CA1143689A

CA1143689A - Print ribbon driving mechanism

Info

Publication number: CA1143689A
Application number: CA000356127A
Authority: CA
Inventors: James M. Rigotti
Original assignee: International Business Machines Corp
Current assignee: International Business Machines Corp
Priority date: 1979-09-27
Filing date: 1980-07-14
Publication date: 1983-03-29
Also published as: EP0026275A2; JPS585794B2; EP0026275A3; EP0026275B1; JPS5651381A; DE3066963D1

Abstract

PRINT RIBBON DRIVING MECHANISM
ABSTRACT OF THE DISCLOSURE
A print ribbon driving mechanism including a switching bail swingingly mounted on a reciprocatively mounted support movable between two opposite spindles carrying print ribbon spools. The spindles have ratchet teeth, and the switching bail has a pair of opposite pawl surfaces for engaging the ratchet teeth as the support and bail are moved in opposite directions.
A trigger lever is provided on each of the spindles which is responsive to the existence of ribbon on the associated spools so that the trigger lever drops into an operative position on depletion of the ribbon from the associated spool, and the switching bail is provided with two opposite camming surfaces adapted to engage the trigger levers in their operative dropped positions for swinging the switching bail into a position to engage the ratchet teeth of the spindle of the dropped trigger lever so as to wind ribbon onto this particular spool.

Description

PRINT RIBBON DRIVING MECHANISM

BACKGROUND OF THE INVENTION

The invention relates to mechanism for driving a print ribbon for a printing machine effective for alternately winding a print ribbon applied across the print head of the machine alternately on one spool at one side in the machine an~ on an opposite spool at the othe.r side of the machine.

Print ribbon driving mechanisms for alternately .: 10 winding a print ribbon on opposite spools have been previously proposed which rely on the tension or resistance tO further turning of a spool when unwound such as to cause a swing lever to be effective.for winding the ribbon on an immediately depleted ribbon ;: 15 spool. An example of such a.ribbon drive construction : is disclo.sed in Nicholas Kondur, Jr., U. S. Patent 4,046,246 which discloses a swingable drive arm that is alternately effective for winding a print ribbon on one : or the other of a pair of ribbon spools. Another example of such a ribbon drive construction is disclosed in Terrance J. Hebron, U. S. Patent 3,880,271. The Hebron structure includes a swingable feed pawl beam which has two detented positions for this purpose in which its two notches alternately rest on a drive stud.
~he beam thus has two princlpal positions in each of which it drives one of a pair of ribbon spools. The International Business Machines Technical Disclosure Bulletin publication, Vol. 21, No. 9, February 1979, pages 3687 and 3688, discloses another example of such a structure. In thi~ structure, a longitudinally movable shifting pawl is alternately effective to drive one or the other of two ribbon spool ratchets, and the mechanism is changed from a condition driving one of the ratchets to a condition driving the other ratchet by a shifter control which is responsive to the amount RO979-014 `~

1 of ribbon on one of the spools. The shifter control drops when the ribbon is depleted on this spool to drive a detent bar from one position to another position to cause the shifting pawl to be changed in its operation to drive one of the ratchet wheels in lieu of the other.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an improved ribbon drive mechanism which avoids certain operat-ing problems resulting from the use of ribbon tension for causing ribbon reversal by being responsive only to the substantial absence of ribbon on one of two opposite ribbon spools without influence of ribbon tension to alternate the drive of the two spools so that a ,ust depleted ribbon spool is driven in a ribbon winding direction.

It is a more specific object of the invention to provide such an improved ribbon drive mechanism which includes a swingable switching bail carried by a recip-rocative support also carrying a printhead, with the con-struction being such that the switching bail is swung from one principal position to another principal position under the control of a device responsive to the lack of ribbon on a ribbon spool and by a reciprocation of the support in order to then drive a spindle carrying a depleted ribbon spool in a ribbon winding direction.

The invention constitutes a double spool ribbon drive particularly for use with a wire print head that recipro-cates back and forth across the print medium. The print head carries an oscillatible switching bail which moves with the print head and which is moved into opposite switched positions by camming surfaces on the bail that strike ;89 1 reversing triggers carried by the ribbon spool spindles.
When the ribbon is depleted on one or the other of ihe spools, the reversing trigger drops and engages a fixed latching surface preventing further rotation of the assoc-iated spindle and spool, and a camming surface on the switching bail contacts the trigger in its dropped position so as to swing the bail and cause it to be effective on this spindle for rewinding the ribbon on the associated spool as the print head reciprocates.

10In a preferred form, the invention incIudes such a reciprocative s~pport carrying a printhead with a switching bail swingably mounted on the support. Two spindles each carrying one of two print ribbon spools are provided with ratchet teeth, and the swingable switching bail is provided with pawl surfaces for engaging the ratchet teeth so as to rotate the spindles RO979014 2a ~4~ 39 and cause the associated ribbon spools to rotate in a rlbbon winding direction when the support and printhead are moved toward the spindle given such a ribbon winding -rotation. Each of the spindles carries a trigger lever which is responsive to the ribbon wound on to the associated ribbon spool so that, when the ribbon is nearly depleted from the spool, the trigger lever falls and engages with a fixed abutmen-t which holds the spindle and the associated spool from fur-ther rotation in a ribbon unwinding direction. This is an operative position of the trigger lever, and the swinging bail is provided with opposite cam surfaces which contact the trigger levers of the two spindles when in their operative positions for swinging the bail so that it has the associated pawl surface in position for engaging the ratchet teeth on the spindle of the ribbon depleted spool for then causing the spindle to rotate the ribbon spool in the ribbon winding direction.
~ , sRIEF DESCRIPTION OE' THE DRAWINGS
.

FIG. 1 is a plan view of a print ribbon driving mechanism inCo!rpOrating the principles of the invention and including a pair of ribbon spool carrying spindles, a trigger lever swingably mounted on each of the spindles and a switching bail swingably mounted on a reciprocative ; 25 support carrying a printhead;

-FIG. 2 is an exploded view of one of the spindles together with the trigger lever swingably mounted on the spindle;

FIG. 3 is a side elevational view of one of the spindles together with its trigger lever and taken from lines 3-3 of FIG. l; and FIG. 4 is a fragmentary view of one of the trigger levers together with its support.

~3~

~E:SCE~IPTION O~' T~l~ Pl~l,F~RRED EMBODIMI',N'l' Tht? print ribb~n dr.iving mechani.sm 1.ncl-ldes a swi.tchinq bail 20 which is oscillatably disposed on the carrier 22 for a printhead 24 of a print.~ng machine.
The printhead ?4 has a nose tip 24a, and a print ribbon 26 passes over the nose tip 24a. The ribbon 26 is disposed on ribbon supply spools 28 and 30 and has its ends fixed to the spools. The spools 28 and 30- are disp(Jsed on the toothed spindles 32 and 34 respectively.
The ~eeth on ~he spindle 32 have radially extending surfaces 32a and alternate surfaces 32b connecting the surfaces 32a and extending at an angle with respect to radial. The teeth on the spindle 34 have radially extending -tooth surfaces 34a connected by alternate tooth surfaces 34b connecting -the tooth surfaces 34a and extending at an angle with respect to radial. As the teeth are seen in plan in FIG. 1, it will be noted that the tooth surfaces 32b and 34b slant inwardly toward the centers of the spindles oppositely with respect to each other, and this is so that the radially extending tooth surfaces 32a and 34a are available for engagement by the bail 20 approaching the spindles 32 and 34 from opposite directions as will be apparent from subsequent descri.ption.

The carrier 22 is slideably disposed on a stationary carrier guide rod 36 so that the carrier 22 and thereby the printhead 24 may reciprocate in directions 37 and 38. The printhead 24 may thus provide lines of print on the printing medium 40 with the lines of print - 30 extending in directions 37 and 38. The printhead 24 for this purpose may be oE the wire type which includes wires 24b that are selectively thrust -through the nose -tip 24a to billow thè ribbon 26 off the tip 24a and into contact with the medium 40 for printing corresponding dots on the medium 40. The carrier 22 is reciprocatively RO979~014 ~3~

driven in directions 37 and 38 by any suitable motive means (not shown).

Spool brackets 42 and ~4 are mounted to the frame 46 oE the machine in which the prin-thead 2~ is installed, and hr~ckets ~2 and 44 r~spectively carry the spindle studs ~8 and 50. The spool bracket 42 having the spindle stud 48 mounted thereon is shown in detail in FIG. 2, and the assembly oE the spindle stud 50 on the spool bracket 44 is similar. The upper surface of the bracket 42 is embossed with a depression 51 providing a vertical shoulder 52, and a similar shoulder 53 is formed on the bracket 44. Spindles 32 and 34 have reversing trigger levers 54 and 55 swingably mounted on them. The levers 54 and 55 and their mountings on the 15 tooth spindles 32 and 34 are similar, and the lever 54 together with its mounting is shown in detail in FIGs.

2, 3 and 4. The lever 54 is swingably mounted on the upstanding portion 56a of a bracket 56 fitting over stud 48 and extends upwardly through an opening 32a in 20 spindle 32. The lever 54 has a toe portion 54a, and the tang 57a of a leaf spring 57 fitting over bracket 56 extends oveir the toe portion 54a for the purpose of providing a swinging force on the lever 54 tending to swing the lever 54 away from the center line of the spindle 32 and stud 48 and urging the lever downwardly into engagement with the upper surface of the bracket 42. A drag spring 58 is attached to the bracket 42 and engages with the teeth of the associated spindle 32, and a similar drag spring (not shown) is used in connection with the spindle 34. Each of the spindles 32 and 34 is provided with a non-round exterior surface, and this surface corresponds with and mates with a corresponding non-round opening 28a in the spool 28 or 30a in the spool 30.

The bail 20 is provided with pawl surfaces 60 and 62 on opposite ends and with camming surfaces 64 and 66

3~

on opposite ends. The bail 20 i5 swin~ably disposed on the carrier 22 b~ me~3ns of a pin 6~, and a pin 70 extends through an opening 72 in the bail 20 for limiting the swincling movement o~ -the bail 20. An overcenter sprincJ 7~ is provided effectively between the bail 20 and the carrier 22 for yie}dably holding the bail 20 in either of its end positions limited by the pin 70.

In operation, the carrier 22 and the printhead 24 are reciprocated in the opposite directions 37 and 38 so that the head 24 may print lines of print on the print medium 40. Initially, the bail 20 may be assumed to be in its position shown in FIG. 1, swung in the clockwise direction about the pin 68 to a limit determined by the pin iO. When the head 24 along with the carrier 22 moves in the direction 38 to complete a line of print on the medium 40 in this direction, the pawl surface 62 moves into~engagement with one of the tooth I surfaces 34a on the spindle 34 and thus rotates the spindle 34 about the spindle axis in the clockwise ; 20 direction as seen in FIG. 1 for a certain arc, for example corresponding to four of the teeth on the spindle 34. The spool 30 has a non-rotative connection with the spindle 34, and the spool 30 thus rotates for the same arc of rotation. The ribbon 26 is fixed at its ends to the spools 28 and 30, and this rotation of the spool 30 thus winds the ribbon 26 onto the spool 30 and unwinds the ribbon from the spool 28 which rotates correspondingly and freely in the clockwise direction (see FIG. 1) about the axis of the spindle 32. The carrier 22 and printhead 24 then reciprocate in the opposite direction 37 for printing a line of print in this direction; however, with the bail 20 being in its illustrated position of FIG. 1 with respect to the carrier 22, the pawl surface 60 is out of line with respect to and passes over and makes no contact with the teeth of t~e spindle 32. The spindle 32 and the spool 28 are thus not rotated with this reciprocation o~ the prin-thead 24 and carrier 22 in direction 37.
Each successive reciprocation of the printhead 24 and bail 20 in the direction 38 winds a corresponding len~th oE the ribbon 26 on-to the spool 30, while the corresponding reciprocations in the direction 37 have no effect on the spindle 32 and spool 28.
.
When the ribbon 26 is d~pleted on the spool 28 until practically none of the ribbon remains on the spool 28, the trigger lever 54 is no longer held by the - ribbon 26 on the spool 28 in the position of the lever 54 in which its lower end 54a is out of contact with the upper surface of the bracket 42. The lever 54 thus swings downwardly due to the action of the spring tang 57a, since the lever 54 is no longer held by the ribbon 26; and the lower end 54a of the lever 54 makes contact and rides on the upper surface of the bracket 42. On a final arc of rotation of the spindle 32 and spool 28 (in the ribbon unwinding clockwise direction as seen in FIG. 1), the lever end 54a moves downwardly into the depression 51 Ind strikes the shoulder 52 which prevents any further rotation of the spindle 32 and spool 28 about the axis of the spindlè 32 in the clockwise direction as sieen in FIG. 1. On the next succeeding reciprocation of the carrier 22 and bail 20 in the direction 37, the camming surface 64 strikes the lower end 54a of the trigger lever 54 in contact with the shoulder 52, and the bail 20 is thus swung .in the counterclockwise direction about the pin 68 to the limit of its movement in this direction as limited by the pin 70. On subsequent movements of the carrier 22 and head 24 in the direction 37, the pawl surface 60 is then in place to strike a tooth surface 32a of the spindle 32, and-the spindle 32 and the spool 28 are thus rotated in` the counterclockwise direction as seen 68~

in FIG. 1 in order to wind the ribbon 26 onto the spool 28 with a corresporl-ling unwinding of -the ribbon 26 from the ~spool 30. The p(~wl surface 62, with the bail 20 being at -the limit of its rotat-ion in the counterclockwise directioll as seen in FIG. l, is out oE line Eor engaging with the teeth of the spin~le 34, and the-spindle 34 and spool 30 thus have a free ribbon unwinding action.
The lever 54 is swung upwardly out of engagement with the upper surface of the bracket 42 by -the ribbon 26 as it winds on the spool 28.

Finally the ribbon will be depleted from the spool 30, and the trigger lever 55 will swing downwardly and engage the abutment surface 53 so as to hold the spool 30 and spindle 34 from any further unwinding action;
and -the cam surface 66 will strike the trigger lever 55 in contact with the shoulder 53 and will again swing the bail 20 back into its illustrated position in which the pawl surface 62 is effective on the teeth of the spindle 34 as above described.

These reciprocations of the bail 20 to the limits of its swingirl~ movement by the actions of the camming surfaces 64 and 66 on the trigger levers 5~ and 55 respectively as the ribbon 26 is depleted from one or the other of the spools 28 and 30 cause the ribbon 26 to be successively and alternately wound on the spools 30 and 28 from the other of the spools.

The ribbon drive mechanism of the invention has numerous advantages. It is not dependent on the tension of the ribbon 26 for reversing the spooling actions of the spools 28 and 30 so that it is not subject to a potential blockage of ribbon movement for one reason or another which could cause an undesirable premature reversal of ribbon movement prior to an exhaustion of -eith~r one of the ribbon spools and so that the print R~979-014 3~
g wires 24b cannot be irnpe(led in their movements toward the medium 40 by the ribbon ?6 arld possibly punch throug]l the ribbon 26 and be prevented by -the r.ibbon from full return movement wi.th a disastrous ribbon and wire j aln resulting. The r:ibbon drive mechanism of the inventi.oll(loes not requi..re the use of senslng arms dragging on the ribbon 26 during spooling to change the winding direction which could cause undesired ribbon tension and which would have to be rotated out of the lG way manually when a new ribbon is installed in the machine. The ribbon loading path is simple particularly si.nce the ribbon is not routed around such tension arms. The ribbon drive has few parts resulting in a very-low cost mechanism; it does not exert a drag on the carrier.22 for the printhead 24 during printing;
the tension on the ribbon 26 is not increased during reversing; and the swingable bail 20 together with the carrier 22 and printhead 74 as an assembly has a desirably low inertia.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:
1. Mechanism for driving a pair of spools having a print ribbon would thereon and extending therebetween and including:
a pair of two rotatably mounted spindles each adapted to carry a print ribbon spool, a reciprocatively mounted support movable between and relative to said spindles, a switching bail swingably mounted on said reciprocatively mounted support and having two pawl portions on opposite ends, one of which is adapted to contact and rotate one of said spindles when said support is moved toward this spindle in one principal swung position of the switching bail, and the other of which is adapted to contact and rotate the other of sai spindles when said support is moved toward this spindle in the second principal swung position of the switching bail, a trigger lever swingably mounted on each of said spindles and adapted to swing into an operative position when the ribbon is depleted on the spool mounted on this spindle, and a pair of camming surfaces on opposite ends of said switching bail impinging on one or the other of said trigger levers in the said operative position of the rigger lever as said support moves toward this trigger lever and the spindle on

Claim 1 Continued which this trigger lever is mounted so that the switching bail is swung into its principal swung position to be effective on this particular spindle and drivingly rotate this spindle on successive reciprocative movements of said support toward this spindle for thereby causing the spool on this spindle to wind the print ribbon thereon.
2. Mechanism for driving a pair of spools as set forth in claim 1 and including fixed abutment means contacted by each of said trigger levers to limit the rotative movement of the spindle on which the trigger lever is mounted in the ribbon unwinding direction and to define said operative position of the trigger lever.
3. Mechanism for driving a pair of spools as set forth in claim 1 and including a printhead carried by said reciprocatively mounted support.
4. Mechanism for driving a pair of spools as set forth in claim 1 and including an overcenter spring for yieldably holding said switching bail in either of its said two principal swung positions.
5. Mechanism for driving a pair of spools as set forth in claim 1, each of said spindles having ratchet teeth with radially extending tooth portions adapted to be engaged by a said pawl portion of the switching bail as it moves toward this particular spindle for rotatably driving this spindle in a ribbon winding direction.

6. Mechanism for driving a pair of spools having a print ribbon wound thereon and extending there-between and including:
6. (continued) a pair of rotatably mounted spindles each spindle being adapted to carry a print ribbon spool, a reciprocatively mounted support movable between and relative to said spindles, spindle driving means carried by said support and switchable in its action for driving one of said spindles or the other of said spindles as said support moves toward the respective spindle in its reciprocative movement, a trigger lever swingably mounted on each of said spindles and responsive to the existence or lack of ribbon on the spool carried by the particular spindle so that the rigger lever is swung into an operative position when the ribbon is depleted on the spool mounted on the particular spindle, and means carried by said spindle driving means and responsive to a contact by said spindle driving means with one or the other of said trigger levers when the support is moving toward the spindle on which the lever is mounted and the lever is in its said operative position for switching said driving means to drive the particular spindle carrying the trigger lever which is in its said operative position.
7. Mechanism for driving a pair of spools as set forth in claim 6 and including a fixed abutment for each of said trigger levers for holding the trigger lever and the associated spindle and spool from further rotative movement about the axis of the spindle in a spool unwinding direction when the trigger lever is in its said operative position.
8. Printing mechanism including:
8. (continued) a pair of two rotatably mounted spindles each adapted to carry a print ribbon spool, a reciprocatively mounted support movable between and relative to said spindles, a printhead of the projectable wire type carried by said support about which the ribbon carried by said spools may pass so that the printhead is effective to print with its said wires projecting against the ribbon, spindle driving means carried by said support and switchable in its action for driving one of said spindles or the other of said spindles as said support moves toward the respective spindle in its reciprocative movement, a trigger lever swingably mounted on each of said spindles and responsive to the existence or lack of ribbon on the spool carried by the particular spindle so that the trigger lever is swung into an operative position when the ribbon is depleted on the spool mounted on the particular spindle, and means carried by said spindle driving means and responsive to a contact by said spindle driving means with one or the other of said trigger levers when the support is moving toward the spindle on which the lever is mounted and the lever is in its said operative position for switching said driving means to drive the particular spindle carrying the trigger lever which is in its said operative position.