JP3038811B2 - Image forming device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION The present invention relates to a toner image obtained by developing an electrostatic latent image formed on a photoreceptor represented by an electrophotographic copying machine, a printer, and a facsimile. The present invention relates to an image forming apparatus for transferring an image onto a sheet or the like, wherein the number of rotations of an OPC photosensitive member or the like is reduced in order to reduce wear of an electrostatic latent image carrier such as an OPC photosensitive member.

[Conventional technology]

Recently, an organic photoconductor called OPC has been used in electrophotographic copying machines instead of an inorganic photoconductor such as selenium. As shown in FIG. 4 (a), the OPC photoreceptor has an undercoat layer UCL, a charge generation layer CGL, and a charge transport layer CTL sequentially provided on a conductive substrate CB.
As shown in FIG. 4 (b), there is a layered photoreceptor having a layer structure or a two-layer structure in which a charge generation layer CGL and a charge transport layer CTL are provided on a conductive substrate CB in this order. It is. The undercoat layer UCL and the charge generation layer CGL usually have a thickness of 1 μm or less, and the charge transport layer CTL has a thickness of 10 to 30 μm. Of these layers, the charge transport layer CTL, which is in direct contact with the cleaning member and the developing member, is an organic material, and is generally fragile and easily worn. The cause of the abrasion includes contact with the developing system and copy paper, but the largest is caused by a cleaning member (blade, fur brush, etc.). For this reason, a binder polymer that is hard to be worn and hard to be damaged is selected in addition to electric characteristics such as charging property and ozone resistance. Generally, polycarbonate resin, polyester resin, methacrylic resin and the like are used.

The Applicant has determined that the OP
In order to prevent the abrasion of the C photoreceptor, a brush for a toner deter bar that removes untransferred toner and paper dust from the photoreceptor or disturbs the photoreceptor to weaken the adhesive force is disposed upstream of the cleaning blade. Have already proposed something (Japanese Utility Model Application No. 62-52088, Japanese Utility Model Application 63-160)
No. 576). According to such a cleaning device, the pressing force and hardness of the cleaning blade can be minimized by appropriately selecting the parameters of the mechanical contact state of the deter bar brush to the photoconductor, and Charge transport layer CTL using the debar bar brush itself
Wear can be minimized. Further, the present applicant, in the cleaning device comprising the cleaning blade and the toner deter bar brush as described above, by selecting the moving speed of the photoconductor and the peripheral speed ratio of the toner deter bar brush in a predetermined range, Charge transport layer
It has been proposed that CTL wear can be minimized (Japanese Patent Application No. 2-39505).

Conventionally, apart from the approach described above, in which the wear of the OPC photoreceptor is reduced as much as possible by improving the cleaning device to prevent the background potential on a white background from rising, the OP
There are approaches to reduce the rotational speed of the C photoconductor as much as possible to reduce its wear. For this purpose, the rotation of the photosensitive drum is stopped when the photosensitive member position corresponding to the rear end of the transfer sheet has passed through the cleaning device (Japanese Patent Application Laid-Open No. 61-32867). Stop the rotation of the photosensitive drum when it reaches
No. 61-32864) are known.

[Problems to be solved by the invention]

By the way, in a conventional image forming apparatus, when a copy button is pressed and control of each part of the entire apparatus is started, driving of a motor for rotating a photosensitive drum is started immediately. In this case, the photosensitive drum is rotated more than necessary to secure a region actually required for forming an electrostatic latent image on the photosensitive member. In addition, an apparatus having a multi-stage paper feed cassette is becoming common. When the cassette closest to the photosensitive drum side is selected and paper is supplied, the cassette located farthest is selected. The number of rotations at which the photosensitive drum rotates extra differs greatly from the case where the paper is supplied. Further, after the toner image formed on the photosensitive drum is transferred to a sheet and the sheet passes through the fixing device and is discharged onto a discharge tray, the photosensitive drum keeps rotating for a while. In this case as well, the rotation is unnecessary except that the untransferred image after the transfer is cleaned and the residual potential of the photosensitive drum is removed by one turn by the discharge lamp. Also, when using in the multi-synthesis copy mode or the duplex copy mode,
While the transfer paper on the first side passes through the fixing device and is conveyed to the double-sided multiplex conveyance device, the photosensitive drum continues to rotate unnecessarily.

As described above, in the conventional image forming apparatus, since the photosensitive drum is rotated more than necessary, particularly when the OPC photosensitive member is used as the electrostatic latent image carrier, the photosensitive member is unnecessarily rotated with the rotation. The background potential of the white background rapidly increased due to abrasion, and the life of the photoconductor was shortened.

SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances, and an object of the present invention is to provide an image forming apparatus having a plurality of paper cassettes and a double-sided multiplex conveying device, and a rotational speed of an electrostatic latent image carrier such as an OPC photosensitive member. Is to provide an image forming apparatus in which the wear is reduced by reducing as much as possible.

[Means for solving the problem]

In order to achieve the above object, a first image forming apparatus according to the present invention is an image forming apparatus that transfers a toner image obtained by developing an electrostatic latent image formed on a photoreceptor surface including a rotating body to a transfer material. The forming apparatus includes a plurality of transfer material supply trays or cassettes, and is configured such that a sheet supply transport path from each tray or cassette to a transfer position merges into one transport path on the way, and The rotation of the body and the drive of the transfer material transport system are configured to be independently controllable, and are supplied from any of the transfer material supply trays or cassettes to any position on the transport path that has joined the one. A detecting means for detecting that the leading end of the transfer material has arrived, and the rotation of the photosensitive member is started based on a detection signal from the detecting means.

In this case, the distance from the mounting position of the detection means on the paper supply conveyance path to the tacking point is the distance from the charger center on the photoreceptor surface to the tacking point, half the width of the charger, The moving distance of the photoconductor surface corresponding to the longer one of the rising time of the charger and the rising time of the photoconductor driving means, and the stoppage time of the transfer material by means of adjusting the posture of the transfer material and taking the transport timing. It is desirable to set the distance to be equal to or greater than the distance obtained by adding the moving distance of the photosensitive member surface to be moved.

Further, a second image forming apparatus of the present invention is an image forming apparatus that transfers a toner image obtained by developing an electrostatic latent image formed on a photoreceptor surface including a rotating body to a transfer material.
A paper circulation conveyance path for circulating the transfer material on which the toner image has been transferred once again to the transfer position is provided, and the rotation of the photoconductor and the drive of the transfer material conveyance system can be controlled independently,
Detecting means for detecting that the rear end of the transfer material on which the toner image has been once fixed arrives near the entrance of the paper circulation conveyance path, and stops rotation of the photoconductor based on a detection signal from the detecting means. It is characterized by having such a configuration.

Further, a third image forming apparatus according to the present invention is an image forming apparatus which transfers a toner image obtained by developing an electrostatic latent image formed on a surface of a photoreceptor formed of a rotating body to a transfer material. And a paper circulating conveyance path for circulating the transfer material on which the toner image has been transferred once and then re-circulating to the transfer position after fixing the transfer material onto which the toner image has been transferred, and reaching the transfer position from each tray or cassette and the circulating conveyance path. The paper supply conveyance path is configured to join one conveyance path in the middle, and the rotation of the photosensitive member and the drive of the transfer material conveyance system can be controlled independently. A first detecting means for detecting that the leading end of the transfer material supplied from any of the transfer material supply tray or cassette or the circulating transfer path reaches any position of the combined transfer path; Also, the paper A second detecting unit is provided for detecting that the rear end of the transfer material on which the toner image has been transferred has reached the vicinity of the entrance of the ring conveying path, and based on a detection signal from the first detecting unit, The rotation of the photoconductor is configured to start, and the rotation of the photoconductor is stopped based on a detection signal from the second detection unit.

In this case, a fixing unit is further provided for fixing the toner image transferred in the paper conveyance path after the transfer to the transfer material, and the rear end of the transfer material on which the toner image is fixed arrives behind the fixing unit. It is desirable to provide a third detecting means for detecting and to stop the rotation of the photoconductor based on a detection signal from the third detecting means.

[Action]

According to the first aspect of the present invention, there is provided a transfer material supply tray or cassette for copying, and the paper transport path from each tray or cassette to the transfer position is configured to join one transport path halfway. And the rotation of the photosensitive member and the driving of the transfer material transport system can be controlled independently, and the transfer material supply tray or cassette of the transfer material supply tray or cassette is located at any position of the transport path where the one is joined. A detection unit is provided for detecting that the leading end of the transfer material supplied from any of the trays has arrived, and the rotation of the photoconductor is started based on a detection signal from the detection unit. Even if there is a variation in the length of the paper transport path from the transfer position to the transfer position, unnecessary rotation of the photoconductor due to this variation can be prevented. In addition, by appropriately selecting the mounting position of the detecting means or appropriately setting the rotation start timing of the photosensitive body based on a signal from the detecting means, unnecessary rotation of the photosensitive body before the image forming operation is minimized. be able to. Therefore, abrasion of the photoconductor due to extra rotation can be reduced.

Further, according to the second aspect of the present invention, a paper circulation path is provided for circulating the transfer material on which the toner image has been fixed once again to the transfer position, and the rotation of the photosensitive member and the drive of the transfer material transfer system are independent. And a detecting means for detecting that the rear end of the transfer material on which the toner image has been transferred once has arrived near the entrance of the paper circulating conveyance path, and a detecting signal from the detecting means is provided. Since the rotation of the photoconductor is stopped based on this, it is possible to prevent the photoconductor from rotating excessively while the transfer material on which the toner image has been transferred is in the paper circulation path. . Therefore, abrasion of the photoconductor due to extra rotation can be reduced.

According to the third invention of the present invention, the first invention and the second invention
Since the inventions are combined, the actions of both can be achieved in a superimposed manner, the unnecessary rotation of the photoconductor can be further prevented, and the abrasion of the photoconductor due to the extra rotation can be further reduced.

〔Example〕

FIG. 1 is a view showing a configuration of an embodiment of an electrophotographic copying machine to which an image forming apparatus according to the present invention is applied, which is provided with a multi-stage paper feed cassette, an automatic document feeder, double-sided copying and multiple image synthesis. It has a function.

In the figure, reference numeral 11 denotes a latent image carrier composed of an OPC photosensitive drum or the like, 12 denotes a pre-charging device such as a corotron for pre-charging the surface of the latent image carrier 11, and 13 denotes a latent image formed on the latent image carrier 11. Inter-image lamp that lights up in areas other than the area, 14
Is an exposure lamp 14a for irradiating the document 21 on the platen 22 with illumination light, a plurality of mirrors 14b forming an optical path for guiding reflected light from the document 21 to the latent image carrier 11, and a latent image of the light image from the document 21. An exposure optical system comprising an imaging lens 14c for forming an image on the position of the carrier 11, a developing device 15 for developing a latent image on the latent image carrier 11 with toner, and a reference numeral 25 for the second and subsequent times of one copy sheet A pre-transfer static elimination lamp for facilitating transfer by eliminating static before the toner-developed latent image carrier 11 reaches the transfer device 17 in copying of
Reference numeral 26 denotes a holding member that holds the copy paper 16 in a position of entering the latent image carrier 11 and corrects the deformation and the like of the copy paper 16, and 17 denotes a corotron or the like that transfers the toner image on the latent image carrier 11 to the copy paper 16. The transfer device 18 transfers the copy paper 16 to the latent image carrier 11 after the transfer process.
A stripping neutralizer 19 such as a corotron that removes the charge on the copy sheet 16 to separate it from the sheet 16. Reference numeral 19 denotes a copy sheet 16 from the latent image carrier 11 when the stripping operation of the copy sheet 16 by the stripper neutralizer 18 is incomplete. Finger for forcibly peeling off the latent image carrier 11
The cleaning device 23 for removing the residual toner is a fixing device that fixes the toner image on the copy paper 16 after the transfer process.

In this embodiment, an automatic document feeder (hereinafter abbreviated as ADF) 30 is provided at the top of the copying machine. The ADF 30 includes a document set tray 31 provided near the platen 22, The original 21 set in the original set tray 31 is placed on the platen in accordance with the timing of each copy cycle.
Document feed roll 32 to be supplied to 22 side and platen cover 24
The transport belt 33 is incorporated in the transport belt 33 for transporting the original 21 sent from the original set tray 31 to the platen 22 to the registration position of the platen 22 and discharging and transporting the original 21 from the registration position of the platen 22 after the completion of the copy cycle.
And a document storage tray 34 formed integrally with the platen cover 24 and storing the documents 21 discharged by the transport belt 33.
It is composed of

Further, in this embodiment, the paper transport system 40 for transporting the copy paper 16 is configured to be capable of performing multiple combined copying and double-sided copying. That is, the paper transport system 40
For example, sheet cassettes 41, 42, and 42 'each containing copy papers 16 of a plurality of sizes, and an intermediate tray 43 temporarily containing copy papers 16 whose first copy cycle has been completed at the time of multiple composite copying and double-sided copying, Feed rolls for sending copy paper 16 from the paper feed cassettes 41, 42, 42 'and the intermediate tray 43
44 to 46, a supply-side transport path 47 for guiding the copy paper 16 from the paper feed cassettes 41, 42, 42 'and the intermediate tray 43 to the transfer site, and disposed near the transfer site in the supply transport path 47. After once positioning the supplied copy paper 16,
A registration gate 48 composed of a resist roll that is sent to the transfer site at a predetermined timing, a discharge tray 49 that discharges and stores the copy paper 16 after a series of copying operations is completed, and the copy paper 16 that has passed the transfer site passes through the fixing unit 23. The discharge-side conveyance path 50 for guiding the copy sheet 16 that has passed through the fixing device 23 to the intermediate tray 43 side, and the discharge-side conveyance path 50 U-turn transport path 51
A first switching gate 52 disposed at the intersection of the two to select one of the transport paths, and an intermediate tray of the U-turn transport path 51
43, a reversing transport path 53 that is used when reversing the copy sheet 16 and is disposed at the intersection of the U-turn transport path 51 and the reversing transport path 53. And a second switching gate 54 for selection. In the drawing, reference numeral 55 denotes a transport roll for transporting the copy paper 16 in each transport path, and reference numeral 56 denotes a transport belt for transporting the copy paper 16.

In such a copying machine, the photosensitive drum 11, the surrounding exposure optical system 14, the fixing device 23, and the transport belt 56, the registration gate 48, and the transport roll 55 immediately before the register gate 48, which are a part of the paper transport system 40, are not shown. The main unit is driven by a main motor. Apart from this, the other parts of the paper transport system 40 are driven by a paper transport system motor (not shown).
The drive of these main motor and paper transport motor is controlled by a microcomputer system of a control unit 70 described later.

On the console panel at the top of the copier, in addition to the start switch 61 for starting the copying operation,
A parallel composition mode switch 62 that is pressed when performing parallel composition on two sheets of copying paper 16, a double-sided copy mode switch 63 that is pressed when performing duplex copying, and a pre-transfer static elimination lamp 25 that is forcibly turned on in the manual feed mode before transfer. Various switches such as a static elimination lamp lighting switch 64 are arranged, and an input signal from each switch is input to the control unit 70.

In this embodiment, the control unit 70 is realized as a microcomputer system as shown in FIG.

In the figure, signals from a start switch 61, a parallel combination mode switch 62, a double-sided copy mode switch 63, and a pre-transfer static elimination lamp lighting switch 64 are input to the CPU 72 via the input interface 71.
Further, a paper supply sensor disposed at the uppermost part of the supply side transport path 47 of the paper transport system 40 and detecting the leading end of the copy paper 16 supplied from any of the paper feed cassettes 41, 42, 42 'and the intermediate tray 43. 91, a fixing device passing sensor 92 that is disposed immediately after the fixing device 23 in the discharge side conveyance path 50 and detects the rear end of the copy-fixed copy paper 16, the first surface is transferred in the multiple image combined copy mode or the duplex copy mode. A U-turn conveyance path 51 is used to detect the rear end of the copy sheet 16 which is fixed and sent to the intermediate tray 43.
The line number from the paper detection sensor that detects the passage timing of the copy paper 16 of the paper transport system 40 such as the double-sided multiplex system carry-in sensor 93 arranged at the entrance is also converted to a CP via the input interface 71.
It is to be input to U72. Based on the input data, the CPU 72 executes various programs including a rotation start timing, a rotation stop timing control program, a parallel synthesis mode program, and the like of the main motor and the like stored in the ROM 73 in advance. Data is exchanged between them. Then, the CPU 72
Outputs various operation signals via an output interface 75, and a variable power section 81 of the optical system 14, a cassette selecting section 82, a main motor power supply 83 for rotatingly driving the latent image carrier 11, an ADF 30, and an exposure of the optical system 14. The lamp 14a, the pre-charger 12, the pre-transfer static elimination lamp 25, the transfer unit 17, the exfoliating static eliminator 18, the inter-image lamp 13, the developing device drive control system 85, and the paper transport system 40 are controlled. The control of the paper transport system 40 includes drive control of the paper transport motor, operation control of the feed rolls 44 to 46, open / close control of the registration gate 48, switching control of the switching gates 52 and 54, drive control of the transport roll 55, and the like. It is.

By the way, in the present invention, as described above, for example, when the OPC photosensitive drum 11 rotates excessively, the photosensitive drum 11 is worn by contact with the cleaning device 20, the developing device 15, and the like, the background potential increases, and the life of the photosensitive drum 11 increases. In order to reduce the length of the photosensitive drum 11, unnecessary rotation of the photosensitive drum 11 is reduced as much as possible. First, as described above, the photosensitive drum 11, the surrounding exposure optical system 14, the fixing device 23, and A main motor for driving a conveying belt 56, a registration gate 48, a conveyance roll 55 immediately before the registration gate 48, which is a part of the system 40,
The paper transport system motor that drives the main part of the paper transport system 40 located at the lower part of the machine main body is composed of another motor, and the main motor is controlled by the drive control by the control unit 70 to charge the photosensitive drum 11 for image formation. It is rotated only at the time of exposure, development, transfer, and cleaning, and at other times, for example, when the transfer paper 16 is moving in the supply conveyance path 47, one side of the paper to be double-sided is transferred and fixed. When the copy paper 16 is moving in the U-turn conveyance path 51, it is not necessary to rotate the photosensitive drum 11 at a time after the copy paper 16 is discharged from the fixing device 23. Therefore, the paper supply sensor 91, the fixing device passage sensor 92, and the double-sided multiplex system carry-in sensor 93 are arranged in the paper conveyance system 40 as described above, and the passage timing of the leading edge or the trailing edge of the copy paper 16 is detected, and the timing is determined. The photosensitive drum 11 is rotated and stopped in response to the command.

This will be described in more detail. In FIG. 1, a feed roll of each of the sheet cassettes 41, 42, 42 'and the intermediate tray 43 is shown.
The paper transport distances from 44, 45, 45 'and 46 to the paper contact point (tack point) of the photosensitive drum 11 immediately before the transfer device 17 are different from each other. Assuming that the rotation of the photosensitive drum 11 starts when the paper 16 is fed by the feed roll 45 'or the like as in the related art, for example, the paper feed cassette located at the bottom
When 42 'is selected, it takes the longest time for the paper 16 to reach the tacking point, so that the photosensitive drum 11 is rotated extra and the wear is the most intense. In order to eliminate such excessive rotation of the photosensitive drum 11, the paper 16 actually conveyed reaches a predetermined point no matter which paper feed cassette or tray 41, 42, 42 ', or 43 is selected. The rotation of the photosensitive drum 11 may be started only when the rotation of the photosensitive drum 11 is reached. The predetermined point is a position where the copy sheet also reaches the tacking point when the position of the surface of the photosensitive drum 11 which is first uniformly charged by the charger 12 reaches the tacking point. This point will be described a little more with reference to FIG. 3. In the figure, a photosensitive drum 11, a charger 12 disposed around the photosensitive drum 11, a tacking point S,
The copy sheet 16, the predetermined point A (the point at which the rotation of the photosensitive drum 11 starts when the copy sheet 16 reaches this point) on the sheet transport path P, and the registration gate 48 are shown. Since the transport speed of the copy paper 16 on the paper path P and the peripheral speed of the photosensitive drum 11 are equal, the developed toner image formed on the photosensitive drum 11 can be transferred onto the copy paper 16 without excess or deficiency. When considering at least only the leading end of the toner image, the charging point 12 on the surface of the photosensitive drum 11
Is required to be set equal to the distance l 'from the predetermined point A on the paper transport path P to the tacking point S. However, in practice, the charger 12
Since the charging is not uniform in half of the width of the charging device, it is necessary to add this distance to the distance l '.
Rise time is required for uniform charging of
In addition, since the rise time is similarly required for stable rotation from the start of the rotation of the motor, it is necessary to add the moving distance of the surface of the photosensitive drum 11 corresponding to the time until these are stabilized to the distance l '. . Not only this, but paper
When 16 is sent through the paper transport path P, it takes some time to adjust the paper position at the registration gate 48, etc.
The photosensitive drum 11 corresponding to the stop time at the registration gate 48
It is necessary to further add the moving distance of the surface to the distance l '. That is, in order to prevent unnecessary wear due to excessive rotation of the photosensitive drum 11, the distance from the point A at which the rotation of the photosensitive drum 11 starts to reach the tacking point S when the copy paper 16 reaches the paper transport path P is reached. l is (a distance l 'from the center of the charger 12 on the surface of the photosensitive drum 11 to the tacking point S) + (half the width of the charger 12) + (charger 12)
The moving distance of the surface of the photosensitive drum 11 corresponding to the longer one of the rising time of the photosensitive drum 11 and the rising time of the main motor for rotating the photosensitive drum 11) + (the photosensitive drum corresponding to the stop time of the copy paper 16 at the registration gate 48) It must be equal to or greater than the sum of (11 surface movement distance), and most preferably equal. In order to start the rotation of the photosensitive drum 11 while satisfying such conditions, it is necessary to position the photosensitive drum 11 in the supply-side transport path 47 after the transport paths from the sheet cassettes 41, 42, 42 'and the intermediate tray 43 have joined. The above-described paper supply sensor 91 is located at the position of the above-described point A or a position before the point A.
And when the paper supply sensor 91 detects the leading end of the copy paper 16 sent from any of the cassettes or trays (when the sensor 91 is placed at the point A) or from the detection, the leading end of the paper 16 is moved to the point A. After the time when the image sensor reaches (when the sensor 91 is arranged before the point A), the drive of the main motor that rotates the photosensitive drum 11 may be started. Such timing control can be easily executed by the microcomputer system of the control unit 70 described above.

By the way, in the above case, if the distance of the supply side transport path 47 after the merging cannot be sufficiently ensured and the arrangement position of the paper supply sensor 91 cannot be selected at or before the point A, the paper supply sensor 91 is When the leading edge of the sheet is detected, the drive of the main motor that rotates the photosensitive drum 11 is started, and the copy sheet 16 is stopped at the registration gate 48 for an extra time corresponding to the distance between the point A and the position where the sheet supply sensor 91 is disposed. It may be configured as follows.

As described above, the paper supply sensor 91 is disposed on the supply side conveyance path 47 after the merging, and the rotation start time of the main motor is controlled based on the signal, so that the excess of the photosensitive drum 11 before the start of the image forming operation is obtained. Rotation can be reduced, and no extra rotation of the photosensitive drum 11 occurs regardless of the size of copy paper selected. When performing a series of continuous copying, such control is usually performed only at the time of the first copy. By the way, even after such a series of image forming operations, it is necessary to stop the rotation of the photosensitive drum 11 as early as possible without performing extra rotation. For this purpose, a fixing device passage sensor 92 is disposed immediately after the fixing device 23 in the discharge side conveyance path 50, and detects the rear end of the copy paper 16 on which the transfer and fixing are performed. If the distance from the tacking point on the paper path to the fixing device passage sensor 92 is equal to or greater than the distance from the tacking point on the photosensitive drum 11 to the cleaning device 20, the fixing device passage sensor 92 moves the rear end of the copy sheet 16 When the detection is detected, the rotation of the main motor is immediately stopped based on this signal, so that unnecessary rotation can be reduced. However, in practice, control is performed so that the rotation of the main motor is stopped after one rotation after the position on the photosensitive drum 11 corresponding to the rear end of the copy sheet 16 has passed through the cleaning device 20. The reason is that the entire surface of the photosensitive drum 11 is discharged by a discharge lamp (not shown). If the distance from the tacking point on the paper path to the fixing device passing sensor 92 is shorter than the distance from the tacking point on the photosensitive drum 11 to the cleaning device 20, the copy paper 16 The rotation of the main motor may be stopped after a time corresponding to the above distance difference or a time obtained by adding a time corresponding to one rotation of the photosensitive drum 11 thereto after receiving the rear end detection signal.

By the way, in the case of using the multi-synthesis copy mode or the duplex copy mode, the copy sheet 16 on which the transfer and fixing of the first side has been completed is transported to the U-turn transport path 51 selected by the switching gate 52. The main motor is driven while the last copy sheet 16 of the series of copies is in the U-turn transport path 51, the reverse transport path 53, the sheet transport system 40 such as the intermediate tray 43, and the photosensitive drum 11.
Is not preferable in terms of the abrasion described above. Therefore, a double-sided multiplex system carrying-in sensor 93 is arranged at the entrance of the U-turn carrying path 51, and the intermediate tray 43 or the reversing carrying path 53 is provided.
To detect the rear end of the copy sheet 16 sent to the printer.
When the double-sided multiplex system carry-in sensor 93 detects the trailing end of the last copy sheet 16 of a series of multiple image combined copy or double-sided copy of the first side, the drive of the main motor is stopped based on the detection signal. To control. In this case, unnecessary rotation of the photosensitive drum 11 is not required until the sheet supply sensor 91 detects the copy sheet 16 conveyed from the intermediate tray 43 to copy the second surface. In this manner, the copy paper 16 is transported only in the paper transport system 40, and the rotation of the photosensitive drum 11 is stopped while the operation related to image formation is not performed around the photosensitive drum 11. Wear of the photoconductor can be reduced.

By actually arranging the above three sensors 91 to 93 as described above and controlling the driving and stopping of the main motor as described above, the charge transport layer CTL of the OPC photosensitive member is changed as shown in the following table. The amount of wear was reduced.

In the above description, the OPC photosensitive drum is assumed as the latent image carrier 11, but the present invention can be similarly applied to the case of an OPC photosensitive belt. Further, the photosensitive drum 11 and the exposure optical system 14 and the like around the photosensitive drum 11 are driven by a main motor, and the paper transport system 40 is described as being driven by another paper transport system motor. However, both are driven by one motor. Even in such a case, the present invention can be applied. In that case, a clutch may be interposed between the motor and the photosensitive drum 11, and the rotation and stop of the photosensitive drum 11 may be controlled at the above-described timing by controlling the clutch.

〔The invention's effect〕

In the image forming apparatus according to the first aspect of the present invention, the image forming apparatus includes a plurality of transfer material supply trays or cassettes, and a sheet supply transport path from each tray or cassette to a transfer position joins one transport path in the middle. And the rotation of the photoreceptor and the driving of the transfer material transport system can be controlled independently, and the transfer material is located at any position on the transport path that has merged with the one. Detecting means for detecting that the leading end of the transfer material supplied from either the supply tray or the cassette has arrived is provided, and the rotation of the photosensitive member is started based on a detection signal from the detecting means. Therefore, even if there is variation in the length of the paper transport path from each tray or cassette to the transfer position, unnecessary rotation of the photoconductor due to this variation can be prevented. Moreover,
By appropriately selecting the mounting position of the detecting means or appropriately setting the photoconductor rotation start timing based on a signal from the detecting means, it is possible to minimize unnecessary rotation of the photoconductor before the image forming operation. it can. Therefore, abrasion of the photoconductor due to extra rotation can be reduced.

In the image forming apparatus according to the second aspect of the present invention, a paper circulating conveyance path for circulating the transfer material on which the toner image is fixed once to the transfer position is provided, and the rotation of the photosensitive member and the driving of the transfer material conveyance system are performed. And a detection means for detecting that the rear end of the transfer material on which the toner image has been transferred once has reached near the entrance of the paper circulation conveyance path. Is configured to stop the rotation of the photoconductor based on the detection signal of the photoconductor, preventing the photoconductor from rotating excessively while the transfer material on which the toner image has been transferred is in the paper circulation conveyance path. can do.
Therefore, abrasion of the photoconductor due to extra rotation can be reduced.

In the image forming apparatus according to the third aspect of the present invention, since the first and second aspects are combined, the actions of both can be achieved in a superimposed manner, and the unnecessary rotation of the photoreceptor can be further prevented. Thus, wear of the photoconductor due to excessive rotation can be further reduced.

The above-described image forming apparatus of the present invention is particularly effective when an OPC photoconductor is used.

[Brief description of the drawings]

FIG. 1 is a diagram showing the configuration of an embodiment of an electrophotographic copying machine to which the image forming apparatus according to the present invention is applied, FIG. 2 is a block diagram showing a control system of the electrophotographic copying machine shown in FIG. FIG. 4 is a view for explaining the position of the point where the rotation of the photosensitive drum starts when the copy paper is reached, and FIG. 4 is a sectional view of the OPC photosensitive member. 11 ... Latent image carrier, 12 ... Precharger, 13 ... Inter-image lamp, 14 ... Exposure optical system, 14a ... Exposure lamp, 1
4b: Mirror, 14c: Image forming lens, 15: Developing device, 16
…… Copy paper, 17… Transfer unit, 18… Peak eliminator, 19
… Finger, 20… cleaning device, 21… original,
22 ... Platen, 23 ... Fixer, 24 ... Platen cover, 25 ... Electric discharge lamp before transfer, 26 ... Holding member, 30 ...
Automatic document feeder, 31 Document set tray, 32 Document feed roll, 33 Transport belt, 34 Document storage tray, 40 Paper transport system, 41, 42, 42 'Paper feed cassette , 43 ... Intermediate tray, 44, 45, 45 ': 46 ... Feed roll, 47 ... Supply side transport path, 48 ... Register gate, 49 ... Discharge tray, 50 ... Discharge side transport path, 51 ... U-turn transport path, 52 ... First switching gate, 53 ... Reverse transport path, 54
… Second changeover gate, 55… Convey roll, 56… Convey belt, 61… Start switch, 62… Parallel composition mode switch, 63… Duplex copy mode switch, 64… Light-off lamp before transfer Switch, 70 Control unit, 71
…… Input interface, 72 …… CPU, 73 …… ROM, 74
… RAM, 75… output interface, 81… magnification change section of optical system, 82… cassette selection section, 83… main motor power supply, 85… developing device drive control system, 91… paper supply sensor,
92: Fixing unit passage sensor, 93: Double-sided multiplex system carry-in sensor

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-253962 (JP, A) JP-A-3-216667 (JP, A) JP-A-61-32867 (JP, A) (58) Investigation Field (Int.Cl. ⁷ , DB name) B41J 29/38 G03G 15/00 G03G 21/00

Claims (5)

(57) [Claims] An image forming apparatus for transferring a toner image obtained by developing an electrostatic latent image formed on a surface of a photoreceptor formed of a rotating body to a transfer material is provided with a plurality of transfer material supply trays or cassettes. The paper supply conveyance path from each tray or cassette to the transfer position is configured to join one conveyance path in the middle, and the rotation of the photoconductor and the drive of the transfer material conveyance system are independent. And a detection unit that detects that the leading end of the transfer material supplied from any of the transfer material supply trays or the cassette has reached any position of the transport path that has joined the one. Means for starting rotation of the photoconductor based on a detection signal from the detection means. A distance from the mounting position of the detection means to the tacking point on the paper supply / conveying path is a distance from the center of the charger to the tacking point on the surface of the photoreceptor, and is half the width of the charger. The moving distance of the photoconductor surface corresponding to the longer one of the rising time of the charger and the rising time of the photoconductor driving means, and the stop time of the transfer material by the means for adjusting the posture of the transfer material and taking the transport timing 2. The image forming apparatus according to claim 1, wherein the distance is set to be equal to or longer than a distance obtained by adding a moving distance of the photosensitive member surface corresponding to the distance. 3. An image forming apparatus for transferring a toner image obtained by developing an electrostatic latent image formed on a surface of a photoreceptor comprising a rotating body to a transfer material, the transfer material having the toner image fixed thereon once. A paper circulation path for circulating the paper to the transfer position again,
The rotation of the photoreceptor and the drive of the transfer material transport system are configured to be independently controllable, and it is determined that the rear end of the transfer material on which the toner image has been transferred once reaches near the entrance of the paper circulation transport path. An image forming apparatus, comprising: detecting means for detecting, wherein rotation of the photoconductor is stopped based on a detection signal from the detecting means. 4. An image forming apparatus for transferring a toner image obtained by developing an electrostatic latent image formed on a surface of a photoreceptor comprising a rotating body to a transfer material, comprising a plurality of transfer material supply trays or cassettes. A paper circulating conveyance path for circulating the transfer material on which the toner image has been once transferred to the transfer position again after fixing,
The paper supply transport path from each tray or cassette and the circulating transport path to the transfer position is configured to join one transport path in the middle, and the rotation of the photoconductor and the drive of the transfer material transport system are performed. Are configured to be independently controllable, and the leading end of the transfer material supplied from any of the transfer material supply tray or cassette or the circulating transport path is located at any position of the transport path that has merged into one. A first detecting means for detecting that the toner image has arrived is provided, and a second detecting means for detecting that the rear end of the transfer material on which the toner image has been once transferred arrives near the entrance of the paper circulation path. The rotation of the photoconductor is started based on a detection signal from the first detection unit, and the rotation of the photoconductor is stopped based on a detection signal from the second detection unit. Features An image forming apparatus. 5. A fixing device for fixing a toner image transferred in a paper transport path after transfer to a transfer material, wherein a rear end of the transfer material on which the toner image is fixed arrives behind the fixing device. 5. The image forming apparatus according to claim 4, further comprising a third detecting unit for detecting, wherein rotation of the photosensitive member is stopped based on a detection signal from the third detecting unit.