Multi-strike ink ribbon feed control

Abstract: Means to control feeding of a multi-strike ink ribbon (19) housed in a reversible cassette (12) is disclosed. The cassette carries a magnetisable element (20; 30,31) and when the cassette is inserted in printing apparatus (10, 26) the element is located in operative alignment with a magnetic sensing device (21; 32,33) and with an electromagnet (25; 34). Upon insertion of the cassette, the polarity of magnetisation is sensed and provided the polarity is correct printing is enabled. If the polarity is incorrect printing is disabled. When the end of the ink ribbon is sensed, the electromagnet (25; 34) is energised to reverse the polarity of magnetisation of the element (20) so that when the cassette is removed and re-inserted with reversed orientation, the correct polarity of magnetisation is sensed and printing is enabled. A counter may be provided to limit the number of permitted reversals of the cassette.

Description: This invention relates to control of the feed of multi-strike ink ribbons and in particular to the control of insertion of cassettes containing such ribbons into printing apparatus. Multi-strike ink ribbons are ribbons in which a part of the ink is removed in a pass of the ribbon past a print head so that the ribbon may be re-used a number of times in which the ink is successively removed. In thermal ink transfer ribbons the ink is in multiple layers carried on a backing substrate and in each pass of the ribbon ink from the exposed layer is removed leaving ink in underlying layers to be removed in successive passes of the ribbon. In printing devices in which printing is carried out during feeding of an item, on which printing is to be effected, past a print head in a single direction it has been required that, when the end of the ribbon is reached after a pass of the ribbon, printing is interrupted to enable the entire ribbon to be rewound. In a multi-strike ink ribbon feed disclosed in our European patent specification 0 315 384 the disadvantage of interrupting the printing for a time sufficient to enable the ribbon to be rewound is overcome by progressively rewinding the ribbon in intervals between printing on items. However whether the entire ribbon is rewound in a single operation or is progressively rewound it is necessary to provide drive means to rotate the spool on which the ribbon is wound. Such drive means add to the cost of the equipment and furthermore occupy space so that the equipment be larger than desired. Ink ribbons may be provided in a cassette which may be removably inserted in operative position in a printing device. The cassette usually has a supply spool filled with ribbon and an empty take-up spool onto which the used ribbon is wound. When the cassette is in operative position in the printing device, means in the printing device draws the ribbon from the supply spool past the print head of the printing device and take up spool is driven by a drive motor in the printing device to wind the used ribbon onto the take-up spool. GB-A-2 219 553 discloses an ink ribbon cassette provided with identifying coding in the form of a magnetised element which is sensed by printing apparatus when the cassette is mounted in said apparatus. According to the invention printing apparatus including a print head (18); an ink ribbon cassette removably mounted relative to said print head; said cassette including first and second spools, and a multi-strike ink ribbon initially wound on one of said first and second spools, the ink ribbon being drawn from the one spool past the print head and wound onto the other of said first and second spools in printing operations; a magnetised element carried by said cassette; sensor means responsive, when the cassette is mounted relative to said print head, to magnetisation of said magnetised element to generate a signal indicative of said magnetisation characterised in that the cassette is mountable in a first orientation relative to the print head to enable the ink ribbon to be drawn from the first spool and wound onto the second spool and in a second orientation, reversed relative to said first orientation, to enable the ink ribbon to be drawn from the second spool and wound onto the first spool; in that initially the magnetised element has a first polarity of magnetisation and the sensor means generates a first signal when the cassette is mounted in said first orientation and a second signal when the cassette is mounted in said second orientation; in that control means permits operation of the printing apparatus in response to the first signal and inhibits operation of the printing apparatus in response to the second signal; and in that magnetisation means is operated by the control means in response to the ink ribbon being substantially unwound from the first spool to reverse the polarity of magnetisation of the magnetised element so that the sensor generates the second signal when the cassette is mounted in the first orientation and the first signal when the cassette is mounted in the second orientation. Embodiments of the invention will now be described by way of example with reference to the drawings in which:- Figure 1 is a schematic side view of an ink ribbon cassette mounted on printing apparatus, Figure 2 is a schematic sectional view on the line 2 - 2 of Figure 1, Figure 3 is a circuit diagram of a circuit for detecting orientation of the cassette, Figure 4 is a schematic side view of a modification of Figure 1, Figure 5 is a schematic sectional view on the line 5 - 5 of Figure 4, and Figure 6 is a circuit diagram of a circuit for detecting orientation of the cassette of Figures 4 and 5. Referring first to Figures 1 and 2, a chassis 10 of printing apparatus has a recess 11 for the reception of an ink ribbon cassette 12. The cassette has a supply spool 13 filled with thermal transfer ink ribbon 19 and the ribbon extends to a take-up spool 14. When the cassette is inserted in the recess of the printing apparatus the take spool drivingly engages with a shaft 15 of a take-up motor drive 16. The ribbon between the supply spool and the take-up spool is guided by ribbon guides 17 to follow a path past a thermal print head 18. The cassette is apertured in side walls thereof to permit the print head to enter the space between the spools when the cassette is inserted in the printing apparatus. During printing operations, items on which printing is to be effected are fed past the print head and are urged by an impression roller (not shown) into ink transfer engagement with an ink layer on the ribbon and a substrate of the ribbon is urged into heat transfer relationship with the heatable elements of the print head. After passing the print head, the ribbon is peeled from the surface of the item by tension applied to the ribbon due to rotational drive by the take-up motor of the take-up spool. Accordingly as items pass the print head and receive an imprint the ribbon is successively drawn from the supply spool 13 and is wound onto the take-up spool. When the end of the ribbon on the supply spool is reached the cassette is removed and may be replaced on the printing apparatus with reverse orientation so that the spool which was the take-up spool and on which the entire ribbon is now wound becomes the supply spool and the spool which was the supply spool and has become empty becomes the take-up spool. This removal, reversal and re-insertion of the cassette may be repeated a number of times until the ink layers of the multi-strike ribbon have been depleted. However it will be appreciated that a user of the printing apparatus may in error replace the cassette in the printing apparatus with the same orientation as in its previous insertion or may continue to re-insert the cassette with reversed orientations after the ink layers have been depleted. For many forms of printing apparatus this would merely be an inconvenience and would lead to poor quality printing which could be remedied by repeating the printing process with a new ribbon. However in postage franking apparatus this could result in mail items passing through the apparatus without receiving a clear and perceivable franking impression. Accordingly for such apparatus it is desirable to provide means which prevent or at least warn an operator that the cassette has an incorrect orientation or has been used to a predetermined limit. For this purpose a magnetisable element 20 is provided in or on the cassette. Initially the element 20 is magnetised with a predetermined first polarity. The printing apparatus is provided with a sensor 21, which may be a Hall effect device, which responds to the magnetisation of the element of a cassette inserted in the printing apparatus. As shown in the circuit diagram of Figure 3, the Hall effect device 21 is powered by connections to 0V and +VCC lines and has an output connected to a voltage sense circuit 22. An output 23 of the circuit 22 is connected to a control circuit 24 which may be a microprocessor. When the element 20 is magnetised with the initial polarity of magnetisation and the cassette is inserted with the correct orientation in the chassis of the printing apparatus such that the spool full of unused ribbon is positioned as a supply spool, the output of the device 21 causes the voltage sensor circuit to produce a first signal on output line 23 to the control circuit 24. However if the cassette is inserted with incorrect orientation, the polarity of magnetisation of the element 20 will be reversed relative to the sensor device 21 and this will cause the voltage sensor circuit to output a second signal to the control circuit. In response to receipt of the second signal the control circuit inhibits operation of the printing apparatus 26 for printing and preferably causes display of an error message to an operator of the apparatus. An electromagnet 25 is located on the chassis of the printing apparatus adjacent the magnetisable element 20 of an inserted cassette 12. The electromagnet is normally unenergised. Energisation of the electromagnet is controlled by the control circuit 24. When the end of the ribbon is reached, i.e. substantially the entire length of ribbon is wound onto the take-up spool and the supply spool is empty, an end of ribbon sensor 27 inputs a signal to the control circuit and the control circuit energises the electromagnet to remagnetise the element 20 with a polarity reversed compared with the previous polarity of magnetisation. Thus when the cassette is removed and re-inserted with reverse orientation, the positions of the spools will be interchanged and the reversed polarity of magnetisation of element 20 will correspond, relative to the chassis of the printing apparatus, to its initial polarisation and be detected by the sensor device 21 to cause the circuit 22 to output the first signal to the control circuit. Accordingly the printing apparatus will be operative. However if the cassette were to be re-inserted without reversal of its orientation the polarity of magnetisation of the element 20 would be sensed as being reversed and the control circuit would inhibit operation of the printing apparatus 26. The control circuit 24 may include a counter which is reset to zero by a reset input 28 generated for example by manual operation of a key by the operator when a new unused ribbon cassette is inserted and the counter is incremented each time the sensor 21 detects that the cassette is re-inserted with reversed orientation. The control circuit will include means to check the count registered by the counter and when it reaches a value corresponding to a limit to re-use of the ribbon the control circuit inhibits further operation of the printing apparatus until a new cassette is inserted and the counter is reset. As described hereinbefore the electromagnet is energised when the end of ribbon is reached in order to reverse polarity of magnetisation of the element 20. However when the counter detects that the limit of re-uses of the ribbon has been reached the electromagnet is not energised and hence the element will remain magnetised with a polarity which prevents the printing apparatus accepting the cassette for further use. It is to be understood that the end of ribbon detector is provided in the printing apparatus to determine when the end of the ribbon has been reached in unwinding from one of the spools and the end of ribbon detector provides an end of ribbon indication to the control circuit 24. In a modified embodiment two magnetisable elements 30, 31 are provided on the ribbon cassette. This embodiment may have the same function as the first embodiment, but may also be operated in a different way which, however, does not fall within the scope of the present invention. This different way is as follows : Initially, prior to use of the cassette, both magnetisable elements 30, 31 are magnetised with a predetermined polarity. Upon first insertion of the cassette into the chassis of the printing apparatus, the polarity of magnetisation of both elements is sensed by sensors 32, 33 and upon sensing of the predetermined polarity of magnetisation of both elements the counter of the control circuit is reset to zero and one element, for example element 30, is magnetised by an electromagnet 34 to reverse its polarity of magnetisation. Thereafter the polarity of magnetisation of both elements 30, 31 remains unchanged. It will be appreciated that two sensor devices 32, 33 are provided for sensing the two magnetisable elements 30, 31. On sensing the polarity of magnetisation of the elements, the sensed polarity is retained either by the voltage sense circuits 35, 36 or by the control circuit 24. When the cassette is removed and re-inserted the polarity of magnetisation of both elements is sensed and if the sensed polarity is reversed as compared with the sensed polarity retained from the previous insertion of the cassette an indication is provided that the cassette has been reversed. However if the sensed polarity is not reversed it indicates that the cassette has not been reversed and operation of the printing apparatus 26 is inhibited until the cassette has been re-inserted with reversed orientation. The magnetisable element 20 and elements 30, 31 are illustrated schematically as rod like elements. However they may be of other form and may comprise a length of magnetisable tape, such as magnetic recording tape utilised for recording signals, and may be secured to a surface of the cassette by adhesive. It will be appreciated that the sensor devices 21, 32, 33 are located at a position on the chassis of the printing apparatus such that each sensor is responsive to the polarity of magnetisation of the element adjacent thereto. Also the electromagnetic 25 or 34 is so located as to be able to reverse the polarity of magnetisation of the element adjacent thereto. Instead of providing a magnetisable element or elements on the cassette, the thermal transfer ink ribbon may carry a magnetisable element in the form of a magnetisable ribbon at each end of the thermal ink ribbon. When the magnetisable ribbon is drawn from the spool it passes a sensor which is responsive to the magnetisation of the ribbon. As described hereinbefore the magnetisable element is magnetised such that the whole element is magnetised with a desired polarity of magnetisation. However if desired the element may be magnetised with a code representation which signifies the number of times the cassette has been reversed. Each time the cassette is reversed the code is incremented to signify the updated number of reversals of the cassette. The electromagnet 25 includes a number of sections which may be selectively energised to magnetise the element 20 with the code representation and the sensor 21 is responsive to the code representation.

Claims: Printing apparatus including a print head (18); an ink ribbon cassette (12) removably mounted relative to said print head; said cassette including first and second spools (13, 14) and a multi-strike ink ribbon (19) initially wound on one of said first and second spools, the ink ribbon being drawn from the one spool past the print head and wound onto the other of said first and second spools in printing operations; a magnetised element (20) carried by said cassette; sensor means (21) responsive, when the cassette is mounted relative to said print head, to magnetisation of said magnetised element to generate a signal indicative of said magnetisation characterised in that the cassette (12) is mountable in a first orientation relative to the print head (18) to enable the ink ribbon (19) to be drawn from the first spool (13) and wound onto the second spool (14) and in a second orientation, reversed relative to said first orientation, to enable the ink ribbon (19) to be drawn from the second spool (14) and wound onto the first spool (13); in that initially the magnetised element (20) has a first polarity of magnetisation and the sensor means (21) generates a first signal when the cassette is mounted in said first orientation and a second signal when the cassette is mounted in said second orientation; in that control means (24) permits operation of the printing apparatus in response to the first signal and inhibits operation of the printing apparatus in response to the second signal; and in that magnetisation means (25) is operated by the control means in response to the ink ribbon being substantially unwound from the first spool to reverse the polarity of magnetisation of the magnetised element so that the sensor generates the second signal when the cassette is mounted in the first orientation and the first signal when the cassette is mounted in the second orientation. Printing apparatus as claimed in claim 1 further characterised in that the control means (24) includes a counter incremented in response to generation of each first signal. Printing apparatus as claimed in claim 2 further characterised in that the control means (24) is operative to inhibit operation of the printing apparatus (26) in response to a predetermined value of count registered by said counter. Printing apparatus as claimed in claim 1 further characterised in that the control means includes a counter incremented in response to generation of each first signal and is operative to inhibit operation of said magnetisation means (25; 34) in response to a predetermined count value registered by said counter. Printing apparatus as claimed in claim 1 further characterised in that the control means operates the magnetisation means (25; 34) to magnetise the magnetised element (20; 30, 31) with a magnetisation pattern representing a code. Printing apparatus as claimed in claim 5 further characterised in that the control means operates the magnetisation means (25; 34) to increment the code each time the orientation of the ribbon cassette (12) is reversed relative to the printing apparatus (10, 26). Printing apparatus as claimed in any preceding claim wherein the magnetised element (20) comprises a magnetisable ribbon carried by the ink ribbon (19). Printing apparatus as claimed in any preceding claim further characterised in that the sensor means (21) includes a Hall effect device.

Inventors: HERBERT RAYMOND JOHN, HERBERT, RAYMOND JOHN
Applicants: NEOPOST LTD, NEOPOST LIMITED
Application year: 1992
Main classification: B41J33
IPC codes: B41J35, B41J33