JPH1035943A - Sheet material carrying device and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To ensure the precise carrying of a sheet material and prevent the deterioration of an image such as wrinkle, image flow or the like to transfer materials having every possible characteristic of thickness, size, material, image, density and the like by providing a control means for controlling the sucking force of a carrying means. SOLUTION: A sheet material carrying device 90 is formed of a suction fan 91 and a carrying motor which are carrying means, a carrying belt 92, and a guide 94. The carrying belt 92 is formed of a rubber-like belt laid over the carrying guide 94, and it has a number of suction ports. A transfer material is carried on the carrying belt 92, and at this time, it is sucked to the belt 92 by a suction duct provided on the guide 94 and a suction fan 91 provided under the carrying belt. This sucking force provide a stable carrying force to the transfer material. The suction fan 91 is controlled in the sucking force of the transfer material by a suction fan control device as control means. Thus, the precise carrying of a sheet material can be ensured.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sheet conveying apparatus and an image forming apparatus having a sheet conveying apparatus between an image forming section and an image fixing section. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus, and more particularly to a multicolor electrophotographic image forming apparatus in which an image forming section such as a plurality of electrophotographic photosensitive members is provided and an image of each color is transferred by these to form a color image.

[0002]

2. Description of the Related Art Conventionally, from the viewpoint of protecting the surface of a sheet material to be conveyed, a suction fan or an electrostatic attraction or the like is used in this type of sheet material conveying device to protect the surface of the sheet material to be conveyed. There is provided a transporting means for transporting while sucking.

In particular, in an electrophotographic image forming apparatus such as a conventional electrophotographic copying apparatus, when a transfer material on which an unfixed image is mounted is conveyed to a fixing section, vibrations and the like are generated from the fixing section. If the transfer material is directly conveyed from the image forming unit to the fixing unit at this time, a shock may be transmitted to the transfer material during image formation, causing a decrease in the accuracy of image formation. Becomes In order to prevent this, it is necessary to provide an independent sheet material conveying device between the image forming unit and the fixing unit. At this time, in order to prevent deterioration of the unfixed image, There is used a sheet material conveying device provided with a conveying means for conveying while sucking only the sheet material.

On the other hand, some recent image forming apparatuses include:
There are many materials that can transfer an image to a transfer material of any material, material, thickness and size. Not only plain paper (about 50 to 100 g / m ² basis weight) but also thick paper ( (Basis weight about 100 to 300 g / m ² ), OH
Transparent films for overhead projectors (hereinafter referred to as trappen) called P paper are also frequently used.

The size of the transfer material (paper feed direction and
Width) is also available in all sizes.

Further, in a color image forming apparatus for forming images of a plurality of colors, due to its characteristics, the image density is
Compared to the case of black and white, the amount of toner used is large, and images of all densities are assumed.

On the other hand, in the above-mentioned conventional sheet conveying apparatus, the attraction force is always set as large as possible irrespective of the characteristics and state of the sheet. this is,
This is because it is necessary to ensure the transportability of the transfer material that requires the most suction force, for example, thick paper such as thick paper. This is because relatively high suction force is required for OHP paper and postcards. It was effective for various materials.

[0008]

However, the above conventional example has the following disadvantages.

That is, a thin sheet material (for example, having a basis weight of 60
g / m ² or less), etc., when suction is performed on thick paper with an appropriate high suction force, the sheet material is subjected to excessive force during conveyance due to the strong suction force and is conveyed properly. I couldn't do that. For example, in an image forming apparatus, the transport direction and the transport speed are inevitably changed when entering the fixing unit, and when the suction force of the transport unit is high, a large restraining force acts to generate a stress on the transfer material. Then, wrinkles or image flow occurred.

As described above, since the appropriate suction force differs depending on the difference in the thickness of the sheet material, a problem has occurred unless the sheet material conveying device is adapted to this. Not only the difference in thickness, but also the appropriate suction force varies depending on the material and size, and furthermore, the appropriate suction force varies depending on the image density on the transfer material. Similar problems have been found to occur.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above problems and to provide a sheet material conveying device which ensures proper conveyance of a sheet material. An object of the present invention is to provide an image forming apparatus with high image quality by preventing the occurrence of image deterioration such as wrinkles and image deletion on a held transfer material.

[0012]

In order to achieve the above object, the present invention is characterized in that control means for controlling the suction force of the conveying means is provided.

[0013] This makes it possible to change the attraction force of the conveying means depending on the state and characteristics of the sheet material, thereby enabling proper conveyance of the sheet material.

It is also preferable that the transport means is a transport means for transporting the transfer material while sucking it by air suction, whereby the control of the suction force can be easily and reliably performed.

It is also preferable that the transfer means is a transfer means for transferring the transfer material while sucking the transfer material by an electrostatic suction method, whereby the transfer material can be transferred with little noise.

An image forming section for forming an unfixed image on a transfer material, a fixing section for fixing an image to be transferred formed on the transfer material, and a transfer material from the image forming section to the fixing section. And an image forming apparatus having a conveying section, wherein the sheet conveying apparatus is used for the conveying section.

Thus, even when the sheet enters the fixing section, the transfer material and its image can be properly conveyed without being damaged.

The control means is a control means for controlling the attraction force according to the characteristics of the transfer material to be conveyed, whereby the control means has an appropriate attraction force corresponding to a transfer material having all characteristics. The transfer material can be transported, and the quality of the transfer material and its image can be maintained.

It is preferable that the characteristics of the transfer material include the size of the transfer material. In this case, the size of the transfer material is
Above a certain size, the adsorption power will be low,
In addition, if the size of the transfer material is smaller than the predetermined size, if the suction force is controlled to be high, the transfer material having a size that receives both the conveyance force of the image forming unit and the conveyance force of the fixing unit may be unnecessarily large. The transfer material is conveyed without applying a suction force, and when the size is smaller than the transfer material, the transfer material is conveyed while adsorbing with a suction force that can be sufficiently conveyed by only the sheet material conveyance device.

It is preferable that the characteristics of the transfer material include the thickness of the transfer material. In this case, if the transfer material is thick, the suction force is increased, and if the transfer material is thin, the suction force is controlled to be low. Transfers the transfer material,
In the case of a transfer material having a weak stiffness, the transfer material is conveyed without deteriorating the quality of the transfer material so that excessive force is not applied during the conveyance.

The characteristics of the transfer material preferably include the material of the transfer material. Thus, for example, in the case of plain paper and OHP sheet having exactly the same other characteristics, the transfer material is transported while being suctioned with an appropriate suction force according to the stiffness and mass of the transfer material.

It is preferable that the characteristics of the transfer material include the density of an image to be transferred of the transfer material. This focuses on the fact that the characteristics of the transfer material after transfer differ depending on the density of the transferred image, even if the characteristics of the transfer material before transfer are completely the same. For example, the density of the transferred image is high. In such a case, if the suction force of the conveying means is controlled to be high, and if the suction force is low, the transfer image density is high.
When the transfer material becomes heavy and firmly needs to be conveyed, the transfer material is conveyed by firmly adsorbing it. When the density of the transferred image is low, the transfer material does not become stiff and does not impair the quality of the transfer material. As described above, the conveyance is performed with the suction force suppressed.

The image forming section has an image forming medium, and detecting means for detecting the density of a latent image formed on the image forming medium, and the density of the transferred image is obtained by the detecting means. It is also preferable to make a determination based on the detection result.

Further, an image forming medium is provided in the image forming section.
A detection unit for detecting the density of a visible image formed after development on the image forming medium, and it is preferable that the density of the transferred image is determined based on a detection result obtained by the detection unit.

It is also preferable that the density of the transferred image is detected by detecting the density of the image formed on the transfer material on the conveying means with a photodetector.

It is also preferable to determine the density of the transferred image from the density of the original image.

It is also preferable that an output image density selecting means is provided on the main body of the image forming apparatus, and the density of the transferred image is determined based on an input signal from the selecting means.

As a result, the density of the transferred image can be detected and determined by various means, and an appropriate suction force can be determined accordingly.

In the image forming section, a plurality of image forming media are provided side by side, images are formed on the image forming media, and the images are sequentially superimposed on a transfer material conveyed by a transfer material conveying device. It is also preferable that the transfer is performed, and then the transfer material is transported to the fixing unit via the transport unit, and the image is fixed on the transfer material at the fixing unit.

Thus, also in the multicolor image forming apparatus, the suction force of the conveying means can be controlled depending on the characteristics of the transfer material, and a multicolor image forming apparatus with high image quality can be provided.

[0031]

Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. However, the dimensions of the components described in this embodiment,
The material, shape, relative arrangement, and the like are not intended to limit the scope of the present invention unless otherwise specified. [First Embodiment] FIG. 1 is a schematic configuration diagram of a sheet conveying apparatus according to a first embodiment of the present invention.

The sheet conveying device 90 includes a suction fan 91 as conveying means, a conveying motor (not shown), and a conveying belt 9.
2. Consists of a guide 94. The transport belt 92 is a belt made of a rubber-like material, which is stretched over a transport guide 94, and has a large number of suction holes. The transfer material P is transported on the transport belt 92. At this time, the transfer material P is attracted to the belt 92 by a suction duct (not shown) provided on the guide 94 and a suction fan 91 provided below the transport belt.

The transfer material can obtain a stable conveyance force by the suction force. Here, the suction fan 91 has a suction force of the transfer material controlled by a suction fan control device (not shown) as a control unit. Specifically, in this embodiment, a DC brushless motor is used as the suction fan. A fan is used, and the suction force is controlled by the applied voltage. [Embodiment 2] Next, as an example of an image forming apparatus according to the present invention, an electrophotographic copying apparatus using the above-described sheet material conveying apparatus will be described. FIG. 2 shows a schematic configuration diagram thereof.

In FIG. 2, a primary charger 2, an exposure unit 3 such as a laser beam exposure device, a developing unit 4, a transfer discharger 6 are provided around a photosensitive drum 1 as an image forming medium.
A cleaner 12 and the like are provided, and an image forming unit is formed as a whole.

The image formed on the photosensitive drum 1 is transferred to a transfer material P fed from a paper feeder 20 under the action of a transfer discharger 6. The transfer material P having completed the transfer is conveyed to a sheet material conveyance device 90 as a conveyance unit. The transfer material conveyed by the sheet material conveyance device 90 is then conveyed to the fixing device 9 as a fixing unit, and the transfer image is fixed on the transfer material. The residual developer is removed from the photosensitive drum 1 after the transfer by the cleaner 12 and the next image forming process is performed.

At this time, the conveying speed V1 of the image forming unit, the conveying speed V2 of the sheet material conveying device, and the conveying speed V3 of the fixing unit
Is substantially constant speed, but considering the influence of the transfer material P on the image, it is configured to be exactly V1>V2> V3. As a result, the transfer material P forms a certain amount of loop between the image forming section, the transport section, and the fixing section, thereby preventing the transfer material from being pulled.

Next, a description will be given of a control means for controlling the attraction force of the conveying means in accordance with the thickness of the transferred transfer material as the control means of the sheet conveying apparatus used in the image forming apparatus according to the present embodiment. I do.

In the image forming apparatus according to the present embodiment, the control means detects the thickness information of the transfer material, and the control device (not shown) compares the thickness information with the preset reference thickness information. It is constituted by a series of means for comparing and determining the applied voltage of the suction fan.

For example, assuming that the voltage applied to the suction fan 91 in the normal state is a voltage (V), when the transfer material P is about the normal thickness, the transfer material P is applied with the value a as it is. As a result, the transfer material P is provided with a normal suction force, and is appropriately conveyed from the image forming unit to the conveying unit to the fixing unit.

When it is determined that the transfer material P is thinner than the normal thickness, for example, when it is determined that the transfer material P is thinner than 50 μm, the control device (not shown) changes the voltage applied to the suction fan 91 to the normal voltage a. Control is performed such that the value b becomes lower than that of (V). As a result, the transfer material P is conveyed on the sheet material conveying device with a lower suction force than in a normal case. At this time, as described above, the suction force is a relatively low value as compared with the normal thickness, but a sufficient suction force is set for the conveyance of the thin transfer material conveyed at this time. Of course.

As a result, the transfer to the fixing device is optimized, and image deterioration such as wrinkles and image deletion is eliminated.

Normally, in the apparatus according to the present embodiment, the thickness information of the transfer material is obtained by input information from an operator from an operation unit, an automatic thickness detecting means, or the like. Here, the automatic thickness detecting means will be described with reference to FIG. FIG. 3 is a schematic diagram of a transfer material thickness detecting unit. FIG. 4 is a flowchart showing the operation in this case.

In FIG. 3, reference numerals 51 and 52 denote a pair of rollers for holding and transporting the transfer material, 51 a transport roller, and 52 a pressure roller. Reference numeral 53 denotes a transmission type photosensor disposed upstream of the roller pair in the transfer material transport direction, and detects the leading end of the transfer material by blocking the optical path of the transfer material.

Each roller pair is provided with a gear 54 that rotates integrally with the roller at the axis width thereof. Since the pitch circle diameter of the gears is substantially equal to the outer diameter of each roller, they mesh with each other, and the phase relationship in the rotational direction of each roller is always constant. The gear 54 is provided with a drive source 55 for driving the rollers 51 and 52. The rollers 51,
Numeral 52 is supported by a support member 57 via a bearing 56. In particular, the pressure roller 52 is supported so as to be movable only in the direction of arrow a, and both ends of the pressure roller 52 are pressed in a direction in which the spring 58 presses the conveying roller 51. Being energized.

Both rollers are made of metal to prevent deformation. Further, when the transfer material is held between the rollers, the eccentricity of the pair of rollers causes an error at the time of measurement, so that the processing needs to be performed with extremely high precision. For example, each roller is 20 μm
This is because, when the rollers are eccentric each other, when the roller pair is formed, the axial distance between the two rollers changes at a maximum of ± 40 μm depending on the phase, so that it is difficult to distinguish between the transfer materials of 100 μm and 200 μm.

A reflection type photosensor 59 is attached to the support member 57 of the transport roller 51. The sensor irradiates infrared light toward a shaft end of the pressure roller 52 with a light emitting element, and receives a reflected light reflected by the light receiving element by a light receiving element, thereby outputting a voltage corresponding to the amount of reflected light. In this case, an output voltage substantially proportional to the distance between the roller pair is obtained from the sensor. However, when trying to measure the displacement of a cylindrical object such as a roller, a mounting error of the sensor affects the measured value. Increasing the diameter of the roller in order to reduce the curvature of the roller is not preferable because it increases the size of the apparatus. Therefore, when the sensor has a light emitting element and a light receiving element, the light emitting element and the light receiving element are arranged in the axial direction. The output from the sensor is converted into a digital signal by an AD converter 61 and then sent to a central processing unit (CPU) 60.

When such a thickness detector is used, a flowchart thereof will be briefly described with reference to FIG.

When the sensor 53 detects the transfer material (S
1) The drive source starts operating (S2), and after a lapse of a predetermined time, reads the output value of the sensor 59 (S3, S4). After reading the predetermined number of times, the values are averaged (S5, S5
6) Determine the magnitude of the average value and a predetermined value. For example, assuming that the predetermined value is 50 μm in this case, the voltage b (V) is applied if the predetermined value is less than that, and the voltage a (V) is applied if it is more than that. [Third Embodiment] As a control means of a sheet material conveying device in an image forming apparatus according to the present embodiment, a control means for controlling a suction force of a conveying means in accordance with a size of a transferred transfer material will be described.

The other components of the image forming apparatus are the same as those of the second embodiment, and the description is omitted.

The image forming apparatus according to the present embodiment is configured such that a control device (not shown) compares the size information of the transfer material with the preset size information to determine the voltage applied to the suction fan. I have.

That is, when the length of the transfer material in the transport direction is equal to or more than a certain length, the suction force is set low, and
When the size is less than a certain length, the suction force is set to be high. Although the threshold value differs depending on the arrangement of transfer and fixing of the apparatus, the certain length here refers to the conveyance force of the image forming unit and the fixing unit even if the suction force of the sheet material conveyance device is low. Is the length that can transfer the transfer material. Conversely, when the size is equal to or less than a certain length, that is, when the size cannot be conveyed only by the conveyance force of the image forming unit and the fixing unit, the suction force is set to be high.

For example, assuming that the voltage applied to the suction fan 91 at normal time is a voltage (V), the length L (hereinafter referred to as the length of the transfer material) of the transfer material P in the transport direction becomes a predetermined value LL. If it is determined to be shorter, the voltage is applied with the value a as it is. As a result, the transfer material P is provided with a normal suction force, and is appropriately conveyed from the image forming unit to the conveying unit to the fixing unit.

The transfer material length L is a predetermined value L
If it is determined that the voltage is longer than L, the control device (not shown) changes the voltage applied to the suction fan 91 to the normal voltage a (V).
Is controlled so as to have a lower value b as compared with. As a result, the transfer material P is conveyed on the sheet material conveying device with a lower suction force than in a normal case. With respect to the conveyance of the transfer material (paper longer than a certain length LL) conveyed at this time, since the conveyance force of the image forming unit and the fixing unit is applied, the transfer material is sufficiently stably conveyed even with such a low suction force. At this time, if the transfer material is conveyed with a high suction force, a severe stress acts on the transfer material, causing wrinkles or an unfixed image to flow.

That is, by performing the above-described control, an appropriate suction force can be obtained based on the size information of the transfer material P, so that the transfer to fixing is optimized, and image deterioration such as wrinkles and image deletion is eliminated.

Normally, in the apparatus as in the present embodiment, the paper size information can be easily obtained from the input information from the operator from the operation section or the automatic paper size detecting means. The details thereof are well known to those skilled in the art, and thus description thereof is omitted in the text. [Fourth Embodiment] As a control means of a sheet material conveying device used in the image forming apparatus according to the present embodiment, a control means for controlling the attraction force of the conveying means in accordance with the material of the transferred transfer material will be described. .

The other components of the image forming apparatus are the same as those of the second embodiment, and the description is omitted.

The image forming apparatus according to this embodiment compares the material information of the transfer material with a look-up table in which material information set in advance is written by a control device (not shown), and applies the voltage applied to the suction fan. To determine.

As a result, an appropriate suction force can be obtained according to the type of the transfer material P, so that the transfer to the fixing is optimized, and image deterioration such as wrinkles and image deletion is eliminated.

Normally, in the apparatus as in this embodiment, the information on the material can be obtained from the input information from the operator from the operation section or from the automatic material detecting means such as the OHP detecting means. . [Fifth Embodiment] As a control unit of a sheet material conveying device in an image forming apparatus according to the present embodiment, a control unit that controls an attraction force of a conveying unit in accordance with a density of a transferred image of a conveyed transfer material will be described. I do.

The other components of the image forming apparatus are the same as those of the second embodiment, and the description is omitted.

Several methods for determining the density of a transferred image will be described below.

First, the case where the density of the transferred image is determined by detecting the density of the latent image formed on the image forming medium will be described.

The density of the latent image on the image forming medium is, for example,
It is detected by measuring the surface potential on a photosensitive drum as an image forming medium. The surface potential value obtained thereby is compared with a potential value with respect to a preset reference density to determine the density of the transferred image.

Next, a case where the density of a transferred image is determined by detecting the density of a visible image formed after development on an image forming medium will be described.

The density of the visible image on the image forming medium can be determined by, for example, irradiating a toner image as a visible image on a photosensitive drum as an image forming medium with light, collecting the reflected light with a lens, and receiving the reflected light with a CCD sensor. , Based on the output signal from the CCD sensor. The resulting concentration,
The density of the transferred image is determined by comparing the density with a preset reference density.

Next, a case in which the density of an image to be transferred is directly detected from an unfixed image of a transfer material will be described.

The density of the unfixed image of the transfer material is determined by a detecting device provided between the image forming section and the sheet material conveying device.

FIG. 5 shows an example of the configuration. In FIG. 5, reference numeral 70 denotes an image density detecting device. 71 is a CCD sensor, 72 is a lamp as a light source, and 73 is a condenser lens. Image density (luminance) information is read by a CCD sensor provided above the transfer material transport path. The CCD sensor is a linear sensor that converts an optical signal into an electric signal, and is generally used in a facsimile or the like, and is similar to a known image reading sensor. The light transferred from the light source 72 is irradiated onto the image transferred onto the transfer material, and the reflected light is received by the sensor 71 by the condenser lens 73, and is transferred by the output signal from the sensor 71 obtained based on the reflected light amount. The density (luminance) of the on-material image is detected. The control unit (not shown) compares the density with a preset reference density and makes a determination.

Next, a case where the density of a transferred image is determined from the density of a document image will be described.

The original image density is measured by irradiating the original with light, collecting the reflected light with a lens, receiving the light with the CCD sensor, and detecting the output signal from the CCD sensor in the same manner as in the case of using the CCD sensor. I do. In this case, detection is generally performed together with the document reading operation. Based on the output signal from the CCD sensor obtained in this way, the density on the transferred image is compared with a preset reference density to determine the transferred density.

Finally, the case where the transfer image density is determined from the input signal from the output image density selecting means will be described.

When the output density desired by the user is input to the output image density selection means provided on the image forming apparatus main body, the density of the image to be transferred is determined from the input signal.

The various cases in which the density of the image to be transferred is determined have been described above. The sheet conveying device is controlled from the image to be transferred as follows.

For example, the density of the transferred image determined as described above is compared with a reference density value previously written in a memory in the main unit by a control device (not shown), and it is determined that the image is a reference density image. Then, a signal from the detection unit is transmitted to a drive control unit (not shown) of the sheet material conveying device 90, and the applied voltage of the suction fan 91 is controlled by the control device. Is applied.

When the transferred image density is higher than the reference density and is determined to be higher, the suction fan is configured so that the applied voltage is higher than that in the normal state. Thus, the transfer material on which the high-density image has been transferred is transported between the image forming unit, the transporting unit, and the fixing unit by a stronger suction force than usual.

On the other hand, when it is determined that the density of the transferred image is lower than the reference density, the suction fan is configured so that the applied voltage is lower than that in the normal state. As a result, the transfer material on which the low-density image has been formed can be transferred from the image forming unit to the transporting unit due to a weaker suction force than normal.
The sheet is transported between the fixing units.

As a result, optimal suction fan control according to the image density, that is, appropriate conveyance can be performed, and image deterioration, rubbing, wrinkling, and the like can be prevented.

As described above, in each embodiment, the case where the control is performed based on the single information of the thickness information, the size information, the material information, and the image density information has been described. Such information formed in such an image forming apparatus is expected to be all, and all such information is combined.

Therefore, it is needless to say that the above-mentioned set value of the suction force of the suction fan depends on the degree of each other, and fine variable control is required. That is, according to the thickness, size, material, and image density information obtained by each of the information detection means described above, the most suitable voltage applied to the suction fan for each transfer material is input in advance in the memory, Alternatively, it is needless to say that it is convenient to make a configuration that can be determined on the spot from each information and strictly controlled by controlling the applied voltage.

Further, in particular, if the detection means of the above configuration is insufficient for accurate determination of a special transfer agent, a special image, for example, an image having an extremely uneven density or an extremely thick transfer material, etc. Or, if it is not possible, instead of the detecting means having the above configuration as the detecting means, or as a replenishing means, the operator manually sends a signal to each device from, for example, an operation panel, the control device of each device. It is also possible to configure so as to be able to input to. [Embodiment 6] FIG. 6 shows a laser beam printer for multicolor copying by an electrophotographic system using a sheet material conveying device as an example of an image forming apparatus according to the present invention. The full-color laser beam printer in the present embodiment is
Four image forming units are arranged, each image forming unit has a photosensitive drum 1a, 1b, 1c, 1d as an image forming medium, and around it, dedicated image forming process means,
For example, chargers 2a, 2b, 2c, 2d, laser beam exposure means 3, developing units 4a, 4b, 4c, 4d, transfer unit 6
a, 6b, 6c, 6d, cleaning units 12a, 12
b, 12c, 12d and the like are provided.

The photosensitive drums 1a, 1b, 1c, 1d are driven by a drive motor (not shown), and are rotated below the photosensitive drums 1a, 1b, 1c, 1d so as to penetrate the respective image forming sections. A moving body, that is, a transfer material transporting device 7 having an endless belt 8 is arranged. The transfer material P is fed to the transfer material transporting device 7 by the paper feeding device 5, and is configured to be transported in the arrow direction through the transfer units 6a, 6b, 6c, and 6d of each image forming unit.

In such a configuration, first, a visible image of yellow toner is formed in the first image forming portion Pa, and the transfer portion, that is, the transfer position, is formed on the transfer material P conveyed by the transfer material conveying device 8. At 8a, a yellow toner image is transferred. On the other hand, while the yellow image is being transferred to the transfer material P, an image using magenta toner is obtained in the second image forming unit, and the transfer material P, which has been transferred in the first image forming unit, is the second image. When carried into the transfer position 8b of the forming section,
This magenta toner image is transferred to a predetermined position on the transfer material P.

Thereafter, in the third and fourth image forming sections, images are formed for cyan and black, and the toner images of four colors are superimposed on the transfer material P.

In this image forming operation, the conveying speed of the endless belt 8 is set to be equal to the peripheral speed of each of the photosensitive drums 1a, 1b, 1c, 1d. Is prevented from occurring.

When the transfer process is completed, the transfer material P is conveyed to the sheet material conveyance device 90 by the endless belt 8 of the transfer material conveyance device 7. The transfer material conveyed while being sucked by the sheet material conveyance device 90 with the controlled suction force is then conveyed to the fixing device 9 as a fixing unit, and the transfer image is fixed on the transfer material.

At this time, the transport speed V1 of the endless belt 8
The conveying speed V2 of the conveying belt, the fixing roller pair 1 of the fixing device
Although the relationship between the conveying speeds V3 of 0 and 11 is configured to be substantially constant, considering the effect on the image of the transfer material P, usually, V1> V2.
> V3. As a result, the transfer material P forms a certain amount of loop between the image forming section, the transport section, and the fixing section, thereby preventing the transfer material from being pulled. The transfer material P is fixed by the fixing device 9, and a multicolor (full color) image is obtained on the transfer material P.

After the transfer, each of the photosensitive drums removes the residual toner by the cleaning units 12a, 12b, 12c, and 12d, and prepares for the subsequent latent image formation.

The configuration and operation of the sheet conveying device 90 are the same as those of the first embodiment, and therefore, the description thereof is omitted.

As described in the second to fifth embodiments, the voltage applied to the suction fan is controlled based on the information on the thickness, size, material, and image density of the transfer material.

In a device such as this embodiment, in which a plurality of images are superimposed on a transfer material, the suction force of the suction fan is controlled by the nature of the device, particularly, the image density on the transfer material. Is valid.

[Other Embodiments] In the above-described embodiments, the suction conveyance of the sheet material conveyance device by the suction fan has been described. Similarly, a stable operation from the image forming section to the fixing section is performed. The present invention is not limited to this embodiment as long as it is a means for achieving the transfer of the transfer material. For example, an apparatus for sucking and transferring the transfer material by the electrostatic suction means is also described with respect to the suction force. It goes without saying that such control can be realized. Although the case where only the suction force is controlled in the sheet material conveyance device has been described, the suction force and the conveyance force of the conveyance motor may be simultaneously controlled.

[0092]

According to the present invention, since the control means for controlling the attraction force of the conveying means is provided, the attraction force of the conveying means can be changed according to the state and characteristics of the sheet material, and the proper conveyance of the sheet material can be achieved. It is possible. Further, if the transfer means is a transfer means for transferring the transfer material while sucking the transfer material by air suction, it is possible to easily and reliably control the suction force. If the transfer unit is a transfer unit that transfers the transfer material while sucking the transfer material by an electrostatic suction method, the transfer material can be transferred with little noise. An image forming unit that forms an unfixed image on a transfer material, a fixing unit that fixes an image to be transferred formed on the transfer material, and a transport unit that transports the transfer material from the image forming unit to the fixing unit. In the image forming apparatus having
Since the above-described sheet material conveyance device is used for the conveyance unit, conveyance from the image forming unit to the fixing unit is appropriately performed, and wrinkles,
It is possible to provide an image forming apparatus with high image quality, which can prevent problems such as image deletion and image rubbing, and can always carry optimal transfer material, and can always obtain good quality images. is there.

Since the control means is a control means for controlling the attraction force in accordance with the characteristics of the transfer material to be conveyed, transfer with an appropriate attraction force is also possible for transfer materials having all characteristics. The material can be conveyed, and the quality of the transfer material and its image can be maintained. When the size of the transfer material is included in the characteristics of the transfer material, if the size of the transfer material is equal to or more than a certain size, the attraction force is reduced, and if the size of the transfer material is less than the certain size, In the case of a transfer material of a size that can be controlled to increase the suction force and receives both the conveyance force of the image forming unit and the conveyance force of the fixing unit, the transfer material can be conveyed without applying unnecessary suction force. In the case of a smaller size, the transfer material can be conveyed while adsorbing with a sufficient conveyable force by only the sheet material conveying device. Accordingly, the transfer of a large-sized transfer material is performed appropriately, and the occurrence of image deterioration such as wrinkles and image deletion can be prevented.

When the characteristics of the transfer material include the thickness of the transfer material, it is possible to control the suction force to be high when the transfer material is thick, and to be low when the transfer material is thin.
When sufficient force is required to convey the transfer material, firmly adsorb it to transfer the transfer material.For thin, stiff transfer material, make sure that excessive force is not applied during transfer. The transfer material can be conveyed without deteriorating the quality. This allows
The transfer of a thin transfer material is also properly performed, and the occurrence of image deterioration such as wrinkles and image deletion can be prevented.

If the characteristics of the transfer material include the material of the transfer material, for example, O.D.
In the case of an HP sheet or the like, the transfer material can be conveyed while being suctioned with an appropriate suction force according to the stiffness and mass of the transfer material.

If the characteristics of the transfer material include the density of the transferred image on the transfer material, even if the characteristics of the transfer material before the transfer are completely the same, the characteristics of the transfer material after the transfer will be the same. Depending on the image density, control can be performed in response to a difference. For example, if the transfer image density is high, the suction force of the transfer means is increased, and if the transfer image density is low, the suction force is reduced. If the transfer image density is high, the transfer image density is high. When the transfer material is conveyed by firmly adsorbing it, the transfer material does not become stiff when the density of the transferred image is low. It can be conveyed while holding down. As a result, even for transfer materials having characteristics such as low image density and low waist,
Appropriate conveyance can be performed, and occurrence of image deterioration such as wrinkles and image deletion can be prevented.

The density of a transferred image may be determined by detecting the density of a latent image or a visible image formed on an image forming medium, or the image density of a transfer material may be directly detected. The determination may be made from the image density or from the input signal from the output image density selecting means.

As a result, the density of the transferred image can be detected and determined by various means, and an appropriate suction force can be determined accordingly.

A plurality of image forming media are provided side by side in the image forming section, images are formed on the image forming media, and the images are sequentially superimposed on a transfer material conveyed by a transfer material conveying device. Transfer, then, through the transport unit, transport the transfer material to the fixing unit, so that the image is fixed on the transfer material in the fixing unit, even in a multicolor image forming apparatus,
The suction force of the conveying means can be controlled depending on the characteristics of the transfer material, and a multicolor image forming apparatus with high image quality can be provided.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a sheet conveying apparatus according to a first embodiment of the present invention.

FIG. 2 is a schematic sectional view of an image forming apparatus according to a second embodiment of the present invention.

FIG. 3 is a schematic diagram showing a thickness detecting unit according to a second embodiment of the present invention.

FIG. 4 is a flowchart of a thickness detecting unit according to a second embodiment of the present invention.

FIG. 5 is a front view showing an image density detecting unit according to a fifth embodiment of the present invention.

FIG. 6 is a schematic sectional view of an image forming apparatus according to a sixth embodiment of the present invention.

Claims (15)

[Claims] 1. A sheet material conveying apparatus comprising a conveying means for adsorbing and conveying a sheet material, wherein a control means for controlling an attraction force of said conveying means is provided. 2. A sheet conveying apparatus according to claim 1, wherein said conveying means is a conveying means for conveying the transfer material while sucking the transfer material by air suction. 3. The sheet conveying apparatus according to claim 1, wherein the conveying unit is a conveying unit that conveys the transfer material while adsorbing the transfer material by an electrostatic attraction method. 4. An image forming unit for forming an unfixed image on a transfer material, a fixing unit for fixing an image to be transferred formed on the transfer material, and a transfer material from the image forming unit to the fixing unit. An image forming apparatus comprising: a conveying unit that conveys the sheet material; wherein the sheet conveying device according to claim 1, 2, or 3 is used as the conveying unit. 5. An image forming apparatus according to claim 4, wherein said control means is a control means for controlling an attraction force in accordance with a characteristic of a transfer material to be conveyed. 6. The image forming apparatus according to claim 5, wherein the characteristics of the transfer material include a size of the transfer material. 7. The image forming apparatus according to claim 5, wherein the characteristics of the transfer material include a thickness of the transfer material. 8. The image forming apparatus according to claim 5, wherein the characteristics of the transfer material include a material of the transfer material. 9. The image forming apparatus according to claim 5, wherein the characteristics of the transfer material include a density of an image to be transferred of the transfer material. 10. An image forming apparatus, comprising: an image forming medium in the image forming section; and a detecting means for detecting the density of a latent image formed on the image forming medium, wherein the density of the transferred image is obtained by the detecting means. The image forming apparatus according to claim 9, wherein the determination is performed based on the detected result. 11. An image forming medium in said image forming section, and detecting means for detecting the density of a visible image formed after development on said image forming medium, said detecting means detecting the density of the transferred image. The image forming apparatus according to claim 9, wherein the determination is performed based on a detection result obtained from the image forming apparatus. 12. The image forming apparatus according to claim 9, wherein the density of the transferred image is detected by detecting the density of the image formed on the transfer material on the transfer means with a photodetector. apparatus. 13. The image forming apparatus according to claim 9, wherein the density of the transferred image is determined from the density of the original image. 14. An image forming apparatus according to claim 9, wherein output image density selecting means is provided on the image forming apparatus main body, and said transferred image density is determined based on an input signal from said selecting means. . 15. An image forming apparatus, wherein a plurality of image forming media are provided side by side, images are formed on the image forming media, and the images are sequentially superimposed on a transfer material conveyed by a transfer material conveying device. The method according to any one of claims 4 to 14, wherein the transfer is performed, and then the transfer material is transported to the fixing unit via the transport unit, and the image is fixed on the transfer material at the fixing unit. Image forming device.