On the Design, Construction and Operation of a Diffraction Rangefinder MS Thesis Presentation Gino Lopes A Thesis submitted to the Graduate Faculty of Fairfield University in partial fulfillment of the requirements for the degree of a Master of Science in the Electrical and Computer Engineering.

Outline Problem Approach Motivation Rangefinding Design and Testing Performance and Comparison Conclusion Future Work

Problem Design a diffraction rangefinder, subject to the following constraints: – Fit on a desktop, – Digitize and display objects, – Be affordable, – Be easy to use, – Not suffer from occlusion issues, characteristic of triangulation rangefinders, – Characterize the performance of the rangefinder

Approach Design a Prototype for testing. – Hardware Diffraction grating. Network Camera instead of USB camera. Laser line generator. Motion control hardware. – Software JAVA was used for everything. – Layout of 3D Scanner Dependent on hardware parameters.

Motivation Diffraction rangefinders represent a new class of rangefinder for digitizing object. Verify predicted performance.

Rangefinding Types of Rangefinders: – Shape to shading: Process of computing the shape of a three-dimensional surface by looking at the brightness of one image of the surface. Shape to shading is difficult to implement.

Rangefinding Continued – Triangulation: Finds the range-to-target by using two different views (angles) of the target, or by making use of off-access illumination. Transmitter and receiver are separated. Subject to shadows.

Rangefinding Continued – Light Detection and Ranging (LIDAR) system: Uses laser pulse time of flight. Receiver and transmitter can be co-axial and shadows and occlusion limitation are minimized. For surface scanning the laser source or target would need to be moved in both the x-axis and y-axis. – To collect enough data points to reproduce the surface detail.

Rangefinding Continued – Diffraction Rangefinders: Measures the distance to a target by reading the curvature of the wave front. Work with (active illumination) using a laser. Less susceptibility to occlusion. Receiver and transmitter can be co-axial. Limitation in range of measurement due to size of the grating.

Design Scanner Design: – Illumination Source: Off the shelf red laser line generator – Vision System: Network Camera 1000 line/mm Diffraction Grating – Motion System: Motor and controller. Rotary Turntable.

2D View of Scanner Layout

2D View Of Scanner Layout Cont.

3D Scanner Prototype

Testing Testing of scanner performance. – Calibration wedge used as a resolution target. Target with known dimensions. Verification of operation

Scanner Test Configuration

Testing Continued Calibration wedge was positioned at 49mm, 92mm, and 135mm from grating.

Wedge at 49mm

After Processing at 49mm

Wedge at 92mm

After Processing at 92mm

Wedge at 135mm

After Processing at 135mm

Scanner Comparison Scanner characteristics was compared against two other scanners on the market. – One from VXTechnologies. – One from Cyberware.

Scanner Comparison Continued 3D Scanner VXTechnologies StarCamCyberware Field of View12" X 7" (310mmX178mm)21" X 16" (533mmX406mm)14" X 17" (350mmX440mm) Resolution0.017" (0.44mm)0.019" (0.48mm)0.015" (0.38mm) Width11.5"16.375” (416mm)188.2 cm (74.1") Height14"11.000” (280mm)205.3 cm (80.8") Length30"9.250” (235mm)Not Given

3D Image of Chess Piece

3D Image of Chess Piece Cont.

Conclusion Average resolution of the 3D Scanner was between 0.43mm and 0.44mm. (Comparable to other rangefinders on the market)

Future Work Replacing the turntable with an improved model. Replacing the Lego motor and RXTX controller with a stepper motor and controller. Increasing the laser fan angle from 60 .

Future Work Continued Replacing the camera with one that allows for turning automatic gain off. – Reduce noise and blooming. Improve image acquisition and processing software user interface. Verify repeatability of scanner.

Data Analysis Using Grating equation to calculate dispersion angle of 1000 line per mm grating. Number of slits per mm (q):1000 One mm in meters:0.001 Center to center distance between slits (p) in meters (1mm/q): Wavelength of light source (lambda) in meters: Diffraction Order (n):1 Dispersion Angle (sin(a)=(n*lambda)p) in degrees: 39 

Data Analysis Cont. Using trigonometry to calculate mm per pixels from acquired data. Calculated dispersion Angle of grating:39 Distance from grating to target (D) in mm:135 Tan(b):0.806 Distance between zero-order and first-order fringes in mm:

Experimental Data Average Number of Pixels: Distance to Target Between Zero Order and First Order on Right Side Between Zero Order and First Order on Left Side 49mm mm mm

Experimental Data Continued Pixels per mm. Distance to Target Between Zero Order and First Order on Right Side (pixels/mm) Between Zero Order and First Order on Left Side (pixels/mm) 49mm mm mm

Experimental Data Continued Average distance resolvable. Distance to Target Between Zero Order and First Order on Right Side (mm) Between Zero Order and First Order on Left Side (mm) 49mm mm mm Average Standard Deviation