Problem
Alpha Omega designed a walk-through metal detector that had to meet standards published by the National Institute of Justice (NIJ) and the Transportation Security Administration (TSA). To test the prototype units we needed a means to present standard test objects to the detector to measure performance. After production started the tester was to be used to test assembled units.
Solution
We constructed a non-metallic three axis "robot" that could place a test object anywhere within the detector opening and move it through the detector over a wide range of speeds. Z-axis motion through the opening was provided by a cart that rolled on fiberglass rails. The cart was moved by a belt that was driven by a large stepper motor mounted at the end of the rails. The rails were 24 feet long to allow the cart to accelerate to four to five meters per second, pass through the detector at a constant speed, and then decelerate. Tests could be run in both directions.
The cart carried a positioning mechanism that was driven along the X (horizontal) axis by another stepper motor also mounted at the end of the rails. When the cart returned to the starting position the mechanism moved the test frame to the next horizontal test position. Another mechanism moved the target carrier along the Y axis (vertical) to the next test elevation.
The entire mechanism was controlled by a computer. A test program allowed manual settings for cart speed and X and Y axis increment distances. For automatic testing this information plus the number of test passes could be programmed. Full testing at all positions at a slow test speed could take several hours.
The robot controller computer fed test object position information to a data collection computer that received detection data from the metal detector under test. The results of the tests were recorded in data records that allowed statistical and graphical analysis of the test data.
Results
The "railroad" provided definitive test data for analyzing different detection methods, allowing us to settle on an effective design. The railroad was also used to measure the speed and distance performance of a hand-held metal detector we designed for the same customer.
