JPH0920439A - Sheet conveyer and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately detect thickness of a sheet in the variety of kinds with no influence by a curl or the like, by providing a thickness detecting means for detecting the thickness of the sheet by pressing the sheet against the first roller and by detecting a distance to the second roller movable in accordance with the thickness of the sheet. SOLUTION: Paired register rollers of constituting a sheet conveyer comprise a conveying roller 1 for giving conveying force to a recording sheet S and a pressure roller 2 movable in accordance with thickness of the recording sheet S. In order to detect a moving amount of the pressure roller 2, a reflecting photosensor 33 is mounted in a support member 29, to provided a light emitting element 33a and a light receiving element 33b of this sensor 33 so as to be opposed to the pressure roller 2. Since luminous energy is changed in proportion to a distance between the sensor 33 and the pressure roller 2, the distance between the pressure roller 2 and the sensor 33 is detected by a change of voltage, to change this output into a digital signal by an A/D converter, thereafter by calculation in a control part 34, sheet thickness can be detected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sheet conveying device capable of detecting the thickness of a conveyed sheet and an image forming apparatus using the sheet conveying device.

[0002]

2. Description of the Related Art In recent years, an image forming technique using an electrophotographic method or an ink jet method has been developed, and one capable of forming an image in full color has also become widespread. On the other hand, a wider variety of recording sheets have been developed corresponding to various image forming systems for use in the above apparatus. In particular, in a color image forming apparatus, it is required to form images on recording sheets of various thicknesses, because high quality images can be obtained by recording on thick paper.

However, it is necessary to optimize various conditions at the time of image formation in order to maintain high image quality while being compatible with recording sheets of various thicknesses. For example, in the electrophotographic system, the amount of heat required when the recording sheet is thin and thick is different in the fixing process in which the toner transferred to the recording sheet is heated and pressed to melt and fix the toner. It is necessary to control the temperature at the time of fixing according to this. In addition, even with recording sheets of the same material, if the thickness is different, the volume resistance value is also different. Therefore, in order to obtain a uniform image, the transfer current that drives the transfer charger also changes according to the thickness of the recording sheet in the transfer process. Need to let.

Further, in the ink jet recording system, the distance between the recording head and the recording sheet has a great influence on the image quality. In order to always maintain a constant image quality, it is necessary to keep the distance between the surface of the recording sheet and the recording head constant regardless of the thickness of the recording sheet. Further, when the image formation is performed by the serial scan method, it is necessary to intermittently convey the recording sheet accurately in an amount equal to the recording width.
When the rotation angle of the conveyance roller is constant, the conveyance amount of the recording sheet changes depending on the thickness of the recording sheet.

In order to solve the above problems, an image forming apparatus equipped with a means for detecting the thickness of a recording sheet has been developed in recent years. For example, as shown in FIG. 7, in the conveyance path of the recording sheet conveyed by the conveyance roller pair 50, 51,
An actuator 53 rotatable about the shaft 52 is provided,
One end of the actuator 53 is configured to come into contact with the recording sheet conveyed by the tension spring 54.

The actuator 53 swings according to the thickness of the sheet being conveyed, and the amount of the swing is detected by a reflection type photosensor 55 provided on the other swinging end side of the actuator 53 to detect the sheet thickness. is there.

The above-mentioned sheet thickness detecting structure has a simple structure and can easily detect even a colored sheet or a transparent sheet such as an OHP sheet because the recording sheet is not directly sensed. Further, by changing the ratio of the distance m from the shaft 52 to the recording sheet and the distance n from the shaft 52 to the sensor 55, it becomes possible to amplify and detect the recording sheet thickness.

[0008]

However, with the above-described sheet thickness detecting structure, it is not easy to accurately detect the thickness of a wide variety of recording sheets. For example, it is necessary to minimize the biasing pressure of the actuator 53 in order to deal with a thin recording sheet. However, it is difficult to accurately detect the thickness of a relatively thick curled recording sheet in such a state. If the biasing pressure is increased in order to suppress the curl, a thin recording sheet may be jammed (paper jam) when it is conveyed. Further, there is a problem in that the size of the device is increased in order to attach the actuator 53.

The present invention has been made to solve the above problems, and
The object of the present invention is to provide a sheet conveying device or the like that can accurately detect the thickness of a wide variety of sheets without being affected by curling and the like.

[0010]

A typical structure according to the present invention for achieving the above object is to provide a conveying force to a sheet in a sheet conveying apparatus capable of detecting the thickness of the sheet to be conveyed. A rotatable first roller, a second roller that is pressed against the first roller and is movable according to the thickness of the sheet, and a distance between the second roller are detected to detect the thickness of the sheet. It is characterized in that a thickness detecting means for detecting is provided.

In the above structure, even if the sheet is curled, a wide variety of sheets are used because the sheet thickness is changed by the displacement of the second roller when sandwiched by the first roller and the second roller. On the other hand, the sheet thickness can be accurately detected without being affected by the curl amount and without polluting the recording surface of the sheet.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION

[First Embodiment] Next, a sheet conveying apparatus and an image forming apparatus according to a first embodiment of the present invention will be specifically described with reference to FIGS. 1 to 4. 1 is a schematic explanatory view of a sheet conveying device capable of detecting a sheet thickness, FIG. 2 is a flowchart showing a sheet thickness detecting procedure, FIG. 3 is an explanatory diagram showing a sheet thickness detection output value, and FIG. FIG. 6 is a schematic configuration diagram of an image forming apparatus using a sheet conveying apparatus having the sheet thickness detecting mechanism.

As an order of description, the overall structure of an image forming apparatus having a sheet conveying device will be described first with reference to FIG. 4, and then the structure of a sheet conveying device having a sheet thickness detecting mechanism will be described with reference to FIGS. This will be described with reference to FIG.

[Overall Configuration of Image Forming Apparatus] The image forming apparatus shown in FIG. 4 is a full-color copying machine according to the electrophotographic system, in which the recording sheet S conveyed by the feeding means is transferred to the registration rollers constituting the sheet conveying apparatus. The pair 1 and 2 send out the image in accordance with the image forming timing, and the conveying belt 3 conveys the image from right to left in FIG. 4, during which a predetermined toner image is transferred by the image forming unit to record the image. Then, the recording sheet S on which the toner image is transferred
Is applied with heat and pressure by the fixing means 4 and the toner is fixed and discharged to the discharge tray 5, or when recording on the back side, the toner is sent to the resending path 6 and the registration roller pairs 1 and 2 are again supplied.
It is configured to be sent to.

The recording sheet S is fed to the pair of registration rollers 1 and 2 in a case where it is fed from a feeding cassette 7 by a pickup roller 8 and a separation roller 9 via a feeding path 10 and in a large capacity feeding. When feeding from the feeding deck 11 via the feeding roller 12 and the like, and when feeding from the manual feed tray 13 to the pickup roller 14, the separation roller 15 and the pre-registration roller pair 16a,
It may be delivered via 16b, etc., and each is selectively deliverable.

The image forming means is composed of four electrophotographic process means Y, M, C and B which can form yellow, magenta, cyan and black toner images arranged along the sheet conveying path. Each of these process means is a rotatable drum-shaped photosensitive drum 17 having a photosensitive layer formed on its surface.
On the other hand, a latent image is formed by scanning light from a laser light source (not shown), which is uniformly charged by the charging device 18 and emits light according to an image signal, by the polygon mirror 19a and the reflection mirror 19b. The developing device 20 develops the latent image with toner to form a visible image. Further, the toner image is transferred to the transfer charger 21.
The toner is transferred onto the recording sheet S to form a color image, and the toner remaining on the photosensitive drum 17 after the toner transfer is removed by the cleaning device 22.

The image information light radiated on the photosensitive drum 17 causes the laser light source to emit light in accordance with an image signal from an external device and an automatic document feeder 23 provided on the upper portion of the apparatus to scan the original. The document is sent onto the platen glass 24, the light source 25 irradiates the original with light, and the reflected light is photoelectrically converted through a reflection mirror 26 and a lens 27.
It is possible to convert into an electric signal at 28 and to make the laser light source emit light according to the signal.

{Structure of Sheet Conveying Device for Detecting Sheet Thickness} In the present embodiment, the recording sheet S conveyed by the pair of registration rollers 1 and 2 constituting the sheet conveying device.
Is configured to be detectable. Next, the configuration will be described with reference to FIGS. 1 to 3.

As shown in FIG. 1, the pair of registration rollers is
A conveying roller 1 that is a first roller that can be driven and rotated to give a conveying force to the sheet, and a second roller that presses the recording sheet S against the conveying roller 1 and is movable according to the thickness of the recording sheet S. The pressure roller 2 is a roller pair, and both rollers 1 and 2 are rotatably supported by the same support member 29 via bearings 28a and 28b, respectively.

A first end having a pitch circle diameter substantially equal to the outer diameter of the carrying roller 1 is provided at one end of the carrying roller 1.
A conveying gear 30 which is a gear is fixed, and this gear 30 meshes with a shaft gear 31a of a motor 31 and can be driven and rotated. Also, a pressure gear 32, which is a second gear having a pitch circle diameter substantially the same as the outer diameter of the pressure roller 2, is fixed to one end of the pressure roller 2, and this pressure gear 32 meshes with the conveyance gear 30. Rotational force is transmitted.

By making the outer diameter of the roller and the diameter of the gear pitch circle equal to each other as described above, the phase relationship in the rotation direction of both rollers 1 and 2 is always constant. The advantage that the phase relationship is constant relates to the operation when detecting the thickness of the recording sheet S, and this point will be described later.

Bearings 28b for supporting both ends of the pressure roller 2 are slidably attached to a pressing hole 2a provided in a supporting member 29 in the direction of arrow a in FIG. The spring 39 urges the conveyance roller 1 side (downward). Therefore, the pressure roller 2 is movable only in the direction of the arrow a, and is biased so as to come into pressure contact with the conveying roller 1 so as to press the recording sheet S against the conveying roller 1 and depending on the thickness of the recording sheet S. It slides in the direction of arrow a.

Therefore, the thickness of the recording sheet S can be detected by detecting the amount of movement of the pressure roller 2. However, if the rollers 1 and 2 are deformed at this time, it is difficult to detect the accurate thickness. become. Therefore, in the present embodiment, both the transport roller 1 and the pressure roller 2 are made of a metal member that is hard to be deformed. Further, when the recording sheet S is sandwiched by the rollers 1 and 2, the eccentricity of the roller pair causes an error when the sheet thickness is detected, and therefore the rollers 1 and 2 must be processed with extremely high accuracy. For example, if each roller 1 and 2 are eccentric by 20 μm, the axial distance of both rollers when a roller pair is configured changes up to ± 40 μm depending on the phase and becomes 100 μm.
This is because it becomes difficult to detect the difference in the thickness of the recording sheet S of 200 μm.

Next, regarding the structure for detecting the moving amount of the pressure roller 2, in the present embodiment, a reflection type photo sensor 33 is attached to the supporting member 29 as a thickness detecting means,
The light emitting element 33a and the light receiving element 33b of the sensor 33 are configured to face the pressure roller 2. The sensor 33 emits infrared light from the light emitting element 33a to the shaft end of the pressure roller 2 and receives the reflected light by the light receiving element 33b, thereby outputting a voltage according to the amount of reflected light. The amount of reflected light is a sensor
Since it changes in proportion to the distance between the pressure roller 2 and the pressure roller 2, the distance between the pressure roller 2 which moves up and down according to the thickness of the recording sheet S and the sensor 33 is detected by a voltage change, and the output is AD converted. The sheet thickness can be detected by converting the signal into a digital signal by a container and then calculating it by the control unit 34 having a built-in CPU, memory and the like.

Here, when it is attempted to measure the displacement of a cylindrical member such as the pressure roller 2, the mounting error of the sensor 33 with respect to the curvature of the roller affects the measured value. In order to reduce this effect, it is conceivable to decrease the curvature of the pressure roller 2 and increase the roller diameter, but the device becomes large. Therefore, in the present embodiment, the light emitting element 33a and the light receiving element 33b of the sensor 33 are arranged parallel to the axial direction of the pressure roller 2. With this arrangement,
The influence of the curvature of the roller can be weakened.

Further, in this embodiment, in order to make the conveying roller 1 and the pressure roller 2 function as a pair of registration rollers, a transmissive photosensor 35 is arranged upstream of the roller pair 1 and 2 in the sheet conveying direction. The conveying roller 1 is driven and rotated after a lapse of a predetermined time after the leading edge of the recording sheet S has passed the position of the sensor 35. That is, the leading end of the recording sheet S is abutted against the registration roller pair to form a loop to correct the skew and convey the recording sheet S according to the image forming timing.

The control section 34 inputs signals from the sensors 35, 33, etc., and executes the program shown in the flow chart shown in FIG. 2 to control the drive of each member such as the motor 31. Is to perform various calculations.

Next, the operation of detecting the thickness of the fed recording sheet S will be described with reference to the flowchart of FIG. In this embodiment, the thickness of the recording sheet S is 150
Depending on whether it is more than μm or less than 150 μm, the control unit 34
Is configured to switch image forming conditions (transfer bias voltage, heating temperature by fixing means, etc.), and the control unit 34
The recording sheet S is previously provided between the transport roller 1 and the pressure roller 2.
The output value of the reflection-type photo sensor 33 when not sandwiched is stored in the memory.

Now, as shown in FIG. 2, the output of the sensor 35 changes when the leading edge of the recording sheet S fed from the feeding means passes through the transmissive photosensor 35 and the sensor 35 is shielded from light. Then, the recording sheet S is detected (S1). The clock pulse is counted from that point, and the sheet S is fed until a predetermined time passes (S2, S3). by this,
The leading edge of the recording sheet S is abutted against the pair of registration rollers 1 and 2, and a skew is corrected by forming a loop.

After that, the motor 31 as a drive source is driven by a signal from the controller 34 (S4), and the conveying roller 1 and the pressure roller 2 are rotated to sandwich and convey the recording sheet S.
At this time, as described above, the pressure roller 2 causes the recording sheet S
Is displaced upward by an amount corresponding to the thickness of the reflective photosensor 33. The amount of displacement changes with the rotation of the roller pairs 1 and 2 due to the eccentricity of the roller pairs 1 and 2. However, the transport roller 1 and the pressure roller 2 have a gear 30, which has the pitch circle diameter as described above,
Since the gears 32 mesh with each other, the sensor 33 outputs a periodic waveform as shown in FIG. Therefore, in order to detect the sheet thickness, by taking in the sheet thickness data every rotation cycle T1 or half cycle T2 of the pressure roller 2 or every quarter cycle T3, for example, the eccentricity of the roller pair 1 and 2 is 10 μm.
Even with each of them, it is possible to calculate a sensor output value that is not influenced by the eccentricity of the roller pair by performing the averaging process described later.

The sheet thickness detecting sensor 33 includes roller pairs 1 and 2.
Starts to rotate and nips the recording sheet S after a lapse of a predetermined time T, and then the cycle T1 or half cycle T2 or quarter cycle T
Store data in memory every 3 minutes. When the number of data points reaches a predetermined number stored in advance (S5 to S
7) Divide the data by the predetermined number to calculate the average value and store it in the memory. Then, the value stored in advance in the memory (the value before the recording sheet S is nipped between the transport roller 1 and the pressure roller 2) is subtracted. The recording sheet S is compared with the voltage value when the roller pair 1 and 2 stored in the memory sandwich the recording sheet S of 150 μm.
The thickness of the sheet is judged (S8, S9) and the judged sheet thickness is 1
Control is performed to meet the respective image forming conditions in the case of 50 μm or more and the case of less than 150 μm (S10, S1).
1).

As described above, by detecting the displacement of the pressure roller 2 when the recording sheet S is nipped, and thereby detecting the thickness of the recording sheet S, even if the recording sheet S is curled, it is affected. It is possible to accurately detect the thickness of a wide variety of sheets, without increasing the size of the apparatus. By attaching the transport roller 1 and the pressure roller 2 to the same support member 29, the parallelism between the rollers 1 and 2 can be easily obtained.

The pair of registration rollers 1 and 2 are used as the pair of rollers for detecting the sheet thickness. The pair of registration rollers 1 and 2 are used for recording from any one of the feeding cassette 7, the large capacity deck 11 and the manual feed tray 13. Even if the sheet S is fed,
Since it is located at the merging portion, the thickness of the recording sheet S fed from any one of them can be detected by one sensor 33, and the cost of the sheet thickness detecting means can be kept low.

Further, the distance between the pair of rollers may be affected by the disturbance due to a shock or the like when the recording sheet S is nipped by the pair of rollers 1 and 2. Since the sensor 35 for detecting the arrival is provided, the sheet thickness is detected without being affected by the disturbance.

[Other Embodiments] In the above-described first embodiment, both the conveying roller 1 and the pressure roller 2 are provided on the recording sheet S.
Although an example is shown in which the rollers are made of metal so that they will not be deformed when they are nipped, in order to increase the conveying force of the recording sheet S, as shown in FIG. Alternatively, a composite of elastic members 36b such as rubber having an outer diameter slightly larger than that of the rigid member 36a may be formed on both sides thereof.
With this configuration, the elastic body portion 36b can apply a reliable conveying force to the recording sheet S, and the recording sheet S is held between the rigid body portion 36a and the pressure roller 2 without deforming the roller. The sheet thickness can be detected.

Further, using the carrying roller 36 shown in FIG.
As shown in FIG. 6, the pressure roller has a rigid body portion 37a made of metal in a portion facing the rigid body portion 36a, and a driven roller portion 37b made of polyacetal or the like having good slipperiness on both sides thereof. Alternatively, the driven roller portion 37b may be configured by pressing the driven roller portion 37b against the conveying roller 36 with a pressing spring 38. By doing so, the transport layer property of the recording sheet S can be further improved.

Further, in the above-described first embodiment, the registration roller pair 1 and 2 is used as the roller pair for detecting the sheet thickness, but the pair of rollers for detecting the sheet thickness is the registration rollers 1 and 2. It is not necessary to limit the number of rollers to other rollers, and other roller pairs may be used. For example, it is possible to use the pair of pre-registration rollers 16a and 16b shown in FIG. When the pair of pre-registration rollers 16a and 16b is used as a roller pair for detecting the sheet thickness, it is farther from the image forming position than the pair of registration rollers 1 and 2, so that other devices can be flexibly controlled.

That is, when the pre-registration roller pair 16a, 16b is used as a roller pair for sheet thickness detection, the recording sheet is stopped at the position of the registration roller pair 1, 2 to form a loop when the sheet is conveyed, as described above. However, at this time, the recording sheet has a pair of pre-registration rollers 16a,
It is pinched and conveyed by 16b. Therefore, the waveform data shown in FIG. 3 can be fetched by the time the loop is formed, and the sheet thickness can be detected when the loop is formed. Therefore, when the sheet thickness is detected and the control of the equipment in the image forming apparatus is changed, the degree of freedom can be widened in forming a sequence because there is a time margin.

From the viewpoint of the structure of the image forming apparatus, if the pickup roller 14, the separation roller 15, the pre-registration roller pairs 16a and 16b, and the registration roller pairs 1 and 2 are attached to the same support member (for example, a pair of side plates). In addition to the parallelism between the rollers being obtained, when the transfer charger 21 is exposed to the front, it is possible to easily perform the jam processing.

Further, in the above-described first embodiment, the example in which the reflection type photo sensor 33 is used as the sheet thickness detecting sensor is shown, but other sensors may be used. For example, the sheet thickness can be similarly detected by using a detection unit that uses a gap sensor, a PSD element (position detection element), or the like. When the irregular reflection method in which the displacement of the pressure roller 2 is detected using irregular reflection light is adopted, polishing the surface of the roller may change the characteristics due to variations in the mounting position of the sensor. (For example, the one having abrasive grains of 300 is used in consideration of the durability of the surface of the roller and the transportability of the sheet).
Further, as an object suitable for irregular reflection, an object using a white material, for example, an object in which a roller is applied in white, or an object using polyacetal or the like may be used.

Further, when the image forming apparatus changes the image forming condition according to the sheet thickness, the thickness of the recording sheet fed by the sensor 33 is automatically detected, and the image is detected according to the detection result. An automatic mode that automatically controls the forming conditions, and the user inputs the thickness of the recording sheet from the operation unit,
If it is configured to have a manual mode that controls the image forming conditions according to the input sheet thickness, an image suitable for the sheet thickness can be automatically obtained by the automatic mode, and use that requires higher image quality. It is possible for a person to meet various uses by the manual mode.
However, in the manual mode, the user may make an erroneous input, so if the input sheet thickness is significantly different from the sheet thickness detected by the sensor 33, a warning display may be displayed on the display. It is preferable to configure.
In this case, the sheet thickness detecting mechanism has a protection function.

Further, in the above-described first embodiment, an electrophotographic color copying machine is exemplified as the image forming apparatus.
It is natural that the image forming means may use other recording methods such as an inkjet recording method other than the electrophotographic method, and the image forming apparatus is not limited to a copying machine, and may be, for example, a printer, a facsimile device, or Of course, it can be used in other image forming apparatuses such as word processors.

[0043]

As described above, the present invention presses a sheet against a rotatable first roller in order to apply a conveying force to the sheet, and a second roller movable according to the thickness of the sheet. Since it is configured to detect the sheet thickness by detecting the distance of the sheet, a wide variety of sheets can be accurately measured without being affected by the curl amount and without polluting the recording surface of the sheet. It becomes possible to detect the thickness.

Further, when the roller pair is connected by a gear having a pitch circle diameter equal to the outer diameter of each roller, the sheet thickness detection accuracy does not depend on the eccentricity of the roller at all, so it is necessary to process the parts with high accuracy. Thus, the cost of the sheet thickness detecting mechanism can be reduced.

[Brief description of drawings]

FIG. 1 is a schematic explanatory view of a sheet conveying device capable of detecting a sheet thickness.

FIG. 2 is a flowchart showing a sheet thickness detection procedure.

FIG. 3 is an explanatory diagram showing a sheet thickness detection output value.

FIG. 4 is a schematic diagram illustrating the configuration of an image forming apparatus using a sheet conveying device having a sheet thickness detecting mechanism.

FIG. 5 is a schematic explanatory view of a sheet conveying device in which a conveying roller is made of a composite body of a rigid portion and an elastic portion and capable of detecting a sheet thickness.

FIG. 6 is a schematic explanatory view of a sheet conveyance device capable of detecting a sheet thickness in which a conveyance roller is composed of a rigid body portion and an elastic body portion, and a pressure roller is composed of a rigid body portion and a material having good slipperiness.

FIG. 7 is an explanatory diagram of a conventional sheet thickness detection mechanism.

[Explanation of symbols]

1 ... conveying roller, 2 ... pressurizing roller, 3 ... conveying belt, 4
... fixing means, 5 ... discharge tray, 6 ... resending path, 7 ... feeding cassette, 8 ... pickup roller, 9 ... separation roller, 10
... Feeding path, 11 ... Large capacity deck, 12 ... Feeding roller, 13 ... Manual feed tray, 14 ... Pickup roller, 15 ... Separation roller, 16a, 16b ... Pre-registration roller, 17 ... Photosensitive drum, 18 ... Charging device , 19a ... Polygon mirror, 19b ... Reflecting mirror, 20 ... Developing device, 21 ... Transfer charging device, 22 ... Cleaning device, 23 ... Automatic document feeder, 24 ... Platen glass, 25 ... Light source, 26 ... Reflecting mirror, 27 ... Lens, 28a, 28
b ... Bearing, 29 ... Support member, 29a ... Long hole, 30 ... Conveyance gear, 31 ... Motor, 31a ... Shaft gear, 32 ... Pressurization gear, 33 ...
Reflection type photo sensor, 33a ... Light emitting element, 33b ... Light receiving element, 34 ... Control section, 35 ... Transmission type photo sensor, 36 ... Conveying roller, 36a ... Rigid body section, 36b ... Elastic body section, 37 ... Pressure roller, 37a … Rigid part, 37b… Followed roller part, 38… Pressure spring,
39 ... Pressing spring

Claims (10)

[Claims] 1. A sheet conveying apparatus capable of detecting the thickness of a sheet to be conveyed, comprising: a rotatable first roller for imparting a conveying force to the sheet; a sheet pressed against the first roller; And a second roller movable in accordance with the thickness of the sheet, and a thickness detecting unit for detecting the distance between the second roller and the sheet to detect the thickness of the sheet. . 2. The thickness detecting means is a photosensor having a light emitting portion and a light receiving portion, and the light emitting portion and the light receiving portion are arranged parallel to the axis of the second roller. 1. The sheet conveying device according to 1. 3. A first gear fixed to the first roller,
The sheet conveying device according to claim 1, wherein the second gear fixed to the second roller meshes with each other to transmit the rotational force. 4. The pitch circle diameter of the first gear is substantially equal to the outer diameter of the first roller, and the pitch circle diameter of the second gear is substantially equal to the outer diameter of the second roller. The sheet conveying device described. 5. The sheet conveying apparatus according to claim 1, wherein at least one of the first roller and the second roller has an elastic body portion and a rigid body portion. 6. The sheet conveying apparatus according to claim 1, wherein the first roller and the second roller function as registration rollers. 7. The sheet according to claim 1, wherein the surface of the second roller is white or blasted, and the thickness detecting means uses a diffuse reflection method. Transport device. 8. An image forming apparatus for conveying a sheet to form an image, the sheet conveying apparatus according to claim 1, and an image forming apparatus for forming an image on the conveyed sheet. An image forming apparatus comprising: 9. The image forming apparatus controls an image forming condition by automatically detecting a sheet thickness by a thickness detecting unit of the sheet conveying apparatus, and an image forming apparatus according to an input sheet thickness. The image forming apparatus according to claim 8, further comprising a manual mode for controlling image forming conditions. 10. The image forming apparatus has an image forming unit capable of forming a color image, and the first roller and the second roller of the sheet conveying apparatus are supported by the same supporting member. The image forming apparatus according to claim 8.