JP3184312B2 - Image forming device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus in which three or more developing means are provided around an image carrier.

[0002]

2. Description of the Related Art Conventionally, three or more developing means are arranged around a photosensitive drum, which is an image bearing member, along a rotation direction thereof, and latent images of respective colors formed on the photosensitive drum are developed. 2. Description of the Related Art There is known an image forming apparatus which forms toner images of respective colors by sequentially developing the toner images on a transfer material and forms a multi-color image by transferring the toner images onto a transfer material.

FIG. 4 shows an example of such a conventional image forming apparatus. In FIG. 4, reference numeral 1 denotes a photosensitive drum having a diameter of 150 mm. Around the photosensitive drum 1, a primary charger 2, three developing units 3, a transfer drum 4 having a diameter of 150mm,
A cleaner 5 and the like are provided. A transfer charger 6 is provided inside the image transfer section of the transfer drum 4 facing the photosensitive drum 1, and a registration roller 7 is provided at a position just before the image transfer section between the transfer drum 4 and the photosensitive drum 1. Have been.
A fixing device 8 is provided at a position distant from a portion of the transfer drum 4 opposite to the image transfer portion.

The developing unit 3 includes a blue developing unit 3B, a black developing unit 3K, and a red developing unit 3R arranged around the photosensitive drum 1. As shown in FIG. Adjacent developing units are arranged at a distance of 35 ° from the center of the photosensitive drum 1. Accordingly, all the circumferential lengths L of the photosensitive drums 1 corresponding to the gaps between the adjacent developing units are L = 150 × π × 35/360 = 45.8 (mm).

[0005] These blue developing device 3B, black developing device 3K,
The red developing device 3R contains a blue developer composed of a blue toner and a carrier, a black developer composed of a black toner and a carrier, and a red developer composed of a red toner and a carrier as two-component developers, respectively. Is provided. Each developing unit 3B, 3K, 3R
The developer is attracted and held on the outer peripheral portion of the developing sleeve 30 by the action of a magnet roller, and the developer is conveyed to the developing section facing the photosensitive drum 1 by rotating the developing sleeve 30. ing.

The operation of the image forming apparatus will be described.
First, the photosensitive drum 1 is uniformly charged by the primary charger 2,
Image light L based on black image information is exposed on the photosensitive drum 1 from a scanner unit (not shown), and an electrostatic latent image for black is formed on the photosensitive drum 1. The latent image is located at the position of the black developing device 3K with the rotation of the photosensitive drum 1, a black developer is supplied through the developing sleeve 30 of the black developing device 3K, and the latent image is developed. Visualized as an image. On the other hand, the transfer paper P is fed from a cassette (not shown), and supplied to the transfer drum 4 by the registration roller 7 at the timing with the black toner image.
Is conveyed while being adsorbed and carried on the outer peripheral surface of the transfer drum 4.
Then, while the transfer paper P on the transfer drum 4 passes through the image transfer portion, the black toner image on the photosensitive drum 1 is transferred onto the transfer paper P by the transfer charger 6.

After the transfer, the photosensitive drum 1 is cleaned by a cleaner 5 to remove the residual toner, and then uniformly charged again by a primary charger 2, and is exposed to image light L of red image information via a scanner unit. Thus, a latent image for red is formed, the latent image is supplied with red toner by a red developing device 3R, developed, and visualized as a red toner image.
This red toner image is transferred onto the transfer paper P to which the above black toner image has been transferred.

Similarly, a blue latent image formed by exposure to image light L of blue image information is developed by a blue developing device 3B and visualized as a blue toner image, and the blue toner image is converted into a black toner image and a red toner image. Is transferred onto the transfer paper P on which is transferred.

When the three toner images are transferred onto the transfer paper P as described above, the transfer paper P is separated from the transfer drum 4 and conveyed to the fixing device 8, where the toner image on the transfer paper P is transferred. Fixing is performed.

[0010]

By the way, in the above-described image forming apparatus, a latent image for a test patch is formed on a non-image area of a photosensitive drum under predetermined conditions, and the latent image is obtained by developing the latent image. It is known to read a toner optical density or the like of a test patch and control image forming conditions such as development conditions according to the read signal. There is also known an image forming apparatus in which one of a plurality of developing devices arranged around a photosensitive drum is used for developing such a test patch latent image.

However, when developing devices for developing such a test patch latent image are arranged at positions other than the most upstream and the most downstream in the rotation direction of the photosensitive drum among the arrangement positions of three or more developing devices. As described below, various problems have occurred.

In general, in such an image forming apparatus, it is desirable that (1) there is no time zone in which two or more developing units must perform a developing operation at the same time.
This is because the developing device group is generally driven by one motor, and if the developing operations of two or more developing devices are performed simultaneously, the torque required for the motor increases. Also, it is necessary to apply a developing bias to two or more developing units at the same time.

In general, in such an image forming apparatus, in order to increase the number of images output within a certain period of time, (2) non-images between latent images of each color for one output image Area of the photosensitive drum in the circumferential direction (referred to as M), and the latent image developed last in the previous output image of the two preceding and succeeding output images and the first developed image in the subsequent output image Transfer paper P so that the length (in the circumferential direction) of the photosensitive drum in the non-image area between the latent images is the same.
It is desirable to control the timing at which the transfer drum 4 is attracted to the transfer drum 4. (3) It is desirable that the diameter of the photosensitive drum 1 be as small as possible in view of cost, size of the apparatus, and the like.

The image forming apparatus shown in FIG. 4 is configured in consideration of the above three points, which will be further described. In order to eliminate the time zone in which two or more developing units must perform the developing operation at the same time, the length L in the circumferential direction of the photosensitive drum corresponding to the gap between the adjacent developing units is set to the minimum value of the latent image. Between the non-image area length M (= N) (depending on the image size), and the developing operation order of each developing unit is determined by the developing unit arranged at the most upstream in the rotation direction of the photosensitive drum. After the operation, the developing operation of the developing device arranged at the most downstream is performed, and for the other developing devices including the developing device arranged at the most downstream, the developing operation of the developing device of one of the other developing devices is performed. Later, it is necessary to perform the developing operation of the developing device disposed one upstream of the developing device.

This will be described in more detail. When the developing operation of a developing device (referred to as Y) disposed downstream of the developing device X in the rotation direction of the photosensitive drum after the developing operation of a developing device (referred to as developing device X) is performed, these two operations are performed. There is no time zone during which the developing operations of the developing devices X and Y are performed simultaneously. Because, when the developing device X has finished developing the rear end of the latent image for the developing device X, the leading end of the latent image for the developing device Y downstream of the developing device X is located upstream of the developing device X. Because it is located.

On the other hand, when a developing operation of a developing device (hereinafter referred to as a developing device Z) disposed upstream of the developing device X is performed after the developing operation of the developing device X, the developing device X The circumferential length (m) of the non-image area between the latent image of the developing device Z and the latent image for the developing device Z is the circumferential length of the photosensitive drum corresponding to the gap between the developing device X and the developing device Z. If the length is shorter than (g), the developing device X and the developing device Z have a time zone in which the developing operation must be performed at the same time. Because, when the developing device X is developing the rear end of the latent image for the developing device X, the latent image for the developing device Z located m upstream from the rear end of the latent image for the developing device X is provided. This is because the leading end of the image has passed the developing unit Z. However, if g <m, on the contrary, even if the developing operation of the developing device Z upstream from the developing device X is performed after the developing operation of the developing device X, the developing operations of the developing device X and the developing device Z are not performed. It does not happen at the same time.

Here, the maximum size of an image that can be formed by the image forming apparatus shown in FIG. 4 is A3 size (420 mm × 2
97 mm). Therefore, the peripheral length of the area of the transfer drum 4 where the transfer paper P is attracted and where the transfer paper P does not exist is the shortest, and is 150 × π−420 = 51.2 (mm). Since the rotation speeds of the transfer drum 4 and the photosensitive drum 1 are the same, the peripheral length of the non-image area of the photosensitive drum 1 is also 5
1.2 mm. Therefore, the non-image area length M between the latent images
(= N) is M = 51.2 (mm), and the length L in the circumferential direction of the photosensitive drum corresponding to the gap between the adjacent developing units.
= 45.8 (mm), so that L <M (= N) is satisfied.

The order of the developing operation of each developing unit is, as described above, the order of the developing unit 3K, the developing unit 3R, and the developing unit 3B. Therefore, the condition of the order of the developing operation is satisfied. . Conversely, in the image forming apparatus as shown in FIG. 4, the conditions such as the length of the photosensitive drum in the circumferential direction corresponding to the gap between the adjacent developing units and the condition of the developing operation order are satisfied. The diameter and the like of the photosensitive drum 1 are determined.

However, in such an image forming apparatus, a developing device disposed at a position other than the uppermost stream and the lowermost stream,
That is, when developing the latent image for a test patch formed in the non-image area of the photosensitive drum 1 using the developing device 3K, the developing cannot be performed without the developing operations of the other developing devices being performed simultaneously. This is because the developing devices (developing devices W) arranged at positions other than the most upstream and the most downstream are performed after the developing operation of the one downstream developing device, and after the developing operation of the developing device W, Since the developing operation of the upstream developing device is performed, if the above L <M is not satisfied, there is a time zone in which the developing operations of the two developing devices are simultaneously performed. Dissatisfaction, the latent image for the test patch was transferred to the photosensitive drum 1
Is formed in the non-image area described above for the following reason.

That is, the length of the test patch in the circumferential direction of the photosensitive drum is about 20 mm from the relation of reading the test patch.
If a test patch latent image is formed before or after the black image latent image, the value of M (= N) (which is 51.2 mm) is reduced by about 20 mm to about 31.2 mm.
mm, and L <M (= N) is no longer satisfied. Therefore, the development of the test patch latent image cannot be performed unless the developing operations of the two developing units are performed at the same time.

As described above, in the image forming apparatus in which three or more developing devices are provided around the photosensitive drum, the developing device for developing the test patch latent image is provided with three or more developing devices. If the developing devices are arranged at positions other than the most upstream and the most downstream, the developing image of the test patch cannot be developed without the time period when the developing operations of the two developing units are performed simultaneously. Existed.

An object of the present invention is to provide an image processing apparatus without unnecessarily increasing the size of an image carrier or reducing the output speed of an image.
An image forming apparatus capable of developing a latent image for a test patch without causing two or more developing means of three or more developing means arranged around the image carrier to simultaneously perform a developing operation. It is to provide a device.

[0023]

[0024]

The above object is achieved by an image forming apparatus according to the present invention. In summary, the present invention provides a test patch for a test patch in which three or more developing means are provided around an image carrier along the rotation direction, and a specific developing means is formed in a non-image area of the image carrier. In the image forming apparatus for developing a latent image, the specific developing unit is provided at the most upstream and / or the most downstream position in the rotation direction of the image carrier, and the developing order of the developing unit is set to a direction toward the upstream of the image carrier. 2
An image forming apparatus, wherein two or more developing units are prevented from operating simultaneously. According to one embodiment of the present invention, the developing operation of the most downstream developing means is performed after the developing operation of the most upstream developing means. According to another embodiment of the present invention, the non-image area between images when developing by the adjacent developing means is longer than the circumference of the image carrier between the adjacent developing means. According to still another embodiment of the present invention, the test patch latent image is formed in a non-image area between a latent image for the most upstream developing unit and a latent image for the most downstream developing unit.

[0025]

[0026]

[0027]

Embodiment 1 FIG. 1 is a sectional view showing a main part of an image forming apparatus according to an embodiment of the present invention. In this embodiment, a blue developing device 3B, a red developing device 3R, and a black developing device 3K are arranged from the upstream side in the rotation direction of the photosensitive drum 1, and the developing operation is performed in the following order. The point is a big feature. Other configurations and operations of this embodiment are basically the same as those of the conventional image forming apparatus described with reference to FIG. 4, and therefore, in FIG. 1, the same members as those in FIG. Omitted.

The blue developing device 3B, the red developing device 3R, and the black developing device 3K disposed around the photosensitive drum 1 use a two-component developer composed of a toner and a carrier. The mixing ratio T of the toner (T) and the carrier (C) of each developer is supplied to the developing device 3R for blue and the developing device 3B for blue.
/ C for detecting A / C.
The TR head irradiates the developer with infrared light and detects the T / C ratio from the amount of reflected light.

As the red developer and the blue developer, the red toner and the blue toner reflect infrared light and the carrier absorbs the infrared light. Since the black toner contains carbon, the black toner and the carrier both absorb infrared light, and this detection method cannot be adopted.
Therefore, only the black developing device 3K employs a method of forming a test patch composed of a toner image in a non-image area of the photosensitive drum 1 and detecting the T / C ratio from its optical density.

In this embodiment, the working order of the developing units is as follows: the developing unit for red 3R in the middle and the developing unit for blue 3
B, and the lowermost black developing unit 3K. Then, a test patch latent image is formed in a non-image area between the blue latent image and the black latent image on the photosensitive drum 1, and the test patch latent image is developed by the most downstream black developing unit 3K.

According to this, as the photosensitive drum 1 rotates, the most upstream blue developing unit 3B develops the blue latent image on the photosensitive drum 1 and develops the rear end of the latent image. Since there is enough time for the test patch latent image formed between the blue latent image and the black latent image to reach the most downstream black developing device 3K, the two developing devices 3B, 3K development work is not performed simultaneously.

As described above, in this embodiment, since the black developing device 3K for developing the latent image for the test patch is disposed at the most downstream of the three developing devices, the developing operations of the two developing devices are performed simultaneously. The development of the latent image for the test patch could be performed without being performed.

Embodiment 2 FIG. 2 is a sectional view showing a main part of an image forming apparatus according to another embodiment of the present invention. In this embodiment, a black developing device 3K, a blue developing device 3B, and a red developing device 3R are provided from the upstream side in the rotation direction of the photosensitive drum 1, and the developing operation sequence is the most upstream black developing device 3K, The red developing device 3R at the lowermost position and the blue developing device 3B at the center are arranged in this order. The test patch latent image is located in a non-image area between the black latent image and the red latent image on the photosensitive drum 1. It is characterized by being formed.

According to this, with the rotation of the photosensitive drum 1, the uppermost black developing unit 3K develops the black latent image and the test patch latent image on the photosensitive drum 1 and then sets the red latent image. Since there is enough time until the leading end of the image reaches the most downstream red developing unit 3R, the developing operations of the two developing units 3K and 3R are not performed simultaneously.

As described above, in this embodiment, since the black developing device 3K for developing the latent image for the test patch is arranged at the uppermost stream of the three developing devices, the developing operations of the two developing devices are performed simultaneously. The development of the latent image for the test patch could be performed without being performed.

Third Embodiment FIG. 3 is a sectional view showing a main part of an image forming apparatus according to a third embodiment of the present invention. In the present embodiment, a glossy black developing device 3Ka, a yellow developing device 3Y, a cyan developing device 3C, a magenta developing device 3M, and a glossless black developing device 3Kb are arranged from the upstream side in the rotation direction of the photosensitive drum 1. It is arranged. A full-color image is output using glossy black toner for black characters and glossy black toner and yellow toner, cyan toner, and magenta toner for the image portion. 5
Of the three developing devices, only the glossy black developing device 3Ka and the glossy black developing device 3Kb develop the latent image for the test patch, and the T / C ratio of these developers according to the read signal of the test patch. Is controlled.

In this embodiment, the developing operation is performed in the following order from the most downstream: the second magenta developing device 3M, the third cyan developing device 3C, the fourth yellow developing device 3Y, the most upstream glossy black Developing unit 3Ka, the most downstream glossy black developing unit 3
Kb. In the non-image area between the glossy black latent image and the glossy black latent image, a glossy black test patch latent image and a glossy black test patch latent image are formed in this order.

According to this, after the most upstream glossy black developing unit 3Ka develops the glossy black latent image and the test patch latent image, the glossy black test patch latent image is formed. Since there is enough time to reach the lowermost glossy black developing device 3Kb, the two developing devices 3Ka, 3K
The developing operation of b is not performed at the same time.

As described above, in this embodiment, the two developing units 3Ka and 3Kb for developing different test patch latent images, respectively, are used.
Are arranged at the uppermost stream and the lowermost stream, so that the test patch latent image can be developed without performing the developing operations of the two developing units at the same time.

As described above, according to the first to third embodiments, among the three or more developing means disposed around the image carrier, the non-image Since the developing means for developing the latent image of the test patch formed in the area is located at the most upstream and / or the most downstream in the rotation direction of the image carrier, the size of the image carrier is unnecessarily enlarged or the image output is performed. The latent image of the test patch can be developed without reducing the speed and without performing the developing operations of two or more developing units at the same time.

[0041]

[0042]

[0043]

[0044]

[0045]

[0046]

[0047]

[0048]

[0049]

[0050]

[0051]

[0052]

[0053]

[0054]

[0055]

[0056]

[0057]

[0058]

[0059]

[0060]

[0061]

[0062]

[0063]

[0064]

[0065]

[0066]

[0067]

[0068]

[0069]

[0070]

[0071]

[0072]

[0073]

[0074]

[0075]

[0076]

As described above, according to the present invention,
Of the three or more developing units arranged around the image carrier, a developing unit that develops a latent image of a test patch formed in a non-image area of the image carrier in addition to the latent image of the image, Since it is located at the most upstream and / or the most downstream in the rotation direction of the image carrier,
It is possible to develop the latent image of the test patch without unnecessarily increasing the size of the image carrier or reducing the output speed of the image, and without simultaneously performing the developing operations of two or more developing units. it can.

[0077]

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a main part of an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view illustrating a main part of an image forming apparatus according to another embodiment of the present invention.

FIG. 3 is a cross-sectional view illustrating a main part of an image forming apparatus according to another embodiment of the present invention.

FIG. 4 is a cross-sectional view illustrating a main part of a conventional image forming apparatus.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 photosensitive drum 3 developing device 3B developing device for blue 3K developing device for black 3R developing device for red 4 transfer drum

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Claims (4)

(57) [Claims] 1. A latent image for a test patch in which three or more developing means are provided around an image carrier along a rotation direction thereof, and a specific one of the developing means is formed in a non-image area of the image carrier. In the image forming apparatus, the specific developing unit is provided at the most upstream and / or the most downstream position in the rotation direction of the image carrier, and the developing order of the developing unit is two in a direction toward the upstream of the image carrier. An image forming apparatus wherein the above-mentioned developing means are prevented from operating simultaneously. 2. The image forming apparatus according to claim 1, wherein the developing operation of the most downstream developing means is performed after the developing operation of the most upstream developing means. 3. The image forming apparatus according to claim 1, wherein the non-image area between the images when the image is developed by the adjacent developing means is longer than the peripheral length of the image carrier between the adjacent developing means. Image forming device. 4. The test patch latent image is formed in a non-image area between a latent image for the most upstream developing unit and a latent image for the most downstream developing unit. 3. The image forming apparatus according to 2.