GigE Vision

       GigE Vision  is a camera standard for real-time machine vision.  Automated Imaging Association (AIA)  developed this standard and was released in May 2006. Within a span of four years the number of units shipped was comparable to the rival 'Firewire' and 'Camera link'  standards.  Camera link is from AIA and firewire is Apple's version of IEEE 1394 standard. After the inception of GigE Vision, revision 1.1 and 1.2 was released. In 2011 Gig E Vision 2.0 was released. It supports 10 GigE, IEEE 1588 Precision Time Protocol, JPEG, JPEG2000 and H.264 image compression standards.

GigE Vision Merits

• Supports common camera control interface GenICam. European Machine Vision Association (EMVA) has developed GenIcam.
• It has plug & play, high data transfer rate and low cost cabling. All the above helps system integrators a lot.
• It has wide range of camera for various applications
• cable length supported is around 100m. This feat is not possible by other standards like Firewire, USB3, camera link and coaXpress.

Camera capture system
          Real time applications  do not  necessarily need  ultra fast acquisition. But images should be acquired and processed within the stipulated time.  Reliability of  a real time system depends upon the parameters like jitter and latency. Latency is normally understood as time delay.  Here it means the time taken to complete a task from start to finish. Jitter gives the time variation when  the same task is repeated multiple times.

         Camera capture system consists of a PC with Network Interface Card (NIC), camera and Ethernet link to connect the PC and camera.  Hardware or software trigger can initiate camera to capture image. As expected, hardware trigger has  lesser latency.  Camera-head process the trigger and start the sensor to accumulate incoming light and convert into electrical charges. These accumulated charges are converted into digital and to be placed in the camera buffer memory. This process is called 'readout'. Entire buffer content is transferred to the PC by breaking them into small chunks and adding Ethernet header for each chunk. NIC receives the packet and raise an interrupt to CPU. If CPU is not busy then it will process the packet  and put the chunk into the computer memory. The time taken from start of trigger to reception of last packet of the image is included to calculate the latency.

GigE Standard
          Single GigE camera connected to PC via direct Ethernet link or multiple GigE camera can be connected to PC through an Ethernet switch. Avoid using hub to multiple cameras

          A dedicated wire or electronic signal which is directly connected to input pin of the camera can act as a hardware trigger. To avoid false start,  trigger debouncing method is incorporated. The price we pay for safety is one microsecond latency. An application software can send a trigger via camera configuration channel and it has lesser responsiveness than camera pin. If a software trigger comes from an application that runs on a non real-time operating systems (ex. Microsoft Windows)  then jitter may vary from few hundredth of microseconds to few milliseconds. So it better to avoid software trigger mode. There are three types of exposures  viz. free running mode, horizontal synchronous mode, reset mode and jitter varies from one frame to one pixel depending upon the type of exposure. Latency of camera is depends on exposure time and sensor readout time. Biggest contributor of latency will be readout time. A 60 frame per second camera takes 16ms to do readout.

           The normal size of Ethernet frame (A packet in physical layer is called frame) will be 1500 bytes. Jumbo packets with a size of 9000 to 16000 bytes are available. A chunk inside a frame will be called as payload. Then GVSP (GigE Vision Stream Protocol) header, UDP (User Datagram Protocol) header, IP header and at last Ethernet header are added to payload. Appended four byte Cyclic Redundancy Code (CRC) will help to detect any errors that creped while the packet was in transit. 8000 byte sized packet will take 16.3 microsecond to get transferred over network.

            Without the involvement of CPU, transfer of data from NIC to memory can be accomplished using Frame Grabber. It contains powerful Direct Memory Access (DMA) engine that helps to reduce latency and jitter to a minimum. Fortunately or unfortunately GigE standard do not have frame grabber. GigE software driver takes care of the role of frame grabber. So choice of GigE software driver plays a vital role in the performance.

 Performance Improvement Tips

• Few network adapter allow 'interrupt moderation'. This instead of raising an interrupt for every packet arrival, it waits for certain number packets to arrive then it raises an interrupt. This helps to reduce CPU overload.
• 9000 byte sized jumbo packets are best even though networks may support 16000 byte size jumbo packets. The reason is CRC calculation above 9000 bytes is very cumbersome.
•  Increase the receiver buffer size as much as possible. This in turn will reduce CPU usage.

A typical GigE camera will have physical dimension of  5cm x 3cm  x 7cm , with 1400 x 1024 image resolution capable taking 75 frames per second (fps). Image exposure duration will be 100 microseconds. The data can be transported over 100m using CAT-5e or CAT-6 cables. It will have a mass of around 120 grams. Monochrome, colour and high speed cameras are available.

Source:

• Automated Imaging Association  http://www.visiononline.org
• Allied Vision Technologies, http://www.alliedvisiontec.com
• Whtie paper on "GigE  Vision overview"  (GigE_Vision_for_Real-Time_0.pdf) This pdf is available with the key word in Google search "Whitepaper GigE". 
• White paper on GigE http://www.alliedvisiontec.com/fileadmin/content/PDF/Support/Application_Notes/ApplNote_GigE_Vision_Setting_Standards.pdf

Machine Vision Magazines

I searched a lot and found out that only three machine vision magazines are available.

1. Vision Systems Design

• Magazine articles are crisp in nature
• "White paper" section needs registration.
• Back volumes are available from  September 1996.
• If we register ourselves then we can get the Digital/Print issue free of cost. Registration process seems to less cumbersome.

 Link: http://www.vision-systems.com/index.html

2. Imaging and Machine Vision Europe 

 

• From the home page go to "feature" section (http://www.imveurope.com/features/)   to find back  volumes. They are available from April 2006 onwards. It is an bimonthly (once in two months).
• Sections like 'Webcast' and "white paper" need registration.
• The layout is good. 
• Articles are little bit lengthy.

Link : http://www.imveurope.com/

3. Inspect 

• Without registration, I was able to download PDF files from 'White paper' section .  I have to register myself to get the same content from other magazines.
• Publication  started from 2009 onwards.
• It is bimonthy magazine with an additional special issue magazine. So totally seven issues per year. It costs around 54 euro per year subscription.
• It is available in English as well as German. It is published by Wiley & Sons .
• They have a print circulation of 20000. Germany consumes 70% of the printed copies.
• Looking into the archives, need registration. I thing one get a PDF version of the book after registration.The registration is very simple. It asks for your name, a password and CAPTCHA to ensure registration done by humans only. 
• Archives are from year  2009 onwards. Year 2011 is not available. Why?

Link : http://www.inspect-online.com/en

Machine Vision - Soliton Technologies

Machine Vision in Printing Industry
        Soliton Technologies, 14 year old, a pioneer in machine vision products and solutions based on India. In this August (2012)
 Soliton is going to launch a automation product that will reduce paper wastage while printing. Reduction is wastage will up to 50 percent compared to earlier  manual methods. A smart camera  would take pictures of the printed newspapers as they come out of the press, detect any errors in the color registration (CMYK). Cyan, Magenta and Yellow are secondary colours used in printing industry and K stands for Black colour. The detected errors are automatically corrected using correction motors present in the press. This process is instantaneous and thus paper wastage is reduced.

Jewellery
     They have done R&D work to develop a automation technology that will able to inspect, sort and defect detection in the manufacture of jewellery.

CASE STUDY in Pencil Manufacturing

     A pencil manufacturing   factory was manufacturing one million pencils per day. It employed 60 people inspect and remove defective pencils.  A good quality pencils, can have lead offset of 300 µm only. If the offset increases further pencil leads will break when sharpened. This length is nearly impossible to judge manually. When production was increased to 2 million pencils per day, the manufacturer went for a fully automated system. It means that within a second 23 pencils should be inspected.  This project was handed over to Soliton.  Machine Building and Automation division of Titan Industries was roped by Soliton to build system that will bring the pencils before the camera with minimal vibration. Each of the two ends are inspected by colour camera connected by IEEE 1394 interface.  Depending upon the type of pencils inspected either florescent or fiber optic light is used. They use LabView from National Instruments with IMAQ vision library provided by National Instruments (NI). Image processing algorithms have to find all defects (lead offset, wood chip-off, crack etc) within a time of 40ms. If a pencil is found defective  it is dropped into reject bin else it is lacquered, finished and boxed.

Smart Camera
Smart cameras do not require a PC for operation. It can operate stand alone. Soliton has launched a smart camera named Soliton Neo. It contains a buit-in camera, powerful DSP processor, LED lights and other required interfaces like Ethernet to connect to a laptop or remote PC. One has to use a custom software and able to control the camera thats it.

 More Info

•  Soliton is a industry sponsor for TIFAC CORE on Machine Vision  setup at Rajalakshmi Engineering College (REC), Chennai. This was inagurated by Dr. Chidambaram, Principal Scientific Advisor to the Government of India on 30th June 2009.
• Instrumentation and Control Engineering students can check analog speedometer webpage and they can try as their final year project.
• Look into Soliton webpage's case study, press release, in the news section. Very interesting project idia one may get

 Sources:

• Soliton Technologies, Bangalore, India, http://www.solitontech.com/
• Soliton Technologies launches smart camera,  http://www.hindu.com/2007/12/02/stories/2007120260951500.htm  
• System speeds pencil inspection and sorting, http://www.vision-systems.com/articles/print/volume-11/issue-12/technology-trends/quality-control/system-speeds-pencil-inspection-and-sorting.html 
• Soliton’s focus on machine vision technology, http://www.thehindu.com/business/companies/article3569849.ece 
• Analog Speedometer,http://www.solitontech.com/tmd/case-studies/automated-analog-speedometer-calibration.html