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Question

Use slow motion video for machine stop time study

Dec 3, 2011 9:45AM PST

<font size="3" face="Times New Roman">
</font><span style="'font-family:" "Calibri","sans-serif";'><font size="3">I need to
take high speed video of a machine to determine how quickly it stops when the
safety device is activated. For example, my theory is to set a camera on
a tripod and frame the view where the point of operation of the machine will be
in the picture and also will be the edge of the safety device (usually a light
curtain). I would start the camera, move my hand into the light curtain
beam which would activate the machine stop circuit and then watch to see at
what frame the dangerous motion of the machine stopped.<?xml:namespace prefix =" o" ns =" "urn:schemas-microsoft-com:office:office"" /><oSilly></oSilly></font>
<font size="3" face="Times New Roman">
</font><span style="'font-family:" "Calibri","sans-serif";'><oSilly><font size="3"> </font></oSilly>
<font size="3" face="Times New Roman">
</font><span style="'font-family:" "Calibri","sans-serif";'><font size="3">Normally,
the machine should stop within 0.100 to 0.450 seconds or so, but I need to
verify that exact time to make sure that the light curtain is mounted at the
correct distance. The safety concept is that the machine motion would stop
before a hand could reach the machine point of operation or other hazard
location.<oSilly></oSilly></font>
<font size="3" face="Times New Roman">
</font><span style="'font-family:" "Calibri","sans-serif";'><oSilly><font size="3"> </font></oSilly>
<font size="3" face="Times New Roman">
</font><span style="'font-family:" "Calibri","sans-serif";'><font size="3">Am I on the
right track? Can this be done with your video editing program? Has
anyone done it like this before? Is there something special about the camera
used? Any ideas or suggestions?<oSilly></oSilly></font>
<font size="3" face="Times New Roman">
</font>

Discussion is locked

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Answer
High Speed Camera
Dec 4, 2011 12:07AM PST
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Answer
Nice post.
Dec 4, 2011 3:28AM PST

I see you tried to embellish your content by adding all those codes. Please don't do that in the future.

ON TO HOW WE SOLVED THE TIME STAMP ISSUE. READY?

We put a high speed counter into the video. Or a clock that the second hand rotates once per second. Pretty common lab equipment for a high speed video lab.

But " within 0.100 to 0.450 seconds" would not have to use such things. If your average 30 or 60 FPS video is used that's 0.033333 seconds per frame so nothing special is required for the camera.
Bob

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Use slow motion video for machine stop time study
Dec 4, 2011 6:17AM PST

Thanks - this is my first time using this so I did not know that if I copy and pasted something it would do that - sorry about that! I have been looking for a video camcorder that shows in the viewfinder on playback the time track at 0.100's of a second, but that means I will have to shoot the video at a very high frame rate - probably 240 fps or higher. It also needs to be somewhat protable because i will be in factories going from machine to machine. My other alternative is a digital video camera that will shoot at 240 fps or higher and then I dump that into a laptop and use a video editing program to see how quick the machine stops. I am looking for suggestions - any ideas?

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So why more than 30 or 60 FPS?
Dec 4, 2011 6:23AM PST

You wrote above "the machine should stop within 0.100 to 0.450 seconds or so,"

At 30 FPS we get an image with the stop from 0.096 to 1.034 seconds.

At 240 FPS our accuracy is from 0.0995 to 1.0042 seconds.

Your own words wrote something much more lax. Why the overkill?
bob

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Use Slow Motion for machine stop time study
Dec 4, 2011 12:31PM PST

The concept for the project is to measure how quickly certain types of machines can come to an emergency type stop if someone activates a safety device. The machine points of operation can rotate, some have crushing motions, some have pinching motions and most have speeds that are very very fast. I plan on framing the shot so that i can see the safety device activated (usually a hand going through a light curtain or opening a gate or guard) and then see how many milliseconds it takes the machine to stop. This will determine if the light curtain is far enough away to fully protect the point of operation. There is a formula that i use that incorporates hand speed. For most machines, the light curtain or safety device would be somewhere between 1 foot and 4 feet away, so the machine would have to stop somewhere between 50 ms and 600 ms or so. Shooting at less than 240 fps leaves the machine motion as a blur and by the time a frame shows it stopped, the difference in time is greater than the ms i need to determine.

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FPS is not how we measure blur.
Dec 5, 2011 1:47AM PST

Also it's more a matter of shutter speed. Noted at http://www.digicamguides.com/learn/shutter-speed.html

Back to 50 ms (I prefer mS in papers.)

"At 30 FPS we get an image with the stop from 0.096 to 1.034 seconds."

So I wonder if I did that number wrong (I did). 1/30 second is .033333... seconds so it can't be used for your 50 mS threshold.

Moving to 60 FPS will meet your 50 mS spec and then you worry about shutter speed.
Bob