Drive mechanism and head rail for a blind

A head rail assembly for a vertical venetian blind having an array of retractable and tiltable slats, the assembly including:

• an elongate head rail having a mechanism at one end for selectively tilting and retracting slats of the vertical blind along the elongate head rail, the mechanism having a rotatable control gear, the rotation of which controls the selective tilting and retracting, wherein the control gear is located at a position along the elongate head rail so that it can be meshed with teeth of an external drive source, wherein the head rail includes a housing forming a generally enclosed structure, the housing including an aperture by which the control gear may mesh with the teeth of an external drive source, wherein the housing has an elongate surface from which the slats are adapted to extend and at least one other elongate surface in which the aperture is formed;
• and
• a motor unit for detachable attachment to the at least one other elongate surface of the head rail, the motor unit having a toothed drive gear for meshing with the control gear;
• wherein the mechanism includes a lost motion mechanism comprising first and second components relatively rotatable about a common axis;
• a spacer disposed between the first and second components;
• and a flexible elongate member having ends attached respectively to the first and second components wherein relative rotation of the first and second components causes the flexible elongate member to wrap around the spacer such that the first and second components can rotate relative to one another by an amount determined by the length of the flexible elongate member, the lost motion mechanism being driven by the control gear to effect at least one of tilting and retracting slats.