Home>Manufacturing Test Center>Test How-To

USB 3.0 making headway into cameras

Paul Kozik, Point Grey Research- June 12, 2012

USB 3.0, once known as Superspeed USB, offers considerable performance improvements over USB 2.0, answering the demand for a high-speed, high-bandwidth computer peripheral bus. Consumers who download large files such as movies and e-books can use USB 3.0 to provide the high bandwidth they need for fast data transfers. Engineers looking to rapidly transfer images from industrial cameras can also benefit from USB 3.0, and several manufacturers of industrial cameras have released entire product lines of USB 3.0-based cameras to meet this need.

Unlike consumers who download data to memory devices such as hard drives and flash drives, engineers need application software and a programming interface to transfer images from a machine-vision camera to a host computer. In response, the AIA (Automated Imaging Association) is developing the USB3 Vision camera interface standard, which will enable interoperability among a variety of imaging components. This standard, combined with the advanced capabilities that USB 3.0 offers, makes USB 3.0 a viable option for engineers who are developing machine-vision systems.

Best in class

Like other digital interfaces, USB 3.0 provides high data-transfer rates over a single cable, providing both ease-of-use and cost-effectiveness. In fact, USB 3.0-based vision systems are competitive with systems based on other interfaces. It can outperform many of them in terms of bandwidth and low CPU usage (see Table 1). USB 3.0 enables DMA (direct-memory access) data transfers, which allow images from the camera to pass directly to host memory without CPU interrupts. That greatly reduces CPU usage during data transfers and frees resources for image-processing applications.

Table 1. Comparisons of digital interface standards used in vision systems.

	FireWire-b	Gigabit Ethernet	USB 2.0	USB 3.0	Camera Link
Bandwidth	80 Mbyte/s	100 Mbyte/s	40 Mbyte/s	400 Mbyte/s	680 Mbyte/s (8-tap)
Cable length	10 m	100 m	5 m	5 m	10 m
Power + data over one cable	Yes (45 W)	Yes with Power over Ethernet (15 W)	Yes (2.5 W)	Yes (4.5 to 7.5 W)	Yes with Power over Camera Link (4 W)
Camera-control standard	IIDC	GigE Vision	N/A	USB3 Vision (in progress)	Camera Link
CPU usage	Low	Medium	High	Low	Medium

USB 3.0 cables improve upon the half-duplex communication offered by USB 2.0 cables, where data flows in only one direction at a time. USB 3.0 cables add five wires for a total of nine wires in the connectors, and the cables use a dual-simplex interface that lets data flow in two directions at the same time. USB 3.0 cables are backward-compatible with USB 2.0, though, so users will be able to connect USB 2.0 peripherals to a USB 3.0-enabled computer, or connect USB 3.0 devices to a legacy computer. USB 3.0 Standard-A, Standard-B, and Micro-AB receptacles are also backward-compatible with USB 2.0. This relationship lets camera manufacturers focus on USB 3.0 technology while still supporting USB 2.0 customers. Figure 1 shows a camera with USB 3.0 connector. USB 3.0 uses both sides of connector. USB 2.0 needs the left side only.

Figure 1. A USB 3.0 cable adds five wires to the USB 2.0 interface. USB 3.0 uses both parts of the USB connector while USB 2.0 uses the left side only.

One of the most compelling features of the USB 3.0 interface for machine-vision cameras is its high bandwidth. Because USB 3.0 provides an effective bulk-transfer rate of approximately 400 Mbyte/s, which is 10 times faster than USB 2.0 and five times that of IEEE 1394b, camera manufacturers can build USB 3.0-based cameras that incorporate the fastest image sensors in low-cost packages. Previously, these sensors were limited to specialized high-speed cameras that offered onboard storage or that used complex interfaces to connect with expensive frame-grabber technology.

To demonstrate the capabilities that USB 3.0 offers to vision applications, we performed a streaming test with two of our Flea3 cameras (a 1920x1080 camera at 60 fps and a 1280x1024 camera at 125 fps) connected to a single PCIe card. The two cameras successfully generated a total of more than 280 Mbyte/s of image data.

In the past, camera vendors often used onboard solid-state or compact-flash storage and limited the user to burst capture behavior constrained by the capacity of the storage medium. USB 3.0 now lets camera vendors support image capture at high frame rates on a continuous basis, making it possible to use these cameras in applications that require 24/7 operation.

USB3 Vision promises plug-and-play

To aid developers of machine-vision systems that use the USB 3.0 interface, the AIA and machine-vision camera, software, and peripheral providers, are developing the USB3 Vision standard to permit interoperability of cameras, accessories, and software from different manufacturers. USB3 Vision is scheduled for release later this year, and components that comply with the standard will offer plug-and-play compatibility and will let developers interchange components with little or minimal effect on an overall system. The establishment of USB3 Vision ensures greater compatibility between cameras and host imaging libraries, a benefit that wasn't available to USB 2.0.

Like the popular GigE Vision standard, which is also maintained by the AIA, USB3 Vision will provide a framework for transmitting high-speed video and related control data. Also like GigE Vsion, USB3 Vision will make use of the GenICam programming interface (developed by the European Machine Vision Association) to capture camera attribute behavior. This will minimize the need to modify the host software to support a new camera model.

Developers who want to employ USB 3.0 should have no trouble finding affordable products for their systems. Peripheral devices for USB 3.0 are becoming readily available on the market, and chipsets used to enable the technology are priced very aggressively due to the high-volume market of hard-drive storage.

USB 3.0 is also currently supported by the majority of new laptop computers. By 2015, all PCs are expected to support it. In terms of operating systems, Windows 8 will provide native support, Intel has just announced its new 7-series chipset with native support, and the Linux community is actively developing a kernel driver to support USB 3.0 on Ubuntu and other Linux operating systems. T&MW

Paul Kozik is the Product Manager at Point Grey, one of the founding members of the USB3 Vision committee. He has worked for a number of imaging companies in a variety of roles including applications engineering, sales, and technical support before transitioning to product management.  Kozik manages all imaging products from initial concept to complete life cycle. He holds a Bachelor of Engineering Science (BESc) degree from the University of Western Ontario.