Screen with head rail, bottom rail and middle rail and a first control unit for the middle rail and a second control unit for the bottom rail

1. A screen ( 1 ; 401 ; 601 ) comprising

a headrail ( 2 ; 402 ; 602 );

a bottom rail ( 6 ; 406 ; 606 ) movable with respect to the head rail;

a middle rail ( 4 ; 404 ; 604 ) arranged movably between the head rail and the bottom rail, at least one collapsible screen material ( 8 ; 408 ; 608 ) supported by the middle rail and the bottom rail;

a first control unit ( 10 ; 410 ; 610 ) comprising a first drive shaft ( 12 ), first control means ( 14 , 16 , 18 ; 414 ; 614 ) for rotating said first drive shaft, at least one first winding element ( 30 , 32 ) rotatable with the first drive shaft for winding and unwinding first lift means ( 34 ) extending between the head rail and the middle rail;

a second control unit ( 20 ; 420 ; 620 ) comprising a second drive shaft ( 22 ), second control means ( 24 , 26 ) for rotating said second drive shaft, at least one second winding element ( 32 ) rotatable with the second drive shaft for winding and unwinding second lift means ( 36 ) extending between the head rail and the bottom rail through the middle rail and the screen material;

and

a shaft rotation limiting system ( 100 ) comprising a threaded shaft ( 102 ) arranged on and rotatable in unison with one of the first and the second drive shafts, a coupling element ( 104 ) threaded on said threaded shaft, wherein the coupling element is associated with and rotatable in unison with the other drive shaft, characterized in that the shaft rotation limiting system ( 100 ) further comprises a toothed shaft ( 106 ) arranged on and rotatable in unison with the other drive shaft and in that the coupling element is a toothed nut ( 104 ) that is in continuous engagement with the toothed shaft ( 106 ).

2. The screen according to claim 1 , wherein the toothed nut ( 104 ) takes up a predetermined catch position on the threaded shaft ( 102 ) and wherein the toothed nut moves out of the catch position upon rotation of either the first shaft ( 12 ) or the second shaft ( 22 ) and wherein the toothed nut moves towards the catch position upon rotation of the other shaft.

3. The screen according to claim 1 , wherein the first drive shaft ( 12 ) and the second drive shaft ( 22 ) rotate in opposite directions for moving the middle rail ( 4 ) and the bottom rail ( 6 ) in the same direction.

4. The screen according to claim 1 , wherein the toothed nut ( 104 ) is translatable along the toothed shaft ( 106 ) upon rotation of the threaded shaft ( 102 ).

5. The screen according to claim 1 , wherein the toothed nut ( 104 ) is rotatable along the threaded shaft ( 102 ) upon rotation of the toothed shaft ( 106 ).

6. The screen according to claim 1 , wherein the threaded shaft ( 102 ) and the toothed nut ( 104 ) are provided with cooperating first arresting means ( 107 , 108 ) defining the predetermined catch position.

7. The screen according to claim 1 , comprising a housing ( 110 ), wherein the shaft rotation limiting system ( 100 ) is accommodated.

8. The screen according to claim 1 , wherein at least one additional collapsible screen material ( 409 ) is supported by the middle rail ( 404 ) and the head rail ( 402 ).

9. The screen according to claim 1 , wherein the first control means ( 610 ) and/or the second control means ( 620 ) are motorized.

10. The screen according to claim 1 , wherein the screen is a window covering.