JP2776089B2 - Method and apparatus for adjusting resistance value of thermal head - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for adjusting a resistance value of a thermal printer used as an output device of a word processor, a personal computer or the like, and a thermal head used for a recording section of a facsimile apparatus.

[0002]

2. Description of the Related Art Printing apparatuses using a thermal head have been widely used because they have advantages such as low noise at the time of printing, unnecessary development and fixing steps, and easy handling.

FIG. 9 shows a main part of a thermal head. In FIG. 9, 5 is a dot resistor, 7 is a thermal head,
8 is a common electrode and 9 is an individual electrode. Dot resistor 5,
The common electrode 8 and the individual electrode 9 are formed on an insulating substrate (not shown). 1 between the common electrode 8 and one individual electrode 9
Two dot resistors 5 are provided. The dot resistor 5 is a heating resistor, and generates heat when a current flows from the common electrode 8 to the dot resistor 5 to the individual electrode 9.

[0004] One dot resistor 5 corresponds to one dot at the time of printing, and the dot is printed in black, for example, by the heat generated by the dot resistor 5. Which dot resistor 5 is energized depends on the content to be printed.

Since power is supplied to each dot resistor 5 from the same common electrode 8, if the resistance value between the dot resistors 5 is different, the amount of heat generated also differs. The dots printed by the dot resistor 5 having a large heat value are dark black, while the dots printed by the dot resistor 5 having a small heat value are light black. Occurs.

When the dot resistor 5 is formed by using a thin film technique such as sputtering, the resistance value can be made uniform, but there is a disadvantage that productivity is low.
In contrast, thick film technology is inexpensive and has high productivity. But,
If the dot resistor 5 is formed using a thick film technique such as screen printing, the resistance value of the dot resistor 5 is not uniform, and density unevenness occurs. Therefore, the resistance value of the dot resistor 5 is adjusted to be substantially the same.

One of the conventional resistance value adjustment methods is as follows.
There is a pulse trimming method (see JP-A-61-83053). This is a method of adjusting the resistance value by applying an electric field within a range that does not cause thermal destruction to the dot resistor 5 by utilizing the property that when an electric field is applied, the resistance value decreases in accordance with the intensity of the electric field. is there. According to this method, the variation of the resistance value of the dot resistor 5 constituting the thermal head is reduced.
It can be adjusted to within the range of ± 3%.

As a method of manufacturing the dot resistor 5 by using the thick film technology, a method has been proposed in which the resistance value can be further uniformed and the dot density can be increased. that is,
For example, the MOD method disclosed in JP-A-1-220402 (Metallo-Organic Deposition). In the MOD method, first, a metal organic resistor material is applied to the surface of an insulating substrate by a coating technique such as screen printing, roll coating, or the like, and then fired to form a dot resistor 5.
When formed by the MOD method, the adjacent dot resistor 5
There is little variation in resistance value between the two. However, it is unavoidable that a certain thickness unevenness occurs when applying the metal organic resistor material, and it is difficult to keep the variation of the resistance value within a range narrower than ± 5% in the entire thermal head. there were.

However, in high-quality printing in which halftones are also displayed, it is required that the variation in resistance value be ± 1% or less in order to make the heat generation of each dot resistor 5 uniform. As a method satisfying the demand, a laser trimming method is known in which a part of the dot resistor 5 is irradiated with a laser to scrape (cut) and equalize the resistance value.

FIG. 10 is a view for explaining conventional laser trimming for the dot resistor 5. 6 is a laser irradiation region, L is irradiated length, the L _T dot resistance body, W is irradiation width, W _T is a dot resistor width. This figure shows a state where the laser is irradiated to the dot resistor 5 by the irradiation width W and the irradiation length L. At the laser irradiation area 6,
The resistor material of the dot resistor 5 is scraped off.

FIG. 11 is a diagram showing the relationship between the laser irradiation width and the rate of change in resistance when cutting the dot resistor. FIG. 11A is a diagram showing general characteristics.
The larger the irradiation area, the larger the area to be cut,
This indicates that the resistance value change rate of the dot resistor also becomes large. FIG. 11B is a specific example as described later.

FIG. 12 is a diagram showing a conventional thermal head resistance adjusting device by laser trimming. In FIG. 12, 1 is a dot resistance detection unit, 2 is a target resistance value setting unit, 3 is a comparison unit, 4 is a laser irradiation control unit, and 5 is a dot resistor. The resistance value of the dot resistor 5 is detected by the dot resistance value detection unit 1, and the detected value is compared with the target resistance value setting unit 2 by the comparison unit 3. The target resistance value setting unit 2 includes:
Set the target resistance value that you want to adjust by adjustment. The laser irradiation control unit 4 gradually raises the resistance value while emitting a laser to burn off (cutting) a part of the dot resistor 5. When the comparison result in the comparison section 3 becomes zero, that is, when the resistance value of the dot resistor 5 being burned out matches the target resistance value, laser irradiation is stopped.

FIG. 13 shows how the resistance value is adjusted by the above-described conventional laser trimming. The horizontal axis indicates the dot number for distinguishing the individual dot resistors 5, and the vertical axis indicates the resistance value of the dot resistor 5. In this example, the resistance value of each dot resistor 5 constituting the thermal head is assumed to have varied within the range of ± 10% around the resistance value R _0. In the figure, a dotted line A indicates a + 10% level (resistance value 1.1R ₀ ), a dotted line B indicates a 0% level (resistance value R ₀ ), and a dotted line C indicates a -10% level (resistance value 0. 0).
9R ₀ ).

Since the adjustment of the resistance value by laser trimming is performed by increasing the resistance value, the target resistance value is set to a value equal to or higher than the maximum value of the resistance values of the dot resistors that are varied. If the value of the level indicated by the dotted line A (1.1R
_{When 0} is set, the dot resistor of dot number 2 is raised by ΔR _2, which is the difference from 1.1R ₀ , by laser trimming. This ΔR ₂ is the resistance correction amount for the dot resistor of dot number 2. Similarly, the resistance correction amount for the dot resistor of dot number 4 is ΔR _4, and the resistance correction amount for the dot resistor of dot number 7 is ΔR ₇ . In this way, the variation of the resistance value is made ± 1% or less.

[0015]

[Problems to be solved by the invention]

(Problem) However, in the conventional laser trimming described above, there is a problem that a large variation occurs in the cutting amount between the dot resistors, thereby deteriorating the print quality.

(Explanation of Problems) In laser trimming, adjustment can be made only in the direction of increasing the resistance value. Therefore, in a dot resistor having a low original resistance value such as the dot number 7 in FIG. 13, the cutting amount by the laser is very large, but in a dot resistor having a high original resistance value such as the dot number 4, It will be hardly cut. If the cutting amount is different, the heat generating surface area of the dot resistor 5 is different, so that the size of each dot when printing is different. In this case, the image quality deteriorates, and it becomes impossible to display a high quality halftone.

An object of the present invention is to solve such a problem.

[0018]

[0019]

[0020]

Means for Solving the Problems In order to solve the above problems, the present
According to the invention, a method of adjusting the resistance value of a thermal head that irradiates a laser to each dot resistor constituting a thermal head to adjust the resistance value to a target resistance value is a method for adjusting the resistance value of each dot resistor element.
The period resistance measured respectively, to set the target resistance value below the minimum value among the initial resistance value of each dot resistor is irradiated with a laser only at power to lower the resistance value, each of
Irradiation was stopped when the resistance value of the dot resistor reached the target resistance value.

[0021] Along with this, the dot resistance value detector for detecting the resistance value of each <br/> dot resistors constituting the thermal head respectively, the lowest among the target resistance value initial resistance value of each dot resistors A target resistance value setting unit that sets
A comparison unit that compares the detected resistance value of each of the dot resistors with the target resistance value, and according to a comparison result in the comparison unit.
Only before lowering the resistance value of each dot resistor
A laser power selecting unit for selecting a laser power to be applied to each resistor and a laser emitting unit for emitting a laser with the selected laser power can be provided.

Further, the method of adjusting the resistance value of the thermal head for irradiating a laser to each dot resistor constituting the thermal head and adjusting the resistance value to the target resistance value is described in the above-mentioned dot resistance.
Measure the initial resistance value of each antibody and calculate the target resistance value as described above.
The initial resistance value of each dot resistor is set to be equal to or less than the minimum value, and only the laser power within the range of decreasing the resistance value of the dot resistor according to the difference from the target resistance value is selected and the irradiation width is selected. Is determined, and the resistance value can be adjusted by irradiating the dot resistor with the irradiation width for a predetermined length.

[0023] Along with this, the dot resistance value detector for detecting the resistance value of each <br/> dot resistors constituting the thermal head, respectively, the initial resistance of the target resistance value of each of the dot resistors
A target resistance value setting unit that sets the value to be equal to or less than the minimum value of the values ,
A comparator for outputting a difference compared detected the resistance value of each dot resistors and said target resistance, only laser power is within the range of lowering the resistance value of the dot resistors in accordance with said difference A laser power selection unit for selecting a laser power to be selected, an irradiation width determination unit for determining an irradiation width according to the difference, and a laser emitting unit for emitting a laser with the selected laser power and the determined irradiation width. In other words, the surface of the dot resistor can be irradiated for a predetermined length.

[0024]

[0025]

[0026]

When setting the [action] target resistance value is set to be lower than the minimum value of the resistance value of the dot resistors are varied, only by using a laser power in the range of lowering the resistance value to adjust the resistance value You can do it. In the irradiation in this case, since the dot resistor is not cut, the uniformity of the printed dots is further improved.

[0027]

【Example】

(First Embodiment) An embodiment of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a view showing a thermal head resistance value adjusting device according to a first embodiment of the present invention. Reference numerals correspond to those in FIG. 12, 4-1 is a laser power selection unit, and 4-2 is a laser emission unit. The invention is based on the discovery that the resistance of the dot resistor 5 can be reduced if the power of the irradiating laser is within a certain range.

FIG. 2 is a graph showing the relationship between the laser power and the rate of change in resistance when a dot resistor is irradiated with a laser. A to D are points on the characteristic curve. If the power of the laser that irradiates the dot resistor (specifically, the laser excitation lamp input current) is gradually increased,
The resistance value of the dot resistor does not change up to a certain laser power P _A (point A) (resistance change rate = 0%). If it exceeds that, it first starts to fall (the resistance value change rate becomes negative).

[0029] As you further increasing the laser power, after the maximum negative value (point B), the degree of negative went smaller, eventually some laser power P _C by the resistance value change rate is 0% Return (point C). The laser power P _C
If it is larger, the irradiated portion will be burned off, and the resistance value change rate of the dot resistor becomes positive (point D). The reason why the resistance value falls in a certain laser power range is presumed to be that the laser light in that range has a strength that is convenient for transforming the dot resistor into a material having a small resistance value. .

FIG. 3 is a diagram showing a specific example of the relationship between the laser power and the rate of change of the resistance value when the dot resistor is irradiated with a laser. FIG. 3A shows the dot resistor width W _T.
= 78 .mu.m, an example in which with respect to the dot resistors size of the dot resistance body L _T = 160 .mu.m, was irradiated by a dot resistance body L _T by irradiation width W = 26 .mu.m, 3 (b)
Is an example in which the same dot resistor is irradiated with an irradiation width W = 13 μm. In each case, irradiation is performed by applying a filter that cuts 32% of the laser beam (the laser does not provide a stable output in a low power region, and therefore has a high power region in which a stable output is obtained). And then use the filter to reduce the required power).

FIG. 4 is a diagram showing the relationship between the laser irradiation width and the resistance value change rate when the laser irradiation is performed at a laser power at which the resistance value change rate is negative. FIG. 4A shows a general tendency, and the degree of negative change in the resistance value also increases substantially in proportion to the irradiation width. FIG.
(B) shows a specific example, which is a laser power of a laser excitation lamp input current of 13 A. For a dot resistor having a dot resistor width W _T = 78 μm and a dot resistor length L _T = 160 μm, shows the relationship when irradiated by dot resistance body L _T. According to this, for example, when the irradiation width is 19 μm, the resistance value can be reduced by 10%.

In the conventional laser trimming, as shown in FIG. 2, the adjustment has been performed using the range to the left of point C (the range of positive change in resistance value). In the first embodiment of the present invention, the following values are used together to equalize the resistance values of the dot resistors constituting the thermal head. For a dot resistor having a resistance value larger than the target resistance value, the resistance value is reduced using the range between the points A and C (the range in which the resistance value change rate is negative) in FIG. For a dot resistor having a resistance value smaller than the target resistance value, the resistance value is increased using the range to the left of point C in FIG. 2 (a range in which the resistance value change rate is positive).

That is, in the first embodiment, a first laser power used to lower the resistance value and a second laser power used to increase the resistance value are determined in advance (for example, FIG. 2, the first laser power = P
_B , the second laser power = P _D ). Then, one of them is selected by the laser power selection unit 4-1.

Next, the operation of each unit in FIG. 1 will be described step by step. FIG. 5 is a diagram showing how the resistance value is adjusted in the first embodiment of the present invention. The coordinate axes and signs are shown in FIG.
It corresponds to the thing. The dot resistance detector 1 detects the resistance value of one dot resistor to be adjusted. Detection is also performed during adjustment of the resistance value. The black circles plotted in FIG. 5 represent the resistance values detected before the adjustment.

The resistance value of each dot resistors, optionally the resistance value R ₀ at the center and varies in the range of ± 10%, variations in the center of the dotted line b-level (resistance value R ₀₎ in the target resistance Set. The comparison unit 3 determines whether the resistance value detected by the dot resistance detection unit 1 is larger or smaller than the target resistance value.

As a result of the comparison, when the resistance value is smaller than the target resistance value, such as the dot resistor of dot number 2 in FIG. 5, the laser power selection unit 4-1 increases the second laser power to increase the resistance. Select (P _D ). A laser is emitted from the laser emitting section 4-2 with the power selected by the laser power selecting section 4-1.
Is irradiated. The resistance value adjustment in this case is performed by cutting a part of the dot resistor 5 as in the conventional laser trimming. The resistance value is measured during cutting, and irradiation is stopped when the resistance value becomes equal to the target resistance value. The resistance value is raised by ΔR ₂ to be R _0, and this ΔR ₂ is the resistance correction amount in this case.

Conversely, when the resistance value is larger than the target resistance value, such as the dot resistor of dot number 4, the first laser power (P _B ) for lowering the resistance is set by the laser power selector 4-1. Select Irradiation is stopped when the resistance value is reduced by the resistance correction amount ΔR ₄ and becomes equal to the target resistance value. Adjustment is similarly made for other dot resistors.

FIG. 6 is a diagram showing an example of how a dot resistor is irradiated with a laser. The reference numerals correspond to those in FIG. 10, and 6A is a laser irradiation area. When irradiating a laser in the first embodiment, any of FIGS. 6A to 6C may be employed. 6A and 6B show a method in which the irradiation width W is fixed and the irradiation length L is changed. If the irradiation width W is determined widely as in (a), the irradiation length L is short. If the width is determined to be narrow as shown in (b), the laser irradiation area 6 may have a length of going back and forth many times.

[0039] Figure 6 (c), the irradiation length L are those equal to the dot resistance body L _T, the irradiation width in Toka W ₁ Toka W ₂ in accordance with the resistance correction amount. In addition, their irradiation width is
The determination is made with reference to the relationship between the laser irradiation width and the resistance value change rate shown in FIG. 4 (when the resistance value is reduced) and FIG. 11 (when the resistance value is increased).

FIG. 11B is a diagram showing a specific example of the characteristic curve of FIG. That is, for a dot resistor 5 having a dot resistor width W _T = 78 μm and a dot resistor length L _T = 160 μm, 32% is applied to a laser having a laser excitation lamp input current of 16 A and a laser power of 16 A.
This is the characteristic when irradiating with a filter that cuts the light.

(Second Embodiment) In the first embodiment, a laser having a laser power for increasing the resistance value of the dot resistor and a laser having a laser power for decreasing the resistance are used together. It can be adjusted using only the laser. The block diagram is the same as that of FIG.
Is different in that only the laser power within the range of points A to C in FIG. 2 is selected.

Even if the laser power is in the range of points A to C in FIG. 2, the resistance value change rate differs depending on the value of the laser power. Therefore, a plurality of laser powers that can be selected can be determined or a single type can be determined. The comparison unit 3 compares the detected resistance value with the target resistance value to determine a difference, and selects a laser power according to the difference. However, when only one type of candidate is prepared, the same laser is always used. It means power. When multiple types are prepared, it is conceivable to switch the laser power one after another as the difference in resistance value decreases due to irradiation, but to avoid complicated control, the selection of the laser power is It may be performed only once according to the initial difference.

FIG. 8 is a diagram showing how the resistance value is adjusted in the second embodiment. The reference numerals correspond to those in FIG. In the second embodiment, the resistance value is adjusted by lowering the resistance value.
The target resistance value is equal to or less than the minimum value of the resistance values of the dot resistors that are varied (for example, the level indicated by the dotted line C...
₀ ).

The resistance value of the dot resistor to be adjusted is continuously detected during irradiation, and irradiation is stopped when the resistance value matches the target resistance value. As a result, the dot resistor of dot number 2 is reduced by ΔR ₂ to 0.9R ₀ , and the dot resistor of dot number 6 is reduced by ΔR ₆ to 0.9R ₀ . According to this embodiment, since the dot resistor is not cut, there is no variation in the heat generation area, and the image quality is improved.

(Third Embodiment) FIG. 7 is a view showing an apparatus for adjusting the resistance value of a thermal head according to a third embodiment of the present invention. Reference numerals correspond to those in FIG. 1, and reference numeral 4-3 denotes an irradiation width determination unit. In this embodiment, the resistance value is adjusted only by irradiating a predetermined length of laser light with a laser power within a range for lowering the resistance value of the dot resistor. Predetermined length can be determined arbitrarily, for example, it may be a dot resistance body L _T.

When the laser power is set to a certain power in the range of points A to C in FIG.
As shown in (1), the rate of change in resistance changes according to the laser irradiation width. Assuming that the irradiation width is W and the resistance value change rate is −20%, the variation within the range of 20% can be adjusted without cutting which deforms the heating area. The characteristic curve of Figure 4, from the upper end of the dot resistors to the lower end, a characteristic curve obtained when irradiated throughout dot resistance body L _T.

FIG. 8 is a diagram also showing how the resistance value is adjusted in the third embodiment of the present invention. The code is shown in FIG.
It corresponds to three. The resistance value of the dot resistor is ±
The variation is in the range of 10% (that is, in the range of 20%). Therefore, by selecting a laser power in a range in which the resistance value is reduced, and by adopting an adjustment method of changing the resistance value in a decreasing direction, if there is an irradiation width in which the resistance value change rate is reduced to −20%, it is possible to obtain any dot. The resistance value of the resistor can be set to the same value.

In this case, the target resistance value is equal to or less than the minimum value of the scattered resistance values.
It will be set to ₀ . When adjusting the resistance value of the dot resistor of the dot number 2, first, the resistance value is detected by the dot resistance value detection unit 1 of FIG. 7 and the comparison unit 3 sets the target resistance value of the target resistance value setting unit 2 ( 0.9R ₀ ). In the third embodiment, instead of simply checking whether the resistance value is larger or smaller than the target resistance value, the difference value is determined to some extent. In the case of dot number 2, the difference is determined to be large by ΔR ₂ .

Based on this, the laser power selection unit 4-
In step 1, an appropriate laser power is selected from predetermined laser powers within a range in which the resistance value is reduced. As can be easily understood from the change in the curves at points A to C in FIG. 2, the resistance value change rate differs depending on the laser power, and the characteristic curve corresponding to FIG. Are also slightly different. Therefore, even if the irradiation width is the same, the amount of resistance to be reduced differs depending on the value of the laser power used. Therefore, a plurality of types of laser powers that can be selected may be determined.
You may decide on the type.

The irradiation width determination unit 4-3 determines the irradiation width according to the difference from the target resistance value while referring to the characteristics in FIG. 4 corresponding to the selected laser power. The laser emitting unit 4-2 emits a laser with the above laser power and irradiation width, and irradiates the dot resistor 5 of the dot number 2. As a result, its resistance is reduced by ΔR ₂ to 0.9R ₀ . Similar irradiation is performed on the other dot resistors 5 so that the resistance value is adjusted to 0.9R ₀ . In the third embodiment, since cutting is not performed, the surface area of the dot resistor is not deformed, uniformity of the printed dots is maintained, and high image quality is obtained.

Incidentally, in the third embodiment shown in FIG.
As described above, the resistance value of the dot resistor 5 is not measured and fed back during the irradiation. This is because, when determining the irradiation width with reference to FIG. 4, the desired resistance value is predicted with considerable accuracy. However, needless to say, feedback control can be performed if necessary.

[0052]

[0053]

[0054]

As described above, the thermal head of the present invention is used.
According to the method and apparatus for adjusting the resistance value of the resistor, the target resistance value is set to be equal to or less than the minimum value of the resistance value of the dot resistor that is varied, and only the laser power within the range of decreasing the resistance value is used. When the value is adjusted, the dot resistor is not cut, so that the image quality is further improved.

[Brief description of the drawings]

FIG. 1 is a diagram showing a resistance adjusting device for a thermal head according to a first embodiment of the present invention.

FIG. 2 is a diagram showing the relationship between laser power and the rate of change in resistance when a dot resistor is irradiated with laser.

FIG. 3 is a diagram showing a specific example of the relationship between laser power and the rate of change in resistance when a dot resistor is irradiated with laser.

FIG. 4 is a diagram showing a relationship between a laser irradiation width and a resistance value change rate when irradiation is performed with a laser power having a negative resistance value change rate.

FIG. 5 is a diagram showing how the resistance value is adjusted in the first embodiment of the present invention.

FIG. 6 is a diagram showing an example of a method of irradiating a laser to a dot resistor.

FIG. 7 is a diagram showing a thermal head resistance value adjusting device according to a third embodiment of the present invention.

FIG. 8 is a diagram showing a state where the resistance value is adjusted in the second embodiment and the third embodiment of the present invention.

FIG. 9 is a diagram showing a main part of a thermal head.

FIG. 10 is a view for explaining conventional laser trimming for a dot resistor.

FIG. 11 is a diagram showing a relationship between a laser irradiation width and a resistance value change rate when cutting a dot resistor.

FIG. 12 is a view showing a conventional thermal head resistance adjusting device by laser trimming;

FIG. 13 is a diagram showing a state where a resistance value is adjusted by conventional laser trimming.

[Explanation of symbols]

1. Dot resistance value detection unit, 2. Target resistance value setting unit, 3.
Comparison section, 4 ... laser irradiation control section, 4-1 ... laser power selection section, 4-2 ... laser emission section, 4-3 ... irradiation width determination section, 5 ... dot resistor, 6,6A ... laser irradiation area, 7 ... thermal head, 8 ... common electrode, 9 ... individual electrodes, L ... irradiation length, L _T ... dot resistance body L _T, [Delta] R _2,
ΔR ₄ , ΔR ₆ , ΔR ₇ ... resistance correction amount, R ₀ ... resistance value,
W, W ₁ , W ₂ ... irradiation width, W _T ... dot resistor width

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁶ , DB name) B41J 2/335 B41J 2/35 H01C 17/242

Claims (4)

(57) [Claims] In a method for adjusting a resistance value of a thermal head for irradiating a laser to each dot resistor constituting a thermal head to adjust the resistance value to a target resistance value, an initial resistance value of each dot resistor is measured. The target resistance value is set to be equal to or less than the minimum value among the initial resistance values of the respective dot resistors, and the laser is irradiated only with the power for reducing the resistance value, and the resistance value of the respective dot resistors is the target resistance value. A method for adjusting the resistance value of a thermal head, comprising: 2. A dot resistance detecting section for detecting a resistance value of each dot resistor constituting a thermal head, and a target resistance value is set to be equal to or less than a minimum value among initial resistance values of each dot resistor. A target resistance value setting unit, a comparison unit that compares the detected resistance value of each of the dot resistors with the target resistance value, and reduces the resistance value of each of the dot resistors according to the comparison result of the comparison unit. A laser power selector for selecting a laser power to be applied to each of the resistors only so as to cause the laser to emit light, and a laser emitting unit for emitting a laser with the selected laser power. apparatus. 3. A method for adjusting a resistance value of a thermal head for irradiating a laser to each dot resistor constituting a thermal head to adjust the resistance value to a target resistance value, wherein an initial resistance value of each dot resistor is measured. The target resistance value is set to be equal to or less than the minimum value among the initial resistance values of the respective dot resistors, and only the laser power within a range for reducing the resistance value of the dot resistor according to the difference from the target resistance value is set. And determining the irradiation width, and adjusting the resistance value by irradiating the dot resistor with a predetermined length with the irradiation width. 4. A dot resistance detecting section for detecting a resistance value of each dot resistor constituting the thermal head, and a target resistance value is set to be equal to or less than a minimum value among initial resistance values of each dot resistor. A target resistance value setting unit, a comparison unit that compares the detected resistance value of each dot resistor with the target resistance value and outputs a difference, and a range in which the resistance value of the dot resistor is reduced according to the difference A laser power selection unit that selects a laser power that selects only the laser power that is within, an irradiation width determining unit that determines an irradiation width according to the difference, and a laser that is selected at the selected laser power and the determined irradiation width. A device for adjusting a resistance value of a thermal head of a thermal head, comprising: a laser emitting portion for emitting light; and irradiating the surface of the dot resistor with a predetermined length.