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Vision cables

Every camera requires one or more cables to connect to a vision system or a PC. Different connection methods in relation to data rates (bandwidth), complexity and transmission can be used.

The choice of cabling for an application is driven by the following considerations:

  • Cable flexibility
  • Transmission distance
  • Connector integrity and material
  • Environment
  • Cable routing

Cable flexibility

Most cables have a degree of flexibility, in that you can bend them to fit into a system chassis or machine. For applications where the camera will be moving, standard cables are not sufficient as they are not designed to withstand continuous bending and flexing over time resulting in higher abrasive wear and failure. In these applications robot or track-grade cables should be specified. These cables are tested with repeated movements to simulate use on a robotic system or drag chain. The parameters that define this type of cable are: the minimum radius angle of the flex and the number of flexes in a given time period.

Track-grade cables are typically designed to survive more than 1 million flexes with a minimum radius. Robotic-grade cables go through an additional torsional flex test which specifies repeated twisting of the cable through up to 360° over a specified length. This simulates the stress on a cable used in connection with robot arms. Most interface cables are available in higher flex formats.

Cabling - transmission distance

In principle cables can be produced to any length within the constraints defined by the interface standard.

Cabling - connector integrity

Industrial applications usually require a secure connection and it is desirable to lock the cables in position. Many industrial and commercial interface solutions specify connectors that lock, such as BNC (bayonet lock) and Hirose (push pull) for analogue systems, MDR26 for CameraLink (screwable) and CAT5e/CAT6 (screwable) for Ethernet and other specifications. This ensures that the connector cannot be accidentally removed by pulling on the cable or in case of vibration.

Interfaces such as USB and FireWire A or B, have no universally agreed locking standard defined. The connectors for these interfaces are often of a simple 'push-fit' design, making them problematic when used in industrial applications. However as this type of cable is usually cheaper due to the large volumes manufactured and therefore is often used despite the mechanical disadvantages.

Two choices of locking connectors exist, screw locks where screws fix the connectors together, and latching that have a push latch that needs to be depressed to remove the cables.

Cable routing

Normally cables are bought off-the-shelf and not wired in-situ. Problems often occur when cables need to pass through bulkheads or tight places where cable connectors do not fit. Limited space therefore often leads to complicated cabling solutions. With many of the new digital interface standards, the ability to self-wire cables is a very complex task and if not manufactured correctly can cause data errors..

Extending cables

Some applications require longer cable lengths than the interface standard allows. Using optimized transmission material on a copper base, data can be transferred securely over medium range distances.

For situations requiring significant cable lengths, selecting an alternative interface might solve the problem, however sometimes there are reasons that make this impossible. For all digital interface standards repeaters enable lengths to be extended typically between 2 and 4 times the standard length. Longer distances can be achieved using fibre optic cable solutions where cable lengths can be extended up to a few hundred meters with multi mode fibre and up to a few kilometres using single mode fibres.