TM 5-6675-319-14
s h a f t.
(a) The right angle gear coupling drives a drive spindle and keyway
(b) The drive nuts, mounted on the drive spindle, are linked to the
center member of the parallelogram.
As the spindles rotate, the drive nut moves,
causing expansion or contraction of the parallelogram and indirectly raising or
lowering the easel.
The easel is suspended from the lower end of the parallelogram
by the easel support brackets and lower carriage. The lens support arm is control-
led by the drive spindles which are free to move along the keyway drive shaft. The
lens support arm is suspended between the upper carriages. Vertical movement is
induced by a ball bearing nut built into the lower carriage. The drive spindles are
t h r e a d e d i n t o t h e l o w e r c a r r i a g e . S i n c e e a c h l o w e r c a r r i a g e i s h i n g e d t o i ts
inversor parallelogram, the nut imparts a vertical movement to the drive spindles as
the parallelogram is actuated.
The actual amount of movement which the drive screw
a c c o m p l i s h e s i s t h e s u m o f t h e s e t w o i n d e p e n d e n t m o t i o n s . T h i s a c t i o n r e s u l t s in
the correlated movement between the lens and easel. At the same time, the drive
screw is being rotated by the drive shafts so that it is being threaded vertically
through the drive nut.
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