JPH0368970A - Image forming device - Google Patents

Abstract

PURPOSE:To make the selective switching action of a developing unit smooth and sure with simple constitution and to reduce a noise caused by meshing by displacing the developing unit by an eccentric cam and holding it by a ratchet mechanism. CONSTITUTION:After the developing unit 4a of a developing device is allowed to be opposed to a photosensitive drum 2 where an electrostatic latent image is formed so as to stick color toner, the units 4b... are successively allowed to be opposed to the photosensitive drum 2 to stick the color toner. The projecting member 54 of a developing unit holding body 46 is brought into contact with the eccentric cam 50 with the rotation of the holding body 46, so that the developing unit 4a is turned and displaced centering around a shaft 42 and drawn back. At such a time, the ratchet pawl 58 of the ratchet mechanism 55 of the developing unit 4a meshes with a ratchet tooth 59, thereby stopping the turning of the developing unit 4a which turns around the shaft 42 in a direction D by a spring 60.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Field of Application) The present invention relates to an image forming apparatus such as a color printer, and more specifically, to an image forming apparatus such as a color printer, and more specifically, to an image forming apparatus such as a color printer. The present invention relates to an image forming apparatus equipped with a developing device.

(Prior Art) Conventionally, in a color printer, developers (toners) of different colors are applied to a developer holder rotatably provided near a photoreceptor drum, which is an image carrier, along the direction of rotation of the developer holder. Some devices use a technique in which a plurality of housed developing devices are arranged to selectively face the photosensitive drum.

Further, the above-mentioned developing device is preferably one using a one-component developing method, which allows the device to be made smaller and lighter, but in this case, the positional accuracy of the developing roller of the developing device used with respect to the photosensitive drum must be maintained at least 5/100 mm or more. There must be.

For this purpose, a method is used in which a guide roller is installed coaxially with the developing roller and hits the photosensitive drum, but in order to ensure that the guide roller hits the photosensitive drum, it is necessary to extend it toward the photosensitive drum. It is structured like this.

Further, when the developing device faces the photosensitive drum, the driving force receiver is configured such that a gear meshes with a driving gear and is driven to rotate.

However, with the above configuration, each time the developer passes the position of the photoreceptor drum as the developer holder rotates, the guide roller, photoreceptor drum, and drive force receiver are in contact with the gears on the drive side. There is a problem in that not only the developing device holder does not rotate smoothly, but also unnecessary vibrations are imparted to the photosensitive drum and the developing device.

Therefore, in recent years, in this type of image forming apparatus, as shown in FIG.
... (only one is shown) is pivotally supported via a support shaft C, and is movable in one direction toward and away from the photosensitive drum d, and also rotates the developing unit holder a in the direction of arrow A. A retracting roller e as a developing device displacement means is arranged opposite to the movement locus of the developing device b... caused by the movement of the developing device b. The developing unit was retracted inside. Further, a ratchet mechanism f was used as a holding means for maintaining this state.

Further, the developing device holder a, which holds the developing device b and rotates around the shaft g, has a stopper arm h attached to the main frame and a lever i provided with the drive side gear U at the position shown in the figure. to arrow B respectively.

It rotates after escaping in the direction of C.

When the stopper arm h rotates and escapes from the position shown in the figure, the ratchet pawl g attached to the side frame j via the support shaft k is moved by the action of the spring m to the fixed ratchet tooth attached to the developer holder a. meshes with n. This results in
The rotation of the developing device, which is biased to rotate in the D direction around the support shaft C, is stopped by the spring 0.

Here, when the developing unit holder a rotates in the direction of arrow A, a retraction roller e attached to the main frame is connected to a driving force receiving gear p that meshes with the driving gear U disposed on the lever i. The coaxial abutment roller r contacts first, and the developing device is rotated in the opposite direction of the arrow and retracted inward. Further, after this, the guide roller S coaxial with the developing roller (not shown) and the retraction roller e come into contact with each other, and the developing device is further retracted inward.

This state is maintained by a ratchet mechanism f consisting of a ratchet pawl g and ratchet teeth n.

However, in such a conventional structure, the displacement is the dimension corresponding to the contact distance between the abutting roller r, which is the abutting member on the side of the developer, and the retraction kite roller e, so the required amount of displacement cannot be achieved. In order to obtain the (retraction amount), some impact will occur, but this cannot be prevented.

Further, since the gap between the ratchet teeth n of the ratchet mechanism f is finite (for example, pitch 0.8), it is impossible to prevent the mesh from returning slightly. Therefore, even though the developing device has been retracted once, when it comes to the retraction roller e, the abutting roller r on the developing device side.

The guide roller S came into contact again, and the ratchet pawl g engaged with the ratchet tooth n again, producing a "clicking" sound.

(Problem to be Solved by the Invention) As described above, in the conventional image forming apparatus, some impact is generated during the switching operation for selectively facing the photosensitive drum d between the plurality of developing units b... Occur. Also,
Even though the developer tray was once retracted, there was a problem in that the developer tray came into contact with the retracting roller e and generated noise.

In addition, in order to prevent this noise from occurring, if the amount of displacement caused by the first contact with the retraction roller e is increased in anticipation of the amount of displacement, the impact at the time of contact will be considerably large, making it impossible to operate smoothly. Not only is this impossible, but it can also cause premature failure. On the other hand, if the impact is made smaller, there is a problem that the developing unit cannot be retracted to a predetermined position.

The present invention has been made to solve the above-mentioned problems, and the object thereof is to have a simple structure, yet enable smooth and reliable selective switching of the developing device, and employ a ratchet mechanism as the holding means. An object of the present invention is to provide an image forming apparatus that can reduce noise.

[Structure of the Invention] (Means for Solving the Problems) In order to solve the above problems, the present invention provides an image carrier, a developing device holder rotatably provided near the image carrier, a plurality of developing devices disposed along the rotational direction of the developing device holder, selectively facing the image carrier and movable in directions toward and away from the image carrier; a developing device displacing means comprising an eccentric cam provided opposite to the moving path of the developing device holder and displacing the developing device in a direction away from the image carrier by contacting an abutting member on the developing device side when the developing device holder rotates; The developing device is configured to include a holding device for holding the developing device displaced by the device displacing device in a displaced state.

(Function) That is, according to the present invention, when the developing device holder rotates, the developing device displacement means that comes into contact with the abutting member on the developing device side and displaces the developing device in a direction away from the image carrier is constituted by an eccentric cam. Therefore, compared to the conventional system in which the developing device displacement means is composed of a roller, the amount of displacement caused by contact can be gradually increased, and the contact can be made smoother and the impact can be suppressed to a small level. With this, a large amount of displacement can be taken. This makes it possible to reliably displace the developing device to a predetermined position, allowing for smooth selective switching of the developing device, and reducing noise caused by re-engagement in devices where the holding means is a ratchet mechanism. Become.

(Example) An example of the present invention will be described below with reference to FIGS. 1 to 5. FIG. 2 shows the configuration of a full-color laser printer employing the developing device of the present invention, and 1 in the figure is the main body of the device. At the upper center of the apparatus main body 1 is a photoreceptor drum 2 whose surface is coated with an organic photoreceptor as an image carrier.
A charging device 3, a multicolor developing device 4, a transfer drum 5, a cleaning device 6, and a static eliminating device 7 are provided around the photosensitive drum 2 along the rotation direction (arrow E direction). are arranged in sequence. Furthermore, a laser exposure device 8 for exposing image information is provided in the upper part of the main body 1 between the charging device 3 and the developing device 4. The multicolor developing device 4 includes developing unit units 4a to 4d containing yellow, magenta, cyan, and black non-magnetic component developers (referred to as toners) t.

Further, a paper feed cassette 10 containing paper P such as plain paper is attached to one side of the apparatus main body 1, and a paper feed means 1
1, the sheets are fed one by one.

Paper P fed from the paper feed cassette 10 is conveyed along a U-turn conveyance path 12 and guided to a paper discharge tray 13 mounted above the paper feed cassette 10. The transfer drum 5, the peeling means 14, and the fixing device 15 are opposed to the U-turn conveyance path 12.

During image formation, the photoreceptor drum 2 rotates in the direction of arrow E, and the surface of the photoreceptor drum 2 is uniformly negatively charged by the charging device 3.

Thereafter, the image information is exposed by the laser exposure device 8, and the charge on the surface of the photoreceptor drum 2 is selectively removed to form an electrostatic latent image.

Next, this electrostatic latent image is transferred to the developing unit 4a (of the developing device 4) containing the preset first color toner t.
4b, 4c, and 4d), the charged non-magnetic component developer (toner) t is deposited and visualized by a non-contact jumping method.

On the other hand, at this time, the paper P fed from the paper feed cassette 10 is wound around the transfer drum 5 with its leading edge held by the gripper 5a. Then, the transfer drum 5 rotates in the direction of the arrow F while a positive bias is applied, and the toner image on the photosensitive drum 2 is transferred onto the paper P at the transfer position H.

Note that the toner t that has not been completely transferred is cleaned by the cleaning device 6, and the memory of the photosensitive drum 2 is removed by the static eliminator 7, and the next cycle begins.

Here, when transferring a plurality of colors, the transfer drum 5 is rotated once again, and during this period, the second color developer unit 4b (4c, 4d) of the developing device 4 is transferred.

4a) are sequentially switched to face the photoreceptor drum 2.

After the transfer has been performed a predetermined number of times in this manner, the peeling means 14 operates to peel the paper P from the transfer drum 5 and enters the paper ejection process. Then, the fixing device 15 fixes the paper P.
The upper toner image is heated and fixed, and the paper is discharged onto the paper discharge tray 13.

Next, the configuration of the developing unit 4a of the multicolor developing device 4 will be explained. Note that other developing unit 4b,
4c and 4d also have the same configuration as the developing unit 4a, so their explanation will be omitted.

The developing device unit 4a as a developing device of the present invention has a third
The configuration is as shown in the figure. In the figure, 20 is a casing, and inside this casing 20 are a photoreceptor drum 2 and 0.
Developing rollers 21 are provided as developer holders facing each other with a small gap G of about 25 mm between them. This developing roller 21 has a portion 60 on the surface of a stainless steel sleeve.
0 sandblasted material is used.

Further, within the casing 20, an elastic foam roller 22 made of urethane sponge or foam rubber is arranged in rolling contact with the developing roller 21, and an aluminum roller 23 is further arranged in rolling contact with the elastic foam roller 22. It is in a state.

In addition, a stainless steel blade 24 with a thickness of 0.15 mm is placed diagonally above the developing roller 21 as a layer forming member.
Further, a urethane blade 25 is in pressure contact with the diagonally lower part.

Note that 26 is a lid member, and 27 and 27 (only one of which is shown) are side frames.

Moreover, the stainless steel blade 24 as a layer forming member is
The upper edge portion is held by a blade holder 28 serving as a holding body, and is arranged parallel to the developing roller 21 .

The blade holder 28 is rotatably supported around support shafts 30 attached to both ends in the longitudinal direction, and is a press-contact member screwed into a stay 31 horizontally suspended between the side frames 27 and 27. When the upper surface is pushed by the force adjusting screws 32, 32, it is rotated in the direction of the arrow in FIG. Then, press contact force adjustment screws 32, 3
2 is such that the pressing force of the stainless steel blade 24 against the developing roller 21 can be adjusted depending on the condition.

Further, the developing roller 21, the elastic foam roller 22, and the aluminum roller 23 are rotatably supported via bushings (not shown) attached to the side frames 27 and 27. And these rollers 21.22.2
3 are configured to interlock with each other by a gear group 40 (see FIG. 1) disposed on the front side of the front side frame 27.

Further, positioning rollers 41, 41 are attached to the support shaft 21a of the developing roller 21, and the entire developing unit 4a is urged to rotate around the shaft 42, so that the positioning rollers 41, 41 are The body drum 2 is in rolling contact with the body drum 2, so that the predetermined gap G can be secured.

Thus, the non-magnetic component toner t that has entered the casing 20 is carried to the right in FIG. roller 21
It is sent between the stainless steel blade 24 and the stainless steel blade 24 that comes into pressure contact with the stainless steel blade 24. Here, the toner t is made into a thin layer, charged, and sent to the photosensitive drum 2 side.

At this time, the developing roller 21 is supplied with -250V and AC voltage.
Since a bias of 1,2 KV is applied, the toner t flies toward the exposed portion of the photosensitive drum 2 facing the developing roller 21 with a minute gap G, that is, toward the electrostatic latent image.
The electrostatic latent image becomes visible.

Note that toner t remaining on the developing roller 21 without flying away
is collected into the casing 20 by the urethane blade 25 and then scraped off by the elastic foam roller 22. The toner then passes under the resistant foam roller 22 and the aluminum roller 23 and returns to the toner reservoir 43 above the aluminum roller 23.

Further, as shown in FIGS. 1 and 4, a developing device 4a,
A developing device holder 46 that holds the developing devices 4b, 4c, and 4d and rotates in the direction of arrow A in the figure about a shaft 45 includes side walls 46a and 46a that are spaced from each other and face each other.
4d is arranged between these side walls 46a, 46a. In order to avoid duplication of explanation, only the developing device 4a will be explained and the other developing devices 4b, 4c, and 4d will be omitted.

Further, an eccentric cam 50 as a developing device displacement means is provided opposite to a path of movement of the developing device holder 46 of the developing device 4a as it rotates. The eccentric cam 50 is rotatable on a shaft 52 horizontally suspended on a main frame 51 on which the shaft 45 of the developing device holder 46 is supported, and is moved to the solid line position shown in FIGS. 1 and 5 by means of a spring 53, i.e. , the small displacement portion of the cam surface 50a is always urged to a position close to the developing device 4a side.

Further, an abutment member 54 made of a friction member such as rubber and having an arcuate abutment surface 54a is disposed at a portion of the developing device 4a corresponding to the position of the eccentric cam 50.

As the developing device holder 46 rotates, the arcuate contact surface 54a of the abutment member 54 comes into contact with the eccentric cam 50, so that the developing device 4a is rotated about the shaft 42 and retracted, as will be described later. It becomes a state. At this time, the displaced developing device 4a is held in the displaced state by a ratchet mechanism 55 serving as a holding means.

The ratchet mechanism 55 has a support shaft 56 attached to the side frame 27.
It is comprised of a ratchet pawl 58 which is rotatable via a lever and biased by a lock spring 57, and five fixed ratchet teeth attached to the developing unit holder 51. Then, when the ratchet pawl 58 meshes with the five ratchet teeth,
A spring 60 prevents the developing device 4a from rotating in the D direction about the shaft 42 with respect to the developing device holder 51.

Further, a stop arm 61 as a holding/releasing means for releasing the engagement operation of the ratchet mechanism 55 is provided between the position of the eccentric cam 50 as the developing unit displacing means and the photosensitive drum 2. This stop arm 61 is attached to a drive shaft 62 and is rotatable in the direction of arrow B and in the opposite direction of arrow B to push down the ratchet pawl 58 so that the ratchet pawl 58 is disengaged from the ratchet teeth 59.

Further, the stop arm 61 is provided with a protrusion 61g,
A protrusion 64 of a lever 64 that rotates around a drive shaft 63
It comes into contact with a.

When the stop arm 61 rotates in the direction of arrow B to keep the ratchet mechanism 55 engaged, the lever 64
The projection 64a of the stop arm 61 is pushed by the projection 61a of the stop arm 61, and the lever 64 is rotated in the direction of arrow C.

This lever 64 is provided with an idler gear 66 as a drive side gear that meshes with a drive gear 65 fitted on the drive shaft 63, and a drive force receiver, which is one of the gears 40, is provided with a gear 67. It is designed to mesh with the

Next, the displacement operation (retracting operation) accompanying switching of the developing units 4a (4b, 4c, 4d) will be explained.

First, the stop arm 61 and idler gear 66 attached to the main frame 51 escape in the directions of arrows B and C, respectively, as shown in FIG.
(4b, 4c, 4d) and the developing device holder 46 starts rotating in the direction of arrow A around the shaft 45.

When the stop arm 61 escapes in the direction of arrow B, the ratchet pawl 58 of the ratchet mechanism 55 is attached to the side frame 27 via the support shaft 56. The ratchet pawl 58 of the ratchet mechanism 55 is attached to the fixed ratchet tooth attached to the developer holder 46 by the action of the spring 57. It meshes with 59.

As a result, the developing device is rotatably attached to the holder 46 by the shaft 42, and the shaft 42 is mounted by the spring 60.
The developing device 4a, which is about to rotate in the D direction around the developer 4a, is stopped from rotating.

Here, when the developing device holder 46 rotates in the direction of arrow A,
An abutting member 54 made of a friction member such as rubber comes into contact with an eccentric cam 50 for retraction attached to the main frame 51.

At this time, the small displacement portion of the cam surface 50a of the eccentric cam 50 first contacts the circumferential surface 54a of the abutment member 54, and then, as the developing unit holder 46 rotates in the direction of arrow A, the eccentric cam 50 bumps. Due to the frictional force between the member 54 and the circumferential surface 54a, the member 54 rotates in the direction of arrow J against the biasing force of the spring 53 about the shaft 52 as shown in FIG. 54. As a result, the developing device 4a
teeth.

It is turned in the opposite direction to the arrow and pulled inward.

In this way, in the present invention, after the small displacement parts first come into contact as shown by the solid line in FIG. 5, the large displacement parts shown by the two-dot chain line gradually come into contact with each other, so that there is almost no impact. Thus, a predetermined displacement measurement including the return amount of the ratchet mechanism 55 can be obtained. This displaced state (retracted state!) is maintained by the ratchet mechanism 55.

When the developing device 4a finishes passing, the eccentric cam 50 returns to the solid line position by the biasing force of the spring 53.

Next, when the developing device 4a passes through the installation position of the eccentric cam 50 in the retracted state, a gap corresponding to the displacement gauge is formed between the developing device 4a and the eccentric cam 50.
4 or the positioning roller 41, etc., and there is no noise caused by the ratchet mechanism being re-engaged as in the conventional case.

Note that the present invention is not limited to the above-mentioned embodiment, and it goes without saying that various modifications can be made without departing from the gist of the present invention.

[Effects of the Invention] As explained above, according to the present invention, the selective switching operation of the developing device can be performed smoothly and reliably despite the simple structure, and the noise can be reduced when the holding means is a ratchet mechanism. This has the advantage that it is possible to provide an image forming apparatus that can achieve the following.

[Brief explanation of drawings]

1 to 5 show an embodiment of the present invention,
Fig. 1 is a diagram schematically showing the configuration of the displacement mechanism of the multicolor developing device, which is the main part of the present invention, Fig. 2 is an internal configuration diagram of a full-color printer to which the present invention is applied, and Fig. 3 is the developing device. FIG. 4 is a schematic side view showing the structure of the main parts of the developing device displacement means, FIG. 5 is a schematic front view, and FIG. 6 is a diagram showing a conventional example. It is. 2... Image carrier (photosensitive drum), 4 a, 4
b. 4c, 4d...Developing device, 46...Developing device holder, 5
4... Abutment member, 50... Developing device displacement means (eccentric cam), 55... Holding means (ratchet mechanism). 7

Claims (1)

[Claims] an image carrier, a developer holder rotatably provided near the image carrier, and a developer holder disposed on the developer holder along the direction of rotation of the developer holder and selectively opposed to the image carrier. and a plurality of developing devices movable in directions toward and away from the image carrier; and a plurality of developing devices provided opposite to the movement path of the developing devices and in contact with an abutting member on the developing device side when the developing device holder rotates. A developing device displacing means comprising an eccentric cam for displacing the developing device in a direction away from the image carrier, and a holding means for holding the developing device displaced by the developing device displacing means in a displaced state. image forming apparatus.