Laser Tracker and IMU Pose Synchronization for Tool Orientation
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Solution Overview
Problem
Existing metrology systems face challenges in achieving high-precision, efficient determination of the pose of tools, particularly in metrology-grade applications, due to limitations in sampling rates and data quality from laser trackers and inertial measurement units (IMUs), leading to degraded pose data when merging these data types.
Innovation Solution
A system that integrates a laser tracker, inertial measurement unit (IMU), and data processor to derive tool pose with submillimeter precision by synchronizing data from the laser tracker's high sampling rate with IMU orientation data, using image-based orientation data to zero and calibrate the IMU, and providing output data at a higher sampling rate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If laser tracker data and IMU data are merged to determine tool pose, then comprehensive pose information is obtained, but data quality degrades due to different sampling rates and precision levels
Solution Approach 1:
The patent extracts only the orientation component from IMU data while using laser tracker for position determination. The imaging unit extracts absolute orientation data from alignment markings. This separation allows each sensor to contribute its strongest capability without compromising overall data quality.
Solution Approach 2:
The system performs preliminary calibration by capturing an initial image to determine absolute tool orientation before merging with IMU data. This pre-established reference frame allows subsequent IMU orientation data to be accurately integrated without drift accumulation.
2Measurement precision
If imaging unit is used to determine tool orientation from alignment markings, then absolute orientation is obtained, but sampling rate is limited below laser tracker's rate
Solution Approach 1:
The imaging unit performs preliminary absolute orientation determination at lower sampling rates. These periodic absolute references are then used to calibrate and correct the continuous IMU orientation data, effectively upsampling the precision-oriented data to match the higher sampling rate requirements.
Solution Approach 2:
IMU orientation data serves as an intermediary that bridges the gap between the low sampling rate imaging unit and the high sampling rate laser tracker. The IMU provides continuous orientation estimates that are periodically corrected by the imaging unit, effectively transferring high-precision orientation information at high sampling rates.
3Productivity
If IMU provides continuous orientation data at high sampling rate, then productivity increases, but data drift occurs without regular zeroing
Solution Approach 1:
The imaging unit provides periodic feedback to correct IMU orientation drift. By capturing images at alignment markings and comparing with previous references, the system generates correction signals that zero out accumulated IMU drift, maintaining long-term orientation accuracy while preserving high sampling rate capability.
Solution Approach 2:
The system performs preliminary calibration using imaging unit data to establish absolute orientation references before relying on continuous IMU measurements. This initial accurate positioning prevents drift accumulation and provides a reference framework for subsequent high-rate IMU data.
4Measurement precision
If laser tracker determines position with micrometer precision, then measurement precision is high, but it is limited to position determination only
Solution Approach 1:
The patent merges laser tracker position determination with separate orientation determination systems (imaging unit and IMU). This combination creates a complete six-degree-of-freedom pose measurement system that leverages the laser tracker's micrometer-level position precision while adding orientation capability through complementary sensors.
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 real-time or quasi-real-time determination of tool pose with submillimeter precision, suitable for high-precision measurement and manufacturing tasks, by leveraging the strengths of each data source while minimizing their limitations.
Implementation Method 1
The tool comprises a laser-trackable target. The laser tracker is configured to track the target and to provide tracking data regarding a target position
Implementation Method 2
a beam source for emitting measuring radiation. A point of an object surface to be measured is illuminated by the measuring radiation and measuring radiation is reflected from this illuminated point
Data Source
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Figure 6a~6c
AI summary
The invention relates to a tool pose determination system, comprising a tool, a laser tracker, a data processor, and an IMU. The tool comprises a laser-trackable target and alignment markings. The markings are distributed such that a tool orientation is derivable based on their pattern. The laser tracker provides tracking data regarding a target position with a first sampling sequence having a first sampling rate. An imaging unit of the laser tracker acquires images with a second sampling sequence having a second sampling rate which is less than the first. The IMU unit to provides IMU orientation regarding the tool orientation. The data processor derives image-based orientation based on the imaged pattern of the markings and references the IMU orientation with the image-based orientation. The data processor provide output data timestamped with a third sampling sequence having a third sampling rate which is more than the second. The output data comprises tool positions based on the tracking data and the tool orientations based on the IMU orientation and the image-based orientation.