Multi-Head Laser Tracking for Accurate 6DoF Robot Pose
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Solution Overview
Problem
Current laser tracking systems for robots face challenges in accurately measuring the position and orientation of robot components in real-time, especially at distances, due to line-of-sight issues and increased positional errors with orientation measurements, which result in vibration and delay when trying to compensate for these errors, making them unsuitable for fine positioning tasks.
Innovation Solution
A tracking system using multiple tracking heads and targets, where the position of each target is determined using distance measurements and elevation/azimuth angles, with signals from base sensors controlling the tracking heads to maintain line of sight, and calibration data transforming positional data into an environment coordinate system, allowing for continuous tracking and accurate determination of the robot's position and orientation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single tracking head is used to measure position and orientation of a robot component, then the device complexity is reduced, but the measurement precision deteriorates due to increased positional error from orientation measurement error at distances
Solution Approach 1:
The system divides the tracking function into multiple independent tracking heads (at least three) that each measure position of targets independently. By segmenting the measurement task across multiple sensors, the system achieves accurate position determination through triangulation while maintaining manageable device complexity.
Solution Approach 2:
The patent introduces passive retroreflective targets as intermediaries between the tracking heads and the robot component. These targets reflect laser beams back to the tracking heads, enabling precise position measurement without requiring active sensors on the moving robot component, thus simplifying the overall system while improving measurement accuracy.
2Measurement precision
If orientation measurements are made using existing laser trackers, then orientation data is obtained, but the measurement precision deteriorates due to sensitivity to acceleration error and prediction error introducing step changes
Solution Approach 1:
The system extracts and measures only position information using multiple tracking heads and passive targets, completely eliminating the need for orientation measurements. By taking out the problematic orientation measurement function, the system avoids acceleration sensitivity and prediction errors while maintaining full capability to determine robot component pose through position-only triangulation.
3Adaptability or versatility
If the end effector is positioned further from the tracking target to increase working range, then the adaptability is improved, but the measurement precision deteriorates due to greater end effector positional error from orientation measurement error
Solution Approach 1:
The patent transitions from 2D orientation measurement to 3D position measurement by using multiple tracking heads to perform triangulation. This dimensional change allows the system to maintain high measurement precision regardless of the distance between the tracking target and the end effector, enabling extended working range without sacrificing accuracy.
4Device complexity
If existing laser trackers with 10ms latency are used, then the device complexity is reduced, but the productivity deteriorates due to delay in real-time tracking required for fine positioning tasks
Solution Approach 1:
The system uses passive retroreflective targets that are pre-positioned on the robot component, eliminating the need for active sensors and complex signal processing on the moving part. This preliminary setup enables immediate laser reflection and position calculation, achieving real-time tracking speeds suitable for fine positioning tasks while keeping the moving component simple.
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
This approach provides improved positional accuracy and orientation measurement, reducing vibration and latency, enabling precise tracking of robot components with six degrees of freedom, suitable for fine positioning tasks like brick laying, by maintaining line of sight and minimizing thermal expansion effects.
Implementation Method 1
Each tracking head has a radiation source arranged to send a radiation beam to a respective target and a base sensor that detects the reflected radiation
Implementation Method 2
Each target includes a retroreflector that reflects the radiation beam to the base sensor of a respective tracking head
Data Source
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Figure 1B
Figure 1C
AI summary
A tracking system for tracking a position and orientation of an object, the tracking system including: a tracking base provided in an environment, the tracking base including: a tracking head support; and, at least three tracking heads mounted to the tracking head support, a target system including at least three targets mounted to the object, each target including a reflector that reflects a radiation beam to the base sensor of a respective tracking head; and, a control system that: causes each tracking head to track a respective target as it moves throughout the environment; determines a position of each target with respect to a respective tracking head; determines an orientation of the target system using at least in part the determined position of each target; and, determines the position and orientation of the object using at least in part the position and orientation of the target system.