JPH0641257Y2 - Development device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Purpose of Invention] [Industrial Application Field] The present invention relates to a developing device in an image forming apparatus, for example, a copying machine, provided with a drum heater for heating a photosensitive drum.

“Problems to be solved by the conventional technology and device” Conventionally, in this type of device, a drum heater is used to prevent moisture absorption of the photosensitive drum, and it is effective in preventing moisture absorption and dew condensation of the optical system. However, since the developing sleeve is close to the drum, it causes eccentricity of the sleeve due to thermal expansion, and when a halftone original or the like is copied, a copy image with unevenness appears due to the pitch of the peripheral length of the developing sleeve. I got it.

It is an object of the present invention to obtain a developing device capable of eliminating the above-mentioned drawbacks of the conventional example and at the same time always obtaining a clear image.

[Constitution of device]

"Means for Solving Problems" The present invention relates to an image forming apparatus equipped with a drum heater for heating an electrophotographic photosensitive drum. When the image forming operation is stopped and the drum heater is energized, the photosensitive member is exposed during development. A developing device is provided with means for moving a developing sleeve that is close to and facing the drum in a direction away from the photosensitive drum and holding the developing sleeve at a position that prevents eccentricity due to heat of the drum heater.

"Operation" The developing sleeve is separated from the photosensitive drum by the means for moving the developing sleeve when the image forming apparatus is not in operation, and the developing sleeve is not affected by the drum heater via the photosensitive drum. The developing sleeve approaches the photosensitive drum by the moving means.

[Examples] The present invention will be described below with reference to the drawings. FIG. 1 shows an embodiment of the present invention, in which 1 is a photosensitive drum around which a device for performing charging, exposing, developing, transferring, and cleaning processes of an electrophotographic process is arranged, and 2 is a center of the photosensitive drum 1. , 3 is a developing device hopper, and 4 is a developing sleeve for sending out the toner stored in the developing device hopper 3, which is close to the photosensitive drum 1 during development. Reference numeral 5 denotes a solenoid connected to the developing device hopper 3, which is a movable piece for pulling the lower end of the developing device hopper 3 to move the developing sleeve 4 in a direction away from the photosensitive drum 1.
It is a means for holding it in a position that prevents eccentricity due to heat. Reference numeral 6 denotes a shaft which is disposed above the developing device hopper 3 in parallel with the photosensitive drum 1 and is fixed to the machine frame, and the developing device hopper 3 is pivotally mounted on the shaft. Reference numeral 8 denotes a spring, one end of which is fixed and the other end of which is in contact with the developing device hopper 3 and is compressed.

When the drum heater 2 is turned on at, for example, about 80 W when the copying is stopped, the drum side of the developing sleeve 4 becomes about 40 ° C. and the developing sleeve 4 is eccentric. Therefore, in the present invention, the solenoid 5 is energized at rest, when the drum heater 2 is turned on, and the developing device hopper 3 is pulled around the shaft 6 by the solenoid 5 against the spring 8 in the direction of the arrow 7. The developing sleeve 4 rotates about the shaft 6 and moves away from the photosensitive drum 1, and it is possible to prevent eccentricity due to heat received by the portion of the developing sleeve 4 close to the photosensitive drum 1 due to the temperature rise of the photosensitive drum 1. Further, although not shown in the drawing, the developing sleeve roller which comes into contact with the non-image area at the end of the photosensitive drum 1 coaxially with the developing sleeve 4 for positioning the developing sleeve 4 and the photosensitive drum 1 is also separated from the photosensitive drum 1. As a result, expansion due to contact can be prevented and the correct gap between the photosensitive drum 1 and the developing sleeve 4 can be maintained. When the solenoid 5 is deenergized, the developer hopper 3 is rotated about the shaft 6 by the force of the spring 8 and is restored to a developable state.

In the embodiment, the developing sleeve 4 is pulled in the direction of separating from the photosensitive drum 1 against the spring 8, but the developing device hopper 3 is moved closer to the photosensitive drum 1 by the solenoid 5 using the spring 8 as a tension spring. Good.

[Effect of device]

As described above, by providing the means for moving the developing sleeve in the direction of separating the developing sleeve from the photosensitive drum when the drum heater is turned on while the image forming apparatus is not operating, it is possible to always obtain a clear image without uneven development. Is possible.

[Brief description of drawings]

FIG. 1 is a perspective view of an embodiment of the present invention. 1 ... Photosensitive drum, 2 ... Drum heater, 3 ... Developing device hopper, 4 ... Developing sleeve, 5 ... Solenoid,
6 ... Axis, 8 ... Spring.

Claims (1)

[Scope of utility model registration request] 1. An image forming apparatus equipped with a drum heater for heating an electrophotographic photosensitive drum, wherein when the image forming operation is stopped and the drum heater is energized, the photosensitive drum is closely opposed to the photosensitive drum during development. A developing device comprising means for moving a developing sleeve away from the photosensitive drum and holding the developing sleeve at a position for preventing eccentricity due to heat of the drum heater.