US3906854A

US3906854A - Print hammer control mechanism

Info

Publication number: US3906854A
Application number: US437253*A
Authority: US
Inventors: Yoshifumi Gomi
Original assignee: Suwa Seikosha KK
Current assignee: Suwa Seikosha KK
Priority date: 1973-01-26
Filing date: 1974-01-28
Publication date: 1975-09-23
Anticipated expiration: 1992-09-23
Also published as: GB1417492A; DE2403788A1; JPS523762B2; JPS49132934A; FR2215325A1; FR2215325B1

Abstract

A printer is provided with a plurality of print hammers, each hammer being maintained in a rest position engaging a deformed elastic body by a hammer control mechanism. The hammer control mechanism includes individual magnetic circuits in combination with a magnetic flux producing element which is provided for selectively maintaining each of the print hammers in the rest position and for selectively releasing print hammers to effect printing. Each magnetic circuit includes a hammer hold portion and a control portion, the hammer hold and control portions being connected in parallel with the magnetic flux producing element. The control portion further includes a permanent magnet and a control coil for effecting release of said hammer from its rest position. Each of the print hammers is released from the rest position by exciting the control coil in the control portion in a first direction to effect a reverse of the polarity of said permanent magnet to thereby decrease the magnetomotive force applied to the print hammer to hold the print hammer in the rest position, the displacement of the print hammer being the product of the release of the energy of the elastic body. The hammer is then returned to a rest position by a return mechanism as the control coil is excited in the opposite direction, the excitation of the coil to return the polarity of the magnet in the control portion resulting in a more responsive hammer control.

Description

United States Patent 1 Gomi [ Sept. 23, 1975 PRINT HAMMER CONTROL MECHANISM [75] Inventor: Yoshifumi Gomi, Matsumoto, Japan [73] Assignees: Kabushiki Kaisha Suwa Seikosha;

Shinshu Seiki Kabushiki Kaisha, both of Tokyo, Japan 22 Filed: Jan. 28, 1974 21 Appl. No.: 437,253

[30] Foreign Application Priority Data Primary Examiner-Clifford D. Crowder Assistant ExaminerEdward M. Coven Attorney, Agent, or FirmBlum, Moscovitz, Friedman & Kaplan [57] ABSTRACT A printer is provided with a plurality of print hammers, each hammer being maintained in a rest position engaging a deformed elastic body by a hammer control mechanism. The hammer control mechanism includes individual magnetic circuits in combination with a magnetic flux producing element which is pro vided for selectively maintaining each of the print hammers in the rest position and for selectively releasing print hammers to effect printing. Each magnetic circuit includes a hammer hold portion and a control portion, the hammer hold and control portions being connected in parallel with the magnetic flux producing element. The control portion further includes a permanent magnet and a control coil for effecting release of said hammer from its rest position. Each of the print hammers is released from the rest position by exciting the control coil in the control portion in a first direction to effect a reverse of the polarity of said permanent magnet to thereby decrease the magnetomotive force applied to the print hammer to hold the print hammer in the rest position, the displacement of the print hammer being the product of the release of the energy of the elastic body. The hammer is then returned to a rest position by a return mechanism as the control coil is excited in the opposite direction, the excitation of the coil to return the polarity of the magnet in the control portion resulting in a more responsive hammer control.

5 Claims, 5 Drawing Figures US Patent Sept. 23,1975 Sheet 1 0f 2 3,906,854

FIG. 4

' PRINT HAMMER CONTROL MECHANISM BACKGROUND OF THE INVENTION This invention relates generally to a control mechanism for the print hammers of an on-the-fly printer, and particularly to a control mechanism for such print hammers wherein displacement of any individual print hammer has no influence upon the operation of any other adjacent print hammer.

While the use of printers wherein the print hammers are held in a rest position by a flux producing element and are forced into contact with a printing surface by a deformed elastic body have taken various forms, embodiments of such printers incorporating a single permanent magnet for a plurality of print hammers have yielded results which are less than completely satisfactory. Because the force which is utilized to overcome the deformed elastic body is the force of a permanent magnet, and because it is necessary to reduce the force in order to release the hammer, a change in the reluctance of the portion of the magnetic circuit including the permanent magnet and the print hammer occurs upon the release of each print hammer.

When the reluctance of a magnetic circuit having a permanent magnet is changed, the operating point of the permanent magnet for the respective hammer is changed in order to effect release of same. The change in the operating point of the permanent magnet, influences the operating point of the permanent magnet at the adjacent columns and the print hammers associated therewith which have not yet been released from the hammer rest position. Although coupling a hammer hold circuit and a hammer control circuit in parallel to a permanent magnet has been shown to be helpful in reducing the change in the operating point of such permanent magnets, it has been recognized that the smaller the change in the operating point of the magnet, the quicker the response speed of the hammer and therefore, the faster printing can be effected. Furthermore higher response speeds and lower power consumption are the optimum conditions desired in a print hammer control mechanism. Accordingly, it is desired to provide a print hammer control mechanism which has higher response speed yet utilizes a minimum of power.

SUMMARY OF THE INVENTION Generally speaking, in accordance with the invention, a printer is provided having a plurality of print I hammers displaceable between a rest position and a print position, an elastic body maintained in a deformed state by each of said print hammers at its rest position, and a magnetic circuit control means associated with each of said columns for selectively holding each said print hammer at its rest position and releasing same for displacement to a print position. The magnetic circuit control means includes a magnetic flux producing element common to at least two of said columns, and a first hammer hold magnetic circuit portion associated with each print hammer including a portion associated with each print hammer including a release coil and a permanent magnet associated therewith, the release coil including means for applying signals thereto. The first and second magnetic circuit portions are connected in parallel with the magnetic flux producing element, each of the magnetic circuit control means being adapted to hold the respective hammers in a rest position and to release the respective hammers on application of a signal to its control coil means by means of said signal applying means in a first direction so as to reverse the polarity of the permanent magnet and thereby decrease the magnetomotive force applied to same hammer. the energy stored in the respective deformed body displacing said respective hammer from said rest position to said print position upon said decrease in said magnetomotive force. A mechanism for returning the respective hammer to a rest position is provided, the coil signal applying means applying a second signal to the coil to thereby return the permanent magnet to its original polarity coincident with the return of the hammer, to effect an improved hammer control.

Accordingly, it is an object of this invention to provide an improved print hammer control mechanism wherein a hammer is held at a rest position by the magnetic force generated by a magnetic flux producing element while storing energy in an elastic body such as a spring.

Another object of the invention is to provide an improved hammer control mechanism for a printer which may be actuated by relatively small control current to thereby effect small power consumption.

Still another object of the invention is to provide a printer having a plurality of hammers controlled by a common magnetic flux producing element and individual column circuit control devices wherein the operation of one of said hammers does not affect operation of any of the adjacent hammers.

Still a further object of the invention is a printer having a plurality of hammers controlled by individual column circuit control devices wherein a high response speed is effected by utilizing a minimum of power.

Still another object of the invention is to provide a printer and a plurality of hammers controlled by a single flux producing element common to each of the hammers, and individual column magnetic circuit control devices each including a permanent magnet.

Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.

The invention accordingly comprises the features of construction, combination of elements, and arrangement of parts which will be exemplified in the construction hereinafter set forth, and the scope of the invention will be indicated in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS For a fuller understanding of the invention, reference is had to the following description taken in connection with the accompanying drawings in which:

FIG. I is a partially sectioned side elevational view of the operative portion of one column of a printer constructed in accordance with the prior art;

FIGS. 2 and 3 are partially sectioned side elevational views of the operative portion of one column of a printer including an improved hammer control mechanism constructed in accordance with the instant invention;

FIG. 4 is a graphical representation of a hysteresis loop of the control permanent magnet utilized in the embodiment depicted in FIGS. 2 and 3; and

FIG. 5 is a side elevational view of a second embodiment of an operative portion of one column of a printer including an improved hammer control mechanism constructed in accordance with theinstant invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1, one column of a multicolumn printer constructed in accordance with prior art is depicted. The printer includes a hammer I mounted for longitudinal displacement on suspending springs 2. A magnetic circuit for the control of the displacement of the hammer is provided having a first portion consisting of yokes 3 and 4 for holding hammer l in a rest position by means of a magnetic field caused by fluit from a permanent magnet 6 and depictcd as loop i. A second portion of the magnetic circuit illustrated by loop ii is formed by permanent magnet 6, yoke 3, yoke 4, an additional yoke 5, and a control coil 8 wound about yoke 5. The rear end of hammer 1 is disposed in contact with transmitting lever 9, which lever is pivoted about pivot 9' and which lever further engages and deforms drive spring 10 when the hammer is in the rest position as illustrated in FIG. 1. The stroke of transmitting lever 9 is limited by a stopper 12 which is struck by said lever before the hammer strikes recording paper and inked ribbon 14 against print drum 13. Reset cam 11 is provided for returning the print hammer and spring to a rest position after the hammer is operated and the printing is completed by rotating cam 11 against the lower portion of the transmitting lever 9 to thereby deform the spring into the rest position. Printing is effected by engagement of the front end of the hammer 1 against the recording paper 15 to force the recording paper against the ink ribbon 1 4 and the surface of a character-carrying drum 13. Drum 13 is continuously rotating and has a series of characters circumferentially spaced in alignment with the column represented by FIG. 1. In practice, one such circumferential arrary of characters will be provided for each column of the printer. The characters may consist of the symbols, numbers or letters desired.

The operation of the prior art arrangement depicted in FIG. 1 is understood by making reference thereto wherein the hammer is depicted at a rest position. At this'position hammer l is held by yokes 3 and 4 due to the holding force generated by the flux loop 1' which includes the hammer, yokes 3 and 4 and permanent magnet 6. The holding force applied to hammer l is sufficient to overcome the driving force of drive spring 10 and is further sufficient to hold the hammer in position despite the influence of changes in temperature, vibration and the like. As hereinabove noted, a second loop ii is formed, including permanent magnet 6, and is con nected in parallel with the first loop 1' through permanent magnet 6. As noted above, a character carrying drum 13 rotates at a predetermined speed. When the selected character approaches alignment with hammer l, a signal is applied to control coil 8. The direction of the signal appliedto the control coil 8 is such as to increase the quantity of magnetic flux flowing in magnetic flux loop ii. When the magnetic flux in loop ii is increased, the flux in loop i between the points A and B is decreased, thus decreasing the holding force on the hammer, allowing the holding force to be overcome by the force of drive spring 10 acting upon the hammer. The print hammer is driven in the direction of the character on the print drum by the spring and continues to be supplied with energy until transmitting lever 9 is brought into contact with stopper 12. If the print hammer strikes against the character drum the printing function is performed. The print hammer rebounds off the print drum and is returned to the rest position, spring 10 being returned to the rest position by reset cam 11.

It is noted that the operation of the prior art hammer is less than completely satisfactory in view of the following. When the hammer is released from its hammer hold position, the operating point of the permanent magnet is changed. Alteration of the operating point of the permanent magnet affects the adjacent columns which have hammer control magnetic circuits cooperating with the same permanent magnet, the hammers of which have not yet been released from their respective hammer hold positions. The change in operating point of the permanent magnet at the released hammer column increases the amount of magnetic flux flowing to the hammer hold portion of the magnetic circuits of the adjacent columns which have not yet been released. This increase in the amount of flux in the adjacent columns causes an increase in the force of loop 1' in the other columns and a stronger signal must then be applied to the control coils in the adjacent columns in order to allow the hammers of such adjacent columns to be released. Moreover, even if the power is sufficient to release the hammer of the adjacent columns, an increase in time is required to supply the current needed for releasing such adjacent hammers. Variations in the time between the application of a print command and the release of associated hammer depending on whether another hammer has previously been released results in a reduction in printing efficiency, and hence a reduction in the response time of such printing.

Reference is now made to FIGS. 2 and 3 wherein a printer control mechanism for eliminating the abovementioned defects is depicted. A print hammer 21 is depicted in FIG. 2 in a rest position where it is held thereby by a hammer hold magnetic circuit consisting of

yokes

23 and 24 having

attractive faces

23a and 24a respectively for holding hammer 21 in a rest position, as illustrated in FIG. 2, by means of the magnetic field caused by the flux from a permanent magnet 26 and depicted as loop iii. A hammer control circuit is illustrated by loop v and is formed by permanent magnet 26, a portion of yoke 24, a portion of yoke 23, a control permanent magnet 27, coil core 25, and a control coil 28 wound about coil core 25, control permanent magnet 27 and yoke 23. Both the hammer hold circuit illustrated as loop iii, and the magnetic control circuit illustrated as loop v are connected in parallel with permanent magnet 26 for holding the hammer and releasing same in the same manner as depicted in FIG. 1. The control permanent magnet 27 is selected so that when the hammer is in a rest position, the polarities of the control permanent magnet 27 and the permanent magnet 26 face each other in the manner depicted in FIG. 2.

In operation, the hammer remains at a rest position, as depicted in FIG. 2. When the selected character on a character carrying drum (not shown) approaches a position opposite the print hammer 21, the control coil 28 is excited in a first direction so as to reverse the direction in the polarity of the control permanent magnet 27 and change the polarity of the control permanent magnet thereby reducing the magnetomotive force be- 27 and the permanent magnet 26 have opposite ,polarities facing each other. The amount of magnetic flux flowing to thehammer hold circuit depicted by .mag-

netic flux loop vii isdecreased rapidly. Uponcomple tion of the printing action by the print hammer, the

print hammer is returned by action of a cam in the,

same manner illustrated in FIG. I. Coincident with the return of the hammer the control coil 28 is excited in a second direction in order to reverse the polarities of the control permanent magnet 27 and return same to its rest position polarities so that the same polarities in the permanent magnet 26 and the control permanent magnet 27 again face each other.

Reference is now made to FIG. 4 wherein a hysteresis loop of the control permanent magnet 27 provided in a control magnetic circuit is depicted. When print hammer 21 is held in a hammer rest position, the operating point of the control permanent magnet 27 is at a point a. When the control coil 28 is energized to effect a release of the hammer, the operating point of the permanent manget is moved from point a to point b. It is noted that the f point of the hysteresis loop is the point at which the control permanent magnet 27 is rapidly reversed and since the point a is so close thereto, a small application of current to the control coil will affect an immediate and rapid reversal of polarities in the control permanent magnet. As explained above, upon excitation of coil 28, flux loop iii is also reduced and the print hammer is released from its rest position. It is appreciated that by providing such a rapid change of polarities of permanent magnet 27, a more rapid response is effected when the excitation coil 28 is energized.

When control coil 28 ceases to be energized, the operating point of the control permanent magnet is moved to point c on the hysteresis loop. At that point, magnetic flux is flowing through the magnetic flux loop vi depicted in FIG., 3. Accordingly, by selecting point c in the hysteresis loop at a proper position, it is possible to eliminate the defect described with respect to a hammer mechanism'shown in FIG. 1, namely, that the operation time of the hammer is altered when the hammer is operated because the hold force for the print hammers in the adjacent columns not having been released is increased.

Upon completing the printing action, the print hammer is returned to its rest position in the usual manner. Coincident therewith, the polarity of the control permanent magnet is returned to the direction depicted in FIG. 2, by applying a signal of a second direction to control coil 28. Upon the return of the polarity of control permanent magnet 27 the operating point thereof is moved along the hysteresis loop from points 0, to d, to e. Upon termination of excitation in that direction, the operating point of the control permanent magnet is returned from point e to point a and the hammer mechanism is returned to the rest position depicted in FIG. 2 Accordingly, the magnetic flux produced from the permanent magnet 26 does not separately flow through the magnetic loop 1' and ii at the time the hammer is attracted such as the conventional hammer mechanism depicted in FIG. 1. Moreover, since the magnetic flux from the permanent magnet 26 can be minimized a small magnet for holding the hammers will become particularly adapted for such use. Further, the response time as well as a decrease inthe power consumed thereby will be effected and, the effect of operating hammers on adjacent columns will be eliminated.

Reference is now made to FIG. 5,wherein a hammer controlmechanism forcontrolling the release of hammer 31 is depicted. A yoke 33 including an electromagnet 36 wound therearound, and having hammer attractice faces 33a and 33b to definea hammer hold, circuit while maintaining hammer 31 at a rest position. core 35 includes a control permanent magnet 37 therein, and a control coil 38 wound therearound. It isunderstood, that the only differences between the hammer control mechanism depicted in FIG. 5 and the one depicted in FIG. 2 is that permanent magnet 4 maintaining the hammer in a rest position is replaced by an electromagnet formed by yoke 33 and coil 36, the operation being the same as the mechanism described above, and providing the same improved response time during operation.

It will thus be seen that the objects set forth above, amont those made apparent from the preceding description are efficiently attained and, since certain changes may be made in the above construction without departing from the spirit and scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense. i

It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetwecn.

What is claimed is:

1. In a printer, respective hammer control means for print hammers which are arranged in a plurality of columns and each of which is displaceable between a rest position and a print position, and having respective deformable elastic bodies maintained in deformed condition by the associated print hammers in the rest position, improved magnetic circuit control means comprising holding means for holding each said print hammer at said rest position, releasing means for selectively displacing said print hammer to said print position, and means for producing a magnetic flux, a first hammer hold magnetic circuit associated with each print hammer including a portion of the associated print hammer and a second control magnetic circuit associated with each print hammer including a control permanent magnet and control coil means, said control coil means including means for applying a pulse thereto, said first magnetic circuit and second magnetic circuit being connected in parallel with said magnetic flux producing means, each of said magnetic circuit control means being adapted to hold said respective hammers in said rest position and to release said respective hammers upon application of a pulse to the control coil means by means of said signal applying means in a direction so as to reverse the polarity of said control permanent magnet and thereby decrease the magnetomotive force applied to said hammer, the energy stored in the respective deformed body displacing said respective hammer from said rest position to said print position upon said decrease in said magnetomotive force.

4. In a printer as claimed in claim 2, and including means for returning said print hammer to a rest position upon completion of said printing operation.

5. A printer as claimed in claim 4, wherein said coil means includes a single excitation coil. and said means I for applying said first mentioned pulse to said excitation coil is further adapted to supply a further pulse of an opposite direction to said excitation coil to reverse the polarity of said control permanent magnet coinci-' dent with the return of said print hammer to said rest position

Claims

2. In a printer as claimed in claim 1, wherein said means for producing a magnetic flux is a permanent magnet.

3. In a printer as claimed in claim 2, wherein said permanent magnet and said control permanent magnet have like polarities coupled to each other when said hammer is in said rest position, and upon application of said control release pulse to said control coil means, the polarities of said control permanent magnet being reversed so as to couple the opposite polarities of said permanent magnet to opposite polarities of said control permanent magnet.

5. A printer as claimed in claim 4, wherein said coil means includes a single excitation coil, and said means for applying said first mentioned pulse to said excitation coil is further adapted to supply a further pulse of an opposite direction to said excitation coil to reverse the polarity of said control permanent magnet coincident with the return of said print hammer to said rest position.