Abstract:
An ink jet print head includes an ink jet print module contained in a cartridge housing. The ink jet print module includes a surface containing a plurality of ink jet nozzles and this surface extends in a aperture of the cartridge housing. An element extends from the housing and supports a set of electrical terminals and electrical connection means provide electrical interconnections between electrical contacts of the set of electrical contacts of the ink jet print module and electrical terminals of the set of electrical terminals supported in the element.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to digital print heads and in particular to ink jet print head cartridges and to housing and the provision ofexternal electrical connections therefor. 
     Ink jet print head cartridges or modules are known in which a casing houses a plurality of ink jet nozzles from which droplets of ink may be ejected selectively as required by ink ejection means and electronic circuits for controlling operation of the ink ejection means. One known form of ink jet print head includes, for each ink ejection nozzle, an ink chamber communicating with the ink ejection nozzle and a resistive element for heating the ink in the ink chamber so as to eject a droplet of ink from the nozzle. A pulse of electrical current is passed through the resistive element to cause the required heating of the ink in the associated ink chamber. Electronic driver circuits of the print head control generation of the pulse of electrical current. The driver circuits are controlled by print control signals generated externally of the print head module by electronic control circuits operating to cause ejection of ink droplets selectively in a sequence of printing cycles from selected ones of the nozzles such as to produce a required imprint on a print receiving medium. 
     The ink jet print head module includes a reservoir of ink and, as ink is ejected in droplets from the nozzles during operation of the print head, the ink in the reservoir is gradually depleted. In known commercially available ink jet print head modules, when the ink in the reservoir has been depleted to a low level the entire module is replaced by a new module containing a reservoir full of ink. Accordingly the module is constructed to be readily removable and replaceable by a user of printing apparatus incorporating such ink jet print modules. The module is provided with a set of electrical contacts which, when the module is removably mounted in the printing apparatus, engage with a corresponding set of electrical contacts of the printing apparatus to connect the external control circuits to the driver circuits of the print head module. 
     In one commercially available ink jet print module, the nozzles of the print head are located in a first planar face of the module and the set of electrical contacts is located on an adjacent face extending substantially perpendicular to the first face. While this construction and relative location of the nozzles and of the set of electrical contacts is satisfactory in many constructions of printing apparatus, it does impose restrictions on the construction of the printing apparatus with regard to the insertion into and removal from the printing apparatus of the print head modules. 
     Generally the commercially available print head modules are used in non-secure printers for example output printers connected to and operated by personal computers. However it is also proposed to use commercially available ink jet print head modules in postage meters for printing postal indicia on mail pieces. It will be appreciated that because postage meters are used to dispense postage value it is required that the print head is operated in a secure manner and postal authorities may require use of an ink that is different from inks used in print head modules used generally for other purposes. Accordingly it is desired to ensure that only authorised print head modules are utilised in the postage meter. 
     SUMMARY OF THE INVENTION 
     According to the invention an ink jet printhead includes an ink jet print module and a cartridge housing; said ink jet print module including a plurality of ink jet nozzles in a first exterior surface of said module; selectively operable driver means to eject ink from selected ones of said nozzles and a set of electrical contacts connected to said driver means and located on a second exterior surface of the module; said ink jet print module being housed in said cartridge housing; said cartridge housing including a wall and an aperture in said wall through which said first surface extends so that said ink jet nozzles are located exterior to the housing; an element extending from said housing and supporting a set of electrical terminals; and electrical connection means providing electrical interconnections between electrical contacts of said set of electrical contacts and electrical terminals of said set of electrical terminals. 
     Preferably the electrical terminals are located on a printed circuit board, said printed circuit board extending from the element into the interior of the housing; said printed circuit board being provided with a set of electrical contact pads corresponding to said electrical contacts of the print head module, the electrical contact pads respectively being in electrical contact engagement with corresponding ones of the electrical contacts and the printed circuit board includes electrical tracks extend interconnecting the electrical terminals and the electrical contact pads. 
     If desired the terminals may be connected respectively to correspondingly located electrical contacts of the print head module or at least some of the terminals may be connected to electrical contacts of the print head module that are not located corresponding to the terminals. 
     The housing may have a planar side wall and the element supporting the terminals may extend substantially perpendicular to the planar side wall. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     An embodiment of the invention will now be described by way of example with reference to the drawings in which: 
     FIG. 1 is a view of a print head module and components of a housing therefor prior to assembly of the housing, 
     FIG. 2 illustrates the print head module inserted in a body component of the housing, 
     FIG. 3 illustrates the assembled housing with the print head module therein, 
     FIG. 4 is an end elevation view of the assembled housing, 
     FIG. 5 is a side elevation view of the assembled housing, and 
     FIG. 6 illustrates a printed circuit component with sets of electrical contacts thereon. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring first to FIG. 1 of the drawings, a known commercially available ink jet print head module  10  consists of a main body  11  and a projection  12  extending from the main body. Two rows of ink jet nozzles  13  are located in a face  14  of the projection  12 . A set of electrical contacts  15  are located on a face  16  of the main body  11 . It will be understood that the sets of electrical contacts comprise a plurality of individual contacts but for clarity in the drawings only a small number of contacts are shown by way of illustration. 
     A housing for the module  10  comprises a body component  17  and a cover component  18 . The body component  17  has a side wall  19  and a peripheral wall  20  extending from the side wall  19  to accommodate the print head module  10  as shown in FIG.  2 . The peripheral wall  20  has an aperture  21  therein through which the projection  12  of the print head module extends (see FIG. 2) so that the face  14  and nozzles  13  are located to the exterior of the housing. Resilient members  22  and  23  are provided in the body component and act on the print head module to locate the face  16  and a face  24  of the print head module in abutment with corresponding parts of the peripheral wall and thereby define the location of the print head module within the housing. The body component is provided with an extension  25  extending from the side wall  19  in a direction opposite to that of the peripheral wall  20 . A printed circuit board  26  is located in the extension  25  and has a set of electrical contact pads  30  (FIG. 6) corresponding to the set of electrical contacts  15  of the print head module. The contact pads  30  of the printed circuit board  26  oppose the contacts  15  of the print head module and respective ones of the contact pads  30  are opposed to and make electrical connection to corresponding ones of the electrical contacts  15 . It is preferred to bond the contacts  30  of the printed circuit board to the contacts  15  of the print head module for example by solder bonds to provide reliable electrical interconnections between the print head module and the printed circuit board. However if desired the action of the resilient member  22  on the print head module may be utilised to urge the contacts  15  into engagement with the contact pads of the printed circuit board whereby the contacts  15  are connected electrically to the printed circuit board. The printed circuit board is also provided with a set of electrical terminals  27  (FIG.  4 ). The terminals  27  are connected by conductive tracks (not shown) respectively to corresponding ones of the electrical contact pads  30  of the circuit board and hence, through the engagement between the electrical contact pads of the circuit board with the contacts  15  of the module, the terminals  27  are connected to the electrical contacts  15  of the print head module. 
     When the printed circuit board  26  is located in the base component  17  and the print head module has been inserted the base component as hereinbefore described, the over component  18  is secured to the base component. Conveniently the cover component may be secured to the base component by means of studs  28  extending from the cover and entering in corresponding bores  29  in the base component. The studs are an interference fit in the bores and hence when the cover is pressed into position on the base component with the studs entering the bores, the interference fit of the studs in the bores retains the cover on the base component and the base and cover provide a sealed housing for the print head module. Preferably the construction of the studs is such that if an attempt is made to remove the cover from the base the studs fracture and thereby prevent replacement of the cover. The fracture of the studs provides an indication that tampering has occurred and probably that the tampering was an attempt to interfere with or replace the print head module with an unauthorised print head module. 
     It will be appreciated that, by location of the print head module within the sealed housing and by constructing printing apparatus in which the print head module is to be used such that only a print head module located within the sealed housing can be operationally received in the apparatus, only authorised print head modules located in the sealed housing can be used in the printing apparatus. 
     In addition, by locating the print head module in a housing with external electrical connections provided by terminals  27  on the printed circuit board  25 , the external electrical connections may be provided at a location that is convenient for the particular printing apparatus in which the print head module is to be used. In the embodiment described hereinbefore the external electrical terminals  27  are offset sideways relative to the print head module. However it will be appreciated that the location of the electrical terminals  27  relative to the trical contacts  15  of the print head module may be different from that of the embodiment described hereinbefore and may be chosen for convenience of insertion and removal of the print head module in the housing to and from the particular printing apparatus. 
     The configuration of the electrical terminals  27  may be the same as the configuration of the electrical contacts  15  and the terminals  27  may be connected on a one-to-one basis to correspondingly located electrical contacts  15 . However where it is desired to prevent operation of the print head module by electrical signals applied to a configuration of electrical contacts corresponding to the electrical contacts  15 , the interconnections between the terminals  27  and the electrical contacts  30  of the printed circuit board  26  may be interchanged thereby providing a simple coding of the signals to the print head module. For example suppose that there are 1 to n electrical contacts  15  and corresponding contact pads  30 , 1 to n terminals  27  and that electrical contact  15   1  of the print head is opposed to contact pad  30   1  of the printed circuit board  26  and is connected to terminal  27   8  and, in a similar manner electrical contact  15   5  is connected to terminal  27   1 . If operation of a first nozzle requires an input signal on electrical contact  15   1  and operation of an eighth nozzle requires an input on electrical contact  15   8 , then an input must be applied to terminal  27   8  in order to operate the first nozzle and an input on terminal  27   1  to operate the eighth nozzle. However if in tampering with the print head module a signal is applied to terminal number  1  as might be expected from the configuration of contact  15  on a standard print head module to operate the first nozzle, the first nozzle will not be operated but instead the eighth nozzle will be operated. Accordingly it will be appreciated that inputs to the terminals of signals configured to operate a standard print head will result in a corrupted image being printed and that in order to print a required image using the print head module contained within the sealed housing it is necessary for the signals to be configured to correspond to the connections of the terminals to the contacts  15 . Also if desired the printed circuit board may incorporate active electrical circuits  31  connected between the terminals  27  and the contact pads  30  and operative to modify electrical signals applied to the terminals  27 . The active circuits may include one or more inverters and may include one or more gate circuits. The effect of providing these active circuits is that signals applied to the terminals  27  which would be expected to operate the print head module if applied directly to the electrical contacts  15  are ineffective to operate the print head module in the desired manner. In order to operate the print head module in the desired manner, signals must be applied to the terminals  27  which, when modified by the active circuits, produce electrical signals at the electrical contacts  15  to operate the print head module as desired.