High Speed Video Cameras: Interview with Dr. Jim Bales, Associate Director of MIT’s Edgerton Center

AAC's Gary Elinoff spoke with Dr. Jim Bales, Associate Director of MIT's Edgerton Center, about the value of high-speed cameras in design and manufacturing.

Dr. Jim Bales asserts that high-speed imaging makes it possible to see what is happening mechanically as they are manipulating electrical control side or vice-versa. Cameras can often allow manufacturing engineers to see the cause of manufacturing defects without the need for extensive, time-consuming analysis.

This conversation with Dr. Bales centers on the uses of these devices and on a four-day course he offers at MIT in Cambridge, MA, for a broad range of industry and academic professionals.

Global Shuttering vs. Rolling Shuttering

In research, design, testing or manufacturing, events often take place at speeds far beyond the capability of the human eye to see. Specialized cameras capture fleeting moments in time and provide a basis of correlating with related electrical events.

An important aspect in any kind of photography is control of the shutter, and modern high-speed cameras employ global shuttering, as opposed to an older method call rolling shuttering. 

Global shuttering is a method wherein all of the pixels in an image are sampled simultaneously. This is compared to rolling shuttering, wherein pixels are sampled row-by-row, creating a blur effect if the subject of the image is moving sufficiently quickly.

 

Image used with permission from MIT Edgerton Center.

 

Dr. Bales points out that rolling shuttering will produce distorted images at the higher speeds with which we are concerned about, and “if you make measurements with them you’re going to get bogus data.” In essence, global shuttering allows for clearer images and more reliable data.

You can learn more about the difference between these kinds of shuttering and the devices that use them in these articles:

• STMicroelectronics Introduces High-Dynamic Range Image Sensors for Automotive Driver Monitoring
• ams Introduces Image Sensor for High-Throughput Manufacturing and Optical Sensing Applications
• Product Brief: New CMOS Imaging Sensor by ams Aims to Be the Future for Machine Vision

High-Speed Video Cameras in Manufacturing

According to Dr. Bales, high-speed cameras can provide critical input on everything from populating a circuit board to injecting coca-cola into a bottle and getting a cap on and a label on.

For example, a machine that makes widgets starts misbehaving in some manner, but the machine is moving too quickly to see what’s going on. So the first thing you try is to slow the machine down from making 100 widgets a minute to making only 10. The problem may go away, but then when you speed it up back to normal, the problem comes back. There’s something about the high speed that induces the problem, but you can’t see what’s going on.

You, the engineer, might be able to solve the problem through analysis or inference. But, as senior manufacturing engineering colleague of Jim once advised, “never infer what you can directly measure.” With a high-speed camera, you can take a vast amount of pictures during a relevant time period, and you are likely to see something that can be corrected, sometimes quite easily. You didn’t have to guess or infer, you can see it in a captured image of a moment in time.

 

Image used with permission from MIT Edgerton Center.

 

In analyzing a problematic motor driver, if something is slipping, the slip might not be happening at the relatively slow speed at amenable to human vision. With a high-speed camera, you can see the true motion of the rotor, moment by moment.

Better yet, video cameras give a synch out signal, frame by frame, so you know the exact time of each frame. You can use this synch out to activate test equipment and make other sorts of electrical measurements, and then employ data loggers to concurrently log all the electrical signals and lock those records to compare them to the images.

In essence, the analyst can lock the two records, the mechanical picture and electrical parameters that you measure, in time. For example, if you see voltage glitch, you can look at motor and see what it was doing at the exact moment of the glitch.

Cameras Not Limited to the Visual Spectrum

What happens when the event you wish to analyze is concurrent with a high-intensity blast of visual spectrum light? An example might be an armor-piercing shell fired at tank armor, with the impact causing a visible spectrum fireball.

In such an event there is also useful output in the X-ray spectrum that can be gleaned by specialized, and rather expensive X-ray cameras. The key is that if the fireball doesn’t extend to X-ray wavelengths, the X-rays emitted, unobscured by the fireball, may well provide the sought after picture of the moment-by-moment effect of the shell on the armor.

Why Should Mechanical and Design Engineers Care?

Take the example of a cellphone case designer. When the cellphone case is dropped on a hard surface and it cracks, precisely how is it breaking? If you can see how the failure mode begins, you may be able to end the problem by adding a little reinforcement to the case to a particular part of the structure, or perhaps, as Jim notes, to “move this support two millimeters towards the back of the case” to prevent that breakage. “When you see the failure mode, you can adjust the design to compensate.”

The Course

The course Dr. Bales is teaching is called "High-Speed Imaging for Motion Analysis: Systems and Techniques" and it is intended to help engineers be able to select and utilize cameras in their jobs—without  needing to understand every aspect of the hardware involved. 

Dr. Bales will be teaching:

• Choosing the right camera
• How to light subjects for photography
• How to choose the right lens

All major manufacturers’ equipment is represented, including:

• Vision Research
• Photron
• Nac

The class aims to teach participants the tradeoffs of all the available industry offerings. The focus of the instruction is not the inside of the camera but rather how to use it. The program is four days long and will run from June 17th to 20th.