Simplifying Measurement Of Complex Shapes

Performing dimensional inspections on complex parts has historically been an awkward process that has involved everything from hand gage measurement to sophisticated optical systems. This process can be difficult and time-consuming, especially when holes, anchors, braces, and other items must be located precisely on surfaces with irregular shapes.

This was the problem faced by the staff of Able Body Corporation (Joplin, Missouri), as they performed dimensional checks on large structures they manufacture for specialty trucks and personal watercraft. Able Body fabricates a wide variety of sheet metal, composite, and thermoformed plastic assemblies for cab roofs, boat hulls, and cabinetry.

Adhering to dimensional specifications is critical to Able Body because the company's fabricated assemblies must ultimately fit customers' vehicles. Until recently, Able Body used an optical level—a device similar to surveying equipment—to record dimensions on large, complex components and assemblies. This technique required the effort of at least two technicians, one to "sight" through the level and another to hold a scale against the part being measured. A typical truck cab required 8 to 16 man-hours to measure with a satisfactory degree of precision.

Not only was the optical process time-consuming, but it was difficult to measure many of Able Body's complex components and assemblies. For instance, technicians could not use the optical technique to measure the underside (called the b-surface) of composite parts. Although a b-surface is typically not visible on the finished product, structural components must be attached to this surface, so it is necessary to verify hole locations.

Able Body was able to greatly simplify dimensional checks by replacing the optical measuring system with a measuring device known as the FaroArm, developed by FARO Technologies, Lake Mary, Florida. Stefanie Curylo of FARO Technologies describes the FaroArm as a portable, articulating measuring device with up to seven degrees of freedom. At the arm "joints," rotational transducers report the X-Y-Z location and I-J-K orientation of the probe stylus located at the end of the arm. This enables the arm to follow complex curves and measure the shape of practically any 3D surface.

The mechanical arm is only half of the measuring system. The other half is a highly flexible software package called AnthroCAM, which enables users to create images of what they are measuring. As parts are measured, the software creates CAD data that contains quality information, from hole patterns to curved surfaces.

To take a measurement, Able Body's operators direct the arm's probe to the desired location and simply touch the part. Pressing a button on the handle at this instant records a dimension. Dimensions taken with the arm have point accuracy as close as ±0.003 inch.

Time savings have been dramatic. Able Body's quality engineers routinely perform measurement chores in half the time on large, complex parts. "The FaroArm is a better solution than optics in most of our measurement situations because it requires only one person to operate, and it provides exact measurement coordinates," says Bill Clinton, quality engineer at Able Body. "We've cut our labor cost for measurement by 50 percent."

Able Body technicians can now check dimensions they could not previously check. "Without a measurement arm, it was very difficult to measure the inner structure of a truck cab's roof skin, due to its awkward shape," says Mr. Clinton. "Today, using a measurement arm, we can do the job in less than two hours."

Able Body also can verify customers' models of new products very efficiently. "Generally, when we receive a die model or clay master from our customer, the model will have hole locations and X-Y-Z coordinates. Before we build the parts, we must verify that the model is correct. We can now take exact measurements and make this determination. If we work from a model that is not quite right, the part won't work when we try to assemble it. By comparing key features of the model with the drawing, we can make an immediate `go' or `no go' decision."

The bottom line, as far as Mr. Clinton is concerned, is that Able Body has increased productivity, enhanced quality, and reduced turnaround time for inspection by incorporating advances in measuring technology in its operation.