JP2000071579A - Heating period constant measuring method of thermal printer device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an optimum heating period constant by driving the specific heat-resistor of a plurality of heat resistors through the application of a constant energy at a predetermined period and taking a specific formula while allowing a thermal head provided with a plurality of heat-resistors and a recording medium to move relatively. SOLUTION: A recording medium with printing dots printed on a plurality of printing lines is transported, thereby reading the density of the same density dot printing from the recording medium. When the density difference in the printing line N in the reading data is made D (N), the non-application time of printing pulses in each printing lines is (t)off, the convergent value in the change of the density difference is Dcnv, and the heating period constant is τ, the heat period constant τ is calculated by the application of formula. Concretely, the measurement of recording density of the printed dots is done in a manner facing in the direction opposite to arrow A in turn from the dots 11a at the first printed position. The density measurement results by a reflection density meter 8 are sent to an analysis device 9 corresponding to respective measured line numbers.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a thermal control technique in a thermal printing apparatus, and more particularly to a method for measuring a thermal time constant of a thermal head.

[0002]

2. Description of the Related Art A thermal printing apparatus has a thermal head composed of a plurality of heating resistors, applies a voltage in accordance with print data to the heating resistors, and uses a resistance heating to generate heat-sensitive paper. Print on etc. The print data is, for example, gradation data, and the printing process is performed by controlling the voltage application time to each heating resistor according to the gradation value. For this reason, in a thermal printing apparatus, development of various control techniques such as applied voltage control, applied time control, and heat control is indispensable for high image quality and high speed printing.

[0003] In particular, in the thermal control technique, since the printing density is affected by the amount of stored heat of each heating resistor, it is necessary to obtain information on the amount of stored heat of the target thermal head in order to perform heat control. Conventionally, the information on the livestock calorific value has been obtained by the following method. (B) Attached to or around the thermal head
For example, the temperature is directly measured by a temperature sensor such as a thermistor. (B) In addition, a thermal time constant of the thermal head is obtained in advance, and the thermal time constant of the thermal head is estimated using the thermal time constant. For example, a printing pulse is continuously applied to the heating resistor,
In this method, the temperature change on the surface of the thermal head is directly measured using a radiant heat thermometer, and the heat storage amount is obtained from the measurement result. (C) A method of estimating the amount of heat generated by the heating resistor to be recorded from the print history of the dots near the heating resistor to be recorded.

[0004]

The above-mentioned various methods have the following problems. First, the method (a) requires a considerable amount of time for measurement, and is not suitable as a thermal control method for high-speed printing.

Further, in the method (b), the recording medium cannot be used for the measurement, and the measurement is performed in a so-called idling state in the air. However, in actual printing,
It is affected by the surroundings of the heating resistor and thermal paper. Therefore, in this method, a large error occurs between the measurement result and the actual thermal time constant of the system.

Further, in the method (c), a print history for each dot is required, and the shorter the recording cycle, the more time is required for heat control. Accordingly, the present invention is to obtain the thermal time constant of the system in a state close to the actual printing state in the method (b) and obtain a thermal time constant having a small error from the thermal time constant of the actual system.

[0007]

According to the first aspect of the present invention, the plurality of heating resistors are moved while relatively moving a thermal head having a plurality of heating resistors and a recording medium. By driving a specific heating resistor among the above at a predetermined period by applying a constant energy, a recording medium on which printing dots are printed on a plurality of printing lines is conveyed, and the dot printing of the same density is performed from the recording medium. The density is read, the density difference in the print line N in the read data is D (N), the non-application time of the print pulse between each print line is t _off , and the convergence value of the change in the density difference is D (N).
_{When cnv} and thermal time constant are τ, from the following formula,

[0008]

(Equation 2)

This can be achieved by providing a method for measuring the thermal time constant of a thermal printing apparatus for determining the thermal time constant τ. Here, the recording medium may be, for example, thermal paper,
Further, printing on plain paper using a thermal transfer ribbon may be performed, as long as a printing line is formed by applying a constant applied energy to a specific heating resistor. Note that the printing line is not a line along the heating resistors formed in the row, but a direction perpendicular to the arrangement direction of the heating resistors, that is, a sub-scanning direction.

The reading of the density is performed using, for example, a reflection densitometer. A method for obtaining the thermal time constant τ from the above formula uses an analyzer or the like.
With this configuration, the thermal time constant τ can be measured in a state corresponding to actual printing, and a more accurate thermal time constant τ can be measured.

According to a second aspect of the present invention, for example, the heat storage amount of the heating resistor is estimated based on the thermal time constant τ obtained from the calculation formula. With such a configuration, the optimal thermal time constant τ can be measured for each system, and an appropriate heat storage amount can be estimated.

[0012]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a system configuration diagram of a thermal printing apparatus used in the thermal time constant measuring method of the present embodiment. The thermal printing apparatus 1 includes a CPU 2, a ROM 3,
It comprises a key input / sensor section 4, a thermal head 5, and a printing mechanism 6. The CPU 2 is a central processing unit that controls printing of the thermal printing apparatus 1 and performs processing according to a program stored in the ROM 3.

The ROM 3 stores the above programs,
The self-printing data, which will be described later, is stored, and the CPU 2 reads out the self-printing data and uses it for measuring the thermal time constant. The key input / sensor unit 4 includes a key and a sensor, and a self-printing instruction is issued from the key.

The thermal head 5 is composed of, for example, a heating resistor driven by a driver circuit, and performs printing on a recording medium such as thermal paper. The printing mechanism 6 is a mechanism for transporting the recording medium at a constant speed. The printing mechanism 6 is also driven under the control of the CPU 2.

The thermal printing apparatus 1 shown in FIG.
Performs print processing of normal print data supplied from the host device in addition to self-printing on a recording medium. FIG. 2 shows a device for reading self-printed data printed by the thermal printing device 1 and measuring the thermal time constant τ, and comprises a sheet 7 as a recording medium, a reflection densitometer 8 and an analyzer 9. Have been. The data printed on the paper 7 is data printed by the above-described self-print data, each dot 11 is data of the same density, and one dot is printed on each print line 10. .

The paper 7 is conveyed in the direction of arrow A shown in FIG. 1 and the density of the printed dots 11 is read by the reflection densitometer 8. That is, the transport speed of the sheet 7 in the direction of arrow A and the reading clock of the reflection densitometer 8 are synchronized, and the density is read by the reflection densitometer 8 for each dot.

The density data read by the reflection densitometer 8 is output to an analyzer 9. At this time, for example, the density data is in the form of a pair with the print line number information in the analysis device 9.
Supplied to

The analyzer 9 analyzes the supplied density data. For example, the density of one dot 11 printed on each print line 10 is compared with the dot density of the previous print line 10, and the dot density of the print line 10 newly measured from the dot density of the previous print line 10 is compared. Is higher, the dot density of the next print line 10 is measured.
The above processing is repeated to analyze how many dots have been counted until the density is saturated.

In the thermal time constant measuring method having the above configuration,
Hereinafter, the specific processing and the calculation method used for measuring the thermal time constant τ will be described. In this example, the thermal time constant of the thermal head is determined by the following procedure. First, using the thermal printing apparatus 1 described with reference to FIG. 1 described above, printing is performed with the applied voltage and the pulse width kept constant. That is, the CPU 2
The self-print data stored in the OM 3 is read and output to the thermal head 5. The self-print data is data for causing only a specific heating resistor to generate heat, and heats, for example, a heating resistor located at one end of one line of the heating resistor constituting the thermal head 5.

At the same time as the printing process by the thermal head 5 described above, the CPU 2 drives the printing mechanism 6 to
Is transported at a constant speed in the above-mentioned arrow A direction. Therefore, the dots 11 shown in FIG.
In the above-described printing process, it is desirable to print as long as possible in the direction of arrow A on the paper 7.

Next, the recording density of the dots printed as described above (so-called sample dots) is measured by the apparatus shown in FIG. This measurement is based on (1)
The measurement is performed in order from the dot 11a (in the line) in the direction opposite to the arrow A. That is, first, the reflection densitometer 8
The density of the dot 11a on the line (print line 10a) is measured, then the density of the dot 11b on the second line (print line 10b) is measured, and the density is measured in the same manner.

The results of the density measurement by the reflection densitometer 8 are associated with the measured line numbers, respectively, and are analyzed.
Sent to Here, the print dot formed by the heating resistor is printed on the dot 1 even if the same applied voltage and the same pulse width are applied to the heating resistor according to the heating history of the heating resistor.
The density of 1 increases in order. However, as described later, the concentration is saturated, and finally the concentration becomes almost constant. Therefore, the analyzing device 9 repeats the process of subtracting the density value of the first printed portion for each measured density value, and analyzes how many dots are counted until the density is saturated.

Next, the result of each measured density value is approximated by the following equation.

[0024]

(Equation 3)

In the above equation (1), D (N), t
_off , D _cnv, τ are the density difference in line N,
It shows a non-application time of a printing pulse between each printing line (hereinafter, referred to as a cooling time), a convergence value of a change in density difference, and a thermal time constant.

Here, τ for optimally approximating the above equation (1) is the thermal time constant of the system to be obtained. That is, the number of dots up to the above-described density saturation is the dot on the N-th line where D (N) converges to 0, and the thermal time constant τ can be obtained by substituting the numerical value corresponding to the above-mentioned equation. The derivation of equation (1) is described below.

First, consider the temperature rise after the completion of energization of printing for a certain line. The temperature rise dk of the thermal head 5 due to the energy E [J] given in a certain line is given assuming that the specific heat c of the constituent material is constant regardless of the temperature.

[0028]

(Equation 4)

Is given by Here, m indicates mass.
Normally, energy to the thermal head 5 is given by applying a pulse voltage to the heating resistor. Therefore, when printing is performed with the applied voltage and the applied pulse width kept constant, the applied energy E becomes constant, and the equation
The temperature rise represented by (2) occurs (the time required for the temperature rise is assumed to be sufficiently short).

However, in practice, there are losses due to Joule heat generated in the electrode conductors and the like, and losses due to various heat conduction resistances. Therefore, it is difficult to use the supplied electric power as it is for raising the temperature of the head. Absent. There is also an energy consumption for printing in that line.
Due to these factors, the temperature rise immediately after the end of energization in printing of one line, that is, at the beginning of the cooling time, does not occur as much as the expression (2).

Therefore, it is assumed that a temperature increase of k occurs for each print line. Then, a temperature rise K (N) immediately before the energization of the Nth line printing with reference to the temperature just before the start of the energization of the first line printing is considered. Now, in this example,
The temperature rise immediately after the end of energization of the (N-1) th line printing is N-
The temperature rise K (N
-1) and the sum of the temperature rise k due to the energization of the (N-1) th line printing. In consideration of this, the temperature rise K (N) immediately before the start of energization of the N-th line printing takes into account the cooling amount due to the cooling time t _off .

[0032]

(Equation 5)

Can be expressed as When N <2, K (N) = 0 (4).

Here, assuming that the relationship between the temperature of the heating resistor of the thermal head and the recording density is linear, the following equation is obtained.
(3)

[0035]

(Equation 6)

Can be expressed as D (N) is a value obtained by converting the temperature rise immediately before the start of energization of the Nth line printing into a recording density, and d is a change amount of the recording density when the temperature rises by k.

Now, since 外 1, Equation (5) becomes:
There is a limit at N = ∞. So

[0038]

[Outside 1]

The limit D _cnv of

[0040]

(Equation 7)

## EQU1 ## from now on,

[0042]

(Equation 8)

Is obtained. Substituting this into equation (5) gives

[0044]

(Equation 9)

Equation (8) is derived. This is equation (1) described above. In the equation (1), D _cnv means a convergence value of the change of the density difference. This can be easily obtained by performing the printing described above for a long time in the sub-scanning direction. That is, as shown in FIG. 3, a value that converges when a change in the density difference with respect to the print line number is graphed is _Dcnv .

Further, t _off is an amount that can be obtained in advance. Therefore, the unknown parameter in equation (1) is τ
Only, and the optimum τ can be obtained. And
This is the desired thermal time constant of the system. The present invention thus determines the thermal time constant τ of the system.

Now, the linearity of the relationship between the temperature and the recording density assumed when introducing the equation (5) will be examined. FIG. 4 shows an example of the relationship between the applied energy and the recording density. This indicates that there is a region where the relationship between the applied energy and the recording density can be expressed as a linear function.

From equation (2), it is clear that the applied energy is proportional to the temperature (ignoring the loss of the applied energy), so it can be said that there is an area where the relationship between the temperature and the recording density is linear. That is, if the present invention is applied to such an area, the above assumption is satisfied.

The process of deriving the above equation (1) has been described above. The thermal time constant τ can be obtained using the equation (1). In addition, according to the present embodiment, the thermal time constant τ of the thermal head can be measured in the same state as the actual printing, and the optimal thermal time constant τ for the system can be calculated.

[0050]

As described in detail above, according to the present invention, the thermal time constant of the thermal head can be measured in the same state as the actual printing state, so that the optimum thermal time constant can be obtained. it can.

Further, by estimating the heat storage amount of the thermal head using the thermal time constant obtained as described above, it is possible to perform optimal thermal control of the thermal head.

[Brief description of the drawings]

FIG. 1 is a system configuration diagram of a thermal printing apparatus to which a thermal time constant measuring method according to an embodiment is applied.

FIG. 2 is a configuration diagram of an apparatus for measuring a print dot density.

FIG. 3 is a diagram illustrating a relationship between print densities corresponding to print line numbers.

FIG. 4 is a diagram showing a relationship between a recording density and an applied energy.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Thermal printing device 2 CPU 3 ROM 4 Key input / sensor part 5 Thermal head 6 Printing mechanism 7 Paper 8 Reflection densitometer 9 Analysis device 10, 10a, 10b Printing line 11, 11a, 11b (printing) dot

Claims (2)

[Claims] 1. A thermal head provided with a plurality of heating resistors and a recording medium are relatively moved, and a specific heating resistor among the plurality of heating resistors is applied at a predetermined cycle by applying a constant energy. By driving, a recording medium on which printing dots are printed on a plurality of printing lines is conveyed, the density of the printing dots is read from the printing medium, and the density difference in the printing line N in the read data is represented by D (N ), When the non-application time of the print pulse between each print line is t _off , the convergence value of the change in density difference is D _{cnv , and the} thermal time constant is τ, the following formula is used. A method for measuring a thermal time constant of a thermal printing apparatus, wherein a thermal time constant τ is obtained. 2. The method of measuring a thermal time constant of a thermal printing apparatus according to claim 1, wherein the heat storage amount of the heating resistor is estimated based on the thermal time constant τ obtained from the calculation formula.