Technical Approach
DSL 3-D Imaging

Contact Information

Ernest Franke, Ph.D., PE
DSL 3-D Imging Program Manager
Manufacturing Systems Department
(210) 522-3678

image of projection of rotating grid

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
image of Light-dark transitions at a pixel

Light-dark transitions at a pixel

image of experimental projector for rotating grid pattern

Experimental projector for rotating grid pattern

image of Reconstruction of a vane

Reconstruction of a vane

Experimental Tests

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

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.


image of application range for DSL 3-D measurement

Application range for DSL 3-D measurement

Related Terminology

digital imaging software  •  3-D imaging  •  reverse engineering  •  rapid prototyping  •  3-D measurement  •  surface roughness measurement  •  surface profile measurement  •  automated optical inspection  •  non-contact surface profile  •   thickness measurement •  equipment surface angle measurement  •  surface measurement systems  •  non-contact surface finish measurement  •  non-contact automated dimensional inspection  •  three dimensional images  •  3-D images  •  dynamic structured light  •  noncontact surface measurement  •  optical measurement  •  lower cost  •   higher accuracy  •  scalable microscopic  •  large area custom •  system development  •  long stand-off

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Southwest Research Institute® (SwRI®), headquartered in San Antonio, Texas, is a multidisciplinary, independent, nonprofit, applied engineering and physical sciences research and development organization with 9 technical divisions.