Maria Montero

High-speed video cameras: interview with Dr. Jim …

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

Dr. Jim Bales states that high-speed images allow you to see what is happening mechanically when you manipulate the electrical control side or vice versa. Cameras can often allow manufacturing engineers to see the cause of manufacturing defects without the need for lengthy and time-consuming analysis.

This conversation with Dr. Bales. focuses on the use of these devices and on a four-day course offered at MIT in Cambridge, MA, for a wide range of academic and industry professionals.

Global formwork vs. rolling formwork

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

An important aspect in any type of photography is shutter control, and modern high-speed cameras employ global formwork, as opposed to an older method called rolling formwork.

Global shooting is a method in which all pixels in an image are sampled simultaneously. This is compared to rotary formwork, where pixels are sampled row by row, creating a blur effect if the object in the image is moving fast enough.

Image used with permission from the MIT Edgerton Center.

Dr Bales notes that rotary formwork will produce distorted images at the highest speeds we are concerned about, and “if you take measurements with them you will get false data.” In essence, global formwork allows for clearer images. And more reliable data.

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

High-speed video cameras in manufacturing

According to Dr. Bales, high-speed cameras can provide critical information on everything from populating a circuit board to injecting Coca-Cola into a bottle and donning a cap and label.

For example, a machine that causes widgets to start misbehaving in some way, but the machine is moving too fast to see what’s going on. So the first thing you try is to reduce the speed of the machine, from doing 100 widgets per minute to just 10. The problem may go away, but when you return it to normal, the problem returns. There is something about the high speed that induces the problem, but you cannot see what is happening.

You, the engineer, could solve the problem through analysis or inference. But, as Jim’s engineering colleague once said, “never deduce what you can measure directly.” With a high-speed camera, you can take a large number of images over a relevant period of time, and you will likely see something that can be corrected, sometimes quite easily. You didn’t have to guess or infer, you can see it in an image captured from a moment in time.

Image used with permission from the MIT Edgerton Center.

When analyzing a problematic motor controller, if something is slipping, the slipping may not be occurring at a speed relatively slow to human vision. With a high-speed camera, you can see the true movement of the rotor, moment by moment.

Better yet, camcorders give a sync signal, frame by frame, so you know the exact time of each frame. You can use this timing to activate test equipment and make other types of electrical measurements, and then use data loggers to simultaneously record all electrical signals and lock those records for comparison with images.

In essence, the analyst can lock the two registers, the mechanical image and the electrical parameters that it measures, in time. For example, if you see a voltage fault, you can look at the motor and see what it was doing at the exact time of the fault.