JPH02278273A - Developing device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a developing device for a printer or copying machine using electrophotographic technology.

[Conventional technology]

FIG. 4 shows a developing device for developing an electrostatic latent image formed on the surface of a photoreceptor by conventional charging exposure. FIG. 5 is a timing chart of a conventional example. A latent image recorded on the surface of the photoreceptor 101 rotating in the N1 direction by the n-light device 111 as a potential difference with the surroundings contacts the developing roller 102 or approaches the developing roller 102 through a small gap called a developing gap, and is at a certain potential. It is visualized by the adhesion of charged toner to the surface.

The developing device is a device that uniformly charges toner to a certain potential and stably supplies the charged toner between the photoreceptor 101 and the developing roller 102. Developing casing 105
The toner stored in the toner is stirred by the stirring member 104, and is stably conveyed to the supply roller 103 regardless of the amount of toner remaining in the pre-occurrence casing 105. The supply roller 103 is made of an elastic body having a certain resistance value and capacitance, and contacts the developing roller 102 with a certain pressure, causing the toner to adhere to the developing roller 102 and being supplied by the bias supply device 106. The toner is charged with the supplied supply bias Va. The toner attached to the developing roller 102 is removed from the developing roller 10.
As the developing roller 102 rotates, the developing roller 102 passes in front of the developing roller 102, and at this time, excess toner adhering to the developing roller 102 is scraped off by the developing roller 102, and is also charged by friction with the developing roller 102. When the toner, whose adhesion (3) and fIII (fIII) are controlled to a constant value, reaches the point of contact with the photoreceptor 101 or the point of proximity, the developing bias vb is supplied to the developing roller 102 by the bias supply device 106. The toner is conveyed from the developing roller 102 to the photoreceptor 101 by a potential gradient generated between the latent image portion on the photoreceptor 101 and the potential Von. The toner remaining after development in the latent image area and the toner in the non-latent image area are transferred to the developing roller 102 again by the rotation of the developing roller 102.
It is conveyed to the contact point between the supply roller 103 and the supply roller 103, and is scraped off by the supply roller 103. Further, the charge of the charged toner of the supply bias supply device is discharged via the supply roller 103 and the uncharged toner in the developer casing 105.

[Problem to be solved by the invention]

However, the above-mentioned developing method has problems such as changes in print density during continuous printing and occurrence of scumming in non-print areas. The cause of this is that while printing continues, the developing roller 10
This is due to the change in the toner band i1M adhering to the surface of the toner 2. If the amount of toner charge is small, the print density will decrease, and if the amount of charge is large, the print density will be excessive and background smudges will occur in non-print areas.

As described above, the toner is supplied with charge by the bias supply device RA106 via the supply roller 103,
Electricity is generated due to friction with the doctor blade.

Further, the non-printing area is charged due to friction with the photoreceptor 101, and in the printing area, the charged toner is developed on the photoreceptor 101, so that the amount of charge of the toner on the developing roller 102 rapidly decreases. In this way, the irregularities of the charge (2) generated on the developing roller 102 are removed by the supply roller 102.
3 and is smoothed by supplying and discharging electric charge.

The charge supply and discharge characteristics by the supply roller 103 are determined by the resistance value, capacitance, and supply bias V of the supply roller 103.
Potential difference between a and developing bias vb, aa development white - la 1
02 and the co-feeding roller 103, contact resistance, toner capacitance, resistance value, etc. However, among the above-mentioned factors, the resistance value and capacitance of the supply roller 103, the contact width between the development roller 102 and the supply roller 103,
Since the contact resistance Ui, toner capacitance, and resistance value are very easily affected by temperature and humidity, it has been difficult to obtain good print quality in a wide range of usage environments.

Conventionally, the following measures have been taken to solve the above-mentioned problems.

(1) Detecting temperature and humidity and switching supply bias Va or developing bias Vb.

However, when the supply bias Va or the developing bias Vb is switched, the ErJ-shaped hardness itself changes. Since the contact width, contact resistance, toner capacitance, and resistance value gradually change depending on the temperature of 4 degrees Celsius, the supply bias Va or the developing device changes depending on the temperature and humidity of A where the photoreceptor 101 and the developing device are placed. It is necessary to control the bias vb.

(2) Remove the toner scraping device.

A conventional example will be explained using FIG. In the rotating direction of the developing roller 202, the contact point between the photoreceptor 201 and the developing roller 202 and the contact point between the supply roller 203 and the developing roller 202 are arranged so as to be in contact with the developing roller 202 with a certain pressure. A scraping roller 213 having conductivity is disposed, and a developing bias Vb is applied to the scraping roller 213 and a scraping bias V is supplied to the scraping roller 213.
A scraping bias Vk is supplied so that the difference Vb-Vk of k becomes the same as the charging polarity of the toner, and the developing roller 20
Rotate in the opposite direction to 2. Then, the developing roller 20
Some of the charged toner that has landed on the roller 2 is scraped off by the scraping roller 213. The scraped toner is scraped into the developing casing 205 by a scraping blade 214 pressed against the scraping roller 213 with a certain pressure.

The developing roller 202 from which the toner has been scraped off comes into contact with the supply roller 203 and new toner is adhered to it.

The above method requires a scraping roller 213, a scraping and reblade 214, a drive device for driving the scraping roller 213, and a high-voltage power supply for the scraping bias Vk, making the structure of the printing machine complex, and the printing device The disadvantage is that it greatly reduces the freedom of layout.

An object of the present invention is to solve this problem and provide a developing device that ensures stable and high print quality.

[Means to solve the problem]

The present invention comprises a rotatable developing roller 2 that is in contact with the photoreceptor 1 or facing the photoreceptor 1 with a certain gap therebetween, and a conductive elastic member set 114 that is rotatable in contact with the developing roller 2. Supplying a bias potential to the supply roller 3, the stirring member 4, the developing roller 2, the supply roller 3, the developer casing 5 that houses the stirring member 4 and the toner, and the developing roller 2 and the supply roller 3. a bias supply device 6 for rotating the developing roller 2 and the supply roller 3; and a drive device for supplying rotation to the developing roller 2 and the supply roller 3. It is characterized in that the difference Vb-Va between the bias Ib and the supply bias Va supplied to the supply roller 3 has the same polarity as the polarity of the toner.

〔Example〕

FIG. 1 shows an embodiment of the invention. FIG. 2 is a timing chart of the present invention. 8. The leading edge of paper conveyed into the printing apparatus from a paper feed roller (not shown in FIG. 8) is detected by an entry sensor 8. After the leading edge of the printing paper is detected by the entry sensor 8 and a certain period of time Tc has passed, the main charging process starts, and after a certain period of time Te has elapsed, the exposure starts for a certain period of time Td.
After the development process has elapsed, the transfer process is turned on after a certain period of time Tt has elapsed, and the entry sensor 8 detects the leading edge of the paper, and a certain period of time Tg has elapsed, and the printing paper has been sufficiently pressed against the gate roller rough. Thereafter, the gate roller 7 starts rotating and conveys the printing paper to a position where the photoreceptor 1 and the transfer charger 9 face each other. The printing paper, on which the toner image formed on the photoreceptor 1 has been transferred through the main charging process, exposure process, and development process, is further conveyed to the fixing device 1.
3, and eventually the trailing edge of the printing paper is detected by the entry sensor 8. After a certain period of time T1 has elapsed, a developing process occurs, after a certain period of time Te', exposure occurs, and after a certain period of time Td', development occurs. The transfer process is turned off after a certain period of time Tt' has elapsed, and the entry sensor 8 detects the trailing edge of the paper, and a certain period of time Tg' has elapsed, and the trailing edge of the printing paper reaches the gate roller. 7, the rotation of the gate roller rough stops and printing ends.When printing continuously, the main charging and developing processes are kept on, and the entry sensor 8 detects the trailing edge of the paper for a certain period of time. When T1 has elapsed, a paper feed signal is sent to the paper feed device, the next printing paper is conveyed into the main unit, and the next printing process starts. When reaching the transfer position, the boundary where main charging, exposure, development, and transfer on the photoreceptor 1 are switched from OFF to ON is located a certain distance ahead of the leading edge of the printing paper in the direction of travel of the printing paper. In addition, Tc'Te',Td', and Tt are the main charges on the photoreceptor 1 when the trailing edge of the printing paper comes to the transfer position,
The boundary where exposure, development, and transfer are switched from on to off is set so that it is a certain distance behind the trailing edge of the printing paper in the traveling direction of the printing paper. The developing process will be explained in detail below using figures.

FIG. 1 shows the configuration of the developing device of the present invention, FIG. 2 shows the timing chart of the present invention, and FIG. 3 shows the developing bias vb and the photoreceptor 1.
FIG. 3 is a diagram showing the relationship between the difference vb-V□n with respect to the potential Von on the surface and the density of development. The ground of photoconductor 1 is -100
connected to the bolt. When the printing apparatus is in a standby state, the surface of the photoreceptor 1 is in a state of -100 volts, and the bias supply device 6 applies a developing bias Vd=O volts to the developing roller 2, and a supply bias Va to the supply roller 3.
=O volts are supplied. When a print start signal is sent to the printing device, the main motor starts rotating, and the photoreceptor 1, developing roller 2, supply roller 3, and stirring member 4 also start rotating. At this time, the photoreceptor 1 and the developing roller 2
Since the electric field created between Vo and Vd is -100 and -, toner having a single charge characteristic is not developed on the photoreceptor 1.

Print paper is conveyed into the printing apparatus from a paper feed roller (not shown). The leading edge of the printing paper is detected by the entry sensor 8, and when a certain period of time Tc has elapsed, the main charging device 11
1, the surface of the photoreceptor 1 is charged to -900 volts. Further, after a certain period of time Te has elapsed, exposure is performed by the exposure device 11, and an electrostatic latent image is written on the surface of the photoreceptor 1 as an area having a surface potential of −100 volts. Fixed time T
After d has elapsed, the bias supply device 6 supplies the developing roller 2.
The developing bias to is switched to Vb=-500 volts, and the supply bias to the supply roller 3 is switched to Va=-650 volts. At this time, the developing roller 2 and the supplying roller 3
Due to the electric field Vd-Va=150 mini 150 volts, the toner with a single charge characteristic is conveyed to the developing roller 2, and the latent image portion of the photoreceptor 1 and the developing roller 2
Since the electric field created between VO-Vd is 400 volts, the toner with a single charge characteristic is developed, and the electrostatic latent image on the photoreceptor 1 is visualized as a toner image, and the non-latent image on the photoreceptor 1 is The electric field Vo- created between the part and the developing roller 2
Vd=-400o-Vd knee 400 volts charged vf Toner with a negative charge will not be developed.

The toner image developed on the photoreceptor 1 is
The image is transferred onto the printing paper at a position facing the transfer charger 9. On the other hand, the toner on the developing roller 2'' which has completed development is conveyed by the rotation of the developing roller 2 and brought to the contact point between the developing roller 2 and the supply roller 3, and is caused by friction with the doctor blade and the photoreceptor 1. The toner charged more than necessary is electrified, and the toner layer on the developing roller 2, which has become thin due to development, is supplied by the supplying roller 3, restored to a constant thickness, and then passed through the doctor blade 12 again to the photosensitive layer. Head towards the point of contact with body 1.

However, the supply bias Va of the supply roller 3 is -65
Since the voltage is 0 volts, the static electricity cannot be removed to -650 volts or more, and the contact time between the developing roller 2 and the supply roller 3 is short, so the static electricity cannot be completely removed to the initial state. Fluctuations in temperature conditions, etc. Therefore, the low resistance value of the supply roller 3 increases, and as the capacitance decreases, the static elimination effect further decreases.

After the trailing edge of the JPJ paper is detected by the entry sensor 8 and a certain period of time Td'' has elapsed, the supply bias Va to the supply roller 3 is switched to -400 volts. The electric field between Vd-Va=-100 volts has the same polarity as the 4\1 polarity of the toner, and the -charged toner on the developing roller 2'' is conveyed onto the supply roller 3. The toner adhering to the supply roller 3 is neutralized while adhering to the supply roller 3, and part of it returns to the developing casing 5, and part of it returns to the point of contact with the developing roller 2 again.

Compared to the conventional example, the potential difference between the toner and the supply roller 3 is large, and the contact time between the toner and the supply roller 3 can be significantly lengthened, making it possible to completely eliminate static electricity from the toner. To the developing roller 2;
Fresh toner can be supplied with respect to potential, and background smearing due to overcharging of toner can be eliminated.

The printing paper passes through the gate roller 7, the next printing paper is conveyed into the main body, the entry sensor 8 detects the leading edge of the printing paper, and when a certain period of time Tc has elapsed, the bias supply device 6 moves the supply roller The supply bias Va of No. 3 is switched to -850 volts, and the developing operation is performed again as described above.

In the above embodiment, the supply bias Va is synchronized with the printing paper.
Although the voltage is set to -400 volts, the same effect can be obtained by switching to the ground level, and a high voltage power supply for changing the supply bias is not required, which further simplifies the configuration.

Further, in the above embodiment, the supply bias Va was set to 1,400 volts in synchronization with the printing paper, but the supply bias Va was fixed and the developing bias Vb was set so that Vb - Va has the same polarity as the charged polarity of the toner. A similar effect can be obtained by switching.

As described above, the supply bias Va of the bias supply device 6 is set so that the polarity of the electric field Vd-Va between the developing roller 2 and the supply roller 3 becomes the same as the charging polarity of the toner.
, or because the developing bias Va is switched during the time corresponding to the time from when the trailing edge of the printing paper passes the transfer position to the time when the leading edge of the next printing paper reaches the transfer position, the supply bias Va is changed. The decrease in print density caused by switching does not appear on the printing paper.

〔Effect of the invention〕

The bias supply bag r116 synchronizes with the printing paper and at non-printing timing, the developing bias vb supplied to the developing device and the supply bias Va supplied to the supply roller 3.
By configuring the printer so that the difference Vb-Va has the same polarity as the toner polarity, it is possible to always ensure stable print quality without background smearing or a decrease in print density, regardless of environmental conditions such as a temperature of 4 degrees Celsius. .

[Brief explanation of drawings]

FIG. 1 is a diagram of an embodiment of the present invention. 1... Photoreceptor 2... Actual elephant roller 3... Supply roller 4... Stirring member 5...Developer casing 6...Bias supply device 7... Registration roller 8... Entry sensor 9...Transfer charger 10... Main charger 11... Exposure device 12...Doctor Blade 13...Fuser FIG. 2 is a diagram of a timing chart of the present invention. 101...Photoreceptor 102...Developing roller 103... Supply roller 104... Stirring member 105...Developer casing 106...bias supply device 107... Registration roller 108... Entry sensor 109...Transfer charger 110... Main charger 111... Exposure device 112...Doctor Blade 113...Fuser FIG. 5 is a timing chart of a conventional example. 201...Photoreceptor 202...Developing roller 203... Supply roller 204... Stirring member 205...Developer casing 206...Bias supply device 212...Doctor Blade 213... scraping roller 214... scraping blade that's all Applicant: Seiko Epson Corporation Agent: Patent attorney Kisanbe Suzuki and 1 other person Figure 3

Claims (1)

[Claims] A developing device for developing an electrostatic latent image formed on a photoreceptor by charging exposure includes a rotatable developing roller that is in contact with the photoreceptor or faces the photoreceptor with a certain gap therebetween; and the developing roller. a supply roller composed of a conductive elastic member that can rotate in contact with the toner, a stirring member, the developing roller, the supply roller, a developing casing that houses the stirring member and the toner, and the developing roller and the supply roller. The bias supply device includes a bias supply device that supplies a certain bias potential, and a drive device that supplies rotation to the developing roller and the supply roller. A developing device characterized in that a difference Vb-Va between a developing bias Vb and a supply bias Va supplied to the supply roller has the same polarity as that of toner.