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Forms Feed Emitter
Below is a conceptual illustration of the forms
feed emitter used in the serial printer. An emitter
disk is driven by the forms feed stepper motor.
The emitter disk has 90 slots, 45 on an outer
track, and 45 on an inner track. The slots of the
outer track are positioned 2 degrees in advance of
the inner track. Each slot is 4 degrees of one emit-
ter disk revolution.
Light Emitting
Diodes
Photocells
Forms Emitter
Disk
Two LEOs (light emitting diodes) are positioned
opposite the two tracks. Two photocells face the
diodes on the opposite side of the disk. The disk
turns freely between the LEOs and the photocells
so that light from the LEOs can be sensed by the
photocells. When the disk is rotating and a slot
appears in front of the LED, light passes through
the slot, the photocell senses it, and current is
conducted. The photocells drive two amplifiers.
The amplifiers convert the low level current signal
from the photocells to a VTL logic level. The sig-
nals from the printer to the attachment are forms
emitter A and forms emitter B.
A
Attachment
A
9-10
As the forms feed stepper motor rotates, the
forms feed emitter produces one pulse for each 2
degrees of rotation. For every 16 pulses the paper
advances 1/6 inch (or one line). These pulses signal
the attachment that a line feed is occurring. (The
attachment uses these pulses to control forms
movement.)
This is a closed loop system:
Forms emitter A is used by the attachment to
control forms-predriver A and forms-predriver
A.
Forms emitter B is used by the attachment to
control forms-predriver
Band
forms-predriver
B.
The pulses are counted by the attachment to de-
~
I
I
B
termine the amount of the motion, and are used
~------i
in a feedback loop that generates forms-predriver
B
pulses (A, A, B, andS) to keep the motor running.
~-----1
Amplifier
I-~I
___
L-_ _
--1 _ _ _
L _ _ _ _ _ _ •
Forms Emitter B
I
I
~
~2°
I
I
I
I
Amplifier l-.!..I ________________
L _ _ ... ..,
Forms Emitter A }-----"
I
I
I
D
Slot in Outer Track
I
I
I
D
Slot in Inner Track
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