Nilfisk SC800 ST User Manual

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Service Manual: SC750, SC800, SC 750 ST, SC800 ST

Form Number 56043150 Page 114

Scrub System, Rev

Functional Description

Scrubbing

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 discs spin toward the center at the front edge of each disc. 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 in the normal scrub mode. When extreme pressure is requested, the actuator moves down farther

causing a gas spring to exert addional downward pressure on the oor.

The Main Machine Controller energizes the brush solenoid to turn on the brush motors when the following inputs have

been met:

• Key switch on

• Operator request

• Machine moving signal (FOR/REV) is received from the Drive Motor Controller (A2 PG Drives Speed Controller)

o 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 is 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.

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Nilfisk SC800 ST Heavy-Duty Cleaning