SLED Light Source for Coordinate Measuring Device Granulation Reduction
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Solution Overview
Problem
Coordinate measuring devices face inaccuracies due to granular intensity distribution from laser diodes, especially at long distances, which affects position detection and tracking of moving targets.
Innovation Solution
A coordinate measuring device utilizing a superluminescent diode (SLED) as a light source, which emits incoherent light in a broad frequency band, simplifies illumination design and reduces granulation, enabling more accurate measurements over longer distances with a closed loop control system for precise alignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a laser diode is used as a light source to maintain light intensity over large distances, then the required light intensity can be maintained, but transverse modes are excited causing asymmetrical granular intensity distribution that vitiates position detection accuracy
Solution Approach 1:
The patent changes the fundamental parameter of light coherence from coherent (laser diode) to incoherent (superluminescent diode). This parameter change eliminates the granular intensity distribution caused by transverse modes while maintaining sufficient light intensity for long-distance measurement, thereby resolving the contradiction between illumination intensity and position detection accuracy
Solution Approach 2:
The patent replaces the expensive, complex laser diode system with a simpler, more economical superluminescent diode. Although SLEDs have shorter coherence length, this is actually beneficial for eliminating granulation effects. The solution trades the long coherence length of lasers for the shorter coherence length of SLEDs, achieving better measurement precision at acceptable light intensity levels
2Illumination intensity
If a laser diode is used to provide sufficient light intensity, then the light intensity requirement is met, but temperature-dependent variations in granulation patterns occur that reduce measurement stability
Solution Approach 1:
The patent changes the coherence parameter from high (laser diode) to low (superluminescent diode), which fundamentally eliminates temperature-dependent granulation variations. The incoherent light source does not exhibit the same thermal sensitivity as coherent laser sources, thereby improving measurement stability and reliability
Solution Approach 2:
The patent converts what would traditionally be seen as a disadvantage (shorter coherence length of SLEDs) into a benefit by eliminating the harmful granulation effects. The incoherent nature of SLED light, which initially seems to reduce directional precision, actually eliminates the temperature-sensitive granular patterns that plague laser-based systems
3Measurement precision
If a PSD with small aperture angle is used for tracking, then position detection is possible, but the field of view is limited requiring an additional target detection unit with larger field of view
Solution Approach 1:
The patent merges the functions of the PSD and target detection unit by using a single camera-based detection system that combines both fine position detection (tracking) and coarse target acquisition. The camera system can resolve fine positional details while simultaneously providing a wide field of view for target detection, eliminating the need for separate PSD and target detection unit components
Solution Approach 2:
The patent implements a universal detection system using a camera that performs multiple functions: it detects targets within a wide field of view, tracks moving targets, and provides fine position measurement. This multi-functional approach replaces the need for separate specialized components (PSD for precise tracking and target detection unit for wide field of view) with a single versatile camera-based system
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
The use of SLEDs provides higher measurement accuracy and stability, reducing temperature-dependent variations in granulation patterns, allowing for precise tracking and detection of moving targets with improved illumination profiles.
Implementation Method 1
A coordinate measuring device utilizing a superluminescent diode (SLED) as a light source, which emits incoherent light in a broad frequency band
Implementation Method 2
The target point to be measured is provided with a retro-reflector (in particular corner cube prism or arrangement of three mirrors placed perpendicularly on one another), the retro-reflector reflecting the measurement beam of the laser tracker incident thereon back to the latter
Implementation Method 3
A part of the reflected measurement beam is conventionally sent onto a PSD (position sensitive device). From the position at which the reflected measurement beam strikes the photosensitive surface of the PSD, the parallel displacement of the reflected measurement beam relative to the emitted measurement beam is deduced
Data Source
AI summary
A coordinate measuring device includes a carrier that can be rotated automatically about two axes and that can be directed toward a measuring aid. The following are arranged on the carrier so as to be able to move together: an optical distance measuring device for measuring the distance to the measuring aid; a light source for emitting light, directly or by means of optical elements, wherein said light is visible as a target point when reflected on the measuring aid; a target detecting unit for determining a position as the position of the imaging of the target point on a position detection sensor. The control apparatus is designed to direct the carrier at the measuring aid by rotating the carrier about the at least two axes of the carrier according to the fine position and the rough position; and the light source is a superluminescent diode (SLED).