Machine Vision: How To Choose The Right Interface?

By November 20, 2012January 24th, 2022Image Processing

Importance of UI in Machine Vision

In a typical Machine Vision application, industrial cameras are responsible for capturing stable images and transmitting them to a PC for evaluation. The transmission occurs via different alternative interfaces and protocols that constitute image transmission interfaces. Over a few decades, Machine Vision camera interfaces have evolved significantly, permitting the cameras to transfer megapixel images at considerably high frame rates. These advancements are opening the doors to endless applications. However, each type of interface comes with its pros and cons. To choose the perfect Machine Vision interface for your application, you must consider four prime factors.

Also, Read 7 APPLICATIONS OF MACHINE VISION

Factors To Be Considered While Choosing a Machine Vision Interface

The four factors that will help your window down your selection are mentioned below:

  1. Bandwidth

Bandwidth is analogous to the size of the channel through which your data flows. It determines the total Megabits/ second (Mb/sec). Large frame rates need a large pipe for efficient performance. If you’re bandwidth limited, you’ll need to reduce the frame rate and image size.

  1. Cable Length

As the name suggests, it is simply the distance between the camera and the industrial computer. Usually, in factory automation applications, cameras can be located within a few meters of the computer.

  1. Cost

The budget allocated for acquiring the interface dictates in most cases. While interfaces such as the USB are relatively cheaper, setting up the latest CoaXPress interface can be a lot more expensive. 

  1. Complexity

Not all interfaces for Machine Vision are plug-and-play and might require complex configuration. It is best to approach a certified systems integrator to help you choose the right interface if you have no prior experience.

Also, Read 3 Uncommon Applications of Machine Vision

Different Types of Machine Vision Interfaces

The four types of Machine Vision interface we will be covering are:

  1. FireWire

FireWire, also known as the IEEE 1394, is a serial bus system that was developed by Apple. It was mostly found on the Macintosh computers by Apple for a long period and acquired widespread prevalence only after the introduction of i. Link by Sony as a part of the IEEE 1394a standard. It provided cheap standardized cable and plug technology and eliminated the need for expensive frame grabbers. While some PCs don’t come with inbuilt FireWire ports, they can be conveniently installed with FireWire hardware available in the market.

FireWire is also quite effective for multi-camera systems. These cameras leverage a peer-to-peer communication protocol and integrated voltage supply to offer the ability to synchronize trigger broadcast and other cameras on a single bus. FireWire competes with the popular USB 2.0 bus.

  1. Gigabit Ethernet (GigE)

GigE’s combination of simplicity, speed, and 100m cable length limit has made it extremely popular among vision engineers. Its most attractive feature is the support for long cable lengths. Also, since every camera is addressed using a unique IP address, there is no limit to how many cameras operate on the same network. Ethernet cables come with robust shielding. This is useful in environments with high electromagnetic interference due to proximity to some powerful motors. 

Since this technology comes from the communication mass market, it is cheap and results in reduced system costs. This relatively cost-effective nature of Cat 5e and Cat 6 cables makes GigE the best Machine Vision interface when a longer cable length is required. However, unlike USB, GigE doesn’t support DMA. This is of trivial consequences in modern PCs but may result in latency for low-power embedded systems.

  1. USB 3.0

USB 3.0 or Universal Serial Bus was initially developed to address the consumer need for a PC-based interface with higher bandwidths. It arrived in the Machine Vision interface market in 2009 with support for up to 440 MB/s of bandwidth, 10 times faster than the traditional USB 2.0 and 5 times faster than the FireWire B. High-flexibility USB cables also help in maximizing the lifespan of the cables in situations where the cameras need to be displaced repeatedly. USB 3.0 supports Direct Memory Access or DMA, thus allowing the data to be written directly to the memory and reducing CPU load. Due to its high bandwidth, ease of use, and low cost, USB 3.0 is ideal for a vast range of applications.

  1. CameraLink

CameraLink is a well-established, serial high-speed point-to-point interface for industrial imaging applications. It provides the user with the highest data rate of over 680 MB/s and minimal latency of all interfaces. CameraLink also supports DMA, which results in reduced load on the CPU when capturing images. 

Two cameras, at max, can be connected to a computer using one frame grabber. Compared to other interfaces for Machine Vision, system costs are relatively higher due to the expensive frame grabber and the necessary power supply for each camera in the system. However, the use of a frame grabber does help in offloading some of the processing done by the CPU. Despite low consumer popularity and high system costs, CameraLink is a widely prevalent interface for Machine Vision in applications that require real-time processing and high bandwidth.

Also, Read Camera Types for Machine Vision Applications

Conclusion

Although the current Machine Vision standards have found acceptability with all camera and industrial vendors, engineers are consistently striving to develop custom interfaces that offer better suitability to certain applications. CoaXPress is one such latest digital interface that promises ultra-bandwidth and versatility. One should thoroughly scrutinize the application requirements, performance, data throughput, and ease of integration. However, consulting with Machine Vision experts is advised before choosing your pick.

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