Browse Prior Art Database

Controlled Power Printhead Driver for Resistive Ribbon

IP.com Disclosure Number: IPCOM000038651D
Original Publication Date: 1987-Feb-01
Included in the Prior Art Database: 2005-Jan-31
Document File: 3 page(s) / 50K

Publishing Venue

IBM

Related People

Hurd, JJ: AUTHOR [+2]

Abstract

The instantaneous power going into a resistive ribbon is measured when used to control the average power to a desired level by a pulse-width modulation technique. The instantaneous power into the printing part of a resistive ribbon for each electrode is the product of the voltage across the printing part of the ribbon and the current into the electrode. The circuit includes a separate first portion for each electrode creating a pulse-width modulated (PWM) waveform having its duty cycle inversely proportional to the electrode current. A second portion of the circuit creates a PWM waveform having its (Image Omitted) duty cycle inversely proportional to the voltage across the printing part of the ribbon.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 49% of the total text.

Page 1 of 3

Controlled Power Printhead Driver for Resistive Ribbon

The instantaneous power going into a resistive ribbon is measured when used to control the average power to a desired level by a pulse-width modulation technique. The instantaneous power into the printing part of a resistive ribbon for each electrode is the product of the voltage across the printing part of the ribbon and the current into the electrode. The circuit includes a separate first portion for each electrode creating a pulse-width modulated (PWM) waveform having its duty cycle inversely proportional to the electrode current. A second portion of the circuit creates a PWM waveform having its

(Image Omitted)

duty cycle inversely proportional to the voltage across the printing part of the ribbon. By having the first portion of the circuit designed to have a relatively constant voltage drop across it for all combinations of ON electrodes, the second portion of the circuit can be common for all electrodes. A composite PWM waveform that effectively multiplies the current times the voltage to gain power control is produced by an AND gate for each electrode. If the operating range is assumed to be that the minimum electrode current is twenty milliamps and the minimum voltage is four volts with each of these having a 100% duty cycle so that the average power is 80 milliwatts, the average power of 80 milliwatts can be produced in various ways by PWM.

(Image Omitted)

Fig. 1 shows a 60-milliamp current PWM waveform with a 33% duty cycle and a 30-milliamp current PWM waveform with a 66% duty cycle; this discloses the current PWM waveform having its duty cycle inversely proportional to the electrode current. Fig. 1 also shows an 8-volt PWM waveform with a 50% duty cycle and a 6-volt PWM waveform with a 67% duty cycle. Fig. 2 shows four different products of voltage and current from the waveforms of Fig. 1 to produce the same average power, which is being controlled, even though the instantaneous power varies substantially. Fig. 3 discloses a circuit 1, which is common to all the electrode drivers. The circuit 1 includes a current ramp generator 2, which continuously cycles at a predetermined period. The signal from the generator 2 is connected to a comparator 3 of a circuit 4 at each electrode. With forty electrodes, there are forty of the circuits 4. An electrode 5 has its current supplied thereto from a head voltage power supply line 6 through a sense resistor 7 of a low resistance, such as 1 ohm, for example, and a switch 8, which is a transistor, of the circuit 4. The switch 8 is turned on only when an AND gate 9 of the circuit 4 has a high output. As long as the output of the ramp generator 2, which has a starting value which tracks the head voltage on the line 6, exceeds the voltage at the bottom of the sense resistor 7, a high output is produced by the comparator 3. The output of the comparator 3 is supplied as an inverse control signal to a reset or clear (CLR) input of a la...