The drive unit
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Over speed device construction and operation
The over speed device ensures that the stairlift comes to a halt if the speed is too high.
Construction
Over speed device components
Over speed gearwheel
The over speed device consists of:
1. catchment gearwheel
2. teeth
3. cam ring
4. idler
5. locking pin
6. opto coupler
7. switch mechanism
8. emergency limit switch
The drive unit gearwheel is connected by means of a rubber
coupling to the catchment gearwheel (1) which is connected
to the teeth (2) and the cam ring (3).
When the stairlift moves along the rail, the catchment
gearwheel (1) with the teeth (2) and cam ring (3) turns at the
same speed as the drive shaft.
Operation
The over speed device
Inside the cam wheel is an idler (4). This idler is shaped like a
Christmas tree. The ‘top’ of the idler runs over the teeth (2)
inside the cam ring (3). As long as the speed of the seat and
thus the rotation speed of the over speed device is not too
high, the idler quietly follows the teeth. At each tooth, the idler
is pushed outwards and is pushed back by a spring when the
teeth move. The teeth and the cam wheel are matched with
each other so that the idler is pushed between the cams in the
cam wheel each time and springs back to let the following
cam pass.
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