Adjustable printer head drive

Claim 1

In combination with a serial printer an adjustable diameter pulley for adjusting belt tension in a belt transmission system which moves a printing head along a printing line comprising: a plastic cylinder having a tapered longitudinal internal surface, a cylindrical external surface acting as a winding surface for a belt and two flat sides perpendicular to said cylindrical surface, said cylinder further having a plurality of longitudinal slits partially extending alternately from either longitudinal end of said cylinder: a core provided with a tapered portion inserted in said cylinder, said core further having a threaded portion extending longitudinally; positioning means for positioning said plastic cylinder on said core, said positioning means comprising an annular ring having its internal surface threaded, said annular ring engaging said threaded portion of said core and being capable of longitudinal motion when screwed on said threaded portion; whereby said positioning means contacts one end of said cylinder urging said cylinder in a longitudinal direction, thus radially expanding the cylindrical external surface of said plastic cylinder whereby the belt tension in the belt transmission system which moves a printing head along the printing line is appropriately adjusted.