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Visual Inspection & Testing
Visual Inspection & Testing
X-Ray-Based Machine Vision Systems
POSTED 05/24/2005 | By: Nello Zuech, Contributing Editor
Whenever I write about x-ray-based systems I fondly remember my first job out of college. I worked for Machlett Labs and was engaged in production engineering activities for their x-ray tube product line. At that time they were “state-of-the-art” and their products were widely used in medical and dental x-ray systems. While vestiges of that era’s technology still exists, the world of x-ray sources has moved forward significantly. The net result is that more distinctive x-ray images are created, which lend themselves to automated interpretation at least for industrial application if not medical applications. In the latter case, it is opined the radiologists are the barrier to advances along these lines as they would then perceive theirs as a diminished role. Also contributing to today’s implementations has been the advances in solid state detectors, imagers and cameras as well as the underlying computer technology. The result has been a migration from film-based x-ray systems to digital imaging-based systems.
In the industrial setting one finds at least six distinct classes of applications of x-ray-based machine vision products.
1. In the semiconductor industry they are used to inspect packages for internal defects and interconnect problems.
2. In the electronic industry they are used to inspect solder joints and multilayer boards for registration issues.
3. In the food industry they are used to find foreign objects in food products – bones in hamburger patties, or chicken or fish.
4. In packaged products they are used to detect contents in a package or carton as well as foreign objects in containers such as filled baby food jars.
5. In the beverage industry they are used to monitor fill height especially in plastic and glass bottles.
6. The last class is non-destructive evaluation generically. This includes inspection of tires and metal-formed products – forgings and castings – for internal conditions.
In each of these classes one finds a range of “machine vision” based products being offered. Some are digital radiographic systems with image enhancements and interactive tools that make it easier for an operator to locate areas of concern in the image and applying the tools, for example, to measure a region, make a decision about the integrity of the part or assembly being inspected.
Given the improved image made possible by the latest in x-ray sources, machine vision techniques can be more readily applied to the x-ray image yielding application-specific systems with automatic defect detection. In some cases it is even possible to apply various pattern recognition techniques leading to systems with automatic defect recognition as well. With the processing speeds now available there are even applications where 3D-based approaches are being used to evaluate conditions.
In each of the respective application classes cited above one will find companies offering application-specific x-ray-based machine vision systems for that class of applications. More often than not, that is the only class of applications those companies address. With the exception of application and marketing challenges and the resources required to establish multiple distribution channels to address more than one market, there is really no reason why one company cannot offer products to address several or even all the above application classes. However, virtually all companies in the x-ray-based machine vision market only address one application class.
Significantly, these companies also do not address applications outside of manufacturing (markets other than machine vision) such as defense or security related applications. There are a couple of merchant system integrators with backgrounds in x-ray technology that may undertake project-specific assignments in more than one application class as well as in security or defense applications.
As with other articles in this series, input was solicited from over 20 vendors of x-ray-based machine vision products associated with one of the abovementioned application classes. For whatever reason, only two responded. Both of these companies are perceived to be more of a merchant system integrator of machine vision-based x-ray systems.
- Scott Stewart – CXR Company, Inc.
- Gary Korkla – Security Defense Systems
What follows are the answers provided to our questions.
1. What are some specific x-ray-based machine vision applications that your company addresses with your x-ray-based machine vision technology?
[Scott Stewart, CXR Company, Inc.] Our x-ray equipment is used mainly by food production companies for locating contaminants in their products. We service sectors such as meat, poultry, dairy, frozen foods, bakery, beverage, and others. We can detect metal, plastic, stone, glass, bone and more. The equipment is also used for foreign particle detection in pharmaceutical products and to detect internal defects in electronic components. Once, we inspected large stuffed teddy bears for imbedded needles!
[Gary Korla – Defense Security Systems] Applications that we have addressed include munitions inspection, investment castings, electronic components, food and pharmaceutical (consumer products) and automotive assemblies.
2. Can you provide a general description of the approach your products employ to arrive at x-ray image data?
[Gary] Depending on the application, sensitivity and resolution required determines the x-ray energy level and type of x-ray system. We then look at the image receptor required, image intensifier, linear diode array, digital panel, etc. and finally the process of automation, line speed, spacing etc…
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[Scott] Currently we employ an x-ray tube, an image intensifier, a CCTV camera and a CCTV monitor. This is much like the systems used by airport security luggage screeners.
3. What are critical x-ray-based machine vision system performance criteria for each of the applications that you address?
[Scott] It is important that the x-ray system has enough power to detect very small contaminants (.8 mm or smaller). It is also important that the equipment be easy to operate, and be suitable for harsh environments such as cold temperatures and wash-down.
[Gary] What acceptance standards are required, i.e., military or commercial and will realtime imaging be accepted, which is not always the case. What does the customer expect in the way of image quality. In the case of food and pharmaceutical, will the system have to comply with USDA or FDA standards?
4. What changes have been taking place in the underlying technologies that are the basis of your x-ray-based machine vision systems that has resulted in improved performance?
[Gary] Improved image receptors that provide higher resolution at significant conveyor speeds. Several new manufacturers of monobloc type x-ray generators capable of higher current at continuous duty cycles required in 24/7 production applications.
[Scott] Among other things, improvements in software are making a big difference in performance.
5. Where do you see breakthroughs coming in the specific underlying technologies that are the basis of your x-ray-based machine vision systems that will result in further improvements in the near future – next three years?
[Scott] Once again, the software.
[Gary] The current technologies in image receptors and x-ray sources are actually quite good. What will happen as interest from consumers increases demand, the costs of these critical components should drop, which will hopefully spark even more interest in automated x-ray systems from the end users.
6. Are there market changes associated with those applications that you address that are driving the adoption of x-ray-based machine vision?
[Gary] Yes, there are higher quality demands by consumers and automation will reduce manufacturing costs creating a win/win situation. In food and pharmaceuticals the increase in foil type packaging prevents the use of metal detectors to inspect finished product, often making x-ray the only viable method of inspection.
[Scott] It seems that food production companies are more and more willing to spend what it takes to achieve the highest levels of quality control. It is simply cost effective to screen product for contaminants rather than risk a recall situation or be forced to scrap entire batches of suspect product.
7. How will x-ray-based machine vision systems have to change to meet emerging x-ray-based machine vision applications or to further penetrate their markets more successfully?
[Scott] Systems will need to keep up with faster production speeds by increasing image processing speed through improved components and software.
[Gary] The cost has to come down.
8. As a supplier of x-ray-based machine vision systems what are some challenges you face in marketing x-ray-based machine vision systems?
[Gary] Educating the end user of the benefits of incorporating automated x-ray inspection technology at an affordable cost.
[Scott] Some food production companies still believe that metal detectors are enough of a screening method for foreign particles. We try to get the message out that x-ray is an affordable and efficient addition to any HACCP program.
9. What are your thoughts on the future of x-ray-based machine vision?
[Scott] Use is increasing. The future looks bright.
[Gary] We think the future for machine vision based x-ray systems is bright, the technology is greatly improved and costs are slowly coming down.
10. What advice would you give to a company investigating the purchase of an x-ray-based machine vision system?
[Gary] To look at the various vendors systems closely, providing samples of their products and making very certain that both the manufacturer and prospective x-ray system vendor agree on the level of detection that must be obtained. Making sure the amount of false rejects is acceptable and that the x-ray vendor is capable of providing after sales support. They must be aware that a “down” x-ray system can delay if not bring production to a standstill. Finally, if possible they should see an automated x-ray system in operation, either at the manufacturer or at an installed site where they can speak with an end user.
[Scott] Look for good service and communication. Talk to others in your industry who have used x-ray equipment. Be sure to find out what steps you need to take regarding radiation safety and control (employee use of dosimeters, shielding, etc.) and equipment registration within your state.