((Principle Of Control System^) - Brother MD-802 Service Manual

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PRINCIPLE OF CONTROL SYSTEM
1. When the power switch O is turned on and the treadle 3 is stepped on, the start signal and the voltage correspond¬
ing to the stepping degree are supplied to the control box © by the treadle unit. The voltage is supplied to the
motor © by the control circuit board in the control box © so that the motor runs in proportion to the stepping
degree to drive the sewing machine.
2. When the treadle © is returned to the neutral position (with foot off), the neutral signal is sent to the control box
© by the treadle unit © and the brake command is given by the control circuit board to decelerate the motor ©.
Then the signal from the synchronizer ©, mounted on the pulley of the sewing machine, is sent to the control
box © and the brakes are applied so that the operation of the sewing machine is stopped at the needle down stop
position set by the synchronizer ©.
3. When the treadle is stepped on again, the thread trimming signal is sent to the control box © by the treadle unit ©
and the command is given by the control circuit board to run the motor © at the thread trimming speed (inching
speed).
Then the signal from the synchronizer © is sent to the control box © and the brakes © are applied so that the
operation of the sewing machine is stopped at the needle up stop position set by the synchronizer ©.