JP2003063047A - Thermal printer and method for detecting form edge - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermal printer capable of detecting the edge of a form without any special sensor. SOLUTION: A thermal head is equipped with a heat element. The thermal printer is provided with a resistance value detecting means for detecting value of resistance of each heat element set in an array in the width direction of a print form, and an edge position identifying means for identifying the edge position in the width direction of the print form based on a resistance value detected by the resistance value detecting means. If the value of resistance varies in accordance with the temperature of the heat element of the thermal head, the resistance value is detected by the resistance value detecting means and the edge position identifying means identifies the edge of the form from the position where the distribution of temperature becomes discontinuous. The electricity supply to each heat element is properly controlled reflecting the position of the edge.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal printer for forming an image on a printer sheet using a thermal head and a method for detecting the edge of the sheet, and more particularly to detecting the edge of the sheet and improving the image quality near the edge. Technology for doing.

[0002]

2. Description of the Related Art Conventionally, there is a thermal printer which forms a full-color image on a paper by heating a dye with a thermal head to change its physical properties to develop a color. The printer of the following method is known as this thermal printer. (1) Sublimation system printer The sublimation system printer uses an ink ribbon coated with a sublimation dye and a dedicated paper coated with an image receiving layer of the sublimation dye as a basic medium, and heats it with a thermal head to form an ink ribbon. An image is formed by sublimating and diffusing the above dye in the image receiving layer on the paper surface.

(2) Melt type printer The melt type printer uses an ink ribbon coated with a pigment mixed with wax and a normal paper as basic media, and heats it with a thermal head to melt the pigment on the ink ribbon. The image is formed by transferring this onto paper. (3) Thermal full-color printer The TA system is a typical system of the thermal full-color printer. This TA-type thermal full-color printer uses a paper that is encapsulated in microcapsules and separated for each color and a coupler and is coated uniformly on the paper surface as the basic medium, and the thermal head is used to clean the paper surface. It is heated to develop color. The above-described three methods are typical printing methods for both monochrome printing and multicolor printing.

Here, an outline of a thermal printer will be described by taking a sublimation printer as an example. FIG. 4 schematically shows the configuration of a conventional sublimation printer. This example is configured such that the paper is unwound from the roll paper and the paper portion printed on the entire surface is separated from the roll paper without leaving an edge (margin) like digital photographs. As shown in the figure, on the upper surface side of the paper 1 unwound from the roll paper, the ink ribbon 2A (unused portion) on the unwinding side, the thermal head 3, the winding side is provided along the paper transport path. The ink ribbon 2B (used portion) and the cutter 4 are sequentially arranged. Between the length W _H of the heat generating portion of the thermal head 3 and the width W _{P of the} paper 1, in general, W _H > W _P
Therefore, the length of the thermal head 3 is set longer than the width of the paper 1.

A platen 5 is arranged on the back side of the sheet 1 at a position facing the thermal head 3.
As a result, the roll paper 1 is appropriately pressed against the heating resistor (not shown) of the thermal head 3. The ink ribbon unwound from the ink ribbon 2A is superposed on the paper 1 unwound from the roll paper, passes between the thermal head 3 and the platen 5, and then is wound around the ink ribbon 2B. Further, on the back side of the sheet 1, an edge detection sensor 6 for detecting an edge of the sheet 1 in the width direction (hereinafter, referred to as “edge of sheet 1”) is arranged.

Here, the necessity of the edge detecting sensor 6 will be described. Ideally, the positional relationship between the heating resistor of the thermal head 3 and the paper 1 should match in dot units. However, it is virtually impossible to match the position of the heating resistor with the width of the paper in dot units for the following reason. (Reason 1) Width W of paper 1 sold as a product
_{As for P} , the variation due to the cutting error is recognized as a tolerance, and as shown in FIG. 5, the width of the sheet varies between the maximum sheet width dimension W _pmax and the minimum sheet width dimension W _pmin . This tolerance varies depending on the paper width, thickness, material, etc., but is usually much larger than the size of the heating resistor 100 (one unit) shown in FIG. Therefore, it is difficult to align the position of the heating resistor with the sheet 1 in dot units.

(Reason 2) According to the sheet conveying method shown in FIG. 4, the sheet 1 is conveyed with a slight deviation from the conveying direction to the left and right and with a slight shake. Therefore, even if the width of the sheet 1 is invariable (constant), the relative positional relationship between the sheet 1 and the heating resistor of the thermal head 3 constantly fluctuates. It is difficult to align the positions of the resistors in dot units.

Further, when forming an image near the edge of the above-mentioned paper, there are the following problems. (Problem 1) When the heating resistor located outside the edge of the sheet is made to generate heat, the sheet does not exist and there is no escape area for the generated heat, so the temperature of the heating resistor itself rises abnormally. Therefore, the resistance value change and the life of the heating resistor are significantly shortened due to abnormal overheating (blank print) of the heating resistor. (Problem 2) Normally, the edges of the paper are discontinuous in terms of thermal behavior, so the temperature tends to rise more easily than at the parts other than the edges, and the transfer / coloring density becomes high, resulting in uneven image quality. Lower. Due to the above-mentioned circumstances, when printing on the entire surface of the paper, it is important to accurately detect the edge of the paper, prevent blank printing, and correct the amount of heat generated at the edge of the paper. It is customary to provide the end detection sensor 6 at the end.

[0009]

By the way, as the above-mentioned edge detecting sensor 6, a CCD as shown in FIG. 6A is used.
There are a method using a sensor array and a method using a reflective photosensor shown in FIG. Here, in the system using the CCD sensor array 300, as shown in FIG. 6A, the CCD sensor elements 301 to 306 image the edges of the sheet 1 and image-process the output of each CCD element. The position of the edge of the sheet 1 with respect to the heating resistor 100 is determined. FIG. 6B shows an example of the output of the CCD sensor element. In this example, the output voltage changes at the boundary of the CCD sensor element 303 corresponding to the CCD sensor element number "3", and it is understood that the edge of the sheet 1 exists at the position of this CCD sensor element 303. .

Further, in the system using the reflection type photo sensor 400, as shown in FIG. 7A, the light is received from a certain area including the edge of the sheet 1, and the position can be determined from the output voltage at that time. it can. FIG. 7B shows an example of the output voltage of the reflective photosensor 400. As shown in the figure, the reflection type photo sensor 4 according to the position of the edge of the sheet 1
00 output voltage characteristic is obtained in advance, and the position Pa of the end portion of the sheet 1 is detected in reverse from the actual output voltage by referring to this characteristic.

However, according to the above-mentioned prior art,
When detecting the edge of the paper, whether the method using the CCD sensor or the method using the photo sensor, the edge detecting sensor 6 for detecting the edge of the paper is specially required. There is a problem in that the structure of the device is complicated, and therefore the device is upsized and the cost is increased. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a thermal printer capable of detecting the edge of a sheet without requiring a special sensor.

[0012]

In order to solve the above problems, the present invention has the following constitution. That is, the thermal printer according to the present invention is a thermal printer configured to form an image on a sheet by using a thermal head, wherein each heat generating resistor of the thermal head is arranged in the width direction of the sheet. A resistance value detecting means for detecting a resistance value of the resistor and an end position specifying means for specifying a position of an end portion in the width direction of the sheet based on the resistance value detected by the resistance value detecting means are provided. It is characterized by

Here, for example, an energization control means for controlling energization of the heating resistor of the thermal head by reflecting the position of the edge of the sheet specified by the edge position specifying means may be further provided. . Further, the energization control unit may suppress energization to the heating resistor of the thermal head located near the edge of the sheet, for example. Further, the resistance value detection means, for example,
The thermal head may be composed of a voltage applying unit for applying a predetermined voltage to the heating resistor of the thermal head and a current detecting unit for detecting a current flowing through the heating unit.

The method of detecting the position of the edge of the sheet of the thermal printer according to the present invention comprises the steps of: (a) sequentially heating the heating resistors on the thermal head arranged in the width direction of the sheet with constant energy; ) Calculating the resistance value of the heating resistor on the thermal head, and (c)
On the basis of the principle that the temperature of the heating resistors changes according to the contact state between the heating resistors of the thermal head and the paper and the resistance value of each heating resistor depends on the temperature, the heating resistors on the thermal head Identifying the edge of the sheet from the resistance value of the body.

Further, the method of detecting the position of the edge of the sheet of the thermal printer according to the present invention comprises the steps of: (a) sequentially heating the heating resistors on the thermal head arranged in the width direction of the sheet with constant energy; ) A step of calculating an energization time until the heating resistor on the thermal head reaches a predetermined temperature, and (c) the heating resistor of the thermal head depending on a contact state between the heating resistor and the paper. Based on the principle that the energization time until the temperature reaches a predetermined temperature changes and the resistance value of each heating resistor depends on the temperature, the edge of the paper is specified from the calculated energization time for each heating resistor. And a step of performing.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. In the thermal printer according to the present embodiment, the thermal head has a sensor function in addition to the original heater function, and the sensor function is used to detect the edge of the paper. The structural features of this sensor function are summarized in the following two points. (Characteristic 1) The material of the heating resistor is selected so that the resistance value of the heating resistor fluctuates greatly with temperature changes, and the thermal head also functions as a thermistor. In addition,
As a heating resistor of a conventional normal thermal head, a material whose resistance change little with temperature change is used. (Characteristic 2) A means for detecting the temperature of the heating resistor as a resistance value is provided. This resistance value is calculated from the value of the current flowing through the heating resistor and the voltage across it. As a thermal head having such a sensor function, for example, the one disclosed in Japanese Patent Application Laid-Open No. 55-115185 can be utilized.

FIG. 1 schematically shows the structure of the thermal printer according to this embodiment. In this figure, FIG.
The same components as the components shown in are denoted by the same reference numerals, and the description thereof will be omitted. The thermal printer shown in FIG. 1 according to the present embodiment includes a thermal head 3A having a sensor function, instead of the thermal head 3 and the edge detecting sensor 6 shown in FIG. Other configurations are similar to those of the related art shown in FIG.

FIG. 2 shows a structural example for realizing the sensor function of the thermal head 3A. As shown in the figure, the thermal head 3A includes a heating resistor group RH including heating resistors R _{H1 to} R _Hn and a switch group SW for controlling energization of each heating resistor. Here, one ends of the heating resistors R _{H1 to} R _Hn forming the switch group SW are commonly connected, and the other ends thereof are connected to the switch SW ₁ respectively.
To SW _n are grounded. These switches SW ₁
To SW _n, as described below, it is controlled to a conducting state alternatively and sequentially in detecting the edge of the paper.

The power supply 10 and the voltage adjusting section 20 are provided with a heating resistor.
Voltage application unit for applying a predetermined voltage to the antibody group RH
Configure (unsigned). The output voltage of the power supply 10 is the voltage
The voltage is adjusted to an appropriate voltage by the adjusting unit 20, and the current detecting unit 3
Heating resistor R through 0_H1~ R _HnApplied to the common connection point of
Be done. The current detection unit 30 includes a voltage adjustment unit 20 and a heating resistor.
Resistance r inserted between group RH_SAnd this resistance r_SFlow
A-D converter 31 for calculating the current i to be converted and performing A-D conversion
Composed of and. This resistance r_SCurrent i flowing through the
Since it is equal to the current flowing through the resistor group RH, in other words,
The current detection unit 30 is a heating resistor R of the thermal head 3A.
_H1~ R_HnTo detect the current flowing through.

The operation of the thermal printer according to the present embodiment will be described below in the case of detecting the edge of the paper 1 in the width direction. FIG. 3A shows a thermal head 3A.
The positional relationship between the heating resistors R _{H1 to} R _Hn and the sheet 1 is shown.
In this example, the heating resistors R _H1 and R _H2 are separated from the sheet 1 and are not in contact with the sheet 1 at all, and a part of the heating resistor R _H3 is in contact with the sheet 1 to generate the heating resistors R _{H4 to} R _{H4. Hn} is in contact with the paper 1 on the entire surface. In FIG. 3A, although it is expressed that there is a gap between the heating resistor and the paper, it is assumed that they are in thermal contact with each other.

When the heating resistor contacts the paper, this heat is generated.
The heat of the resistor is absorbed by the paper, and the temperature of the heat-generating resistor decreases.
To do. Therefore, in FIG.
Not heating resistor R_H4~ R_HnTemperature rise is suppressed,
The increase in the resistance value also tends to be suppressed. Conversely, the paper
Heating resistor R that does not come into contact with 1 at all_H1, R_H2The temperature is empty
Since air acts as a heat insulation layer, it contacts the entire surface of paper 1.
Heating resistor R _H4~ R_HnMarkedly higher than
The resistance value also tends to increase. Also, some are for
Heating resistor R that contacts paper_H3The temperature is between the two
And the resistance value is also a value in between.

FIG. 3B shows the characteristics showing the relationship between the energization time and the temperature of each heating resistor in parallel. As shown in the figure, the temperature of any heating resistor tends to rise with energization time, but the degree of temperature rise tends to differ depending on the contact state with the paper. Therefore, it is possible to grasp the end portion of the sheet 1 from the resistance values of the heating resistors R _{H1 to} R _Hn of the thermal head. According to the present invention, the resistance value of each heating resistor forming the heating resistor group R _H is
This is based on the principle that the portion that comes into contact with the sheet 1 and the portion that does not come into contact with the sheet 1 are different, and the resistance value is determined according to the contact state.

Hereinafter, the heating resistors R _H1 to
The detection operation of each resistance value of R _Hn will be described. Heating resistor R _H1
When detecting the resistance value of the switch, the switch SW ₁ connected in series with this heating resistor is closed, and the other switches SW _{2 to} SW
Open n. At this time, as shown in FIG. 2, the voltage (V _TH −) obtained by subtracting the voltage drop V _S due to the resistance r _S from the output voltage V _TH of the voltage adjusting unit 20 is applied to the heating resistor R _H1.
V _S ) is applied. The current i flowing through the heating resistor R _H1 is equal to the current flowing through the resistor r _S, hence the resistance r _S
It is calculated from the voltage V _S across both ends and the resistance value of the resistor r _S.
At this time, the heating resistor R _H1 generates heat with constant energy and exhibits a resistance value according to the temperature. A voltage (V _TH -V _S) being applied to the heating resistor RH1 from above, the current flowing through the heating resistor R _H1 i is obtained, the resistance value of the heating resistor RH1 is calculated from these. Similarly, the resistance values of the other heating resistors R _{H2 to} R _Hn are sequentially acquired. As a method for detecting the temperature of the heating resistor, the above-mentioned Japanese Patent Laid-Open No.
The method disclosed in Japanese Patent Laid-Open No. 5-115185 can be utilized.

When the resistance value of each heating resistor is detected in this way, an end specification processing section (end position specifying means) (not shown) positions where the resistance value distribution of the heating resistor becomes discontinuous. By searching for the heat generating resistor in the position, the process for specifying the position of the heat generating resistor as the position where the edge of the sheet exists is executed. This processing is performed based on the above-mentioned principle that the temperature of the heating resistors changes depending on the contact state between the heating resistors of the thermal head and the paper and the resistance value of each heating resistor depends on the temperature. However, the method of identifying the edge is not limited to the method of using the discontinuity of the resistance value, and if the edge of the paper can be identified from the resistance value of each heating resistor, for example, a predetermined threshold value It is also possible to specify the edge of the sheet by using another method such as a method of comparing with.

When the position of the end of the sheet 1 is specified by the end specification processing unit (not shown), the energization control means (not shown) of the thermal head 3A reflects the specified position of the end of the thermal head. The power supply to each heating resistor 3A is controlled. Specifically, the energization control unit of the thermal head 3A is provided with a heating resistor located near the edge of the sheet 1 so that the temperature does not rise in a portion not in contact with the sheet 1 and uneven density occurs in the image. The power supply to is properly suppressed. As a result, high-quality printing without density unevenness is performed over the entire surface of the sheet 1.

In the above description, the resistance value of each heating resistor is calculated, but the temperature may be calculated, and the method of calculating the temperature will be described below. In FIG.
The output voltage V _TH of the voltage adjusting unit 20 and the current i flowing through the resistance r _S and the heating resistor group R _H satisfy the following expression (1). V _TH = i (R _H + r _S ) ... (1) However, in the formula (1), “R _H ” is heat generated in the energized state that forms the “heating resistor group R _H ” shown in FIG. The resistance value of the resistor is represented, and “r _S ” represents the resistance value of the resistor r _S shown in FIG.

Since there is a relationship of V _S = i · r _S ,
The formula (1) is transformed into the following formula (2), and the formula (3) is obtained from the formula (2). _{V TH = i · R H +} V S ··· (2) R H = (V TH -V S) / i ··· (3) further, and a constant for converting the resistance value R _H of the temperature T _H alpha Then, the following equation (4) is obtained from the equation (3). T _H = α · _RH = α · (V _TH −V _S ) · r _S / V _S (4) From the above, the temperature of the heating resistor can be calculated,
By sequentially measuring the temperature of the heating resistor near the edge of the sheet, it becomes possible to know at which heating element position the edge of the sheet is located. In addition, when detecting the edge of the paper, the energization time used for temperature measurement (resistance measurement) of the heating resistor is
It is desirable that the thermal paper is set so that it does not develop color, and that the sublimation printer or the melting printer does not cause transfer.

In the above description, a constant energy is applied to the heating resistor to detect (measure) the resistance value and temperature of the heating resistor at this time, but until the heating resistor reaches a predetermined temperature. The pulse width that defines the energization time may be measured. That is, the pulse width for the heating resistor in the portion in contact with the paper is long, the pulse width for the heating resistor in the portion not in contact with the paper is short, and the pulse width for the heating resistor in contact with the edge of the paper is It shows a tendency to have an intermediate value. Thus, the energization time until the temperature of the heating resistors reaches a predetermined temperature changes depending on the contact state between the heating resistors of the thermal head and the paper, and the resistance value of each heating resistor depends on the temperature. By using the principle, it is possible to grasp the edge of the paper from the pulse width that defines the energization time for each heating resistor. In this case, the edge of the paper can be grasped from the position where the pulse width becomes discontinuous.

Although the embodiment of the present invention has been described above, the present invention is not limited to this embodiment, and is included in the present invention even if there are design changes and the like within a range not departing from the gist of the present invention. Be done.

[0030]

As described above, according to the present invention, the resistance value detecting means for detecting the resistance value of each heating resistor of the thermal head, which is arranged in the width direction of the paper, Since the end position specifying means for specifying the position of the end portion in the width direction of the paper based on the resistance value detected by the resistance value detecting means is provided, it is possible to detect the end portion of the paper without requiring a special sensor. Is possible.

[Brief description of drawings]

FIG. 1 is a diagram schematically showing a configuration of a thermal printer according to an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a characteristic configuration of a thermal printer according to an embodiment of the present invention.

FIG. 3 is a diagram for explaining an operation (detection of an edge portion of a sheet) according to the embodiment of the present invention.

FIG. 4 is a diagram showing a configuration example of a thermal printer according to a conventional technique.

FIG. 5 is a diagram for explaining a problem with a conventional technique.

FIG. 6 is a diagram for explaining a method of detecting an edge of a sheet when an edge detecting sensor (CCD sensor array) according to a conventional technique is used.

FIG. 7 is a diagram for explaining a method for detecting an edge of a sheet when a sensor for edge detection (reflection type photosensor) according to the related art is used.

[Explanation of symbols]

1 ... Paper (roll paper), 2A ... Ink ribbon (unwinding side), 2B ... Ink ribbon (winding side), 3A ... Thermal head, 4 ... Cutter, 5 ... Platen, 10 ... Power supply (one of voltage application parts) Part), 20 ... voltage adjusting part (a part of the voltage applying part), 30 ... current detecting part, 31 ... AD converting part, R
_H ... Heating resistor group, R _{H1 to} R _Hn ... Switch, SW ... Switch group, SW _{1 to} SW _n ... Switch, r _S ... Resistance.

Claims (6)

[Claims] 1. A thermal printer configured to form an image on a sheet by using a thermal head, wherein the heating resistors of the thermal head are arranged in the width direction of the sheet. A resistance value detecting means for detecting a value, and an end position specifying means for specifying a position of an end portion in the width direction of the sheet based on the resistance value detected by the resistance value detecting means, Thermal printer. 2. An energization control unit for controlling energization of the heat generating resistor of the thermal head by reflecting the position of the edge of the sheet specified by the end position specifying unit. The thermal printer according to claim 1. 3. The thermal printer according to claim 2, wherein the energization control unit suppresses energization of a heating resistor of the thermal head located near an edge of the sheet. 4. The resistance value detecting means includes a voltage applying section for applying a predetermined voltage to a heating resistor of the thermal head, and a current detecting section for detecting a current flowing through the heating element. The invention according to any one of claims 1 to 3, characterized in that
The thermal printer described in the section. 5. A step of: (a) causing each of the heating resistors on the thermal head arranged in the width direction of the paper to sequentially generate heat with constant energy; and (b) calculating a resistance value of the heating resistors on the thermal head. And (c) on the basis of the principle that the temperature of the heating resistors changes according to the contact state between the heating resistors of the thermal head and the paper and the resistance value of each heating resistor depends on the temperature. A step of identifying an edge of the sheet from a resistance value of a heating resistor on the thermal head; and a method of detecting an edge of a sheet of a thermal printer. 6. (a) a step of sequentially heating each heating resistor on the thermal head arranged in the width direction of the paper with constant energy, and (b) heating resistors on the thermal head are heated to a predetermined temperature. Calculating the energization time until reaching the temperature, and (c) changing the energization time until the temperature of the heating resistor reaches a predetermined temperature according to the contact state between the heating resistor of the thermal head and the paper. Based on the principle that the resistance value of each heating resistor depends on the temperature, the step of specifying the edge of the sheet from the calculated energization time for each heating resistor is included. Paper edge detection method.