Vision systems are becoming commonplace in many manufacturing operations for tasks such as quality assessment and process control. These systems bring the added benefits of high-speed, continuous, and uninterrupted operation. Unfortunately, food processing has not realized the same level of success with vision system implementation as other manufacturing sectors. This is because the food processing environment places a unique set of hardware requirements on the system design. While the costs associated with the electronics required to fabricate a new vision inspection system have dropped, the real expense is in the hardening of such a system for a food processing environment. The design and fabrication of the enclosures and conduits must withstand the rigors of the food processing environment and protect the sensitive electronics contained inside from the routine washdown and sanitation practices.

For the past decade, the Georgia Tech Research Institute has been developing vision inspection systems for various food processing applications from chicken breasts to the bread buns they are served on. During this time, these imaging systems have evolved to meet the unique set of requirements placed upon them.

Some of the first vision systems that were built were simply stainless steel or fiberglass boxes with all of the electronics housed inside. These systems performed tasks such as foreign object detection or on-line detection of systemic defects in chicken. These early systems used compact fluorescent lighting and required air conditioners to keep the electronics cool. While the enclosures themselves worked well, the cooling systems did not.

Addressing the heat issue with the enclosures led to the first innovation in the system design. LED lighting was used to replace the compact fluorescent lights. Strobing the LEDs at a 15% or less duty cycle significantly reduced the amount of heat accumulation in the enclosures to the extent that in some applications external cooling was no longer required. In addition, the lifespan of the strobed LEDs is extended well beyond that of the compact fluorescent lighting leading to lower maintenance and replacement costs. This innovation has led to a more robust, reliable vision system design.

The traditional square enclosure design works well for a variety of inspection applications; however, it is less than optimal for conducting over-line product quality inspection. The direct nature of the lighting results in specular reflections off the product and an uneven illumination intensity across the field-of-view resulting in shadows and hotspots in the images. Without additional shrouding, the traditional square enclosure does a poor job of keeping ambient lighting from interfering with the desired illumination and affecting the images acquired by the system. This was especially apparent when working with a wet, shiny product such as poultry.

To solve the issues of both the ambient light interference and the non-uniformity of the illumination intensity, a new system was designed. In the 1990s, the concept of a “dome” or “cloudy day illuminator” was adopted to minimize the specular reflections and shadows and improve the uniformity of the light distribution across the field-of-view.

The dome design uses the concept of reflected illumination instead of shining the lights directly on the product. The lights are oriented toward the inner surface of the dome enclosure and away from the product. This orientation reflects and scatters the light allowing for more even light distribution across the entire field-of-view of the vision system. This is very similar to how a professional photographer uses the umbrella to diffuse the flash when taking a family portrait.

The dome design has proven to be very beneficial for conducting quality-based vision inspection. The scattered nature of the lighting allows the system to capture accurate and consistent images during operation. However, the dome design itself is complicated to build. There are potential issues with the possibility of contaminants and water getting captured or trapped in various locations on the dome, and this solid stainless design is expensive to fabricate.

The current evolution of the over-line inspection system addresses all of the problems with the previous designs, from the potential contaminant traps to the issues with manufacturing and cost of fabrication. A series of innovations were made in order to meet these requirements. The most radical of which was a decision to move away from the solid stainless steel design and use a plastic design with a stainless steel frame. The entire dome section was replaced with a high-density polyethylene instead of stainless steel. This greatly reduced the cost and weight of the system. Stainless steel is still used for the frame walls to hold the dome section and camera enclosure and keep the system rigid, but the bulk of the system is now plastic. This design decision not only reduces the cost and complexity of the system, but it also allows for rapidly changing the dimension of the system design in order to accommodate different width food processing lines. This means that the dome does not have to be re-designed for each different processing application.

In addition, the lighting enclosures were detached from the rest of the system, thus becoming individual components. This allowed for quick and easy servicing or replacement of the lights without having to remove the system from the line. To eliminate the possibility of trapping contaminants, the light enclosures themselves were re-designed. Instead of a stainless steel tray with a polycarbonate window, the entire lighting fixture is now contained in a polycarbonate tube. The shape of the tube itself makes it such that no water or contaminants will be able to accumulate on the surfaces. The tube is also filled with nitrogen so that there will be no condensation forming on the electronics and no thermal expansion of the enclosure which could lead to cracks or leaks in the assembly.

In conclusion, designing vision-based inspection systems for food processing operations is no easy task. Such systems must be designed to keep the lighting uniform and repeatable, keep the system’s internal electronics cool, be able to withstand the harsh environments found within the plant (e.g., daily washdown), and be simple and inexpensive to fabricate. In order for vision systems to truly take off in food processing, they need to meet all of the above requirements. The current system design meets all of these requirements and helps to usher in a new era of automated food processing technologies.

Colin Usher is a research scientist in the Georgia Tech Research Institute’s Food Processing Technology Division. His areas of expertise are software development, intelligent systems, computer imaging, robotics, and automation technologies.