JP2007119235A - Image forming apparatus - Google Patents

Abstract

Image formation that can eliminate image defects such as color misregistration, image rubbing, trailing edge splash, discharge image, etc. regardless of the type of recording medium by always properly controlling the loop of the recording medium during transfer and fixing. Providing equipment.
A loop detecting unit for detecting a loop amount generated in a recording medium between the image forming unit and the fixing unit; a time measuring unit for measuring an on / off time of a signal detected by the loop detection time; Speed switching means capable of switching the recording medium conveyance speed by the fixing means in at least two stages, and in a state where the recording medium S is being conveyed, the loop amount detected by the loop detection means 23 and the time measuring means 25 The speed switching means is switched according to the detection time measured by the above, and the loop amount of the recording medium S is controlled.
[Selection] Figure 2

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile machine that forms an image by, for example, electrophotography. In particular, the present invention relates to an image forming apparatus that forms a toner image in an image forming unit, transfers the toner image to a recording medium, and fixes the transferred image on the recording medium.

  2. Description of the Related Art Conventionally, as a color image forming apparatus that forms a color image at high speed, there is what is called an in-line method. That is, in the in-line type color image forming apparatus, a photosensitive drum is arranged for each color of yellow (Y), magenta (M), cyan (C), and black (Bk) along the conveyance belt. Then, the images of the respective colors formed on the respective photosensitive drums are sequentially superimposed and transferred onto a recording medium conveyed by the conveyance belt, or the toner images of the respective colors are sequentially transferred onto the intermediate transfer belt so as to overlap each other. Finally, the toner images are transferred to the recording medium all at once.

  As a main problem in this in-line type color image forming apparatus, there is a color shift between colors of a color image. One of the causes of this color misregistration is a speed difference between the speed of the conveyance belt that conveys the recording medium (that is, the transfer speed) and the fixing speed in the fixing unit.

  This is because the speed of the recording medium is governed by the fixing speed after entering the fixing, and the recording medium cannot be fed at a constant speed after entering the fixing.

Therefore, generally, as described in Patent Document 1, a loop is formed on the recording medium before the entrance of the fixing unit, and the loop amount at that time is made constant (hereinafter referred to as “loop control”). ) Minimizes the difference in speed between transfer and fixing.
JP-A-7-234604

  However, even if the speed difference between transfer and fixing is eliminated, in order to always perform stable loop control with the diversification of media, the support for double-sided printing, and the speedup of the device, it is necessary to adapt to the paper type and print mode. It becomes necessary to set and control the optimum loop.

  In particular, when passing thin paper or high-resistance media in a low-humidity environment, the transfer separation state becomes unstable due to charging up of the recording medium during double-sided printing, and the leading edge of the recording medium enters the fixing nip. Variations sometimes occurred.

  For example, when the speed of the apparatus increases, the state of the recording medium entering the fixing nip portion becomes unstable, so that the recording medium enters the fixing nip portion on the left and right (in the direction orthogonal to the recording medium traveling direction). There may be a difference in both sides of the recording medium. As a result, a left-right difference is likely to occur in the formed loop, and an image defect may occur due to the left-right difference of the loop.

  In this case, not only the color misregistration but also the paper conveyance state (loop amount) at the time of fixing becomes unstable, so that image rubbing at the time of fixing, trailing edge splash, discharge image, etc. may occur.

  Furthermore, when the distance between the transfer and fixing is short, it is difficult to secure an appropriate loop amount and a transfer distance between the transfer and fixing that can absorb the difference between the left and right loops. Improvement is required.

  Accordingly, an object of the present invention is to always control the loop of the recording medium properly between the transfer and fixing, thereby eliminating image defects such as color misregistration, image rubbing, trailing edge splash, and discharge image regardless of the type of the recording medium. It is an object of the present invention to provide an image forming apparatus.

The above object is achieved by the image forming apparatus according to the present invention. In summary, according to the first aspect of the present invention, in an image forming apparatus that forms an image in an image forming unit, transfers the image to a recording medium, and fixes the transferred image to the recording medium.
Conveying means for carrying and conveying the recording medium to the image forming unit in order to transfer the image formed by the image forming unit to the recording medium;
Fixing means for fixing the image to the recording medium while conveying the recording medium to which the image has been transferred, fed from the conveying means;
A loop detection unit for detecting a loop amount generated in the recording medium between the image forming unit and the fixing unit;
Time measuring means for measuring the on / off time of the signal detected by the loop detection time;
A speed switching means capable of switching the recording medium conveyance speed by the fixing means in at least two stages;
In a state where the recording medium is being transported, the speed switching means is switched according to the loop amount detected by the loop detecting means and the detection time measured by the time measuring means to control the loop amount of the recording medium. Control means;
An image forming apparatus is provided.

According to a second aspect of the present invention, in the image forming apparatus for forming an image in the image forming unit, transferring the image to a recording medium, and fixing the transferred image to the recording medium.
Conveying means for carrying and conveying the recording medium to the image forming unit in order to transfer the image formed by the image forming unit to the recording medium;
Fixing means for fixing the image to the recording medium while conveying the recording medium to which the image has been transferred, fed from the conveying means;
A loop detection unit for detecting a loop amount generated in the recording medium between the image forming unit and the fixing unit;
Time measuring means for measuring the on / off time of the signal detected by the loop detection time;
A speed switching means capable of switching the recording medium conveyance speed by the fixing means in at least two stages;
In a state where the recording medium is being conveyed, if the loop amount generated in the recording medium during the conveyance from the image forming unit to the fixing unit has not changed over a predetermined time, the speed switching unit is switched, Control means for switching the recording medium conveying speed of the conveying means;
An image forming apparatus is provided.

  According to the present invention, it is possible to provide an image forming apparatus that does not cause image defects such as color misregistration, image rubbing, trailing edge splash, and discharge image regardless of the type of recording medium.

  The image forming apparatus according to the present invention will be described below in more detail with reference to the drawings.

Example 1
FIG. 1 shows a schematic configuration of an electrophotographic color image forming apparatus which is an embodiment of the image forming apparatus of the present invention. First, the overall configuration of the color image forming apparatus of this embodiment will be described with reference to FIG.
(overall structure)
Referring to FIG. 1, in this embodiment, the color image forming apparatus includes four drum-shaped electrophotographic photosensitive members (hereinafter referred to as “photosensitive drums”) 1 (1a, 1b, 1c, 1d). I have. Around each photosensitive drum 1, charging means 2 (2a, 2b, 2c, 2d) for uniformly charging the surface of the photosensitive drum 1 are arranged in order according to the rotation direction. Further, around the photosensitive drum 1, exposure such as a laser beam scanner device that forms an electrostatic latent image by irradiating a laser beam on the photosensitive drum 1 whose surface is uniformly charged based on image information. Means 3 (3a, 3b, 3c, 3d) is arranged. Further, a developing device 4 (4a, 4b, 4c, 4d) is provided around the photosensitive drum 1 as a developing unit that causes toner to adhere to the electrostatic latent image on the photosensitive drum 1 to be visualized as a toner image. Is arranged. Around the photosensitive drum 1, transfer means 5 (5a, 5b, 5c, 5d) such as a transfer roller for transferring the toner image on the photosensitive drum 1 to a recording medium is disposed. Further, around the photosensitive drum 1, cleaning means 6 (6a, 6b, 6c, 6d) for removing post-transfer toner remaining on the surface of the photosensitive drum 1 after transfer is disposed. The photosensitive drum 1, the charging unit 2, the exposure unit 3, the developing unit 4, the transfer unit 5, the cleaning unit 6, and the like constitute an image forming unit.

  In this embodiment, the photosensitive drum 1, the charging unit 2, the developing unit 4, and the cleaning unit 6 are integrated into a cartridge to form a process cartridge 7 (7a, 7b, 7c, 7d). Yes.

  The recording medium S fed from the feeding unit 8 is transported to the image forming unit by a transport unit 9 constituted by an electrostatic transport belt 9a, and each color toner image is sequentially transferred to record a color image. . Thereafter, the recording medium S is image-fixed by the fixing unit (fixing unit) 10 and discharged to the discharge unit 13 by the discharge rollers 11 and 12.

  In the case of double-sided printing, before the recording medium S is fixed by the fixing unit 10 and discharged by the discharge rollers 11 and 12, the discharge rollers 11 and 12 are reversed to be conveyed to the double-sided conveyance path 15. (Arrow D direction). The recording medium S conveyed to the double-sided conveyance path 15 passes through the oblique feeding roller 16 on the front surface of the apparatus main body, and is conveyed vertically downward to the U-turn roller 17, and an image forming unit is formed by the U-turn roller 17 and the registration roller 8 d. It is conveyed to.

  Next, the configuration of each unit will be described sequentially.

(Recording medium feeding configuration)
The feeding unit 8 includes a feeding cassette 8a, a multi feeding tray 8b that is a multi feeding device, a multi feeding unit 8c, and a registration roller 8d.

  The feeding cassette 8a stores a plurality of recording media S and is loaded on the inner bottom of the apparatus main body. At the time of image formation from the feeding cassette 8a, the recording medium S is separated and conveyed one by one by the cassette pickup roller 8a1, and conveyed to the image forming unit by the cassette conveying roller 8a2 and the registration roller 8d.

  Next, the multi-feed tray 8b is normally stored in front of the apparatus main body, but when used, the multi-feed tray 8b is rotated and opened from the apparatus main body, and a plurality of recording media S are set. At the time of image formation from the multi-feed tray 8b, the recording medium S is separated and conveyed one by one by the multi-pickup roller 8c1, and conveyed to the image forming unit by the multi-conveying roller 8c2 and the registration roller 8d.

  At this time, feeding from a multi-feeding device 8b that uses a recording medium such as cardboard, envelope, special paper, etc., which is relatively difficult to electrostatically attract to the surface of the electrostatic conveyance belt 9a or has a strong stiffness. The route is configured as follows.

  That is, the recording medium S has a curved shape such that when the recording medium S reaches the surface of the electrostatic conveyance belt 9a, the leading end and the trailing end are along the belt surface and the central portion is floated.

  The feeding path from the feeding cassette 8a shown in FIG. 1 has a curve that warps against the surface of the electrostatic conveyance belt 9a. However, since the recording medium S fed from the feeding cassette 8a is relatively weak and uses the recording medium S that is easily attracted to the surface of the electrostatic transport belt 9a, the cassette as shown in FIG. It has been found that taking the feed route is not a problem.

  Separation and conveyance of sheets in the feeding cassette 8a and the multi-feeding unit 8c are performed by a feeding motor (not shown) in the feeding unit 8 via a gear drive train.

(Image formation configuration)
The photosensitive drum 1 as an image carrier is configured by applying an organic photoconductor layer (OPC) to the outer peripheral surface of an aluminum cylinder. Both ends of the photosensitive drum 1 are rotatably supported by flanges, and a driving force is transmitted from one driving motor (not shown) to one end in a counterclockwise direction indicated by an arrow in FIG. Driven by rotation.

  Each charging means 2 is a conductive roller formed in the shape of a roller. The roller is brought into contact with the surface of the photosensitive drum 1 and a charging bias voltage is applied by a power source (not shown) to thereby surface the surface of the photosensitive drum 1. Is uniformly charged.

  The exposure means 3 is a laser beam scanner device in this embodiment, and has a polygon mirror 31 (31a, 31b, 31c, 31d), and this polygon mirror 31 corresponds to an image signal from a laser diode (not shown). Image light is irradiated.

  The developing unit 4 includes a toner storage unit that stores toner of each color of black, cyan, magenta, and yellow. Further, the developing means 4 is provided with a developing roller 41 (41a, 41b, 41c, 41d) as a developer carrier which is adjacent to the surface of the photosensitive drum and is rotationally driven by a driving unit (not shown). The developing roller 41 is developed by applying a developing bias voltage from a developing bias power source (not shown).

  Further, inside the electrostatic conveyance belt 9a, which will be described later, transfer members 5a, 5b, 5c, and 5d that abut against the electrostatic conveyance belt 9a facing the four photosensitive drums 1a, 1b, 1c, and 1d, respectively. It is attached. These transfer members 5 are connected by a power supply for transfer bias (not shown), and a positive charge is applied from the transfer member 5 to the recording medium S via the transfer conveyance belt 9a. By this electric field, the negative color toner images on the photosensitive drum 1 are sequentially transferred to the recording medium S in contact with the photosensitive drum 1 to form a color image.

  The toner image detection sensor 20 detects a toner pattern for measuring a color misregistration amount formed on the transfer conveyance belt 9a, calculates a color misregistration amount based on the detection result, and forms an image based on the calculation result. Correct the position.

(Recording medium transport configuration)
The recording medium S is conveyed from the feeding unit 8 to the image forming area by the conveying unit 9.

  An electrostatic conveyance belt 9a as a recording medium carrier constituting the conveyance means 9 is stretched and supported by four rollers of a driving roller 9b and driven rollers 9c, 9d, 9e, and all the photosensitive drums 1a, 1b, 1c and 1d are arranged opposite to each other. By this drive roller 9d, the recording medium S is conveyed to the transfer position by the electrostatic conveyance belt 9a, and the toner image on the photosensitive drum 1 is transferred.

  In addition, an adsorption roller 9f that holds the recording medium S together with the belt 9a and attracts the recording medium S to the electrostatic conveyance belt 9a is disposed at the most upstream position of the electrostatic conveyance belt 9a. When the recording medium S is conveyed, an electric field is formed between the suction roller 9f and the grounded roller 9c facing each other by applying a voltage to the suction roller 9f. As a result, dielectric polarization is generated between the electrostatic transport belt 9a and the recording medium to generate an electrostatic attracting force on both.

(Fixing configuration)
The fixing unit 10 serving as a fixing unit applies heat and pressure to the unfixed toner image formed on the recording medium S to fix it.

  The cylindrical fixing belt 10a having an elastic layer includes a heating element (not shown) inside and is guided by a belt guide member 10c. The elastic pressure roller 10b sandwiches the fixing belt 10a and forms a fixing nip portion N having a predetermined width with a predetermined pressure contact force with the belt guide member 10c.

  The pressure roller 10b is rotationally driven by a driving means (not shown), and the cylindrical fixing belt 10a is rotated accordingly, and power is supplied from a circuit (not shown) to the heating element so that the surface of the fixing belt 10a has a predetermined temperature. Controlled.

  In a state where the fixing nip N rises to a predetermined temperature and is temperature-controlled, the recording medium S on which the unfixed toner image conveyed from the image forming unit is formed is the fixing belt 10a and the pressure roller 10b of the fixing nip N. It is sent between. The recording medium S is introduced with the image surface facing upward, that is, facing the fixing belt surface. That is, the recording medium S is nipped and conveyed through the fixing nip N together with the fixing belt 10a with the image surface closely contacting the outer surface of the fixing belt 10a in the fixing nip N.

(Loop formation configuration)
Next, a configuration in which a loop is formed in the recording medium S by the fixing unit 10 will be described with reference to FIG.

  When the image on the recording medium S is fixed, the recording medium clamping force at the fixing nip N is stronger than the clamping force of the transfer unit. Therefore, if the conveyance speed at the fixing unit 10 and the conveyance speed at the transfer unit are different, recording is performed. The medium S is conveyed at the fixing speed.

  Therefore, as shown in FIG. 2, the image forming apparatus of the present embodiment is provided with a loop detection unit 23 that detects the loop amount of the recording medium S between the fixing unit 10 and the transfer unit. The loop detection means 23 is rotatable about the shaft portion 23a, and whether or not the flag 21 of the rotation source portion shields the detection sensor 22 formed of an optical sensor from the recording medium S is determined. It is detected whether the loop amount has reached a certain level. The on / off state of the signal detected by the loop detecting means 23 is measured by a timer (time measuring means).

  On the other hand, the driving speed of the elastic pressure roller 10 b of the fixing unit 10 can be switched at least in two or more stages by the control unit 200 including the speed switching unit 201. Then, the loop amount of the recording medium S is made constant by switching the driving speed according to the detection result of the detection sensor 22. In this embodiment, switching in two stages is possible.

  That is, when there is no loop in the recording medium S to be conveyed, the detection sensor 22 is in an on state, and when the loop amount becomes larger than a predetermined amount, the flag 21 is turned off to shield the detection sensor 22. Accordingly, when the detection sensor 22 is on, the conveyance speed of the recording medium S by the fixing unit 10 is increased, and when the detection sensor 22 is turned off, the conveyance speed by the fixing unit 10 is decreased. As a result, the loop amount of the recording medium S near the entrance of the fixing unit 10 can be made constant.

  Next, the conveyance state of the recording medium S during loop control will be described.

  FIG. 2 is a cross-sectional view showing a paper conveyance state during transfer and fixing, and a solid line A in the drawing shows a normal loop formation state. On the other hand, dotted lines B and C indicate the loop state when a left-right difference occurs in the loop (hereinafter referred to as “one loop”).

  In normal times, there is no difference between the right and left (both sides of the recording medium S in the direction orthogonal to the traveling direction of the recording medium S) in the timing of the recording medium leading edge entering the fixing nip N. Therefore, a solid line A loop is formed in order to enter the nip uniformly on the left and right. Therefore, good recording medium conveyance can be obtained, and there is no occurrence of image defects such as blurring or discharge images.

  On the other hand, when double-sided or thin paper, moisture-absorbing soft paper, dry high-resistance paper, or the like is used, the conveyance of the recording medium S after transfer separation becomes relatively unstable, and the fixing inrush timing is reduced. There may be a slight left-right difference in the timing at which the leading edge of the recording medium enters the fixing nip N. In this case, a left-right difference occurs in the distance between the transfer and fixing of the recording medium S, and a loop must be formed and transported with the left-right difference generated. This right / left difference makes it difficult to form an appropriate loop over the entire length. As a result, a single loop such as dotted lines B and C in FIG. 2 may be generated. In this case, color misregistration, image blurring, and image defects such as discharge images may occur.

  This will be further described with reference to FIGS.

  FIG. 3 is a diagram illustrating a conveyance state of the recording medium S between the image forming unit (transfer separating unit) and the fixing unit at the time of forming a predetermined loop, that is, between the transfer and fixing. 4 and 5 are diagrams showing a state in which a single loop is generated. When a left-right difference occurs at the leading edge, the recording medium conveyance state is as shown in FIG. 4, and this loop state is maintained until the trailing edge of the recording medium S passes through the transfer separation portion.

  In addition, when the difference between the left and right ends is large, the one loop may be further deteriorated.

  When this left-right difference is large, it is difficult to maintain the loop. For example, when the recording medium S is continuously pushed in on the side where the loop is larger, a left-right difference is caused in the color misregistration. Alternatively, as a result of continuing to be pushed in, the state shown in FIG. 5 is reached and the recording medium S is pushed in until a loop cannot be formed. In this case, the trailing edge of the recording medium S, the image is rubbed, or the transfer / conveyance separation state becomes unstable, which may cause image defects due to abnormal discharge.

  If the difference between the right and left of entry can be eliminated, appropriate loop control can be easily performed. Therefore, it is possible to obtain the transportability of the recording medium S during stable transfer and fixing, and to suppress the occurrence of image defects. However, it is difficult to completely eliminate variations in transport and left-right differences as various media, both sides support, and speeding up of the apparatus are increased. The present invention solves the above-mentioned problems by appropriately performing loop control even when a slight difference between the left and right rushes occurs.

  Hereinafter, the loop control according to the present invention will be described.

  The process speed of the image forming apparatus used in the present embodiment is 180 mm / sec for the electrostatic conveyance belt 9a. Further, the second speed used for fixing loop control has a speed difference of ± 3% with respect to the process speed of the electrostatic conveyance belt 9a of 180 mm / sec. That is, the speed High is 186 mm / sec and the speed Low is 174 mm / sec.

The media used is thin paper (basis weight 60 g / m ² ), and the test environment is a low temperature and low humidity environment (specifically, 15 ° C., 10% RH). In this case, completely left-over paper that has been allowed to stand for a week or more in a low-temperature and low-humidity environment is used.

  In the case of using an apparatus having a relatively high process speed as described above, the recording medium S is used particularly when the recording medium S that has been left for a long time in a low-temperature and low-humidity environment is used during double-sided conveyance. In some cases, the transfer of the paper becomes unstable. In rare cases, a single loop may occur.

  6 and 7 show the sensor output and the fixing speed control output when there is no one-loop and when there is one-loop during continuous duplex printing.

  FIG. 6 shows sensor output and fixing speed control output when a normal loop is formed.

  When a small loop → large loop is detected, the speed is switched from low to high after a predetermined delay time. Similarly, when a large to small loop is detected, control is performed so that a constant loop amount is always maintained stably by switching from High to Low after a predetermined delay time.

  In this embodiment, 4 ms is set as the delay time. If the delay time is too short, control may be violated, and if the delay time is too long, the amplitude of the loop may increase, causing other adverse effects. In all the embodiments described below, the delay time is unified at 4 ms.

  The output shown by the solid line in FIG. 7 shows the sensor output and the fixing speed control output when one loop occurs in the conventional control. The dotted line in FIG. 7 shows the sensor output and the fixing speed control output when the control according to the present invention is performed.

  FIG. 6 shows an appropriate loop control, which can obtain good transportability, and there is no occurrence of transport failure or image failure.

  The output indicated by the solid line in FIG. 7 is a sensor output when a so-called single loop has occurred. In FIG. 7A, since the speed is Low, the loop amount increases with time. Originally, when it is detected that the loop is large, the speed is switched to High, and the loop size is eliminated.

  However, when a single loop is formed, a sufficiently large loop is formed after a predetermined time has passed at a low speed. Nevertheless, the sensor output may detect that the loop is small (the loop C in FIG. 2 detects the small loop in the sensor even though the loop is large). In this case, the speed Low is maintained to further increase the loop. As a result, the control is further performed to enlarge the loop. Therefore, in this case, the recording medium S is pushed in more and more, causing image problems such as color misregistration, trailing edge splashes, and abnormal discharge images.

  The output indicated by the dotted line in FIG. 7 shows the output waveform when the control of the present invention is used.

  In the present invention, when the recording medium S continues to detect the loop small for a predetermined time T or more while the loop control is being executed between the transfer and fixing, it is determined that a loop formation defect due to one loop has occurred, and is forced. Switch to Speed High. Control is performed at a high speed until the loop detecting means detects a predetermined loop, and control is shifted to normal loop control after the loop detecting means detects the predetermined loop.

  In the present embodiment, the predetermined time T = 100 ms.

  The predetermined time T varies optimally depending on the process speed, the distance between the transfer and fixing, the configuration of the apparatus (depending on the shape of the conveyance path of the recording medium S), the response speed of the control, and the like.

  In the setting used in the present embodiment, the switching time until the predetermined loop amount is detected from the ON state of the loop sensor output at the time of control execution until it is detected again (this is referred to as “loop control response time t Is defined as about 25 to 50 ms. Therefore, when this switching was not performed three times in succession, it was determined that the control was abnormal, and the value was set within a range of 75 to 150 ms, which is three times the response time. However, the optimum value differs depending on the device configuration and the like.

  As for the method for determining the predetermined time T, the predetermined time T can be variably controlled by the response speed t of the loop control defined above. In this case, a response time t at the time of loop control is detected, and an optimum predetermined time T is determined based on the result of the detected response time t. For example, it is set in a range of T = 2t to 5t, or an average of response times t is always calculated and fed back to a predetermined time T. As a result, optimum control can be performed according to the paper type and print mode, and stable loop control is always possible.

  In this embodiment, when the speed Low is detected for 100 ms or more during the control, it is forcibly switched to the speed High as shown in (B) in FIG. As a result, the one loop is gradually eliminated with time, and the sensor detects a normal loop (shown by a one-dot chain line in FIG. 7 (C)). Then, when a regular loop is detected, the control returns to the conventional control and this control is repeated.

  As a result, even when a single loop occurs, optimal loop control is possible.

  As described above, at the time of loop control having at least two speeds or more, if the speed and speed Low continue for a predetermined time or longer, it can be forcibly switched to the speed High and returned to the predetermined loop amount. become. In addition, it is possible to always suppress the generation of one loop and form a stable loop, and it is possible to suppress the occurrence of various problems such as discharge, rubbing, and color misregistration that occur during transfer separation.

  In this embodiment, the image forming apparatus using the electrostatic conveyance belt 9a has been described. However, the present invention may be applied to an image forming apparatus using an unillustrated intermediate transfer belt instead of the electrostatic conveyance belt 9a. There is a similar effect. By adopting this control, it is possible to form a stable loop between the transfer and the fixing similarly by using it for the transfer control between the transfer and the fixing in the image forming apparatus of the intermediate transfer system. In addition, it is possible to suppress the occurrence of various problems such as discharge, rubbing, and color misregistration that occur during transfer separation.

Example 2
A second embodiment of the present invention will be described with reference to FIG.

  Since the basic configuration of the present embodiment is the same as that of the first embodiment, the same components as those of the first embodiment are denoted by the same reference numerals and description thereof is omitted. Only the configuration different from that of the first embodiment will be described.

  The present embodiment is characterized in that when the speed Low is detected for a predetermined time (T) or longer, the speed is switched to High and driven for a predetermined time (T ′), and then returns to the normal loop control.

  In the first embodiment, when the speed Low is detected for a predetermined time (T) or more, the speed is switched to the high speed, and one loop is gradually resolved and the sensor waits until the sensor detects the regular loop. 7 (C)), the control returns to the conventional control. For this reason, the timing for returning to the normal control varies depending on the loop formation state, or the loop detection varies depending on the state of one loop, and the normal loop state cannot be detected. In this case, it may be considered that the regular loop cannot be detected and the wire is pulled too much at the speed High. However, in this embodiment, after switching to the speed High and driving for a predetermined time (T ′), the control returns to the normal loop control, so that it is possible to surely shift to the normal loop control.

  In the present embodiment, T is set to 100 ms as in the first embodiment, and T ′ is also set to T ′ = 100 ms. However, T and T ′ can be set independently. Since the optimum value varies depending on the process speed, speed Low, and High set speed, it can be set at an arbitrary value.

  In order to more reliably avoid one loop and execute control, it is preferable to set T <T ′. In this embodiment, when T = 100 ms, T ′ is good in the range of 100 to 200 ms. It was confirmed that a good transportability could be obtained.

  In this way, by driving for a predetermined time (T ′) and then forcibly returning it, the loop control can be more reliably performed, the occurrence of one loop can be suppressed, and a stable loop can be formed. In addition, it is possible to suppress the occurrence of various problems such as discharge, rubbing, and color misregistration that occur during transfer separation.

Example 3
A third embodiment of the present invention will be described with reference to FIGS.

  The feature of this embodiment is that it has three stages of fixing speeds used for loop control.

  Specifically, the process speed of the electrostatic forming belt 9a is set to 180 mm / sec as the process speed of the image forming apparatus. On the other hand, the third speed used for fixing loop control has a speed difference of −3%, + 3%, and + 6% with respect to the process speed of the electrostatic transport belt 9a of 180 mm / sec. That is, speed Low = 174 mm / sec, speed High-1 = 186 mm / sec, and speed High-2 = 191 mm / sec were set.

  In FIG. 9, as in the first embodiment, when the loop small (speed Low) is continuously detected for a predetermined time (here, T = 100 ms), it is determined that a loop formation failure due to one loop has occurred. . Therefore, the speed is forcibly switched to High-2, and the control is performed at Speed High-2 until the loop detection means detects a predetermined loop amount ((B) of FIG. 9). Then, after the loop detection means detects the predetermined loop amount, control is shifted to normal loop control controlled at the speed Low and the speed High-1 ((C) in FIG. 9).

  As a result, when a single loop occurs, it is possible to return to the proper loop state in a shorter time by controlling at the speed High-2, which is a driving speed faster than the speed High-1, and the normal loop Control can be performed.

  In FIG. 10, similarly to the second embodiment, when loop small (speed Low) is detected for a predetermined time (here, T = 100 ms), a loop formation failure due to one loop has occurred. to decide. Therefore, after forcibly switching to the speed High-2 and driving for a predetermined time (T '), the control is shifted to the loop control controlled at the normal speed Low and the speed High-1.

  Here, the predetermined time (T ′) = 50 ms.

  In this way, after driving for a predetermined time (T ') at a speed High-2, which is a driving speed faster than the speed High-1, it is forcibly returned. Thus, in this embodiment, the predetermined time (T ′) can be reliably returned to the predetermined loop state in a shorter time than in the second embodiment.

Example 4
In the present embodiment, as an embodiment, the condition for executing the above-described first to third embodiments is characterized in that it is executed only when double-sided printing is performed according to the print mode or when the thin paper mode is selected.

  This makes it possible to reliably perform optimal loop control even during double-sided printing, which is difficult to transport, or when printing thin paper, special paper, etc., and suppress the occurrence of single loops to form stable loops. Is possible. Therefore, it is possible to suppress the occurrence of various problems such as discharge, rubbing, and color misregistration that occur during transfer separation.

  Further, in this embodiment, as another embodiment, it is determined whether or not to execute based on the detection result of the temperature / humidity sensor or the like as a condition for executing the above-described first to third embodiments.

  As a result, by executing the control of this embodiment only in a low-temperature and low-humidity environment or in a high-humidity environment, it is possible to reliably perform optimal loop control even in an environment where transportability is severe. Generation of a loop can be suppressed and a stable loop can be formed. Therefore, it is possible to suppress the occurrence of various problems such as discharge, rubbing, and color misregistration that occur during transfer separation.

  As described above, in this embodiment, the image forming apparatus includes the timer (timer) that monitors the on / off time of the signal detected by the loop detector. The loop amount by the loop detecting means and the detection time by the time measuring means are monitored. The speed switching means is switched according to the monitored loop amount and detection time to control the loop amount of the recording medium. With such a configuration, it is possible to form an image without occurrence of image defects such as color misregistration, image rubbing, trailing edge splash, and discharge image regardless of the type of recording medium.

1 is a schematic configuration diagram of an embodiment of an image forming apparatus according to the present invention. FIG. 6 is a cross-sectional view illustrating a conveyance state of a recording medium between a transfer unit and a fixing unit. FIG. 6 is a perspective view illustrating a conveyance state of a recording medium between a transfer unit and a fixing unit. FIG. 6 is a perspective view illustrating a conveyance state in which a single loop of a recording medium occurs between a transfer unit and a fixing unit. FIG. 6 is a perspective view illustrating a conveyance state in which a single loop of a recording medium occurs between a transfer unit and a fixing unit. It is a figure which shows the sensor output at the time of normal loop formation, and the output of fixing speed control. It is a figure which shows the output of a sensor output and fixing speed control for demonstrating the control aspect of one Example when one loop generate | occur | produces. It is a figure which shows the output of a sensor output and fixing speed control for demonstrating the control aspect of the other Example when one loop generate | occur | produces. It is a figure which shows the output of a sensor output and fixing speed control for demonstrating the other control aspect when one loop generate | occur | produces. It is a figure which shows the output of a sensor output and fixing speed control for demonstrating the other control aspect when one loop generate | occur | produces.

Explanation of symbols

1 (1a, 1b, 1c, 1d) Photosensitive drum (image carrier)
2 (2a, 2b, 2c, 2d) Charging roller (charging means)
3 (3a, 3b, 3c, 3d) Laser beam scanner (exposure means)
4 (4a, 4b, 4c, 4d) Developing device (developing means)
5 (5a, 5b, 5c, 5d) Transfer roller (transfer means)
8 Feeding part 9 Conveying means 9a Electrostatic conveying belt 10 Fixing part (fixing means)
23 Loop detecting means 25 Timer (time measuring means)
200 Control means 201 Speed switching means

Claims (9)

In an image forming apparatus that forms an image in an image forming unit, transfers the image to a recording medium, and fixes the transferred image to the recording medium.
Conveying means for carrying and conveying the recording medium to the image forming unit in order to transfer the image formed by the image forming unit to the recording medium;
Fixing means for fixing the image to the recording medium while conveying the recording medium to which the image has been transferred, fed from the conveying means;
A loop detection unit for detecting a loop amount generated in the recording medium between the image forming unit and the fixing unit;
Time measuring means for measuring the on / off time of the signal detected by the loop detection time;
A speed switching means capable of switching the recording medium conveyance speed by the fixing means in at least two stages;
In a state where the recording medium is being transported, the speed switching means is switched according to the loop amount detected by the loop detecting means and the detection time measured by the time measuring means to control the loop amount of the recording medium. Control means;
An image forming apparatus comprising:   The control unit monitors the loop amount detected by the loop detection unit and the detection time measured by the time measuring unit in a state where the recording medium is being conveyed, and the detection time is equal to or longer than a predetermined time. 2. The image forming apparatus according to claim 1, wherein when this is detected, the speed switching unit is switched regardless of the detected loop amount to control the loop amount of the recording medium.   The control means monitors the loop amount detected by the loop detection means and the detection time measured by the time measuring means in a state where the recording medium is being conveyed, and based on the detection result of the loop detection means. When loop control is performed so that a constant loop is always obtained, and it is detected that the detection time is equal to or longer than a predetermined time, the speed is detected until the predetermined loop amount is detected again regardless of the detected loop amount. The image forming apparatus according to claim 1, wherein the switching unit is switched.   The control means monitors the loop amount detected by the loop detection means and the detection time measured by the time measuring means in a state where the recording medium is being conveyed, and based on the detection result of the loop detection means. Loop control is performed so that a constant loop is always obtained, and when the detection time is detected for a predetermined time or more, the speed switching means is switched only for a predetermined time regardless of the detected loop amount. The image forming apparatus according to claim 1. In an image forming apparatus that forms an image in an image forming unit, transfers the image to a recording medium, and fixes the transferred image to the recording medium.
Conveying means for carrying and conveying the recording medium to the image forming unit in order to transfer the image formed by the image forming unit to the recording medium;
Fixing means for fixing the image to the recording medium while conveying the recording medium to which the image has been transferred, fed from the conveying means;
A loop detection unit for detecting a loop amount generated in the recording medium between the image forming unit and the fixing unit;
Time measuring means for measuring the on / off time of the signal detected by the loop detection time;
A speed switching means capable of switching the recording medium conveyance speed by the fixing means in at least two stages;
In a state where the recording medium is being conveyed, if the loop amount generated in the recording medium during the conveyance from the image forming unit to the fixing unit has not changed over a predetermined time, the speed switching unit is switched, Control means for switching the recording medium conveying speed of the conveying means;
An image forming apparatus comprising:   When the loop amount generated in the recording medium while being conveyed from the image forming unit to the fixing unit detects that the loop is small for a predetermined time or more, the recording medium conveying speed of the conveying unit is increased by the speed switching unit. The image forming apparatus according to claim 5, wherein the image forming apparatus is switched.   The image forming apparatus according to claim 1, wherein the predetermined time measured by the time measuring unit is changed according to a print mode.   The image forming apparatus according to claim 1, wherein the predetermined time measured by the time measuring unit is changed according to a type of a recording medium. The image forming apparatus according to claim 1, wherein the predetermined time measured by the time measuring unit is changed according to a use environment.

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