Abstract: A compact print wheel position sensing device for parallel-wheel printers includes pairs of optoelectronic printed circuit emitters 22 and receivers 24 arranged in two lines inside and outside, respectively, a tubular shaft 21 provided with radial holes 23 aligned with each emitter/receiver pair and carrying wheels 19 which mesh with corresponding parallel print wheels 11. Each wheel 19 has a set of angularly spaced transparent regions, alternating with opaque regions, which permit transmission between the corresponding emitter/receiver pair at each printing position of the respective print wheel. A logic device includes a memory arranged for storing printing wheel position orders and having double reading heads for each division.

Abstract: A device for projecting ink droplets through a set of projection holes to print a pattern under selective electrical or light pulse control.A first plate formed with a large number of holes is placed in close proximity to the surface of the printing medium. A second plate a small distance from the first defines therewith a chamber in which the ink is locally heated by electrical current controlled by light selectively impinging on a photoconductive part of said second plate in register with each hole or each group of holes so as to form a pattern with constant or variable parts.