CA1125661A - Vibration dampening printing element guide means - Google Patents

Abstract

Docket No. 2603 Title of the Invention VIBRATION DAMPENING PRINTING ELEMENT GUIDE MEANS

Abstract of the Disclosure In a matrix print head, a plurality of elongated printing elements, mounted in a frame, are driven axially by electromagnetic means to effect printing on record media positioned adjacent to the printing ends of the printing elements. Printing element support members are mounted loosely in complementary slots in the frame, in order to dampen the bending and vibration of the printing elements, and thus reduce or eliminate consequent fatigue failure.

Description

~s~

Backq~und of the Inventior~
. _ _ In the field of high-speed printing devices which are especlally suitable for use in connection with electronic data processing systems, the wire matrix type of printer has come into increasiny use. In this type of printer, letters, numbers and symbols are formed from a series of dots produced by the impact of the ends of a plurality of wire elements on record media, most customarily in combination with an ink ribbon which provides the ink needed to produce a mark on the record medium being printed upon.
One problem which has arisen in connection with US2 of printers of the wire matrix type is that of fatigue breakage of the print wires and associated springs employed to return the wire to a non~printing position after a printing stroke.
This breakage results from bending and vibration of the print wires caused by the high force employed to drive the wires over a short distance to impact upon the record medium being printed upon or the ink ribbon associated therewith. In order to reduce or eliminate such breakage, in some prior structures, the individual print wires have been confined within print head blocks or Ullits, or within tubes or coil springs anchored in the printer framework. However, such structures have the disadvantages of increasing the parts and labor costs, and also tend to impede the movement of the printer wires by frictional engagement between the wires and the tubes or other supporting structure. This, in turn, has led in some instances to further structural alterations of the printers to provide means for lubricating the wires within the tubes, thereby additionally increasing the cost and complexity of the assembly.

5~

In another approach to solution of this problem, tubular elements have been placed on the print wires to ride freely thereon and exercise a vibration dampening function, as disclosed and claimed in Canadian Patent No. 1,106,689 which issued August 11, 1981, inventors Nelson et al., assigned to the assignee of the present application.
In a further approach to solution of this problem, a dampening element, of generally conical configuration, is centrally disposed in a print head frame, within the volume defined by a plurality of printing elements, in order to dampen the bending and vibration thereof, as disclosed and claimed in Canadian patent No. 1,109,334 which issued September 22, 1981, inventors Schrag et al., assigned to the assignee of the present application.
This invention relates to a printer of the matrix type, and more particularly relates to such a printer which includes means for dampening vibration and bending of the print elements to reduce or eliminate fatigue failure.
In accordance with the invention, there is provided a printing mechanism comprising: frame means including an elongated portion of substantially rectangular cross-sectional configuration having first lateral support means at one end thereof and integral therewith, having second lateral support means at the other end thereof and integral therewith, and having a plurality of stations provided with slots on the elongated portion thereof disposed intermediate of said first and second lateral support means, printing end bearing means associated with said second lateral support means and having a plurality of printing element receiving apertures disposed -therein, an intermediate support member of substantially rec-tangular configuration disposed in the slots of each of said stations, the length and depth of each intermediate support ~ 3 member being sufficiently less than the corresponding dimensions of the slots of the station to enable said intermediate support ; member to move freely in two directions within the station, and the width of each intermediate support member being only enough less than the width of the slot of the corresponding station to enable free sliding lateral movement of said support member; a plurality of elongated printing elements extending in curved paths through and supported by apertures in said first and second lateral support means, said intermediate support members and said printing end bearing means, the apertures in said intermediate support members being of larger diameter on one surface than on the opposite surface to accommodate the curved paths of the elongated printing elements, the total mass ; of the elongated printing elements being less than the total mass of the intermediate support members which latter total mass is distributed in spaced-apart locations, corresponding to the locations of said stations, along the elongated printing elements; and driving means position~3d adjacent the first lateral support means and associated with each printing element for driving each printing element axially in a printing operation, ~- the intermediate support members being free to slide laterally in said slots in response to lateral movement of said printing elements to dampen undesired transverse movement and vibration of said printing elements.
One advantage of the present invention is that dampen-ing of the bending and vibration of the print elements is achieved without substantial frictional drag on the print , elements.
Another advantage of the present invention is that dampening means for the print elements are provided which re-quire no extra cost in terms of parts or assembly.
It is accordingly an object of the present invention t~ -4-5~6~

to provide a print head including elongated printing elements having vibration dampening means for the printing elements which are both inexpensive and effective in operation.
Another object is to provide a print head having elongated printing elements and also having vibration dampening means which do not impose a substantial frictional load on the -4a-5~6~

print elements.
A further object is to provide a print head including printing element support members which are loosely mounted in the print head frame, in order to dampen the bending and vibration of the printing elements, and thus reduce or eliminate consequent fatigue failure.
A further object is to provide a print head which is durable and reliable in operation.
With these and other objects, which will become apparent from the following description, in view, the invention includes certain novel features of construction and combinations of parts, one form or embodiment of which is hereinafter described with reference to the drawings which accompany and eorm a part of this specification.

~, ~" .

. _ 5 ~ 2S~6~

rief Description of the Drawings Fig. ~ is a sectional view of a print head in accordance with the present invention' Fig. 2 is an elevation view, partly broken away, showing the frame, the elongated printing elements, and the dampening means, of the print head, Fig. 3 is an enlarged cross-sectional view, taken along line 3-3 of Fig. 2;
Fig. 4 is an enlarged cross-sectional view, taken along line 4-4 of Fig. 2;
Fig. 5 is an enlarged cross-sectional view, taken along line 5-5 of Fig. 2; and Fig. 6 is an enlarged bottom view of the frame of Fig. 2, taken along line 6-6, showing the printing end of the print head.

~ ' .
.
~:' ... .

l2S~6~

~ E~Otl of the Preferre~ Embodiment .~
Referring now particularly to Fig. l of the drawings, a print head lO of the wire matrix type is shown. This print head is similar in general configuration to the print head disclosed in United States Patent No. 3,929,214, issued December 30, 1975, to which reference may be had for a more detailed description of certain aspects of the print head structure.
A frame 12 is provided to support a plurality oE
elongated print elements or prin-t wires 14, only two of which are shown, for purposes of simplification and ready understan-ding of the drawings. Each wire 14 has a cap 16, which may be made of plastic or other suitable material, attached to its impact-receiving end to enlarge the area oE the impact-receivinq surface. Each wire 14 also has a spring 18 disposed at its upper end, which e~erts an upward force upon the cap 16 to resiliently bias the wire upwardly, as shown in Figs. 1 and 3, relative to the f~ame 12. The spring 18 has been omitted from one of the wires of Fig. l, in order that the cap 16 may be more ~learly depicted.
The frame 12 includes three side walls 20, 22 and 24, a print end support member 26 and an upper end support member 28. Both of the members 26 and 28 are formed integral with the side walls 20, 22 and 24 of the frame 12, in the illustrated embodiment, although it is clear that they could equally well be formed separately and secured to the frame 12.
In addition to the support members 26 and 28, a plurality of intermediate support members, two in the illus-trated embodiment, are provided. ~ first intermediate support member 30 is provided with a plurality of apertures 32 in a 566~

predetermined pattern, through which apertures the print wires 14 are passed. The apertures are of large~ diameter on one surface of the support memheL- than on the opposite surface, ln order to accommodate the slightly curved path of the print wires 14 and to facilitate insertion of the wires into the apertures. The member 30 includes a portion 34 of reduced size which is shaped generally in accordance with the circumferential pattern of the apertures 32 in the member 30, and also includes an enlarged portion 36 of generally rectangu~
lar configuration. The edge portions 38 and 40 of the enlarged portion 36 of the member 30 cooperate with slots 42 and 44 formed in side walls 20 and 22 of the frame 12 for loosely positioning the member 30 in the frame 12. The width of the slots 40, 42 is only slightly greater than the width of the enlarged poction 36 of the member 30, to enable said member to slide freely in said slots. ~lowever, the length and depth of the enlarged portion 36 o~ the member 30 are sufficiently less than the corresponding dimensions defined by the slots 42, 44 to enable the member 30 to move with considerable ~0 latitude and Ereedom in all directions at substantially right angles to the longitudinal axis of the frame 12.
Since the print wires 14 follow varying curved paths through the frame 12, it will be seen that the member 30 is Eree tG move in directions which are substantially, but not ` precisely, perpendicular to the longitùdinal axes of the print wires 1~1. As will subsequently be described in greater detail, vibration and lateral movement of the print wires 14 cause the member 30, which is "floating" in the slots 42, 44, to move transversely within such slots, in response to forces applied thereto by the wires 14.

Z~16~

A notch 4G is formed in one corner of the enlarged portion 36 of the member 30 and cooperates with a key ~8 in the slot ~4 to lnsure that the member 30 is placed correctly in the slots.
In the illustrated embodiment, a second intermediate support member 50 having print ~ire apertures 52, a reduced portion 54, an enlarged portion 56, edge portions 58 and 60, and a notch 6~ cooperating with a key 68, is positioned in slots 62, 64 in the side walls 20, 22 o the frame 12. This second intermediate support member 50 functions in the same manner as the member 30, described above.
The members 26, 28, 30 and 50 guide the various print wires 14 to follow desired paths, and to accomplish the translation of the wires Erom a circular formation at the upper end, as seen in Fig. 3, to a linear formation at the printin~ end, as seen in F`ig. 6. This translation is accomplished by passing each wire 14 through a separate aperture 70 in the upper member 28, through apertures 32 and S2 in the members 30 and 50, and in~o a defined position within a bearing 72 in the print end support member 26, as shown in Fig. 6. The bearing 72 is of a material which resists wear, and has a low coefficient of friction.
A pair of mounting flanges 78 and 80 extend laterally from the upper ends of side walls 20 and 22. The frame 12 is circular in cross-sectional shape above the flanges 78l 80 as seen in Fig. 1, and terminates in the upper end support member 28, which is of circular configuration. An apertured post 82 extenc3s from the member 28 and provides means for assembling the driving means for the wires 14 to the frame 12, as will subsequently be described in greater detail.

_ g _ _ . _ .. ..... . ..

As shown in Fig. 1, a plate 84 is provided with a central aperture 86 and is secured to the flanges 78, 80 on the frame 12 by suitable fastening means 88. The circular portion o~ the frame 12 extends through the aperture 86. A
plurality of holes 90 are provided in the plate 84 for mounting a corresponding plurali~y~ nine in the illustrated embodiment, of actuating means for the wire printing elements 14.
A coil 92, a center pole 94, an "L" shaped outer pole 96 and an armature 98 form the electromagnetic actuating means used in the print head. An armature shim 100 spaces the armatures 98 away from the poles 94 for the purpose of effec-~- ting faster armature release.
A unitary connector 102 is mounted by means of a screw 104 and a washer 106 to the post 82 of the frame 12. The connector 102 has a circular centraL portion 108 with an annular groove 110 provided in its bottom surface. ~n O-ring 112 is inserted in the groove 110 to act as a shock absorber and to provide a reference surface for the cap 16 of the print wire 14 striking the end of the armature 98. Nine arms 114 are formed integral with the central portion 108 of the connector 102 and extend therefrom. Each aem 114 has associated with it a first armature receiving structure 116 and a second armature receiving structure 118. One end of each armature 98 is received and held in place by the structure 116 and the other end of each armature is received and guided by the str~lcture 118.
With the connector 102 installed in the position shown, the arms 114 apply forces to the cantilevered distal ends of the armatures, causing their print wire impacting ends to rotate about the fulcrum formed by the top edge of the pole 96 and upwardly into engagement with the O-ring 112. The caps 16 . ;.!~1,~
5~

associated with the print wires 14 are maintained in contact with the ends of the armature 98 by means of the forces applied by the springs 18.
~ s discussed in ~reater detail in the previously-cited United States Patent No. 3,929,214, the unitary connector 102 serves a number of Eunctions in the assembly and operation of the print head 10, including retaining the armatures 98 in proper relationship to the remainder of the structure, acting as a biasing means for the armatures, providing means for adjusting the air gap between the armatures 98 and corres-ponding center poles 92, formir.q a reference surface for the armatures 96 and print wire caps 16 to assure that all actuated print wires 14 impact the record medium at substantial-ly the same time during a printing cycle, and, by means of the O-ring 112, absorbing energy from the armatures 98 and the print wires 14 on return motion after actuation.
~ As is also described in greater detail in the ; previously-mentioned United States Patent No. 3,929,214, characters such as numbers, letters or symhols are generated by the print head by a sequence of print cycles. Selective actuation of predetermined combinations of print wires 14 through energization of their corresponding coils 92 during each cycle results in the formation of the desired character on the record medium, with the print head bein~ shifted one - position with respect to the record medium after each cycle to be properly located for the next printing cycle.
When a coil 92 i5 energized, a magnetic flux is created which causes armature 98 to be drawn into contact with center pole 94. The movement of armature 98 transmits energy into print wire 14, causing it to move in an axial ~ 2~

, direction in the frame 12. rrhe force imparted into the wire 14 causes it to move aqainst the spring 18 and its inertia causes it to continue to move downwardly out of contact with the armature 98 after said armature bottoms out against center pole 94. The impact clelivering end of the print wire extends beyond bearing 72 and strikes the record medium, causing a dot to be imprinted. The energy stored in the moving print wire 14 is partially absorbed by the impac~ed record medium and partially returned to the print wire 14, aiding the spring 18 in returning the print wire 14 to its rest position.
At approximately the same time that the print wire 14 is impacting the record medium, the coil 92 is de-energized.
The moment exerted on the armature 98 by the arm 114 causes it ; to rotate away from the center pole 94 and to return into contact with the O-ring 112.
~ In the past, a recurring peoblem encountered in i~ print heads of the wire matrix type has been that of print wire fatigue failures. Breakage both of print wires such as the wires 14 and springs 5uch as the springs 18 by fatigue failure has been encountered.
It is thought that several factors contribute to print wire fatigue failures, among which are the following: ~ ;
First, the quality of wire used in fabricating the print wires;
second, the number of stress cycles induced in the print wires;
and third, the magnitude of the induced stresses. Since there are economic considerations which in effect limit the quality of the wire which may be employed, means for improving conditions relating to the second and third factors mentioned above assume increasing importance.

6~L

An inherent corlsideration in the design ~f print he~ds of the wire matrix type is the relatively high length-to-diameter ratios o~ the print wires. The print wires such as the wires 14 are small in diameter in order to produce proper character line width, a typical diameter being 0.014 inches. Print wire length is relatively long (typically three inches), in order to enable the print wires to be fanned out from their tight linear pattern at the bearing 72 to the larger circular pattern required to coact with the armatures 98.
Due to the large ratio of wire length to wire diameter, and the fact that a relatively large impact force (approximately 4.5 lbs.) is required to print, the wire 14 has a tendency to buckle. A further factor increasing the tendency of the wire to buckle is the initial curvat~re of the wire through the frame of the print head which is required Eor access to the wire of the actuating means.
In order to obtain the required impact force for satisfactory printing, it is necessary to reduce the effective length-to-diameter eatio of the print wire by adding inter-mediate guide members for the print wire. This lower ratioincreases the critical buckling force, so that buckling still occurs, but only at a much higher force. Thus a relatively hlgher force may be applied to the wire, which enables the delivery of more printing force to the printing media. The lower ratio also increases the natural lateral oscillation ~` frequency of the print wire to the point at which this frequency is close to the operating frequency of the prlnting cycle. As these two frequencies approach the same point, resonance develops and the amplitude of lateral oscillation increases to the point that it creates stresses in the print . .

.

~5~16~

wire above the critical le~el for extended operation without fatiyue failures~ The higher natural Erequency also adds many fatigue cycles to the wire beyond those required in the printing cycle, consequently decreasing the fatigue life of the print wires.
By permitting the intermediate support members 30 and 50 shown in the drawings to translate laterally in all directions, these members add additional effective mass to the print wire at each gulde or support member location and consequently reduce the natural frequency of the lateral oscillations of the print wires. In the illustrated embodi-ment, the total mass of the intermediate support members is substantially in excess of the total mass of the print wires, though this factor is not, in itself, believed to be critical. It should be noted that the "effective" mass of a - support member at any given time, with respect to the print wires 14, may differ from its actual mass, since the support member may be partially supported by those wires which are not being fired at that instantr and therefore will not exert its full dampening effect upon the wires which afe ; being fired at that time.
The support members 30 and 50 are located laterally by the combined array of print wires 14 extending through the intermediate support members and by the fixed support members 26 and 28 at either ends of the frame 12, which are located close to the ends of the print wires 14. This ~ ~`
arrangement also optimi2es the lateral location of the intermediate support members 30 and 50 for best alignment of, and minimum frictio})al drag on, the print wires 14.
While the form of the invention shown and described 2S~6~

herein i5 admirably adapted to fulfill the objects primarily stated, it is to be understood that it is not .intended to confine the invention to the form or embodiment disclosed herein, for lt is susceptible of embodiment in various other forms within the scope of the appended claims.

.

. :

;' ~ .' ` ~ ` ` .

:`~, .
i . .

~!

.
' . ` ' , ~ .
' - , '

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows.

1. A printing mechanism comprising: frame means in-cluding an elongated portion of substantially rectangular cross-sectional configuration having first lateral support means at one end thereof and integral therewith, having second lateral support means at the other end thereof and integral therewith, and having a plurality of stations pro-vided with slots on the elongated portion thereof disposed intermediate of said first and second lateral support means;
printing end bearing means associated with said second lat-eral support means and having a plurality of printing element receiving apertures disposed therein; an intermediate support member of substantially rectangular configuration disposed in the slots of each of said stations, the length and depth of each intermediate support member being sufficiently less than the corresponding dimensions of the slots of the sta-tion to enable said intermediate support member to move freely in two directions within the station, and the width of each intermediate support member being only enough less than the width of the slot of the corresponding station to enable free sliding lateral movement of said support member;
a plurality of elongated printing elements extending in curved paths through and supported by apertures in said first and second lateral support means, said intermediate support members and said printing end bearing means, the apertures in said intermediate support members being of larger diameter on one surface than on the opposite surface to accommodate the curved paths of the elongated printing elements, the total mass of the elongated printing elements 1 (concluded) being less than the total mass of the intermediate support members which latter total mass is distributed in spaced-apart locations, corresponding to the locations of said stations, along the elongated printing elements; and driv-ing means positioned adjacent the first lateral support means and associated with each printing element for driving each printing element axially in a printing operation, the intermediate support members being free to slide laterally in said slots in response to lateral movement of said printing elements to dampen undesired transverse movement and vibration of said printing elements.