FireWire cameras tackle linescan applications
Camera designers can choose from a number of interfaces when developing their products.
Camera designers can choose from a number of interfaces when developing their products. Depending on each application, these can range from Camera Link-, USB 2.0-, Gigabit Ethernet-, and FireWire-based designs. While each specific interface has different price/performance trade-offs, the trend to lower camera costs has resulted in a number of vendors embedding gate arrays or processors into their designs.
In this way, much of the image processing can be performed within the camera itself, reducing the requirement for host processing and allowing simpler, less-expensive interfaces to be used. In the design of 1394a cameras, for example, many companies have used PHY and LINK devices from Texas Instruments (TI; Dallas, TX, USA; www.ti.com) to implement the FireWire interface.
In developing their latest 1394a-compatible camera, however, Kerry Van Iseghem and his colleagues at Imaging Solutions Group (ISG; Fairport, NY, USA; www.isgchips.com) have taken a different approach. The company's LightWise LW-SLIS-2048A linescan camera uses the SLIS-2048a, a 2k × 1 sensor from Panavision SVI (Homer, NJ, USA; www. panavisionsvi.com) to digitize data at rates up to 60 MHz with 12-bit pixel resolution.
Using an onboard FPGA for developing custom algorithms and signal processing, the camera has optoisolated programmable I/O for trigger/strobe functions.
"Rather than implement the FireWire interface using TI's PHY and LINK chips," says Van Iseghem, "we chose to implement the link-layer controller in software on an 8051 microcontroller from Cirrus Logic (Austin, TX, USA; www.cirrus.com). This controller eliminates the use of a LINK chip, since the 1394a can be implemented with an 8051 and an external PHY chip. "As well as providing a 1394a interface, the on-board USB 2.0 circuitry of the 8051 controller allows the camera to be configured with a USB 2.0 interface without additional circuitry." According to Van Iseghem, the company has applied for patent protection for the idea.
Already the camera is finding use in high-speed linescan applications. Consol Energy (Pittsburgh, PA, USA; www.consolenergy.com), a producer of coal, gas, and electricity, is using the LW-SLIS-2048A camera to inspect belt splices in a mining application. In the mining industry, coal is extracted and then moved from the mine on conveyor belts that can be more than two miles in length. As mining progresses, belt sections are spliced onto the existing belt to keep the belts as close as possible to the mining faces. Pieces of belt are joined with metallic splices that have a lifetime of only three to six months. These splices must be constantly monitored to determine when they have to be replaced. It is difficult to inspect these splices manually as the belts run at up to 1000 ft/min.
"If these splices were to break while coal is being transported," says Van Iseghem, "the resultant downtime could cost the company hundreds of thousands of dollars." To reduce this downtime and to provide a splice management tool to the belt group, Consol Energy used ISG's camera to constantly monitor the integrity of each splice. Mounted above the conveyor belts, the linescan camera continuously digitizes and processes image data in the camera's on-board FPGA.
To detect whether a splice is present, an algorithm is run in the on-board electronics. This algorithm is a complicated function of edge sums and was tested extensively on a mock belt and a wide variety of operating belts. It is robust with respect to splice age, splice condition, and varying amounts of mud and moisture on the belt. The algorithm identifies both the leading and trailing edges of a splice. A pointer can then be set to send specific lines of belt data that includes the splice over the 1394 interface to a host PC. The host PC also runs custom ISG software that allows the user to configure parameters that control the splice detection algorithm and set camera operating parameters.
Although a number of companies including Point Grey Research (Vancouver, BC, Canada; www.ptgrey.com) have already migrated to 1394b-based designs, ISG has no plans to introduce a 1394b camera. Citing the lack of off-the-shelf 1394b LINK chips and the higher bandwidth and lower cost of Gigabit Ethernet, Van Iseghem's company plans to launch a range of Gigabit Ethernet-compatible cameras later this year.