Data interfaces always become the focus of attention among people involved in the machine vision industry, for example at the VISION 2011 trade fair, to be in Stuttgart November 8-10. The attention--and debates--occur whenever new attempts at standardization are made or when new standards crop up in the consumer sector. Both are true at present.
The increasingly more efficient image sensors in digital cameras call for even faster data transmission methods. To date, Camera Link has been the ideal solution in many cases for high-speed applications. However, this no longer appears to be sufficient. New standardization attempts such as CoaXPress and Camera Link HS have been initiated. Version 2.0 of the GigE Vision Standard is due to be adopted in the third quarter of this year. Another interesting area for the machine vision industry is the extended USB 3.0 interface, which is currently making inroads into the consumer sector.
Matching applications and interfaces
Additional standard interfaces do not necessarily make life easier for application engineers since “every interface has its strengths and weaknesses, and it is difficult to make general statements," says Rupert Stelz, Image Capture Group Leader at Stemmer Imaging. The challenge therefore is to find the right product with the ideal data interface for a specific application.
Experts will tackle this challenge at VISION 2011, which will be held at the Stuttgart Trade Fair Centre from 8 to 10 November 2011.The special segment “International machine vision standards” in Hall 6 will unravel the confusion surrounding interfaces. It will be held for the fourth time and is being organized jointly with the Automated Imaging Association (AIA), the European Machine Vision Association (EMVA), and the Japan Industrial Imaging Association (JIIA). The special show will present specific applications and demonstrators under the motto “Standards at close hand”. “Visitors will be able to talk directly with developers, ask them questions, and make suggestions. This direct interaction is unique”, says Patrick Schwarzkopf, General Secretary of the EMVA.
CoaXPress was adopted by the CoaXPress consortium in the version JIIA NIF-001-2010 in December 2010. After a three-month publication period, AIA, EMVA, and JIIA confirmed CoaXPress as the international standard. With the CoaXPress interface it is possible using a single standard coaxial cable to transmit image data, communication data and control data, as well as the power supply between the high-speed camera and frame grabber. The data transmission speed per cable from the camera to the host (downlink) is up to 6.25 Gbit/s and in the opposite direction (uplink) 20 Mbit/s for communication and control data. The jitter of the interface is in the microsecond range, and the cable may be up to 100 metres long.
“The development of CoaXPress is slightly more advanced than Camera Link HS,” says Stelz. This can also be seen by the fact that the first products from different manufacturers are already available and in stock. For example, Active Silicon will celebrate a premiere with the first CoaXPress frame grabber in the new FireBird family at VISION 2011. Adimec will also present, for example, its dual CoaXPress camera Quartz for the first time at VISION 2011. “Manufacturers of CoaXPress products are currently improving in conjunction with the JIIA the implementation and conformity tests for the products”, says Dr. Joost van Kuijk, Marketing Manager at Adimec, Netherlands.
Experts are also vigorously working on the Camera Link HS interface standard. This standard is being promoted by a subcommittee of the Camera Link Committee. The established Camera Link interface is available in an extended version 2.0, but must be regarded separately from Camera Link HS. CameraLink HS offers a scalable downlink bandwidth during data transmission from 2.4 to 48 Gbit/s in x1 to x20 configurations and in steps each of 2.4 Gbit/s. Depending on the speed, the cable may measure 15 metres or up to 40 metres. The jitter is in the nanosecond range.
“We are currently involved in a research project which is focusing on extensions of Camera Link HS”, says Dr. Gerhard Holst, Director of Research at PCO AG. “We believe this is vital for the future,” continues Dr. Holst, “because fast data transmission is becoming increasingly more important for users of our cameras and existing standards can no longer keep pace. The approach which PCO is using to transmit large amounts of image data volumes is based on Camera Link HS, but with 10 GigE or 40 GigE hardware. The concept must be extended easily and scalably so that as many interfaces as required by the application can be used.”
The Camera Link HS Standard has not yet been finally adopted; however, there are already products on the market, for example from Teledyne DALSA. The market or rather the corresponding task with consideration of the advantages and disadvantages will decide which standard will ultimately prevail. “CoaXPress is more firmly in favor of the generic software interface GenICam. The GenICam-GenTL interface is mandatory in this case. In the case of Camera Link HS, it has only agreed to use proprietary software development kits (SDK) for the software interface,” says Stelz.
Debating the market share
Some camera manufacturers are waiting to see what will happen. “We are actively monitoring CoaXPress and HS-Link. Although both interfaces target the eradication of the limitations of the current Camera Link version, frame grabbers are still required,” says Mirko Benz from Product Management at Baumer Optronic. According to the expert, suitable components are still in a very early state of development whereas Camera Link has been used successfully and reliably for many years. Benz concludes: “In our opinion, the proven Camera Link interface will therefore remain the preferred alternative for the majority of high-speed applications in the foreseeable future.”
“We believe that CoaXPress has too many limitations,” says Dr. Holst, “and that Camera Link HS is very similar in principle. However, the power supply via the same cable is an advantage for machine vision applications.” According to Stelz, there are definitely overlapping areas between the two new standards. While CoaXPress scores points with its simple and cost-efficient cable concept, the end version of Camera Link HS will permit higher bandwidths and will implement a trigger concept, which allows linescan camera applications that obtain their trigger from a central frame grabber. “I am therefore assuming,” concludes Stelz, “that both standards will win through and acquire their market shares.”
Written by Silvia Stoll, Messe Stuttgart
--Posted by Vision Systems Design