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Photogrammetric Method for Determination 
  
   
  
  
   
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
   
     
of Short-time Decelerations 
Bertil Aldman, M. Doctor, Official Swedish Council on Road Safety 
Research ; 
Ejnar Sigmark, Civ. Engineer, R. Institute of Technology, Div. of 
Photogrammetry, Stockholm 70 
Velocity changes occuring in car collisions can reach very high values 
during relatively short times. The actual decelerations occur in less than 
100 milliseconds but vary within wide limits in different parts of the 
car. The method most frequently used for a wide study of these things 
has been to use accelerometers of strain gauge type and a high speed 
film camera with frequencies between 1-—3000 frames/sec. For the 
study of special details this method is less useful because the mass of 
the accelerometers will interfear with the result. Also the geometric 
property of the high speed camera makes it less suitable for measuring 
purposes as can be proofed using the Hallert grid method, [1]. 
By using photogrammetry very short decelerations can be measured. 
In this paper a method will be described for determinating the stretch- 
ing of a textile band, one end of which is loaded with a weight of metal 
and the other end is fastened to a wagon which can be given a certain 
speed and then be brought to a sudden stop. This trial imitates what 
happens to a safety belt in a car collision. 
On the weight, on the band and on the wagon are mounted small 
signals of highly polished, spherical metal buttons. These are illuminat- 
ed by a stroboscope with a frequency of about 300 flashes/sec. The 
stroboscope used was a Philips PR 9100. Every flash had a duration of 
about 3 microseconds. The frequency can be controlled against the A. 
C. net or a tonegenerator. 
The camera used was a Wild stereocamera with 40 cm base adjusted 
to take stereopairs according to the normal case. The camera constant 
was 91 mm and the size of the pictures 6,5 X 9 cm. The maximum 
aperture is f:12. This is a rather small aperture and therefore high 
speed plate must be used. 
The room in which the trial toke place was darkened to awoid dis- 
turbing reflected light. In the moment when the wagon starts the came- 
ra shutter is opened and remains so until the collision is over. On both 
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