High speed imaging as a tool in trouble shooting and researchAntero Komppa AMBERTEC Oy (Ltd), Espoo, Finland
To see is to know
The human eye - when connected to properly working brain - is a magnificent tool for troubleshooting and operational analysis. However, very often it is too slow to see what really happened. Ordinary video recording (25 or 30 frames per second) may offer some help but e.g. for tuning up of many processes or machinery it is not fast enough. For instance, the web of a modern paper machine runs above 1500 m/min and by normal video imaging the paper web there would travel above 1000 mm between two full video frames. It is possible to use a stroboscope to "freeze" periodic phenomena but when examining phenomena that appear only once the stroboscope does not help at all.
According to the experience from a variety of cases from industries and research the majority of the reasons behind the disturbances in fast running machinery can be revealed very quickly and effectively through the use of modern high speed imaging. Such cases do include trouble due to wrong timing, vibrations, misplacement of components, unexpected changes of the materials or components during handling etc. In many of these cases the high speed imaging was the only way to solve the problem because the disturbance took place for a short while only and could not be seen in any of the usual measurements for process control or ordinary video recording techniques.
High speed, yet low cost
Due to historical reasons, high speed imaging does have a reputation of a difficult and expensive method. This was true when fast movies were exposed on ordinary movie film which required the wet developing process and it was true even with the fast video recording on special video tapes; the devices were heavy, expensive and vulnerable.
Today these historical methods have been replaced by digital high speed imaging in which the images are stored directly into a random access memory or onto a hard disk. The modern high speed imaging devices are low cost, rugged, lightweight, portable tools - easy to learn and use. An excellent example of these is the AMBERTEC FastVision 2200 (Figure 1), which is able to shoot up to 2250 frames per second - almost a hundred times faster than ordinary video. This system has excellent triggering capabilities thus making it very versatile for various applications where automatic starting or stopping of the recording can be used.
Actual events are short in duration
At first, many of the customers
do require that they could continuously record events for up to several
minutes. Usually this is based on a misunderstanding of the events
and the imaging technique itself: the interesting part of the phenomena
usually take less than half a second. Even a car collision at a speed
of 110 km/h is over in about one second (Figure 2). So we should
rather use intelligent triggering to catch the interesting part than to
shoot minutes of frames just to be sure that something would take place
during that time. The FastVision 2200 is able to shoot more
than 15000 frames in 7 seconds so it would take about 90 minutes to watch
a 1 minute long record at a normal 25 f/s playback rate!! On the
other hand the recording time (7 seconds at full speed) is long enough
so that even the fast events can be caught with manual triggering.
Figure 2. Car collision test, vehicle speed 110 km/h.
The car hits the rail and gets upon it. The rail prevents the car from getting off the road but will be damaged and torn off the pole. The damages of the car can be monitored in detail from the recorded frames, e.g. a) the headlight hits the pole and gets demolished, b) the steering assembly gets loose, c) the rear shield of the headlight in the air.
Another misunderstanding regards to the frame rate required. The collision test in Fig. 2 was recorded at a rate of 275 frames per second and one can easily analyse and identify the parts breaking up from the vehicle. As a matter of fact it would be rather boring to watch this case at a recording rate of 2250 frames /second: virtually nothing would change from frame to frame.
The high recording speed
is required in cases of very fast phenomena. In Fig. 3 there is a
machine gun firing 20 bullets per second. The full speed of the camera
makes it possible to catch the bullet leaving the muzzle.
Figure 3. Gun firing 20 bullets per second
A portion of the flash (2nd frame) escapes from the muzzle just before the bullet (3rd frame) followed by the major part of the flash. Last frame shows the next bullet.
Thanks to the digital operation it is easy to review each of the records immediately and to find and cut out the interesting part of the record for permanent storage. Therefore the hard disk space will not be filled up with large files of nonsense.
What is the resolution necessary?
The usual resolution of a
high speed imaging systems of today is 256x256 pixels. There are
systems available with better resolution but at lower speeds or high speed
high resolution ones at a VERY high price level. As a rule, the customers
do first require a very high resolution until they do see the quality of
a 256 resolution image. This is enough for most cases as can be seen
from Fig. 4. Figure 3 is recorded using 256 x 128 pixel resolution
and even there the details are visible well enough.
Figure 4. Trouble in PC board automatic assembly machine
Due to a faulty shock absorber in the component inserting tool the capacitor does not remain in the holes of the PC board thus stopping the automatic assembly line.
The conventional rules of
photography and cinematography do apply to the high speed imaging as well:
Do bring the object close enough using a suitable lens combination or by
moving the camera and do arrange suitable illumination of the object to
allow good depth of field and contrast of the image! Many of the
"snapshooters" of today may no more recognise these simple rules as the
modern automatic snapshot cameras have made the traditional photographing
skills almost unnecessary. These are easy to learn however and most
of the people do learn the essentials of high speed imaging during a half
day of training. During playback of the record, the brightness and contrast
can be further adjusted to some extent but any serious imaging errors cannot
be corrected. Fortunately the records are easy to browse through
on the spot already and a short test record prior to the important one
would confirm that everything is ready for the actual work.
Could I benefit from high speed imaging?
Briefly: YES, you could!!
The high speed imaging applications do range from sleeping people up to
target hitting missiles. The former might sound irrational but there
the researchers are actually studying the rapidly moving eyes during the
REM-phase of the sleep (sorry, we are not able to record the dreams, yet…).
Figure 5. Trouble on a candy
Figure 6. Reel change on
a paper machine
Figure 7. Tissue towel wrinkling
on the packaging line
One of the most profitable
uses of the high speed imaging is in trouble shooting of processes or machines:
In many cases a malfunction of a machine has been studied for many days,
even several weeks before somebody finally would try the high speed imaging
as their last alternative. Quite often, however, the problem can
be solved as a matter of minutes only after the operators or the maintenance
crew have seen the high speed imaging record of the case. The reason
may be defective machinery (like in Fig. 4), a tune-up problem (like in
Figures 5, 6 and 7) or virtually any malfunction in the process.
The production downtime in
the fast running process industries of today is very costly and therefore
many mills have purchased a high speed imaging system as a troubleshooting
tool for routine use: If you do have the imaging device at the mill
site you can take it to the trouble spot without a loss of time. Usually
it is more expensive to find out the reason of the trouble than to fix
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