US3833870A

US3833870A - Print hammer firing circuit

Info

Publication number: US3833870A
Application number: US00406722A
Authority: US
Inventors: L Wallace
Original assignee: International Business Machines Corp
Current assignee: International Business Machines Corp
Priority date: 1973-10-15
Filing date: 1973-10-15
Publication date: 1974-09-03
Anticipated expiration: 1991-09-03
Also published as: GB1437929A; DE2446741A1; FR2247352B1; JPS5068232A; FR2247352A1

Abstract

A circuit for firing print hammers of the type in which a plurality of hammers are provided in a magnetic core structure having a common yoke portion and a plurality of individual yoke portions. A common holding coil provides holding flux for holding the hammers in the normal or retracted position. An individual bucking coil associated with each hammer provides an impulse of bucking flux for overcoming the holding flux and causing the hammer to fire under spring tension, whereafter the holding flux restores the hammer to its retracted position. A proportional coil or winding, linked to the common portin of the magnet yoke, is connected so that the sum of the hammer firing currents in the bucking coils flows through the proportional coil or winding. This flux cancels out the effects of flux induced by the bucking flux in adjacent individual magnetic yokes, and thereby reduces hammer flight time variations.

Description

United States Patent 11 1 1111 3,833,870 Wallace 1 1 Sept. 3, 1974 PRINT HAMMER FIRING CIRCUIT [57] ABSTRACT [75] Inventor: Leonard .1. Wallace, Vestal, NY. [73] Assignee: International Business Machines A circull for finng prim hammers type in which Corporation Armonk, NY. a plurality of hammers are prov1ded 1n a magnetlc core structure havmg a common yoke port1on and a Filedi 1973 plurality of individual yoke portions. A common hold- [21] APPL NOJ 406,722 ing coil provides holding flux for holding the hammers in the normal or retracted position. An individual bucking coil associated with each hammer provides an U.S. C, impulse of bucking flux for vercoming the [5 Int. Clflux and causing the hammer to fire under pring ten. Field of Search 155-5, 1316- 4; sion, whereafter the holding flux restores the hammer 101/93 335/263 to its retracted position. A proportional coil or winding, linked to the common portin of the magnet yoke, References Cited is connected so that the sum of the hammer firing cur- UNITED STATES PATENTS rents in the bucking coils flows through the propor- 3,285,165 11/1966 Richter 317 010. 4 {1011111 coil of winding- This flux Cancels out the effects 3,423,641 1/1969 Feldt 317 137 of flux induced by the bucking flux in adjacent indi- 3,505,950 4/1970 Harper 101/93 C vidual magnetic yokes, and thereby reduces hammer 3,735,696 5/1973 Dayger et a1 101/93 C flight time variations,

Primary Examiner-J. D. Miller Assistant Examinerl-larry E. Moose, Jr. Attorney, Agent, or Firm-Paul M. Brannen 6 Claims, 4 Drawing Figures Pmmiuw w 3.833.870

sun 1:: 2

PATENIEB E 3.833.870

sum ear 2 HOLD ---='BUCKI FLX FIG. 4

PROPORTIONAL FLUX PRINT HAMMER FIRING CIRCUIT FIELD OF THE INVENTION DESCRIPTION OF A PREFERRED EMBODIMENT Referring to the drawings, particularly FIGS. 1 and 2,

This invention relates generally to electromagnetic 5 there is shown a print hammer assembly having a comapparatus, and particularly to an improved electromag netic print hammer firing circuit.

DESCRIPTION OF THE PRIOR ART Print hammer firing circuits of the type comprising a common hold coil or winding on a common position of a magnetic yoke structure, and an individual bucking coil associated with the individual yoke leg or branch provided for each hammer, are well known in the art, and various circuit arrangements have been utilized in controlling print hammers of this type, as shown for example in U.S. Pat. No. 3,423,641.

SUMMARY OF THE INVENTION Generally stated, it is an object of this invention to provide an improved hammer firing circuit for electromagnetic print hammers.

More particularly, it is an object of the present invention to provide compensating means on a print hammer assembly which will compensate for the adverse effects normally encountered when a plurality of hammers are fired simultaneously.

Another object of the invention is to provide compensating means for the purpose described above, which is simple and economical to provide.

In practicing the invention, a print hammer assembly in which there are a plurality of individual hammers, each having associated therewith an individual magnetic core portion, and those portions being connected to a common magnetic core structure, is provided with a compensating coil or winding linking the common portion of the core structure. This winding is connected in series with the individual bucking coils associated with individual hammers and core portions, so that the instantaneous sum of all the hammer firing currents flow through the compensating winding in a direction such that the compensating flux aids the flux generated by the bucking coils and opposes the flux generated by a common holding coil. By suitable selection of the number of turns on the windings, the compensating flux will counteract the effects of simultaneous firing of a plurality of hammers.

The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of a preferred embodiment of the invention, as illustrated in the accompanying drawings.

DESCRIPTION OF THE DRAWINGS mon core portion of magnetic material which is formed of two

portions

3 and 5, the end portion of portion 3 being divided into a plurality of separate legs or sec tions 7, one for each of the individual print hammers 9.

The magnetic structure is energized by flux generated by the current through a holding coil or winding 11, the holding coil'and the common portion of the yoke being common to all of the hammers in the unit. The holding flux could also be generated by a permanent magnet suitably disposed with respect to the common portion of the yoke. As stated previously, the magnetic circuit is subdivided into individual legs or sections 7 for each of the print hammers, and each of these legs or branches is provided with an individual bucking coil 13, which when energized bucks out or neutralizes the effects of the flux from the holding coil or winding 11 so that the associated hammer is operated. Each of the hammer units 9 is provided with an armature element l5 welded or otherwise affixed to the hammer structure 9 which bears at its lower end a type element 17 that is either engraved or otherwise formed as an integral portion of the element 9, or is a type slug which is welded in place. Two flexural elements 19 and 21 serve to support the hammer and to provide the force to propel the hammer. The force and hence the flight time can be adjusted by changing the amount of interference between the fulcrum spring 23 and the flexural element 19. A screw 25 is provided to adjust the amount of tension.

Thus far, the arrangement shown and described is well known in the prior art. Normally, the armature 15 is in an attracted position because of the magnetic flux generated by the current flowing through winding 11. However, when it is desired to have the print hammer mechanism operate, current is passed through the bucking winding 13 for the particular hammer which is to be actuated, which thereby sets up an opposing flux that cancels or decreases the amount of holding flux provided to the armature l5, whereupon it will be released and the hammer mechanism will be impelled to cause the type face 17 to impact the document and ribbon against a suitable platen, not shown for the sake of simplifying the drawings.

It has been found that variations in the current supplied to the bucking coils can be mainly attributed to cross-coupling between adjacent coils or adjacent hammers. Also variations in the hold coil current are mainly attributed to back-induced voltages caused by the firing of the circuits and energization of the bucking coil. The voltages and resultant current caused by such induction in the hold and bucking coils is proportional to the number of hammers fired.

In accordance with the present invention, there is provided means for compensating for the effects of a number of hammers being fired simultaneously to thereby reduce the flight time variation caused by the magnetic coupling when a plurality of hammers are fired simultaneously. In accordance with the present invention, this means includes a compensating winding 27, mounted on the common portion or yoke of the magnetic core structure as shown in FIGS. 1 and 2.

FIG. 3 shows the manner in which the compensating winding 27 is connected to produce the desired result. As shown in this figure, all of the windings are illustrated in relationship to the magnetic core 5. The holding coil 11 is continuously energized as shown to produce the holding flux in the common portion and also in the individual branches of core 5. The winding 27 is connected so that the current flow therethrough is in the opposite sense to the flow of current through holding winding 11, as indicated by the conventional dot symbology used in denoting transformer winding relations. One side of the bucking windings 13 is commonly connected to the energy source through the winding of coil 27 as shown. Each of the windings 13 is adapted to be selectively energized by the closing of a suitable switch such as the switches 31. Although these switches are shown as conventional manually operated switches, this is for the sake of convenience and it will be understood that in the usual case, suitable electronic switches are employed. It is apparent from the drawing that the amount of current flowing through the winding 27 will depend upon how many of the switches 31 are closed at any one time to thereby simultaneously energize a plurality of the bucking windings 13. Also it will be seen that this current flow in winding'27 will be in a sense such that the flux generated thereby will oppose the flux generated by the hold winding 11.

The flux relationships are also seen from consideration of FIG. 4, which is a diagrammatic illustration of the various flux paths in the hammer assembly. The holding flux produced by winding 11 is shown in FIG. 4 as a series of solid arrows traveling in a clockwise direction. The bucking flux set up by energization of the bucking coils is shown as a dash line which travels through the core in a counterclockwise direction, and in the same direction, namely counterclockwise, there is shown a dot-dash line to indicate the proportional flux set up by the winding 27.

of the printer assembly at higher speeds of operation.

While the invention has been particularly shown and described with reference to a preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.

I claim:

1. In an impact printer of the type wherein means including a plurality of print hammers are activated by an electromagnetic assembly comprising a magnetic core structure having a common core portion and individual core portions associated with each hammer, holding flux generating means linking the common portion of said magnetic core structure for generating a hold flux in said core structure, bucking flux generating means associated with and linking each individual core portion for generating bucking flux in said individual core portions to thereby activate the associated print hammer, the combination with the foregoing of compensating flux generating means linking said common portion of said core for generating flux in opposition to said holding flux and proportional to the instantaneous sum of said bucking flux.

2. The combination as claimed in claim 1, in which each of said flux generating means comprises an electromagnet.

3. The combination as claimed in claim 1, in which said holding flux generating means comprises a continuously energized electromagnet.

4. The combination as claimed in claim 1, in which said bucking flux generating means comprises an individual electromagnet for each of said individual core portions.

5. The combination as claimed in claim 2 in which the electromagnets comprising the bucking flux generating means are connected in parallel and then in series with the electromagnet generating the compensating flux, so that all of the current in the bucking electromagnets flows through the compensating flux electromagnet.

6. The combination as claimed in claim 5, inlwhich each of the bucking flux electromagnets is governed by an associated switch, whereby one or more electromagnets can be energized at any given time.

Claims

6. The combination as claimed in claim 5, in which each of the bucking flux electromagnets is governed by an associated switch, whereby one or more electromagnets can be energized at any given time.