JPS6155663A - Image forming device - Google Patents

Abstract

PURPOSE:To reduce form carrying power and increase durability of driving parts and obtain images of high quality by detecting the arrival of a form at a carrying device by the first sensor to raise the carrying speed and detecting the arrival of the form at a fixing part by the second sensor to reduce the carrying speed. CONSTITUTION:When the arrival of the front end of a form 3 is detected before a carrying device D by a sensor 41, power is supplied to a motor 44 to set the speed of the carrying device D to the same first speed as a transfer speed, and the form is considered to be fed out to a belt 10 when the detection signal of the sensor 41 exists again. When a sensor 42 detects the arrival of the form at the position just before a fixing part C, a speed converter 45 switches the carrying speed to the same second speed as a fixing speed, and the form 3 is considered to pass the fixing part completely to stop the motor when the detection signal of the sensor 42 disappears. Since the high-speed carrying operation time is set to a required minimum, the power consumption is minimized to increase the durability of driving parts, and oscillation is suppressed to obtain images of high quality.

Description

[Detailed Description of the Invention] [Technical Field] The present invention relates to an image forming apparatus, and more specifically, it is an improvement in the control of the conveyance speed in a conveyance device for a sheet-like recording material disposed in the image forming apparatus. be.

[Prior Art] In a conventional image forming apparatus of this type, a paper sheet-like recording material (hereinafter referred to as a recording sheet) conveying device has two types of conveying speeds in the process of conveying the recording sheet for image formation. It may be set.

In this type of conveying device, a means for obtaining a sending force through frictional contact with a rotating body such as a roller, drum, or belt is generally used to convey the recording paper on which an image is formed. If the conveyance speeds of the two conveyance means are clearly set to be different when the conveyance path is divided into two on a continuous conveyance path, problems may occur with respect to the image on the recording paper. That is, the impact applied to the recording paper due to the speed difference between the two conveyance means has an adverse effect on the image on the recording paper, such as scattering.

Therefore, by providing a sufficient distance between both conveying means, a variable-speed recording paper conveying device is placed between them, and during conveyance, the conveying speed is changed from a value approximating the feeding speed of one to the feeding speed of the other. It is conceivable to switch to a value that approximates the speed. By the way, if sequence control is performed in which the first stage is set to a high transport speed during normal operation and then switched to the second stage's slow transport speed during transport, the transport time at high speed must be lengthened, and the drive Durability of switching means such as clutches in the system, durability of gears, etc.

Problems such as power consumption due to increased load and noise and vibration are likely to occur.

FIG. 1 shows an example of a conventional conveyance device in an electrophotographic image forming apparatus and the work steps provided on its conveyance path. In FIG. , the latter feeding means also serves as an image fixing section C, and a conveyance device B is disposed between the two.

In this way, a latent image is electrostatically formed on the photosensitive drum 1 and then developed with toner, but the transfer drum 2 can temporarily hold the recording paper 3 by its outer circumference, and the paper 3 is transferred. When the photosensitive drum 1 is in the section A, the developed image on the photosensitive drum 1 can be transferred onto the paper 3 by the charging action of the transfer charger 4 disposed inside the transfer drum 2.

The separation claw 5 separates the paper 3 after the transfer from the transfer drum 2 and guides it to the subsequent conveyance device B. At this time,
The paper 3 is subjected to a feeding action by the rotation of the transfer drum 2.

The drive unit of the conveyance device B is composed of a drive roller 7, driven rollers 8 and 9, which are attached to a drive shaft 6, and an endless belt 10 for conveyance stretched between these. The conveyance speed of the bell (10) can be changed via the drive shaft 6.

The recording paper 3 sent out from the conveyance device B is guided to the image fixing section C at the subsequent stage. While the paper 3 is held between these rollers 12 and 13, the image is fixed by the heat, and the paper is sent out to a tray or the like (not shown). In this case, the rotational speed of the rollers 12 and 13, that is, the fixing speed, is set to be slower than the transfer speed in the transfer section A, and the reason for this is as follows.

For example, when a transparent resin sheet is used as the recording paper 3 in a thermal fixing device, the fixing speed must be slowed down because its thermal conductivity is poorer and the heat capacity is larger than that of plain paper. It is necessary to supplement the amount of heat supplied over time. In addition, when the single layer of toner transferred to the recording paper No. 3 becomes a multilayer structure due to multiple transfers such as color copying, the thermal conditions are different from those for a single layer toner image, so the fixing speed during image formation must be adjusted. It is also known to be configured to be slow. That is, for the reasons described above, the fixing speed is set slower than the process speed represented by the transfer speed.

Furthermore, in FIG.
% 11 is provided with a paper passage detection sensor 15, and a detection signal from this sensor 15 is transmitted to the drive control means 14, so that the drive control means 14 outputs the variable speed drive means 1.
1 is supplied with a control signal, and the rotational speed of the drive roller 7, that is, the fixing speed, is controlled in a predetermined sequence via the variable speed drive means 11.

FIG. 2 shows an example of a variable speed drive mechanism in the conveying device for the recording paper 3 in the image forming apparatus shown in FIG. f31. here,
Rotational driving force supplied from a drive source (not shown) is transmitted to the drive shaft 21. Gear 22 and gear 23 are connected to drive shaft 2
The rotary driving force from the drive shaft 21 is transmitted to a gear 24 and a gear 25 which are fixed to the drive shaft 1 and mesh with each other. The gear 24 is an input side gear of the electromagnetic clutch 26,
In the released state, it is held rotatably along the clutch shaft 27, but when the electromagnetic clutch 26 is energized, the gear 2
4 is transmitted to the clutch shaft 27, thereby rotating the gear 28 fixed to the clutch shaft 27. In addition.

In this example, gear 24 and gear 28 have the same number of teeth. Furthermore, gear 28 and gear 29 are meshed, and gear 2
By applying rotational driving force to gear 9, this gear 29
The drive roller 7A is connected via the transport drive shaft 6 to which the
, 7B, . . . , 70, and the rotation of the drive rollers 78 to 7D can rotate the endless belt 10A-100 that is hung around the outer periphery of the drive rollers 78 to 7D.

Therefore, the recording paper 3 is placed on the belt IO1 as shown in FIG.
That is, these endless bells) are transported by IOA~100, and are transported at approximately the same speed as the moving speed of the bell h IOA~+00. On the other hand, a one-way clutch 30 is attached to the gear 25, and this clutch 30
It is supported on a shaft 31 via. Note that this one-way clutch 3o does not transmit the rotation of the gear 25 to the shaft 31 when the rotation speed of the shaft 31 is faster than the rotation speed of the gear 25 in the normal rotation direction. When 1131 is on the load side, that is, on the driven side, it transmits the rotation of the gear 25 to the shaft 31. A gear 33 is fixed to the shaft 31, and is meshed with a gear 34 fixed to the transport drive shaft 6.

Therefore, in such a two-line drive transmission system, one stage of deceleration is performed between the drive shaft 21 and the conveyance drive shaft 6 on the left side in FIG. The drive is transmitted with the reduction ratio. On the other hand, on the right side of the figure, gear 23 and gear 25. A total of two stages of deceleration is performed by the combination of both the door gear 33 and the gear 34. That is, in the two drive transmission systems in the figure, the left side is a high speed transmission system, and the right side is a low speed transmission system, and by exciting the electromagnetic clutch 26, a high conveyance speed can be achieved.

Next, a sequence operation of the thus configured conveying device and its transmission mechanism will be explained.

First, when the image forming apparatus starts operating, the transporting device also starts operating at the same time, and the transporting speed at this time is set to approximately the same speed as the transfer speed. In other words, 1 image transfer section A
The recording paper 3 on which the image has been transferred is guided to the conveyance device B. At this time, the conveyance speed of the conveyance device B is almost equal to the transfer speed, so no impact occurs in the transfer section due to the speed difference.

Therefore, the leading edge of the recording paper 3 reaches the paper passage detection sensor 15.
When the paper crosses the position, a signal from the paper passage detection sensor 15 is sent to the drive control means 14, and from there a speed switching signal is supplied to the speed change mechanism of the variable speed drive means 11, so that the transport speed of the transport device B is fixed. Since the speed is changed to a low speed that is approximately equal to the speed, the paper 3 is guided to the nip portion between the fixing rollers 12 and 13 without being subjected to impact here as well.

When the fixing progresses and the trailing edge of the paper 3 crosses the paper passage detection sensor 15, a detection signal from the sensor 15 is transmitted to the variable speed drive means 1 via the drive control means 14 in the same manner as described above.
1, and the conveyance speed is returned to the same speed as the original process speed, that is, the transfer speed after an appropriate time delay. Note that the above-mentioned examples are examples in which a function for temporarily reducing the conveyance speed is added to a conventional image forming apparatus in which the transfer speed and the conveyance speed are almost the same and do not change.

However, in such a conventional recording paper transport device δ, a high transport speed or a process speed in the original operating state is used.

During the conveyance process, sequence control is performed in which the speed is temporarily switched to low speed for a process that requires low speed, so the time spent at high speed becomes longer, and this causes the drive part to The following disadvantages arise.

1) When using a high-speed conveyance speed that consumes a large amount of power, the drive is transmitted by the high-speed transmission system shown on the left side of FIG. Since the transmission system has a smaller reduction ratio than the low-speed transmission system shown on the right side, the rotational force required for driving is conversely large, and the drive shaft 21
Since the load on a drive source such as a motor (not shown) that drives the motor increases, the overall power consumption increases.

2) Bearings due to the high speed side driving time which reduces the durability of the conveyor component parts.

Severe wear and tear on gears, belts, etc.

3) Vibration and noise are a problem Since the high-speed, high-load drive is long, problems due to noise and vibration are likely to occur.In other words, since the image forming device is used in an office as an office machine, Although quiet equipment is expected, such high levels of noise and vibration make it impossible to meet market demands. Furthermore, the vibrations induce vibrations in the imaging plane, causing image blur. In particular, in color electrophotographic image forming equipment, it is necessary to expose images separated from a single original image onto a photoconductor multiple times, but due to vibrations, the relative position of each color separated image on the photoconductor may be delicate. This may cause color shift or color unevenness in the post-development and transfer steps. In other words, it is difficult to maintain image quality when there is vibration.

[Purpose] In view of the above-mentioned drawbacks found in the recording paper conveyance device in the conventional image forming apparatus, the present invention reduces power consumption in the recording paper conveyance device and further improves the durability of its component parts. Another object of the present invention is to provide an image forming apparatus that suppresses vibrations and noise and provides high image quality.

[Example] Below, an example of the present invention will be described in detail based on the drawings.

FIG. 3 shows an embodiment of the present invention, where D is a conveying device according to the present invention disposed between an image transfer section A and an image fixing section C. The image forming operation in section C is the same as that in FIG. 1, and its explanation will be omitted. Furthermore, in the conveying device, the drive roller 7, driven rollers 8, 9, belt 1O, etc., and the minute St claw 5 are the same as in the examples of FIGS. 1 and 2, but in this example, the conveyance of this conveyance section FtD A first sensor 41 and a second sensor 42 for paper detection are provided at the entrance and the conveyance exit, respectively, so that these sensors 41 and 42 detect when the paper 3 passes through these positions.

That is, these sensors 41 and 42 detect the period from when the leading edge of the recording paper 3 passes through the detection position until the trailing edge of the recording paper 3 finishes passing through the detection position.

43 is a control means for controlling the switching of the conveyance speed and driving and stopping the motor 44; 45 is the motor 44 and the drive shaft 6;
The control means 43 sends a conversion signal to the conversion device 45 in response to a position detection signal as described later from the sensor 41 or 42, thereby converting the conveyance speed. control so that The mechanism of this speed converter 45 is the same as that shown in FIG. 2.

Next, the operation of the sequence control in the control means 43 of the conveyance apparatus constructed as described above will be explained with reference to FIG.

When the image forming apparatus is powered on, the motor 44 and the electromagnetic clutch 26 are turned off in initial setting (step) 100. Next, image forming operation determination (step) 101
When it is determined whether or not the image forming operation has been started by the operator and the operator presses the operation button, the image forming operation is started.
In paper S1 passage determination (step) 102, it is determined based on the paper leading edge detection signal from the first sensor 41 whether or not the paper 3 has reached the front side of the conveying device. If the paper 3 has not reached this position, this determination is repeated until the paper 3 has arrived, but if it is determined that the paper 3 has reached the above position, the motor and clutch operation settings (step) are performed.
103 sends a signal to the motor 44 and the speed converter 45, energizes the motor 44 and the electromagnetic clutch 26, and sets the transport speed in the transport device to a first speed that is the same as or slightly faster than the transfer speed, and transports the paper 3. .

Next, in paper first passage determination (step) 104, the presence or absence of a paper detection signal from the first sensor 41 is determined again. In passage determination (step) 105, it is detected based on the detection signal from the second sensor 42 whether or not the leading edge of the paper 3 has arrived.

Thus, if it has not arrived, steps 104 and 1
If the determination in step 05 is repeated or if arrival is detected, a signal is sent to the speed converter 45 in step 106.
The clutch 26 is turned off, and the conveying speed in the conveying device is set to a second speed that is the same as or slightly slower than the fixing speed.

Furthermore, in step 104, the signal is
If so, the paper 3 is 1° after it has passed, and at this point the process proceeds to step 106, where the conveyance speed is set to the second speed. Thus, paper second pass key 11 (step) 107
The presence or absence of the paper 3 is determined again based on the detection signal from the second sensor 42, and if it is determined that there is no paper, it is assumed that the paper 3 has passed and the process proceeds to step 108, where the motor 44 is stopped. . Therefore, the conveying operation in this conveying device remains stopped until the next image formation.

In the embodiment described above, the motor 44, which is the drive source for the conveying device, is repeatedly driven and stopped during the copying operation, but this is because the motor 44 is independent of other devices in the image forming apparatus. This is possible only if you have However, some image forming apparatuses use a common drive source for the transport device and another device, and therefore, the drive source cannot be stopped according to the sequence of each individual device. The drive source 44 is driven only during the copying operation, and in the normal process state, the electromagnetic clutch 26 is demagnetized and the conveyance speed is set to the f52 conveyance speed, and after the first sensor 41 detects the leading edge of the paper 3, the second sensor 42
The electromagnetic clutch 2 is activated only until the front end of the paper 3 is detected.
6 may be excited to set the conveyance speed to the first conveyance speed.

Next, another embodiment of the present invention will be described with reference to FIG. Here, 50 and 51 are a pair of paper feed guide plates, and after the recording paper 3 is guided between these paper feed guide plates 50 and 51, it is held between registration rollers 52 and 53. The registration rollers 52 and 53 ensure synchronization between the transport position of the paper 3 and the rotational position of the transfer drum 2. 54 is a sensor for detecting paper passage (
The sensor 54 detects when the leading edge and trailing edge of the sheet 3 pass through the sensor position, that is, the slit 51A provided on the guide plate 51, and sends each detection signal to the drive control means. 55.

56 is a magnet fixedly attached to the transfer drum 2, and 57 is a rotational position detection means (hereinafter referred to as a Hall IC) constructed using a Hall element. The image forming sequence is started from the home position with the drum 2 at the home position. That is, as the drum 2 rotates, when the magnet 5B is rotated to the position of the Hall IC 57, the Hall IC 5? detects the magnetic force of the magnet 56 and sends a position detection signal to the control means 55.

On the other hand, the control means 55 includes, for example, a pulse generator that rotates a disk having slits at equal intervals in the circumferential direction at a constant speed and generates pulse signals at a constant cycle by detecting light passing through the slits. It has a counter for counting, a memory, an arithmetic device, etc.

Therefore, suppose that the pulse in the pulse generator when the leading edge of the paper 3 is detected by the detection sensor 54 is the n3th pulse, and similarly, the pulse when the trailing edge is detected by the sensor 54 is the n2nd pulse. , the time interval of the Halless is t, the length of the paper 3, and the conveyance speed on the paper detection sensor 54 are V, then L= (N2 - nl )XtXv' - (1
) holds true.

However, in the image forming apparatus 1, the registration rollers 52 and 53 and the rotation of the drum 2 are synchronized as described above, but now the paper 3 has finished being transferred in the image transfer section A. Then, if the time taken by the transport device to move the distance corresponding to the length L of the paper 3 at the transfer speed or a speed V slightly faster than the transfer speed is TS, then TS = L/V+ ... (2)
Similarly, the fixing speed or a speed slightly slower than the fixing speed v2
If the time taken to move the distance ML is T4, then T4 = L/V2 =
(3) Therefore, by substituting equation (1) into equations (2) and (3), TS = (nz −nl)XtXv/V+
−(4)T4 = (N2 −nl)Xt
Xv/V2 − (5) is obtained. That is, the control means 55 calculates TS and T from equations (4) and (5).
4 operations are possible.

On the other hand, the transfer drum 2 and the registration rollers 52, 53 (i
fffJ- Since it is driven synchronously with reference to the pulse from the pulse generator, the time from when the Hall IC 57 detects the home position until the paper 3 reaches the position immediately in front of the transport device is T. Then, TI is a constant value given in advance, and therefore, if the number of pulses during that period is N, this number of pulses N is also a constant value.

Furthermore, while the paper 3 moves from the position immediately in front of the transport device to the position immediately in front of the fixing device C, this distance is also set in advance, and the time it takes to move between the transport devices at the above-mentioned speed vI. T2. If the number of pulses during that period is N2, these values are also constant values.

Furthermore, if the time for moving between the conveying devices at the above-mentioned v2 is TS + the number of pulses during that time is N5, these values are also constant values, so the control means 55 sets the number of pulses NI IN2 F3 and N.

is stored in the memory in advance, and the motor 44 is driven and stopped and the speed converter 4 is driven and stopped at the timing of the above-mentioned delay time TI, "2 +73 +74" and T5.
5, the electromagnetic clutch 26 (see FIG. 2) is turned on and off.

Next, the control operation in the control means 55 will be explained based on the flowchart in FIG.

In the image forming apparatus, operation is started in step 200 in response to the image forming operation start signal, and at that time, the photosensitive drum 1 and the transfer drum 2 are rotated idly for initialization. The Hall rc57 is waiting for the magnet 56 on the transfer drum 2 to pass, and in step 201, the Hall IC5? is a magnet 5G
When the passage of is detected, this detection signal is transmitted to the control means 55. In the control means 55, a pulse has already been generated by the pulse generator, and in step 202, the pulse when the detection signal is transmitted is defined as the no-th pulse. Thereafter, in synchronization with the rotation of the transfer drum 2, the paper 3 is fed from a paper feed mechanism (not shown) between the upper paper feed guide 50 and the lower paper feed guide 51.Next, in step 203, the paper detection sensor 54 The leading edge and trailing edge of the paper 3 moving at the speed V are detected, and respective signals are transmitted to the control means 55. In the control means 55, the generated pulse at the time when the leading edge and trailing edge of the paper are detected is set as the nl+12th pulse, and that number is reserved in a temporary memory. In addition, here, the delay time T3 is 'r3= (N2-nl) as mentioned above.
XtXY/V+, and if we change this to the number of pulses, we get
The number of equivalent pulses N3 for the delay time T3 is N5=(N2 n
1) Xv/vI.

Similarly, the number of equivalent pulses N4 of delay time T4 is N4= (n
z-nl)XV/V2. Therefore, these equivalent pulse numbers are calculated in step 204. Thereafter, the paper 3 is gripped by the transfer drum 2 at appropriate timings by the registration rollers 52 and 53, receives the image on the photosensitive drum 1, and is separated by the separation claws 5. However,
When the leading edge of the paper 3 comes just in front of the conveyance device, in step 205 the control means 55 determines whether the number of pulses has reached Nl + nO, and if the number of pulses is (N++no), the motor is switched on in step 206. 44, and further energizes the electromagnetic clutch 2 in the speed converter 45 to drive the conveying device at a speed v1 that is the same as or slightly faster than the transfer speed. Thereafter, the paper 3 is transported by the transport device at a speed vI, but the control means 55 performs step 20? and 2
08, the number of generated pulses is N, +N2+no, that is, the time when the leading edge of the paper 3 reaches the terminal part of the conveyance device, or n=N1+N3+Qo, that is, the time when the trailing edge of the paper 3 reaches just before the conveyance device. Whichever step is determined earlier is adopted, and in step 20G, the electromagnetic clutch 26 in the speed conversion device 45 is demagnetized, and the conveying speed is changed to a speed v2 that is the same as or slightly slower than the fixing speed. Thereafter, the leading edge of the paper 3 is guided to the fixing section C. Next, in steps 210 and 211, the time point when the rear end of the paper 3 reaches the terminal part of the conveying device, that is, the number of generated pulses n is N1 + N2 + N4 + no or N1 + N3
+N5 +n6, whichever step is determined earlier, is adopted and the motor 44 is stopped in step 212.
It is ready for the next image formation.

Note that in the above embodiment, the motor 44, which is the drive source of the conveying device, is repeatedly driven and stopped during the copying operation, but such control is performed so that the drive source is independent from other devices in the image forming apparatus. This is possible only if

However, in some image forming apparatuses, the transport device and another device share a common drive source, and in such cases, it is not possible to stop the drive sources according to the sequence of each individual device. Therefore, in this case, the drive source is driven only during the copy operation, and normally the electromagnetic clutch 26
is demagnetized and the conveyance speed is set to the above-mentioned second conveyance speed v2,
When step 20B is reached, only the electromagnetic clutch 2B is operated and turned on, and the motor 44 is not stopped during one image forming operation without going through steps 210 and 211.
Step 212 may be omitted.

Yet again. The delay times T3 and T4 may change depending on the size of the paper 3, but instead of the paper detection sensor 54 as in this example, the delay times T3 and T4 are determined by a paper size identification signal from the paper holding cassette in the paper supply means. It is also possible to determine times T3 and T4.

Furthermore, in this example, the timing reference signal is obtained from the home position detection signal of the drum 2, but the timing reference signal is not limited to this, and any signal obtained in synchronization with the movement of the paper 3 on the drum 2 may be used. For example, a paper passage detection means may be provided separately, or a drive signal from the registration rollers 52 and 53 or a signal generated when the paper 3 is separated from the drum 2 by the separating claw 5 may be used.

〔effect〕

As explained above, according to the present invention, when the paper sent out from the image transfer section reaches just before the conveyance device, the feed speed at the image transfer section, that is, the conveyance speed is equal to or slightly faster than the transfer speed. Since the conveyance device is driven by switching to the transfer mode, the conveyance device itself has the effect of pulling out the paper from the transfer section, and the occurrence of bending of the paper is prevented. In addition, when an endless belt device is used for conveyance as in this embodiment, there is no risk of extreme tensile force acting due to slippage between the paper and the belt, and there is no impact or other inconvenience caused by speed differences. The paper can be conveyed smoothly without any problems.

In addition, when the paper is transported by the transport device and reaches the end of the transport path, which is just before the fixing section, the transport speed is changed to a transport speed that is equal to or slightly slower than the fixing speed in the fixing section. Therefore, there is no possibility that the sheet will be slightly stretched from the fixing unit side, causing the sheet to bend.

Particularly, if an endless belt is used for conveyance as in this embodiment, the slip between the paper and the endless belt will alleviate the tensile force, and no extreme tensile force will be applied. Therefore, there is almost no impact due to the difference in speed, and the paper can be moved smoothly.

Furthermore, with the sequence control according to the present invention, in a conveying device capable of switching to a plurality of conveying speeds, it is possible to reduce the high-speed conveying operation time to the necessary amount to the minimum time. Since the clutch is in an energized state and the reduction ratio from the drive source is small, the drive load becomes large, resulting in an increase in power consumption.However, according to the present invention, the high-speed conveyance operation time is reduced to the necessary minimum. Therefore, power consumption can be reduced to a minimum.

Furthermore, the durable life of sliding mechanical parts such as bearings, belts, and gears used in the conveyance device is correlated with the drive speed, but the life can be extended by shortening the high-speed conveyance operation time.

Furthermore, the vibration and noise of a driving device generally increase as the driving speed increases, but the sequence control according to the present invention can minimize the time during which they occur, thereby reducing the amount of vibration caused by vibrations. Image blur, color shift, and color unevenness in images can also be minimized.

Yet again. By arranging the paper passage detection means at the front and rear stages of the transport path of the transport device, optimal switching control can be performed depending on the size of the paper used. That is,
In the embodiment, the high-speed conveyance operation can be switched to the low-speed conveyance operation as soon as the passage of the leading edge of the paper is detected by the paper second detection means, and the low-speed conveyance operation can be switched to the low-speed conveyance operation as soon as the passage of the trailing edge of the paper is detected by the paper@1 detection means. It is also possible to switch to operation. Therefore, in the case of especially long paper, that is, even if the leading edge is just before fixing in the latter stage, the trailing edge is still upstream of the first paper detection means, the trailing edge of the paper is detected by the first paper detection means. Detection control is possible by detecting paper with a second paper detection means, and for paper with short dimensions, detection control is possible by detecting with a second paper detection means, and regardless of the paper size, high-speed conveyance operation can be immediately switched to low-speed conveyance operation. As a result, high-speed transport operation time can be kept to a minimum.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing the general configuration of a conventional image forming apparatus together with an example of the configuration of a conveyance device, FIG. 2 is a 4IIi diagram showing a speed conversion mechanism in the conveyance device, and FIG. FIG. 4 is a flowchart showing a conversion control operation in the control means of the conveying device according to the present invention; FIG. 5 is a schematic diagram showing an example of the configuration of the conveying device in the apparatus; FIG. 5 is a diagram showing another embodiment of the image forming apparatus of the present invention. FIG. 6 is a schematic diagram showing the 411 configuration of the transport device. FIG. 6 is a flowchart showing the speed change control operation in the control means of the transport device 11. A... Image transfer section. B, D... Conveyance device, C... Image fixing unit, 1... Photosensitive drum, 2... Transfer drum, 3... Recording paper, 4... Transfer charger, 5... Separation claw, 6... Drive shaft, 7.78-7D... Drive roller, 8.8... Followed roller, 10jOA-100... Belt, 11... Variable speed drive means, 12...・Heating roller, 13... Roller, 14... Drive control means, 15... Paper detection sensor, 21... Drive shaft, 22.23, 24.25... Gear, 26... Electromagnetic Clutch, 27...Clutch shaft, 28.29, 33.34...Gear, 30...One-way flanch, 31...Shaft, 41...First sensor, 42...Second sensor. 43... Drive control means, 44... Motor, 45... Speed conversion means, 50.51... Paper feed guide plate, 51A... Slit, 52.53... Registration roller, 54. ...Paper detection sensor, 55...Drive control means, 56...Magnet, 57...Hall IC. Ku

Claims (1)

[Claims] 1) An image transfer section that sends out a paper sheet at a predetermined transfer speed and transfers an image onto the paper sheet, and an image transfer section that receives the paper sheet from the image transfer section and that is slower than the transfer speed. In an image forming apparatus, the image forming apparatus includes a conveying device that sends out the sheet according to a fixing speed, and an image fixing unit that performs the fixing on the sheet from the conveying device, wherein the leading edge of the sheet is fixed to the conveying device. a first detection means for detecting a first point in time when the sheet is fed to a position immediately before the sheet and a second point in time when the trailing edge of the sheet passes through the position immediately before the sheet; a second detection means for detecting a third point in time at which the transfer speed has been transferred; An image forming apparatus comprising: means for controlling one of the conveyance speeds to a second speed that is lower than the fixing speed. 2) The image forming apparatus according to claim 1, wherein the conveyance operation of the conveyance device is stopped until the paper sheet reaches the first time point. 3) The image forming apparatus according to claim 1 or 2, characterized in that the conveying operation is stopped when the trailing edge of the sheet passes through the trailing edge of the conveying device. Image forming device. 4) In the image forming apparatus according to any one of claims 1 to 3, the control means includes means for generating a clock signal of a predetermined frequency;
An image forming apparatus characterized in that the second and third time points are obtained by counting the clock signals.