Brother International MD-817 Service Manual - Page 9

Principle, Control, System

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( PRINCIPLE OF CONTROL SYSTEM ) 0 O 0000 00O0 0 0 00 III 0 1. When the power switch 0 is turned on and the treadle is depressed, the start signal and a voltage corresponding to how 0 far the treadle is depressed, are supplied to the control box by the treadle unit. The voltage is supplied to the motor 0 by the control circuit board in the control box 0 so that the motor runs in proportion to the depression of the treadle to drive the sewing machine. 0 2. When the treadle is returned to the neutral position (with foot taken off), the neutral signal is sent to the control box 0 by the treadle unit 0 and the brake command is given by the control circuit board to decelerate the motor 0. Then the signal from the synchronizer 0, mounted on the pulley of the sewing machine, is sent to the control box 0 and the brakes are ap- plied so that the operation of the sewing machine is stopped with the needle in the down stopping position set by the syn- chronizer 0. 3. When the treadle is stepped on again, the thread trimming signal is sent to the control box 0 by the treadle unit 0 and the command is given by the control circuit board to run the motor 0 at the thread trimming speed (inching speed). Then the signal from the synchronizer 0 is sent to the control box 0 and the brakes 0 are applied so that the operation of the sewing machine is stopped with the needle in the up position set by the synchronizer G.

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(
PRINCIPLE
OF
CONTROL
SYSTEM
)
0
O
0000
00O0
0
0
00
III
1.
When
the
power
switch
0
is
turned
on
and
the
treadle
0
is
depressed,
the
start
signal
and
a
voltage
corresponding
to
how
far
the
treadle
is
depressed,
are
supplied
to
the
control
box
0
by
the
treadle
unit.
The
voltage
is
supplied
to
the
motor
0
by
the
control
circuit
board
in
the
control
box
0
so
that
the
motor
runs
in
proportion
to
the
depression
of
the
treadle
to
drive
the
sewing
machine.
2.
When
the
treadle
0
is
returned
to
the
neutral
position
(with
foot
taken
off),
the
neutral
signal
is
sent
to
the
control
box
0
by
the
treadle
unit
0
and
the
brake
command
is
given
by
the
control
circuit
board
to
decelerate
the
motor
0.
Then
the
signal
from
the
synchronizer
0,
mounted
on
the
pulley
of
the
sewing
machine,
is
sent
to
the
control
box
0
and
the
brakes
are
ap-
plied
so
that
the
operation
of
the
sewing
machine
is
stopped
with
the
needle
in
the
down
stopping
position
set
by
the
syn-
chronizer
0.
3.
When
the
treadle
is
stepped
on
again,
the
thread
trimming
signal
is
sent
to
the
control
box
0
by
the
treadle
unit
0
and
the
command
is
given
by
the
control
circuit
board
to
run
the
motor
0
at
the
thread
trimming
speed
(inching
speed).
Then
the
signal
from
the
synchronizer
0
is
sent
to
the
control
box
0
and
the
brakes
0
are
applied
so
that
the
operation
of
the
sewing
machine
is
stopped
with
the
needle
in
the
up
position
set
by
the
synchronizer
G.