BACKGROUND OF THE INVENTION

1. Field of the Invention

⁵ The invention relates to print ribbons that are encoded so as to provide data about the print ribbon to a printing system, such as a printer, copier, typewriter, etc., that uses the print ribbon.

2. Description of Related Art

Print ribbons for use in printing mechanisms of various types of

¹⁰ machines are well known. Typically, the ribbon comprises a flexible substrate and ink coated on a surface of the flexible substrate. When used with a printing mechanism that is an impact printer, the ink is transferred from the flexible substrate to a receiving medium such as, for example, paper when pressure is applied to the ribbon. When used with a printing

¹⁵ mechanism that is a thermal transfer printer, the ink is transferred from the flexible substrate to the receiving medium by applying heat to selected portions of the ribbon.

In order to increase the versatility of a printing system using print ribbons, it is common to use different types of print ribbons with the

^° printing system. For example, a person might use a multi-pass ribbon to produce most of their images at a relatively low quality, and use a single- pass ribbon when high quality images are desired. This enables the person to reduce their costs (i.e., by using a single multi-pass ribbon for normal daily use), while preserving the ability to make high quality images (i.e.,

^ ⁵ with the single-pass ribbon, which would be expended quickly if it were used exclusively). Similarly, a person may wish to switch between a low cost black ink print ribbon and a more expensive print ribbon that prints in one or more colors.

A problem that arises when more than one type of print ribbon

^ is used with a printing mechanism is that the quality of the image can vary between the different types of ribbons. This problem arises because the flexible substrate and/or the ink used with different types of ribbons have different characteristics including transfer characteristics. Thus, in order to produce images having the optimal quality regardless of the type of print

³⁵ ribbon used by the printing mechanism, the operating parameters (i.e., the control settings) of the printing mechanism printhead should be adjusted

(i.e., customized) for each type of print ribbon. For example, the pressure or amount of heat applied by the printhead to the print ribbon should be adjusted.

It is known to provide machine-readable indicia such as bar codes on print ribbons or on a portion of the cartridge that contains a print ribbon, wherein the bar code indicates the type of print ribbon being used. A reading device located in the printing system reads the bar code, and then a controller of the printing system uses the appropriate printing parameters to form images with the print ribbon whose type has been identified.

Conventional printing systems, however, have a limited versatility because of the encoding technique that they use. In conventional systems, the bar code represents the type of print ribbon (for example, the bar code represents a number that corresponds to the type of print ribbon). Once the bar code reader reads the bar code and the controller identifies the print ribbon type, the controller retrieves the printing parameters appropriate for that print ribbon from a look-up table (stored in a memory of the printing system). A limitation of this technique is that when new print ribbons are developed, having a new set of optimal printing parameters that should be used by the printing mechanism, the look-up tables in previously available printers do not contain the new optimal set of parameters for use with the new ribbon. Additionally, the print ribbon identification software cannot identify the new ribbon because the identification code of the new ribbon did not exist when the printer was manufactured. Accordingly, it becomes necessary to update the look-up table and ribbon-type-identification software in the printing system each time a new type of ribbon having new optimal printing parameters is developed. An alternative technique is to mark the new type of ribbon with a code that is identical to the code of a previously existing ribbon-type if the previous and new types of ribbons have relatively similar printing parameters. This technique is limited in its ability to optimize print quality.

U.S. Patent No. 4,797,016 to Lahr discloses a printer ribbon having machine-readable markings arranged on its substrate to provide selected information such as ribbon footage used and ribbon type. The ribbon includes a transferable ink deposited on a first side of the flexible substrate and a plurality of machine-readable marks deposited on a second

side of the substrate. The machine-readable marks are distributed over the length of the ribbon from a start end to a finish end so that the ribbon footage can be determined. See column 6, lines 39-43. General information also can be provided at the beginning of the tape. See column 6, lines 43-51.

U.S. Patent No. 5,073,053 to Kashiwagi discloses a color ink ribbon having discriminating marks parallel to a lengthwise direction of the color ink ribbon. The marks are positioned on the same straight line and are formed at one edge of the color ink ribbon. An end-of-tape mark also is provided.

U.S. Patent No. 4,336,751 to Melissa et al. discloses a printer/plotter system for producing a multiple color hard copy output in response to digital input data. The system includes an ink ribbon having multiple zones of different colors carrying encoded identifying indicia. See column 2, lines 10-19.

U.S. Patent No. 5,144,331 to Amano discloses a drive control method for a thermal transfer printer adapted to carry out printing by detecting a mark formed upstream or downstream of an ink layer on an elongated ink medium for indicating the color of the ink layer. The detecting marks are discriminated from one another by differentiating the number of bars constituting a color.

U.S. Patent No. 5,087,137 to Burnard et al. discloses an ink ribbon cartridge in which a bar code is included on either a supply-spool or on a take-up spool for the print ribbon. The bar code represents a number that is used to reference a set of control parameters stored in memory. See column 4, lines 50-56. The control parameters include printhead temperature, printing speed, ribbon speed, and single vs. multi-pass ribbon.

SUMMARY OF THE INVENTION It is an object of the invention to provide a print ribbon encoded in a manner that enables new types of ribbons to be developed and used with existing printing systems without requiring reprogramming or other software updating of the printing system. It is also an object of the invention to provide a printing system and method of using such a print ribbon.

It is another object of the invention to provide a print ribbon encoded with machine-readable indicia in a manner so that the machine-

readable indicia can be read with a high degree of certainty, and so that any errors in the reading process can be detected and preferably corrected.

It is another object of the invention to provide a print ribbon encoded in a manner that enables information regarding many variables to be indicated in a limited amount of space that is available on the print ribbon.

It is another object of the invention to provide a print ribbon encoded with machine-readable indicia in a manner that enables reading of the machine-readable indicia to be resistant to ribbon slipping or stretching and that does not require a clock to be synchronized between the reading process and the ribbon motion.

It is a further object of the invention to provide a print ribbon encoded so that machine-readable indicia can be read from the print ribbon regardless of the position of the ribbon and regardless of the direction of ribbon movement, enabling ribbon cartridges to be exchanged readily in an imaging device using the print ribbon when it is desired to print with a different type of print ribbon.

In order to achieve the above and other objects, and to overcome the shortcomings in previous devices, a print ribbon having a flexible substrate and transferrable ink located on a portion of one of the first and second surfaces of the flexible substrate includes machine- readable indicia on one of the first and second surfaces, the machine- readable indicia being provided in accordance with one or more of the inventive features detailed hereafter. According to one aspect of the invention, the machine-readable indicia includes a code pattern, with at least a portion of the code pattern indicating a value of a control setting to be used by a controller of a printing system using the print ribbon so that the printing operation is performed using the control setting without retrieving the control setting from a storage device. According to this first aspect of the invention, it is not necessary to store control settings or sets of control settings in a memory such as a look-up table. Instead, the printing system derives the control settings directly from the machine-readable indicia on the particular print ribbon located in the printing system. Usually, the code pattern includes a plurality of code pattern portions, each code pattern portion indicating a value of a control setting to be used in the printing process. This enables the control setting indicated by each of the plurality

of code pattern portions to be varied independently of the control settings indicated by the other code pattern portions. Accordingly, when new types of print ribbon are developed, each of the optimal control settings can be indicated in the machine-readable indicia located on the new type of print ribbon. The printing system using the print ribbon then can derive the optimal set of control settings for use with the new type of print ribbon.

The control settings indicated by the print ribbon code pattern can include, for example, a value of a first energy pulse to be supplied to a heating element and a value of a second energy pulse to be supplied to the heating element of the imaging device when the printing system is, for example, a thermal printer. Additionally, control settings can be provided that indicate variations in the values of the first and/or second energy pulses that should be made during the printing process. According to a second aspect of the invention, the code pattern can include a first pattern portion that indicates at least one control setting to be used by a printing mechanism to print with the print ribbon and a second pattern portion that indicates instructions for modifying the at least one control setting during the printing process. For example, in some printing systems it is desirable to vary a pulse width used for actuating printing elements that print with the print ribbon as the printhead containing the printing elements moves across an image-receiving surface, such as a sheet of paper. The manner in which the width of the energy pulse should be varied as the printhead moves can be indicated by the second pattern portion of the code pattern. The second pattern portion can indicate an equation, for example, the slope of a line, which indicates the rate at which an initial pulse width (indicated by the first pattern portion) is varied during printhead movement.

According to a third aspect of the invention, the code pattern includes a first portion that provides information for use in printing with the print ribbon, and a second portion that provides information about the first portion so that a printing system using the print ribbon can verify that the first portion was read correctly. The second portion can be located at the end of the code pattern (i.e., after the first portion) or can be interspersed with the first portion depending on the type of reading verification technique that is utilized. For example, when the code pattern is a bar code pattern including a plurality of bars, each having either a

large width or a small width, the second portion of the bar code pattern can indicate a total number of bars in the first portion having the large width (or having the small width).

The code pattern in each of the first through third aspects of the invention can be a bar code pattern.

According to a fourth aspect of the invention, the machine- readable indicia located on the print ribbon is a bar code pattern including alternating light and dark data bars with each of the data bars having widths of either X or nX, depending on the data that the data bars indicate, wherein n has a value greater than 1. The use of both light and dark bars to represent data enables more data to be provided on the limited space available on the print ribbon than in systems that only use dark bars to represent data (the dark bars in previous systems being separated by constant-sized spaces that do not represent data). The bar code pattern according to the fourth aspect of the invention also is advantageous over previous systems in which dark data bars directly abut one another, i.e., no spaces are provided between adjacent dark data bars, because it does not require a clock to synchronize reading of the bar code pattern (i.e., the present pattern is "self-clocking"). According to the fourth aspect of the invention, the data contained in the light and dark data bars can be detected simply by measuring the time between edges of the data bars (which can be detected easily by sensing when the bar code reader output changes from high to low or from low to high) and comparing the measured time with a reference time to determine whether the data bar was wide or narrow.

The bar code pattern can be provided on a leader portion of the ribbon, which does not include ink on either surface thereof. Alternatively, the bar code pattern can repeat multiple times throughout the length of the ribbon so that the bar code pattern can be read regardless of the position of the ribbon in a ribbon cartridge when the ribbon cartridge is inserted into the printing system. This eliminates the need to place ribbon cartridges in the printing system having the ribbon entirely rewound so that the bar code on the leader portion can be read.

According to another aspect of the invention, when the printing system can use multi-pass and single pass print ribbon, one of the bars in the bar code pattern indicates whether the ribbon is a multi-pass ribbon. When ribbons are multi-pass ribbons, they can include bar code patterns

on the leader portions located at both ends of the ribbon, with the bar code patterns arranged in opposite directions on each of the leader portions so that the bar code pattern can be read regardless of the direction in which the ribbon is moved by the imaging device. According to another aspect of the invention, a bar at one end of the bar code pattern can constitute a multi-pass bar having a width larger than the widths of the other data bars in the pattern. For example, the other data bars can have widths of X or 2X, while the multi-pass bar has a width of 4X (when indicating a multi-pass ribbon). According to this aspect of the invention, the printing system determines in which direction to read the bar code pattern by determining the orientation of the multi¬ pass bar relative to the other bars or to a start bar having a width of 3X. For example, if the multi-pass bar is the first bar in the bar code pattern, the bar code pattern is decoded in the same order in which the bars are read. If, however, the multi-pass bar code is the last bar in the code pattern, the bar code pattern is decoded in an order reversed from the reading order. Accordingly, it is possible to determine the order in which the ribbon is moving (forward or backward) from the position of the multi¬ pass bar relative to the reading order of the bar code pattern. BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention will be described in detail with reference to the following drawings in which like reference numerals refer to like elements and wherein:

Fig. 1 is a perspective view of a portable copier that uses a print ribbon according to the invention;

Fig. 2 is a perspective view of a scanner and drive system of the Fig. 1 copier;

Fig. 3 is a top view of the Fig. 2 scan carriage and a print ribbon cartridge used therewith; Fig. 4 is a front view of the scan carriage and print ribbon cartridge of Fig.3;

Fig. 5 is a top view of a bar code on a print ribbon according to a first embodiment of the invention;

Fig. 6 is a side view of a ribbon in which the bar code and the transferable ink are located on opposite sides of a support substrate;

Fig. 7 is a side view of a ribbon in which the bar code and the

transferable ink are located on a same side of a transparent support substrate;

Fig. 8 shows a bar code located on a leader portion of a print ribbon; Fig. 9 is a block diagram of a copier control system using the print ribbon of the invention;

Fig. 10 is a flow chart showing a process for reading and interpreting the bar code on a print ribbon of the invention;

Fig. 11 shows a bar code located on both leader portions of a multi-pass print ribbon;

Fig. 12 shows a print ribbon bar code having a bar code portion that is used to check whether the print ribbon information-containing portion of the bar code was correctly read;

Fig. 13 shows a print ribbon bar code having a bar code pattern in which the checking portion is interspersed with the print ribbon information-containing portion;

Fig. 14 is a flow chart showing a modification of the Fig. 10 flow chart in which a checking process is performed: and

Fig. 15 shows a print ribbon in which a bar code repeats multiple times throughout the length of the print ribbon.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The invention is applicable to print ribbons that can be used with various types of printing systems, such as, for example, printers, copiers, facsimile machines, typewriters, etc., in which the optimal printing parameters used by the printing system to perform printing can vary depending on the properties of the print ribbon and the ink contained on the print ribbon. The invention is applicable to printing systems having printing mechanisms (i.e., printheads) that rely on, for example, thermal energy to transfer ink from the print ribbon during image formation, or having printing mechanisms that use pressure to transfer the ink from the print ribbon during the printing process. For example, the invention can be included on print ribbons that can be used with thermal printing mechanisms or impact-type printing mechanisms. Additionally, the manner in which the heat and/or pressure is controlled in the printheads can vary depending on the particular control algorithm used by the printing system. Thus, the information that needs to be encoded on the print ribbon can vary depending on the type of printing mechanism with

which the print ribbon is used and depending on the control algorithm used by the printing mechanism. Accordingly, while a particular type of printing system (a portable copier that uses a thermal printhead to form images on a sheet of paper using a particular control algorithm) will be described in conjunction with the invention, it is apparent that the invention can be used with other types of printing systems. Additionally, the information that can be indicated on a print ribbon using a code pattern according to the present invention can differ from the information indicated in the print ribbons described hereafter. Figs. 1-4 illustrate a portable copier 1 that uses a ribbon cartridge 70 containing a print ribbon having thermally transferable ink on one surface thereof that can be used to print images on, for example, a sheet of paper when a thermal printhead 65 of the copier is actuated. The copier 1 includes a housing having opening 455 through which the print ribbon cartridge 70 can be inserted and removed. A copy sheet input chute 460 is rotatably attached to the copier housing so that chute 460 can be moved to an open position shown in Fig. 1 during ribbon replacement and copying and to a closed position (not shown) in which chute 460 closes opening 455. The copy sheet input chute 460 includes a copy sheet guide 462 for positioning and guiding a copy sheet so that it moves between the ribbon and a supporting platen (not shown) of the copier 1 during an imaging operation.

Figs. 2-4 illustrate the system for driving the printhead and document scanner. Scan carriage 40 is driven by lead screw 50 along guide rod 53 in a scan direction 55 and in a reverse direction opposite to the scan direction. Disposed above scan carriage 40 is a document indexer having rolls 10 mounted on shaft 15 for advancing a document (containing an original image) along a document transport path in the direction of arrow 20. Disposed below scan carriage 40 is a copy sheet indexer having rolls 25 mounted on shaft 30 for advancing a copy sheet along a copy sheet transport path in the direction of arrow 35. Motors 90a, 90b rotate document index shaft 15, copy sheet index shaft 30 and lead screw 50. Output shaft 100 of motor 90a drives gear 105, which is engaged with gear 110 and with gear 130 mounted on lead screw 50. Rotation of shaft 10 is transmitted by gear 110 through one-way clutch 113 to jack shaft 115, and then to gears 120, 125 and document shaft 15. Motor 90a causes document shaft 15 to rotate, advancing the document along the document

transport path in the direction of arrow 20. Further, motor 90b independently drives copy sheet index shaft 30 via output shaft 135 and gears 140, 145 and 150. Motors 90a, 90b are preferably DC motors, that generate movement signals by encoder wheels 95a, 95b and sensors 97a, 97b, which are used to monitor and control the motors as is well known.

Scan carriage 40 includes vertical face 45 on which shafts 75a, 75b are disposed, supporting removable print ribbon cartridge 70. After a used cartridge 70 is removed, a replacement cartridge easily can be installed by aligning ribbon cartridge opening 73a, 73b with shafts 75a, 75b and imparting a linear motion to ribbon cartridge 70 to engage shafts 75a, 75b.

Thermal printhead 65, which includes a line of printing elements 160 (Fig. 3), preferably resistor elements, engages the ribbon of ribbon cartridge 70 and prints on the copy sheet advanced by rolls 25. Printhead 65 is mounted on mounting arm 85, which includes a journal portion 80 that enables arm 85 to pivot about pin 83, which is mounted on and extends outward from carriage face 45. Mounting arm 85 is spring biased in a downward direction allowing thermal printhead 65 to push the ribbon and copy sheet against an elastomeric platen (not shown) to transfer ink from the ribbon to the sheet when printing elements 160 on printhead 65 are heated. When carriage 40 completes each scan, that is, reaches the end of its movement in the direction of arrow 55, a mechanism (not shown) lifts and latches printhead up and out of contact with the ribbon and copy sheet. Thus, when carriage 40 moves in its non-imaging direction (opposite arrow 55), a gap exists between printhead 65 and the ribbon, the copy sheet, and the elastomer platen. When carriage 40 reaches the end of its movement in the direction opposite arrow 55, the printhead latch is released, thus re-engaging printhead 65 against the ribbon, copy sheet, and elastomer platen under the influence biasing of arm 85. Scan carriage 40 also supports contact image sensor 60 on carriage surface 47. Image sensor 60 includes a line of input photosites 155 (Fig. 3) for reading images from the document as scan carriage 40 moves in scan direction 55. Photosites 155 of image sensor 60 and printing elements 160 of thermal printhead 65 preferably are aligned with each other along axis 165, as shown in Fig.3.

Fig.4 illustrates the relative position of print ribbon cartridge 70

with respect to a sheet of copy paper 170 and a glass platen 180 upon which the original document 175 to be copied is placed.

Referring to Fig. 2, in use, motor 90a rotates in a first direction to rotate lead screw 50 through the illustrated gearing arrangement, so as to drive scan carriage 40 in scan direction 55. During movement in the scan direction, one-way clutch 113 slips relative to jack shaft 115, so that document index shaft and document index rolls 10 remain stationary. At the end of the scan, that is, when scan carriage 40 has completed its movement in scan direction 55, motor 90a reverses, rotating lead screw 50 in the opposite direction and causing scan carriage 40 to move in the reverse direction. During this return scan, one-way clutch 113 is engaged, allowing motor 90a to rotate document index shaft 15 and document index rolls 10 via jack shaft 115 and gears 120, 125, thereby indexing the document. Preferably, the gear ratios are designed so that full travel of scan carriage 40 in the reverse direction corresponds to a single indexing rotation of document index shaft 15.

For further details on the illustrated portable copier, see U.S. Patent Application Serial No. 08/139,776, filed October 22, 1993, and entitled "Portable Copier and Method of Using a Portable Copier", by Denis J. Stemmle and Egon Babbler, the disclosure of which is incorporated herein by reference.

A controller 600 (Fig.9) in copier 1 controls printhead 65 by supplying the appropriate amount of energy to each resistor (heating) element 160 so that printing is performed having an optimal print quality. As mentioned earlier, it often is necessary to have knowledge of the characteristics of the print ribbon inserted in the copier so that printhead 65 can be controlled to produce high quality images with the installed print ribbon.

A preferred algorithm that controls the energy supplied to heating elements 160 uses heat transfer calculations to determine the energy level of each heating element during printing. For example, as a heating element is caused to print dots repeatedly, its energy level (which is related to temperature) increases, whereas a heating element that is not used very often tends to remain at a lower energy level. It is necessary to take the energy level of each heating element into consideration when determining the amount of energy to be supplied to each heating element so that each heating element is controlled to print dots having equal sizes,

thereby ensuring high, uniform print quality. For example, the frequency with which a particular heating element is actuated effects its energy level as detailed above. Additionally, the energy levels of adjacent heating elements affect each other. The rate at which energy is dissipated from the heating elements also effects their energy levels. Energy is dissipated to, among other things, the print ribbon. Accordingly, it is necessary to have knowledge of the heat transfer characteristics (e.g., the coefficient of heat transfer) of the print ribbon installed in copier 1 so that the control algorithm can determine the rate at which energy is dissipated from each heating element to the print ribbon. It also is necessary for the controller to have information about the print ribbon (including the ink on the print ribbon) so that an appropriately sized energy pulse can be supplied to the heating elements to cause them to print a dot having a predetermined size (this energy pulse may be further modified in view of the energy level of a particular heating element as detailed earlier).

For more details on one type of preferred algorithm used to determine the energy levels of each heating element during printing (thereby determining the size of the pulse to be supplied to each heating element), see U.S. Patent Application No. 08/139,791, filed October 22, 1993, by Robert P. Robideau and Dennis J. Stemmie, and entitled "Heat Management Method and Apparatus for a Thermal Printhead," the disclosure of which is incorporated herein by reference. In this algorithm, in order to optimize print quality "offdot" pulses are supplied to heating elements that have cooled below a predetermined temperature in order to prevent these heating elements from cooling by an excessive amount. The offdot pulse is insufficient to cause a dot to be formed with the print ribbon. When it is desired to print with a heating element, an "ondot" pulse is provided to the heating element.

It is necessary to provide the controller with "baseline" ondot and offdot pulses, which vary depending on the type of ribbon installed in the copier. It also can be desirable to vary the ondot and offdot pulses as the printhead sweeps across the sheet of paper. For example, as the printhead sweeps across the sheet of paper, the values (i.e., the durations) of the ondot and offdot pulses usually can be reduced because the printhead temperature increases during the print cycle (this variation in the ondot and offdot pulses can be in addition to or an alternative to variations made in the baseline ondot and offdot pulses due to the

calculated energy levels of specific heating elements). The amount by which the ondot and offdot pulses should be varied also is effected by the type of print ribbon (including the ink) that is used.

As mentioned earlier, the heat management algorithm that calculates the energy level of each heating element also determines the amount of heat that is transferred from each heating element to the print ribbon. Accordingly, the coefficient of heat transfer to the print ribbon, which depends on the type of print ribbon and ink, also needs to be supplied to the copier controller. It also can be desirable to include a customer ID code on each print ribbon so that the copier can confirm that the print ribbon was manufactured by an authorized manufacturer or distributed by an authorized distributor and therefore controlled withi n known specifications for important parameters. Preferred embodiments of a print ribbon encoded according to the present invention will now be described.

Figs. 5 and 8 show a print ribbon 200 having one end wound around a supply spool 71a, which is rotatably provided in cartridge 70 as is well known. A majority of the print ribbon 200 includes transferable ink on one surface thereof. The end of print ribbon 200 opposite from supply spool 71a includes a leader portion 215, which does not include any transferable ink thereon. In accordance with one embodiment of the invention, the bar code 202 is included on the leader portion 215, as shown in Fig. 8. Alternatively, the bar code can be provided on the portion of the print ribbon that is coated with transferable ink as shown in Figs. 6 and 7. Fig. 6 shows an embodiment where the print ribbon 200 includes a flexible substrate 204, having transferable ink 206 applied on one surface of the substrate, and the bar code 202 applied on the opposite surface of substrate 204. Alternatively, as shown in Fig. 7, when substrate 204 is transparent, the bar code 202 and transferable ink 206 both can be applied to the same surface of substrate 204, with bar code 202 located between substrate 204 and transferable ink 206. In this embodiment, when optically readable bar codes are used, the substrate 204 should be transparent so that the bar code can be read through the transparent substrate 204.

The bar code 202 illustrated in Fig. 5 includes 23 bars, labeled B1- B23. In the preferred embodiment, the bars are alternating dark and light bars. The dark bars could be formed by applying black, non-transferable ink to the print ribbon substrate or leader. The light bars could be formed by applying a silver, reflective material to the print ribbon substrate or leader. This type of bar code can be read by an optical reader 300 (see Fig. 3), which includes a light emitter and a photodetector. The photodetector detects whether the emitted light is reflected from the light bars or is absorbed by the dark bars. Other types of bar code readers (and appropriate bars) could be used, for example, magnetic and infrared type bar code readers.

As illustrated in Fig. 5, the odd-numbered bars are dark bars and the even-numbered bars are light bars. Both the light and dark bars encode data. The narrow bars, which have a width of about 0.10 inches could represent a data bit having a value of 0, while the wide bars, which have a width of about 0.15 inches, could represent a data bit having a value of 1. In Fig. 5, bits B1, B3-B5, B8-B11, B14, B15, B17, B18 and B21-23 are narrow bars, while data bars B2, B6, B7, B12, B13, B16, B19, and B20 are wide bars. The use of both light and dark bars to represent data enables more data to be provided on the limited space available on the print ribbon than in systems that only use dark bars to represent data. In such previous systems, the dark bars typically are separated by constantsized spaces that do not represent data. The bar code pattern also is advantageous over previous systems in which dark data bars directly abut one another, i.e., no spaces are provided between adjacent dark data bars. Such previous systems required very accurate clocking techniques to ensure that the bar code was read properly. The Fig. 5 bar code is advantageous over such systems because it does not require a highly accurate clock to synchronize reading of the bar code pattern. The content of the data bars (i.e., the width of the data bars) is determined simply by measuring the time between edges of the data bars, which can be detected by sensing when the bar code reader output changes from high to low (light bar to dark bar) or from to low or high (dark bar to light bar). The measured time is compared to a reference time to determine whether the data bar was wide or narrow. For example, at regular sampling intervals by the bar code reader sensor, if between 5 and 17 similar readings are made, the bar is

interpreted as a narrow bar, whereas if between 18 and 24 similar readings are made by the point of transition to the other state, the bar is interpreted to be a wide bar. Because the wide data bars are 50% wider than the narrow data bars, it is unlikely that any stretching of the ribbon would adversely affect the accuracy of the read bar code (the print ribbon would break before it was stretched by 50%). Also, this system is substantially immune to variations in ribbon speed within the tolerance of ±25% speed variation that can occur if the ribbon slips or stretches relative to the printhead. In accordance with one aspect of the invention, the bar code provides data that can be used by the controller of the printing system to directly derive control settings to be used by the printing system during the printing process. In the context of the invention, "directly derived" means that the control settings are calculated, for example, using equations as opposed to being retrieved from a memory (such as a look-up table). The bar code is divided into a plurality of portions. Each bar code portion provides a numerical value (represented in binary form by the narrow and wide bars) that can be used by the printing system controller to derive the control setting, preferably without reference to a look-up table or other storage device, which conventional devices used to store a plurality of possible control settings that can be used by different types of print ribbons.

The bar code shown in Fig. 5 provides information regarding multiple control settings and a customer identification code. Bits B1-B5 provide a value to be used to derive an ondot pulse. The ondot pulse control setting is a pulse width that is appropriate for use to print a dot at the beginning of a print line for the installed print ribbon. Typical values for an ondot pulse might range from between 120 microseconds and 256 microseconds, for example. By providing 5 bits (B1-B5) to encode the ondot pulse data, 32 possible settings are available for the ondot pulse control setting. A simple equation can be used by the printing system controller to derive the ondot pulse control setting so that it is set between 120 microseconds and 256 microseconds based on the value of bits B1-B5. For example: when bits B1-B5 all are narrow bars, the value will be 120 microseconds; when bits B1-B5 all are wide bars, the value will be 256 microseconds; and when bits B1-B5 are a combination of narrow and wide

bars, the value will be set between 120 microseconds and 256 microseconds.

Bits B6-B7 provide information regarding an ondot modification instruction. The ondot modification control setting varies the ondot pulse for each of the heating elements in the printhead as the printhead sweeps across a sheet of paper to print a scan line. It has been determined that as the printhead sweeps across the copy sheet, the temperature of the printhead and heating elements increases due to the printing that has taken place. Accordingly, the ondot pulse required to produce a uniform shaped spot decreases as the printhead sweeps across the sheet of paper. The ondot modification portion of the bar code enables four possible rates of decline in the ondot control setting to be selected. The ondot modification instruction can reference an equation, for example, a slope that is used to calculate a decrease in the ondot pulse width as the printhead moves in scan direction 55. For example, if 3400 dots could be made by each heating element as it moves across the sheet, and the first possible dot energy was established to be a 200 microsecond pulse width, the pulse width might be reduced by 2 microseconds every 100 dots. In this case, the last hundred dots would have a pulse width of 132 microseconds. Bits B8-B12 provide information regarding the offdot pulse. As detailed earlier, the offdot pulse is a pulse that is insufficient to cause dot formation. The offdot pulse is used to prevent less active heating elements from cooling below a predetermined temperature. The control settings for the offdot pulse can be determined in a manner similar to that described above with respect to the ondot pulse (although the offdot pulse widths would be shorter than the ondot pulse widths). As with the ondot pulse, 32 possible values of the control setting can be selected.

Bits B 13-B 14 provide information regarding an offdot modification instruction and are used in a similar manner as bits B6-B7 described earlier.

Bits B15-B18 provide information regarding the heat transfer coefficient of the print ribbon. As detailed above, the heat transfer coefficient of the ribbon is used to determine how much energy is transferred from the heating elements to the print ribbon during the printing operation. In the illustrated embodiment, 16 possible heat transfer coefficients can be encoded depending on the values of bits B15- B18.

Bits B19-B22 provide information regarding the supplier of the print ribbon. This information can be used to determine whether the print ribbon was distributed by an authorized supplier. Unlike the previous portions of the bar code, the customer identification portion compares the read data to a look-up table stored in the printing system.

Bit B23 indicates whether the print ribbon is a multi-pass print ribbon. For example, if bit B23 is narrow, the ribbon is a single-pass ribbon, whereas if bit B23 is wide, the ribbon is a multi-pass ribbon. For printing systems equipped with automatic rewind mechanisms, the multi-pass bit will instruct the controller to engage the auto rewind mechanism when the end of ribbon is reached if the ribbon is a multi-pass ribbon.

Figure 9 is a block diagram of the control system for the copier 1 of Fig. 1. A controller 600, which can be, for example, a microprocessor having a RAM and a ROM, or can be an application specific integrated circuit (ASIC), controls the scanning of an original document via image sensor 60, the reading of bar codes on print ribbon 200 using bar code reader 300 and the printing on copy sheets by printhead 65. Controller 600 can control other portions of the copier, such as motors 90a, 90b; however such interconnection is not shown in the drawings for the sake of simplicity. As detailed earlier, numerous control algorithms can be used to control the printhead depending on the type of printhead and the quality of print desired. Accordingly, the control routine for controlling the printhead will not be described herein.

Figure 10 is a flow chart showing the basic steps for determining control settings to be used by the printing system by reading the bar code on a print ribbon. In step S1, the bar code pattern is read from ribbon 200 using bar code reader 300. In step S2, the data for each portion of the bar code pattern is identified. For example, referring to the bar code in Figure 5, the value for the ondot pulse represented by bars B1-B5 is identified as "01000." The data for each of the other bar code portions are identified in similar fashion. In step S3, the control setting to be used by the printing system is derived from the data read for each code pattern portion. Typically, this is done by inserting the read value for each bar code portion into an equation to calculate each control setting. Then, in step S4, the printhead 65 is controlled by controller 600 using the determined control settings.

An advantage of this encoding technique is that when new types of print ribbons are developed, each of the optimal control settings can be indicated in the bar code independently of one another. Thus, unlike previous systems in which the bar code merely contained a number that referenced a set of control settings appropriate for the print ribbon identified by that particular bar code, the present invention enables information regarding each control setting to be independently provided on the ribbon.

Although the previously described embodiment directly derived the control settings from the numerical values indicated in some portion or portions of the bar code pattern without reference to a look-up table, it is also possible for some portion or portions of the bar code pattern to reference a separate look-up table in the controller memory. This also enables each of the control settings to be varied independently from one another. For example, the value indicated by bits B1-B5 could be used to reference a first look-up table that stores a plurality of possible ondot pulses, the numerical value indicated by bits B6-B7 could be used to reference an ondot modification instruction look-up table that provided a variety of ondot slopes or modification equations that could be used with different types of print ribbons, and so on.

When the ribbon is a multi-pass ribbon that can be repeatedly used and moved in either direction between supply and take-up spools in cartridge 70, it is preferable to include the bar code at both ends of the print ribbon. Fig. 11 illustrates the print ribbon having leader portions 215 and 217 at opposite ends of the print ribbon. Both the leader portions 215 and 217 include bar code 202. However, the barcode is arranged to read in opposite directions on the leader portion 215 and the leader portion 217. As shown in Fig. 11, the first bar (indicated by S) of the bar code on leader portion 215 is located on the left side of the bar code, while the last bar, which could be the multi-pass indicating bar (labeled M), is provided on the right side of the bar code (of course, the multi-pass bar could be located in the central portion of the bar code pattern). This differs from the bar code 202 located on leader portion 217 in which the multi-pass indicating bar M is located on the left side of the bar code, and the first bar S is located on the right side of the bar code. This enables the bar code to be read regardless of the direction in which cartridge 70 is installed in the printing system.

Fig. 12 illustrates another aspect of the invention. The bar code of Fig. 12 has two portions: a first portion comprised of bits B1-B10; and a second portion comprised of bits B11-B14. The first portion contains information that can be used by the printing system controller to control the printhead to optimize printing with the particular type of installed print ribbon as detailed earlier. The second portion of the bar code includes information that can be used to determine (i.e., check) whether the first portion of the bar code was read properly by the bar code reader 300. In the Fig. 12 embodiment, the second portion of the bar code is a binary representation of the total number of wide bars contained in the first portion of the bar code. The first portion of the bar code includes four wide data bars: B3, B4, B7, and B10. Accordingly, the second portion of the bar code is the binary representation of the number 4 (i.e., "0100").

The second portion (i.e., the checking portion) of the bar code can be located entirely at the end of the bar code as shown in Figure 12, or it can be dispersed throughout the bar code, in which case each separate part of the checking portion could represent the total number of wide (or narrow) bars contained in the information portion of the bar code located immediately prior to that checking portion. Fig. 13 shows a bar code that contains three print control information portions P1-P3 and three checking portions C1-C3 interspersed with the print control information portions PI¬ PS. Each checking portion can contain a bar code pattern that is the binary representation of the total number of wide bars in its corresponding print ribbon information portion. For example, checking portion C1 can be the binary representation of the total number of wide bars in portion P1, etc. (The actual bars are not shown in Fig. 13 for simplicity.)

It also is possible to use other types of confirming techniques to encode the ribbon. For example, Hamming codes also can be interspersed throughout the bar code. An advantage with Hamming codes is that they enable the controller to confirm whether the bar code was read correctly and also enable the controller to determine which bar was incorrectly read so that the correct information can be received without attempting to read the bar code a second time. For more information on Hamming codes see, for example, "Data Communications: A User's Guide," 2nd edition, Ken Sherman, pages 154-156, Reston Publishing Co., Prentice Hall, Reston VA. (1985, 1981), the disclosure of which is incorporated herein by reference.

Fig. 14 is a flow chart similar to Fig. 10, with modifications to illustrate the process for checking whether the first portion of the bar code was read properly. After the bar code pattern is read in step S1, the printing system controller (i.e., controller 600) determines whether the bar code pattern containing the instructions for print control (i.e., the first bar code pattern portion) was read correctly (step S10) using the checking portion of the bar code pattern (i.e., the second bar code pattern portion). When the bar code is read correctly, flow proceeds to steps S2-S4 as described with respect to Fig. 10. When the bar code is not read correctly, "flo proceeds to step S12 where a determination is made as to whether the mis-read bar code reading can be corrected. When the reading can be corrected (for example, using techniques that are known to those familiar with Hamming codes), flow proceeds to step S14 in which the correct code reading is registered. Flow then continues through steps S2-S4. When the reading cannot be corrected, flow proceeds to step S16 where default values are set for the printing control settings. Alternatively, if the printing system has auto rewind capability, the print ribbon can be rewound and another attempt can be made at reading the bar code. As another alternative, when the bar code pattern repeats multiple times throughout the print ribbon (as detailed hereafter), the print ribbon could be fed further so that another repetition of the bar code pattern passes by and is read by the bar code reader.

Fig. 15 illustrates a print ribbon encoded according to another aspect of the invention. The ribbon of Fig. 15, like the previous print ribbons, encodes numerical values that can be used by the printing system controller to derive control settings, preferably without reference to look¬ up tables. Unlike the previous print ribbon, the light bars do not represent data. They merely are spaces provided between each dark data bar. Thus, the Fig. 15 bar code requires more space to encode data than the previously described bar codes. The data bars have one of four possible widths: X, 2X, 3X and 4X. The first bar SB is a start bar that indicates the start of the bar code. The start bar SB has a width of 3X. The second bar MB is a multi-pass bar. When this bar has a width of X, it indicates that the print ribbon is a single-pass ribbon. When the multi-pass bar MB has a width of 4X, it indicates that the print ribbon is a multi-pass ribbon. The remaining bars, labeled B1-B25 provide information regarding seven parameters (labeled P1-P7) that can be used to control the printing process

for the installed print ribbon. The bars B26-B30 constitute a checking portion CP of the bar code and is the binary representation of the total number of wide bars in the first portion of the bar code (bars B1 -B25).

Unlike the previous print ribbons, the bar code repeats multiple times on the Fig. 15 print ribbon throughout the portion of the print ribbon that is coded with the transferable ink. Each repetition of the bar code pattern abuts an adjacent repetition. Because the bar code repeats throughout the length of the print ribbon, it is not necessary for the leader portion to be located adjacent to the reading device 300 when the ribbon is installed. Instead, a partially used print ribbon can be inserted into the copier and the bar code can be read immediately. Since the ribbon moves by an amount approximately equal to the length of the sweep by printhead 65 across the copy sheet during a single sweep (i.e., 8 inches) the bar code should have a length no less than about 95% of the sweep so that the bar code reader will be guaranteed to read the entire bar code in one sweep of the scanner 40. The software for reading the bar code can arrange the data read from the bars in the correct order even if reading begins midway throughway the bar code by using the start bars SB as a reference point. Additionally, when multi-pass ribbons are used, the software can correctly arrange the read data regardless of the direction in which the print ribbon is moving by determining whether the multi-pass bar MB was read immediately before the start bar SB or vice versa.

While this invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. For example, when the code is repeated throughout the ribbon, it will be evident that a code pattern in which both dark bars and light bars contain data also can be used. Accordingly, the preferred embodiments of the invention as set forth herein are intended to be illustrative, not limiting. Various changes may be made without departing from the spirit and scope of the invention as defined in the following claims.