US3698528A

US3698528A - Compact print head assembly with antirebounding means

Info

Publication number: US3698528A
Application number: US25358A
Authority: US
Inventors: Peter H De Graff
Original assignee: NCR Corp
Current assignee: NCR Voyix Corp; National Cash Register Co
Priority date: 1970-04-03
Filing date: 1970-04-03
Publication date: 1972-10-17
Anticipated expiration: 1989-10-17
Also published as: CA920424A; GB1310851A; FR2092548A5; CH523145A; JPS5122845B1; BE765097A; DE2115956A1; ZA711841B

Abstract

A printing bar arrangement for high-speed operation wherein the bars are slidably nested and supported in relation to one another and include tip portions capable of printing alpha-numeric characters upon precise striking of one or more of the separate bars. The printing bars are fixedly connected to blocks, also slidably nested, which blocks are positioned to be driven by appropriate solenoid mechanism wherein the coupling forces derived from an offset drive line are absorbed within the blocks to provide an even and parallel operation of the printing bars.

Description

United States Patent De Graft 1 Oct. 17, 1972 [54] COMPACT PRINT HEAD ASSEMBLY 2,632,386 3/1953 l-lyland ..197/1 R X WITH ANTIREBOUNDING MEANS 2,694,362 11/1954 Paige ..197/1 R X [72] lnventor: Peter H. De Graft, Newfield, NY.

[73] Assignee: The National Cash Register Company, Dayton, Ohio [22] Filed: April 3, 1970 [211 Appl. No.: 25,358

52 US. Cl ..197/1 [51 1 Int. Cl. ..B4lj 7/70 [58] Field of Search ..197/l, 6.1

[56 References Cited UNITED STATES PATENTS 3,099,711 7/1963 Foley et al ..l9.7/l R UX 3,209,681 10/1965 Sanborn ..l01/93 C 3,386,377 6/1968 Dalton ..1 Ol/93 C 3,108,673 10/1963 Green ..197/1R Primary ExaminerRobert E. Pulfrey Assistant Examiner-R. E. Suter AttorneyLouis A. Kline, Wilbert Hawk, Jr. and George J. Muckenthaler [57] ABSTRACT A printing bar arrangement for high-speed operation wherein the bars are slidably nested and supported in relation to one another and include tip portions capable of printing alpha-numeric characters upon precise striking of one or more of the separate bars. The printing bars are fixedly connected to blocks, also slidably nested, which blocks are positioned to be driven by appropriate solenoid mechanism wherein the coupling forces derived from an offset drive line are absorbed within the blocks to provide an even and parallel operation of the printing bars.

5 Claims, 18 Drawing Figures PATENTED 17 I972 3,698 528 sum 1 (IF 6 FIG. 16 I FIG. I?

FIG. l8

INVENTOR PETER H. DEGRAFF HIS ATTORNEYS RATENIEDBBI 17 m2 SHEET 2 OF 6 HIS ATTORNEYS PATENTED 17 I973 3.698.528

sum 3 [1F 6 lNVENTOR PETER H. DEGRAFF HIS ATTORNEYS PATENTEDBN 1'! I972 F I 6. l2

SHEET 5 OF 6 U Fl 203 I60 1 [I] I6! 50 PETQQ E'T BZ GRAFF OKM HIS ATTORNEYS COMPACT PRINT HEAD ASSEMBLY WITH ANTIREBOUNDING MEANS BACKGROUND OF THE INVENTION tronic controls, becomes apparent in high-speed print- 1 ing operations. Conventionalprinters have utilized type hammers or print wheels for one-the-fly printing; however, these mechanisms have proven costly when incorporated into a small machine. It was therefore the conception of a multi-bar, direct solenoid actuated, serial type impact printer which would answer the need as stated above. Some of the specific problems which needed solutions in establishing a successful printer of this design and arrangement were the optimization of the solenoid design with respect to the geometry of the solenoid-print bar or element system, the off-center drive of the print bars, and optimization of print element mass, travel, restore means, and dynamic behavior of the entire system.

Known printing systems or arrangements have included the use of movable segments for forming the desired characters wherein selected segments are locked in extended position by individual latching levers. Other devices have been used which accomplish direct character formation by means of wires, bars, or pins which are selectively actuated to strike or bear upon the ribbon and/or the record medium.

The prior art teaches the use of a print head with selective character-forming dies, which head rotates through the various quadrants to effect the printing of alphanumeric characters. The character-forming dies are driven by solenoids engageable with pivoted arms against a spring bias to an extended, or printing, position, as shown in U.S. Pat. No. 3,209,681, issued Oct. 5, 1965, on the application of Alfred W. Sanborn.

Another example of solenoid-operated print hammers wherein the hammers are mounted in closelyspaced side-by-side relationship is shown and described in U.S. Pat. No. 3,386,377, issued June 4, 1968, on the application of John F. Dalton.

U.S. Pat. No. 3,1 12,693, issued Dec. 3, 1963, on the application of David R. Williams, teaches the use of a transducer unit for printing type elements actuated by an electrostrictive material member, and each type element comprises a raised portion or portions on its face to accommodate for printing in either seven or 14 bar arrangements. Additionally, U.S. Pat. No. 3,242,855, issued Mar. 29, 1966, on the application of Frank R. N011 and Harry B. Vollmer, shows printing apparatus including a type assembly comprising at least one electrostrictive actuating element for hurling a free-mass type head from a rest position to a printing position. Each head has a type character in the form of a bar on its face, and the heads are arranged in a manner to form the printed matter by actuation of specific heads.

Also shown in the prior art is U.S. Pat. No. 3,367,469, issued Feb. 6, 1968, on the application of George H. Fathauer, wherein a digital printer is equipped with plural similar print heads with line type elements and mechanism for selecting a particular combination of such elements to print the characters. The print head utilizes a permanent magnet, a pawland-cam arrangement, and a print solenoid. Another example of the prior art is taught in U.S. Pat. No. 3,401,781, issued Sept. 17, 1968, on the application of Everett J. West, which shows a printer employing parallel print bars each with a printing edge stacked in side-by-side relationship, support arms in a parallelogram linkage arrangement, and solenoid drivers for actuating the bar structures.

While these prior-art structures show and describe the use of solenoid-driven printing bars, it is essential that improvements be made in this day and age of higher-speed printing operations.

SUMMARY OF THE INVENTION This invention relates to direct character formation as a darkened impression on common media by electromechanical means at rates sufficiently high to accomplish serially repetitive formation of certain of such characters without the need for discrete incremental positioning of the printing device or media, and more particularly to a bar type serial printer which is direct actuated and which is compactly arranged for small business machines. The print head includes plurality of print elements or bars which are slidably nested to be supported and contained in side-by-side relationship,

. each of the bars having a tip portion for effecting the An additional set of bars is located within the print formation of at least one portion of a character, and the total of the bars being arranged to be driven for effecting all of the alphabetic and numeric symbols. The individual bars are permanently attached to block members also slidably contained and positioned to be directly actuated by solenoid type mechanism. Each bar is selectively driven by means of a solenoid through a plunger and a push rod, the push rod being in direct contact with the block member. The drive line is offset from the print bar and, by reason of the block member arrangement, is designed to provide a straight and direct impact on the print bar without twisting or other undesirable forces being introduced to the several bars.

The basic design includes the nesting of seven bars, with the tip portions being arranged to form the horizontal and vertical parts of those characters which are made up by means of two or more impressions of a printing system. Although the vertical tip portions are canted at an angle, the characters formed follow a generally vertical configuration in the printed matter. The seven bars with their tip portions are capable of forming all of the numerals and the majority of the letters of the alphabet.

Also included within an extension of the seven-bar print head assembly is another set of bars slidably nested, the bars being set at acute angles with the tip portions extending in an X formation and adaptable to be actuated to complete the letters of the alphabet.

head assembly, which bars have tip portions formed to make the punctuation marks.

The print head construction follows a parallel theme throughout, the line of drive being from the solenoid actuating means through the push rods and the bearing blocks and to the print bars. The bearing blocks contain the offsets required to direct the drive to the compact set of nested print bars.

In line with the above discussion, the principal object of the present invention is to provide a printing device utilizing print elements and actuating systems of low total mass to effect character formation and printing while the print head is traveling in uninterrupted motion.

Another object of the present invention is to provide a print-element-actuating mechanism which includes a direct line drive from the actuator to the print element.

A further object of the present invention is to provide a wholly self-contained, compact, and movable print head.

An additional object of the present invention is to provide direct actuation, within said compact, wholly self-contained, movable print head, of said printing elements, so that print element travel, from rest position to printing impact and return to rest position, is accomplished in a wholly controlled fashion without rebound upon reaching the restored position or without undesired oscillation of any sort at any point in the printing cycle.

Another object of the present invention is to provide total control of the printing elements during printing operation without inclusion of any lever, toggle, latch, cam, follower, or aggregate thereof intervening solely for the purpose of control or in combination with any other related purpose.

A further object of the present invention is to provide total control of printing element movement solely as a result of the geometric design and dynamic behavior of the design as executed within the instant invention.

And a further object of the present invention is to provide totally-controlled, non-rebounding, characterforming printing elements and actuating means therefor in a compact grouping within a wholly-selfcontained, compact, and movable print head, so that said printing elements are one equal to another with respect to the movable mass of each.

Still a further object of the present invention is to provide equal mass printing elements of such individually low total moving mass and therefore rapid mechanical response as to effect repeated character formation and printing at high rates.

Still an additional object of the present invention is to provide compact grouping of the aforedescribed printing elements such that the printed output provided by the device is competitive in size with that obtained from prior-art devices such as the typewriter; to wit, horizontal character spacing of 12 characters per inch and vertical line spacing of six to eight lines per inch.

Still another object of the present invention is to provide said wholly-self-contained, compact, and movable print head in such form as to allow simple and conventional means to be utilized for lateral movement and control of said movement of said print head to yield a complete printing machine without recourse to complex, expensive, or new associated devices, technique, or machinery.

Still a further object of the present invention is to provide said print head with self-contained print element actuating means such that the only connection to parent equipment or controlling logic is by means of small electrical wires.

And still another object of the present invention is to provide a technique by which may be obtained multiple printed bar positions within the character outline described by the seven basic print bars of the instant printing device.

And a final object of the present invention is to provide, within the concept of the instant invention, an extension thereof which, together with the basic structure, yields a printing head capable of printing all 26 alphabetical characters, 10 numeric characters, and a plurality of conventional and special symbols without sacrifice of any one or any combination of the previously or subsequently mentioned objects or advantages.

Additional advantages and features of the present invention will become apparent and fully understood from a reading of the following description taken together with the annexed drawings, in which:

FIG. 1, on the sheet with FIGS. 2, 3, 4, l6, l7, and 18, is a perspective view taken from the right front side and showing the basic compact print head;

FIG. 2, on the sheet with FIGS. 1, 3, 4, 16, 17, and 18, is a top view of the print head shown in FIG. 1;

FIG. 3, on the sheet with FIGS. 1, 2, 4, l6, l7, and 18, is a front view of the print head shown in FIG. 1;

FIG. 4, on the sheet with FIGS. 1,2, 3, 16, 17, and 18, is a right side view of the print head shown in FIG.

FIG. 5 is a rear view of the print head shown in FIG.

FIG. 6 is an enlarged view, similar to FIG. 3 but with the front plates removed, taken on the line 6-6 of FIG.

FIG. 7 is a view taken on the line 7-7 of FIG. 6;

FIG. 8 is a view taken on the line 8-8 of FIG. 6;

FIG. 9 is a view taken on the line 99 of FIG. 8;

FIG. 10 is a view taken on the line l010 of FIG. 8;

FIG. 11 is a top view ofa modification which is an extension of the concept shown in FIG. 2;

FIG. 12 is a front view of the modification shown in FIG. 11;

FIG. 13 is a rear view of the modification shown in FIGS. 11 and 12;

FIG. 14 is a sectional view through the print head portion of the modification and taken on the line 14- 14 of FIG. 15;

FIG. 15 is a view taken on the line 15-15 ofFIG. 12;

FIG. 16, on the sheet with FIGS. 1, 2, 3, 4, l7, and

18, is a line representation of an alpha character and a numeric character for one condition of head operation;

FIG. 17, on the sheet with FIGS. 1, 2, 3, 4, l6, and 18, is a representation similar to FIG. 16 for another condition of operation; and

FIG. 18 is a representation for a further condition of operation.

Referring to FIG. 1, there is shown a compact print head assembly which includes print elements and actuators or drivers for the print elements, all contained or packaged in a cluster-like manner. The print head assembly will be described as applicable for a back printer as seen by the machine operator; however, other printing positions, such as front or top, may be both desirable and efficient. Wires or leads connect the actuators to appropriate control systems (not shown). The assembly shown in FIG. 1 contains a seven-bar print head wherein the bars include tip portions of both horizontal and vertical nature for forming desired characters on paper or like media.

the printing The print head assembly, as shown in the perspective view of FIG. 1 and the top, side, and front views of FIG. 2, 3, and 4, respectively, has a generally rectangular housing made up of a front or face plate member 12,

side plates

14 and 16, top and

bottom plates

18 and 20, and a rear plate 22. These members are secured together to form a box-like housing by means of screws 24 and interlocks 26 suitably arranged and positioned to maintain a tight and secure enclosure for the movable internal parts. The housing rear plate 22 also serves as an anchor or attachment plate for several of the actuators or drivers, which in the instant invention are electromagnetic solenoids.

ln a seven-bar print head configuration, there are seven solenoid assemblies, four of these being positioned forwardly and three rearwardly. The four forward solenoid assemblies, 30, 32, 34, and 36, actuate or drive what will be referred to as the two, three, five, and six or vertical bars, the solenoids also being shown as positioned in FIGS. 7 and 8. The three rear solenoid assemblies, 38, 40, and 42, actuate or drive the one, four, and seven or horizontal bars, which solenoid assemblies are vertically aligned in a central position in the assembly (see FIGS. 4 and 5). In this respect, the solenoid assembly 30 actuates or drives the two bar 44 (see FIGS. 9 and 10), the solenoid assembly 32 actuates the three bar 46, the solenoid assembly 34 actuates the five bar 48, and the solenoid assembly 36 actuates the six bar 50. Likewise, the solenoid assembly 38 actuates or drives the one" bar 52, the solenoid assembly 40 actuates the four bar 54, and the solenoid assembly 42 actuates the seven or center bar 56.

Referring back to FIGS. 3 and 4, the print bars are seen as protruding through the face of the print head, there being the center bar 56 surrounded by the six circumventing

bars

52, 44, 46, 54, 48, and 50. The seven bars are nested or clustered together in a manner which provides support and control of any one or more of the bars as they are moved to and fro in a printing operation. The print bars or elements 52, etc., are made of a high-density hardened powdered metal and are ultrasonically affixed to their respective plastic supports or bearing blocks. Proceeding from the housing 10, the rear housing plate 22 also serves as an anchor or mounting plate for one end of the forwardly-positioned

solenoid assemblies

30, 32, 34, and 36,there being a centrally-located mounting plate 60 for supporting the forward end of the rearwardly-positioned

solenoid assemblies

38, 40, and 42. Boards 62 and.64 are printed circuit boards of common art type which serve to anchor external connecting wires and to carry electrical connections to the aforementioned solenoid assemblies. The use of screws, spacers, and tapped studs for securing the parts completes a compact assembly for the print elements and solenoids.

Six bearing blocks 70, 71, 72, 73, 74, and 75 (FIG. 6) are slidably contained within the housing or guide box structure 10 with protrusions of the print bars, which print bars are rigidly affixed each to a bearing block, and extending through an appropriately-shaped aperture 76 (FIG. 8) in the front plate 12. Each bearing block/print bar assembly is yieldingly urged to the right (FIGS. 7 and 8) to a rest, or non-printing, position in the proximity of the rear plate 22 of the print head housing, which also serves as the front solenoid mounting plate, by the expansive tendency of an associated restore spring 77 seated against the front plate 12 through appropriate apertures in a spring template 66.

As in FIGS. 6 and 8, a print bar system may be seen as composed of a print bar 52, a bearing block, as 70, rigidly affixed to the print bar, a push rod 78, a solenoid armature or plunger, such as 79, and the restore spring 77, all slidably contained within their surrounding elements; to wit, respectively, the front plate 12, the guide box structure or housing 10 and the five bearing blocks 71, 72, 73, 74, and 75, the front solenoid mounting plate 22, the rear solenoid mounting plate 60, a push rod cover 58, and a solenoid coil form 68.

One print bar structure varies from the above-taught structure, and that is the center horizontal print bar system. The center horizontal print bar system may be seen as composed of the center horizontal print bar 56, a restore spring retaining washer or stop 85, a washer 83, a push rod 86 rigidly affixed to said center horizontal print bar, the rod being directed through a collar or push rod guide 81, a solenoid armature 88, and a restore spring 89, all slidably contained within their surrounding elements; to wit, respectively, six surrounding print' bars, which print bars in turn are slidably contained within the front plate, and other elements as mentioned above, the front solenoid mounting plate, the center bar solenoid housing, and a center bar solenoid coil form, which form slidably contains the core of the armature.

As between the front solenoid mounting plate 22 and the rear solenoid mounting plate 60, the front solenoid mounting plate is utilized to act as the locator and holder of the housings or cans for the

solenoid assemblies

30, 32, 34, and 36, of which solenoid housings such as 59in FIGS. 7 and 8 each serve as containers for and as part of the magnetic circuit of one each solenoid coil form and coil assembly, and the non-magnetic cap therefore serves as a dust cover and adjusting screw holder, each such solenoid coil form and coil assembly being so arranged by and retained in position by the aforementioned respective solenoid housing, cap, and front solenoid mounting plate as to cooperate with and serve to motivate one print bar system of the four vertical print bars of the seven-print-bar matrix against the counteracting expansive tendency of each respective restore spring. The rear solenoid mounting plate 60 is utilized to act as the locator and holder of the housings for the three

solenoid assemblies

38, 40, and 42, each such steel solenoid housing or can, as 59, serving as a container for and as part of the magnetic circuit of each solenoid coil form and coil assembly, the solenoid coil form and coil assemblies being arranged and retained by the aforementioned respective solenoid housings and caps and rear solenoid mounting plate in such manner as to cooperate with and serve to motivate one print bar system of the three horizontal print bars of the seven-print-bar matrix, which three horizontal print bars include the aforementioned center horizontal print bar acting against the counteracting expansive tendency of each respective restore spring. The coil forms are made of non-magnetic stainless steel for maximum bore life, and a graphite-molybdenum coating is applied to the solenoid plungers and push rods for protection and ease of operation. The push rods are made of non-magnetic stainless steel, although other materials, such as ceramic, have been considered.

A single print bar system so described as slidably contained with one degree of freedom in the fore-andaft sense may be seen to be urgeable leftwardly, as seen in FIGS. 7 and 8, against the expansive tendency of a respective restore spring 77, when so urged by the electrical energization of a related solenoid coil. As so taught is the operation of each and all of the seven noted print element systems, each such print element system being totally independent in a slidable sense and in an operable sense from each and every other such print element system. By means of the electrical energization of a given solenoid winding, its respective print element system is caused to move as allowed in a slidable sense and, at the end of said slidable movement, which end of movement is determined by a fixed backing surface 97 (FIG. 4), to impinge upon inked ribbon, paper, and platen elements common to prior printing art such as the typewriter, or to impinge upon equivalent media and backing or like materials as might be appropriate to a particular application of the device of the instant invention so as to derive a printed output.

In allowing for additional printing elements or bars, as such additional printing elements or bars will be discussed later, there may be mounted on either or both the front solenoid mounting plate 22 and the rear solenoid mounting plate 60 additional solenoid housings and caps and solenoid coil form and coil assemblies, which assemblies and housings may be arranged and retained by said front solenoid mounting plate and/or said rear solenoid mounting plate to cooperate with and motivate, in the manner described, said additional printing elements or bars as might be provided to operate in a cooperative fashion with the basic sevenbar matrix of the discussion above in a manner to yield additional printing repertoire to that available from said basic seven-bar matrix and in addition to those available added print bar printing positions of the basic seven-bar matrix to be discussed later.

Referring to FIG. 8, there is shown a print element system, specifically the print element system associated with the upper horizontal print bar of the seven-bar matrix, which print element system as illustrated is operationally identical in every sense to the remaining five print element systems which surround the aforementioned center horizontal print element system. To reiterate the components of a print bar system as said components are displayed by FIG. 8: a print bar 52 extending with a leftward protrusion through an appropriate aperture 76 in the front plate 12, a bearing block 70 rigidly affixed to the print bar, a push rod 78, a solenoid armature 79, and a restore spring 77. Said components of the example print element system may be seen to be contained with single degree slidable freedom, as are all other print element systems within the device of the instant invention, within, respectively, the front plate 12, the guide box structure as represented by the upper plate 18 of the guide box structure or housing, the front solenoid mounting plate 22, the solenoid assembly 38, and the solenoid coil form 68. Slidable freedom of the subject components of the print element system portrayed in FIG. 8 is illustrated by the dotted outline of the print bar 52 and a portion of the bearing block 70 represented by said dotted outline to be in the excursion or media impingement position, displaced leftwardly, as in FIG. .8, from the rest, or restored, position of the same elements portrayed by the solid outline thereof. The movement of the solenoid armatures represented by 79, 80, and 88, which are the actuators of the

bars

52, 54, and 56, respectively, is shown in dotted lines at the printing position, it being understood that the additional parts in the drive line are likewise displaced leftwardly.

The bearing block arrangement, shown in FIG. 6 with the front plate 12 and the spring template 66 removed, is that of a slidable nesting of the blocks which securely retain and guide the printing bars in a parallel manner during the printing operation. The push rods have an expanded tip portion 92 bearing upon an insert 93, which is made a permanent part of each block, so as to provide a durable point of contact for the push rod.

FIGS. 9 and 10 show the construction of the print head along sectional planes to define the limits and the configuration of the print bars in relation to the bearing blocks, and of the push rods and solenoids in relation to each other. Beginning with the solenoid assembly 30 (FIG. 10), which has a plunger and a coil form 120, and continuing clockwise, the solenoid assembly 32 has a plunger 111 and a coil form 121; the solenoid assembly 40 has a push rod and a coil form the

solenoid assemblies

34 and 36 have

armature plungers

112 and 113 and

coil forms

122 and 123; and the solenoid assembly 38 has a push rod 78 and a coil form 124, these parts surrounding the centrally located print bar assembly push rod 86. The

plungers

110, 111, 112, and 113 have

push rods

132, 133, 134, and (FIG. 7) striking against the inserts 93 in their respective bearing blocks. Adjusting screws to 146 inclusive are inserted in the one end of the respective solenoid caps for equalizing the extent of travel of the armatures, the push rods, and the print bars, so that the tip portions of the bars strike the paper or other recording medium with the same force for imprinting at equal density. The throw of the armature, as seen by the positions of the solid lines and the dotted lines thereof and also the tip portions of the print bars, can be varied from 0.020 inch to 0.080 inch to accommodate the desired operating characteristics by appropriate adjustment of said adjusting screws.

The printed character, as effected by the impingement of the tip portions of the print bars against the record material 95, is 0.058 inch wide and 0.098 inch high to obtain 12 characters per inch. A modification in the size of the print bars, when it is desired to print ten characters to the inch, is effected with a character 0.070 inch wide and 0.125 inch high. It is also possible to vary the printing rate by regulating the print head sweep rate across the space allowed for printing, the sweep rate being controlled by suitable means and responsive to the conditions as to whether the tencharacter spacing or the l2-character spacing is selected.

A modification or extension of the seven-bar construction is shown in FIGS. 11 to 15 inclusive, wherein additional print bars and solenoids are incorporated into a compact print head assembly capable of printing the balance of the alpha characters and also the punctuation symbols, which cannot otherwise be derived

side plates

152 and 153, a top guide block 154, and a bottom guide block 155 (FIG. 15). A rear plate 156 serves as an enclosing side of the print bar portion and also serves'as a supporting member or anchor for the majority of the solenoids or those nearest the print bar section of the assembly. These plates are secured together to form the housing, the securing being accomplished by means of screws and interlocking lip portions suitably arranged and positioned to maintain a tight and secure enclosure for the internal moving parts.

Since the seven-bar components are a part of the extended assembly and have been described heretofore, only the additional structure will be discussed in regard to the various figures, the previously-described parts being mentioned in relation to the modified structure as is deemed necessary.

Adjacent the seven-bar configuration in the print head housing 150 is the punctuation mechanism, comprising print elements or

bars

160, 161, and 162 (see FIG. 14), the

bars

160 and 162 being secured to bearing

blocks

163 and 164 and the bar 161 being slidably contained along a central axis between the bars 160 and 162 (see FIG. 15). In this respect, the punctuation bars are seated and contained within the print head in similar fashion as the

bars

52, 54, and 56 in the sevenbar configuration. The actuating devices for the

bars

160, 161, and 162 are the

electromagnetic solenoid assemblies

168, 169, and 170 (FIG. 13), the

solenoid assemblies

168 and 170 each being positioned along a plane spaced from and parallel with the central bar 161 and offset from their

respective bars

160 and 162, and the solenoid assembly 169 being axially located with respect to the print bar 161. Except for details of construction of the print bars, the punctuation portion of the print head-is substantially the same as that of the three-in-line design of the seven-bar assembly, in that the drive line from the solenoids includes a solenoid plunger, and a push rod engaging each of the bearing blocks 163 and 164 and biasly held by

springs

175 and 176.

The center print bar 161 (FIG. 15) is driven by means of a solenoid plunger 177 and a push rod 178 restrained in one direction by means of the spring 179 pressing against a stop or washer 180 on the solenoid side and against a detent sleeve 181 on the print bar side, which, in turn, engages a push rod guide 182.

Adjacent the punctuation portion of the print head in the housing 150 is a four-bar portion of the print head assembly carrying inclined tips for forming portions of characters which require these inclined marks in the printing of the characters. The four print bars are shown in a frontal view in FIG. 12 as 200, 201, 202, and 203, and in a sectional view in FIG. 14, the bars being permanently secured to the bearing blocks 205, 206, 207, and 208, respectively, all slidably contained and nested in similar fashion as the previously-described blocks. The upper guide block 154 and the lower guide block 155 extend from one side plate 152 to the other side plate 153 just forward of the rear plate 156, the block guides serving to maintain the bearing blocks in .19 parallel relationship in their to-and-fro travel. An apertured spring plate 212 is positioned adjacent the front or face plate 151, the plate 212 acting as a locating template for the several springs which are substantially aligned with the solenoid drive push rods, the springs being placed in the plate 212 in similar manner as shown in FIGS. 7 and 8 for the seven-bar assembly. The

four springs are urged toward the left, or front, of the ing screw for each of the solenoids is inserted into the end thereof to regulate the throw of the plunger, as above described. Appropriate wires or leads are connected to the solenoid coils, as shown in FIGS. 5 and.

13. As in the case of the slanted design carried out in the seven-bar system, the punctuation marks are set at compatible with the seven-bar imprint.

Four distinct phases may be seen to occur during the operation of the subject print element system, or any other print element system within the scope of the present invention, which four phases are:

Phase 1. The acceleration and movement of th movable elements of the subject print element system leftwardly, as seen in FIG. 8, which movable elements are the print bar 52 and the bearing block rigidly fixed thereto, the push rod 78, and the solenoid armature 79, from the rest, or restored, position, as said acceleration and movement are caused by electrical energization of the appropriate solenoid coil 67 to cause an attractive force in the electromagnetic sense between the solenoid armature 79 and the solenoid housing 59 primarily but not solely at the air gap therebetween in such manner and intensity as to overcome the rightwardly-acting, as in FIG. 8, expansive tendency of the restore spring 77. Said electrical energization of the appropriate solenoid coil 67 is applied and maintained throughout the duration of acceleration and movement of the subject print element system and is terminated only at the point of said movement whereat Phase 1 ends and the following-described Phase 2 begins.

Phase 2. The portion of the impingement event of the print bar 52 (specifically, of the left tip of said print bar as illustrated in FIG. 8), against the fixed assemblage of paper 95, ribbon 96, and platen 97 (see FIG. 4) as beginning with first contact therebetween and ending with the complete stoppage of motion of the aforementioned movable elements of the print element system.

Phase 3. Acceleration and movement in the restore sense, or rightward direction, as in FIG. 8, of the movable elements as said acceleration and movement are caused by the expansive tendency of the restore spring 77 and, for the duration of contact of the print bar 52 with the assemblage of paper, ribbon, and platen, the restitutional force exerted on the print bar 52 and thereby on all of the movable element of the print element system as that restitutional force may be seen to arise in chorus from the elastic properties of each and all the paper, ribbon, and platen in reaction to and as a consequence of the impingement described in Phase 2 above, said restitutional force acting in cooperation with the aforementioned expansive tendency of the restore spring 77 to overcome the residual electromagnetic forces, if any, of the now-de-energized solenoid coil 67 and cooperating electromagnetic elements including the solenoid armature 79 and the solenoid housing 59. The acceleration and movement in this Phase 3 continue to the point of travel whereat the right end of the solenoid armature 79, as seen in FIG. 8, begins contact with the fixed restore pad or adjusting screw 144.

Phase 4. From the point of travel of the abovedescribed movable elements marking the end of Phase 3 above,- to the point of the cycle at which the kinetic energy of the movable elements has been expended, which kinetic energy accrued thereby during the actions of acceleration and movement noted in Phase 3 above, the expenditure of said accrued kinetic energy occurs as will be described below.

From the phases of operation of a print element system as above taught, the following true actions, interactions, and results may be seen to occur:

a. That energization by proper electrical impulse of the solenoid coil 67 causes the three basic movable elements of the related print element system the armature, the push rod, and the bearing block/print bar unit to accelerate and move toward printing impact and to accomplish printing impact and that the acceleration and movement is of a relatively gentle magnitude and that the only significant force acting in opposition to this acceleration and movement is the force arising from the restore spring 77.

b. That the opposing restore spring force acts along an axis coincident with the line of action of the electromagnetically-generated force developed at and imparted by the solenoid armature 79 and transmitted to the bearing block 79/print bar 52 assembly by the push rod 78.

c. That the axially coincident forces as described produce little or no net torque on the bearing block/print bar assembly, which torque, if present, would be a root cause of undesirable frictional forces as between the bearing block/print bar assembly and the elements of containment thereof. V

d. That the acceleration and motion of a print element system thereby obtained and constrained will proceed without significant impediment to the point of impact.

e. That the effect of the motivating electromagnetic force acting at one end of the assemblage of the constituents of a print element system, and the effect of the opposing restore spring force acting at the other end of the assemblage, is to prevent separation therebetween or any independent movement of any individual constituent of the assemblage, so that the constituents of the assemblage accelerate and move in unison to and through the printing impact.

f. That the print element system constituents act in chorus during the printing impact to deliver the accrued kinetic energy of all three constituents (the solenoid armature, the push rod, and the bearing block/print bar assembly) toward accomplishment of the printing operation.

g. That the energy of printing is the combined energy of all moving parts within the device of the instant invention in combination with the motive force simultaneously provided by the respective actuating solenoid, which motive force may be seen to be produced at a position of the solenoid armature with respect to the remaining solenoid elements whereat the aforementioned air gap is of minimum dimensional value and therefore provide this motivating and print contributory force at a maximum intensity as derived in the known electromagnetic sense in common solenoid art. Although the electrical energization of the motivating coil is stopped at the precise end of Phase 1, the aforementioned minimum air gap and the residual electromagnetic forces still present through the brief duration of Phase 2 act in chorus to contribute a significant energy to the printing event.

h. That the result of the primary beginning event of Phase 3 (namely, the restore force contributed as taught by the restitutional forces of the paper, the ribbon, and the platen) acts to overcome the residual impinging forces caused by the known inductive residual action of the solenoid coil and its companion electromagnetic components (namely, the solenoid housing and the solenoid armature), which residual forces tend to be present to a rapidly declining degree after energization of the motivating solenoid coil has ceased, as such cessation occur at the beginning of Phase 2.

i. That the restore spring force carries on, after demise of these restitutional forces and said residual forces, to accelerate said movable constituents of the print element system toward the restored position.

j. That the acceleration as caused by the restore spring acts at a point in the print element system in opposition to the inertial forces of each and all the constituents as produced by said acceleration, so that the constituents again move in unison with no separation therebetween and with no independent movement of any constituent or group of constituents with respect to other constituents of the same subject print element system.

k. That the acceleration of phase 3 is of a relatively gentle magnitude and that no significant torque or frictional forces produced by such torque act upon any given constituent or on the print element system as a result of inertial forces arising therefrom.

1. That the deceleration of the moving constituent of the print element system, upon commencement of Phase 4, is abrupt and is of a relatively large magnitude due to the relative solidity and hardness of the fixed restore pad or adjusting screw.

m. That, due to the abrupt change of velocity of the moving print element system upon reaching the restored position, the inertial forces which result are relatively large.

ii. That the inertial force of the bearing block/print bar assembly operates in the direction of travel of said assembly through the center of gravity thereof.

0. That the line of action of the inertial force of the bearing block/print bar assembly and the line of action of the force which is acting to decelerate the assembly are displaced one from the other as shown in FIG. 8, showing the elements in the printing position and in the restored position, with arrows representing the subject force vectors added to the picture, so as to show an appreciable net torque T on the assembly.

p. That the appreciable net torque acts to rotate the assembly counter-clockwise, as seen in FIG. 8, and thereby to develop appreciable pressures of contact between the assembly and the surrounding elements of containment therefor.

q. That these pressures of contact in turn result in appreciable frictional forces, which forces serve directly and automatically and without additional apparatus of any sort or type to restrain all of the previously moving constituents of the print element system from any leftward motion, as in FIGS. 7 and 8, as any leftward motion, if existing, would serve to increase the tendency of counter-clockwise rotation.

r. That any motion in a leftward sense, as in FIGS. 7 and 8, while kinetic energy from the restore motion remained in the subject print element system, would be undesirable in that it would result in an unknown and uncontrollable position for the system until such time as the motion had settled out in oscillatory bounces, as are common in and a problem to prior-art devices.

s. That the snubbing of the print element system derived and accomplished as taught is highly desirable.

t. That the duration of Phase 4 comprises less than percent of the total print cycle.

It is here noted that the above-taught dynamic effect of an offset center of gravity utilized for snubbing action in cooperation with and only with inrline actuating forces is best seen in FIGS. 7 and 8, where the forces are shown acting in relation to the center of gravity.

Of the basic seven print element systems within the seven bar printing matrix of the instant device, one only remains without benefit of an offset center of gravity in the sense of the above-taught benefits of dynamic snubbing action, this one being the center horizontal print element system. It should be noted that the actuation of any one or any combination of the remaining and surrounding six print element systems in unison with the center system, as such actuation occurs in every printing instance except for the printing of a central dash or minus sign, produces the same dynamic snubbing action and consequent total lack of rebound from rest or restored position for the center horizontal print element system. The dynamic snubbing of the center system results from the use of the surrounding print bars, as contained by the aperture of the front plate, as contacting and supporting elements for the center print bar. This contact by another print bar is intensified in pressure during the dynamic snubbing (Phase 4) of the surrounding print bar, which pressure and resultant friction act directly to snub any rebounding tendency of the subject center print bar.

A summary of the respective minimum time durations of the phases of operation of the subject print element system or of any print element system within the device of the instant invention is as follows:

Phase 1: 1,200 microseconds Phase 2: 150 microseconds Phase 3: 1,600 microseconds Phase 4: 80 microseconds The above time durations prevail when the device of the instant invention has been adjusted to function at a maximum printing rate under Printing Condition A as outlined below.

Although the maximum printing rate is not normally applied or desired under generally continuous printing operation of a business machine, there are a number of variables which determine the maximum operating rate in the instant invention. The first of these is the accelerating distance or the distance from rest position to impact position of one or more of the print bars. Since the printing rate is substantially in inverse proportion to the accelerating distance, a selected distance of 0.030 inch would produce, say, 150 characters per second, whereas a greater distance, of 0.060 inch, would print characters per second. The minimum accelerating distance at which the maximum printing rate is achieved is 0.020 inch, and the maximum accelerating distance of 0.080 inch would produce a reduced printing rate.

Another of these variables is the rise in temperature which normally accompanies high-speed operation of moving parts, so that the design of a system must include parameters which alleviate heating problems. Heat dissipation is best accomplished in the compact print head assembly by the semi-open construction of the solenoid section and by use of the bearing block configuration and material.

A third variable which affects the maximum printing rate is the duty cycle, which is the ratio of the working time to the total time of one imprint. In the preferred embodiment, the print head is at rest approximately 40 percent of the time, this being the head restore time between print sweeps, so that the printing time is approximately 60 percent of the print cycle.

Adjustments may be made upon the device, or printing conditions may be imposed upon it, to produce a printing rate capability of less than the maximum number of characters per second. If these adjustments are imposed to reduce the printing rate to a rate less than the maximum practical rate, then the aforestated time durations of

Phases

1, 2, and 3 shall increase in inverse proportion to the amount of decrease from the maximum number of printed characters per second, whereas and wherewith the time duration of Phase 4 shallincrease to a lesser degree.

An additional variable is the amount of driving vo1tage which affects the duration of solenoid energizing pulse needed for good print density. Within recognized limits, a higher driving voltage allows a shorter solenoid energizing pulse and a higher printing rate.

In regard to the maximum printing rate, the following three conditions may be considered.

PRINTING CONDITION A Printing condition A consists of the printing of immediately adjacent repetitive characters of any of the repertoire A, C, E, F, G, H, J, L, O, P, S, U, 2, 3, 4, 5, 6, 7, 8, and 9 and similar characters, none of which contain laterally centered vertical elements.

As shown in FIG. 16, the letter L and the FIG. 8 are imprinted by firing the appropriate print bars, the characters being spaced at 0.0833 inch with a width of 0.058 inch to provide 12 characters per inch. The FIG. 8 utilizes all bars of the seven-bar print head assembly (FIG. 3), the bars being numbered in accordance with the prior described vertical and horizontal arrangement of the bars and their respective solenoid drivers. In this respect, the four, five, and six bars are tired to form the letter L. So long as any of the above characters are being printed, the head assembly moves at a constant rate in its printing condition travel across the machine, and, by reason of this constant rate of travel, the maximum printing rate is obtained in line with the variables imposed as described above.

This condition consists of the printing of immediately adjacent characters, which include all of those noted under Condition A, above, and additionally the characters B, D, I, T, Y, and l and similar characters, which characters contain vertically centered printed elements in absence of left printed elements and which centered printed elements are obtained by the means of delayed actuation of said left elements so as to cause printing impact thereof at the later time of character printing as when the print head device has moved translationally to the right as from when other, if present, elements of the character were printed, assuming a rightward motion of said print head device during the formation of the printed line and with respect to the finished printing.

This condition is shown in FIG. 17, wherein the one and four bars are fired in regular timed sequence and the firing of the five and six bars is delayed to form the letter I. It is understood, of course, that the delayed firing or offset in the printing position requires the print head assembly to make an additional mark during its travel, so that the printing rate is thereby reduced. The FIG. 6 is shown to include a character as printed under Condition A. The character spacing is the same as above, but the vertical portion of the letter I is at 0.054 inch from the left side of the FIG. 6.

PRINTING CONDITION C This condition includes the printing of characters which include all of those noted under Conditions A and B, above, and additionally the characters M, Q, R, W, and and similar characters, which characters contain centered printed bar elements in conjunction with left printed bar elements, which condition implies repeated laydown within the same character space of the left print elements first in the normal printing position as in the character S followed immediately as said in the centered printing position as in the character 8.

Another example of characters printed under this condition is shown in FIG. 18, wherein the letter R and the military zero are spaced as above, but the vertical or center bars are at 0.029 inch from the left side of the character. The repeated delay in firing of the print bars to form these characters requires additional time, and the printing rate is thereby further reduced.

Printed bar positions as described above are illustrated in FIG. 16 for Condition A, in FIG. 17 for Condition B, and in FIG. 18 for Condition C. In each figure, the spacing is shown for the characters printed by a preferred embodiment of the instant invention, wherewith said characters are in a nominal and normal to the art spacing of 12 characters per inch and where thus the nominal center-to-center character spacing is 0.0833 inch and the nominal printed character width is 0.058 inch, half character width being 0.029 inch, which dimension applies to the centered printed bar position.

Now applying the minimum print element cycle time, which minimum cycle time is the sum of the duration of Phases 1 through 4 above and which sum is 3,030 microseconds, the imposed maximum printing rates for said preferred embodiment of the instant invention may be derived as follows.

Under stated Printing Condition A, the minimum space between printed impressions made by any given bar is 0.0833 inch, and the minimum print element cycle time as composed of Phases 1 through 4 determines a maximum lateral translational velocity for the print head of:

0.0833 inch/0.00303 second 27.5 inches per second.

Thus a print head representing a preferred embodiment of the instant invention, when applied to the printing task with a lateral velocity of 27.5 inches per second while printing, accomplishes printing laydown of any of the characters noted as applicable to Condition A, above, at a maximum rate of 27.5 X 12/10 characters per second, or 330 characters per second.

By similar argument, the maximum printing rate imposed by condition B, with reference to FIG. 17, is:

0.054/0.00303 X 12/10 214 characters per second.

Again, and by similar argument, the maximum print rate imposed by Condition C, with reference to FIG. 18, is:

0.029/0.00303 X 12/10 l 15 characters per second.

This is the actual printing performance of a preferred I embodiment of the instant invention, which embodiment is capable of a printing repertoire which includes the alphabetic characters A, B, C, D, E, F, G, H, I, J, L, M, O, P, Q, R, S, T, U, W, and Y, the numeric characters l, 2, 3, 4, 5, 6, 7, 8, 9, and 0, and at least 20 additional symbols all derived from seven only printing elements, which elements by their preferred arrangement are able to form, at a maximum printing rate, 12 alphabetic characters and all numbers except a centered numeral 1, and additionally, by means of timing control and without movement of the printing head of any sort other than lateral, nine additional alphabetic characters and a large variety of special symbols. The basic seven-bar printer accommodates 21 letters and all numbers, so that five letters, K, N, V, X, and Z, remain to be covered by the extension or X arrangement of the print bars 200, 201, 202, and 203. Of these five letters, K, N, V, and Z are formed with a combination of one or more bars of the seven bars and the fourbar extension thereof, so that the delayed or offset aspect of the print head is important in the printing cycle. The seven-bar head and the extension or X" bar provide a completed assembly printing device by using the eleven bars for forming letters and numerals as stated above. Although it is possible to omit either the punctuation bars or the X bars for limited applications, the head can be a simple seven-bar structure, it can be modified as an ll-bar device, or it becomes a complete assembly with the punctuation bars. It is notable that the complete eleven-bar print head can produce a full alphanumeric repertoire within the constraints of Printing Condition B and without recourse to the constraints of the slower Condition C.

It is thus seen that herein shown and described is a high-speed print head assembly having side-by-side matrices for printing alphanumeric characters wherein each and all of the print element systems, comprising a print bar and drive means therefor, are totally independent in a slidable manner and in an operable sense from each and every other such print element system, and which assembly or mechanism accomplishes all the features and advantages mentioned above. While only one basic embodiment has been disclosed for the printing of alphanumeric characters, certain variations on the above may occur to those skilled in the art, so it is contemplated that all such variations having these features are within the scope of the invention.

What is claimed is: l. A compact print head assembly comprising a plurality of block members juxtaposed and individually slidable and bearing on adjacent members in parallel manner with respect to each other, a plurality of nested printing elements each secured to a respective block member and slidable parallel therewith from a non-printing position to a printing position and returnable to the non-printing position, each, block member and its respective printing element forming a member-element assembly, solenoid means for selectively actuating each member-element assembly from the non-printing position to the printing position in a line parallel with the path of movement of the printing elements, a centrally-positioned printing element surrounded by and in contact with adjacent printing elements, means for actuating said centrally-positioned printing element wherein said means for actuating said centrally-positioned element is aligned with said centrally-positioned element, and spring means aligned with the path of movement of the solenoid actuating means for retaining the members and elements in a non-printing position and for restoring the members and elements from the printing position to the non-printing position after actuation thereof, the center of gravity of each member-element assembly being offset from the path of movement of its actuating means and its retaining and restoring means, each of the member-element assemblies being in contact with adjacent member-element assemblies to effectively prevent rebounding of the assemblies from the non-printing position toward the printing position. 2. A compact print head assembly for a serial type printer, comprising a housing, a plurality of block members nested in said housing and adapted to be selectively slidable a predetermined distance, a plurality of printing bars, each of said bars being secured to a respective block member and each of the printing bars having a tip portion arranged in a manner to form a printed character upon themovement of two or more bars along a predetermined path from a non-printing position to a printing position, said bars being in contact with adjacent bars along said path,

means within the housing and engaging the block members for retaining the printing bars in a nonprinting position and for restoring said bars from a printing position to a non-printing position,

means for selectively actuating the printing bars from a non-printing position to a printing position, said actuating means including solenoid elements movable to provide a line of drive aligned with said retaining and restoring means and offset therefrom and parallel to the path of movement of the printing bars, said block members bearing on adjacent members to absorb unbalanced forces by reason of the offset in the drive line from the actuating elements to the printing bars, and a central printing bar surrounded by said plurality of printing bars, and

central printing bar actuating and restoring means in line with said central printing bar.

3. Printing apparatus comprising a housing, a

plurality of bearing blocks each individually slidably contained within the housing and supported by adjacent blocks for parallel operation thereof, a

plurality of print bars secured to respective bearing blocks, the bars occupying a centralized area in nested relationship therein and slidably contacting adjacent bars for parallel operation thereof, and said bars having tip portions extending through the housing and adaptable to be moved in a path from a non-printing position to a printing position,

resilient means for retaining the bearing blocks and the print bars in a non-printing position and for restoring the bearing blocks and the print bars from a printing position to a non-printing position, and

means for selectively driving the print bars from a non-printing position to a printing position, said driving means being on a plane aligned with the resilient means and driving along a line of drive offset from and parallel with the path of movement of the print bars.

4. A compact print head assembly for making impressions and forming characters of the alpha-numeric system, comprising a housing, a

plurality of generally rectangular bearing blocks contained therein and slidably contacting adjacent blocks for parallel operation and individually slidable a predetermined distance, a

plurality of print bars each print bar being secured to a bearing block adjacent one side and having a tip portion extending through the housing, said print bars being carried in contacting relationship by said bearing blocks and adapted to be individually slidable the predetermined distance from a nonprinting position to a printing position,

resilient members in said housing for urging the be aring blocks and the print bars to the non-printing position, said resilient members contacting said bearing blocks at a point adjacent a side opposite to the side to which the print bars are secured, and a plurality of solenoids supported from the housing and having drive means connected with the bearing blocks and aligned with said resilient members for driving the print bars in selective manner from the non-printing position to the printing position.

5. A print head assembly comprising a housing, a

plurality of bearing blocks slidably contained and nested within the housing and slidably contacting adjacent blocks for parallel operation thereof, a

plurality of print bars sEhEd to the bearing blocks,

the print bars being secured adjacent one side of each bearing block and being nested together and selectively movable along a path from a non-printing position to a printing position and each of said print bars having a tip portion for impressing a mark in the printing position,

spring means within the housing and engaging the bearing blocks adjacent a side opposite the side to which the print bar is secured for retaining the print bars in the non-printing position, and

solenoid means aligned with the spring mean for

Claims

1. A compact print head assembly comprising a plurality of block members juxtaposed and individually slidable and bearing on adjacent members in parallel maNner with respect to each other, a plurality of nested printing elements each secured to a respective block member and slidable parallel therewith from a non-printing position to a printing position and returnable to the non-printing position, each block member and its respective printing element forming a member-element assembly, solenoid means for selectively actuating each member-element assembly from the non-printing position to the printing position in a line parallel with the path of movement of the printing elements, a centrally-positioned printing element surrounded by and in contact with adjacent printing elements, means for actuating said centrally-positioned printing element wherein said means for actuating said centrally-positioned element is aligned with said centrally-positioned element, and spring means aligned with the path of movement of the solenoid actuating means for retaining the members and elements in a non-printing position and for restoring the members and elements from the printing position to the non-printing position after actuation thereof, the center of gravity of each member-element assembly being offset from the path of movement of its actuating means and its retaining and restoring means, each of the member-element assemblies being in contact with adjacent member-element assemblies to effectively prevent rebounding of the assemblies from the non-printing position toward the printing position.

2. A compact print head assembly for a serial type printer, comprising a housing, a plurality of block members nested in said housing and adapted to be selectively slidable a predetermined distance, a plurality of printing bars, each of said bars being secured to a respective block member and each of the printing bars having a tip portion arranged in a manner to form a printed character upon the movement of two or more bars along a predetermined path from a non-printing position to a printing position, said bars being in contact with adjacent bars along said path, means within the housing and engaging the block members for retaining the printing bars in a non-printing position and for restoring said bars from a printing position to a non-printing position, means for selectively actuating the printing bars from a non-printing position to a printing position, said actuating means including solenoid elements movable to provide a line of drive aligned with said retaining and restoring means and offset therefrom and parallel to the path of movement of the printing bars, said block members bearing on adjacent members to absorb unbalanced forces by reason of the offset in the drive line from the actuating elements to the printing bars, and a central printing bar surrounded by said plurality of printing bars, and central printing bar actuating and restoring means in line with said central printing bar.

3. Printing apparatus comprising a housing, a plurality of bearing blocks each individually slidably contained within the housing and supported by adjacent blocks for parallel operation thereof, a plurality of print bars secured to respective bearing blocks, the bars occupying a centralized area in nested relationship therein and slidably contacting adjacent bars for parallel operation thereof, and said bars having tip portions extending through the housing and adaptable to be moved in a path from a non-printing position to a printing position, resilient means for retaining the bearing blocks and the print bars in a non-printing position and for restoring the bearing blocks and the print bars from a printing position to a non-printing position, and means for selectively driving the print bars from a non-printing position to a printing position, said driving means being on a plane aligned with the resilient means and driving along a line of drive offset from and parallel with the path of movement of the print bars.

4. A compact print head assembly for making impressions And forming characters of the alpha-numeric system, comprising a housing, a plurality of generally rectangular bearing blocks contained therein and slidably contacting adjacent blocks for parallel operation and individually slidable a predetermined distance, a plurality of print bars, each print bar being secured to a bearing block adjacent one side and having a tip portion extending through the housing, said print bars being carried in contacting relationship by said bearing blocks and adapted to be individually slidable the predetermined distance from a non-printing position to a printing position, resilient members in said housing for urging the bearing blocks and the print bars to the non-printing position, said resilient members contacting said bearing blocks at a point adjacent a side opposite to the side to which the print bars are secured, and a plurality of solenoids supported from the housing and having drive means connected with the bearing blocks and aligned with said resilient members for driving the print bars in selective manner from the non-printing position to the printing position.

5. A print head assembly comprising a housing, a plurality of bearing blocks slidably contained and nested within the housing and slidably contacting adjacent blocks for parallel operation thereof, a plurality of print bars secured to the bearing blocks, the print bars being secured adjacent one side of each bearing block and being nested together and selectively movable along a path from a non-printing position to a printing position and each of said print bars having a tip portion for impressing a mark in the printing position, spring means within the housing and engaging the bearing blocks adjacent a side opposite the side to which the print bar is secured for retaining the print bars in the non-printing position, and solenoid means aligned with the spring means for selectively actuating the print bars to the printing position by exerting a driving force for driving the bearing blocks and the print bars in a line parallel with the line of movement of the actuating means, said line of movement of the actuating means being offset from the path of the print bars, and said driving force being directed within and through the bearing blocks along a path in line with the actuating means and then offset therefrom to the print bars.