PRINTING SYSTEM FOR DOT-MATRIX PRINTER

Abstract: A printing system for a dot-matrix printer for printing a dot-matrix character or graphic pattern with a print head having head pins. The printing system includes a memory for storing preceding data printed by the head pins, a register for storing input data, a processing circuit for processing the stored preceding data from the memory and the input data from the register to modify the input data by omitting certain data items thereof, and a print head driver for enabling the print head to print the modified input data. When the printing system operates in a high-speed printing mode, the charac­ ter or graphic pattern with certain dots skipped can be printed at a higher speed. When the printing system operates in a normal-speed printing mode, the character or graphic pattern with certain dots skipped can be printed at a lower speed with low noises.

Description: SPECIFICATION PRINTING SYSTEM FOR DOT-MATRIX PRINTER BACKGROUND OF THE INVENTION The present invention relates to a printing system for use in a dot-matrix printer. The speed of printing in dot-matrix printers is determined by the repetitive cycle time of a dot printing head. For increasing the printing speed with print heads having limited printing capability, it has been conventional practice to skip or omit certain dots when printing a pattern or to use a font of dot patterns from which certain dots are removed. However, the conventional printing practice has been disadvantageous in that printed characters are of poor quality. Examples of prior dotmatrix printing processes are disclosed in Japanese Patent Publications No. 57-18632 published on April 17, 1982, No. 5733594 published on July 17, 1982, and No. 57-51113 published on October 30, 1982. SUMMARY OF THE INVENTION It is an object of the present invention to provide a printing system for a dot-matrix printer, which can perform highspeed printing and low-noise printing orations without substantially lowering the quality of printed characters, so that no high-speed font of dot patterns will be necessary. According to the present invention, there is provided a printing system for a dot-matrix printer for printing a dotmatrix character or graphic pattern with a print head having head pins. The printing system includes a memory for storing preceding data printed by the head pins, a register for storing input data, a processing circuit for processing the stored preceding data from the memory and the input data from the register to modify the input data by omitting certain data items thereof, and a print head driver for enabling the print head to print the modified input data. The above and other objects, features and advantages ofthe present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which a preferred embodiment of the present invention is shown by way of illustrative example. BRIEF DESCRIPTICN OF THE DRAWINGS FIG. 1 is a block diagram of a printing system according to the present invention; FIG. 2 is a block diagram of a processing circuit in the printing system of FIG. 1; FIg. 3 is a timing chart of operation of a print head driven in a normal printing mode; FIG. 4 is a timing chart of operation of the print head driven in a dot-skip mode; FIG. 5 is a diagram showing a print head and a dot pattern printed by the print head in the normal printing mode; and FIG. 6 is a diagram illustrative of a dot pattern printed in the dot-skip mode. DESCRPTION OF THE PREFERRED EMBODIMENT FIg. S shows a print head of a dot-matrix printer and a letter "B" printed thereby in a normal printing mode. The print head has a vertical array of printing elements or head pins for printing one vertical column of dots at a time. The print head may have two vertical columns of printing elements or head pins which are staggered with respect to each other. FIG. 1 illustrates a printing system according to the present invention. Image data LD arranged in a pattern corresponding to the printing elements of the print head are stored in a dot-column register 1 as print data for one vertical column of dots. The print data for the previously printed vertical dot column are stored in a data memory 2. The data from the dot-column register 1 and the data from the data memory 2 are processed by a processing circuit 3 for each head pin in the manner described later, and the processed data are shifted as data to be printed into a print data register 4. In a high-speed printing mode, a high-speed printing control circuit 5 is enabled to drive a print head driver 6 to print the print data at a speed higher than a normal printing speed. The print data in the print data register 4 are stored into the data memory 2 for enabling the processing circuit 3 to process a next column of dots to be printed. FIG. 2 illustrates the processing circuit 3 in greater detail. The processing circuit 3 is composed of exclusive-OR gate 7 and an AND gate 8, for example, for preventing the print data item for each dot from being printed in any consecutive dot positions in the high-speed printing mode. More specifically, if the preceding data item for any head pin in the data memory 2 has been printed, the present data for the head pin is processed as data not to be printed regardless of the data stored in the dotcolumn register 1. when the preceding data item has not been printed, the data for the head pin is processed as data equal to the data stored in the dot-column register 1. The following table shows present data to be printed resulting from combinations of preceding data stored in the data memory 2 and present data stored in the dot-column register 1: Table EMI4.1 <SEP> g <tb> Preceding <SEP> data <SEP> ' <SEP> Present <SEP> data <SEP> Present <SEP> data <tb> Printed <SEP> stored <SEP> to <SEP> be <SEP> printed <tb> <SEP> 1 <SEP> 1 <SEP> 0 <tb> <SEP> 1 <SEP> 0 <SEP> 0 <tb> <SEP> o <SEP> 1 <SEP> 1 <tb> <SEP> Q <SEP> O <SEP> <SEP> O <SEP> <tb> 1: Dot printed or to be printed, O: Dot not printed or not to be printed FIG 3 shows the period in which a desired print head pin is driven in a normal-speed printing mode. The illustrated period represents the limited capability of the print head, and governs the printing speed of the printer. FIG. 4 shows that the data for second dot column is skipped and not printed in the highspeed printing mode according to the present invention. FIG. 6 illustrates a letter printed at a higher speed than the normal speed at which the letter is printed as shown in FIG. 5. The letter printed in the high-speed printing mode can be printed at a speed twice higher than the normal speed, without substantially lowering the printing quality. When not in the high-speed printing mode, the high-speed rinti control circuit 5 is disabled, and desired data are printed in the normal-speed printing mode. The high-speed printing mode and the normal-speed printing mode can be selected by a DIP switch provided in the printer, or by a command signal from a master control device. While the present invention has been described with respect to the high-speed printing mode, it is possible to employ the principle of the present invention in a normal-speed printing mode by eliminating the high-speed printing control circuit 5 and also by skipping or omitting certain dots, thereby reducing the printing density of printed letters and lowering the level of noise produced in the printing operation. Although a certain preferred embodiment has been shown and described, it should be understood that many changes and modifications may be made therein without departing from the scope of the appended claims.

Claims: What is claimed is: 1. A printing system for a dot-matrix printer for printing a dot-matrix character or graphic pattern with a print head having head pins, said printing system comprising: (a) a memory for storing preceding data printed by said head pins: (b) a register for storing input data; (c) a processing circuit for processing said stored preceding data from said memory and said input data from said register to modify said input data by omitting certain data items thereof; and (d) a print head driver for enabling said print head to print said modified input data. 2. A printing system according to claim 1, including a printing speed control circuit for controlling said print head driver to print said modified input data selectively in high- and normal-speed printing modes. 3. A printing system according to claim 1, wherein said processing circuit comprises an exclusive-OR gate and an AND gate for processing said preceding data and said input data.

Inventors: HATAKEYAMA, MOTONOBU OKI ELECTRIC IND. CO., LTD., MATSUMURA, TAKESHI OKI ELECTRIC IND. CO., LTD., SHIMOYAMA, NORIO OKI ELECTRIC IND. CO., LTD., YOSHIMURA, KOHTAROH OKI ELECTRIC IND. CO., LTD.
Applicants: OKI ELECTRIC INDUSTRY COMPANY, LIMITED
Application year: 1985
Main classification: G06K15
IPC codes: G06K15, B41J2