Thermal printer

Abstract

To provide a technology which can easily adjust an amount of energy applied to a thermal head.SOLUTION: A thermal printer 1 forms an image to a label with a thermal head 21 and includes: a concentration sensor 41 which is disposed at the upstream side relative to the thermal head 21 in a label transport direction and measures a concentration of the image printed by the thermal head 21; and a processor which adjusts an amount of energy applied to the thermal head 21 based on the measured concentration.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] Embodiments of the present invention relate to a thermal printer.

Background Art

[0002] Conventionally, a thermal printer that performs printing on a medium using a thermal head having a heating element is known. Thermal printers include those that perform printing by a direct thermal recording printing method and those that perform printing by a thermal transfer method. In the direct thermal recording printing method, printing is performed by heating a medium that changes color with heat using a thermal head. In the thermal transfer method, printing is performed by heating ink using a thermal head.

[0003] In such a thermal printer, the printing density changes depending on the type of ink or medium, the usage time of the thermal head and platen, etc. Therefore, in order to obtain a desired printing density, it is necessary to adjust the amount of energy applied to the thermal head.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The problem to be solved by the embodiments of the present invention is to provide a technique that can easily adjust the amount of energy applied to a thermal head.

Means for Solving the Problems

[0006] In one embodiment, a thermal printer that forms an image on a medium using a thermal head comprises a density sensor positioned upstream of the thermal head in the transport direction of the medium and measuring the density of the image printed by the thermal head, and a processor that adjusts the amount of energy applied to the thermal head based on the measured density. [Brief explanation of the drawing]

[0007] [Figure 1] This is a schematic perspective view showing a thermal printer used as an inline printer according to the first embodiment. [Figure 2] This is a schematic side view showing the internal configuration of a thermal printer according to the first embodiment. [Figure 3] This is a block diagram showing the configuration of the control system of a thermal printer according to the first embodiment. [Figure 4] This is a flowchart showing the operation of the concentration adjustment process according to the first embodiment. [Figure 5] This is a schematic diagram showing a label with an adjustment image printed on it according to the first embodiment. [Figure 6] This is a schematic diagram showing a label being transported upstream according to the first embodiment. [Figure 7] This figure shows the estimation table according to the first embodiment. [Figure 8] This figure shows an example of measurement results according to the first embodiment. [Figure 9] This is a schematic diagram showing the configuration of the concentration sensor in a thermal printer according to the second embodiment. [Figure 10] This is a schematic diagram showing the configuration of the concentration sensor in a thermal printer according to the third embodiment. [Modes for carrying out the invention]

[0008] Embodiments of the present invention will be described below with reference to the drawings. In each figure, identical components are denoted by the same reference numerals.

[0009] <First Embodiment> (Thermal printer configuration) The configuration of the thermal printer according to the first embodiment will now be described. Figure 1 is a schematic perspective view showing the thermal printer used as an inline printer according to this embodiment. Figure 2 is a schematic side view showing the internal configuration of the thermal printer according to this embodiment. Figure 3 is a block diagram showing the configuration of the control system of the thermal printer according to this embodiment.

[0010] As shown in Figure 1, the thermal printer 1 according to this embodiment is used as an inline printer installed in a workplace or the like. Specifically, in this embodiment, the thermal printer 1 is fixedly installed on a transport device C that transports an item O, and prints on a label L that is attached to the item O. The label L is supplied to the thermal printer 1 by another device (not shown). Similarly, the label L printed by the thermal printer 1 is attached to the item O by another device (not shown).

[0011] As shown in Figure 2, the thermal printer 1 is a thermal transfer printer that transfers ink to a label L by heat. The thermal printer 1 comprises a housing 10, a thermal head 21, a ribbon winding shaft 22, a ribbon support shaft 23, a platen roller 31, a peeling roller 32, an opposing roller 321, a capstan roller 33, an opposing roller 331, and a peeling bar 34.

[0012] Furthermore, as shown in Figure 3, the thermal printer 1 includes a ribbon winding motor 29, a sheet supply motor 39, a density sensor 41, a label sensor 42, an MPU (Micro Processor Unit) 51, a RAM (Random Access Memory) 52, a ROM (Read Only Memory) 53, and a communication I / F (Interface) 54.

[0013] The housing 10 is formed in a roughly box shape that defines an internal space for housing the above-mentioned components. The housing 10 has a label discharge port 101 and a sheet supply / discharge port 102. The label discharge port 101 is an opening formed by cutting off the front side (right side in Figure 2) located on the bottom side of the housing 10. The sheet supply / discharge port 102 is an opening formed by cutting off the rear side (left side in Figure 2) located on the bottom side of the housing 10. A sheet 30 with multiple labels L continuously attached is supplied from the sheet supply / discharge port 102. Each of the multiple labels L attached to the sheet 30 is discharged from the label discharge port 101. The sheet 30 from which the labels L have been peeled off is discharged from the sheet supply / discharge port 102.

[0014] The ribbon support shaft 23 rotatably supports the ink ribbon 20, which is a roll of ink-coated strip material. The ribbon winding shaft 22 is rotated by the ribbon winding motor 29 to wind up the ink ribbon 20 that has been unwound from the roll. The ribbon support shaft 23 and the ribbon winding shaft 22 are located at the same position relative to each other in the vertical direction. The ribbon support shaft 23 is located behind the ribbon winding shaft 22.

[0015] The thermal head 21 is located below the ribbon support shaft 23 and the ribbon winding shaft 22, and has a plurality of heating elements adjacent to each other in the width direction of the label L. The ink ribbon 20, unwound from the roll, is wound onto the ribbon winding shaft 22 via the thermal head 21. The plurality of heating elements generate heat in response to the input pulse wave, thereby allowing the thermal head 21 to transfer the ink applied to the ink ribbon to the label L and form an image. Methods for adjusting the amount of energy applied to the thermal head 21 according to this embodiment include increasing or decreasing the current value of the pulse wave and increasing or decreasing the duty cycle of the pulse wave.

[0016] The capstan roller 33 is provided on the rear side of the platen roller 31 and the peeling roller 32. The capstan roller 33 conveys the sheet 30 supplied from the sheet supply / discharge port 102 to the front side where the thermal head 21 is located. The sheet 30 conveyed by the capstan roller 33 is positioned above the capstan roller 33 so that the back surface without the plurality of labels L attached thereto contacts the capstan roller 33. The opposing roller 331 is provided so as to oppose the capstan roller 33 with the sheet 30 interposed therebetween. The capstan roller 33 cooperates with the opposing roller 331 to convey the sheet 30 while sandwiching it.

[0017] The platen roller 31 is located on the front side of the capstan roller 33 and the peeling roller 32, and is configured to press the label L against the thermal head 21. The platen roller 31 conveys the sheet 30 to the front side where the label discharge port 101 is provided above it, and also conveys the sheet 30 to the rear side where the sheet supply / discharge port 102 is provided below it.

[0018] The peeling bar 34 is located on the front side of the platen roller 31 and is provided near the label discharge port 101. The peeling bar 34 is formed to be longer than the width of the label L, and a corner portion is formed at the front end portion over the entire longitudinal direction thereof. The sheet 30 conveyed to the front side is folded back so as to be conveyed to the rear side with the corner portion of the peeling bar 34 as a base point. The peeling bar 34 can be bent at an acute angle so as to project the sheet 30 forward by the corner portion contacting the back surface of the sheet 30. Since the label L cannot follow the bending, the peeling bar 34 can discharge the printed label L from the label discharge port 101 by projecting the sheet 30 forward.

[0019] The peeling roller 32 is positioned between the platen roller 31 and the capstan roller 33 in the front-rear direction. The peeling roller 32 transports the sheet 30 from which the label L has been peeled off toward the rear side where the sheet supply / discharge port 102 is located. The sheet 30 being transported to the peeling roller 32 is positioned below the peeling roller 32 so that its back surface is in contact with the peeling roller 32. The opposing roller 321 is positioned opposite the peeling roller 32, sandwiching the sheet 30 between them. The peeling roller 32 works in cooperation with the opposing roller 321 to transport the sheet 30 while gripping it. The sheet supply motor 39 rotates the platen roller 31, the peeling roller 32, and the capstan roller 33.

[0020] The density sensor 41 has a light-emitting element and a light-receiving element, and is positioned upstream of the thermal head 21 and platen roller 31 in the transport direction, and is installed inside the housing 10 so as to be able to read the printed surface of the label L. The density sensor 41 measures the optical density of the image printed on the label L by having the light-receiving element detect the light emitted from the light-emitting element and reflected by the label L.

[0021] The label sensor 42 is a sensor that detects marks on the sheet 30. These marks indicate the downstream end of each label L in the transport direction on the sheet 30. The MPU 51 calculates the position of the transported label L based on the detection result from the label sensor 42 and the transport speed of the sheet 30. The label sensor 42 is installed inside the housing 10 so as to be able to detect marks on the sheet 30, and in this embodiment, it is installed upstream of the concentration sensor 41 in the transport direction.

[0022] The communication interface 54 communicates with the host device of the thermal printer 1. The MPU 51 works in cooperation with the RAM 52 to control the ribbon winding motor 29, the sheet supply motor 39, and the thermal head 21 to form the image received from the host device onto the label L. Furthermore, the MPU 51 performs a density adjustment process to adjust the amount of energy applied to the thermal head 21 so that an appropriate print density is obtained, based on the measurement results from the density sensor 41. The ROM 53 stores the program and data used for processing by the MPU 51.

[0023] (Operation of concentration adjustment process) The operation of the density adjustment process according to the first embodiment will now be described. Figure 4 is a flowchart showing the operation of the density adjustment process according to this embodiment. Figure 5 is a schematic diagram showing a label with an adjustment image printed on it according to this embodiment. Figure 6 is a schematic diagram showing a label transported to the upstream side according to this embodiment. Figure 7 is a diagram showing the estimation table according to this embodiment. Figure 8 is a diagram showing an example of the measurement results according to this embodiment. Prior to the operation of the density adjustment process shown in Figure 4, it is assumed that the user of the thermal printer 1 has set the media type and given instructions to start the density adjustment process.

[0024] As shown in Figure 4, first, the MPU 51 prints the adjustment image IA (see Figure 5) onto the label L (S101). While the adjustment image IA is being printed, the label L is transported downstream in the transport direction.

[0025] As shown in Figure 5, the adjustment image IA includes multiple density images printed at different densities. The multiple density images are printed in the transport direction, with the density increasing towards the upstream side. In this embodiment, each of the multiple density images is printed so that a rectangular area is filled with the same density, but it is sufficient if an area of ​​a predetermined shape is filled with the same density. In this embodiment, the adjustment image IA includes five density images 1 to 5, and the numbers attached to the density images indicate that the density is higher the larger the number.

[0026] The adjustment image IA is printed in a position where its width AW overlaps, at least partially, with the measurement range SW of the density sensor 41 in the width direction of the label L, in order to enable measurement by the density sensor 41. In this embodiment, the density sensor 41 is located to the left when viewed from the upstream side in the transport direction (upper side in Figure 5). Therefore, the adjustment image IA is printed to the left when viewed from the upstream side in the transport direction, in accordance with the density sensor 41. It is desirable that the adjustment image IA be printed so that the measurement range SW fits within the width AW.

[0027] Furthermore, the adjustment image IA is printed within a range of length AL in the transport direction from the upstream end of the label L in the transport direction. Length AL in the transport direction is the length obtained by subtracting the distance GP (see Figure 1) from the total length LN of the label L in the transport direction from the printing position of the thermal head 21 to the corner of the peeling bar 34. This prevents the label L from being peeled off by the peeling bar 34 while the adjustment image IA is being printed.

[0028] After printing the adjustment image IA, the MPU 51 controls the sheet supply motor 39 so that the label L on which the adjustment image IA is printed is transported downstream in the transport direction, that is, in the opposite direction to the direction in which the label L is transported during printing, as shown in Figure 6 (S102).

[0029] Next, the MPU 51 causes the density sensor 41 to measure a density image (S103), and calculates the optical density from the measured value indicated by the output voltage value from the density sensor 41 (S104).

[0030] The optical density is calculated using an estimation table as shown in Figure 7. The estimation table associates the range of measured values, which are divided into multiple stages, with the optical density set for each type of medium. In Figure 7, the measured value of 3.5 represents the range of measured values ​​between 3.5 and 3.8V, and the optical density of thermal paper (0.7) and the optical density of transfer paper (1.2) are associated with this range of measured values. The MPU 51 calculates the optical density of the measured density image as the optical density that corresponds to the range of measured values ​​that the measured values ​​from the density sensor 41 fall within, among the optical densities set for the medium type that were set prior to the operation of the density adjustment process.

[0031] In this way, by calculating the optical density based on the measured values ​​for each type of medium, the error between the measured values ​​and the optical density, mainly due to the reflectance of the medium, can be reduced. The optical density for each medium may also be calculated using coefficients, formulas, etc., set for each medium.

[0032] After calculating the optical density, the MPU51 determines whether all density images included in the adjustment image IA have been measured (S105).

[0033] If all density images have been measured (S105, YES), the MPU 51 controls the sheet supply motor 39 so that the label L with the adjustment image IA printed on it is discharged from the label discharge port 101 (S106). The MPU 51 also selects a density adjustment value based on the optical density calculated for all density images included in the adjustment image IA (S107).

[0034] As shown in Figure 8, each of the density images 1 to 5 is pre-assigned a density adjustment value. The density adjustment value maintains, reduces, or increases the amount of energy. In Figure 8, a positive density adjustment value indicates an adjustment amount that increases the amount of energy, a negative density adjustment value indicates an adjustment amount that decreases the amount of energy, and a density adjustment value of 0 indicates that the current amount of energy is maintained without increasing or decreasing it. Furthermore, for density images, a smaller density adjustment value is assigned to the lower the density, and a larger density adjustment value is assigned to the higher the density. In this embodiment, density image 3, which has a density intermediate between density image 1 and density image 5, is assigned a density adjustment value of 0.

[0035] Furthermore, an appropriate optical density corresponding to the desired print density is set for each type of media. In this embodiment, an optical density of 1.6 is set as the appropriate optical density for thermal paper, and an optical density of 1.8 is set as the appropriate optical density for transfer paper. These appropriate optical densities are shown as numerical values ​​enclosed in black frames in Figure 8. Note that the appropriate optical density may also indicate a range of optical densities. The MPU51 selects a density adjustment value associated with a density image in which the calculated optical density corresponds to the appropriate optical density.

[0036] The MPU51 adjusts the amount of energy applied to the thermal head 21 based on the selected concentration adjustment value.

[0037] As described above, the thermal printer 1 according to this embodiment can adjust the amount of energy applied to the thermal head 21 without increasing the size of the thermal printer 1 by arranging the density sensor 41 upstream of the thermal head 21 in the transport direction. Furthermore, the thermal printer 1 according to this embodiment can adjust the amount of energy applied to the thermal head 21 to achieve a print density suitable for each type of medium by calculating the optical density for each type of medium.

[0038] <Second Embodiment> A thermal printer according to the second embodiment will now be described. Figure 9 is a schematic diagram showing the configuration of the concentration sensor in the thermal printer according to this embodiment.

[0039] As shown in Figure 9, the thermal printer 2 according to this embodiment differs from the thermal printer 1 according to the first embodiment in that it is equipped with a density sensor 61 instead of a density sensor 41, and prints an adjustment image IB instead of an adjustment image IA.

[0040] The density sensor 61 differs from the density sensor 41 in that it is configured to be movable in the width direction of the label L, that is, in a direction perpendicular to the transport direction of the label L. In addition, the MPU 51 of the thermal printer 2 prints an adjustment image IB, which includes multiple density images arranged in the width direction of the label L, during the density adjustment process.

[0041] In this way, by measuring the density of multiple density images arranged in the width direction using a density sensor 61 that is movable in the width direction, the print density can be adjusted without peeling off the label L, even when the thermal head 21 and the peeling bar 34 are in close proximity.

[0042] <Third Embodiment> A thermal printer according to the third embodiment will now be described. Figure 10 is a schematic diagram showing the configuration of the concentration sensor in the thermal printer according to this embodiment.

[0043] As shown in Figure 10, the thermal printer 3 according to this embodiment differs from the thermal printer 2 according to the second embodiment in that it is equipped with a concentration sensor 71 instead of a concentration sensor 61.

[0044] The concentration sensor 71 differs from the concentration sensor 61 in that it is configured as a line sensor extending in the width direction of the label L, that is, in a direction perpendicular to the transport direction of the label L.

[0045] In this way, by configuring the density sensor 71 as a line sensor, it is possible to measure multiple density images in a shorter time compared to the density sensor 61, which sequentially measures multiple density images while moving in the width direction.

[0046] In the embodiments described above, the thermal printers 1-3 were described as printing on the label L using a thermal transfer method, but they may also print on the medium using a direct thermal recording printing method. Furthermore, the medium is not limited to the label L, but can be any medium that can be printed on by the thermal head 21.

[0047] While embodiments of the invention have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications are permitted without departing from the spirit of the invention. These embodiments and their variations are included within the scope and spirit of the invention, as well as within the scope of the invention and its equivalents as described in the claims.

[0048] (Note 1) The thermal printer is characterized in that the processor calculates the density for each of the plurality of density images based on the measurement value from the density sensor and the type of medium. (Note 2) The thermal printer according to Appendix 1, characterized in that the processor calculates the density for each of the plurality of density images based on a table in which the density for each of the plurality of measurement ranges is associated with the density for each of the plurality of medium types. (Note 3) A thermal printer characterized in that each of the plurality of density images is printed so as to be aligned in the transport direction. (Note 4) A thermal printer characterized in that each of the plurality of density images is printed so as to be aligned in a direction perpendicular to the transport direction. (Note 5) The thermal printer is characterized in that the concentration sensor is movably provided in a direction perpendicular to the transport direction. (Note 6) The thermal printer according to Appendix 4, characterized in that the concentration sensor is a line sensor extending in a direction perpendicular to the transport direction. [Explanation of Symbols]

[0049] 1. Thermal printer 21 Thermal Head 41, 61, 71 Concentration Sensor

Claims

1. A thermal printer that forms an image on a label attached to a sheet using a thermal head, A density sensor is positioned upstream of the thermal head in the transport direction for transporting the label towards the discharge port formed in the thermal printer, and measures the density of the image printed by the thermal head. The system includes a processor that adjusts the amount of energy applied to the thermal head based on the measured concentration, A peeling bar is provided downstream of the thermal head, which folds the sheet in the opposite direction of the conveying direction and peels the label from the sheet at its corner. Prior to measurement by the concentration sensor, the processor prints an adjustment image onto the thermal head. The thermal printer is characterized in that the adjustment image is printed within a range from the upstream end of the label in the transport direction to a distance obtained by subtracting the distance between the thermal head and the peeling bar from the transport length of the label in the transport direction.

2. The thermal printer according to claim 1, characterized in that the adjustment image includes a plurality of density images printed at different densities.

3. The thermal printer according to claim 2, characterized in that the processor transports the medium upstream in the transport direction after the adjustment image has been printed, so that the density sensor can measure the adjustment image.

4. Each of the aforementioned plurality of density images is associated with an adjustment value for the amount of energy. The thermal printer according to claim 2 or 3, characterized in that the processor adjusts the amount of energy by an adjustment value associated with a density image in which a density corresponding to a predetermined density range has been measured.

Images