Cassette for a printing ribbon for typewriters

Abstract: A cassette (11) for a printing ribbon (33) for typewriters comprises a casing (12) accommodating a supply spool (34), a receiving spool (36) and a brake and take up device (39) which operates on a tube (37) of the supply spool (34) and on the ribbon (33) which is unwound from the supply spool (34). The tube (37) is rotatable on a sleeve (38) projecting from the bottom (13) of the casing (12) . The brake and take up device (39) comprises a shoe (47) for applying a braking action to an internal surface (41) of the tube (37). A wire spring (48) has an intermediate portion (52) which engages in a seat (56) of coupling means (46) of the shoe (42). In a first position the shoe (42) is urged against the surface (41) of the tube (37) and brakes the supply spool (34). In a second position the shoe (42) is spaced from the internal surface (41) of the tube (37) and the supply spool (34) is free to rotate. The spring (48) also performs the slack ribbon take-up function and for that purpose comprises an end (54) having an L-­ shaped bent portion (55) which in turn is engaged with the ribbon (33) to regulate the tension and unwinding of the ribbon (33) which is unwound from the supply spool (34).

Description: The present invention relates to a cassette for a printing ribbon for typewriters comprising a casing supporting for rotation a supply spool on which a printing ribbon is wound and a receiving spool on to which the ribbon is wound again after having been used, and in which the supply spool includes a tube. A brake shoe is fulcrumed in the casing internally to the tube and biased toward an internal surface of said tube for braking the supply spool, and a ribbon guide is connected with the brake shoe and cooperates with the ribbon which is being unwound from the supply spool. U.S. Patent No. 4,350,454 relates to a cartridge of the above type in which the brake shoe and the ribbon guide are supported by a rigid lever arm, which is pivoted on the casing. The biasing of the arm lever is effected either by a coil spring or, in alternative, by a flexible hub included in the brake shoe. Upon the unwinding of the ribbon, the tension on the ribbon will cause the arm to be rotated against the action of the coil spring or the flexible hub until the frictional engagement between brake and tube is reduced to release the supply spool. In use, therefore, the tension on the ribbon continuously alternates between a maximum when the supply spool is locked and a minimum when the spool is released. A cassette of this type has the disadvantage that the ribbon can be subject to deformation upon the advancing of the printing ribbon and loosening upon the arrest of the ribbon. Swiss Patent No. CH 668 942 relates to a cassette for a printing ribbon comprising a casing and a supply spool with a tube on which a printing ribbon is wound. The supply spool tube is internally toothed and is rotatably supported on a stub axle carrying on one side a corresponding tooth. A wire spring is positioned to urge the spool tube teeth into engagement with the stub axis tooth to brake the supply spool and regulate the ribbon tension. In particular the wire spring has one end fixed to the casing, another end co-operative with the printing ribbon which is being unwound from the supply spool and an intermediate portion co-operative with the external surface of the tube for braking the supply spool. During the feed movement of the printing ribbon, the tension of the ribbon will overcome the tension of the wire spring and the intermediate portion will disengage the external surface of the tube to permit the supply spool teeth and the stub axis tooth to disengage and allow the supply spool to rotate. This arrangement has the disadvantage that the 'brake' acts in a very intermittent, jerky fashion, in the manner of a dog-clutch for example. This cassette also has the disadvantages that the braking action of the wire spring on the tube is not reliable in view of the surfaces of limited dimensions which are in reciprocal contact between wire and tube and the unavoidable resulting wear. As a result, the ribbon in this cassette will be subject to intermittent tension which can cause deformation or loosening in the ribbon. European Patent Application EP-A-0 075 084 discloses a cassette for a printing ribbon comprising a casing with a supply spool, a receiving spool and an omega-shaped spring which is applied against the external surface of an extension portion of the supply spool. The omega-shaped spring comprises two arms of which a first arm is fixed to the casing and the second arm has an L-shaped bent portion which is engaged to guide and tension the ribbon as it is unwound from the supply spool. The tension of the spring holds the omega-shaped part bearing against the external surface of the tube and the supply spool is braked. As the ribbon is advanced, the tension of the ribbon causes the second arm of the spring to flex, thereby expanding the omega-shaped part thereof. The latter no longer bears against the external surface of the tube and the supply spool is free to rotate. The second arm of the spring oscillates continuously, tensioning the ribbon which is unwound from the spool and alternativing braking actions with release actions. That device suffers from disadvantages. In fact, in order for the omega-shaped spring to operate effectively, the extension portion of the tube must be of suitable size and thus the cassette will have to be thicker than is necessary, with the result that it is bulky and cumbersome. In addition, the spring being formed by piano wire, engagement of the omega-shaped portion with the extension portion of the tube, after a brief period of operation, gives rise to play between the components. The braking effect decreases whereby there is a reduction in the control over the rotational movement of the supply spool with a lower degree of tensioning of the ribbon. United States Patent US-A-4 505 605 also discloses a cassette for a printing ribbon in which the brake-take up device comprises two springs. A first spring has one end bent at an angle of 90° and introduced into a central hole in a supply spool. The tension of the ribbon holds the external part of the ribbon which is wound on the supply spool constantly pressed against a wall of the container to apply friction to the ribbon and keep it at a predetermined tension. For that purpose a part of the wall has a series of projections or ribs projecting from the wall by variable amounts such as to compensate for the variations in tension of the spring due to the reduction in diameter of the supply spool. A second spring is engaged with the ribbon which is unwound from the supply spool, to perform the function of providing a take-up effect and tensioning of the ribbon. That brake-take up device also suffers from disadvantages. Indeed, during printing cycles in which the ribbon is advanced, the rubbing effect on the ribbon which is pressed against the projections or ribs due to the action of the first spring causes wear at the outside surface of the ribbon, with the risk of losing pigments. In addition, with the ribbon being of greatly reduced thickness, it undergoes deformation to such an extent as to have parts which become limp, causing a deterioration in the quality of printing. The cassette of the present invention is characterised as defined in claim 1 of the appendant claims. Further preferred features of the invention are defined in the dependent subclaims. The following description sets forth a preferred embodiment of the invention which is given by way of non-limiting example, with reference to the accompanying drawings in which: Figure 1 is a partial plan view of a cassette for a printing. ribbon with a brake-take up device according to the invention, Figure 2 is a partial plan view of some details from Figure 1 in an operative position on an enlarged scale, Figure 3 is a partial plan view of the Figure 2 details in another operative position, Figure 4 is a view in section on an enlarged scale of part of the cassette shown in Figure 1, Figure 5 is a partial front view of some details from Figure 4, and Figure 6 is a partly sectional view of further details of the Figure 1 cartridge on an enlarged scale. Referring to Figure 1, a cassette for a printing ribbon is generally indicated by reference numeral 11 and comprises a casing 12 of plastics material, having a bottom 13, rear walls 14, 16, 17, 18 and 19, two right-hand side walls 21 and 22, a front wall 23 and two left-hand side walls 24 and 26. The casing 12 is closed upwardly by a cover 27 and comprises two arms 28 and 29 projecting from the rear walls 14 and 19, having two openings 31 and 32 which each permit a printing ribbon 33 to pass therethrough. The casing 12 is capable of accommodating a supply spool generally indicated by reference numeral 34 and on to which the ribbon 33 is wound, and a receiving spool generally indicated by reference numeral 36, on to which the ribbon 33 is wound again after having been used. The supply spool 34 is rotatable by means of a tube 37 on a sleeve 38 projecting from the bottom 13 of the casing 12. A brake and take up device generally indicated by reference numeral 39 operates and co-operates with an internal surface 41 of the tube 37 and comprises a brake shoe 42 which is movable within the tube 37. The brake shoe 42 is pivotally mounted on the sleeve 38 and rotates in both directions by means of a pin 43 (see Figures 2, 3, 4 and 5) which is positioned at one end and capable of being accommodated in a hole 44 in the sleeve 38. At the other end the brake shoe 42 comprises coupling means 46 and an external surface 47 co-operable with the internal surface 41 of the tube 37. The brake-take up device 39 comprises a spring 48 (see Figures 1, 2, 3, 4 and 5) of the wire type and having an L-shaped bent end 49 accommodated in a hole 50 in a fixed support 51 of the casing 12. A tongue portion 65 on the casing 12 is normally disposed over the end 49 of the spring 48 and prevents undesired vertical movements of the spring 48. An intermediate portion 52 of the spring 48 is co-operable with a fixed pin 53 projecting from the sleeve 38 and with the coupling means 46 to provide prestressing of the spring 48. Finally a terminal portion or take-up element 54 of the spring 48 has an L-shaped bent portion 55 against which the ribbon 33 is engaged and guided as it is unwound from the supply spool 34. The coupling means 46 comprise a fork element on the brake shoe, which defines a seat 56 which can always be engaged by the intermediate portion 52 of the spring 48. The spring 48 is therefore capable of positively controlling the brake shoe 42 to position it from a first position in which it brakes the supply spool 34, as shown in Figure 2, to a second position in which it permits the supply spool 34 to rotate freely, as shown in Figure 3, and vice-versa, as will be described in greater detail hereinafter. The sleeve 38 has an external surface 57 delimited by vertical ribs 58 of semi-cylindrical shape and capable of co-operating over their full height with the internal surface 41 of the tube 37, being such as to reduce the contact surface area as between the sleeve 38 and the internal surface 41 of the tube 37 and to permit an easy sliding movement, even when there are wear particles between the components. The ribs 58 are positioned only over one half of the circumference of the sleeve 38 and are disposed in opposite relationship to the brake shoe 42. In the half opposite to that provided with the ribs 58, the sleeve 38 has a space delimited by a lowered edge 59, substantially halfway along the height of the tube 37. The hole 44 is provided in the lowered zone and the shoe 42 extends like a flag from the edge 59 to the upper edge of the tube 37 and is supported movably on the edge 59. The seat 56 of the fork element 46 holds the portion 52 in line with the upper edge of the tube 37. The cover 27 also has a recess 60 to permit free movement of the fork element 46. A wire spring 61 which is pivotally mounted by an intermediate portion thereof about a fixed pin 62 on the bottom 13 has one end 63 engaged against a fixed pin 64 on the bottom 13. The other end 66 of the spring 61 has an L-shaped bent portion which is accommodated in a central hole 67 (see Figure 1) of a tube 68 of the receiving spool 66. The tension of the spring 61 always holds the tube 68 in a displaced position in which it is pressed, with the ribbon 33 which is being wound on to the receiving spool 36 again, against the teeth of a drive wheel 69 for the unidirectional feed movement of the ribbon 33. The wheel 69 is fixed and coaxial with a sawtooth wheel 71 (see Figures 1 and 6) which is positioned at a higher level with respect to the receiving spool 36 and which therefore does not interfere with the ribbon 33 when it is being wound on to the tube 68 again. The sawtoothed wheel 71 co-operates with a resilient blade portion 72 mounted on a fixed support 73 of the casing 12 and capable of preventing rotary movement of the wheel 69 in the reverse direction and thus unwinding of the ribbon 33 from the spool 68. When the cassette 11 is mounted on a typewriter, the wheel 69 can be coupled to a drive shaft 74 of the machine, which rotates the wheel 69 for the unidirectional feed movement of the ribbon 33. The wheel 69 is also fixed with respect to a gripping portion 76 which projects from the cover 27 for manual feed movement of the ribbon 33. The casing 12 comprises a through slot or groove 77 (see Figures 1 and 4) which is provided in the bottom 13 and which is capable of accommodating the lower end of the L-shaped bent portion 55 of the spring 48 to facilitate the movement of the bent portion and to prevent contact from occurring between the bent portion and the bottom 13. The ribbon 33 is unwound from the supply spool 34, is engaged with the L-shaped bent portion 55 and by way of the opening 31 issues from the casing 12 to pass back into the casing 12 again by way of the opening 32, is guided around a fixed pin 78 on the bottom 13 and is then rewound on to the tube 68 of the receiving spool 36. When the cassette 11 (see Figures 1, 2, 3 and 6) is removed from the typewriter or is mounted but printing cycles are not being performed, the tension of the spring 48 holds the ribbon 33 in a constantly tensioned condition. In addition the intermediate portion 52 holds the brake shoe 48 in its first position in which the external surface 47 is engaged against the internal surface 41 of the tube 37, as shown in Figure 2. The supply spool 33 will thus be braked. As soon as the printing cycles begin, the toothed wheel 69 is rotated by the drive shaft 74, for example as described in our EP - A 0 333 375. The tube 68 of the receiving spool 36 is driven in rotation by the toothed wheel 69 and causes unidirectional forward movement of the ribbon 33. The tension of the ribbon 33 overcomes the tension of the spring 48 and causes the spring 48 to flex by means of the end 54 and the L-shaped bent portion 55. The intermediate portion 52 of the spring 48 then entrains the brake shoe 42 in an anti-clockwise rotary movement and positions it in its second position in which the external surface47 of the shoe 42 is spaced from the internal surface 41 of the tube 37, as shown in Figure 3. The supply spool 34 is free to rotate and the ribbon 33 is free to advance. The spring 48 which also performs the function of a take-up means to regulate the tensioning of the ribbon 33, with its end 54 and the L-shaped bent portion 55, will continuously oscillate between intermediate positions delimited by the solid line and the broken line, as shown in Figure 1, alternating braking actions with slackening actions in regard to the spool 39, while the ribbon 33 is always. normally and uniformly tensioned. As soon as the printing cycles come to an end, the toothed wheel 69 is stopped and the ribbon 33 is not advanced any further, the tension of the spring 48 gradually causes the brake shoe 42 to rotate in the clockwise direction, by means of the intermediate portion 52, to position it in the first position in which the external surface 47 of the shoe 42 is again engaged against the internal surface 41 of the tube 37 and the supply spool 34 is braked. At the same time the spring 48 still continues with its take-up function and by means of the end 54 and the L-shaped bent portion 55 holds the ribbon 33 in a constantly tensioned condition, being resisted by the reverse action applied by the blade portion 72 to the sawtoothed wheel 71. It will be appreciated that the cassette 11 for the ribbon 33 may be the subject of modifications and improvements both in regard to the shape and the arrangement of the various components and elements without departing from the scope of the present invention. In particular the external surface 47 of the brake shoe 42 may be substantially both to co-operate with the smooth internal surface 41 of the tube 37, as described hereinbefore, or it may be knurled to co-operate with the smooth or knurled internal surface 41 of the tube 37. Finally it may be provided with a tooth capable of meshing with an internal tooth arrangement provided on the internal surface 41 of the tube 37. The brake shoe 42 may be supported by parts of the cover 27 of the casing 12 which are independent of the sleeve 38 on which the tube 37 of the supply spool 34 is rotatably mounted. In addition, the brake shoe 42 may be coupled to the take-up element by means of intermediate cam or lever elements to modify the braking action of the shoe 42 on the tube 37 with respect to the accumulation and tensioning effect applied by the spring 48 to the ribbon 33 as it is unwound from the supply spool 34. For the purposes of its braking action, the shoe 42 may involve a linear movement which is produced by means of sliding couplings rather than rotational couplings. Finally it will also be apparent that the supports disposed on the casing 12 may also be provided by the cover 27 rather than by the bottom 13, without departing from the scope of the invention. The printing ribbon cassette illustrated is simple, reliable in use and of limited bulk, and makes it possible for the ribbon always to be correctly tensioned both in the rest position and in the operating position, thus enhancing printing of optimum quality.

Claims: A cassette (11) for a printing ribbon (33) for typewriters comprising a casing (12) supporting for rotation a supply spool (34) on which a printing ribbon (33) is wound and a receiving spool (36) on to which the ribbon is wound again after having been used, and in which the supply spool includes a tube (37); a brake shoe (42) fulcrumed in the casing (12) internally to the tube (37) and biased toward an internal surface (41) of said tube for braking the supply spool; and a ribbon guide (55) connected with the brake shoe (42) and cooperative with the ribbon (33) which is being unwound from the supply spool (34), characterized by a spring wire (48) having one end portion cooperative with a projecting portion (51) of the casing (12) spaced apart from the maximum diameter of the supply spool, an intermediate portion (52) cooperative with an arrest member (53) of the casing and a coupling member (46) of the brake shoe, a second end portion provided with the ribbon guide (55), and a free portion adjacent to the said second end portion; wherein the arrest member is located internally to the tube to prestress the intermediate portion of the spring wire (48) for the biasing of the brake shoe; wherein the said free portion is provided to flex and regulate the tensioning of the printing ribbon (33) and the bias of the brake shoe, while the printing ribbon (33) unwinds from the supply spool (34); and wherein said coupling member comprises a seat (56) on the brake shoe which holds the intermediate portion (52) of the wire spring in line with an upper edge of the said tube (37). A cassette according to claim 1, characterized in that the arrest member (53) comprises a pin close to said tube. A cassette according to claim 1 or 2, characterized by a support sleeve (38) on which the supply spool (34) is rotatable, wherein the said sleeve (38) comprises a recess having a hole (44) and wherein said brake shoe (42) is lodged in said recess and comprises a shoe pin (43) pivotable in the hole (44) for its braking movement. A cassette for a printing ribbon according to claim 3, wherein the support sleeve (38) includes vertical ribs (58) of semi-cylindrical shape and cooperative with the internal surface (41) of the tube (37) to reduce the area of contact between the sleeve (38) and the internal surface (41) of said tube (37). A cassette according to claim 3 or 4, characterized in that the arrest member (53) and the seat (56) are positioned opposite each other in said recess and cooperate with two sections of the intermediate portion of the spring wire (48). A cassette according to any preceding claim wherein the ribbon guide (55) comprises an L-shaped bent portion at the second end portion of the spring wire (48), on which the printing ribbon (33) is guided as it is unwound from the supply spool (34). A cassette according to claim 6, wherein the casing (12) comprises a slot (77) to accomodate an end (54) of the L-shaped bent portion to facilitate the free movement of said second end. A cassette according to claim 7, wherein the slot (77) is provided in a bottom wall (13) of the casing (12) and wherein said casing (12) further comprises a cover (27) having a recess (60) to permit free movement of said coupling member (46). A cassette according to any of the preceding claims, wherein the coupling member (46) comprises a fork element which is engaged by the intermediate portion (52) of the spring wire (48) for a positive connection between the spring wire and the brake shoe. A cassette for a printing ribbon according to any of the preceding claims, wherein as soon as the printing cycles terminate, the tension of the spring wire (48) moves the brake shoe (42) gradually from a releasing position to a braking position to brake the supply spool (34), at the same time holding the printing ribbon (33) in a constantly tensioned condition by means of the ribbon guide (55).

Inventors: GILLIO CLAUDIO, GILLIO, CLAUDIO
Applicants: OLIVETTI & CO SPA, ING. C. OLIVETTI & C., S.P.A.
Application year: 1990
Main classification: B41J32
IPC codes: B41J32, B41J33, B41J35