GB1567120A

GB1567120A - Ink ribbon feed mechanisms

Info

Publication number: GB1567120A
Application number: GB931578A
Authority: GB
Original assignee: Oki Electric Industry Co Ltd
Current assignee: Oki Electric Industry Co Ltd
Priority date: 1978-03-09
Filing date: 1978-03-09
Publication date: 1980-05-08

Description

(54) IMPROVEMENTS IN OR RELATING TO INK RIBBON FEED MECHANISMS (71) We, OKI ELECTRIC INDUSTRY CO., LTD., a Japanese body corporate of 7-12 Toranomon l-chome, Minato-ku, Tokyo, Japan, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be peformed, to be particularly described in and by the following statement:- The present invention relates to ink ribbon feed mechanisms for printers.

According to the present invention there is provided an ink ribbon feed mechanism, comprising a pair of ratchet wheels which in use of the mechanism have respective associated ink ribbon spools between which an ink ribbon is to be fed, pawl means for intermittently driving one of the ratchet wheels to effect ribbon feed, back-stop means arranged to prevent rotation of the driven ratchet wheel opposite to its driven direction, stopper means normally engaging the non-driven ratchet wheel to prevent rotation thereof in a sense to cause ribbon to unwind from its said associated spool, the stopper means being disengageable from the non-driven wheel in response to driving of said driven ratchet wheel, and reversing means operable to cause the pawl means, back-stop means and stopper means each to change the ratchet wheel upon which it is arranged to act whereby to - reverse the ribbon feed direction.

An ink ribbon feed mechanism embodying the invention will now be particularly described by way of example with reference to the accompanying drawings in which: Fig. 1 is a plan view of the ink ribbon feed mechanism; Fig. 2 is a section on line I-I of Fig. 1; and Figs. 3, 4 and 5 are plan views of part of the ink ribbon feed mechanism of Fig. 1 at different stages during its operation.

The illustrated ink ribbon feed mechanism includes a feed pawl 1 pivotally supported by a shaft la and having a plate spring 2 fixed to it. A reciprocating movement (indicated by arrow Ain Fig. 1) is imparted to the feed pawl 1 by means of a plate 3 which is itself reciprocated by a drive mechanism (not shown) in response to the movement of a carrier 18 on which printing elements are mounted. Ratchet wheels 4a, 4b mounted on shafts 17a, 17b respectively are provided, one on each side of a lever 5.

The lever 5 has a rectangular body portion with arms extending from its corners. The lever 5 is pivotally supported by a shaft 6 substantially mid-way between the roots of the two upper arms (as viewed in Fig. 1) which constitute back-stoppers 7a, 7b. The arms projecting from the lower corners of the body portion of the lever 5 form stoppers 8a, 8b. The back-stopper 7a and the stopper 8a are engageable in the teeth of the ratchet wheel 4a and the back-stopper 7b and the stopper 8b are likewise engageable in the ratchet wheel 4b.

A frame 9 (see Fig. 2) supports guides 14a, 14b of a change arm 10 to which a further guide 11 is fixed. The guide 11 of the change arm 10 is inserted in an oblong hole 12a formed in a detent element or lever 12 and a detent spring 13 is stretched between the shaft 6 and one end of the detent lever 12.

Apin 19 is fixed to the other end of the detent lever 12 and inserted into a hole provided centrally in the lower end of the body portion of the lever 5, whereby the lever 5 is linked to the detent lever 12.

Printing paper 16 is arranged to pass between the printing element carriage 18 and a platen 15. An ink ribbon 20 passing between spools mounted on the shafts 17a and 17b extends between the carriage 18 and the paper 16.

Initially a ribbon supply spool is positioned on the shaft 17a and during a forward feed run of the ribbon 20, ribbon is drawn off the supply reel by rotation of a take-up spool on the shaft 17b by the pawl 1.

When the forward feed run is complete and the end of the ribbon reached, the mechanism is automatically changed over to a reverse feed run in which the said supply spool now becomes the take-up spool and is rotated by the pawl 1 to rewind the ribbon.

During the forward feed run the lever 5 is pivoted about the shaft 6 such that the pawl 1 and the back-stopper 7b engage the ratchet 4b and the stopper 8a co-operates with the ratchet 4a, while during the reverse feed run the lever 5 is pivoted such that the pawl 1 and the back-stopper 7a engage the ratchet 4a and the stopper 8b co-operates with the ratchet 4b. Engagement of the stopper 8a or 8b with its associated ratchet wheel 4a or 4b prevents further ribbon unwinding rotation of the ratchet wheel (see, for example, Fig. 3).

The distance between the shaft 6 and the stoppers 8a, 8b is made longer than the distance between the shaft 6 and the back-stoppers 7a, 7b by such an amount that when either back-stopper is in contact with the tip of the saw-tooth of the associated ratchet wheel (that is, the ratchet wheel 4b for back-stopper 7b during forward feed, and ratchet wheel 4a for the back-stopper 7a during reverse feed) the operative stopper is disengaged from its associated ratchet wheel which carries the spool off which ribbon is unwinding (see, for example, Fig.

4).

The plate spring 2, which is fixed to the feed pawl 1, contacts the back-stoppers 7a, 7b with respective arms, the amount of deflection of each arm differing because of the difference in distance between said feed pawl 1 and the back-stoppers 7a, respectively due to the pivoting of the lever 5. Therefore, on the direction of feed of the ink ribbon 20 being reversed, the feed pawl 1 will snap out of engagement with the ratchet wheel 4b and engage in the ratchet wheel 4a. A grommet is attached near to the end of the ink ribbon 20 (Fig. 5) to bring about this feed reversal in a manner to be described hereinafter.

Operation of the described said ink ribbon feed mechanism will now be explained with reference to the plan views of the Figs. 3 through 5. In Fig. 3, the mechanism is shown with the lever 5 and pawl 1 tilted for forward feed and the back-stopper 7b engaged in the ratchet wheel 4b and the stopper 8a engaged in the ratchet wheel 4a. During normal operation, the ratchet wheel 4b is driven round one saw-tooth at a time by means of the feed pawl in response to the transverse movement of the plate 3 (as indicated by an arrow B of Fig. 4). The plate 3 moves in response to the reciprocating movement of the carriage 18. As the feed pawl 1 rotates the ratchet wheel 4b, the back-stopper 7b is lifted to contact the tip of a saw-tooth of the ratchet wheel 4b as shown in Fig. 4.At this stage, the stopper 8a is disengaged from the ratchet wheel 4a, allowing the ratchet wheel 4a to rotate due to the pull on the ink ribbon 20. As the rotation of the ratchet wheel 4b by the feed pawl 1 proceeds, the back-stopper 7b engages in the next saw-tooth of the ratchet wheel saw-tooth of the ratchet wheel 4b whereon the stopper 8a engages in the ratchet wheel 4a. Thereby the situation shown in Fig. 3 is restored.

The arrangement is such that when the feed pawl 1 is not actively rotating the ratchet wheel 4b, the back-stopper 7b is engaged in the ratchet wheel 4b and the stopper 8a is engaged with the supply ratchet wheel 4a, and thereby any further rotation of the wheels 4a, 4b which would cause slackening of the ink ribbon 20 is - prevented. The stopper 8a disengages from the ratchetwheel 4a able to rotate while the take-up raised by the rotation of the ratchet wheel 4b. Therefore, at no time is the ratchet wheel 4a unable to rotate while the take-up ratchet 4b is stopped and so the ink ribbon 20 cannot slacken.

In the above description, the ink ribbon 20 is taken up by the ratchet wheel 4h (Figs.

3 and 4) but the direction of movement of the ink ribbon 20 can be reversed (Fig. 5) so that it is taken up by the ratchet wheel 4a.

This reversal of ribbon feed direction is brought about by the grommet 21 which is fixed near the end of the ink ribbon 20 on the side of the ratchet wheel 4a, moving the change arm 10 in a direction indicated by arrow C as the end portion of the ink ribbon 20 winds off the supply spool. The movement of the change arm 10 turns the detent lever 12 about the pin 19, which motion, together with the action of the detent spring 13, rotates the lever 5 in a direction indicated by arrow D. The back-stopper 7a now engages in the ratchet wheel and as the arms of the plate spring 2 are deflected by different amounts, the feed pawl 1 snaps from the ratchet wheel 4b, formerly the take-up side, onto the ratchet wheel 4a. The reciprocating movement of the plate 3 is now transferred, via the feed pawl 1, to the ratchet wheel 4a which is moved intermittently, and so the ratchet wheel 4a becomes the take-up wheel, drawing the ink ribbon 20 in the opposite direction. The stopper 8a can have a plurality of pawl heads.

As described above in relation to the stopper 8a and ratchet wheel 4a, the stopper 8b is always engaged with the ribbon supplying ratchet wheel 4b except when disengaged in response to the movement of the back-stopper 7a and this prevents any backward movement of the ratchet wheel 4a. Thus the stopper which engages on the supply ratchet wheel controls the rotation of the spool and so no excess ink ribbon can be fed which would cause slack forming in the ink ribbon. This is advantageous in that the feeding of the ink ribbon can be stabilized and the quality of the printing can be improved. The described mechanism is particularly useful in high-speed printers used for processing computer data.

WHAT WE CLAIM IS: 1. An ink ribbon feed mechanism, comprising a pair of ratchet wheels which in use of the mechanism have respective associated ink ribbon spools between which an ink ribbon is to be fed, pawl means for intermittently driving one of the ratchet wheels to effect ink ribbon feed, back-stop means arranged to prevent rotation of the driven ratchet wheel opposite to its driven direction, stopper means normally engaging the non-driven ratchet wheel to prevent rotation thereof in a sense to cause ribbon to unwind from its said associated spool, the stopper means being disengageable from the non-driven wheel in response to driving of said driven ratchet wheel, and reversing means operable to cause the pawl means, back stop means and stopper means each to change the ratchet wheel upon which it is arranged to act whereby to reverse the ribbon feed direction.

2. A mechanism according to claim 1, in which the back-stop means are incorporated in a lever biased to engage the back-stop means with the driven ratchet wheel and movable to enable the back-stop means to ride up over the ratchet wheel teeth when the wheel rotates in its driven direction upon operation of the pawl means. said stopper means being arranged to disengage the non-driven wheel in response to movement of the lever caused by said riding up of the back-stop means.

3. A mechanism according to claim 2, in which the lever also incorporates the stopper means and is pivotally supported by a shaft, the distance of the stopper means from said shaft being longer than the distance of the back-stop means therefrom such that the stopper means disengages the non-driven wheel prior to the back-stop means reaching the tip of a tooth of the driven ratchet wheel during said riding up.

4. A mechanism according to claim 3, in which the lever comprises a body portion and four arms two of which constitute said back-stop means and the other two of which constitute the stopper means, the lever being pivoted about said shaft in one sense to engage one back-stop arm with one ratchet wheel and one stopper arm with the other wheel in order to effect ribbon feed in one direction, and in the opposite sense to engage the other back-stop arm with said other ratchet wheel and the other stopper arm with said one wheel in order to effect ribbon feed in the reverse direction.

5. A mechanism according to claim 4, in which the said shaft is located substantially midway between the roots of the two back-stop arms, and a detent element is connected to the lever substantially midway between the roots of the two stopper arms.

6. An ink ribbon feed mechanism according to claim 4 or claim 5, wherein the pawl means engages the lever via a plate spring which is fixed to the pawl means.

7. An ink ribbon mechanism according to claim j, wherein the operative back-stop means is pressed against the driven ratchet wheel by means of the detent element and a detent spring.

8. A feed mechanism to any one of claims 4 to 7, wherein the reversing means comprises change-over means to pivot the lever about said shaft to change over the operative back-stop and stopper arms, the change-over means being arranged to be actuated by a grommet mounted on the ink ribbon near to one end.

9. An ink ribbon feed mechanism according to claim 8 when dependent on claim 5, wherein the change-over means is linked to the detent element through which it interacts with the lever.

10. An ink ribbon feed mechanism, substantially as hereinbefore described with reference to the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. ink ribbon. This is advantageous in that the feeding of the ink ribbon can be stabilized and the quality of the printing can be improved. The described mechanism is particularly useful in high-speed printers used for processing computer data. WHAT WE CLAIM IS:

1. An ink ribbon feed mechanism, comprising a pair of ratchet wheels which in use of the mechanism have respective associated ink ribbon spools between which an ink ribbon is to be fed, pawl means for intermittently driving one of the ratchet wheels to effect ink ribbon feed, back-stop means arranged to prevent rotation of the driven ratchet wheel opposite to its driven direction, stopper means normally engaging the non-driven ratchet wheel to prevent rotation thereof in a sense to cause ribbon to unwind from its said associated spool, the stopper means being disengageable from the non-driven wheel in response to driving of said driven ratchet wheel, and reversing means operable to cause the pawl means, back stop means and stopper means each to change the ratchet wheel upon which it is arranged to act whereby to reverse the ribbon feed direction.