Machine Vision Lights Boost Canning Line Inspection Speeds

Machine vision is increasingly crucial for companies navigating labor shortages to stay competitive in an ever-evolving global economy. In areas such as food and beverage inspection, for example, the machine vision vendor community must innovate to keep pace with evolving production processes and faster line rates.

Typically comprised of cameras, cables, lenses, industrial computers, and software, machine vision systems cannot “see” without lighting. Systems for high-speed, 360° can and bottle inspection have existed for some time, but innovative lighting designs are needed to increase throughput while maintaining accuracy. Specifically, for software to perform inspections, cameras need to acquire quality images, a process that relies on effective lighting. Instead of relying on longer exposure times, lighting designers are creating faster systems with brighter lighting. One such system increased the inspection rate from 4000 to 6000 ppm while cutting the exposure time from between 40 and 50 µs to only 12 µs, with zero motion blur or gain.

EAMVision’s inspection system can image multiple frames of the beverage can at once. Courtesy Michael Wheeler/Photonics Media.

Strobing a machine vision LED can freeze images of high-speed objects, and today’s LED controllers typically support this functionality. They are also designed, tuned, and tested to meet the thermal constraints of running for an indefinite period (continuous mode) with no associated duty cycle. In strobe/pulse mode, the LEDs are switched on through a controller when needed. Controllers allow the fine-tuning of pulse timing, which offers more flexibility than adjusting the camera timing.

In addition, pulse mode operation allows LEDs to be overdriven past the manufacturer’s rating, which produces more light — but also more heat — than continuous mode. Lights running in this mode may feature an integrated strobe driver for complete LED control. The driver monitors the strobe operation and maximizes light output during high-speed machine vision inspections. However, the controller must ensure that the lights run in overdrive for a set amount of time to prevent them from burning out.

Lights operating in overdrive can help in a wide range of challenging machine vision applications, particularly where objects or conveyor lines are moving at high speeds. A bright strobe is needed to freeze an object’s motion, but designers do not want to rely on long exposure times to achieve this goal. One challenging application is 360° can and bottle inspection. It can be difficult to capture high-quality images of a fast-moving target. A new lighting design from Smart Vision Lights combines its standard OverDrive mode with Deca OverDrive, delivering up to 10× the light output of a continuous operation light. By leveraging these lights, one systems integrator decreased exposure time while also maintaining the speed and accuracy required for the system.

2000 more parts per minute

In its 360° inspection system, machine vision systems integrator EAMVision used a through-beam fiber optic sensor from Banner Engineering to detect the presence of a can or bottle. Detection triggers four 5-MP cameras to capture images of the entire circumference of the inspection target and transmit them to an industrial PC running a custom inspection application for image processing. The system takes four images from each camera, unwarps them, and stitches them together to create a flat projection of an entire label of a can for inspection.

“A unique challenge of these 360° inspection systems is meeting the speed and rate requirements, which is challenging when it comes to imaging a continuously moving target without motion blur,” said Peter Gallagher, business development manager at EAM- Vision. “As the speed of the inspection target increases, that challenge increases as well, but we’ve solved this by decreasing exposure time, which is where lighting selection becomes crucial.”

In its 360° inspection system, machine vision systems integrator EAMVision used a through-beam fiber optic sensor from Banner Engineering to detect the presence of a can or bottle. Using lighting from Smart Vision Lights, the overall speed of the system increased from 4000 to nearly 6000 ppm. Courtesy Michael Wheeler/Photonics Media.

Decreasing exposure time while maintaining the benefits of overdrive lighting, EAMVision installed four Smart Vision Lights bar lights equipped with Dual OverDrive mode capabilities. This allowed the integrator to capture specific label information. A label that passed (top) and a label that failed (bottom). Courtesy Michael Wheeler/Photonics Media.

In the previous setup, four bar lights operating in OverDrive mode helped the system capture images with 40 µs and 50 µs of exposure time on the cans, with some variation occurring due to pixel blur. Decreasing exposure time while maintaining the benefits of overdrive lighting, EAMVision installed four Smart Vision Lights bar lights equipped with Dual OverDrive mode capabilities. This allowed the integrator to decrease exposure time to 12 µs with no additional gain and no motion blur, increasing the overall speed of the system from 4000 to nearly 6000 ppm.

“Using these lights in applications like this allows us to build inspections systems that keep up with some of the fastest automation out there,” Gallagher said.

Easing short duty cycle concerns

On its own, Smart Vision Lights’ OverDrive mode delivers >5× the output of continuous mode, which is more than what is offered by many other manufacturers, and Deca mode offers a 1-ms light pulse that is 10× brighter than continuous mode. Integrated into a Dual OverDrive design, these two modes form a single unit, allowing users to select the appropriate lighting mode via the strobe duration. Dual OverDrive mode always begins with a 1-ms burst in Deca mode, but if the exposure exceeds this, the light falls to standard OverDrive.

To prevent lights from burning out, Dual OverDrive lights have shorter duty cycles than continuous mode lights, but the short duty cycle may not affect users as expected, if at all. For instance, a high-speed application with a 100-µs pulse width at a 3% duty cycle can repeat the Deca OverDrive pulse every 3.3 µs, which equates to 300 fps. Even an application with a 500-µs pulse width and a 3% duty cycle can run at 60 fps, which suits a wide range of machine vision applications while delivering more light than 5 ms in continuous mode.

EAMVision was able to replace the LED lights in less than one day, which minimized downtime. In addition, the lights were designed with ease of use, space, and flexibility in mind. They are offered in multiple formats, with direct connection and control through a camera’s trigger output. An integrated cable connects to the camera, light, and controller and reaches up to 15 m.

“Complex problems can arise when creating a high-performance inspection system,” Gallagher said, “but innovations like these LED lights allow us to solve these challenges and help push the capabilities of machine vision systems forward.”

Meet the author

Steve Kinney is the Director of Training, Compliance, and Technical Solutions for Smart Vision Lights. A machine vision expert, he has worked for Pulnix America, Basler, JAI, CCS, and now Smart Vision Lights. Kinney has additionally been an active A3 member and is a current member of the A3 board of directors and vice chair of the Vision & Imaging Technology Strategy Board.

Kinney has also been a major material contributor and instructor for the A3 Certified Vision Professional (CVP) program in both the Basic and Advanced CVP Camera + Image Sensor Technology courses; email: steve.kinney@smartvisionlights.com.