enigma2k wrote:It is just logical that they will always get dusty as they are in the dust bin.
No, it isn't that
logical!... The dirt is supposed to pass
the optical sensors, not stick
to them! If more than light dust/dirt passes the sensors, the Karcher determines which of it's "intensive clean" programmes to employ. If 'sight' between the sensors is constantly reduced, Karcher knows something is obscuring them - possibly a full bin, so it'll go and empty. If the sensors are still obscured, there's a problem with trapped dirt/threads. A light coating of dust doesn't affect normal operation, but if the dirt coating the lenses gets too thick, it will.
For me, it happens when: If the base station bag is almost full and base-station suction is possibly less than optimal, sometimes the robots' bin will not empty completely; that dirt will compress at the front of the suction channel blocking the sensors. Other times, wet/damp dirt trodden in from outside can stick in the channel/on the sensors. Rarely, a thread of carpet webbing comes up, wraps around the brush, and flutters across the sensors (this causes the 'backing-up' motion you describe, thinking it's stuck on a tassle or cable). In these cases, it will eventually stop and a fault will show. These all happen very, very rarely.
It's just good practice to keep the brush and sensors clean and wash the fabric filter occasionally... and empty the base-station bag in good time so there's maximum 'emptying' suction. It's all mentioned in your manual under the "Maintenance and Care" section. It's still a lot less maintenance/hassle than other robots I could mention! Okay, the Karcher doesn't suck like a Neato/Vorwerk (nothing does), but it does require less maintenance that most other robotic cleaners, does a very respectable cleaning job, and in all likely-hood the Karcher will still be running long after your Vorwerk is worn-out/broken beyond repair and in the bin (in my personal opinion!).