Color panel identification and synchronization in a thermal printer

Abstract: The invention pertains to a device capable of recognizing any color dye frame from a color ribbon for use in a thermal printer. The device comprises an LED (light emitting diode) (10) capable of producing a white light, positioned so that the ribbon (44) passes between the LED (10) and a photo-transistor (22). The device is adapted to collect the light generated by the LED (10) as it passes through the color dye frame (12,14,16,18,20) and generate a specific exit voltage associated with the color of the dye frame. An analog to digital converter transforms the voltage into a digital value and a micro-computer (28) processes the digital value and compares the digital value to a stored set of values associated with each color dye frame.

Description: The invention pertains to a color sensor system to identify and synchronize the color panels of an ink ribbon loaded in a thermal printer. The color sensor system can detect any specific color panel and synchronize the first color frame to be printed while wasting as few ribbon frames as possible. More particularly it pertains to a novel panel identification solution for a quicker and more cost effective technology. BRIEF DESCRIPTION OF RELATED ART In the field of printer technology, a number of different methods have been developed for applying ink to paper, plastic cards or other print media in a controlled manner. One of the most common methods is through the use of ink ribbons. A flexible ribbon-shaped substrate is impregnated or coated with an ink that adheres to paper or a plastic card. The act of printing depletes the print substance so that the substrate must periodically be replaced. The use of replaceable ribbons, supply spools, and take-up spools is therefore common in many different types of printers. In one type of thermal printer which prints colored images, a carrier contains a repeating series of spaced frames of different colored heat transferable dyes. In such an apparatus, the carrier is disposed between a receiver, such as coated paper, and a print head formed of, for example, a plurality of individual heating elements. When a particular heating element is energized, it is heated and causes dye from the carrier to transfer to the receiver. The density or darkness of the printed color dye is a function of the energy delivered from the heating element to the carrier. Thermal dye transfer printers offer the advantage of true "continuous tone" dye density transfer. This result is obtained by varying the energy applied to each heating element, yielding a variable dye density image pixel on the receiver. The carrier often includes a repeating series of spaced yellow, magenta, and cyan dye frames. The carrier may also include a varnish frame to protect the color from UV rays and protect against abrasion and a black frame. First, the yellow frame and the receiver are moved until they are positioned under the print head and as they are advanced, the heating elements are selectively energized to form a row of yellow image pixels on the receiver. This process is repeated until a yellow dye image is formed in the receiver. Next, the magenta frame is moved under the print head and the receiver is also moved under the print head. Both the receiver and the magenta frame are moved as the heating elements are selectively energized and a magenta image is formed superimposed upon the yellow image. Finally, as the cyan dye frame and the receiver are moved under the print head, the heating elements are selectively energized and a cyan dye image is formed in the receiver superimposed upon the yellow and magenta dye images. These yellow, magenta and cyan dye images combine to form a colored image. Since the carrier has a repeating series of yellow, magenta and cyan dye frames, it is important to identify the leading yellow frame of each series (See Figure 2). One way to identify the leading yellow frame is to employ a conventional sensitometer. The sensitometer identifies a yellow dye frame by producing a particular analog signal in response to light passing through the yellow dye frame. A sensitometer is effective but can be a complex and expensive to implement in a printer. Another way to identify a yellow dye frame is by a code field. A code field is composed of a series of spaced black bars disposed in a clear interframe area between each dye frame. This code field can identify the particular color of the following frame. A reader station can be provided which includes a plurality of photodetectors which are aligned to produce a particular output signal representing the color of the following dye frame. Such a system can perform quite satisfactorily but requires decoding electronics and involves additional manufacturing steps for forming each code field in the clear interframe areas of the carrier. A third way to identify the color of each dye frame is by using a red light source that provides two logical levels representing only two "colors" which are: transparent (for yellow, magenta, varnish, etc) and dark (for cyan, black, etc). This solution often requires a wheel with holes and an optical sensor to calculate the distance to move the film to align the yellow frame with the print head. A fourth way to identify the color of each dye frame is by using both a yellow and a red light source transmitted through each dye frame. The problem with this method is that the method fails to detect a difference between the yellow dye frame and the varnish dye frame and also fails to detect a difference between the cyan dye frame and the black dye frame. The logical levels of this method are as follows: Frame Yellow Light Logical Level Red Light Logical Level Yellow Transmits 1 Transmits 1 Varnish Transmits 1 Transmits 1 Magenta Blocked 0 Transmits 1 Cyan Blocked 0 Blocked 0 Black Blocked 0 Blocked 0 JP-A-60154093 discloses a similar device but which makes use of a red and a green light source. A fifth way to identify the color of each dye frame is by using a black bar mark located at the beginning of the yellow dye frame. This solution needs an infra-red sensor to detect the black bar mark, a wheel with holes and an optical sensor to calculate the distance to the film must move to synchronize the other dye frames with the print head. This solution represents an expensive technology. What is needed is a cost effective technology that is capable of detecting the actual color of each dye frame without the use of a code system on the ribbon itself or between a clear interframe area between each dye frame. SUMMARY OF THE INVENTION The invention pertains to a device capable of recognizing any color dye frame from a color ribbon for use in a thermal printer. The device comprises an LED (light emitting diode) capable of producing a white light, positioned so that the ribbon passes between the LED and a photo-transistor. The device is adapted to collect the light generated by the LED as it passes through the color dye frame and generate a specific exit voltage associated with the color of the dye frame. An analog to digital converter transforms the voltage into a digital value and a micro-computer processes the digital value and compares the digital value to a stored set of values associated with each color dye frame. Because ribbon having color dye frames is always organized according to a specific sequence, i.e. yellow, magenta, cyan, black, the ribbon can be automatically driven and synchronized so that once the first yellow dye frame is aligned with the print head, all subsequent dye frames will also be aligned with the print head. The foregoing and additional features and advantages of the present invention will become apparent by way of non-limitative examples shown in accompanying drawings and the detailed description that follows. In the figures and written description, numerals indicate the various features of the invention, like numerals referring to like features throughout both the drawings and the written description. BRIEF DESCRIPTION OF THE DRAWINGS The invention is shown by way of example in the accompanying drawings in which: Figure 1 is a perspective view of the preferred embodiment of the LED, phototransistor and the ribbon having color dye frames; Figure 2 is a graph of the spectral-phototransistor responsivity; and Figure 3 is a schematic of a thermal printing system. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The invention pertains to the recognition of any color dye frame from a color ribbon to use in a thermal printer. The device comprises an LED (light emitting diode) 10 capable of producing a white light, positioned so that the ribbon passes under the LED; a photo-transistor 22 positioned under the ribbon and adapted to collected the light generated by the LED as it passes through the color dye frame, and further adapted to generate a specific exit voltage associated with the color of the dye frame; an analog to digital converter 26 to transform the voltage into the digital value; and a micro-computer 28 to process the digital value and to associate the digital value to a color dye frame. (See Figure 3). Commercially, the LED and the photo-transistor used in this invention are inexpensive and have a long life span. Moreover, another advantage of the present invention is that the ribbon type can be identified as a panel sequence as the ribbon passes through the system. The sequence of color dye frames are repeated along the ribbon. Each sequence contains the following color dye frames: yellow 12, magenta 14, cyan 16, black 18, and varnish 20. Perpendicular to the ribbon's surface 22 is an LED 10, capable of producing white light, that may be based of InGaN (Indium Gallium Nitride). (See Figure 1). The light from the LED 10 crosses a colored dye frame on the ribbon and produces a light having a wave length corresponding to the color of the panel. This light is then detected by a photo-transistor 22. The maximum light intensity of the LED 10 is 420mCd. The diffusion angle depends on the distance between the LED 10 and the receptor of the photo-transistor 22. In the preferred embodiment, the diffusion angle is a minimum of 35 degrees. In the preferred embodiment, the photo-transistor 22 has an acceptance angle of 50 degrees minimum and a light linear sensitivity for wave lengths of 300nm to 900nm. (See Figure 2). A resistor 24 is located between the collector of the photo-transistor 22 and a potential of 5 Volts whereby the photo-transistor 22 produces a voltage according to the color dye frame detected. The following table represents the exit voltage of each color dye frame detected: Color of the ribbon Voltage of the phototransistor Yellow 1 Volts Magenta 2.5 Volts Cyan 3.5 Volts Black 4.5 Volts Varnish 0 Volts The detection system described above is integrated in a thermal printing system. (See Figure 3). The voltage from the photo-transistor 22 is an analog value that is converted into a digital value by an analog to digital converter 26. The analog to digital converter 26 has a variable voltage range from 0 to 5V for a range of digital values 2 8 (from 0 to 255). The relation between the digital value and the voltage can be described in the following formula: Voltage = 5Volts • digital value/(2 8 ) The present invention detects the transition between a current dye frame and a subsequent dye frame. The suite of voltages are recognized so that the micro-computer 28 knows which dye frame on the ribbon 44 is being detected and stops the rotation of the drive motor 32 . The distance between the photo-transistor 22 and the print head 36 is equivalent to the length of one dye frame (See Figure 2) so that when a transition between one dye frame and another is being detected, the beginning of the current panel is under the print head, ready to execute the printing command. When a print command is sent by the operator to the micro-computer 28 and the yellow dye frame is not under the print head, the ribbon 44 will be fed off a supply spool 40 and be driven until the photo-transistor 22 detects the transition between the yellow and magenta dye frame (from 1 V to 2.5V). When the photo-detector 22 detects the transition between the yellow and magenta dye frames, the print head 36 can begin printing yellow 12 onto the media 38. When the yellow panel 12 is finished printing the ribbon 44 is driven until the phototransistor 22 detects the transition of the magenta 14 and cyan 16 panels (from 2.5V to 3.5V) then the print head 36 begins printing magenta 14 onto the media 38. When the magenta 14 panel is finished printing the ribbon 44 is driven until the phototransistor 22 detects the transition of the cyan 16 and black 18 panels (from 3.5V to 4.5V) then the print head 36 begins printing cyan 16 onto the media 38. When the cyan 16 panel is finished printing the ribbon 44 is driven until the phototransistor 22 detects the transition of the black 18 and varnish 20 panels (from 4.5V to OV) then the print head 36 begins printing black 18 onto the media 38. When the black 18 panel is finished printing the ribbon 44 is driven until the phototransistor 22 detects the transition of the varnish 20 and yellow 12 panels (from OV to 1V) then the print head 36 begins printing varnish 20 onto the media 38. When the varnish 20 panel is finished printing the ribbon 44 is driven until the phototransistor 22 detects the transition of the yellow 12 and magenta 14 panels (from 1V to 2.5V) then the yellow 23 panel is ready for the next printing operation. A new cycle can start again when a printing command is sent to the micro-computer. During the printing the micro-computer 28 controls the roll up of the ribbon 44 by the take-up spool 34 and the drive motor 32; the energy provided for each heating element of the print head 36 to transfer the color from the dye frame on to the printing media 38; the driving of the printing media 38 with the use of drive motor 32; and the reception of the digital value coming from the analog to digital converter 26. While certain exemplary embodiments have been described in detail and shown in the accompanying drawings, it is to be understood that such embodiments are merely illustrative of and not restrictive on the broad invention, and that this invention is not to be limited to the specific arrangements and constructions shown and described, since various other modifications may occur to those with ordinary skill in the art.

Claims: A colored dye frame detection device, comprising: an LED (10) adapted to produce white light, the LED being disposed adjacent to a ribbon to illuminate a repeating sequence of colored dye frames (12, 14, 16, 18, 20) on the ribbon; and a photo-detector (22) having a collector, the photo-detector being disposed adjacent to a ribbon and opposite the LED and adapted to detect the intensity of the light from the LED after the light passes through a dye frame, the photo-detector being further adapted to provide an output voltage in proportion to the intensity of the light passing through a dye frame. The device of claim 1, further comprising: an analog to digital converter coupled to the photo-detector, the analog to digital converter being adapted to convert the output voltage of the photo-detector into a digital value to be processed by a micro-computer. The device of claim 2, the micro-computer being capable of discerning the colors yellow, magenta, cyan, black, and varnish.

Inventors: DOAN TRUNG DUNG, DOAN, TRUNG DUNG
Applicants: ZIH CORP, ZIH CORPORATION
Application year: 2001
Main classification: B41J35
IPC codes: B41J2, B41J35