HCBC Structured Light CMM for Sub-5 Micron Accuracy
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Solution Overview
Problem
Current non-contact three-dimensional optical sensors using a single scanned projected laser line for coordinate measuring machines (CMMs) do not match the accuracy of traditional stylus-type CMMs, and structured light patterns like Gray code, while offering potential for increased scan rate and accuracy, face challenges with optical blur affecting digital resolution elements and signal saturation.
Innovation Solution
A non-contact coordinate measuring machine employing a Hybrid Cyclic Binary Code (HCBC) structured light system with a rotating cylindrical code drum and optical sensors, which projects hybrid cyclic binary code patterns and non-structured reference light to improve measurement accuracy by compensating for optical diffraction and defocus effects, and normalizing sensor signals to reduce signal saturation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a single scanned projected laser line is used for non-contact measurement, then the area scan rate is increased beyond stylus probe capability, but the measurement accuracy does not match traditional stylus-type CMMs
Solution Approach 1:
The measurement process is segmented into multiple sequential projections of structured light patterns (Gray code patterns) across different areas of the object surface. Each pattern projects information about a specific spatial region, allowing the system to cover large areas while maintaining measurement accuracy through divided encoding zones
Solution Approach 2:
The system transitions from one-dimensional laser line scanning to two-dimensional structured light pattern projection. By encoding spatial information in both horizontal and vertical dimensions simultaneously through grid-based Gray code patterns, the system achieves higher area scan rates while maintaining accuracy through multi-dimensional encoding
2Productivity
If structured light patterns are projected to increase area coverage and scan rate, then more area is measured faster, but optical blur affects digital resolution elements and causes signal saturation
Solution Approach 1:
The system applies different optical characteristics to different regions of the projected pattern. By varying the local spatial frequency and bar width of Gray code patterns across different zones of the object surface, the system optimizes each region's measurement quality while compensating for optical blur effects that vary across the field of view
Solution Approach 2:
The system performs preliminary calibration and characterization of optical blur effects before actual measurement. By pre-determining the point spread function and blur characteristics of the optical system, the system can compensate for these effects in real-time during structured light projection, preventing signal degradation before it occurs
3Measurement precision
If Gray code patterns with minimum period are used, then the encoding resolution is maximized, but the patterns become sensitive to optical blur and defocus
Solution Approach 1:
The system dynamically adjusts the spatial period and frequency parameters of the projected Gray code patterns based on the measurement requirements and optical conditions. By varying the bar width and pattern density, the system optimizes the balance between encoding resolution and robustness to optical blur, using finer patterns where resolution is critical and coarser patterns where optical quality degrades
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 HCBC system enhances measurement accuracy to match or exceed traditional stylus-type CMMs, achieving positional coordinate measurement errors less than 5 microns, and improves signal dynamic range by compensating for optical non-linearity and saturation.
Implementation Method 1
One or two digital cameras view the reflected light from the object's surface at a different angle from the laser light direction, enabling the distance to points on the surface to be measured by triangulation
Implementation Method 2
A non-contact coordinate measuring machine employing a Hybrid Cyclic Binary Code (HCBC) structured light system with a rotating cylindrical code drum and optical sensors, which projects hybrid cyclic binary code patterns
Implementation Method 3
achieving positional coordinate measurement errors less than 5 microns, and improves signal dynamic range by compensating for optical non-linearity and saturation
Data Source
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AI summary
Technologies for determining positional coordinates on the surface of an object are disclosed. In some embodiments the technologies utilize a code drum to encode incident light into structured light and non-structured light that is projected on the surface of the object being measured. The code drum may include a plurality of hybrid cyclic binary code (HCBC) patterns, wherein the plurality of HCBC patterns include a plurality of weighted numbering system patterns, and a plurality of unweighted numbering system patterns. Systems and methods for measuring positional coordinates on a surface of an object being measured are also described.