IMU Calibration Fixture for Accurate Biomechanical Skeleton Alignment

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Solution Overview

Problem

Angular offsets between inertial measurement unit (IMU) measurement axes and corresponding biomechanical skeleton axes lead to substantial position errors in motion capture, causing inaccuracies in determining limb and joint positions.

Innovation Solution

A calibration fixture and method that utilize a base plate with finger and thumb rests, partitions, and optional IMUs to stabilize the hand position, allowing accurate determination of angular offsets and correcting IMU data for precise biomechanical skeleton modeling.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If IMU is attached to a motion capture subject, then motion capture data can be collected, but the IMU measurement axes become skew to the biomechanical skeleton axes causing position errors

Engineering Contradiction:

Improvemotion capture data collectionVSAvoidposition accuracy

Core Design Contradiction:

ProductivityVSMeasurement precision

Solution Approach 1:

The patent applies preliminary action by performing calibration before motion capture data collection. The calibration process determines offset angles between IMU measurement axes and biomechanical skeleton axes in advance, so these corrections can be applied during actual motion capture to eliminate position errors while maintaining productivity

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent changes the parameter of measurement axis orientation by introducing offset angle corrections. The calibration process measures and compensates for angular deviations between IMU axes and skeleton axes, transforming the measurement data to align with the biomechanical model and thereby improving position accuracy

Inventive Principle:

Principle #35Parameter changes

2Measurement precision

If angular offset calibration is performed to improve position accuracy, then measurement precision improves, but device complexity and calibration procedure complexity increase

Engineering Contradiction:

Improveposition accuracyVSAvoidcalibration fixture complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The calibration fixture is segmented into modular components including a base plate with finger rests, partition walls for hand positioning, and separate IMU mounting structures. This segmentation allows for easier manufacturing, assembly, and adjustment while maintaining the precision needed for accurate offset angle determination

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The calibration fixture incorporates self-positioning features such as finger rests and partition walls that guide the subject's hand into the correct orientation without requiring complex external positioning devices. The fixture essentially calibrates itself by providing mechanical constraints that define the reference orientation

Inventive Principle:

Principle #25Self-service

Data Source

PatentUS12539055B2Calibration of an inertial measurement unit for improving the accuracy of a biomechanical skeleton

Publication Date: 2026.02.03 AIQ SYNERTIAL LTD

AI summary

A calibration fixture provides a repeatably accurate tool for measuring offset angles between measurement axes for inertial measurement units (IMUs) used in motion capture. The measured offset angles may be used to correct angles measured by the IMUs to create a biomechanical skeleton that accurately represents movements of a motion capture subject. The disclosed embodiments are applied segments of a biomechanical skeleton providing a mathematical model of a human arm and hand.