Although photographic evidence was crucial to his reports, Clarke had no satisfactory way to reproduce and transmit his images without incurring unacceptable losses in resolution and contrast quality while relying on Polaroid prints. Now he can transmit them worldwide as digitally captured by storing them as files on a local area network server.
Clarke uses three digital imaging systems, including a scanning electron microscope, in his lab at Case. The most used system, however, is the Kodak MegaPlus camera, model 1.6i/AB, which he relies on for grayscale imaging. The camera employs a 9 x 13-mm charge-coupled device (CCD) sensor to produce 10:bit digital grayscale images measuring 1534 x 1024 pixels.
The camera’s pixel array size was what initially attracted Clarke to the MegaPlus. He was looking for something that would match the images he had been getting with 4 x 5-in instant print film. To achieve this same field size, Clarke crops the camera’s image down to 1024 x 1280 pixels. The cropping results in 1.3 MB bitmap grayscale image files.
According to Clarke’s calculations, 4 x 5-in instant print resolution is approximately equivalent to six lines per mm at a magnification of 500 times the numerical aperture. His experiments with the MegaPlus camera indicated a resolution of 5.6 lines per mm. The experiments were conducted using a Nikon 60 mm f/2.8 micro Nikkor lens on a copy stand imaging an office copier resolution test chart (a version of the NBS Microcopy Test Chart) in a 3.5 x 4.5-in field size.
Upon selecting the MegaPlus, Clarke quickly found ways to increase the flexibility of the camera system. For large field sizes, he mounts a Vivitar 28-mm f/2.8 lens on the camera. The 60-mm micro Nikkor yields magnifications on the camera’s CCD sensor of 0.1-1.0 times, which when enlarged are equivalent to 1-10 times 4 x 5-in instant prints. He has also machined a special mount that allows him to add an Olympus bellows on the camera. With it, he can use a 100-mm f/6.3 Zeiss Luminar lens to yield 1.0-2.5 times magnifications on the sensor. With a 63-mm f/4.5 Zeiss Luminar lens, he can get 2.5-5.0 times on the sensor for the equivalent of 25-50 times magnification on a 4 x 5-in print. The camera can be transferred from the copy stand and mounted on a nearby Zeiss Universal Microscope in less than a minute to capture images of even greater magnification.
“this gives us far more flexibility than we had in the past,” Clarke says. “We can image small regions on large parts at high magnification, which we couldn’t do before when we were working with a view camera system. Now we have a two-stage compound system.”
The MegaPlus camera, when cabled to a Pentium PC, produces images that are immediately viewable on a 1024 x 1280-pixel monitor, which provides a particularly fast way of producing photomacrographs of fracture surfaces and relevant features, such as broken gear teeth.
Metal surfaces are often highly reflective. Establishing proper lighting and exposure to capture sufficient detail is a bit tricky with Polaroid film. In the past, it wasn’t uncommon to expose three or four sheets of instant film for every usable picture, Clarke says. The digital system allows Clarke to quickly establish proper illumination, focus, and depth of field while viewing camera output in real time on the computer monitor.
“With the Kodak system, it’s almost like viewing live video, except that you’re looking at it in HDTV resolution,” Clarke says. He believes that time savings with the digital camera average at least 75%. The camera has paid for itself several times over, Clarke says, both by eliminating waste and making the metallurgists and technicians more productive in the lab.
When a metallurgical report is complete, it goes onto the company’s network server as a Microsoft Word file containing image links. This keeps the Word document small. The images are downloaded when a person opens the report on the network. This generally takes a few minutes.
“We can also send users a brief report on e-mail. Then they can pick up the images, look at them on their monitor, and download them if they need to,” notes chief engineer Gordon Walter.
“Recently, we sent two of the 1.3-megabyte image files to France,” continues Walter. “That only took a couple of minutes. Until now, the only way we could move an image that fast was to fax it, but this way is far superior to faxed images. With a fax, you lose image detail.”
In other settings, the images might choke a local area network. But that hasn’t been a problem at the Case Technology Center, where the LAN is a Token Ring network designed to accommodate engineering drawings that are quite a bit larger than the MegaPlus camera’s image files.
To print the images, the company is currently using networked laser printers with 8 MB of RAM and 600 dpi resolution. Network printers with higher resolution and grayscale range could upgrade the company’s print capabilities when they become competitive in price with the current laser printers.
The Case failure analysis department is creating a reference library of microstructure images that have been captured digitally. Image Central software from Advanced Imaging Concepts Inc., Princeton, N.J., is being used to create the database with reference images and associated data.
“The idea is to document different types of failures and keep the images in the system so people can go in and see what a typical failure of type X looks like and compare it with the part they’re examining,” Clarke explains. Images will remain on the network long-term for reference, so that even if a written report is lost, users can call up the report and its supporting documentation.
Clarke is also setting up a system that would allow him to transfer failure analysis reports to Case’s key suppliers in a secure fashion using encrypted files. Suppliers now receive only hard-copy versions of his reports.
Summing up the impact the switch to digital imaging has had at Case, “we’re looking at a major improvement in the way test images are acquired and used throughout the company,” Walter says.