JPH0373865B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an image forming method and apparatus, and more particularly to a method for suppressing development during non-development by changing the developing bias between developing and non-developing.

Conventionally, in electrophotographic devices, it is necessary to take a period after image formation to clean the residual developer on the latent image carrier or to return the exposure optical system to its normal position. If so, an unnecessary developed image is formed and developer is wasted. Conventionally, therefore, an additional exposing means and means for removing the charge on the latent image carrier have been required to prevent image formation during this period.

The purpose of the present invention is to solve such problems,
The purpose is to provide an image forming method that suppresses the consumption of developer without providing any special means other than the image forming period.

The gist of the present invention is to provide an image forming method in which an image is obtained by developing an electrostatic latent image by flying toner from a developer carrier onto a rotating latent image carrier. During development, an alternating bias voltage is applied to the developer carrier to cause the toner to fly and adhere to the electrostatic latent image area, and development is performed.
When rotating the latent image carrier during non-development, when the electrostatic latent image does not pass through the developing section, an alternating bias voltage different from the above is applied, and an alternating bias voltage that does not cause toner to adhere to the latent image carrier is applied. An image forming method characterized by applying a voltage to a developer carrier. More specifically, it is possible to improve the image quality by changing the DC component of an alternating bias voltage (DC superimposed on AC) between developing and non-developing, or by distorting the AC component into an asymmetrical waveform. It performs formation.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Details of embodiments according to the present invention will be described below with reference to the drawings.

FIG. 1 shows the principle of a developing method in an embodiment according to the present invention. Reference numeral 1 denotes a latent image holder such as an electrostatic image, and 2 its back electrode, which moves in the direction of the arrow. Reference numeral 3 denotes a developer carrier which carries a so-called 1-formed developer 4 consisting only of toner particles without a carrier. The thickness of the toner layer in the development area A is thinner than the gap between the developer carrier 3 and the latent image holder 1, so that a gap is formed between the surface of the toner layer and the latent image holder. In this example,
The carrier 3 consists of an electrically conductive material, for example metal or electrically conductive rubber. 5 is a power source for applying an external alternating voltage between both members 2 and 3.

FIG. 2 shows the magnitude relationship between the electrostatic image potential and the applied external alternating voltage. In the figure, V _D is the potential of the image area (the area to which toner should ultimately be attached) of the latent image carrier 1, and V _L is the potential of the non-image area (the area to which toner should not be ultimately attached). It is. Although a rectangular wave is shown as an example of the external alternating voltage in the figure, the present invention is not limited to this, and alternating voltages having other waveforms such as a sine curve or a sawtooth wave can be used. The horizontal axis in FIG. 2 is time, and the external alternating voltage acts in phase t ₁ to promote the transfer of developer from the developer carrier 3 to the latent image carrier 1 through the gap. do. Arrows a and b in the figure represent the size of the transition to the non-image area V _L and the image area V _D , respectively. On the other hand, in phase _t2 , the developer acts to draw back the developer from the latent image holding member 1 to the developer carrying member 3 through the gap (reverse transfer). Arrows c and d in the figure represent the magnitude of the reverse transition to the non-image area V _L and the image area V _D, respectively.

In FIG. 1, a latent image carrier 1 and a developer carrier 3
The development on the latent image carrier 1 is completed by repeating phases t ₁ and t ₂ while moving from the closest area A to area B where the distance between the two gradually increases. At this time, in area A, the developer is transferred from the developer carrier to the latent image holder in both the image area and the non-image area, and in the process of passing through area B, the developer transferred to the non-image area. The agent is completely drawn back to the developer carrier. Images obtained through such a process are extremely excellent in fine line reproducibility and gradation reproducibility. The details of this developing method are described in detail in Japanese Patent Laid-Open Nos. 55-18656 to 18656-9 filed by the present applicant.

FIGS. 3a, b, and c show a method for providing stable image quality by changing the external alternating voltage in response to fluctuations in the latent image potential due to some factor.

Figure 3a shows the image area potential V _D and the non-image area potential V _L
(Hereafter, these will be referred to as dark potential and bright potential, respectively.)
This is the case when the values tend to shift by approximately the same amount.
To solve this problem, it is sufficient to shift the alternating voltage by the same amount as the variation thereof, that is, to shift the DC level of the alternating voltage. An example of this is shown in the figure.

Figure b shows a case where only the bright potential V _L tends to move. In this case, the phase of the external alternating voltage
The voltage value at t ₂ may be changed in accordance with the fluctuation of the bright potential.

Figure c shows a case where only the dark potential V _D tends to fluctuate, and the voltage value at phase t ₁ of the external alternating voltage may be changed in accordance with the fluctuation of the dark potential. These alternating external voltages may be changed by dial adjustment by the operator. In this case,
An added benefit is that it is possible to obtain an image density that matches the original density and the user's preference.

In this way, when the latent image on the latent image holding member passes through the development area, the operator of the image forming apparatus manually or automatically adjusts the development bias, as shown in FIG. This causes toner transfer and countertransference to occur.

On the other hand, there is a transfer process in which the developed image is transferred onto the transfer material after the above-mentioned development is completed, a cleaning process in which toner remaining on the latent image holding body is cleaned after the transfer, and a process after scanning the original for forming the latent image. During the process of returning the optical system to its normal position, the latent image usually does not pass through the development area. Therefore, during such a non-image period, it is preferable to suppress the transfer of toner from the developer carrier to the latent image carrier, and to promote the process of reverse transfer. For this reason, the _phase
By applying an alternating bias with a large voltage applied at t ₂ , the above-mentioned suppression of toner transfer and promotion of reverse transfer can be achieved.

FIG. 4 shows a diagram of an embodiment of the invention. FIGS. 4a and 4d show model circuit examples for alternating voltages, and FIGS. 4b, c, e, and f show voltage waveforms thereof. FIG. 4a shows an example of a circuit in which a DC voltage is superimposed on a sine wave AC voltage, and FIG. 4B shows an output waveform diagram thereof.
The input consists of two AC power supplies 5 and 6, one of which is made variable in voltage, thereby making the DC component of the alternating voltage variable. During development, the voltage is alternately varied as shown in FIG. 3a in accordance with the potential on the latent image holder, so that good development is always carried out.

On the other hand, during the non-image period (during non-development), the alternating voltage is greatly changed from the state shown in FIG. 4B to the state shown in FIG. That is, as explained in Fig. 2,
Make the transition electric fields a and b small (or none at all),
On the other hand, fogging is prevented by increasing the reverse transition electric fields c and d. Figure 4d shows the (-) of the sinusoidal AC voltage.
Only the side is reduced by a diode 8 and resistors 9 and 10, and by sliding the resistor 9 at the output terminal, the (-) side voltage is made variable during development. This output waveform is as shown in FIG. As shown in FIG. 4(f), the (-) side voltage is suppressed to a small value, toner transfer is minimal or not at all, and development is suppressed by the electric field acting only in the reverse transfer direction. This switching from e to f in FIG. 4 is performed by the switching means 11 in response to a signal from the sequence controller 7 which controls the image forming sequence.

Next, a fifth embodiment of an image forming apparatus incorporating such a variable alternating voltage application means and its adjustment means will be described.
Shown in the figure. 12 is an electrostatic latent image carrier having a selenium (Se) layer; 13 is its back electrode;
2 and 13 form a drum shape. 14 is a non-magnetic stainless steel sleeve having a magnet roll 15 inside. Electrostatic latent image holder 12 and sleeve 14
This minimum spacing is maintained at 300μ by well-known gap maintaining means. 16 is a one-component magnetic developer in the developing container 17, which is made by kneading and pulverizing 70 wt% styrene maleic acid resin, 25 wt% ferrite, 3 wt% carbon black, and 2 wt% negative charge control agent (Cr ^- ). Additionally, 0.2wt% of colloidal silica is externally added to improve fluidity. 18 is an iron blade, and sleeve 1
Main pole 15a (N
The thickness of the magnetic developer 16 applied to the sleeve 14 is controlled by magnetic force (see Japanese Patent Laid-Open No. 55-93177 for further details). The gap between the blade 18 and sleeve 14 is 250μ
The thickness of the developer layer applied by the blade 18 onto the sleeve 14 is about 80 microns. Reference numeral 19 denotes a variable alternating voltage power supply, which is applied between the back electrode 13 and the conductor portion of the sleeve 14. Further, in order to prevent uneven application of the developer, the blade 18 and the sleeve 14 are set at the same potential.

The average value of electrostatic image potential is dark potential +700V,
Bright potential +50V, external alternating voltage, frequency 800Hz,
+50V to peak-to-peak 1200V sine wave
A DC voltage variable up to +350V is superimposed on the control circuit 20, which is connected to the power source 19 and includes the circuit example shown in FIG. It is now possible to select the image style.

The photosensitive drum 12 is positively charged by the charging means 21, and then the optical image of the document 23 is irradiated onto the photosensitive drum by the exposure optical system 22. At this time, the original 23 moves in the direction of arrow R in the figure. Further, development is performed by the illustrated developing device 24, and the obtained developed image is transferred onto a transfer device 26 by a transfer means 25, and the remaining developer is cleaned by a cleaning means 26. After completing such a copying process, the original 23 moves in the direction of arrow L in the figure and returns to its normal position. At this time, the photosensitive drum is continuously rotating in the direction of the arrow in the figure, and there is no hidden material on the drum. There are no images, making it a non-image period. During this non-image period (when development is required), the frequency is supplied from the power supply 19 as an external alternating voltage.
A DC voltage of +750 V is superimposed on a sine wave of 800 Hz and peak-to-peak Vpp of 1200 V to form a waveform as shown in FIG. 4C to suppress development.

Furthermore, when an organic photoconductor OPC is used as the photoreceptor 12, after it is primarily charged to be monopolar and subjected to image exposure, it is applied with a development bias of -100V to a sine wave with a frequency of 800Hz and a peak-to-peak Vpp of 1300V.
When developing was carried out by superimposing a DC voltage of 100 V, and during non-development, the DC voltage was set to -500 V, no toner adhered to the drum and no toner scattering occurred during the non-image period.

In the sequence controller 7 of FIGS. 4a and 4d and the control circuit 20 of FIG. 5, the bias during development and during non-development are switched in the sequence shown in FIG. Furthermore, in Fig. 6, the start point of development is delayed from the end point of the previous rotation because the leading edge of the electrostatic image, which is first formed by the start of image exposure, reaches the developing section from the exposure section. The reason why the end of development is delayed from the start of post-rotation is that it takes a certain amount of time for the rear end of the electrostatic image to reach the development section from the exposure section. This is for this reason. Therefore, it goes without saying that the time to start applying the developing bias to the sleeve is delayed from the end of the previous rotation, and the time to switch between the developing bias and the non-developing bias is also delayed from the start of the subsequent rotation.

Furthermore, Japanese Patent Application Laid-open No. 14266/1983 discloses a method of switching to a DC bias or electrically floating the bias during non-development. However, in the above-mentioned method, the toner tends to solidify in a nearly stationary state during non-development, or the fine powder toner tends to cover the sleeve surface.

In contrast, in the present invention, alternating voltages are applied to the toner even during non-development, so the toner is always stirred and excited, and when the bias is switched during development, transfer and reverse transfer occur immediately. It is possible to cause

As detailed above, in the present invention, the voltage is alternately switched between developing and non-developing times, and the electric field for reverse transition that returns the toner from the image carrier to the developer carrier is increased during non-developing. There is no fogging on the image carrier during development and no toner scattering. Furthermore, the mechanism is simple and development can be suppressed without the need for a separate high-pressure switch or exposure means.

In addition, by manually or automatically varying the bias during development, it is possible to extremely easily adjust the image density of (a) a developing method that is free from background fog and has extremely high gradation; You can further increase the fruit of your life.

(b) Depending on the usage conditions, environmental conditions, the density of the original or original light image, etc., it is very easy to obtain the desired image density desired by the operator.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram explaining the principle of the developing method according to the present invention, FIG. 2 is an explanatory diagram showing the phase and waveform of the alternating bias voltage applied to the latent image potential, and FIGS. FIG. 2 is an explanatory diagram showing three modes of adjusting the alternating bias voltage according to the variation of the latent image potential, FIGS. 4 a and d are connection diagrams of an example of a circuit that performs the adjustment, and FIG. 4 b , c, e, f are output waveform diagrams according to the circuit example, and FIG. 5 is a sectional view of an embodiment of a developing device to which the developing method according to the present invention is applied.
FIG. 6 is a sequence diagram for implementing the present invention. In the figure, 1, 12... image carrier, 3, 14...
Developer carrier, 4, 16... Toner, 7... Sequence controller, 19... Alternating voltage power supply, 20...
Represents a control circuit.

Claims (1)

[Claims] 1. In an image forming method in which an image is obtained by developing an electrostatic latent image by flying toner from a developer carrier onto a rotating latent image carrier, the electrostatic latent image passes through a developing section. Sometimes, development is performed by applying an alternating bias voltage to the developer carrier to make the toner fly and adhere to the electrostatic latent image image area, and the latent image carrier is rotated during non-development when the electrostatic latent image does not pass through the developing area. An image forming method comprising: applying an alternating bias voltage different from the above, which does not cause toner to adhere to the latent image carrier, to the developer carrier. 2. The image form according to claim 1, wherein an AC bias voltage on which a DC voltage is superimposed is applied to the developer carrier, and the value of this DC voltage is changed between during development and during non-development. Method.