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USB3 Vision

USB 3.0 has found interest of the machine vision market as it delivers a host based (i.e. no frame grabber) solution for faster cameras.

As such a group of companies under the leadership of AIA (Automated Imaging Association) decided in 2011 to cooperate in the development of a machine vision standard for USB, called USB3 Vision. However, despite the name, the standard is not technically limited to USB 3.0. The VISION show in November 2012 saw many companies announce the first products to meet this new standard with many more to follow. USB3 Vision has now matured with a growing choice of products, good interoperability between cameras and a choice of software vendors supporting the standard.

Like GigE Vision, the new standard will be a mere protocol standard or "on the wire" standard. This means that only the data package layout and a bootstrap register map is defined. This ensures that a USB3 Vision device needs a certain "basic intelligence" without having to reload firmware. No manufacturer specific drivers will need to be installed on the host, provided that USB3 Vision compliant software is installed Thus the integration on niche operating systems such as Linux is no longer an obstacle and easy migration between manufacturers is possible when using independent USB3 Vision software. USB3 Vision uses the GenICam GenApi device description for camera control as used on GigE Vision, CoaXPress, CameraLink 2.0 and CameraLink HS. It is expected that the camera will be controlled via the control channel, and data transferred as bulk data. Asynchronous events may be sent from the camera to the computer using the event channel also based on the bulk transfer. The new standard is very different from the standards used for USB web cameras, etc. to meet the specific requirements of industrial imaging.

USB: cables and connectors

According to the USB 2.0 standard the maximum length of a USB 2.0 cable is 5 m. Longer cables can be used if they are made of high quality material and where transmission distances are longer, hubs or active repeaters can be installed. Testing by our integration team and cable suppliers have shown that cable lengths of 7 metres are possible and can be guaranteed using higher quality screening and cable design.

On the other hand we have found that USB 3.0 running at the full speed might limit cables to 5 metres. As such we highly recommend the use of machine vision validated USB cables, rather than the cheaper consumer cables. Optical repeaters and extenders are available today and extend the range of USB 3.0 to several hundred metres.

As with USB 2.0, hubs can help either to connect several cameras or extend the reach. The maximum theoretical distance using passive copper cables is approximately 30 m. In this case, the hubs should be powered externally.

Our certified USB 2.0 cables or USB 3.0 cables are validated for use with the higher data rates and industrial environment we find in machine vision applications. These screened twisted-pair cables have two wires for differential data signals and two for power supply. The power supply from the bus (up to 2.5 W - 5 V and 500 mA with USB 2.0 and 900 mA with USB 3.0) is sufficient for most USB cameras. Tests have shown that there are significant differences between the cables available in the market

Because USB was developed for the mass market there are no defined standards for locking mechanisms or connectors for robotic applications. On request, we will be pleased to deliver connectors with locks and highly flexible cables. USB3 Vision includes the definition/recommendation for an optional locking mechanism.

Here you can see examples of USB cables with locking mechanisms for application in industrial environments.

As described earlier, the new offspring USB3 Vision is hosted by AIA (Automated Imaging Association) and was adopted by the G3 pool of the three leading machine vision associations AIA, EMVA and JIIA. Further information about this standard is available at: http://www.machinevisiononline.org/vision-standards.cfm.