CCD cameras and frame grabbers became the staples of industrial imaging in the mid-80s. However, improvements in CCD sensors and the increased accuracy of frame grabbers during the ‘90s have advanced the state of the art. As a result, industrial applications for video imaging have blossomed in recent years.

The CCD camera is the heart of industrial imagers. These cameras give industrial machines the ability to detect objects. For example, they can give robotic machines "vision" or allow automatic inspection machines to detect flaws in products running on a conveyor belt. You can find CCD cameras in a variety of formats- - finished cameras housed in a case and modular cameras that you can mount inside a system. If you can’t find an off-the-shelf camera that meets your needs, you can find chip sets that let you design the CCD sensor directly into your system.

CCD cameras come in many shapes and sizes and cover a wide price range. They can cost from $125 for a Hitachi VK-C25 module to more than $100,000 for a Kodak Ektapro RO image-capture machine. A signal from a CCD sensor must be manipulated to format it for capture by a frame grabber before it becomes a suitable image for capture on a CRT monitor.

Both Hitachi and Sharp Electronics offer CCD cameras in modular form factors. Hitachi has a four-chip set that works with most complementary color CCD-area-image sensors with as many as 768 effective horizontal pixels. The chip set consists of the HA118184F, a correlated double sampling/AGC chip; the HD49319F, a nine-bit CMOS A/D converter or a 10-bit CMOS A/D converter; the HD49811TFA, a CMOS digital signal processor (DSP) with timing generator and D/A conversion; and the H8/337, an 8- or 16-bit CMOS embedded controller.

Both Sharp and Hitachi chip sets use correlated double sampling in the first stage of processing to remove low-frequency noise from the CCD sensor output. In the next stage, an AGC circuit compensates for the dc voltage coming from the CCD sensor. Then, a knee circuit puts a bend in the slope of the gain curve to emphasize low-level signals. The resultant signal gets passed on to the A/D converter, which, in turn, passes the digital signal along to the DSP chip.

The heart of the Hitachi chip set is the H49811TFA DSP chip, which provides the timing generator that controls the charge transfer of the CCD elements. The chip also produces the luminance (Y) and chrominance (C) signals in YCrCb 4:2:2 format. A D/A-converter block permits the chip to reconstruct the digital YCrCb data into an NTSC signal for driving a frame-grabber board (see box, "Frame-grabber boards"). The chip also provides "de-kneeing"of the gain-curve slope. Hitachi offers the chip set for $50.70 (5000).

Hitachi also packages the four-chip set in its VK-C25 (250,000 effective pixels) and VK-27 (380,000 effective pixels) digital video-camera modules. The VK-C25 has 320-line resolution and the VK-C27 has 400-line resolution. Each module is a functional video camera consisting of a CCD sensor/lens board and a digital video signal-processing board connected by a ribbon cable. The module comes as a finished camera, including case. An auto-iris function with a 1/60- to 1/10,000-sec shutter speed, backlight compensation, and white balance uses the DSP board. The auto-iris keeps the visual output at a fixed level, even when the brightness of the surroundings changes. The VK-C25 costs $125 (5000).

Sharp Electronics delivers many of its chips in camera module format. It offers a wide variety of CCD and peripheral chips to build digital cameras. However, the company says that 90% of its orders are for custom-built modules that you can install easily.

A look at finished cameras

When you choose a CCD camera, you should consider its size, resolution, cost, optics, and sensitivity. You should also think about color or monochrome and any special requirements you may have for the camera. Pulnix produces a wide variety of finished digital cameras for high-speed production and inspection machinery, robots, military aircraft, and vehicles. Pulnix cameras range in size from 1 to 1/3 in. and have resolutions of 768×484 to 1024×1024 pixels. They cost $2200 to $2500 and $8000 to $9000, respectively.

Pulnix uses an interline-progressive-scan technique to transfer the charge from an area-array-CCD sensor to the horizontal-readout register (Reference 1). The interline-transfer scheme places an opaque analog register next to every transparent vertical-analog-element in the array. The transparent elements load their charge into the adjacent opaque registers on command from the controlling electronics. This transfers the charges to the horizontal readout register using a bucket-brigade transfer. Progressive scanning makes certain that each charge arriving at the horizontal readout register gets transferred out of the CCD before another charge transfer can take place.

If you’re looking for a low-profile CCD camera for microscopy, radiology, surveillance, or other low-light-level applications, you should look at Xybion’s ISS-255 camera. The $10,500 camera has a mount that measures 4.25×1.99 in. and is 4 in. high, and it has a sensitivity of 10^-6 fc. A unique feature lets you rotate the sensor in 90° increments, so the video output is properly oriented for viewing, regardless of the package-mounting orientation. The camera has an effective image of 753×488 pixels and, when equipped with an auto-iris lens, has as much as nine orders of magnitude in dynamic range.

Another low-profile video camera is Chinon’s $499 VCC-620 model. The camera measures 2.8×7.7×1.8 in. and weighs 8.9 oz. The color video camera has a 1/3-in. color CCD sensor, which produces 250,000-pixel (512-horizontal×492-vertical) resolution. The camera has a 1/60- to 1/15,000-sec electronic shutter and a 78° field-of-view optical lens.

Electrim Corp offers seven camera models that have resolutions ranging from 192×330 to 1134×972 pixels, with horizontal pixels interlaced. The cameras come with their own ISA bus control card, which eliminates the need for a frame-grabber board. Sub array scanning allows the board to capture moving objects within still images, producing full-motion video. All timing, video signals, and power are carried on a single multiconductor cable, which connects the camera head to an ISA bus computer. The camera head contains only the lens, optics, CCD sensor, and an op amp. The EDC-1000 model measures 1.95×1.2×1.20 in.

Electrim cameras are being used for imaging applications in microscopy, astronomy, factory automation, robotic vision, and industrial inspection. Camera prices range from $400 to $1250, and all of the cameras use either full-frame or frame-transfer CCD detection.

If you have the luxury of having an IEEE-1394 serial bus connection to your computer or industrial system, you can consider two camcorders from Sony Corp. The IEEE-1394 serial bus can transport digital data at 100, 200, or 400 Mbps. Isochronous, just-in-time delivery permits low-cost implementations for critical timing situations.

The DCR-VX1000 and the DCR-VX7000 models offer the digital picture and sound afforded by the digital video format, a format agreed to by 55 manufacturers worldwide. The DCR-VX1000 gets the most out of the digital video format by offering 20× digital zoom and a 180,000-pixel color viewfinder. A dichroic prism splits light into its red, green, and blue components, which are directed to one of the three 410,000-pixel CCDs. The result is a high resolution of 1,230,000 pixels.

The DCR-VX700 camcorder offers a single 410,000-pixel CCD sensor. The camcorder also offers a 180,000-pixel color viewfinder and a 20× precision digital zoom. Both models have an IEEE 1394 serial bus interface. The DCR-VX1000 costs $4999, and the DCR-VX700 costs $2999.

1.Gallant John, "CCDs let you design vision into applications," EDN, Oct 12, 1995, pg 87.