JPH11138903A - Image forming system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming system in which an image having good gradation and color reproducibility can be obtained stably using contact DC developing method or noncontact AC+DC developing method. SOLUTION: An image forming system comprises a developer of contact DC developing method. A controller 12 in the image forming system comprises an LD current control circuit 3a, i.e., means for controlling the quantity of irradiating light of a light irradiating means 3, and a laser power control means 3b for determining irradiation of light of the light irradiating means 3 at the time of image formation. A toner image for detecting density is formed on a photosensitive drum prior to image formation and when the density of image is detected by a density sensor, the laser power control means 3b compares the detected density with a preset reference level and determines the quantity of irradiating light of the light irradiating means 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus using an electrophotographic method, and more particularly to an image forming apparatus characterized by a method of determining a developing voltage during image formation.

[0002]

2. Description of the Related Art FIG. 15 shows a conventional image forming apparatus using an electrophotographic method. In FIG. 15, reference numeral 100 denotes a photosensitive drum serving as an image carrier. After a surface of the photosensitive drum 100 is uniformly charged to a predetermined potential by a charging roller 101, light corresponding to image information is emitted by a light irradiation unit 108 such as a laser. By performing exposure by irradiation, an electrostatic latent image corresponding to image information is formed on the surface of the photosensitive drum 100. The electrostatic latent image is developed by the developing device 102 using the toner T, and is visualized as a toner image.

[0003] A toner image formed on the photosensitive drum 100 is electrostatically transferred onto a transfer material P supplied to the photosensitive drum 100 by a transfer roller 106 provided on the downstream side of the developing device 102 in the rotation direction of the photosensitive drum 100. Transcribed. The transfer material P on which the toner image has been transferred is sent from the photosensitive drum 100 to a fixing device (not shown), where it is heated and pressurized.
It is fixed as a permanent image. Photosensitive drum 1 after transfer
At 00, the transfer residual toner remaining on the surface is removed by the cleaning device 107 installed on the downstream side of the transfer roller 106.

The charging roller 101 and the developing roller 10
A predetermined voltage is applied to the transfer roller 4 and the transfer roller 106 from a power supply (not shown).

The developing device 102 includes a developing roller 104 which is a toner carrier (generally a developer carrier), a toner supply roller 105 for supplying toner T to the surface of the developing roller 104, and a toner on the surface of the developing roller 104. A developing blade 103 for regulating the amount is provided.

In recent years, the developing device 102 has a photosensitive drum 1
A contact DC developing method in which a developing roller 104 is elastically brought into contact with the surface of the developing roller 00 and a DC voltage is applied to the developing roller 104 has been adopted in many cases.

The advantage of the contact DC developing method is that the structure of the apparatus is simple, and no AC voltage is applied to the developing roller 104. That is, adhesion of toner (so-called fog) to a non-image area is small, and development efficiency is high.

Here, the developing efficiency is defined as the developing blade 10
3, the amount of toner (toner coat amount) initially present on the surface of the developing roller 104 after the regulation, and the amount of toner transferred from the surface of the developing roller 104 to the image area on the surface of the photosensitive drum 100 by development. This is the ratio with the amount of toner attached.

The development efficiency of the contact DC development method is extremely high.
Conventional non-contact AC + DC superposition type developing method (non-contact A
While the development efficiency of the (C + DC development method) is about 50 to 60%, almost 100% of the development efficiency is obtained.

[0010] The high developing efficiency means that the residual toner that has not contributed to the development of the image area is removed from the developing roller 1.
Since the number of chances of being present on the surface of the toner 04 is reduced, accumulation of stress in the toner remaining after development, prevention of deterioration, and prevention of charge-up are achieved, leading to an advantage that image deterioration hardly occurs. Further, the contact DC development method can use a non-magnetic one-component toner, and can easily cope with colorization.

[0011]

However, the conventional image forming apparatus using the contact DC developing method has the following problems.

FIG. 16 shows the relationship (VD characteristic) between the developing electric field, which is the contrast between the developing voltage and the potential of the electrostatic latent image on the surface of the photosensitive drum 100, and the image density.

As shown in FIG. 16, in the contact DC developing method, development can be performed with a lower contrast than in the non-contact AC + DC developing method, but the rise of the image density on the low developing electric field side is sharper. That is, compared to the non-contact AC + DC developing method, the electrostatic latent image is less likely to be developed in a highlight region where the latent image potential is shallower, and as a result, the image tends to be less visible.

This is a characteristic not found in the non-contact AC + DC developing method. The reason is that the contact DC development method can be developed if there is a development contrast of a predetermined amount or more,
If the contrast is lower than this, development becomes impossible, and as a result, a sharp rise in image density occurs on the low developing electric field side.

That is, in the contact DC developing method, the latent image potential is sufficiently deep so that a predetermined amount of contrast can be easily obtained, for example, an image based on a binary electrostatic latent image such as a character image. For the formation, a very good image quality can be provided, but the electrostatic latent image is shallow, and a multi-valued static image having a gradation such as a graphic or a photograph having an electrostatic latent image for which a predetermined amount of contrast cannot be obtained. This indicates that the image forming apparatus is not suitable for forming an image in a highlight area of an electrostatic latent image or forming an image using an electrostatic latent image such as a minute spot having an insufficient light amount, even if it is binary. For these reasons, the contact DC developing method has the following problems.

For example, even if a developing voltage corresponding to the predetermined value is set in order to always maintain the image density at a predetermined value, if the charge amount of the toner on the developing roller 104 fluctuates due to environmental fluctuation or toner deterioration, The VD characteristic changes in the direction indicated by the arrow X in FIG. 16, and the highlight region of the image becomes unreproducible or the image density becomes too high, resulting in a very unstable image. As a result, it is possible to stably and favorably perform image formation using a multi-valued electrostatic latent image having gradations such as the above-mentioned graphics and photographs, and binary image formation such as minute spots having a shallow latent image potential. It will be difficult to do.

In the non-contact AC + DC developing method, selective development is performed for a shallow latent image potential as already known, and therefore, it tends to be more advantageous than the contact DC developing method. Non-AC +
Also in the DC development method, if the variation in the charge amount of the toner on the developing roller 104 due to environmental fluctuations is large, the variation in the charge amount of the toner actually contributing to development is less than that in the contact DC development method. However, the problem of difficulty in image formation stability due to a multi-valued or binary electrostatic latent image as described above occurs.

When the contact DC developing method is applied to the formation of a color image, there is a problem that the color reproducibility in a high density region becomes unstable. The reason is as follows.

As described above, when the charge amount of the toner fluctuates due to environmental fluctuations or the like, the VD characteristic changes in the direction of arrow X as shown in FIG. Then, even if the developing voltage is set so that a predetermined value (maximum value) of image density is sufficiently obtained,
The toner amount (toner weight per unit area of the photosensitive drum surface, M / S) obtained by developing the latent image on the surface of the photosensitive drum 100 is as follows.
As shown by the one-dot chain line in FIG. 17, saturation does not reach at the equilibrium point of the maximum value of the image density, and tends to increase as the developing electric field increases, and the toner amount (M / M
S) fluctuates even if the fluctuation of the image density is small.

As a result, when a color image is output, the degree of color mixing of the toners of each color in the fixing device changes, and the color reproducibility becomes unstable. Although this problem is not so noticeable as in a color image, it appears as a difference in glossiness of an image (that is, a difference in glossiness in a black image area) even in black and white image output.

As described above, in order to perform stable image output other than character output using the conventional contact DC developing method in particular,
There are still issues that need to be resolved.

In a color image forming apparatus or a black-and-white image forming apparatus for outputting images such as graphics and photographs, gradation control is performed prior to image formation in order to adjust gradation characteristics to predetermined characteristics. However, conventionally, the toner used in this gradation control does not contribute to the image output,
Was discarded uselessly.

Accordingly, it is an object of the present invention to provide an image which uses a contact DC developing method or a non-contact AC + DC developing method to develop an image, and which can stably obtain an image having good gradation and color reproducibility. It is to provide a forming device.

Another object of the present invention is to provide an image forming apparatus capable of eliminating wasteful consumption of toner used for gradation control.

[0025]

The above object is achieved by an image forming apparatus according to the present invention. In summary, the present invention provides:
An image carrier, a charging unit for charging the surface of the image carrier to a predetermined potential, and irradiating the surface of the image carrier charged to the predetermined potential with light in accordance with image information, thereby forming a surface on the image carrier. Light irradiating means for forming an electrostatic latent image, and developing the electrostatic latent image with a developer or a developer containing a toner carried on a developer carrier in contact with or in proximity to the image carrier,
In an image forming apparatus having a developing unit for forming a toner image on an image carrier, a light irradiation amount control unit for controlling a light irradiation amount of the light irradiation unit, and a density detecting unit for detecting a density formed on the image carrier. Density detecting means for detecting the image density of the toner image, and light irradiation amount determining means for determining the light irradiation amount of the light irradiation means at the time of image formation, the light irradiation amount determining means,
The density of the toner image for density detection by the density detection means;
The image forming apparatus is characterized in that the amount of light irradiation of the light irradiation unit at the time of image formation is determined by comparing with a preset reference density.

According to the present invention, the light irradiation amount control means controls the determined light irradiation amount so as to gradually increase from a predetermined value. The light irradiation unit is a laser exposure unit, and the light irradiation amount control unit is a laser drive current control unit that controls a laser emission amount by controlling a laser drive current in the laser exposure unit. The light irradiation amount determination unit is a laser drive current determination unit that determines a laser drive current during image formation. The laser drive current control means digitally controls the laser emission amount by digitally controlling the laser drive current value using a plurality of laser drive current values set in advance. Further, the laser drive current determining means compares the image density of the toner image for density detection corresponding to the development contrast formed by the laser light controlled by the laser drive current control means with the reference density. The amount of light irradiation during the image formation can be selected and determined from a plurality of laser drive current values set in advance.

The density detecting toner image on the image carrier is transferred to another member, and the density detecting means detects the image density of the density detecting toner image on the image carrier. This can be performed on the toner image for density detection transferred to the separate member instead of the toner image. After detecting the image density of the toner image for density detection by the density detecting means, the toner of the toner image for density detection can be collected by the developer carrier of the developing means. The formation of the density detecting toner image is performed until the position of the image carrier at the start of application of the developing voltage to the developer carrier of the developing unit reaches the light irradiation position in the next image forming process. further,
While the light irradiation amount is being determined by the light irradiation amount determining means,
When the toner image for density detection on the image carrier is present at the transfer position to another member, the transfer means for transferring the toner image for density detection on the image carrier to another member has the same polarity as the charge polarity of the toner. Polar transfer voltage can be applied. Preferably, the shape factor SF-1 of the toner is 100 to 140,
SF-2 is 100 to 120.

DETAILED DESCRIPTION OF THE INVENTION

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an image forming apparatus according to the present invention will be described in more detail with reference to the drawings.

Embodiment 1 FIG. 1 is a schematic structural view showing an embodiment of the image forming apparatus of the present invention.

In FIG. 1, reference numeral 1 denotes a photosensitive drum as an image carrier which rotates in the direction of arrow A in the figure.
Is uniformly charged to a predetermined potential by a charging roller 2 rotating in the direction of arrow D, and then light irradiation (exposure) is performed by light irradiation means 3 such as a laser to write image information, and the surface of the photosensitive drum 1 is written. An electrostatic latent image corresponding to the image information is formed.

In this embodiment, the light irradiating means 3 is used as shown in FIG.
The laser optical system shown in FIG. Light irradiation means 3
Are a semiconductor laser 20, a photodiode 21, a collimator lens 22, a polygon mirror 23, a scanner motor 24, a cylinder lens 25, a toroidal lens 26 (the fθ lens is constituted by the cylinder lens 25 and the toroidal lens 26), a reflection mirror 27, and a BD mirror. 28, an optical fiber 29, and a scanner drive circuit 30.

The scanner circuit 30 includes a horizontal synchronizing circuit and a scanner driving circuit. The horizontal synchronization circuit is BD
Based on the optical signal input from the mirror 28 via the optical fiber 29, the horizontal synchronization is performed when the surface of the photosensitive drum 1 is subjected to laser exposure corresponding to the image signal. The scanner drive circuit drives a scanner motor 24 that drives the polygon mirror 23 at a predetermined rotation speed.

Laser driving is a well-known method, APC.
The output value is controlled to a predetermined value by (Auto Power Control) control. The APC control will be briefly described. As shown in FIG. 3, the semiconductor laser 20 is controlled at a constant current by an LD current drive circuit 31 arranged in the controller 12.

First, the semiconductor laser (L
D) Photodiode (PD) with 20 monitor beams
At 21, the output voltage Vp of the photodiode 21 is converted from an analog signal to a digital signal by an A / D converter 32 arranged in the controller 12, and this digital signal is output to a reference voltage generation circuit 33. The comparison is made by the CPU 14 with the reference voltage Vb. And CPU1
4 is an LD current drive circuit 31 so that Vp becomes Vb.
Is controlled.

The light irradiation means 3 is controlled by an LD current control circuit 3a and a laser power control means 3b (FIG. 4). The LD current control circuit 3a performs the above-described LD current driving circuit 3 during the light irradiation amount determination process which is one of the features of the present invention.
1 is a light irradiation amount control means for controlling the constant current value Icc driven by 1 in multiple stages, and a laser power control means 3b
Similarly, during the light irradiation amount determination process, the light irradiation amount for determining the light amount irradiated by the light irradiation unit 3 during image formation based on the output from the density sensor 8 and the control current of the LD current control circuit 3a. It is a determining means. Details of the control of the light irradiation means 3 will be described later.

In FIG. 1, reference numeral 4 denotes a developing device for developing an electrostatic latent image on the surface of the photosensitive drum 1. Developing device 4
Are in contact with the surface of the photosensitive drum 1 at a predetermined contact pressure and rotate in the direction of arrow B in the figure, and have elasticity (the peripheral speed is set to 120% of the peripheral speed of the photosensitive drum 1). A toner supply roller 7 (which has a peripheral speed of 60% with respect to the peripheral speed of the photosensitive drum 1) rotating in the direction of arrow C in the figure to separate and supply toner to the surface of the developing roller 5; And a developing blade 6 for regulating the amount of toner supplied to the surface of the developing blade to a predetermined value. A direct current voltage (DC voltage) is applied to the developing roller 5 by a power supply 11 in order to form a developing electric field with the photosensitive drum 1.

The toner image formed on the surface of the photosensitive drum 1 by development is transferred to a transfer material supplied to the photosensitive drum 1 by a transfer roller 9 rotating in a direction indicated by an arrow E in FIG. It is electrostatically transferred to P. The transfer residual toner remaining on the surface of the photosensitive drum 1 due to the transfer is removed by the cleaning device 10. In FIG. 1, reference numeral 8 denotes a density detection sensor for detecting the image density of a density detection toner image (density detection image) formed on the surface of the photosensitive drum 1 prior to image formation.

In this embodiment, the process speed of the image forming apparatus is set to 100 mm / sec.
An OPC photosensitive drum having a negative charging polarity of 0 mm was used. As for the latent image condition, the image exposure is performed by the light irradiating means 3, and the charged potential of the photosensitive drum 1 is set to -7 in the non-image area.
00V. The light irradiation means 3 has a maximum output of the semiconductor laser 20 of 5 mW, a wavelength of 770 to 800 nm, and a spot diameter on the surface of the photosensitive drum 1 of about 60 μm in the main scanning direction.
It was adjusted to be about 80 μm in the sub-scanning direction. As the charging roller 2, a roller made of silicone rubber which has been subjected to a conductive treatment so as to have a volume resistivity of 10 ⁶ Ωcm was used. In order to secure the surface potential of the photosensitive drum 1 to the above-mentioned −700 V, the charging roller 2 is applied with a DC voltage of −700 V and 1800 V
A voltage obtained by superimposing an AC voltage of pp, 400 Hz is applied.

The toner T contained in the developing device 4 was a non-magnetic one-component toner having a negatively charged polarity. Since the toner is a non-magnetic toner, the supply roller 7 for supplying the toner to the developing roller 5 is a rubber roller using insulating foamed urethane rubber, and has a diameter of 16 mm in this example. The toner is carried on the developing roller 5 by a mirror force based on the charge amount of the toner T, and the charge amount is mainly determined by the toner T in a contact area between the supply roller 7 and the developing roller 5.
Owes to the friction.

In this embodiment, the developing roller 5 is an elastic roller made of conductive silicone rubber having a volume resistivity of about 10 ⁵ Ωcm, and has a diameter of 16 mm. The surface roughness Rz of the developing roller 5 was adjusted to about 7 to 8 μm. The developing blade 6 is a metal blade made of stainless steel, the edge of the tip is bent in an L shape, and the corner is brought into edge contact with the developing roller 5.

According to this embodiment, the developing roller 5, the developing blade 6, and the toner supply roller 7 are electrically connected so that they have the same potential. Further, a DC voltage of −350 V is applied to the developing roller 5 at a predetermined timing as a developing voltage by the power supply 11 during the light irradiation amount determination process of the present invention. This will be described later.

On the other hand, the transfer roller 9 is a semiconductive EPD.
Made of M foamed rubber, carbon black and metal double oxide were mixed in appropriate amounts to adjust the resistance. The transfer roller 9 also has a power supply 11 based on the control of the controller 12.
As a result, a predetermined voltage is applied as a transfer voltage at a predetermined timing. Since the transfer voltage has no direct relation to the present invention, detailed description thereof will be omitted.

As shown in FIG. 1, the cleaning device 10 has a urethane blade 10a, which is brought into counter contact with the surface of the photosensitive drum 1 so as to remove transfer residual toner on the surface of the photosensitive drum 1. .

Next, the controller 12 will be described with reference to FIG.

The controller 12 includes a CPU 14 for controlling the operation of the entire image forming apparatus, ROMs 17 to 19 for storing other operation sequences, and temporary work for executing image information and operation sequences from outside. It has a RAM 15 used as an area. Further, the controller 12 includes an LD current control circuit 3a, a laser power control means 3b, an LD current drive circuit 31, a reference voltage generation circuit 3
3, an A / D converter 32 and an A / D converter 34, each of which is connected to the CPU 14. Also, the CPU 14
It is connected to the light irradiation means 3 via the LD current control circuit 3a and the LD current drive circuit 31, and is also connected to the power supply 11 to control these operations. Descriptions of transfer and fixing devices not particularly related to the present invention are omitted.

The operation sequence in the controller 12 will be described.

The ROM 17 stores a sequence (1) for controlling the driving operation of the entire image forming apparatus.
When the power is turned on to the image forming apparatus, the CPU 14 immediately
The contents are read into the ROM 17 and executed. The ROM 18 stores a laser power control sequence for the light irradiation amount determination step. The sequence relating to the image processing of the input image data is stored in the ROM 19.

The above laser power control sequence is read based on the control of the sequence (1), and the LD current control circuit 3a, the laser power control means 3b, the LD current drive circuit 31, the reference voltage generation circuit 33, the density sensor 8, A
The operation control of the / D converter 32, the A / D converter 34, the scanner drive circuit 30 disposed in the light irradiation means 3, and the like is performed as shown in FIG.

The control according to the present invention will be described with reference to FIG.

When the power is turned on to the image forming apparatus, the CP
U14 reads the contents of the ROM 17 and the like, starts up the controller 12, and starts up the image forming apparatus based on the sequence (1) stored in the ROM 17. CP
U14 first drives a main motor (not shown),
The rotation drive of the photosensitive drum 1, the charging roller 2, the developing roller 5, the toner supply roller 7, the transfer roller 9, and the like is started. Next, the above-described voltage is applied to the charging roller 2 to obtain a charging potential of −700 V on the surface of the photosensitive drum 1. Further, the CPU 14 executes a laser power control sequence for determining the light irradiation amount stored in the ROM 18, and performs a light irradiation amount determining process as described below.

The CPU 14 controls the LD current control circuit 3a based on the laser power control sequence, controls the LD current drive circuit 31, and as shown in FIG. ) Icc, I1, I
2, I3, I4,... At predetermined time intervals.

The process speed of the image forming apparatus is 100
mm / sec, and the diameter of the photosensitive drum 1 is 30 mm. Therefore, the above-mentioned predetermined time is set to 0.1 second, and the surface of the photosensitive drum 1 is moved by 10 m per each driving constant current value in the rotation direction.
An exposure with a width of m is performed. Since there are five types of driving constant current values,
Exposure is performed with a total width of 50 mm to form five stages of latent image potentials having a width of 50 mm on the surface of the photosensitive drum 1. Since the circumferential length of the photosensitive drum 1 is 94.2 mm, an electrostatic latent image is formed for about a half circumference. The predetermined time is 0.1
It is not limited to seconds, but can be set arbitrarily. That is, it does not matter if the number is increased or decreased or the type of the drive current value is increased or decreased.

In the first embodiment, the driving constant current value is set to I1 = 5.
0 mA, I2 = 60 mA, I3 = 70 mA, I4 = 80
mA, I5 = 90 mA. As a result, according to the semiconductor laser 20 used in this embodiment, as shown in FIG. 6, the laser output is controlled to 1 mW at I1, 2 mW at I2, 3 mW at I3, 4 mW at I4, and 5 mW at I5. can do.

It is clear from FIG. 6 that the laser drive current is set to be equal to or higher than the threshold value of the laser emission, that is, the laser drive control during the light irradiation amount determination process is performed at the laser emission threshold or higher. This is performed with a drive current value that is equal to or less than the drive current value corresponding to the maximum laser output.

As described above, by controlling the laser drive current, the irradiation amount (the third quadrant shown in FIG. 7) on the surface of the photosensitive drum 1 can be controlled as shown in FIG. In this embodiment, the collimator efficiency of the light irradiation means 3 is set to 3
5%, and the optical efficiency of the scanning system was 90%. Numerical values such as the collimator efficiency are not limited to these, and may be set according to the sensitivity of the photosensitive drum 1.

According to the above driving constant current value, FIG.
The laser irradiation amount on the surface of the photosensitive drum 1 is I1 = 50 mA
0.8 μJ / cm ² when I 2 = 60 mA, approximately 1.6 μJ / cm ² when I 2 = 60 mA, and approximately 2.4 μJ when I 3 = 70 mA.
J / cm ² , about 3.2 μJ / cm when I 4 = 80 mA
^2, is about 4μJ / cm ² when I5 = 90 mA.

Further, as shown in FIG. 8, from the relationship between the surface laser irradiation amount (μJ / cm ² ) of the photosensitive drum 1 and the latent image potential (non-laser irradiation potential: −700 V) in this embodiment, the semiconductor laser 20 The latent image potential of the photosensitive drum 1 with respect to each drive constant current value of I is -640 V at I1, -300V at I2, -170V at I3, and -1 at I4.
00V and 55 at I5, and the developing contrast is I50 since the developing DC voltage is -350V.
1, 340V, I2 + 50V, I3 + 180V, I4 + 250V, I5 +3
00V.

As described above, the CPU 14 increases the amount of laser light in a stepwise manner based on the laser power control sequence and raises the surface potential of the photosensitive drum 1 from -700 V to-
Change to 50V. Further, the CPU 14 applies a developing voltage of −350 V to the developing roller 5 from the developing roller 5 to the photosensitive drum 1 by applying a latent image potential that changes from −700 V to −50 V obtained by controlling the light irradiation unit 3. A developing contrast that gradually changes from −340 V to +300 V is formed, and the electrostatic latent image on the surface of the photosensitive drum 1 is gradually developed.

That is, the surface potential of the photosensitive drum 1 is changed by changing the amount of laser light by the light irradiating means 3, and as a result, the development contrast is changed, and the surface of the photosensitive drum 1 is developed accordingly. Go. In this method of controlling the laser light amount, the laser light amount may be increased digitally by a predetermined width (1 mW in this embodiment) as described above, or may be increased continuously in an analog manner.

Next, the density sensor 8 detects the image density of the density detection toner image developed by the increasing development contrast. The CPU 14 converts the analog image density D detected by the density sensor 8 into a digital signal by the A / D converter 34, and further controls the laser power control means 3b to change the detected value to a preset set value. b. Then, based on the result, C
The PU 14 computes and calculates the minimum LD drive current value that obtains the result of D = b, and determines the LD drive current during image formation.

Here, the method of determining the LD drive current value is as follows.
The LD drive current value that satisfies> b may be determined by performing arithmetic processing from the relationship between the LD drive current value and the detected density D. When the LD drive current value is changed in an analog manner, D>
The LD drive current value satisfying b may be determined as the LD drive current value during image formation.

When the LD drive current value is determined in this way, the CPU 14 turns off the light irradiating means 3, the developing voltage, the charging roller 2, and the main motor sequentially, and ends the laser power control sequence. If the sequence (1) has been completely completed, the CPU 14 sets the image formation to a standby state.

The set value b may be set arbitrarily. However, according to the laser power control sequence according to the present invention, when the set value b is set to the maximum image density, the development of the surface of the photosensitive drum 1 is performed. The toner amount is set to 70 to 70% of the maximum developable amount (the amount of development when the amount of developed toner on the surface of the photosensitive drum 1 is in an equilibrium state even when the developing voltage is increased).
It can be set to 80%. However, this value fluctuates depending on the amount of charge of the toner on the surface of the developing roller 5, and therefore, due to environmental fluctuation.

Next, the effects of the present invention will be described with reference to specific examples.

FIG. 9 shows the relationship between the LD drive current value I and the detection output of the density sensor 8 in this embodiment. Low temperature and low humidity L / L (15 ° C, 10% Rh) environment, normal temperature and normal humidity N / N
(25 ° C., 60% Rh) environment, high temperature and high humidity H / H (30
(° C., 80% Rh) environment. The horizontal axis in FIG. 9 also shows the development contrast (V) corresponding to the LD drive current value I. The detection output is shown in the detection output (vertical axis) in FIG. 9 in the same manner as in the conventional example, using the image density corresponding to the detection output instead.

In the contact DC developing method, as shown in FIG. 9, in an environment of H / H and N / N, the development contrast becomes a negative side, that is, a side on which the development of the negative polarity toner is suppressed. Also, there is an electric field region where the toner develops. This is because, since the toner T on the surface of the developing roller 5 is charged, if the electric field for suppressing the development is small, the toner T only contacts the surface of the photosensitive drum 1 and develops.

On the other hand, in the L / L environment, the charge amount of the toner T rises more than in other environments due to low humidity, and the mirroring power of the toner T on the developing roller 5 increases, so that the toner T Adhesion increases compared to other environments. As a result, development efficiency is reduced, and developability in a low development contrast region is reduced.

That is, in the contact DC development method, the toner T depends on the environment in which the image forming apparatus is installed.
Depending on the charge amount, there is a possibility that the characteristics shown in FIG. 9 are shifted and fluctuated in the horizontal axis direction as described in the conventional example.

In the conventional example, if the developing voltage is set in a state where the image density is sufficiently stable and in an equilibrium state, the fluctuation of the maximum image density value itself can be suppressed to an acceptable level. As described above, the image density in the highlight area greatly varies. At the time of forming a large number of dots, since there is superposition of optical spots corresponding to each dot, the light intensity in the superposed area of the optical spots is increased, and as a result, the electrostatic latent image is deepened,
It is possible to obtain a sufficient development contrast.
The latent image potential per dot is higher than the latent image potential when a large number of dots are formed, since the overlapping between the spots is eliminated, the absolute value thereof becomes higher, and a sufficient development contrast cannot be obtained.

That is, in the L / L environment, development becomes impossible in the highlight region due to the decrease in the development electric field, and depending on the set value of the development voltage, as shown in FIG. Under the environment of H / H and N / N, the image density of the highlight area increases. That is, in the conventional image forming apparatus, the image density in the highlight area greatly changes due to the environmental change. This tendency becomes more conspicuous as the resolution of the laser exposure area on the surface of the photosensitive drum, that is, the DPI, is increased. In an optical system such as a semiconductor laser generally used at present, when the resolution is set to 600 dpi or more, the amount of light per dot is increased. Is particularly remarkable because the diameter decreases with the miniaturization of the spot diameter. That is, in the conventional image forming apparatus, when the contact DC developing method is used, the image quality is insufficient with respect to the gradation.

On the other hand, in the present invention, it is possible to suppress the above-described change in the characteristic shown in FIG. 9 due to the change in the charge amount of the toner T. In this embodiment, the LD drive current value in the L / L environment is set to 90 mA (I5), and the H / H and N / N
In the environment of (1), the LD drive current value is 70 mA (I3).
, It is possible to obtain an optimum development contrast corresponding to each environment, obtain a stable maximum image density, and stably change the developability of a highlight area due to a change in the charge amount of the toner T. I do. That is, the gradation is stabilized.

Further, another advantage of the present invention is that
It is also possible to stabilize the toner amount on the surface of the photosensitive drum 1 (developing amount indicated on the Y axis on the right side of FIG. 10: M / S on the drum) to a predetermined value. In the conventional example, as described in the section of the problem to be solved by the present invention, FIG.
As can be understood from the figure, even if the maximum image density is stable,
There is a possibility that the development amount of the toner on the photosensitive drum fluctuates. It is considered that the developing voltage should be set in a region where the developing efficiency is 100%. However, since the density is sufficient, wasteful toner consumption is generated. In addition, there is a problem that the gradation is insufficient in the highlight region.

On the other hand, in the present invention, as is apparent from the above description, the maximum image density is stabilized, and at the same time, as described in the conventional example, the characteristic of the image density with respect to the development contrast varies with the development contrast. However, it is possible to always ensure a substantially constant development amount for the electrostatic latent image on the photosensitive drum surface.

In this embodiment, as shown in FIG.
/ L, development amount of about 0.5 mg / cm ² in N / N environment,
With H / H, a development amount of about 0.53 mg / cm ² can be obtained. That is, it is possible to prevent the problem caused by the fluctuation in the development amount even when the image density is constant as shown in the conventional example.

According to the present invention, the variation in the charge amount of the toner is
Although image characteristics can be stabilized, this means that an image forming apparatus that is resistant to environmental changes can be provided.

As described above, according to the present invention, the conventional problems can be solved, the reproducibility of halftones can be stabilized, and a stable output of a photographic image, a graphic image, and a color image can be achieved. It has become possible to provide a possible image forming apparatus.

Although the voltage applied to the transfer roller 9 during the execution of the laser power control sequence is not particularly described above, the transfer roller 9 has the same polarity as the charged polarity of the toner in order to prevent toner contamination. It is desirable to apply a negative polarity voltage.

Second Embodiment In the first embodiment, the image density detection is performed on the surface of the photosensitive drum 1. In the second embodiment, however, the density detection toner image developed on the photosensitive drum is executed by executing the laser power control sequence. After transferring to an intermediate transfer body, transfer belt or transfer material, etc.
Image density detection was performed on the toner image for density detection on another member such as the intermediate transfer member, the transfer belt or the transfer material.

FIG. 11 shows a case where the present invention is carried out on an intermediate transfer member. 11, the same parts as those in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted.

FIG. 11 shows that the toner image developed on the surface of the photosensitive drum 1 is once primarily transferred onto the surface of the intermediate transfer member 40 rotating in the direction of arrow F in the figure, and then in the direction of arrow G in the figure. Secondary transfer is performed on the surface of the transfer material P by the rotating transfer roller 41. This is a configuration generally used in a color image forming apparatus provided with developing devices 42 for four colors of magenta, cyan, yellow, and black. Intermediate transfer member 40,
A primary transfer voltage and a secondary transfer voltage are applied to the transfer rollers 41 at predetermined timing by the power supply 11, respectively.

In the present embodiment, the laser power control sequence is executed based on the output from the density sensor 8 disposed near the intermediate transfer member 40. The execution contents of the laser power control sequence in the present embodiment are the same as those in the first embodiment, and therefore the description is omitted. However, the density sensor 8 is located near the surface of the intermediate transfer member 40 from the primary transfer region to the secondary transfer region. It is arranged between the areas.

In this manner, in an image forming apparatus requiring high color reproducibility, such as a color image forming apparatus, by detecting the image density of the transferred toner image, Can be controlled to a substantially predetermined value, and fluctuations in the amount of toner on the surface of the transfer material due to fluctuation factors such as transfer efficiency that occur at the time of transfer can be removed, and the object of the present invention can be more reliably achieved.

In the present embodiment, the image density of the toner image on the surface of the intermediate transfer body 40 is detected. However, the image density of the toner image on the surface of the transfer material P after the secondary transfer may be detected. However, according to the examination by the present applicants, the toner image density on the surface of the transfer material P varies with the distance between the density sensor 8 and the transfer material P due to vibrations during the transfer of the transfer material P or the like. Therefore, the detection accuracy of the density sensor 8 tends to decrease depending on the location of the density sensor 8. That is, when the present invention is carried out after the transfer from the photosensitive drum 1, it is preferable to carry out the transfer on the surface of the intermediate transfer member or the transfer belt.

Third Embodiment In the first embodiment, the toner T used in the execution of the laser power control sequence is removed by the cleaning device 10.
In the third embodiment, instead of being removed by the cleaning device 10, the toner is removed by the developing device 4 and collected by the developing device 4. Therefore, the image forming apparatus according to the present embodiment is a so-called cleaner-less image forming apparatus in which the cleaning device 10 is removed. This makes it possible to prevent wasteful consumption of toner as in the conventional example.

In this embodiment, a spherical toner is used as the toner T because it is cleanerless. This spherical toner can be prepared by using a known polymerization method or the like.

The degree of sphericity of the spherical toner used in the present embodiment is as follows.
Those in which 2 is 100 to 120 are preferable. More preferably, SF-1 is 100 to 130, SF-2 is 10
0 to 115.

In the present invention, the shape factor SF−
1. SF-2 is FE-SEM (S-80) manufactured by Hitachi, Ltd.
0), 100 toner particle images are sampled at random, and the image information is introduced into an image analyzer (Luzex3) manufactured by Nicole via an interface and analyzed, and is calculated by the following equation. Defined as a value.

SF-1 = ｛(MXLNG) ² / ARE
A｝ × π / 4 × 100 SF-2 = {(PERI) ² / AREA｝ × π / 4 × 1
00 where AREA: toner projection area, MXLNG: absolute maximum length, PERI: circumference

The shape factor SF-1 of the toner indicates the degree of spherical shape. If the shape factor SF-1 is larger than 140, the shape gradually changes from spherical to irregular. SF-2 indicates the degree of unevenness. If it is larger than 120, the unevenness on the toner surface becomes remarkable. This shape factor SF
As long as -1, SF-2 is within the above range, transfer efficiency, that is, (amount of toner on transfer material after transfer) / (amount of toner on photosensitive drum before transfer) × 100 is ensured to be 95% or more. Thus, the cleaning device 10 required in the first embodiment can be removed.

In this embodiment, the spherical toner is used as shown in FIG.
The image forming apparatus of FIG. 12 is obtained by removing the cleaning device 10 from the image forming apparatus.
The toner used during the execution of the laser power control sequence was collected in the developing device. This sequence differs from the sequence of the first embodiment in the following points.

(1) After the execution of the laser power control sequence, the developing voltage V1 is turned on, and then a transfer reverse voltage having the same polarity as the toner charging polarity is applied to the transfer roller 9 (step b). In the case of the present embodiment, the transfer reverse voltage is a negative voltage.
The purpose of the application of the transfer reverse voltage is to prevent the toner T from adhering to the transfer roller 9. The application timing of the transfer reverse voltage is not limited to the above, and may be at least applied when the toner T is conveyed on the surface of the photosensitive drum 1 to the transfer roller 9.

(2) In this embodiment, since the developing toner is collected by the developing roller 5 after the light irradiation amount is determined, the light irradiation amount determining process is performed in a manner that the contact area of the photosensitive drum 1 with the developing roller 5 is reduced. The rotation is preferably performed in the direction of arrow A in FIG. This condition is sufficiently satisfied by using the control time of the LD drive current value used in the first embodiment.

If the above conditions are not satisfied, the laser power control sequence, that is, the control of the LD drive currents I1 to I5 shown in the first embodiment is performed over one rotation of the photosensitive drum 1, and the laser power is controlled. During the first half of the LD drive current control during the power control sequence (I1 to I
About 3) of the developing toner reaches the exposure position without being cleaned. For this reason, in the latter half of the LD drive current control (I4, I5) in the laser power control sequence,
The laser exposure must be cut off, the desired latent image potential cannot be obtained, and the development contrast may be unstable (as a phenomenon, the development contrast may decrease).
This is because the detection density in the latter half of the laser power control sequence may decrease.

Therefore, in the present embodiment employing the cleanerless system, in the process of the laser power control sequence shown in FIG. 12, steps a to c are performed in such a manner that the contact area of the photosensitive drum 1 with the developing roller 5 corresponds to FIG. The rotation is performed in the direction of the middle arrow A until the position of the light irradiation means 3 is reached.
By the time the contact area reaches the position of the light irradiation means 3, the exposure of the light irradiation means 3 is turned off, and the laser power control sequence is terminated. As a result, it is possible to prevent a decrease in control accuracy of the laser power control sequence.

(3) There is an ON step of the developing toner collection voltage. Specifically, the developing toner collection voltage was a positive developing voltage V2 having a polarity opposite to the charging polarity of the toner. In this process, since the toner image on the surface of the photosensitive drum 1 is negatively charged, a developing electric field is formed on the side of the surface of the photosensitive drum 1 that collects the toner on the developing roller 5, and the toner on the surface of the photosensitive drum 1 Is collected by the developing roller 5.

As described above, by using the above-described spherical toner and the sequence shown in FIG. 12, the second object of the present invention is achieved, and wasteful consumption of toner used for gradation control can be eliminated.

Embodiment 4 Embodiments 1 to 3 described above have dealt with the cases where the present invention is applied to an image forming apparatus using a contact DC developing method.
Although the present invention has a great effect in the contact DC developing method, the present invention is also effective when applied to the non-contact AC + DC developing method (non-contact AC + DC superimposing type developing method). On the other hand, it has the effect of further stabilizing the image density.

FIG. 13 shows the fourth embodiment. In this embodiment, since the non-contact AC + DC developing method is used, a developing sleeve 50 made of aluminum is used in place of the developing roller 5, and a regulating means (not shown) makes the distance between the photosensitive drum 1 and the developing sleeve 50 from about 150 μm to 500 μm.
The distance is set to a predetermined distance within the range of about 300 μm in this example.

In accordance with this, the toner regulating member also
Developing blade 5 having plate-shaped urethane rubber 51 at its tip
Changed to 2. Further, the power supply 11 applies a 160 VPP, 2000 Hz AC voltage to the developing sleeve 50 to a -350 V D voltage.
A voltage on which the C voltage is superimposed is applied.

Even in the non-contact A + DC developing method, the developing contrast is determined by the difference between the electrostatic latent image potential of the image area on the surface of the photosensitive drum 1 and the developing voltage DC component. Should be executed for In general, the VD characteristics in the non-contact AC + DC developing method are L / L (low temperature and low humidity environment), N /
It fluctuates in each environment of N (normal temperature and normal humidity environment) and H / H (high temperature and high humidity environment).

Conventionally, the DC component of the development contrast is fixed to a predetermined value, such as VN in FIG. 14, so that the development characteristics greatly fluctuate due to environmental fluctuations, as is apparent from FIG. In the present invention, problems such as image collapse due to an increase in high-density area density in an H / H environment and low density in an L / L environment occurred.
Since the laser power control sequence as shown in 3 is performed on the development contrast DC component, an optimum LD drive current value can be obtained in each environment.

In the example shown in FIG. 14, H / H and N / N
70mA (equivalent to 180V development contrast) in environment, L
The LD drive current value is determined such that / mA is 90 mA (equivalent to a development contrast of 300 V), and a predetermined image density can be obtained.

As described above, the present invention is effective not only for the contact DC developing method but also for the non-contact AC + DC developing method. Further, it goes without saying that the present invention is also effective for a two-component developing method using a two-component developer in which a toner and a carrier are mixed as a developer.

In the first to third embodiments, the light irradiating means 3 is a laser optical system. However, the present invention is not limited to this. For example, an LED optical system, a fluorescent lamp using a liquid crystal shutter, etc. Can be applied to the optical system. In the case of the LED optical system, the amount of light emitted from the LED may be controlled in the same manner as in the above embodiment. In the case of the optical system of the liquid crystal shutter, the operation of the liquid crystal shutter is controlled so that the amount of light emitted to the photosensitive drum surface May be controlled.

[0105]

As described above, according to the present invention,
By using a contact DC developing method or a non-contact AC + DC developing method for developing an image, an image forming apparatus capable of stably obtaining an image with good gradation and color reproducibility can be provided. Further, wasteful consumption of the toner used in the gradation control can be eliminated.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing one embodiment of an image forming apparatus of the present invention.

FIG. 2 is a perspective view showing a laser optical system of the image forming apparatus of FIG.

FIG. 3 is a block diagram showing a mechanism of APC control in laser driving of the laser optical system.

FIG. 4 is a block diagram illustrating a controller in the image forming apparatus of FIG. 1;

FIG. 5 is a flowchart illustrating a control method such as laser power control in the image forming apparatus of FIG. 1;

FIG. 6 is an explanatory diagram showing a relationship between a drive current value of a semiconductor laser and a laser output.

FIG. 7 is a diagram illustrating a relationship among the sensitivity of the photosensitive drum, the laser chip surface light amount, the light amount after the collimator, and the photosensitive drum surface light amount.

FIG. 8 is an explanatory diagram showing a relationship between a laser irradiation amount on the photosensitive drum and a latent image potential on the photosensitive drum surface at that time.

FIG. 9 is a diagram showing a relationship between an LD drive current value I and a detection output of a density sensor in the control of FIG. 6;

FIG. 10 is a graph obtained by adding a change in a development amount to the graph of FIG. 9;

FIG. 11 is a schematic configuration diagram showing another embodiment of the image forming apparatus of the present invention.

FIG. 12 is a flowchart illustrating laser power control and toner collection control in still another embodiment of the image forming apparatus of the present invention.

FIG. 13 is a schematic configuration diagram showing still another embodiment of the image forming apparatus of the present invention.

FIG. 14 illustrates an example of a configuration of the image forming apparatus illustrated in FIG.
FIG. 6 is a diagram illustrating a relationship between a D drive current value I and a detection output of a density sensor.

FIG. 15 is a schematic configuration diagram illustrating a conventional image forming apparatus.

16 is a diagram illustrating a relationship between a developing electric field and an image density in the image forming apparatus of FIG.

FIG. 17 is a diagram illustrating a relationship between a developing electric field, an image density, and a development amount.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photosensitive drum 2 Charging roller 3 Light irradiation means 3a LD drive current circuit 3b Laser power control circuit 4 Developing device 8 Density detection sensor 12 Controller 14 CPU 20 Semiconductor laser 30 Scanner drive circuit 31 LD current drive circuit

Claims (10)

[Claims] An image bearing member, a charging means for charging the surface of the image bearing member to a predetermined potential, and irradiating the surface of the image bearing member charged to the predetermined potential with light in accordance with image information to form an image. Developing the electrostatic latent image with a light irradiating unit for forming an electrostatic latent image on the surface of the carrier, and a developer or a developer containing toner carried on a developer carrier in contact with or in proximity to the image carrier An image forming apparatus having a developing unit for forming a toner image on the image carrier; a light irradiation amount controlling unit for controlling a light irradiation amount of the light irradiating unit; and a density formed on the image carrier. Density detecting means for detecting the image density of the toner image for detection, and light irradiating amount determining means for determining the light irradiating amount of the light irradiating means at the time of image formation; The detection density of the toner image for density detection by the detection means is set in advance. An image forming apparatus, wherein a light irradiation amount of a light irradiation unit at the time of the image formation is determined by comparing with a predetermined reference density. 2. The image forming apparatus according to claim 1, wherein the light irradiation amount control unit controls the determined light irradiation amount so as to gradually increase from a predetermined value. 3. The laser irradiation means, wherein the light irradiation means is a laser exposure means, and the light irradiation amount control means controls a laser driving current in the laser exposure means, thereby controlling a laser light emission amount. 3. The image forming apparatus according to claim 1, wherein said light irradiation amount determining means is a laser driving current determining means for determining a laser driving current at the time of image formation. 4. The laser drive current control means digitally controls the laser emission amount by digitally controlling the laser drive current value using a plurality of laser drive current values set in advance. 3 is an image forming apparatus. 5. The laser drive current determining means compares the image density of a toner image for density detection corresponding to a development contrast formed by a laser beam controlled by the laser drive current control means with the reference density. By doing
4. The image forming apparatus according to claim 3, wherein the light irradiation amount at the time of image formation is selected and determined from a plurality of laser drive current values set in advance. 6. A density detecting toner image on the image carrier is transferred to another member, and the density detecting means detects the image density of the density detecting toner image on the image carrier. The image forming apparatus according to claim 1, wherein the image formation is performed on the toner image for density detection transferred to the separate member instead of the toner image. 7. The method according to claim 1, wherein after detecting the image density of the density detecting toner image by the density detecting means, the toner of the density detecting toner image is collected by a developer carrier of the developing means. The image forming apparatus according to the item. 8. When the application of the developing voltage to the developer carrier of the developing means is started, the position of the image carrier reaches the light irradiation position in the next image forming process. The image forming apparatus according to claim 7, wherein the processing is performed up to the time. 9. When the light irradiation amount is being determined by the light irradiation amount determining means and the toner image for density detection on the image carrier is present at a transfer position to another member, the light irradiation amount is determined. 2. A transfer voltage having the same polarity as the charged polarity of the toner is applied to a transfer unit that transfers the toner image for density detection to another member.
The image forming apparatus according to any one of Items 1 to 5, 10. A toner having a shape factor SF-1 of 10
0-140, SF-2 is 100-120.
10. The image forming apparatus according to any one of Items 9 to 9, wherein