process is simple, but the measurement precision and manufacturing precision are insufficient for aerospace applications
Solution Approach 1:
The calibration process is divided into distinct segments: (1) measuring fixture features with CMM to establish a fixture coordinate system, (2) measuring IMU features with CMM to establish an IMU coordinate system, and (3) calculating the rotation matrix from these two coordinate systems. This segmentation allows each step to be performed with appropriate precision using specialized equipment rather than requiring a single complex calibration system.
Solution Approach 2:
The patent introduces a fixture coordinate system as an intermediary reference frame between the IMU and the vehicle body. The CMM measures both the fixture features and IMU features relative to this common reference, enabling precise determination of the rotation matrix without requiring direct complex measurements between the IMU and vehicle body.
2Manufacturing precision
If manufacturer calibration information is used, then the calibration process is straightforward, but the accuracy and precision are not sufficient for high-precision aerospace applications
Solution Approach 1:
The patent performs preliminary high-precision measurements of both the fixture features and IMU features using a CMM before the IMU is installed in the vehicle. This preliminary characterization creates accurate coordinate systems that can be used later without requiring complex on-site calibration procedures, thereby improving ease of manufacture while maintaining high precision.
Solution Approach 2:
The patent transforms the calibration problem from directly measuring angular relationships to measuring positions of multiple features in 3D space with a CMM. By changing the measurement parameters from direct angular measurements to positional measurements of multiple fiducial features, the system achieves higher precision through the CMM's positional accuracy while simplifying the overall calibration process.
Data Source
AI summary
Systems and methods for aligning inertial measurement units (IMUs) with mounting structures. A system can include fiducials attachable to a fixture, a coordinate measuring machine (CMM) for measuring positions of the fiducials, inclinometers attachable to the fixture, and a rate table for receiving the fixture and posing the fixture with the inclinometers and/or the IMUs. A method can include determining a first rotation matrix between a coordinate frame associated with the fiducials and a reference coordinate frame, determining a second rotation matrix between the reference coordinate frame and a coordinate frame associated with a rate table, determining a third rotation matrix between the coordinate frame associated with the rate table and a coordinate frame associated with an IMU, and multiplying the three rotation matrices by data from an IMU. The reference coordinate frame can be a coordinate frame associated with the fixture or associated with one or more inclinometers.