JPH04213470A - Image forming device - Google Patents

Abstract

PURPOSE:To always control gradation reproduction to the optimum and to obtain an image excellent in quality by forming a pattern for testing on a photosensitive body, developing it with toner, and then, measuring the reflection density of a toner image via a slit. CONSTITUTION:A pattern signal for testing is sent to a dot generator 41 according to the instruction of a control part 51, and a test detecting pattern is written on the photosensitive body 9 regardless of the writing of original data to the photosensitive body 9. The electrostatic latent image of the test detecting pattern on the photosensitive body 9 is actualized with the toner by a developing unit 12. The toner image formed on the photosensitive body is moved accompanying with the rotation of the photosensitive body 9, and passes a micro density measuring part 38. In the measuring pattern 38, the reflecting light quantity of the toner image illuminated by an illuminating means has micro measurement according to a constant clock through a microslit, while the toner image of the pattern passes, and the result is sent to an image processing part 50.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to electrophotography, which involves projecting recording image light onto a photoreceptor to form an electrostatic latent image on the photoreceptor, and developing the electrostatic latent image to form a visible image. The present invention relates to image forming apparatuses such as copying machines and printers.

0002

2. Description of the Related Art In an electrophotographic image forming apparatus that obtains an image by attaching toner to an electrostatic latent image, changes in the charging characteristics and photoelectric characteristics of a photoreceptor due to environmental changes, deterioration over time, etc. Due to changes in the characteristics of the developer used for development and changes in the characteristics of the development process itself, the state of the final image becomes unstable. Under such circumstances, process control has conventionally been carried out in order to continuously obtain stable images. The conventional method is to form a pattern on a photoreceptor for process control, irradiate it with light from an LED light source, and detect the amount of reflected light with a photosensor (for example, as described in 1-206368). This method is also used in image forming apparatuses that form images using analog optical systems, and detects the average density of a pattern having a certain width. Being able to obtain the averaged density is a reasonable detection method because when controlling toner density etc. based on the density information, we want to know the overall density state rather than the detailed reproduction state. Met.

0003

[Problems to be Solved by the Invention] However, it is not only average conditions such as density that affect image quality, but also more detailed conditions such as density uniformity, graininess, unevenness, directionality, dots, etc. There is also the uniformity of shape. In particular, digital copying involves converting an original image into an image electrical signal using an imaging device such as a CCD, converting it into digital image data, and recording the digital image data using a digital recording device such as a laser printer. In digital recording devices such as laser printers that record digital image data generated externally or internally, reproduction in small dot units becomes a problem, and in the case of conventional analog image forming devices, In comparison, the state of reproduction of details directly reflects the state of reproduction of the overall image. Therefore, it is necessary to know information such as recording density and uniformity of more detailed images of recorded images, but these cannot be detected by conventional methods.

Furthermore, when actually forming an image, it is not uncommon for two or more toner layers to be formed. When considering image reproduction, the fact that toner is attached in multiple layers does not pose a problem in terms of the image density in that part, but it becomes an important problem when considering the overall image quality. Therefore, a method has been proposed in which the toner adhesion amount is directly measured to control gradation reproducibility.

Although this method is accurate, it is expensive because it uses a laser, and has the disadvantage that the entire device becomes large.

An object of the present invention is to detect the recording density quality of more detailed images and to always control optimum tone reproduction characteristics without requiring particularly expensive and large equipment.

[0007]

[Means for Solving the Problems] The present invention provides a document reading means (30) that scans a document in the main scanning direction and the sub-scanning direction and outputs an image signal for each read pixel; Image processing means (50) that receives an image signal to be output and performs gamma conversion;
In an image forming apparatus that forms an electrostatic latent image on a uniformly charged photoreceptor (9) in response to an image signal output by a photoreceptor (9) and develops it with toner, a density detecting means (38) for forming a test pattern on the toner, developing it with toner, and then measuring the reflection density of the toner image through a slit (38b); )
A control means (51, 56) is provided for determining a value corresponding to the amount of toner adhesion from the measured reflection density and selecting a gamma conversion characteristic curve of the image processing means (50) in accordance with the determined value.

Note that symbols in parentheses indicate corresponding elements or matters in the embodiments shown in the drawings and described later.

[0009]

[Operation] FIG. 12 shows a typical tone reproduction curve. In the case of an image forming apparatus that obtains images by electrophotography, the gradation reproduction of input data and final image reflects the gradation characteristics of each process in between. The gradation reproduction curve shown in Figure 12 is drawn by dividing each of these processes,
This represents the gradation reproduction characteristics at each stage when the input data passes through the image processing section, writing section, development, transfer, and fixing to obtain the final image.

[0010] Here, what is called the final gradation reproduction curve is the one shown in the first quadrant (a). The fourth quadrant is the intermediate reproduction curve of the image processing system, and shows the characteristics when input data is converted by the gamma conversion section and halftone processing section of the image processing means (50). . The third quadrant is the gradation reproduction curve of the image forming section, in which the output from the image processing means (50) is modulated in the writing section, a latent image is written and developed, and a toner image is obtained on the photoreceptor. The characteristics when used are shown (c). The second quadrant is the gradation reproduction curve of the transfer/fixing section, which shows the gradation reproduction characteristics when the toner image after development undergoes transfer/fixing to obtain the final image (a). In this way, the relationship shown in the first quadrant between the input data and the final image obtained through the above steps is established.

Therefore, depending on what kind of final gradation reproduction characteristics are desired, the characteristics of the fourth, third, and second quadrants are controlled to obtain the desired gradation reproduction characteristics. Obtainable. In addition, if any of the characteristics from the fourth quadrant to the second quadrant changes due to changes in the environment or changes in characteristics over time, it is possible to maintain the tone reproduction characteristics of the final image by changing other characteristics. can.

According to the invention of the present application, the photoconductor (9) can be used when some characteristics affecting the gradation reproduction characteristics of the third quadrant (c) in FIG. 12 change due to environmental changes or changes in characteristics over time.
A test pattern was formed on the photoreceptor (9) to measure the change in the amount of toner adhesion on the photoreceptor (9), and the amount of toner adhesion after development was measured using a slit (38b).
), the amount of reflected light is determined from the measured data.
Concentrations can be detected in a narrower area. Therefore, detailed information on the toner image on the photoreceptor (9) can be obtained without requiring particularly expensive and large equipment. In addition, the obtained data was used for the fourth quadrant (
The feed is sent to the image processing means (50) whose characteristics are shown in d).
Since the gamma conversion characteristic curve is selected by performing a backward step, control can be performed so that appropriate characteristics are always obtained as the final image characteristics, and thereby an image with excellent image quality can be obtained.

Other objects and features of the invention will become apparent from the following description of embodiments with reference to the drawings.

[0014]

[Example] The main body mechanism of one embodiment of the invention of the present application is shown in Fig. 1.
The electrical system is shown in Figure 2. This is a digital copying machine, and its mechanical section mainly consists of an image reading section 3 that reads the image of the original document 1.
0, and an image recording section 40 that records images on recording paper.

[0015] Original 1 is placed on a platen (contact glass)
2 and illuminated by an exposure lamp 3. The reflected light from the original 1 passes through the first mirror 4a, the second mirror 4b, the third mirror 4c, and the lens array LEN, and then enters the CCD 5, which is a line image sensor. Exposure lamp 3 and 1st
Mirror 4a, second mirror 4b, and third mirror 4c are mounted on carriages Car1 and Car2, respectively, and are driven from right to left by carriage drive motor 23 when reading document 1, and are placed on platen 2. The entire surface of the written document 1 is scanned. The CCD 5 has many CCD elements lined up in a row, and charges are serially output from each element in accordance with an externally applied clock.

The light reflected from the original 1 is converted into an electrical signal by the CCD 5, and is subjected to necessary processing such as shading correction, gamma conversion, and halftone reproduction processing by the image reading section 30 and image processing section 50, and is then recorded as an image. The signal is input to a dot generator 41 which is an LD (laser diode) drive circuit of the section 40.

The LD drive circuit energizes the LD (laser diode) of the LD (laser diode) unit 31, and the LD unit 31 emits laser light modulated by the modulation circuit 42. be done. The laser beam emitted from the LD unit 31 is reflected by a polygon mirror (rotating polygon mirror) 6, passes through an f.theta. lens 7 and a mirror 8, and is irradiated with an image onto a rotating photoreceptor drum 9.

The polygon mirror 6 is connected to a polygon motor 10.
The polygon motor 10 rotates at a constant speed to rotationally drive the polygon mirror 6. As the polygon mirror 6 rotates, the laser beam is raster-scanned in a direction perpendicular to the rotational direction (clockwise) of the photoreceptor drum 9, that is, in a direction along the drum axis.

The photosensitive drum 9 has a photoconductive layer provided on an electrically grounded conductive substrate, and the surface of the photosensitive drum 9 is connected to a negative high voltage generator (not shown). After being uniformly charged by the charging charger 11, a potential distribution corresponding to the on/off pattern is formed according to the on/off of the laser beam irradiated from the image recording section 40. . In addition, since the laser beam is modulated to be turned on/off in accordance with the black/white of the pixel at the scanning position of the image to be written, the potential distribution formed on the photoreceptor drum 9 will vary depending on the image to be recorded. This corresponds to the density distribution of . As a result, an electrostatic latent image is formed on the surface of the photoreceptor drum 9 according to the density of the document 1, and when this electrostatic latent image is developed by the developing unit 12, a toner image is formed on the surface of the photoreceptor drum 9. Ru. On the other hand, the recording paper 17 stored in the cassette 16 is fed by the paper feeding operation of the paper feeding roller 18, and is sent toward the photosensitive drum 9 by the registration roller 20 at a predetermined timing. While the recording paper 17 passes under the photoreceptor drum 9, the toner image is transferred to the recording paper 17 by the action of the transfer charger 13, and the recording paper 17 is transferred to the photoreceptor drum 9 by the action of the separation charger 14. more peeled off.

The peeled recording paper 17 is transferred to the fixing unit 2.
The toner that was sent to recording paper 17 and transferred there is transferred to recording paper 17.
The recording paper 17 with the toner fixed thereon is placed in the tray 2.
2.

Further, toner remaining on the surface of the photoreceptor even after transfer is removed by a brush 15 provided in the cleaning unit 15.
a and blade 15b, and the entire surface of the photoreceptor is exposed to light by a static elimination lamp QL, in preparation for the next copying process.

The digital copying machine described above has two modes (
It can operate in normal mode, check mode). Normal mode
In the mode, it operates as described above.

In the check mode, a test pattern is formed and its micro density is measured before dot generation based on the image data of the original. first,
According to the instructions from the control unit 51, the dot generator 4
1, a test pattern signal is sent. This results in
Instead of original image data being written on the photoreceptor 9, a pattern for test detection is written on the photoreceptor 9. The electrostatic latent image of the test detection pattern on the photoreceptor 9 is transferred to the developing device 12.
The image is visualized using toner. The toner image formed on the photoreceptor moves as the photoreceptor 9 rotates and passes through the micro density measuring section 38 .

In the micro-density measuring section 38, the amount of reflected light from the toner image of the test detection pattern illuminated by the illumination means is passed through the micro-slit to measure the toner image of the pattern (toner image pattern). During the passage of the image sensor, micro-measurements are performed according to a constant clock, and the results are sent to the image processing section 50.

The configuration of the optical sensor section of the micro concentration measuring section 38 is shown in FIG. In this example, the photosensors 38a are arranged in the sub-scanning direction (direction parallel to the rotation axis of the photoreceptor 9). In front of the photosensor 38a is a slit plate 38b with slits formed therein, in front of this slit plate 38b is a condensing lens 38c, in front of this condensing lens 38c is an entrance 38d; is opposite to the area (ring shape) of the photoreceptor 9 where the pattern is formed. Further, an illumination means 38e for illuminating an area on the photoconductor 9 where a pattern is formed is provided on the back side of the micro-density measuring section 38 in the direction of rotation of the photoconductor. Measurement range (in front of slit 38d)
illuminate evenly. The slit width of the slit plate 38b is narrower than the width in the sub-scanning direction of a pattern for test detection, which will be described later. This allows concentration to be detected in fine units.

The reflected light on the photoreceptor 9, which is made into parallel light by the condenser lens 38c, passes through the slit of the slit plate 38b and reaches the photosensor 38a, where the reflected light from each part is converted into an electrical signal. The levels of these electrical signals correspond to the intensity of reflected light.

An example of a pattern for test detection is shown in FIG. This pattern is an example of a pattern for power modulation. (a) is a diagram of the latent image on the photoreceptor 9 viewed from a direction perpendicular to the photoreceptor 9, and the shaded area is the image portion. In FIG. 4, the power is increased from the upper part to the lower part. Although (a) is a binary representation, each pattern actually differs in the depth direction of the latent image. (b) shows the depth (surface potential) of the electrostatic latent image. Note that the dotted line is the development start potential. In this example, six types of patterns are arranged in the sub-scanning direction in descending order of power, but from among the gradations possible in the system, there are enough patterns to monitor the gradation reproduction characteristics. A pattern may be used in which an arbitrary number is selected and arranged in an arbitrary order. Alternatively, a pattern example as shown in FIG. 5 may be used. This is an example of pulse width modulation.

FIG. 6 shows an example of data obtained when the pattern example shown in FIG. 4 is measured by the micro density measuring section 38. If the number of points measured for one pattern is n, the number of data obtained is n×m (m is the number of patterns). Each is 8-bit data. The obtained data is fed back to the adhesion amount processing section 56 of the image processing section 50.

The configuration of the adhesion amount processing section 56 is shown in FIG. The concentration data is sent from the control section 560 to the data input section 56.
1 is input to the adder 562,
Data for one pattern (D11 to D1n) is added. The result is LUT5 as data A representing the total concentration.
65. The density data is also input to a comparator 563, where it is compared with a threshold value Thr generated by a threshold value generating device 568 for determining an image portion, and the result is sent to an adder 564. The adder 564 obtains a value B corresponding to the width of the image portion within one pattern by adding the signals when the value is equal to or greater than Thr. The relationship between A and B and the toner adhesion amount is determined in advance and reflected in LUT 565, so it can be calculated from data A representing the total density and value B corresponding to the width of the image area within one pattern. Data S representing the amount of adhesion is obtained according to LUT 565. this day
The data S is input to a comparator 566.

The comparator 566 also includes a control section 5.
A circuit 570 that generates an address by a signal from 60
Accordingly, a signal representing the data order is sent as an address to the reference threshold value generator 569, and the reference threshold value Tm is inputted accordingly. The comparator 566 compares the data S with the reference threshold Tm, and the comparison result data R is R.
Written to AM567. Similar processing is carried out in D11 to D
The process is repeated up to 1 m by the number of patterns, and data R1 to Rm are written into the RAM 567 as signals representing the reference threshold value Tm and the magnitude of the adhesion amount data. According to this data, the gamma determining section 571 determines the gamma curve,
One of the gamma conversion characteristic curves prepared in advance in the ROM 571b of the gamma determination section 571 is selected, and a signal corresponding to this curve is output to the control section 560. This signal is outputted by the control section 51 to the gamma conversion section 53, and a gamma conversion curve is determined.

[0031] Here, the processing of the adhesion amount processing section 56 will be specifically explained. Assuming that eight patterns are used to detect the toner adhesion amount, the data representing the adhesion amount for each pattern is S1 to S8, and the reference threshold value corresponding to each pattern is T1 to T8. shall be. This reference threshold value is T
1 to T8 are values corresponding to eight patterns used for toner adhesion amount detection on the standard gamma curve. Curve a is a graph showing the amount of toner adhesion above. Now, the data S1 to S8 are shown in FIG. 8, and the estimated gamma curve is represented by b. By comparing the values at eight points, the positional relationship between both curves can be known. The value representing the magnitude relationship between the reference threshold Tm and the data representing the toner adhesion amount Sm is set to "1" if the toner adhesion amount is large, and "0" if the toner adhesion amount is equal or small.
In the case shown in FIG. 8, the value R1 represents the magnitude relationship between the reference threshold value and the data representing the amount of toner adhesion.
~R8 has “0”, “0”, “0”, “1”, “
1”, “1”, “1”, and “0” are substituted.

Next, using this data, processing is performed in the gamma determination section 571. The gamma determination section 571 is composed of a ROM table 571b in which a gamma conversion characteristic curve prepared in advance is stored, a CPU 571a that controls the entire system, and the like. Here, FIG. 9 shows and describes the control operation of the CPU 571a in the check mode. That is, in part A, the total sum of m data is calculated (
Steps 1 to 6), and in part B, a gamma curve is selected from among the gamma conversion characteristic curves shown in FIG. 10 based on the value of Sum (steps 7 to 11). For example, Thr1=6,T
If hr1=2, in the above example, Sum=4(=
0+0+0+1+1+1+1+0), d is selected as the gamma conversion characteristic curve. This corresponds to the graph (d) of the fourth quadrant of the gradation reproduction curve shown in FIG. 12 described above. Then, a signal representing the selected gamma conversion characteristic curve d is fed to the gamma conversion section 53 in FIG.
be backed up.

Similarly, when feeding back data to the halftone processing section 54, the data written in the RAM 567 is
The data is used to determine the threshold value when performing halftone processing.

Note that similar processing may be performed by pattern matching without determining the total sum Sum. That is, as shown in FIG. 11, gamma conversion characteristic curves to be selected for all patterns that may appear are determined in advance, and
A gamma conversion characteristic curve to be used for processing may be determined by showing this together.

[0035]

As explained above, according to the invention of the present application, detailed information on the toner image on the photoreceptor (9) can be obtained without the need for particularly expensive and large equipment, and it is also possible to obtain detailed information on the toner image on the photoreceptor (9). To constantly appropriately control tone reproduction characteristics against changes in tone reproduction characteristics due to changes in characteristics, and to obtain images with excellent image quality.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing an outline of a mechanical section of an embodiment of the invention of the present application.

FIG. 2 is a block diagram showing an outline of the configuration of the electrical system of the embodiment.

[Fig. 3] Sensor of the micro concentration measuring section 38 shown in Fig. 1.
FIG. 2 is a block diagram showing elements of a component.

4 is a plan view showing the position of an example of a test pattern formed on the photoreceptor 9 shown in FIG. What you see from (
b) shows the depth of the latent image.

FIG. 5 shows another image formed on the photoreceptor 9 shown in FIG.
FIG. 2 is a plan view showing the position of an example of a test pattern;
) shows the latent image on the photoreceptor 9 viewed from a direction perpendicular to the photoreceptor 9, and (b) shows the depth of the latent image.

6 is a waveform diagram showing an example of concentration data obtained by the micro concentration measuring section 38 shown in FIG. 1. FIG.

7 is a block diagram showing the configuration of the adhesion amount processing section 56 shown in FIG. 2. FIG.

FIG. 8 is a graph showing the relationship between input data and toner adhesion amount.

9 is a flowchart showing the gamma determination processing content of the gamma determination unit 571 shown in FIG. 7. FIG.

10 is a graph showing a gamma conversion characteristic curve stored in advance in the ROM 571b shown in FIG. 7;

FIG. 11 is a plan view showing an example of an area map for determining a gamma conversion characteristic curve corresponding to all patterns that may appear in advance.

FIG. 12 is a graph showing a tone reproduction curve.

[Explanation of symbols]

1: Original 2: Contact glass 3: Illumination light Car 1: Carriage 4a to 4c: Mirror
5: CCD 6: Polygon mirror 7: fθ lens
8: Mirror 9: Photoreceptor 10: Motor
11: Main charger 12: Developing device 13: Transfer charger 14: Separation charger 15: Cleaning unit
16: Recording paper cassette 17: Recording paper 18: Paper feed roller
19: Paper feed roller 20: Registration roller 21: Fixing unit
22: Paper ejection tray 23: Carriage drive motor
24: Original presser 30: Image reading section 31: LD unit 38
: Micro concentration measuring section
38a: Photo sensor 38b: Slit plate 38c: Condensing lens
38d: Inlet port 38e: Illumination means 40: Image recording unit 41: Dot generation device
42: Modulation circuit 50: Image processing section 51: Control section 52: Shading correction section
53: Gamma conversion section 54: Halftone processing section
55: Test pattern data generation circuit 56: Adhesion amount processing section 560: Control section
567: RAM 571: Gamma determination section 571a: CPU
571b: ROM

Claims (1)

[Claims] 1. Original reading means for scanning an original in the main scanning direction and sub-scanning direction and outputting an image signal for each read pixel; Image processing means for receiving the image signal outputted by the original reading means and performing gamma conversion; In an image forming apparatus that forms an electrostatic latent image on a uniformly charged photoreceptor in response to an image signal output by the image processing means and develops it with toner, a test is performed on the photoreceptor. A density detecting means for forming a pattern and developing it with toner, and then measuring the reflection density of the toner image through a slit; An image forming apparatus comprising: a control means for determining a value corresponding to the amount and selecting a characteristic curve of gamma conversion of the image processing means in accordance with the value.