US3422945A

US3422945A - Printing machine character selection structure employing differential means

Info

Publication number: US3422945A
Application number: US649940A
Authority: US
Inventors: Manning Kirk Bethune
Original assignee: Friden Inc
Current assignee: Friden Inc
Priority date: 1967-06-29
Filing date: 1967-06-29
Publication date: 1969-01-21
Anticipated expiration: 1986-01-21

Description

Jan. 21, 1969 M. K. BETHUNE PRINTING MACHINE CHARACTER SELECTION STRUCTURE EMPLOYING DIFFERENTIAL MEANS Sheet Filed June 29, 1967 INVENTOR. MANNING KIRK BETHUNE AGENT M. K. BETHUNE 3,422 945 ACHINE CHARACTER SELECTION STRUCTURE MPLOYING DIFFERENTIAL MEANS Jan. 21, 1969 PRINTING M E Shee't Filed June 29, 1967 Jan. 21, 1969 M. K. BETHUNE 3,

PRINTING MACHINE CHARACTER SELECTION STRUCTURE EMPLOYING DIFFERENTIAL MEANS Sheet Filed June 29, 1967 United States Patent 3,422,945 PRINTING MACHINE CHARACTER SELEC- TION STRUCTURE EMPLOYING DIFFEREN- TIAL MEANS Manning Kirk Bethune, Rochester, N.Y., assignor to Friden, Inc., a corporation of Delaware Filed June 29, 1967, Ser. No. 649,940 US. Cl. 19716 14 Claims Int. Cl. B41j 23/02, 1/32; H041 15/24 ABSTRACT OF THE DISCLOSURE A structure for effecting selection of an individual one of plural alphanumeric and symbol character printing type confined within a type box is effected by selective positioning of the type box in 'a vertical direction within a type-box support frame and by selective positioning of the support frame laterally on support ways. The selective positioning of the type box is effected by a rack and pinion gear rotationally driven through microchain connection to a first type-selective differential gear assembly, the lateral positioning of the type box support frame being likewise effected by microchain lateral drive of the frame from a second type-selective differential gear assembly mechanically interconnected by the microchain drive with the first type-selective differential gear assembly. The type box support frame is additionally laterially displaced for character spacing by a further microchain drive coupling through the second differential gear assembly to a power source providing character-space-controlled forward drive motion of the type-box support frame in printing a line of copy and its return to initiate printing of a succeeding line of copy.

The present invention relates to printing machine character selection structures and, more particularly, to such structures adapted to effect selection at relatively high printing rates of successive characters to be printed.

There is an ever increasing need in data translation systems for data printers operable at much higher printing rates than is readily attainable by printers having the usual office typewriter structure. While the highest printing rates may generally be attained by printing an entire line of characters in one print cycle, as by use of a conventional drum printer, there is a need in many applications for printing data character-'by-character at a faster rate than was heretofore possible.

It has heretofore been proposed that successive character printing at enhancing printing rates be accomplished by transversing a selective-character print head longitudinally of a stationary paper carrying platen. These proposed constructions selectively move a character selective element against spring bias thereof in each of mutually perpendicular directions, and contemplate an increase of printing rate upon character selection and print operations by bidirectional reciprocal movements of print head mechanical elements of small size and light weight and thus of low inertial mass. The latter, together with the inertial mass of the necessary positional drive mechanical components proposed for print head actuation, nevertheless place to more or less extent a subtantial and undesirable limit on the maximum printing rate attainable by them. Further, the ones of these proposed structures having the higher printing rates are usually deficient either in the accuracy with which they are able to print characters with uniform spacing and in precise alignment along a printed line of copy or in the attainment of reliable and trouble-free operation .with minimum service attention over prolonged periods of printer use, or both lack of accuracy and reliability.

It is an object of the present invention to provide a new and improved printing machine character selection structure which enables increased printing rates while avoding one or more of the disadvantages and limitations of prior such structures.

It is a further object of the invention to provide a novel printing machine character selection structure which ensures reliable and highly accurate printing of successive characters with close-tolerance alignment and spacing along a printing line and at significantly improved printing rates.

It is an additional object of the invention to provide an improved printing machine character selection structure in which the printing rate of successively printed characters is substantially increased by use of character selective bi-directional power drive of a print head in each of two mutually perpendicular directions and through reciprocal drive elements of relatively low inertial mass yet of high mechanical strength capable of consistently and reliably transmitting large and rapidly fluctuating drive forces.

In accordance with the present invention, a printing machine character selection structure comprises a print selection means including support means for guided movement thereof in each of two mutually perpendicular directions and adapted by displacement to preselected positions in each such direction to select at each of such positions in each of such directions and individual alphanumeric character or symbol to be printed, differential gear train means, a first character-selective step-motion drive source, a first-position drive means non-differentially coupling said first drive source through said gear train means to said print selection means to effect bi-directional drive setting thereof to such preselected position in one of the two directions, a second character-selective step motion drive source, and a second-position drive means differentially coupling said second drive source through said gear train means to the print selection means to effect bi-directional drive setting thereof to such preselected positions in the other of the two directions.

These and other objects of this invention will become apparent from the following detailed description and drawing thereof in which:

FIG. 1 is a front elevational view schematically illustrating a printing machine character selection structure embodying the present invention in a particular form;

FIG. 2 is an enlarged fragmentary and partially brokenaway side elevational view of a type box used in the construction, and particularly illustrates the support of char acter print type carried by the type box;

FIG. 3 illustrates in developed plan view the construction of a differential gear train mechanism employed in the present structure;

FIG. 4 illustrates such mechanism in isometric view;

FIG. 5 is a fragmentary cross-sectional view illustrating a detail of the mechanism;

FIG. 6 is a fragmentary side elevational view illustrating the construction of a print hammer and print-hammer drive used in the present structure;

FIG. 7 illustrates in isometric view a structure for effecting print-character spacing along a line of copy and the return of the type box and its associated support frame to initiate printing of a succeeding line of copy; and

FIG. 8 being a fragmentary cross-sectional elevational view illustrating certain details of construction of an escapement mechanism employed in the FIG. 7 structure.

Referring now more particularly to FIG. 1 of the drawings, which illustrates a printing machine character selection structure embodying the present invention, a type box 10 supports a plurality of alphanumeric and symbol character printing type 11. The latter are shown by way of example as arranged in eight rows and eight columns of type and, as illustrated by the fragmentary and partially cross-sectioned side elevational view of FIG. 2, have square type heads 12 with a planar face 13 carrying individual print characters 14. 'Each type head is supported by a support pin 15 received in and guided for longitudinal movementby an aperture 16 provided in the body of the type box 10 and by an aperture 17 coaxial with the aperture and provided in a rear plate 18 of the type box 10. The type box 10 has bores 19 of square cross section to receive the type heads 12 and maintain the latter against angular rotation as each type head is moved in a manner presently to be explained from a non-print position shown in full lines to a print position shown in broken lines. Each print head 12 is normally biased to its non-print position by a helical wire spring 20 received in a bore 21 of cylindrical cross section provided in the type box 10, the spring 20 being compressed between the base surface of the bores 21 and a collar 22 affixed to the pin 15.

The type box 10 has coplanar side fins (not shown) extending along the length ofeach side and which are slidably received within mating grooves (not shown) provided in

opposed side walls

23 and 24 of a support frame 25. The latter is conveniently fabricated of a metal or rigid plastic casting of relatively small mass having an integrally formed base portion 26 joining the

side walls

23 and 24 and maintaining them in fixed spaced relation. This construction permits the type box 10 to be movably positioned within the support frame 25. The latter, carrying the type box 10, is supported for lateral movement by means of rearwardly extending pairs of integrally formed

projection pairs

30 and 31 having coaxial apertures to receive rigid support rods or ways 32 fixedly secured between the side frames (not shown for simplicity) of the printing machine structure. For convenience of description and as indicated in FIG. 1, it will be hereinafter assumed that the median plane of the type box 10 cccupies a vertical position although it will be understood that such median plane could occupy any angular position from the vertical depending on each particular application of the invention. Also, and as will become more evident hereinafter, the type box 10 normally occupies an at-rest vertical position in the support frame 25 such that the upper edge of the type box is located just below the character print line and is movable upwardly from such position to select any of the eight rows of type. Likewise the support frame 25 moves longitudinally on the ways 32 to successive character print near-median positions, but at each such position is movable to left and right of the near-median position.

At the initiation of each print cycle, the type box 10 is moved upwardly within the support frame 25 from its at-rest position to select the uppermost row of type and may be further moved upwardly by any of a number of equal-valued steps to select a correspondingly lower row of type. Such positioning of the type box 10 thus selects a particular row of type 11 and positions the selected row on the character print line. Likewise the support frame 25 with its type box 10 is permitted to remain at its characterprint near-median position or is laterally moved on the ways 32 to the left or right of the near-median position, thereby to select a particular column of the type 11. These positional movements of the type box 10 and support frame 25 select an individual one of the type in the type box 10 for the individual character printing operation. The manner in which the type selective positioning of the type box 10 and support frame 25 is accomplished will now be described.

Considering first the controlled vertical positioning of the type box 10 within the supoprt frame 25, there is affixed to the type box 10 a vertically depending rack 33 which is reciprocally guided by a cooperating guide groove 34 formed in the end of a guide block 35 integrally formed on the side wall 24 of the support frame 25 as shown. The rack 33 is drivingly engaged by a segmental gear 36 secured to and rotatably supported by a shaft 37 journaled in upstanding spaced trunnions 38 integrally formed on the base portion 26 of the support frame 25. A drive sprocket wheel 39 is also affixed to and rotatably supported by the shaft 37. A closed looped chain 40 of relatively small link construction, often called and hereinafter referred to as a microchain, is wrapped around the sprocket wheel 39 and passes over a plurality of

sprocket wheels

41, 42 and of a differential gear train mechanism 43 hereinafter described more fully and extends around an idler sprocket wheel 44 rotationally supported in a manner presently to be described. The operation of the type box positioning structure just described will be considered hereinafter, but before doing so the manner in which the character print positioning of the support frame 25 is accomplished will be next described.

The idler sprocket wheel 44 is rotationally supported on a shaft 49 secured between the arms of a fork 50, preferably guided for longitudinal motion by a guide member (not shown), to which is secured one end of a microchain 51. The latter extends over a sprocket wheel 42' and a sprocket wheel 45 of a differential gear train mechanism 43' to be connected at its opposite end to a link connecting yoke 52 provided on the side wall 24 of the support frame 25. The differential gear train mechanism 43' has the same construction as the mechanism 43, and for this reason components of the mechanism 43' which correspond to the same components of the mechanism 43 are identified by the same reference numerals primed. Longitudinal positioning of the support frame 25 to successive character-print positions is accomplished by a positioning drive structure 53, hereinafter described more fully, which is mechanically connected as indicated by the broken line 54 to the shaft of the sprocket wheel 41' of the mechanism 43'. A microchain 55 is connected at one end by a link connecting yoke 56 to the hammer support frame 100 and is wrapped around the sprocket wheel 41' of the mechanism 43', extends over an idler sprocket wheel 57 rotationally supported on a stud shaft 58 secured on a projection 59 affixed to the mechanism 43, and has its opposite end secured to a link connecting yoke 60 on the opposite side of the hammer support frame 100.

Before considering the operation of the type selective positioning structure just described, reference is made to FIG. 3 which shows the construction of the differential gear train mechanism 43 in developed plan view and to FIG. 4 which illustrates this mechanism in isometric view. The differential gear mechanism includes

parallel side plates

63 and 64 which are assembled in fixedly spaced position by spacer members (not shown) and which rationally journal a shaft 65 to which the sprocket wheel 41 is secured and a shaft 66 to which the sprocket wheel 45 is secured. The

side plates

63 and 64 also journal an input drive shaft 67 which is coupled by a coupler 68 to the output shaft 69 of a first character-selective step-motion drive source or mechanism 70 having, for example, the construction and mode of operation disclosed and claimed in the Donald G. Bastian application Ser. No. 649,941, filed concurrently herewith and assigned to the same assignee as the present application. Briefly considered, the drive mechanism 70 includes an input drive shaft 71 which is driven at constant angular velocity through a conventional electromagnetically controlled single-revolution helical-wire-spring cycle-control clutch C (such as that shown in the United States Patent No. 3,243,533) from a suitable drive source indicated as a motor M (FIG. 1). For the character selection structure herein described, the mechanism 70 is controlled by four code magnets selec tively energized alone and in permutational combinations by four code bits of a multi-bit input code representative of characters to be printed. This control is such that the rotional motion of its input shaft 71 is changed to a character-selective step angular motion of its output shaft 69, the output motion starting from an at-rest angular position and having an incremental step value alone or such incremental step added to each of a total of seven additional equal-valued angular displacements. The incremental step corresponds to that required to raise the type box from its at-rest position to one at which the uppermost row of type is aligned with the character print line while the seven additional displacements raise the type box to levels corresponding to the seven lower rows of type. The output shaft 69 dwells at its displaced position during a character-print interval and then returns to its at-rest position to complete a cycle of reciprocal angular motion.

Any character-selective step angular motion thus imparted to the input shaft 67 of the mechanism 43 produces a corresponding stepped angular planetary motion of a bevel sun gear 72 which, as shown by the enlarged crosssectional fragmentary view of FIG. 5, is rotationally supported; on a cap screw 73 secured to a collar 74 which is affixed by a set screw 75 to the input shaft 67. The sun gear 72 drivingly engages a bevel gear 76 freely rotatable on the shaft 67 and having an integral pinion gear 77 drivingly engaging a pinion gear 78 secured to the shaft 65. The sun gear 72 also drivingly engages a bevel gear 79 freely rotatable on the shaft 67 and having an integral pinion gear 80 which engages an idler gear 81 rotatably supported on a stud shaft 82 supported by the side plate 64, the idler gear 81 in turn engaging a pinion gear 83 fixedly secured on the shaft 66. Any stepped angular planetary motion thus imparted to the sun gear 72 by the input shaft 67 does not permit differential motion of the bevel gears 76 and 79, since this would require the same direction of angular motion of the

sprocket wheels

41 and 45 but such common direction of angular motion of these sprocket wheels is only permitted by operation of the differential gear mechanism 43'. Accordingly, any stepped angular planetary motion imported to the bevel sun gear 72 results in drive of the

sprocket wheels

41 and 45 in opposite angular directions. This results in angular drive motion of the sprocket wheel 39 and segmental gear 36 in a clockwise direction as seen in FIG. 1, and in an amount which is proportional to the stepped angular motion of the input shaft 67 of the mechanism 43 from its at-rest angular position. Any rotational displacement of the segmental gear 36 from its at-rest position effects a corresponding vertical displacement of the rack 33 so that any one of the eight rows of type in the type box 10 may be selected. The character-row selective cycle of operation is completed by reverse drive of the input shaft 67 and thereby the type box is returned to its at-rest position.

The lateral positioning of the support frame 25 in its near-median position or the laterial displacement to the left or right therefrom in selecting any one of the eight columns of type in the type box is similarly accomplished by the differential gear train mechanism 43'. The latter operates under control of a character-selective steppedmotion drive source or mechanism 70' also having, for example, the construction and mode of operation disclosed in the aforementioned Bastian application. In particular, the drive mechanism 70 is driven through the clutch C from the source M and is controlled by three code bits of the multi-bit input code representative of characters to be printed. Under such code-bit control, the mechanism 70 drives the input shaft 67 of the gear mechanism 43' through a total of eight equal-valued angular displacements of which one corresponds to the near median angular position of the shaft 67 and three lie to one side and four to the other of such position. For type column selection by lateral positioning of the support frame 25, the sprocket wheel 41' is maintained stationary by the character-print-position drive structure 53 and the stepped angular planetary drive motion of the bevel sun gear 72 accordingly imparts differential drive motion to the pinion gear The pinion gear 80 through the idler gear 81' and a pinion gear secured to the shaft 66 (not shown but corresponding to the pinion gear 83 of FIGS. 3 and 4) drives the sprocket wheel 45' by stepped angular motion in clockwise or counterclockwise direction according to any stepped planetary motion by the planetary gear 72 from its near-median angular position. For such angular drive motion of the sprocket wheel 45', the microchain 51 and the closed-loop microchain 40 operate effectively as a single length of microchain having one end secured by the link connecting yoke 52 to the side wall 24 of the support frame 25 and having its opposite end connected to the support frame 25 through the sprocket wheel 39 and its shaft 37 supported by the trunnions 38 of the support frame 25. In this, the upper loop of the microchain 40 in moving to left or right effects rotation of the

sprocket wheels

41 and 45 in the same angular direction and these unidirectional drive motions of the

sprocket wheels

41 and 45 are permitted by the differential gear motions of the bevel gears 76 and 79 and sun gear 72 of the differential gear train mechanism 43. This is true even though the differential gear train mechanism 43 also effects a concurrent vertical positioning of the type box 10 to select a row of the type 11 thereof in the manner earlier explained. Thus the type box 10 is positioned vertically and the support frame 25 is concurrently positioned laterally to select a particular one of the type 11 for each character print operation.

When the type box 10 and support frame 25 have been thus positioned to select one of the type 11 for a character print operation, a spring-loaded print hammer 87 (FIG. 1 and FIG. 6) is released to impact the end of the support pin 15 of the selected type and thus move the selected type to print position. To this end, the print hammer release occurs in timed relation to the completion of the character selection operation just described and is effected through a spline shaft 88 driven through the single cycle electromagnetically controlled helical wire spring clutch C from the input drive source M of the drive mechanism 70 as indicated by the broken line 90. In particular, and referring to FIGS. 1 and 6, the print hammer 87 is pivotally supported on a shaft 91 carried by a print hammer support carriage having integral support lugs 101 apertured for support and lateral displacement of the carriage 100 on rigid rods or ways 102 secured to the side frames (not shown) of the printing machine structure. The print hammer support carriage 100 is mechanically connected by

yokes

56 and 60 to the microchain 55 for lateral positional movement to each successive character print position. As more clearly shown in FIG. 6, the print hammer 87 is provided with an integral arm 103 having an end engaging a cam 104 rotatably journaled on the support carriage 100 and having an aperture 105 of square cross-sectional configuration through which the spline shaft 88 slidably extends. A spring 106 is positioned between the print hammer arm 103 and the support carriage 100 and is compressed by counter-clockwise driven motion of the cam 104 (as seen in FIG. 6) by the spline shaft 88 to effect spring loading of the print hammer 87. When the arm 103 drops off of the step of the cam 104, the spring 106 impulses the print hammer 87 to effect a character print operation by inertial impact of the print hammer 87 with the support pin 15 of the selected one of the type 11. This impact moves the latter to print position against a conventional type ribbon 107 conventionally raised to and lowered from a print position forwardly of a sheet of paper 108 wrapped about a platen 109 which is rotatably supported in conventional manner in the printer structure and is indexed in conventional manner for line space operations in response to each return of the support frame 25 to the left-hand margin to begin a new line printing operation.

In effecting each such character print operation, the electromagnet of the clutch C is energized concurrently with energization of the code magnets of the step-motion drive mechanisms 70 and 70' and accordingly initiates a cycle of rotation of the spline shaft 88 and cam 104 to position the step of the latter to the arm 103 of the print hammer 87 in correctly timed relation to the completion of each new character selective positioning of the type box and support frame 25 as earlier described. Immediately following the print hammer operation, a print hammer restore spring 110 positioned between a lug 111 on the carriage 100 and the hammer arm 103 restores the print hammer 87 to a position such that its hammer head is slightly spaced from the vertical plane defined by the ends of the type support pins and thus permit unrestrained repositioning of the type box 10 and support frame to their respective at-rest and near-median positions in preparation for a further character-print selection operation.

Each cycle of character print operation is preferably initiated and terminated by displacements of the support frame 25 in an amount equal to one-half the desired value of character spacing, thus enabling the character spacing operation to utilize time intervals used in moving the type box 10 and support frame 25 to character selective positions and returning them to their respective atrest and near-median positions.

This character space lateral positioning of the support frame 25 and the print hammer structure of FIG. 6 is accomplished by a character space drive structure shown in FIG. 7. The shaft 65 of the differential gear train mechanism 43 extends through and is secured to the rotatable central hub 113 of a conventional spring motor 114 having a helical wire spring anchored at its ends to the hub 113 and to an enclosing casing 115 of the motor. The shaft 65' further extends through and is secured, as shown in the fragmentary cross-sectional view of FIG. 8, to a central ratchet wheel 116 of an escapement structure 117 and terminates in a conventional 90 electromagnetically controlled helical wire spring clutch 118 (such as one of the type shown in the aforementioned Blodgett patent) which is mechanically connected by a shaft 119 for rotational drive by a pulley 120 and belt 121 from a drive source such as the motor M.

Upon manual or code-controlled closure of a pair of electrical contacts 122 in convention manner to initiate return of the support frame 25 and the hammer structure of FIG. 6 to the left-hand margin in readiness to begin printing a new line of copy, an electromagnet 123 of the clutch 118 is energized to attract its armature 124 and permit the clutch 118 to provide a drive connection between the shafts 119 and 65'. The sprocket wheel 41 is thereupon driven in counterclockwise direction as seen in FIG. 7 and the print hammer structure of FIG. 6 is moved toward the left-hand margin stop, a spring biased pawl 125 pivoted to an escapement wheel 126 and engaging the teeth of the ratchet wheel 116 permitting counterclockwise rotation of the latter at this time. The electrical contacts 122 are only briefly closed but the electromagnet 123 remains energized through its now closed contacts 127 until the support frame 25 has been moved to engage a left-hand stop which thereupon opens a pair of electrical contacts 128 to interrupt the energizing circuit of the electromagnet 123 and permit its armature to engage a stop detent of the clutch 118 and interrupt the drive connection between the shafts 119 and 65'. The support frame 25 is moved to the left by the rotation of sprocket wheel 41' which, through the differential of FIG. 4, causes a corresponding counterclockwise rotation of sprocket wheel 45'. That is, rotation of sprocket wheel 45' causes movement of the microchain 51, which is attached to the support frame 25 by yoke 52. Accordingly, the support frame 25 is returned to the left. The sprocket wheel rotates an amount which corresponds to the rotation of sprocket wheel 41' as during the return motion there is no input signal from drive shaft 67. A careful examination of FIG. 1 will show that although idler sprocket wheel 44 moves to the right during the return of the support frame 25 to the left there is no rotation of the sprocket wheel 44. Instead

sprocket wheels

42 and 45 rotate. Drive sprocket wheel 39 does not rotate and therefore there is no vertical motion transmitted to rack 33.

Having now described the position selecting mechanism and the carriage restore mechanism independently, it should be obvious that the support frame 25 will move an appropriate amount and direction depending upon the input signals from sprocket wheel 41' and/or input shaft 67. More specifically, and as an example: the support frame must move one letter space to the right for each character to be printed; if at the same time the character selected for printing is one which is in a column which requires movement of the support frame 25 one letter space to the left, then the net result is that the support frame 25 will not move. That is, it got simultaneous signals to move one letter space to the left and one letter space to the right. The differential of FIG. 4 accepts both signals and transmits no relative motion to the frame 25. However, it must be clearly understood that sprocket wheel 41 and microchain did transmit a motion of one letter space to the right to the print hammer structure of FIG. 6.

During return of the support frame 25 to the left-hand margin, the rotational drive of the shaft winds the spring motor 114. Now when the clutch 118 interrupts the drive connection between the

shafts

119 and 65, the wound spring motor 114 tends to drive the shaft 65' and sprocket wheel 45' in clockwise direction as seen in FIG. 7. Such drive is restrained, however, by the escapement structure 117 wherein the pawl 125 now drivingly connects the ratchet wheel 116 to an escapement wheel 126, but the latter is restrained from clockwise rotation by an escapement lever 131 pivoted at 132 and biased by a spring 133 into engagement with escapement wheel 126 as shown. The escapement lever 131 is rocked about its pivot 132 upon energization of an electromagnet 134 concurrently with energization of the code magnets of the drive mechanisms and 70' of FIG 1, the rocking motion of the escapement lever permitting a one-tooth angular rotation of the escapement wheel 126 under drive of the wound spring motor 114. This one-tooth escapement effects a corresponding angular rotation of the sprocket wheel 41' to displace the hammer support frame laterally to the right by one-half of a character space value. The magnet 134 is only briefly energized with the code magnets, but is of the slow release type permitting spring return of the escapement lever 131 after an interval corresponding to that required for print operation of the print hammer 87. The return of the escapement lever 131 permits a further one-tooth displacement of the escapement wheel 126 to displace the hammer support frame 100 laterally to the right by a further onehalf character space value. This spring-motor drive and escapement controlled positioning of the hammer support frame 100 continues through successive character print operations to the end of a line of print whereupon the support frame 25 and the print hammer structure are restored to the left-hand margin by a repetition of the foregoing described operation.

It will be apparent from the foregoing description that a printing machine character selection structure embodying the invention is one of the balanced type providing positive bi-directional drive of a character-selective structure in each of two mutually perpendicular directions and avoids any form of the heretofore required spring biasing of the structure in each of such directions. This substantially reduces the input power needed for selective positioning of the character-selective structure, and has the further important advantage of attaining printed character alignment and spacings with high precision. The natural damping of the chain form an inter-element drive used in a preferred form of the invention has the advantage that it minimizes undesired vibration which tends to occur especially at high character printing rates. A structure embodying the invention is characterized by a sturdy construction exhibiting high reliability in operation and requiring minimized maintenance and service attention over prolonged periods of use.

While specific form of the invention has been described for purposes of illustration, it is contemplated that numerous changes may be made without departing from the spirit of the invention.

What is claimed is:

1. A printing machine character selection structure comprising:

print selection means including support means for guided movement of said print selection means in first and second independent directions and adapted to select at each of a plurality of preselected positions in each of said directions an individual alphanumeric character or symbol to be printed,

differential gear train means,

a first character-selective step motion drive source, a first position drive means non-differentially coupling said first drive source through said gear train means to said print selection means to effect bi-directional drive setting thereof to selected ones of said preselected positions in said first of said two directions,

a second character-selective step-motion drive source, and a second-position drive means differentially coupling said second drive source through said gear train means to said print selection means to effect bi-directional drive setting thereof to said preselected positions in the second of said two directions.

2. A printing machine character selection structure according to claim 1 wherein said support means supports said first position drive means for character-selective movement of said print selection means in said first direction while said support means remains stationary and said first drive source is non-differentially coupled through said gear train to said first position drive means.

3. A printing machine character selection structure according to claim 2 wherein:

said first-position drive means comprises a rack connected to said print selection means and a sector gear drivingly engaging said rack, and

said first drive source is non-differentially coupled through said differential gear train means rotationally to drive said sector gear.

4. A printing machine character selection structure according to claim 2 wherein:

said first-position drive means comprises a rack connected to said print selection means and a sector gear drivingly engaging said rack,

said first drive source is non-differentially coupled through said differential gear train means rotationally to drive said sector gear, and

means including a belt-like closed drive loop of flexible fabrication mechanically drivingly connects output gearing of said first-mentioned differential gear train means to said sector gear and said loop forms a portion of a second belt-like closed drive loop of flexible fabrication which mechanically drivingly connects output gearing of said second differential gear train means to said print selection means.

5. A printing machine character selection structure according to claim 2 wherein said second drive source is differentially coupled through said gear train means to said support means for character-selective concurrent movement of said print selection and support means in said second direction.

6. A printing machine character selection structure according to claim 5 wherein:

a second differential gear train means nondifferentially couples said second drive source differentially through said first-mentioned gear train means to said support means, and

a third character-space step-motion drive source is differentially coupled through both said first-mentioned and second gear train means to said support means for character-space movement thereof in said other direction.

7. A printing machine character selection structure according to claim 6 wherein said second differential gear train means is of the bevel gear type having at least one bevel planetary gear driven in planetary motion by said second drive source.

8. A printing machine character selection structure according to claim 6 wherein a belt-like closed loop of flexible fabrication mechanically drivingly connects output gearing of said first-mentioned differential gear train means to said first-position drive means and said loop forms a portion of a second belt-like closed loop of flexible fabrication which mechanically drivingly connects output gearing of said second differential gear train to said support means.

9. A printing machine character selection structure according to claim 1 wherein said differential gear train means is of the bevel gear type having at least one bevel planetary gear driven in planetary motion by said first drive source.

10. A printing machine character-selection structure according to claim 1 wherein the drive motion of each said first and second drive sources comprises an angular reciprocal motion character-selective positioning means for effecting print selection in each of said first and second directions and wherein said drive sources provide a selectable step range of angular motion for effecting reciprocal movement of said print selection means in said first and second directions.

11. A printing machine character selection structure according to claim 1 wherein said print selection means is comprised by a type box structure supporting a rowand-column array of printing type individually selected by type row and column positioning of said type box structure in each of said two directions.

12. A printing machine character selection structure according to claim 11 wherein:

said type box structure is supported on said support means for guided movement in said first of said two directions and said support means carries said first-position drive means for type selective movement of said type box stnucture in said first direction independently of any movement of said support means in said second direction, wherein said first drive source is nondifferentially coupled through said differential gear train means to said first position drive means, and

said second drive source is differentially coupled by said second position drive means through said differential gear train means to said support means.

13. A printing machine character selection structure according to claim 12 wherein said second position drive means comprises:

a differential gear train means non-differentially coupling said second drive source differentially through said first-mentioned gear train means to said support means, and wherein a third character-space step-motion drive source is differentially coupled through both said first-mentioned and second differential gear train means to said support means for character space movement thereof in said second direction.

14. A printing machine character selection structure according to claim 13 wherein said first-mentioned differential gear train means includes a differential planetary 11 12 gear driven in planetary movement by said first drive 2,757,775 8/1956 Hickerson- 19749 source and wherein said second dilferential gear train 3,205,996 65 reenwo d 19716 XR means includes a diflerential planetary gear driven in 3,283,870 11/1966 GPllwltzer 197*62 planetary movement by said second drive source. 3,307,676 3/1967 Hlckerson 197 49 XR References Cited 5 ROBERT E. PULFREY, Primary Examiner.

UNITED STATES PATENTS E. S. BURR, Assistant Examiner. 631,833 8/1899 Treadgold 197 55 1,127,487 2/1915 Mohr 197--11 10 17833;19753, 49