Control System - Brother S-7200B Service Manual

9. CONTROL SYSTEM

Turn on the power switch (1).
A. When the treadle is depressed
1. When the treadle (2) is depressed, a voltage corresponding to the amount of treadle depression is transmitted by the
treadle unit (3) to the control box (4).
2. The DD motor (5) that is directly linked to the sewing machine receives a voltage that corresponds to the treadle
depression amount from the control box (4), causing the DD motor (5) to operate at the speed represented by the treadle
depression amount, and this makes the sewing machine operate.
B. When the treadle is returned to the neutral position
1. When the treadle (2) is returned to the neutral position (when the operator's foot is removed from the treadle), a signal
indicating that the treadle is at the neutral position is transmitted by the treadle unit (3) to the control box (4), and the
electrical brake is then applied to slow the DD motor (5).
2. The encoder circuit board that is installed to the DD motor (5) sends a signal to the control box (4) so that the electrical
brake is applied in order to stop the sewing machine at the stopping position (needle up or needle down) set by the pulley
(6) that is attached to the DD motor (5).
C. When the treadle is depressed backward
1. When the treadle (2) is depressed backward, a signal indicating thread trimmer operation is transmitted by the treadle unit
(3) to the control box (4), and the DD motor (5) slows down to the thread trimming speed (inching speed).
2. The encoder circuit board that is installed to the DD motor (5) sends a signal to the control box (4) so that the electrical
brake is applied in order to stop the sewing machine at the needle up stopping position set by the pulley (6) that is
attached to the DD motor (5). The thread trimming operation is carried out immediately before the sewing machine stops at
the needle up stop position.
S-7200B
9. CONTROL SYSTEM
2320M
48