JP2017177587A - Thermal print head and thermal printer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form high-quality images on a recording medium.SOLUTION: A thermal print head includes: substrates 26, 27; a plurality of heating resistors 12 disposed on one surface of the substrates 26, 27 in a main scanning direction S1 side by side; a plurality of control elements 8 disposed side by side on one surface of the substrates 26, 27 in the main scanning direction S1 with a pitch different from a pitch in a disposition range of the prescribed number of heating resistors 12; and a plurality of individual wiring electrodes 14 disposed between the plurality of heating resistors 12 and the plurality of control elements 8 on one surface of the substrates 26, 27, and connecting the plurality of heating resistors 12 and the plurality of control elements 8. The plurality of heating resistors 12 are subjected to correction processing for correcting resistance values of the heating resistors in accordance with wire resistance values of the plurality of individual wiring electrodes 14, and thereby, at the time of image formation, heat can be generated while making a heat generation amount almost constant regardless of unevenness of the value of current flowing in the plurality of heating resistors 12, so that high-quality images can be formed on a recording medium P.SELECTED DRAWING: Figure 10

Description

  The present invention relates to a thermal print head and a thermal printer provided with the thermal print head.

  The thermal print head generates heat from a plurality of heating resistors arranged in a heat generating area along the main scanning direction, and images of characters, figures, etc. are recorded on a recording medium such as thermal recording paper by the heat of the plurality of heating resistors. This is an output device to be formed. Thermal print heads are widely used in thermal printers (that is, recording devices) such as barcode printers, digital plate-making machines, video printers, imagers, and seal printers.

  As a general thermal print head, for example, there is one in which one pixel of an image is formed by two heating resistors adjacent in the main scanning direction. In such a thermal print head, a circuit board and a head substrate are arranged side by side along a sub-scanning direction orthogonal to the main scanning direction on one surface of a heat sink long in the main scanning direction.

  On one surface of the head substrate, a plurality of heating resistors long in the sub-scanning direction and a plurality of U-shaped folded electrodes are arranged side by side in the main scanning direction, and two heating resistors adjacent in the main scanning direction are arranged. Each one of these end portions is connected to each other via a folded electrode.

  Also, on one surface of the head substrate, a plurality of linear individual wiring electrodes and a plurality of linear common wiring electrodes are alternately arranged in the main scanning direction one after another, and a plurality of strip-shaped common band electrodes that are long in the main scanning direction. Are arranged in the main scanning direction. In the head substrate, one end of the individual wiring electrode is connected to the other end of one heating resistor for every two heating resistors, and the other end of the other heating resistor is connected to the common wiring electrode. To the corresponding common strip electrode.

  Thus, the head substrate is formed with a plurality of heating elements each having two heating resistors by the plurality of heating resistors and these various electrodes. In the head substrate, in a plurality of heating elements, a portion between the folded electrode of the two heating resistors, the individual wiring electrode, and the common wiring electrode becomes a heating portion that generates heat by energization, and the plurality of heating portions are arranged in order. A belt-like region along the scanning direction is a heat generating region.

  On one surface of the circuit board, a plurality of driving ICs (Integrated Circuits) each having a switching function of a plurality of heating elements are arranged in the main scanning direction, and a plurality of negative electrodes for connecting an external power source are arranged. ing. In addition, a pair of positive electrodes for connecting an external power source is disposed on both sides of each of the plurality of driving ICs on one surface of the circuit board. In the circuit board, a plurality of driving ICs are connected to the other end portions of a plurality of corresponding individual wiring electrodes and a plurality of minus electrodes via a plurality of bonding wires, and a pair of plus electrodes for each driving IC is provided. It is connected to both ends of the corresponding common strip electrode via a pair of bonding wires.

  As a result, in the thermal print head, when the driving IC is turned on in a state where a voltage is applied from the external power supply to both ends of the common strip electrode during image formation, current flows from both ends of the common strip electrode to the center portion. The current flows in sequence to the two heat generating resistors through the common wiring electrode to cause the heat generating portion to generate heat.

  However, in the thermal print head, when the resistance value of the common strip electrode is relatively large, a voltage drop called a so-called common drop occurs when a current flows from both ends to the central portion of the common strip electrode. And the voltage drop which arises in a common strip | belt-shaped electrode is larger in the center part than the both ends of the common strip | belt-shaped electrode.

  For this reason, in the thermal print head, when a voltage drop occurs in the common strip electrode, the value of the current flowing from the common strip electrode to each heating resistor varies due to this, and the amount of heat generated in each heating section varies, and as a result, Printing unevenness, which is density unevenness, occurs in an image formed on a recording medium. Therefore, the conventional thermal print head has a common strip electrode that is relatively thick to reduce the resistance value, thereby reducing the voltage drop that occurs when current flows from both ends of the common strip electrode to the center (for example, Patent Documents). 1).

JP 2006-95943 A (page 5, page 6, FIG. 1, FIG. 3)

  By the way, in recent years, for example, a thermal print head having a relatively small size of a recording medium that can be used for image formation is used as a head unit, and a plurality of head units are sequentially arranged in the main scanning direction and connected to each other, thereby recording a relatively large size. There is a thermal print head called a long type configured so that an image can be formed on a medium.

  Such a thermal print head has, for example, one or a plurality of first head units formed in a trapezoidal shape whose width gradually decreases in the sub-scanning direction. The thermal print head is formed in an inverted trapezoidal shape that gradually widens in the sub-scanning direction, and the arrangement positions of the plurality of heating resistors are shifted in the sub-scanning direction from the arrangement positions of the plurality of heating resistors of the first head unit. One or more second head units are also included.

  The thermal print head connects the first head unit and the second head unit alternately and sequentially in the main scanning direction so that the pitch of the plurality of heating resistors in the main scanning direction is applied to the inside of the unit and the unit boundary portion. Almost equal. Thus, in the thermal print head, when an image is formed on a recording medium, the image is prevented from being separated or overlapped.

  However, since the second head unit of the thermal print head is formed in an inverted trapezoidal shape, a portion where a plurality of driving ICs are arranged as compared with a width in the main scanning direction of a portion where a plurality of heating resistors are arranged. The width in the main scanning direction is narrow. For this reason, in the second head unit, a plurality of driving ICs are arranged side by side at a pitch narrower than the pitch of the arrangement range of the heating resistors for each predetermined number connected to them.

  As a result, in the second head unit, for each driving IC, a resistance value (hereinafter also referred to as a wiring resistance value) along with the lengths of the corresponding predetermined number of individual wiring electrodes and the predetermined number of common wiring electrodes. Are different. Therefore, in the second head unit, even if each common strip electrode is made relatively thick and the resistance value is made small, it is caused by variations in the wiring resistance values of the plurality of individual wiring electrodes and the plurality of common wiring electrodes during image formation. Thus, the current flowing through the plurality of heating resistors varies, and the amount of heat generated by the plurality of heating portions varies. For this reason, the thermal print head has a problem in that an image is printed unevenly on a recording medium, and it is difficult to form a high quality image.

  Therefore, the present invention proposes a thermal print head and a thermal printer that can form a high-quality image on a recording medium.

  In order to solve such problems, in the present invention, a substrate, a plurality of heating resistors arranged side by side in the main scanning direction on one surface of the substrate, and a predetermined number of heating resistors can be connected to each other on one surface of the substrate. Between the plurality of control elements arranged in a different pitch from the pitch of the arrangement range of the predetermined number of heating resistors in the main scanning direction, and between the plurality of heating resistors and the plurality of control elements on one surface of the substrate A plurality of individual wiring electrodes that are arranged and connect the plurality of heating resistors and the plurality of control elements, and the plurality of heating resistors have a heating element resistance value according to the wiring resistance values of the plurality of individual wiring electrodes. Correction processing was performed to correct.

  Therefore, according to the present invention, during image formation, heat can be generated with the heat generation amount substantially constant regardless of variations in the value of the current flowing through the plurality of heating resistors.

  According to the present invention, a substrate, a plurality of heating resistors arranged side by side in the main scanning direction on one surface of the substrate, and a predetermined number of heating resistors can be connected to each other. A plurality of control elements arranged side by side with a pitch different from the pitch of the arrangement range of the predetermined number of heating resistors, and arranged between the plurality of heating resistors and the plurality of control elements on one surface of the substrate, A correction process for providing a plurality of individual wiring electrodes for connecting the heating resistor and the plurality of control elements, and correcting the heating element resistance value according to the wiring resistance values of the plurality of individual wiring electrodes on the plurality of heating resistors. As a result, it is possible to generate heat with an almost constant heating value regardless of variations in the value of current flowing through a plurality of heating resistors during image formation, thus forming a high-quality image on a recording medium. Thermal print head to obtain and It can be realized over circle printer.

It is a top view which shows the structure of the elongate thermal print head which concerns on embodiment of this invention. It is a fragmentary sectional view which shows the structure of the elongate type thermal print head which concerns on embodiment of this invention. It is a partial top view which shows the structure of the 1st head substrate and 2nd head substrate which concern on embodiment of this invention. It is a partial top view which shows the structure of the 1st head unit which concerns on embodiment of this invention, and a 2nd head unit. 1 is a partial cross-sectional view showing a configuration of a thermal printer provided with a long thermal print head according to an embodiment of the present invention. It is a top view which shows the structure of a 1st head unit. It is a characteristic curve figure with which it uses for description of the correction | amendment process of the heating element resistance value performed to the several heating resistor of a 1st head unit. It is a top view which shows the structure of a 2nd head unit. It is a characteristic curve figure with which it uses for description of the wiring resistance value of the some wiring electrode of a 2nd head unit. It is a characteristic curve figure with which it uses for description of the correction | amendment process of the heating element resistance value performed to the several heating resistor of a 2nd head unit. It is a top view which shows the structure of the thermal print head which concerns on other embodiment of this invention.

  Embodiments of a thermal print head and a thermal printer according to the present invention will be described with reference to FIGS. Incidentally, FIG. 2 is a cross-sectional view taken along the line V1-V1 of FIG. Note that this embodiment is merely an example, and the present invention is not limited to this.

  As shown in FIGS. 1 to 4, the thermal print head 1 is a long type that is long in the main scanning direction S1 that can form an image on a relatively large recording medium, and is alternately arranged in the main scanning direction S1. For example, two first head units 2 and one second head unit 3 are arranged. Incidentally, the 1st head unit 2 and the 2nd head unit 3 can function as a thermal print head by these single units.

  The first head unit 2 is, for example, formed in a trapezoidal shape that is long in the main scanning direction S1 and gradually narrows in the sub-scanning direction S2 perpendicular to the main scanning direction S1. The first head unit 2 includes a first heat radiating plate 5, a first head substrate 6, a first circuit substrate 7, and a plurality of driving ICs 8. The first heat radiating plate 5 is formed in a trapezoidal shape from a metal having good heat radiating properties such as aluminum, and the first circuit board 7 and the first head substrate 6 are arranged in order in the sub-scanning direction S2 on one surface.

The first head substrate 6 has a support substrate 10 formed in a trapezoidal shape by a ceramic such as Al ₂ O ₃ , and a glaze layer 11 made of a glass film such as SiO ₂ is disposed on one surface of the support substrate 10. Yes. On one surface of the glaze layer 11, a plurality of heating resistors 12 that are long in the sub-scanning direction S2 are arranged at a predetermined pitch in the main scanning direction S1 at one end of the head substrate in the sub-scanning direction S2.

  Further, on one surface of the glaze layer 11, a plurality of U-shaped folded electrodes 13 are arranged at a predetermined pitch in the main scanning direction S1 in the sub-scanning direction S2 of the plurality of heating resistors 12. As a result, the first head substrate 6 is connected to the two heating resistors 12 adjacent to each other in the main scanning direction S1 through the folded electrode 13 at one end in the sub-scanning direction S2. One heating resistor 12 forms one pixel of the image.

  Further, on one surface of the glaze layer 11, a plurality of linear individual wirings extending to the other end of the head substrate in the sub-scanning direction opposite to the sub-scanning direction S2 opposite to the sub-scanning direction S2 of the plurality of heating resistors 12. The electrodes 14 and the plurality of linear common wiring electrodes 15 are alternately arranged in the main scanning direction S1. Further, on one surface of the glaze layer 11, a plurality of strip-like common strip electrodes 16 that are long in the main scanning direction S1 are arranged in the main scanning direction S1 at a predetermined pitch in the vicinity of the other end of the head substrate.

  The first head substrate 6 has one end of the individual wiring electrode 14 at the other end of the one heating resistor 12 in the sub-scanning direction, for example, every two heating resistors 12 adjacent along the main scanning direction S1. Are connected, and the other end of the individual wiring electrode 14 is routed to the vicinity of the corresponding common strip electrode 16. In the first head substrate 6, the other heating element 12 in the sub-scanning opposite direction of the other heating resistor 12 is provided via the common wiring electrode 15 for every two heating resistors 12 adjacent along the main scanning direction S 1. , Are connected to corresponding common strip electrodes 16.

  Thus, the first head substrate 6 includes a plurality of heating resistors 12 and these various electrodes (that is, a plurality of folded electrodes 13, a plurality of individual wiring electrodes 14, a plurality of common wiring electrodes 15, and a plurality of common strip electrodes 16). Thus, a plurality of heating elements each having two heating resistors 12 are formed. In the first head substrate 6, in the plurality of heating elements, the portion between the folded electrode 13 of the two heating resistors 12, the individual wiring electrode 14, and the common wiring electrode 15 becomes a heat generating portion that generates heat by energization. A belt-like region along the main scanning direction S1 in which the heat generating portions are sequentially arranged is a heat generating region 17.

  A protective film 18 is formed on one surface of the glaze layer 11 to cover the plurality of heating resistors 12 and the plurality of electrodes. The first head substrate 6 is attached to the other surface of the support substrate 10 at one end portion in the sub-scanning direction S2 on one surface of the first heat radiating plate 5 via an adhesive 19 that is a thermoplastic resin such as double-sided tape or silicon resin. Is glued.

  The first circuit board 7 is formed, for example, by attaching a trapezoidal flexible substrate to a trapezoidal ceramic plate. The first surface of the first circuit board 7 is bonded to the other end of the first heat radiating plate 5 in the direction opposite to the sub-scanning direction via an adhesive 19. Incidentally, the first circuit board 7 is mounted with a connector (not shown) that is connected to an external control circuit or an external power source and inputs a control signal and driving power.

  The plurality of driving ICs 8 are control elements each having a switching function capable of individually controlling a plurality of heating elements (that is, controlling a predetermined number of heating resistors 12 every two). On one surface of the first circuit board 7, a plurality of driving ICs 8 are arranged at a predetermined pitch in the main scanning direction S1 at one end of the circuit board in the sub-scanning direction S2 (that is, at the boundary with the first head substrate 6). Has been placed.

  Further, on one surface of the first circuit board 7, there are a plurality of negative electrodes (not shown) for connection to a negative terminal of an external power source and a control terminal (not shown) in the vicinity of each of the plurality of driving ICs 8. ) Is arranged. Further, on one surface of the first circuit board 7, a pair of plus electrodes 20 for connection to a plus terminal of an external power source are arranged on both sides of each of the plurality of driving ICs 8.

  Therefore, the first circuit board 7 includes a plurality of driving ICs 8 connected to the other ends of the corresponding plurality of individual wiring electrodes 14, a plurality of minus electrodes, and a control terminal via a plurality of bonding wires 21 and 22, respectively. Yes. In the first circuit board 7, a pair of plus electrodes 20 for each driving IC 8 is connected to both ends of the corresponding common strip electrode 16 through a pair of bonding wires 23. The plurality of driving ICs 8 are sealed together with a plurality of bonding wires 21 to 23 at a boundary portion between one surface of the first head substrate 6 and one surface of the first circuit substrate 7 by a sealing body 24 made of epoxy resin. .

  On the other hand, the second head unit 3 is, for example, formed in an inverted trapezoidal shape that is long in the main scanning direction S1 and gradually widens in the sub-scanning direction S2. The second head unit 3 includes a second heat radiating plate 25, a second head substrate 26, a second circuit substrate 27, and a plurality of driving ICs 8. Although the shape is different from that of the first head unit 2, basically, The configuration is almost the same as that of the first head unit 2.

  That is, the second heat radiating plate 25 is formed in an inverted trapezoidal shape with a metal having good heat radiating properties such as aluminum, and the second circuit board 27 and the second head substrate 26 are arranged in order in the sub-scanning direction S2 on one surface.

The second head substrate 26 has a glaze layer (not shown) made of a glass film such as SiO _{2 on} one surface of a support substrate (not shown) formed in a reverse trapezoidal shape with ceramics such as Al ₂ O _3. Has been. However, on one surface of the glaze layer, a plurality of heat generation similar to the case of the first head substrate 6 is provided at one end of the head substrate closer to the sub-scanning direction S2 than the arrangement position of the plurality of heating resistors 12 of the first head substrate 6. Resistors 12 are arranged at a predetermined pitch in the main scanning direction S1.

  Further, on one surface of the glaze layer, a plurality of folded electrodes 13 similar to the case of the first head substrate 6 are arranged in a predetermined pitch in the main scanning direction S1 in the sub-scanning direction S2 of the plurality of heating resistors 12. Yes. As a result, the second head substrate 26 is also connected to the two heating resistors 12 adjacent to each other along the main scanning direction S1 through the folded electrode 13 at one end in the sub-scanning direction S2. One heating resistor 12 forms one pixel of the image.

  Further, on one surface of the glaze layer, a plurality of individual wiring electrodes 14 and a plurality of common wiring electrodes 15 similar to the case of the first head substrate 6 are provided in the main scanning direction S1 in the direction opposite to the sub scanning of the plurality of heating resistors 12. They are arranged alternately one after another. Further, on one surface of the glaze layer, a plurality of common strip electrodes 16 similar to the case of the first head substrate 6 are arranged in the main scanning direction S1 at a predetermined pitch near the other end of the head substrate.

  The second head substrate 26 has one end of the individual wiring electrode 14 connected to the other end of one heating resistor 12, for example, every two heating resistors 12 adjacent along the main scanning direction S1, The other end of the individual wiring electrode 14 is routed to the vicinity of the corresponding common strip electrode 16. Further, the second head substrate 26 has a common belt-like shape in which the other end of the other heating resistor 12 passes through the common wiring electrode 15 for every two heating resistors 12 adjacent along the main scanning direction S1. It is connected to the electrode 16.

  Accordingly, the second head substrate 26 also includes a plurality of heating elements each having two heating resistors 12 by the plurality of heating resistors 12 and these various electrodes. The second head substrate 26 also has a plurality of heat generating elements where the portions between the folded electrodes 13 of the two heat generating resistors 12 and the individual wiring electrodes 14 and the common wiring electrode 15 generate heat when energized. A belt-like region along the main scanning direction S1 in which the heat generating portions are arranged in sequence is a heat generating region 28.

  Further, a protective film (not shown) that covers the plurality of heating resistors 12 and the plurality of electrodes is formed on one surface of the glaze layer. The second head substrate 26 is supported on one end of the second heat radiating plate 25 in the sub-scanning direction S2 via an adhesive (not shown) made of thermoplastic resin such as double-sided tape or silicone resin. The other side is glued.

  The second circuit board 27 is formed by adhering an inverted trapezoidal flexible substrate to an inverted trapezoidal ceramic plate, and an adhesive is provided on the other surface of the first heat dissipating plate 5 in the sub-scanning opposite direction. The other side is bonded. Incidentally, the second circuit board 27 is also mounted with a connector (not shown) that is connected to an external control circuit and an external power source and inputs a control signal and driving power.

  Similarly to the case of the second circuit board 27, a plurality of driving ICs 8 are provided on one surface of the second circuit board 27 at one end of the circuit board in the sub-scanning direction S2 (that is, at the boundary with the second head substrate 26). Are arranged at a predetermined pitch in the main scanning direction S1. A plurality of minus electrodes (not shown) and control terminals (not shown) are arranged on one surface of the second circuit board 27 in the vicinity of each of the plurality of driving ICs 8. Further, on one surface of the second circuit board 27, a pair of plus electrodes 20 are arranged on both sides of each of the plurality of driving ICs 8.

  Therefore, also in the second circuit board 27, the plurality of driving ICs 8 are connected to the other end portions of the corresponding individual wiring electrodes 14, the plurality of minus electrodes, and the control terminals through the plurality of bonding wires 21 and 22, respectively. Yes. In the second circuit board 27, a pair of plus electrodes 20 for each driving IC 8 is connected to both ends of the corresponding common strip electrode 16 through a pair of bonding wires 23. The plurality of driving ICs 8 are sealed together with a plurality of bonding wires 21 to 23 at a boundary portion between one surface of the second head substrate 26 and one surface of the second circuit substrate 27 by a sealing body 29 made of epoxy resin. .

  In the thermal print head 1, for example, the first head unit 2 and the second head unit 3 are alternately arranged in the main scanning direction S1 on a head frame (not shown) that can be attached to and detached from the thermal printer 40, and face each other. The side surfaces to be touched are close to each other or are in contact with each other. That is, the thermal print head 1 has the first head unit 2 and the second head unit 3 fixed to the head frame individually by means of attachments such as screws (not shown) and attached to the head frame so that the whole becomes a long type. Is assembled.

  Thereby, in the thermal print head 1, the first head unit 2 and the second head unit 3 are brought closer to the head frame as much as possible in the sub-scanning direction S2 with the heat generation regions 17 and 28 parallel to the main scanning direction S1. In addition, the pitch of the plurality of heating resistors 12 in the main scanning direction S1 is fixed to be substantially equal in the first head substrate 6 and the second head substrate 26 regardless of their boundary portions. Thus, the thermal print head 1 has the first head unit 2 and the second head unit 3 connected with high accuracy.

  As shown in FIG. 5, the thermal print head 1 is attached to a thermal printer 40 together with a head frame (not shown) to which the first head unit 2 and the second head unit 3 are fixed. The thermal printer 40 rotates around the roller shaft 42 with the platen roller 41 having the roller shaft 42 parallel to the main scanning direction S1 and the outer peripheral surface being in contact with the heat generating regions 17 and 28 of the thermal print head 1. It is provided as possible.

  Then, the thermal printer 40 sandwiches the recording medium P between the platen roller 41 and the heat generation areas 17 and 28 by the rotation of the platen roller 41 during image formation, and sends it in the medium conveyance direction along the sub-scanning direction S2. . At this time, the thermal printer 40 appropriately turns on the plurality of driving ICs 8 with a voltage applied to both ends of each of the plurality of common strip electrodes 16 of the thermal print head 1 by an external power source (not shown).

  As a result, the thermal printer 40 causes a current to flow from both ends of each of the plurality of common strip electrodes 16 to the central portion in the thermal print head 1, and the current is passed from the plurality of common wiring electrodes 15 to every two heating resistors 12, The plurality of individual wiring electrodes 14 and the plurality of driving ICs 8 are sequentially passed to an external power source, and the heat generating portions of the two heat generating resistors 12 are heated. In this way, the thermal printer 40 has the heating part for each of the two heating resistors 12 of the thermal print head 1 while the recording medium P is brought into contact with the heating areas 17 and 28 by the platen roller 41 and is conveyed in the medium conveying direction. By selectively generating heat, a desired image is formed on the surface of the recording medium P.

  By the way, the plurality of driving ICs 8 provided in the thermal print head 1 can be connected to an equal predetermined number of heating resistors 12 and are formed in the same rectangular shape. Further, the plurality of driving ICs 8 have, for example, the length of the end surface along the IC longitudinal direction that is longer than the length in the main scanning direction S1 of the arrangement range of the predetermined number of heating resistors 12 connected to one driving IC 8. Also, a short predetermined length is selected.

  The plurality of driving ICs 8 are arranged on one surface of the first circuit board 7 and one surface of the second circuit board 27 so that the IC longitudinal direction is parallel to the main scanning direction S1, and a predetermined pitch (hereinafter, referred to as the main scanning direction S1). (This is also referred to as an IC pitch). Incidentally, the IC pitch is an interval between the center positions of the plurality of driving ICs 8 in the IC longitudinal direction (hereinafter also referred to as IC center positions). In the following description, a predetermined number of heating resistors 12 connected to one driving IC 8 are collectively referred to as an IC unit heating resistor, and the IC unit heating resistors are arranged along the main scanning direction S1. The range is also called an IC unit resistor arrangement range.

  The number of common strip electrodes 16 provided in the thermal print head 1 is the same as the number of driving ICs 8, and the length in the main scanning direction S 1 is slightly longer than the length of the end face of the driving IC 8. The length is selected. The plurality of common strip-like electrodes 16 are arranged on one surface of the first head substrate 6 and one surface of the second head substrate 26 so as to be arranged at an IC pitch in the main scanning direction S1, so that the central portion is one driving IC 8. Both end portions are opposed to a pair of plus electrodes 20 on both sides of the one driving IC 8.

  In addition, each of the plurality of IC unit heating resistors is connected to one driving IC 8 via a predetermined number of individual wiring electrodes 14, and the one driving unit via a predetermined number of common wiring electrodes 15. It is connected to one common strip electrode 16 facing the IC 8 for use. Incidentally, in the following description, when it is not necessary to distinguish the individual wiring electrode 14 and the common wiring electrode 15, these are also referred to as wiring electrodes. In the following description, a predetermined number of individual wiring electrodes 14 and a predetermined number of common wiring electrodes 15 that connect an IC unit heating resistor to one driving IC 8 and one common strip electrode 16 are integrated into an IC. It is also called a unit wiring electrode.

  However, in the thermal print head 1, unlike the conventional thermal print head, in the first head substrate 6 and the second head substrate 26, the plurality of common strip electrodes 16 have a thickness substantially equal to the thickness of the plurality of common wiring electrodes 15, for example. So as to be relatively thin. For this reason, each of the plurality of common strip electrodes 16 has a relatively large resistance value (hereinafter also referred to as a strip electrode resistance value).

  Therefore, when a current flows from both ends to the center during image formation, a voltage drop (common drop) in which the voltage value gradually decreases from the both ends to the center is generated in the common strip electrode 16. As a result, in the IC unit heating resistor, the value of the current flowing from the common strip electrode 16 to the predetermined number of heating resistors 12 via the predetermined number of common wiring electrodes 15 is located at both ends in the main scanning direction S1. The heating resistor 12 gradually decreases from the heating resistor 12 to the heating resistor 12 located in the center.

  In the IC unit heating resistor, the smaller the value of the current flowing through the heating resistor 12, the smaller the amount of heat generated by the heating section. That is, in the IC unit heat generating resistor, the heat generation amount of the heat generating portion gradually decreases from the heat generating resistor 12 positioned at both ends in the main scanning direction S1 to the heat generating resistor 12 positioned at the central portion.

  For this reason, in the thermal print head 1, when the first head unit 2 and the second head unit 3 are manufactured, a heating element resistance correction process called so-called bit trimming is performed on the plurality of heating resistors 12. As a result, in the thermal print head 1, during the image formation, the heat generation amount of the plurality of heat generating portions is made substantially constant regardless of the value of the current flowing through the plurality of heat generating resistors 12.

  Actually, as shown in FIG. 6, the first head unit 2 is entirely formed in a trapezoidal shape. Therefore, in the first head unit 2, the plurality of driving circuits for the first circuit board 7 are compared with the width in the main scanning direction S1 at one end portion of the head board on which the plurality of heating resistors 12 of the first head board 6 are arranged. The width in the main scanning direction S1 of one end portion of the circuit board on which the IC 8 is arranged is wide.

  Therefore, on one surface of the first circuit board 7, for example, a plurality of driving ICs 8 have a pitch in the main scanning direction S1 of the plurality of IC unit resistor arrangement ranges AR1 (that is, IC unit heating resistors) (hereinafter referred to as IC units). Are also arranged side by side with an IC pitch equal to the resistor pitch). Incidentally, the IC unit resistor pitch is the interval between the center positions of the plurality of IC unit resistor arrangement ranges AR1 (that is, IC unit heating resistors) in the main scanning direction S1 (hereinafter also referred to as IC unit resistor center positions). It is.

  More specifically, a plurality of driving ICs 8 on one surface of the first circuit board 7 are individually centered on the virtual center line L1 parallel to the sub-scanning direction S2 passing through the center position of each IC unit resistor. Are arranged to match. For this reason, the plurality of IC unit wiring electrodes all have the shortest wiring electrodes located near the central virtual line L1.

  Each of the plurality of IC unit wiring electrodes has a wiring electrode position shifted from the central imaginary line L1 in the main scanning direction S1 and each time the wiring electrode position is shifted in the main scanning direction opposite to the main scanning direction S1. However, the length of the wiring electrode at the line target position is equal to the central virtual line L1.

  By the way, in the thermal print head 1, while the heating element resistance value of each heating resistor 12 is about several thousand [Ω], for example, the wiring resistance value of each wiring electrode is compared with about several tens [Ω]. Small. In each of the plurality of IC unit wiring electrodes of the first head unit 2, the length of the wiring electrode gradually increases from the central portion to both ends, and accordingly, the wiring resistance value gradually increases.

  However, in each of the plurality of IC unit wiring electrodes, the difference between the minimum value and the maximum value of the wiring resistance values of the plurality of wiring electrodes is remarkably reduced to about several [Ω]. That is, in the first head unit 2, the wiring resistance values of the plurality of wiring electrodes vary for each IC unit wiring electrode, but the variation in the wiring resistance values of the plurality of wiring electrodes is the value of the current flowing through the plurality of heating resistors 12. The effect on the environment is negligible.

  Therefore, as shown in FIG. 7, in the correction process for correcting the heating element resistance values of the plurality of heating resistors 12 of the first head unit 2, first, the heating element resistances of the plurality of heating resistors 12 are measured by a predetermined resistance measuring instrument. The value (characteristic curve A in FIG. 7) is measured. Further, in the heating element resistance correction process, the strip electrode resistance values of the plurality of common strip electrodes 16 are measured by a resistance measuring device, and the voltage at the time of energization of the plurality of common strip electrodes 16 is determined based on the strip electrode resistance values. Calculate the amount of descent.

  Further, in the heating element resistance value correction process, based on these heating element resistance values and voltage drop amounts, target resistance values (characteristic curves in FIG. 7) that are target values for correction of heating element resistance values for each of the plurality of heating resistor elements 12 are obtained. B). In the heating element resistance correction process, the target resistance value is substantially equal for each IC unit heating resistor in accordance with the voltage drop of each of the plurality of common strip electrodes 16, and actually a predetermined value for each IC unit heating resistor is set. The target resistance values of the number of heating resistors 12 gradually increase in a quadratic function from the center to both ends in the main scanning direction S1.

  In the heating element resistance value correction process, according to the target resistance value of each of the plurality of heating resistors 12, the plurality of heating resistors 12 are crystallized by applying, for example, a resistance value correction pulse for each desired number of times. . Incidentally, the resistance value correction pulse is a pulse having a relatively short pulse width and a relatively large amplitude (that is, a voltage value).

  Thus, in the heating element resistance value correction process, the heating element resistance values of the plurality of heating resistors 12 of the first head unit 2 are corrected to the target resistance value. That is, in the heating element resistance value correction process, for example, since the heating element resistance values at the time of formation of the plurality of heating resistors 12 are relatively varied, the heating element resistance values of the plurality of heating resistors 12 are reduced as a whole. In consideration of the voltage drop amount of the common strip electrode 16, the distribution was corrected so as to have a quadratic function for each IC unit heating resistor.

  On the other hand, as shown in FIG. 8, the entire second head unit 3 is formed in an inverted trapezoidal shape. Therefore, in the second head unit 3, the plurality of driving circuits for the second circuit board 27 are compared with the width in the main scanning direction S1 at one end of the head board on which the plurality of heating resistors 12 of the second head board 26 are arranged. The width in the main scanning direction S1 of one end of the circuit board on which the IC 8 is arranged is narrow. Therefore, on one surface of the second circuit board 27, for example, a plurality of driving ICs 8 are arranged side by side with an IC pitch narrower than the IC unit resistor pitch (that is, the IC pitch is different from the IC unit resistor pitch). Yes.

  More specifically, for example, one driving IC 8 in which the order of arrangement in the main scanning direction S1 is in the middle on one surface of the second circuit board 27 is one in which the order of arrangement in the main scanning direction S1 is in the middle. The IC center positions are arranged on the central imaginary line L1 of the IC unit resistor arrangement range AR1. Incidentally, in the following description, one driving IC 8 in which the order of arrangement in the main scanning direction S1 is in the middle is also referred to as a central driving IC 8 as appropriate, and one IC in which the order of arrangement in the main scanning direction S1 is in the middle. The unit resistor arrangement range AR1 is also referred to as a central IC unit resistor arrangement range AR1 as appropriate.

  Further, on one surface of the second circuit board 27, for example, a plurality of driving ICs (hereinafter also referred to as main scanning side driving ICs) 8 in the main scanning direction S1 from the central driving IC 8 are central IC unit resistors. The IC center position is shifted from the arrangement range AR1 in the direction opposite to the main scanning with respect to the central virtual line L1 of the plurality of IC unit resistor arrangement ranges AR1 in the main scanning direction S1. The plurality of driving ICs 8 in the main scanning direction S1 from the central driving IC 8 are further away from the central driving IC 8 in the main scanning direction S1, and the central virtual line L1 of the plurality of IC unit resistor arrangement ranges AR1 in the main scanning direction S1. The shift amount of the IC center position with respect to is increased.

  Further, on one surface of the second circuit board 27, for example, a plurality of driving ICs (hereinafter also referred to as main scanning opposite side driving ICs) 8 in the direction opposite to the main scanning direction from the central driving IC 8 are provided with a central IC unit resistance. The IC center position is shifted in the main scanning direction S1 from the central virtual line L1 of the plurality of IC unit resistor arrangement ranges AR1 in the direction opposite to the main scanning from the body arrangement range AR1. The plurality of driving ICs 8 in the direction opposite to the main scanning from the central driving IC 8 are separated from the central driving IC 8 in the direction opposite to the main scanning, and the central virtual line L1 of the plurality of IC unit resistor arrangement ranges AR1 in the main scanning opposite direction. The shift amount of the IC center position with respect to is increased.

  For this reason, the IC unit wiring electrode corresponding to the central driving IC 8 is gradually increased in length from the central portion to both ends in the main scanning direction S1 as in the case of the first head unit 2. Yes.

  In addition, the plurality of IC unit wiring electrodes corresponding to the plurality of main scanning side driving ICs 8 have, for example, the shortest length of the wiring electrode located at the end in the opposite direction of the main scanning, and the position of the wiring electrode from the end is the main scanning. Each time the direction S1 is shifted, the lengths of these wiring electrodes are gradually increased. The plurality of IC unit wiring electrodes corresponding to the plurality of main scanning side driving ICs 8 are generally longer in the length of the plurality of wiring electrodes as they are positioned in the main scanning direction S1.

  Further, each of the plurality of IC unit wiring electrodes corresponding to the plurality of driving ICs 8 on the opposite side of the main scanning has, for example, the shortest length of the wiring electrode located at the end in the main scanning direction S1, and the position of the wiring electrode from the end is the main. Each time the scanning direction shifts, the lengths of these wiring electrodes are gradually increased. The plurality of IC unit wiring electrodes corresponding to the plurality of main scanning opposite-side driving ICs 8 are generally longer in the length of the plurality of wiring electrodes as they are positioned in the opposite main scanning direction.

  By the way, as shown in FIG. 9, the IC unit wiring electrode corresponding to the central driving IC 8 has a wiring resistance value that gradually increases with the length of the wiring electrode from the center to both ends in the main scanning direction S1, The difference between the minimum value and the maximum value of these wiring resistance values is as small as several [Ω]. On the other hand, the wiring resistance values of the plurality of IC unit wiring electrodes corresponding to the plurality of main scanning side driving ICs 8 increase as the wiring electrodes are positioned away from the end in the main scanning opposite direction in the main scanning direction S1. ing. Also, the wiring resistance values of the plurality of IC unit wiring electrodes corresponding to the plurality of main scanning opposite side driving ICs 8 are larger as the wiring electrodes are located away from the end in the main scanning direction S1 in the main scanning opposite direction.

  However, as for the plurality of IC unit wiring electrodes corresponding to the plurality of main scanning side driving ICs 8, the wiring resistance values of the plurality of wiring electrodes generally increase as they are positioned in the main scanning direction S1. Actually, among these, the IC unit wiring electrode located at the end in the main scanning direction S1 has an overall wiring resistance value of 50 as compared with the IC unit wiring electrode corresponding to the central driving IC 8. It has increased to about [Ω].

  In addition, the plurality of IC unit wiring electrodes corresponding to the plurality of main scanning opposite side driving ICs 8 are located in the opposite direction of the main scanning, and the wiring resistance values of the plurality of wiring electrodes generally increase. Actually, among these, the IC unit wiring electrode positioned at the end in the main scanning opposite direction has a wiring resistance value of the plurality of wiring electrodes as a whole as compared with the IC unit wiring electrode corresponding to the central driving IC 8. It has increased to about [Ω].

  In the second head unit 3, when the wiring resistance value of the plurality of wiring electrodes for each IC unit wiring electrode varies in the range of about 50 [Ω], the variation in the wiring resistance values of the plurality of wiring electrodes is as follows. The value of the current flowing through the plurality of heating resistors 12 varies. That is, in the second head unit 3, the larger the wiring resistance value of the wiring electrode, the lower the current flowing through the heating resistor 12 connected thereto as well as the value of the current flowing through the wiring electrode.

  For this reason, as shown in FIG. 10, in the correction process for correcting the heating element resistance values of the plurality of heating resistors 12 of the second head unit 3, first, as in the case of the first head unit 2 described above, a plurality of heating elements are generated. The resistance value of the heating element of the resistor 12 (characteristic curve C in FIG. 10) is measured. Further, in the heating element resistance value correction process, as in the case of the first head unit 2 described above, the amount of voltage drop when the plurality of common strip electrodes 16 are energized is calculated.

  Further, in the heating element resistance correction process, as in the case of the first head unit 2 described above, the target resistance value of each of the plurality of heating resistors 12 is obtained based on the heating element resistance value and the voltage drop amount. Also in this case, in the heating element resistance value correction process, the target resistance values are substantially equal for each IC unit heating resistor, and the target resistance values of the predetermined number of heating resistors 12 for each IC unit heating resistor are actually It gradually increases in a quadratic function from the center to both ends in the main scanning direction S1.

  However, in the heating element resistance value correction process, the wiring resistance values of a plurality of wiring electrodes are measured for each IC unit wiring electrode by a resistance measuring instrument. In the heating element resistance correction process, for example, an approximate value of a difference between the wiring resistance value of the wiring electrode located at the center of the IC unit wiring electrode corresponding to the central driving IC 8 and each of the wiring resistance values of the plurality of wiring electrodes ( A characteristic curve D) in FIG. 10 is obtained as a correction wiring resistance value used for correcting the target resistance value.

  Further, in the heating element resistance value correction process, for example, the correction wiring resistance value of the corresponding wiring electrode is subtracted from the target resistance value of the plurality of heating resistors 12 to obtain the target resistance value of the plurality of heating resistors 12. to correct. In the heating element resistance correction process, the plurality of heating resistors 12 are changed according to the corrected target resistance value (characteristic curve E in FIG. 10) which is the corrected target resistance value of each of the plurality of heating resistors 12. Each resistance value correction pulse is applied a desired number of times for crystallization.

  Thus, in the heating element resistance value correction process, the heating element resistance values of the plurality of heating resistors 12 of the second head unit 3 are corrected so as to be substantially the corrected target resistance value. That is, in the heating element resistance value correction process, for example, since the heating element resistance values at the time of formation of the plurality of heating resistors 12 are relatively varied, the heating element resistance values of the plurality of heating resistors 12 are reduced as a whole. In consideration of the voltage drop amount of the common strip electrode 16 and the variation of the wiring resistance values of the plurality of wiring electrodes, the distribution becomes a quadratic function for each IC unit heating resistor, and the plurality of heating resistances as a whole. The distribution was corrected so as to gradually decrease from the center portion to both ends of the arrangement portion of the body 12.

  In this way, the thermal print head 1 is formed so that the amount of heat generated by the plurality of heating portions is substantially constant regardless of the value of the current flowing through the plurality of heating resistors 12 during image formation. In particular, in the thermal print head 1, even if the values of the currents flowing through the plurality of heating resistors 12 vary due to variations in the wiring resistance values of the plurality of wiring electrodes as in the second head unit 3, The calorific value can be made almost constant.

  In the above configuration, in the thermal print head 1, the first head unit 2 that is alternately arranged in the main scanning direction S <b> 1 is formed in a trapezoidal shape, and the second head unit 3 is formed in an inverted trapezoidal shape. In the first head unit 2, a plurality of heating resistors 12 are arranged on one side in the main scanning direction S1, and a plurality of driving ICs 8 and a plurality of common strip electrodes 16 are respectively provided in the main scanning direction S1 with IC unit resistances. A plurality of wiring electrodes for arranging the plurality of heating resistors 12 with the plurality of driving ICs 8 and the plurality of common strip electrodes 16 are arranged with an IC pitch equal to the body pitch.

  Further, in the second head unit 3, a plurality of heating resistors 12 are arranged side by side in the main scanning direction S1, and a plurality of driving ICs 8 and a plurality of common strip electrodes 16 are respectively provided in the main scanning direction S1 as IC unit resistances. A plurality of wiring electrodes for arranging the plurality of heating resistors 12 with a plurality of driving ICs 8 and a plurality of common strip electrodes 16 are arranged side by side with an IC pitch different from the body pitch.

  In the first head unit 2, the heating element resistance value correction process is performed on the plurality of heating resistors 12 according to the voltage drop that occurs when the plurality of common strip electrodes 16 are energized. Further, in the second head unit 3, the heating element resistance values are corrected in the plurality of heating resistors 12 according to the voltage drop generated when the plurality of common strip electrodes 16 are energized and the variation in the wiring resistance values of the plurality of wiring electrodes. Treated.

  According to the above configuration, when the thermal print head 1 is provided in the thermal printer 40 to form an image, a plurality of heat generating portions are caused to generate heat, regardless of variations in current values flowing through the plurality of heat generating resistors 12. It is possible to generate heat with substantially constant. Thereby, the thermal print head 1 can form a high-quality image without causing printing unevenness on the recording medium P.

  In the above-described embodiment, in the second head unit 3 of the long thermal print head 1, the voltage drop generated when the plurality of heating resistors 12 are energized to the plurality of common strip electrodes 16 and the plurality of wiring electrodes. The case where the heating element resistance value correction process is performed according to the variation in the wiring resistance value has been described. However, the present invention is not limited to this. For example, in the thermal print head 50 shown in FIG. 11, the plurality of heating resistors 12 may be subjected to the heating element resistance correction process in the same manner as the second head unit 3. .

  That is, according to the present invention, a plurality of heating resistors 12 are arranged side by side in the main scanning direction S1 on one surface of the thermal trapezoidal (or rectangular) thermal print head 50 as a whole. The present invention also includes a plurality of driving ICs 51 having a length of an end surface along the IC longitudinal direction on one surface of the thermal print head 50 that is equal to or longer than the length of the main unit scanning direction S1 of the IC unit resistor arrangement range. Strip electrodes (not shown) are arranged in the main scanning direction S1 at an IC pitch different from the IC unit resistor pitch (that is, an IC pitch wider than the IC unit resistor pitch).

  In the present invention, a plurality of wiring electrodes 52 that connect the plurality of heating resistors 12 to the plurality of driving ICs 51 and the plurality of common strip electrodes may be disposed on one surface of the thermal print head 50. According to the present invention, according to the thermal print head 50, the wiring resistance value varies with the lengths of the plurality of wiring electrodes 52 due to such a configuration, and therefore, the plurality of heating resistors 12 as in the case of the second head unit 3 described above. By performing the heating element resistance value correction processing on the plurality of heating portions, even if the values of the currents flowing through the plurality of heating resistors 12 vary due to variations in the wiring resistance values of the plurality of wiring electrodes, The calorific value can be made almost constant.

  In the above-described embodiment, the case where the plurality of common strip electrodes 16 provided in the second head unit 3 and the thermal print head 50 are formed relatively thin has been described. However, the present invention is not limited to this, and the plurality of common strip electrodes 16 provided in the second head unit 3 and the thermal print head 50 are formed relatively thick to reduce the strip electrode resistance value, thereby reducing the voltage drop during energization. You may let them. According to the present invention, with respect to the number of heating resistors 12 of the number of the second head units 3 and the thermal print heads 50, the heating element resistance values of the plurality of wiring electrodes depend only on the variation of the wiring resistance values. Correction processing can be performed.

  In addition, in the present invention, for example, a plurality of driving ICs 8 and 51 are arranged on the one surface of the second head unit 3 or the thermal print head 50 in the main scanning direction S1 at an IC pitch different from the IC unit resistor pitch. However, only one common strip electrode that is relatively longer than the common strip electrode 16 is disposed. Further, according to the present invention, one end of the plurality of heating resistors 12 is connected to one common strip electrode without arranging the plurality of folded electrodes 13 on one surface of the second head unit 3 or the thermal print head 50. A plurality of common wiring electrodes having the same length are disposed, and a plurality of individual wiring electrodes 14 having different lengths are connected to connect the other end portions of the plurality of heating resistors 12 to the plurality of driving ICs 8 and 51. You may do it.

  In the second head unit 3 and the thermal print head 50 configured as described above, when the common strip electrode is formed relatively thin, the voltage drop generated when the common strip electrode is energized with respect to the plurality of heating resistors 12. Further, the heating element resistance value correction process may be performed according to the wiring resistance value variations of the individual wiring electrodes 14. In the second head unit 3 and the thermal print head 50 having such a configuration, the common strip electrode is formed to be relatively thick to reduce the strip electrode resistance value, thereby reducing the voltage drop during energization. The heating resistor 12 may be subjected to a correction process of the heating element resistance value according to variations in the wiring resistance values of the plurality of individual wiring electrodes 14. According to the present invention, even with such a configuration, the heat generation amounts of the plurality of heat generating portions can be made substantially constant.

  Furthermore, in the above-described embodiment, in the correction processing for correcting the heating element resistance values of the plurality of heating resistors 12 of the second head unit 3, the target resistance value of each of the plurality of heating resistors 12 is set for each wiring electrode. The case where correction is made by subtracting the correction wiring resistance value obtained in the above has been described. However, the present invention is not limited to this, and in the correction processing for correcting the heating element resistance values of the plurality of heating resistors 12 of the second head unit 3, the target resistance value of each of the plurality of heating resistors 12 is set to the wiring electrode. You may correct | amend by subtracting the measured value of every wiring resistance value.

  Further, in the above-described embodiment, the case where a plurality of driving ICs 8 are arranged on one surface of the first circuit board 7 and one surface of the second circuit board 27 has been described. However, the present invention is not limited to this, and a plurality of driving ICs 8 may be disposed on one surface of the first head substrate 6 and one surface of the second head substrate 26.

  The present invention can be used for a thermal printer such as a digital plate making machine, a video printer, an imager, and a seal printer, and a thermal print head provided in the thermal printer.

  DESCRIPTION OF SYMBOLS 1 ... Thermal print head, 2 ... 2nd head unit, 8, 51 ... Driving IC, 12 ... Heating resistor, 14 ... Individual wiring electrode, 15 ... Common wiring electrode, 16 ... Common belt shape Electrode, 26... Second head substrate, 27... Second circuit board, 40... Thermal printer, 50.

Claims (4)

A substrate,
A plurality of heating resistors arranged side by side in the main scanning direction on one surface of the substrate;
A predetermined number of the heating resistors can be connected to each other, and a plurality of the heating resistors arranged side by side at a different pitch from the pitch of the predetermined number of the heating resistors in the main scanning direction on the one surface of the substrate. A control element of
A plurality of individual wiring electrodes arranged between the plurality of heating resistors and the plurality of control elements on the one surface of the substrate, and connecting the plurality of heating resistors and the plurality of control elements;
The plurality of heating resistors are
A thermal print head subjected to a correction process for correcting the heating element resistance value according to the wiring resistance values of the plurality of individual wiring electrodes. A plurality of common strip electrodes arranged on the one surface of the substrate in the main scanning direction at a pitch equal to the pitch of the control elements;
A plurality of common wiring electrodes arranged between the plurality of heating resistors and the plurality of common strip electrodes on the one surface of the substrate and connecting the plurality of heating resistors and the plurality of common strip electrodes; Prepared,
The plurality of heating resistors are
The thermal print head according to claim 1, wherein a correction process is performed to correct the heating element resistance value according to a wiring resistance value of the plurality of individual wiring electrodes and a wiring resistance value of the plurality of common wiring electrodes. The plurality of heating resistors are
Correction processing for correcting the heating element resistance value according to a voltage drop generated when energizing the plurality of common strip electrodes, a wiring resistance value of the plurality of individual wiring electrodes, and a wiring resistance value of the plurality of common wiring electrodes The thermal print head according to claim 2. A substrate, a plurality of heating resistors arranged side by side in the main scanning direction on one surface of the substrate, and a predetermined number of the heating resistors can be connected to each other, and the one surface of the substrate is connected to the main scanning direction in the main scanning direction. Between a plurality of control elements arranged side by side at a pitch different from the pitch of the arrangement range of the predetermined number of the heating resistors, and between the plurality of heating resistors and the plurality of control elements on the one surface of the substrate A plurality of individual wiring electrodes arranged to connect the plurality of heating resistors and the plurality of control elements, and the plurality of heating resistors according to the wiring resistance values of the plurality of individual wiring electrodes. A thermal printer that has a thermal printhead that has been subjected to correction processing to correct the heating element resistance.

Images