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Coil Current Regulator for Print Wire Actuator

IP.com Disclosure Number: IPCOM000059644D
Original Publication Date: 1986-Jan-01
Included in the Prior Art Database: 2005-Mar-08
Document File: 3 page(s) / 38K

Publishing Venue

IBM

Related People

Holloway, JF: AUTHOR [+2]

Abstract

A technique is described whereby a coil current regulator, as used in the actuating coil circuits of the printing mechanism of matrix printers, is designed in such a way so as to minimize coil heating, while maintaining required coil actuating performance. The current regulator, consisting of a ramp reference generator, a modulator and an actuator driver, is unique in that it allows the performance of the magnetic actuator to be independent of the coil heating and ambient temperatures as well as being independent of power supply voltage variations. The design also permits actuator output force adjustments to be made easily. The coil current regulator, as shown in Fig. 1, consists of ramp reference generator 10, modulator 11 and actuator driver 12.

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Coil Current Regulator for Print Wire Actuator

A technique is described whereby a coil current regulator, as used in the actuating coil circuits of the printing mechanism of matrix printers, is designed in such a way so as to minimize coil heating, while maintaining required coil actuating performance. The current regulator, consisting of a ramp reference generator, a modulator and an actuator driver, is unique in that it allows the performance of the magnetic actuator to be independent of the coil heating and ambient temperatures as well as being independent of power supply voltage variations. The design also permits actuator output force adjustments to be made easily. The coil current regulator, as shown in Fig. 1, consists of ramp reference generator 10, modulator 11 and actuator driver 12. The regulator is controlled by two digital signals, +Ramp and -SEL (select pulse), as shown in the timing diagram of Fig. 2. The -SEL signal, when at a down level, turns on actuator driver 12. This causes regulated current to flow in the actuator coil. The +Ramp signal causes the ramp voltage to ramp downward, timed to coincide with the start of the actuator armature motion. Ramp reference voltage restores to normal when the +Ramp signal is at a down level. The slope of the ramp reference voltage is selected to keep the degree of core saturation in the actuator nearly constant as the armature closes. By holding the core saturation constant, a near maximum actuator force is produced, while minimizing core and copper losses in the actuator. The ramp reference generator 10 circuit, as shown in Fig. 3, is capable of driving many modulator circuits. When the +Ramp signal goes to a down level, open collector hex inverter 14 is turned off. Timing capacitor 15 is charged in the positive direction by current through resistor 16 and diode 17. Voltage across capacitor 15 is limited by forward biasing the collector base diode of transistor 18. The time constant, resistor 16 and capacitor 15, is short compared to the time between actuator pulses. When the +Ramp signal goes to an up level, capacitor 15 charges toward zero volts through resistor 19 and the turned-on inverter 14. The time constant, resistor 19 and capacitor 15 are selected so that the slope of the ramp reference voltage produces the desired degree of core saturation as the armature closes. The modulator 11 circuit, as shown in Fig. 4, controls the on and o...