JPH031175A - Image forming device - Google Patents

Abstract

PURPOSE:To hold the density of a reproduced image constant by checking the image potential of an electrostatic latent image and adjusting an image forming process according to the potential. CONSTITUTION:A multilevel image information generation part 13 generates and outputs image information 32 for forming an image from pattern data 31 and a reference potential generation part 12 outputs target potential information 33 on a binary electrostatic latent image formed on a photosensitive body according to the image information 32. A surface potential detection part 21 measures the surface potential of a photosensitive body where the electrostatic latent image is formed and outputs surface potential information 37 to an exposure quantity control part 32, and an exposure quantity control part 22 inputs and compares target potential information 33 from a reference potential generation part 12 and the surface potential information 37 with each other and outputs exposure control information 38 to a storage part 16. Then when an image is recorded, the image forming process is changed according to the control information 38 to record the image. Consequently, the density of the reproduced image is held constant.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an image forming apparatus such as a laser beam printer, and particularly relates to an image forming apparatus that performs density correction control and forms an image by an electrophotographic process. be.

[Prior Art] There is an image forming apparatus, such as a laser beam printer, which binarizes and records multivalued image information sent from a scanner or the like using a dither method, error diffusion method, pulse width modulation, or the like. FIG. 1O is a diagram showing an image signal processing block of a conventional laser beam printer. A conventional example will be explained based on FIG. 10. Reference numeral 101 is image information having multivalue density information sent from a scanner or the like, and is input to a binarization processing section 102. The binarization processing unit lO2 performs binarization processing on the input multivalued image information using a dither method, error diffusion method, pulse width modulation, etc., and outputs binary image information 103 to the exposure unit 105. There is.

The exposure unit 105 drives a semiconductor laser based on the input binary image information, and irradiates the photosensitive drum with laser light modulated by the image signal. This photosensitive drum is uniformly charged by a charging section 104, and an electrostatic latent image is formed on its surface by laser light from an exposing section 105. The electrostatic latent image thus formed on the surface of the photoreceptor drum is turned into a visible image by a developing section 107, and is fixed onto a recording medium such as a recording paper by a transfer fixing section 109 to form an image.

[Problem to be solved by the invention] Generally, in such an image forming process, charging characteristics and exposure characteristics change due to differences in the environment in which the device is placed, and the density of the formed image becomes large. It may change. In such a case, in the conventional apparatus, the operator has no choice but to check the reproduced image and adjust the density of the reproduced image using a density adjustment knob or the like according to the density of the reproduced image.

The present invention has been made in view of the above-mentioned conventional example, and it is possible to keep the reproduced image density constant by examining the image potential of an electrostatic latent image and adjusting the image forming process based on the potential. The purpose of the present invention is to provide an image forming apparatus that is

[Means for Solving the Problems] In order to achieve the above object, an image forming apparatus of the present invention has the following configuration. That is, the image forming apparatus forms an image on a recording medium by an electrophotographic process, and includes a pattern generating means for generating a predetermined image pattern, and a storage means for storing a reference potential of an electrostatic latent image for each of the image patterns. and a comparison means for detecting the potential of the electrostatic latent image corresponding to the image pattern and comparing it with the reference potential, and performing an image forming process corresponding to the image pattern based on the comparison result by the comparison means. control information storage means for storing control information to be controlled;
and a control means for controlling the recording of the image by changing the image forming process based on the control information when recording the image.

According to another invention, there is provided an image forming apparatus for forming an image on a recording medium by an electrophotographic process, comprising: a pattern generating means for generating a predetermined image pattern; and a pattern generating means for generating an image recorded based on the image pattern. an image input means for reading and inputting; a storage means for storing reference density values corresponding to each of the image patterns; a comparison means for comparing the reference density value and the image density value read by the image input means; Subscript information storage means for storing control information for controlling an image forming process based on a comparison result by the comparison means, and for recording an image by changing the image forming process based on the control information when recording an image. and control means for controlling.

[Operation] In the above configuration, the reference potential of the electrostatic latent image for each of the predetermined image patterns is stored, and the potential of the electrostatic latent image corresponding to the image pattern is detected and compared with each reference potential. . Based on this comparison result, control information for controlling the image forming process is stored in accordance with the image pattern, and when recording an image, the image forming process is changed based on the control information to create an image. It works to record.

According to another configuration of the invention, a predetermined image pattern is generated, and a recorded image is read and input based on the image pattern. A reference density value corresponding to each of these image patterns is stored, and this reference density value is compared with an image density value obtained by reading an image formed by the corresponding image pattern. Control information for controlling the image forming process is stored based on the comparison results, and when recording an image, the image forming process is changed based on the control information and the image is recorded. .

[Embodiments] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[Description of Laser Beam Printer (Figs. 1 and 2)] Fig. 1 is a block diagram showing the configuration of the image processing and image forming portion of the laser beam printer of the embodiment, and Fig. 2 is a block diagram showing the configuration of the part that performs image processing and image formation of the laser beam printer of the embodiment. FIG. 3 is a diagram showing the relationship between a recording section and a control section.

In FIG. 1, reference numeral 11 denotes a density pattern generating section which generates pattern data 31 of a predetermined density. This pattern data 31 is input to the multivalued image information generating section 13 and the reference potential generating section 12. The multivalued image information generation section 13 creates image information 32 for forming an image based on this pattern data 31 and outputs it to the selection section 14 . on the other hand,
The reference potential generation section 12 outputs target potential information 33 of a binary electrostatic latent image formed on the photoreceptor based on the image information 32. Reference numeral 14 denotes a selection section which inputs image data 34 from an external device and image information 32 from the multivalued image information generation section 13, and selects the image data 34 when performing normal image printing.
When performing density adjustment, the image information 32 is selected and output as an image signal 35.

15 is a binarization processing unit which inputs the multivalued image signal 35 and binarizes it using the dither method or pulse width modulation (PWM).
It is output as a modulated signal 36 to the exposure section 18 of the recording section 23. The exposure section 18 forms a binary electrostatic latent image on the photoreceptor uniformly charged by the charging section 17 in accordance with the modulation signal 36 .

This electrostatic latent image is formed and fixed on the recording paper by the developing section 19 and the transfer/fixing section 20.

The configuration of this recording section is basically the same as the configuration shown in FIG.

A surface potential detection section 21 measures the surface potential of the photoreceptor on which an electrostatic latent image has been formed by being exposed by the exposure section 18, and outputs it to the exposure amount control section 22 as surface potential information 37. The exposure amount control section 22 inputs and compares the target potential information 33 and the surface potential information 37 from the reference potential generation section 12 described above, and generates exposure control information in order to control the exposure amount associated with the modulation signal 36. 38 is output to the storage section 16. This exposure control information 38 is information based on the difference between the target potential information 33 and the surface potential information 37. For example, when the difference is "0", the value is equal to the density pattern 31, and the target potential information 3
3 is smaller than the density pattern 31, and when the target potential information 33 is larger, it may be set to a larger value than the density pattern 31. In this way, the storage unit 16
The exposure control information 38 stored in is sequentially read out in accordance with the input of image data from an external device, and is output as a signal 39 to the binarization processing section 15. As a result, the binarization processing unit 1
5 determines the signal level of the modulated signal 36 by, for example, changing the binarization process method.

As explained above, the surface potential detection section 21, the exposure amount control section 22, the storage section 16, the binarization processing section 15, and the exposure section 18
Through the loop passing through, the surface potential of the photoconductor on which the binary latent image is formed in the exposure section 18 is stored in the storage section 16 as control information such that it becomes a predetermined value corresponding to the target potential information 33.

Next, the density pattern generation section 11 generates density pattern data 3.
1 is changed and output, and exposure control information 38 corresponding to the density pattern information is stored in the storage section 16 using the control loop as described above. When the input multi-valued image data is composed of, for example, 3 bits, such processing is repeated 256 times from "0" to "255" for the density pattern data 31, and each density pattern is Corresponding exposure control information 38 is stored in the storage unit 16.

When the exposure control information is thus stored in the storage unit 16 and image recording is performed based on the image data 34 from the external device, the selection unit 14 selects the multivalued image data 34 from the external device and converts it into a binary image. It is sent to the processing section 15. 2
The value processing unit 15 uses the exposure control information 39 from the storage unit 16.
The image data is binarized based on the image data, and the exposure amount in the exposure section 18 is determined.

FIG. 2 is a diagram showing the connection between the recording section 23 and the control section 201 and the configuration of the recording section in this embodiment.

In the figure, 201 is a control section including a binarization processing section 15, a surface potential detection section 21, an exposure amount control section 22, a storage section 16, etc., the details of which will be described later with reference to FIG. 202
is a potential signal from the potential sensor 207, and the surface potential of the electrostatic latent image on the photoreceptor 206 is detected based on this signal. 20
Reference numeral 3 denotes a semiconductor laser driven by a modulation signal 36. Laser light 204 output from this laser 203 is reflected by a polygon mirror 205 and scanned over a photoreceptor 206 as shown in the figure. Reference numeral 208 denotes an electrostatic latent image formed on the photoreceptor 206 based on the density pattern data output from the density pattern generating section 11.

[Description of Control Section (FIGS. 3 to 6)] FIG. 3 is a block diagram showing a specific circuit configuration of the control section 201 shown in FIG. 2.

In the figure, 41 is a CPU such as a microprocessor, which executes control of the control unit 201 according to a control program and various data stored in a program ROM 42. The CPU 41 and the program ROM 42 are connected to the exposure amount control section 22 and the density pattern generation section 11. It executes operations corresponding to the reference potential generation section 12, multivalued image information generation section 13, and the like. 43 is a selector, which corresponds to the selection section 14 in FIG. This selector 43 is
According to the selection signal 44 from boat IA, the multi-level image data 34 or boat 1. Select one of the density pattern data 32 input to the RAM 4.
It is output to 9. 45 is an image clock that is synchronized with the image data 34; 47 is a clock output from an oscillator 46, which is used as a synchronization clock when the density pattern data 32 is input.

A RAM 49 stores exposure control information, and corresponds to the storage section 16 in FIG. 50 is a latch circuit, RAM
352 to latch the exposure control information read from 49;
is a D/A converter that converts the digital value stored in the latch circuit 50 into an analog signal. The image signal 57 thus converted into an analog signal is compared with the triangular wave 56 from the triangular wave generator 51 in a comparator 53 and pulse width modulated. A switch circuit 55 outputs a modulated signal 36 to the recording section 23 based on the pulse width modulated signal (binary signal) from the comparator 53.

The operation of the circuit of this embodiment will be explained based on the configuration shown above. First, the recording of the density pattern data 32 will be described.

When recording the density pattern data 32, the CPU 41 selects the selector 43 from 1 to 1 based on the selection signal 44. Select the input, and set the density pattern data 32 to "O" at first, for example.
Output with . This pattern data 32 is input as an address of the RAM 49, and the value stored in advance at the address specified by this pattern data 32 or the CP
The initial value output by U41 from boat P5 is output to bus 54 and latched by latch circuit 50. On the other hand, the triangular wave generator 51 outputs a triangular wave 56 based on the clock signal 47, and the comparator 53 converts the data of the latch circuit 50 into D/
It is compared with the analog signal 57 converted to 8. In this way, the pattern data 32 is pulse width modulated and output to the recording section 23, and an electrostatic latent image corresponding to the pattern data 32 is formed on the photoreceptor 206.

Next, the potential of the electrostatic latent image at this time is detected by the potential sensor 207, and the potential signal 202 is input as a digital signal to the boat P1 via the amplifier 58 and the A/D converter 59. The CPU 41 compares this digital value with a reference potential value (stored in advance in the ROM 42) corresponding to the pattern data, and outputs exposure control information to the boat P5 based on the comparison result. Then, the potential of the electrostatic latent image is detected again based on the potential signal 202, and it is determined whether the difference from the reference potential is less than a predetermined value. Then, when the potential of the electrostatic latent image becomes approximately equal to the reference potential, the exposure control information being output to the bus 54 is stored in the address corresponding to the pattern data 48 in the RAM 49 by the write signal 60.

Next, the value of the pattern data 32 is incremented by 1, and the same operation as described above is performed to store the exposure control information in the RAM 49. For example, if the image data is 8 bits, this operation is
It is executed repeatedly 56" times. In this way, the RAM 49
When the exposure control information is stored in the address, a recording operation is started in which actual image data is input and an image is recorded.

When inputting image data 34 to record an image,
The selector 43 of the CPU 4 t is selected by the selection signal 44.
Instructs to select large input. In this way, the input image data is input to the address of the RAM 49, and the exposure subwriting information corresponding to the image data 34 stored in the RAM 49 is read out by the above-described operation. This exposure control information is latched by a latch circuit 50, converted into an analog signal by a D/A converter 52, and inputted to a comparator 53. Image clock 4 is connected to the other terminal of comparator 53.
A triangular wave 56 synchronized with 5 is input, and this triangular wave 56 and an exposure control information signal (image signal) 57 are compared and output as a modulated signal 36.

FIG. 4 is a diagram showing the relationship between the potential signal 202 and the exposure control information 38 for the pattern data 32.

Here, the selection signal 44 is at a high level, and the Is large input of the selector 43 is selected. T I NT n indicates the output time of the pattern data 32, and the exposure control information 38 is created for each pattern data, and the potential signal 2
It can be seen that 02 is brought closer to the reference value (indicated by the dotted line).

FIG. 5 is a diagram for explaining pulse width modulation in the comparator 53, where 56 indicates a triangular wave signal and 57 indicates an exposure control signal (image data signal). Reference numeral 36 denotes a binary signal (modulation signal) which has been pulse width modulated in this way, and the semiconductor 1 noser 203 is driven based on this signal.

FIG. 6 shows the CPU 4 of the embodiment. This is a flowchart showing the process of creating exposure control information by I.A control program for executing this control is stored in the program ROM 42.

In step Sl, the selection signal 44 is set to high level so that the selector 43 selects the Is large input. Step S
In step S3, the pattern data 32 is outputted, and in step S3, exposure control information is outputted to the bus 54 from step S3. In this way, when an electrostatic latent image based on this pattern data 32 is formed on the photoreceptor 206, the potential signal 20
Enter 2. Then, it is determined whether a reference potential corresponding to this butter data can be obtained, and if it does not substantially match the reference potential, the process proceeds to step S8, and the bus 54
Change the exposure control information output to .

In this way, when the reference potential and the potential signal 202 corresponding to the pattern data are almost equal, step S4
The process then proceeds to step S6, where the write signal 60 is transferred to the RAM 49.
Output to. As a result, the exposure control information on the bus 54 at that time is stored in the address addressed by the pattern data 32 in the RAM 49.The process then proceeds to step S7 to check whether all pattern data has been output.

If the output of all pattern data has not been completed, the process advances to step S8, the pattern data 32 is updated, and the process returns to step S2.

When the output of all pattern data is completed in step S7, the process proceeds to step S9, where the selection signal 44 is set to low level and the process ends. As a result, exposure control information for all pattern data is stored in the RAM 49.

Note that since the operation during image recording is executed based on the image recording operation described above, the explanation thereof will be omitted here.

[Description of the second embodiment (FIGS. 7 and 8)] FIG. 7 is a diagram showing the connection between the recording section 23 and the control section 201a of the second embodiment.

In the first embodiment described above, before performing image formation using image data from an external device, exposure control information is stored in the ROM.
However, in this second embodiment, pattern data is recorded on a portion of the photoreceptor that is not used during normal image recording, so that exposure control can be performed even during image recording. .

In FIG. 7, parts common to those in FIG. 2 described above are indicated by the same numbers.

The control unit 201a is the control unit 20 shown in FIGS. 2 and 3.
1, but as shown in the flowchart of FIG.
2) are slightly different. 208a is the photoreceptor 20
This is an electrostatic latent image based on pattern data formed outside the image recording area of No. 6.

Next, the control operation in this control section 201a will be explained with reference to the flowchart of FIG. 8 and the circuit of FIG. 3.

The process shown in FIG. 8 is started by an interruption that occurs when the laser beam moves out of the image area while scanning the photosensitive drum 206. In step Sll, the selection signal 44 is set to high level so that the selector 43 selects the pattern data 32.

Next, the process proceeds to step S12, where the pattern data 32 is output to form an electrostatic latent image in a non-image area on the photoreceptor 206. In step S13, as is clear from FIG. 7, the position of the photoconductor part where the electrostatic latent image is formed in step SL2 and the photoconductor part whose potential is detected by the potential sensor 207 is different, so that the current pattern is Until the part where the electrostatic latent image is formed by the data reaches the potential sensor 207 part,
The same pattern data is repeatedly recorded each time each separate entry is input, and the electrostatic latent image portion is still visible on the potential sensor 207.
It is checked whether the part has been reached, and if it has not been reached, the process advances to step S19.

The electrostatic latent image part based on the pattern data is the potential sensor 2.
When reaching the 07 part, step 513 to step S1
Proceeding to step 4, data obtained by digitizing the potential signal 202 from the potential sensor 207 is input. In step S15, this value is compared with a reference potential value stored in the ROM 42 to determine whether the exposure amount is appropriate. If the exposure 1 is appropriate, the process proceeds to step 318 and the pattern data is updated; however, if the exposure amount is not appropriate, the process proceeds to step S16, where the exposure control information is changed and output to the bus 54. Then, in step S17, a write signal 60 to the RAM 49 is output, and the exposure amount control information is written to the RAM 49.

In this way, if it is determined that the exposure amount is not appropriate,
At the next interrupt timing, the potential of the electrostatic latent image is measured based on the same pattern data, and the exposure amount is controlled using the same pattern data until the exposure amount reaches a proper value. When the exposure amount becomes appropriate, it is updated to the next pattern data in step S18, and exposure amount control corresponding to the pattern data is implemented.

When the processing in step S17 or step S18 is completed, the process proceeds to step S19, the selection signal 44 is set to low level, and the process returns to the main routine.

In this way, according to the second embodiment, even during image formation, the potential of the electrostatic latent image can be checked for each scan and the exposure amount can be adjusted. Fluctuations in the amount can be more appropriately corrected and kept constant.

[Description of Third Embodiment (Figure 9)] In the embodiment described above, the surface potential of the photosensitive drum in a laser beam printer is measured, and the density is corrected by comparing it with a reference potential for a standard density. However, the sampling of the density information of the formed image is not limited to the surface potential of the photosensitive drum.A third embodiment of the present invention will be described below with reference to FIG. 9.

In the figure, 70 is an image forming apparatus such as a laser beam printer, which forms images using an electrophotographic process 72 such as charging, exposure, development, transfer, and fixing. Reference numeral 75 denotes an interface unit with an external device, which inputs and outputs information such as image information. Reference numeral 73 denotes an image forming process control unit that controls the electrophotographic process. A memory 74 stores sequence programs for the image forming process control section 73 and the like.

72 is an exposure control unit that controls exposure in the electrophotographic process, and in a laser beam printer, controls switching of a laser diode, light amount, etc.; 80 is a detachable density correction unit connected to the image forming apparatus 70; be. Reference numeral 82 denotes a density reading unit that photoelectrically reads the image sample printed on the image forming apparatus 70 using, for example, COD, and reads the density thereof. Reference numeral 84 denotes a reference density generation section that generates a standardized density pattern. A density comparison section 83 compares the density value of the image sample read by the density reading section 82 with the standardized density from the reference density generation section 84.

Reference numeral 81 denotes an interface unit that inputs and outputs information between the image forming apparatus 70 and the density correction unit 80, and transmits the comparison result by the density comparison unit 83 and the density pattern information from the reference density generation unit 84 to the image forming apparatus 70. It is output to.

The operation based on the above configuration will be explained.

The density pattern output by the reference density generation section 84 in the density correction device 80 is transmitted to the interface sections 81 and 75.
0 image forming device 7 sent to image forming device 70 through
The image forming process control section 73 of No. 0 prints and outputs a sample image according to the image information having the reference density. The image forming process control section 73 of No. 9 refers to the process conditions stored in the memory 74 and controls the exposure control section The exposure amount information is transmitted to 71.

Next, the density correction section 82 reads the density of the sample of the outputted image using the density reading section 82, and compares it with the reference density from the above-mentioned reference density generation section 84 using the density comparison section 83. Then, the comparison result is sent to the interface section 81.
．． It feeds back to the image forming apparatus 70 through 75.

In the image forming process control 73 of the image forming section 70, the memory 74 is
Change the image forming process conditions stored in , and output the image sample again.

By repeatedly performing these operations, the memory 74
It is possible to change the image process conditions stored in the image processing device to condition values that enable image formation at standardized density.

Further, by removing the density correction section 80, the image forming apparatus 50 can output an image according to image information sent from an external device, such as a host computer, through the interface section 75.

In this embodiment, only the exposure amount is changed in the image forming process, but the invention is not limited to this. The amount of charge, the transfer potential for transferring the developer to the recording medium, the fixing temperature for fixing the developer to the recording medium, etc. may be changed. Various formation process conditions can be set.

As explained above, according to this embodiment, image density information in the image forming process is compared with standardized density information, and process conditions are corrected based on the difference in density, so that, for example, aging of the photosensitive drum can be improved. This has the effect of improving the reproducibility of output images due to sensitivity deterioration due to changes, environmental changes, and process characteristics unique to the device.

[Effects of the Invention] As explained above, according to the present invention, the density of the reproduced image can be kept constant by checking the image potential in the electrostatic latent image and adjusting the image forming process based on the potential. In addition, there is an effect that images can always be recorded with appropriate image density.

[Brief explanation of the drawing]

Fig. 1 is a functional block diagram of the image forming apparatus of this embodiment, Fig. 2 is a diagram showing the configuration of the recording section and the connection with the control section of the laser beam printer of the embodiment, and Fig. 3 is a diagram showing the specific details of the control section. 4 is a timing diagram showing an exposure amount correction operation corresponding to pattern data, FIG. 5 is a timing diagram showing pulse width modulation using a sawtooth wave, and FIG. FIG. 7 is a flowchart showing the control processing of the control section; FIG. 7 is a diagram showing the configuration of the recording section and the connection with the control section of the second embodiment; FIG. 8 is a flowchart showing the control processing of the second embodiment; FIG. 9 is a block diagram showing a schematic configuration of an image forming apparatus according to a third embodiment, and FIG. 10 is a functional block diagram showing a configuration of a conventional laser beam printer. In the figure, 11...Density pattern generating section, 12...Reference potential generating section, 13...Multi-value image information generating section, 14...
- Selection section, 15... Binarization processing section, 16... Storage section, 17... Charging section, 18... Exposure section, 19... Developing section, 20... Transfer/fixing section , 21...Surface potential detection section, 22...Exposure amount control section, 23...Recording section, 3
2...Pattern data, 36...Modulation signal, 41.
...CPU, 42...Program ROM, 43...
Selector, 44...Selection signal, 49-RAM, 20
1, 201a...Control unit, 202...Potential signal, 2
03... Semiconductor laser, 204... Laser light, 20
5... Polygon mirror 206... Photosensitive drum. Figure 4 Figure 5

Claims (2)

[Claims] (1) An image forming apparatus that forms an image on a recording medium by an electrophotographic process, comprising a pattern generating means for generating a predetermined image pattern, and a memory for storing a reference potential of an electrostatic latent image for each of the image patterns. means for detecting a potential of an electrostatic latent image corresponding to the image pattern;
a comparison means for comparing with the reference potential; a control information storage means for storing control information for controlling an image forming process in accordance with the image pattern based on the comparison result by the comparison means; when recording an image; An image forming apparatus comprising: a control means for changing an image forming process based on the control information to control recording of an image. (2) An image forming apparatus that forms an image on a recording medium by an electrophotographic process, comprising: a pattern generating unit that generates a predetermined image pattern; and an image that reads and inputs an image recorded based on the image pattern. input means; storage means for storing reference density values corresponding to each of the image patterns; comparison means for comparing the reference density values with image density values read by the image input means; and comparison results by the comparison means. a control information storage unit that stores control information for controlling an image forming process based on the image forming process; and a control unit that controls the image forming process to be changed and recorded based on the control information when recording an image. An image forming apparatus comprising: