Browse Prior Art Database

Digital Correction of Hammer Firing Times

IP.com Disclosure Number: IPCOM000076844D
Original Publication Date: 1972-May-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 2 page(s) / 56K

Publishing Venue

IBM

Related People

Meier, JH: AUTHOR [+2]

Abstract

Correction of hammer firing times in a printer is effected by monitoring the speed of a motor driving a type belt immediately before an emitter signal which is to initiate hammer firing, and then introducing a short, variable delay between the emitter pulse and the hammer firing. The variable delay is made a function of the monitored motor speed and the nominal hammer flight time, so that impact occurs always at the proper place with respect to the type element (or the paper which is the moving element in the case of a scatter printer).

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Digital Correction of Hammer Firing Times

Correction of hammer firing times in a printer is effected by monitoring the speed of a motor driving a type belt immediately before an emitter signal which is to initiate hammer firing, and then introducing a short, variable delay between the emitter pulse and the hammer firing. The variable delay is made a function of the monitored motor speed and the nominal hammer flight time, so that impact occurs always at the proper place with respect to the type element (or the paper which is the moving element in the case of a scatter printer).

Motor speed is monitored, as shown in Fig. 1, by using a counter 10 which counts pulses from a crystal oscillator 12 during a time interval determined by a fixed number of pulses from an emitter 14, driven by the type-belt motor. The counter is an up and down counter advanced by oscillator pulses and caused to fill up, reset and start counting up again during the measuring interval as shown in Fig. 2.

During printing, a latch 16 is turned on and inhibits reset of the counter 10 through inverter 18 and AND 20. A zero-to-two counter 22 driven by the emitter through AND 24 causes the counter 10 to start counting down, and when the counter 10 reaches zero, a single-shot 26 is turned on through AND 28 to fire the print hammer.

It is readily seen that when the motor slows down, the intervals between emitter pulses, and hence the measuring intervals, increase. Thus, the count at the moment of rev...