Heliostat Surface Shape Measurement Using Starlight Translation
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Solution Overview
Problem
Current methods for determining the surface shape of heliostats using starlight are incomplete, as they fail to provide slope information over areas where light reflected from the heliostat surface falls between cameras in a sparse array, especially when using a point source like a star.
Innovation Solution
A system and method employing a fixed array of cameras with large aperture lenses configured in a zig-zag line, oriented perpendicular to the translation direction, which captures simultaneous exposures as the aberrated star image translates across the heliostat array receiver, ensuring every point on the reflector surface is sampled in two dimensions, allowing for the integration of surface slopes using Snell's law.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a sparse array of cameras is used to image heliostats in starlight, then the device complexity is reduced, but the measurement precision deteriorates because light reflected from many regions falls between cameras and yields no slope information
Solution Approach 1:
The patent transitions from a two-dimensional sparse camera array to a three-dimensional solution by incorporating temporal dimension through Earth's rotation. The heliostat remains stationary while the star image moves across the camera array over time, effectively sampling the entire reflector surface without requiring a dense spatial camera distribution.
Solution Approach 2:
The system utilizes the dynamic motion of the star image across the camera array caused by Earth's rotation. Instead of requiring all cameras to be active simultaneously, the moving star image sequentially activates different camera subsets, transforming a static sparse array into a dynamic sampling system that achieves complete surface coverage.
2Device complexity
If cameras are spaced further apart to reduce the number of cameras, then the device complexity decreases, but the measurement precision worsens due to gaps in sampling coverage
Solution Approach 1:
The patent adds the temporal dimension to the sampling process. Cameras that are spatially separated can still achieve complete coverage because the moving star image brings different regions of the reflector into view of different cameras at different times, effectively filling the spatial gaps through temporal sequencing.
Solution Approach 2:
The systematic periodic motion of Earth's rotation causes the star image to move predictably across the camera array. This periodic action ensures that all regions of the reflector surface are systematically sampled over time, with each camera capturing data from specific angular ranges that collectively cover the entire surface.
3Device complexity
If a point source like a star is used instead of an extended source, then the measurement process is simplified, but the measurement precision deteriorates because point source light reflects to a single location and creates gaps in coverage
Solution Approach 1:
The patent transforms the static point-source limitation into a dynamic advantage. While a point source does reflect to a single location, the motion of this reflected image across the camera array over time allows sequential sampling of all surface regions, converting a spatial coverage problem into a temporal sampling solution.
Solution Approach 2:
The continuous motion of the star image across the camera array ensures uninterrupted sampling of the reflector surface. By maintaining continuous exposure and recording throughout the star's transit, the system achieves complete surface coverage without gaps, transforming the discontinuous nature of point-source reflection into a continuous measurement process.
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 enables a complete and accurate mapping of the heliostat surface shape by ensuring every point is captured in the recorded images, achieving high-resolution surface slope measurements with improved accuracy and coverage.
Implementation Method 1
For any point on the reflector surface that appears bright in the view from a given camera, the slope of the mirror surface at that point may be determined using Snell's law
Implementation Method 2
setting the heliostat in fixed orientation such that aberrated and overlapping star images formed are translated due to Earth's rotation in a translation direction across the heliostat array receiver
Implementation Method 3
the slopes at every point P on the reflector surface are then determined by equation 1, in which the intensities measured from viewpoints m,n are summed, weighted simply by the sign of the x or y coordinate
Data Source
AI summary
A method for measuring a shape of a reflector surface of a heliostat at night using a bright star at different elevation and azimuthal settings according to an embodiment of the current invention includes setting the heliostat in fixed orientation such that aberrated and overlapping star images formed are translated due to Earth's rotation in a translation direction across the heliostat array receiver; viewing images of the bright star using a fixed array of cameras placed at or near an array receiver of the heliostat, wherein each camera of the fixed array of cameras has a large aperture lens, and simultaneous exposures are made quickly enough and repeated for long enough, so that, as they translate past the cameras, the aberrated star image is fully sampled in two dimensions, and wherein every point on the reflector surface of the heliostat appears in one or more of the recorded images as being bright from reflected starlight; and processing the recorded images from the fixed array of cameras with a data processor to obtain the surface shape by integration of the surface slopes.