JPH06102385B2 - Image printer - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image printer capable of multi-gradation printing, and an image printer applicable as a hard copy device in the field of computer graphics, video system, and communication such as facsimile. It is about.

Conventional configuration and its problems Recently, due to the improvement in the manufacturing technology of integrated heads, the density of head elements has increased and high-resolution hard copy has become possible. On the other hand, however, the number of head elements has increased. Along with this, the instantaneous power required at the time of printing also increases, and a large-capacity power supply is required to satisfy the required power, which is a major obstacle to downsizing and weight saving of the apparatus.

A divided printing method is used as one of the methods for reducing the power required for printing by using a head having a large number of elements. This method does not print on all the elements of the head at the same time, but divides the head into n blocks and prints sequentially for each block. The instantaneous power required for printing is 1 / n. Can be suppressed to

However, when the above-described divisional printing drive method is used, the printing speed is relatively slower in multi-tone printing than in binary printing, so that heat is easily dissipated at the block boundary portion. As shown in FIG. 5, between the dots corresponding to the switching position 3 of the block of the thermal head 2 in the printed image 1, linear noise (switching line) 5 that is not sufficiently printed occurs along the paper feeding direction 4. However, there is a drawback that the image quality is greatly deteriorated.

The cause of the switching line will be described with reference to FIG. In FIG. 2, .phi.1 and .phi.2 are waveforms indicating block sequential driving. SL is a line-shaped thermal head, T
1 and T2 are temperature distributions generated by the thermal head when uniform gradation data is printed, and DEN is the density distribution of dots printed by the head. In the example shown in the figure, the head is divided into a left half of 0 to 255 and a right half of 256 to 511, and the left block is driven for phase φ1 and the right block is driven for phase φ2 sequentially.

Now, considering the case of printing uniform gradation data (binary recording), the density distribution DEN of printing is obtained according to the temperature distributions T1 and T2 generated by the head. It is assumed that T1 and T2 also take into consideration the effect of heat diffusion to the peripheral parts such as the printing paper connected to the head. Here, as indicated by T1 and T2, the elements 0, 255 and 256, 511 at both ends of each block have different temperature distributions from the other elements. Ie 1-254 and 257
As for the elements between 510 and 510, both adjacent elements also generate heat at the same time, so that the gap between the elements also reaches a certain temperature due to thermal diffusion of each other. Therefore, the density of each printed dot can also be obtained to some extent as shown by DEN in FIG.

However, 0,255 and 25 located at both ends of each block
The elements of 6,511 generate heat only to the elements adjacent to them, and the heat is diffused further in the direction in which heat is not generated, and the temperature distribution shown by T1 and T2 is exhibited. as a result,
The print density DEN around the element is lower than the gap between other elements as shown in FIG. In the case of 0 and 511 elements at both ends of the entire head, since it is the end of the image, the image quality will not be greatly deteriorated, but the gap between the elements 255 and 256 located at the joint between the two blocks is The density is extremely low compared to the gap between them, and a white linear defect is generated just in the center of the image, which significantly deteriorates the image quality. When the thermal diffusion to the periphery of the element at the end of the block is further large, not only the gap between the elements but also the print dot itself by the corresponding element may have a lower density than other elements. This causes a large deterioration in image quality.

As a method for suppressing such a switching line, there is a method of incrementally correcting the applied voltage applied to each element. When such incremental correction of the applied voltage is performed, the energy per unit time increases, so the density peaks of both pixels sandwiching the block boundary rise, and the density itself at the block boundary portion also slightly increases. However, the gap between the density peaks of both pixels sandwiching the block boundary did not change much, and the density decrease at the block boundary still existed, and the switching line could not be sufficiently suppressed.

As described above, when an image is printed by multi-gradation recording by the conventional divided printing method, a switching line that causes noise occurs between the blocks of the head, which causes a problem of image quality deterioration.

An object of the present invention is to solve the above problems and to provide an image printer in which deterioration of image quality due to a switching line which occurs when an image is printed in multi-gradation recording by a division printing method is reduced. Has an aim.

According to the image printer of the present invention, a thermal head having a plurality of elements arranged in a line and a thermal head composed of the plurality of elements are divided into a plurality of blocks, and each element in the same block is energized at the same time. An image printer having a driving circuit for sequentially energizing divided blocks and performing recording, and capable of continuously recording dot printing in multiple gradations in the line direction, in each block of the thermal head. The energization pulse width data is preset in the element of the block which is recorded in advance for a total of two elements each including one element located in the boundary portion of each block adjacent to each other in the boundary portion. The first correction coefficient larger than 1 is multiplied, and the energization pulse width data for the element of the block to be recorded later is smaller than the first correction coefficient and larger than 1. It is characterized in that a correction means for multiplying by a second correction coefficient is provided, and the correction means performs the incremental correction of the energization pulse time.

Description of Embodiments An embodiment of the image printer configuration of the present invention is shown in FIG.
In FIG. 3, 6 is an image input section, 7 is a CPU, 8 is a correction coefficient section, 9 is a line memory for recording data corresponding to the number of elements of the thermal head, and 10 is a divisional energization drive of the thermal head in block units. Reference numeral 11 denotes a thermal head in which a plurality of heat generating elements are arranged in a line, and the division driving unit 11 performs the gradation recording according to the data in the line memory 9.

The image input unit 6 converts the input image signal into gradation data and inputs it to the CPU 7. The CPU 7 converts the gradation data into energization pulse width data for energizing and driving the head element and outputs it to the line memory 9. Further, regarding the gradation data for both elements sandwiching the boundary portion of the head block, the correction coefficient unit 8 is referred to, and the gradation data is multiplied by the correction coefficient set in advance, and the energization pulse width data subjected to the incremental correction And output to the line memory 9.

Further, each element in the thermal head 11 is driven by the division drive unit 10 for an energization time according to energization pulse width data of each element stored in the line memory 9. Therefore, since each element in the thermal head 11 is energized for a variable time, the heat generation energy of each element becomes multi-gradation, and if a sublimable dye is used, multi-gradation recording can be performed for each pixel. .

The image printer according to the present embodiment has a division driving unit for each block for a plurality of blocks forming the thermal head 11.
Thermal head 11
Is an image printer capable of continuously recording dot printing in multiple gradations in the line direction. The characteristic is that two elements in total, which are adjacent to each other at the boundary of each block forming the thermal head 11 and located at the boundary of each block, are preceded by a total of two elements. The elements of the block to be recorded are multiplied by the energization pulse width data by a preset first correction coefficient larger than 1, and the elements of the block to be recorded later are energized by the energization pulse width data. Correction means for multiplying a second correction coefficient smaller than the correction coefficient of 1 and larger than 1 is provided (in the embodiment, the CPU 7 and the correction coefficient part 8 correspond to each other), and this correction means performs the incremental correction of the energizing pulse time. Yes, the dots at the boundary of the divided blocks of the head as described in the conventional example,
Also, in order to compensate for the low density portion that occurs in the gap, the density data of the boundary dot is multiplied by a correction coefficient, and the gradation data that is incrementally corrected from the actual value is printed to divide it. The effect of the switching line generated between the dots of the block is reduced.

As shown in FIG. 2, the element at the end point of the divided block of the head diffuses heat because the element adjacent to one side thereof does not generate heat, and the density of the print dot and its peripheral portion decreases. For this reason, the gradation data of only the boundary dots are incrementally corrected, and the current is supplied for a longer time than the actually supplied gradation data to promote the diffusion of heat to the heat-generating dots of the element and its surroundings. Correct the density of the dots and their surroundings. That is, the density of the dots themselves rises due to the heat generated by the elements at the end points of the divided blocks, the gap between the dots narrows due to the diffusion of heat around the dots, and the density between the dots rises. Therefore, it is necessary to suppress the correction width to such an extent that the increase in dot density does not give a visually uncomfortable feeling, but by performing the incremental correction, it is possible to visually narrow the gap between the dots at the boundary of the block, and The influence of the switching line can be reduced.

The effects of this embodiment will be described in more detail below. When the element at the block boundary portion of the thermal head is subjected to the incremental correction by the energizing pulse width as in this embodiment, the energy is increased and the power supply time becomes longer, so that the temperature peak rises and the heat With the addition of time diffusion
An increase in print density and an increase in print dot diameter occur simultaneously. That is, after the correction, the density peaks of both pixels sandwiching the block boundary shift toward the block boundary, and the correction can be made almost the same as the gap of the density peaks of the other pixels. Furthermore, since it is possible to increase the recording density of both pixels sandwiching the boundary of the block and to enlarge the area of both pixels as compared with the case without correction,
The density at the boundary of the block is increased, and the switching line can be almost completely removed.

Further, in the present embodiment, the energization pulse width data is incrementally corrected in a multiplying manner, so that the increment amount is proportionally adjusted, such as a small increment in the low gradation part and a large increment in the high gradation part. , It is possible to accurately correct each gradation. Actually, since the appropriate correction coefficient value changes depending on the gradation, it is possible to further improve the image quality by changing the correction coefficient value for each gradation or for each gradation having a certain width. This can be easily realized by preparing the correction coefficient part in advance as a table of gradation data and referring to the correction coefficient from the table according to the gradation data of the corresponding element.

Further, the two elements 255 and 256 adjacent to each other at the boundary of the divided blocks have different temperature distribution histories in terms of time, and in some cases, it is necessary to consider the influence of the thermal history.

That is, in the divided driving sequence of the head, as shown in FIG. 2, the left half is printed with the phase φ1 and the right half is printed with the phase φ2. Usually, after φ2, there is a pause period of the head due to paper feeding or the like, and then the sequence of printing of the next line is performed.

Therefore, in the element 255 at the right end of the left block of the head, the extra heat diffusion in the direction of the element 256 on the right side is large. On the other hand, in the element 256 at the left end of the right block, the element 255 on the left side of the element has been driven until immediately before, and therefore the extra heat diffusion in the direction of the element 255 is not so large due to the influence of the residual heat. Due to the difference in thermal history as described above, the manner in which the concentrations of both elements and their surroundings decrease is also different.

Therefore, a correction coefficient is provided independently for each of the two dots on the boundary, and for element 255, energization pulse width data is multiplied by correction coefficient k1 for incremental correction, and for element 256, energization pulse width data is multiplied by correction coefficient k2. Perform incremental correction. The correction coefficient k1 and the correction coefficient k2 are (k1>k2>
There is a relationship like 1), and dots on both sides of the boundary and
The correction can be performed in consideration of the density balance of the peripheral portion, and the image quality can be further improved.

Note that, in the present embodiment, an example in which the thermal head is divided and driven by two blocks has been described for the sake of simplicity. However, the technical idea of the present embodiment naturally means that the thermal head is not limited to two blocks. It is self-evident that it can be applied even if it is divided into three or more blocks. In that case, the point is that the elements of the block to be recorded ahead of two elements in total, which are one element located at the boundary of each block and adjacent to each other at the boundary of the adjacent blocks, are recorded. Is multiplied by a first correction coefficient which is larger than 1 which is set in advance, and the elements of the block to be recorded later have the energization pulse width data which is smaller than the first correction coefficient and is smaller than 1. It may be multiplied by a larger second correction coefficient.

EFFECTS OF THE INVENTION As is apparent from the above description, the image printer of the present invention is configured such that the thermal head having a plurality of elements arranged in a line and the thermal head having the plurality of elements are divided into a plurality of blocks, and the same block is provided. In the image printer capable of recording dots by multi-gradation continuously in the line direction, the circuit has a driving circuit for simultaneously energizing each element of the above and driving by sequentially dividing and energizing for each block. ,
When performing divided printing, the print data given to two elements adjacent to each other at the boundary of the divided blocks of the thermal head is multiplied by the correction coefficient to perform the incremental correction of the energization pulse time, thereby increasing the energy and the power. Since the supply time of the ink becomes longer, a rise in the temperature peak and a time diffusion component of the heat are added, and an increase in the print density and an increase in the print head diameter occur simultaneously. Therefore, after the correction, the density peaks of both pixels sandwiching the boundary of the block deviate toward the boundary part of the block, and the correction can be made almost the same as the interval of the density peaks of the other pixels. Furthermore, since it is possible to increase the recording density of both pixels sandwiching the boundary of the block and to enlarge the area of both pixels compared to when there is no correction, the density of the boundary of the block is increased and the switching line is almost perfect. Can be removed.
Further, as a result, a small-capacity power supply can be used by the division printing, so that many effects such as size reduction, weight reduction and cost reduction of the apparatus can be expected.

[Brief description of drawings]

FIG. 1 is a printing state diagram showing a state of a head switching line generated in an image printed by a division driving method, and FIG. 2 is an explanatory diagram showing a temperature distribution around the head and a printing density generated by driving the head. FIG. 3 is a block diagram showing the configuration of an image printer according to an embodiment of the present invention. 7 ... CPU, 8 ... correction coefficient part, 9 ... line memory, 1
0 …… Split drive, 11 …… Thermal head

Claims (2)

[Claims] 1. A thermal head in which a plurality of elements are arranged in a line and a thermal head including the plurality of elements are divided into a plurality of blocks, and each element in the same block is energized at the same time. An image printer having a driving circuit for separately energized driving for recording and capable of continuously recording dot printing in multiple gradations in the linear direction, in an image printer adjacent to each other at a boundary portion of each block of the thermal head. For a total of two elements consisting of one element located at the boundary of each block, the energization pulse width data is stored in the element of the block that is recorded in advance,
A second correction coefficient smaller than the first correction coefficient and larger than 1 is applied to the energization pulse width data for the element of the block to be recorded later, which is multiplied by the first correction coefficient which is set to be greater than 1. An image printer characterized in that a correction means for multiplying by is provided, and the correction means performs the incremental correction of the energization pulse time. 2. The image printer according to claim 1, wherein the correction coefficient for the incremental correction is set as a table and is changed according to the gradation of the print data.