DE102009053093A1 - Method for determining color of color section of multi-color band for thermal transfer printer utilized for printing smart card, involves outputting signal that depicts determined color of illuminated section of multi-color band - Google Patents

Abstract

The method involves generating a light sequence that has two different wavelength ranges, and illuminating a multi-color band with the light sequence. A light portion of the light sequence reflected by or passing through the band is received by a light-sensitive sensor element. A bit pattern is generated from two output signals of the sensor element, where two bits in the bit pattern are assigned to the respective wavelength ranges. Color of the illuminated section of the band is determined, where the section corresponds to the bit pattern. A signal depicting the determined color is output. The sensor element is formed as photodiode and phototransistor. An independent claim is also included for a thermal transfer printer comprising LEDs and a device for determining color of a color section.

Description

background

A method and apparatus for determining a color will be described. In particular, a method and apparatus for determining the color of a color portion of a multi-color ribbon for, for example, a thermal transfer printer is described.

For example, to print color images with a thermal transfer printer, a so-called four-color printing method is used. In these methods, one of the four basic colors is added to the image in several printing steps. By superimposing the four primary colors any color images can be printed. For example, in the CMYK color model used, these four primary colors are cyan, magenta, yellow, and black. In some applications, a transparent coating layer is additionally used to protect the printed surface from environmental influences or to obtain a glossy surface.

In order for the thermal transfer printer to process the base colors, the colors are provided in the form of a multi-color ribbon. The multi-color ribbon has a substrate carrying a plurality of color portions arranged one behind the other. The size of the individual color sections corresponds to the size of the object to be printed. Depending on the length of the multi-color ribbon, the color pattern of the primary colors is repeated several times.

In order to match the individual printing steps, it is necessary to precisely align the color sections of the multi-color ribbon relative to the object to be printed. For this purpose, the controller of the thermal transfer printer must accurately capture the transitions between the individual color sections. In addition, the controller of the thermal transfer printer must detect the color of the current color section.

The positioning takes place in available arrangements by a simple light barrier with a processor with a relatively complicated software algorithm for synchronization of the transfer band over one or more black segments and comparison with entries in a configuration table. Due to the different diameter of the ribbon winding roll at runtime, however, there is no linear relationship between the segment position and necessary steps of the ribbon motor. Moreover, in the prior art regarding the color segment length, their order on the film and the additional existing number and location of the black and Farblossegmente further variable to be considered to process, which ultimately leads to a relatively inaccurate positioning, time losses and additional tape consumption by the synchronization to lead.

As far as for detecting these data color sensors were used, these consist of at least three photodiodes. Each of the photodiodes is sensitive to a different wavelength range. For example, a first photodiode receives red light, a second photodiode receives green light, and a third photodiode receives blue light. Depending on the intensity of the respective wavelength ranges, the resistance of the individual photodiodes changes. To evaluate the three resistance values and to assign the colors, complex electronics are required. Although the color sensors can recognize a variety of colors, but are expensive due to the required evaluation.

problem

It is therefore the task to reliably detect the color transitions and / or the colors of the color sections of the multicolor tape with little effort.

Suggested solution

A method is proposed with which a color of a color section can be determined, wherein the color section is part of a multi-color ribbon, for example for a thermal transfer printer. According to the method, a light sequence is generated which has at least two different wavelength ranges. The multicolor band is illuminated with the light sequence, wherein the multicolor band is illuminated first with a first wavelength range and then with a second wavelength range. A photosensitive sensor element is provided to receive a light portion of the light sequence reflected or transmitted by the color portion, the sensitivity of the photosensitive sensor element being selected to include at least the first and second wavelength ranges. From at least two output signals of the photosensitive sensor element, a bit pattern is generated, wherein a first bit is assigned to one of the two wavelength ranges and a second bit to a second of the two wavelength ranges of the light sequence. From the generated bit pattern, a color of the illuminated color portion is detected, and a signal representing the detected color is output.

Embodiments and properties

Thus, only a simple photosensitive sensor element is needed to determine whether a portion of light of a wavelength range is reflected or transmitted by the color portion. The photosensitive sensor element can have a broadband sensitivity. That is, the sensor element can receive the entire wavelength range that is reflected or transmitted and change its output state accordingly. The sensor element does not have to be especially sensitive to the respective color. Thus, the spectral sensitivity of the photosensitive sensor element may include the entire wavelength range of visible light. The initial state of the photosensitive sensor element may thus be substantially independent of the wavelength of the received light. The signal applied to the output terminal of the photosensitive sensor element may be, for example, a voltage level, current or charge.

For generating the bit pattern, a controller may be used which converts the at least two signals, which are successively output at the output terminal of the photosensitive sensing element, into a bit pattern, which signals may correspond to a logical '0' or a logical '1'.

The number of bits of the generated bit pattern may correspond to the number of different wavelength ranges with which the multi-color band is successively illuminated.

When determining the color, the generated bit pattern can be compared with predetermined bit patterns, wherein each of the predetermined bit pattern is assigned a color of the multi-color band.

For generating the light sequence, a clock signal tuned to a clock signal used in generating the bit pattern may be used.

Furthermore, a light sequence with three different wavelength ranges can be used, wherein a first wavelength range of the color corresponds to yellow, a second wavelength range corresponds to the color cyan and a third wavelength range corresponds to the color blue.

A device is also proposed with which a color of a color segment can be determined, wherein the color segment is for example part of a multi-color ribbon for a thermal transfer printer. The device has a light source which is suitable for illuminating the multicolor band with a light sequence, wherein the light sequence has at least two different wavelength ranges. In addition, the device has a photosensitive sensor element which is suitable for receiving a light component reflected or transmitted by the multicolor band, and wherein the sensitivity of the photosensitive sensor element is selected such that it comprises at least the first and second wavelength ranges. Furthermore, the device has a controller, wherein at least one output terminal of the controller is connected to the light source and at least one input terminal of the controller is connected to the photosensitive sensor element. The controller is adapted to drive the light source, to convert at least two successive output signals of the photosensitive sensor element into a bit pattern, to determine a color of an illuminated color section associated with the bit pattern, and to output a signal representing the detected color.

The controller may be provided to specify a clock signal underlying the light sequence, which is tuned to a clock signal used in generating the bit pattern.

The light source may have one or more LEDs. The light source can also be a "RGB" tri-color LED or several single LEDs in the colors red, blue, green.

The sensor element may be a photodiode or a phototransistor.

Three output terminals of the controller may be connected to the light source, with the three output terminals being arranged to output one drive signal for the light source corresponding to a logical '1' or a logic '0'.

The controller may be provided to convert a first output signal applied to the at least one input terminal of the controller into a logic '1' or a logical '0' and a second output signal applied to the at least one input terminal of the controller into one to convert logical '1' or a logical '0'.

Further, a thermal transfer printer is proposed which comprises the device according to the invention for determining a color of a color section, wherein the printer has at least one multi-color ribbon having a plurality of color sections and the device for determining the color of the color section is arranged such that the light source illuminates the multi-color band and the photosensitive Sensor element receives the light reflected or transmitted by the multi-color band.

In this case, the multi-color tape may be mounted in the thermal transfer printer so that it is interchangeable.

The multi-color ribbon may have different colors arranged in color portions on the multi-color ribbon. In this case, the color sections can be arranged in the unwinding direction one behind the other.

The thermal transfer printer may be further configured to print smart cards.

Brief description of the drawings

Other objects, features, advantages and applications will become apparent from the following description of non-limiting embodiments to be understood and the accompanying drawings.

1 illustrates a method of determining the color of a color patch.

2 shows a block diagram of a device with which the in 1 explained method is executable.

3 shows a block diagram of a controller that is used to perform the in 1 described method is used.

Detailed description of embodiments

1 illustrates a method for determining the color of a color patch. In step S10, a light sequence is generated. This light sequence has at least two different wavelengths (ranges). In one embodiment, the light sequence has three different wavelengths (ranges). These three wavelengths (ranges) may correspond, for example, to the colors yellow, cyan and blue. Of course, it is also possible to use different wavelengths (ranges) for the light sequence. However, to facilitate understanding, only the colors yellow, cyan, and blue will be used hereinafter to refer to and differentiate between the different wavelengths (ranges).

When ordering the colors in the light sequence, it is important to remember that a certain pre-determined order will be kept, since the order of the colors is matched to the coding of the colors stored in the controller.

In step S20, the light sequence is used to illuminate a color portion of the multicolor tape. In the embodiment described here, the color portion is first illuminated with yellow light, then with cyan light and then with blue light. The three illumination intervals are the same length and do not overlap. After completion of a light sequence, the light source is turned off. The interval in which the light source is switched off corresponds in its duration to one of the illumination intervals. Thus, in the embodiment described here, the light sequence consists of a total of four equally long intervals.

In step S30, a light portion reflected from the color portion of the multi-color ribbon or shining through the color portion is received with a photosensitive sensing element. The photosensitive sensor element may be, for example, a broadband phototransistor. In this case, the term "broadband" refers to the fact that the phototransistor is suitable for receiving at least the majority of the wavelength ranges of the yellow, cyan and blue light and for changing its switching state when it receives light.

In step S40, the photosensitive sensor element outputs a voltage level. The voltage level depends only on whether the photosensitive sensor element receives light or not. When light is received because the color portion has a color that reflects or shines through the irradiated wavelength range, a voltage level corresponding to a logical '1' is output. If no light is received, because the color portion has a color that does not reflect or shine through the irradiated wavelength range, a voltage level corresponding to a logical '0' is output.

Step S80 indicates that steps S20, S30 and S40 are repeated for all colors of the light sequence. So first run for yellow light, then run for cyan light and then run for blue light.

In step S50, the voltage levels are converted to a bit pattern. This step may overlap in time with the preceding steps S20, S30 and S40. For example, it is possible that a first bit is already read, while the color portion of the multi-color tape is still illuminated with yellow light. Each bit of the bit pattern is assigned an illumination interval and thus a wavelength range.

If, for example, a yellow color segment is illuminated, a first voltage level associated with a yellow light corresponds to a logical '1' since the yellow color segment reflects or shines light components which are contained in the yellow light. The first bit is thus '1'. The same applies to the cyan light. The second bit is therefore also '1'. However, since the yellow color section neither reflects nor shines through the blue light, the third bit is '0'. Thus, the bit pattern '110' results.

In step S60, the detected bit pattern is compared with the bit patterns stored in the controller, which are assigned to a specific color. For example, the bit pattern '110' is assigned the color yellow.

In step 70, a signal representing the detected color is output. For example, when the color yellow is determined from the generated bit pattern '110', a signal is output that includes at least the information that the illuminated color portion is yellow. This signal can be output, for example, to an engine control unit. The engine control unit can then use the signal to drive a motor which rolls off or rolls up the multicolor belt.

Each illumination interval and thus each wavelength range is assigned a voltage level and thus one bit of the bit pattern. If the bit assumes the value '1', this means that the photosensitive sensor element has received a light component in the corresponding illumination interval. Furthermore, each bit pattern is assigned a specific color. Therefore, the order of the colors in the light sequence is matched to the bit patterns of the colors deposited in the controller. Interchanging the colors in the light sequence would result in the order of the detected bit pattern also being reversed and a wrong color signal being output.

Since the photosensitive sensor element distinguishes only light and dark (light / no light), the wavelength of the received light component is essentially insignificant.

2 shows a block diagram of a device 10 with the in 1 explained method is executable. The device 10 consists of a light source 12 arranged such that a multi-color ribbon passing thereto 16 is illuminated. The light source 12 creates a light sequence that consists of different colors.

For example, the light source 12 consist of an RGB LED that can emit different wavelength ranges that correspond to red, green or blue light. Alternatively, however, it is also possible to have three separate LEDs 13a . 13b . 13c provide, of which a first LED 13a blue light emitted, a second LED 13b emitted green light and a third LED 13c emitted red light. In the 2 illustrated light source 12 also has the transistors 14a . 14b . 14c and the resistors 15a . 15b . 15c . 15d . 15e . 15f on, which are intended, that of the controller 30 over the wires 62 . 64 . 66 amplify output drive signals. The LEDs 13a . 13b . 13c can thus be controlled with sufficient power. The resistors 15a - 15c should be adjustable to make a basic initial adjustment of the sensor. Thus, the different radiation powers of the LEDs and the different spectral sensitivity of the photosensitive component can be matched to each other. For this purpose, a "test" state is provided in the logic block with which each individual LED can be switched to continuous operation for adjustment. Furthermore, the module can also be used to adjust the level of the 2.5 or 3.3 V outputs of the logic board to the LED supply voltage, which must be 5 V due to the forward voltage of the blue LED. Practically, the realization of this module is possible by standard driver blocks with open-collector or open-drain output. However, it is also useful to use special, adjustable LED driver ICs and is considered disclosed. These adjustable LED driver ICs can also be set via an existing SPI or I ² C bus.

Each of the collector terminals of the transistors 14a . 14b . 14c is by one of the resistors 15a . 15b . 15c and over the line 9a with the supply voltage connection 11 connected. Each of the emitter terminals of the transistors 14a . 14b . 14c is by one of each of the three LEDs 13a . 13b . 13c and over the line 9b connected to ground potential. Each of the base terminals of the three transistors 14a . 14b . 14c is by one of the resistors 15d . 15e . 15f and one of each of the lines 62 . 64 . 66 with the controller 30 connected.

For example, lies at the base terminal of the first transistor 14a over the line 62 a logic '1', the first transistor turns on 14a by. This is the current path from the supply voltage connection 11 over the line 9a , the resistance 15a , the first transistor 14a , the first LED 13a closed to the ground connection and the first LED 13a shines.

In the embodiment described here, the control of the LEDs takes place 13a . 13b . 13c in such a way that first the second LED 13b and the third LED 13c be controlled. The green light of the second LED overlaps 13b and the red light of the third LED 13c to yellow light. Then the first LED 13a and the second LED 13b driven. The blue light of the first LED 13a and the green light of the second LED 13b overlap to cyan light. Then the first LED 13a driven, which emits blue light. The duration of the individual areas is essentially the same long. To set the duration, a from the clock signal of the controller 30 derived signal can be used.

The multicolor ribbon will be in the direction of the arrow 16f passed by the light source, so that successively all color portions of the multi-color tape can be illuminated by the light source. According to the currently lit color section 16a . 16b . 16c . 16d . 16e of multicolor ribbon 16 becomes the light of the light source 12 let through or absorbed. The multicolor ribbon 16 is arranged so that it is from the light source 12 is illuminated. According to the embodiment of the 2 , is the multicolour ribbon 16 between the light source 12 and a photosensitive sensor element 17 arranged. Alternatively, it is also possible that the light source 12 and the multi-color band 16 are arranged such that the angle of incidence of the light is greater than zero, that is, the light impinges obliquely on the multi-color band. The incident light can thereby, depending on the wavelength of the incident light and the color of the illuminated color portion of the multi-color band 16 reflected or absorbed.

The transmitted light portion is from the photosensitive sensor element 17 receive. In this case, the photosensitive sensor element 17 arranged so that it is not directly illuminated by the light source, but only indirectly by the multi-color band 16 transmitted light component. The photosensitive sensor element 17 For example, it may be a phototransistor or a photodiode. It is also possible to use another photosensitive element such as a solar cell. The decisive factor is that the element is capable of that of the light source 12 to receive emitted light and output a signal reproducing this.

At the in 2 illustrated embodiment, the photosensitive sensor element 17 from a phototransistor 18 and an amplifier circuit. The emitter terminal of the phototransistor 18 is over a line 9d connected to ground potential. The collector terminal of the phototransistor 18 is over a first resistance 20 and a line 9c with the supply voltage connection 11 connected and via a second resistor 22 with a first, inverting differential input 24a an operational amplifier 24 , The second, non-inverting differential input 24b of the operational amplifier 24 is with a voltage divider 26a . 26b connected. The voltage divider 26a . 26b is over the line 9c with the supply voltage connection 11 and over the line 9e connected to ground potential. The output terminal of the operational amplifier 24 forms the output terminal of the photosensitive sensor element 17 ,

In the unlit state is the phototransistor 18 not conductive. Because of the first resistance 20 Thus, no current flows, is essentially supply voltage potential at the first, inverting differential input 24a of the operational amplifier 24 at.

When the phototransistor 18 is illuminated, its switching state and the phototransistor changes 18 becomes conductive. This is the second resistance 22 over the phototransistor 18 connected to ground potential. Thus lies at the first, inverting differential input 24a of the operational amplifier 24 essentially ground potential.

Because the second, non-inverting differential input 26b of the operational amplifier 24 over the voltage divider 26a . 26b is maintained at a constant voltage level causes a voltage change at the inverting differential input 24a a change in the output voltage. The output terminal of the photosensitive sensor element 17 is over the line 68 with the controller 30 connected.

Receives the photosensitive sensor element 17 Light, indicates the output signal of the operational amplifier 24 the logical value '1'. Receives the photosensitive sensor element 17 no light, because the light from the multi-color band 16 is fully absorbed, the output signal has the logic value '0'.

In the controller 30 an algorithm is executed, which is the light source 12 and the at the output terminal of the photosensitive sensor element 17 applied voltage level converted into a color signal. 3 shows a block diagram illustrating a possible circuit of the controller 30 represents. Although a circuit is described here, it will be appreciated that this function can also be implemented with a μ processor equipped with a corresponding software program. Alternatively, it is also possible to use a universal circuit, for example a suitably configured FPGA.

The circuit consists of a 2-bit counter 34 , a 3-bit shift register 44 and multiple AND gates 36 . 38 . 40 . 42 . 46 . 48 . 50 . 52 . 54 , The counter 34 has a clock input on which it passes over the line 90 a in a clock generator 32 generated clock signal receives. The clock signal can be the working clock of the controller 30 or a clock signal derived therefrom. At each rising edge of the clock signal, the counter adds 34 the value '1' for the counter reading. The counter 34 is executed as a 2-bit counter. When the counter reaches the binary value '11', the counter assumes the value '00''at the next rising edge. Further, the counter points 34 two outputs on which the meter reading corresponding logical signals are output. The counter 34 can output the following four logical signals: '00', '01', '10' and '11'. The logical value '0' corresponds to a low signal and the logical value '1' to a high signal.

The outputs of the meter are over the wires 92 and 94 with the AND gates 36 . 38 . 40 and 42 connected. The AND gates 36 . 38 . 40 and 42 are with negated inputs 110 . 112 . 114 . 116 encoded such that the four logical signals of the counter 34 each one AND gate is assigned. So that's the first AND gate 36 the signal '00', the second AND gate 38 the signal '01', the third AND gate 40 the signal '10' and the fourth AND gate 42 assigned to the signal '11'.

The AND gates 36 . 38 . 40 and 42 have the outputs 36a . 38a . 40a . 42a on which a signal to drive the light source 12 is issued. In addition, each of the outputs 36a . 38a . 40a . 42a , about the inverter 70 . 71 . 72 . 73 . 74 . 75 . 76 , the wires 62 . 64 . 66 and the resistors 15d . 15e . 15f with the base terminals of the transistors 14a . 14b . 14c connected. Because the transistors 14a . 14b . 14c the LEDs 13a . 13b . 13c are thus the logical signals of the counter 34 assigned different colors.

For example, is the logical condition ('0', '0') of the first AND gate 36 fulfilled, will be at the exit 36a a high signal is output. The inverters 70 . 71 . 72 convert this high signal into a low signal. Over the lines 62 . 64 . 66 is at the base terminals of the three transistors 14a . 14b . 14c the light source 12 thus a low signal. The three transistors 14a . 14b . 14c Therefore do not go through, the three LEDs 13a . 13b . 13c are not driven and the multi-color band 16 is not lit.

Is the logical condition ('0', '1') of the second AND gate 38 fulfilled, will be at the exit 38a a high signal is output. The inverter 73 converts this high signal into a low signal. About the line 62 is at the base terminal of the first transistor 14a a low signal. Over the lines 64 . 66 is at the base terminals of the second and third transistors 14b . 14c a high signal. The second and the third transistor 14b . 14c switch on, the second and the third LED 13b . 13c are addressed and the multi-color band 16 is illuminated with yellow light.

Is the logical condition ('1', '0') of the third AND gate 40 fulfilled, will be at the exit 40a a high signal is output. The inverter 74 converts this high signal into a low signal. About the line 66 is at the base terminal of the third transistor 14c a low signal. Over the lines 62 . 64 is at the base terminals of the first and second transistors 14a . 14b a high signal. The first and the second transistor 14a . 14b switch on, the first and the second LED 13a . 13b are addressed and the multi-color band 16 is lit with cyan light.

Is the logical condition ('1', '1') of the fourth AND gate 42 fulfilled, will be at the exit 42a a high signal is output. The inverters 75 . 76 convert this high signal into a low signal. Over the lines 64 . 66 is at the base terminals of the second and third transistors 14b . 14c a low signal. About the line 62 is at the base terminal of the first transistor 14a a high signal. The first transistor 14a turns off, the first LED 13a is addressed and the multi-color band 16 is illuminated with blue light.

The shift register 44 is intended for generating the bit pattern. The shift register 44 has three inputs, of which the first input via the line 90 with the clock signal, the second input via the line 96 with the exit 42a of the fourth AND gate 42 and the third input over the line 68 to the output terminal of the photosensitive sensor element 17 connected is. It can be in the signal flow through the line 68 Also switching elements to improve the signal quality such as a Schmitt trigger be provided.

Because the counter 34 and the shift register 44 over the line 90 are connected to the same clock signal, their operation is synchronized. However, the counter will 34 with the rising edge and the register 44 with the falling edge of the clock signal 32 driven. Thus, the counter works 34 and the register 44 delayed. This can be compensated for delays resulting from a different gate transit time, the control of the light source 12 , and the photosensitive sensor element 17 result.

On the falling edge of the clock signal, this is via the line 68 adjacent output signal of the photosensitive sensor element 17 in the shift register 44 read. At the next falling edge of the clock signal, the next output of the photosensitive sensor element becomes 17 in the shift register 44 read. The successively received signals "push" the read signals further. Thus, successively, the bits b1, b2 and b3 of the shift register 44 Assigned values ('0' or '1').

In this way, three successive output signals of the photosensitive sensor element 17 compiled to a bit pattern. Because the counter 34 and the shift register 44 are synchronized, is in the shift register 44 the first bit of the bit pattern is read when the counter 34 the signal '01' and the multi-color band 16 illuminated with yellow light.

Accordingly, the second bit of the bit pattern becomes the shift register 44 read in when the counter 34 the signal '10' and the multi-color band 16 illuminated with cyan light. The third bit of the bit pattern is in the shift register 44 read in when the counter 34 the signal '11' and the multi-color band 16 illuminated with blue light.

Thus, after reading in the three bits of the bit pattern, the first bit b1 of the shift register corresponds 44 the first color, the second bit b2 of the shift register 44 the second color and the third bit b3 of the shift register 44 the third color.

When the logical condition ('1', '1') of the fourth AND gate 42 is met, so the light sequence is essentially complete, is on the line 96 a high signal indicating the shift register 44 for issuing the generated bit pattern.

The shift register 44 is over the wires 98 . 100 . 102 with the AND gates 46 . 48 . 50 . 52 . 54 connected. The AND gates 46 . 48 . 50 . 52 . 54 are through the negated inputs 118 . 120 . 122 . 124 . 126 . 128 . 130 encoded such that each AND gate is associated with a generated bit pattern. The coding of each of the AND gates 46 . 48 . 50 . 52 . 54 corresponds to one of the stored bit patterns and thus a specific color of the color section. Thus, the AND gates become 46 . 48 . 50 . 52 . 54 used that in the shift register 44 generated bit patterns with those in the controller 30 stored bit patterns to compare.

The fifth AND gate 46 has a '110' coding. Thus, the logical condition of the fifth AND gate is 46 fulfilled when the bit pattern b1, b2, b3 corresponds to the values '110'. Will this bit pattern from the shift register 44 is spent over the line 80 a high signal is output. This high signal is assigned the color yellow.

The sixth AND gate 48 has the code '100'. Returns the shift register 44 a corresponding bit pattern is sent over the line 82 outputs a high signal associated with the color magenta.

The seventh AND gate 50 has the coding '011'. Returns the shift register 44 a corresponding bit pattern is sent over the line 84 outputs a high signal associated with cyan.

The eighth AND gate 52 has the encoding '000'. Returns the shift register 44 a corresponding bit pattern is sent over the line 86 outputs a high signal associated with the color black.

The ninth AND gate 54 has the encoding '111'. Returns the shift register 44 a corresponding bit pattern is sent over the line 88 a high signal is output, which is assigned to the state colorless.

With the method described and the device described, the color of a color section of a multicolor strip can be determined in a simple manner. The use of conventional color sensors can therefore be dispensed with. For example, it can be a simple phototransistor of the type LPT 80 can be used, which has a spectral sensitivity in the range of 430 nm to 1070 nm.

In contrast to conventional color sensors, which consist of at least three photodiodes, associated amplifier circuits and a complex evaluation, the device described can be implemented with few components. Also, the device described only outputs simple signals. Thus, the processing of the output color signal is much easier.

For example, unlike conventional color sensors whose sensitivity must be adapted to changing environmental conditions, it is not necessary to adapt the device described to different types of ribbon.

Further, the detected signal need not be compared with values stored in tables to determine a color of the color section. The algorithm for determining the color of the color sections and for positioning the multi-color band can thus be significantly simplified.

Claims (10)

Method for determining a color of a color segment ( 16a . 16b . 16c . 16d . 16e ) where the color section ( 16a . 16b . 16c . 16d . 16e ) Part of a multicolour tape ( 16 ) for a thermal transfer printer, the method comprises the following steps: Generating a light sequence having at least two different wavelength ranges; - Illuminating the multicolour tape ( 16 ) with the light sequence, wherein the multicolor band ( 16 ) is illuminated first with a first wavelength range and then with a second wavelength range; Receiving one from the multi-color ribbon ( 16 ) reflected or transmitted light component of the light sequence with a photosensitive sensor element ( 17 ), wherein the sensitivity of the photosensitive sensor element ( 17 ) comprises at least the first and second wavelength ranges; Generating a bit pattern from at least two output signals of the photosensitive sensor element ( 17 ), wherein a first bit is assigned to one of the two wavelength ranges, and a second bit is assigned to a second of the two wavelength ranges of the light sequence; - determining the color of the illuminated color segment corresponding to the generated bit pattern; and - outputting a signal representing the detected color. Method according to claim 1, wherein to generate the bit pattern a controller ( 30 ) is used which the at least two output signals, which successively at the output terminal of the photosensitive sensor element ( 17 ), converted into a bit pattern, the output signals corresponding to a logical '0' or a logical '1', and / or the number of bits of the generated bit pattern corresponds to the number of different wavelength ranges with which the multicolor band ( 16 ) is illuminated successively. Method according to one of the preceding claims, wherein to determine the color, the generated bit pattern is compared with predetermined bit patterns and each of the predetermined bit patterns is compared to a color of the multicolor tape ( 16 ) assigned. Method according to one of the preceding claims, wherein a clock signal which is used for generating the light sequence, is tuned to a clock signal which is used in generating the bit pattern. Device for determining a color of a color segment ( 16a . 16b . 16c . 16d . 16e ), wherein the color section ( 16a . 16b . 16c . 16d . 16e ) Part of a multicolour tape ( 16 ) for a thermal transfer printer, the device comprising: - a light source ( 12 ), which is suitable, the multicolour tape ( 16 ) to illuminate with a light sequence, wherein the light sequence has at least two different wavelength range; A photosensitive sensor element ( 17 ), which is suitable for one of the multi-color tape ( 16 ) receive and output a signal, the sensitivity of the photosensitive sensor element comprising at least the first and second wavelength ranges; - a controller ( 30 ), wherein at least one output terminal of the controller is connected to the light source and at least one input terminal of the controller to the photosensitive sensor element ( 17 ) and the controller ( 30 ): - the light source ( 12 ), - at least two successive output signals of the photosensitive sensor element ( 17 ) to convert a bit pattern to a first one of the two wavelength ranges and a second bit to a second of the two wavelength ranges, to determine a color of the illuminated color portion associated with the bit pattern, and to output a signal representing the detected color. Apparatus according to claim 7, wherein the light source ( 12 ) one or more LEDs ( 13a . 13b . 13c ) and / or the photosensitive sensor element ( 17 ) a photodiode or a phototransistor ( 18 ) having. Device according to one of claims 5 or 6, wherein three output terminals of the controller ( 30 ) with the light source ( 12 ) and the three output terminals are provided for each drive signal for the light source 12 output that corresponds to a logical '1' or a logical '0' and / or the controller ( 30 ) is provided to convert a first output signal applied to the at least one input terminal into a logic '1' or a logical '0' and a second output signal applied to the at least one input terminal into a logic '1' or a to transform logical '0'. Thermal transfer printer comprising a device according to one of claims 5 to 7, wherein the thermal transfer printer comprises at least one multicolor belt ( 16 ) with several color sections ( 16a . 16b . 16c . 16d . 16e ) and the device for determining the color of the color segment ( 16a . 16b . 16c . 16d . 16e ) is arranged such that the light source ( 12 ) the multicolour tape ( 16 ) and the photosensitive sensor element ( 17 ) from the multicolour tape ( 16 ) receives reflected or transmitted light. A thermal transfer printer according to claim 8, wherein said multi-color ribbon ( 16 ) is mounted in the thermal transfer printer in such a way that it is exchangeable and / or the multicolour belt ( 16 ) different Has colors in the color sections ( 16a . 16b . 16c . 16d . 16e ) on the multicolour tape ( 16 ) are arranged. Thermal transfer printer according to one of claims 8 or 9, wherein the thermal transfer printer is adapted to print smart cards.

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