JP2015014694A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem in which: when developing bias is reduced after completion of the development of an image on the preceding sheet and the developing bias is increased to meet the development of an image on the subsequent sheet in order to prevent scattering of toner between the sheets on a photoconductor drum, since a certain amount of time is required for the rise and fall of the developing bias, as the high-speed operation is further realized in the future, there is a possibility that the developing bias cannot be sufficiently reduced between images or the developing bias cannot be sufficiently increased by the start of development of an image on the subsequent sheet.SOLUTION: An image forming apparatus detects the leading edge of the subsequent sheet with a top sensor 105 and then increases the rotation speed of a resist roller 104, causes the leading edge of the subsequent sheet to catch up with the rear edge of the preceding sheet before the rear edge of the preceding sheet reaches a transfer roller 106 to eliminate the gap between the sheets, and stops the on/off control of developing bias between the sheets. The image forming apparatus further increases the operation speed of a thermal fixing device 130 after the rear edge of the preceding sheet has passed through the transfer roller 106.

Description

  The present invention provides an image forming process means having an appropriate principle and method such as electrophotography, electrostatic recording, and magnetic recording. The present invention relates to an image forming apparatus such as a printer, a copier, a recording machine, or a facsimile machine that forms and supports the image and heat-fixes the image as a fixed image on a recording sheet to output an image formed product.

  FIG. 10 shows a configuration of a main part of a conventional image forming apparatus.

  In FIG. 10, 122 is a photosensitive drum which is an image carrier, and 124 is a charging bias generation circuit, which is for placing a uniform charge necessary for the electrophotographic process on the photosensitive drum 122.

  Reference numeral 107 denotes a laser beam reflecting mirror for reflecting the laser beam output from the laser optical box 108 and forming an electrostatic latent image corresponding to the image data on the photosensitive drum 122. Reference numeral 121 denotes a developing roller. The developing roller 121 is disposed opposite to the photosensitive drum 122 and carries toner necessary for developing the electrostatic latent image on the photosensitive drum 122. Reference numeral 126 denotes a development bias generation circuit for generating a development bias necessary for developing the electrostatic latent image on the photosensitive drum 122.

  The iron component in the toner is attracted by the magnetic force of the magnet 125 embedded in the developing roller 121, and the toner is attracted onto the developing roller 121. Then, the toner attracted to the developing roller 121 is transported uniformly by the blade 129.

  When a bias is applied to the developing roller 121, an electric field is generated on the developing roller 121 and the photosensitive drum 122, and when the magnetic force of the magnet 125 becomes stronger, the toner flies toward the photosensitive drum 122. Then, the transfer positive bias 127 is applied to the toner on the photosensitive drum 122 at the timing when the recording paper P comes onto the transfer roller 106, and the toner is transferred onto the recording paper P.

On the other hand, depending on the relationship between the charging bias and the developing bias, the toner may be placed on the background portion not irradiated with the laser. Then, a part of the toner adheres to the transfer roller 106 due to the positive bias of the transfer between the sheets. As this increases,
1. The toner stains on the back of the recording paper.
2. The edge (recording paper edge) is contaminated with toner.
3. The transfer roller 106 is scraped by the abrasive in the toner and its diameter changes.
The problem occurs.

  As a countermeasure against the above problem, there is a method in which the developing bias is lowered between sheets so that toner does not fly to the photosensitive drum 122 (see Patent Document 1).

Japanese Patent Laid-Open No. 11-133809

  In recent years, speeding up of throughput has been demanded, and there has been a demand for speeding up the conveyance speed of recording paper and shortening between papers. Increasing the conveyance speed of the recording paper increases the rotational speed of the photosensitive drum, and shortening the gap between the sheets decreases the image interval on the photosensitive drum. For this reason, the time from the development of the image of the preceding paper to the start of the development of the image of the subsequent paper is shortened.

  In the prior art, in order to prevent the toner from jumping to the photosensitive drum between papers, the development bias is lowered after the development of the image on the preceding paper, and the development bias is raised so as to be in time for the development of the image on the subsequent paper. ing. A certain amount of time is required for the falling and rising of the developing bias. For this reason, if the speed is further increased in the future, there is a possibility that the development bias does not fall between images or the development bias does not rise until the development of the image on the subsequent sheet starts.

  When the developing bias does not fall between the images, unnecessary toner adheres to the photosensitive drum, which is transferred to the transfer roller, and the transfer roller becomes dirty. When the next paper is passed there, there is a problem that dirt adheres to the back side of the succeeding paper.

  Further, if the development bias cannot be fully raised before the development of the image on the succeeding paper, there is a problem that the image at the leading edge of the succeeding paper is not developed or the image becomes thin.

  In view of the above-described problems, an object of the present invention is to provide an image forming apparatus capable of preventing a transfer roller from being soiled by toner at a time between sheets and obtaining a good image free from back soiling. is there.

  According to the first invention of the present application, the object is to form a toner image on the surface of the photoconductor using an electrophotographic method, transfer the toner on the photoconductor to a recording sheet using a transfer member, In an image forming apparatus using a method of thermally fixing on a recording sheet, an upstream roller driving unit that drives a roller disposed in a conveyance path upstream of a transfer member, a photosensitive member rotating unit that rotates a photosensitive member, A downstream roller driving unit that drives a roller disposed in a conveyance path downstream of the transfer member; a recording sheet detection unit that is disposed in a conveyance path upstream of the transfer member and detects the conveyed recording sheet; Paper transport control means for accelerating and decelerating the rotation speeds of the upstream roller driving means and the downstream roller driving means based on the input from the paper detection means, exposure means for latent images on the photosensitive member surface, and exposure Means light source An image output means for turning on / off a latent image on the surface of the photoconductor and an image output start timing notifying means for notifying the image output means of the image output start timing; After detecting the leading edge of the succeeding paper, the rotational speed of the upstream roller driving means is increased so that the leading edge of the succeeding paper catches up with the trailing edge of the preceding paper before the trailing edge of the preceding paper reaches the transfer member, This is achieved by adjusting the notification timing of the image output start timing in accordance with the acceleration of the succeeding sheet, and increasing the speed of the downstream roller driving means after the trailing edge of the preceding sheet has passed the transfer member.

  As described above, according to the present invention, it is possible to provide an image forming apparatus capable of preventing a transfer roller from being contaminated by toner at a time between sheets and obtaining a good image free from back contamination. Even when the subsequent sheet is accelerated, the notification timing of the image output start timing is adjusted, and the positional relationship between the toner image on the surface of the photoreceptor and the subsequent sheet is matched to output a good image on the subsequent sheet. It is possible to provide an image forming apparatus capable of performing the above.

1 is a cross-sectional view illustrating an example of an image forming apparatus of the present invention. FIG. 3 is a diagram showing the relationship between each roller and each motor in Examples 1 and 2. The block diagram of a control system. 2 is a flowchart in the first embodiment. 2 is a flowchart in the first embodiment. a), b), c) The positional relationship diagram of the recording paper in the first and second embodiments. The conveyance speed at the registration rollers in Examples 1 and 2. 10 is a flowchart in the second embodiment. 10 is a flowchart in the second embodiment. 1 is a configuration diagram of a conventional image forming main part.

[Example 1]
FIG. 1 is a cross-sectional view of the image forming apparatus of this embodiment. In FIG. 1, reference numeral 122 denotes a photosensitive drum made of an organic photosensitive member or an amorphous silicon photosensitive member, which is rotationally driven at a predetermined peripheral speed (process speed) in the clockwise direction. The peripheral surface of the rotating photosensitive drum 122 and the charging roller 123 is uniformly charged to a predetermined polarity and potential. In response to the time-series electrical digital pixel signal of the target image information output from the laser optical box 108 and input from an image signal generator (not shown) such as an image reading device or a computer to the charged surface. The modulated (on / off-converted) laser light is changed and irradiated by the laser light reflecting mirror 107, scanning exposure is performed, and an electrostatic latent image corresponding to the image information is formed.

  The scanning exposure start timing in the sub-scanning direction is notified from the image forming apparatus to the image signal generating apparatus by a sub-scanning direction synchronization signal. The electrostatic latent image thus formed corresponding to the target image is developed by the developing roller 121.

  Next, one sheet of recording paper is fed from the paper feeding cassette by the paper feeding roller 102, transported by the transport roller 103 and the registration roller 104, and sent to the photosensitive drum 122, whereby the recording paper is photosensitive drum. A mirror image toner image on the 122 side is formed. The transfer roller 106 transfers a toner image from the photosensitive drum 122 to the recording paper by supplying a charge having a polarity opposite to that of the toner from the back of the recording paper.

  The recording sheet that has received the transfer of the toner image in this manner is separated from the photosensitive drum 122 and sent to the heat fixing device 130, where the toner image is heat fixed by the heater 132, the fixing film 133, and the pressure roller 134. The recording paper that has undergone thermal fixing is conveyed by the FU roller 110 and the FD roller 111 and discharged to the FD tray 113.

  FIG. 2 is a diagram illustrating a relationship between each roller of the image forming apparatus according to the present exemplary embodiment and a motor that drives the roller. In the image forming apparatus according to the present exemplary embodiment, a conveyance motor 301, a drum motor 302, and a fixing motor 303 are used. The transport motor 301 drives the paper feed roller 102, the transport roller 103, and the registration roller 104. The drum motor 302 drives the photosensitive drum 122 and the transfer roller 106. The fixing motor 303 drives the pressure roller 134, the FU roller 110, and the FD roller 111. Stepping motors are used for the transport motor 301 and the fixing motor 303. Thus, the rotation speeds of the conveyance motor 301 and the fixing motor 303 can be changed only by changing the cycle of the clock output from the CPU of the image forming control unit 200.

  FIG. 3 is a block diagram of a control system in the present embodiment. The image forming apparatus control unit 200 includes a microprocessor that controls the entire image forming apparatus, a ROM that stores a control program, a RAM that stores data, a gate element, and the like, and a top sensor 105 for detecting a recording sheet. , A paper discharge sensor 109, a conveyance motor 301 for driving each roller, a drum motor 302, a fixing motor 303, a developing bias generating circuit 126 for applying a developing bias to the developing roller 121, and a heater for thermally fixing toner. 132, a thermistor 131 for detecting the temperature of the heater, an image signal output means 400 for starting on / off of the laser beam corresponding to the target image, based on the sub-scanning direction synchronization signal, and the like are connected.

Functionally, in order to form an image on a recording sheet and thermally fix it, an image formation control unit 201 that controls a high-voltage, scanner, fixing, and sub-scanning direction synchronization signal.
Paper conveyance control means 202 for controlling paper conveyance based on information from the sensors and image formation control means 201 arranged in the paper conveyance path
Etc.

  The sub-scanning direction synchronization signal is output based on detection of the leading edge of the recording paper by the top sensor 105. Specifically, simultaneously with the output of the sub-scanning direction synchronization signal, when the image signal output means 400 starts emitting laser light, the image is transferred onto the photosensitive drum 122 so that the image is transferred from the leading edge 0 mm of the recording paper. It is formed. When the recording sheet is conveyed at a constant speed, the time Ttop from when the top sensor 105 detects the leading edge of the sheet to when the sub-scanning direction synchronization signal is output can be expressed by the following Equation 1.

  Here, Ld is the creeping distance from the laser irradiation position on the photosensitive drum 122 to the transfer nip, Lf is the distance from the top sensor 105 to the transfer nip, and Vf is the conveyance speed of the recording paper. In addition, it is assumed that the peripheral speed of the photosensitive drum 122 and the conveyance speed of the recording paper are the same, and the top sensor 105 is arranged so that Lf is longer than Ld.

  Specific processing performed by the image forming apparatus control unit 200 will be described with reference to the flowcharts of FIGS. FIG. 4 is a flowchart of processing that starts when the leading edge of the recording paper reaches the top sensor 105, and FIG. 5 is a flowchart of processing that starts when the trailing edge of the recording paper reaches the top sensor 105. First, the recording paper leading edge reference process will be described with reference to the flowchart of FIG.

  When the leading edge of the recording sheet reaches the top sensor 105, it is first checked in step 1 whether there is a preceding sheet. If there is no preceding sheet, the conveyance motor 301 is not accelerated or decelerated, and the process is terminated.

  If it is determined in step 1 that there is a preceding sheet, acceleration of the carry motor 301 is started in step 2 and the process proceeds to step 3.

  In step 3, the output timing of the sub-scanning direction synchronization signal output to the image signal output means 400 is advanced, and the process proceeds to step 4. Adjustment of the output timing of the sub-scanning direction synchronization signal will be described later.

  In step 4, it is determined whether or not it is the deceleration timing of the transport motor 301. If it is the deceleration timing, the process proceeds to step 5. The determination of the deceleration timing of the transport motor 301 will be described later.

  In step 5, the conveyance motor 301 is decelerated, the conveyance speed at the registration roller 104 is matched with the conveyance speed at the photosensitive drum 122, and the process ends.

  Next, the recording paper trailing edge reference process will be described with reference to the flowchart of FIG. When the trailing edge of the recording sheet reaches the top sensor 105, it is first determined in step 1 whether the development bias is OFF or not. If the development bias is OFF, the process proceeds to step 2.

  In step 2, it is confirmed whether there is a subsequent sheet. If there is no subsequent sheet, the process proceeds to step 5, where the developing bias is turned off and the process is terminated. If there is a subsequent sheet, go to Step 3.

  In step 3, the process waits for the trailing edge of the recording paper to reach the transfer nip and then proceeds to step 4.

  In step 4, the fixing motor 303 is accelerated, the conveyance speed at the thermal fixing device 130 is made faster than the conveyance speed at the photosensitive drum 122, and the process ends.

  6A, 6B, and 6C are image diagrams of a recording sheet conveyance state in this embodiment.

  FIG. 6a is a view at the time when the leading edge of the recording paper reaches the top sensor 105, and is an image diagram at the start time in the flowchart of FIG. P1 is the preceding paper, P2 is the succeeding paper, X1 is the distance between the transfer nip and the trailing edge of the preceding paper P1, and X is the distance between the transfer nip and the top sensor 105. Thereafter, in steps 2 to 4 in the flowchart of FIG. 4, the conveyance motor 301 is accelerated / decelerated, whereby the recording paper has the positional relationship shown in FIG. 6B.

  In FIG. 6b, the trailing edge of the preceding paper P1 and the leading edge of the succeeding paper P2 are located in the transfer nip. Specifically, the distance between the trailing edge of the preceding paper P1 and the leading edge of the succeeding paper P2 is 0 mm. Here, in order to achieve the object of the present invention, it is sufficient that there is no space between the preceding paper and the succeeding paper. Therefore, even if the trailing edge margin portion of the preceding paper P1 and the leading margin portion of the succeeding paper P2 overlap each other. Good. From this state, by increasing the speed of the fixing motor 303 in step 4 of the flowchart of FIG. 5, the recording paper has the positional relationship shown in FIG. 6c.

  In FIG. 6c, a space between the trailing edge of the preceding paper P1 and the leading edge of the succeeding paper P2 is secured. For this reason, the trailing edge of the preceding paper P1 and the leading edge of the succeeding paper P2 can be detected by the paper discharge sensor 109, and jamming of the recording paper can also be performed.

  Adjustment of the output timing of the sub-scanning direction synchronization signal in step 3 of the flowchart of FIG. 4 will be described. By accelerating / decelerating the transport motor 301, the following paper is jammed by the distance X2 in FIG. 6a as compared with the case of transporting at a constant speed. Therefore, the image formed on the photosensitive drum 122 must be formed earlier by the distance X2. In order to form an image on the photosensitive drum 122 earlier by the distance X2, the sub-scanning direction synchronization signal may be output earlier by the distance X2. When the succeeding sheet is accelerated, the time Ttop2 from when the top sensor 105 detects the leading edge of the sheet until the sub-scanning direction synchronization signal is output can be expressed by the following Expression 2.

  Here, Ld is the creeping distance from the laser irradiation position on the photosensitive drum 122 to the transfer nip, Lf is the distance from the top sensor 105 to the transfer nip, and Vf is the conveyance speed of the recording paper. Further, it is assumed that the top sensor 105 is arranged such that the circumferential speed of the photosensitive drum 122 and the conveyance speed of the recording paper are the same, and Lf is longer than the total of Ld and X2.

  A method for determining the deceleration timing of the conveyance motor 301 in step 4 of the flowchart of FIG. 4 will be described.

  FIG. 7 is a diagram showing a change in the conveyance speed at the registration roller 104. V1 is a speed equivalent to the conveyance speed on the photosensitive drum 122, and V2 is a speed higher than the conveyance speed on the photosensitive drum 122. Ta is the time required for increasing the speed of the transport motor 301, Td is the time required for decelerating the transport motor 301, and T2 is the time for maintaining the speed V2.

  In order for the leading edge of the succeeding sheet to catch up with the trailing edge of the preceding sheet, the succeeding sheet may advance the distance X in FIG. 6 while the preceding sheet proceeds the distance X1 in FIG. For this purpose, T1 is the distance from the leading edge of the succeeding sheet to the top sensor 105 until the trailing edge of the preceding sheet passes through the transfer nip. Find T2 like this. Note that the distance between the papers may be zero, but zero mm may be difficult due to the number of rotations of the motor, a dimensional error in the paper conveyance path, and the like. At that time, the object can be achieved even if the preceding paper and the succeeding paper are controlled to overlap to the trailing edge and the margin at the leading edge. T2 coincides with the time staying at step 4 in the flowchart of FIG. Therefore, the determination of the deceleration timing of the conveyance motor 301 in step 4 of the flowchart of FIG. 4 can be determined by whether or not T2 has elapsed after the acceleration of the conveyance motor 301 is completed. V1 and V2 are predetermined speeds, and Ta and Td are times determined by the characteristics of the transport motor 301 and the like, and can be determined in advance. T1 can be obtained by subtracting the time from detection of the trailing edge of the preceding paper by the top sensor 105 to detection of the leading edge of the succeeding paper from the time when the distance X is advanced at the conveyance speed on the photosensitive drum 122. .

  With the above control, if there is no margin for the time required for the development bias to be turned on / off, the distance between the papers is eliminated and the development bias is turned on / off to prevent the transfer roller from being contaminated with toner during the paper gap. It is possible to provide an image forming apparatus that can obtain a good image that is prevented and has no back-stain.

[Example 2]
In the first embodiment, the conveyance motor 301 is always accelerated if there is a preceding sheet. In the second embodiment, it is determined whether or not the speed of the transport motor 301 is increased according to the interval between the preceding sheet and the following sheet. In addition, the fixing motor 303 is also accelerated only when the subsequent sheet is accelerated, and when it is increased, the temperature of the thermal fixing device 130 is raised to improve the fixing property of the toner to the recording sheet.

  The cross-sectional view of the image forming apparatus of the present embodiment, the block diagram of the control system, and the relationship between each roller and the motor that drives the roller are the same as in the first embodiment.

  Specific processing performed by the image forming apparatus control unit 200 in this embodiment will be described with reference to the flowcharts of FIGS. FIG. 8 is a flowchart of processing that starts when the leading edge of the recording paper reaches the top sensor 105, and FIG. 9 is a flowchart of processing that starts when the trailing edge of the recording paper reaches the top sensor 105. First, the recording paper leading edge reference process will be described with reference to the flowchart of FIG.

  When the leading edge of the recording sheet reaches the top sensor 105, it is first checked in step 1 whether there is a preceding sheet. If there is no preceding sheet, the conveyance motor 301 is not accelerated or decelerated, and the process is terminated.

  If it is determined in step 1 that there is a preceding sheet, the process proceeds to step 2 to determine whether or not there is time to turn off the developing bias.

  Specifically, the total of the development bias fall time and rise time is compared with the paper interval time measured by the top sensor 105. If the paper interval time is longer, it is determined that there is time to turn off the development bias. Then, the acceleration / deceleration of the transport motor 301 is not performed, and the process is terminated. If the time between sheets is shorter, it is determined that there is no time to turn off the developing bias, and the process proceeds to step 3 to start acceleration of the carry motor 301 and proceeds to step 4.

  In step 4, the output timing of the sub-scanning direction synchronization signal output to the image signal output means 400 is advanced, and the process proceeds to step 5. The method for adjusting the output timing of the sub-scanning direction synchronization signal is as described in the first embodiment.

  In step 5, it is determined whether or not it is the deceleration timing of the transport motor 301. If it is the deceleration timing, the process proceeds to step 6. The method for determining the deceleration timing of the transport motor 301 is as described in the first embodiment.

  In step 6, the conveyance motor 301 is decelerated, the conveyance speed at the registration roller 104 is matched with the conveyance speed at the photosensitive drum 122, and the process is terminated.

  Next, the recording paper trailing edge reference process will be described with reference to the flowchart of FIG.

  When the trailing edge of the recording sheet reaches the top sensor 105, it is first determined in step 1 whether the development bias is OFF or not. If the development bias is OFF, the process proceeds to step 2.

  In step 2, it is confirmed whether or not there is a subsequent sheet. If there is no subsequent sheet, the process proceeds to step 6 where the developing bias is turned off and the process is terminated. If there is a subsequent sheet, go to Step 3.

  In step 3, it is determined whether or not there is time to turn off the developing bias. A specific determination method is the same as step 2 in the flowchart of FIG. If it is determined that there is time to turn off the developing bias, the process proceeds to step 6 where the developing bias is turned off and the process ends. If it is determined that there is no time to turn off the developing bias, the process proceeds to step 4.

  In step 4, the process waits for the trailing edge of the recording paper to reach the transfer nip and then proceeds to step 5.

  In step 5, the fixing motor 303 is accelerated, and the conveyance speed in the thermal fixing device 130 is made faster than the conveyance speed in the photosensitive drum 122, and the process proceeds to step 7.

  In step 7, the temperature of the thermal fixing device 130 is increased and the process is terminated. Here, the temperature to be raised is a temperature that is equivalent to the fixability when the fixing motor 303 is not accelerated.

  By the control as described above, it is possible to provide an image forming apparatus that can prevent the transfer roller from being smeared with the toner at the time of paper separation and obtain a good image free from back dirt.

100 Image forming device
101 Paper presence sensor
102 Feed roller
103 Conveyor roller
104 cashier
105 Top sensor
106 Transfer roller
107 Laser beam reflection mirror
108 Laser optical box
109 Output sensor
110 FU Roller
111 FD roller
112 FU tray
113 FD tray
120 toner cartridge
121 Developing roller
122 Photosensitive drum
123 Charging roller
124 Charging bias generation circuit
125 magnet
126 Development bias generator
127 Transfer positive bias
128 Negative transfer bias
129 blade
130 Fuser
131 thermistor
132 Heater
133 Fixing film
134 Pressure roller
200 Image forming device control means
201 Image formation control means
202 Paper transport control means
301 Conveyor motor
302 drum motor
303 Fixing motor
400 Image signal output means
P Recording paper
P1 Leading paper
P2 trailing paper

Claims (9)

  In an image forming apparatus using a system in which a toner image is formed on the surface of a photosensitive member using an electrophotographic method, toner on the photosensitive member is transferred to a recording sheet using a transfer member, and heat-fixed on the recording sheet. An upstream roller driving unit that drives a roller disposed in the conveyance path upstream of the transfer member, a photosensitive member rotation unit that rotates the photosensitive member, and a roller disposed in the conveyance path downstream of the transfer member. A downstream roller driving unit, a recording sheet detecting unit that is disposed in a conveyance path upstream of the transfer member and detects the conveyed recording sheet, and an upstream roller driving unit and a downstream unit based on an input from the recording sheet detecting unit The paper conveyance control means for accelerating and decelerating the rotational speed of the side roller driving means, the exposure means for latent image forming on the surface of the photoconductor, and the light source of the exposure means are turned on / off so that the image is Painting An output means and an image output start timing notifying means for notifying the image output means of the image output start timing, and the number of rotations of the upstream roller driving means after the leading edge of the succeeding paper is detected by the recording paper detecting means The leading edge of the succeeding sheet catches up with the trailing edge of the preceding sheet before the trailing end of the preceding sheet reaches the transfer member, and the notification timing of the image output start timing is adjusted according to the increasing speed of the succeeding sheet. An image forming apparatus characterized in that the downstream roller driving means is accelerated after the trailing edge of the preceding paper has passed the transfer member.   2. The image according to claim 1, wherein the number of rotations of the upstream roller driving unit is reduced so that the peripheral speed of the photosensitive member and the conveyance speed of the succeeding sheet coincide with each other before the succeeding sheet enters the transfer member. Forming equipment.   2. The image forming apparatus according to claim 1, wherein when the trailing edge of the preceding sheet and the leading edge of the succeeding sheet pass through the transfer member, the distance between the preceding sheet and the succeeding sheet is 0 mm.   2. The image according to claim 1, wherein when the trailing edge of the preceding paper and the leading edge of the succeeding paper pass through the transfer member, the trailing edge margin portion of the preceding paper overlaps with the leading edge margin of the succeeding paper. Forming equipment.   If the distance between the trailing edge of the preceding paper and the leading edge of the succeeding paper detected by the recording paper detecting means is less than a predetermined distance, the upstream roller driving means is accelerated, and if the distance is equal to or longer than the predetermined distance, the upstream roller driving means. 5. The image forming apparatus according to claim 1, wherein the image forming apparatus is not accelerated.   6. The image forming apparatus according to claim 5, wherein the predetermined distance is a distance obtained from a product of a sum of a falling time and a rising time of the developing bias and a conveyance speed of the recording paper.   In order to form a toner image on the surface of the photoreceptor, a developing bias is applied, and when the upstream roller driving means is accelerated, the developing bias is maintained at a voltage during printing, 6. The image forming apparatus according to claim 5, wherein when the speed of the upstream roller driving unit is not increased, the developing bias is turned off or the voltage is lowered between the image on the preceding sheet and the image on the succeeding sheet.   When the upstream roller drive means is accelerated, the downstream roller drive means is increased after the trailing edge of the preceding paper has passed through the transfer member, and when the upstream roller drive means is not increased, the downstream roller drive means is increased. 6. The image forming apparatus according to claim 5, wherein the image forming apparatus is not fast.   9. The image forming apparatus according to claim 8, further comprising a thermal fixing unit for thermally fixing the toner transferred to the recording paper, wherein the temperature of the thermal fixing unit is increased when the downstream roller driving unit is accelerated. .