LEDs in Machine Vision Systems|
In modern manufacturing, quality control and product inspection is increasingly being done using Machine Vision technology. Machine vision is a simple enough concept to understand. At the simplest level, machine vision is the combining of computer vision with industrial automation to speed up processes. In lay terms, a camera is used to take a “picture” of an item which is then sent to the computer, which then processes the image and compares it against a good proof in order to detect anomalies or deviations that may signal a defect in the scanned item. In effect, machine vision technology allows the computer to “see” the item and decide if it conforms to the desired specifications. Of course, this is not exactly vision in the true sense, but a process more akin to digital photography, and like photography it is dependent upon good light quality and processor strength.
Machine vision systems hold many benefits over traditional human inspectors. They can operate twenty four hours a day, produce highly consistent results, operate at very high speeds and provide in-depth inspection of minute details that otherwise would be difficult and time consuming for a human being. Some of the tasks these systems are capable of performing include continuous monitoring of products on conveyor systems, identification of defects and surface irregularities, product counting and even reading of numbering and lettering.
There are several aspects of machine vision that are critical to optimal reliability and operation of the system as a whole. Since the process is highly dependent upon producing images with high resolution and clear detail, just as in normal digital photography, lighting plays perhaps the most crucial role of all. Traditionally, halogen lights have been used in machine vision systems in combination with fibre-optics and specialized housings. These arrangements however have several drawbacks including the generation of prodigious amounts of heat and overall short lamp life. In fact, relamping such systems accounts for a large part of these systems operational costs.
LEDs have made a significant appearance in machine vision systems due in part to the drawbacks mentioned above and also their ability to produce light in highly specific color spectrums and their overall versatile nature. As the cost of LEDs drops their performance versus price continues to improve as well, making them an even more attractive lighting alternative in machine vision technology. Costs are further reduced due to the need for less apparatus. Whereas a halogen based system often needs specially constructed enclosures, complex light directing devices, reflectors and system dedicated cooling machinery, LEDs reduce or eliminate the need for such added equipment and thus expense. In fact, LEDs are now the dominant light source in machine vision systems primarily because they operate at such cooler temperatures and require much less supporting hardware to be utilized effectively.
Effective machine vision requires a higher degree of lighting accuracy and efficiency to form detailed images than the human eye. To increase the effectiveness of machine vision it is necessary to produce sufficient light intensity and ensure that uniform coverage is also produced as well. This intensity and uniform coverage helps in bringing out all the features and characteristics of the object being scanned, providing an accurate picture with which the machine can then make detailed and reliable comparisons and records with. LEDs provide a degree of control and intensity not easily achieved with the halogen lamps previously used. Rather than rely on complex light directing devices, LEDs can be arranged in an application specific manner, providing light exactly where it is needed. LEDs also offer the ability to be coupled with electronics that allow lighting to be “pulsed”, creating a lighting solution well suited to the needs of high speed imaging that is often associated with machine vision.
LEDs can be arranged in a wide variety of ways, allowing operators to produce exactly the kind of lighting pattern desired. Since different applications and material will affect how well an image is formed, directing the light in precise patterns and directions optimizes the ability of the equipment to form an accurate image. Backlighting to produce defined product edges, line lighting to produce a uniform bar of light useful for scan pattern imaging and angled field light rings to highlight surface defects are just some of the applications in which LEDs hold a distinct advantage over incandescent lamps.
LEDs also provide a specific advantage in their ability to produce light in a well defined part of the light spectrum. Many machine vision systems operate best with light within a certain part of the light spectrum such as infrared or red. With halogen lamps this usually meant that lenses and filters were needed. LEDs however can be constructed to produce light only within a certain part of the light spectrum, doing away with the need for yet more hardware. Adding further benefit, LEDs experience a very slow degradation in light intensity over time. Halogen lamps typically begin degrading very quickly and within 1500 hours require replacement to maintain the efficiency of the system. LEDs, however, typically retain up to 80% of their intensity for up to 50,000 hours, greatly improving the efficiency and reliability of the machine vision system.
Incorporating high powered LED light systems like Magnalights LED10W-18R 180 Watt LED light can produce significant advantages when combined with an effective machine visioning system in high paced industrial applications. Although often application specific, the high versatility and good color rendering of such LED lights offer a lot of potential for improvement when properly selected and applied. Compared to the cost of an entire halogen lighting apparatus which includes the lamp, directional hardware, cooling and enclosure, the initial outlay for LEDs costs averages out to be almost the same. The reduced operating costs of the LEDs, however, combined with their longevity and improved light quality produce a distinct performance advantage as well, resulting in a better price versus performance ratio. As LEDs continue to improve and advance, and demand for LEDs continues to rise, they will become and even more cost effective alternative to regular incandescent light in machine vision systems.