Method of operating a thermal printer

Abstract

The invention relates to a method for operating a thermal printer (2), at least comprising the step: (S300) preheating a printhead (4) of the thermal printer (2) by controlling the printhead (4) with a preheating control signal (VAS), wherein at least one preheating value of the preheating control signal (VAS) has a shorter signal duration and / or a lower signal amplitude than a pressure value of a pressure control signal (DAS) for generating an imprint on a printed product (8).

Description

[0001] The invention relates to a method for operating a thermal printer. Furthermore, the invention relates to a computer program, a thermal printer, and a control unit for such a thermal printer.

[0002] A printer is a device designed to read text and / or graphics in machine-readable form and transfer them to a substrate to produce a printed product.

[0003] A substrate is understood to be a printing material that can be printed using a printing process carried out by the printer, while the final result is referred to as a printed product.

[0004] Thermal printing is a printing process that relies on the application of heat to a specific point on the substrate. Common applications include cash register printers, ticket printers, and parking ticket printers. In this case, the printer is designed as a label printer, capable of continuously printing labels from rolls or fanfolds.

[0005] For example, such a thermal printer can be designed as a ticket printer.

[0006] However, various performance parameters, such as the print speed of such a thermal printer, are temperature-dependent. The warmer the printhead of the thermal printer is, the less energy is required for printing and the faster the printing process can be carried out. Low ambient temperatures reduce the print speed because longer heating is required to generate the necessary activation energy or to reach a color change temperature at which the thermal paper changes color due to the heat.

[0007] Therefore, there is a need to show ways in which the operation of such a thermal printer can be improved even at low temperatures.

[0008] The object of the invention is solved by a method for operating a thermal printer, at least with the step: preheating a printhead of the thermal printer by controlling the printhead with a preheating control signal, wherein at least one preheating value of the preheating control signal has a shorter signal duration and / or a lower signal amplitude than a pressure value of a pressure control signal for generating an imprint on a printed product.

[0009] To preheat the printhead, heating elements within the printhead are controlled with signals that have a shorter duration and / or lower amplitude than the values ​​used to bring the heating elements up to their target printing temperature. At temperatures below the target printing temperature, no printing occurs because the color change temperature, at which the thermal paper undergoes a color change due to heat, is not reached. This allows the printhead to be preheated before the actual printing process without additional heating elements. This improves operation at low temperatures, such as printhead temperatures in the range of 10°C to 60°C, and even below 32°C, as it increases printing speed.

[0010] According to one embodiment, the preheating value of the preheating control signal is a first time duration, and the pressure value of the pressure control signal is a second time duration. Thus, the preheating value of the preheating control signal differs from the pressure value of the pressure control signal by a shorter signal duration, while both values ​​can have the same signal amplitude. In this way, the pressure value of the pressure control signal and the preheating value of the preheating control signal can be provided particularly easily by varying the switch-on duration.

[0011] However, it is also possible, as an alternative or in addition to the signal duration, to select a signal amplitude of the preheating value of the preheating control signal that is smaller than the pressure value of the pressure control signal.

[0012] According to a further embodiment, the first duration is 1 / 10 to 1 / 1000, in particular 1 / 100 to 1 / 300, and especially 1 / 30 to 1 / 50, of the second duration. For example, the first duration can be in the range of several hundred µs, while the second duration is in the range of a few µs. This ensures that there is no unintentional printing on the substrate during preheating.

[0013] According to another embodiment, the printed product is a linerless printed product. The linerless printed product is created by printing on a linerless substrate. A linerless substrate is understood to be a carrier-free, continuous substrate wound onto a roll, which can be printed on one side using a thermal printing process. Such a linerless substrate has an adhesive coating on its reverse side, while a release layer is provided on its front side. When wound onto a roll, this release layer comes into contact with the adhesive coating on the reverse side, preventing unwanted sticking of the wound-up linerless substrate. With linerless substrates, the tendency for streaking is further increased when the thermal printer's printhead is cold, as silicone from the linerless substrate partially detaches and accumulates on the printhead.The buildup of silicone can prevent printing in those areas. This results in unwanted streaks appearing in the print direction. Preheating can counteract this streaking on the printed product, which would otherwise occur when operating a thermal printer within a temperature range of 10°C to 60°C, or at lower temperatures, such as when the printhead temperature is below 32°C. This improves the print quality.

[0014] According to another embodiment, the method includes the following further steps: Reading a temperature value indicative of a temperature, comparing the temperature value with at least one lower reference value, and performing the step of preheating a printhead of the thermal printer if the temperature value is less than the lower reference value.

[0015] In other words, preheating only occurs if a measured temperature, for example at the printhead, is lower than the lower reference value. The lower reference value can be within a temperature range of 10°C to 60°C. For example, it could be 32°C. This avoids unnecessary heating when the thermal printer is in a warm environment. This saves energy and allows for faster startup of the thermal printer, as a preheating phase can be skipped.

[0016] According to a further embodiment, a signal sequence is used in the preheating step of a thermal printer's printhead, wherein the signal sequence contains at least the preheating control signal and is at least a binary signal sequence with at least one logic one level and one logic zero level. During operation, in the present embodiment, the heating elements of the thermal strip are controlled by the signal sequence using a shift register during a first sub-step of the preheating mode. A first heating element of the thermal strip is preheated due to the logic one signal level, while, for example, the second, third, and fourth heating elements are not preheated due to the logic zero signal level. For example, a fifth heating element of the thermal strip is preheated due to the logic one signal level, while, for example, the sixth, seventh, and eighth heating elements are not preheated due to the logic zero signal level.In a further step, a cyclic bit shift (also called bit rotation) of one bit is performed. For example, the last bit of the signal sequence is shifted to the beginning of the sequence, and the heating elements of the thermal strip are controlled with the now modified signal sequence. Consequently, the second heating element of the thermal strip is preheated due to the signal level being logic one, while the first, third, and fourth heating elements are not preheated due to the signal level being logic zero. Similarly, the sixth heating element of the thermal strip is preheated due to the signal level being logic one, while the fifth, seventh, and eighth heating elements are not preheated due to the signal level being logic zero. In a further step during the preheating mode, another cyclic bit shift of one bit is performed, and so on, so that immediately adjacent heating elements are preheated sequentially, with a time offset.During the first step, the first heating element is preheated, while the second heating element, being directly adjacent to the first, is not. In the second step, the second heating element is preheated, while the first and third heating elements, being even closer to the second, are not, and so on. This allows the heating elements of the thermal strip to cool down in between. This ensures that the heating elements do not overheat and reach an unintentionally high temperature, above which an unwanted color change could occur.

[0017] Furthermore, the invention includes a computer program product, a thermal printer and a control unit for such a thermal printer.

[0018] The invention will now be explained using the figures. They show: Figure 1 shows a schematic representation of the components of a thermal printer. Figure 2 shows a schematic representation of a signal sequence for operating the device. Figure 1 shown thermal printer. Figure 3 schematically illustrates a procedure for operating the printer shown in the Figure 1 thermal printer shown.

[0019] It will initially be on Figure 1 Reference made to.

[0020] The image shows components of a thermal printer 2.

[0021] The components are a printhead 4, a drive roller 6, a control unit 10 and a temperature sensor 14.

[0022] The printhead 4 can print on a substrate 20 using thermal printing to produce a printed product 8. In the present embodiment, the printhead 4 has a thermal strip 12 with a plurality of heating elements 16, each with a heating resistor, arranged in a row.

[0023] The drive roller 6 serves to convey the printed product 8 to an outlet 18 of the thermal printer 2.

[0024] In the present embodiment, the printed product 8 is a linerless printed product, which is provided by printing on linerless substrate.

[0025] The substrate 20, in the present embodiment a linerless substrate, is provided on its back side with an adhesive coating 24, while on its front side a separating layer 22 is provided, which, when wound up, e.g. to a roll, comes into contact with the back side with the adhesive coating 24 and prevents unwanted sticking of the linerless substrate wound up to the roll.

[0026] In the present embodiment, the control unit 10 is designed to read a temperature value W, e.g. a temperature of the printhead 4 of the thermal printer 2.

[0027] The temperature value W is detected by the temperature sensor 14, which in the present embodiment is thermally connected to the print head 4.

[0028] The control unit 10 is further configured to compare the temperature value W with a lower reference value UR and an upper reference value OR. The lower reference value UR can, for example, lie in a temperature range of 10°C to 60°C, while the upper reference value OR can, for example, lie in a temperature range of 12°C to 65°C. However, both the lower reference value UR and the upper reference value OR can also lie in a different temperature range in which an optimal operating temperature of the printhead 4 is found. In the present embodiment, for example, the lower reference value UR is 32°C and the upper reference value OR is 35°C.

[0029] If the temperature value W in the present embodiment is, for example, greater than the upper reference value OR, the control unit 10 operates the thermal printer 2 in a printing mode to print on the substrate 20 in order to provide the printed product 8.

[0030] In the present embodiment, the printhead 4 is controlled by the control unit 10 with a print control signal DAS, which has a print value that activates the heating elements 16 of the thermal printhead 12, causing them to heat up. Control with this print value ensures that a color change temperature is reached, so that in print mode the substrate 20 is printed to produce the printed product 8. Simultaneously, the control unit 10 controls a motor 26 of the drive roller 6 to convey the printed product 8 towards the output 18.

[0031] If, in the present embodiment, the temperature value W is smaller than the lower reference value UR, the control unit 10 operates the thermal printer 2 in a preheating mode to preheat the printhead 4.

[0032] In the present embodiment, the printhead 4 is controlled by the control unit 10 with a preheating control signal VAS, which has a preheating value that activates the heating elements 16 of the thermal printhead 12, causing them to heat up. However, the ink changeover temperature is not reached during the preheating mode; that is, the substrate 20 is not printed and no printed product 8 is produced during the preheating mode. Furthermore, the control unit 10 does not control the motor 26 of the drive roller 6 during the preheating mode. Thus, the printed product 8 is not conveyed towards the output 18 during the preheating mode.

[0033] In the present embodiment, the preheating value of the preheating control signal VAS has a first duration T1 that is shorter than the second duration T2 of a pressure value of a pressure control signal DAS. The first duration T1 can be 1 / 10 to 1 / 1000, in particular 1 / 100 to 1 / 300, and especially 1 / 30 to 1 / 50, of the second duration T2. ​​In the present embodiment, the first duration T1 is 5 µs, while the second duration T2 is 200 µs. However, in the present embodiment, the respective signal amplitudes of the pressure control signal DAS and the preheating control signal VAS are the same.

[0034] As soon as the temperature value W reaches the upper reference value OR, the preheating mode is ended and the system switches to printing mode.

[0035] It will now also be applied to Figure 2 Reference made to.

[0036] Shown is a predetermined signal sequence SF, which is used to preheat the printhead 4 during the preheating mode.

[0037] In this embodiment, the signal sequence SF has a predetermined length, e.g., one or more bytes.

[0038] In the present embodiment, the signal sequence SF is a binary signal sequence with the two signal levels logic one and logic zero. In contrast to the present embodiment, the signal sequence SF can also be multi-level, i.e., have more than two signal levels, e.g., three or four signal levels.

[0039] In the present embodiment, the signal sequence SF has the following pattern: A logic one signal level is followed by three logic zero signal levels. In contrast to the present embodiment, the number of logic zero signal levels can also be different, e.g., one, 10, 100, or 1000. Furthermore, the number of logic zero signal levels itself can vary according to a predetermined pattern. For example, a logic one signal level can be followed by 100 logic zero signal levels, followed by a logic one signal level, followed by 1000 logic zero signal levels, followed by a logic one signal level, followed by 1000 logic zero signal levels, and so on.

[0040] In the first step of operation, during the preheating mode in this embodiment, the heating elements 16 of the thermal strip 12 are controlled by a shift register using the signal sequence SF. A first heating element 16 of the thermal strip 12 is preheated due to a logic level of one, while the second, third, and fourth heating elements 16, with a logic level of zero, are not preheated. A fifth heating element 16 of the thermal strip 12 is preheated due to a logic level of one, while the sixth, seventh, and eighth heating elements 16 are not preheated due to a logic level of zero.

[0041] In a further step during the preheating mode, a cyclic bit shift (also bit rotation) by one bit takes place in the present embodiment: In the present embodiment, the shift is to the left, i.e., the last bit of the signal sequence SF is shifted to the beginning of the signal sequence SF.

[0042] In contrast to the present embodiment, a bit shift of several bits, e.g., two, three, or five, can also be performed. Furthermore, in contrast to the present embodiment, a rightward bit shift can be performed, i.e., the first bit of the signal sequence SF is shifted to the end of the signal sequence SF.

[0043] Consequently, the second heating element 16 of the thermal strip 12 is preheated due to the signal level of logic one, while the first, third, and fourth heating elements are not preheated due to the signal level of logic zero. Similarly, the sixth heating element 16 of the thermal strip 12 is preheated due to the signal level of logic one, while the fifth, seventh, and eighth heating elements 16 are not preheated due to the signal level of logic zero.

[0044] In a further step during the preheating mode, in the present embodiment, another cyclic bit shift of one bit, etc., takes place, so that immediately adjacent heating elements 16 are preheated successively with a time offset. Thus, during the first step, the first heating element is preheated, while the second heating element 16, as an immediate neighbor to the first heating element 16, is not. In the second step, the second heating element is then preheated, while the first and the third heating elements 16, as immediate neighbors to the second heating element 16, are not, and so on.

[0045] This allows the heating elements 16 of the thermal strip 12 to cool down temporarily. This ensures that the heating elements 16 do not overheat and reach a temperature at which an unwanted color change occurs.

[0046] In the present embodiment, each phase of the signal sequence SF with a logic level of one is a preheating control signal VAS. In other words, in the present embodiment, the phase of the signal sequence SF with a logic level of one has the first duration T1 of 5 µs.

[0047] In the present embodiment, the phases of the signal sequence SF with the signal levels logic one and logic zero are of equal length. Thus, in this embodiment, the heating elements 16 each have 15 µs to cool down. In contrast to the present embodiment, the phases of the signal sequence SF with the signal levels logic one and logic zero can also be of different lengths.

[0048] It will now be further elaborated with reference to the Figure 3 A procedure for operating the thermal printer 2 is explained.

[0049] In a first step S100, the temperature value W measured by the temperature sensor 14 is read by the control unit 10.

[0050] In a further step S200, the control unit 10 compares the temperature value W with the lower reference value UR and the upper reference value OR.

[0051] If the temperature value W is less than the lower reference value UR, the control unit 10 then, in a further step S300, activates the thermal printer 2 in preheating mode.

[0052] In the present embodiment, the printhead 4 of the thermal printer 2 is controlled by the preheating control signal VAS with the preheating value which has the first time duration T1 of 5 µs.

[0053] In the present embodiment, during a first step of the preheating mode, the heating elements 16 of the thermal strip 12 are controlled by a shift register using the signal sequence SF. A first heating element 16 of the thermal strip 12 is preheated due to a logic level of one, while the second, third, and fourth heating elements 16 are not preheated due to a logic level of zero. A fifth heating element 16 of the thermal strip 12 is preheated due to a logic level of one, while the sixth, seventh, and eighth heating elements 16 are not preheated due to a logic level of zero.

[0054] In a further step, during the preheating mode, a cyclic bit shift (also bit rotation) by one bit takes place, i.e., the last bit of the signal sequence SF is shifted to the beginning of the signal sequence SF.

[0055] Consequently, the second heating element 16 of the thermal strip 12 is preheated due to the signal level of logic one, while the first, third, and fourth heating elements 16 are not preheated due to the signal level of logic zero. Similarly, the sixth heating element 16 of the thermal strip 12 is preheated due to the signal level of logic one, while the fifth, seventh, and eighth heating elements 16 are not preheated due to the signal level of logic zero.

[0056] In a further step of the present embodiment, during the preheating mode, another cyclic bit shift of one bit, etc., takes place, so that immediately adjacent heating elements 16 are preheated successively with a time offset. Thus, during the first step, the first heating element is preheated, while the second heating element 16, as an immediate neighbor to the first heating element 16, is not. In the second step, the second heating element is then preheated, while the first and third heating elements 16, as more immediate neighbors to the second heating element 16, are not, and so on.

[0057] If, however, the temperature value W is greater than the upper reference value OR, the control unit 10 then, in a further step S400, activates the thermal printer 2 in print mode.

[0058] In the present embodiment, the printhead 4 of the thermal printer 2 is controlled with the pressure control signal DAS with the pressure value, wherein in the present embodiment the pressure value has the second time duration T2 of 200 µs.

[0059] In contrast to the present embodiment, the sequence of steps can also be different. Furthermore, several steps can be executed simultaneously. Additionally, in contrast to the present embodiment, individual steps can be skipped or omitted.

[0060] This allows the printhead 4 to be preheated before an actual printing process without additional heating elements, which improves operation at low temperatures, e.g. in a range of 10°C to 60°C, such as below 32°C, as this increases the printing speed.

[0061] Furthermore, preheating can counteract streaking on the linerless print product, which would otherwise occur when operating the thermal printer 2 at low temperatures, e.g., in a range of 10°C to 60°C, such as at temperatures below 32°C. This can improve the print quality. Reference symbol list

[0062] 2 Thermal printer 4 Printhead 6 Drive roller 8 Printed product 10 Control unit 12 Thermal strip 14 Temperature sensor 16 Heating element 18 Outlet 20 Substrate 22 Separation layer 24 Adhesive coating 26 Motor DAS Pressure control signal OR Upper reference value RR Reference value SF Signal sequence UR Lower reference value VAS Preheating control signal WT Temperature value S100 step S200 step S300 step S400 step

Claims

1. Method for operating a thermal printer (2), at least comprising the step: (S300) Preheating a printhead (4) of the thermal printer (2) by controlling the printhead (4) with a preheating control signal (VAS), wherein at least one preheating value of the preheating control signal (VAS) has a shorter signal duration and / or a lower signal amplitude than a print value of a print control signal (DAS) for generating an imprint on a printed product (8).

2. Method according to claim 1, wherein the preheat value of the preheat control signal (VAS) is a first time period (T1) and the pressure value of the pressure control signal (DAS) is a second time period (T2).

3. Method according to claim 2, wherein the first time period (T1) is 1 / 10 to 1 / 1000, in particular 1 / 100 to 1 / 300, in particular 1 / 30 to 1 / 50, of the second time period (T2).

4. Method according to any one of claims 1 to 3, wherein the printed product (8) is a linerless printed product.

5. Method according to any one of claims 1 to 4, comprising the further steps of: (S100) reading a temperature value (W) indicative of a temperature, and (S200) comparing the temperature value (W) with at least one lower reference value (UR) and performing step (S300) preheating the printhead (4) of the thermal printer (2) if the temperature value (W) is less than the lower reference value (UR).

6. Method according to one of claims 1 to 5, wherein in step (S300) preheating a printhead (4) of the thermal printer (2) a signal sequence (SF) is used, wherein the signal sequence (SF) contains at least the preheating control signal (VAS), wherein the signal sequence (SF) is at least a binary signal sequence with at least one logic one level and one logic zero level.

7. Computer program product configured to execute a method according to any one of claims 1 to 6.

8. Thermal printer (2) with at least one printhead (4), wherein the printhead (4) can be controlled by a preheating control signal (VAS) and by a print control signal (DAS), wherein at least one preheating value of the preheating control signal (VAS) has a shorter signal duration and / or a lower signal amplitude than a print value of the print control signal (DAS) for producing an imprint on a printed product (8).

9. Thermal printer (2) according to claim 8, wherein the preheat value of the preheat control signal (VAS) is a first time period (T1) and the pressure value of the pressure control signal (DAS) is a second time period (T2).

10. Thermal printer (2) according to claim 9, wherein the first time period (T1) is 1 / 10 to 1 / 1000, in particular 1 / 100 to 1 / 300, in particular 1 / 30 to 1 / 50, of the second time period (T2).

11. Thermal printer (2) according to one of claims 8 to 10, wherein the printed product (8) is a linerless printed product.

12. Thermal printer (2) according to one of claims 8 to 11, with a control unit (10), wherein the control unit (10) is configured to read a temperature value (W) indicative of a temperature, to compare the temperature value (W) with at least one lower reference value (UR) and to perform preheating of the printhead (4) of the thermal printer (2) when the temperature value (W) is less than the lower reference value (UR).

13. Thermal printer (2) according to one of claims 8 to 12, with a control unit (10), wherein the control unit (10) is configured to provide a signal sequence (SF), wherein the signal sequence (SF) contains at least the preheating control signal (VAS), wherein the signal sequence (SF) is at least a binary signal sequence with at least one logic one level and one logic zero level.

14. Control unit (10) for a thermal printer (2) according to one of claims 8 to 13.

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