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The drive unit
Figure 4-9: The bogie system
The top bogie rollers (1) are spring-mounted so that the rollers can roll over the rail without any play and the stairlift
remains stable in the rail even when there is no one sitting on it. The ball joints incorporated in the assembly ensure
that the rollers always follow the profile of the rail.
For safety reasons the motor is equipped with an electromechanical friction based brake which is normally ON. This
means that the brake is actively released by the electronics. As soon as the power is removed the brake will engage
and lock the drive shaft.
In addition a safe drive is guaranteed by:
•
An over speed device (OSD)
This is a mechanically locking brake that engages if the speed of the seat becomes too high. The red
pennon will follow the pinion until a certain speed is exceeded. Then a gearwheel fitted directly underneath
the drive gearwheel will be locked. At the same time an electrical signal (opto coupler switch) is send to the
electronics. The electronics will then execute an emergency stop sequence by placing the motor in active
brake mode followed by an action to activate the friction brake of the motor.
Figure 4-10: Over speed device (OSD)
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