TM 11-6720-24235
cam, the pressure roller releases the film from the puck
b. Magazine Drive Mechanism. The linkage gear
thus stopping film transport.
(12), which delivers mechanical power from the body to
the magazine, meshes with the input gear (13). Also on
2-10. Functioning of Scan Drive Circuits
the input gear shaft are the supply sprockets (42) and
pulley (43) which drive pulley(45) via belt (50). On the
The scan drive circuits comprise a pulse width
same shaft with pulley (45) are the takeup sprockets
modulated amplifier which controls scan motor B1. The
(41) and gear (44) which meshes with idler gear (46)
inputs to amplifier AR1 are a v/h signal voltage (fig. 2-
which, in turn, meshes with gear (47) and thus drives the
1) and the voltage generated by tachometer-generator
takeup spool (51). The clutch (48) is attached to and
G1.
The tachometer generates a voltage that is
functions with gear (47). The brake (49) is mounted on
proportional to the speed at which the scan motor is
the spindle of the supply spool (52) and furnishes drag
rotating. A variable v/h signal voltage from the scaling
on the film supply to prevent excess film slack. The
networks at a gradient of 0.4 volt/cycle/second for
rotation of the lift cam (29) raises and lowers the cam
autocycle mode of operation or at a fixed 0.8
follower (36). The rocker arm (37), operated by the up
volt/cycle/second for pulse mode with the pulse intervals
and down motion of the cam follower, causes the adas
variable, is proportional to velocity-over-height at which
pressure plate (38) to provide pressure on the film
the aircraft is traveling. The v/h signal voltage and the
during adas exposure (para 2-3). Film is threaded
voltage from the tachometer-generator are compared in
through the magazine as follows: fresh film from the
scan amplifier AR1. The amplitude and polarity of the
supply spool is threaded about the supply sprockets (42)
amplifier output governs the needed acceleration or
and routed under the film keeper (40) forming the supply
deceleration of the scan motor so that it will rotate the
slack loop (53). The film is routed from the film keeper
prism and advance the film at the required scan rate for
between the pressure roller (35) and the puck (31)
the photographing of present terrain.
forming the takeup slack loop (54), threaded about the
takeup sprockets (41) and collected by the takeup spool.
a. The output of amplifier AR1 is an error voltage
Film transport is accomplished when the linkage gear
resulting from the difference between the two inputs.
(12) drives the input gear (13) causing the supply
The polarity is positive when the v/h voltage is greater,
sprockets to rotate in a clockwise direction. The supply
and negative when the tachometer-generator voltage is
sprockets pull film from the supply spool and routes it to
greater. When scan control relay K1 is energized, the
the supply slack loop thus increasing the supply slack
error signal from amplifier ARI is applied to the collector
loop size. The pulley (43) rotates the takeup spool and
of chopper transistor Q6 and also to the dynamic motor
takeup sprockets in a clockwise direction via the belt
brake circuit, which includes transistors Q12 and Q13.
(50) and the gear arrangement (44, 45, 46, and 47)
The function of chopper transistor Q6 is to convert the
allowing the film to be collected from the takeup slack
dc level of the error voltage to a 400 hertz square wave
loop and thus decreasing the takeup slack loop size. As
dc pulse.
the supply slack size increases, the cam follower rides
on the high side of the lift cam. When the supply slack
b. The amplitude of the square wave from chopper
loop increases a predetermined amount, the cam
Q6 is proportional to the error signal and it is connected
follower rides on the low side of the lift cam. This
by emitter follower transistor Q4 to a differentiates
condition causes the pressure roller to press the film
capacitor C4. The differentiated pulse (fig. 2-5) then
against the continuously rotating puck thus transporting
becomes the input to the base of switching transistors
the film from the supply slack loop, under the pressure
Q5 and Q7. Note that Q5 receives a positive-going
plate (39) and film keeper and to the takeup slack loop.
differentiated dc pulse and Q7 a negative-going
As the film passes under the pressure plate and the film
differentiated dc pulse. Transistors Q5 and Q7 conduct
keeper it is exposed to the target image. The prism
at approximately 0.3 volt. The output at the collector of
(22), which is rotated at the same rate as the film is
Q5 positive half cycles and at Q7 for negative half
transported, transmits the target image through the lens,
cycles is amplified as a pulse width. Transistor Q3
aperture, and slit (not shown) to the film. When the cam
serves as the summing point of both circuits and its
follower reaches the high side of the lift
positive output is the base drive for power transistor Q1,
located on the heat sink assembly. Transistor Q1, in
turn, drives scan motor B1.
2-10
