JP2747065B2 - 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.

<Problem to be Solved by the Invention> Among the above conventional apparatuses, the former has a configuration for keeping 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, which cannot be achieved by the prior art.

<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 the amount of application, a first stage consisting of a plurality of stages of halftone reproduction energies in which the output energy of the light beam output unit is predetermined in order to confirm halftone reproducibility. First beam control means for controlling the halftone reproduction energy, potential detection means for detecting the surface potential of the exposed photoconductor, and EV characteristics indicating the relationship between the exposure energy and the surface potential of the photoconductor are stored in advance. Memory means, The relationship between the first halftone reproduction energy in a plurality of stages and the photoreceptor surface potential detected corresponding to the first halftone reproduction energy is compared with the EV characteristics stored in the storage means, and they are different from the EV characteristics. In this case, the first feedback correction control means and the first feedback correction control means for controlling any one of the light beam output means and the charging means so as to obtain the average value of the deviation and correct the average value of the deviation. In order to confirm the corrected halftone reproducibility, the second beam control means for controlling the output energy of the light beam output means to the second halftone reproduction energy, and the second halftone reproduction energy and correspondingly The relationship between the detected photoconductor surface potential is compared with the EV characteristic stored in the storage unit, and the relationship is determined by the EV characteristic.
Any one of the light beam output means, the developing bias adjusting means and the charging means, which is not controlled by the first feedback correction control means, so that when the characteristics are deviated, the deviation is corrected. And a second feedback correction control means for controlling the image forming apparatus.

Also, the present invention provides the image forming apparatus, wherein
The feedback correction control means controls the light beam output means, and the second feedback correction control means controls the developing bias adjustment means.

Further, according to the present invention, in the image forming apparatus, the first feedback correction control means controls a light beam output means, and the second feedback correction control means controls a charging means.

Further, according to the present invention, in the image forming apparatus, the first feedback correction control means controls the charging means, and the second feedback correction control means controls the developing bias adjusting means.

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. A developing unit for applying a developer to the latent image to make the image visible, and an image forming apparatus including a developing bias adjusting unit for adjusting the amount of developer applied by the developing unit,
A first beam control means capable of controlling the output energy of the light beam output means to a first halftone reproduction energy comprising a plurality of predetermined halftone reproduction energies in order to confirm halftone reproducibility; Potential detecting means for detecting the surface potential of the photoconductor, storage means in which EV characteristics representing the relationship between the exposure energy and the surface potential of the photoconductor are stored in advance, the first halftone reproduction energy in a plurality of stages, and The relationship between the photoreceptor surface potentials detected in correspondence thereto is compared with the EV characteristics stored in the storage means, and if they deviate from the EV characteristics, an average value of the deviation is obtained. First feedback correction control means for controlling the light beam output means so that the average value of the deviation is corrected;
A second beam control means capable of controlling the output energy of the light beam output means to a second halftone reproduction energy in order to confirm the halftone reproducibility after being corrected by the first feedback correction control means; (2) The relationship between the halftone reproduction energy and the photoconductor surface potential detected correspondingly is compared with the EV characteristic stored in the storage means. A second feedback correction control means for controlling the charging means so that the deviation is corrected, and a light beam output means for confirming halftone reproducibility after being corrected by the first and second feedback correction control means. A third beam control means for controlling the output energy of the third beam to the third halftone reproduction energy;
The relationship between the halftone reproduction energy and the photoreceptor surface potential detected corresponding to the halftone reproduction energy is stored in the storage means.
And a third feedback correction control means for controlling the developing bias adjusting means so as to correct the deviation when the relation is deviated from the EV characteristic as compared with the characteristic. It is a forming device.

Further, according to the invention, in any one of the image forming apparatuses described above, the light beam output means changes the output energy stepwise by pulse width modulation.

<Operation> The surface potential of the photosensitive member is detected by exposing the photosensitive member with halftone reproduction energy, and by comparing the surface potential with the EV characteristic, the variation in the sensitivity of the photosensitive member is detected and corrected.

For this purpose, first, the surface potential of the photoreceptor exposed with the first halftone reproduction energy including a plurality of halftone reproduction energies is detected, and when it is deviated from the EV characteristic, the average value of the deviation is calculated. In order to mainly correct, any one of the photosensitive member charging voltage and the light beam output energy related to the image density is subjected to the first feedback correction control. And
After the correction control, the photoconductor is exposed with the second halftone reproduction energy to detect its surface potential. If the surface potential deviates from the EV characteristic, in order to supplementarily correct the deviation,
Any one of the photoreceptor charging voltage, light beam output energy, and development bias, which is not related to the first feedback correction control, related to the image density is further subjected to the second feedback correction control.

More specifically, the main correction of the light beam output means and the auxiliary correction of the developing bias adjustment means, the main correction of the light beam output means and the auxiliary correction of the charging means, or the charging means It is preferable that the main correction is performed and the developing bias adjustment unit is corrected auxiliary.

Further, the light beam output means may be mainly controlled, and the developing bias adjusting means and the charging means may be supplementarily corrected and controlled, and in addition thereto, the developing bias adjusting means may be supplementally controlled.

<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 generating 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 potential, 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 by the laser beam, the electric charge of the exposed portion is removed. Therefore, an electrostatic latent image corresponding to the exposure content is formed. A developing device 10 is disposed downstream of the photoconductor drum 1 in the rotation direction (the direction indicated by the arrow A1 direction). The developing device 10 applies toner as a developer to the electrostatic latent image, Is visualized as a toner image. A developing bias adjusting circuit 11 is connected to the developing device 10 in order to control the applied toner amount. 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 driving circuit 6 drives the semiconductor laser 7 by pulse width modulation, changes the laser beam output time to, for example, five steps, and multi-values one pixel to perform halftone expression.

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

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. Then, the amount of adhered toner is proportional to the magnitude of the surface potential. Therefore, halftone expression is possible.

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 first 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 S1). The laser driving circuit 6 outputs the first halftone image signal (1 /
4) Based on D, pulse width modulation is performed so that the irradiation energy of the laser beam output from the semiconductor laser 7 becomes (1/4) E per pixel (step S2). At this time, the modulation signal of the laser drive circuit 6 is supplied to a feedback control unit.
Also given to 13.

The surface potential _VM1 after the surface of the photoreceptor drum 1 has been exposed with the irradiation energy of (1/4) E is measured by the potential sensor 12 and given to the feedback control unit 13 (step S).
3).

In the feedback control unit 13, (1/4) E and V _M1
Is compared with an EV characteristic curve as shown in FIG. 3 stored in the EV characteristic storage unit 14, and the deviation voltage ΔV ₁ = V
Request _M1 -V _D1 (step S4). And the deviation voltage ΔV
_A control signal is supplied to the laser drive circuit 6 so as to correct ₁ so that the irradiation energy E of the laser beam output from the semiconductor laser 7 is corrected to E '(step S5).

In the above embodiment, in order to correct the deviation voltage [Delta] V _1,
Although the laser drive circuit 6 is controlled, the bias voltage of the developing bias adjustment circuit 11 may be corrected and controlled instead.

Next, the second halftone image signal output unit 15
The halftone image signal (3/4) D is supplied to the laser drive circuit 6 (step S6). The laser drive circuit 6 controls the irradiation energy of the beam output from the semiconductor laser 7 based on the second halftone image signal (3/4) D.

In this case, the laser drive circuit 6 performs step S5
Because it has received feedback correction control described in
Laser beam irradiation energy per pixel (3/4)
Pulse width modulation is performed so as to be E '(step S7). The modulation signal of the laser drive circuit 6 at this time is also supplied to the feedback control unit 13.

The surface potential _VM2 after the surface of the photosensitive drum 1 has been exposed with the irradiation energy of (3/4) E '
And is provided to the feedback control unit 13 (step S8).

In the feedback control unit 13, (3/4) E
(A E rather than E '.) And the relationship between the measured potential V _M2, compared with the E-V characteristic curve as shown in Figure 3 stored in the E-V characteristic storage unit 14, the deviation voltage ΔV ₂ = V _M2 −V _D2 is obtained (step S9). Then, so as to correct the deviation voltage [Delta] V _1, supplies a control signal to the charging voltage generating circuit 3,
Correction control of the charging voltage is performed (step S10).

By performing such control, the halftone reproducibility is improved mainly by the laser beam output (step S
5) Further, the halftone reproducibility close to a white background is supplementarily improved by the charging voltage.

Note that, in step S5, in case of giving a control signal to the charging voltage generating circuit 3 in order to correct the deviation voltage [Delta] V _1, the feedback control in step S10 may be performed with respect to the development bias adjustment circuit 11.

Further, in step S5, in case of performing the feedback correction control for correcting the deviation voltage [Delta] V ₁ to the laser drive circuit 6, the feedback correction control in Step S10, even if the developing bias adjustment circuit 11 Good.

Further, the same control as in steps S6 to S10 is repeated once again, and the developing bias adjustment circuit 11 is adjusted so that the variation in the sensitivity of the photosensitive drum 1 is corrected based on the third halftone image signal to be corrected. Feedback correction control may be performed.

As described above, when the photosensitive drum 1 is exposed with three types of halftone reproduction energies, the surface potential after exposure in each case is detected, and feedback correction control is performed based on the surface potential, first, the first intermediate The irradiation energies E and E 'of the laser beam based on the irradiation with the tone reproduction energy.
It is preferable that the main correction is made, the charging voltage is supplementarily corrected based on the second halftone reproduction energy, and the developing bias is supplementarily corrected based on the third halftone reproduction energy.

In such a case, the main correction may be performed by correcting the charging voltage, and the second auxiliary correction may be performed by correcting the irradiation energy of the laser beam. However, the correction of the developing bias does not appear in the output of the potential sensor 12, and therefore must always be corrected last.

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 half of the surface potential is an important part in the halftone expression, and the potential between the reference EV characteristic and the actual EV characteristic is likely to be the largest. Many.

Therefore, in this embodiment, the first halftone image signal (1/1 /
4) D is a signal such that the irradiation energy (1/4) E of the laser beam output from the semiconductor laser 7 is obtained.

The reference EV characteristic stored in the EV characteristic storage unit may be, for example, a value calculated by calculation, or may be measured before shipment from the factory when the photosensitive drum is in the initial state. It may be something.

Further, as described above, the first halftone image signal (1/4) D that has been corrected first is not limited to one type, and for example, three-stage signals (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
The signal is changed into three stages of (1/4) E, (2/4) E and (3/4) E in accordance with the three-stage signals. The potential sensor 12 sequentially detects the surface potential of the photosensitive drum 1 exposed with the irradiation energy for each stage, and the feedback control unit 13 compares the theoretical EV characteristic with the actual EV characteristic. The average value avΔV of the shift may be calculated.

That is, if expressed by the equation, ΔV ₁₁ = V _M11 −V ₁₁ ΔV ₁₂ = V _M12 −V ₁₂ ΔV ₁₃ = V _M13 −V ₁₃ avΔV = (ΔV ₁₁ + ΔV ₁₂ + ΔV ₁₃ ) / 3. Here, V _M11 : the surface potential detected when exposed with the energy of (1/4) E V _M12 : the surface potential detected when exposed with the energy of (2/4) E V _M13 : (3 / 4) This is the surface potential detected when exposed with the energy of E.

Then, in order to perform main feedback correction of the average value avΔV of the deviation, the developing bias is adjusted, the output voltage of the charging voltage generating circuit 3 is adjusted, or the irradiation energy of the laser driving circuit 6 is adjusted. Is also good.

Then, after that, steps S6 to S1 described in FIG.
The same control as 0 is performed, and the auxiliary feedback correction control is performed on any one of the remaining two or the other two other than the one on which the main feedback correction control is performed.

In the above embodiment, the case where the laser beam output from the semiconductor laser 7 is controlled in five stages by pulse width modulation has been described as an example, but the laser beam is controlled in a plurality of stages capable of halftone expression by pulse width modulation. do it.

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-1-109365 (JP, A) JP-A-58-111959 (JP, A) JP-A-1-289979 (JP, A) JP-A-62-187363 (JP) JP-A-61-189574 (JP, A) JP-A-55-155367 (JP, A) JP-A-57-27279 (JP, A) JP-A-59-136754 (JP, A) 60-52868 (JP, A) JP-A-3-1175 (JP, A)

Claims (6)

(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 An image forming apparatus including a bias adjusting unit, wherein the output energy of the light beam output unit is controlled to a first halftone reproduction energy comprising a plurality of predetermined halftone reproduction energies in order to confirm halftone reproduction. One-beam control means; potential detecting means for detecting the surface potential of the exposed photoreceptor; and E-representing the relationship between exposure energy and the surface potential of the photoreceptor.
The storage means in which the V characteristic is stored in advance, and the relationship between the first halftone reproduction energy in a plurality of stages and the photoreceptor surface potential detected corresponding thereto are compared with the EV characteristic stored in the storage means, respectively. , They are EV
When there is a deviation from the characteristic, an average value of the deviation is obtained, and a first feedback correction control unit that controls one of the light beam output unit and the charging unit so that the average value of the deviation is corrected; A second beam control means for controlling the output energy of the light beam output means to a second halftone reproduction energy for confirming the halftone reproducibility after being corrected by the feedback correction control means; And the relationship between the photoreceptor surface potential detected correspondingly and E in the storage means.
Any one of the light beam output means, the developing bias adjusting means, and the charging means may be compared with the -V characteristic so that if the relationship is different from the EV characteristic, the difference is corrected.
An image forming apparatus comprising: a second feedback correction control unit that controls a device that is not controlled by the first feedback correction control unit. 2. The image forming apparatus according to claim 1, wherein the first feedback correction control means controls the light beam output means, and the second feedback correction control means controls the developing bias adjustment means. Is what you do. 3. The image forming apparatus according to claim 1, wherein the first feedback correction control means controls a light beam output means, and the second feedback correction control means controls a charging means. It is. 4. The image forming apparatus according to claim 1, wherein the first feedback correction control means controls a charging means, and the second feedback correction control means controls a developing bias adjustment means. It is. 5. A photoreceptor having a photoconductive surface, a charging means for uniformly charging the surface of the photoreceptor, and a light source 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 And controlling the output energy of the light beam output means to a first halftone reproduction energy comprising a plurality of predetermined halftone reproduction energies in order to confirm halftone reproduction in the image forming apparatus including the bias adjustment means. First beam control means for detecting the surface potential of the exposed photoreceptor; E-representing the relationship between the exposure energy and the surface potential of the photoreceptor.
The storage means in which the V characteristic is stored in advance, and the relationship between the first halftone reproduction energy in a plurality of stages and the photoreceptor surface potential detected corresponding thereto are compared with the EV characteristic stored in the storage means, respectively. , They are EV
When there is a deviation from the characteristic, an average value of the deviation is obtained, and the first feedback correction control unit that controls the light beam output unit so that the average value of the deviation is corrected. A second beam control means capable of controlling the output energy of the light beam output means to a second halftone reproduction energy in order to confirm the halftone reproducibility after the second halftone reproduction energy, The relationship between the photoconductor surface potentials detected and stored in the storage means is stored in E.
A second feedback correction control means for controlling the charging means so as to correct the deviation when the relation is different from the EV characteristic, as compared with the -V characteristic; A third beam control means for controlling the output energy of the light beam output means to a third halftone reproduction energy in order to confirm the halftone reproducibility after the correction by the control means; and a third halftone reproduction. The relationship between the energy and the surface potential of the photoreceptor detected corresponding to the energy is stored in the storage means.
A third feedback correction control unit that controls the developing bias adjustment unit so as to correct the deviation when the relationship deviates from the EV characteristic as compared with the -V characteristic;
An image forming apparatus comprising: 6. An image forming apparatus according to claim 1, wherein said light beam output means changes output energy stepwise by pulse width modulation. It is.