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Constant Current Signal for Driving a Print Head Coil Using Predictive Pulse Width Modulation

IP.com Disclosure Number: IPCOM000041126D
Original Publication Date: 1987-Sep-01
Included in the Prior Art Database: 2005-Feb-02
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Heybruck, WF: AUTHOR [+3]

Abstract

In the past, wire matrix print head drive circuits have monitored the current used to drive the print head coil and relied upon a feedback signal to increase or decrease the driving current. The present invention empirically predicts the optimum pulse width modulated current waveform to energize a coil, eliminating the need to sense the actual current through the coil. Without the need for a feedback signal, the coil driver circuit is simplified.

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Constant Current Signal for Driving a Print Head Coil Using Predictive Pulse Width Modulation

In the past, wire matrix print head drive circuits have monitored the current used to drive the print head coil and relied upon a feedback signal to increase or decrease the driving current. The present invention empirically predicts the optimum pulse width modulated current waveform to energize a coil, eliminating the need to sense the actual current through the coil. Without the need for a feedback signal, the coil driver circuit is simplified.

The amount of current to drive the coil in a wire matrix print head varies with the duty cycle and temperature of the coil. Using these characteristics as variables, an optimum current waveform using pulse width modulation is defined for a wide range of acceptable duty cycles and temperatures. A sample generic TTL waveform is illustrated in Figure 1.

Referring to Figure 2, the TTL waveform illustrated in Figure 1 is applied to the predictive chopper driver circuit in Figure 2. Either the Fire Wire line or Enable line are connected to the microprocessor controlling print head operations. One of these lines receives the TTL level signals to switch on and off a current control device, such as the PFET or NFET. The Fire Wire line may be used for overlapping wire firing signals, and the Enable line may be used for non- overlapping wire fire signals.

If further control or modification of the current pulse waveform is necessary, the mi...