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	Projection of rotating grid

The theory of 3-D measurement is based on quadric surfaces defined by a projected rotating grid pattern. The X, Y, Z coordinates of a point on a surface are calculated from the intersection of a pixel ray from the camera and a quadric surface.

Calculation Method

The distance from the projected grid axis of rotation to a point on the surface is found by counting the number of light-dark transitions as the grid makes a revolution.

Calibration Method

• Record image data at three or more reference planes

• Determine contour lines of constant radius from the projected center of rotation

• Calculate equations for 3-D quadric surfaces generated by iso-contour lines
   

Light-dark transitions at a pixel

Experimental Tests

	Experimental projector for rotating grid pattern

Tests were conducted using a breadboard grid projector system that can be configured with different lenses to meet specified measurement requirements for different size parts. Software was developed for image analysis and 3-D calculations and tested using a Pentium computer with a CCD camera to capture images of parts. The system was calibrated, and measurements were made for parts ranging in size from 1 sq. in. to approximately 25 sq. ft.

3-D Measurement Method

• Record a sequence of images as the grid rotates

• For any pixel, determine the radius from the projected center of rotation (quadric surface number)

• Calculate the intersection of the ray from the camera and the quadric surface at the location on the target

• Interpolate between quadric surfaces to obtain increased accuracy

	Reconstruction of a vane

3-D measurements include

• Gage blocks

• Reference planes

• Small machined parts

• Small forged parts (coins)

• Airfoils (flaps and elevators)

• Models of ships

• Turbine and torque converter vanes

Results of 3-D Measurement

Dynamic Structured Light (DSL) (patent pending) has been developed as a method for 3-D measurement. DSL 3-D measurement can be scaled from precise measurement of small parts to surface measurement of large assemblies. Design tradeoffs between size of working volume, measurement accuracy, and measurement time were investigated, and a design procedure was developed for selecting system parameters to meet specified requirements of part size and accuracy.

Application range for DSL 3-D measurement

For more information about DSL 3-D imaging capabilities at SwRI or how you can contract with SwRI, please contact Ernest Franke, PhD, PE, at efranke@swri.org or (210) 522-3678.

| Manufacturing Systems Department | Automation and Data Systems Division | SwRI Home |

Southwest Research Institute^® (SwRI^®), headquartered in San Antonio, Texas, is a multidisciplinary, independent, nonprofit, applied engineering and physical sciences research and development organization with 12 technical divisions.

August 24, 2009