Multi-Channel Deep-Memory Digitizing Architecture for Automated Inspection of Large Composite Surfaces

The manufacturing inspection process of large composite surfaces a coordinated real-time control/acquisition system. Existing ultrasonic inspection systems use a single ultrasonic transducer or in some cases effectors containing two ultrasonic channels. The large amount of surface area presented by the fuselage barrels compels the use of ultrasonic arrays containing up to 102 elements (channels) in order to meet the scan times necessary to satisfy production rates. The exterior inspection system uses an array containing 64 elements and the interior system has a dedicated manipulator containing 96 array elements and an additional 6 channels to cover the radius of the hat stiffeners. The surface coverage rates necessary to meet the desired scan times are approximately 12 inches/sec. Digital waveform data will be acquired on each of the array elements and individual transducers at each 0.05 inch increment along the surface. This data acquisition rate will digitize approximately 24,500 waveforms per second. In addition to placing enormous data storage demands on the data system, waveforms must be moved from the digitizer module and written to disk at a very high rate. The system also has the requirement to retrieve waveforms from the storage system for signal analysis and display during the acquisition process, eliminating the possibility of using a stream-store or similar device. Current inspection systems use a hard real-time operating system (RTOS) to arm and fire the digitizer at each spatial position, and rely on interrupts from the digitizer hardware to efficiently move the digitized waveforms to memory in a deterministic time. The problem that arises from this methodology is that the hardware requires a driver written for the specific RTOS. This requires expensive and unique development environments including compilers, debuggers, and necessitates testing in the kernel mode. Developing a driver can be a very complex task and requires cooperation from the hardware vendor to provide low level register information. The solution under development by the Boeing Automated Systems Group uses a deep memory paradigm, consisting of a programmable digitizer capable of storing waveforms in system memory using direct memory access (DMA) and a circular buffer scheme. The digitizer can acquire more waveforms than the available on-board memory, requiring only that the controller offload data at a high rate, but eliminating the need for a deterministic response. The digitizer has an extremely fast rearm time and will not miss an event trigger even at the fastest rates. Software communication with the digitizer is through the provided Windows driver model (WDM) driver running on an embedded PC with standard embedded Windows XP, eliminating the need to develop a device driver. Initial testing produced waveform rates well in excess of specifications. This concept allows use of commercial off the shelf (COTS) hardware and software while leveraging many existing system components of the automated ultrasonic scanning system (AUSS) developed by the Automated Systems Group. Significant cost and development time savings were realized in addition to exceeding waveform analysis requirements. This newly developed system architecture will support the 787 manufacturing inspection process in the United States, Australia, and Italy.