JPS6261150B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic brush developing device equipped with a rotating body that approaches or contacts the surface of an image carrier in an image forming apparatus such as an electrophotographic copying machine or an electrostatic recording device.

In the case of a magnetic brush developing device, the gap between the surface of the image carrier such as a photoreceptor or dielectric and the surface of the developing roller is
It is set to a certain value. The developer on the developing roller comes into contact with the surface of the image carrier while passing through this gap, and develops an electrostatic latent image formed on the surface of the image carrier by the Carlson method, electrostatic recording method, or the like. Since the gap between the image carrier surface and the developing roller surface is extremely narrow, if relatively large diameter particles are present in the developer, they may be crushed and solidified. Further, when a larger amount of developer passes through this gap, a similar phenomenon occurs. This is usually called developer blocking. This phenomenon is particularly likely to occur when a one-component developer consisting only of toner is used, since the toner particles tend to stick together due to heat or stress. When such blocking occurs, the developer is prevented from uniformly adhering to the developing roller, resulting in poor development. Therefore, if pressure above a certain level is applied between the image carrier surface and the developing roller,
An invention in which the magnetic brush developing device is separated from the surface of the image carrier to prevent the occurrence of blocking is disclosed in Japanese Patent Application No. 51-63409.
52-146642). this is,
The application was filed by the same applicant as the applicant.
In such a magnetic brush developing device that can be retracted from the surface of the image carrier, if a drive source for rotating the developing roller is installed in the magnetic brush developing device, the magnetic brush developing device itself and its own weight will become large and the developing The magnetic brush developing device may not be separated by the pressure caused by the agent, and the intended purpose may not be achieved. Therefore, the drive source for the developing roller is preferably provided outside the magnetic brush developing device. However, if the driving source is provided outside the magnetic brush developing device, the separation of the magnetic brush developing device from the image carrier will be affected by the force transmitted from the driving source, making it impossible to achieve the intended purpose. There are cases.

According to the present invention, a magnetic brush developing device including a rotating body that is close to or in contact with the surface of an image carrier and a driven gear that rotates this rotating body is swingably supported on an image forming apparatus main body by a support shaft. By this, the rotating body is held so as to be retractable from the surface of the image carrier, and power is transmitted to the rotating body by meshing a driving gear provided on the main body of the image forming apparatus with a driven gear of the magnetic brush developing device. The magnetic brush developing device is characterized in that the positions of both gears and the support shaft are related so that the direction of the force transmitted from the drive gear to the driven gear is substantially directed toward the support shaft.

According to this invention, since the driving force is received from outside the magnetic brush developing device, the weight and volume of the magnetic brush developing device can be reduced, and as a result,
The magnetic brush developing device can be easily and reliably retracted from the image carrier. In addition, by determining the positional relationship between gears and spindles,
The adverse effect of external driving force on the retraction of the magnetic brush developing device from the image carrier can be minimized.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a magnetic brush developing device that can be easily and reliably evacuated from an image carrier.

Hereinafter, the present invention will be described in further detail with reference to the accompanying drawings. FIG. 1 is a schematic diagram showing an example of a magnetic brush developing device to which the present invention is applied. Inside the magnetic brush developing device 1, a hopper 2 and a developing roller 3 are provided. A one-component magnetic toner 4 is housed in the hopper 2, and this toner is supplied from the lower opening of the hopper 2 to the surface of the developing roller 3, and is supplied by the magnetic force of the magnet housed inside the developing roller. is adsorbed onto the surface of the developing roller. Magnetic brush developing device 1
On the outside of the side plate supporting the developing roller 3, there is a gear 5 fixed to the rotating shaft of the developing roller 3, and a driven gear 6 meshing with the gear 5 is rotatably supported by the side plate. This driven gear 6
A driving gear 7 supported by the copying machine body is engaged with the developing roller 3.
Power is transmitted from the driven gear 6 and gear 5 to rotate counterclockwise. The entire magnetic brush developing device 1 is swingably supported by a support shaft 8 provided on the copying machine main body. A gap between the developing roller 3 and the photosensitive drum 10 is maintained by contacting the developing roller 3 with the photosensitive drum 10 .

The toner magnetically adhered to the surface of the developing roller 3 is transported as the developing roller 3 rotates.
The developing roller 3 and the photoreceptor drum 10 contact the surface of the photoreceptor drum at a position close to each other, and develop the electrostatic latent image on the photoreceptor drum. When pressure above a certain level is applied between the developing roller 3 and the photosensitive drum 10,
For example, when toner clumps occur or there is a large amount of toner, the magnetic brush developing device 1 swings counterclockwise around the support shaft 8 due to the pressure, absorbing the pressure. Prevents toner blocking.

In such a device, the direction of the force transmitted from the drive gear 7 to the driven gear 6 is a direction perpendicular to the tangent of the tooth profile at the pitch point of the drive gear 7 in the meshing portion. That is, as shown in FIG. 2, the direction PB is perpendicular to the tangent line PA passing through the pitch point P of the tooth profile 11, which is a cross section of the tooth surface. The angle θ formed by this tangent line PA and the radius line PC of this gear passing from the center O of the gear to the pitch point P is called the pressure angle, and is unique to that gear. Therefore,
In other words, in terms of the direction of force PB, the tangent line PD of this gear passing through the pitch point P is perpendicular to the radius line PC, so it can be said that the direction is clockwise from the tangent line PD at an angle equal to the pressure angle θ. For this reason,
When the driving gear 7 and the driven gear 6 are arranged horizontally, for example, as shown in FIG. 3, the direction of the driving force PB is downward, and the direction of the moment about the support shaft 8 is clockwise. This acts to constantly press the magnetic brush developing device 1 against the photosensitive drum 10 side. Therefore, in order for the magnetic brush developing device 1 to retreat from the photoreceptor drum 10, it must resist this moment and rotate counterclockwise with a force greater than this moment. It is extremely difficult to generate force between the developer roller and the photoreceptor drum.
If a large amount of developer were to pass through this gap, such a large force would be generated, but the moment due to the driving force would also become large in opposition to this force, so that this force would be canceled out.

The present invention is characterized in that the moment caused by such a driving force is minimized so that the separating action of the magnetic brush developing device can be performed easily and reliably. For this purpose, the positional relationship between both gears and the support shaft is taken into consideration so that the direction of the force transmitted from the driving gear to the driven gear is approximately toward the support shaft, which is the swinging fulcrum of the magnetic brush developing device. . In other words, as shown in FIG.
These are related so that the support shaft 8 is located in the vicinity of a direction PB at an angle equal to the pressure angle θ in a clockwise direction passing through the pitch point P from PD. Support shaft 8
The preferred position is from the force direction PB to the pitch point P
Within a range of ±15°, more preferably ±5
It is in the range of ゜. When the spindle 8 is located at a position of ±0° with respect to the direction of force PB, that is, on PB,
The moment about the support shaft 8 due to the driving force is zero. Therefore, this condition can be said to be the best condition. On the other hand, as shown in the figure, the support shaft 8
When it is located on the + side of PB, that is, on the clockwise side, the direction of the moment due to the driving force is clockwise, and acts to press the magnetic brush developing device against the photoreceptor drum. On the contrary, the direction
When it is located on the minus side, that is, on the counterclockwise side of PB, the direction of the moment becomes counterclockwise, and acts to separate the magnetic brush developing device from the photosensitive drum. Where to position the support shaft 8 within the above range is determined by other conditions, but in any case, within the above range, the influence of the moment due to the driving force can be minimized. . For the same reason,
The influence of moment changes due to various load fluctuations caused by insufficient lubrication of the drive system can also be minimized.

The inventors of the present application used a magnetic brush developing device as shown in FIG. 1 with a total weight of 3.1 kg, and
rotation speed 130r.pm, torque 3Kg・cm~5Kg・
cm, pressure angle 20°, position of support shaft 8 80mm from point P
When I experimented by setting it at ±2 degrees from PB,
Appropriate rocking motion is obtained around the support shaft 8 with little influence of the moment due to the driving force, and excess developer also passes smoothly between the developing roller 3 and the photosensitive drum 1, preventing blocking. Nakatsuta.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an example of a magnetic brush developing device to which this invention is applied, FIG. 2 is an explanatory diagram showing the theoretical basis of this invention, and FIG. 3 is a diagram showing an example of a magnetic brush developing device to which this invention is not applied. It is a figure showing the direction of driving force. P...Pitch point at the meshing part of the driving gear and driven gear, PB...Direction of driving force, PD...Tangential line passing through the pitch point of the driving gear.

Claims (1)

[Claims] 1. The image forming apparatus is equipped with a rotating body that is close to or in contact with the surface of the image carrier, and a driven gear that rotates the rotating body, and is swingably supported by the image forming apparatus main body by a support shaft. In the magnetic brush developing device, the rotating body is held retractably from the surface of the image carrier, and power is transmitted to the rotating body by meshing a driving gear provided on the main body with the driven gear. The gears and the support shaft are arranged in a relationship such that the direction perpendicular to the tangent to the tooth profile at the pitch point of the drive gear at the meshing portion of the drive gear and the driven gear substantially faces the support shaft. Magnetic brush developing device.