Triangulation Distance Measurement with High Dynamic Range Sensor
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Solution Overview
Problem
Conventional 3D coordinate measurement systems face challenges in achieving precise measurements on surfaces with varying reflectivity, such as mirror-like surfaces, due to strong inhomogeneity of reflected light and the phenomenon of laser speckle, which limits the precision and reliability of distance data.
Innovation Solution
A method and device for structured light triangulation that employs a high dynamic range image sensor with a detection sequence comprising multiple exposure sub-sequences with varying saturation limits, and uses a broad area laser to reduce speckle noise, allowing for reliable light information capture across the entire illuminated region and improved eye safety.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional single-exposure detection is used, then the device complexity is low, but the measurement precision deteriorates on surfaces with varying reflectivity due to strong inhomogeneity of reflected light and laser speckle
Solution Approach 1:
The detection process is segmented into multiple exposure sub-sequences, each capturing light intensity information at different saturation levels. This segmentation allows the system to handle surfaces with varying reflectivity by combining data from multiple exposures, thereby improving measurement precision without requiring complex hardware modifications.
Solution Approach 2:
The system employs periodic exposure sub-sequences with varying saturation limits to capture reflected light information. By periodically switching between different exposure levels, the system accumulates sufficient light information across varying surface reflectivities, enhancing measurement precision while maintaining a manageable detection sequence structure.
2Productivity
If higher laser power is used, then the productivity of distance measurement increases, but eye safety deteriorates
Solution Approach 1:
The system uses periodic pulsed laser illumination with controlled duration and intensity. By delivering high power in short pulses rather than continuous operation, the system achieves fast distance measurement (high productivity) while limiting total energy exposure to safe levels, thereby maintaining eye safety.
Solution Approach 2:
The system maintains continuous measurement capability through rapid sequential exposure sub-sequences. This allows the useful action of distance measurement to continue without interruption while using lower peak laser powers, achieving both high productivity and eye safety.
3Measurement precision
If broad area laser is used to reduce speckle noise, then the measurement precision improves, but the device complexity increases
Solution Approach 1:
The system changes the spatial parameters of the laser beam by using a broad area laser instead of a conventional narrow beam. This parameter change reduces laser speckle noise and improves measurement precision on surfaces with varying reflectivity, while the complexity increase is offset by the simplicity of the broad area laser source itself.
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 fast and precise distance measurements over a large dynamic range, reducing motion blur and speckle noise, and improving eye safety by allowing higher laser power usage, while maintaining reliable data capture on surfaces with varying reflectivity.
Implementation Method 1
detecting a reflection of the measuring light from the object with respective pixels of an image sensor
Implementation Method 2
the phenomenon of laser speckle, which limits the precision and reliability of distance data
Implementation Method 3
Method and device for triangulation-based distance measurement
Data Source
Figure 1~2a
Figure 2b~3a
Figure 3b~4b
AI summary
Method for determining distances to an object to be measured based on the principle of triangulation and using a high dynamic range image sensor, in particular with a piecewise-linear multi-slope sensitivity characteristic, the method comprising generating and emitting a measuring light beam, directing the measuring light beam to the object to be measured, detecting a reflection of the measuring light from the object with respective pixels of the image sensor during a defined detection sequence (t0-te) and deriving distance information based on the detected reflection. The detection sequence (t0-te) comprises a number of at least two exposure sub-sequences each defining a particular exposure period and saturation limit for the pixels of the sensor, wherein the exposure periods and saturation limits are defined so that the final total charge for substantially every pixel is below the saturation limit of the last exposure sub-sequence. To this end, a successive exposure sub-sequence comprises a higher saturation limit than its prior exposure sub-sequence and each saturation limit defines a maximum charging level of the pixels for the respective exposure sub-sequence. The pixels are at least partly exposed by the reflected measuring light whereby the charge of each exposed pixel changes, and the charge of each pixel reaching at least one of the maximum charging levels during the detection sequence (t0-te) is limited to the respective saturation limit for the period of the corresponding exposure sub-sequence.