JP2730779B2 - Image forming device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus capable of forming a halftone image.

<Prior Art> One of the prior arts of interest to the present invention is disclosed in JP-A-63-24.
There is an electrophotographic apparatus described in Japanese Patent No. 0568.

The electrophotographic apparatus described in this publication measures the residual potential on the photoreceptor surface after exposure, and controls the developing bias according to the measured value, so that the density of the developed image is maintained at a constant density regardless of the residual potential. Is what you can do.

Further, as another prior art, there is an apparatus described in JP-A-63-293566.

In the apparatus described in this publication, the laser output is controlled based on the bright portion potential in order to detect the bright portion potential of the image formed on the photoreceptor and correct a change in sensitivity of the photoreceptor. With such a configuration, stable gradation expression is possible.

<Problems to be Solved by the Invention> Among the above conventional devices, the former is a configuration for making the image density constant when forming a black and white binary image. Therefore, when forming a halftone image, it is not possible to correct halftone reproducibility that varies due to a difference in sensitivity of the photoconductor.

On the other hand, the latter device controls the laser output to correct the change in the sensitivity of the photoconductor, but controls the laser output based on the bright portion potential of the image formed on the photoconductor. It is difficult to satisfactorily correct the tone reproducibility. This is because, when the laser output is controlled based on the light portion potential, the gradation expression near the white level is stabilized, but the reproducibility of the entire halftone is not always corrected.

Therefore, an object of the present invention is to provide an image forming apparatus having good halftone reproducibility even when the sensitivity of the photoreceptor varies due to the environment or the like.

<Means for Solving the Problems> The present invention provides a photoreceptor having a photoconductive surface, charging means for uniformly charging the surface of the photoreceptor, and exposing the charged photoreceptor surface to static electricity. Light beam output means for forming an electrostatic latent image, developing means for applying a developer to the electrostatic latent image formed on the surface of the photoreceptor to make it visible, and developer provided by the developing means In an image forming apparatus including a developing bias adjusting unit for adjusting an applied amount, a beam for controlling output energy of a light beam output unit to a predetermined plurality of halftone reproducing energies in order to confirm halftone reproducibility. Control means; potential detecting means for detecting the surface potential of the photoreceptor exposed at each of the plurality of halftone reproduction energies; and EV characteristics representing the relationship between the exposure energy and the surface potential of the photoreceptor are stored in advance. Memory Means and a plurality of photoreceptor surface potentials corresponding to a plurality of exposure energies detected by the potential detection means are compared with the EV characteristics stored in the storage means. And a feedback correction control means for controlling the developing bias adjusting means so as to obtain an average value of the deviation and correct the average value of the deviation.

Further, the present invention provides a photoconductor having a photoconductive surface,
A charging unit for uniformly charging the surface of the photoconductor, a light beam output unit for exposing the charged photoconductor surface to form an electrostatic latent image, and an electrostatic unit formed on the surface of the photoconductor. An image forming apparatus including a developing unit for applying a developer to a latent image to visualize the latent image. Beam control means for controlling the tone reproduction energy, potential detecting means for detecting the surface potential of the photoreceptor exposed to the plurality of intermediate tone reproduction energies, and representing the relationship between the exposure energy and the surface potential of the photoreceptor. A storage unit in which the EV characteristic is stored in advance, and a plurality of photoconductor surface potentials corresponding to a plurality of exposure energies detected by the potential detection unit are stored in the storage unit.
And a feedback correction control means for controlling the charging means so that the average value of the deviation is obtained when the deviation from the EV characteristic is compared with the V characteristic, and the average value of the deviation is corrected. Further, the present invention provides a photoconductor having a photoconductive surface, a charging unit for uniformly charging the surface of the photoconductor, and exposing the charged photoconductor surface to light. An image forming apparatus comprising: a light beam output unit for forming an electrostatic latent image on the surface of the photosensitive member; and a developing unit for applying a developer to the electrostatic latent image formed on the surface of the photoconductor to visualize the electrostatic latent image. Beam control means for controlling the output energy of the light beam output means to a predetermined plurality of halftone reproduction energies in order to confirm the halftone reproducibility; Body surface potential , A storage unit in which an EV characteristic representing the relationship between the exposure energy and the surface potential of the photoconductor is stored in advance, and a plurality of exposure energies corresponding to a plurality of exposure energies detected by the potential detection unit. Stored in the storage means.
And a feedback correction control unit for controlling the light beam output unit so as to obtain an average value of the deviation when the deviation from the EV characteristic is compared with the -V characteristic and to correct the average value of the deviation. An image forming apparatus comprising:

Still further, according to the present invention, in each of the above image forming apparatuses, the light beam output means changes output energy stepwise by pulse width modulation.

<Operation> By detecting the surface potential of the photoreceptor exposed at a plurality of predetermined halftone reproduction energies and comparing it with the EV characteristic, the sensitivity variation of the photoreceptor in proportion to the exposure energy can be reduced. To detect. Then, in order to obtain the average value of the variation and correct the average value of the variation,
Feedback control is performed on any of the developing bias related to the image density, the charging voltage of the photoconductor, or the output energy of the light beam output unit.

<Embodiment> A digital copying machine will be described below as an embodiment of the present invention with reference to the drawings.

FIG. 1 is a block diagram showing a configuration of a main part of a digital copying machine according to this embodiment. The digital copying machine is provided with a photosensitive drum 1 having a photoconductive surface, a charging charger 2 for uniformly charging the surface of the photosensitive drum 1, and a charging voltage generating circuit 3. The charging voltage generation circuit 3 applies a predetermined charging voltage to the charging charger 2 to uniformly charge the surface of the photosensitive drum 1 to a constant voltage, for example, 700V.

The original image is read by a CCD sensor 4 via an optical system (not shown), processed by a signal processing circuit 5, and provided to a laser drive circuit 6. The laser drive circuit 6 is a signal processing circuit 5
The semiconductor laser 7 is driven by using the signal from the controller as a modulation component. The laser beam output from the semiconductor laser 7 is scanned by the rotating polygon mirror 8 and irradiated on the photosensitive drum 1 to expose the photosensitive drum 1.

When the photoreceptor drum 1 is exposed to the laser beam, the charge of the exposed portion is removed, and an electrostatic latent image corresponding to the exposure content is formed. Rotation direction of photoconductor drum 1 (arrow A1
A developing device 10 is disposed downstream, and a toner as a developer is applied to the electrostatic latent image by the developing device 10, and the electrostatic latent image is visualized as a toner image. .
To control the amount of toner applied by the developing device 10, a developing bias adjusting circuit 11 is connected to the developing device 10.
The developing bias adjustment circuit 11 applies a predetermined bias voltage to the developing device 10.

The toner image is transferred to a sheet by a known mechanism (not shown).

With respect to the rotation direction A1 of the photosensitive drum 1, a potential sensor 12 is provided downstream of the exposure position by the laser beam and upstream of the developing device 10 so as to face the surface of the photosensitive drum 1. Is arranged. The potential sensor 12
This is for detecting the surface potential of the photosensitive drum 1 after the exposure, and the potential detected by the potential sensor 12 is given to the feedback control unit 13. The feedback control unit 13 includes an EV characteristic storage unit 14 described later.

Further, a halftone image signal output unit 15 is provided,
The halftone image signal output from the output section 15 is applied to a laser drive circuit 6, and the laser drive circuit 6 drives the semiconductor laser 7 using the applied halftone image signal as a modulation component.

The output of the laser drive circuit 6 at this time is also supplied to the feedback control unit 13.

In this embodiment, the laser drive circuit 6 drives the semiconductor laser 7 by pulse width modulation, changes the laser beam output time to, for example, five stages, and performs halftone expression by multi-leveling one pixel.

More specifically, referring to FIG. 2, the laser beam for one pixel output from the semiconductor laser 7 is (4/4) E, (3/4) E, (2 / 4) E or (1/4) E or laser light is not output (0/4)
E.

Incidentally, when the photosensitive drum 1 charged to a constant potential is exposed to a laser beam, between the irradiation energy E of the laser beam and the surface potential V of the exposed photosensitive drum 1 is shown in FIG. There is a relationship represented by an EV characteristic curve (curve indicated by a solid line). That is, the irradiation energy of the laser beam is (4/4) E, (3/4) E, (2/4) E, (1/4) E,
(0/4) If we reduced the E, the surface potential of the photosensitive drum 1 becomes large as _{V 4, V 3, V 2} , V 1, V 0 accordingly. The amount of adhered toner is compared with the magnitude of the surface potential. Therefore, it is possible to express a halftone.

However, the relationship between the actual irradiation energy E and the surface potential V is represented by a broken line instead of the EV characteristic curve (solid line) in FIG. 3 due to variations in the sensitivity of the photosensitive drum 1 and changes in the surrounding atmosphere. There are times when it shifts like a relationship.

If this deviation is not corrected, the halftone reproducibility will deteriorate.

Therefore, in this embodiment, the control operation shown in the flowchart of FIG. 4 is performed in the configuration shown in FIG. Next, a description will be given with reference to FIG. 1 and FIG.

The halftone image signal (1/4) D to be corrected is supplied from the halftone image signal output unit 15 to the laser drive circuit 6 (step S
1). In response, the laser drive circuit 6 performs pulse width modulation so that the irradiation energy of the irradiation energy of the laser beam output from the semiconductor laser 7 is (1) E per pixel (step S2). The modulation signal of the laser drive circuit 6 at this time is also supplied to the feedback control unit 13.

The surface potential V _M of the surface of the photosensitive drum 1 is exposed by the irradiation energy (1/4) E is measured by the potential sensor 12,
It is provided to the feedback control unit 13. (Step S
3).

In the feedback control section 13 compares the potential V ₁ determined from the E-V characteristic curve as shown in Figure 3 stored in the V _M and E-V characteristic storage unit 14, the deviation voltage [Delta] V = V _M - V ₁
Is obtained (step S4). Then, a control signal is supplied to the developing bias adjusting circuit 11 so as to correct the deviation voltage ΔV, and the developing bias is adjusted (step S5).

In the above embodiment, in order to correct the deviation voltage ΔV,
Although the developing bias is adjusted, the surface voltage of the photosensitive drum 1 charged by the charging charger 2 may be changed by adjusting the output voltage of the charging voltage generating circuit 3 instead. Alternatively, the output energy E of the semiconductor laser 7 may be changed to E ′ by adjusting the drive of the laser drive circuit 6.

In the case where the laser beam output from the semiconductor laser 7 is controlled in five steps by pulse width modulation, as shown in FIG. the surface potential V ₁ of the 1 becomes substantially 1/2 of the original potential V _0. As described above, the area where the surface potential is about 1/2 is an important part in the halftone expression and the reference E
The potential between the −V characteristic and the actual EV characteristic is likely to be the largest.

Therefore, in this embodiment, the halftone image signal (1/4) D to be corrected output from the halftone image signal output unit 15 is
The signal is set in advance so that the irradiation energy of the laser beam output from the semiconductor laser 7 becomes (1/4) E.

The reference EV characteristic stored in the EV characteristic storage unit 14 may be, for example, a value calculated by calculation, or may be the value when the photosensitive drum 1 is in an initial state before industrial shipment. What was actually measured may be used.

Instead of the above-described embodiment, the halftone image signal output from the halftone image signal output unit 15 is, for example, a three-stage signal (1/1 /
4) D, (2/4) D and (3/4) D, and the irradiation energy of the laser beam output from the semiconductor laser 7 is changed to (1/4) E according to the three-step halftone image signal. , (2 /
4) Change to three stages of E and (3/4) E. And
Photoconductor drum 1 exposed with irradiation energy for each stage
May be detected by the potential sensor 12 and the feedback control unit 13 calculates the average value of the deviation between the theoretical EV characteristic and the actual EV characteristic.

That is, if expressed by the equation, ΔV ₁ = V _M1 −V ₁ ΔV ₂ = V _M2 −V ₂ ΔV ₃ = V _M3 −V ₃ ΔV ₀ = (ΔV ₁ + ΔV ₂ + ΔV ₃ ) / 3. However, V _M1 : the surface potential detected when exposed with the energy of (1/4) E V _M2 : the surface potential V _M3 detected when exposed with the energy of (2/4) E V _M3 : (3/4 ) Surface potential detected at the time of exposure with the energy of E. In order to correct the average value ΔV ₀ of this deviation, the developing bias is adjusted, the output voltage of the charging voltage generating circuit 3 is adjusted, or The drive of the laser drive circuit 6 may be adjusted.

In the above embodiment, the case where the laser beam output from the semiconductor laser 7 is controlled in five steps by pulse width modulation has been described as an example. What is necessary is to control.

The laser beam may be controlled using pulse amplitude modulation instead of pulse width modulation.

If the original image contains, for example, many blackish halftones or many whiteish halftones, the halftone image signal to be corrected in accordance with the original image, that is, the laser beam May be changed.

In the above embodiment, the halftone image signal is directly supplied from the halftone image signal output unit 15 to the laser drive circuit 6.
The output may be provided to the laser drive circuit 6 via the signal processing circuit 5.

<Effects of the Invention> Since the present invention is configured as described above, it is possible to correct a variation in halftone reproducibility due to a difference in sensitivity between photoconductors and a change in an ambient atmosphere, etc., thereby obtaining a good and stable halftone scale. An image forming apparatus capable of reproducing a tone can be provided.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a main configuration of a digital copying machine according to an embodiment of the present invention. FIG. 2 is a waveform diagram showing five stages of laser beam outputs when a semiconductor laser is pulse width modulated. FIG. 3 is a diagram showing an EV characteristic curve representing the relationship between the irradiation energy E of the laser beam and the surface potential V of the photoconductor exposed with the irradiation energy E. FIG. 4 is a flowchart showing a control operation which is a feature of this embodiment. In the figure, 1... Photosensitive drum, 2... Charging charger, 3... Charging voltage generating circuit, 6.
7 semiconductor laser, 10 developing device, 11 developing bias adjustment circuit, 12 potential sensor, 13 feedback control unit, 14 EV characteristic storage unit, 15 halftone image signal Output section.

Continuation of the front page (56) References JP-A-3-1175 (JP, A) JP-A-60-260066 (JP, A) JP-A-57-27279 (JP, A) JP-A-58-111959 (JP) JP-A-61-189574 (JP, A) JP-A-61-213865 (JP, A) JP-A-62-187363 (JP, A) JP-A-55-155367 (JP, A) 61-3160 (JP, A) JP-A-1-276166 (JP, A) JP-A-63-309978 (JP, A) JP-A-59-30551 (JP, A)

Claims (4)

(57) [Claims] 1. A photoreceptor having a photoconductive surface, a charging unit for uniformly charging the surface of the photoreceptor, and a device for exposing the charged photoreceptor surface to form an electrostatic latent image. Light beam output means, developing means for applying a developer to the electrostatic latent image formed on the photoreceptor surface to make it visible, and developing for adjusting the amount of developer applied by the developing means In the image forming apparatus including the bias adjusting unit, a beam control unit that controls the output energy of the light beam output unit to a predetermined plurality of halftone reproduction energies in order to confirm halftone reproducibility, A potential detecting means for detecting the surface potential of the photosensitive member exposed with the halftone reproduction energy, and E- representing the relationship between the exposure energy and the surface potential of the photosensitive member.
A storage unit in which the V characteristic is stored in advance, and a plurality of photoconductor surface potentials corresponding to a plurality of exposure energies detected by the potential detection unit are compared with an EV characteristic stored in the storage unit. And a feedback correction control means for controlling a developing bias adjusting means so as to obtain an average value of the deviation when the deviation is different from the V characteristic and to correct the average value of the deviation. apparatus. 2. A photoreceptor having a photoconductive surface, charging means for uniformly charging the surface of the photoreceptor, and light for exposing the charged photoreceptor surface to form an electrostatic latent image. In an image forming apparatus including a beam output unit and a developing unit for applying a developer to the electrostatic latent image formed on the photoreceptor surface to visualize the image, in order to confirm halftone reproducibility, Beam control means for controlling the output energy of the light beam output means to a predetermined number of halftone reproduction energies; and potential detection means for detecting the surface potential of the photosensitive member respectively exposed with the plurality of levels of halftone reproduction energy. E- representing the relationship between the exposure energy and the surface potential of the photoreceptor
A storage unit in which the V characteristic is stored in advance; and a plurality of photoconductor surface potentials corresponding to a plurality of exposure energies detected by the potential detection unit are compared with the EV characteristic stored in the storage unit. An image forming apparatus comprising: a feedback correction control unit that determines an average value of the deviation when the deviation is different from the V characteristic and controls the charging unit so that the average value of the deviation is corrected. 3. A photoreceptor having a photoconductive surface, charging means for uniformly charging the surface of the photoreceptor, and exposing the charged photoreceptor surface to form an electrostatic latent image. In order to confirm halftone reproducibility in an image forming apparatus including a light beam output unit and a developing unit for applying a developer to the electrostatic latent image formed on the photoreceptor surface to visualize the image, Beam control means for controlling the output energy of the light beam output means to a predetermined number of halftone reproduction energies; and potential detection means for detecting the surface potential of the photosensitive member respectively exposed with the plurality of halftone reproduction energies. Which represents the relationship between the exposure energy and the surface potential of the photoreceptor.
A storage unit in which the V characteristic is stored in advance, and a plurality of photoconductor surface potentials corresponding to a plurality of exposure energies detected by the potential detection unit are compared with an EV characteristic stored in the storage unit. And a feedback correction control means for controlling an optical beam output means so as to obtain an average value of the deviation when the deviation is different from the V characteristic, and to correct the average value of the deviation. apparatus. 4. An image forming apparatus according to claim 1, wherein said light beam output means changes output energy stepwise by pulse width modulation. It is.