JPS5880677A - Method for setting control level of developer density controller - Google Patents

Abstract

PURPOSE:To exactly set a level of a developer density control, by rotating a photosensitive body and a toner by charging to the same polarity when setting a control level, rotating a developing sleeve in the same way, and forming an electric field between the photosensitive body and the sleeve. CONSTITUTION:On a developer scraping plate 4 contacting with the downstream side of a developing position of a developing sleeve 3 provided so as to be opposed to a photosensitive body 2, a funnel-like hopper 5 is provided, and a nonmagnetic bobbin 7 which is connected to its lower opening and has a coil 6 at the outside is provided. An LC oscillating circuit is formed by inductance L of the coil 6 and a capacitor C, and a variation of L of a variation of specific volume of iron powder of a developer for dropping the bobbin 7 is set to a variation of oscillation frequency, and density is detected. When setting a control level of a developer density level, bias voltage is applied between the developing sleeve 3 and the photosensitive body 2, only the developing sleeve is rotated, and the control level is set to a prescribed quantity.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a developer concentration control device for an electrophotographic copying apparatus that supplies a developer consisting of carrier and toner to an electrostatic latent image formed on a photoreceptor through a developing sleeve. This invention relates to a control level setting method.

When a developer consisting of carrier and toner is used to develop an electrostatic latent image formed on a photoconductor, as the number of copies increases, the toner in the developer is consumed and the developer concentration (developer Since the weight ratio of toner in the developer decreases, it is necessary to constantly replenish toner to maintain a predetermined developer concentration. There is a method of replenishing toner by estimating the amount of toner consumed for an average original and replenishing it in a fixed amount according to the number of copies, but actual originals vary in image area and proportion of line and solid areas. However, with this method, it is difficult to always maintain the developer concentration within a predetermined range. Therefore, a developer concentration sensor is installed in the developing device to detect the developer concentration in the developing device, and a developer concentration control device is provided that automatically replenishes the insufficient amount of toner by comparing it with a set level. things are being done.

An example of a developer concentration control device will be explained with reference to FIG.
A funnel-shaped hopper 5 is provided on the developer scraping plate 4 provided in contact with the downstream side of the development position of the development sleeve 8 provided in the development tank 1 facing the photoreceptor drum 2. A non-magnetic bobbin 7 is connected to the coil 6 and has a coil 6 wound thereon. An Lc oscillation circuit is formed by the inductance L of the coil 6 and the capacitor C, and the inductance L of the coil changes depending on the concentration of the developer flowing down inside the bobbin 7, that is, the specific volume-volume of the iron powder in the developer. The change in oscillation frequency is converted into a change in oscillation frequency, and the concentration of the developer is detected. This sensor is superior in that it is simple in configuration and is less susceptible to environmental changes. A comparison circuit 10 compares the output of the frequency detector 8 connected to the coil 6 and the output of the reference circuit 9, and inputs the signal to the drive circuit 11 to drive the toner replenishing roller 18 provided at the bottom of the toner hopper 12. By controlling the amount of rotation, the concentration of the developer in the developing tank 1 is controlled.

The control level of the developer concentration control device described above is set by putting the developer into the developer device and rotating the sleeve. However, if the time from the start of rotation of the sleeve to the setting is short, It is known that when copying is performed, the developer concentration decreases below the set value, resulting in a lower image density.

The embodiment will be explained with reference to FIG. The horizontal axis of the figure shows the number of continuous copies, the vertical axis shows the developer concentration, and the time from the start of sleeve rotation to the setting of the control level is taken as a parameter.
Curves are shown for 1 minute, 2 minutes, 3 minutes, and 5 minutes.

According to this, when the developer concentration is initially set to 1-5% by weight, as the number of copies is increased, the time required to set it becomes 1%.
In the case of 21 minutes, it decreases to about 0.8%, and in the case of 21 minutes, it decreases to about 1%.
．． It can be seen that the time decreases to 2%, and there is almost no decrease when the time is 8 minutes or more.

The reason for this is not clear, but it is thought to be because the physical properties of the developer change from the initial physical properties during continuous copying due to changes in the magnetic susceptibility of the carrier and the zero particle size of the toner due to the magnetic force from the magnet in the sleeve. Therefore, it is necessary to set the control level of the developer concentration control device at least about 8 minutes after the rotation of the sleeve starts. However, if the sleeve is rotated for 2 to 8 minutes while the photoreceptor drum is stopped, the magnetic brush comes into contact with one position on the photoreceptor circumferential surface, so that the photoreceptor drum 2 is rotated as shown in FIG. As a result of experiments, it has been confirmed that in the magnetic brush contact portion 14 on the circumferential surface of the magnetic brush, areas 14b with large toner stains occur on both sides of the magnetic brush contact area 14, with a part 14a without toner stains in between. When copying was performed using this photoreceptor, the first copy had toner stains 14b.
Black band-like no(turns) appeared and the image quality deteriorated.

By the way, development using XXXX coat carrier (XXXX' is DuPont's product name for fluorinated polymers such as polytetrafluoroethylene, copolymers thereof, and modified resins) as a developer carrier. When normal copying is performed using a printing agent, the xxxx' resin on the carrier surface is scraped and adheres to the surface of the photoconductor (called clear filming), the friction coefficient of that area decreases and the toner becomes difficult to sit on. There is a phenomenon in which the image density decreases, but if the photoreceptor drum is stopped and the developing sleeve is rotated to set the control level of the developer concentration control device as described above, this clear filming will not occur. There is an acceleration, an increasing drawback. According to the experimental results, “××
When I set the developer concentration control level of the developer using the ×× coated carrier 2 minutes after the start of sleeve rotation and made continuous copies, clear filming occurred after about 500 copies, and the image density decreased. It was about half compared to the normal area.

In this case, it was observed that the area where clear filming occurred spread around the contact area between the magnetic brush and the photoreceptor shown in FIG. 8 above.

The present invention provides a control level setting method that solves the above-mentioned problems associated with setting the control level of a developer concentration control device of an electrophotographic copying apparatus that uses a developer consisting of a carrier, particularly an XXXXIXXX carrier, and toner. The purpose is to provide.

In order to achieve this object, the present invention provides a developer concentration control device for an electrophotographic apparatus that performs development by supplying a developer consisting of a carrier and toner to an electrostatic latent image formed on a photoreceptor through a developing sleeve. At the time of setting the control level of
The photoreceptor is charged to the same polarity as the toner and rotated, and the developing sleeve is also rotated so that an electric field is formed between the photoreceptor and the sleeve.

The above control level setting method is particularly effective when using a developer using a medium carrier XXXXIXXX where clear filming occurs.

Furthermore, if a bias voltage is applied between the developing sleeve and the photoreceptor at the time when the control level is set using the above method, good results can be obtained without staining the drum and reducing the developer concentration.

Next, embodiments of the present invention will be described in detail.

Example 1 Using the apparatus shown in FIG. 1, a developer for an FT-7500 copying machine (X
When setting the control level of the developer concentration control device, a bias voltage is applied between the developing sleeve and the photoreceptor, and only the developing sleeve is rotated to adjust the control level to t. The S content was set at % by weight.

In this case, the polarity of the developer toner is positive, the sleeve is negative, the photoreceptor ground surface is positive, and the /quias voltage is +s.
I made it oo v.

When the surface of the photoreceptor was observed after the setting, no toner stains as shown in FIG. 3 were observed. Although the bias voltage was varied up and down (9)■ around +600V, no staining occurred.

When the sleeve surface was observed at this time, it was found that toner was adhered to the entire surface of the sleeve in a black color.

Also, when I checked the developer concentration after performing continuous copying, I found that the initial developer concentration, which was set at 1.5% by weight, had decreased to 1.8% by weight, and the image density of the copies was t, S% by weight. The image density was about 0.02 lower than the original image density.

Example 2 Using the above device and developer, the photoreceptor and developing sleeve are rotated at the time of setting the developer concentration control level, and the photoreceptor surface has the same polarity as the toner polarity (positive polarity in this example). The setting was carried out 2 minutes after the start of rotation without applying a bias voltage to the developing sleeve.

Thereafter, the surface of the photoreceptor drum was observed and found to be in good condition with no toner stains.

Further, the stain on the sleeve was a little black, which was not as bad as in Example 1. The decrease in developer concentration due to continuous copying could be suppressed to about 0.08% by weight (initial 15% by weight decreased to 1.42% by weight). Also, the image density decreased by 0.05%.

Example 3 In Example 2, when a bias having the same polarity as the toner polarity was applied to the developing sleeve, the photoreceptor was removed.

Good results were obtained with no toner stain on the ram and no decrease in developer concentration.

In this example, the photoreceptor potential was +800V and the sleeve bias was +600V.

In both Example 2 and Example 8, continuous copying was carried out, and no occurrence of 1-fail filming was observed up to 1,000 copies. This is considered to be an effect of the photosensitive drum and sleeve being rotated at the same time.

As is clear from the above description, the present invention is applied when the photoconductor charging polarity is the same polarity as the toner polarity, that is, it is applied to reversal development, and when the photoconductor charging polarity is opposite to the toner polarity. It does not apply to regular development, which is polar.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram showing an example of a conventional developer concentration III control device, and Fig. 2 shows changes in the rotation time of the knob 1 of the control level setting cloth of the developer simultaneous 1 concentration reservoir control device shown in Fig. 1. FIG. 8 is a curve diagram showing the effect of continuous copying on the decrease in developer concentration. FIG. 7 is a perspective view showing the state of toner stains on the photoreceptor drum when the agent concentration control level is set. 2... Photoreceptor drum 8... Developing sleeve 6,
~18...Developer concentration control device

Claims (3)

[Claims] (1) In a control level setting method of a developer concentration control device of an electrophotographic apparatus in which an electrostatic latent image formed on a photoreceptor is developed by being held, conveyed, and supplied by a Sabamo developing sleeve consisting of a carrier and toner. , at the time for setting the control level of the developer concentration control device, the photoreceptor is rotated while being charged to the same polarity as the toner;
A control level setting method characterized in that the above-mentioned developing sleeve is also rotated so that an electric field is formed between the photoreceptor and the sleeve. (2) The control level setting method according to claim 1, wherein the carrier for the developer is a ××XX× coat carrier. (3) Claim 1 or 2 characterized in that a bias voltage is applied between the developing sleeve and the photoreceptor at the timing for setting the control level.
Control level setting method described in section.