Incremental printing of symbolic information – Thermal marking apparatus or processes – Gradational recording
Reexamination Certificate
1998-09-21
2001-04-24
Le, N. (Department: 2861)
Incremental printing of symbolic information
Thermal marking apparatus or processes
Gradational recording
Reexamination Certificate
active
06222572
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a thermal recording apparatus which performs recording pixels each having a predetermined density by selectively driving a plurality of heating-elements mounted on a thermal head.
More particularly, the invention relates to a thermal recording apparatus, in which a pixel is formed by a plurality of dots arranged in a matrix form, capable of greatly increasing the number of gradation levels while maintaining resolution and providing a smooth change in the gradation of each pixel by forming a dot pattern in accordance with the energy amount of a dot formed in the matrix, the energy amount being quantized in multi levels.
2. Description of Related Art
Conventionally, there have been proposed various thermal recording apparatus using a thermal head for printing images with multi gradation levels.
For example, Japanese Patent (JP) publication No. 6(1994)-30887 discloses a thermal printer which selectively causing a plurality of heating resistance elements mounted on a thermal head to generate heat for printing out images is provided with means for driving the resistance elements on an every second pixel basis, which can produce an even density distribution in the printed images. The printer is also provided with means for energizing the resistance elements associated with odd pixels and those associated with even pixels at different time points, yet a plurality of resistance elements out of each of the odd and even resistance elements at the same time.
JP publication No. 7(1995)-46828 discloses a thermal transfer type recording apparatus including a thermal head provided with a plurality of heating-elements arranged in line, the thermal head being moved relative to a substantially perpendicular direction with respect to the arrangement direction of the heating-elements, yet the heating-elements being selectively caused to generate heat for transferring an ink to a desired position on printing paper, whereby to provide a gradation of each pixel in accordance with a dot matrix region of ink transferred. This apparatus further includes a memory which stores in advance plural dot patterns formed by dots in the matrix form to be transferred and the energy supply level of each heating-element, the energy supply level being quantized to multi levels, a determining means which determines, per pixel, the dot pattern constituted of dots in a matrix assigned to the pixel and the energy supply level of each heating-element corresponding to each dot based on the density for the multi-gradation level signal, referring to the memory, and means for causing the generation of heat and the movement of the thermal head in accordance with the pattern and energy supply level of the pixel, determined by the determining means. The memory stores a pattern of dots arranged in the relative movement of the thermal head as a pattern formed by a plurality a dots to be transferred in a matrix. The memory stores, preferably, the dot patterns in a low, middle, and high density ranges respectively, in which the pattern in a low density range comprises a single dot to be printed, the pattern in the middle density range comprises dots arranged in the direction of the relative movement of the thermal head, and the pattern in the high density range comprises at least one dot in addition to the dots arranged as above. The apparatus uses both a pseudo half tone printing method for printing images with gradation or gray levels and a heat energy control method. The apparatus also uses the patterns of dots arranged in the direction of the relative movement of the thermal head to printing paper for a pattern comprising a plurality of dots to be printed in a matrix to provide a gradation level. Accordingly, the apparatus can print half tone images improved in resolution and image quality.
However, in the thermal printer disclosed in JP publication No. 6-30887, one pixel is constituted of a plurality of dots and the heating-element corresponding to each dot is driven to control the gradation level of each pixel, so that the resolution and the number of gradation levels are degraded if one pixel is formed by a small number of dots.
In the thermal transfer recording apparatus disclosed in JP publication No. 7-46828, the pattern is formed by a part of dots in a matrix of each pixel. As a result, there occur problems that there is a limitation in a minimum number of dots forming one pixel and that the constant matrix size can not provide the large increment of the number of gradation levels without degrading resolution.
SUMMARY OF THE INVENTION
The present invention has been made in view of the above circumstances and has an object to overcome the above problems and to provide a thermal recording apparatus which prints a pixel in a dot matrix formed by a plurality of dots and forms a dot pattern by quantizing the amount of energy supplied to a heating-element whereby to form the dot matrix, resulting in the great increment of the number of gradation levels with a constant resolution and a smooth change in the gradation of each pixel.
Additional objects and advantages of the invention will be set forth in part in the description which follows and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
To achieve the objects and in accordance with the purpose of the invention, there is provided a thermal recording apparatus including a heat recording device provided with a plurality of heating-elements, a dot pattern memory for storing a dot pattern defined by a plurality of dots arranged in a matrix form, forming a pixel to be printed with the heat recording device, a gradation level pattern memory for storing a plurality of gradation level patterns formed per pixel by determining a minimum and maximum values of dot formation energy to be supplied to the heating-element, and providing the minimum energy value to one of the print dots forming a pixel and to remaining print dots in a predetermined sequence until the maximum energy value is provided to all of the print dots, and a heat-generation drive device for selectively driving the heating-elements of the heat recording device in accordance with the dot pattern of the print dots stored in the dot pattern memory and the gradation level pattern stored in the gradation level pattern memory.
In the above thermal recording apparatus, each pixel is formed by a plurality of dots in a matrix form, and the level of energy amount of each dot is quantized and stored in the gradation level pattern memory. As the increase of the gradation density, the number of dots to be provided in the matrix is increased one by one in a predetermined sequence, when a minimum value of the energy level is sequentially assigned to each dot. If the minimum energy value is provided to all of the dots, the energy level of each dot is changed in a predetermined sequence to the next large level until a maximum energy level is provided to all of the dots, thereby forming dot patterns. Thus, the dot patterns are stored in advance in the dot pattern memory. The heating-elements corresponding to the dot pattern are driven to generate heat to print dots of a predetermined energy level, performing multi gradation recording of each pixel.
Since the energy level of each dot constituting a matrix is quantized, accordingly, a large number of gradation levels can be provided even by the same matrix size as conventional one. In addition, the number of gradation levels can be increased even by small matrix size. Consequently, a smooth change in gradation levels can be achieved without degrading resolution.
According to another example of the present invention, there is provided a thermal recording apparatus including an input device for inputting character data, a thermal head provided with a plurality of heating-elements to print ch
Brother Kogyo Kabushiki Kaisha
Feggins K.
Le N.
Oliff & Berridg,e PLC
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