Variable print density encoder system

Abstract

In a printer system in which hammers mounted along a shuttle assembly which reciprocates relative to a print paper are selectively energized to impact the paper and print dots thereon, the dot density is made variable by an encoder system responsive to the position of the shuttle assembly as it traverses a linear path of motion. The encoder system includes a decoder for generating a succession of fence post pulses as the shuttle assembly reaches each of a succession of different positions along the linear path of motion and circuitry for generating a succession of hammer firing pulses in response to and having a desired phase relationship with the fence post pulses. The hammer firing pulses may occur at a frequency the same as or different from the frequency of the fence post pulses to provide a desired print density. A stored initial offset value is used to initially establish the desired phase relationship between the hammer firing pulses and the fence post pulses. Thereafter, a stored pulse interval value is used to generate the hammer firing pulses at the desired frequency. The desired phase relationship is maintained by measuring the time distance between selected ones of the hammer firing pulses and the preceding fence post pulses, comparing the measured time interval with a stored value representing the desired offset and applying any difference as an error signal to alter the time interval between the immediately following pair of hammer firing pulses.