JPH11190919A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a toner from becoming too thick and changing in hue, due to the change in the temperature of a photoreceptive drum. SOLUTION: When a temperature detected by an environmental sensor 18 is below a specified temperature, conditions under which images are formed are altered according to the surface temperature of the photoreceptive drum 1 detected by a surface potential sensor 12 or temperature detection sensor 12A for the photoreceptive drum 1. For example, in the case the surface temperature of the photoreceptive drum 1 rises making development contrast low corresponding to it, can prevent the toner image from increasing in density and changing in hue.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an image forming apparatus such as a copying machine and a laser beam printer.

[0002]

2. Description of the Related Art Generally, in an image forming apparatus such as an electrophotographic copying machine or a laser beam printer, a surface of a photosensitive drum (image carrier) is charged, and each process such as exposure, development, and transfer is performed. Then, the toner image is transferred onto the recording material, and then the toner image is heated and transferred onto the recording material to complete the image formation.

In the above-mentioned charging, for example, when a corona charger is used, the surface of the photosensitive drum is uniformly charged by keeping the grid voltage applied to the grid constant (for example, -700 V).

[0004]

However, since the characteristics of the photosensitive drum as an image carrier change with a change in temperature, the density of the toner image becomes too high with the change in temperature, and the color of the toner image becomes too high. Or change.

That is, for example, in a low-temperature environment, the sensitivity of the photosensitive drum increases as the temperature of the photosensitive drum increases due to heat from the heat fixing means and heat generated by indoor heating. In such a state, when the grid potential is controlled to be constant as described above, as shown in FIG. 5, the photosensitive drum surface potential V1 when the exposure amount is maximized decreases as the photosensitive drum surface temperature increases. . For this reason, for example, if the control is performed by the measurement value of the potential measurement control performed when the main power is turned on, the contrast potential at the time of development is widened even when controlled by the same grid potential, so that the image becomes gradually darker. In addition, there is a problem that the color is also changed.

Accordingly, the present invention provides a method for increasing the density of a toner image even when the temperature of an image carrier changes,
It is an object of the present invention to provide an image forming apparatus that does not change color.

[0007]

According to another aspect of the present invention, there is provided an image forming apparatus, comprising: an image carrier; a charging unit configured to charge a surface of the image carrier; Exposure means for exposing the carrier surface to form an electrostatic latent image,
Developing means for attaching toner to the electrostatic latent image to form a toner image; transfer means for transferring the toner image from the image carrier to a recording material; and fixing the toner image on the recording material. An image carrier detecting unit for detecting a state of the image carrier, a fixing temperature detecting unit for detecting a temperature of the heat fixing unit, and the developing unit. Environment detecting means for detecting temperature and humidity near the means,
When the temperature detected by the environment detecting unit is equal to or lower than a predetermined temperature, the temperature of the image carrier derived from at least one of the image carrier detecting unit, the fixing temperature detecting unit, and the environment detecting unit is reduced to the temperature. The image forming conditions are controlled accordingly.

According to a second aspect of the present invention, in the image forming apparatus, the image carrier detecting unit is a surface potential detecting unit for detecting a charged state of the image carrier.

The image forming apparatus according to a third aspect is characterized in that the image carrier detecting means is a surface temperature detecting means for detecting a surface temperature of the image carrier.

According to a fourth aspect of the present invention, in the image forming apparatus, the predetermined temperature is in a temperature range where a change in sensitivity of the image carrier is small.

According to a fifth aspect of the present invention, the temperature of the image carrier is detected at a short interval on a low temperature side and at a long interval on a high temperature side.

[0012]

Embodiments of the present invention will be described below with reference to the drawings.

First Embodiment FIG. 3 shows an example of an image forming apparatus according to the present invention. FIG. 1 is a longitudinal sectional view showing a schematic configuration of an electrophotographic four-color full-color digital copying machine.

In FIG. 3, when a copy key (not shown) is pressed, the original 30 placed on a platen glass 31 is exposed and scanned by an exposure lamp 32 in the reader unit, so that the original 30 is scanned. Is condensed on a full-color sensor 34 such as a CCD via a lens 33 to obtain a color-separated image signal. The full-color sensor 34 separates the original 30 into a number of pixels and generates a photoelectric conversion signal corresponding to the density of each pixel.

FIG. 2 shows a block diagram of the image processing. In the figure, the image signal output from the full-color sensor 34 is input to an analog signal processing unit 51 and the gain and offset are adjusted, and then the A / D conversion unit 52 outputs, for example, 8 bits ( 0 to 255 levels: 25
(6 gradations) are converted into RGB digital signals, and the shading correction unit 53 uses a signal obtained by reading a reference white plate (not shown) for each color to eliminate sensitivity variations among the CCD sensor cell groups arranged in a line. To
A well-known shading correction is performed by optimizing a gain corresponding to each CCD sensor cell.

The line delay section 54 corrects a spatial shift contained in the image signal output from the shading correction section 53. This spatial shift is caused by the line sensors of the full-color sensor 34 being arranged at a predetermined distance from each other in the sub-scanning direction. Specifically, based on the B (blue) color component signal, the R (red) and G (green) color component signals are line-delayed in the sub-scanning direction, and the phases of the three color component signals are synchronized.

The input masking section 55 converts the color space of the image signal output from the line delay section 54 into an equation shown in FIG.
The matrix is converted to the NTSC standard color space by the matrix operation shown in (1). In other words, the color space of each color component signal output from the full-color sensor 34 is determined by the spectral characteristics of the filter of each color component, and is converted into the NTSC standard color space.

The LOG conversion section 56 is constituted by a look-up table (LUT) composed of, for example, a ROM or the like.
The RGB luminance signal output from the input masking unit 55 is converted into a CMY density signal. The line delay memory 57
The image signal output from the LOG converter 56 is delayed by a period (line delay) during which the black character determination unit (not shown) generates the control signals UCR, FILTER, SEN, and the like from the output of the input masking unit 55.

The masking / UCR section 58 extracts a black component signal K from the image signal output from the line delay memory 57, further performs a matrix operation for correcting the turbidity of the recording color material in the printer section, and the YMCK signal And outputs, for example, an 8-bit color component image signal in the order of M, C, Y, and K for each reading operation of the reader unit. The matrix count used for the matrix calculation is set by a CPU (not shown).

The gamma correction unit 59 is used to mask and UC the image signal to match the ideal gradation characteristics of the printer unit.
The image signal output from the R unit 58 is subjected to density correction. The output filter (spatial filter processing unit) 60 performs edge enhancement or smoothing processing on the image signal output from the γ correction unit 59 according to a control signal from the CPU.

The LUT 61 is for matching the density of the original image with the density of the output image, and is composed of, for example, a RAM, and its conversion table is set by the CPU. The pulse width modulator (PWM) 62 outputs a pulse signal having a pulse width corresponding to the level of the input image signal, and the pulse signal is input to a laser driver 41 that drives a semiconductor laser (laser light source).

The image forming apparatus has a pattern generator (not shown) on which a gradation pattern is registered so that a signal can be directly passed to the pulse width modulator 62.

The laser light E emitted from the semiconductor laser is swept by the rotary polygon mirror 3a and is exposed by a lens 3b such as an f / θ lens and a fixed mirror 3c for directing the laser light E toward the photosensitive drum 1 as an image carrier. A spot image is formed on the drum 1. Thus, the laser beam E scans the surface of the photosensitive drum 1 in a direction substantially parallel to the rotation axis of the photosensitive drum 1 (main scanning direction), and repeatedly scans the photosensitive drum 1 in the rotation direction of the photosensitive drum 1 (sub-scanning direction). By doing so, an electrostatic latent image is formed.

In the printer section, an electrophotographic drum-type photosensitive member (hereinafter, referred to as "photosensitive drum") is used as an image carrier.
1 is provided. The photosensitive drum 1 has a photosensitive layer of amorphous silicon, selenium, OPC, or the like, and is driven to rotate in a direction indicated by an arrow by driving means (not shown). Around the photosensitive drum 1, a pre-exposure lamp 11 and a primary charger (corona charger) as a charging unit are arranged substantially in order along the rotation direction.
2, laser exposure optical system 3, surface potential sensor (surface potential detecting means) 12, four developing devices containing toners of different colors, that is, yellow developing device 4y and cyan developing device 4
c, magenta developing device 4m, black developing device 4bk,
On-photosensitive-drum light amount detection means 13, transfer means (transfer device)
5, cleaning means 6 and the like are arranged. The primary charger 2 has a wire 2b disposed in the shield 2a and a grid 2c disposed in an opening of the shield 2a facing the surface of the photosensitive drum 1. By the grid potential applied to the grid 2c, the charged photosensitive drum 1 is
Is determined.

In the printer section, when forming an image, the photosensitive drum 1
Is rotated in the direction of the arrow, is uniformly discharged by the pre-exposure lamp 11, and is then uniformly charged by the primary charger 2. Thereafter, an electrostatic latent image corresponding to the above-described image information signal is formed.

Next, a predetermined developing device of the developing means 4 is operated to reversely develop the electrostatic latent image on the photosensitive drum 1 with a two-component developer mainly composed of toner and carrier. Then, a negatively charged visible image (toner image) based on a resin is formed. Developing units 4y, 4c, 4m, 4
bk is selectively brought closer to the photosensitive drum 1 in accordance with each separation color by the operation of the eccentric cams 24y, 24c, 24m and 24bk. Here, the reversal development is a development method in which a toner charged to the same polarity as the electrostatic latent image is adhered to an exposed area on the surface of the photosensitive drum 1 and is visualized.

Further, the toner image on the photosensitive drum 1 is transferred from a recording material cassette 7 to a recording material supplied to a position facing the photosensitive drum 1 via a transport system and a transfer device. In the present embodiment, the transfer device 5 includes a drum-shaped transfer drum 5a as a recording material carrier, a transfer brush charger 5b as a transfer unit, a suction brush charger 5c for electrostatically adsorbing the recording material, and Suction roller 5 facing this
g, an inner charger 5d, an outer charger 5e, and a transfer peeling sensor 5h, and a recording material carrying sheet 5f made of a dielectric material is provided in the peripheral opening area of the transfer drum 5a which is rotatably supported. Are integrally extended in a cylindrical shape. The recording material supporting sheet 5f uses a dielectric sheet such as polycarbonate.

As the transfer drum 5a rotates, the toner image on the photosensitive drum 1 is transferred onto a recording material carried on a recording material carrying sheet 5f by a transfer brush charger 5b. This transfer is sequentially performed for the above four colors, and the toner images of a desired number of colors are transferred onto the recording material so as to overlap. After the transfer of the toner image, the recording material is separated from the transfer drum 5a by the action of the separation claw 8a, the separation push-up roller 8b, and the separation charger 5h, and discharged to the tray 10 via the heat roller fixing device (heat fixing means) 9. Thus, a full-color image is obtained.

On the other hand, the photosensitive drum 1 after the transfer of the toner image
The residual toner not transferred to the recording material and remaining on the surface is removed by a cleaning device 6 having a cleaning blade 6a and a squeeze sheet 6b, and is then subjected to an image forming process.

Further, in order to prevent scattering of powder on the recording material carrying sheet 5f of the transfer drum 5a and adhesion of oil on the recording material, etc., the fur brush 14 and the fur brush via the recording material carrying sheet 5f are used. The cleaning is performed by the action of the backup brush 15 facing 14. Such cleaning is performed before or after image formation, or at any time when a jam (paper jam) occurs.

Next, a method (potential control) for obtaining the grid potential and the developing bias potential from the contrast potential will be described.

FIG. 4 shows the relationship between the grid potential applied to the grid 2c of the primary charger 2 and the photosensitive drum surface potential. FIG. 3 shows the relationship at room temperature. The grid potential is set to −300 V, and the surface potential Vd when scanning is performed with the emission pulse level of the semiconductor laser minimized, and the photosensitive drum surface potential Vl when the emission palace level of the semiconductor laser is maximized is determined by the surface potential sensor 12.
Measured by Similarly, when the grid potential is -500 V,
Measure Vd and Vl when set to -700V. −
By interpolating and extrapolating 300V data and -500V data, -500V data and -700V data, the relationship between the grid potential and the photosensitive drum surface potential can be obtained. Control for obtaining this potential data is called potential measurement control. In this potential measurement control, the main power of the image forming apparatus is turned on, and the thermistor (fixing temperature detecting means) 9
(a) when the temperature of the fixing roller 9b of the heat roller fixing device 9 detected at a is 130 ° C. or less, the feasible temperature (170 ° C.)
And after a predetermined time has elapsed.

The developing bias Vdc is set by providing a difference between Vd and Vback (here, set to 150 V) set so that fog toner does not adhere to the image. The contrast potential Vcont is a difference voltage between the developing bias Vdc and Vl.

In order to obtain the contrast potential required at the time of image formation, the temperature and humidity in the image forming apparatus are detected by an environment sensor (environment detection means) 18 (see the lower right of the photosensitive drum 1 in FIG. 3). The following Table 1 shows the moisture content (g) 0.86 3.03 10.52 15.22 21.56 Vcont 310 290 270 260 250 Vback 150 150 150 150 150 150 Contrast potential 460 440 420 410 By interpolating and extrapolating 400, a necessary contrast potential that satisfies the water content in the device is obtained.

The temperature signal T and the humidity signal H output from the environment sensor 18 to the CPU are calculated and replaced by another numerical value of the amount of water W in the air. The water content in the air is the weight (g) of water contained in 1 kg of air, and is an absolute value. This is obtained according to the following equation.

H = (P / P _S ) × 100 (%) (2) W = {0.622P / (π−P)} × 1000 (3) The procedure is as follows: First, P is obtained. P _S call by reference to the T signal by table 2 in memory. The details of Table 2 are shown in FIGS. 8, 9, and 10. Next, W obtained by substituting P obtained by equation (2) into equation (3). For example, when the temperature T = 30 ° C. and the humidity H = 80%, the water content W = 2
1.6 (g / kg). Next, the optimum contrast potential is obtained by referring to the obtained W with Table 1.

Based on the contrast potential, it can be calculated from the relationship shown in FIG. 4 how many grid potentials are required and how many development bias potentials are required. Here, when the grid potential is −500 V or less, data interpolated from −300 V data and −500 V data, and when −500 V or more, −500 V data and −700.
The data interpolated from the V data is used.

When the above control is completed, a message "Copy (image formation) is possible" is displayed on the operation panel (not shown).
Displayed above, and becomes copy standby.

During the copying operation, a stable density after output is guaranteed by the contrast potential setting calculated by the above method.

In the first embodiment, a thermistor (surface temperature detecting means) 12 for detecting the surface temperature of the photosensitive drum is further provided at the position of the surface potential sensor 12 shown in FIG.
A is provided. However, the thermistor 12A is disposed outside the image forming area at the end of the photosensitive drum 1 in the axial direction of the photosensitive drum 1.

FIG. 1 is a flowchart for explaining the present embodiment.

This embodiment is applied when the temperature detected by the environment sensor 18 is 25 ° C. or less when the main power of the image forming apparatus is turned on.

Photosensitive drum 1 used in this image forming apparatus
Has characteristics as shown in FIG. 14 with respect to the drum surface temperature.

In FIG. 1, when the temperature detected by the environment sensor 18 is １５15 ° C., every minute,
At 5 ° C., the surface temperature of the photosensitive drum is measured every three minutes (S1) (S2), and when the difference from the previously measured surface temperature of the photosensitive drum is a predetermined temperature change (S4, S5, S5).
6), Vl of potential measurement values at six points obtained by potential measurement control
Vl ′ = Vl × Vt / V17 Vl ′: corrected Vl Vl: three points obtained by the potential measurement control Vl Vt: Vl V17 calculated from the temperature change table in FIG. 4: obtained by the potential measurement control Grid potential -700
The correction of V1 at V is performed, and the grid potential and the developing bias potential that satisfy the necessary contrast potential are calculated again.

In the copy operation, after one job (four-color image formation for full-color image formation) is completed,
An image is formed with the newly calculated grid potential and developing bias potential.

As a result, a stable density can always be provided irrespective of the temperature change of the photosensitive drum 1, that is, the sensitivity change.

<Second Embodiment> In the first embodiment,
Although the surface temperature of the photosensitive drum 1 was detected, the main power supply time of the image forming apparatus, the thermistor 9a and the environment sensor 1 were detected.
8 to 7 (when the temperature of the thermistor 9a is the same as that of the environment sensor 18), the surface temperature of the photosensitive drum can be calculated.

In this case, the temperature T in the image forming apparatus calculated from the environment sensor 18 and the time Δ
t, the temperature T in the image forming apparatus calculated from the table in FIG. 7 and the time Δt ′ required for the change ΔT, when Δt ≦ Δt ′, when Td ′ = Td + ΔTd, and when Δt> Δt ′, The correction of Td ′ = Td + ΔT (and rewriting of the table in FIG. 7) may be performed to estimate the surface temperature of the photosensitive drum, and then the flow described in the first embodiment may be performed.

If the temperature of the heat roller fixing device 9 is at a predetermined temperature (here, 170 ° C.), it is determined that the temperature of the photosensitive drum 1 is the same as the temperature detected by the environment sensor 18.

As a result, a stable density can be always provided irrespective of the temperature change of the photosensitive drum 1, that is, the sensitivity change.

When the potential of the photosensitive drum 1 predicted from the photosensitive drum surface temperature in the first and second embodiments does not fall within a predetermined range, an error other than the drum temperature characteristic due to contamination of the optical system or the like. There is also an effect that can be detected.

<Embodiment 3> In the image forming apparatuses of Embodiments 1 and 2 described above, the laser power of the laser exposure optical system 3 is fixed, and the grid potential and the developing bias potential are set under optimum conditions. The present invention is also effective in an image forming apparatus in which the developing bias potential is fixed and the grid potential and the laser power are controlled so as to be optimal.

Hereinafter, control of potential (measurement) in the image forming apparatus will be described.

FIG. 11 shows the relationship between the grid potential and the photosensitive drum surface potential when the development contrast Vdc is kept constant.

The surface potential sensor 12 measures the photosensitive drum surface potential Vd when scanning is performed with the grid potential set at -600 V and the emission pulse level of the semiconductor laser minimized. Similarly, the grid potential is set to -700 V, -800 V
Measure Vd when set to. -600V data and -700V data, -700V data and -800
By interpolating and extrapolating V data, the relationship between the grid potential and the photosensitive drum surface potential Vd can be obtained.

Next, the laser power (light emission amount) was set to 2.5 m.
The surface potential Vl is set to W and the surface potential Vl when the light emission pulse level of the semiconductor laser is maximized is measured by the surface potential sensor 12. Similarly, Vl when the laser power is set to 3.0 mW and 3.5 mW is measured. 2.5mW data and 3.0mW data, 3.0mW data and 3.5mW
By interpolating and extrapolating the above data, the relationship between the laser power and the photosensitive drum surface potential Vl can be obtained.

This potential measurement control is performed after the main power supply of the image forming apparatus is turned on and the temperature of the fixing roller detected by the thermistor 9a reaches a fixing-possible temperature (170.degree. It is performed after the lapse.

When the present invention is applied to this image forming apparatus, Vl '= Vl.times.Vt / Vl3 Vl' is corrected for the Vl measurement values at three points obtained by the potential measurement control by changing the laser power. Vl Vl: three points obtained by the potential measurement control Vl Vt: Vl V13 calculated from the temperature change table of FIG. 4 V3: laser power obtained by the potential measurement control 3.0
Correction of Vl at mW is performed, and the laser power satisfying the required contrast potential is calculated again. The result is shown in FIG.

Also in this case, a stable density could always be provided irrespective of the temperature change of the photosensitive drum 1, that is, the sensitivity change.

[0060]

As described above, according to the present invention,
When the temperature detected by the environment detection unit is equal to or lower than a predetermined temperature, according to the temperature of the image carrier guided from at least one of the image carrier detection unit, the fixing temperature detection unit, and the environment detection unit, By controlling the image forming conditions, even when the temperature of the image carrier changes,
It is possible to effectively prevent the density of the toner image from increasing and the color from changing.

[Brief description of the drawings]

FIG. 1 is a flowchart illustrating Embodiment 1;

FIG. 2 is a block diagram illustrating image processing.

FIG. 3 is a longitudinal sectional view illustrating a schematic configuration of the image forming apparatus according to the first embodiment.

FIG. 4 is a diagram illustrating a relationship between a grid potential and a photosensitive drum surface potential at room temperature.

FIG. 5 is a diagram showing a relationship between a photosensitive drum surface potential and a photosensitive drum surface potential in a low-temperature environment.

FIG. 6 is a diagram showing a relationship between a grid potential and a photosensitive drum surface potential at a low temperature.

FIG. 7 is a diagram illustrating a relationship between a room temperature and a photosensitive drum temperature.

FIG. 8 is a diagram showing a relationship between temperature and water content.

FIG. 9 is a graph showing the relationship between temperature and water content.

FIG. 10 is a graph showing the relationship between temperature and water content.

FIG. 11 is a diagram illustrating a relationship between a grid potential and a photosensitive drum surface potential when a development contrast is fixed.

FIG. 12 is a diagram showing a relationship between laser power and photosensitive drum surface potential.

FIG. 13 is a diagram showing a matrix for converting a color space of an image signal into a standard color space.

FIG. 14 is a diagram showing a relationship between a drum surface temperature and a surface potential.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Image carrier (photosensitive drum) 2 Charging means (primary charger) 3 Laser exposure optical system 4 Developing means 5 Transfer means (transfer device) 6 Cleaning means 7 Recording material cassette 9 Thermal fixing means (Heat roller fixing device) 9a Fixing Temperature detector (thermistor) 12 Image carrier detector (surface potential detector, surface potential sensor) 18 Environment detector (environment sensor)

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yasuhiro Saito 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc.

Claims (5)

[Claims] An image carrier, a charging unit for charging the surface of the image carrier, an exposure unit for exposing the charged surface of the image carrier to form an electrostatic latent image, and the electrostatic latent image. Developing means for forming a toner image by adhering toner onto the recording medium; transferring means for transferring the toner image from the image carrier to a recording material; and heat fixing means for fixing the toner image on the recording material. An image forming apparatus comprising: an image carrier detecting unit for detecting a state of the image carrier; a fixing temperature detecting unit for detecting a temperature of the heat fixing unit; and a temperature and humidity near the developing unit. And an environment detecting means for detecting the temperature of the image carrier, when the temperature detected by the environment detecting means is equal to or lower than a predetermined temperature, the image carrier detecting means, the fixing temperature detecting means, and the environment detecting means. At least One of the in accordance with the temperature of the image carrier derived from the sensing means, for controlling the image forming conditions, the image forming apparatus characterized by. 2. The image forming apparatus according to claim 1, wherein the image carrier detecting unit is a surface potential detecting unit for detecting a charged state of the image carrier. 3. The image forming apparatus according to claim 1, wherein said image carrier detecting means is a surface temperature detecting means for detecting a surface temperature of said image carrier. 4. The image forming apparatus according to claim 1, wherein the predetermined temperature is a temperature range where a change in sensitivity of the image carrier is small. 5. The image forming apparatus according to claim 1, wherein the timing of detecting the temperature of the image carrier is performed at short intervals on the low temperature side and at long intervals on the high temperature side.