US3907091A

US3907091A - Type disc-interposer assembly for a printer

Info

Publication number: US3907091A
Application number: US415277A
Authority: US
Inventors: Johann Hans Meier; Jerry Wesley Raider
Original assignee: International Business Machines Corp
Current assignee: IBM Information Products Corp
Priority date: 1972-06-02
Filing date: 1973-11-12
Publication date: 1975-09-23
Anticipated expiration: 1992-09-23

Abstract

A rotating, circular type carrier for a serial printer is equipped with axially movable type elements arranged on its periphery and having type members on one face, and a metal interposer disc with radial spokes is placed on the same axis of rotation such that the spokes line up with the other face of the elements; the inclined rear surfaces of the spokes are struck by a hammer so that the impact energy is transmitted from the hammer through a spoke to the corresponding element and the hammer is cammed back by the inclined surface of the rotating spoke.

Description

[ Sept. 23, 1975 United States Patent n91 Meier et a1.

Ragland et Willcox et al.......

Folkens 972 Cattaneo lllilill TYPE D ISC-INTERPOSER ASSEMBLY FOR 3,442,365

A PRINTER [75] Inventors: Johann Hans Meier, Vestal;

Jerry both of Wesley Raider, Endieott, NY.

Primary Exarn'iner-Edgar S. Burr Assistant Exami'nerR. T. Radler Attorney, Agent. or Firm- Francis V. Giolma [22] Filed:

[21] Appl. No.: 415,277

ABSTRACT Related US. Application Data A rotating, circular type carrier for a serial printer is [63] Continuation of Ser.

abandoned.

June equipped with axially movable type elements arranged on its periphery and having type members on one face, and a metal interposer disc with radial placed on the same axis of rotation such that the spokes line up with the other face of the elements; the inclined rear surfaces of the spokes are struck b hammer so that the impact ene t; men k fgh C o .mn P wd S ne we... Y

the hammer through a spoke to [56] References Cited merit and the hammer is cammed back b f' t 't' k UNITED STATES PATENTS sur ace of he rota mg spo e 25 Claims, 5 Drawing Figures US Patent Sept. 23,1975 Sheet 1 of2 3,907,091

FIG.

US Patent Sept. 23,1975 Sheet2 of2 3,907,091 r TYPE DISC-INTERPOSER ASSEMBLY FOR A PRINTER This application is a continuation of application Ser. No. 259,320, filed June 2, I972, now abandoned.

FIELD OF THE INVENTION The invention relates generally to on-the-fly rotating print disc printers and it has reference in particular to means for reducing print hammer nipping of adjacent type fingers in a rotating disc printer.

DESCRIPTION OF THE PRIOR ART SUMMARY OF THE INVENTION Generally stated, it is an object of this invention to provide an improved print disc assembly for a printer.

Another object of the invention is to provide an improved printing apparatus utilizing a plurality of type slugs each having an interposer portion positioned be tween it and a print hammer for transmitting energy from the print hammer to the type slug by Hertzian stresses and stress waves across the thickness of the interposer.

More specifically, it is an object of this invention to provide for using a spoked interposer disc with a print disc having type-carrying fingers, and to transfer the print energy from a print hammer to the fingers of the print disc through the interposer disc spokes.

Another object of the invention is to provide for using with a continuously-rotating print disc an interposer having resilient spokes against which type carrying fingers of the print disc are preloaded.

It is also an object of this invention to provide for using a slotted interposer disc with a continuously' rotating type disc having radial type fingers so that the interposer spokes transfer energy from a print hammer to the type disc fingers, and locate a relatively stiff spring support between the type disc and the interposer disc to prevent large deformations of the interposer and hence, nipping.

An important object of the invention is to provide for using a resilient spoked interposer between a print hammer and a type carrying disc, with the interposer being impacted by the hammer to impact the type disc and the interposer disc having cam surfaces engaged by the hammer for restoring the hammer towards its rest position.

It is also an important object of this invention to provide a spoked interposer between a multi-finger print disc and a print hammer with the interposer spokes being in contact with type carrying fingers of the print disc before being struck by the print hammer.

Another important object of the invention is to provide for using a spoked interposer between a fingered print disc and a print hammer with a relatively stiff spring back up disc between the interposer and the print disc having a diameter greater than the root of the interposer slots.

Still another object of the invention is to provide for using a resilient spoked interposer disc between a print hammer and a flexible fingered type carrying disc, with relatively stiff support discs on either side of the interposer.

Another important object of the invention is to provide camming surfaces on an interposer for a flexible print disc by deforming the spokes of the interposer, grinding away edge portions of the deformed surfaces, and then releasing the spokes to allow them to restore to their original position with the ground surface portions providing inclined cam surfaces to be impacted by a print hammer.-

An importantobject of the invention is to provide for assembling aiflat fingered print disc and a fiat spoked interposer disc on a hub with a wedge disc therebetween so that the print disc is deformed and the fingers of the print disc are prestressed against the spokes of the interposer disc.

Still another object of the invention is to provide for using a relatively stiff flat disc spring member between a flat spoked interposer disc and a flat fingered print disc for preventing rebound of the interposer spokes from striking the print disc to cause double strikes.

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 drawing.

DESCRIPTION OF THE DRAWING In the drawing:

FIG. 1 is a schematic isometeric view in part of a printer mechanism embodying the invention in one of its forms;

FIG. 2 is an enlarged partial cross-sectional view DESCRIPTION OF PREFERRED EMBODIMENTS As shown in FIG. 1, a rotatable Print Wheel Assembly 10 is positioned to move past a Document 12 which is backed up by a Platen 14, in conjunction with a Print Hammer 16 operated by a Solenoid 18 to impact the print wheel against the document for printing.

The Print Wheel Assembly 10 comprises a Print Disc 20 having radial Slots 21 defining a plurality of type carrying elements such as the radial Fingers 22 having Type Slugs 23 mounted thereon for impacting the Document 12. Referring to FIGS. 1 and 2, it will be seen that the Type Wheel Assembly comprises a Hub 24 having a Recess 26 disposed to fit on a Shoulder 28 on the end of a rotatable Shaft 30 having a rotating Support Plate 32 for the type disc assembly secured thereto. The Hub 24 is fastened to the Shoulder 28 by means of a knurled Screw 34 having a threaded Portion 36, threadably engaged in an opening in the Shaft 30. The Hub 24 is provided with a radial Flange 38 having a

peripheral Rib

40 and 21 Projection 42 disposed to be positioned in a Recess 44 of the Support Plate 32 to position the hub with respect to the Support Plate 32.

Instead of having the Print Hammer 16 impact the Type Slugs 23 or the Type Fingers 22 directly an lnterposer Disc 46 is positioned on the Hub 24 between the Type Disc and the Print Hammer 16. The lnterposer Disc 46 has a plurality of radial Slots 48 defining a plurality of interposer portions such as the radial lnterposer Spokes 50, which are impacted by the Hammer 16 and in turn impact the Type Slug 23 against the Document 12. A relatively stiff, flat disc Spring 52 is positioned on the hub between the Type Disc 20 and the lnterposer Disc 46 to prevent rebound of the Interposer Spokes 50 from causing double strikes of the Type 23. The Spring Disc 52 is provided with a Channel-shaped Rim 54 of rubber or other resilient material to provide a non-fretting contact surface between the lnterposer Disc 46 and the flat Spring 52. A Wedge Ring 56 is positioned between the Type Disc 20 and the flat Spring Disc 52, being tapered towards its outer edge so as to provide for deforming the Type Disc 20 to bring the Type Slugs 23 into contact with the Interposer Spokes 50 in the rest position. This effect is obtained by the peripheral Rib 40 of the Hub 2 4 pressing against the Type Disc 20 and forcing it against the Wedge Ring when the assembly is clamped between the Rib 40 of Flange 38 and a circular Clamp Plate 60, which is secured to the Flange 38 by means of Screws 62. A damping Disc 63 of plastic material is positioned between the lnterposer Disc 46 and the Clamping Plate 60 having a thickened Rim Portion 64 to provide a stop for the lnterposer Fingers 50 and absorb most of the energy from them upon their rebound from the Type Fingers 22 after being struck by the Hammer 16.

In order to prevent nipping or interference between the Print Hammer 16 and an adjacent one of the Interposer Spokes 50, the surface portions of the lnterposer Spokes 50, which are engaged by the Print Hammer 16, are inclined as shown in FIG. 4 to provide a camming action. Since the print wheel assembly rotates in a counterclockwise direction, the inclined rear surface Portion 66 of the lnterposer Spokes 50 provides an inclined plane which cams the Hammer 16 backwardly as the interposer spoke moves past the hammer towards the left, thus preventing interference between the Print Hammer 16 and the next lnterposer Spoke 50 to the right, as it approaches the print hammer. The inclined surface portions may be provided in a number of suitable ways. It has been found expedient to place the interposer Disc 46 in a jig wherein it may be clamped so as to twist the Fingers 50 by raising the left-hand edges (downwardly, as shown in FIG. 4). The rear surface may then be ground to remove the raised edge portion and when the interposer disc is removed from the jig and the spokes return to their original positions, the left-hand edges will be reduced in thickness, as shown, providing an inclined plane cam surface.

As shown in FIGS. 1 and 3 the Clamp Plate 60 is eccentrically mounted. This is done to provide an additional mass at about the 11 oclock position, as shown in FIG. 3, to compensate for the unbalance caused by the type fingers, with the resilient material filling the,

Slots 2] to the outer radius of the molded area. This provides a damping action for the Type Fingers 22 to minimize rebound. As shown in FIG. 3, the lnterposer Spokes 50 are substantially aligned with the Type Fingers 22. They are not, however, exactly aligned, since the interposer fingers to right of the Gap 70 are positioned slightly ahead of the Type Fingers 22, whereas at the other end of the Gap 70, the interposer fingers are positioned slightly behind the type fingers in the direction of rotation, which is as has been explained, counterclockwise.

Referring to FIG. 5, an alternate construction is shown in which the inclined rear surface of the Interposer Spokes 71 is provided by merely twisting the lnterposer Spokes 71 bodily so that in th'; free position they occupy a position substantially as shown and the rear surfaces 74 are inclined to provide a camming action for the Print Hammer 16.

From the above description and the accompanying drawing it will be apparent that we have provided in a simple and effective manner for preventing nipping in a rotating print disc assembly. By using an interposer disc with spokes in contact with the type fingers on the type disc, operating speeds of double that obtainable otherwise may be obtained. In one embodiment with a print disc having a diameter on the order of 3 H2 inches, the type disc may be made from stainless steel 10 mils thick. The interposer disc having a diameter of approximately 3.4 inches may be made of spring steel about 20 mils thick, while the flat spring disc 52, which is made of spring steel, may be 30 mils thick. A hammer force on the order of 20 pounds for a 15 microsecond interval, causes an interposer spoke to be impacted against a type slug, causing the type finger to deflect and the type slug to accelerate and impact the document, which may by way of example, be an action type or pressure sensitive paper, against the platen. The interposer fingers rebound and are stopped by the damping disc. The flat disc spring prevents any rebound of the interposer spokes from again striking the type members.

By way of explanation, since the lnterposer Disc 46 is described as twice as thick as the Print Disc 20, the lnterposer Spokes 50 are at least eight times as stiff, i.e., have a spring constant at least eight times as high as the Print Disc Fingers 22, the relative stiffness being proportional to the cube of the thickness ratio. This means that while the lnterposer Spokes 50 can deflect they are so much stiffer than the Print Disc Fingers 22 that when the Print Hammer 16 strikes an lnterposer Spoke 50 the spoke deflects very little, the primary transfer of energy from the Print Hammer 16 to the Type Finger 22 being accomplished by the buildup of Hertzian stresses at the contact point between the Print Hammer 16 and lnterposer Spoke 50, stress waves across the thickness of the lnterposer Spoke, and a second Hertzian stress buildup at the contact point between the lnterposer Spoke 50 and the Type Slug 23 on the corresponding Type Finger 22. At the completion of the energy transfer, i.e. when the Type Slug 23 leaves the lnterposer Spoke 50, the interposer spoke displacement is very small, being on the order of 3 to 5 mils. The Type Slug 23 is accelerated to strike the Document 12 and deflects on the order of 45 mils. Thus it is seen that the kincticcnergy of the Print Hammer I6 is converted substantially into strain energy in u the Print Hammer 16. in thelnterposer Spoke 50, and in the corresponding Type Slug 23; and then it is substantially reconvened into kinetic energy of the Type Slug. V g

While the invention has been particularly shown and described with reference to preferred embodiments 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.

What is claim is: a

1. Printing apparatus for use in a printer having a rotatable print carrier supportwhich is movable across a document and having a print hammer operable from a rest position to effect impact of a type carrying element on said support which is intermediate said document and said print hammer against said document for printing thereon comprising;

a rotatable print disc having a plurality of resilient axially-movable type carrying elements with two faces, .said typecarrying elements having type characters on one face adjacent said document,

an interposer disc disposed to rotate with said print disc and having the same plurality of resilient radial spokes positioned adjacent and normally in contact with the other faceof the type carrying elements, said radial spokesbeing stifferthan said type carrying elements and having cam surfaces for engagement withgsaid print hammer which are operable to restore. said print hammer to said rest position by cam action as they rotate past said print hammer, and

means securing the print disc and interposer disc on said rotatable support in predetermined fixe'd' rotational relation to each other so that said print disc and interposer disc rotate together at the same angular velocity and said interposer spokes impart an axial velocity to said print disc typecarrying elements when impacted by said print hammer, causing said print disc type carrying elements to sepa rate from saidint'er'poser spokes before impacting saiddocument to print.

2. The invention as defined in claim 1 characterized by said type carrying elements comprising radial fingers defined by radialslots extending inwardly from the periphery of the print disc, and said print'dis'c and interposer disc being secured in fixed relation with each other to a hub which is detachably secured to said rotatab'le support.

3. Theinvention as defined in claim 2 characterized by a wedge means secured on said hub between said print disc and said interposer disc whereby said fingers of said print disc are positioned to be normally in contact with and are pressed against the spokes of saidinterposer disc so as to be preloaded thereby.

4. The invention as defined in claim 3 characterized by a'flat disc spring positioned between said wedge means and said interposer disc to normally engage the spokes of said interposer disc.

5. The invention as defined in claim 4 characterized by an energy absorbing plastic disc secured on said hub and in contact with said interposer disc adjacent the periphery thereof on the side away from said print disc.

6. The invention as defined in claim 5 characterized by a resilient cap positioned about the periphery of said flat disc spring.

7. The invention as defined in claim 1 characterized by said interposer disc lying substantially in a single plane, and said spokes of said interposer disc being twisted about a radial axis out ofthe plane of said disc to provide inclined cam surfaces on the sides away from said print disc.

8. Theinvention as defined in claim 1 characterized by said print disc having. a band of resilient material bonded to the fingers and covering a central portion of said print-disc and at least Bi'POltlOll of the slots between the spokes.

9. Printing apparatus comprising,

a platen positioned on one side of a'document to provide support for the document and define a print line,

a type-element carrier moving in a direction parallel to the print line and supporting type carrying ele- 'ments movable in the direction perpendicular to the platen at the desired point of impact, said type carrying elements having two faces with type characters on the face adjacent said platen and document,

flexible interposers attached to said type-element carrier, each interposer corresponding to onetype element and contacting'the other face of said type element away from said platen and documents,

means biasing said type elements and interposers against each other so as to normally preload said type elements against said interposers,

a print hammer operable to impact said interposers and cause said interposer to impart velocity to the corresponding type element, whereby said type element separates from said corresponding interposer and impacts its type character against said document and platen. 10. The invention as claimed in claim 9 characterized by said interposers having inclined cam surfaces on the side of said print hammer. 1

11. Serial printing apparatus comprising,

a platen positioned on one side of a document to provide a support for the document and define aprint line thereon, v V v a carriage movable along said print line in spaced relation with said platen and document,

a type-element carrier rotatably mounted on said carr riage and having type elements movable perpendicular' to the print surface, said type elements having type characters on the one face adjacent said platen and document,

an interposer array rotatably mounted on said carriage, coaxially and in fixed rotational relation with said type element carrier so as to rotate together at the same angular velocity and having flexible components aligned with and normally in contact with said type elements, said interposer array being adjacent to said type element carrier on the side of said type element carrier away from said platen and document, and

a print hammer mounted on said carriage operable to impact one of said flexible components of said interposer array and cause said flexible component of said interposer array to impart velocity to the corresponding type element in contact therewith causing it to separate from said interposer flexible component and to impact the type character of said type element against said document and platen.

12. The invention as defined in claim 11 characterized by said components of said interposer array having inclined cam surfaces on the side of said print hammer.

13. Printing apparatus for use in a printer in which a type carrying element is movable to present a plurality of type along a print line on a document, and a print hammer is operable to effect impact of said typecarrying element and document for printing thereon, compl'lSH'lg,

a movable type carrying element having a plurality of type bearing portions movable both past said document to present different type to print positions along said print line and toward said document with a predetermined spring constant to print thereon,

an interposer mounted to move past said document with and at the same rate as said type carrying element and having an interposer portion normally positioned in contact with each type bearing portion, between said print hammer and said type carrying element, to transfer energy to said type from said print hammer when impacted by said print hammer primarily by stress waves travelling through said interposer portion, said interposer portion having a spring constant substantially higher than that of said movable type carrying element so as to cause said movable type carrying element to separate from said interposer portion and impact said document.

14. The invention as defined in claim 13 characterized by saidtype carrying element comprising a disc and said type carrying portions comprising radial finger s. I I I l5. Theinvention as defined in claim 13 characterized by said interposer portions comprising radial spokes against which said corresponding print disc fingers alre preloaded. l y v l6. The invention as defined in claim 15 characterized by the spokes of said interposer being sufficiently thicker than said fingers of said type disc, so as to be more than five times stiffer than the fingers of said type disc.

17. The invention as defined in claim 16 characterized by a spring disc mounted between said print disc and said interposer and being stiffer than said interposer.

18. The invention as defined in claim 17 characterized by a spacer positioned between said print disc and said spring disc adjacent said support to provide for biasing the fingers of said print disc against the spokes of said interposer adjacent said type.

19. Printing apparatus comprising,

a platen positioned on one side of a document to provide support for the document and define a print line, v v

a type element carrier movable in a direction parallel to said print line and supporting a plurality of type bearing portions movable in a direction perpendicular to said platen, said type bearing portions having type on the one face adjacent said platen and document,

interposer means attached to said type element carrier having a plurality of cantilever interposer portions, corresponding one for one with each type bearing portion positioned in contact with said type bearing portions on the face of said type bearing portions away from said platen and document to transmit energy to said type primarily by stress waves, and

a print hammer operable to impact a selected one of said interposer portions to impart a velocity to said corresponding type'bearing portion causing it to separate from said interposer portion and to impact -said type against said document and platen.

20. The invention as defined in claim 19 characterized by said type carrying element comprising a disc of a resilient material having a plurality of radial fingers bearing said type.

21. The invention as defined in claim 20 characterized by said interposer means comprising a disc having radial spokes corresponding to said type carrying element fingers but being stiffer than said type carrying element fingers.

22. The invention as defined in claim 21 characterized in that said interposer means spokes are sufficiently thicker than said type carrying element fingers so as to be from 5 to 10 times as stiff as said type carrying element fingers.

23. The invention as defined in claim 22 characterized by a disc spring positioned between said type carrying element and said interposer means in contact with said interposer means and being stiffer than said interposer means spokes.

24. The invention as defined in claim 23 characterized by a damping disc positioned to engage said interposer means on the side away from said type carrying element. A

25. The invention as defined in claim 22 characterized by said interposer means spokes having inclined cam surfaces on the side toward said print hammer.

Claims

1. Printing apparatus for use in a printer having a rotatable print carrier support which is movable across a document and having a print hammer operable from a rest position to effect impact of a type carrying element on said support which is intermediate said document and said print hammer against said document for printing thereon comprising; a rotatable print disc having a plurality of resilient axiallymovable type carrying elements with two faces, said type carrying eLements having type characters on one face adjacent said document, an interposer disc disposed to rotate with said print disc and having the same plurality of resilient radial spokes positioned adjacent and normally in contact with the other face of the type carrying elements, said radial spokes being stiffer than said type carrying elements and having cam surfaces for engagement with said print hammer which are operable to restore said print hammer to said rest position by cam action as they rotate past said print hammer, and means securing the print disc and interposer disc on said rotatable support in predetermined fixed rotational relation to each other so that said print disc and interposer disc rotate together at the same angular velocity and said interposer spokes impart an axial velocity to said print disc type carrying elements when impacted by said print hammer, causing said print disc type carrying elements to separate from said interposer spokes before impacting said document to print.

2. The invention as defined in claim 1 characterized by said type carrying elements comprising radial fingers defined by radial slots extending inwardly from the periphery of the print disc, and said print disc and interposer disc being secured in fixed relation with each other to a hub which is detachably secured to said rotatable support.

3. The invention as defined in claim 2 characterized by a wedge means secured on said hub between said print disc and said interposer disc whereby said fingers of said print disc are positioned to be normally in contact with and are pressed against the spokes of said interposer disc so as to be preloaded thereby.

4. The invention as defined in claim 3 characterized by a flat disc spring positioned between said wedge means and said interposer disc to normally engage the spokes of said interposer disc.

7. The invention as defined in claim 1 characterized by said interposer disc lying substantially in a single plane and said spokes of said interposer disc being twisted about a radial axis out of the plane of said disc to provide inclined cam surfaces on the sides away from said print disc.

8. The invention as defined in claim 1 characterized by said print disc having a band of resilient material bonded to the fingers and covering a central portion of said print disc and at least a portion of the slots between the spokes.

9. Printing apparatus comprising, a platen positioned on one side of a document to provide support for the document and define a print line, a type-element carrier moving in a direction parallel to the print line and supporting type carrying elements movable in the direction perpendicular to the platen at the desired point of impact, said type carrying elements having two faces with type characters on the face adjacent said platen and document, flexible interposers attached to said type-element carrier, each interposer corresponding to one type element and contacting the other face of said type element away from said platen and documents, means biasing said type elements and interposers against each other so as to normally preload said type elements against said interposers, a print hammer operable to impact said interposers and cause said interposer to impart velocity to the corresponding type element, whereby said type element separates from said corresponding interposer and impacts its type character against said document and platen.

10. The invention as claimed in claim 9 characterized by said interposers having inclined cam surfaces on the side of said print hammer.

11. Serial printing apparatus comprising, a platen positioned on one side of a document to provide a support for the document and define a print line thereon, a carriage movable along said print line in spaced relation with said platen and document, a type-element carrier rotatably mounted on said carriage and having type elements movable perpendicular to the print surface, said type elements having type characters on the one face adjacent said platen and document, an interposer array rotatably mounted on said carriage, coaxially and in fixed rotational relation with said type element carrier so as to rotate together at the same angular velocity and having flexible components aligned with and normally in contact with said type elements, said interposer array being adjacent to said type element carrier on the side of said type element carrier away from said platen and document, and a print hammer mounted on said carriage operable to impact one of said flexible components of said interposer array and cause said flexible component of said interposer array to impart velocity to the corresponding type element in contact therewith causing it to separate from said interposer flexible component and to impact the type character of said type element against said document and platen.

13. Printing apparatus for use in a printer in which a type carrying element is movable to present a plurality of type along a print line on a document, and a print hammer is operable to effect impact of said type carrying element and document for printing thereon, comprising, a movable type carrying element having a plurality of type bearing portions movable both past said document to present different type to print positions along said print line and toward said document with a predetermined spring constant to print thereon, an interposer mounted to move past said document with and at the same rate as said type carrying element and having an interposer portion normally positioned in contact with each type bearing portion, between said print hammer and said type carrying element, to transfer energy to said type from said print hammer when impacted by said print hammer primarily by stress waves travelling through said interposer portion, said interposer portion having a spring constant substantially higher than that of said movable type carrying element so as to cause said movable type carrying element to separate from said interposer portion and impact said document.

14. The invention as defined in claim 13 characterized by said type carrying element comprising a disc and said type carrying portions comprising radial fingers.

15. The invention as defined in claim 13 characterized by said interposer portions comprising radial spokes against which said corresponding print disc fingers are preloaded.

16. The invention as defined in claim 15 characterized by the spokes of said interposer being sufficiently thicker than said fingers of said type disc, so as to be more than five times stiffer than the fingers of said type disc.

19. Printing apparatus comprising, a platen positioned on one side of a document to provide support for the document and define a print line, a type element carrier movable in a direction parallel to said print line and supporting a plurality of type bearing portions movable in a direction perpendicular to said platen, said type bearing portions having type on the one face adjacent said platen and document, interposer means attached to said type element carrier having a plurality of cantilever interposer portions, corresponding one for one with each type bearing portion positioned in contact with said type bearing portions on the face of said type bearing portions away from said platen and document to transmit energy to said type primarily by stress waves, and a print hammer operable to impact a selected one of said interposer portions to impart a velocity to said corresponding type bearing portion causing it to separate from said interposer portion and to impact said type against said document and platen.

24. The invention as defined in claim 23 characterized by a damping disc positioned to engage said interposer means on the side away from said type carrying element.