Handbook of High Speed Photography - IET Labs, Inc.
Handbook of High Speed Photography - IET Labs, Inc.
Handbook of High Speed Photography - IET Labs, Inc.
Create successful ePaper yourself
Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.
Figure 1-4. Multiple-flash analysis <strong>of</strong> shaft rotational motion.<br />
DIRECTION OF<br />
SHAFT ROTATION<br />
An«ANGULAR DISPLACEMENT<br />
OF SHAFT AT THE<br />
INSTANT OF nTH LIGHT<br />
FLASH.<br />
Typical pattern obtained from a multiple-flash photograph <strong>of</strong> the end <strong>of</strong> a<br />
moving shaft. A single bright mark placed on the shaft's periphery re<br />
veals its position at the instant each Strobotac flash occurs.<br />
Given: Average angular velocity = 1800 rpm = 10.8° per millisecond<br />
Strobotac flash rate = 21,600 flashes per minute = 12 flashes<br />
per revolution<br />
tp =time between Strobotac flashes = 2.78 milliseconds<br />
Camera shutter speed approximately 1/30 second<br />
To determine the shaft's average angular velocity at different positions,<br />
measure the angles between adjacent mark positions on the photograph<br />
and divide by tp. Consider this average value over each displacement<br />
interval as the approximate angular velocity at the midpoint <strong>of</strong> the inter<br />
val. Since this example is symmetrical, only half <strong>of</strong> the calculations<br />
need be made. For example:<br />
Angles<br />
Measured<br />
From<br />
Photograph<br />
Average<br />
Angular Velocity<br />
In Degrees<br />
Per Millisecond<br />
(Angle/tp)<br />
Shaft<br />
Displacement<br />
At Midpoint<br />
Of Interval<br />
A,, (360-An) = 21° ^1,0=7.55 10°, 350°<br />
(A2"Al)> (AirAio) = 24° w2,l =8-63 33°, 327°<br />
(A3-A2), (A10-A9) = 28° W3?2= 10.1 59°, 301°<br />
(A4-A3), (A9-A8) = 32° W4)3=ll.5 89°, 271°<br />
(A5-A4), (A8-A7) = 36° W5?4 = 12.9 123°, 237°<br />
(A6-A5), (A7-A6) = 39° W6>5 = 14.0 160°, 200°
Change language