What are the most common connector styles used for MV systems?

Machine vision (MV) is an important tool in Industry 4.0, autonomous driving, and other advanced technologies. Various standard data connectors and application-specific vision system connectors support it.

MV hardware consists of a camera or other imaging sensor and a computer that analyzes the images. Reliable, high-speed connectivity is required to link them. Examples of standard connectors used in MV systems include universal serial bus (USB) 3.1, various implementations of Gigabit Ethernet (GigE), CoaXPress (CXP), and several types of Camera Link (CL) (Table 1).

Table 1. Example of common machine vision connector types. (Table: Edmund Optics)

The Association for Advancing Automation hosts the USB3 Vision, GigE Vision, and Camera Link standards. CoaXPress is hosted by the Japan Industrial Imaging Association (JIIA).

One common thread is the GenICam programming interface hosted by the European Machine Vision Association (EMVA). GenICam seeks to provide a generic application programming interface (API) for all types of cameras and interconnects like GigE Vision, Camera Link, USB3 Vision, etc. The GenICam standard includes modules for specific tasks like:

GenApi for configuring the camera.
Standard Feature Naming Convention (SFNC) that includes recommended names and types for common features.
Pixel Format Naming Convention (PFNC).
GenTL is a transport layer interface that grabs images.

USB3 Vision is used in various MV applications, such as medical imaging, factory quality control, process monitoring, and automotive and aerospace systems. Its camera control registers are based on the EMVA GenICam standard. USB3 Vision defines locking connectors that add screw-locks to standard USB connectors for industrial use.

The USB3 Vision standard does not match the computer USB standard for backward compatibility. However, some USB 3.1 Gen 1 cameras can be backward compatible by making them run at the slower 400 megabits per second (Mbps) speed of USB 2.0. Some additional features of USB3 Vision include:

USB3 Vision can transfer data at speeds approaching 3 gigabits per second (Gbps).
USB3 Vision connectors are simple to use.
USB3 Vision can provide power over the cable.
USB3 Vision is compatible with PCs, laptops, and smartphones with a USB 3.0 interface.

GigE Vision uses standard Ethernet cables. It balances speed and cost and is suitable for many MV applications — Standard Cat 5e and Cat 6 cables support high-speed camera connections. Standard Ethernet switches, hubs, and repeaters can support multiple cameras in an industrial network. Like USB3 Vision, GigE Vision camera control registers are based on the EMVA GenICam standard.

Newer implementations of GigE Vision support 5 and 10 Gbps data rates. Some cameras support link aggregation, which uses multiple Ethernet ports in parallel to increase the available data rate. Cameras are available that support the network Precision Time Protocol (PTP), which can synchronize the clocks of multiple cameras connected to the same network.

CoaXPress (CXP) was designed to support extended cable lengths in industrial environments and deliver high-speed and expandable transmission rates. High-frame rate industrial cameras need more than 4 W of power, and CXP can deliver up to 13 W at 24 V. Like other connectivity choices, CXP delivers higher bandwidth over shorter cable runs. Each coax cable can deliver up to 12.5 Gbps, and multiple cables can be used to increase the available bandwidth. Using multiple coax cables increases the available power since each cable can deliver up to 13 W.

Camera Link (CL) is a high-speed, low-latency serial interface developed for industrial machine vision applications. The two primary types of connectors used for CL cables are the mini delta ribbon (MDR) and the shrunk delta ribbon (SDR) (Figure 1).

Figure 1. Camera Link SDR (two left) and MDR (three right) connectors are available in various configurations. (Image: 3M)

CL is compliant with the EMVA GenICam standard. Several variants of CL use the same connectors but deliver different levels of performance, including Base, Medium, Full, Deca, and PoCL. Base CL uses a single cable and is limited to 4 W. Medium, Full, and Deca CL configurations use two cables and can deliver up to 8 W, 4 W per cable.