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There are also other practical factors to consider when evaluating USB 3.0 for vision applications. An important one is the control protocol implemented on the camera. FireWire cameras use the 1394-based Instrumentation and Industrial Digital Camera (IIDC) standard, which enables any IIDC-compliant camera to be used with any vision software package that also supports IIDC. GigE Vision is the common standard for many Gigabit Ethernet cameras and provides the same benefits as IIDC in terms of software compatibility. USB 2.0, on the other hand, has no such common protocol. The USB Video Class (UVC) is not appropriate for industrial digital cameras, leading some manufacturers to create their own proprietary camera control interface and others to use IIDC. The Automated Imaging Association (AIA), which historically has had no involvement in USB 2.0, announced at its January business conference a new USB 3.0 standard committee to evaluate appropriate protocols like IIDC and GenICam.

Another consideration is cable length. The maximum length is not explicitly specified in the USB 3.0 standard. However, the standard does describe the relationship between wire gauge and maximum length in order to achieve USB 3.0 voltage drop requirements. For example, a cable can be up to 5.3 meters long when using an American Stranded Wire Gauge (AWG) of 20. In the majority of cases, the host computer system is located within this distance. A variety of high-performance and cost-effective solutions will rapidly become available to address situations where it is not. For FireWire-based applications, for example, where the maximum recommended distance for FireWire cables is 4.5 meters, products that increase the distance between the camera and host system are now commonplace. These include optical repeaters for spans greater than 100 meters, longer cables up to 20 meters, and more recently, 1394-over-GigE technology. Similar USB 3.0 solutions will be introduced. USB 3.0 hubs and repeaters already are in production, and work on signal-corrected long-distance cables, equilizer technology like EqcoLogic’s EQCO5000, and long-haul optical solutions is in progress. Other USB 3.0 cable and connector products geared toward industrial and machine vision are under development, including screw-locking connectors, high-flex chain cables, and so on.

Obviously if one interface can cover all requirements, ranging from size of the camera, bandwidth, cable length, price, and so on, it would be the clear technical winner. But in reality customer requirements are too diverse to be met by just one interface. In fact it is often what the interface does not do that makes the decision, rather than what it does do. Customers want more pixels at faster frame rates, superior reliability, a migration path for future retrofits, and perhaps most importantly, lower overall system cost. CCD and CMOS sensor manufacturers are providing more high-quality multi-megapixel image sensors that can run at increasingly fast speeds. While there is no single digital interface that works best for all vision applications, on technical merits alone USB 3.0 will be a strong contender, and will certainly become an important camera interface in the years to come. AI

Michael Gibbons is Product Marketing Manager at Point Grey Research, Inc.(Richmond, BC), where he is responsible for marketing and product management. He has more than seven years of experience in the field of advanced digital imaging, and is a graduate of the University of British Columbia (Commerce) and the British Columbia Institute of Technology (Embedded Systems).