JPH0574821B2 - - Google Patents

Description

Detailed Description of the Invention A. Purpose of the Invention [Field of Industrial Application] This invention relates to a developing device that develops an electrostatic latent image on an image bearing member with a developer, particularly a developing device that faces a photosensitive drum serving as an image bearing member. The present invention relates to an image forming apparatus having a developing device in which a developer carrier (hereinafter referred to as a rotating body) such as a sleeve or a magnetic roll is provided in a developing device and the rotating body is rotated only during development.

[Conventional technology]

In the above-mentioned developing device, in order to prevent developer (toner) from scattering, a plate-shaped electrode member (hereinafter referred to as a plate electrode) for preventing toner scattering is installed on the downstream side of the developing device, as shown in Fig. 2. )4
It has been proposed that a bias potential be applied to this from an electrode E.

When the photosensitive drum 1 rotates, an air layer 1 of several mm from its surface moves at approximately the same speed as the circumferential speed of the photosensitive drum. When a bias having the same polarity as the toner T is applied to the plate electrode 4, the toner floating near the rotating body 3 is pushed toward the photosensitive drum by the bias electric field. This bias is set to such a potential that the toner is taken into the air layer 1, and is, for example, about 500 V to 1500 V when the triboelectric average of the toner is 10 μc/g and the circumferential speed of the drum is 145 mm/sec. However, as a matter of course, this value changes somewhat depending on the distance between the plate electrode 4 and the photosensitive drum 1.

The toner pushed toward the photosensitive drum in this manner adheres to the drum and develops an image when the surface of the photosensitive drum is an image area, and as shown in FIG. 2, the purpose is achieved by suppressing toner scattering.

[Problem that the invention seeks to solve]

However, when the rotating body 3 is started, acceleration acts on the toner on the rotating body, and a larger amount of scattered toner is generated than during constant speed rotation development. Under the bias condition of V ₀ , as shown in T' in FIG. 3, the particles fly out of the developing section and contaminate the inside of the machine.

Also, when the rotating body 3 stops rotating, similar development occurs as described later.

Therefore, it is possible to start and stop the rotating body at a slow speed, but this method has the disadvantage that the copying speed is determined by the time required for starting and stopping as the copying speed increases. It was hot.

An object of the present invention is to provide an image forming apparatus that solves the above problems.

B. Structure of the Invention [Means for Solving the Problems] This invention provides a developing unit having a developer carrying member arranged around an image carrying member in order from upstream in the moving direction of the image carrying member, and a developer dispersing device. The image forming apparatus is provided with an electrode member for prevention, from the start of rotation of the developer carrier until the starting end of the image area to be developed by the developer on the image carrier comes to the development position. and/or the potential applied to the electrode member during the time when the rear end of the image area leaves the development position and the developer carrier stops; This image forming apparatus is characterized in that the image forming apparatus is controlled so that the image forming temperature is higher than that of the image forming apparatus.

[Effect]

There is a period t ₁ from the start of the rotating body 3 until the image area of the photosensitive drum 1 reaches the developing position (the position where the starting edge of the image area substantially faces the rotating body 3), and when the trailing edge of the image area leaves the developing position. By making the bias potentials V ₁ and V ₂ at t ₂ higher than the bias potential V ₀ applied to the plate electrode 4 in the image area as shown in FIG. The force of pushing the floating toner into the air layer 1 in the image area is increased, the floating toner is carried to the cleaner, and the above-mentioned toner scattering phenomenon is eliminated.

〔Example〕

The values of the above bias potentials V ₀ , V ₁ , and V ₂ are based on (1) the rotational circumferential speed of the photosensitive drum 1, (2) the toner moving speed or the rotational circumferential speed of the rotating body 3, and (3) the rotational circumferential speed of the rotating body 3. This is determined experimentally by combining conditions such as the time it takes to reach a stable toner movement speed.

The bias potential V ₀ at a stable rotating body speed during normal image area development is 500 to 1500 V, and V ₁ at startup may be about 2 to 6 times that value.

As one example, the circumferential speed of the photosensitive drum is 145 mm/sec,
Rotating body peripheral speed 270 mm/sec, startup rise time t ₁ = 0.3
In the case of seconds, good results were obtained with V ₀ = 1 KV and V ₁ = 2 KV.

The above example is a case where a bias voltage with the same polarity as the toner is applied to the plate electrode 4, but when we tried applying a bias voltage with the opposite polarity to the toner, we found that the voltage value to be applied was the same polarity as the toner. The voltage or timing of application was the same as when applying a voltage of the same polarity as the toner, and sufficient effects were obtained. However, in this case, since toner adheres to the plate electrode 4, it has been found that providing a means for collecting and removing the adhered toner works effectively.

Next, when the rotating body is stopped, negative acceleration is generated in the toner on the rotating body 3. Also, since there is a change between the photosensitive drum speed and the toner movement speed,
After all, the three conditions mentioned above change in the same way as when the developing device (rotating body) is started up, and the toner scattering increases for the reason mentioned above, so it is necessary to change the bias value.

When the developer stops at the same speed as when it starts, the degree of toner scattering is not as large as when the developer starts, so there is a relationship between V ₀ , V ₁ , and V ₂ of V ₀ <V ₂ ≦V ₁ . _V2 of 1000V to 3000V is sufficient.
When the circumferential speed of the drum, the rotational speed of the rotating body, etc. were as in the above embodiment, good results were obtained with _V2 of about 1500V.

Further, in this case, the time _t2 from steady rotation to stop of the rotating body 3 was approximately 0.3 to 0.5 seconds. The reason why the bias voltage applied to the plate electrode in the non-image area is set to zero is to prevent toner from scattering from the developing device and to avoid contamination of the plate electrode as much as possible.

C. Effects of the Invention As explained above, in an image forming apparatus that uses a developing device having a developer carrier such as a sleeve or a magnetic roller that rotates only during development and is equipped with a plate electrode for preventing toner scattering, the plate electrode By controlling the applied potential to be higher during transitions between starting and stopping of the rotating body than during normal development, it was possible to sufficiently suppress toner scattering within the machine that occurs during these transitions.

[Brief explanation of the drawing]

Fig. 1 is a timing chart showing the control of bias potential application to the plate electrode of the present invention, Fig. 2 is an explanatory diagram of the flow of toner during constant speed rotation development of the rotary body, and Fig. 3 is the activation of the rotary body. FIG. 4 is an explanatory diagram of the action of the plate electrode, and FIG. 5 is a timing chart showing the conventional control of applying a bias potential to the plate electrode. 1... Photosensitive drum, 3... Developer sleeve (rotating body), 4... Plate electrode, T... Toner,
T′...Scattered toner, E...Bias power supply.

Claims (1)

[Claims] 1. An image forming apparatus in which a developing device having a developer carrier and an electrode member for preventing developer scattering are disposed around an image carrier in order from upstream in a moving direction of the image carrier, The developer carrier is rotated only during development, and the period from the start of rotation of the developer carrier until the starting end of the image area to be developed by the developer on the image carrier comes to the development position; /Or, the potential applied to the electrode member is higher than the potential applied to the electrode member during development of the image area until the rear end of the image area leaves the development position and the developer carrier stops. An image forming apparatus characterized in that it is controlled as follows.