JPH07232455A - Image forming device - Google Patents

Abstract

PURPOSE:To reduce the deterioration of an image and form a multiple tone image which is of fidelity to an image data and of high picture quality by controlling the unevenness among recording systems including recording elements and so correcting image signals as to control the unevenness between tone characteristics and respective recording elements. CONSTITUTION:Correction factors for correcting the uneveness generated in driving a plurality of recording elements driven successively in compliance with image signals having tone characteristics in the same state are stored in a correction value memory 14. The driving of a plurality of recording elements and correction factors read out of the correction value 14 are operated in communication with each other, and the driving of a recording means is controlled based on the correction factors read out of the correction value memory 14 and the tone characteristics of a video data 11.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus for forming an image using a plurality of recording elements.

[0002]

2. Description of the Related Art There are various types of printer heads that obtain an output image in a dot representation format. Specific examples are the wire printer head, electrostatic printer head, ink jet printer head, thermal printer head, LE.
For example, a D array printer head. Above all, an LED array printer head in which 8 to several tens of LEDs are arranged as a dot generating element per mm is attracting attention in recent years because an extremely high resolution can be obtained. If this is used instead of the optical scanning mechanism of the conventional electrophotographic copying machine, the Ls arranged in a straight line
A printer device is constructed in which an ED is selectively turned on in accordance with a video signal, a latent image is formed on a surface of a photoconductor that is almost in contact with the ED, and a visible image is obtained through a developing process and a transfer process to a sheet. be able to. It is known that in such a printer device, it is possible to make a portion where the LED is turned on a black visible image or a white visible image by changing the charging condition and the toner. .

[0003]

However, since the output device of the dot expression format expresses an image by a combination of a large number of dot output pixels, if a high resolution image output is to be obtained, the dot output will be drastically changed. The number of elements increases.

As the number of dot output elements increases, the unevenness of the density of the formed image due to the variation of the dot output elements occurs, and the finally obtained formed image deteriorates.

Further, even if the variation of the dot output element itself is small, the variation of the recording system including the dot output element causes the variation of the obtained image, which also causes the problem of the deterioration of the image.

In particular, when multi-gradation image formation is performed based on image data having gradation characteristics, due to variations in the recording system including such dot output elements, multi-level gradation faithful to the image data. There is a problem that a toned image cannot be formed. In addition, the gradation characteristics of the image data,
The mismatch between the gradation characteristics of the recording element is also an important issue in faithful image formation.

The present invention has been made in view of the above problems, and in an image forming apparatus composed of a plurality of recording elements, it suppresses variations between recording systems including the recording elements, and also has gradation characteristics. By correcting the image signal so as to suppress the variations between the recording elements, deterioration of the image is reduced, and it is possible to obtain a high-quality multi-gradation image that is faithful to the image data and has a simple structure. An object is to provide an image forming apparatus.

[0008]

An image forming apparatus according to the present invention for achieving the above object has the following constitution. That is, a recording unit including a plurality of recording elements that are sequentially driven according to an image signal having a gradation characteristic, and a variation in shading obtained by driving the plurality of recording elements in substantially the same state are corrected. Storage means for storing the correction coefficient,
A reading unit that sequentially reads the correction coefficient from the storage unit in conjunction with the sequential driving of the plurality of recording elements, and a drive of the recording unit based on the correction coefficient and the gradation characteristic read by the reading unit. And control means for controlling.

[0009]

According to the above-mentioned structure, the correction coefficient for correcting the shading variation obtained by driving a plurality of recording elements sequentially driven according to the image signal having the gradation characteristic in substantially the same state is provided. It is stored in the storage means. The driving of the plurality of recording elements and the reading of the correction coefficient from the storage unit are operated in association with each other, and the driving of the recording unit is controlled based on the correction coefficient and the gradation characteristic read from the storage unit.

Since the correction coefficient for correcting the shading variation obtained by driving a plurality of printing elements in substantially the same state is read in conjunction with the driving of the printing elements to control each printing element, the printing elements are mutually controlled. It is possible to correct not only the unevenness in density between areas but also the unevenness in density due to factors other than the recording elements in the recording system, and the variation between the gradation characteristics of image data and the gradation characteristics of each recording element or recording system. Can be corrected. That is, since the correction coefficient for correcting the variation in shading obtained by driving the recording elements in substantially the same state is obtained, the gradation characteristics of the image data and the gradation characteristics of each recording element can be matched. Easy to implement.

Further, since it is possible to make correction at the time of recording without storing the image signal previously corrected by the correction coefficient, the image signal can be corrected with a simple structure.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a circuit diagram showing a head drive unit of a printer head drive apparatus according to one embodiment. 1a, 1b ... 1n is L
Each LE included in the ED array printer head 1
D, which is used as the printer head. A resistor R for limiting the current of the LEDs 1a, 1b ... 1n
a, Rb ... Rn are connected in series with each LED. Drn transistors Tra, Trb ... Trn form a driver circuit for each LED, and the signals on the signal lines 2a, 2b ... 2n respectively are HI.
When it is at the level, it conducts and turns on the LED, and when it is at the LO level, it cuts off and turns off the LED.

.. 3n includes a down counter circuit which counts down according to the clock pulse signal CLK until a count value output becomes 0 according to the clock pulse signal CLK. While the count value output of the counter is not 0, Output Q
HI level is output to 0, Q1 ... Qn, and the count value output is 0
Then, the subsequent counting operation is stopped and outputs Q0, Q1 ... Qn
Is a head drive time control circuit (hereinafter referred to as a control circuit) that outputs an LO level to. Then, each output Q0, Q1 ...
Qn controls the head drive time of each driver circuit via the signal lines 2a, 2b ... 2n. Control circuits 3a, 3b ... 3
The initial value is set to n by inputting each input data signal D0.
The weighted values of 0, D01, D10, D11 ... Dn0, Dn1 are set at the rising timing of the clock pulse CLK when the load signal LD is at the HI level.

The structure of an example of such a control circuit is shown in the circuit diagram of FIG. Although the control circuit 3n is shown here, the other circuits are the same. In the figure, 301 is a counter set to operate in a countdown mode, 302 to 304 are OR gates, and 305 and 306 are inverters. When the initial value is loaded into the counter 301, the HI level is output to any of the output terminals QA to QB unless the set value is 0. In this state, the output of the OR gate 304 is at the HI level, and the HI level is output to the output Qn of the control circuit 3n. At the same time, in this state,
The output of the OR gate 304 is inverted via the inverter 305 to energize the count energizing terminal T of the counter 301 to a countable state. HI for initial setting timing
The load signal LD that has been at the level is inverted to the LO level before the next clock pulse signal CLK is input. Accordingly, the HI level signal input via the inverter 306 deactivates the load terminal LD of the counter 301.

In this state, the clock pulse signal C continues.
When LK is input, the count value output is counted down each time it rises, and when the count value output eventually reaches 0, the LO level is output to the output Qn of the control circuit 3n. At this time, the count energizing terminal T of the counter 301 is deenergized by the output of the inverter 305, so that no further countdown operation is performed. Therefore, the output Q of the circuit 3n
n holds the LO level until a value other than 0 is set at the timing of the next initialization.

It is also shown that the control circuit used in the embodiment can be constructed by combining the logic circuit elements of TI, which are commercially available, as shown in FIG. Of course, similar control can be performed by other circuits instead of the control circuit of FIG. For example, in order to variably control the time constant of the known one-shot circuit, a plurality of resistors are provided in parallel with the time constant determining circuit, and these resistor circuits are individually held by the switch means which is interlocked with the input data signals Dn0, Dn1 ... Open,
The configuration may be such that the closing control is performed, or a plurality of resistors are provided in series with the time constant determination circuit and these are individually short-circuit controlled. As described above, the control circuit may have any configuration as long as it is triggered at a predetermined timing and the drive signal level (or the signal level for not driving) of the output signal Qn can be variably controlled by the input data signal. Good.

FIG. 2 shows an operation timing chart of the circuit configured as shown in FIG. Here, since the driving method of each LED is the same, the operation timing will be described by taking the control circuit 3n as an example. The waveform of the clock pulse signal CLK is shown, and the case where one dot pixel is formed every four cycles of this clock is shown. Of course, this cycle is not limited to 4 clocks. The dot pixel numbers n1 to n4 indicate the respective time periods and the order in which the n-th LED forms a dot pixel. Input data signals for initialization are shown for Dn0 and Dn1. Here, Dn0 is a signal having a lower weight, and Dn1 is a signal having an upper weight. The control circuit 3n supplies the clock pulse signal CL when the load signal LD is at the HI level.
At the rising edge of K, the input data signals Dn0 and Dn1 are loaded. That is, it is the initial setting.

In the embodiment, since the counter 301 is a binary down counter, the initial setting value in the figure is 3.
Since this value is other than 0, the output Qn outputs the HI level. After that, it counts down each time the clock pulse signal CLK rises, the count operation ends when the count value output becomes 0, and the LO level is output to the output Qn. Therefore, during the time 3T, the output Qn becomes HI level and the LED 1n lights up for three cycles of the clock pulse signal CLK. At the timing of the dot pixel number n2, the initial setting value becomes 2, and by the same operation, the LED 1n lights for the time 2T, that is, two cycles. Further, at the timing of the dot pixel number n3, the initial setting value becomes 1 and the LED 1n lights up for one cycle. Furthermore, the dot pixel number n4
At the timing of, the initial setting value is 0, and the output Qn is H
Since it does not reach the I level, the LED 1n does not light at all during the section.

As described above, the configuration of the embodiment is different for each LE.
For D, the maximum lighting time was set to 3T, and other 4T drive time control was performed for 2T, T and no lighting. The LED array printer head 1 of the embodiment can be configured to form a latent image by photosensitization on a photosensitive surface around a rotating drum, for example. If the straight lines of the LEDs 1a to 1n are arranged so as to be parallel to the rotation axis of the drum, the LEDs 1a to 1n on a straight line are driven according to the image information and synchronized with the rotation of the drum. By repeating the driving once, a latent image for one screen can be formed.

Specifically, in FIG. 1, the image information of the embodiment is the input data signal D00,
A pair of D01, a pair of input data signals D10 and D11 for the LED1b, and a pair of input data signals Dn0 and Dn1 for the LED1n. Assuming that the drum is rotating at a constant speed, the movement of the photosensitive surface of the drum during the period of 4 clocks will allocate the photosensitive surface having a predetermined area to the LED 1a, for example. If this is made into a substantially rectangular shape, one side in the rotation axis direction has a width of a predetermined length that can be cut off between adjacent LEDs, and
The side is given by the moving distance of the photosensitive surface that moves within the time of four cycles of the clock pulse signal CLK. The value 3 of the input data signal for the given area
The LED lit by exposes about 75% of its area,
Further, the LED turned on with the value 2 of the input data signal is relatively controlled so as to expose about 50% of its area. Of course, when the value of the input data signal is 0, the photosensitive surface is not exposed.

When the latent images having different exposure area ratios obtained in this way are developed and transferred and fixed on a sheet, when the input data signal value is 3, the darkest black is obtained, and when the values are 2, 1 When the resulting visible image is viewed macroscopically, an image having four gradations can be obtained.

In the embodiment, since the maximum value of the 2-bit input data signal is 3, there is always a blank control section in which the LED is not turned on in the dot pixel output period of 4 cycles.
It is obvious that this does not occur if the output period of the dot pixel is set to 3 cycles. That is, the blank can be eliminated by performing the initialization for each clock pulse having the gradation number -1.

Further, in the embodiment, the structure in which the LEDs 1a to 1n are simultaneously driven and controlled is shown. Therefore, at the timing of the load signal LD, the image data D00, D01 to Dn0, D
This corresponds to the configuration in which all n1 are prepared. However, to describe another method instead of this, first, the load signal LD is not made common to the control circuits 3a to 3n, and, for example, the load terminals LD of the control circuits 3a to 3n are sequentially activated individually in time series. You can do it. This is so-called skiyaning control. By doing so, there is provided common storage means for reading corresponding image data in synchronization with the initialization of each control circuit, and common image data output from the storage means is sequentially fetched. The drive time of the head can be individually controlled. Therefore, LED1
For a to 1n, the start timing of the light emission is scanning-driven, and the light emission time depends on the image data individually fetched.

The rotation of the drum may be intermittently controlled when the latent image is formed on the photosensitive surface of the drum. That is, LED1
The photosensitive drum is stopped while the exposure control of a to 1n is performed, and the intermittent control is such that after the exposure of the relevant row is completed, it advances by one row before the exposure of the next row is started. . When the photosensitive drum is stopped for exposure, the entire unit light receiving area of the dot pixel is exposed at the same time, but the difference in exposure time results in gradation of the visible image. When the exposure amount changes as a function of time (unsaturated range) when the surface of the photoconductor is exposed with an appropriate illuminance,
Gradation can be obtained in the resulting visible image.

As described above, the case where the LED array is used for the printer head has been described in the description of the embodiment, but any one can change the size and density of the output pixel dot depending on the activation time of the dot generation mechanism. It is possible to obtain gradation in an output image by using the printer head drive device according to the present invention.

In the above embodiment, the time width signal correlated with the image data is used as the time width for driving the dot output element, but it may be used as the time width for not driving the dot output element. This makes it possible to easily deal with the case where the latent image exposed on the photoconductor is output as a black visible image or a white visible image. Of course, there is also a method of taking the complement of the original image data and using this as the image data. The meaning of the time width signal of the present invention to control the driving time of the dot output element includes the control of the driving time based on the time width of no driving or the control of the driving time based on the complement image data.

Furthermore, the printer head drive apparatus according to the present embodiment is not limited to the control for positively obtaining the gradation of the output image as described above, but also the variation of the relative characteristics of each dot output element and the image receiving portion ( For example, it is possible to simultaneously perform control for correcting the light emission capability of each LED and the correspondence between the exposure characteristics of the photoconductor surface. Such a characteristic variation can be obtained by, for example, driving all the dot output elements for the same time width, and obtaining a correction value from the obtained variation in the shade of the visible image for one screen. . As a result, it is possible to correct the variation in shade of the visible image. In this case, the correction value exists for one screen, but the effect of the actual correction is great even if the correction value is remarkable because it is caused by the variation existing among a plurality of dot output elements. There are as many correction values as there are dot output elements,
This correction value may be applied to the input image data in advance.

Specifically, there is a method in which a correction value table is provided in a microprocessor or the like and the correction values are added to or subtracted from the image data in advance. If high speed is required, there is a method shown in FIG.

The figure is a block diagram of an embodiment of a printer head drive device using the scanning method. For example, video data is externally written to the video RAM 10 that stores pixel data for one screen through the data bus 11. Address bus 16 for video RAM address
The full-bit output given from the address counter 12 via is used. Although not shown, the address counter 12 is synchronously, count-up, and reset controlled via the control line 13 at the time of writing the video data or at the time of reading the video data described later.

Next, when outputting an image, the lower bits of the address counter 12 are the correction value memory 14 and the decoder 15.
Is commonly input to. As a result, the decoder 15 sequentially outputs the selection signals 15-1 to 15-n from the load terminals LD of the control circuits 3a to 3n from 3a to 3n.
At the same time, the correction value memory 14 outputs a frame of correction data to be given to the control circuits 3a to 3n to the data bus 20. At the same time, the video RAM 10 has the control circuits 3a to 3n.
A frame of video data to be provided to the data bus 17
Output to. In the correction value memory, when one frame of correction data for the control circuits 3a to 3n is read, the same frame is read again from the first address, whereas in the video RAM 10, the upper bit is updated for each frame. Then, different frames of video data are output. Reference numeral 18 denotes an adder circuit that adds each read correction data to each read video data.

Of course, a subtraction circuit may be used to subtract the correction data, or a multiplication / division circuit may be used to provide the correction data with a correction magnification. As a result, the image signal is corrected. The corrected video data output from the adder circuit 18 is the data bus 19
Is commonly given to the control circuits 3a to 3n via. Outputs 15-1, 15-2, ... 15-n of the decoder 15 are selection energizing signals for individually fetching the corrected video outputs, and a control circuit individually initialized according to the corrected video data. 3a to 3n independently drive the dot output elements via the control lines 2a to 2n.

Further, if the correction data can be externally written in the correction value memory 14, the correction data can be corrected very easily, and it is possible to easily deal with the fluctuation of the printer head drive characteristic caused by the use.

Regarding the correction value for one screen, 1
If unevenness occurs as a result in the dot pixels that make up the visible image of the screen, there is some variation between the dot output and image receiving characteristics of that part, and the drive time corresponding to that part It is possible to improve the overall image quality by controlling the. For example, even if all the correction values corresponding to the position of the output dot pixels for one screen are stored in the memory, the economical efficiency of the configuration is not deteriorated.

As described above, according to the above embodiment, the control for displaying the halftone for each dot output element is possible with a simple structure. Therefore, it is possible to inexpensively construct a dot printer device capable of obtaining a high density image having a halftone at a high speed. If the binary image data is directly converted into the drive time control of the dot head, there is an effect that the consistency is excellent when the binary image data is adopted in the conventional facsimile or the computer output device.

Further, according to this embodiment, variations in driving characteristics existing in individual dot output elements can be easily corrected, so that the image quality of a dot output image having a halftone can be improved. It is a thing.

[0037]

As described above, according to the image forming apparatus of the present invention, in an image forming apparatus composed of a plurality of recording elements, an image is formed so as to suppress variations between recording systems including the recording elements. It becomes possible to correct the signal, image deterioration is reduced, and high image quality is obtained. Furthermore,
According to the image forming apparatus of the present invention, it is possible to perform a correction for matching the gradation characteristics of the image data with each recording element at the same time as the above correction, and it is possible to perform high-quality multi-gradation faithful to the image data. It becomes possible to form an image.

Further, according to the present invention, since the stored correction coefficient is read in association with the driving of the recording element to control each recording element, the uneven density due to the variation of the recording system can be easily generated. Can be prevented with.

[0039]

[Brief description of drawings]

FIG. 1 is a diagram illustrating a circuit configuration example of a printer head drive device according to an embodiment.

2 is a timing chart showing the operation of the printer head drive device of FIG.

FIG. 3 is a circuit diagram showing an example of a counter circuit.

FIG. 4 is a block diagram showing a printer head drive device according to one embodiment of a scanning system.

[Explanation of symbols]

 1 LED array printer head 1a, 1b ... 1n LED Ra, Rb ... Rn Current limiting resistance Tra, Trb ... Trn Transistor 3a, 3b ... 3n Counter circuit 10 Video RAM 11, 17, 19, 20 Data bus 12 Address counter 13 Control line 14 correction value memory 15 decoder 16 address bus 18 adder circuit

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location B41J 2/52 G06F 3/12 L G06T 5/00 H04N 1/23 103 A G06F 15/68 310 J

Claims (1)

[Claims] 1. A recording unit including a plurality of recording elements that are sequentially driven according to an image signal having gradation characteristics, and a variation in shading obtained by driving the plurality of recording elements in substantially the same state. Storage means for storing a correction coefficient for storing the correction coefficient, a reading means for sequentially reading the correction coefficient from the storage means in association with sequential driving of the plurality of recording elements, the correction coefficient read by the reading means, and An image forming apparatus comprising: a control unit that controls driving of the recording unit based on gradation characteristics.