Explanation of the USB3 Vision camera protocol | Top 5 reasons why to use an USB3.0 camera | Top 10 checklist for implementing an industrial USB3 Vision system

Introduction to the industrial machine vision USB3 Camera System


USB3 Vision standard is an imaging interface standard for industrial USB3 vision cameras. The majority of camera manufacturers have already adopted this standard, and the number of compatible, accessories growing quickly. A big advantage of the USB3 interface is that, any of the PCs, laptops and smartphones have a USB 3.0 interface built in nowadays. In the field of vision technology, USB 3.0 is also replacing dated interfaces such as the FireWire, Cameralink and USB2.0.

The speed of the USB3 Vision Camera Interface

The USB 3.0 interface, also known as Super-Speed USB, is the following line of the well-known plug and play Universal Serial Bus spec that builds on the assets of USB 2.0 and washed out its weaknesses. The operative bandwidth accessible with the use of USB 3.0 when transferring bulks of data totals 350-450 MB/s, conditional on the host controller. This is roughly about ten times higher than the USB2.0 camera USB 2.0 cameras and 4 times higher than GigE cameras.

The protocol of an industrial USB3 Vision Camera

USB 3.0 makes use of nine wires in total in the USB 3.0 plug and cable as well as the Unicast Dual-Simplex data interface that permits transferring data in both ways. The USB 2.0 interface still makes use of an unidirectional transfer model, where GigE, FireWire and USB 3.0 all allow transferring data in both ways, this is a huge improvement. A host directed procedure then sends route packets and notifications explicitly in an allochronic manner. The procedure enables the cameras to send a message to the host controller to know when it is prepared to transfer data. This mechanism reduces system overheat and CPU load relative to the polling mechanism in USB 2.0 modules. Likewise this makes USB 3.0 a similar interface to Firewire at once.

USB3 Vision camera standard

Well-established manufacturers of USB 3.0 applications and accessories, jointly invented the USB 3 Vision Standard and launched the interface into the market. The new standard has strong benefits for all their users. Also software and hardware can be exchanged in and out, which allows for greater modification possibilities and therefore flexibility. There is also certainty that all functions are available, and that image transmission is stable. The Automated Imaging Association is accountable for the interface and publication.

Top 5 reasons to select the USB3 Vision camera interface


•    The USB3 Vision System stability: A universal standard for the requirements for accessories and cables averts potential failures during data transmissions.
•    Low CPU: Due to Zero Copy the required CPU load is very low when capturing images.
•    Low jitter times and latency: The duplex communication options enable the host to initiate actions at any given time without suffering from delays.
•    The present bandwidth will no longer be adequate to operate on the current and specifically upcoming requirements posed by vision systems. Higher resolutions, framerates and alternate image formats are increasingly requiring more bandwidth and cannot be processed by dated interfaces.
•    Interfaces such as FireWire are dated and nearing the ‘end of life’ stage in the product life cycle. The past shows that hardware based on technology approaching the end of this and becomes more difficult to buy. As aforementioned this is currently happening with the FireWire interface.
 

How to install an USB 3.0 camera system


There are a few variables to be taken into consideration before setting up a system compatible with USB 3.0 cameras:
•    Which cables are required? Which cable length? Do you require a passive or active USB 3.0 cable(s)?
•    How many industrial USB 3.0 vision cameras are used in one system?
•    What are the requirements for the PC hardware? Are there specific components that need to be installed or need upgrading?
At the initial release of the USB3 vision standard. Users struggled to accomplish a stable setup, mainly caused by problems with accessories. These struggles are solved and nowadays USB3 is an easy and stable interface.
 

The key to a stable USB3 camera setup


For all USB3 Vision Standard accessories the minimum performance is specified. To solidify the complete power of the new technology and achieve uppermost stability, it is of importance to select individual components carefully, this includes the camera. USB3 accessories such as cables, cards and other components are broadly accessible in the market of consumer electronics, whilst being reasonably priced. Because these components are cheaper some users will be drawn to use these in their machine vision applications. These accessories are normally not certified based on the USB3 Vision Standard and will be most likely unable to operate on the strict requirements of an industrial application. Often resulting into lost mages or even worse, a complete breakdown of your system. This will frequently be blamed on a defective camera, even though poorly chosen accessories caused the problem. All accessories in our webshop are USB3 Vision certified and therefore we advise to use these.

Certified and tested USB3 camera accessories

The interaction between individual components is extremely important in the setup of a USB 3.0 camera based image processing system and must be taken in consideration. For this reason, for example, Daheng Imaging has tested all accessory components together with their camera models and are only being sold after it passes these tests. Any limitations that arise during the interaction between accessories and camera will be documented and these components will not be sold with this camera, or only when the limitation are clearly defined. The foremost advantage of this is that users can assume stability and reliability whilst using standardized accessories in their systems.

The key components

As aforementioned in the prior section, the interactions between individual components in a USB 3.0 image processing system is very critical and components must be picked cautiously. Components that necessitate special attention are described below.

USB3 Vision cables

Dissimilar to standards such as GigE Vision or CameraLink, USB3 Vision describes cable connections and the main necessities for compatible cables. The maximum cable length is determined by the ratio between the high-frequency features, and the relationship between the maximum possible cable length and the thickness of the copper wire before the USB 3.0 voltage drop happens.
Cables need to meet different technical conditions based on the purpose or applications they are used for. A screw-down USB 3.0 Micro B plug is used on the side o the camera, whilst a USB 3.0 Standard A will be used on the PC or hub side. Considering the USB 3.0 Standard A plug and the USB 2.0 jack are very much alike, specific symbols or a blue tag on the jack or plug are used to provide an indication the presence of USB 3.0 functionality.

USB3 Vision cable length

Regarding the length of the cable, it is of importance that the cable has been fully examined for compatibility with USB3 Vision. Passive cables have a maximum length of 4.5 meters, where active and hybrid cables have a maximum length of 20 meters, but the two latter are way more expensive and not supported by GeT Cameras. Applications that need such a long cable, should take a look at GigE cameras. There is a possibility that these are more affordable in that specific setting. Daheng Imaging certifies and tests its cables and has a wide range of cables that can be found under accessories.

Host Adapter

The amount of USB3.0 bandwidth accessible is determined by what kind of motherboard chipset and USB 3.0 chipset will be used. The option to connect your cameras to motherboards via the USB 3.0 connection is always there. When there are not any integrated USB 3.0 connections available, then PCI Express cards can be installed. To make use of the maximum amount of bandwidth, GeT Cameras recommends using USB3 PCI express adapters that can be found under accessories on our website.
Motherboard and Chipset
Motherboards with chipsets from the original Intel 7, Intel 8 or Intel 9 series have built-in support for USB 3.0 due to the USB 3.0 host controller. Chipsets from the above series are recommended to setup a stable USB 3.0 system.

USB3 Hubs

Hubs are being used to connect a host on the computer to several USB 3.0 cameras. This is also called a star network. In this setup the hub is only able to work with the bandwidth of a USB 3.0 upstream port, it must be taken in consideration that individual downstream ports on the hub are also only able to transfer that bandwidth. So, as an example if you connect four USB 3 cameras to one USB3 hub, each camera has (400/4) 100 mb/s bandwidth left.
 

Top 10 design rules for implementing a USB3 Vision Camera


To guarantee a smooth USB3 interface transition, the next points should be taken into consideration:
•    Make use of the host controllers GeT Cameras offers. The product listings include information regarding bandwidth, and hubs and cables limitations.
•    Only make use of certified USB 3.0 accessories. Low-quality accessories can potentially cause problems with your transition and even through your while vision system.
•    At all times make use of the latest drivers for your host controllers when they have been tested by the camera manufacturer.
•    Circumvent the usage of hubs when this is unquestionably not required.
•    Circumvent the usage of active USB3 Vision cables
•    Reduce the cable length as much as possible (maximum cable distance of 4,5meters)
•    It is advised against twisting or kinking the cable needlessly, this could potentially reduce the efficiency of your transmission. If a cable ought to be twisted or relocated, make sure to use a cable which is intended for working with cable drag chains or robotics.
•    The bandwidth of all connected cameras together also needs to be taken into consideration. The bandwidth of all cameras together is not able to surpass the maximum possible bandwidth of the host controller. If the bandwith exceed, use extra host controllers.
•    Take care of electromagnetic compatibility (EMC) problems in your setting or system setup that can lead to disruptions.
•    Control or monitor the CPU load on your computer.

USB3 Design Rules to keep in mind

The following design rules when installing a USB3 camera system should be kept in mind.

Excessively high CPU load on the computer

Using a large number of USB 3.0 cameras with a single system brings other risk of overloading the computer and its CPU. This can disrupt the vision system. Therefore, should the CPU load always be monitored.

High speed and high resolution cameras bandwidth consumption

If you are using a USB 3.0 camera that has a very high frame rate and/ or resolution and therefore consumes the maximum USB 3.0 bandwidth, it must be taken in consideration that the motherboard, host controller, and/ or hub supports the maximum USB3 bandwidth.

EMC related interruptions

EMC is able to cause disruptions to every electronic setup, including USB3. Usually, this is caused by disruptive signals in close proximity of the camera system incorrectly grounding the camera and termination signals can cause the EMC related problems.

USB3 cable problems

Poor-quality USB 3.0 cables could potentially cause error message such as incomplete and lost images or even a complete drop of the connection between the host and camera can occur. This can leave the user thinking that the USB 3 system is not stable and/ or reliable. This risks get bigger as the cable length increases. For this motive it is of great importance to pick your cable as short as possible.
 

Setup of a multi-camera USB3 vision camera system


There are two methods to set up a USB 3.0 multi-camera system: a point-to-point network and a star network.

Star network

When using a star network, the cameras are connected to a hub. The hubs is connected to the PC’s host controller. It should be taken into account that the host controller’s maximum bandwidth should not be exceeded.
This is due to that individual cameras from different ports all consume from the single bandwidth of the host that is connected to the hub. The entire bandwidth in this application is also dependent on the speed and/ or resolution of each separate camera. Using passive cables exceeding a cable length of 4.5 meters is advised against for this setting, where else the entire system will be susceptible to interruptions.

Point-to-point network

With a point-to-point  network you connect each camera directly to a host controller. It should be taken into consideration that the host controller and motherboard or PC its bandwidth is not surpassed, each separate camera needs a certain capacity of bandwidth. This is determined by the speed and/ or resolution of the camera. Using a passive cable with a cable length longer than 4.5 meters is not recommended in this setting, the entire system will then be prone to disruptions.
 

The future of USB3.0 Vision cameras


We expect USB 3 to solidify its position in the marketplace by attaining a bigger market share over the next years and becoming with GigE the dominating interface. This replicates the USB 3.0 Vision standard as a flexible and standard interface. Great benefits of this standard are that it is simple to use and setup and widely available. When all variables and technical requirements are taken into consideration, then building a stable USB3 vision camera system should be easy and affordable.

  M. Reijngoudt         Comments (0)

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