Custom linear guide rails
NB Corporation of America
Hanover Park, IL
ADC USA, Inc. (Ithaca, NY) develops and supplies high-precision motion systems and instruments for large government laboratories and corporations around the world. ADC was contracted by NASA’s Langley Research Center (Hampton, VA) to design, build, and install the major components for a 40 × 40 × 40-foot indoor radar range. NASA’s goal was to refurbish and upgrade their old indoor radar range. They want to clear out what they had and replace it with newer, better-designed equipment. The goal was to put multiple targets inside the radar range without having to get a forklift to bring them in and out – not only things such as airplanes, but anything that is detected by radar.
The indoor range measures radar cross-section (RCS) and antenna measurement range. The range will include specialized active antennas, microwave circuits, and devices that are governed by underlying electromagnetic physics. RCS is a strong function of the orientation of the radar and target. The size of a target’s image on radar is measured by RCS. The radar cross-sectional area of an object does not necessarily bear a direct relationship with the physical cross-sectional area of that object, but depends upon other factors. Or, technically, the RCS of a target is the effective area that intercepts the transmitted radar power and then scatters that power isotropically back to the radar receiver.
Orienting the target – positioning it accurately within the radar range – is crucial to the measurement process. ADC had to build a transportation system into and out of the radar range that provided absolute accurate positioning. To bring targets into and out of the radar range, they proposed building railroad tracks approximately 110 feet long that would be all metal-welded. Two rails would be positioned about four feet apart and would traverse the distance to and through the indoor radar range. The track would be placed inside the building containing the range of the radar. NASA could roll equipment into the range and shoot it with radar to see what the radar looks like.
Because NASA wanted to put multiple targets inside the radar range without having to get a forklift to bring them in and out, ADC developed the design of a switching station outside the perimeter of the range. The switching station would actually be a turntable similar in operation to switching stations for railroad trains. Targets atop track sections could be moved on and off the turntable, which would then turn to align that track section with the 110-foot-long track that would bring them into the radar range.
The Experimental Test Range (ETR) rail system begins in the model prep area of the facility and ends 10 feet past the center of the test chamber. The total length of the rail system is 112 feet, with laser position encoding for the final section of the rail system using the WayCon, LLD-150-Profibus. Linear guide rails are used to support the carriages, and each carriage is positioned with a rack and pinion drive. Rails mount to steel weldments that are supported with 8”-diameter feet. Capacity of the rail system is 7,300 pounds.
The design includes a place to dock positioning components when they are not in use. Curved linear guide rails support the switching station so that the platform can be rotated manually. Hardened tapered pins are used to align the switching station with mating rail segments. NB Corporation of America machined the custom rails. They are case hardened steel shafts that have tapered ends to improve transfer across the switching station platform. The rail diameter is 2”. They are supported by NB shaft supports that are precision-machined aluminum extrusions available with or without pre-drilled mounting holes. They offer continuous shaft support and consistent shaft centerline. Spacing between sections is equal to the pitch of the rack so that transfer is completely motorized.
ADC was particularly concerned about the positioning accuracy requirements. They tested several vendors’ linear guides and blocks that would carry the target platforms. NB TOPBALL slide units were chosen. The NB TWD 32UU includes a clear anodized, corrosion-resistant aluminum block and a TOPBALL self-aligning slide bushing. Closed and adjustable clearance styles incorporate machined snap ring grooves in combination with standard retaining rings for slide bush retention. Their open style incorporates bottom plates and mounting screws to retain bushings in the proper position. All styles are provided with standard machined reference edges for proper alignment and installation.
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