JP2006347135A - Thermal printer and method of thermal printing - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress the generation of density unevenness due to a print load during yellow print. <P>SOLUTION: An amount of transportation load during recording of each line is calculated on the basis of a thermal energy value corresponding to image data. An amount of transportation load fluctuation is determined for a case where surface temperature of a protective layer of recording paper 2 exceeds a glass transition point of the protective layer and a case where the temperature does not exceed the glass transition point. This makes it possible to determine a more accurate amount of transportation load fluctuation corresponding to actual transportation load fluctuation. A corrected heat energy value is determined on the basis of an amount of transportation speed fluctuation calculated from the amount of transportation load fluctuation. The density unevenness can be prevented reliably by charging the corrected energy value into the line where the density unevenness is generated. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a thermal printer and a thermal printing method for thermally recording an image on a recording paper using a thermal head.

  2. Description of the Related Art A thermal printer is known that heats a thermal recording paper provided with a thermal heating layer with a thermal head to color and record an image. In the thermal head, a large number of heating elements are arranged in a line along the main scanning direction. The thermal printer records an image line by line while relatively moving the thermal head and the thermal recording paper in the sub-scanning direction. Each heating element is driven based on image data for one line, and gives thermal energy to the thermal recording paper.

  The coefficient of friction between the thermal recording paper and the thermal head varies with the thermal energy. That is, when the thermal energy is large, the temperature of the heating element increases and the friction coefficient decreases, whereas when the thermal energy is small, the temperature of the heating element decreases and the friction coefficient increases. Therefore, in the portion where the image data changes greatly in the adjacent line and the density of the original image changes suddenly, the fluctuation of the thermal coefficient is large, so the fluctuation of the friction coefficient is also large. When the friction coefficient varies, the conveyance load of the thermal recording paper varies, so the conveyance pitch of the thermal recording paper changes. As a result, there is a problem in that the thermal energy applied per unit area changes and density unevenness occurs.

For example, as shown in Patent Document 1, when recording is performed on a plurality of recording areas by simultaneously operating a dedicated thermal head for each color of yellow, magenta, and cyan, the load fluctuation caused by the above density change A color thermal printer is described in which density unevenness does not occur even if the ink occurs. In this color thermal printer, the load amount is obtained for each line recorded by the thermal head of each color, and the load fluctuation amount is obtained from the difference between the load amount of the line to be recorded and the load amount of the adjacent line. The thermal energy applied to the thermal heads of the respective colors is corrected based on the load fluctuation amount of the thermal heads of other colors. For this reason, even when the conveyance pitch of the thermal recording paper changes due to fluctuations in the conveyance load, the thermal energy is also corrected in accordance with the change, thereby preventing density unevenness from occurring.
JP 2003-326754 A

  By the way, a belt or the like is used for a drive system for conveying recording paper, and these have a self-determining function of dynamic characteristics. For this reason, the load fluctuation of the thermal head affects the drive system, thereby causing fluctuations in the transport speed of the drive system. As a result, when the relative speed between the thermal head and the recording paper is high, not much heat energy is input to the recording paper, the density becomes thin, and conversely, when the relative speed between them is low. A large amount of heat energy is input to the recording paper, and the density becomes high. Therefore, sufficient correction cannot be performed simply by considering only the load fluctuation amount of the thermal head as described above, and density unevenness cannot be sufficiently prevented.

  Further, a synthetic resin having a glass transition point is used for the protective layer located above the yellow thermosensitive coloring layer of the recording paper. As shown in FIG. 1, the gradation of the image data is obtained during yellow printing. When the level is 22, the load due to printing (printing load) becomes maximum. Therefore, when the surface temperature of the recording paper in the recording of a certain line changes from the surface temperature of the recording paper in the recording of the previous line across the glass transition point, the conveyance load amount between the lines is actually A transport load fluctuation amount larger than a value obtained by using the difference between the two as the transport load fluctuation amount occurs. Therefore, when correcting the image data based on the transport load fluctuation amount, it is not possible to perform sufficient correction simply by setting the difference in the transport load amount between lines as the transport load fluctuation amount. Occurrence cannot be sufficiently prevented.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a thermal printer and a thermal printing method for preventing density unevenness caused by a conveyance speed fluctuation of a driving system and a printing load during yellow printing.

  In order to achieve the above-mentioned object, the present invention is to heat each of the heating elements in accordance with image data by a thermal head in which a plurality of heating elements are arranged along the main scanning direction, and to protect the surface with a protective layer made of synthetic resin. In a thermal printer for recording an image line by line by feeding a recording paper covered with a mark in the sub-scanning direction crossing the main scanning direction, the recording paper is given to the recording paper based on the image data when recording each line. Power heat energy is calculated, a transport load amount F (i) at the time of each line recording is obtained based on the heat energy, and the transport load amount F (i-1) and the i-th line of the immediately preceding (i-1) line. A transport load fluctuation amount calculating unit for obtaining a difference F (i) −F (i−1) from the transport load quantity F (i) of the current as a transport load fluctuation quantity ΔF (i), and the transport load fluctuation quantity ΔF (i). Based on the above, find the amount of fluctuation in the conveyance speed Based on the correction data, a conveyance speed fluctuation amount calculation unit, a correction data calculation unit that obtains correction data for image data based on the conveyance speed fluctuation amount when the conveyance load fluctuation amount ΔF (i) exceeds a certain value, and A printing unit that corrects the amount of heat generated by each heating element and performs printing, and at the time of recording from the (i-1) -th line to the i-th line when calculating the transport load fluctuation amount ΔF (i), It is determined whether or not the surface temperature of the recording paper crosses the glass transition point of the protective layer. When the glass transition point is crossed, F (i) + F (i−1) − (printing of the glass transition point) When the load does not cross the glass transition point, F (i) -F (i-1) is set.

In the thermal printing method of the present invention, the thermal energy to be given to the recording paper is calculated based on the image data when recording each line, and the transport load amount F (i) at the time of recording each line based on the thermal energy. And the difference F (i) −F (i−1) between the transport load amount F (i−1) of the immediately preceding (i−1) line and the transport load amount F (i) of the i th line is transported. Obtained as a load fluctuation amount ΔF (i), and based on the conveyance load fluctuation amount ΔF (i), a conveyance speed fluctuation amount was obtained.
When the transport load fluctuation amount ΔF (i) exceeds a certain value, correction data for image data is obtained based on the transport speed fluctuation amount, and printing is performed by correcting the heat generation amount of each heating element based on the correction data. In calculating the transport load fluctuation amount ΔF (i), whether or not the surface temperature of the recording paper straddles the glass transition point of the protective layer when recording from the (i-1) th line to the ith line. F (i) -F (i-1) when not crossing the glass transition point, and F (i) + F (i-1)-( It is characterized in that it is a conveyance load at the time of printing at the glass transition point.

  According to the present invention, the conveyance load amount is calculated based on the thermal energy corresponding to the image data, and the conveyance is performed depending on whether the surface temperature of the protective layer of the recording paper crosses the glass transition point of the protective layer. By obtaining the load fluctuation amount, it is possible to obtain a more accurate conveyance load fluctuation amount according to the actual conveyance load fluctuation. Further, density unevenness can be reliably prevented by obtaining corrected thermal energy based on the transport speed fluctuation amount calculated from the transport load fluctuation amount and putting this corrected heat energy into a line where density unevenness occurs. .

  FIG. 2 is a schematic view showing a main part of a color thermal printer embodying the present invention. In this color thermal printer, a long color thermal paper (hereinafter simply referred to as recording paper) 2 fed from a recording paper roll (not shown) is used. The recording paper 2 is fed by the transport unit 3 in a paper feeding direction and a recording direction opposite to the paper feeding direction.

  The conveyance unit 3 includes a conveyance roller pair 4, a belt transmission unit 5, and a conveyance motor 6. The conveyance roller pair 4 includes a capstan roller 4 a that is connected to the conveyance motor 6 via the belt transmission unit 5, and a nip roller 4 b that is pressed against the recording motor 2 via the recording paper 2. The nip roller 4b is provided so as to be movable between a pressure contact position where the nip roller 4b is pressed against the capstan roller 4a and a retreat position where the nip roller 4b is separated.

  The belt transmission unit 5 includes a capstan pulley 5a, an intermediate small pulley 5b, a first timing belt 5c wound around these pulleys 5a and 5b, an intermediate large pulley 5d, a motor pulley 5e, and these pulleys 5d, 5e, and a second timing belt 5f wound around. The intermediate small pulley 5b and the intermediate large pulley 5d are integrally formed, and the rotation of the motor is decelerated by the intermediate pulleys 5b and 5d and transmitted to the capstan roller 4a. Each of the timing belts 5c and 5f has a spring coefficient. The transport motor 6 is controlled by the controller 10 via the driver 6a.

  FIG. 3 is a schematic diagram showing a simplified printing load variation model of the transport unit 3. Each pulley 5a, 5b, 5d, 5e and the capstan roller 4a are made of a rigid body and are not related to the printing load. Each of the timing belts 5c and 5f and the recording paper 2 is an elastic body, and is an element of fluctuations in the conveyance speed due to the printing load. Here, the spring coefficient in the first timing belt 5c is k1, the attenuation term is c1, the spring coefficient in the second timing belt 5f is k2, the attenuation term is c2, the spring coefficient in the recording paper 2 is k3, and the attenuation term is c3. .

中間小プーリ５ｂと中間大プーリ５ｄの運動方程式：

モータプーリ５ｅの運動方程式：

ただし、（１）,（２）,（３）中の微分は、ラインｉについての微分を表している。Ｉ₁，Ｉ₂，Ｉ₃はそれぞれ、キャプスタンローラ４ａとキャプスタンプーリ５ａ、中間小プーリ５ｂと中間大プーリ５ｄ、モータプーリ５ｅの慣性モーメントを表している。ｒ₀は中間小プーリ５ｂ、ｒ₁はキャプスタンプーリ５ａ、ｒ₂は中間大プーリ５ｄ、ｒ₃はモータプーリ５ｅ、ｒ₄はキャプスタンローラ４ａの半径を表している。θ₁，θ₂，θ₃はそれぞれ、キャプスタンローラ４ａとキャプスタンプーリ５ａ、中間小プーリ５ｂと中間大プーリ５ｄ、モータプーリ５ｅの角変動量を表している。Ｆ（ｉ）は第ｉラインにおける印画負荷による搬送負荷量を、ｐはモータ負荷を表している。 The equations of motion of the capstan roller 4a, the capstan pulley 5a, the intermediate small pulley 5b, the intermediate large pulley 5d, and the motor pulley 5e can be expressed as follows.
Equation of motion of capstan roller 4a and capstan pulley 5a:

Equation of motion of intermediate small pulley 5b and intermediate large pulley 5d:

Equation of motion of motor pulley 5e:

However, the differentiation in (1), (2), and (3) represents the differentiation with respect to the line i. I ₁ , I ₂ , and I ₃ represent the moments of inertia of the capstan roller 4a and the capstan pulley 5a, the intermediate small pulley 5b, the intermediate large pulley 5d, and the motor pulley 5e, respectively. r ₀ is an intermediate small pulley 5b, r ₁ is a capstan pulley 5a, r ₂ is an intermediate large pulley 5d, r ₃ is a motor pulley 5e, and r ₄ is a radius of the capstan roller 4a. θ ₁ , θ ₂ , and θ ₃ represent the angular fluctuation amounts of the capstan roller 4a and the capstan pulley 5a, the intermediate small pulley 5b, the intermediate large pulley 5d, and the motor pulley 5e, respectively. F (i) represents the conveyance load amount due to the printing load on the i-th line, and p represents the motor load.

  As shown in FIG. 4, the spring coefficients k1 and k2 are determined according to the load, that is, the transport load amount F (i). c1 and c2 represent attenuation coefficients of the belts 5c and 5f. Note that the belt used in this embodiment takes into account that the relationship between the load and the spring coefficient of the belt is non-linear. However, when modeling the transport section in an idealized manner, the non-linearity of the spring coefficient is not always considered. do not have to.

ただし、

であり、式（４）の微分は、ラインｉについての微分を表している。 The equations of motion (1), (2), (3) can be rewritten as state equations as follows.

However,

And the derivative of equation (4) represents the derivative with respect to line i.

  In the recording paper 2, a cyan thermosensitive coloring layer, a magenta thermosensitive coloring layer, a yellow thermosensitive coloring layer, and a protective layer are sequentially formed on a support. The yellow thermosensitive coloring layer which is the uppermost layer as the thermosensitive layer has the highest thermal sensitivity and develops yellow with small energy. The cyan thermosensitive coloring layer, which is the lowermost layer, has the lowest thermal sensitivity and develops cyan with large heat energy. The yellow thermosensitive coloring layer loses its coloring ability when irradiated with 420 nm blue-violet light. The magenta thermosensitive coloring layer develops magenta with intermediate heat energy between the yellow thermosensitive coloring layer and the cyan thermosensitive coloring layer and loses the coloring ability when irradiated with near-ultraviolet rays of 365 nm.

  A thermal head 7 is disposed on the downstream side of the transport unit 3 in the paper feeding direction. The thermal head 7 includes a heating element array 7a in which a large number of heating elements are arranged in a line, and is fixed in the printer.

  A platen roller 8 is arranged at a position facing the thermal head 7 so as to sandwich the recording paper 2 between the thermal head 7. The platen roller 8 is movable in the vertical direction and is urged in a direction in which it is pressed against the thermal head 7 by a spring (not shown). The platen roller 8 is connected to a platen motor 9 composed of a pulse motor. The platen motor 9 is rotationally controlled by the controller 10 via a driver 9a.

  When the recording paper 2 is transported in the recording direction by the transport unit 3, the thermal head 7 causes each heat generating element of the heat generating element array 7 a to generate heat to a predetermined temperature, and each thermosensitive coloring layer in the recording area of the recording paper 2. To develop color. The platen roller 8 is lowered by a shift mechanism (not shown) using a cam, a solenoid or the like at the time of paper supply and paper discharge, thereby forming a gap for passing the recording paper 2 between the thermal head 7.

  On the downstream side in the paper feeding direction of the thermal head 7, an optical fixing device 11 is disposed facing the recording paper 2. The optical fixing device 11 includes a yellow fixing lamp 12, a magenta fixing lamp 13, and a reflector 14. The yellow fixing lamp 12 emits blue-violet light having an emission peak of 420 nm, and the magenta fixing lamp 13 emits ultraviolet light having an emission peak of 365 nm. By irradiating fixing light from these fixing lamps 12 and 13, the yellow thermosensitive coloring layer and the magenta thermosensitive coloring layer of the recording paper 2 are fixed so as not to develop color even when heated.

  A cutter 16 is provided on the downstream side of the optical fixing unit 11 in the paper feeding direction. The cutter 16 separates the full color image from the unrecorded area. As a result, the sheet-like recording paper is discharged from the discharge port (not shown) to the outside of the printer.

  The controller 10 controls each unit to record a full-color image on the recording paper 2 by three-color surface sequential recording of yellow, cyan, and magenta in the same recording area. In order to prevent density unevenness caused by fluctuations in the conveyance speed during recording, image data is corrected according to the processing procedure of FIG. When the relative speed between the thermal head 7 and the recording paper 2 is increased, the density is decreased. Therefore, the thinned portion is increased. Conversely, when the relative speed is decreased, the density is increased. Therefore, a process of thinning the darkened portion is performed.

  For this reason, the controller 10 includes a frame memory 21, a line memory 22, a conveyance load fluctuation amount calculation unit 25 for obtaining a conveyance load fluctuation amount based on the thermal energy of each line, and a conveyance for obtaining a conveyance speed fluctuation amount based on the conveyance load fluctuation amount. A speed variation calculation unit 26, a correction data calculation unit 27 for obtaining correction data for image data based on the conveyance speed variation, a line memory 28, and an energization time calculation control unit 29 are provided.

  The image data written in the frame memory 21 is sent to the line memory 22 line by line. The line memory 22 stores image data for a plurality of lines, for example, 5 lines. The image data input to the line memory 22 is sent to the transport load fluctuation amount calculation unit 25 line by line.

  The transport load fluctuation amount calculation unit 25 includes an energy / data conversion LUT memory 25a, a dynamic friction coefficient LUT memory 25b, a spring coefficient conversion LUT memory 25c, and a RAM 25d. The energy / data conversion LUT memory 25a includes a table in which the gradation level (0 to 255) of the image data is used as an address, and the heat energy applied to the recording paper 2 from the heating element of the thermal head 7 as data, and the heat energy. Is a table in which the address is the address and the gradation level of the image data is the data. In the dynamic friction coefficient LUT memory 25b, a table showing the relationship between the thermal energy of each heat generating element and the surface of the recording paper 2 and the dynamic friction coefficient of the heat generating element is written. In this table, the dynamic friction coefficient decreases as the heat energy of the heating element increases. The table is obtained in advance for each type of recording paper by experiments or the like, and is written in the dynamic friction coefficient LUT memory 25b. Then, a corresponding table is selected according to the type of recording paper 2 to be used. In the spring coefficient conversion LUT memory 25c, a table corresponding to FIG. 4 and indicating the relationship between the transport load amount F (i) and the spring coefficient of the belt used in the transport unit 3 is written. The RAM 25d temporarily stores the calculation result and the like in the transport load fluctuation amount calculation unit 25.

なお、発熱素子は本実施形態では、例えば３２５６個用いているが、この発熱素子の数は記録紙のサイズ等に応じて適宜変更してよい。 The conveyance load fluctuation amount calculation unit 25 converts the image data of the i-th line and the j-th dot taken in from the line memory 22 with reference to the energy / data conversion LUT memory 25a into thermal energy E (i, j), Is stored in the RAM 25d. Then, the dynamic friction coefficient μ (E (i, j)) corresponding to the thermal energy E (i, j) is read from the dynamic friction coefficient LUT memory 25b and multiplied by the pressing force P with which the thermal head 7 presses the recording paper 2. Thus, with respect to the image data of the i-th line and the j-th dot, the conveyance load amount applied to the recording paper 2 by the corresponding heating element is obtained. The transport load amount is obtained for all the heating elements by the following equation (6), and the transport load amount F (i) received by the recording paper 2 when the thermal head records the image of the i-th line on the recording paper 2. Is calculated.

In the present embodiment, for example, 3256 heating elements are used, but the number of heating elements may be changed as appropriate according to the size of the recording paper.

Next, according to the procedure of FIG. 6, the transport load fluctuation amount ΔF (i) is calculated based on the transport load amount F (i) (step 50). Here, the conveyance load fluctuation amount ΔF (i) at the time of magenta and cyan printing is obtained by the following equation.
ΔF (i) = F (i) −F (i−1)
At the time of yellow printing, since it is necessary to consider the glass transition point, it is necessary to calculate the transport load fluctuation amount ΔF (i) based on the following conditions.
The dynamic friction coefficient μ (E (i, j) where μ ₀ is the dynamic friction coefficient at the time of printing at the gradation level 0, μ _g is the dynamic friction coefficient at the time of printing at the glass transition point, and μ ₂₅₅ is the printing at the gradation level 255. ) And the dynamic friction coefficient μ (E (i−1, j)) in the (i−1) -th line satisfy the condition C1:
μ ₀ ≦ μ (E (i, j)) ≦ μ _g and μ ₀ ≦ μ (E (i−1, j)) ≦ μ _g
Or, condition C2:
_{μ g <μ (E (i} , j)) ≦ μ 255 cutlet _{μ g <μ (E (i} -1, j)) ≦ μ 255
When satisfying, the conveyance load fluctuation amount ΔF (i) caused by the recording of the i-th line is
ΔF (i) = F (i) −F (i−1)
And When the conditions C1 and C2 are not satisfied, that is, the condition C3:
μ ₀ ≦ μ (E (i, j)) ≦ μ _g and μ _g <μ (E (i−1, j)) ≦ μ ₂₅₅
Or, condition C4:
μ ₀ ≦ μ (E (i−1, j)) ≦ μ _g and μ _g <μ (E (i, j)) ≦ μ ₂₅₅
In this case, the conveyance load fluctuation amount ΔF (i) resulting from the recording of the i-th line is
ΔF (i) = F (i) + F (i−1) −2 × (conveyance load at the time of printing at the glass transition point)
And

  When the calculated transport load fluctuation amount ΔF (i) is not “0” or “nearly 0”, that is, when it is expected that density unevenness will occur due to the transport load fluctuation amount ΔF (i), the transport load amount F Based on (i), the spring coefficient k1, k2 of the belt used in the drive system is calculated by the spring coefficient LUT memory 25c. Then, the calculated transport load fluctuation amount ΔF (i), spring coefficients k1, k2 and thermal energy E (i, j) are sent to the transport speed fluctuation amount calculation unit 26.

ここで、モータ負荷ｐは搬送負荷量Ｆ（ｉ）に比べてかなり大きく、モータ負荷による負荷変動は生じないと仮定した。算出した搬送速度変動量Ｈ（ｉ）はＲＡＭ２６ａに書き込まれる。そして、第（ｉ＋１）ラインの画像データをラインメモリ２２から読み出し、搬送負荷変動量が「０」もしくは「ほぼ０」になる（そのときのラインを第（ｉ＋ｉ'）ラインとする）まで、これまでと同様の処理を行う。 The conveyance speed fluctuation amount calculation unit 26 includes a RAM 26a. The RAM 26a temporarily stores the calculation result and the like in the conveyance speed fluctuation amount calculation unit 26. The transport speed fluctuation amount calculation unit 26 calculates a transport speed fluctuation amount H (i) of the drive system caused by the transport load fluctuation based on the transport load fluctuation amount ΔF (i). By giving an impulse response U (F (i)) corresponding to the transport load variation ΔF (i) as an input to the general solution of the state equation (4), the transport speed variation is based on the following equation (7). H (i) can be calculated.

Here, it is assumed that the motor load p is considerably larger than the conveyance load amount F (i), and load fluctuation due to the motor load does not occur. The calculated conveyance speed fluctuation amount H (i) is written in the RAM 26a. Then, the image data of the (i + 1) th line is read from the line memory 22, and this is changed until the transport load fluctuation amount becomes “0” or “nearly 0” (the line at that time is the (i + i ′) line). Perform the same processing as before.

ただし、

である。ここでＩは６×６の単位行列とする。この搬送速度変動量は、補正データ演算部２７に送られる。 The transport speed fluctuation amount from the i-th line where the transport load fluctuation occurs to the (i + i ′) line where the transport load fluctuation amount is “0” or “nearly 0” is determined by the transport speed fluctuation amount calculation unit 26 ( It can be obtained by performing convolution integration according to equation (8).

However,

It is. Here, I is a 6 × 6 unit matrix. This conveyance speed fluctuation amount is sent to the correction data calculation unit 27.

ここで、Ｇは１×６の行列で、行列Ｇの各成分は、搬送速度変動量と補正熱エネルギとを関係づける、実験で求めた係数である。そして、この補正熱エネルギＥ_cと熱エネルギＥ（ｉ,ｊ）とを足し合わせたものを、補正後の印画エネルギ（以下、「補正印画エネルギ」とする。）とする。補正印画エネルギは、補正データとして、データ変換ＬＵＴメモリ２６ａによって画像データに変換され、ラインメモリ２８に送られる。 The correction data calculation unit 27 includes a data conversion LUT memory 27a. In the data conversion LUT memory 27a, a table is written in which the thermal energy is used as an address and the gradation level of image data is used as data. First, the correction data calculation unit 27 uses the following equation (10) based on the conveyance speed fluctuation amount sent from the conveyance speed fluctuation amount calculation unit 26 to calculate the correction thermal energy E _c to be input to the line where density unevenness occurs. calculate.

Here, G is a 1 × 6 matrix, and each component of the matrix G is a coefficient obtained by an experiment that relates the amount of conveyance speed fluctuation and the corrected thermal energy. Then, the sum of the corrected thermal energy E _c and the thermal energy E (i, j) is defined as corrected printing energy (hereinafter referred to as “corrected printing energy”). The corrected printing energy is converted into image data by the data conversion LUT memory 26 a as correction data and sent to the line memory 28.

  When the transport load fluctuation amount ΔF (i) is equal to “0” or “almost 0”, the transport speed fluctuation does not occur and density unevenness does not occur. When the conveyance speed fluctuation amount is not stored in the RAM 26a in the conveyance speed fluctuation amount calculation unit 26, the thermal energy E (i, j) is returned to the image data again by the energy / data conversion LUT 25a memory, The image data is sent to the line memory 28. When the conveyance speed fluctuation amount is stored in the RAM 26 a, the correction data is calculated by the correction data calculation unit 27, and then the correction data is sent to the line memory 28.

  When the image data and the correction data are written in the line memory 28, the energization time calculation control unit 29 accordingly obtains the energization time control data for each heating element based on the image data and the correction data, and supplies this to the thermal head 7. send. The head drive unit of the thermal head 7 causes each heating element to generate heat with the energization time control data. In synchronization with the driving of the heat generating elements, the transport unit 3 and the platen roller 8 are controlled via the drivers 6 a and 9 a, and an image is recorded on the recording paper 2.

  Next, the operation of this embodiment will be described. First, yellow image data, magenta image data, and cyan image data of an image to be recorded are taken into the frame memory 21, and then a print instruction is given. By this instruction, the recording paper 2 is sent to the position of the thermal head 7, and after the thermal head 7 is pressed against the recording start position of the recording paper 2, the yellow printing process is started. The yellow image data stored in the frame memory 21 is sent line by line to the line memory 22 for writing. Then, the yellow image data of the first line is read from the line memory 22 and sent to the transport load fluctuation amount calculation unit 25.

  When yellow image data is input to the transport load fluctuation amount calculation unit 25, the yellow image data of the first line and the jth dot is converted into thermal energy E (1, j). Based on the thermal energy E (1, j), the dynamic friction coefficient μ (E (1, j)) is calculated. The dynamic friction coefficient μ (E (1, j)) is multiplied by the pressing force P, and the conveyance load amount F (1) received by the recording paper is calculated by Expression (6).

Based on the transport load amount F (1), a transport load fluctuation amount ΔF (1) is calculated. When the dynamic friction coefficient μ (E (1, j)) and the dynamic friction coefficient μ (E (0, j)) stored in the RAM 25d in advance satisfy the condition C1 or the condition C2, the conveyance caused by the recording of the first line. The load fluctuation amount ΔF (1) is
ΔF (1) = F (1) −F (0)
(F (0) is a transport load amount stored in the RAM 25d as an initial value in advance). When the condition C1 or the condition C2 is not satisfied, that is, in the case of the condition C3 or the condition C4, the conveyance load fluctuation amount ΔF (1) due to the recording of the first line is
ΔF (1) = F (1) + F (0) −2 × (conveyance load during printing of glass transition point)
And

  If the calculated transport load fluctuation amount ΔF (1) is not “0” or “nearly 0”, the spring coefficients k1 and k2 of the belts used in the drive system are calculated based on the transport load amount F (1). The calculated transport load fluctuation amount ΔF (1), spring coefficients k1, k2 and thermal energy E (1, j) are sent to the transport speed fluctuation amount calculation unit 26.

When the conveyance load fluctuation amount ΔF (1) is input to the conveyance speed fluctuation amount calculation unit 26, the conveyance speed fluctuation amount H (1) is obtained based on the conveyance load fluctuation amount ΔF (1). The calculated transport speed fluctuation amount H (1) is written in the RAM 26a. Thereafter, the same processing as before is performed until the transport load fluctuation amount becomes “0” or “almost 0” (the line at that time is the (1 + i ′) line). When the conveyance load fluctuation amount becomes “0” or “almost 0”, the conveyance speed fluctuation amount from the first line to the (1 + i ′) line is obtained by Expression (8). Then, the correction data calculation unit 27 calculates the correction heat energy E _c according to the equation (10) based on the conveyance speed fluctuation amount. Then, the sum of the corrected thermal energy E _c and the thermal energy E (1, j) to E (1 + i ′, j) obtained by the transport load fluctuation amount calculation unit 25 is defined as corrected printing energy. The corrected printing energy is converted into image data by the data conversion LUT memory 27a as yellow correction data, and sent to the line memory 28.

  When the calculated transport load fluctuation amount ΔF (1) is equal to “0” or “almost 0”, the following processing is performed. When the conveyance speed fluctuation amount is not stored in the RAM 26a, the thermal energy E (1, j) is converted into yellow image data again, and then the yellow image data is sent to the line memory 28. When the conveyance speed fluctuation amount is stored in the RAM 26 a, the yellow correction data is calculated by the correction data calculation unit 27, and then the yellow correction data is sent to the line memory 28.

  When the yellow image data and the yellow correction data are written in the line memory 28, each heating element of the thermal head 7 generates heat accordingly, and a yellow image is recorded on the recording paper 2.

  When the recording of all the lines of the yellow image is completed, the feeding of the recording paper 2 in the recording direction is stopped, and then the recording paper 2 is fed in the paper feeding direction. When the recording paper is fed in the paper feeding direction, the platen roller 8 is moved away from the thermal head 7 by a shift mechanism (not shown). Simultaneously with the conveyance in the paper feeding direction, the yellow fixing lamp 12 of the optical fixing device 11 is turned on to fix the yellow thermosensitive coloring layer in the recording area of the recording paper 2. When the optical fixing is completed with respect to the recording area, the conveyance motor 6 stops. Thereafter, the recording paper 2 is fed in the recording direction, and the magenta and cyan printing processes are started. The magenta and cyan printing processes are the same as the yellow printing process except for the method of calculating the conveyance speed fluctuation amount.

  When each color printing process is completed and the heated portion of the recording paper 2 is discharged out of the apparatus, the cutter 16 operates after the transport motor 6 is stopped. As a result, the recording area is separated from the unrecorded area, and a sheet-like color print is obtained.

  In this embodiment, a 1-head 3-pass color thermal printer has been described as an example. However, the present invention may be applied to a 3-head 1-pass color thermal printer as shown in FIG. In addition, the same code | symbol is attached | subjected to the same structural member as this embodiment. In this case, platen motors 33, 34, and 35, and conveyance units 36, 37, and 38 (reference numerals of the pulleys and rollers are omitted) are provided on the platen rollers 30, 31, and 32 of the respective colors. Then, in the print stages 41 to 43 for each color, the amount of variation in the conveyance load of each line is obtained, and the amount of variation in the conveyance speed is calculated based on the amount of variation. The thermal energy calculated from the image data is input to the recording paper for the lines that do not occur, thereby suppressing the occurrence of density unevenness based on the conveyance load fluctuation amount at the time of recording each line. Reference numeral 44 denotes a yellow fixing device, and 45 denotes a magenta fixing device.

  In the present embodiment, the color thermal printer has been described. However, other printers in which the conveyance load fluctuates due to the fluctuation amount of the thermal energy of each line, for example, sublimation type, thermal melting type using yellow, magenta, and cyan color ink sheets. The present invention may be implemented in a thermal transfer printer.

It is a graph which shows the relationship between the total heat energy thrown into a recording paper, and the load by the printing at the time of yellow printing. 1 is a schematic view showing a color thermal printer of the present invention. It is the schematic which shows the conveyance speed fluctuation model by printing load. It is a graph which shows the relationship between the spring coefficient of a belt, and load. It is a flowchart which shows the process sequence for preventing the density | concentration nonuniformity generation | occurrence | production by a conveyance speed fluctuation | variation. It is a flowchart which shows the procedure which calculates conveyance load fluctuation amount. It is the schematic of another embodiment which shows the color thermal printer of a 1 pass 3 head system.

Explanation of symbols

2 Recording paper 3 Conveying section 4 Conveying roller pair 4a Capstan roller 4b Nip roller 5 Belt transmission section 5a Capstan pulley 5b Intermediate small pulley 5c First timing belt 5d Intermediate large pulley 5e Motor pulley 5f Second timing belt 6 Conveying motor 7 Thermal head DESCRIPTION OF SYMBOLS 10 Controller 11 Optical fixing device 25 Conveyance load fluctuation amount calculating part 26 Conveying speed fluctuation amount calculating part 27 Correction data calculating part 30-32 Platen roller 33-35 Platen motor 36-38 Conveying part

Claims (2)

A heating head in which a plurality of heating elements are arranged along the main scanning direction causes each of the heating elements to generate heat in accordance with image data, and a recording sheet whose surface is covered with a synthetic resin protective layer is placed in the main scanning direction. In a thermal printer that records images line by line by sending them in the sub-scanning direction intersecting
The thermal energy to be applied to the recording paper is calculated based on the image data when recording each line, and the transport load F (i) at the time of recording each line is determined based on the thermal energy. -1) The difference F (i) -F (i-1) between the conveyance load amount F (i-1) of the line and the conveyance load amount F (i) of the i-th line is defined as the conveyance load fluctuation amount ΔF (i). A required transport load fluctuation calculation unit;
A transport speed fluctuation amount calculation unit for obtaining a transport speed fluctuation amount based on the transport load fluctuation amount ΔF (i);
A correction data calculation unit for obtaining correction data for image data based on the conveyance speed fluctuation amount when the conveyance load fluctuation amount ΔF (i) exceeds a certain value;
A printing unit that performs printing by correcting the heat generation amount of each heating element based on the correction data;
In calculating the transport load fluctuation amount ΔF (i), whether or not the surface temperature of the recording paper crosses the glass transition point of the protective layer during recording from the (i-1) th line to the i-th line. Determine
When straddling the glass transition point, F (i) + F (i−1) − (conveying load amount at the time of printing of the glass transition point), and when not straddling the glass transition point, F (i ) -F (i-1). A heating head in which a plurality of heating elements are arranged along the main scanning direction causes each of the heating elements to generate heat in accordance with image data, and a recording sheet whose surface is covered with a synthetic resin protective layer is placed in the main scanning direction. In a thermal printing method of recording an image line by line by sending it in the sub-scanning direction intersecting
Calculating the thermal energy to be given to the recording paper based on the image data when recording each line;
Based on the heat energy, the conveyance load amount F (i) at the time of recording each line is obtained,
The difference F (i) −F (i−1) between the transport load amount F (i−1) of the immediately preceding (i−1) line and the transport load amount F (i) of the i th line is defined as the transport load fluctuation amount. As ΔF (i),
Based on the conveyance load fluctuation amount ΔF (i), a conveyance speed fluctuation amount is obtained,
When the transport load fluctuation amount ΔF (i) exceeds a certain value, correction data for image data is obtained based on the transport speed fluctuation amount,
Based on the correction data, the amount of heat generated by each heating element is corrected and printed,
In calculating the transport load fluctuation amount ΔF (i), whether or not the surface temperature of the recording paper crosses the glass transition point of the protective layer during recording from the (i-1) th line to the i-th line. Determine
When the glass transition point is not straddled, F (i) -F (i-1) is set. When the glass transition point is straddled, F (i) + F (i-1)-(printing of the glass transition point). The thermal printing method is characterized in that the transport load amount at the time).

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