Variable Control of Print Hammer On-Time
Original Publication Date: 1982-Feb-01
Included in the Prior Art Database: 2005-Feb-08
Line printers fire a hammer or a group of hammers at different time intervals within a single print line. Fire point is determined according ing to when selected characters align with proper hammers for the positions to be printed. With the fire point fixed because of character alignment, turnoff point in time can be made variable for density control. For a fixed hammer ON duration, this is achieved by storing the hammer address number in a programmable shift register or FIFO (first-in, first-out) memory. The control then clocks through all the shift register positions until the hammer number later appears at the output in clock cycles for hammer resetting. The ON-time is thereby determined by the shift register length times the period of the shift register clock.