| 摘要 |
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. A double electronic switch is connected to the heads to read the divisions in numerical sequence, each division being read twice per cycle, the earlier reading head controlling electromagnetic latches for stopping each print wheel at the ordered position and the later reading head subsequently delivering the order signal for comparison with the resulting wheel position, thereby compensating for mechanical actuation delay of said electromagnetic latches. |
