From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Descriptive document outlining the features and operation of the Ashdown Rotoscope for motion study.
| Identifier | ExFiles\Box 143\3\ scan0181 | |
| Date | 15th April 1940 guessed | |
| Page Three THE ASHDOWN ROTOSCOPE (Covered by British and Foreign Patents) Standard “Bladed” Shutter. THE Ashdown Rotoscope has now been in steadily increasing use in industry for so long that it is recognised as the standard stroboscope in the British Empire and the principal foreign countries for all purposes of motion study and the most modern and safe method for checking speeds. It has in most countries superseded and eliminated cheap types of slotted-disc stroboscope as well as the very costly types of high-frequency electric instrument developed in France and America, and imported into this country. The application of the stroboscope to motion problems is now well known to engineering students and physicists, but as an explanation to those not particularly familiar with this form of instrument, it might be mentioned that the Ashdown Rotoscope, by a simple process, “gears up” the observer’s vision to the speed of any moving body if its action takes place at a reasonably periodic rate, and with sufficient speed, so that the individual glimpses merge into a continuous picture. For instance, if a view be taken through the Ashdown Rotoscope of, say, an aeroplane propeller at 2,000 r.p.m.; a shaft at 500 r.p.m.; a reciprocating cam with 1,200 up-and-down movements per minute; a grinding spindle at 12,000 r.p.m.; a fly’s wings beating at 9,000 per minute; a chain at 1,500 f.p.m.; dust-laden air passing through a chamber, etc., etc.; the respective motions would come to rest in any position. This would give actual information regarding the true action probably not known, and unobtainable in any other way. Moreover, at this point the speed would, in each case, be immediately determined by reference to the indicated speed of the instrument; i.e. without physical contact of any kind having been made with the moving object. Briefly expressed, therefore, the Ashdown Rotoscope is capable of giving a “slow motion” view, without photography, of any moving body whether rotational, reciprocating or vibratory, whereby its motion can be studied on the spot for the detection of any faults, or the rapid modification of any mechanical design by actual knowledge of what is taking place under any condition of load and speed Page Ten If a steadily maintained double, treble, or any fixed multiple appearance is shown, this apparent number of images from the actual can be taken as the divisor. There are two great advantages of this “multiple view” method:— The first is that speed checking can be done on relatively slow objects at speed settings where “flashing” (the flicker caused by the speed being below the period of retentivity of vision) is entirely eliminated. The second is that the Ashdown Rotoscope can thus be used as a “safety first” speed checker for any machines or line shafts which bear multi-arm pulleys, by the simple expedient of setting the instrument approximately to r.p.m. x number of arms (or other equi-distant points), after which a careful adjustment to the “static” appearance is made, and the speed at this point divided by the number—which can, incidentally, be clearly seen and counted. WE ARE PREPARED TO FURNISH AT A LOW PRICE SPECIAL MARKED PULLEYS (SPLIT) FOR ANY SHAFT FOR DIRECT READING OF THE SPEED IN R.P.M. When the stationary appearance is given of the object, a very slight movement of the controller from this position puts the shutter slightly out of synchronism with the object, and the latter is then observed appearing to move at the actual difference in speed between itself and that of the instrument. By this means, the “slow-motion” viewing is obtained. The Ashdown Rotoscope can be regulated for accuracy. This is done by moving the little lever on the side of the instrument, which puts in the “sounder.” Audible “clicks” are then heard, the correct rate of which is 120 per minute: chosen because of the ease by which this can be checked with a stop-watch, and adjustment made immediately a discrepancy is noted—instead of waiting for the completion of a full minute’s running. Correction is made, if necessary, by inserting the setting-key in the hole at the side of the instrument, and turning it in the indicated direction for “fast” or “slow.” The controlling wheel should be turned only when the instrument is running, and the instrument must be started fully wound—particularly when accurate speed-computation is required. See that the observing conditions are the best that can be obtained from the points of view of the object being clean, and observed from the best position if a study of the action is to be made: also in the matter of securing good local lighting fully directed on the object, where the “foundation” lighting is not strong enough. | ||