Abstract:
An ink ribbon cassette with two projecting arms between which an ink ribbon is held exposed for printing. The cassette has a positioning slit in one of the arms, extended perpendicular to the running direction of the ink ribbon, and two side fixing projections. The former fixes the cassette in the running direction of the ribbon while the latter fix the cassette in the vertical direction, thus securing improved mounting of the cassette and preventing undesirable movement of the cassette.

Description:
This application is a continuation of application Ser. No. 814,773 filed 12/30/85 now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an ink ribbon cassette in which an internally contained ink ribbon is guided by a guide arm and exposed to the experior thereof, and to a loading mechanism therefor. 
     2. Description of the Prior Art 
     Impact printers often employ so-called use ink ribbon which loses ink in an area once hit by a type letter. Such an ink ribbon is usually contained in a cassette, and is advanced by a minimum pitch since economy in use of the ribbon is desired recently. However, the advancement with such a minimum pitch may cause defective printing since the area in which the ink is already lost may be hit by the type letter again if the ribbon is displaced by unexpected vibration during a printing operation. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide an ink ribbon cassette which can be loaded with precise positioning. 
     Another object of the present invention is to enable more precise positioning and loading of an ink ribbon cassette. 
     Still another object of the present invention is to enablew smooth positioning and loading of an ink ribbon cassette. 
     Still another object of the present invention is to prevent movement of an ink ribbon cassette caused by operations of a ribbon advancing member. 
     Still another object of the present invention is to increase the supporting force for an ink ribbon cassette. 
     Still another object of the present invention is to provide a loading mechanism for an ink ribbon cassette, which enables the ink ribbon cassette to be loaded in an exact position with a simple structure. 
     Still another object of the present invention is to achieve more precise positioning of an ink ribbon cassette. 
     Still other objects of the present invention will become fully apparent from the following description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The attached drawings illustrate an embodiment of the present invention, wherein 
     FIG. 1 is a perspective view of an entire cassette ane a portion of a mounting mechanism for it; 
     FIG. 2 is a bottom plan view of the cassette; 
     FIG. 2A is a block diagram showing a spring biasing a take-up reel toward a ribbon feed roller; and 
     FIG. 3 is a perspective view indicating preferred dimensions of the cassette. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 illustrates an embodiment of the present invention, wherein an ink ribbon cassette 1 is loaded on a pivotable plate 2, constituting a supportfor the ink ribbon cassette, fixed on a carriage of an unrepresented printer. Under the pivotable plate 2 there is provided an eccentric cam 3,of which rotation causes vertical pivotting of the plate 2, thus inducing integral pivotting of the ink ribbon cassette loaded on said pivotable plate. 
     As shown in FIG. 2, in a main body 4 of the ink ribbon cassette 1, there are provided a feed spool 6 wound on a reel 5, and a take-up reel 10 for winding a ribbon 7 which is drawn from the spool 6, guided to the exteriorfrom the front end of a guide arm 8 and then to the interior from the frontend of another guide arm 9. The take-up reel 10 is rotatably supported at an end of a lever 12 which is rotatable about a pin 11, and is biased in adirection A by a spring 30, toward a ribbon feed roller 13, as illustrated in FIG. 2A. On the periphery of said ribbon feed roller 13 there are provided pins 13a to wind the ribbon on the reel 10 by contacting the ribbon. The ribbon feed roller 13 is driven by an unrepresented driving claw protruding from the carriage and engaging with a cross-shaped groove 13b of the ribbon feed roller 13. The ribbon feed roller 13 is provided atthe lower right corner, in FIG. 2, of the main body 4. The take-up reel 10 becomes larger as it takes up the ribbon, and the lever 12 is therefore moved in a direction opposite to A, so that the take-up reel does not touch the wall of the cassette. The positioning of the ribbon feed roller 13 at the lower right corner allows maximizing the amount of ribbon to be taken up. On the lower face of the arm 9 there is formed a positioning slit 14, which is parallel to the direction of the arm 9 and is perpendicular to the advancing direction of the ribbon between the arms 8,9. In the slit 14, a central slit recess 14a formed inside of the bottom face of the main body 4 is connected to the bottom face by slant faces 14b, and a positioning flat protrusion 16a projecting from a support arm 16 is guided by the slant faces 14b and fitted in the slit recess 14a to support the cassette. As shown in FIG. 1, support arms 15, 16 protrude from the pivotable plate 2, corresponding to the arms 8, 9 of the ink ribbon cassette, and projections 15b, 16b support the bottom face of the arms 8, 9. 
     On both lateral faces of the cassette main body 4, there are provided flat pins 17, 18 for fixing the cassette to the pivotable plate 2. The pins 17,18 are rectangular in cross section perpendicular to the projecting direction thereof, and are provided with a tapered face such as 18a shown in FIG. 3, for achieving smooth engagement in portions corresponding to fixing pawls 20. In the positions corresponding to the pins 17, 18, the pivotable plate 2 is provided with fixing pawls 20 rotatably biased by springs 19 in a direction B about shafts 21. Each of said fixing pawls 20 is provided with a push lever 22, which, when depressed, rotates the fixing pawl 20 in a direction opposite to B, thus disengaging the pawl 20 from the pin 17 or 18. 
     The ink ribbon cassette 1 can be mounted on the pivotable plate 2 by merelypressing the cassette 1 against the pivotable plate 2. The fixing pawls 20,of which slant faces 20a are pressed by the pins 17, 18, rotate in a direction opposite to B against the force of the springs 19, and, when thepins 17, 18 pass, again rotate in the direction B to engage with said pins 17, 18. The springs 19 of the fixing pawls 20 press the cassette against the pivotable plate, and the rear end 4a of the cassette main body 4 against a rear bent portion 2a of the pivotable plate 2, thus defining theposition of the cassette in the front-rear direction. On the upper face of the pivotable plate 2 there is provided a plate spring 23 to press the cassette main body 4 upward. The spring 23 firmly presses the pins 17, 18 against the fixing pawls 20 and generates a moment to engage the lower face of the arms 8, 9 with the projections 15b, 16b of the support arms 15, 16 as explained before. In this manner the cassette position in the vertical direction is defined. 
     In a state where the cassette is mounted on the pivotable plate 2, the flatprotrusion 16a of the support arm 16 snugly engages with the slit recess 14a, thus avoiding the movement of the cassette 1 in the lateral directionperpendicular to the arms 8, 9. 
     Also in the mounted state of the cassette, a rear pin 24, protruding opposite to the arm 9 at the left-hand end, in FIG. 1, of the rear end 4a of the cassette main body 4, engages with a positioning notch 2b formed inthe rear bent portion 2a of the pivotable plate. 
     The rear pin 24 prohibits the movement of the cassette main body 4 at the rear end thereof with respect to the pivotable plate 2, and improves the positioning accuracy of the cassette in cooperation with the slit 14. 
     The ribbon feed roller 13 is provided with an integral manual feed knob 13cexposed from the upper face of the cassette, thus allowing take-up of the slack of the ribbon 7. 
     The ribbon feed roller 13, which is rotated by the driving claw provided onthe carriage as explained before, is scarcely affected by the driving forcethereof because of the position of the roller close to the rear pin 24 on aline connecting the rear pin 24 and the slit 14, thus minimizing the movement of the ribbon cassette resulting from the ribbon advancement. 
     FIG. 3 shows preferred dimensions of the ink ribbon cassette of the presentembodiment, but it will be readily understood that the dimensions can be modified. 
     The above-explained embodiment has the following advantages. 
     First, the cassette 1 does not move in the advancing direction C of the exposed ink ribbon since the positioning slit 14 is provided in the arm 9 which is close to the printing position of the ink ribbon. The movement ofthe cassette 1 in direction C is further reduced by the fact that the slit recess 14a extends along the arm 9 and engages with the flat protrusion 16a. 
     Upon molding the cassette, the slit 14 and the rear pin 24 can have a very high relative positional precision, since the rear pin 24 is placed closest to the slit 14 at the rear end of the cassette main body 4. Consequently, the mounting precision of the cassette can be significantly improved. 
     Also, the fixing pins 17, 18 provided on both lateral faces of the main body 4 have a flat form, allowing engagement with the fixing pawls 20 through large areas. Consequently, the cassette 1 can be firmly fixed to the pivotable plate 2. 
     It is to be understood that the present invention is not limited to the foregoing embodiment. For example, the ink ribbon is not limited to one-time ink ribbon, but can be a correctable ribbon or any other ribbons.