Table-based optical measurement is a quick, simple, and accurate method for both measuring and reverse engineering flat and folded/formed sheet metal components; gaskets, seals, and O-rings; laminations; paper, acetate, and electronic drawings; as well as other opaque and semi-transparent flat materials.

Figure 1. The InspecVision Planar measurement system consists of an LED backlit table and a 50-Megapixel camera sitting over the top. (Image courtesy of Exact Metrology, Inc.)

The basic elements of the Planar measurement system from InspecVision Ltd. are an LED backlit table and an up-to 50-megapixel camera sitting over the top. The camera “sees” the edges of one or more parts randomly placed on the table. Within about 30 seconds it takes a snapshot of a part, which it can either compare to a CAD file for inspection, or output as a DXF or DWG CAD file for reverse engineering.

Typical users of this system include sheet metal fabricators using X/Y CNC, laser, plasma, punch, water-jet cutting, and forming machines who supply a wide variety of industries such as automotive, aerospace, electronics, and communications.

2D Inspection

Joe Wright, General Manager, Exact Metrology (Moline, IL), described a typical inspection scenario where the system would be installed on a factory floor near a group of punch presses. Since there are no moving parts and the data is captured at a rate of about 4 megapixels per second, the system is not affected by vibration, he said. That means the presses could keep running while the part is being inspected.

The punch press operator could upload a CAD file by scanning it into the machine using a bar code. There is no need for a certified technician to take measurements once the integrated computer has been programmed for the desired dimensions, including hole sizes and locations, linear dimensions, and radiuses.

The operator can pull a finished part (or parts), place it on the table without any fixturing and without regard to any particular orientation. The control software will virtually orient the part before comparing it to the CAD file. The measurement accuracy ranges from 12 microns for a small (500 mm × 330 mm) table to 50 microns for a large (2355 mm × 1570 mm) table.

Important features include:

  • Multiple identical parts can be scanned simultaneously. If you place, for example, 10 parts on the table, and part 5 in the corner does not pass, the display will segregate that part on the screen.

  • Since the parts don’t have to be touched to be measured, the machine can also be used for O-rings. Trying to measure an O-ring with a tactile device like a coordinate measuring machine (CMM) or even calipers, you run the risk of distorting the piece and producing an error.

  • Although the table is made of glass, scratches can be calibrated out so they will not affect the measurements.

  • It will generate reports automatically, including measured data and nominal data and it will indicate PASS or FAIL for each item.

  • A color deviation diagram comparing CAD data to measurement data will be displayed and/or printed.

  • Deviations can be projected onto the part itself, using augmented reality.

  • It will output SPC data for analysis.

2D Reverse Engineering

Figure 2. Multiple identical parts can be scanned simultaneously without regard to orientation. (Image courtesy of Exact Metrology, Inc.)

Reverse engineering falls into two categories. The first involves imaging an already manufactured piece and the second is converting a paper, acetate, or electronic image file to a CAD file.

“I’m in the Midwest and I have shops that will run punch processes or do laser cutting. A farmer might come in and say: ‘Hey I got this piece that broke. Sit it on the table and cut me a new one.’ My end customer would use the table for getting the data to control their cutting. Versus the old school where you’re grabbing tape measures and calipers, you start drawing this thing out and then you have to create a CAD to get it. This will skip that whole step,” said Wright.

To generate a drawing for a manufacturer, a part can be placed on the table, and an image file will be ready within 30 seconds. The software then allows the user to edit and clean the data, for example, standardizing hole sizes, cleaning up edges, and removing burrs.

I asked Wright what kind of tolerances a manufacturer could achieve. He said that the best you could expect is the 12 to 50 microns of the system itself. Then to determine the tolerances needed for manufacturing a part, you can overlay multiple parts to see the dimensional variability of the typical sample pieces. If you had, say, a 30-piece study of the part that you’re trying to reverse engineer, you could overlay those 30 pieces and get a process deviation to help you specify your tolerances.

From Drawing to CAD File

Figure 3. Worker preparing to cut a custom sheet metal part. (Vadim Ratnikov/Shutterstock)

If you have a scaled drawing on paper or acetate, it too can be placed on the table and imaged to produce a CAD file. It can even be used to create files for reproducing graphics, perhaps a logo. You lay the drawing on the backlit table. If the light can be seen through it and the drawing is black print on white paper, the print can be picked up as edges. However, the drawing has to be scalable — either one to one or some fixed ratio — it can’t be just a hand drawn picture of a part. Once it is scanned, the drawing will be imported to a DXF file format.

2.5D Inspection

Figure 4. Sheet metal with small bends can be inspected with 2.5D imaging. (Image courtesy of Exact Metrology, Inc.)

Typical punching machine products can include features like louvres or small bends. The add-on SurfScan projector shines structured light onto the part being imaged. It integrates with the system software to allow accurate inspection of both the 2D shape and its “2.5D” features with a single click.

3D Inspection

The Opti-Scan inspection system can measure surfaces and edges in 3D. This non-contact structured white light scanning system uses a high-speed, high-resolution camera and an LED DLP projector to scan the surfaces of an object.

Patterns of light are beamed from the projector onto the part to produce a fringe pattern. The fringe data is recorded by the camera and used to create either a 3D point cloud or a polygonal mesh of the scanned surface. The processed imaging data can be sent to several different file types for use in virtually any 3D inspection or reverse engineering software package.

With 2D imaging, one shot captures the full picture. With 3D, the imaging is still line-of-sight so you have to use a three-axis table that can rotate and tilt the object to get data from every angle. The data is then stitched together to obtain the full 3D image.

Opti-Scan 3D can be added to existing Planar systems, transforming Planar into a complete 2D and 3D measurement system.

Important features include:

  • Single click automated inspection.

  • White light scanning technology.

  • Surface and edge measurements in 3D.

  • Texture mapping — can create a fully textured mapped point cloud in full color.

  • Scans objects at a rate of approximately 250,000 measurements per second.

Summing it Up

The Planar system is designed for fast, accurate, and rugged measurements of fabricated sheet metal parts. It is well-suited for quick, accurate first article inspection, quality reporting, and reverse engineering. The system is ideal for shop floor use — it is not affected by vibration caused by nearby machines; it requires minimal operator input; and because of its speed and accuracy, it can increase production throughput across a wide range of applications.

This article was written by Ed Brown, Associate Editor of Photonics & Imaging Technology. For more information, visit here .