JPH05177868A - Optical writing printer - Google Patents

Abstract

PURPOSE:To especially uniformize printing density and to form an image having constant resolving power in an optical writing printer performing optical writing on a photosensitive body using a printing head wherein a plurality of light emitting elements are arranged in an array form. CONSTITUTION:When image data is written in a frame memory 26, the number of the black dots contained in the image data is counted by a counter/ comparator part 25 to calculate data of a printing ratio. A CPU 20 outputs the corresponding image data to an LED head circuit on the basis of the data of the printing ratio to optically write the same on a photosensitive drum to control an optical writing time. By this constitution, the lights from light emitting elements are uniformized in brightness and image density after the formation of an image becomes constant regardless of the change of the printing ratio.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical writing printer for performing optical writing on a photosensitive member by using a print head having a plurality of light emitting elements arranged in an array.

[0002]

2. Description of the Related Art As a printer device for performing optical writing using a print head having a plurality of light emitting elements arranged in an array,
For example, an LED printer is known. An LED printer is a printer that uses a so-called LED head in which LED (light emitting diode) elements are arranged in an array as a light emitting element for optical writing on a photoconductor, and when the number of LED elements is B4 size, printing is performed. Density 240D
The number of PIs is about 2400. But the LED
The elements require a large current for light emission, and a large current is required to drive all the LED elements at the same time. Therefore, light emission is usually controlled by time division driving (for example, four division driving).

FIG. 8 shows a time chart when driving an LED element arranged in a print head. As shown in the figure, the strobe (ST
B) The signal is output four times to drive, for example, 2400 LED elements in four time divisions. That is, the clock signal (CL
The print data is input dot by dot to the shift register (not shown) in synchronization with the output of K), and when 2400 print data are input to the shift register, this data is latched by the latch signal (LA) and then the STB signal is output. The corresponding LED element is driven based on the print data of "1" to "600" in synchronization with the output of 1 and then the printing of "601" to "1200" in synchronization with the output of STB signal 2 The corresponding LED element is driven based on the data. Furthermore, S
In synchronization with the output of the TB signal 3, "1201" to "180"
The corresponding LED element is driven based on the "0" th print data, and "1801" -is synchronized with the output of the STB signal 4.
LE corresponding to the "2400" th print data
Drive the D element.

As shown in the figure, the output time τ of the STB signal is constant in the conventional optical writing printer. Further, the output time τ of the STB signal described above is conventionally set to a time at which the photoconductor potential can obtain a prescribed light attenuation when all the LED elements driven by the output of the corresponding STB signal are made to emit light.

[0005]

However, the printing rate of the LED elements (the ratio of the light emitting elements actually emitting light to the number of light emitting elements driven by the corresponding STB signal) is not always constant. That is, since the LED element emits light based on the print data, the print ratio is 100% when a solid black image is created in reverse development, but the print ratio may be 75% depending on the supplied print data. , 50%
There are also times. Further, the printing rate may be 25% or less. Further, this printing rate is different once every time optical writing is performed on the photoconductor. FIG. 9 is a diagram in which, when the output time τ of the STB signal is constant (for example, 128 μs), the printing rate is changed and the light emission luminance (relative value) of one LED element is measured. As shown in the figure, the emission brightness of the LED element increases as the printing rate decreases. It is considered that this is because the current flowing through the circuit changes depending on the printing rate, and a voltage drop occurs instantaneously, and especially when the printing rate is large, the voltage drop also increases.

Further, FIG. 10 is a diagram showing the luminance difference for each printing rate based on FIG. 9 when the luminance when the printing rate is 100% is 100. As can be seen from the figure, it can be seen that the relative value of luminance increases as the printing rate decreases. Therefore, in the conventional optical writing printer, the light emission brightness of the LED element varies depending on the printing rate, and the output time τ of the light emitting element is constant even though the amount of light received by the photoconductor changes depending on the printing rate. When the electrostatic latent image formed on the image is developed, the print density becomes non-uniform and the resolution is lowered.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems of the prior art, and provides an optical writing printer which can make an image having a constant resolution and uniform printing density even if the printing rate changes. To aim.

[0008]

SUMMARY OF THE INVENTION According to the present invention, the above-described object is to face the charged photoconductor with a light dot generating means in which a plurality of light emitting elements are arranged in an array, and to cause the light emitting elements to be turned off by a strobe signal in response to a print signal. In the optical writing printer for performing optical writing on the photoconductor by dividing and emitting light, and for printing by developing the electrostatic latent image formed on the photoconductor by developing means, each division of the N time divisions. A comparing means for comparing the number of dots allocated therein and the number of dots to be printed during each division, and a time changing means for changing the time of the strobe signal based on the comparison value obtained by the comparing means. Characterize.

[0009]

EXAMPLES An example of the present invention will be described in detail below with reference to the drawings. This embodiment describes an example of an LED printer as an optical writing printer.
Shows the overall configuration of the LED printer. In the figure, L
The ED printer 1 includes a so-called image forming unit 4 including a photoconductor drum 2 and an LED head 3, a paper transport mechanism 7 including a paper feed cassette 5 and a paper feed roller 6, an interface controller board 8 and a head controller board 9. It is composed of a control circuit unit 10.

The image forming section 4 uses a photosensitive drum 2 which is rotatable in the direction of arrow a, a charger 11, an LED head 3, and a reversal developing system which are sequentially arranged near the peripheral surface of the photosensitive drum 2. The developing device 12, the transfer device 13, and the cleaner 14 are included. Further, the paper transport mechanism 7 is configured to transfer a predetermined amount of paper P.
Is formed on the photosensitive drum 2. The above-described paper feed cassette 5 for storing the paper P, the paper feed roller 6 for carrying out the paper P from the paper feed cassette 5, the slip roll 15 for carrying the paper P, and the paper P for a temporary standby. Paper P at the same timing as the toner image
It is composed of a standby plate 18 for re-feeding the sheet. Further, the fixing roll 17 fixes the toner image, which has been subjected to the transfer process described later by the transfer device 13, onto the paper P, and the paper discharge roll 16 is a roll for discharging the paper after the fixing process to the outside of the machine. Is.

On the other hand, the interface controller board 8 converts the character code output from the host computer connected to the LED printer 1 into dot pattern data, and stores this data in the frame memory 8 '(FIG. 1). ) Is provided. In addition, the head controller board 9 is controlled to output the data in the frame memory output from the interface controller circuit 8'to the LED head 3 described above, and also controls the photosensitive drum 2, the paper feed roller 6, and the slip. Output of a control signal for controlling the rotation of the roll 15, the fixing roll 17, etc. at a predetermined rotation speed, and the fixing roll 1
A control circuit for outputting a temperature control signal or the like to 7 is provided.

FIG. 1 is a circuit block diagram of the interface controller circuit 8 '. Interface controller circuit 8'is CPU 20, system ROM
(SROM) 21, system RAM (SRAM) 22,
It is composed of a character generator (hereinafter referred to as CG) 23, a character processing unit 24, a counter / comparison unit 25, and the frame memory 26 described above. The CPU 20 as a time changing unit executes print control processing according to a program stored in the system ROM 21, and writes a character code or print control information output from a host device such as a host computer (not shown) into the system RAM 22. In addition, processing such as changing the output time of the STB signal is performed.

The system RAM 22 has a capacity for storing image data for several pages of paper, and when a predetermined amount of data is written, the CPU 20 thereafter performs a data analysis process. For example, in the case of a character code, image data (dot pattern data) corresponding to the character code is read from the CG 23 and written in the frame memory 26 by the processing of the character processing unit 24. Further, when it is the print control information, the command is analyzed, and the process instructed by the command is executed. The process at this time is, for example, a process of rotating or reducing characters. The frame memory 26 has a memory capacity capable of storing image data of one page of paper, and the character processing unit 24 described above is used.
The image data output via is stored.

The counter / comparison unit 25 as a comparison means, when writing the image data in the frame memory 26, a counter for counting the number of dots (black dots) to be printed in the image data included in each line, and a comparator. It is composed of. Specifically, since the present embodiment drives the image data of one line in four time divisions, black dots are present in each of 600 image data which is 1/4 of the image data of one line, for example, 2400 data. The number of contained dots is counted, and the corresponding number of data, for example, the ratio of black dots to 600 data is compared (calculated). The comparison data of the counter / comparison unit 25 (hereinafter referred to as print ratio data) is the character processing unit 24.
Is output to the CPU 20 via. The CPU 20 determines the output time τ of the STB signal based on the printing rate data output from the counter / comparing unit 25.

When image data for one page of paper is stored in the frame memory 26, this image data is output to the printer controller board 9 and further output from the printer controller board 9 to the LED head 3 described above. FIG. 3 is a diagram showing a circuit configuration of the LED head circuit 3 ′ in the LED head 3. The LED head circuit 3'includes a shift register 30, a latch circuit 31, an AND gate 32,
The output of the driver circuit 33 is output via the resistor R to the LED elements arranged in a line in the LED head 3 via the resistor R. The LED elements are LED arrays 34-1 to 34-n arranged in a line in an array.
Are formed respectively. In addition, this LED array 34-1
Corresponding to ~ 34-n, the shift register 30 is also specifically configured by cascade connection of n shift registers 30-1 to 30-n. In addition, each LED array 34-
The number of LED elements formed in 1 to 34-n is about 80, for example.

Image data output through the printer controller board 9 is supplied to the LED head circuit 3'in synchronization with a clock signal (CLK), and image data (D) for one line is supplied to the shift register 30. Written. The image data written in the shift register 30 is latched by the latch circuit 31 in synchronization with the latch signal (LA), and the image data held in the latch circuit 31 is synchronized with the outputs of the STB signals 1 to 4 in the driver circuit. It is output to the corresponding LED element via 33, and L is output according to the image data.
The ED element is controlled to emit light.

Next, the printing process by the LED printer 1 of this embodiment will be described. As described above, the character code output from the host device is stored as image data in the frame memory 26 under the control of the CPU 20 based on the print control information. At this time, the counter / comparing unit 25 counts the number of black dots included in the image data stored in the frame memory 26 as described above, and the result is CP.
It is supplied to the U20 as the data of the printing rate. For example, 1
When the number of black dots included in the "1" to "600" th image data, which is the first quarter of the 2400 image data of the line, is 450, the printing rate data is "75".
(75%) "data is output to the CPU 20, and if, for example, 300 black dots are included," 50 (50%) "data is output to the CPU 20 as the print rate data. Of "601" to "1200" th, the number of black dots included in the image data, "1201" to
The number of black dots included in the “1800” -th image data and the number of black dots included in the “1801” to “2400” -th image data are also counted in the same manner, and the data of the print ratio, which is the calculation result, is stored in the CPU 20. Is output.

In this manner, the CPU 20 outputs the print ratio data corresponding to each image data of 1/4 in one line (corresponding to each STB signal), and the CPU 20 outputs the STB signal output time according to this data. Determine τ.

At this time, the relationship between the output time τ at which the CPU 20 outputs the STB signal and the print rate is obtained by measuring the output time τ when the print rate is changed so that the LED elements emit the same brightness. .. Fig. 4 shows a print rate of 100%, 75
%, 50%, 25%, and a measured value of the output time τ for obtaining the same brightness when only one dot emits light. Further, FIG. 5 shows the relative values when the output time τ was measured for all the printing rates in this way and the printing rate was 100% when the result was 100.

Therefore, the CPU 20 stores the data of the relation shown in the drawing in the memory, determines the output time τ from the data of the printing rate output from the counter / comparison section 25, and outputs the corresponding STB signal. Output time τ. That is, the output time τ of the STB signal determined in this way corresponds to the printing rate when the corresponding STB signal is output.

FIG. 6 shows an example of the STB signals 1 to 4 output to the LED head circuit 3'based on the output time τ controlled by the CPU 20 in this way. STB shown in the figure
The output time τ3 of the signal 3 is shorter than the output times τ1 and τ2 of the STB signals 1 and 2, and it can be imagined that the printing rate of the LED element driven by the STB signal 3 at this time is low. Also,
The output time τ4 of the STB signal 4 is longer than the output times τ1 and τ2 of the STB signals 1 and 2, and it can be imagined that the printing rate of the LED element driven by the STB signal 4 at this time is high.
FIG. 7 is a diagram when the optical density is written on the photosensitive drum 2 based on the light emission time of the LED element controlled as described above and the image density when printed on the paper P is compared with the conventional example.
As can be seen from the figure, according to this embodiment, the image density is constant even if the printing rate changes.

In the present embodiment, the image forming section 4 was explained using the so-called reversal development method, but the same can be applied to the case of the image forming section 4 using the so-called positive development method. That is, in the case of the reversal development method, for example, a negative (−) uniform charge is applied to the photoconductor drum 2 by the charger 11, and the electrostatic latent image formed on the photoconductor drum 2 by the LED head 3 is a character. The charges of the portion corresponding to the portion are erased (low potential portion).
When the developing device 12 to which the bias voltage is applied develops with negatively charged toner, the toner corresponding to the voltage difference between the bias voltage and the low potential part adheres to the low potential part and develops. Therefore, in the case of the reversal development method, the larger the printing rate is, the more current is required to drive the LED head circuit 3 '. However, in the positive development method, the electrostatic latent image formed on the photoconductor drum 2 by the LED head 3 erases the electric charge in the portion corresponding to the back shadow portion. Therefore, conversely to the above, the larger the printing rate (so-called white dot). LED is less
The current for driving the head circuit 3'is reduced, and ST
Contrary to the reversal development method, the output time τ of the B signal needs to be controlled so that the output time τ becomes shorter as the printing rate increases.

In the present embodiment, the optical writing process on the photosensitive drum based on the image data of one line is driven in four time division, but it is not limited to four time division drive.

[0024]

As described in detail above, according to the present invention, the output time τ of the STB signal is changed according to the change in the print rate of the image data, so that the image density can be made constant regardless of the print rate. , The image resolution can be made constant.

[Brief description of drawings]

FIG. 1 is a circuit block diagram of an optical writing printer according to an embodiment.

FIG. 2 is an overall configuration diagram of an optical writing printer according to an embodiment.

FIG. 3 is a circuit diagram of an LED head circuit of an optical writing printer according to an embodiment.

FIG. 4 is a diagram showing measurement data of an output time τ with respect to a printing rate.

FIG. 5 is a diagram showing the relationship between the print rate and the output time τ.

FIG. 6 is a diagram showing an example of an output time τ of an STB signal.

FIG. 7 is a diagram comparing a relationship between image density and change in print ratio with a conventional one.

FIG. 8 is a time chart showing the operation of a conventional optical writing printer.

FIG. 9 is a diagram showing measurement data of an output time τ with respect to a printing rate of a conventional example.

FIG. 10 is a diagram showing the relationship of the output time τ with respect to the printing rate of the conventional example.

[Explanation of symbols]

 1 LED Printer 2 Photosensitive Drum 3 LED Head 4 Image Forming Section 5 Paper Feed Cassette 6 Paper Feeding Roll 7 Paper Transport Mechanism 8 Interface Controller Board 8'Interface Controller Circuit 9 Printer Controller Board 20 CPU 21 System ROM 22 System RAM 23 Character Generator 24 Character Processing Section 25 Counter / Comparison Section 26 Frame Memory

Claims (3)

[Claims] 1. A photosensitive element comprising a plurality of light emitting elements arranged in an array and facing a charged photosensitive member, and the light emitting elements are caused to emit light in N time divisions in response to a strobe signal in accordance with a print signal. An optical writing printer that performs optical writing on a body and develops an electrostatic latent image formed on the photoconductor by a developing means to perform printing, wherein the number of dots assigned during each division of the N time division and the dot number An optical writing printer, comprising: comparing means for comparing the number of dots printed during each division; and time changing means for changing the output time of the strobe signal based on the comparison value obtained by the comparing means. 2. The optical writing printer according to claim 1, wherein the developing unit is a reversal developing unit, and the time changing unit sets the output time of the strobe signal to be shorter as the number of dots printed during each division is smaller. 3. The developing unit is a normal developing unit, and the time changing unit sets the output time of the strobe signal shorter as the number of dots printed during each division increases.
The optical writing printer described.