Nilfisk-Advance Advance SC750 ST

Service Manual: SC750, SC800, SC 750 ST, SC800 ST
Form Number 56043150 Page 77
Scrub System – Cylindrical
Functional Description
The scrub system moves the scrub head up and down and turns the scrub motors on and o at the operator’s request, to
provide oor scrubbing acon. The brushes spin toward one another at the boom. The head is moved up and down by
an electric actuator motor that has integrated posion switches. The weight of the scrub head provides the downward
pressure for scrubbing. The actuator linkage is sloed to allow the brush head to “oat” when going over low and high
spots on the oor. A spring is used to li just a bit of weight in order to obtain opmal scrub pressure weight. Note: The
cylindrical scrub system does not have an “extreme pressure” mode.
• The Main Machine Controller energizes the brush solenoid to turn on the brush motors when the following
inputs have been met:
o Key switch on
o Operator request
o Machine moving signal (FOR/REV)is received from the Drive Motor Controller (A2 PG Drives Speed Con-
troller)
 Approximately 24 volts received from the main controller (J3 Pin 6) is switched to baery nega-
ve by the Drive Motor Controller, dropping the voltage to 0 volts.
Here is how the circuit works for the scrub motors: The Main Machine Controller turns on the scrub motors indirectly
by energizing the Brush Contactor. The brush contactor coil is fed baery posive voltage through the key switch. The
voltage goes through the coil and on to the controller. Inside the controller, it switches the circuit to baery negave to
energize the relay. When the relay energizes, posive baery voltage is applied through its contacts to the brush motors.
Since the other side of the motors is connected to baery negave, they turn on.
The Main Machine Controller also monitors the amount of electrical current (Amps) that is owing through the brush
motor ground circuit. If it is higher or lower than expected a fault code will be set. It monitors the amperage indirectly
on a “sense” wire by measuring the dierence in voltage (Voltage Drop) between a point near the motors and the main
baery negave terminal. As actual current increases, the voltage drop measured increases. The controller then converts
the voltage value to “Amps”. The monitoring circuit relies on a calibrated ground wire that is a specic gauge and length.
An electric actuator is used to move the scrub head up and down. The actuator has a DC permanent magnet electric mo-
tor which is driven by the Main Machine Controller. The motor turns a threaded sha. When the threaded sha turns, it
moves a threaded rod up and down. Since the rod is aached to the deck, it moves the deck up and down.
Inside the actuator housing, there are also three posion switches which are monitored by the Main Machine Controller.
One for the “retracted” posion, one for the “middle” posion (Normal scrub pressure) and one for the “Extended” posi-
on (Extreme scrub pressure). Each switch is normally closed. The threaded rod has a collar on it that opens each switch
as it passes by it. When the Main Machine Controller sees the middle posion switch open, it knows that the deck is in
the normal scrub posion. If that was its goal posion, the controller turns o the motor to stop the deck in that posi-
on.