Abstract:
A ribbon cassette for electronically controlled typewriters or similar machines equipped with a signal generator, the ribbon cassette being disposed on a carriage moveable along the platen. The present invention is also directed to the combination of such a ribbon cassette with such a machine.

Description:
BACKGROUND OF THE INVENTION 
     The subject of the invention is a ribbon cassette for electronically controlled typewriters or similar machines equipped with a signal generator, the ribbon cassette being disposed on a carriage movable along the platen. The invention is also directed to the combinatioin of such a ribbon cassette with such a machine. It happens in such machines again and again that it is not recognized at all whether or not a ribbon cassette is inserted. It should be recognizable additionally, without the operator having to continually check, whether the ribbon supply is at an end or whether the transport step for the ribbon was adjusted optimally. If the transport step is not adjusted in accordance with the ribbon type, the result is either poor reproductions or the use of unnecessarily large amounts of ribbon. 
     In DE-GM No. 79 10 078 a device is described which recognizes when the ribbon is used up. However, this known machine requires that the type carrier carriage also pull a Bowden wire. Adjusting to different transport steps is not known from this publication. 
     It is known from DE-G No. 81 13 008 to select automatically one of two ribbon transport steps by means of a design feature on the ribbon cassette. This is done purely mechanically. The end of the ribbon is not detected. Also, DE-OS No. 31 09 299 is a known device by means of which an automatic adjustment of the transport step takes place. But this known device has the disadvantage that position tolerances can have an unfavorable effect, for instance, between ribbon cassette and carriage. In addition, the carriage has to move a greater mass. Also, electrical connections must be provided from this movable device to the stationary machine logic, which requires additional electrical lines. This device is also not suited to detect the ribbon end. 
     It would cause additional costs if it were intended to realize in these devices a transport step adjustment or a ribbon end detector. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to create a simple device making it possible both to signal whether a ribbon cassette is inserted at all and to adjust the transport step automatically if required. This is provided by the ribbon cassette according to the present invention, without loading the carriage with an additional mass. An advantage is that the expense of the ribbon cassette is not increased. There is also no additional loading of the carriage with switches, light barriers or cables. 
     By means of the ribbon cassette according to the present invention, a signal is provided to indicate whether or not a ribbon cassette has been inserted. Further the machine can be adjusted automatically to the transport step appropriate for the type of ribbon. Also, a warning signal is emitted when the ribbon is used up, or the machine can be automatically shut off. 
     Overall, greatly different operating states of a typewriter or printer can be detected or set with the present invention, without the operator having to pay special attention to the ribbon. The interpretable information, resulting from the interaction of the switching element on the cassette with the signal generator provided on the machine according to the present invention, can be obtained, for example, during the usual operation of turning-on such machines. Signaling the end of the ribbon, or the shutting off of the machine when the ribbon end is reached, makes it necessary for the switching element to interact with the signal generator in certain time intervals during the operation of the machine. This can be done, for instance, when the carriage reaches the left margin. But it is also possible by actuating a certain key, e.g. the backspacer, to run an intermediate routine during which the signal generator is activated. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The drawing indicates schematically one exemplary embodiment of the invention, showing a part of a ribbon cassette and the signal generator provided on the machine side. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     The ribbion cassette 1 comprises a coil 2 of ribbon 3 on a supply spool, from which the ribbon 3 is unwound and led to the outside through an opening 4. Not shown in the drawing are the inlet opening and the rewind spool. A lever 6, a tab 7 of which rests on the coil 2 on the supply spool, is mounted so as to pivot about an axis 5. In the embodiment shown, an extension of the lever 6 with a switching element 8 projects through a cutout 9 in a wall 10 of the ribbon cassette 1 to the outside. 
     Installed in the typewriter itself is a signal generator 11. The embodiment shown includes a forked light barrier 12 and a slide 14 which is spring-loaded in the direction of arrow A. In the slide 14 are windows 15 which alternately let the light beam of the forked light barrier 12 go through or interrupt it. 
     The signal generator 11 is mounted in relation to the switching element 8 in the ribbon cassette so that the switching element 8 activates the signal generator 11 in certain time intervals during the operation of the machine. For example, the signal generator 11 may be disposed on the left side of the machine frame so as to be activated whenever the carriage arrives in its position at the beginning of the line. But it is also possible by actuating a certain key, e.g. the backspacer, to activate an intermediate routine in which the signal generator 11 is acted upon by the switching element 8. 
     Through the interaction of switching element 8 and signal generator 11, information important for the operation of the machine can be imparted to the machine. For example, if no ribbon cassette 1 is present, the signal generator 11 is not activated. Thus, the machine logic does not permit operation of the machine. The same occurs if the tab 7 of lever 6 slides off the coil 2 on the supply spool, as a result of the diameter of the coil 2 becoming too small to support the tab 7. The switching element 8 then assumes a position below the line B, which also results in the slide 14 of the signal generator 11 being unable to be acted upon when the carriage with the ribbon cassette 1 reaches a certain position, namely a position at which a signal pulse would normally be generated. Therefore, if the diameter of the coil 2 on the supply spool decreases during operation of the machine to the point that the tab 7 of lever 6 can drop, this results in production of a signal &#34;ribbon used up, insert new ribbon cassette&#34;. The tab, however, may be designed so that the ribbon supply remaining at that time still suffices to print a predetermined number of characters. 
     As to its length L, the switching element 8 may be differently designed, depending on the type of ribbon 3 installed in the ribbon cassetee 1. If L is short, the slide 14 is moved a short distance only so that only one status change is generated, for example from BRIGHT to DARK. This signal can be utilized to set the transport step for the ribbon 3 to a clearly defined length. If L is longer, the slide 14 is moved a greater distance so that several status changes can be generated, for instance by the slide 14 containing several windows 15. This signal sequence then sets a predetermined other transport step for the ribbon 3 by means of the machine logic. Of course, several different ribbon types can thus be recognized, and the transport steps set accordingly. 
     A modification of the embodiment shown can involve replacing the forked light barrier 12 of the signal generator 11 by a different device. In cases in which it is not necessary to also signal the end of the ribbon 3 coiled on the supply spool, the switching element can also be mounted as a stationary element on the ribbon cassette to indicate the type of ribbon to control the transport step. 
     Thus, the advantages described above can be obtained at minimal cost. In particular, the extra costs for the ribbon cassette 1 are negligible, because the lever 6 with the tab 7 and the switching element 8 can be designed as simple injection-molded parts, which can also be assembled automatically on the ribbin cassette 1. 
     It will be obvious to those skilled in the art that various changes may be made without departing from the scope of the invention. Accordingly, the invention is not to be considered limited to what is shown in the drawings and described in the specification.