GB2078672A

GB2078672A - Braking Unwinding Spool in Ribbon Cassette

Info

Publication number: GB2078672A
Application number: GB8039273A
Authority: GB
Original assignee: TA Triumph Adler AG
Current assignee: TA Triumph Adler AG
Priority date: 1980-06-21
Filing date: 1980-12-08
Publication date: 1982-01-13
Also published as: CH647721A5; SE442974B; IT8026920A0; GB2078672B; IT1150072B; DE8016521U1; SE8007794L

Abstract

A ribbon cassette (1) for use in typewriters comprises a casing (2) in which a supply spool (4) is mounted for rotation together with a toothed disc (20) on a common pin (3). A tensioning and guiding device (10) which also acts as a brake for the supply spool (4) consists of a bent wire having a first section (11), fixed at its free end to the casing at (2a), a second section (12) extending substantially perpendicularly to the first section and a junction portion (14) which is adapted to engage in the toothed disc (20) to prevent rotation of the supply spool. Ribbon unwound from the supply spool is guided round the free end (15) of the second section, which free end may carry a roller (17). The tensioning and guiding device is arranged such that, when tension is applied to the ribbon to unwind it from the supply spool, the second section (12) pivots about portion (14) by a predetermined extent before the detent portion becomes disengaged from the toothed disc on movement of the first section. A take up spool (7) is driven by spikes on a wheel (8) penetrating into the ribbon being wound onto spool (7). The spool (7) is carried on a pivotable lever (5) so that spool (7) pivots towards the supply spool (4) as the diameter of the ribbon wound on spool (7) increases. The device (10) delays movement of the supply spool until slightly after drive wheel (8) has started rotating so that the raising of the ribbon (16) to its printing position is not hindered. <IMAGE>

Description

SPECIFICATION Improvements in or Relating to Printing Ribbon Cassettes The present invention relates to printing ribbon cassettes.

The invention is particularly, but not exclusively, suitable as a ribbon cassette for use in a typewriter. However the cassette may be used in other forms of printing apparatus.

Typewriter ribbon cassettes are known in which the ribbon is wound on a supply spool.

From the spool it is drawn off by means of a driving device, is guided past the printing location and drawn into the cassette once again. With some of these cassettes, the used ribbon is again wound onto a return spool. This return spool can be mounted on a pivotable spring loaded lever which, with an increase in the diameter of ribbon wound on the return spool, is pivoted towards the supply spool against the spring force. This arrangement has the advantage that the cassette casing can be more compact because the diameter of the supply spool decreases whilst the diameter of the return spool increases and, because it is pivotably mounted, the increased diameter return spool can move into the region vacated by the reduced diameter supply spool.

However, with such cassettes, it is absolutely necessary to brake the unwinding spool. This is essential since the ribbon must be prevented from unwinding from the spool unintentionally and forming loops or being supplied to the printing location at an incorrect tension. The unwinding ribbon must also run over set guides at least one of which serves as a ribbon tensioner.

The present invention provides a ribbon cassette comprising a casing having disposed therein a supply spool of printing ribbon, a toothed disc mounted for rotation with the supply spool, and a tensioning and guiding device comprising an elongate resilient member having first and second sections which adjoin at a detent portion which is adapted to engage in the toothed disc to prevent rotation of the supply spool, the free end of the first section being fixed to the casing and the free end of the second section being arranged to form a guide for ribbon unwound from the supply spool thereof, the second section being arranged to move by a predetermined extent before the detent portion becomes disengaged from the toothed disc when tension is applied to the ribbon in order to unwind it from the supply spool.

In order that the invention may be well understood an embodiment thereof will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a plan view of a typewriter ribbon cassette with an upper part of its casing removed showing a full supply spool; Figure 2 is a view similarto Figure 1 showing a nearly full return spool; and Figure 3 is a respective view on a reduced scale of a tensioning and guiding device as fitted to the cassette of Figures 1 and 2.

A cassette 1 is provided with a casing, a lower part of this casing is shown in the drawings while the upper part has been removed to expose the interior of the cassette.

The cassette has a mounting pin 3 for the supply spool 4. The mounting pin 3 is made integral with the cassette casing 2. A pivotable lever 5, which is biased by a tension spring 6, carries the take-up or return spool 7. The latter is driven by means of a wheel 8 which carries pointed pins 9 which penetrate into the ribbon being wound onto the take-up spool 7. The drive for the wheel 8 is taken from outside the cassette in known manner, for example by means of a motor on the shaft of which is mounted a coupling which engages with the shaft of the wheel 8. However, no drive means for wheel 8 is illustrated in the drawings.

A tensioning and guiding device comprises an elongate resilient member or wire 10, the shape of which can be seen from Figure 3. One free end of the wire 10 is fixed to the part 2a of the cassette casing wall 2. The wire 10 consists substantially of first and second sections 11 and 12 which extend substantially perpendicularly to one another. The free end of the first section 11 is provided with an angled portion 13 for insertion in a recess formed in part 2a of the wall 2 of the cassette 1.A detent portion 14 is angled relative to both sections 11 and 1 2 and is provided at the junction between the two sections 11, 12 so that the plane of the section 12 lies deeper than that of the section 1 The sections 11 and 12 act as a ribbon brake and ribbon tensioner in the manner still to be described.

At the free end of the second section 12, there is a further angled portion 1 5 which is once again directed upwardly. This angled portion 1 5 serves as a guide for the ribbon 1 6 and can be provided with a roller 17 in order to prevent friction. In an intermediate region of the first section 11, the wire 10 is supported by engagement with a projection 1 8 from the cassette wall 2 and is therefore under a predetermined tension.

As can be seen from Figures 1 and 2, the first section 11 of the wire up to the angled detent portion 14 lies on an upper side of the supply spool 4 and the second section 1 2 lies on the other side below the supply spool 4. Moreover, the angled portion 14 engages in the teeth 1 9 on a toothed disc 20 which is mounted on the mounting pin 3 together with the supply spool 4 and is rotatable together with the supply spool 4.

The ribbon 16 runs from the supply spool 4 around the angled portion 1 5 or roller 1 7 to a further deflecting member 30 fixed to the casing and thus rigidly arranged in the cassette. From there the ribbon is guided to the cassette outlet 21, proceeds to the printing location which lies substantially in the region designated by the arrow 22, but which is not illustrated in detail.

The used ribbon is drawn back into the cassette 1 once again through the opening 23 around further deflecting members 24 and 25 until it is finally wound onto the take-up spool 7.

By means of the previously described drive, a tension in the direction of the arrow 26 is produced on the ribbon 16 by the wheel 8 so that the second section 1 2 of the wire 10 is first of all under load, and therefore the second section 1 2 pivots in the direction of the arrow 27. However, the angled detent portion 14 still remains in engagement with the teeth 1 9 on the disc 20 until the second section has moved by a predetermined extent. Thus, the supply spool 4 is not rotated immediately a certain tension occurs in the ribbon 16. Only during a further movement of the ribbon transport does the angled detent portion 14 become disengaged from the teeth 19 on the disc 20 whereupon the braking of the supply spool 4 is removed.The deflection of the angled detent portion 14 takes place in such a manner that the section 1 a of the wire 10 is moved in the direction of the arrow 28. The resultant of the two movements 27 and 28 is illustrated in Figure 1 by the arrow 29.

The movement referred to is achieved in such a manner that initially the second section 12 of the wire 10 performs a pivotal movement substantially tangentially to the supply spool 4 and then the first section 11 of the wire 10 performs a similar tangential movement with respect to the supply spool 4 but which is substantially perpendicular to the direction of movement of the second section 12. Thus, the tension 26 of the ribbon 16 first of all causes the resilient second section 12 of the wire 10 and then the resilient first section 11 of the wire 10 to move. Only with the second movement is the supply spool 4 released for rotation.Thus, movement of the mass, which is represented by the supply spool 4, is delayed to a later instant after drive means for wheel 8 is started whereby the raising of the ribbon 1 6 to the level of the lines of print is no longer hindered.

The desired operation of the tensioning and guiding device can be influenced by various factors. One of these relates to the resilience or spring force and the tensioning of the wire 10. A further factor is the position of the deflecting member 30. Experiments have shown that a particularly favourable effect is achieved when the deflecting member 30 lies laterally of the supply spool 4 and displaced a distance which corresponds substantially to half the radius r of the full supply spool 4 from the centre of the supply spool.

Further it will be noticed that the arrangement of the present cassette prevents the coated side of the ribbon being supplied to the printing locations from contacting any ribbon tensioner or guide member. Thus the ink particles are not prematurely removed from the film and therefore clear characters of consistent tone are printed.

This is particularly important when the ribbon comprises a thin foil coated on one side with a colouring agent.

Another important feature of the present cassette is that the second section 12 of the tensioning device carries out a prelimimary movement as a result of a pull on the ribbon before the detent portion 14 leaves the teeth 1 9 of the disc 20 fixed to the supply spool 4. Thus essentially more favourable acceleration characteristics of the masses to be moved are achieved. Thus the device reacts positively to ribbon tension 26 due to operation of the drive means of wheel 8, whilst permitting the ribbon to be readily raised to its printing position.

Claims

1. A ribbon cassette comprising a casing having disposed therein a supply spool of printing ribbon, a toothed disc mounted for rotation with the supply spool, and a tensioning and guiding device comprising an elongate resilient member having first and second sections which adjoin at a detent portion which is adapted to engage in the toothed disc to prevent rotation of the supply spool, the free end of the first section being fixed to the casing and the free end of the second section being arranged to form a guide for ribbon unwound from the supply spool thereof, the second section being arranged to move by a predetermined extent before the detent portion becomes disengaged from the toothed disc when tension is applied to the ribbon in order to unwind it from the supply spool.

2. A cassette as claimed in claim 1, wherein the first section of the elongate member is disposed to one side of the supply spool and the second section is disposed to the other side of the supply spool.

3. A cassette as claimed in claim 1 or 2, wherein the detent portion comprises a portion angled relative to the first and second sections.

4. A cassette as claimed in any one of the preceding claims, wherein the first section is tensioned by engagement with a projection extending from the cassette casing.

5. A cassette as claimed in any one of the precedin, claims, wherein the path of ribbon unwound from the supply spool is past the free end of the second section and then past a deflecting member fixed to the casing, the deflecting member being disposed laterally of the supply spool and displaced a distance equal to half the radius of a full supply spool to the rear of the cassette from the centre of the supply spool.

6. A cassette as claimed in any one of the preceding claims for use in a typewriter.

7. A typewriter ribbon cassette provided with a device made of wire for tensioning and guiding the ribbon, characterised in that, the wire fixed to one of the cassette walls has two sections which are arranged substantially perpendicular to one another, wherein an angled portion at the junction of the two sections engages resiliently in a toothed disc on the supply spool and the second section of the wire carried an angled portion at its free end for guiding the ribbon.

8. A ribbon cassette substantially as herein described with reference to the accompanying drawings.