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the tracing velocity. By this means, the smoother 
areas of the model can be traced rapidly, the 
velocity reducing automatically to accommodate 
the rougher areas. 
Tracing velocity will drop to zero in the 
absence of image correlation. Thus, the C.R.T. 
carriage comes to rest in areas devoid of image 
detail or beyond the limits of the model. 
Profiling — Figure 4 
Stereomat includes a horizontal transport 
system for the C.R.T. having independent servo- 
motor drive in the X and Y directions. 
To profile automatically in the X direction, 
the tracing-velocity signal is applied to the X 
motor, giving a linear motion to the C.R.T. 
carriage. As the carriage moves horizontally, 
the Z motor maintains the pattern centre in 
contact with model surface, in response to the 
X parallax signals. The Y motor forms a part of 
a positioning servo, that holds the carriage 
rigidly in the Y direction. The pattern centre is 
thereby constrained to trace out a straight pro- 
file in the X direction. The Y position is se- 
lected by an automatic stepping system. When 
the carriage reaches the edge of the model, a 
limit switch operates. The profiling direction 
is thereby reversed, and the stepping system is 
actuated to shift the carriage to a new Y position 
for the next profile. 
By reversing the roles of the X and Y 
transport motors, profiles may be traced in the 
  
AUTOMATIC STEREO 
Y direction. 
"Synchro read-out” is provided for X, Y, 
and Z positions of the carriage. The read-out 
signals may be coupled to a computer or to an 
external profile-drawing "co-ordinatograph", as 
required. 
Contouring — Figure 5 
The XY transport system also provides the 
movements of the carriage necessary for con- 
touring, while the Z motor holds the C.R.T. 
rigidly at the required height. The stepping 
system is used to shift the C.R.T. vertically 
to each contour position. 
During contouring, X parallax is cleared 
by horizontal movement of the C.R.T. The di- 
rection of motion required to clear X parallax 
is always perpendicular to the direction of motion 
required for tracing the contour. Since a con- 
tour may assume any angle in the XY plane, a 
steering “resolver” is required to direct the X 
parallax and the tracing-velocity signals to 
appropriate transport motors. 
A resolver is a variable transformer with 
two inputs, A and B, and two outputs, C.and D. 
The angle of the resolver shaft determines how 
the input signals are distributed between the 
output terminals. For example, if output C were 
A sin © + B cos O, then output D would be A 
cos © t B sin 9. 
When contouring, the tracing-velocity 
signal is applied to one input of the steering 
RIGHT IMAGE SIGNAL 
  
  
Y 
  
  
  
  
   
   
   
    
  
   
  
  
    
    
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
CORRELATION == 
x CIRCUITRY LEFT IMAGE SIGNAL 
A X [s 
TRACING | PARALLAX | SIGNAL PHOTO 
T.S.M VELOCITY | SIGNAL | (SHAFT POSITION) CELLS 
A SIGNAL SIGNAL n * 7 
v \ / 
REF v ne » —Ó PHOTOGRAPHIC 
Y REF  RESOLVER \ j TRANSPARENCIES 
i <> > LENSES 
VELOCITY \ / 
CONTROL \ / 
k 1 
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| AMP AMP 
À » GENERATOR i ; 
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vy y RAY TUBE 
+ » » DEFLECTION 
+ » » COIL ASSEMBLY 
'X' MOTOR 'Y' MOTOR 
Figure 5. System Block Diagram Contour Mode 
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