' means of 
> provided 
Ort points 
ent of the 
, averaged 
rity error 
dial gauge 
rammetric 
couplings. 
couplings 
ise as and 
re cheked. 
i. 
e passage 
ie Cardan 
e the po- 
ling to be 
xes of the 
g and the 
g and the 
ase bridge 
  
— 13 — 
rod axis. These eccentricities were determined by measuring the inclination 
changes of the rod when the position of the Cardan coupling was caused to 
rotate 180° round both the primary and secondary axes. 
The results of the experiment were as follows: 
Eccentricity left camera right camera 
er 8,9 um 12 um 
ey 12,7 um 39 um 
€x 12 vm 16,4 um 
The mean error of each determination, deduced «a posteriori » from the 
repetitions of the tests, is + 1 pm. 
Also the bearings of the sleeve within which the rod slides, were examined 
«globally ». Their irregularities however resulted irrelevant. 
As can be easily demonstrated, the A X and the A Y projection errors, 
due to coupling eccentricities, result from the following formulae, where the 
o angle is the rod slope in the YZ plane, and the angle ¢ is the slope in the 
plane containing the rod, which is parallel to the X axis. 
; 1 
A} Lm Ey | ] —! | 
COS €) 
D 
2) 
; 1 
AX —e 1 — £y tán © — e,. tan o tan o 
3 7 ; } ; 
cos © ) 
Substituting the values of ej, ey, e, experimentally obtained, the re- 
sulting maximum projection errors, even when the rods are very sloped, are 
inconspicuous. 
b) The plate-holder and its movement. 
The Santoni Stereocartograph mod. IV has a fixed optical system which 
observes the plates, from the principal point of the camera, always perpen- 
dicularly. 
Consequently it is the plate which must be movable so as to permit its 
complete survey. 
In accordance with what has been previously stated, the analitical study 
of the instrument has considered only the organs of the camera which are 
moving during the plotting stage, 1. e. the plate-holder and the parallelogram 
linkage (Fig. 10) which controls it when the former is moving, and which is 
in turn driven by the rod. 
The theoretical conditions for the correct operation of this organ are the 
tollowing: 
1) the linkage from the plate-holder to the rod must be free of back- 
lash: : 
2) the surface described by the centre of the coupling during plotting 
notions must be plane: 
: 3) no anomalous rotations must take place about the three axes pas- 
sg through the coupling centre, which are respectively parallel to the axis 
? the camera, the x axis and the y axis of the photographs (Fig. 10) 
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
        
   
    
   
    
    
       
     
   
   
  
  
     
  
  
  
   
     
      
    
   
    
   
  
    
    
  
    
   
     
  
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