Interferometer Pulse Validation for Laser Tracker Precision

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Solution Overview

Problem

Laser trackers face challenges in maintaining measurement precision due to the robustness and reliability issues of interferometers, particularly when detecting distance changes, as they can lose or incorrectly count interferometer pulses, leading to erroneous measurements, especially at large distances or during rapid target movement.

Innovation Solution

Implement a method to check the correctness of interferometric measurements by generating a time-resolved output variable curve from the interferometer data, comparing movement parameters to defined criteria, and providing feedback on measurement errors, allowing for automated correction and adaptation of measurement results.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If interferometer is used to measure distance changes, then measurement precision is improved, but reliability deteriorates due to pulse loss or incorrect counting

Engineering Contradiction:

Improvedistance change measurement precisionVSAvoidmeasurement reliability

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The patent implements a feedback mechanism where the measured distance change is continuously compared against expected movement criteria (maximum velocity, acceleration limits). When deviations are detected indicating pulse loss or counting errors, the system generates feedback signals to correct or flag the erroneous measurements, thereby maintaining reliability while preserving the high precision of interferometric measurement

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent applies preliminary action by establishing movement criteria (maximum velocity, acceleration, displacement limits) before measurement begins. These pre-defined constraints are used to validate interferometer readings in real-time, allowing the system to proactively identify and correct potential measurement errors before they compromise overall reliability

Inventive Principle:

Principle #10Preliminary action

2Measurement precision

If interferometer pulses are counted to determine distance change, then measurement precision is improved, but difficulty of detecting and measuring worsens due to pulse loss at large distances or rapid movement

Engineering Contradiction:

Improvedistance change measurement precisionVSAvoidinterferometer pulse detection difficulty

Core Design Contradiction:

Measurement precisionVSDifficulty of detecting and measuring

Solution Approach 1:

The patent introduces an intermediary validation layer between the interferometer pulse counting and the final distance measurement. This intermediary system uses movement criteria (velocity, acceleration, displacement limits) to assess whether detected pulses are plausible, effectively mediating between raw interferometer data and reliable distance measurements, especially challenging conditions like large distances or rapid target movement

Inventive Principle:

Principle #24Intermediary (Mediator)

3Productivity

If laser tracker is used for target tracking, then productivity is improved, but measurement precision deteriorates due to incorrect interferometer readings during rapid target movement

Engineering Contradiction:

Improvetarget tracking efficiencyVSAvoiddistance measurement precision

Core Design Contradiction:

ProductivityVSMeasurement precision

Solution Approach 1:

The patent applies dynamics by making the measurement validation adaptive to the target's motion characteristics. The system dynamically adjusts validation thresholds based on real-time movement parameters (velocity, acceleration), allowing faster tracking speeds while maintaining precision through adaptive criterion adjustment rather than fixed limits

Inventive Principle:

Principle #15Dynamics

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 enhances the accuracy of distance change measurements by identifying and correcting errors, ensuring that only plausible movements are recorded, thereby improving the reliability and precision of laser tracker measurements.

Implementation Method 1

a generation and detection of a superposition of the reflected measurement radiation with a reference radiation

Methodology Applied

Scientific EffectInterference: Interference

Data Source

PatentUS9638519B2Method for determining a change in distance to a movable and reflective target by means of interferometer to determine if the movement of the reflective target is really executable

Publication Date: 2017.05.02 LEICA GEOSYSTEMS AG

AI summary

Embodiments of the invention relate to a method for determining a change in distance to a moving and reflective target. Embodiments of the invention can be performed by means of interferometry and may include the generation of laser radiation, the emission of the measurement radiation to the target, and the detection of at least part of the measurement radiation reflected at the target. In some embodiments, a superposition of the reflected measurement radiation with the reference radiation is generated and detected, an interferometer output variable is derived on the basis of the detected superposition, and/or a time-resolved output variable curve is produced from the derived interferometer output variable. In some embodiments, the output variable curve is continually checked in that the output variable curve is continually read out in a time-resolved manner.