Fiducial Marker Calibration via Pose Graph Optimization
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Solution Overview
Problem
Existing methods for calibrating fiducial markers relative to objects in manufacturing environments are costly and time-consuming, often requiring expensive laser trackers and being sensitive to environmental changes.
Innovation Solution
A calibration system using one or more cameras and a processor to estimate the poses of fiducial markers by formulating and solving a pose graph, with first fiducial markers at unknown locations and calibration fiducial markers at known locations, allowing for efficient and accurate calibration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If laser trackers or scanning equipment are used for calibration, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent uses camera images (optical copies) of fiducial markers to perform calibration, replacing the need for physical laser trackers and scanning equipment. The camera captures 2D images of the fiducial markers, and the system computationally reconstructs 3D pose information from these images, achieving accurate calibration without expensive laser-based hardware.
Solution Approach 2:
The patent replaces mechanical laser tracking systems with an optical imaging system (camera). Instead of using physically actuated lasers that require precise mechanical control and positioning, the system uses a camera to capture images of fiducial markers, eliminating the need for complex mechanical laser tracking apparatus.
2Measurement precision
If laser tracking methods are used for calibration, then measurement precision is improved, but loss of time increases
Solution Approach 1:
The patent pre-places fiducial markers at known locations on the workpiece before the calibration process begins. These markers serve as pre-prepared reference points that the camera can quickly detect and use for pose estimation, eliminating the need for time-consuming laser scanning of the entire workpiece surface during calibration.
Solution Approach 2:
The patent skips the time-consuming step of scanning the entire workpiece surface with laser equipment. Instead, the system directly captures images of the pre-placed fiducial markers and computes their poses, rapidly completing the calibration process in a fraction of the time required by traditional laser tracking methods.
3Measurement precision
If laser trackers are used for calibration, then measurement precision is improved, but adaptability to environmental changes worsens
Solution Approach 1:
The patent uses optical imaging (camera photographs) to capture fiducial marker positions, creating a digital record that can be processed computationally. This approach is less sensitive to environmental factors like vibrations, temperature changes, and air currents that affect laser-based systems, as the camera captures a static image that can be analyzed without requiring continuous precise optical alignment.
Data Source
AI summary
In an example, a method for calibrating fiducials relative to a workpiece is disclosed and involves receiving, from one or more cameras, images of the fiducials, each image acquired from a different camera pose, where the fiducials comprise (i) one or more first fiducials fixed at one or more unknown locations on the workpiece and (ii) calibration fiducials disposed at known locations on the workpiece; estimating poses of the fiducials, where estimating the poses of the fiducials comprises, in each image, estimating, for each fiducial visible in the image, a pose of the fiducial relative to the camera(s); formulating a pose graph comprising nodes for the images and for the fiducials, the poses estimated for the fiducials, the calibration fiducials as landmarks with known poses, and constraints between the calibration fiducials and the images; and solving the pose graph to determine poses of the first fiducial(s) that satisfy the constraints.