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Total Variable Energization Control for Impact Printer Hammer

IP.com Disclosure Number: IPCOM000051900D
Original Publication Date: 1981-Mar-01
Included in the Prior Art Database: 2005-Feb-11
Document File: 3 page(s) / 47K

Publishing Venue

IBM

Related People

Polk, DR: AUTHOR [+3]

Abstract

The present approach involves the tailoring of an impact printer hammer firing pulse to provide a total energization scheme for the impact printer hammer wherein the total energy provided by the pulse may be varied. This permits control of the whole waveform of the firing pulse during the firing cycle so as to eliminate undesirable variations due to random changes in the electrical circuit parameters. To this end, a tailored hammer firing pulse waveform generation scheme is provided which eliminates the costly generation of the waveform through the periodic accessing of a look-up table. Instead, in accordance with the present system, the desired waveform is incrementally generated using an algorithm for generating the next increment of the waveform in place of the look-up table storing the entire waveform.

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Total Variable Energization Control for Impact Printer Hammer

The present approach involves the tailoring of an impact printer hammer firing pulse to provide a total energization scheme for the impact printer hammer wherein the total energy provided by the pulse may be varied. This permits control of the whole waveform of the firing pulse during the firing cycle so as to eliminate undesirable variations due to random changes in the electrical circuit parameters. To this end, a tailored hammer firing pulse waveform generation scheme is provided which eliminates the costly generation of the waveform through the periodic accessing of a look-up table. Instead, in accordance with the present system, the desired waveform is incrementally generated using an algorithm for generating the next increment of the waveform in place of the look- up table storing the entire waveform. In order to control hammer flight time and impact force, it is necessary to have an accurate forcing function. The electrical component of the hammer forcing function is coil current versus time. Most hammer driver circuits try to control an absolute level of current in the coil, with the rate of change of current being a function of inductance, resistance and voltage. As these parameters change, the hammer flight time and impact force vary, thereby causing a degradation in printer performance.

An energization scheme for impact hammers is provided that controls the entire current waveform in the hammer coil. Thus, performance perturbations due to changes in the electrical circuit parameters (supply voltage, inductance, resistance) are eliminated. In order to control the rate of rise and fall of current, the following conditions must be satisfied: di over dt </- Vsmin - Vd - Vemf over Lmax (1) and Icoil < Vsmin - Vd - Vemf over R(T) (2) where Vsmin = Minimum Voltage Supply Vd = Maximum Voltage Drops in Circuit Vemf = Enduced Voltage in Coil Lmax = Maximum Hammer Coil Inductance R(T) = Total Resistance of Circuit and Coil

By taking the various electrical parameters to their worst-case values and then tailoring the input current rate of rise to not exceed those conditions of Equation (1), it is possible to always have the coil current track the input command. Hence, an accurate and controllable forcing function can be achieved.

A circuit for the implementation of the control system is shown in Fig. 1. A waveform generator drives the non-inverting input of operational amplifier A(1), causin...