iDOS (Inspection of Double Omega Stringers)

Abstract

Spirit AeroSystems, Inc. has developed a precision inspection system for automatically inspecting the thickness of composite stringers utilizing an array of laser displacement sensors. These parts have complex geometry and many changes in ply layup count. In addition, these parts are long with the longest stringer being approximately seventeen feet. An Olympus 38DL – a hand-held Non-Destructive Inspection (NDI) device – was initially used to inspect thickness. Manual thickness measurement with an ultrasonic thickness measurement sensor (Olympus 38 DL) is a tedious and labor intensive measurement process. The manual measurement process presented a bottleneck and high resource load for Spirit’s production of stringers and straps. Challenges associated with part orientation and ply ramp location proved prohibitive for consistent inspection. Spirit’s response for an improved technique is the inspection of Double Omega Stringers, or iDOS. iDOS utilizes two laser displacement sensors, calibrated to each other through a built-in calibration standard. iDOS is easily programmable to calculate the thickness at any required cross-section of a given part. The two lasers are mounted on a moving gantry that extends out into the inspection volume, which is located between two precision conveyor belts each twelve foot long. A simple projection laser is utilized to identify the starting location of the stringer or strap in relation to the line displacement array. An integrated vision system confirms part-machine alignment prior to beginning the automated inspection. Once the part is properly located on the conveyor system, the operator presses the start button, inputs the part number and timekeeping record number. Through a collaborative effort the system was developed and made production ready within 7 months, research risks were mitigated upfront through experimental testing. Utilizing the combination of a linear traverse and conveyor system, full coverage of a wide variety of part types was obtained with readily obtainable off-the-shelf components. Thickness measurements are performed with laser displacement sensors synchronized via precision motion control. As much as 136 million data points are collected per part, the large data volume is used to provide a stable and robust measurement of key thickness locations on the part. iDOS provides a precise and fully autonomous inspection solution to a once highly manual and time consuming process.