Gyroscope Sensor Femur Axis Tracking Calibration
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Solution Overview
Problem
Current MEMS systems for tracking bones in computer-assisted orthopedic surgery face challenges in accurately determining the orientation of the femoral head due to its hidden location, requiring sensitive 6DOF tracking methods that are prone to errors with low-cost sensors and unnatural leg motions.
Innovation Solution
A system utilizing a three-axis gyroscope sensor unit secured to the femur, which performs specific rotational movements to calibrate and normalize gyroscope readings, allowing for accurate tracking of the femoral mechanical axis through axis calibration and normalization, and displaying orientation data for precise navigation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If dead reckoning is used to retrieve 6DOF from gyroscope and accelerometer readings, then orientation data can be obtained, but sensor errors cause high sensitivity and reduced reliability
Solution Approach 1:
The patent segments the 6DOF tracking problem into two independent parts: 3DOF orientation tracking using gyroscopes and 3DOF position tracking using optical navigation. This segmentation allows each subsystem to be optimized independently, with the gyroscope focusing solely on orientation measurements without being affected by position drift errors.
Solution Approach 2:
The patent transitions from attempting to retrieve all 6DOF from low-cost sensors to using gyroscopes exclusively for the orientation dimension (3DOF), while obtaining position data through a different dimension (optical tracking). This dimensional separation eliminates the accumulation of errors that plagues dead reckoning systems.
2Measurement precision
If axial rotation kinematic methods are used to retrieve the femur axis, then orientation can be determined, but very specific and unnatural leg motion is required
Solution Approach 1:
The patent changes the motion parameters from requiring specific axial rotations about the femoral axis to allowing natural leg movements in multiple directions. The gyroscope captures orientation changes during any motion, and the femoral axis is derived through mathematical normalization of the orientation data, eliminating the need for constrained motion patterns.
Solution Approach 2:
The patent replaces the mechanical constraint system (requiring specific leg motions and physical guides) with a sensor-based system. The gyroscope electronically tracks orientation during natural movement, and computational algorithms extract the femoral axis, substituting mechanical guidance with sensor fusion and mathematical processing.
3Loss of information
If optical navigation is used to locate the femoral head by moving the femur, then the hidden landmark can be found, but 6DOF tracking requires complex sensor integration
Solution Approach 1:
The patent extracts the orientation measurement function from the position tracking system. By using gyroscopes dedicated to capturing rotational movements, the system separates orientation data acquisition from position tracking, eliminating the need for complex 6DOF sensor integration while still enabling femoral head location through the extracted orientation information.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables reliable and accurate tracking of the femoral axis, reducing sensor errors and natural motion constraints, thereby improving the precision of bone navigation in computer-assisted surgery.
Implementation Method 1
a sensor unit comprising gyroscopes producing gyroscope readings related to orientation data about three axes of rotation
Data Source
AI summary
A system tracks an object in computer-assisted surgery. The system comprises a sensor unit secured to the femur. Gyroscopes on the sensor unit produce readings related to orientation data about three axes of rotation. A tracking unit receives the gyroscope readings. An axis calibrator on the tracking unit comprises a calculator for adding at least part of the gyroscope readings for specific movements of the object about a desired axis. An axis normalizer on the tracking unit determines an orientation of the desired axis with respect to the sensor unit from the added gyroscope readings. A tracking processor tracks the desired axis from the gyroscope readings. An interface displays orientation data for the object from a tracking of the desired axis. A method for tracking an object with a gyroscope sensor unit is also provided.