“You need to be able to create an image and access a license plate number on a car quickly, get that information back to wherever you need it, and get it ready for the next one that’s whizzing by,” said Morse.
Quality sensors have become available at lower prices, and big manufacturers like CMOSIS, Sony, and Aptina strive for the improved speeds.
Another speed innovation lies in the cameras’ communication features, which now are able to take data very quickly to where a user wants it. Gigabit Ethernet, a technology that transmits Ethernet frames at a rate of a gigabit per second, enables users to take an image away from a chip rapidly and transfer it back to wherever he or she wants to process it, often to a standard computer.
Many companies offer GigE cameras, and the options appeal to customers like Richard Schwarzbach, president of the Sebastian, FL-based systems integrator, InoSys, Inc. The InoSys founder, who builds and integrates between 10 and 20 systems per year, frequently installs PPT Vision multicamera systems, which have the hardware, I/O, and drivers necessary to hook up GigE vision cameras. Schwarzbach recently finished building a large system with seven GigE, high-resolution (3.5 megapixel and 4.2 megapixel) cameras (see Figure 2).
“With GigE, you plug an Ethernet cable into it, you plug it into a port on a PC, and you have communication with a camera,” he said.
The GigE cameras have provided the necessary speed — Schwarzbach recently finished a job that processed 600 parts per minute — along with other additional improvements. On certain jobs, Schwarzbach cannot always place the camera in the right orientation to help a customer who, for example, may need to see a bottle standing up and not laying on its side.
“Normally you’d have to take that image and mirror it inside of the computer, but these cameras are smart enough that you can mirror right in the camera and it takes no time. You’re talking microseconds.”
In the past, says Ben Dawson, Director of Strategic Development for Machine Vision at Teledyne DALSA, a machine-vision manufacturer headquartered in Billerica, MA, there was not enough bandwidth on either the interface link or the computer to handle high-speed demands. “Now customers routinely use four cameras, effectively 40 megabytes per second, with no problem at all,” he said. “In some cases the cameras generate 50 to 60 megabytes per second. A camera has to feed that need.”
A high-quality picture has always been important to machine vision customers, but consumers have high expectations, too. The latest iPad, for example, features a 5-megapixel iSight camera.
Some manufacturers, however, require superior color resolution for tasks like edge-to-edge measurements of colored objects or verification of the uniformity of a colored part. One technology that has improved resolution is a specialist end of the market called 3- chip technology.
Most machine vision color cameras have a standard lens, along with one sensor, which picks up the light. The onechip cameras use a Bayer Pattern of alternating red/green and blue/green filters over individual pixels.
Three-chip technology uses three, separate charge-coupled device (CCD) sensors and a prism. Each CCD is covered by a different color filter, and handles one of the three primary colors: red, green, and blue. The prism splits the light coming through the lens, and focuses the different wavelengths to the appropriate CCD.
In a 3-chip camera, color (red, green and blue) is fully sampled at every pixel in the image. These types of cameras, however, are only usually used where accurate color recognition is critical, like when providing high-quality images for the food industry or for the print industry. Because each of the three monochrome sensors is dedicated to a different color (rather than one sensor covering all of the colors), there are less resolution problems and no bleeding, fringes, or edge defects. The alignment of the prisms used to send light to the three CCD chips, however, contributes to the high cost of these cameras as well as the cost of two additional sensors. The light must pass through the prism and lens, hitting the same corresponding pixels on each of the carefully placed sensors.
“What I would like to see, and I don’t see anything on the horizon, is a way to inexpensively get full-resolution color,” said Dawson. “I get complaints from customers who use a Bayer Pattern color camera, but can’t afford a full-resolution camera. The typical customer that has problems is looking at manufactured objects with fine color details.”
Although the 3-chip technology has been around for 30-plus years, the nature of the cameras is changing to some degree, according to Morse. The three chips are not always designated to red, green, and blue. Some of the chips correspond to “UV+ visible light + IR” instead, and each will be configured to sense a particular material.