JPH04337960A - Laser printer printing control device - Google Patents

Abstract

PURPOSE:To print characters and graphics with high quality by the laser printer of low resolution by allocating the plural bits of data to one picture element to be printed and selecting the kind of a pulse train for the unit of one picture element. CONSTITUTION:A pulse memory 13 stores pulse trains as data in advance, and the data stored in the pulse memory 13 are outputted as pulses for switching a laser after parallel/serial conversion at a shift register 12. In this case, since the frequency of a clock to decide the shift cycle of the shift register 12 is set at a value higher than the frequency of one dot, the pulse shorter than the pulse width of one dot can be obtained. Bit map memories 9 and 10 store code data for allocating the plural bits to one dot and for selecting the kind of the pulse train and in the case of printing, the output data of the bit map memories 9 and 10 are outputted to the address input terminal of the pulse memory 13 so that one kind of the pulse train can be selected.

Description

[Detailed description of the invention]

0001

FIELD OF INDUSTRIAL APPLICATION The present invention is utilized in electrophotographic printers such as laser printers to improve printing quality by increasing printing density in the main scanning direction.

0002

[Prior Art] A conventional device is disclosed in Japanese Patent Application Laid-Open No. 54-11412.
As described in No. 6, the recording density was increased by varying the clock frequency of the clock oscillation circuit that determines the scanning speed of the laser beam and the rotational speed of the photoreceptor drive section.

0003

[Problems to be Solved by the Invention] In the above-mentioned prior art, the printing density is changed by changing the speed of the drive unit in the sub-scanning direction, and since the speed of the electrophotographic printing process is changed, the quality of printing is affected. The problem was that it changed.

An object of the present invention is to obtain high print quality without changing the speed of the drive unit.

[0005]

[Means for Solving the Problem] In order to achieve the above object, a pulse memory that stores a plurality of types of pulse trains of one dot or less in the main scanning direction, a means for reading pulse trains from the pulse memory, and a paper to be printed are provided. A plurality of bits are allocated to each dot in a bitmap memory for storing dot data corresponding to the dot data, and means is provided for selecting one type from among the plurality of types of pulse trains based on the plurality of bits of data read from the bitmap memory.

[0006]

[Operation] The printing density in the sub-scanning direction of a laser printer is determined by the rotational speed of the motor of the drive unit and the scanning speed of the laser beam, and is constant in a normal laser printer. On the other hand, the printing density in the main scanning direction can be increased by decreasing the pulse width for switching the laser, in accordance with the pulse width. A pulse train is previously stored in the pulse memory as data, and the data stored in the pulse memory is converted from parallel to serial by a shift register to become a pulse for switching the laser, and is output. By setting the frequency of the clock that determines the shifting period of the shift register to a value higher than the frequency of one dot, a pulse shorter than the pulse width of one dot can be obtained. The bitmap memory stores code data for selecting the type of pulse train by allocating multiple bits per dot, and when printing, the output data of the bitmap memory is output to the address input terminal of the pulse memory and multiple bits are assigned. One type of pulse train can be selected from the pulse trains.

[0007]

Embodiment An embodiment of the present invention will be described below with reference to FIGS. 1 to 5.

FIG. 1 shows a configuration diagram of a printing control device. The host device 4 transfers to the printing control device 1 the size of characters to be printed, character data such as character codes, graphic data such as graphic type, size and position information, and control codes necessary for printing.

The data such as characters, graphic data and control codes are transferred to the bus 12 via the host interface 3, and the microprocessor 2 is transferred to the program ROM.
The character, graphic data, and control code are interpreted and processed by a program stored in the computer 7.

The RAM 5 is a memory used by the microprocessor 2 to temporarily store data necessary for processing. The character pattern memory 6 is a memory in which coordinate data indicating the shape of the outline of a character to be printed is stored. The bitmap memories 9 and 10 are memories for storing dot data corresponding to positions on paper to be printed, and the character pattern data stored in the character pattern memory 6 is processed by the microprocessor according to the algorithm stored in the program ROM 7. It is used to store the dot data converted by step 2, or to store the data converted into dots corresponding to the graphic when data for printing a figure is transferred from the host device 4. The print control circuit 11 transfers the dot data stored in the bitmap memories 9 and 10 to the printer engine 1.
4 controls reading at a timing synchronized with printing. The engine interface 8 is an interface circuit for instructing the printer engine 14 to start printing and for receiving information indicating the status of the printer engine 14 from the microprocessor 2.

The bitmap memory is composed of two planes 9 and 10, and one dot is represented by a 2-bit code. The 2-bit code data read from the bitmap memory is output to the address input terminal of the pulse memory 13, and the parallel data output from the pulse memory 13 is output to the shift register 12. The shift register 12 converts parallel data into serial data and outputs it to the printer engine 14. By setting the frequency of the clock that determines the period for shifting data in the shift register 12 to a value higher than the frequency of one dot, a pulse shorter than the pulse width of one dot can be obtained.

FIG. 2 shows a part of a character or figure to be printed, where a dashed line 20 indicates the theoretical boundary line of the character or figure, and the shaded area indicates that it is to be filled in black. Further, the dotted grid indicates the boundary of one dot printed by the printer engine 14.

The hatched area in FIG. 3 indicates the area that is filled in when the theoretical boundary line of the character or figure shown in FIG. Because the image is digitized, the quality of the diagonal lines, which should be smooth, is compromised.

FIG. 4 is a digitized version of the characters or figures shown in FIG. 2 according to the present invention. In general, when the theoretical position of the character or figure to be printed and the dot position do not match, the boundary line is made into a pulse shape of about 24 dots/mm or more to create a pseudo intermediate value, and when viewed from a distance. It is known that the quality of time is improved (D
digital formats for typefa
ces, written by Peter Karow, published by URW). In the horizontal direction, without changing the density in the vertical direction, that is, in the sub-scanning direction,
That is, when the boundary of one dot is far from the boundary of a character outline or figure in the main scanning direction, switching is performed with a pulse shorter than one dot to achieve a pseudo intermediate value. Here, two types of pulse trains are used depending on the ratio of the area of the theoretical black part to be filled in to one dot.

FIG. 5 shows the 2-bit code data output from the bitmap memories 9 and 10 and the pulse memory 1.
3 shows the correspondence between the pulses stored in No. 3 and the area ratio of the black part of the character or figure in the one-dot grid. When filling in characters or figures specified by the host device 4, the area to be filled within a 1-dot grid ranges from 0% to 25%.
When it is %, it is white and its code is 00. When the area to be filled within the grid of one dot is from 75% to 100%, it is black and the code is 11. 25% to 50%, 5
Codes from 0% to 75% are 01 and 10, respectively, representing intermediate values, and code 10 is a darker intermediate value than code 01. The pulse memory 13 is connected to the bus 12 and can be changed by writing from the microprocessor 2, so it can be changed according to the printing characteristics of the printer engine 14 or according to the user's preference.

Furthermore, by increasing the number of planes of the bitmap memory to three or more planes, increasing the capacity of the pulse memory, and increasing the types of pulse trains, it is possible to further increase the number of intermediate values and improve the quality.

FIG. 6 shows another embodiment of the present invention.

The print control device 1 sends dot data such as characters and graphics to be printed to the printer engine 14. The interface 32 communicates with the print control device 1 and sends the status of the printer engine 14 to the print control device 1 and receives a print start signal from the print control device 1. The printing control device 1 sends dot data through a plurality of signal lines, and the data is input to the address input terminal of the pulse memory 13. The parallel data output from the pulse memory 13 is output to the shift register 12. The shift register 12 converts the parallel data into serial data and outputs it to the laser control circuit 30, and the laser 31 is switched by the output. By setting the frequency of the clock that determines the period for shifting data in the shift register 12 to a value higher than the frequency of one dot, a pulse shorter than the pulse width of one dot can be obtained. The relationship between the pulses stored in the pulse memory 13 and the input data is the same as that described in FIG. 1 above. Data determining the pulses generated by the pulse memory 13 is transmitted from the printing control device 1 to the interface 32.
Can be rewritten via .

[0019]

[Effects of the Invention] According to the present invention, quality can be improved by expressing intermediate values in a pseudo manner using a pulse train, so there is no need to increase the motor rotation speed of the drive unit of a laser printer or the laser scanning speed. , it is possible to prevent print quality from deteriorating due to changes in the electrophotographic printing process and provide a low-cost, high-quality printing device.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a print control device according to an embodiment of the present invention.

FIG. 2 is a diagram showing an example of a portion of characters or figures to be printed.

FIG. 3 is a diagram showing an example in which characters or figures to be printed are filled in using a conventional technique.

FIG. 4 is a diagram showing an example in which characters or figures to be printed are filled in using the present invention.

FIG. 5 is a diagram showing an example of a pulse shape and a code indicating the pulse.

FIG. 6 is a block diagram of a printer engine according to another embodiment of the present invention.

[Explanation of symbols] 1...Printing control device, 9, 10...Bitmap memory, 1
1... Print control circuit, 12... Pulse memory, 14... Printer engine.

Claims (4)

[Claims] Claim 1: A printing control device comprising a bitmap memory that stores data to be printed and a data readout control circuit that controls reading out of the data stored in the bitmap memory in raster format; 1. A print control device for a laser printer, characterized in that a means for generating a pulse train in a main scanning direction is provided, a plurality of bits of data are assigned to one pixel to be printed, and the type of pulse train can be selected for each pixel. 2. The laser printer according to claim 1, comprising:
1. A print control device for a laser printer, characterized in that means for generating a plurality of types of pulse trains is rewritable. 3. A laser printer comprising a laser that generates a laser beam and a laser control circuit that switches the laser according to data sent from a printing control device, wherein a pulse generation means that generates a plurality of types of pulse trains is provided to control the printing. A laser printer characterized in that a pulse train generated by the pulse generating means can be selected based on data sent from the device. 4. A laser printer according to claim 3, wherein the pulses generated by the pulse train generating means can be changed from a printing control device.