JP2008209624A - Image forming apparatus capable of double-sided recording - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a recording paper conveyance device for an image forming apparatus capable of double-sided recording that ensures a satisfactory quality image by controlling loops in a recording paper, which arise due to driving speed differences when a plurality of rollers, such as a fixing roller, a transport roller, a paper ejection roller, and an inverting roller, are driven with a common driving source. <P>SOLUTION: The plurality of rollers, e.g., the fixing roller 15, the transport roller 19, the paper ejection roller 17, and the inverting roller 18, are fitted in a single unit and are driven by the common driving source. This eliminates the need for loop control, until the leading end of the usable maximum recording paper (the longest paper) reaches the fixing roller 15. After the start of a fixing process by a fixing device FX, loop control is exerted for the longest paper, until the trailing end of the longest paper passes along the transport roller 19. A difference ΔL1, between the counter resist roller 13 and the transport roller 19 in the amount of transport, is held as a loop. In order that the loop LP 1 be held so as to prevent troubles, such as bending of recording papers in a conveyance path, the loop LP1 is maintained at the difference ΔL1 to the amount of transport or smaller. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus capable of double-sided recording, such as an electronic copying machine, a printer, or a multifunction machine thereof, and more particularly to a recording paper conveying apparatus thereof.

  In an electrophotographic image forming apparatus, a laser beam modulated with an image signal is projected onto a charged photoreceptor to form an electrostatic latent image of the image, and the formed electrostatic latent image is developed with toner. Thus, a toner image is formed on the photoreceptor. Next, the toner image is transferred onto a recording sheet, the toner image transferred onto the recording sheet is fixed, and discharged to a discharge tray. To fix the toner image, a fixing device is widely used in which a heating roller and a pressure roller are pressed against each other, a recording sheet on which the toner image is transferred is passed between them, and the toner on the recording sheet is thermally melted and pressed. ing.

  In such an image forming apparatus, there is an image forming apparatus capable of double-side recording that forms images on both sides of a recording sheet. First, an image is formed on the first side of the recording sheet, and the recording sheet is discharged after being fixed. Is conveyed to a reversing path inside the image forming apparatus to form an image on the second surface of the recording paper, and a fixing process is performed.

  For this reason, the image forming apparatus is provided with a fixing roller that always rotates normally during operation, a conveyance roller that repeats forward and reverse rotation, a conveyance roller that repeatedly starts and stops according to the timing of image formation, and the like. Control is being performed.

These various rollers are driven forward / reversely using a dedicated motor (see Patent Document 1), while the fixing roller and the discharge roller use a one-way clutch to rotate the motor forward / reversely. A fixing roller that rotates in one direction (see Patent Document 2), a paper discharge roller and a conveyance roller that are driven by a dedicated motor (see Patent Document 3), and the like are known. In addition, there is a technique in which the fixing speed is made variable and the recording paper loop amount on the input side of the fixing device is adjusted (Patent Document 4).
JP 2002-154727 A. JP 2002-169403 A. Japanese Patent Application Laid-Open No. 09-26677. JP2003-345150A.

  Among the conventional image forming apparatuses capable of double-sided recording, those in which the discharge roller and the fixing roller of the fixing device are driven from a common motor and those in which the reverse roller and the conveyance roller are driven from a common motor are known. The paper discharge roller, the fixing roller, and the reverse roller are not driven from a common drive source.

  In an image forming apparatus capable of double-sided recording, a fixing roller, a reversing roller (which may also be used as a paper discharge roller), and a conveying roller in a reversing path are close in position inside the double-sided recording apparatus. It is difficult to drive from a common drive source because it always rotates forward, the reverse roller repeats forward and reverse rotation, and the transport roller repeatedly starts and stops in accordance with the image forming timing. This necessitates the use of a plurality of motors, resulting in inconveniences such as noise generation and increased manufacturing costs.

  Further, in the case of controlling the rotation speed of the fixing roller of the fixing device described above, the fluctuation in the speed appears as the fluctuation in the speed of the reversing roller and the conveying roller, and the speed required for the transfer portion in the image forming apparatus is stabilized. This hinders the ability to absorb the fluctuations in the speed of the recording paper in the reversing path and causes image noise. SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus that can solve the above-described problems, can perform stable image formation, and does not generate image noise and can perform double-sided recording.

  The present invention solves the above-mentioned problems, and the invention of claim 1 comprises an image forming device, a transfer device, a fixing device, a paper discharge device, a recording paper reversing device, and a registration roller. The formed electrostatic latent image is developed with toner to create a toner image, the obtained toner image is transferred to a recording sheet by a transfer unit, and the toner image on the recording sheet is fixed by a fixing device and discharged. When performing double-sided recording, an image forming apparatus capable of double-sided recording in which an image is formed on the first surface and the discharged recording paper is reversed by a recording paper reversing device and an image is also formed on the second surface. The image forming apparatus capable of duplex recording includes a fixing roller of the fixing device, a reversing roller of a recording paper reversing device, a conveying roller disposed in a conveying path in the recording paper reversing device, and a discharging roller of a paper discharging device. Driven by a single drive source That a double-sided recording an image forming apparatus comprising the drive mechanism.

  The drive mechanism driven by the single drive source may be configured to be assembled into a single unit and attached to the image forming apparatus.

  The driving mechanism driven by the single driving source includes a fixing roller driving speed changing mechanism, and the recording paper loop before reaching the fixing roller by changing the fixing roller driving speed by the driving speed changing mechanism. The amount shall be controlled.

  In the image forming apparatus capable of double-sided recording, a recording paper loop is formed between a conveying roller and a registration roller arranged on the most downstream side in the conveying path in the recording paper reversing device. The loop amount LP1 is assumed to maintain the relationship of the following formula (1).

LP1 ≧ (LM) · {(Vmax−Vmin) / V0} (1)
However, LP1: loop amount of recording paper
L: Length in the transport direction of the maximum usable recording paper size
M: disposed at the most downstream side in the conveyance path in the recording sheet reversing apparatus
Distance between transport roller and fixing roller
V0: Standard conveyance speed V0 of the fixing roller
Vmax: Maximum value of the conveyance speed of the fixing roller
Vmin: The minimum value of the conveyance speed of the fixing roller.

  In the image forming apparatus capable of double-sided recording, a recording paper loop is formed between a conveying roller and a registration roller arranged on the most downstream side in the conveying path in the recording paper reversing device, and the recording paper The relationship of the following formula (2) may be maintained for the loop amount LP1.

LP1 ≧ (LM). {(Vmax−V0) / V0} (2)
However, LP1: loop amount of recording paper
L: Length in the transport direction of the maximum usable recording paper size
M: disposed at the most downstream side in the conveyance path in the recording sheet reversing apparatus
Distance between transport roller and fixing roller
V0: Standard conveyance speed V0 of the fixing roller
Vmax: Maximum value of the conveyance speed of the fixing roller.

  In the image forming apparatus capable of double-sided recording, a drive play F is provided between a transport roller drive shaft and a transport roller arranged on the most downstream side in the transport path in the recording paper reversing device. It is assumed that the relationship of the following formula (3) is maintained.

F ≧ (LM) · {(Vmax−Vmin) / V0} (3)
F: Driving play between the transport roller drive shaft and the transport roller
L: Length in the transport direction of the maximum usable recording paper size
M: disposed at the most downstream side in the conveyance path in the recording sheet reversing apparatus
Distance between transport roller and fixing roller
V0: Standard conveyance speed V0 of the fixing roller
Vmax: Maximum value of the conveyance speed of the fixing roller
Vmin: The minimum value of the conveyance speed of the fixing roller.

  Further, the image forming apparatus capable of double-sided recording is configured such that the length of the recording sheet conveyance path from the conveyance roller disposed at the most downstream side in the conveyance path in the recording sheet reversing apparatus to the fixing device is the maximum usable recording. It is preferable that the length is not less than the length of the paper size in the conveyance direction.

  According to the present invention, the fixing roller of the fixing device, the reversing roller of the recording paper reversing device, the transporting roller disposed in the transporting path in the recording paper reversing device, and the discharging roller of the paper ejecting device are provided as a single drive source. When the drive mechanism is assembled into a single unit, assembly and installation are facilitated. And since it can drive with a single drive source, generation | occurrence | production of a noise can be reduced rather than the case where a several motor is used, and it becomes possible to reduce manufacturing cost.

  Further, the driving mechanism driven by the single driving source controls the loop amount of the recording paper before reaching the fixing roller by changing the fixing roller driving speed by the fixing roller driving speed changing mechanism. An image forming apparatus capable of double-sided recording capable of controlling the loop amount of recording paper and forming an image with good image quality without changing the driving speed affecting the driving speed of other reversing rollers, transport rollers and paper discharge rollers. Can be provided.

  Embodiments of the present invention will be described below. FIG. 1 is a cross-sectional view for explaining the structure of a main part of a recording paper transport device 10 of an image forming apparatus according to an embodiment of the present invention.

  In FIG. 1, a recording paper transport device 10 includes a paper feed tray 11, a paper feed roller 12, a registration roller pair 13, a transfer roller 14, a fixing roller 15, a transport roller 16, a paper discharge roller 17, a reverse roller 18, and a transport roller 19. Etc. are provided. In FIG. 1, a fixing roller 15, a transport roller 16, a paper discharge roller 17, a reverse roller 18 and a transport roller 19 are rollers driven by the same drive source.

  The reverse roller 18 arranged on the downstream side in the transport direction of the paper discharge roller 17 functions as a paper discharge roller in the case of single-sided recording, but in the case of performing double-sided recording, the recording paper P on which an image is recorded on the first surface. Is conveyed to the reversing path 20, and a conveying roller 19 disposed below the reversing path 20 conveys the recording paper P conveyed from the reversing path 20 to the registration roller pair 13.

  The recording paper P fed from the paper feed tray 11 by the paper feed roller 12 rotating at a predetermined paper feed timing is temporarily stopped by the registration roller pair 13. In FIG. 1, the conveyance of the recording paper P is started by the registration roller pair 13 that starts driving rotation in accordance with the image forming timing in the image forming unit IM, which is shown only partially. In the image forming unit IM, a first toner image corresponding to the first image is formed on the transfer belt 21, and when the toner image on the transfer belt 21 reaches the transfer unit TR where the transfer roller 14 is disposed, the transfer roller 14 is transferred to the first surface of the recording paper P. The recording sheet P on which the first toner image has been transferred is conveyed and fixed by the fixing roller 15 of the fixing device FX, and is discharged to a discharge tray outside the apparatus via the transfer roller 16, the discharge roller 17, and the reverse roller 18. Paper. In the case of single-sided recording, the first process forms the first image on the first side of the recording paper P, and the single-sided recording process for one recording paper is completed.

  In the case of double-sided recording, when the above-described single-sided recording process is completed and the rear end of the recording paper P on which the image is formed on the first surface passes through the reverse switching claw 22, the reverse roller 18 starts reverse rotation, and the recording paper P is conveyed to the reverse path 20 with the rear end first. The recording paper P is transported to the registration roller pair 13 with the trailing edge at the top by the transporting roller 19 disposed on the lower side of the reverse path 20 and temporarily stops.

  The conveyance of the recording paper P is started by the registration roller pair 13 that starts driving rotation in accordance with the image forming timing of the image forming unit IM, and the image forming unit IM has a second image corresponding to the second image on the transfer belt 21. When the toner image is formed and the toner image on the transfer belt 21 reaches the transfer portion TR where the transfer roller 14 is disposed, the toner image is transferred to the second surface of the recording paper P by the action of the transfer roller 14. The recording sheet P on which the second toner image has been transferred is conveyed and fixed by the fixing roller 15 of the fixing device FX, and is discharged to a discharge tray outside the apparatus via the transfer roller 16, the discharge roller 17, and the reverse roller 18. Paper.

  With the above processing, the first image is formed on the first surface of the recording paper P and the second image is formed on the second surface, and the double-side recording processing of one recording paper P is completed.

  FIG. 2 is a perspective view for explaining the power transmission gear train of the recording paper transporting apparatus 10 shown in FIG. 1, in which the fixing roller 15 (see FIG. 1, not shown in FIG. 2) is moved from the motor 30 to the power transmission gear train 31. , 32. Switching between the forward and reverse rotation directions and starting / stopping are not performed.

  The reverse roller 18 is driven through power transmission gear trains 31, 32, 33, 34, electromagnetic clutches 35, 36, gear trains 37, 38, 39, and a shaft 40. Here, the forward / reverse switching of the reversing roller 18 is performed using the two electromagnetic clutches 35 and 36, but the forward / reverse switching can be performed by one electromagnetic clutch and a torque limiter.

  The conveying roller 19 is driven through power transmission gear trains 31, 32, 33, 41, 42, an electromagnetic clutch 43, and gear trains 44, 45. The start / stop of the conveying roller 19 is achieved by the electromagnetic clutch 43 disposed in the middle of the power transmission gear train.

  FIG. 3 is a perspective view illustrating a configuration in which the power transmission gear train shown by the chain line is combined into one unit 50 in the power transmission gear train shown in FIG. 2. Since the configuration of the power transmission gear train is the same as that described with reference to FIG. 2, the description thereof is omitted here. By assembling the power transmission gear train into one unit, assembly, adjustment, maintenance management and the like can be easily performed.

  Next, the loop control of the recording paper P in the recording paper transport device 10 will be described. As described above in the background art, the conveyance speed of the recording paper P in the fixing device and the conveyance speed of the recording paper in the transfer unit are not the same, and the difference in speed is due to dimensional error of parts, dimensional change due to temperature change, recording It fluctuates due to various factors such as a difference in the thickness of the paper and a difference in slip rate due to a difference in the amount of adhered toner.

  In a state where there is no loop (sag) of the recording paper P between the fixing device FX and the transfer unit TR, if the conveyance speed of the fixing device FX is faster than the conveyance speed of the transfer unit TR, the recording paper P is forcibly pulled. In addition, a transfer shift that disturbs the toner image occurs, and in the case of a color image, a color shift occurs.

  On the other hand, when the conveyance speed of the fixing device FX is slower than the conveyance speed of the transfer unit TR, the loop of the recording paper P expands, and in an extreme case, the recording paper P sticks to the paper passing guide and is transferred in the reverse direction. Deviation and color deviation occur. Further, when the recording paper P comes into contact with the paper passing guide and rubs, image noise may occur.

  For this reason, it is necessary to maintain the loop of the recording paper P appropriately. Loop control is not particularly necessary when there is sufficient space in the paper passing path. However, as the size of the apparatus continues to decrease, the allowable amount of the loop decreases, and the recording paper P is detected by detecting the loop amount of the recording paper P. A method of controlling the transport speed of P has come to be adopted.

  In the loop control of the recording paper P, the conveyance speed of the recording paper P cannot be controlled by the registration roller pair or the transfer unit TR. Therefore, the conveyance speed of the recording paper P is controlled upstream of the transfer unit TR. As a method of changing the conveyance speed, the motor speed is switched by two or more stages such as three stages. For this reason, the conveyance speed of the recording paper P fluctuates, but various rollers are arranged and loop control is performed so that the fluctuation in speed does not adversely affect image formation.

  First, the loop amount of the recording paper P in the U-turn guide UG disposed near the conveyance roller 19 and the registration roller pair 13 in the reverse path 20 will be described.

  FIG. 4 is a diagram for explaining the difference in length in the transport direction when the recording paper P is not curved and when the recording paper P is curved. P1 shows a state in which the recording paper is not curved, and P2 shows the recording paper P. When the recording paper P is curved (P2), the length in the transport direction is shortened by ΔL as compared to the case where the recording paper P is not curved (P1).

  FIG. 5 is a diagram for explaining the state of the recording paper P in the U-turn guide UG disposed near the registration roller 13. The posture of the recording paper P is determined by points A and B of the U-turn guide UG and enters the portion indicated by R below. The recording paper P supported by the points A and B and the R portion draws a loop as shown by a thick line in FIG. 5 due to its rigidity (paper waist and strength). If there is resistance (an element that delays the conveyance of the recording paper) on the leading end side of the recording paper P being conveyed, the loop expands outward, and if the leading end side is conveyed quickly, the loop shrinks. Areas SP (SP1 and SP2) on both sides of the loop indicated by bold lines in FIG. 5 act as areas that absorb the load on the recording paper due to the fluctuation of the loop, and transfer deviation and magnification caused by the speed fluctuation of the recording paper P. Prevent image noise such as errors.

  FIG. 6 is a diagram for explaining the state of the recording paper P in the vicinity of the registration roller 13. In FIG. 6, a thick solid line Pa indicates a state where the leading edge of the recording paper P has reached the nip portion of the registration roller 13 in a stopped state. In order to correct the inclination of the recording paper P, the transport roller 19 stops with a slight paper feed. The recording paper P is in a state indicated by a thick broken line Pb in FIG.

  The registration roller 13 and the conveyance roller 19 start to rotate at the timing of image formation. The registration roller 13 rotates at the standard speed. However, when the loop control is started, the conveyance roller 19 is influenced by the rotation, and starts rotating at a speed different from the standard speed.

  If the rotation of the registration roller 13 is faster than the rotation of the conveying roller 19, the loop of the recording paper P swells. The bulge limit of the loop of the recording paper P that does not cause the paper folding due to the bulge or the rotation irregularity of the registration roller 13 due to the pushing of the paper is shown by a thick dashed line Pc in FIG. The difference between the state indicated by the thick broken line Pb in FIG. 6 and the state indicated by the thick dashed line Pc is curved with P1 when the recording paper P described above with reference to FIG. 4 is not curved. In this case, the length difference ΔL1 in the conveying direction of P2 is obtained.

  Also, if the rotation of the registration roller is slower than the rotation of the conveying roller, the recording paper is pulled and the loop becomes small, and the state indicated by the thick dashed line in FIG. A difference in length in the conveyance direction between the state before the rotation of the registration roller 13 indicated by the thick broken line Pb in FIG. 6 and the state indicated by the one-dot broken line Pd in FIG. It is a capacity and is a difference ΔL2 in the length in the transport direction.

  Here, the speed error of the fixing device FX and the loop control of the recording paper P will be described. The fixing roller 15 of the fixing device FX has various factors such as tolerance of the roller outer diameter and rubber thickness, dimensional change due to temperature rise, toner inclusion ratio, change in slip rate due to recording paper type and humidity, and recording paper thickness. Therefore, the conveyance speed of the recording paper P in the fixing device FX is difficult to stabilize and may have a speed tolerance of about ± 2%. For example, when a speed tolerance of about ± 2% is assumed, the average transport speed Vm is set while switching the transport speed V between + 3% and −3% by setting a transport speed V of ± 3% higher than that. Is controlled to approach the standard transport speed V0.

  FIG. 8 is a diagram for explaining an example in which the driving speed of the motor 30 for driving the fixing roller 15 of the fixing device FX is switched in two steps so that the average transport speed Vm of the recording paper approaches the standard value. The vertical axis represents the difference (%) between the standard transport speed V0 and the transport speed V.

  Assume that the conveyance speed V of the recording paper P in the fixing device FX set in consideration of various factors as described above is a conveyance speed V that is + 2% faster than the standard conveyance speed V0. In this case, the motor driving speed is switched to two stages of + 3% and −3% so as to cancel the speed error of + 2%, and the average conveyance speed Vm is controlled to be −2%. Here, since the average transport speed Vm of the recording paper P in the fixing device FX cannot be directly detected, the transport speed is estimated from the loop amount (deflection amount) of the recording paper P generated by the change in the transport speed.

  Next, the conveyance speed control of the longest sheet Pmax in the fixing device FX when the recording sheet Pmax having the longest conveyance direction length (hereinafter, the longest sheet) Pmax is used will be described.

  FIG. 9 is a diagram illustrating a state in which the leading edge of the longest sheet Pmax has reached the nip portion of the fixing roller 15 of the fixing device FX. Until the leading edge of the maximum usable recording paper (longest paper) Pmax reaches the nip portion of the fixing roller 15, the loop control of the longest paper Pmax is not necessary. Rotate with V0.

  Next, when the registration roller 13 starts rotating and fixing processing by the fixing device FX is started, the sheet is conveyed by the distance indicated by A in FIG. 9 until the trailing edge of the longest sheet Pmax passes through the conveying roller 19. Meanwhile, loop control of the longest paper Pmax is required.

  The distance shown as A in FIG. 9 is the distance L between the conveyance direction length L of the longest sheet Pmax and the nip portion of the fixing roller 15 and the conveyance roller 19 disposed on the most downstream side in the conveyance path 20 in the recording sheet reversing apparatus. The distance A is expressed by (A = LM).

  The maximum value at which the conveyance speed of the longest sheet Pmax by the conveyance roller 19 deviates from the standard conveyance speed V0 of the fixing roller 15 is the difference between the maximum speed Vmax and the minimum speed Vmin of the fixing roller 15. When the difference ΔV between the maximum value Vmax of the conveyance speed and the minimum value Vmin of the conveyance speed is multiplied and divided by the standard conveyance speed V0, the trailing edge of the longest sheet Pmax is the conveyance roller 19 after the loop control of the longest sheet Pmax is started. The difference ΔL1 in the amount of conveyance that occurs between the registration roller 13 and the conveyance roller 19 until it passes through is expressed by the following equation (a).

ΔL1 = (LM). (Vmax-Vmin) / V0 (a)
= A ・ ΔV / V0
The difference ΔL1 in the conveyance amount is held as a loop LP1 generated in the longest paper Pmax in the conveyance path, but in order to hold the loop LP1 so as not to cause a problem such as paper breakage in the recording paper in the conveyance path, It is necessary to maintain LP1 below the transport amount difference ΔL1.

  That is, the loop amount LP1 is set to be smaller than the difference ΔL1 in the conveyance direction when the recording paper P is not curved and when it is curved as described with reference to FIG. 4 (LP1 <ΔL1). .

  If the above matters are arranged, the loop LP1 is expressed by the following equation (1).

LP1 ≧ (LM). ({Vmax−Vmin) / V0} (1)
LP1: Loop amount generated on the recording paper
L: Maximum recording paper length in the transport direction
M: disposed at the most downstream side in the conveyance path in the recording sheet reversing apparatus
Distance between transport roller and fixing roller
V0: Standard conveyance speed of the fixing roller
Vmax: Maximum conveyance speed of the fixing roller
Vmin: Minimum conveyance speed of the fixing roller.

  In Formula (1) relating to the conveyance speed control of the longest paper Pmax in the fixing device FX described above, the standard conveyance speed V0 of the fixing roller may be used instead of the minimum conveyance speed Vmin of the fixing roller. In this case, the loop LP1 is expressed by the following equation (2).

LP1 ≧ (LM). {(Vmax−V0) / V0} (2)
LP1: Loop amount generated on the recording paper
L: Maximum recording paper length in the transport direction
M: disposed at the most downstream side in the conveyance path in the recording sheet reversing apparatus
Distance between transport roller and fixing roller
V0: Standard conveyance speed of the fixing roller
Vmax: Maximum Conveying Speed of Fixing Roller FIG. 10 is a diagram for explaining loop control of the recording paper P that is conveyed in contact with the conveying roller 19 and the registration roller 13. The loop control of the recording paper P with reference to FIG. 9 is an explanation for the rear end side of the recording paper P in the recording paper transport device, but the recording paper transported in contact with the registration roller 13 and the transfer roller 15. P loop control is also required. The section B in which loop control is necessary is the distance between the trailing edge of the preceding recording sheet Pad and the leading edge of the succeeding recording sheet Ptr from the distance S1 between the registration roller 13 and the transfer roller 14 (between the recording sheets). Distance) is a distance obtained by subtracting D1, and B = (S1 -D1).

  The maximum value at which the conveyance speed of the longest sheet Pmax by the conveyance roller 19 deviates from the standard conveyance speed V0 of the registration roller is the difference between the maximum conveyance speed and the minimum conveyance speed of the registration roller. When the difference ΔV between the maximum value Vmax and the minimum value Vmin is multiplied and divided by the standard conveyance speed V0, the loop control of the longest paper Pmax is started and the trailing edge of the longest paper Pmax passes through the conveyance roller 19. A difference ΔL2 in the conveyance amount generated between the registration roller 13 and the conveyance roller 19 becomes a loop amount LP2 generated in the longest sheet Pmax.

ΔL2 = B · {(Vmax−Vmin) / V0}
= B ・ ΔV / V0
However, ΔL2: generated between the registration roller 13 and the conveying roller 19
Difference in transport amount
B: From the distance S1 between the registration roller and the transfer roller,
The distance between the trailing edge of the longest paper to be printed and the leading edge of the longest paper to follow
(Distance between recording sheets) Value obtained by subtracting D1 (S1 -D1)
V0: Standard transfer speed of registration rollers
Vmax: Maximum transfer speed of registration rollers
Vmin: Minimum transfer speed of the registration roller.

ΔV: Difference between maximum value Vmax and minimum value Vmin of registration roller conveyance speed
= (Vmax-Vmin)
The difference ΔL2 in the conveyance amount is held as a loop LP2 that occurs in the longest paper Pmax in the conveyance path. To hold the loop LP2 in the conveyance path so as not to cause trouble such as paper breakage in the recording paper, It is necessary to keep LP2 below the transport amount difference ΔL2. Therefore, it is necessary that the following condition is satisfied in consideration of the condition of ΔL1.

B · {(Vmax−Vmin) / V0} ≦ ΔL1, and B · {(Vmax−Vmin) / V0} ≦ ΔL2.

  FIG. 11 illustrates a “drive play” provided in the drive transmission system of the transport roller 19 in order to avoid the influence of the length of the transport direction being shortened by ΔL due to the curvature of the recording paper P described above with reference to FIG. FIG. 11A shows a mechanism constituted by a transmission pin 51 and a fan-shaped cam 52, and FIG. 11B shows a mechanism constituted by a one-way clutch 56.

  In the mechanism constituted by the pin 51 and the fan-shaped cam 52 shown in FIG. 11A, the transmission pin 51 is planted on the shaft of the conveying roller 19, while the gear 54 has a recess that engages with the transmission pin 51. The provided fan-shaped cam 52 is formed, and the recording paper P is transported when the gear 54 rotates counterclockwise.

  When the drive shaft 53 rotates counterclockwise, the transmission pin 51 comes into contact with the counterclockwise end surface of the concave portion of the fan-shaped cam 52 and rotates the gear 54 counterclockwise. When the drive shaft 53 rotates clockwise, the transmission pin 51 does not rotate the gear 54 until it contacts the clockwise end surface of the concave portion of the sector cam 52. A space between the counterclockwise end surface and the clockwise end surface of the concave portion of the sector cam 52 is referred to as “driving play F”.

  Even when the drive shaft 53 rotates, the recording pin P is not conveyed by the amount of the driving play F in the concave portion of the fan-shaped cam 52, so that the rotation of the conveying roller 19 is slowed in the loop control, and the recording sheet is pulled. However, the tensile force applied to the recording paper by the drive play F can be reduced, and the occurrence of image noise can be prevented without providing the aforementioned ΔL2. The amount of driving play F is preferably set to an amount necessary for the trailing edge of the recording paper to pass through the conveyance roller. As a result, it is possible to avoid the influence that the length in the conveyance direction is shortened by ΔL due to the curvature of the recording paper.

  The driving play F, the longest paper Pmax, the distance M between the transport roller 19 and the fixing roller 15 arranged on the most downstream side in the transport path in the recording paper reversing device, the standard transport speed V0 of the fixing roller 15, the fixing roller 15 The relationship of the following formula (3) is set between the maximum value Vmax and the minimum value Vmin of the conveyance speed.

F ≧ (LM) · {(Vmax−Vmin) / V0} (3)
However, F: Driving play
L: Maximum recording paper length in the transport direction
M: disposed at the most downstream side in the conveyance path in the recording sheet reversing apparatus
Distance between transport roller and fixing roller
V0: Standard conveyance speed of the fixing roller
Vmax: Maximum conveyance speed of the fixing roller
Vmin: Minimum conveyance speed of the fixing roller.

In the mechanism constituted by the one-way clutch shown in FIG. 11B, 56 one-way clutches are arranged between the drive shaft and the gear. In this configuration, even if the rotation of the conveying roller 19 is slow and the recording sheet is pulled, the pulling rotation of the conveying roller 19 is freed by the one-way clutch 56 and the tensile force applied to the recording sheet P can be reduced. Generation of image noise can be prevented without providing ΔL2.

  In the configuration described above, the description has been made on the assumption that the front end side of the recording paper P is in the nip portion of the fixing roller 15 of the fixing device FX and the rear end side of the recording paper P is in contact with the conveying roller 19. However, if the recording paper P enters between the fixing roller 15 and the conveying roller 19, there is no restriction imposed on at least the rear end side of the recording paper. Since the restriction on the leading end side of the recording paper can be avoided by adjusting the interval of the recording paper to be conveyed, the margin of the recording paper conveyance path such as ΔL1 and ΔL2 can be reduced.

  12 shows a state in which the recording paper P is interposed between the fixing roller 15 and the transport roller 19, that is, the length of the transport path in the recording paper reversing device is the maximum transportable paper length in the transport direction. This indicates the above case, and the restriction imposed on the trailing edge of the recording paper is eliminated.

  In the case of a small image forming apparatus, if the maximum processable recording paper size is A4, the A4 size recording paper has a length of 297 mm in the conveyance direction, and therefore from the nip portion of the fixing roller 15 of the fixing device FX. If the distance M of the recording paper conveyance path to the conveyance roller 19 is set to 300 mm, which is slightly longer than 297 mm, the recording paper of A4 size and smaller is subject to the restriction that the trailing edge side of the recording paper receives. Can be used without any trouble.

  A recording paper conveyance device of an image forming apparatus capable of double-sided recording, which drives a plurality of rollers such as a conveyance roller, a discharge roller, and a reverse roller in addition to a fixing roller of a fixing device from a common driving source, and is stable and constant. Adjust the driving speed of the other rollers with respect to the transfer roller and fixing roller of the transfer unit in the image forming apparatus driven at high speed without causing abnormal slack or tension on the recording paper in the transport path. This is a recording paper transport device of an image forming apparatus capable of duplex recording capable of stable image formation.

FIG. 3 is a cross-sectional view illustrating a configuration of a main part of a recording paper conveyance device of the image forming apparatus. FIG. 2 is a perspective view for explaining a power transmission gear train of the recording paper transport device shown in FIG. 1. The perspective view explaining the structure which put together the power transmission gear train shown by the chain line in one unit in the power transmission gear train shown in FIG. FIG. 6 is a diagram for explaining a difference in length in a conveyance direction when a recording sheet is not curved and when the recording sheet is curved. The figure explaining the state of the recording paper in the U-turn guide near a registration roller. The figure explaining the state of the recording paper near the registration roller The figure explaining the limit which becomes small in the loop of the vicinity of a registration roller. FIG. 6 is a diagram for explaining an example in which the driving speed of the fixing roller of the fixing device is switched in two stages and the average conveyance speed is brought close to a standard value. FIG. 4 is a diagram illustrating a state in which the leading end of the longest paper reaches the nip portion of the fixing roller of the fixing device. FIG. 4 is a diagram for explaining loop control of a recording sheet conveyed while being in contact with a conveyance roller and a registration roller. The figure explaining an example of the "drive play" mechanism provided in the drive transmission system of the conveyance roller. FIG. 3 is a diagram illustrating a recording sheet conveyance device of an image forming apparatus in which a recording sheet enters between a fixing roller and a conveyance roller and the restriction on the rear end side of the recording sheet is eliminated.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Recording paper conveying apparatus 11 Paper feed tray 12 Paper feed roller 13 Registration roller pair 14 Transfer roller 15 Fixing roller 16 Carrying roller 17 Paper discharge roller 18 Reverse roller 19 Transport roller 20 Reverse path 21 Transfer belt 22 Reverse switching claw IM Image forming unit FX fixing device TR transfer part UG U-turn guide P Recording paper

Claims (7)

An image forming device, a transfer device, a fixing device, a paper discharge device, a recording paper reversing device, and a registration roller are provided. The electrostatic latent image formed on the photosensitive member by the image forming means is developed with toner to create a toner image. When the obtained toner image is transferred to a recording sheet by a transfer unit, the toner image on the recording sheet is fixed by a fixing device and discharged, and an image is formed on the first side. In an image forming apparatus capable of double-sided recording, wherein the discharged recording paper is reversed by a recording paper reversing device to form an image on the second side as well.
The image forming apparatus capable of double-sided recording includes a fixing roller of the fixing device, a reversing roller of a recording paper reversing device, a conveying roller disposed in a conveying path in the recording paper reversing device, and a discharging roller of a paper discharging device. An image forming apparatus capable of double-sided recording, comprising a drive mechanism driven by a single drive source. 2. The image forming apparatus according to claim 1, wherein the driving mechanism driven by the single driving source is assembled into a single unit and attached to the image forming apparatus. The drive mechanism that is driven by the single drive source includes a fixing roller driving speed changing mechanism, and changes the fixing roller driving speed by the driving speed changing mechanism to determine the loop amount of the recording paper before reaching the fixing roller. The image forming apparatus according to claim 1, wherein the image forming apparatus is capable of duplex recording. In the image forming apparatus capable of double-sided recording, a recording paper loop is formed between a conveyance roller disposed on the most downstream side in a conveyance path in the recording paper reversing device and a registration roller, and the loop amount of the recording paper LP1 must maintain the relationship of the following formula (1): LP1 ≧ (LM) · {(Vmax−Vmin) / V0} (1)
However, LP1: loop amount of recording paper
L: Length in the transport direction of the maximum usable recording paper size
M: disposed at the most downstream side in the conveyance path in the recording sheet reversing apparatus
Distance between transport roller and fixing roller
V0: Standard conveyance speed V0 of the fixing roller
Vmax: Maximum value of the conveyance speed of the fixing roller
4. The image forming apparatus according to claim 3, wherein Vmin is a minimum value of the conveying speed of the fixing roller. In the image forming apparatus capable of double-sided recording, a recording paper loop is formed between a conveyance roller disposed on the most downstream side in a conveyance path in the recording paper reversing device and a registration roller, and the loop amount of the recording paper LP1 must maintain the relationship of the following equation (2): LP1 ≧ (LM) · {(Vmax−V0) / V0} (2)
However, LP1: loop amount of recording paper
L: Length in the transport direction of the maximum usable recording paper size
M: disposed at the most downstream side in the conveyance path in the recording sheet reversing apparatus
Distance between transport roller and fixing roller
V0: Standard conveyance speed V0 of the fixing roller
4. The image forming apparatus according to claim 3, wherein Vmax is a maximum value of the conveying speed of the fixing roller. In the image forming apparatus capable of double-sided recording, a drive play F is provided between a transport roller drive shaft and a transport roller arranged on the most downstream side in the transport path in the recording paper reversing device. Is that the relationship of the following expression (3) is maintained: F ≧ (LM) · {(Vmax−Vmin) / V0} (3)
F: Amount of driving play between the transport roller drive shaft and the transport roller
L: Length in the transport direction of the maximum usable recording paper size
M: disposed at the most downstream side in the conveyance path in the recording sheet reversing apparatus
Distance between transport roller and fixing roller
V0: Standard conveyance speed V0 of the fixing roller
Vmax: Maximum value of the conveyance speed of the fixing roller
4. The image forming apparatus according to claim 3, wherein Vmin is a minimum value of the conveying speed of the fixing roller. The image forming apparatus capable of double-sided recording is configured such that the length of the recording sheet conveyance path from the conveyance roller arranged at the most downstream side in the conveyance path in the recording sheet reversing apparatus to the fixing device is the maximum usable recording sheet size. The image forming apparatus capable of double-sided recording according to any one of claims 1 to 6, wherein the image forming apparatus has a length equal to or greater than a length in a conveyance direction.

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