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] The present invention relates to a thermal printer. [Background technology]

[0002] Conventionally, thermal printers that print on a medium using a thermal head with a heating element are known. Thermal printers include those that print using a direct thermal recording printing method and those that print using a thermal transfer method. The direct thermal recording printing method prints by using a thermal head to heat a medium that changes color when heated. The thermal transfer method prints by heating ink with a thermal head.

[0003] In such thermal printers, the print density varies depending on the type of ink and medium, the length of time the thermal head and platen have been used, and other factors, so it is necessary to adjust the amount of energy applied to the thermal head to obtain the desired print density. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2019-113884 A Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present invention is to provide a technique for easily adjusting the amount of energy applied to a thermal head. [Means for solving the problem]

[0006] In one embodiment, a thermal printer forms an image on a medium using a thermal head, and includes a density sensor arranged upstream of the thermal head in the transport direction of the medium, which measures 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 description of the drawings]

[0007] [Figure 1] 1 is a schematic perspective view showing a thermal printer used as an in-line printer according to a first embodiment. [Diagram 2] 1 is a schematic side view illustrating an internal configuration of a thermal printer according to a first embodiment. [Diagram 3] 2 is a block diagram showing the configuration of a control system of the thermal printer according to the first embodiment. FIG. [Figure 4] 5 is a flowchart showing an operation of a density adjustment process according to the first embodiment. [Diagram 5] FIG. 2 is a schematic diagram showing a label on which an adjustment image according to the first embodiment is printed. [Figure 6] FIG. 4 is a schematic diagram showing a label being transported to the upstream side according to the first embodiment. [Figure 7] FIG. 4 is a diagram showing an estimation table according to the first embodiment. [Figure 8] FIG. 4 is a diagram showing an example of a measurement result according to the first embodiment. [Figure 9] 10 is a schematic diagram illustrating a configuration of a density sensor in a thermal printer according to a second embodiment. FIG. [Figure 10] FIG. 11 is a schematic diagram illustrating the configuration of a density sensor in a thermal printer according to a third embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In each drawing, the same components are denoted by the same reference numerals.

[0009] First Embodiment (Thermal Printer Configuration) The configuration of a thermal printer according to a first embodiment will be described. Fig. 1 is a schematic perspective view showing a thermal printer used as an in-line printer according to this embodiment. Fig. 2 is a schematic side view showing the internal configuration of the thermal printer according to this embodiment. Fig. 3 is a block diagram showing the configuration of a control system of the thermal printer according to this embodiment.

[0010] As shown in Fig. 1, a thermal printer 1 according to this embodiment is used as an in-line printer installed in a workplace or the like. Specifically, in this embodiment, the thermal printer 1 is fixedly installed with respect to a conveying device C that conveys an item O, and prints on a label L to be 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] 2, the thermal printer 1 is a thermal transfer printer that uses heat to transfer ink to a label L. The thermal printer 1 includes a housing 10, a thermal head 21, a ribbon take-up 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 FIG. 3, the thermal printer 1 is equipped with a ribbon take-up 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 substantially box-like shape that defines an internal space for accommodating the above-mentioned components. The housing 10 is formed with a label discharge port 101 and a sheet feed / discharge port 102. The label discharge port 101 is an opening formed by cutting out the front side (right side in FIG. 2) located on the bottom side of the housing 10. The sheet feed / discharge port 102 is an opening formed by cutting out the rear side (left side in FIG. 2) located on the bottom side of the housing 10. A sheet 30 to which a plurality of labels L are continuously attached is supplied from the sheet feed / discharge port 102. Each of the plurality of labels L attached to the sheet 30 is discharged from the label discharge port 101. The sheet 30 from which the label L has been peeled off is discharged from the sheet feed / discharge port 102.

[0014] The ribbon support shaft 23 rotatably supports the ink ribbon 20, which is a strip-shaped member coated with ink and wound into a roll. The ribbon take-up shaft 22 is rotated by a ribbon take-up motor 29 to take up the ink ribbon 20 unwound from the roll. The ribbon support shaft 23 and the ribbon take-up shaft 22 are provided at the same position relative to each other in the up-down direction. The ribbon support shaft 23 is located rearward of the ribbon take-up shaft 22.

[0015] The thermal head 21 is disposed below the ribbon support shaft 23 and the ribbon take-up shaft 22, and has multiple heating elements adjacent to each other in the width direction of the label L. The ink ribbon 20 unwound from the roll is taken up by the ribbon take-up shaft 22 via the thermal head 21. The multiple heating elements generate heat in response to the input pulse waves, and the thermal head 21 thereby transfers the ink applied to the ink ribbon to the label L to form an image. Methods for adjusting the amount of energy applied to the thermal head 21 in this embodiment include increasing or decreasing the current value of the pulse waves, and increasing or decreasing the duty ratio of the pulse waves.

[0016] The capstan roller 33 is provided rearward of the platen roller 31 and the peeling roller 32. The capstan roller 33 transports the sheet 30 supplied from the sheet supply / discharge port 102 toward the front side where the thermal head 21 is located. The sheet 30 transported by the capstan roller 33 is positioned above the capstan roller 33 so that the back side of the sheet 30 to which the multiple labels L are not affixed contacts the capstan roller 33. The opposing roller 331 is provided facing the capstan roller 33 with the sheet 30 sandwiched therebetween. The capstan roller 33 cooperates with the opposing roller 331 to transport the sheet 30 while holding it therebetween.

[0017] The platen roller 31 is located forward 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 transports the sheet 30 to the front side where a label discharge port 101 is provided on the upper side thereof, and transports the sheet 30 to the rear side where a sheet supply / discharge port 102 is provided on the lower side thereof.

[0018] The peeling bar 34 is located forward of the platen roller 31 and is provided in the vicinity of the label discharge port 101. The peeling bar 34 is formed to be longer than the width of the label L, and a corner is formed at the front end over the entire length of the peeling bar 34. The sheet 30 conveyed forward is folded back so as to be conveyed rearward, using the corner of the peeling bar 34 as a base point. The peeling bar 34 can bend the sheet 30 at an acute angle so as to protrude forward by abutting the corner against the back surface of the sheet 30. Since the label L cannot follow the bending, the peeling bar 34 can eject the printed label L from the label discharge port 101 by protruding the sheet 30 forward.

[0019] The peeling roller 32 is provided so as to be located 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 to the rear side where the sheet feed / discharge port 102 is located. The sheet 30 transported to the peeling roller 32 is positioned below the peeling roller 32 so that the back surface of the sheet 30 contacts the peeling roller 32. The opposing roller 321 is provided so as to face the peeling roller 32 with the sheet 30 sandwiched therebetween. The peeling roller 32 cooperates with the opposing roller 321 to transport the sheet 30 while holding it therebetween. A 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 provided inside the housing 10 so as to be positioned upstream of the thermal head 21 and the platen roller 31 in the transport direction and 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 detecting light emitted from the light-emitting element and reflected by the label L with the light-receiving element.

[0021] The label sensor 42 is a sensor that detects a mark on the sheet 30. This mark indicates the end of each label L on the sheet 30 on the downstream side in the conveying direction. The MPU 51 calculates the position of the conveyed label L based on the detection result by the label sensor 42 and the conveying speed of the sheet 30. The label sensor 42 is provided in the housing 10 so as to be able to detect the mark on the sheet 30, and in this embodiment, is provided upstream of the concentration sensor 41 in the conveying direction.

[0022] The communication I / F 54 communicates with a host device of the thermal printer 1. The MPU 51 cooperates with the RAM 52 to control the ribbon take-up motor 29, the sheet supply motor 39, and the thermal head 21, and forms the image received from the host device on the label L. Furthermore, the MPU 51 executes a density adjustment process that adjusts the amount of energy applied to the thermal head 21 so as to obtain an appropriate print density, based on the measurement result by the density sensor 41. The ROM 53 stores programs and data used in the processes by the MPU 51.

[0023] (Density adjustment process) The operation of the density adjustment process according to the first embodiment will be described. FIG. 4 is a flowchart showing the operation of the density adjustment process according to this embodiment. FIG. 5 is a schematic diagram showing a label on which an adjustment image according to this embodiment is printed. FIG. 6 is a schematic diagram showing a label transported to the upstream side according to this embodiment. FIG. 7 is a diagram showing an estimation table according to this embodiment. FIG. 8 is a diagram showing an example of a measurement result according to this embodiment. It is assumed that, prior to the operation of the density adjustment process shown in FIG. 4, the user of the thermal printer 1 has set the medium type and instructed to start the density adjustment process.

[0024] 4, first, the MPU 51 prints (S101) an adjustment image IA (see FIG. 5) on the label L. During printing of the adjustment image IA, the label L is transported downstream in the transport direction.

[0025] As shown in FIG. 5, the adjustment image IA includes a plurality of density images printed at different densities. The plurality of density images are printed side by side in the transport direction so that the density increases toward the upstream side. In this embodiment, each of the plurality of density images is printed so that a rectangular area is filled with the same density, but it is sufficient that 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 larger the number attached to the density image, the higher the density.

[0026] To enable measurement by the density sensor 41, the adjustment image IA is printed in a position in the width direction of the label L where the width AW of the adjustment image IA at least partially overlaps with the widthwise measurement range SW of the density sensor 41. In this embodiment, the density sensor 41 is provided in a position (upper side in FIG. 5) shifted to the left side as viewed from the upstream side in the transport direction. Therefore, the adjustment image IA is printed in a position shifted to the left side as viewed from the upstream side in the transport direction, in line with the density sensor 41. Note that it is desirable to print the adjustment image IA so that the measurement range SW falls within the width AW.

[0027] The adjustment image IA is printed within a transport direction length AL from the upstream end of the label L in the transport direction. The transport direction length AL is the total length LN of the label L in the transport direction minus the distance GP (see FIG. 1) from the printing position of the thermal head 21 to the corner of the peel bar 34. This prevents the label L from being peeled off by the peel 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, i.e., in the opposite direction to the direction in which the label L is transported during printing, as shown in FIG. 6 (S102).

[0029] Next, the MPU 51 causes the density sensor 41 to measure the 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 FIG. 7. The estimation table associates a measurement range divided into multiple stages with an optical density set for each type of medium. In FIG. 7, a measurement value of 3.5 indicates a measurement value range of 3.5 or more and less than 3.8V, and an optical density of 0.7 for thermal paper and an optical density of 1.2 for transfer paper are associated with this measurement value range. The MPU 51 calculates the optical density of the measured density image as the optical density of the measured density image, which is associated with the measurement value range within which the measurement value by the density sensor 41 falls, among the optical densities set for the medium type set prior to the operation of the density adjustment process.

[0031] In this way, by calculating the optical density based on the measured value for each medium type, it is possible to reduce the error between the measured value and the optical density, which is mainly caused by the reflectance of the medium. Note that the optical density for each medium may be calculated using a coefficient, a formula, etc., set for each medium.

[0032] After calculating the optical density, the MPU 51 determines whether or not all density images included in the adjustment image IA have been measured (S105).

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

[0034] As shown in Fig. 8, density adjustment values ​​are associated in advance with each of density images 1 to 5. The density adjustment value maintains, reduces or increases the amount of energy, and in Fig. 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 a density image, a smaller density adjustment value is associated with a lower density, and a larger density adjustment value is associated with a higher density. In this embodiment, a density image 3, which is an intermediate density between density image 1 and density image 5, is associated with a density adjustment value of 0.

[0035] Further, for each medium type, an appropriate optical density corresponding to the desired print density is set. 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 ​​surrounded by black frames in FIG. 8. The appropriate optical density may indicate a range of optical density. The MPU 51 selects a density adjustment value associated with a density image in which the calculated optical density corresponds to the appropriate optical density.

[0036] The MPU 51 adjusts the amount of energy to be applied to the thermal head 21 based on the selected density adjustment value.

[0037] As described above, the thermal printer 1 according to this embodiment is able to 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. Also, the thermal printer 1 according to this embodiment is able to adjust the amount of energy applied to the thermal head 21 so as to obtain a print density suitable for the medium type by calculating the optical density for each medium type.

[0038] <Second embodiment> A description will now be given of a thermal printer according to the second embodiment. Fig. 9 is a schematic diagram showing the configuration of a density sensor in the thermal printer according to the present embodiment.

[0039] As shown in FIG. 9, the thermal printer 2 of this embodiment differs from the thermal printer 1 of the first embodiment in that it has a density sensor 61 instead of the density sensor 41, and in that it 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, i.e., in a direction perpendicular to the conveying direction of the label L. In addition, in the density adjustment process, the MPU 51 of the thermal printer 2 prints an adjustment image IB including multiple density images aligned in the width direction of the label L.

[0041] In this way, by measuring the density of multiple density images arranged in the width direction using the 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 peel bar 34 are closer to each other.

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

[0043] As shown in FIG. 10, the thermal printer 3 according to this embodiment differs from the thermal printer 2 according to the second embodiment in that it includes a density sensor 71 instead of the density sensor 61.

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

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

[0046] In the above embodiment, the thermal printer 1-3 is described as printing on the label L by a thermal transfer method, but it may be a direct thermal recording printing method for printing on the medium. Also, the medium is not limited to the label L, and may be any medium that can be printed on by the thermal head 21.

[0047] Although the embodiments of the invention have been described, these embodiments are presented as examples 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 can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope and spirit of the invention, and are included in the scope of the invention and its equivalents described in the claims.

[0048] (Appendix 1) The thermal printer is characterized in that the processor calculates a density for each of the plurality of density images based on a measurement value by the density sensor and a type of the medium. (Appendix 2) The thermal printer described in Appendix 1, characterized in that the processor calculates the density for each of the multiple density images based on a table in which the density for each of the multiple measurement value ranges is associated with the density for each of the multiple density images. (Appendix 3) The thermal printer is characterized in that the plurality of density images are printed so as to be aligned in the transport direction. (Appendix 4) A thermal printer, characterized in that the plurality of density images are printed so as to be aligned in a direction perpendicular to the transport direction. (Appendix 5) The thermal printer is characterized in that the density sensor is provided movably in a direction perpendicular to the transport direction. (Appendix 6) 5. The thermal printer according to claim 4, wherein the density 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 medium by a thermal head, a density sensor that is disposed upstream of the thermal head in a transport direction of the medium and that measures the density of an image printed by the thermal head; a processor for adjusting an amount of energy applied to the thermal head based on the measured density; A thermal printer comprising:

2. 2. The thermal printer according to claim 1, wherein the processor causes the thermal head to print an adjustment image including a plurality of density images printed at different densities prior to the measurement by the density sensor.

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

4. an adjustment value for the amount of energy is associated with each of the plurality of density images; 4. The thermal printer according to claim 2, wherein the processor adjusts the amount of energy using an adjustment value associated with a density image in which a density that falls within a predetermined density range has been measured.

5. the medium is a label affixed to a sheet; a peeling bar is provided downstream of the thermal head for folding back the sheet in the opposite direction to the conveying direction and peeling the label off the sheet by a corner of the peeling bar; 2. The thermal printer according to claim 1, wherein the adjustment image is printed within a range from a downstream end of the label in the transport direction to a distance obtained by subtracting the distance between the thermal head and the peel bar from the length of the label in the transport direction.

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