Stair lifts are well known and are particularly used for transporting loads such as persons and/or goods up or down over a stairs by being carried on a chair or a platform. In general a stair lift comprises of a guide or rail to be attached along a staircase and a motorized carriage or trolley which carries and guides the load along the rail.
Stair lifts may be driven by friction drive rollers which are in frictional engagement with the guide. These have proven to be less expensive than form fitted drive means such as sprocket and chains or rack and pinion.
For example, a stair-climbing device is known from patent publication EP-0,881,188-A1. This publication shows a stair-climbing device comprising a guiding rail and a trolley movable on the guiding rail. The stair-climbing device is further provided with a motor that drives a drive roller supported by the trolley, wherein the drive roller is in frictional engagement with the guiding rail. Each longitudinal side of the guiding rail is in frictional engagement with a guiding roller to keep the trolley in a predetermined position with respect to the guided rail. Each drive roller is provided with a means for pressing the drive roller into frictional engagement.
Drawback of these known stair lifts is that they are mechanically complex.