JP2510548B2 - Image forming device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an image forming apparatus.

[Conventional technology]

In an image forming apparatus such as a conventional copying machine, an image signal from an image reading element such as a CCD is used. The conversion of digital image data into digital image data by an analog-digital converter (A / D converter) and the like and then correcting the gradation of the digital image data is widely known as γ conversion. This γ conversion table is created based on the relationship between the recording result density from the recording device and the video signal, and is stored in a ROM or the like to be used as a γ conversion ROM for gradation correction. However, in the case of an electrophotographic printing machine such as a laser beam printer, the characteristics of the photoconductor and the developer change due to environmental conditions such as temperature and humidity and aging. However, there is a drawback that conversion cannot be performed and a proper image cannot be obtained.

〔Purpose〕

The present invention has been made in view of the above points, and an object of the present invention is to provide an image forming apparatus capable of always obtaining an appropriate image regardless of environmental changes.

In detail, the measuring means for measuring the surface potential of the photoconductor, and the setting means for setting the difference of the surface potential of the light portion and the dark portion of the photoconductor to the target value based on the measurement result of the measuring means are input. Gamma conversion means for gamma-converting multivalued digital image data according to conversion information, output means for outputting gamma-converted image data as an image signal, and image forming means for forming an image by electrophotography based on the image signal. Monitoring means for monitoring environmental conditions; and after setting by the setting means, surface potential data is obtained by the measuring means for a plurality of image data levels, and the surface potential data is obtained based on the obtained surface potential data and the output of the monitoring means. It is an object of the present invention to provide an image forming apparatus characterized in that the image forming apparatus is provided with changing means for changing the conversion information of the gamma converting means.

Embodiments Embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

Description of Block Diagram of Color Copier (FIG. 1) FIG. 1 is a block diagram of the color copier of this embodiment.

Reference numeral 1 denotes a sync signal processing unit which, based on a signal from a BD (beam detector) detector 20 of the printer unit 200, synchronizes various timing signals with a horizontal sync signal 22 output from a gradation control circuit 21. create. Reference numeral 2 is a contact type CCD sensor block, which reads a document according to the reader horizontal synchronizing signal (RHSYNC) and the driving signal 4 generated by the synchronizing signal processing unit 1 and converts the image signal into an electric signal and outputs it. A signal processing unit 3 performs a waveform shaping process in order to prevent attenuation of high frequency components of the electric signal 5.

Reference numeral 6 is an image processing block. The image signal from the signal processing 3 is first input to the analog processing unit 7. In the analog processing unit 7. The signal from the contact CCD sensor block 2 is 1
Since cyan (C), green (G), and yellow (Y) signals are sequentially output for each pixel, the C, G, and Y colors are first separated. Next, since the developing units of the printer unit 200 correspond to yellow (Y), magenta (M), and cyan (C), the image is first displayed as red (R), green (G), and blue (B) signals. Convert to. This is performed by arithmetic processing according to the formulas C-G = B and Y-G = R. Further, the signals separated into R, G, and B are converted into 8-bit density signals by the A / D converter because the output voltage changes linearly with respect to the density. The above processing is executed by the analog processing unit 7.

The image signal for each color digitized by the analog processing unit 7 is divided into 5 channels, and the video signals of the respective channels are not synchronized, so that one image data is stored in the connection memory 8. Is synthesized. The image data synthesized by the connecting memory 8 and converted into the YMC signal is sent to the image processing unit (IPU) 9 in synchronization with each color. The IPU9 performs a shading process to correct the light distribution and a masking process to correct the color. Further, a desired color signal is selected by the control unit 10 of the reader unit 100, and is sent from the IPU 9 to the printer unit 200 through the 8-bit image data 11 on which a predetermined color conversion process has been performed.

On the other hand, in addition to the image signal, the control unit 10 drives the motor driver 13 for manipulating the document to control the rotation of the motor 12. In addition, the CVR 15 and the copy key for controlling the lighting of the exposure lamp 14 and the operation unit 16 for performing other operations are also controlled.

The image data 11 output from the reader unit 100 is input to the gradation control circuit 21 of the printer unit 200. Gradation control circuit 2
In 1, since the image clock of the reader unit 100 and the image clock of the printer unit 200 have different speeds, they have a function of synchronizing them and a function of making the image data correspond to the color reproduction density of the printer unit 200. . Output data from the gradation control circuit 21 is input to a laser driver 22 and a laser 23 is driven to form an image.

The control unit 25 of the printer unit, which communicates with the reader unit 100 via the communication control line 24, controls each control element of the printer unit 200. Reference numeral 26 denotes a potential sensor for detecting the electric charge charged on the photosensitive member 29, and reference numeral 27 denotes a potential measurement unit that converts an output from the potential sensor 26 into a digital signal and inputs the digital signal to the control unit 25. The potential data input to the control unit 25 is read by the CPU 25-1 of the control unit 25 and used for control. On the other hand, a signal from the sensor 28 for detecting the image leading edge signal (ITOP) is input to the control unit 25 and used for control. Also, the humidity sensor 98 to correct the development characteristics
And the temperature sensor 99 is input through the A / D converter 25-3 of the controller 25. Here, the humidity sensor in this embodiment
As shown in FIG. 12, 98 has a characteristic that it changes with temperature when the vertical axis shows resistance and the horizontal axis shows absolute humidity. Therefore, it is expressed as a ratio of saturated water vapor amount at each temperature. Relative humidity ΔH
Is expressed as ΔH = f (T, H) T: temperature, H: humidity sensor value. Usually, the f function is expressed by a cubic expression. The temperature sensor 99 and the humidity sensor 98 of T and H are converted into A / D by the control unit 25-3, and the relative humidity is calculated.

Then, at the calculated relative humidity, control described later is performed.

FIG. 7 is a block diagram of a copying machine using the contact type color CCD sensor of this embodiment.

The copying apparatus 80 includes a reader unit 100 and a printer unit 200. Reference numeral 83 denotes a document scanning unit which moves and scans in the direction of arrow A in order to read the image of the document 84 on the document table, and at the same time, an exposure lamp 85 in the document scanning unit 83.
Lights up. The reflected light from the document is guided to the converging rod lens array 86 and is condensed on the contact color CCD sensor 87. The contact color CCD sensor 87 is 62.5 μm (1/16 m
m) as one pixel, and 1024 pixel chips are arranged in a staggered pattern of 5 chips, and each pixel is 3 in 15.5 μm x 62.5 μm.
It is divided and C, G, and Y color filters are attached to each.

The optical image focused on the contact color CCD sensor 87 is converted into an electrical signal for each color. These electrical signals are subjected to a predetermined process described later by the processing block 88. The color separated image electrical signal formed by the image processing block 88 is transmitted to the printer 200 and printed.

The color image data from the reader unit 100 is subjected to PWM processing and the like to finally drive the laser. The laser light modulated according to the image data is scanned at high speed by the polygon mirror 89 rotating at high speed, reflected by the mirror 90, and the surface of the photosensitive drum 91 is subjected to dot exposure corresponding to the image. One horizontal scan of the laser beam corresponds to one horizontal scan of the image, and has a width of 1/16 mm in this embodiment. On the other hand, since the photosensitive drum 91 is rotating at a constant speed in the arrow direction, the planar image is successively exposed by the above-mentioned laser beam scanning in the main scanning direction and the constant speed rotation of the photosensitive drum 91 in the sub-scanning direction. Prior to exposure, the photosensitive drum 91 is uniformly charged by the charger 97,
A latent image is formed by exposing the charged photoreceptor to light. A latent image formed by a predetermined color signal is visualized by developing devices 92 to 95 corresponding to a predetermined color.

Considering, for example, the first exposure scanning of the original in the color reader, first, the dot image of the yellow component of the original is exposed on the photosensitive drum 91 and developed by the yellow developing device 92. Next, the yellow image is formed on the paper wound on the transfer drum 96 by the photosensitive drum 91.
A yellow toner image is transferred and formed by the transfer charger 98 at the contact point between the transfer drum 96 and the transfer drum 96. By repeating the same process for M (magenta), C (cyan), and BK (black), and superimposing each image on the paper,
A color image is formed with four-color toner.

At this time, since the characteristics of the developer of each developing device differ depending on the humidity condition, the image density with respect to humidity when printed under the same image forming conditions is as shown in FIG. Further, the image density with respect to the surface potential of the photosensitive drum using humidity as a parameter is as shown in FIG.

Description of gradation control circuit (FIGS. 2 and 3) FIG. 2 is a block diagram of the gradation control circuit 21.

The 8-bit image data 11 output from the IPU 9 of the reader unit 100 is input to the buffer memory 30 in synchronization with the synchronization signal RHSYNC from the synchronization signal processing unit 1 and the image clock RCLK. The image data stored in the buffer memory 30 is read from the buffer memory in synchronization with the HSYNC and CLK signals 32 by the synchronization controller 31. This allows the reader unit
The synchronization deviation and speed conversion between 100 and the printer unit 200 are performed and output to the selector 33.

The selection signal 34 from the CPU 25-1 of the control unit 25 causes the selector 3
When the A input 3 is selected, the image data is input to the address of the look-up table RAM (LUTRAM) 38. At this time, when the CPU 25-1 reads the LUTRAM 38 by the control signal 36, the LUTRAM 38 outputs the data corresponding to the address input. The output data is output to the selector 39,
The selection signal 34 is input to the next selector 40. When the selection signal 42 of the selector 40 selects the A input, it is output to the D / A converter 41 and converted into an analog signal.

The analog-converted image signal is compared with the triangular wave 47 from the triangular wave generator 44 by the comparator 43. The image signal PWM-modulated by the comparator 43 is the OR circuit 4
5, output to the laser driver 22 through the AND circuit 46.
The blanking signal 48 from the synchronization control unit 31 is
This is a signal for turning on the laser 23 in the BD detection unit in order to detect BD. A signal 49 is an inhibit signal of the laser 23 output from the CPU 25-1 and is used to prevent the deterioration of the life of the laser 23.

A pattern generator 50 outputs a predetermined pattern for checking an image signal. To the pattern generator 50, the transfer drum synchronizing signal ITOP, the horizontal synchronizing signal HSYNC of the printer unit 200, and the control signal from the CPU 25-1 are input. When outputting the pattern signal, the CPU 25-1 switches the selection signal 42 of the selector 40 to the B input, outputs the data from the pattern generator 50 to the D / A converter 41, and checks the image signal.

The synchronization control unit 31 is based on the reference clock of the crystal oscillator,
Either CLK51 or 3CLK52 as the triangle wave generation clock. Output by the instruction of CPU25-1, B from BD detector 20
Input the D signal to output the blanking signal 48 and the printer unit 200.
The horizontal synchronizing signal HSYNC and the image clock CLK are output. The triangular wave generator 44 uses CL based on the input clock.
Outputs triangular wave 47 synchronized with K51 or 3CLK52.

FIG. 3 is a timing chart showing the timing of these BD signal, blanking signal 48 and the like.

A clock having a cycle twice or more that of the image clock is input to the synchronization control unit 31 from the crystal oscillator, and BD signal and HSYNC and CLK synchronized with the clock are output. The blacking signal 48 is generated by a counter that resets at the trailing edge of the BD signal and measures a time shorter than the BD signal period.

Operation explanation of reader unit (Fig. 4) Fig. 4 shows an operation flow chart of the CPU 10-1 of the control unit 10 of the reader unit 100.
Built in 2.

When the power of the reader unit 100 is turned on, first, step S1
To execute the initial display routine. This is the check of each I / O, the initialization of the RAM 10-3, and the movement processing of the original scanning start point. At step S2, it is checked whether the reader unit 100 is connected to the printer unit 200. At step S3, it is checked whether the print switch of the operation unit 16 has been pressed. When the switch is pressed, the process proceeds to step S4 to output a print-on command to the printer unit 200. In step S5, the IPOP signal is input from the printer section 200. When the ITOP signal is input, in step S6, the image is scanned in the designated color mode and the video signal is output to the printer section 200.

Description of Operation of Printer Unit (FIG. 5) FIG. 5 is a flow chart of a processing program by the control unit 25 of the printer unit 200, and this program is stored in the ROM 25-2.

When the printer unit 200 is powered on, the initial routine is executed in step S10. Here, initial operations such as checking each I / O, initializing RAM, and removing drum potential of the machine body are performed. In step S11, the connection with the reader unit 100 is checked, and if the connection is confirmed, the process proceeds to step S12 to check whether the heater of the fixing unit has reached a predetermined temperature (whether warm-up is completed). When the warm-up is completed, the process proceeds to step S13, and it is determined whether there is a print instruction from the reader unit 100. When the print instruction is input, a PGON process described later is executed in step S14.

In step S15, the write data of the LUTRAM 38 is calculated based on the result of step S14 as described later, and step S1 is executed.
Write to LUTRAM38 with 6. This selects the B input of the selector 33 by the selection signal 34, while the selector 39 causes the CPU 25-
The one data bus 36 is connected to the data input of the LUTARM 38. Here, the CPU 25-1 inputs the address of the LUTRAM 38 to the address bus 35, the write data to the data bus 37, and the write pulse by the control signal 36 to write to the LUTRAM 38.

In step S17, it is checked whether the writing to the LUTRAM 38 is completed, and if completed, the ITOP signal is output to the reader unit 100 in step S18. As a result, the reader unit 100 of FIG.
In the program flow chart, the control shifts from step S5 to step S6. The designated color mode is executed in step S19. In that case, needless to say, the LUT is switched by switching the selector for each color. Next, the printing operation is performed in steps S20 and S21, and when one color image is formed and the color mode is completed, the process returns to step S11 again.

Explanation of PGON processing (FIGS. 6 and 7) FIG. 6 shows the PGON processing of step S14 in FIG. 5, that is, driving the pattern generator 50 to output a predetermined pattern and read the surface potential of the photosensitive drum. It is a processing flow chart.

In step S30, the data from the pattern generator 50 is D / A
The selection signal 42 selects the B input of the selector 40 for input to the converter 41. In step S31, the pattern generator 5
A potential generated on the photoconductor 29 by the laser beam emitted based on the data output by 0, for example, "00" is input through the potential measuring unit 27. It is assumed that the triangular wave generator 44 is set in advance so that the limit pulse generated by the laser is generated by the comparator 43 when the input of the D / A converter 41 is “0”. As a result, the laser driver 22 and the laser 23 irradiate the photoconductor 29 with uniform light.

In addition, in step S31, the pattern generator 50 outputs "F" in hexadecimal.
The triangular wave generator 44 is set in advance so that the laser 23 emits light in a cycle shorter than the cycle of the triangular wave when the F "data is output, that is, the dots can be accurately reproduced. Then read the potential corresponding to the data “FF”.

In step S32, the data from the pattern generator 50 "0
_Find the difference between the read potentials V ₀₀ and V _FF corresponding to "0" and "FF" and see if the difference reaches a predetermined value. If not, proceed to step S33, where the primary high voltage 97 in FIG. Change the voltage,
Return to step S31 again to check.

When the difference reaches a predetermined value in step S32, the process proceeds to step S34, and the pattern generator 50 is turned on. As a result, the pattern generator 50 starts to operate as an m-ary counter of HSYNC in synchronization with ITOP, and sequentially outputs data obtained by dividing the data "00" to "FF" into a predetermined number of stages m. This data is input to the D / A converter 41 through the selector 40, and drives the laser 23 as an analog signal. Step S35, S36
Then, the electric potential of the photoconductor 29 which is generated by this and changes in the number of m steps is read and sequentially stored corresponding to the output data of the pattern generator 50. In this embodiment, m = 16.

As described above, the relationship between the surface potential of the drum and the image humidity when the humidity is used as a parameter is as shown in FIG. Therefore, the relationship between the input data of the laser and the image density can be obtained from the relationship between the input data to the laser and the surface potential of the photoconductor obtained as described above. Therefore, the relationship between the input image humidity data and PG is newly written in the LUT in order to make this an ideal linear characteristic. Further description will be given below.

Description of LUT creation process (Figs. 10 and 11) Fig. 10 is a diagram showing the calculated value of the concentration data with respect to the calculated value from the measured value by the potential sensor. The calculated value from the measured value = (measured data- V _FF ) / (V ₀₀ −V _FF ) Concentration data calculated value = (concentration / maximum concentration) × “FF” V ₀₀ ; “00” output potential sensor measurement value V _FF ; “FF” output potential sensor Is the measured value of. This curve is preset in ROM 25-2 with several types of humidity data as parameters.

FIG. 11 is a flow chart showing the LUT creation process.
In step S40, the 10th value is output according to the output value of the humidity sensor 98.
Select one of the curves in the figure and select step S14 in Figure 6.
16-stage PG output V ₀ to _F for concentration data D ₀ to _F
Are calculated using the curves selected in step S40 (step S41).

Next, in step S42, when the input data is D _O and V ₀ , D ₁
16 LUT data are created so that V _F is output when V ₁ , ... D _F. Further, in step S43, the LUT data is converted from the data obtained in step S42 to "00" by line approximation.
It is completed up to "FF" and used as write data of the LUTRAM 38 in step S15 in FIG.

In this embodiment, a RAM is used as the backup table.
However, it is also possible to use a ROM in which a plurality of data groups are written in advance and select appropriate data from the data stored in the ROM based on the calculation result of the CPU.

As described above, according to this embodiment, a stable image can be obtained because the relationship between the potential on the photoconductor and the image data is constant and the change in the developer characteristics is taken into consideration according to the environmental conditions such as temperature and humidity. To be Further, in the case of a color image, since variations in color can be prevented, there is an effect that an image with no change in tint can always be obtained.

〔The invention's effect〕

As described above, according to the present invention, there is an effect that images can be reproduced stably regardless of environmental changes. That is, the conversion information of the gamma conversion means is based on the surface potential data corresponding to a plurality of image data levels obtained after the difference between the surface potentials of the light portion and the dark portion of the photoconductor is set to the target value, and the detection environment condition. Since it has been changed, it is possible to accurately obtain the data of the surface potential of the photoconductor for a plurality of image data levels, regardless of changes in the characteristics of the photoconductor and environmental conditions,
Optimal density reproduction is possible for each value of the input multilevel digital value.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 (a) and 1 (b) are block diagrams of a color copying machine of the present embodiment, FIG. 2 is a block diagram of a gradation control circuit, and FIG. 3 is a synchronous control block. Timing chart of signals, FIG. 4 is an operation flow chart of the control section in the reader section, FIG. 5 is an operation flow chart of the control section in the printer section, and FIG. 6 is a flow of data output and potential reading processing of the pattern generator. Chart, FIG. 7 is a cross-sectional view of a color copying machine, FIG. 8 is a diagram showing the relationship between image density and humidity when printing is performed under the same image forming conditions, and FIG. 9 is when printing under the same image forming conditions. Fig. 10 is a diagram showing the relationship between the image potential and the surface potential of the photoconductor drum, Fig. 10 is a diagram showing the concentration data for the measured data of the potential sensor that has been set in ROM in advance, and Fig. 11 is written in LUTRAM. No data creation processing of the flow chart, FIG. 12 is a diagram showing input and output characteristics of the humidity sensor in which the temperature as a parameter. 1 ... Synchronous signal processing unit, 2 ... Adhesion unit CCD sensor block, 3 ... Signal processing unit, 7 ... Analog processing unit, 8 ... Connecting memory, 9 ... IPU, 10 ... Control unit, 11 ... … Image data, 16… Operating part, 20… BD detector, 21… Gradation control circuit, 22… Laser driver, 23… Laser, 25… Control part, 26… Potential sensor, 27… … Potential measuring unit, 29 …… photoconductor, 30 …… buffer memory, 31 …… synchronous control block, 33,39,40 …… selector, 38 …… lookup table RAM (LUTRAM), 41 …… D / A conversion 43 ... Comparator, 44 ... Triangular wave generator, 50 ... Pattern generator, 100 ... Reader, 200 ... Printer.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-54-86353 (JP, A) JP-A-58-127955 (JP, A) JP-A-59-146456 (JP, A) JP-A-62- 23070 (JP, A) JP 61-45677 (JP, A) JP 62-108269 (JP, A) JP 63-158273 (JP, A) JP 54-92742 (JP, A) JP-A-59-146456 (JP, A) JP-B 5-55875 (JP, B2) JP-B 6-68647 (JP, B2)

Claims (3)

(57) [Claims] 1. A measuring means for measuring the surface potential of a photoconductor,
Setting means for setting the difference between the surface potentials of the light portion and the dark portion of the photosensitive member to a target value based on the measurement result of the measuring means, and gamma conversion means for gamma-converting the input multivalued digital image data according to the conversion information. Output means for outputting gamma-converted image data as an image signal, image forming means for forming an image by electrophotography based on the image signal, monitor means for monitoring environmental conditions, and after setting by the setting means. A measuring means for obtaining surface potential data for a plurality of image data levels, and changing means for changing the conversion information of the gamma converting means based on the obtained surface potential data and the output of the monitoring means. A characteristic image forming apparatus. 2. The image forming apparatus according to claim 1, wherein the monitor means monitors humidity as an environmental condition. 3. The changing means, when changing the conversion information, has means for using data selected from a plurality of table data corresponding to the humidity monitor information. The image forming apparatus according to the item.