JP2006091729A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of preventing the generation of transfer irregularity and transfer omission and capable of securing gloss and color mixture while suppressing the enlargement of the apparatus and the lowering of productivity as much as possible even when cardboard, OHT, or the like is used as a transfer material. <P>SOLUTION: An intermediate transfer belt is driven at a first speed up to primary transfer operation, and after the primary transfer, the intermediate transfer belt is decelerated to a second speed to execute secondary transfer. As a different point from conventional technology, "lock control signal" is applied to a driving means of the intermediate transfer belt, and in a deceleration period, the driving shaft of the driving means is switched to a lock control state for prescribed time. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a color image forming apparatus using an electrophotographic system, an electrostatic recording system or the like, and more particularly to a color image forming apparatus using an intermediate transfer member which is a second image carrier.

  In the image forming apparatus, as a technique for forming a good image on the transfer material without being affected by the thickness, material, surface property, etc. of the transfer material, in addition to the first image carrier made of a photoconductor, An image forming apparatus including an intermediate transfer member that is a second image carrier has been proposed.

  FIG. 1 is a schematic configuration diagram showing a configuration of a color image forming apparatus showing the embodiment. Around the photosensitive member 1, a primary charger 4, an exposure device 5, a color developing unit 7, a black and white developing unit 8, a transfer charger 9, and a cleaner device 6 are arranged. The color developing unit 7 is a rotary type and includes three developing devices 7Y (yellow developing device), 7M (magenta developing device), and 7C (cyan developing device) for full color development. On the other hand, the black and white developing unit 8 is fixed at a position where it abuts on the photoreceptor 1.

  When an image is formed by the color image forming apparatus of FIG. 1, first, a toner image developed on the photoreceptor 1 is transferred to an intermediate transfer belt 2 as an intermediate transfer body by a primary transfer device 9. This is called primary transfer. When a monochrome image is formed, this primary transfer is performed once with only black toner. On the other hand, when forming a color image, it is necessary to superimpose three other color toners. Therefore, the primary transfer is repeated four times in the order of each toner color, so that multiple toner images are formed. It is formed on the intermediate transfer belt 2.

  The toner image transferred to the intermediate transfer belt 2 is further transferred to a sheet by the secondary transfer device 15. Here, in the primary transfer device 9 and the secondary transfer device 15, a high voltage for transferring the toner image to the next medium is applied. The high voltage value for transferring the toner image from the secondary transfer device 15 to the intermediate transfer belt 2 is determined in consideration of a voltage drop due to the resistance of the transfer material. For example, the resistance value differs between the case of using thick paper or OHT (transparent sheet for OHP) as the transfer material and the case of using plain paper. Therefore, by applying different high-pressure values according to the respective transfer materials, optimum transfer characteristics that do not cause image unevenness or omission are obtained.

JP 09-146434 A

  When forming a color image using thick paper or OHT as the transfer material, in order to obtain an image that ensures sufficient gloss and color mixing properties, in addition to the control of the transfer high pressure value described above, the fixing operation as the next step is performed. Must be slower than plain paper.

  Here, if the speed of only the fixing device 3 is controlled to be slow and controlled at the same speed as that for plain paper without lowering the speed of the intermediate transfer belt 2, these differences are caused by the speed difference between the fixing device 3 and the secondary transfer position 15. There is a problem that the transfer material is loosened between the units, and the toner image on the transfer material interferes with a member in the apparatus and is rubbed to cause an image defect. Further, when the speed differences between these units interfere with each other, uneven speeds occur in each unit, and image defects such as unevenness in fixing property and transfer property are caused.

  If the distance between the secondary transfer device 15 and the fixing device 3 is longer than the length of the transfer material in the conveyance direction, the above-described problems do not interfere with each other even if they operate at different speeds. However, this method leads to an increase in the size of the apparatus.

  In addition, when using thick paper, OHT, or the like as the transfer material, the above-mentioned problems can be solved by performing not only the fixing operation but also all the image forming operations at a low speed, but this method significantly reduces the productivity. End up.

  Therefore, it is preferable to reduce the speed of the image forming apparatus in the middle of the image forming process for the purpose of reducing the productivity as much as possible. However, when this deceleration is performed during the primary transfer or the secondary transfer, the durability is particularly advanced. In the apparatus, image defects such as transfer unevenness and transfer omission appear remarkably.

  The present invention has been made in view of the above circumstances. The purpose of the present invention is that when using thick paper, OHT, or the like as a transfer material, transfer unevenness or transfer omission is suppressed while minimizing the enlargement of the apparatus and the decrease in productivity. It is another object of the present invention to provide an image forming apparatus that can prevent glossiness and ensure gloss and color mixing.

  In order to achieve the above object, the invention described in claim 1 includes a first image carrier, an image forming means for forming an image on the first image carrier, a second image carrier, Primary transfer means for transferring an image on the first image carrier onto the second image carrier, secondary transfer means for transferring an image on the second image carrier to a transfer material, Fixing means for fixing the image transferred onto the transfer material by a secondary transfer means by heating and pressurizing, and a peripheral length L1 of the second image carrier is set in the conveying direction of the transfer material. In the image forming apparatus, the length L3 in the transport direction from the position of the secondary transfer unit to the fixing unit is shorter than the length L2 in the transport direction of the transfer material. Of the first image carrier and the second image carrier, at least the Drive means for moving the image bearing member, the speed of the drive means can be changed, and the drive shaft can be switched to a free state or a lock state. The drive means operates at a first speed during a primary transfer process period in which an image on the first image carrier is transferred onto the second image carrier, and the drive means after the primary transfer process. Is subjected to a secondary transfer step in which the image on the second image carrier is transferred onto the transfer material by the secondary transfer means after the motor is decelerated to a second speed slower than the first speed. Thus, the drive shaft of the drive means is switched to the lock control state for a predetermined time in a period during which the drive means decelerates from the first speed to the second speed.

  According to a second aspect of the present invention, in the first aspect of the present invention, the second moving speed of the driving unit varies depending on the material and thickness of the transfer material.

  According to a third aspect of the present invention, in the first or second aspect of the invention, the predetermined time during which the drive shaft is controlled to be locked depends on a speed difference between the first moving speed and the second moving speed. It is characterized by being set.

  According to a fourth aspect of the present invention, in the invention according to any one of the first to third aspects, the predetermined time during which the drive shaft is controlled to be locked is set according to rotation information of the moving means. Features.

  The invention according to claim 5 is the invention according to any one of claims 1 to 4, wherein the predetermined time during which the drive shaft is controlled to be locked is set according to torque information applied to the moving means. It is characterized by.

  According to the present invention, in contrast to an image forming apparatus using an intermediate transfer member as a second image carrier, even when OHT or cardboard is used as a transfer material, enlargement of the apparatus and reduction in productivity are suppressed as much as possible. However, uneven transfer and transfer omission can be prevented, and gloss and color mixing can be ensured.

  In forming an image, first, a voltage is applied to the charging device 4 to uniformly charge the surface of the photoreceptor 1 at a predetermined charged portion potential. Subsequently, exposure is performed by an exposure device 5 composed of a laser scanner based on the image data so that the image portion on the charged photoreceptor 1 becomes a predetermined exposure portion potential to form a latent image. The exposure device 5 forms a latent image corresponding to the image by turning on and off based on the image data.

  The color developing devices 7Y, 7M, and 7C and the black and white developing device 8 develop the latent images on the photoreceptor 1 with Y, M, C, and K toners, respectively. When developing toner of each color, the color developing unit 7 is rotated in the direction of arrow R by a motor (not shown), and the developing device for that color is aligned so as to contact the photoreceptor 1.

  The toner images of each color developed on the photoreceptor 1 are sequentially transferred to the intermediate transfer belt 2 as an intermediate transfer member by the primary transfer device 9, and the four color toner images are superimposed. A belt cleaner 14 is provided at a position facing the transfer belt driving roller 10 with the intermediate transfer belt 2 interposed therebetween, and residual toner on the intermediate transfer belt 2 is scraped off by a blade.

  The toner image transferred to the intermediate transfer belt 2 is further transferred to a sheet by the secondary transfer device 15. In full-color printing, toners of four colors are superimposed on the belt and then transferred onto the recording paper. The recording paper is drawn out from the recording paper cassette 16 by a pickup roller 17 to a conveyance path, and is fed to a nip portion, that is, a contact portion between the secondary transfer device 15 and the belt 2 by a pair of conveyance rollers 18 and 19.

  Further, the toner remaining on the photosensitive member 1 is easily cleaned by a preliminary cleaning device, and is removed and collected by the cleaner device 6. Finally, the photosensitive member 1 is removed by a static eliminator (not shown). In this manner, the charge is discharged to near 0 volts, and the next image forming cycle is prepared.

  Incidentally, the image forming timing of the color copying machine is controlled with reference to a predetermined position on the intermediate transfer belt 2. The intermediate transfer belt 2 is stretched around rollers 10, 11, 12, and 13. Among these, the intermediate transfer belt drive roller 10 functions as a drive roller that is coupled to a drive source (not shown) and drives the intermediate transfer belt 2, and the intermediate transfer belt tension rollers 11 and 12 adjust the tension of the belt 2. The backup roller 13 functions as a tension roller, and the backup roller 13 functions as a backup roller of a transfer roller 15 as a secondary transfer device.

  In the vicinity of the tension roller 12, a reflective sensor 20 for detecting the reference position is disposed. The reflective sensor 20 detects a marking such as a reflective tape provided at the end of the outer peripheral surface of the belt 2 and outputs an I-top signal.

  The peripheral length of the photoreceptor 1 and the peripheral length of the belt 2 have an integer ratio represented by 1: n (n is an integer). With this setting, the photoreceptor 1 rotates an integer during one revolution of the belt 2 and returns to the same state as before one revolution of the belt, so that the four colors are superimposed on the intermediate transfer belt 2. In this case (the belt rotates four times), it is possible to avoid color misregistration due to uneven rotation of the photoreceptor 1.

  In the intermediate transfer type image forming apparatus as described above, after detecting the I-top signal, exposure is started by the exposure device 5 including a laser scanner after a predetermined time has elapsed. Further, as described above, the photosensitive member 1 rotates an integer during one revolution of the belt 2 and returns to the same state as before the belt one revolution, so that a toner image is always formed at the same position on the belt 2. Although the toner image size varies depending on the paper size, there is a range on the intermediate transfer belt 2 where the toner image is never placed.

  The fixing device 3 includes a fixing roller, which is a fixing member having a halogen heater, which is a heat generating means, and a pressure roller, which is also a fixing member having a halogen heater, which is also a heat generating means. It is configured as a pair of fixing members arranged so as to be rotatable while being pressed against each other.

  An unfixed image formed with a developer material such as toner transferred onto a sheet is heated and pressed through a nip portion between a fixing roller and a pressure roller controlled to a predetermined temperature, thereby being recorded on the recording paper. To be established.

  Next, FIG. 2 shows a block diagram of the control system of this apparatus.

  This apparatus is entirely controlled by the system controller 101. The system controller 101 mainly plays a role of driving each load in the apparatus, collecting and analyzing sensors, and exchanging data with the operation unit 102, that is, the user interface. The internal configuration of the system controller 101 is equipped with the CPU 101a in order to play the above-described role, and the CPU 101a similarly performs a predetermined image forming sequence by a program stored in the ROM 101b mounted on the system controller 101. Execute various sequences. At this time, the RAM 101c is also mounted to store rewritable data that needs to be stored temporarily or permanently. The RAM 101c stores, for example, a high voltage set value for a high voltage control unit 105 described later, various data described later, image formation command information from the operation unit 102, and the like.

  The operation unit 102 obtains information such as a copy magnification and a density setting value set by the user, as well as the state of the image forming apparatus, for example, information on the number of images formed, whether or not an image is being formed, and occurrence of a jam. And data for indicating the location and the like to the user.

  In this apparatus, a DC load such as a motor, a clutch / solenoid, and a sensor such as a photo interrupter and a micro switch are arranged at various locations inside the apparatus. That is, the transfer material is conveyed and each unit is driven by appropriately driving the motor and each DC load, and various sensors monitor the operation.

  Therefore, the system controller 101 controls each motor by the motor control unit 107 based on signals from various sensors 109, and at the same time, operates the clutch / solenoid by the DC load control unit 108 to smoothly perform the image forming operation. We are proceeding to. Also, by sending various high voltage control signals to the high voltage control unit 105, a primary charger 310, which is various chargers constituting the high voltage unit 106, an auxiliary charging device (not shown), a primary transfer belt device, and a secondary transfer belt device. An appropriate high voltage is applied to the developing roller in the developing unit.

  Further, each of the fixing rollers of the fixing device 3 includes a heater 111 for heating the rollers, and these heaters are ON / OFF controlled by an AC driver 110. Each fixing roller is provided with a thermistor 104 for measuring the temperature. The A / D 103 converts the resistance value change of the thermistor 104 according to the temperature change of each fixing roller into a voltage value, and then converts the resistance value to a digital value. Input to the controller 101. The aforementioned AC driver 110 is controlled based on this temperature data.

  Next, the intermediate transfer belt 2 according to the present invention and its peripheral configuration will be described with reference to FIG.

  The distance indicated by L in FIG. 3 is the circumferential length of the intermediate transfer belt 2, and the distance indicated by L2 on the intermediate transfer belt 2 is the length of the image on the largest size sheet.

  The circumferential length L of the intermediate transfer belt 2 is configured to be longer than the length L2 in the conveyance direction of the largest size sheet because a multicolor image must be formed on the surface thereof. Here, in this embodiment, the peripheral length L of the intermediate transfer belt 2 is 565 mm, and the conveyance direction length L2 of the maximum size sheet is 483 mm.

  The intermediate transfer belt 2 and the photosensitive member 1 are driven by a driving unit 201 using a DC motor as a driving source, and are rotated in a direction indicated by an arrow in FIG. The driving means 201 will be described in detail below.

  The following three control signals shown in S201 to S203 are input from the motor control unit 107 to the driving unit 201.

  S201 is a “rotation / stop signal”, and is a signal for controlling the rotation and stop of the driving means 201. Upon receiving the “rotation / stop signal” = H signal, the driving unit 201 rotates the DC motor according to the setting of a speed control signal S203 described later. The driving means 201 stops the rotation of the motor when it receives a “rotation / stop signal” = L signal.

  S202 is a “free / lock signal”, and is a signal that controls whether the drive shaft of the drive unit 201 is in a free state or a locked state. Upon receiving the “free / lock signal” = H signal, the drive unit 201 controls the drive shaft of the drive unit 201 to a free state, and stops the rotation / rotation of the DC motor according to the above-described S201 “rotation / stop signal” Do. Further, when receiving the “free / lock signal” = L signal, the drive means 201 controls the drive shaft of the drive means 201 to the locked state, and is fixed so as not to move even if an external force is applied to the drive shaft. In the present embodiment, this lock control is performed by a short brake that fixes both ends of the coil of the DC motor in the driving means 201 to the GND level.

  In the case where the “free / lock signal” remains H (free) while the drive unit 201 is rotating, the rotation of the drive unit 201 is stopped by switching the above-described S201 “rotation / stop signal” to L (off). It takes a long time for the inertial force of the load driven by the drive unit 201 to work until the drive unit 201 is completely stopped. In the apparatus according to the present embodiment, the stop time is about 1000 ms.

  On the other hand, when the rotation of the drive unit 201 is stopped by setting the “free / lock signal” to L (lock) while the drive unit 201 is rotating, the drive shaft of the drive unit 201 is forcibly controlled to be locked. The stop time of the means 201 is abruptly shortened. In the apparatus according to the present embodiment, the stop time is reduced to about 100 ms. Therefore, the “free / lock signal” is generally provided when it is necessary to urgently stop the drive shaft of the drive means 201.

  S203 is a “speed control signal” and is a signal for controlling the driving speed of the driving means 201. In the present embodiment, the speed control signal is a clock, and the driving means 201 is driven at a rotational speed proportional to the frequency of this clock.

  The speed control signal can also be configured as an H or L 1-bit or multiple-bit logic signal. In this case, it is necessary to prepare a reference clock frequency in the drive unit 201 in advance, and the reference clock may be rotated by dividing the reference clock at a predetermined division ratio according to the logic of the speed control signal. .

  The driving means 201 outputs a “synchronous rotation detection signal” S204 to the motor control unit 107. The synchronous rotation detection signal is a signal indicating whether or not the driving unit 201 is rotating within a predetermined number of rotations set by the above-described S203 “speed control signal”. In the present embodiment, L is output when the driving unit 201 rotates within ± 0.1% of the set number of rotations, and H is output when it deviates from this range. Here, the fact that the driving means 201 rotates within a predetermined range is referred to as synchronous rotation here. The system controller 101 (not shown) monitors the “synchronous rotation detection signal” S204 via the motor control unit 107. If the synchronous rotation detection signal remains in the H state for a predetermined time, the apparatus is urgently stopped. Then, a message indicating that the drive unit 201 is abnormal is displayed on an operation unit (not shown). When the drive unit 201 is started or when the rotation speed is changed, the synchronous rotation signal is always H until the target rotation speed is reached, but abnormality detection is not performed at this timing.

  The fixing device 3 is driven by the driving unit 202. Similarly to the driving unit 201, the driving unit 202 uses a DC motor as a driving source, and rotates the fixing device in the arrow direction shown in FIG. The control signal between the driving means 202 and the motor control unit 107 is exactly the same except that the above-mentioned “free / lock signal” does not exist, “rotation / stop signal” S205, “speed control signal”. S206, “synchronous rotation detection signal” S207. Details regarding the signals in S205 to S207 are the same as those described in connection with the driving unit 201 described above, and are therefore omitted.

  Next, control of the image forming apparatus according to the embodiment of the present invention will be described.

  The driving unit 201 is configured so that the peripheral speed of the photosensitive member 1 and the intermediate transfer belt 2 is V1, regardless of the type of transfer material, until the primary transfer step of transferring the toner image on the photosensitive member 1 to the intermediate transfer belt 2. It is controlled to become. In the present embodiment, V1 = 400 mm / s.

  When the transfer material is plain paper, the driving unit 201 controls the peripheral speeds of the photosensitive member 1 and the intermediate transfer belt 2 at V1 as described above until the end of the image forming operation.

  On the other hand, when the transfer material is OHT, thick paper, or the like, the driving unit 201 decelerates the peripheral speed of the photosensitive member 1 and the intermediate transfer belt 2 to V2 lower than V1 in a process in the middle of the image forming operation. The image forming operation after the secondary transfer process that is controlled and performed thereafter is performed at the peripheral speed of V2.

4 to 8 illustrate the image forming operation. In the present embodiment, every time the intermediate transfer belt 2 makes one turn, the toner image is primarily transferred one by one in the order of magenta, cyan, yellow, and black. Multiple color images are completed on the surface of the transfer belt 2.
Here, when the transfer material is plain paper, the black toner image is primarily transferred and the color image is completed on the intermediate transfer belt 2 on the fourth turn of the intermediate transfer belt 2. The image on the belt 2 is secondarily transferred to a transfer material.

  However, when the transfer material is OHT or thick paper, the primary transfer and the secondary transfer are not performed simultaneously as described above, and the secondary transfer is performed every fifth turn of the intermediate transfer belt 2. Each of the above operations will be described below with reference to FIGS.

  FIG. 4 shows a state in which the intermediate transfer belt 2 is rotated three times, and the three-color toner images (magenta, cyan, yellow) are primarily transferred onto the surface, and immediately before the black toner image is primary-transferred. FIG.

  A position indicated by F in FIG. 4 indicates the front end position of the toner image on the intermediate transfer belt 2, and R indicates the rear end position. F ′ is the leading end position of the black image formed on the photoreceptor. As shown in FIG. 5, a black toner image is formed such that the image leading edge F on the intermediate transfer belt 2 and F ′ on the photosensitive member 1 and the image leading edge F on the intermediate transfer belt 2 coincide and overlap. The primary transfer is performed to complete a multi-color image of all four colors on the intermediate transfer belt 2.

  As described above, when the transfer material is plain paper, a black toner image is primarily transferred on the fourth turn of the intermediate transfer belt 2 as shown in FIG. Is completed, the image on the intermediate transfer belt 2 is secondarily transferred onto the transfer material.

  When the transfer material is plain paper, the fixing speed in the fixing device 3 is equal to the speed of the intermediate transfer belt 2. Therefore, the fixing operation, the secondary transfer, and the primary transfer can be performed simultaneously.

  On the other hand, when the transfer material is OHT or thick paper, the transfer material passing speed in the fixing device 3 is set to the image formation of the intermediate transfer belt 2 in order to obtain an image that secures sufficient gloss and color mixing. It must be slower than the peripheral speed inside.

  If the distance between the secondary transfer device 15 and the fixing device 3 is configured to be longer than the length L2 in the maximum sheet conveyance direction, the speed of the secondary transfer device 15 and the fixing device 3 is the same. Even if not, the transfer material does not exist between these units at the same time, so that the transfer material is not loosened and the image is not defective. Primary transfer can be performed simultaneously.

  However, in an apparatus that is designed to be small so that the distance between the secondary transfer device 15 and the fixing device 3 is smaller than the length in the conveyance direction of the maximum sheet, as in the present image formability device, the secondary transfer device 15 and the fixing device 3 are smaller. Since the transfer material is loosened between the transfer device 15 and the fixing device 3, the secondary transfer and the fixing operation cannot be performed simultaneously while performing the primary transfer at the same speed as that of the plain paper.

  Here, if the fixing operation, the secondary transfer, and the primary transfer processing operation are performed at a low speed, the productivity is significantly reduced. For the purpose of reducing the productivity as much as possible, it is preferable to reduce the speed of the image forming apparatus in the middle of the image forming process. However, when this deceleration is performed during the primary transfer or the secondary transfer, the durability is particularly advanced. In the apparatus, image defects such as transfer unevenness and transfer omission appear remarkably.

  Therefore, when the transfer material is plain paper, as shown in FIG. 7, the intermediate transfer belt 2 performs only the primary transfer of the black toner image from the photoreceptor 1 to the intermediate transfer belt 2 in the fourth turn, After the primary transfer is completed, the intermediate transfer belt 2 is decelerated, and then the secondary transfer and fixing operations are performed on the fifth turn of the intermediate transfer belt 2 as shown in FIG.

  The deceleration of the intermediate transfer belt 2 is performed by controlling a driving unit 201 that is a driving source of the intermediate transfer belt 2. That is, until the trailing edge of the image on the intermediate transfer belt 2 passes through the primary transfer device 9, a speed control signal is inputted so that the peripheral speed of the intermediate transfer belt 2 becomes V 1. The speed control signal is changed so that the peripheral speed is V2 (200 mm / s in the present embodiment).

  The deceleration must be completed before the start of the secondary transfer. That is, it is necessary to finish the deceleration before the leading edge of the image on the intermediate transfer belt 2 arrives at the secondary transfer device 15, but the permissible time is short, and is 700 ms in this embodiment.

  The allowable time until the deceleration is completed is determined by the distance between the primary transfer device 9 and the secondary transfer device 15, the peripheral speed of the intermediate point belt 2, and the like. As it goes up, it becomes shorter and more severe. If the time required for completing the deceleration of the driving unit 201 exceeds the allowable time, the leading edge position F of the image formed on the intermediate transfer belt 2 advances by that amount, and therefore the secondary position on the transfer material. The transferred image does not have a leading edge margin and becomes a defective image with a leading edge missing. If the image forming apparatus is controlled so that the intermediate transfer belt 2 is further rotated one turn and the second transfer is performed on the sixth turn, the above problem can be solved. However, in this method, the productivity is lowered and the intermediate transfer is performed. There is also a problem that the image of the belt 2 deteriorates.

  Therefore, in the present invention, the speed control signal S203 to the drive unit 201 is changed at the timing of decelerating the drive unit 201, and the control signal of the “free / lock signal” S202 is further controlled to the logic of the lock control. The deceleration of the drive means 201 is shortened.

  If the time for locking the free / lock signal S202 is too short, it cannot be sufficiently decelerated. If it is too long, the drive means 201 stops, and in any case, the drive means is decelerated to the target speed. It takes a long time to make it happen. Therefore, it is important to set the time width for locking the free / lock signal S202 to an appropriate time width in accordance with the magnitude of the inertia of the load connected to the driving unit 201. The above contents will be further described with reference to FIG.

  The diagram shown in FIG. 9A is a timing diagram when only the speed control signal S203 is changed and the driving means 201 is decelerated from V1 to V2.

  A point A shown in FIG. 9A indicates a point at which the rear end of the image on the intermediate transfer belt 2 passes through the primary transfer device 9 and starts the deceleration of the driving unit 201. At this timing, the speed control signal S203 is switched from a frequency of 2000 kHz corresponding to the peripheral speed V1 of the intermediate transfer belt to a frequency of 1000 kHz corresponding to the peripheral speed V2.

  At this time, the rotation synchronization detection signal 204 output from the drive unit 201 changes to the H state until the target peripheral speed V2 is reached.

  Here, the allowable time until the peripheral speed of the drive unit 201 takes the target peripheral speed V2 is indicated by Tper. In this embodiment, the allowable time Tper is 700 ms, but the time required for the drive means 201 to decelerate exceeds Tper as T1 (approximately 850 ms).

  The FG waveform of the drive unit 201 shown in FIG. 9 is obtained by extracting a rotation detection signal (FG signal) from a Hall element built in the drive unit 201 and performing frequency-voltage conversion on the rotation detection signal.

  In the present embodiment, the FG waveform of the driving unit 201 is not output to the motor control unit 107 or the like, but may be configured to be output as necessary.

  As shown in FIG. 9A, the driving means 201 gradually decreases in speed from the switching point of the speed control signal S203 and reaches the target speed V2. As the inertia of the load connected to the driving unit 201 increases, the slope of the FG signal waveform becomes gentler, and the deceleration time T1 further exceeds the target point B for completion of deceleration.

  In order to solve this problem, in the present invention, as shown in FIG. 9B, the speed control signal S203 of the driving means 201 is changed, and the free / lock signal S202 is switched to the lock logic for a predetermined time.

  The free / lock signal S202 is switched to lock (L signal) simultaneously with deceleration, and then switched to free (H signal) again after a predetermined set time Tb has elapsed. Here, in this embodiment, Tb = 50 ms. While the free / lock signal S202 is controlled to be locked, the driving means 201 exerts a large force to stop, so that the speed is abrupt as in the FG signal of the driving means 202 shown in FIG. 9B. To drop. Since the free / lock signal S202 is switched to free (H signal) so that the drive control is resumed from a speed close to the target circumferential speed V2, the time T1 required to complete the deceleration is shown in FIG. It is shortened as shown in (b). In the present embodiment, the time required for completing the deceleration is T1 = 100 ms.

  In this embodiment, when the transfer material is both OHT and thick paper, the passing speed of the fixing device 3 is V2. For example, when the passing speed of the thick paper is slower than the passing speed at the time of OHT. The lock control time of the free / lock signal S202 when the intermediate transfer belt 2 is decelerated from V1 to V3 is preferably set to be longer than 50 ms. That is, it is effective to control the lock longer as the deceleration difference is larger in order to shorten the time T1 required to complete the deceleration.

  As described above, the driving unit 201 can change the peripheral speed to V2 at the target point B of completion of deceleration in the rotation of the fifth transfer of the intermediate transfer belt 2, and is formed on the intermediate transfer belt 1. It is possible to obtain a good image in which the leading edge of the printed image and the leading edge of the image of the transfer material coincide with each other at regular timing.

<Embodiment 2>
Next, a second embodiment of the present invention will be described.

  The present embodiment is different from the first embodiment in that the time for controlling the above-mentioned free / lock signal S202 to the locked state is controlled according to the information related to the rotation of the driving means 201. As shown in FIG. 10, a driving unit FG signal S209 is output from the driving unit 201 to the motor control unit 107 as information related to the rotation of the driving unit 201. The system controller 101 controls the time during which the free / lock signal S202 is locked while monitoring the frequency of the FG signal via the motor control unit 107.

  This control will be further described with reference to FIG.

  First, the system controller 101 (not shown) changes the speed control signal S203 and locks the free / lock signal S202 when the drive unit 201 is decelerated so that the peripheral speed of the intermediate transfer belt 2 changes from V1 to V2. (L signal).

  The frequency of the FG signal S209 received from the driving unit 201 is changed from a frequency F1 corresponding to the peripheral speed V1 of the intermediate transfer belt 2 to a frequency F2 ′ corresponding to a peripheral speed slightly higher than the target peripheral speed V2. At this point, the free lock signal S202 is switched again to free (H signal).

  Thus, since the free / lock signal S202 is switched to free (H signal) so that the drive control is resumed from a speed close to the target circumferential speed V2, the time T1 required to complete the deceleration is: It can be shortened as shown in FIG.

  As described above, by controlling the free / lock signal S202 in accordance with the information related to the rotation of the driving unit 201, the deceleration time of the driving unit 201 is not affected by fluctuations in the load connected to the driving unit 201 or the like. Can be reliably shortened.

  Then, the driving unit 201 can change the peripheral speed to V2 at the target point B for completion of deceleration in the rotation of the fifth transfer of the intermediate transfer belt 2, and the image formed on the intermediate transfer belt 1 can be changed. A good image can be obtained in which the leading edge and the leading edge of the transfer material image coincide with each other at regular timing.

<Embodiment 3>
Next, a third embodiment of the present invention will be described.

  The present embodiment is different from the first embodiment in that the time for controlling the above-described free / lock signal S202 to the locked state is controlled according to information on the magnitude of the load applied to the driving unit 201. .

  The greater the load applied to the drive means 201, the greater the force against the drive force of the drive means 201. Therefore, the deceleration time when the drive means 201 is decelerated tends to be shorter, and conversely the load applied to the drive means 201 is smaller. The deceleration time becomes longer.

  Therefore, as shown in FIG. 12, a torque signal S210 is output from the driving unit 201 to the motor control unit 107 as information on the magnitude of the load applied to the driving unit 201, and the system controller 101 passes the motor control unit 107 through the motor control unit 107. Thus, the lock control time for decelerating the drive means 201 is controlled while monitoring the torque signal S210. In the present embodiment, the torque signal S210 is an analog voltage that changes linearly in proportion to the load of the driving unit 201.

  FIG. 14 is a graph showing the relationship between the voltage level of the torque signal S210 and the time for controlling the free / lock signal S202 to the locked state. This table is provided in a memory built in the system controller.

  For example, when the level of the torque signal S210 is E1, the lock control time is controlled to Tb1, and when the level of the torque signal S210 is E2 greater than E1, the lock control time is controlled to Tb2 shorter than Tb1.

  The above control will be further described with reference to FIG.

  FIG. 15 is a diagram showing a case where the voltage level of the torque signal S210 is E1, and the lock control time of the free / lock signal S202 is controlled to Tb1.

  When the voltage level is E2 as indicated by the dotted line, the lock control time is controlled to Tb2 as indicated by the dotted line.

  The system controller 101 (not shown) obtains the lock control time based on the torque signal S210 immediately before the drive unit 201 is decelerated so that the peripheral speed of the intermediate transfer belt 2 is changed from V1 to V2. Then, the speed control signal S203 is changed, and the free / lock signal S202 is controlled to the lock logic for the obtained lock control time tTb.

  Thus, since the free / lock signal S202 is switched to free (H signal) so that the drive control is resumed from a speed close to the target circumferential speed V2, the time T1 required to complete the deceleration is: It can be shortened as shown in FIG.

  As described above, by controlling the free / lock signal S202 in accordance with the information related to the magnitude of the load applied to the driving unit 201, the driving unit is not affected by fluctuations in the load connected to the driving unit 201 or the like. The deceleration time of 201 can be reliably shortened.

  Then, the driving unit 201 can change the peripheral speed to V2 at the target point B for completion of deceleration in the rotation of the fifth transfer of the intermediate transfer belt 2, and the image formed on the intermediate transfer belt 1 can be changed. A good image can be obtained in which the leading edge and the leading edge of the image of the transfer material coincide with each other at regular timing.

1 is a longitudinal sectional view of a color image forming apparatus showing Embodiment 1 of the present invention. FIG. 2 is a block diagram showing a configuration of a control system of the color image forming apparatus showing Embodiment 1 of the present invention. FIG. 3 is a schematic configuration diagram of an intermediate transfer belt and a photoreceptor driving unit using the present invention. It is a figure which shows the image formation operation | movement of Embodiment 1 of this invention. It is a figure which shows the image formation operation | movement of Embodiment 1 of this invention. It is a figure which shows the image formation operation | movement of this invention when a transfer material is plain paper. FIG. 5 is a diagram illustrating an image forming operation of the present invention when the transfer material is special paper such as OHT or cardboard. FIG. 5 is a diagram illustrating an image forming operation of the present invention when the transfer material is special paper such as OHT or cardboard. FIG. 5 is a diagram illustrating a deceleration operation of an intermediate transfer belt when a conventional method and the present invention method are used. FIG. 6 is a schematic configuration diagram of an intermediate transfer belt and a photosensitive member driving unit according to a second embodiment of the present invention. FIG. 10 is a diagram illustrating a deceleration operation of the intermediate transfer belt when the control method according to the second embodiment of the present invention is used. FIG. 5 is a schematic configuration diagram of an intermediate transfer belt and a photosensitive member driving unit according to Embodiment 3 of the present invention. FIG. 10 is a diagram illustrating a deceleration operation of the intermediate transfer belt when the control method according to the third embodiment of the present invention is used. It is a figure which shows the relationship between the torque signal of the drive means in Embodiment 3 of this invention, and the lock control time of a drive means.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photoconductor 2 Intermediate transfer belt 3 Fixing device 9 Primary transfer device 15 Secondary transfer device

Claims (5)

A first image carrier; image forming means for forming an image on the first image carrier; a second image carrier; and an image on the first image carrier to the second image. A primary transfer means for transferring onto the carrier; a secondary transfer means for transferring the image on the second image carrier to the transfer material; and the image transferred onto the transfer material by the secondary transfer means. Fixing means for fixing by heating and pressurizing, the peripheral length L1 of the second image carrier is longer than the length L2 in the transport direction of the transfer material, and the second transfer means In the image forming apparatus, the length L3 in the transport direction from the position to the fixing unit is shorter than the length L2 in the transport direction of the transfer material.
Drive means for moving at least the second image carrier among the first image carrier and the second image carrier, the drive means being capable of changing speed, and a drive shaft Can be switched to a free state or a locked state, and a primary transfer process period in which an image on the first image carrier is transferred onto the second image carrier by the primary transfer means. The driving means operates at a first speed, and after the primary transfer step, the driving means is decelerated to a second speed slower than the first speed, and then the second transfer means carries a second image. Performing a secondary transfer process in which an image on the body is transferred onto the transfer material, and driving the drive means during a period in which the drive means decelerates from the first speed to the second speed. The shaft is locked for a specified time. Ri image forming apparatus characterized by changing.   The image forming apparatus according to claim 1, wherein the second moving speed of the driving unit varies depending on a material and a thickness of the transfer material.   3. The image formation according to claim 1, wherein the predetermined time during which the drive shaft is controlled to be locked is set according to a speed difference between the first movement speed and the second movement speed. apparatus.   The image forming apparatus according to claim 1, wherein the predetermined time during which the drive shaft is controlled to be locked is set according to rotation information of a moving unit.   The image forming apparatus according to claim 1, wherein the predetermined time during which the drive shaft is controlled to be locked is set according to torque information applied to the moving unit.

Images