JPS6388579A - Image forming device - Google Patents

Abstract

PURPOSE:To eliminate color irregularity by specifying the width of the variation rate of the rotating speed of a latent image carrier. CONSTITUTION:A speed reducer 19 is a speed reducer made of a one-stage worm gear with a 1:15 speed reduction ratio. A motor 18 uses a synchronous motor and the rotating speed of the motor itself is nearly unchanged. An irregularity of the rotation of a latent image carrier 1 results from the improper setting of the speed reducer and the majority of variation in the rotating speed of the speed reducer occurs to speed reducers consisting of plural-stage gear trains. For the purpose, this speed reducer 19 is composed of one state of a worm gear, so rotational variation is extremely small. When irregularity in image density is investigated with respect to the permissible value of a rotating speed variation rate, it is inconspicuous with the naked eye within a range of + or -2.6%.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to image forming apparatuses such as copying machines and printers that apply electrophotography.

BACKGROUND ART Conventionally, in this type of image forming apparatus, a rotatably supported cylindrical photoreceptor is used as a latent image carrier that carries a latent image. Specifically, with the photoreceptor and 1
Materials such as e-Te and a-5i are used. As a developing device for developing this latent image, a developing device such as a magnetic brush method is well known. Alternatively, recently, a non-contact developing method has been proposed as a developing device for a color image forming apparatus, in which development is performed by causing charged toner to fly under the action of an electric field, in place of the magnetic brush developing method, which is a contact developing method.

This non-contact development method develops toners of multiple colors on a photoreceptor, and then transfers these toner layers onto paper all at once, so a transfer drum etc. is not required. It is attracting attention as the device becomes smaller and smaller. For example, Japanese Patent Laid-Open No. 60-95456 discloses an image forming apparatus using such a developing method.

FIG. 3 shows the configuration of a similar digital copying machine.

Reference numeral 1 denotes a cylindrical latent image carrier, which rotates in the direction of the arrow. 2 is a charger for charging the surface of the latent image carrier 1; 3 is a BD array for exposing the latent image carrier 1 to image signals; 4.5.6 is a developing device having toner of Y, M, and C colors, respectively, and the toner is carried on the surface of a rotatable cylindrical roller 7.8.9.

The toner carried on the roller 7.8.9 is kept out of contact with the latent image carrier, and the toner is kept in contact with the latent image carrier.
Due to the effect of the electric field generated in the gap between the latent image carrier 1 and the rollers 7, 8, 9, the particles fly and adhere to the exposed areas on the latent image carrier, thereby developing the latent image.

Reference numeral 13 denotes a cleaning device for removing toner remaining on the latent image carrier. 14 is a transfer paper, 15 is a pair of registration rollers, 16 is a transfer charger, and 17 is a static eliminator. Further, the transfer paper 14 is conveyed in the direction of the arrow along a predetermined conveyance path (not shown). Reference numeral 18 denotes a synchronous motor for rotationally driving the latent image carrier 1, rollers 7, 8, 9, registration rollers 15, and the like. Since this motor 18 normally rotates at a rotation speed of around 1800 r, p, m, several tens of revolutions are transmitted from the output shaft of the reducer through a reducer 19 having an appropriate reduction ratio. The number of revolutions is increasing. The speed reducer 19 has a spur gear train structure. This type of reducer is easily available as a commercial item.

Also, as a matter of course, the latent image carrier 1, the rollers 7 and 8
．． Since the rotational speeds of the components 9 and the like are different from each other, they are individually driven via another reduction mechanism (not shown) after the reduction gear 19. Specifically, these reduction mechanisms are chain and sprocket drive mechanisms, and the chain is driven at a constant linear speed by the constant rotation of the output shaft of the reduction gear 19, and the rollers 7, 8, 9, and registration rollers 15 are connected to the chain. The rotational speed of these rotating parts is set to a desired value by meshing sprockets with an appropriate number of teeth fixed to, etc. Of these speed reducers, the speed reducer 19 has the largest reduction ratio, and therefore, this speed reducer is comprised of a multi-stage gear train. The other reduction gears have a one-stage chain and sprocket structure as described above. In addition,
In the figure, the dash-dotted lines connecting the output shaft of the reducer 19 and the rollers 7, 8, 9, etc. schematically indicate that their drive is taken from the output shaft of the reducer 19.

Now, the operation of this device will be briefly explained. First, during the first rotation of the latent image carrier 1, the LED array performs exposure according to the Y image signal, lowering the surface potential of that area, and then fully charging the exposed area with the Y developing device. Develop with toner (reverse development). Then, after recharging the latent image carrier 1 with the charger, in the second rotation, M is developed from above Y with the same setting ( ).Then, in the third rotation, development of M is performed from above Y and M. In this way, Y, M, and C are developed on the latent image carrier 1, and then the toner image is transferred all at once to the transfer paper.

Problems to be Solved by the Invention Now, in such a digital copying machine, the following problems have been found. For example, when thin lines are formed at regular intervals on the latent image carrier 1, as shown in FIG. As shown in the figure, unevenness in image density occurs at a nearly constant pitch. Therefore, when expressing halftones by the dithering method, if a certain intermediate color is drawn over a range exceeding the above-mentioned pitch, unevenness of color shading naturally occurs, resulting in a very unsightly image. Such unevenness also occurred in black-and-white copying machines, but black-and-white copying machines were mainly used for forming characters, and the density unevenness was simply less noticeable. However, in addition to characters, color image forming apparatuses are often used to output figures painted in a certain color, and this color unevenness has been an extremely serious problem.

The present invention aims to solve such color unevenness, which is a particular problem in color image formation.

Means for Solving the Problem The means for solving this problem is to reduce the rate of variation in the rotational speed of the latent image carrier to a certain value or less.

action The effects of this technical means are as follows.

In the process of investigating the cause of the color unevenness mentioned above, it was found that variations in the rotational speed of the latent image carrier are closely related to the color unevenness. In other words, if there is a variation in rotational speed, if the speed at which the latent image passes through the developing section is slow, the development time will be longer and the image density will be higher (darker), and if the speed is faster, the development time will be shorter. This causes the image density to become low (thin).

Also, if the speed at which the latent image carrier passes through the exposure area is fast, the surface potential of the latent image carrier does not decrease sufficiently, and therefore the image density in that area tends to be low, and conversely, if the speed is slow, the image density tends to be high. becomes. Therefore, if the rotational speed fluctuation occurs at a relatively constant period, unevenness in image density occurs at a pitch related to the period. Therefore, color unevenness can be reduced by reducing the variation in the rotational speed.

EXAMPLES Hereinafter, the present invention will be described in detail based on drawings of examples.

FIG. 1 shows an embodiment of the present invention. The same reference numerals as in FIG. 3 represent the same parts.The reducer 19 has a reduction ratio of 1/15, and has a speed of 1800 r, p, m.

A rotation speed of 120 r, p, m is obtained from the motor rotation speed. This speed reducer is different from the conventional example in that it is a speed reducer using a single stage worm gear. As is well known, the feature of the worm gear speed reducer is that the fluctuation in the rotational speed of its output shaft is extremely small compared to the conventional spur gear train speed reducer 19.

Further, the rotating parts such as the latent image carrier 1 and the registration rollers are driven at an appropriate rotational speed by a combination of a chain and a sprocket, as in the conventional example.

Now, in the conventional example shown in FIG. 3, the above-mentioned passing motor 19 uses a synchronous motor, and the rotational speed of the remoter itself hardly changes. The reason why rotational unevenness occurs in the latent image carrier 1 is because the speed reducer is inappropriately selected. In FIG. 3, a reduction gear (not shown) is also used as described above, but among these reduction gears, most of the rotational speed fluctuations are caused by the reduction gear 19. The reason is that it is composed of a multi-stage gear train.

However, in this embodiment, since the speed reducer 19 is constituted by a single-stage worm gear, rotational fluctuations are extremely small. Specifically, in the conventional principle machine, the rotational fluctuation rate is 7.2% above.
However, in this example, it was 1.2%.

As a result, in this embodiment, the rotational fluctuation rate of the latent image carrier 1 was able to be reduced to ±2.3%, whereas the conventional rate was 9.8%.

An example of an output image in this embodiment is shown in FIG.

The unevenness of image density seen in the conventional example is not observed at all with the naked eye.

Next, we investigated the allowable value of rotational speed fluctuation rate, and found that
If it is within the upper 2.6%, it will not be particularly noticeable to the naked eye.

In this embodiment, a worm gear speed reducer is used to reduce fluctuations in rotational speed, but other methods may also be used. In particular, a differential speed reducer with a -film configuration is effective. For example, the product name Harmonic Drive (T, M
The differential speed reducer known as ) is effective because it can reduce the speed by several tens of minutes in one stage and has small fluctuations in rotational speed.

Further, in this embodiment, the rotating parts such as the latent image carrier and registration rollers are driven by chains and sprockets after the motor is provided with a speed reduction mechanism. It is particularly effective to drive directly by the output without using a chain, in order to suppress fluctuations in rotational speed.

Alternatively, by directly detecting the speed fluctuation of the latent image carrier 1,
The rotational speed of the motor may be controlled to keep it constant.

Effects of the Invention As described above, according to the present invention, the rotational fluctuations of the latent image carrier or other rotating parts can be sufficiently reduced with a simple configuration, and the problems of the conventional art can be completely solved. It has an effective effect.

[Brief explanation of the drawing]

FIG. 1 is a principle diagram of an image forming apparatus according to an embodiment of the present invention, FIG. 2 is a diagram showing an image produced by the image forming apparatus of FIG. 1, and FIG. 3 is a principle diagram of a conventional image forming apparatus. , FIG. 4 is a diagram showing an image produced by a conventional image forming apparatus. 1...Latent image carrier 4.5.6...Developing device 18...Motor 19...Name of reducer agent Patent attorney Toshio Nakao Idiot 1 person 7---
Row image rod body 2-row t device 3-/LED array L5.6-1 view I#8X'y, s, q---Roller 10.17. /Z-a Flow t J I3~Cleaning

Claims (5)

[Claims] (1) including a rotatable latent image carrier carrying a latent image, a developing device for developing the latent image on the latent image carrier, and a motor for driving at least the latent image carrier; An image forming apparatus in which the variation rate of the rotational speed of a latent image carrier is 5% or less. (2) A speed reducer is connected to the motor, and rotating parts such as a latent image carrier and a registration roller are driven through an output shaft of the speed reducer, and the speed reducer connected to the motor is configured in one stage. The image forming apparatus according to claim 1, which is a speed reducer. (3) The image forming apparatus according to claim 2, wherein the speed reducer is a worm gear. (4) The image forming apparatus according to claim 2, wherein the speed reducer is a one-stage differential speed reducer. (5) The image forming apparatus according to claim 2, 3, or 4, wherein the motor is provided with a speed reducer, and the latent image carrier is directly driven by the output shaft of the speed reducer. .