Method and means for testing the condition of an ink ribbon

Abstract: Detection apparatus is provided for testing the electrical resistance of an ink ribbon (16) stored in a housing (14) of a ribbon cassette (12). The cassette (12) may be mounted in a printer (10). The detection apparatus comprises first and second conductors (50,52) which contact the ink ribbon (16), and a circuit (54) which is coupled to the first and second conductors (50,52). The circuit (54) includes an operational amplifier (62) which compares a first signal corresponding to the electrical resistance of at least part of the ink ribbon (16) with a second signal corresponding to a predetermined resistance of the ink ribbon (16). When the first signal is equal to or greater than the second signal, the operational amplifier (62) generates an alarm signal which activates a display (74) to warn an operator of the need to change the ribbon cassette (12). A method for measuring the electrical resistance of the ribbon (16) is also disclosed.

Description: This invention relates to ink ribbon cassettes, and more particularly, to a method and apparatus for determining when a ribbon cassette should be replaced. The use of ribbon cassettes in printers has become quite common. Ribbon cassettes are advantageous because they can be easily installed in and removed from the printer. A problem in the prior art is that it was difficult to determine when the ribbon cassette needed to be replaced. The printer would print data having a desired density during normal operation. However, the printer would print data having an undesirable density if the ink ribbon in the ribbon cassette did not have a sufficient ink content. This often resulted in the printer printing illegible data on a document before an operator was made aware that the ribbon cassette needed to be replaced. This was particularly true where the printer was not continuously attended by the operator. Any documents having illegible printing would have to be discarded and new documents would have to be reprinted. DE-U-89 14 893.2 discloses an apparatus for reinking a used ribbon in a cassette. The ribbon passes between electrodes of an electrical sensor to determine the conductivity of the ribbon, prior to the ribbon entering the ink coating device. The sensor is effective to stop the ribbon drive, thereby preventing unnecessary double coating of the ribbon, in dependence on the determined ribbon conductivity. It is an object of this present invention to provide a method and means for testing the condition of an ink ribbon. According to one aspect of the present invention there is provided a method for testing the condition of the ribbon of an ink ribbon cassette, characterized by the steps of generating an electrical signal dependent on the electrical resistance of said ribbon between first and second portions thereof spaced apart along said ribbon, and generating an alarm signal when said electrical resistance exceeds a predetermined value. According to another aspect of the present invention there is provided an ink ribbon cassette including an ink ribbon and a housing for said ribbon, characterized by first and second electrical conductors arranged to contact first and second portions of said ribbon spaced apart along said ribbon, said conductors being accessible externally of said housing whereby the electrical resistance of said ribbon between said conductors may be measured. According a further aspect of the present invention there is provided a printer comprising a cassette receiving means for receiving a ribbon cassette containing an ink ribbon, the cassette having first and second electrical conductors arranged to contact first and second portions of said ink ribbon spaced apart along said ink ribbon, wherein said cassette receiving means includes means adapted to couple said electrical conductors to a circuit arranged to detect the electrical resistance of said ink ribbon between said first and said second portions thereof. The invention has the advantages of being inexpensive to manufacture and easy to implement. An embodiment of the present invention will now be described with reference to the accompanying drawings in which:- Fig. 1 is an isometric view of a printer and a ribbon cassette according to the present invention, with portions of the ribbon cassette broken away to reveal its construction; Fig. 2 is a top view of the ribbon cassette, partly broken away, showing an ink ribbon, a stuffing chamber, first and second ribbon guide arms, and first and second conductors associated with the ribbon cassette and contacting the ink ribbon; Fig. 3 is an end view, taken in the direction of arrow B in Fig. 2 and partly broken away, showing the first and second conductors mounted in the ribbon cassette; and Fig. 4 is a general schematic diagram of a circuit used to generate an alarm signal when the electrical resistance of the ink ribbon equals a predetermined resistance. Fig. 1 shows a printer 10 in which a ribbon cassette 12 according to this invention may be used. The ribbon cassette 12 (which is also seen in Figs. 2 and 3) includes a housing 14 which is used to store and support an ink ribbon 16. The ink ribbon 16 includes a conventional carbon solid ink (not shown) which enables the ink ribbon 16 to have a measurable electrical resistance. In a preferred embodiment, the ink ribbon 16 is 12.2 metres long, endless and reusable. The ribbon cassette 12 further includes a drive roller 18 and a cooperating roller 20 which cooperates with the drive roller 18 to move the ink ribbon 16 in the direction indicated by arrow A in Fig. 2. The ink ribbon 16 is drawn out of a stuffing chamber 22 through a first ribbon guide arm 24 and is guided back into the stuffing chamber 22 through a second ribbon guide arm 26. A portion of the ink ribbon 16 is exposed at all times between the first and second ribbon guide arms 24 and 26 for use in printing. The printer 10 (Fig. 1) comprises a cassette receiving opening or means 28 for receiving the ribbon cassette 12. The cassette receiving means 28 has a shape which is generally complementary to the shape of the housing 14 of the ribbon cassette 12. As depicted schematically in Fig. 1, the printer 10 also includes a controller 30 for controlling the operation of the printer 10. The controller 30 is coupled to drive means 32 for driving the drive roller 18 of the ribbon cassette 12. The drive means 32 includes a drive sprocket or pin 42 which engages a complementary-shaped interior aperture 18-1 of the drive roller 18. When the drive roller 18 rotates in an anticlockwise direction (as indicated by arrow C in Fig. 2), the ink ribbon 16 is drawn out of the stuffing chamber 22 in the direction of arrow A through the first ribbon guide arm 24 and is guided back into the stuffing chamber 22 through the second ribbon guide arm 26. The controller 30 is also conventionally coupled to a print member 34 for impacting the ink ribbon 16 against a document 36 and a platen 40 in order to print data 38 on the document 36. The document 36 is provided from a supply roll 37 which is mounted on a supply spool 39 driven by a motor (not shown) in the printer 10. The print member 34 is conventionally mounted on a carriage 44 which is slidably mounted on a support rod 46. The motor in the printer and its associated drive pulleys (not shown) are controlled by the controller 30 and are also coupled to the carriage 44 to move the carriage 44 and the print member 34 along the support rod 46. The print member 34 is associated with the cassette receiving means 28 so that the exposed portion of the ink ribbon 16 becomes operatively positioned relative to the print member 34 when the ribbon cassette 12 is mounted in the printer 10. The print member 34 forces the ink ribbon 16 against the document 36 and the platen 40 in order to print the data 38 on the document 36 when the document 36 is positioned at a print station 41 between the print member 34 and the platen 40. The preferred embodiment of the invention has a detection apparatus 48 which includes a first conductor 50 and a second conductor 52 which extend through a wall of the housing (14) to enable the electrical resistance of the ink ribbon 16 to be measured. The first and second conductors 50 and 52 are made of a suitable conductive material such as copper and are secured in a first receiving boss 51 and a second receiving boss 53, respectively, which may be integrally molded as part of the housing 14 of the ribbon cassette 12 as best illustrated in Fig. 3. In the preferred embodiment, the first and second conductors 50 and 52 are spaced approximately 10cm apart. The first conductor 50 has a first end 50-1 and a second end 50-2, and the second conductor 52 has a first end 52-1 and a second end 52-2. As best illustrated in Figs. 1 and 2, the first ends 50-1 and 52-1 contact the ink ribbon 16 in the stuffing chamber 22. The detection apparatus 48 also includes a circuit 54 (the details of which are shown in Fig. 4) for generating an alarm signal when the electrical resistance of the ink ribbon 16 equals a predetermined resistance. As seen in both Figs. 1 and 4, the circuit 54 includes a third conductor 56 and a fourth conductor 58 which are located in the printer 10. The third conductor 56 and fourth conductor 58 contact the second ends 50-2 and 52-2 of the first and second conductors 50 and 52, respectively, when the ribbon cassette 12 is mounted in the printer 10. The circuit 54 further includes comparator means or circuit 60 for generating the alarm signal when the electrical resistance of the ink ribbon 16 exceeds the predetermined resistance. The comparator circuit 60 comprises an operational amplifier 62 having a first input conductor 62-1, a second input conductor 62-2, and an output conductor 62-3. The second input conductor 62-2 of the operational amplifier 62 is coupled to the third conductor 56. The circuit 54 further comprises a first resistor 64, a second resistor 66, a third resistor 68, and a fourth resistor 70. The first resistor 64 has one end 64-1 thereof coupled to a source of potential 72 and a remaining end 64-2 thereof coupled to the third conductor 56. The second resistor 66 has an end 66-1 coupled to the source of potential 72 and a remaining end 66-2 coupled to the first input conductor 62-1. The third resistor 68 has an end 68-1 coupled to the first input conductor 62-1 and a remaining end 68-2 coupled to fourth conductor 58. The fourth resistor 70 has an end 70-1 coupled to a reference voltage of 5 volts, and a remaining end 70-2 is coupled to the output conductor 62-3. The output conductor 62-3 of the operational amplifier 62 is coupled to the controller 30, and the fourth conductor 58 is coupled to ground. The electrical resistance of the ink ribbon 16 is measured between the first and second conductors 50 and 52 which are coupled to the third and fourth conductors 56 and 58, respectively, when the ribbon cassette 12 is mounted in the printer 10. The ink ribbon 16 is shown as a resistor in Fig. 4. The operational amplifier 62 will generate the alarm signal at the output conductor 62-3 when the voltage at the second input conductor 62-2 is equal to or exceeds the voltage at the first input conductor 62-1. As the ink ribbon 16 is used, the electrical resistance of the ink ribbon 16 increases and raises the voltage level at the third conductor 56, thereby causing a first signal corresponding to the measured resistance of the ink ribbon 16 to be generated at the second input conductor 62-2. The predetermined resistance mentioned previously herein may be programmed or adjusted by selecting the appropriate resistor values for the first, second, third, and fourth resistors 64, 66, 68, and 70. When the voltages on the input conductors 62-1 and 62-2 are equal or the voltage on the input conductor 62-2 exceeds the voltage on the input conductor 62-1, the operational amplifier 62 generates the alarm signal at the output conductor 62-3. The alarm signal generated at the output conductor 62-3 is received by the controller 30 which causes a message to be displayed on a display 74 coupled to the controller 30. The message alerts the printer operator that the ink ribbon 16 needs to be replaced. The controller 30 may be arranged to sample the alarm signal only when the ink ribbon 16 is not being advanced. Also, the controller 30 may sample the alarm signal several times before the message is displayed on the display 74 in order to verify that the ink ribbon 16 has a low ink content. Circumstances under which the alarm signal might be generated will now be described. Assume that the printer 10 prints the data 38 legibly when measured resistance of the ink ribbon 16 is 1.5K ohms or below. As the ink ribbon 16 is used, the ink on the ink ribbon 16 is removed which causes the data 38 to be printed illegibly or not at all. In the example being described, this would occur when the measured resistance of the ink ribbon 16 equals or exceeds a resistance of 1.5K ohms. For a ink ribbon 16 whose resistance is 1.5K ohms, the circuit 54 may be programmed as follows. In order to program the circuit 54 with the predetermined resistance of 1.5K ohms, the resistors 64, 66, 68, and 70 would be selected to have resistances of 2.2K, 2.2K, 1.5K, and 10K, respectively. It may be desired to select a predetermined resistance of 1.5K so that the alarm signal will be generated prior to the data 38 being printed illegibly. In order to program the circuit 54 with the predetermined resistance of 1.5K ohms, the first, second, third, and fourth resistors 64, 66, 68 and 70 (Fig. 4) could be selected to have resistances of 2.2K, 2.2K, 1.5K, and 10K respectively. In view of the foregoing it will be clear to a person skilled in the art that modifications may be incorporated without departing from the scope of the present invention. For example, the ribbon cassette 12 may include openings (now shown) which permit probes (not shown) from a voltmeter or ohmmeter, for example, to be inserted therethrough in order to contact the ink ribbon 16. The electrical resistance of the ink ribbon 16 could then be measured when the ribbon cassette 12 is stored on a shelf in inventory.

Claims: A method for testing the condition of the ribbon (16) of an ink ribbon cassette (12), characterized by the steps of generating an electrical signal dependent on the electrical resistance of said ribbon (16) between first and second portions thereof spaced apart along said ribbon, and generating an alarm signal when said electrical resistance exceeds an predetermined value. An ink ribbon cassette (12) including an ink ribbon (16) and a housing (14) for said ribbon, characterized by first and second electrical conductors (50,52) arranged to contact first and second portions of said ribbon spaced apart along said ribbon, said conductors being accessible externally of said housing whereby the electrical resistance of said ribbon between said conductors may be measured. A ribbon cassette (12) according to claim 2, characterized in that said first and second conductors (50,52) extend through a wall of said housing (14). A printer (10) comprising a cassette receiving means (28) for receiving a ribbon cassette (12) containing an ink ribbon (16), the cassette having first and second electrical conductors (50,52) arranged to contact first and second portions of said ink ribbon spaced apart along said ink ribbon, wherein said cassette receiving means includes means adapted to couple said electrical conductors (50,52) to a circuit (54) arranged to detect the electrical resistance of said ink ribbon between said first and said second portions thereof. A printer according to claim 4, characterized in that said circuit (54) is arranged to generate an alarm signal when said electrical resistance of said ink ribbon between said first and said second portion thereof exceeds a predetermined value. A printer according to claim 5, characterized by display means (74) coupled to a controller (30) for generating a message that said ribbon cassette needs to be replaced in response to said alarm signal. A printer according to claim 6, characterized in that said controller (30) is arranged to sample said alarm signal only when said ink ribbon (16) is not being advanced. A printer according to claim 6 or claim 7, characterized in that said alarm signal is sampled several times before displaying a message on said display means (74).

Inventors: MENZENSKI GREGORY, MENZENSKI, GREGORY
Applicants: AT & T GLOBAL INF SOLUTION, AT&T GLOBAL INFORMATION SOLUTIONS INTERNATIONAL INC.
Application year: 1991
Main classification: B41J31
IPC codes: B41J31, B41J35, B41J17