JP2005266373A - Image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming device which is operable in a single color mode without stopping an image forming operation even if a fault occurs in a speed detection means provided in an object to be driven in an image forming device, such as a color machine to require high-accuracy speed control. <P>SOLUTION: There are provided a first speed detection means for detecting a rotating speed of a driving motor, a second speed detection means for detecting a rotating speed of an object to be driven to which a driving force of the driving motor is transmitted via a driving force transmission member, and a speed abnormality detection means for detecting abnormality in the rotating speed of the object to be driven by comparing a result of the detection by the second speed detection means with a predetermined reference value. A reference speed value of the driving motor is calculated from a speed command value of the driving motor and a result of the detection by the first speed detection means to perform reference speed control, and rotation variations of the object to be driven is detected from the speed reference value and the result of the detection by the second speed detection means to perform variation suppression control. If the speed abnormality detection means judges the rotating speed of the object to be driven as abnormal, the rotating speed control of the object to be driven is performed using only the reference speed value as a rotation variation suppression value, so that an image forming operation can be continued as it is. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus such as a copying machine, a facsimile machine, or a printer, and more specifically, includes a detection unit that detects a speed abnormality of a driven body that requires speed control with high accuracy, such as an image carrier. The present invention relates to an image forming apparatus.

  Image forming apparatuses such as electrophotographic copying machines, printers, facsimiles, and the like form a developer image by attaching charged toner to an electrostatic latent image formed on a photosensitive drum, and directly form the developer image. Alternatively, once the image is transferred to an intermediate transfer member, the image is formed by transferring and fixing it onto a recording sheet.

  In order to form a clear image in this image forming apparatus, it is necessary to keep the rotational speed of the photosensitive drum constant, and when there is a speed variation such as rotational fluctuation, the transferred image is not clear. Various defects occur. Therefore, speed control for maintaining a constant speed rotation of the photosensitive drum has been performed even before a load change occurs.

  On the other hand, the photosensitive drum is driven to rotate when the driving torque from the motor is transmitted to its rotating shaft. However, since the power transmission path includes a gear train, a coupling, and the like, backlash occurs in the rotational direction. There is a problem that the constant speed rotation of the photosensitive drum is hindered, and there is a problem that there is a backlash due to backlash or the like. For this reason, in feedback control performed only by speed detection means installed directly on a rotating shaft such as a DC motor, high-precision constant-speed rotation control of the photosensitive drum or the like to be controlled cannot be expected.

  Therefore, a method is used in which a rotational speed detection device is directly installed on a driven body such as a photosensitive drum instead of a rotating shaft such as a DC motor to perform constant-speed rotational control with high accuracy. In the apparatus, when the speed detection apparatus itself installed directly on the driven body does not operate normally, a method is employed in which the operation of the apparatus is stopped to eliminate waste of image formation.

However, even in the case of a temporary load fluctuation or a recoverable failure state, if all the image forming operations are stopped, the user's device usage efficiency is lowered. In order to solve such a problem, Patent Document 1 proposes an image forming apparatus that can discriminate between a motor failure and a load abnormality, and can appropriately cope with a temporary overload state during initial operation.
JP-A-10-74022

  However, there is a failure of the speed detection device itself instead of a motor failure. For example, a feedback signal may not be obtained due to a broken or dirty encoder for speed detection, and an image forming operation may be stopped due to an overload condition. In such a case, if the image forming apparatus is immediately stopped for maintenance and inspection, the work efficiency is significantly reduced.

  On the other hand, the speed fluctuation that is a problem in the image forming apparatus is a low-frequency speed fluctuation in one rotation of the driven body. There is a large difference in visible sensitivity characteristics between color and monochrome with respect to this low frequency fluctuation. In contrast to the low-frequency speed fluctuation, the visible sensitivity is low in color (not displayed), whereas in monochrome, the visible sensitivity curve for the monochromatic mode in FIG. 12 shows that the line speed is 50 Hz or less at 73 mm / sec. As a result, the visual sensitivity is increased because the human eye is no longer perceived, and sufficient image quality can be obtained without high-precision speed control.

  As the line speed increases, the frequency becomes higher. Therefore, in the case of using in a single color mode that does not require the accuracy of constant speed rotation even if the speed detection device provided on the driven body such as the photosensitive drum of each color or the intermediate transfer belt is broken in a color copying machine or the like. If the speed control is performed using a speed detection device set directly on the drive motor, sufficient image quality can be ensured.

  The present invention has been made in view of such a situation, and in an image forming apparatus such as a color machine that needs to perform speed control with high accuracy, even if a speed detection device provided on a driven body fails, An image forming apparatus capable of operating in a mode (for example, a single color mode) that does not require high-precision speed control by a speed detection device provided in the motor itself without stopping the image forming operation. It is.

  In order to achieve the above object, an image forming apparatus according to a first invention of the present application includes a driven body such as an image carrier, a drive motor that rotationally drives the driven body, and power that transmits the driving force of the drive motor to the driven body. A transmission member, first speed detection means for detecting the rotation speed of the drive motor, second speed detection means for detecting the rotation speed of the driven body to which the driving force of the drive motor is transmitted via the power transmission member, Based on the speed command value and the detection result of the first speed detection means, the reference speed value of the drive motor is calculated to perform reference speed control, and further, the rotation of the driven body is determined from the speed reference value and the detection result of the second speed detection means. Speed control means for calculating fluctuation values and performing fluctuation suppression control, and speed abnormality detection means for detecting abnormalities in the rotational speed of the driven body by comparing the detection result of the second speed detection means with a predetermined reference value. Configured .

  In the image forming apparatus, it is preferable to use a speed command value as a predetermined reference value, and when the difference between the detection result of the second speed detection means and the speed command value exceeds a predetermined allowable range, a speed abnormality detection is performed. The means is configured to determine that the rotational speed of the driven body is abnormal.

  The speed control means of the image forming apparatus includes a reference speed calculation means for calculating a reference speed value of the drive motor from a speed command value of the drive motor and a detection result by the first speed detection means, a reference speed value and a second speed detection means. And a rotation fluctuation calculating means for calculating a rotation fluctuation value of the driven body from the detection result obtained by the above.

  Two methods are applicable as the control method of the drive motor. One is to input a value obtained by adding the calculated reference speed value and the rotation fluctuation value as a rotation fluctuation suppression value with respect to the speed command value, and to perform fluctuation suppression control of the driven body. When the speed abnormality detecting means determines that the rotational speed of the driven body is abnormal, the fluctuation control of the driven body is performed using only the reference speed value as the rotational fluctuation suppression value, and the image forming operation can be continued as it is. It is a method.

  The other one inputs a value obtained by adding the speed command value of the drive motor and the rotation fluctuation value as a rotation fluctuation suppression value, and performs fluctuation suppression control of the driven body. If the speed abnormality detection means determines that the rotational speed of the driven body is abnormal, the fluctuation control of the driven body is performed using only the reference speed value as the rotational fluctuation suppression value, and the image forming operation can be continued as it is. Is the method.

  In the image forming apparatus provided with the speed abnormality detecting means, it is preferable to provide a selecting means for entrusting the user with a decision as to whether or not to continue the image forming operation.

  The image forming apparatus according to the second invention of the present application shows a configuration when the drive motor is a stepping motor. This image forming apparatus includes a driven body such as an image carrier, a stepping motor that rotationally drives the driven body, a power transmission member that transmits the driving force of the stepping motor to the driven body, and a driving force of the stepping motor that drives the power transmission member. The second speed detecting means for detecting the rotational speed of the driven body transmitted via the reference speed control of the stepping motor based on the speed command value of the stepping motor, and the rotation fluctuation of the stepping motor from the detection result by the second speed detecting means Speed control means for calculating the value and performing fluctuation suppression control, and speed abnormality detection means for detecting the abnormality of the rotational speed of the driven body by comparing the detection result of the second speed detection means with the speed command value It is configured.

  In the image forming apparatus according to the second invention of the present application, when the difference between the detection result of the second speed detection unit and the speed command value exceeds a predetermined allowable range, the speed abnormality detection unit detects the rotational speed of the driven body. It is configured so as to be determined as abnormal.

  The speed control means of the image forming apparatus is configured as follows. That is, a rotation fluctuation calculating means for calculating the rotation fluctuation value of the driven body from the speed command value of the stepping motor and the detection result by the second speed detection means is provided, and a value obtained by adding the speed command value and the rotation fluctuation value is obtained. A fluctuation suppression control of the driven body is performed as the rotation fluctuation suppression value. When the speed abnormality detecting means determines that the rotational speed of the driven body is abnormal, the fluctuation control of the driven body is performed based only on the speed command value, and the image forming operation can be continued as it is. It is configured as follows.

  Further, the image forming apparatus provided with the speed abnormality detecting means is preferably provided with a selecting means for entrusting the user with a decision as to whether or not to continue the image forming operation. According to the image forming apparatus having the above configuration, the following operational effects can be obtained.

  According to the image forming apparatus of the first invention of the present application, the first speed detecting means for detecting the rotational speed of the drive motor and the rotational speed of the driven body to which the driving force of the drive motor is transmitted via the power transmission member. The second speed detection means that detects the actual speed and controls the fluctuation suppression, so that the driven body can be controlled with high accuracy, and the detection result of the second speed detection means Since an abnormality in the rotational speed of the driven body can be detected by comparing with a predetermined reference value, the reliability of image formation can be improved.

  In addition, when it is configured to detect the speed fluctuation by detecting the rotation fluctuation range with respect to the speed command value, it is determined that the speed is abnormal when the speed fluctuation becomes large, so a mode that requires a high-definition image is required. It is possible to eliminate useless image formation.

  In the image forming apparatus according to claim 3, the rotational speed fluctuation suppression control of the driven body is performed based on a value obtained by adding the reference speed value and the rotational fluctuation value. In addition to accurate speed control, even if the second speed detection means provided on the driven body fails, it is possible to perform fluctuation suppression control of the driven body using only the reference speed value as the rotational fluctuation suppression value. it can. As a result, it is possible to operate in a mode that does not require highly accurate speed control without stopping the image forming operation.

  Even if the rotational speed fluctuation suppression control of the driven body is performed based on the rotational fluctuation value from the speed command value for the drive motor as in the fourth aspect, substantially the same effect can be expected.

  In the image forming apparatus according to claim 5, when the speed abnormality detection unit determines that the rotational speed of the driven body is abnormal, the fluctuation suppression control of the driven body is performed using only the reference speed value as the rotational fluctuation suppression value. Since the selection means for continuing or stopping the image forming operation is provided, it is possible to prevent useless image formation while enhancing the use efficiency of the image forming apparatus by leaving the judgment to the user.

  When a stepping motor is used as the drive motor as in the second invention of the present application, the stepping motor rotates following the speed command value, and if the tracking cannot be performed, the motor itself stops. The first speed detection means provided directly on the drive motor in the image forming apparatus is not necessary. As a result, the driven body can be speed-controlled with high accuracy only by the detection result of the second speed detecting means.

  In addition, since it is configured to detect the speed fluctuation by detecting the rotation fluctuation value with respect to the speed command value, it is determined that the speed is abnormal when the speed fluctuation becomes large, and in a mode that requires a high-definition image. It is possible to prevent unnecessary image formation.

  In this image forming apparatus, fluctuation suppression control of the rotational speed of the driven body is performed based on the rotational fluctuation value, so that not only high-precision speed control is possible, but also the second speed provided on the driven body. When the speed detecting means fails, the fluctuation suppression control of the driven body can be continued only with the speed command value. As a result, it is possible to continue the operation in the monochrome mode that does not require highly accurate speed control without stopping the image forming operation.

  In the image forming apparatus according to claim 9, when the speed abnormality detection unit determines that the rotational speed of the driven body is abnormal, it is possible to perform fluctuation suppression control of the driven body based on only the speed command value, and image formation Since the selection means for continuing or stopping the operation is provided, the user can make a selection decision himself, and as a result, it is possible to prevent useless image formation while improving the use efficiency of the image forming apparatus. .

  Note that if the driven body is a photoreceptor or an intermediate transfer body that is an image carrier, the image forming operation is not stopped even when it cannot be used in a color mode that requires high-definition speed control. Therefore, it is possible to continue image formation in the monochrome mode that does not require high-definition speed control. As described above, when the image forming apparatus according to any one of claims 1 to 10 is applied to a color machine, even if the speed detection device mounted on the driven body breaks down and the speed control becomes unstable, the monochrome mode can be used. Use, for example, the output of a monochrome document can be continued, and an effect of excellent utilization efficiency can be obtained.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is an overall configuration diagram of a color image forming apparatus 100 in which an image forming apparatus according to the present invention is implemented. The color image forming apparatus 100 is called a tandem type color image forming apparatus, and includes a document conveying section 91, an image reading section 92, an image processing section (not shown), an image forming section 94, a paper feeding section 95, and a fixing apparatus 96. A paper discharge unit 97 and a re-conveying path 98 for automatic double-sided copying are provided.

  The image forming unit 94 is provided with an endless belt-like intermediate transfer belt 7 that is stretched by a plurality of roller groups and supported so as to be able to be driven around. Along the outer peripheral surface of the intermediate transfer belt 7, yellow, magenta, Four image forming units 10Y, 10M, 10C, and 10K that form cyan and black toner images are arranged in tandem.

  The image forming units 10Y, 10M, 10C, and 10K have photoreceptors 1Y, 1M, 1C, and 1K as image carriers on which latent images are formed, respectively, along the outer peripheral surface of each photoreceptor. In order of operation, charging devices 2Y, 2M, 2C, and 2K that charge the surfaces of the photoreceptors 1Y, 1M, 1C, and 1K almost uniformly, and an exposure device 3Y that writes an electrostatic latent image on each photoreceptor surface. , 3M, 3C, 3K, developing devices 4Y, 4M, 4C, 4K that transfer toner to each latent image formed on the surface of the photoconductor to form a toner image, and toner images on the surface of the photoconductor are transferred to the intermediate transfer belt. 7, primary transfer devices 5Y, 5M, 5C, and 5K for transferring onto the surface 7 and cleaning devices 6Y, 6M, 6C, and 6K for cleaning the surface of the photoreceptor after the transfer are disposed.

  The document conveying section 91 and the image reading section 92 are mounted on the upper part of the main body of the color image forming apparatus 100. The document transport unit 91 includes a feed roller including a document table 11, a pickup roller 12, and a transport roller 13. Documents placed on the document table 11 of the document conveying section 91 with the writing surface facing upward are separated one by one by the pickup roller 12 and sent to the document conveying path by the conveying roller 13. When the original passes through the slit glass 14 disposed on the upper surface of the image reading unit 92, an image is read by the optical system of the image reading unit 92.

  The image reading unit 92 includes a scanning unit A composed of a light source L for illuminating a document and a mirror 21, a traveling body B composed of two roof mirrors 22 and 23 for guiding reflected light, an imaging lens 24, and a CCD image sensor 25 (hereinafter referred to as “scanning unit A”). The CCD sensor). In the image reading unit 92, when the document passes over the slit glass 14, the document is read by the scanning unit A, and the reflected light is CCD-converted by the traveling body B having the two roof mirrors 22 and 23 and the imaging lens 24. The light is guided onto the sensor 25 to form an optical image.

  The optical image read by the CCD sensor 25 is sent to an image processing unit (not shown). In the image processing unit, the electronic image data is subjected to analog processing, A / D conversion, shading correction, color correction, halftone processing, and the like, and then the digitized image information data of each color is converted into each image forming unit 10Y, 10M. , 10C, 10K to the exposure devices 3Y, 3M, 3C, 3K.

  In the exposure apparatuses 3Y, 3M, 3C, and 3K, the semiconductor laser is electrically modulated based on each image data, corrected to parallel light through a collimator lens, and then reflected by a polyhedral reflecting mirror (polygon mirror) and an fθ lens. Sub-scanning is performed on the photoreceptors 1Y, 1M, 1C, and 1K. Further, main scanning is performed by rotating the photoconductors 1Y, 1M, 1C, and 1K, and electrostatic latent images are reproduced on the photoconductors 1Y, 1M, 1C, and 1K.

  Prior to exposure, a predetermined surface charge is applied to the photoreceptors 1Y, 1M, 1C, and 1K by corona discharge of the charging devices 2Y, 2M, 2C, and 2K. By irradiation with laser light for each color, The charge of the exposed portion is reduced according to the exposure amount, and as a result, electrostatic latent images corresponding to the image information data are formed on the respective photoreceptors 1Y, 1M, 1C, and 1K.

  The electrostatic latent image is visualized with toner of each color developer supplied from the developing devices 4Y, 4M, 4C, and 4K, and becomes a toner image. The toner images of the respective colors formed on the photoreceptors 1Y, 1M, 1C, and 1K are sequentially transferred to the same position on the intermediate transfer belt 7 rotated by the primary transfer devices 5Y, 5M, 5C, and 5K, and synthesized. A color image is formed.

  On the other hand, a plurality of paper trays 50 for storing the recording paper P are provided with a movable plate 51 whose free end is always urged upward by an urging means such as a spring, and the recording paper placed thereon. The uppermost P is in contact with the pickup roller 52 that constitutes a part of the paper feeding means.

  The recording paper P that has come into contact with the pickup roller 52 is taken out of the paper tray 50 by the contact pressure, separated one by one, and fed. The fed recording paper P is guided to a plurality of intermediate rollers 26 and conveyed to a registration roller 27. The conveyed recording paper P is corrected by the registration rollers 27 to bend the recording paper P, and is fed to the secondary transfer device 8 at a paper feed timing. A color image of the synthesized toner on the intermediate transfer belt 7 is formed. It is transferred onto the recording paper P at once.

  The recording paper P onto which the color image has been transferred is conveyed to the fixing device 96 while being guided by a conveyance guide plate (not shown). The color image on the recording paper P is heated and fixed by the fixing device 96. The recording paper P heated for melting the developer image is cooled by a cooling fan (not shown) for fixing the developer image, and is sandwiched between paper discharge rollers 28 and placed on a paper discharge tray 29 outside the apparatus. The

  By the way, with respect to the rotational driving of the drum-shaped photoconductors 1Y, 1M, 1C, and 1K that are exposed to the laser light modulated by the image information to form an electrostatic latent image, the formed toner image is made clear. Therefore, highly stable and uniform speed control is required. FIG. 2 is a configuration diagram schematically showing the drive control unit 30 of the photoreceptors 1Y, 1M, 1C, and 1K. Hereinafter, the configuration and operation of the drive control unit 30 will be described by limiting it to the photoreceptor 1K that forms a black toner image. The same applies to the other photoconductors 1Y, 1M, and 1C, and other descriptions are omitted.

  A disc-shaped speed detection plate 32 made of a transparent plate is coaxially mounted on the rotary shaft 31 disposed at the center of the photoreceptor 1K. On this speed detection plate 32, fine bars that block light are arranged at equal intervals along the circumference. A photocoupler 33 is disposed sandwiching the bar from both sides, and a driven body speed encoder 34 is formed which forms a second speed detecting means as a whole.

  A gear is attached to one end of the rotating shaft 31 of the photosensitive member 1K, and is connected to a rotating shaft 37 of a brushless DC motor 36 (hereinafter simply referred to as a DC motor) as a driving motor via a gear train 35. When the DC motor 36 rotates, the rotational driving force is transmitted to the photoreceptor 1K via the gear train 35, and the photoreceptor 1K is rotationally driven.

  On the other hand, the rotation shaft 37 of the DC motor 36 is also provided with a motor speed encoder 38 having the same configuration as that of the rotation shaft 31 of the photoreceptor 1K, thereby forming a first speed detection means. When the DC motor 36 is driven, the photosensitive member 1K is also rotationally driven through the gear train 35, and a detection speed signal is simultaneously generated from the motor speed encoder 38 and the driven body speed encoder 34. This detection speed signal is input to the control device 40.

  A block diagram showing the functional configuration of the control device 40 is shown in FIG. FIG. 4 is a block diagram illustrating an operation example of the control device 40. 3 to 8, the same reference numerals as those in FIG. 2 represent the same items. A control device 40 shown in FIG. 3 includes a sequence control unit 41 that determines a control procedure, a motor speed detection unit 42 that detects the speed of the DC motor 36, and a driven body speed that detects the rotational speed of the photosensitive member 1K that is a driven body. In addition to the control means configured by the speed control unit 45 for driving the detection unit 43 and the DC motor 36 at a predetermined speed, the speed abnormality detection unit 44 is included.

  Hereinafter, variable speed control by frequency / voltage conversion of the DC motor 36 will be described as an example with reference to FIGS. 3 and 4. The control method is not limited to this, and a constant rotation control method using servo control or PLL is also conceivable.

  The sequence control unit 41 determines a motor speed command value according to the content of the image forming operation, and the motor speed command value is input to the speed control unit 45 as a DC voltage value. The waveform output of the motor speed encoder 38 is shaped by the motor speed detection unit 42, and the motor rotation speed of the DC motor 36 is converted into a DC voltage value and input to the speed control unit 45. The speed control unit 45 adds the direct current voltage of the motor speed command value and the direct current voltage value of the motor rotation speed, and calculates the reference speed value of the DC motor 36 based on the difference.

  The waveform output of the driven body speed encoder 34 is also shaped by the driven body speed detection unit 43, and the current rotation speed of the photosensitive member 1 </ b> K is converted into a DC voltage value and input to the speed control unit 45. The rotational speed of the photosensitive member 1K should be the same value as the DC motor rotational speed if there is no gear train 35 as a power transmission member, but includes rotational fluctuations due to backlash or backlash of the gear train 35. It is. Therefore, the speed control unit 45 of the control device 40 adds the rotation speed of the photosensitive member 1K to the speed reference value, and calculates the rotation fluctuation suppression value based on the difference.

  The calculated rotation fluctuation suppression value is converted into a driving time width of the DC motor 36, for example, a pulse width or the number of clocks, and is input to the DC motor 36 from the speed control unit 45 of the control device 40. As a result, the constant speed drive control of the photosensitive member 1K can be performed with high accuracy.

  On the other hand, the speed abnormality detector 44 detects an abnormality in the rotational speed fluctuation of the photosensitive member 1K. The detection method compares the DC voltage value indicating the rotation speed of the photosensitive member 1K detected by the driven body speed detection unit 43 with the DC voltage value indicating the speed command value instructed by the sequence control unit 41, and the difference is found. Generally, it is determined that the speed is abnormal when exceeding a predetermined range set in advance, but the present invention is not limited to this.

  FIGS. 5 and 6 are block diagrams showing a functional configuration and an operation example of the control device 40 when the speed abnormality detection unit 44 determines that the rotational speed of the photoreceptor 1K is abnormal. In this case, the result of determining that the speed is abnormal is transmitted to the sequence control unit 41. In accordance with the result, the sequence control unit 41 blocks the input of the output result of the driven body speed detection unit 43 to the speed control unit 45 as indicated by the crosses in FIGS. As a result, the DC motor 36 is driven to suppress fluctuation using only the reference speed value as the rotation fluctuation suppression value, and the image forming operation continues without interruption.

  FIG. 7 shows an operation example of the control device 40 which is the speed control means according to the fourth aspect. In this control device 40, the rotation speed of the photoreceptor 1K is compared with a motor speed command value, and a rotation fluctuation suppression value is calculated based on the difference. Further, the current motor rotation speed is compared with the motor speed command value, and the reference speed value of the DC motor 36 is calculated based on the difference. The speed control unit 45 is configured so that one of the calculated values can be selected by the changeover switch 47 and the speed can be instructed to the drive unit of the DC motor 36.

  During normal motor speed control, the calculated rotation fluctuation suppression value is input to the DC motor 36 after converting the driving time width of the DC motor 36 into, for example, a pulse width or the number of clocks. When the speed abnormality detection unit 44 determines that the rotation speed of the photosensitive member 1K is abnormal, the detection result is transmitted to the sequence control unit 41. The sequence control unit 41 switches the switch 47 according to the result. As a result, the DC motor 36 is rotationally driven at the reference speed using only the reference speed value as the fluctuation suppression value, and the image forming operation continues without interruption.

  In the above embodiment, when an abnormality is determined by the speed abnormality detecting unit 44, the reference value of the motor speed of the sequence control unit 41 is automatically changed and the rotation driving of the DC motor 36 is continued. However, it is also possible to stop the image forming operation by issuing a failure signal. The user can also select whether or not to continue the image forming operation with a selection button (not shown).

  An example of the optimum speed control method of the color image forming apparatus 100 according to the present invention when the selection unit is provided will be described below with reference to the flowchart shown in FIG. A reference speed value is calculated from the speed signal detected by the motor speed encoder 38 attached to the rotating shaft 37 of the DC motor 36 and the speed command value (S-1). On the other hand, a rotation fluctuation suppression value is calculated from the speed signal detected from the driven body speed encoder 34 and the calculated reference speed value (S-2). This rotational fluctuation suppression value is compared with a predetermined reference value, usually a speed command value, and it is determined whether or not the speed is abnormal (S-3).

  If the rotational fluctuation value is within the allowable range from the predetermined reference value, the rotational speed control of the driven body is normal, and the value obtained by adding the reference speed value and the rotational fluctuation suppression value is the speed of the DC motor 36 at that time. The command value is input to the motor drive unit (S-4). Thereby, the DC motor 36 is driven at a highly stable constant speed (S-5).

  When it is determined that the motor speed is abnormal based on the speed signal detected from the driven body speed encoder 34, it is determined whether or not to continue the operation in the failure mode according to the user's selection (S-6). When the user selects to continue the operation, the fluctuation suppression control is performed only by the reference speed value calculated from the detection result from the motor speed encoder 38 without inputting the rotation fluctuation suppression value to the speed control unit 45 (S-7). ), The DC motor 36 is driven at a constant speed. When the operation in the failure mode is stopped by the user's selection, a service call is made (S-8).

  A drive control unit 60 of the color image forming apparatus 100 according to the second embodiment is shown in FIG. 9, and a block diagram showing a functional configuration of the control apparatus 61 is shown in FIG. The drive control unit 60 of the photoreceptor 1K of the color image forming apparatus 100 has the same configuration as the drive control unit 30 shown in FIG. 2 except that the stepping motor 46 is used as a drive motor.

  Further, since the stepping motor 46 rotates following the speed command value and stops if it cannot follow, the color image forming apparatus 100 according to the first aspect of the invention as shown in the functional block diagram of FIG. The motor speed encoder 38 which is the first speed detecting means provided directly on the DC motor 36 is not necessary. As a result, the object can be achieved by performing the speed control only by the driven body speed encoder 34 as the second speed detecting means. The speed control method will be described with reference to FIGS.

  FIG. 11 is a block diagram showing an operation example of the control device 61 shown as the second embodiment. (A) is a case at the time of normal speed control, (b) is a block diagram which shows rotational speed control operation | movement when the speed abnormality detection part 44 judges that it is speed abnormality.

  The sequence control unit 41 determines a motor speed command value according to the content of the image forming operation, and the motor speed command value is input to the speed control unit 45 as a DC voltage value. The waveform output of the driven body speed encoder 34 is shaped by the driven body speed detection unit 43, and the current rotation speed of the photosensitive member 1 </ b> K is converted into a DC voltage value and input to the speed control unit 45. The speed control unit 45 compares the rotation speed of the photosensitive member 1K with a motor speed command value, and calculates a rotation fluctuation suppression value from the difference.

  The calculated rotation fluctuation suppression value is converted into a driving time width of the stepping motor 46, for example, a pulse width or a pulse interval, and is input to the driving unit of the stepping motor 46. As a result, the rotation fluctuation suppression control of the photosensitive member 1K can be performed with high accuracy (FIG. 11A).

  On the other hand, the speed abnormality detector 44 detects an abnormality in the rotational speed of the photoconductor 1K. In this case, the abnormality determination result is transmitted to the sequence control unit 41. The sequence control unit 41 blocks the input of the output result of the driven body speed detection unit 43 to the speed control unit 45 according to the result (FIG. 11B). As a result, the stepping motor 46 is rotationally driven with the motor speed command value as a target value, and the image forming operation continues without interruption.

  In the above embodiment, when the abnormality is determined by the speed abnormality detection unit 44, the motor speed command value of the sequence control unit 41 is automatically changed and the rotation of the stepping motor 46 is continued. However, it is also possible to stop the image forming operation by issuing a failure signal. As in the case of the DC motor 36, the user can select whether or not to continue the image forming operation with a selection button (not shown).

  The image forming apparatus according to the present invention is not limited to the above-described embodiment, and various methods for controlling the speed of the driven pair are known. Therefore, it goes without saying that the control method can be changed. Further, the driven member is not limited to the photosensitive member and the intermediate transfer member, and can be applied to those that normally require highly stable constant speed rotation control.

1 is an overall configuration diagram of a color image forming apparatus according to an embodiment of the present invention. FIG. 2 is a configuration diagram schematically illustrating a drive control unit of a photoconductor. It is a block diagram showing the function structure of a control apparatus. It is a block diagram which shows the operation example of a control apparatus. It is a block diagram which shows the function structure of a control apparatus when a speed abnormality detection part judges that it is abnormal in the rotational speed of a photoconductor. It is a block diagram which shows the operation example of a control apparatus when a speed abnormality detection part judges that it is abnormal in the rotational speed of a photoconductor. It is a block diagram which shows the operation example of another control apparatus. 6 is a flowchart illustrating an example of an optimum speed control method for the color image forming apparatus according to the present invention. It is the block diagram which showed typically the drive control part of the color image forming apparatus which is another embodiment. It is a block diagram showing the function structure of the control apparatus which is another embodiment. It is a block diagram which shows the operation example of the control apparatus which is other embodiment. (A) is a case at the time of normal speed control, (b) is a case where the speed abnormality detection part judges that it is speed abnormality. It is a curve which shows the visibility limit with respect to the rotational speed nonuniformity in a monochrome mode.

Explanation of symbols

1Y, 1M, 1C, 1K photoconductor (driven body)
7 Intermediate transfer belt (driven body)
10Y, 10M, 10C, 10K Image forming units 30, 60 Drive control unit 34 Driven body speed encoder (second speed detection means)
35 Gear train (power transmission member)
36 DC motor (drive motor)
38 Motor speed encoder (first speed detection means)
40, 61 Control device (speed control means)
41 Sequence control unit 42 Motor speed detection unit 43 Driven body speed detection unit 44 Speed abnormality detection unit (speed abnormality detection means)
45 Speed controller 46 Stepping motor (drive motor)
47 changeover switch 94 image forming unit 100 color image forming apparatus P recording paper

Claims (10)

A driven body;
A drive motor for rotationally driving the driven body;
A power transmission member for transmitting the driving force of the drive motor to the driven body;
First speed detecting means for detecting the rotational speed of the drive motor;
Second speed detection means for detecting the rotational speed of the driven body, to which the driving force of the drive motor is transmitted via the power transmission member;
From the speed command value of the drive motor and the detection result by the first speed detection means, the reference speed value of the drive motor is calculated to perform reference speed control, and from the reference speed value and the detection result by the second speed detection means Speed control means for calculating a rotation fluctuation value of the driven body and performing fluctuation suppression control;
An image forming apparatus comprising: a speed abnormality detection unit that detects a rotation speed abnormality of the driven body by comparing a detection result of the second speed detection unit with a predetermined reference value.   When the predetermined reference value is the speed command value of the drive motor, and the difference between the detection result of the second speed detection means and the speed command value exceeds a predetermined allowable range, the speed abnormality detection means The image forming apparatus according to claim 1, wherein the image forming apparatus determines that the rotational speed of the driven body is abnormal. The speed control means is
A reference speed calculation means for comparing the speed command value of the drive motor and the detection result by the first speed detection means, and calculating the reference speed value of the drive motor from the difference;
Comparing the reference speed value and the detection result by the second speed detecting means, and having a rotation fluctuation calculating means for calculating a rotation fluctuation value of the driven body from the difference,
Performing the fluctuation suppression control of the driven body using the value obtained by adding the reference speed value and the rotation fluctuation value as the rotation fluctuation suppression value with respect to the speed command value,
When the speed abnormality detection means determines that the rotational speed of the driven body is abnormal, the fluctuation suppression control of the driven body is performed using only the reference speed value as the rotational fluctuation suppression value, and the image forming operation is continued. The image forming apparatus according to claim 1, wherein the image forming apparatus is configured as described above. The speed control means is
A reference speed calculation means for comparing the speed command value of the drive motor and the detection result by the first speed detection means, and calculating the reference speed value of the drive motor from the difference;
Comparing the reference speed value and the detection result by the second speed detecting means, and having a rotation fluctuation calculating means for calculating a rotation fluctuation value of the driven body from the difference,
Performing the fluctuation suppression control of the driven body using the value obtained by adding the speed command value and the rotation fluctuation value as a rotation fluctuation suppression value,
When the speed abnormality detection means determines that the rotational speed of the driven body is abnormal, the fluctuation suppression control of the driven body is performed using only the reference speed value as the rotational fluctuation suppression value, and the image forming operation is continued. The image forming apparatus according to claim 1, wherein the image forming apparatus is configured as described above.   When the speed abnormality detection means determines that the rotational speed of the driven body is abnormal, the driven body fluctuation suppression control is performed using only the reference speed value as the rotational fluctuation suppression value, and the image forming operation is continued. 5. The image forming apparatus according to claim 3, further comprising selection means for determining whether or not to perform the operation. A driven body;
A stepping motor that rotationally drives the driven body;
A power transmission member for transmitting the driving force of the stepping motor to the driven body;
Second speed detection means for detecting the rotational speed of the driven body, to which the driving force of the stepping motor is transmitted via the power transmission member;
A speed control means for controlling a reference speed of the stepping motor according to a speed command value of the stepping motor, calculating a rotation fluctuation value of the stepping motor from a detection result by the second speed detection means, and performing fluctuation suppression control;
An image forming apparatus comprising: a speed abnormality detecting unit that detects a rotation speed abnormality of the driven body by comparing a detection result of the second speed detecting unit with the speed command value.   When the difference between the detection result of the second speed detection means and the speed command value exceeds a predetermined allowable range, the speed abnormality detection means determines that the rotational speed of the driven body is abnormal. The image forming apparatus according to claim 6. The speed control means is
Comparing the speed command value and the detection result by the second speed detecting means, and having a rotation fluctuation calculating means for calculating a rotation fluctuation value of the driven body from the difference,
Performing the fluctuation suppression control of the driven body using the value obtained by adding the speed command value and the rotation fluctuation value as a rotation fluctuation suppression value,
When the speed abnormality detecting means determines that the rotational speed of the driven body is abnormal, the fluctuation suppression control of the driven body is performed using only the speed command value as the rotational fluctuation suppression value, and the image forming operation is continued. The image forming apparatus according to claim 7, wherein:   When the speed abnormality detecting means determines that the rotational speed of the driven body is abnormal, the driven body fluctuation suppression control is performed using only the speed command value as the rotational fluctuation suppression value, and the image forming operation is continued. The image forming apparatus according to claim 8, further comprising a selection unit that determines whether or not to perform the operation.   The image forming apparatus according to claim 1, wherein the driven member is a photosensitive member or an intermediate transfer member that is an image carrier.

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