Lighting the Way for Vision

Proper lighting is the key to useful machine vision. Not long ago, the cost and complexity of machine vision limited its use to specialty machines and isolated inspections. Today, however, machine vision has proven itself as a practical and affordable method to monitor and control production in factory automation. The basics of vision sensing have not changed: The camera remains a light collector with the digital imager as the core data collection device. Each imager consists of thousands or sometimes millions of microscopic light meters. Thus lighting is the most significant factor when designing robust vision inspections. An object or target must have enough optical contrast for a vision sensor to see it. Put another way, there must be a detectable change (or delta) in the light received from the target compared to everything else in the camera’s field-of-view (FOV). Controlled lighting creates this contrast. There are many stories about the vision application that ran flawlessly during first shift, but began failing “good” items over second and third shifts after the sun set. Plant windows and skylights produce drastically changing, uncontrolled light that interferes with the repeatable contrast necessary for successful vision sensing. Even the flashing warning beacons on forklifts moving around the plant floor contribute to the overall light pollution. Thus, a repeatable vision application demands lighting that remains controlled and consistent. It must also be immune to the inconsistent and fluctuating light levels in its environment. One of the three techniques commonly used to combat fluctuating ambient light involves controlled high-intensity lamps. The lamps flood the target or feature with excessive radiant energy rendering any ambient light insignificant to the camera. The second technique resembles the first, except for the use of highintensity infrared light to optically shroud the object. A high-pass infrared filter goes over the camera lens