JPH1184760A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device capable of outputting an image without roughness and with good gradation from a low density to a high density. SOLUTION: In this image forming device, which develops a dot distribution electrostatic latent image formed on a photoreceptor drum (image carrier) 43 corresponding to an image signal to be recorded with toner, a CCD sensor 1 evaluating a toner dot image on a transfer paper P before a fixing process is provided so that the transfer process condition or developing process condition is changed based on the evaluation result by the sensor 1. Thus, since the toner dot image is evaluated on the paper P before the fixing process and the transfer process condition or the developing process condition is changed based on the evaluation result, fine control which is conventionally impossible can be performed and the image without roughness and with the good gradation from a low density to a high density can be outputted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an image forming apparatus for developing a dot distribution electrostatic latent image formed on an image carrier corresponding to a recorded image signal with toner.

[0002]

2. Description of the Related Art An electrophotographic photosensitive member is scanned and exposed by a laser beam modulated in accordance with an image signal to be recorded, and a dot distribution electrostatic latent image (a static image in which a dot-like latent image is distributed corresponding to an image). An image forming method for forming an electrostatic latent image is known. Among them, the so-called pulse width modulation (PWM) method of modulating the width of the driving pulse current of the laser (that is, the duration time) in accordance with the density of the recorded image is based on high recording density (that is, high resolution) and high resolution. The tonality can be obtained.

[0003] However, although the developed dot toner image on the photoreceptor is clear, the image composed of minute dots formed on the transfer paper has roughness in a halftone area having a reflection density of 0.3 or less. It has happened.

[0004] Then, as a result of examining the cause of the above-mentioned roughening, the following was found.

That is, as shown in FIG. 11, a dot-shaped toner image adheres to a transfer sheet at each pixel P. Here, the transferred area is indicated by T, and it can be seen that the toner here is very scattered.

As described above, the low-density area appears rough due to the two-dimensional distribution of the scattered transfer images of the individual dot-shaped toner images. Particularly when a color image is formed by superimposing a plurality of color toners. However, this "Gasatsuki" was particularly conspicuous and reduced the image quality.

Further, an electrostatic latent image having a dot distribution is formed on the photoreceptor by using the PWM method, and a two-component developer magnetic brush is brought into contact with the photoreceptor to reversely develop the electrostatic latent image on the photoreceptor. However, in the image composed of the formed minute dots, roughness occurs in a halftone region having a reflection density of 0.3 or less.

[0008] Then, as a result of examining the cause of the above-mentioned roughening, the following was found.

Normally, when a latent image in a low density portion is formed by a dot distribution latent image, when viewed microscopically, the latent image on the photosensitive member is not a broad latent image like an analog latent image, but as shown in FIG. Is a two-dimensional distribution of local dot-like latent images. FIG. 13 shows this. In FIG. 13, P indicates one pixel, and dot-like latent images L1 to L4 corresponding to a low-density image are formed in each pixel P by a laser beam modulated by the PWM method. D1 to D4 denote toner adhering areas (that is, developed areas) of the dot-like latent images L1 to L5.

In the state shown in FIG. 13, the dot-like latent image L2
Are completely developed, but the dot-like latent images L1 and L3 have a large or small amount of developed toner. Then, the dot-like latent image L4 is not developed at all.

As described above, when the defective developed image of the dot-like latent image is 2
The low-density area looks rough due to the dimensional distribution, and particularly when a color image is formed by superimposing toners of a plurality of colors, this "roughness" is particularly conspicuous and lowers the image quality.

[0012]

The causes of the two-dimensional distribution of the scattered transfer image of the dot-shaped toner image include inadequate transfer bias and the configuration of the transfer guide (position and grounding). Conditions) may not be suitable for the transfer paper (hardness, thickness, electrical resistance, etc.), and improper static elimination conditions when the transfer paper is separated from the photoreceptor. The state changes each time the environment changes or the photoconductor changes, and the level is extremely delicate, so it has been found that the level cannot be detected by the sensor installed conventionally.

The defective developed image of the above-mentioned dot-like latent image is 2
The causes of the dimensional distribution include inadequate development bias values (DC component and AC component), insufficient stirring of the developer in the developing device, and inadequate amount of developer. It is considered that the mixing ratio of the two-component developer is not appropriate, that the toner or carrier of the developer is deteriorated, etc., and that the degree is extremely delicate. It turned out that the level could not be detected by the installed sensor.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to provide an image forming apparatus capable of outputting an image having good gradation from low density to high density without roughness. Is to do.

[0015]

According to a first aspect of the present invention, there is provided a dot-distributed electrostatic latent image formed on an image carrier corresponding to an image signal to be recorded with toner. In the image forming apparatus, a device for evaluating a toner / dot image on transfer paper before a fixing process is provided, and a transfer process condition is changed based on an evaluation result by the device.

According to a second aspect of the present invention, there is provided an image forming apparatus for developing, with toner, a dot distribution electrostatic latent image formed on an image carrier corresponding to a recorded image signal. An apparatus for evaluating a toner / dot image is provided, and a developing process condition is changed based on an evaluation result by the apparatus.

Therefore, according to the present invention, the toner / dot image is evaluated on the transfer paper before the fixing process, and the transfer process conditions or the development process conditions are changed based on the evaluation result. The fine control can be performed, and an image having good gradation from low density to high density can be output without roughness.

It should be noted that one pixel in the present invention indicates the minimum unit of gradation information, and is driven by a minimum recording unit, that is, a time length pulse corresponding to the minimum recording unit in a PWM system or the like which is multi-value recording. The pixel which is the highest density pixel, the pixel consisting of the portion exposed by the light driven by the shorter pulse and the non-exposed portion is a half tone density pixel, and Pixels having the lowest density (white background) are used. On the other hand, in a dither method or the like in which a pseudo gradation is output by binary recording, for example, when a pseudo gradation is output in a minimum recording unit of 2 × 2, a minimum recording of 4 is performed. A set of units is one pixel.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION

[First invention] An embodiment of the first invention will be described below with reference to the accompanying drawings.

<Embodiment 1> FIG. 7 shows the relationship between the spot diameter of a light beam and the thickness of a photosensitive member in an electrophotographic image forming apparatus according to the present invention.

The spot diameter of the light beam is 1/1 of the peak intensity.
represented by portions until reduced to e ^2. The light beam used is a scanning optical system using a semiconductor laser, LE
There is solid scanner such as D or a liquid crystal shutter, the Gaussian distribution is also the light intensity distribution, there is a Lorentz distribution, etc., the portion up to 1 / e ² of the respective peak intensities and spot size.

The light spot generally has an elliptical shape as shown in FIG. 7, and the spot diameter in the present invention means either the main scanning spot diameter or the sub-scanning spot diameter in the figure. Can also be applied.

The spot diameter of the light beam is 1 / the peak intensity.
e It is represented by a magnitude of strength of ² or more, and used at 70 μm or less. By the way, at 70 μm or more, 400 dpi, 256
When a gradation image signal is applied, the influence of the overlap of adjacent images increases, and gradation reproducibility becomes unstable, which is not preferable.

When the electrophotographic photoreceptor according to the present invention is manufactured, the substrate itself has conductivity, for example, aluminum, aluminum alloy, copper, zinc, stainless steel, chromium, titanium, nickel, magnesium , Indium, gold, platinum, silver, iron and the like can be used.
In addition, a subbing layer having an injection inhibiting function and an adhesive function can be provided between a dielectric substrate such as plastic and a photoconductive layer by vapor deposition of aluminum, indium oxide, tin oxide, gold, or the like. The undercoat layer is casein, polyvinyl alcohol, nitrocellulose, ethylene-acrylic acid copolymer, polyvinyl butyral, phenol resin,
The film thickness formed of polyamide, polyurethane, gelatin or the like is set to 0.1 μm to 10 μm, preferably 0.3 μm to 3 μm.

The photoconductive layer is composed of a charge generation layer and a charge transport layer, and may be of a function-separated type or a single layer type in which charge generation and charge transport are performed in the same layer.

As the charge generating material, for example, selenium
Tellurium, pyrylium dyes, thiopyrylium dyes, phthalocyanine pigments, anthantrone pigments, azo pigments, indigo pigments, quinacridone pigments, cyanine pigments and the like can be used.

As the charge generation material and the charge transport material, a binder polymer is used as needed. Examples of binder polymers include styrene, vinyl oxide,
Vinyl chloride, acrylic acid ester, methacrylic acid ester, vinylidene fluoride, polymerization pair and copolymer of vinyl compound such as trifluoroethylene, polyvinyl alcohol, polyvinyl acetal, polycarbonate, polyester, polysulfone, polyphenylene oxide, polyurethane, cellulose resin, Phenol resins, melamine resins, silicon resins, and the like are included.

Incidentally, additives other than the above compounds can be used in the photoconductive layer in order to improve mechanical properties and durability. As such additives, an antioxidant, an ultraviolet absorber, a stabilizer, a crosslinking agent, a lubricant, a conductivity controlling agent, and the like are used.

Here, FIG. 4 shows a schematic mechanism of the laser operation unit 300 for scanning a laser beam.

When a laser beam is scanned by the laser operation unit 300, first, the laser beam emitted from the laser element 302 by the light emission signal generator 301 based on the input image signal is transmitted to the collimator lens system 30.
The light beam is converted into a substantially parallel light beam by 3 and further scanned by a rotating polygon mirror 304 rotating in the direction of arrow b, and is imaged in a spot shape on a scanned surface 306 such as a photosensitive drum by fθ lens groups 305a, 305b and 305c. Is done. The scanning surface 306 is formed by the scanning of the laser light.
An exposure distribution for one scan of an image is formed on the upper side. If the scanned surface 306 is scrolled by a predetermined amount perpendicular to the scanning direction, an exposure distribution according to an image signal is formed on the scanned surface 306. can get.

In this embodiment, the laser PWM
Since the multi-value recording using the area gradation of one pixel was performed using the method (pulse width modulation method), the PWM method will be briefly described below.

FIG. 5 is a circuit block diagram showing an example of the pulse width modulation circuit, and FIG. 6 is a timing chart showing the operation of the pulse width modulation circuit.

In FIG. 5, reference numeral 401 denotes a TTL latch circuit for latching an 8-bit digital image signal;
A high-speed level converter for converting a TL logic level to an ECL logic level, a high-speed D / A converter for converting an ECL logic level to an analog signal, a level converter for converting an ECL logic level to a TTL logic level,
06 is a clock oscillator (O) for oscillating the clock signal 2f.
SC), 407 is a triangular wave generator, and 408 is a 1/2 frequency divider for dividing the clock signal 2f by 1/2. ECL logic circuits are provided everywhere to operate the circuit at high speed.

The operation of the pulse width modulation circuit configured as described above will be described with reference to the timing chart shown in FIG.

The signal (a) is the clock signal 2f and the signal (b) is the image clock signal f, which are related to the image signal as shown. Also, in order to keep the duty ratio of the triangular wave signal at 50% inside the triangular wave generator 407, the clock signal 2f is once frequency-divided by １ ／ before generating the triangular wave signal (c). And
This triangular wave signal (c) is converted into an ECL level to become a triangular wave signal (d).

On the other hand, the image signal is from 00h (white) to FF
It changes at 256 gradation levels up to (black). The image signal (e) indicates the ECL voltage level obtained by D / A converting some image signal values. For example, the first pixel indicates a voltage of FFh at a black pixel level, the second pixel indicates a voltage of 80h at a halftone level, the third pixel indicates a voltage of 40h at a halftone level, and the fourth pixel indicates a voltage of 20h at a halftone level.

The comparator 404 shown in FIG. 5 compares the triangular wave signal (d) with the image signal (e) to obtain pulse widths T, t2, t3, t according to the pixel density to be formed.
4. Generate a PWM signal such as 4. Then, this PWM signal is converted to a TTL level of 0 V or 5 V and becomes a PWM signal (f) and input to the laser driver circuit 500. 1 corresponding to the PWM signal value thus obtained.
By changing the exposure time per pixel, a maximum of 256 gradations can be obtained with one pixel.

In the present embodiment, the gradation control by the PWM method is used, but an area gradation method such as a dither method or laser light intensity modulation can be used, and these may be combined.

Thus, the photosensitive drum 4 shown in FIG.
The electrostatic latent image formed in 3 is developed by a developing device 41 to be visualized as a toner image, and the toner image is electrostatically transferred onto a transfer material P by a transfer charger (a transfer roller may be used) 40. Thereafter, the transfer material P is electrostatically separated by the separation charger 50 and is conveyed to the fixing device 47, where the fixing device 47
As a result, the toner image is thermally fixed, and an image is output.

On the other hand, the surface of the photosensitive drum 43 after the transfer of the toner image is subjected to removal of adhered contaminants such as untransferred toner by the cleaner 42, and is repeatedly subjected to image formation.

In FIG. 1, reference numeral 1 denotes a CCD sensor having a light emitting source (500,000 pixels: 12 μm × 1 pixel)
When the machine is started (before copying), about 100 standard dot latent images are developed as a toner image by the developing device 41, and the toner image is transferred by the transfer charger 40. The dot / toner image on the transfer material P, which is electrostatically transferred onto the material P, is electrostatically separated by the separation charger 50, and is sent to the position of the CCD sensor 1, is read, and the size and position of each image are read. Then, the three-dimensional shape (estimated by the amount of reflected light) is read, the average value and the variation thereof are determined, and the transfer bias is increased or decreased so that these values become the desired values. This operation is repeated several times while the transfer material P passes one sheet (which may be increased as appropriate) to determine the optimum value of the transfer bias, so that the transfer is performed in the order of initial → intermediate → final as shown in FIG. The scattering of the toner image T on the paper P has been reduced, and it has become possible to control a very delicate image.

Second Embodiment Next, a second embodiment of the first invention will be described.

The toner image T on the transfer paper P is optimized by changing the output of the static elimination needle (or a separate charger or static eliminator) 50 shown in FIG. 3 alone or in combination with the transfer roller 40. I tried to do. Table 1 shows the results.

[0044]

As shown in Table 1, when the transfer bias is too large, the separation of the transfer material P from the photosensitive drum 43 or the dot / toner on the photosensitive drum 43 before the transfer material P comes into contact with the photosensitive drum 43 are considered. The image T is scattered due to the flying transfer, and if the transfer bias is slightly small, poor transfer of the solid image portion occurs (at this time, the dot portion is clearly transferred).

Further, when the bias of the static elimination needle is large, scattering due to transfer failure or re-transfer or peel discharge generated by reversing the polarity of toner charging occurs. The transfer current and the charge removal current interfere with each other through the back surface of the transfer material P. Therefore, for example, if the charge removal needle voltage is small while the transfer voltage is constant, the transfer current increases as a whole, and the scattering due to the above-described flying transfer occurs, and if the charge removal needle voltage is large, the scattering occurs due to peeling discharge.

As described above, it can be understood that the transfer process is a process that is very difficult to control in consideration of the delicate image quality of dots. In addition, these conditions are also affected by the environment, paper type, and charging characteristics of the toner. Therefore, each time these conditions change, the transfer process should be changed to a suitable one.

According to the present embodiment, the optimum transfer process condition can be determined by finding the OK condition (条件) in Table 1.

<Third Embodiment> Next, a third embodiment of the first invention will be described.

In the second embodiment, at the time of starting up the machine (before copying), a plurality of CCD sensors 1 are used or moved so that about 100 of the photosensitive drums 43 are located on the far side and the near side in the longitudinal direction. Is developed by the developing device 41, the toner image is electrostatically transferred onto the transfer material P by the transfer charger 40, electrostatically separated by the separation charger 50, and sent to the position of the CCD sensor 1. The degree of scattering of each dot / toner image on the transfer material P at the position of the CCD sensor 1 is read, and their average value and variation are calculated. Then, the information is stored in the main body. Then, this information can be read by the serviceman when performing maintenance, and can be used for operations such as balancing the back side and the front side of the transfer guide. Further, a switch or the like for forcibly executing the above-mentioned process is installed in order to check whether or not the back side and the front side of the dot image are balanced after the work by the service person.

It should be noted that better results can be obtained by performing a wide range of measurements using a plurality of CCD sensors 1. [Second invention] An embodiment of the second invention will be described below with reference to the accompanying drawings.

<Embodiment 1> In the present embodiment, FIG.
As shown in the figure, a CCD sensor having a low light emission source (500,000 pixels: 12 μm × 12 μm per pixel, 600 ×
At the time of machine start-up (before copying), about 100 standard dot latent images are developed by the developing device 41 using
The dot / toner image sent to the position of the CCD sensor 1 is read, and the size, position, and three-dimensional shape (estimated by the amount of reflected light) of each are read, and their average values and variations are calculated. Is increased or decreased so as to have a desired value. For example, Table 2 shows the result of evaluating the macro-graininess of an image when a low-density dot latent image was developed for a DC component.
Shown in

From the results in Table 2, it can be seen that when the DC component is varied, there is an optimum value with no dot roughness and good dot reproducibility. In addition, since this optimum value largely depends on the environment, the degree of deterioration of the developer, and the chargeability of the toner, it is desirable to set the DC component periodically.

The reason why the degree of roughness varies with the DC component will be described with reference to FIG.

Normally, when a minute dot is developed, its outline (ie, the size of the dot toner image) greatly depends on the DC component of the developing bias. As is clear from FIG. 12, the latent image of the low-density portion dot is extremely shallower than the high-density portion.

Further, the shape of the dot latent image in the low-density portion is slightly different depending on the local electrical characteristics and the surface state of the toner layer of the photosensitive member and the developer carrier, especially in the vicinity of the hatched portion in FIG. Often. Therefore, by setting as shown in FIG. 9 (b) rather than setting the DC component of the developing bias in FIGS. 9 (a) and 9 (c), there is less variation as in the output image shown in FIG. Image with less roughness) can be output.

By repeating the above operation several times to determine the optimum value of the developing bias, more delicate image control becomes possible.

<Second Embodiment> Next, a second embodiment of the second invention will be described.

FIG. 10 shows a developing device 41 for visualizing the dot distribution electrostatic latent image formed on the photosensitive drum 43.
An example using a two-component developing device as shown in FIG.

The inside of the developer container 27 is partitioned by a partition wall 19 into a developing chamber (first chamber) R1 and a stirring chamber (second chamber) R2, and a toner storage chamber R3 is formed above the stirring chamber R2. A replenishment toner (non-magnetic toner) 20 is stored in the toner storage chamber R3. A supply port 21 is provided in the toner storage chamber R3, and an amount of supply toner 20 corresponding to the toner consumed by the development is dropped and supplied into the stirring chamber R2 via the supply port 21.

On the other hand, in the developing chamber R1 and the stirring chamber R2, the developer 2 containing the toner particles and the magnetic carrier particles is mixed.
2 are accommodated.

As the toner, a known toner obtained by adding a colorant, a charge controlling agent and the like to a binder resin can be used, and a toner having a volume average particle diameter of 5 to 15 μm can be suitably used. Here, the volume average particle diameter of the toner used is, for example, one measured by the following measurement method.

As a measuring device, Coulter Counter T
Interface to output number average distribution and volume average distribution using A-II type (manufactured by Coulter) (manufactured by Nikkaki)
And CX-i personal computer (manufactured by Canon Inc.)
And the electrolyte is 1% N using 1st grade sodium chloride.
An aqueous aCl solution is prepared.

The measuring method is as follows.
A surfactant (preferably an alkylbenzene sulfonate) is added as a dispersant in 0.1 to 5 ml in 150 ml,
Further, a method of adding 0.5 to 50 mg of a measurement sample is used.

The electrolytic solution in which the sample was suspended was subjected to a dispersion treatment for about 1 to 3 minutes using an ultrasonic disperser, and the above-mentioned Coulter Counter TA-II was used to form an aperture of 100 μm.
The volume distribution is determined by measuring the particle size distribution of the particles of 2 to 40 μm using an aperture. Then, the volume average particle diameter of the sample is determined from the determined volume distribution.

On the other hand, as the magnetic carrier, those obtained by applying a very thin resin coating on the surface of magnetic particles are preferably used, and the average particle diameter is preferably 5 to 70 μm. The average particle size of the carrier is indicated by the maximum length in the horizontal direction, a microscopic method is used as a measuring method, 300 or more carriers are randomly selected, the diameter is measured and arithmetically averaged to obtain the carrier particle size. .

As shown in FIG. 10, the developing chamber R1
A transport screw 23 is accommodated therein, and the developer 22 in the developing chamber R1 is transported in the longitudinal direction of the developing sleeve 25 (diameter φ32 mm) by the rotational driving of the transport screw 23.

The transport screw 24 is provided in the storage room R2.
The transport screw 24 transports the developer 22 along the longitudinal direction of the developing sleeve 25 by its rotation. The direction in which the developer is conveyed by the screw 24 is the opposite direction to that by the screw 23.

An opening (not shown) is provided in the partition wall 19 on the front side and the back side, and the developer 22 conveyed by the screw 23 is delivered to the screw 24 from one of the openings, and Is conveyed to the screw 23 from the other one of the openings.
The toner is charged to a polarity for developing the latent image by friction with the magnetic particles.

An opening is provided in a portion of the developer container 27 close to the photosensitive drum 43, and a non-magnetic developing sleeve 2 made of aluminum, non-magnetic stainless steel, or the like is provided in the opening.
5 are provided. The developing sleeve 25 rotates in the direction of arrow b in the drawing to carry and transport the developer 22 in which the toner and the carrier are mixed to the developing unit 26. Then, the magnetic brush of the developer 22 carried on the developing sleeve 25 contacts the photosensitive drum 43 rotating in the direction of arrow a in the developing unit 26,
The electrostatic latent image formed on the photosensitive drum 43 is developed by the developing unit 26.

An oscillating bias voltage obtained by superimposing a DC voltage on an AC voltage is applied to the developing sleeve 25 by a power supply (not shown). The dark portion potential (non-exposed portion potential) and the bright portion potential of the latent image are applied. (Exposure portion potential) is located between the maximum value and the minimum value of the vibration bias potential. by this,
An alternating electric field whose direction changes alternately is formed in the developing section 26. In this alternating electric field, the toner and the carrier vibrate violently, and the toner shakes off the electrostatic constraint on the developing sleeve 25 and the carrier to form an electrostatic latent image. Correspondingly, it adheres to the photosensitive drum 43.

The difference (peak-to-peak voltage) between the maximum value and the minimum value of the vibration bias voltage is preferably 1 to 5 kV, and the frequency is preferably 1 to 10 kHz. As a waveform of the oscillation bias voltage, a rectangular wave, a sine wave, a triangular wave, or the like can be used. The DC voltage component has a value between the dark portion potential and the light portion potential of the latent image, and the absolute value of the DC voltage component is closer to the dark portion potential than to the minimum bright portion potential. It is preferable to prevent fog from adhering to the surface. It is desirable that the minimum gap between the developing sleeve 25 and the photosensitive drum 43 (the minimum gap position exists in the developing section 26) is 0.2 to 1 mm.

In FIG. 10, reference numeral 28 denotes a developer layer thickness regulating blade, which regulates the layer thickness of the two-component developer 22 carried and transported by the developing sleeve 25 to the developing section 26. The amount of the developer regulated by the developer layer thickness regulating blade 28 and conveyed to the developing unit 26 is determined by a developing magnetic pole S1 described later.
22 formed by a magnetic field in the developing unit 26 due to
The height of the magnetic brush above the surface of the developing sleeve 25 is 1.2 to 3 times the minimum gap value between the developing sleeve 25 and the photosensitive drum 43 when the photosensitive drum 43 is removed. Is preferred.

A roller-shaped magnet 29 is fixedly arranged in the developing sleeve 25, and the magnet 29 is
6, and a developing magnetic pole S1 facing the developing magnetic pole S6. The developing magnetic pole S1 causes the developing agent 2
Two magnetic brushes are formed, and the magnetic brush comes into contact with the photosensitive drum 43 to develop the dot distribution electrostatic latent image. At this time, the toner adhering to the ears (brushes) of the magnetic carrier and the toner adhering to the surface of the developing sleeve 25 instead of the ears are transferred to the exposed portion of the electrostatic latent image and developed.

The strength of the developing magnetic field by the developing magnetic pole S1 on the surface of the developing sleeve 25 (magnetic flux density in a direction perpendicular to the surface of the developing sleeve 25) has a peak value of 500 to 2
Desirably, 000 gauss.

In this embodiment, the magnet 29 has N1, N2, N3, and S2 poles in addition to the developing magnetic pole S1.

With this configuration, the developer 22 pumped by the N2 pole by the rotation of the developing sleeve 25 is conveyed from the S2 pole to the S1 pole by the rotation of the developing sleeve 25, and the developer layer thickness regulating blade 28 in the middle thereof. Regulated to form a thin layer. Then, the developer 22 raised in the magnetic field of the developing magnetic pole S1 develops the electrostatic latent image on the photosensitive drum 43. Thereafter, the developing sleeve 2 is moved by the repulsive magnetic field between the N3 pole and the N2 pole.
5 falls into the stirring chamber R1, and the developer 22 on the stirring chamber R1
The developer 22 dropped into the inside is stirred and conveyed by screws 23 and 24.

Using such a two-component developing device 41, about 100 standard dot latent images are developed by the developing device 41 when the machine is started (before copying), and sent to the position of the CCD sensor 1. Reads dot / toner images, size, position, three-dimensional shape of each one (estimated by the amount of light reflected)
, The average value and the variation thereof are calculated, and when the average value or the variation is lower than the reference value, the operation of dropping and replenishing the replenishing toner 20 into the stirring chamber R2 via the replenishing port 21 is started. This operation is repeated several times, and the optimal dot
The toner supply operation is performed until the toner image converges.

It should be noted that better results can be obtained by performing a wide range of measurements using a plurality of CCD sensors 1. Further, a method of periodically moving the CCD sensor 1 was also effective.

<Third Embodiment> Next, a third embodiment of the second invention will be described.

In the second embodiment, at the time of starting up the machine (before copying), a plurality of CCD sensors 1 are used or moved so that about 100 of the photosensitive drums 43 are located on the far side and the near side in the longitudinal direction. The standard dot latent image is developed by the developing device 41, and the dot / toner image sent to the position of the CCD sensor 1 is read, and the size, position, and three-dimensional shape of each image (estimated by the amount of reflected light) Is read out, the average value and the variation thereof are calculated, and when the difference between the values is larger than the reference value on the back side and the near side, the operation of increasing the rotation of the screws 23 and 24 is started. Then, the operation is repeated several times, and the screws 23 and 24 are rotated quickly until the optimal dot / toner image is converged on both the back side and the front side.

If a wide range of measurement is performed using a plurality of CCD sensors 1, better results can be obtained.

[0081]

As apparent from the above description, according to the present invention, the toner / dot image is evaluated on the transfer paper before the fixing process, and the transfer process condition or the development process condition is determined based on the evaluation result. Since the control is changed, fine control that has been impossible in the past can be performed, and an effect that an image having good gradation from low density to high density can be output without roughness can be obtained.

[Brief description of the drawings]

FIG. 1 is a sectional view of a main part of an image forming apparatus according to a first invention.

FIG. 2 is a perspective view for explaining the principle of the image forming apparatus according to the first invention.

FIG. 3 is a perspective view for explaining the principle of the image forming apparatus according to the first invention.

FIG. 4 is a diagram illustrating a configuration of a laser beam scanner.

FIG. 5 is a circuit block diagram illustrating an example of a pulse width modulation circuit.

FIG. 6 is a timing chart showing an operation of the pulse width modulation circuit.

FIG. 7 is a diagram illustrating a relationship between a spot diameter of a light beam and a film thickness of a photoconductor.

FIG. 8 is a sectional view of a main part of the image forming apparatus according to the second invention.

FIG. 9 is a schematic diagram for explaining the principle of the second invention.

FIG. 10 is a sectional view of a developing device for describing Embodiments 2 and 3 of the second invention.

FIG. 11 is a diagram showing one pixel of a conventional transfer image.

FIG. 12 is a schematic diagram for explaining a conventional problem.

FIG. 13 is a schematic diagram for explaining a conventional problem.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 CCD sensor 40 Transfer charger 41 Developing device 43 Photosensitive drum (image carrier) 50 Separation charger

[Table 1]

[Table 2]

Claims (2)

[Claims] 1. An image forming apparatus for developing a latent image having a dot distribution formed on an image carrier corresponding to an image signal to be recorded with toner, evaluates a toner dot image on a transfer sheet before a fixing process. An image forming apparatus, wherein a transfer process condition is changed based on an evaluation result by the device. 2. An image forming apparatus for developing, with toner, a dot distribution electrostatic latent image formed on an image carrier corresponding to a recorded image signal, wherein the toner / dot image is evaluated on the image carrier. Wherein the developing process conditions are changed based on an evaluation result by the device.