Abstract:
A cassette containing a printing head removably installed in an ink jet printing machine. The cassette includes a housing which encloses the printing head in a protective manner when the cassette is removed from the machine and when the cassette is installed in the machine and the printing head is in an inoperative position. The head and housing are provided with locking elememts for securing the head in the housing when the cassette is to be removed. 
     The machine includes a carriage for moving the printing head past a record carrier during printing operations, locking elements for locking the printing head onto the carriage when the cassette is installed in the machine, a receptacle for holding the housing in the machine, and a mechanism for releasing the locking elements when the printing head is in the inoperative position to permit removal of the cassette from the machine.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a cassette for the printing head of an ink jet printer for a typewriter. 
     Demands, on the one hand, for high script quality close to typewritten script, i.e. letter quality, and also for high print quality are increasing steadily for printing mechanisms employing dot matrix printing heads. For this purpose, a printing head may be provided with two rows of ink jet openings which are arranged parallel to one another in the direction of the matrix columns, with these ink jet openings being arranged in such a manner that one row is offset with respect to the other. For the production of draft quality print, ink droplets are discharged selectively from the ink jet openings of one row, while for the production of letter quality print, ink droplets are ejected from the ink jet openings of both rows. Since this requires different, printer controls, it is advisable to use different printing heads which are equipped with corresponding code markers. These code markers cooperate automatically with a decoding circuit in the machine when the printing mechanism is changed. In this way, errors on the part of the operator are excluded. 
     DE-AS [Federal Republic of Germany Published Application ] No. 2,142,409 discloses exchanging printing heads in ink jet printers if the interior of the printing head is soiled or one of the discharge openings is clogged. The printing head is here coupled, by means of plug-in connections which establish the electrical and mechanical connections, with a carriage which moves along the record carrier. Since exchange of the printing head is possible in any desired position of the carriage and the discharge nozzles are not protected against soiling, it can easily happen that they clog and thus that individual jet discharge openings no longer participate in the printing process. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a cassette for the printing head of an ink jet printer in a typewriter which allows easy exchange of the printing head without subsequent malfunction in the printing operation and which prevents errors on the part of the person operating the machine. The above and other objects are achieved, according to the invention, by the provision of an ink jet printing head cassette assembly comprising an ink jet printing head for use in an office machine equipped with a carriage for moving the printing head past a record carrier during a printing operation, the carriage being provided with holding elements for holding the printing head and the carriage being arranged for moving the printing head into a rest position at the conclusion of a printing operation, the machine further being equipped with a receptable having holding members and with means for establishing electrical, mechanical and ink supply plug-in connections with the printing head when the printing head is mounted on the carriage, the assembly further comprising: a housing arranged to be inserted, together with the printing head, into the receptable when the assembly is installed in the office machine so that the housing is held by the holding members of the receptable and the printing head is held by the holding elements of the carriage, the housing being disposed for receiving and protecting the printing head when the printing head is in the rest position and when the housing is removed from the receptable; and holding means associated with the housing and the printing head, for securely holding the printing head in the housing when the housing is removed from the receptable. 
     The cassette according to the present invention permits simple and safe manipulation in the exchange of printing heads, with the printing head being exchangeable only while the carriage is in the rest position and the printing head is always being protected, particularly against soiling, when it is removed from the carriage. 
     According to an advantageous embodiment of the invention, operator errors are made impossible since the respective electronic control system is exchanged together with the printing head. According to a further feature of the invention, when the printing head is exchanged, the covering device is also exchanged so that clogging and soiling of the discharge nozzles is substantially avoided. Moreover, the cassette including the printing head and the electronic control system can be manufactured and mounted in a separate sterile environment so that the usual manufacturing influences are kept away from these sensitive parts. 
     The present invention will now be described in greater detail with the reference to an embodiment. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a perspective view of an ink jet printer incorporating the present invention. 
     FIG. 2 is a perspective detail view of a portion of the structure of FIG. 1, looking toward the back of FIG. 1. 
     FIG. 3 is a perspective detail view illustrating an advantageous feature of the present invention. 
     FIG. 4 is a detail elevational view of a second embodiment of the locking device of an arrangement according to the invention. 
     FIGS. 5A and 5B are detail views of an element of the structure of FIG. 4. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows a carriage 7 which moves on guide rails 3 and 5 adjacent to record carrier 1 and is driven by a motor, e.g. a stepping motor 11, in a known manner via a cable 9. Record carrier 1 passes around a platen 13 (shown in FIG. 2) which is driven by a conventional stepping motor (not shown). FIG. 1 shows a cassette 15 for the printing head 17 of an ink jet printer in a typewriter, with the printing head 17 being composed of a dot matrix printing head component 19 with discharge nozzles 21 and an intermediate ink container 23 permanently connected to component 19. Printing head 17 can be coupled with movable carriage 7 by means of a plug-in connection which establishes both the electrical and mechanical connections. Moreover, printing head 17 includes means for the additional, immediate and automatic establishment of a plug-in connection with an ink supply line. 
     Cassette 15 is composed of a housing 29 which is seated in a receptacle 25 disposed in a side wall 27 of the machine and can be held there, with printing head 17 in its inoperative position being protected whether it is disposed within or outside of receptacle 25. Holding means are provided at printing head 17 and at housing 29 with which printing head 17, when it is dismounted from carriage 7, is secured in housing 29 and, if housing 29 is mounted in the machine, printing head 17 is secured by holding members in receptacle 25 and by holding members in carriage 7. 
     Housing 29 of cassette 15 has an opening 31 for moving carriage 7 and printing head 17 in and out of cassette 15. For this purpose, guide grooves 33 and 35 are provided in housing 29 to both sides of opening 31 and these guide grooves can be brought into interlocking engagement with guide bars 37 and 39 which are provided as an integral part of printing head 17. After moving printing head 17 into housing 29, head 17 is arrested by means of a locking member 41. This locking member 41 is a blocking lever 43 equipped with a blocking tongue 45 which, when housing 29 is being removed from receptacle 25, latches behind a detent edge 47 of printing head 17. Blocking lever 43 is mounted on the upper surface 49 of housing 29 in a recess 52 of a bearing block 54 so as to be pivotable about an axis 51 and can be loaded by a spring 53 in such a manner that blocking tongue 45 can be brought through an opening 55 in housing 29 to a position in front of detent edge 47 of printing head 17. This causes printing head 17 to be positively arrested, i.e. locked, in housing 29 so that printing head 17 and housing 29 form an independent transporting unit. 
     The free end 57 of blocking lever 43 projects over side wall 27 in such a manner that an intermediate lever 61 which is mounted at receptable 25 so as to be pvioted about fulcrum 59 between two end positions causes blocking lever 43 to be moved, by way of an abutment tongue 62 of lever 43, between its blocking position and an unblocking position. Recess 52 in bearing block 54 and blocking lever 43 are designed in such a way that blocking lever 43, when cassette 15 is removed from receptable 25, can be moved out of its blocking position only by means of a special tool to release printing head 17. In this way, the machine operator is prevented from arbitrarily removing head 17 from housing 29. Such a separation should be made only by a customer service representative. 
     Intermediate lever 61 is pivotal about an axis 59 and, with cassette 15 inserted, rests against an abutment 63 provided at the machine frame. In this position, as shown in FIG. 1, blocking tongue 45 is out of engagement with detent edge 47 of printing head 17 so that carriage 7 can be moved out of its rest position in the housing at any time and returned into the housing after each printing process. 
     If printing head 17 is to be exchanged, i.e. if cassette 15 and printing head 17 are to be removed from the machine, intermediate lever 61 must be pivoted away downwardly against the force of a spring 64 until blocking lever 43 is released so that blocking tongue 45 can drop in through opening 55. 
     Such pivoting of intermediate lever 61 is effected by way of a manually operated control lever 65, shown in detail in FIG. 2, which is mounted in side wall 27 so as to be pivotal about axis 67 between two end positions. To exchange cassette 15, control lever 65 is pivoted clockwise as seen in FIG. 2, against the force of a spring 69, to thus be displaced from its fixed rest abutment 71 in the machine frame. This causes an abutment edge 73 of control lever 65 to press down on an inclined surface 75 of intermediate lever 61 in such a manner that blocking lever 61 is pivoted downwardly and lever 43 is released and enabled to drop into its blocking position. 
     Manually actuatable control lever 65 is coupled, via intermediate members 77 and a coupling 89, 95 with a locking device 81 for printing head 17 at movable carriage 7, when the latter is in its inoperative position. This locking device 81 is provided with a locking shaft 83 which is rotatably mounted in carriage 7 and is equipped with a latch hook 85 with which printing head 17, composed of dot matrix printing head component 19 intermediate ink container 23, can be firmly arrested on carriage 7 via an abutment 87 carried by container 23. 
     Locking shaft 83 is provided with a coupling half 89 which has a prismatic recess 91 whose side faces 93 are conically tapered toward its outer end. The other coupling half 95 is mounted so as to be rotatable in the machine frame and is provided with a gripper pin 97 which has a shape corresponding to the prismatic recess 91. Coupling half 95 is connected with control lever 65 by way of a step-up gear constituted by intermediate members 77. For this purpose, intermediate members 77 include a toothed wheel 101 fixed to gripper pin 97 and gear teeth 99 formed on control lever 65 and arranged to mesh with the teeth of wheel 101. 
     Depending on the pivoting direction of control lever 65, the two coupling halves 89 and 95, and thus locking shaft 83, can be pivoted in such a manner that latch hook 85 is brought into or out of engagement with abutment 87 at intermediate ink container 23. Within the scope of the present invention, latch hook 85 can be replaced by a modified hook which presses printing head 17 firmly against carriage 7. One embodiment of such a modified hook will be described below with reference to FIGS. 4, 5A and 5B. It must then be assured that the electrical and ink-supplying plug-in connections are coupled together accurately. 
     Control lever 65 can be blocked in its starting, or rest, position shown in FIG. 2 by a blocking lever 103. This blocking lever 103 is mounted so as to be pivotal about an axis 105 in the machine frame and is provided with an abutment arm 109 which, when carriage 7 is moved into the inoperative position in housing 15, can be pressed by carriage 7, against the force of a return spring 111, to release control lever 65. At the same time, lever 103 is moved away from an abutment 113 which is part of the machine frame. Whenever carriage 7 is in its inoperative position, blocking lever 103 is pivoted by carriage 7 to release control lever 65, with the two coupling halves 89, 97 always being coupled together. If printing head 17 is to be removed, it is only necessary to rotate control lever 65 clockwise until it abuts at abutment 115. This causes latch hook 85 and its latch tongue 86 to be rotated away from abutment 87. According to FIG. 2, printing head 17 can then be extracted toward the top. This removal is effected, as shown in FIG. 1, by removing cassette 15 and printing head 17 as a unit. 
     Referring to FIG. 1, cassette 15 can be inserted by being pushed into receptacle 25 which is provided with an insertion opening 117 equipped with guides 119, 121 for guide elements 123, 125 which form part of housing 29. Cassette 15 can be arrested in its inserted position in receptacle 25 by means of a blocking lever 127 which is mounted so as to be pivotal about an axis 133 at the machine housing and has a blocking tongue 129 which can be pivoted into position above insertion opening 117. Blocking tongue 129 is disposed at an arm 131 of blocking lever 127. Arm 131 is held in the position in which blocking tongue is above opening 117 by lever 65 when lever 65 is in its rest position. A spring 135 is connected between blocking lever 127 and the machine housing to bring blocking lever 127 out of the range of insertion opening 117 as soon as manually actuated control lever 65 is pivoted from its rest position into its release position. An abutment edge 137 of arm 131, which rests against control lever 65 when lever 65 is in its rest position, then comes to rest against an abutment 139 which is part of the machine housing. When control lever 65 is pivoted back into its rest position, control lever 65 engages a camming surface 141 at blocking tongue 129 of blocking lever 127 in such a manner that lever 127 is pivoted into the region of insertion opening 117. This again accurately secures cassette 15 which is disposed in receptacle 25. 
     A covering device 143 is also disposed in housing 29 of cassette 15 for covering discharge nozzles 21 of dot matrix printing head 19. This reliably prevents soiling of discharge nozzles 21 and clogging of the nozzles during intervals between printing operations and also during exchange of printing heads. Covering device 143 may be of any desired configuration and may be comprised, for example, of a rotatably mounted covering roller 145 which is saturated with a cleaning fluid. 
     Additionally, as shown in FIG. 3, codable control means 147 may be provided on housing 29. These control means can be brought into operative engagement with a detection device 149 mounted in wall 27 so as to extend into the receptacle 25 of the machine. This detection device 149 furnishes control signals via a decoding circuit to the printer control so as to generate the desired type of script. This completely eliminates the chance of operator errors. 
     FIGS. 4, 5A and 5B show a locking device between carriage 7 and intermediate ink container 23, provided with one embodiment of the modified hook mentioned earlier herein. Locking shaft 150 carries an eccentric circular cam 152 which is fast to shaft 150 and which frictionally engages in a bore provided in locking hook 153. Hook 153 carries an abutment tongue 155 arranged to engage an abutment 156 carried by ink container 23. 
     FIG. 5A shows the locking device in its locked position, with tongue 155 pressing down on abutment 186 in order to press ink container 23 against carriage 7 and thus to assure secure coupling of associated electrical, mechanical and ink-conducting connecting means. 
     FIG. 5B shows the locking device in its unlocked position, permitting removal of printing head 17, together with cassette 15, from the machine. This position of hook 153 is defined by an abutment 151 carried by carriage 7. 
     For locking and unlocking, shaft 150 executes a rotation of the order of 180° while hook 153 is confined to a rotation of the order of 30° by abutments 151 and 156. 
     For movement from the unlocked position of FIG. 5B to the locked position of FIG. 5A, hook 153 rotates with shaft 150 during the first 30° of shaft rotation until the vertical arm of hook 153 reaches abutment 156. Then, during the remaining 150° of shaft rotation, cam 152 slides in the bore in hook 153 and pulls the hook down to cause it to press downwardly on abutment 156. 
     For unlocking, shaft 150 is rotated in the opposite direction. If there is a sufficient locking force between hook 153 and abutment 156, the first part of this rotation will be associated with a sliding movement between cam 152 and the bore in hook 153 until hook 153 has been raised sufficiently to reduce this force. Then hook 153 rotates with shaft 150 until reaching abutment 151. Thereafter, shaft 150 completes its rotational movement, accompanied by a sliding movement between cam 152 and the bore in hook 153. 
     One suitable example of the electrical, mechanical and ink supply plug-in connections between printing head 17 and carriage 7 are disclosed in the U.S. patent application, Ser. No. 417,897 filed Sept. 14, 1982 now Pat. No. 4,496,959. 
     Electronically controlled printers and typing systems of a large variety of capabilities and types are well known, a typical example being a system such as disclosed in the U.S. patent application Ser. No. 144 716, filed Apr. 28, 1980 now abandoned. 
     It will be understood that the above description of the present invention is susceptible to various modifications, changes and adaptations, and the same are intended to be comprehended within the meaning and range of equivalents of the appended claims.