Patent Publication Number: US-2023144792-A1

Title: Image forming apparatus

Description:
BACKGROUND 
     Field 
     The present disclosure relates to an image forming apparatus using an electrophotographic method, such as a printer, a copying machine, and a facsimile machine. 
     Description of the Related Art 
     Some available image forming apparatuses have a configuration in which a developing roller is movable between a position at which the developing roller is brought into contact with a photosensitive member and a position at which the developing roller is separate from the photosensitive member. An image forming apparatus discussed in Japanese Patent Application Laid-Open No. 2006-292868 includes a separation cam that separates a developing roller from a photosensitive member, and a developing clutch that switches rotating and stationary states of the developing roller. The separation cam and the developing clutch are synchronized with each other and operated by a stepping motor. In the image forming apparatus discussed in Japanese Patent Application Laid-Open No. 2006-292868, the developing roller is brought into contact with the photosensitive member after the rotation of the developing roller is started. 
     There are available image forming apparatuses in which the developing roller is brought into contact with the photosensitive member, it is desirable that the developing roller is fully coated with toner. Accordingly, it is desirable to bring the developing roller into contact with the photosensitive member after the developing roller is fully rotated. 
     In some available image forming apparatuses, if the stepping motor is stopped after the developing roller is rotated and before the developing roller is brought into contact with the photosensitive member, the developing roller is rotated before the developing roller is brought into the photosensitive member, enabling the developing roller to be coated with toner. However, a period from a time when driving of the stepping motor is started to a time when rotation of the developing roller is started and a period from a time when driving of the stepping motor is started to a time when the developing roller is brought into contact with the photosensitive member vary depending on the tolerance of parts and the like. This may make it difficult to reliably stop the stepping motor at a timing after the developing roller is rotated and before the developing roller is brought into contact with the photosensitive member. 
     SUMMARY 
     The present disclosure is directed to providing an image forming apparatus configured to bring a developing roller into contact with a photosensitive member after the developing roller is fully rotated in a configuration in which the developing roller is movable between a position at which the developing roller is brought into contact with the photosensitive member and a position at which the developing roller is separate from the photosensitive member. 
     One aspect of the present disclosure is as follows. 
     According to an aspect of the present disclosure, an image forming apparatus includes a photosensitive member, a developing roller, a first motor configured to drive the developing roller, a drive-train configured to transmit a driving force of the first motor to the developing roller and including a drive switching unit, wherein the drive switching unit is configured to switch between a transmission state where the driving force is transmitted to the developing roller and a non-transmission state where the driving force is not transmitted to the developing roller, a development switching unit configured to switch between a contact state where the developing roller is brought into contact with the photosensitive member and a separated state where the developing roller is separate from the photosensitive member, and configured to operate in conjunction with an operation of the drive switching unit, a second motor configured to drive the development switching unit and the drive switching unit, a control unit configured to control the first motor and the second motor, and a current detection unit configured to detect a current flowing through the first motor, wherein, in a case where the drive switching unit transitions from the non-transmission state to the transmission state and a magnitude of the current detected by the current detection unit has changed, the control unit is configured to execute a stop operation to stop the second motor before the developing roller is brought into contact with the photosensitive member while driving the first motor. 
     Further features of the present disclosure will become apparent from the following description of exemplary embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a schematic sectional view of an image forming apparatus. 
         FIG.  2    is a block diagram illustrating a configuration of a motor control unit. 
         FIG.  3    is an explanatory diagram illustrating a structure of an A-motor. 
         FIG.  4    illustrates driving and movement of a developing roller. 
         FIG.  5    illustrates each timing of driving the developing roller and moving the developing roller with respect to a photosensitive member. 
         FIG.  6    is an explanatory diagram illustrating an operation of driving the developing roller and bringing the developing roller into contact with the photosensitive member according to a first exemplary embodiment. 
         FIG.  7    is a flowchart illustrating a seal removal sequence according to the first exemplary embodiment. 
         FIG.  8    is an explanatory diagram illustrating an operation of driving the developing roller and bringing the developing roller into contact with the photosensitive member according to a second exemplary embodiment. 
         FIG.  9    is a flowchart illustrating the seal removal sequence according to the second exemplary embodiment. 
         FIG.  10    is a schematic view of a cartridge. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Exemplary embodiments of the present disclosure will be illustratively described in detail below with reference to the accompanying drawings. The dimensions, materials, shapes, relative arrangements, and the like of components described in the following exemplary embodiments should be appropriately changed depending on the configuration of an apparatus to which the present disclosure is applied and various conditions. Therefore, the scope of the present disclosure is not limited only to the exemplary embodiments unless otherwise specified. 
     (Image Forming Apparatus) 
     A first exemplary embodiment of the present disclosure will be described. An image forming apparatus  100  according to the present exemplary embodiment will be described with reference to  FIG.  1   .  FIG.  1    is a schematic sectional view of the image forming apparatus  100 . The image forming apparatus  100  according to the present exemplary embodiment is a tandem color laser printer using an electrophotographic process. A configuration example of the image forming apparatus  100  will be described with reference to  FIG.  1   . 
     The image forming apparatus  100  is configured to output a full-color image by forming toner images of four colors, yellow (Y), magenta (M), cyan (C), and black (K), in a superimposed manner. The image forming apparatus  100  includes laser scanners ( 11 Y,  11 M,  11 C,  11 K) each serving as an exposure device and cartridges ( 12 Y,  12 M,  12 C,  12 K) to form images of the respective colors. The cartridges ( 12 Y,  12 M,  12 C,  12 K) are each configured to be detachably attached to an apparatus body  100 A of the image forming apparatus  100 . 
     The cartridges ( 12 Y,  12 M,  12 C,  12 K) include photosensitive members ( 13 Y,  13 M,  13 C,  13 K) and photosensitive member cleaners ( 14 Y,  14 M,  14 C,  14 K), respectively. The photosensitive members ( 13 Y,  13 M,  13 C,  13 K) are each configured to rotate in a direction indicated by an arrow in  FIG.  1   . The photosensitive member cleaners ( 14 Y,  14 M,  14 C,  14 K) are each provided to be in contact with the corresponding photosensitive member. The cartridges ( 12 Y,  12 M,  12 C,  12 K) further include charging rollers ( 15 Y,  15 M,  15 C,  15 K) and developing rollers ( 16 Y,  16 M,  16 C,  16 K), respectively. 
     The photosensitive members ( 13 Y,  13 M,  13 C,  13 K) are photosensitive drums each serving as an image carrying member configured to carry an electrostatic latent image. The photosensitive member cleaners ( 14 Y,  14 M,  14 C,  14 K) are cleaning members that are brought into contact with the photosensitive members ( 13 Y,  13 M,  13 C,  13 K), respectively, and are configured to remove toner serving as developer from the surfaces of the photosensitive members ( 13 Y,  13 M,  13 C,  13 K), respectively. The charging rollers ( 15 Y,  15 M,  15 C,  15 K) are charging members that charge the surfaces of the photosensitive members ( 13 Y,  13 M,  13 C,  13 K), respectively. The developing rollers ( 16 Y,  16 M,  16 C,  16 K) are developer carrying members (developing members) that carry toner and develop the electrostatic latent image formed on the surfaces of the photosensitive members ( 13 Y,  13 M,  13 C,  13 K). 
     The image forming apparatus  100  further includes an intermediate transfer belt  19  that is in contact with the photosensitive members ( 13 Y,  13 M,  13 C,  13 K), and primary transfer rollers ( 18 Y,  18 M,  18 C,  18 K). The intermediate transfer belt  19  is located such that a part of the intermediate transfer belt  19  is sandwiched between the primary transfer rollers ( 18 Y,  18 M,  18 C,  18 K) and the photosensitive members ( 13 Y,  13 M,  13 C,  13 K). 
     The image forming apparatus  100  further includes an A-motor  101 , a B-motor  102 , and a C-motor  103 . 
     In the present exemplary embodiment, the A-motor  101  rotates the developing rollers ( 16 Y,  16 M,  16 C,  16 K), the B-motor  102  rotates the photosensitive members ( 13 Y,  13 M,  13 C), and the C-motor  103  rotates the intermediate transfer belt  19  and the photosensitive member  13 K. The A-motor  101 , the B-motor  102 , and the C-motor  103  are direct-current (DC) brushless motors. Which member each of the A-motor  101 , the B-motor  102 , and the C-motor  103  rotates is not limited to this configuration. 
     The image forming apparatus  100  further includes a cassette  22  that stores sheets  21  serving as recording materials. Paper, a resin film, and the like are used as the sheets  21 . A feed roller  25 , a conveyance roller  26   a , a separation roller  26   b , and registration rollers  27  are provided downstream of the cassette  22  in a conveyance direction of the sheets  21 . A conveyance sensor  28  is provided downstream of the registration rollers  27  in the conveyance direction of the sheets  21 , and a secondary transfer roller  29  is provided downstream of the conveyance sensor  28  so that the secondary transfer roller  29  is in contact with the intermediate transfer belt  19 . A fixing device  30  is provided downstream of the secondary transfer roller  29 . 
     A controller (printer control unit)  31  is a control unit of the image forming apparatus  100 . The controller  31  includes a central processing unit (CPU)  32  including a read-only memory (ROM)  32   a , a random access memory (RAM)  32   b , and a timer  32   c , and one or more various input/output control circuits (not illustrated). A display panel  33  displays an image based on a signal from the CPU  32  of the controller  31 . The image displayed on the display panel  33  includes characters and graphics. The display panel  33  displays information relating to usage of the image forming apparatus  100  and information relating to the state of the image forming apparatus  100 , including the state of the cartridges ( 12 Y,  12 M,  12 C,  12 K). 
     Next, an image forming operation for forming an image on each sheet  21  will be briefly described. In dark places in the cartridges ( 12 Y,  12 M,  12 C,  12 K), the surfaces of the photosensitive members ( 13 Y,  13 M,  13 C,  13 K) are uniformly charged by the charging rollers ( 15 Y,  15 M,  15 C,  15 K), respectively. A driving force of the B-motor  102  is drive-transmitted by a drive transmission unit including a gear, thus rotating the photosensitive members ( 13 Y,  13 M,  13 C). Similarly, a driving force of the C-motor  103  is drive-transmitted by a drive transmission unit including a gear, thus rotating the photosensitive member  13 K and the intermediate transfer belt  19 . 
     Next, the laser scanners ( 11 Y,  11 M,  11 C,  11 K) irradiate the surfaces of the photosensitive members ( 13 Y,  13 M,  13 C,  13 K) with a laser beam based on image data. Electric charge in a portion irradiated with the laser beam is removed to thereby form the electrostatic latent image on the surfaces of the photosensitive members ( 13 Y,  13 M,  13 C,  13 K). 
     A developing bias is applied to the developing rollers ( 16 Y,  16 M,  16 C,  16 K) carrying toner, so that toner adheres to the electrostatic latent image formed on the surfaces of the photosensitive members ( 13 Y,  13 M,  13 C,  13 K) from the developing rollers ( 16 Y,  16 M,  16 C,  16 K). Adherence of toner to the surfaces of the photosensitive members ( 13 Y,  13 M,  13 C,  13 K) based on the electrostatic latent image forms toner images of the respective colors on the surfaces of the photosensitive members ( 13 Y,  13 M,  13 C,  13 K). 
     A primary transfer bias is applied to the primary transfer rollers ( 18 Y,  18 M,  18 C,  18 K). Thus, the toner images formed on the surfaces of the photosensitive members ( 13 Y,  13 M,  13 C,  13 K) are attracted onto the intermediate transfer belt  19  at a nip portion (primary transfer portion) formed by the photosensitive members ( 13 Y,  13 M,  13 C,  13 K) and the intermediate transfer belt  19 . 
     The CPU  32  controls an image forming timing for each of the cartridges ( 12 Y,  12 M,  12 C,  12 K) depending on the moving speed of the intermediate transfer belt  19 . The toner image is transferred onto the surface of the intermediate transfer belt  19  from each of the cartridges ( 12 Y,  12 M,  12 C,  12 K), so that a full-color image is finally formed on the surface of the intermediate transfer belt  19 . 
     By contrast, the sheets  21  stored in the cassette  22  are conveyed by the feed roller  25 . The sheets  21  are separated one by one by the conveyance roller  26   a  and the separation roller  26   b  and the separated sheet  21  is conveyed toward the registration rollers  27 . The sheet  21  passes through the registration rollers  27  and is conveyed toward the secondary transfer roller  29 . The toner image formed on the surface of the intermediate transfer belt  19  is transferred onto the sheet  21  at a nip portion (secondary transfer portion) formed by the secondary transfer roller  29  and the intermediate transfer belt  19 . The fixing device  30  performs a heat fixing process on the toner image transferred onto the sheet  21 . The sheet  21  onto which the toner image is fixed is discharged to the outside of the image forming apparatus  100 . 
     In the present exemplary embodiment, the image forming apparatus  100  includes an environmental temperature sensor  40  for measuring the environmental temperature of outside air, and is capable of performing the image forming operation depending on the measured environmental temperature. For example, the magnitude of the developing bias or primary transfer bias can be changed depending on the external environmental temperature. 
     &lt;Configuration for Driving A-Motor&gt; 
     Next, a configuration for driving the A-motor  101  will be described with reference to  FIG.  2   .  FIG.  2    is a block diagram illustrating a configuration of a motor control unit  120 . 
     In the present exemplary embodiment, the A-motor  101  is a brushless motor that is controlled using vector control. The motor control unit  120  is a circuit for rotating the A-motor  101 . The CPU  32  of the controller  31  controls the A-motor  101  via the motor control unit  120 . The motor control unit  120  includes an arithmetic processing unit using, for example, a microcontroller  121 . The microcontroller  121  includes therein a communication port  122 , an analog-to-digital (AD) converter  129 , a counter  123 , a non-volatile memory  124 , a reference clock generation unit  125 , a crystal oscillator  126 , a pulse-width modulation (PWM) port  127 , and a current calculation unit  128 . The counter  123  performs a counting operation based on a reference clock generated by the reference clock generation unit  125 . For example, measurement of an input pulse cycle and generation of PWM signals are performed based on the counting operation. 
     The PWM port  127  includes six terminals and outputs PWM signals, including three high-level signals (U-H, V-H, W-H) and three low-level signals (U-L, V-L, W-L). The motor control unit  120  includes a three-phase inverter  131  including three high-level switching elements and three low-level switching elements. For example, transistors and field-effect transistors (FETs) can be used as the switching elements. 
     Each switching element is connected to the PWM port  127  through a gate driver  132 , and ON/OFF of each switching element is controllable with the PWM signal output from the PWM port  127 . Each switching element is turned on with the PWM signal at a high level (H) and is turned off with the PWM signal at a low level (L). 
     U-phase, V-phase, and W-phase outputs  133  of the inverter  131  are respectively connected to coils  135 ,  136 , and  137  of the A-motor  101 , thus controlling coil currents to be passed through the coils  135 ,  136 , and  137 . 
     A coil current having flowed through each of coils  135 ,  136 , and  137  of the A-motor  101  is detected by a current detection unit. The current detection unit includes a current sensor  130 , an amplifier unit  134 , the AD converter  129 , and the current value calculation unit  128 . Initially, a current flowing through each of the coils  135 ,  136 , and  137  is converted into a voltage by the current sensor  130 . The amplifier unit  134  amplifies the voltage and applies an offset voltage. The voltage is then input to the AD converter  129  of the microcontroller  121 . 
     For example, assuming that the current sensor  130  outputs a voltage of 0.01 V per 1 A, an amplification factor in the amplifier unit  134  is 10, and an offset voltage to be applied is 1.6 V, an output voltage of the amplifier unit  134  when a current of −10 A to +10 A flows is 0.6 to 2.6 V. The AD converter  129  outputs, for example, a voltage of 0 to 3 V as an AD value of 0 to 4095. Thus, the AD value when a current of −10 A to +10 A flows is approximately 819 to 3549. As for the polarity of a current, it is assumed that the current is positive in a case where the current flows from the three-phase inverter  131  to the A-motor  101 . 
     The current value calculation unit  128  performs predetermined arithmetic processing on AD-converted data (hereinafter referred to as an AD value), to calculate a current value. More specifically, an offset value is subtracted from the AD value and the resultant is multiplied by a predetermined coefficient, thus obtaining the current value. The offset value corresponds to the AD value of the offset voltage of 1.6 V and is approximately 2184. The coefficient is approximately 0.00733. In the present exemplary embodiment, the AD value that is loaded when no coil current is passed therethrough, and is stored is used as the offset value. The coefficient is preliminarily stored as a normal coefficient in the non-volatile memory  124 . 
     The microcontroller  121  controls the three-phase inverter  131  through the gate driver  132  thus passing a current through each of the coils  135 ,  136 , and  137  of the A-motor  101 . The microcontroller  121  causes the current sensor  130 , the amplifier unit  134 , and the AD converter  129  to detect the current flowing through the coils  135 ,  136 , and  137 , and calculates the rotor position and speed of the A-motor  101  based on the detected current. These configurations enable the microcontroller  121  to control the rotation of the A-motor  101 . 
     Next, the structure of the A-motor  101  will be described with reference to  FIG.  3   .  FIG.  3    is an explanatory diagram illustrating the structure of the A-motor  101 . 
     The A-motor  101  includes a 6-slot stator  140  and a 4-pole rotor  141 . The stator  140  includes the coils  135 ,  136 , and  137  of U-phase, V-phase, and W-phase, respectively. The rotor  141  is formed of a permanent magnet and includes two pairs of N pole and S pole. The coils  135 ,  136 , and  137  of U-layer, V-layer, and W-layer are connected to the respective outputs  133  of the inverter  131 . 
     &lt;Configuration for Driving and Moving Developing Rollers&gt; 
     Next, a configuration for driving the developing rollers ( 16 Y,  16 M,  16 C,  16 K) to rotate and a mechanism for moving the developing rollers ( 16 Y,  16 M,  16 C,  16 K) relative to the photosensitive members ( 13 Y,  13 M,  13 C,  13 K) will be described with reference to  FIG.  4   .  FIG.  4    illustrates driving and movement of the developing rollers ( 16 Y,  16 M,  16 C,  16 K). 
     The image forming apparatus  100  includes the A-motor (first motor)  101  configured to drive the developing rollers ( 16 Y,  16 M,  16 C,  16 K) and a drive-train for transmitting the driving force of the A-motor  101  to the developing rollers ( 16 Y,  16 M,  16 C,  16 K). 
     More specifically, the image forming apparatus  100  includes, as the drive-train, drive transmission units (YA, YB, MA, MB, CA, CB, KA, and KB) and mechanical clutches ( 105 Y,  105 M,  105 C,  105 K). The drive transmission units YA, MA, CA, and KA can be referred to as upstream drive transmission units. The drive transmission units YB, MB, CB, and KB can be referred to as downstream drive transmission unit. Each of the mechanical clutches ( 105 Y,  105 M,  105 C,  105 K) is located between the corresponding one of the upstream drive transmission units (YA, MA, CA, and KA) and the corresponding one of the downstream drive transmission units (YB, MB, CB, and KB). The upstream drive transmission units (YA, MA, CA, and KA) and the downstream drive transmission units (YB, MB, CB, and KB) are a gear-train including at least one gear. The cartridges ( 12 Y,  12 M,  12 C,  12 K) may include a part of the drive-train. 
     The image forming apparatus  100  further includes developing movement mechanisms ( 106 Y,  106 M,  106 C,  106 K) and a D-motor (second motor)  104 . The D-motor  104  is configured to drive the developing movement mechanisms ( 106 Y,  106 M,  106 C,  106 K) and the mechanical clutches ( 105 Y,  105 M,  105 C,  105 K). In the present exemplary embodiment, the D-motor  104  is configured to control the rotation position (e.g., a stepping motor). 
     The mechanical clutches ( 105 Y,  105 M,  105 C,  105 K) each serve as a drive switching unit configured to switch between a transmission state where the driving force of the A-motor  101  is transmitted to the developing rollers ( 16 Y,  16 M,  16 C,  16 K) and a non-transmission state where the driving force is not transmitted. The mechanical clutches ( 105 Y,  105 M,  105 C,  105 K) are driven by the D-motor  104  to thereby switch the transmission state and the non-transmission state of the mechanical clutches ( 105 Y,  105 M,  105 C,  105 K). 
     The developing movement mechanisms ( 106 Y,  106 M,  106 C,  106 K) each serve as a development switching unit (development contact/separation mechanism) configured to switch the positional relationship between the photosensitive members ( 13 Y,  13 M,  13 C,  13 K) and the developing rollers ( 16 Y,  16 M,  16 C,  16 K) between a contact position and a separated position. A state where the photosensitive members ( 13 Y,  13 M,  13 C,  13 K) and the developing rollers ( 16 Y,  16 M,  16 C,  16 K) are brought into contact with each other is referred to as a contact state. A state where the developing rollers ( 16 Y,  16 M,  16 C,  16 K) are separate from the photosensitive members ( 13 Y,  13 M,  13 C,  13 K) is referred to as a separated state. The developing movement mechanisms ( 106 Y,  106 M,  106 C,  106 K) can be configured to switch the state of the photosensitive members ( 13 Y,  13 M,  13 C,  13 K) and the developing rollers ( 16 Y,  16 M,  16 C,  16 K) between the contact state and the separated state. 
     In the present exemplary embodiment, the developing movement mechanisms ( 106 Y,  106 M,  106 C,  106 K) are configured to press a part of the cartridges ( 12 Y,  12 M,  12 C,  12 K). Thus, the developing rollers ( 16 Y,  16 M,  16 C,  16 K) move relative to the photosensitive members ( 13 Y,  13 M,  13 C,  13 K). A cam that presses a part of the cartridges ( 12 Y,  12 M,  12 C,  12 K) can be used as the developing movement mechanisms ( 106 Y,  106 M,  106 C,  106 K). 
     The developing movement mechanisms ( 106 Y,  106 M,  106 C,  106 K) and the mechanical clutches ( 105 Y,  105 M,  105 C,  105 K) are coupled with switch transmission units (YC, MC, CC, KC), respectively. In the present exemplary embodiment, the switch transmission units (YC, MC, CC, KC) are a gear-train including at least one gear. Thus, in a case where the mechanical clutches ( 105 Y,  105 M,  105 C,  105 K) are operated, the developing movement mechanisms ( 106 Y,  106 M,  106 C,  106 K) are also operated. More specifically, the developing movement mechanisms ( 106 Y,  106 M,  106 C,  106 K) are operated after a lapse of a predetermined period from a time when the mechanical clutches ( 105 Y,  105 M,  105 C,  105 K) are operated. 
     In the case of performing the image forming operation, in response to the D-motor  104  being driven, the mechanical clutches ( 105 Y,  105 M,  105 C,  105 K) are sequentially switched from the non-transmission state to the transmission state and the driving force of the A-motor  101  is transmitted to the developing rollers ( 16 Y,  16 M,  16 C,  16 K). 
     The developing movement mechanisms ( 106 Y,  106 M,  106 C,  106 K) are sequentially operated in conjunction with the operation of the mechanical clutches ( 105 Y,  105 M,  105 C,  105 K), respectively. The developing movement mechanisms ( 106 Y,  106 M,  106 C,  106 K) sequentially switch the state of the developing rollers ( 16 Y,  16 M,  16 C,  16 K) with respect to the photosensitive members ( 13 Y,  13 M,  13 C,  13 K) from the separated state to the contact state. 
     In this case, the developing movement mechanism  106 Y operates in such a manner that the developing roller  16 Y is brought into contact with the photosensitive member  13 Y after the mechanical clutch  105 Y shifts from the non-transmission state to the transmission state. The developing movement mechanisms ( 106 M,  106 C,  106 K) and the mechanical clutches ( 105 M,  105 C,  105 K) also operate similarly. 
     After completion of the image forming operation, the D-motor  104  is driven to sequentially operate the developing movement mechanisms ( 106 Y,  106 M,  106 C,  106 K). The developing movement mechanisms ( 106 Y,  106 M,  106 C,  106 K) sequentially switch the state of the developing rollers ( 16 Y,  16 M,  16 C,  16 K) with respect to the photosensitive members ( 13 Y,  13 M,  13 C,  13 K) from the contact state to the separated state. The mechanical clutches ( 105 Y,  105 M,  105 C,  105 K) are sequentially operated in conjunction with the operation of the developing movement mechanisms ( 106 Y,  106 M,  106 C,  106 K). After that, the state of the mechanical clutches ( 105 Y,  105 M,  105 C,  105 K) is sequentially switched from the transmission state to the non-transmission state, thus blocking the transmission of the driving force of the A-motor  101  to the developing rollers ( 16 Y,  16 M,  16 C,  16 K). As a result, the developing rollers ( 16 Y,  16 M,  16 C,  16 K) are sequentially stopped. 
     &lt;Timing of Driving and Moving Developing Rollers&gt; 
     Each timing of driving the developing rollers ( 16 Y,  16 M,  16 C,  16 K) and moving the developing rollers ( 16 Y,  16 M,  16 C,  16 K) relative to the photosensitive members ( 13 Y,  13 M,  13 C,  13 K) will be described with reference to  FIG.  5   . 
       FIG.  5    is an explanatory diagram illustrating each timing of driving the developing rollers ( 16 Y,  16 M,  16 C,  16 K) and moving the developing rollers ( 16 Y,  16 M,  16 C,  16 K) relative to the photosensitive members ( 13 Y,  13 M,  13 C,  13 K). In  FIG.  5   , the horizontal axis represents the number of steps of the D-motor  104 .  FIG.  5    illustrates each timing of driving and stopping the developing rollers ( 16 Y,  16 M,  16 C,  16 K) and each timing of bringing the developing rollers ( 16 Y,  16 M,  16 C,  16 K) into contact with the photosensitive members ( 13 Y,  13 M,  13 C,  13 K) and separating the developing rollers ( 16 Y,  16 M,  16 C,  16 K) from the photosensitive members ( 13 Y,  13 M,  13 C,  13 K). 
     As described above, driving and stopping of the developing rollers ( 16 Y,  16 M,  16 C,  16 K) are controlled by the mechanical clutches ( 105 Y,  105 M,  105 C,  105 K). Bringing the developing rollers ( 16 Y,  16 M,  16 C,  16 K) into contact with the photosensitive members ( 13 Y,  13 M,  13 C,  13 K) and separating the developing rollers ( 16 Y,  16 M,  16 C,  16 K) from the photosensitive members ( 13 Y,  13 M,  13 C,  13 K) are controlled by the developing movement mechanisms ( 106 Y,  106 M,  106 C,  106 K). 
     A position sensor is connected to the D-motor  104  to detect a home position (HOME) for switching between driving and stopping of the developing rollers ( 16 Y,  16 M,  16 C,  16 K) and switching between contacting and separating of the developing rollers ( 16 Y,  16 M,  16 C,  16 K) with respect to the photosensitive members ( 13 Y,  13 M,  13 C,  13 K). 
     The controller  31  uses the CPU  32  to control the D-motor  104  with a timing when a signal from the position sensor is detected set to the home position. More specifically, the controller  31  operates the D-motor  104  by a predetermined number of steps from the timing when the signal from the position sensor is detected, thus switching between driving and stopping of the developing rollers ( 16 Y,  16 M,  16 C,  16 K) and between contacting and separating of the developing rollers ( 16 Y,  16 M,  16 C,  16 K) with respect to the photosensitive members ( 13 Y,  13 M,  13 C,  13 K). 
     For example, during the image forming operation, as illustrated in  FIG.  5   , the D-motor  104  is operated until the number of steps reaches FULL and the developing rollers ( 16 Y,  16 M,  16 C,  16 K) are driven and brought into contact with the photosensitive members ( 13 Y,  13 M,  13 C,  13 K), respectively. 
     In this case, along with the rotation of the D-motor  104 , driving of the developing roller  16 Y, contacting of the developing roller  16 Y, driving of the developing roller  16 M, contacting of the developing roller  16 M, driving of the developing roller  16 C, contacting of the developing roller  16 C, driving of the developing roller  16 K, and contacting of the developing roller  16 K are performed. Then, the number of steps of the D-motor  104  reaches FULL. The developing movement mechanisms ( 106 Y,  106 M,  106 C,  106 K) and the mechanical clutches ( 105 Y,  105 M,  105 C,  105 K) are coupled with the switch transmission units (YC, MC, CC, KC), respectively. Accordingly, when the D-motor  104  is rotated in one direction, the sequence of operations described above is not changed. 
     After completion of the image forming operation, the D-motor  104  is operated until the number of steps reaches HOME from FULL, and the developing rollers ( 16 Y,  16 M,  16 C,  16 K) are stopped and separated from the photosensitive members ( 13 Y,  13 M,  13 C,  13 K), respectively. 
     In this case, along with the rotation of the D-motor  104 , separating of the developing roller  16 Y, stopping of the developing roller  16 Y, separating of the developing roller  16 M, stopping of the developing roller  16 M, separating of the developing roller  16 C, stopping of the developing roller  16 C, separating of the developing roller  16 K, and stopping of the developing roller  16 K are performed. Then, the number of steps of the D-motor  104  reaches HOME. 
     The image forming operation is performed in conjunction with the above-described operations, thus reducing the time for rotating the developing rollers ( 16 Y,  16 M,  16 C,  16 K) and the time to bringing the developing rollers ( 16 Y,  16 M,  16 C,  16 K) into contact with the photosensitive members ( 13 Y,  13 M,  13 C,  13 K), while reducing First Print Out Time (FPOT). 
     As a result, degradation of toner and parts such as the developing rollers ( 16 Y,  16 M,  16 C,  16 K) can be suppressed. 
     A timing when driving and stopping of the developing rollers ( 16 Y,  16 M,  16 C,  16 K) are actually switched may vary depending on the number of steps of the D-motor  104  due to the tolerance of various parts of the image forming apparatus  100  and the like. Similarly, a timing when the developing rollers ( 16 Y,  16 M,  16 C,  16 K) are actually brought into contact with and separated from the photosensitive members ( 13 Y,  13 M,  13 C,  13 K) may also vary. A region where a desired operation can be performed in some cases and cannot be performed in other cases on the operation of the D-motor  104  depending on the degree of variations in timing as described is hereinafter referred to as an indefinite region. 
     For example, as illustrated in  FIG.  5   , if stopping and driving of the developing roller  16 Y are switched at the earliest, the timing thereof corresponds to the left end of the indefinite region, and if stopping and driving of the developing roller  16 Y are switched at the slowest, the timing thereof corresponds to the right end of the indefinite region. Similarly, if separating and contacting of the developing roller  16  are switched at the earliest, the timing thereof corresponds to the left end of the indefinite region, and if separating and contacting of the developing roller  16  are switched at the slowest, the timing thereof corresponds to the right end of the indefinite region. Here, in order to prevent the timing when stopping and driving of the developing roller  16 Y are switched and the timing when separating and contacting of the developing roller  16 Y are switched from being replaced with each other, the developing movement mechanism  106 Y and the mechanical clutch  105 Y are coupled with the switch transmission unit YC. For example, the developing roller  16 Y is brought into contact with the photosensitive member  13 Y after the developing roller  16 Y is driven, and the developing roller  16 Y is then stopped after being separated from the photosensitive member  13 Y. The image forming apparatus  100  is configured to prevent the developing roller  16 M from being driven earlier than the developing roller  16 Y. This relationship also holds true for the other developing rollers  16 M,  16 C, and  16 K. 
     &lt;Cartridges&gt; 
     The cartridges ( 12 Y,  12 M,  12 C,  12 K) according to the present exemplary embodiment will be described in more detail below. 
     In the present exemplary embodiment, stations for forming images of the respective colors include the cartridges ( 12 Y,  12 M,  12 C,  12 K) and members that operate on the cartridges ( 12 Y,  12 M,  12 C,  12 K). These stations have the same configuration, except for the colors of toner stored in the cartridges ( 12 Y,  12 M,  12 C,  12 K). Accordingly, if there is no need to distinguish the stations from each other, symbols (Y, M, C, K) denoting the respective colors of stored toner are omitted. 
       FIG.  10    is a schematic view of the cartridge  12  according to the present exemplary embodiment. The cartridge  12  includes a drum unit  12 CU including the photosensitive member  13  and the charging roller  15 , and a developing unit  12 DU including the developing roller  16 . In the present exemplary embodiment, the developing unit  12 DU is movable relative to the drum unit  12 CU. In response to the developing unit  12 DU being moved relative to the drum unit  12 CU, the developing roller  16  is moved to the contact position at which the developing roller  16  is brought into contact with the photosensitive member  13  and the separated position at which the developing roller  16  is separate from the photosensitive member  13 . In the present exemplary embodiment, the developing unit  12 DU is pressed by the developing movement mechanism  106 , thus moving the developing unit  12 DU relative to the drum unit  12 CU. 
     The developing unit  12 DU includes a developing frame  23  serving as a storage portion. The developing frame  23  includes a toner chamber  23   b  that stores toner T, a developing chamber  23   a  that is provided with the developing roller  16 , and a partition wall  23   c  that partitions the toner chamber  23   b  from the developing chamber  23   a . The partition wall  23   c  has an opening  23   d  through which the toner chamber  23   b  communicates with the developing chamber  23   a . The toner T stored in the toner chamber  23   b  is supplied to the developing roller  16  through the opening  23   d.    
     The developing unit  12 DU includes a seal member  24   a  that covers the opening  23   d , and an unsealing member  24   b  that moves the seal member  24   a . The seal member  24   a  is attached to the partition wall  23   c  of the developing frame  23  so as to cover the opening  23   d  in a state where the cartridge  12  is not used yet (state where the cartridge  12  is new). Thus, the toner T is prevented from moving from the toner chamber  23   b  to the developing chamber  23   a . In the present exemplary embodiment, the unsealing member  24   b  is rotatably supported by the developing frame  23  and is stored in the toner chamber  23   b . When the unsealing member  24   b  is rotated, the seal member  24   a  is wound around the unsealing member  24   b . As a result, the seal member  24   a  retracts from a position at which the opening  23   d  is covered, so that the opening  23   d  is exposed. 
     A position at which the opening  23   d  is covered with the seal member  24   a  can be referred to as a sealed position, and a position at which the opening  23   c  is exposed can be referred to as an unsealed position. In other words, the seal member  24   a  is moved from the sealed position to the unsealed position by the unsealing member  24   b  driven by the A-motor  101 . 
     In the present exemplary embodiment, when the new cartridge  12  is attached to the inside of the image forming apparatus  100 , the controller  31  starts a seal removal sequence to move the seal member  24   a  to the sealed position from the unsealed position. More specifically, the controller  31  is configured to cause the CPU  32  to control the A-motor  101  and the D-motor  104 , and drives the A-motor  101  and the D-motor  104  to apply the driving force of the A-motor  101  to the developing unit  12 DU. The driving force of the A-motor  101  applied to the developing unit  12 DU drives the developing roller  16  and the unsealing member  24   b , thus moving the seal member  24   a  from the sealed position to the unsealed position. 
     When the seal member  24   a  is located at the unsealed position, the toner T stored in the toner chamber  23   b  is supplied to the developing roller  16  through the opening  23   d.    
     The controller  31  determines whether the cartridge  12  is a new cartridge based on information stored in, for example, a memory  12 MU of the cartridge  12 . 
     In the present exemplary embodiment, when the cartridge  12  is replaced with a new one, the drum unit  12 CU and the developing unit  12 DU are replaced at the same time. In another embodiment, the developing unit  12 DU and the drum unit  12 CU may be separately detachably attached to the apparatus body  100 A. In such a case, in a case where the developing unit  12 DU is detached from the apparatus body  100 A and is replaced with a new one, the seal removal sequence is executed. The developing unit  12 DU may include a memory corresponding to the memory  12 MU. 
     &lt;Contact Between Developing Roller and Photosensitive Member&gt; 
     When the developing roller  16  is brought into contact with the photosensitive member  13 , it is desirable that the developing roller  16  is fully coated with toner. For example, external additive for toner is uniformly supplied to the photosensitive member cleaner  14  in a rotational axis direction of the photosensitive member  13 , enabling the photosensitive member cleaner  14  to stably clean the surface of the photosensitive member  13 . In such a case, if the developing roller  16  is not fully coated with toner, the external additive cannot be uniformly supplied to the photosensitive member cleaner  14 . This phenomenon is more likely to occur when the cartridge  12  is a new cartridge, or when the developing unit  12 DU is a new developing unit. 
     Accordingly, it is desirable to bring the developing roller  16  into contact with the photosensitive member  13  after the developing roller  16  is rotated for a certain period of time. During a period in which the seal removal sequence is executed, the toner T stored in the toner chamber  23   b  cannot be sufficiently supplied to the developing roller  16 , which may lead to a state where the developing roller  16  cannot be fully coated with toner. Therefore, it is desirable to perform the seal removal sequence in a state where the developing roller  16  is separate from the photosensitive member  13 . 
     Here, the D-motor  104  is stoppable by any number of steps. If the D-motor  104  is stopped after the developing roller  16  is rotated and before the developing roller  16  is brought into contact with the photosensitive member  13 , the developing roller  16  can be rotated in a state where the developing roller  16  is separate from the photosensitive member  13 . 
     Here, a period from a time when the image forming operation is started to a time when image formation on the first sheet  21  is completed is referred to as a first printing period. To shorten the first printing period and prevent the wear of the developing roller  16 , it is desirable to shorten the period from the time when the developing roller  16  starts rotation to the time when the developing roller  16  is brought into contact with the photosensitive member  13 . 
     However, if the period from the time when the developing roller  16  starts rotation to the time when the developing roller  16  is brought into contact with the photosensitive member  13  is short as in the image forming apparatus  100  according to the present exemplary embodiment, it is difficult to preliminarily determine the timing of stopping the D-motor  104 . On the other hand, if the period from the time when the developing roller  16  starts rotation to the time when the developing roller  16  is brought into contact with the photosensitive member  13  is long, a first printing period increases and the number of rotations of the developing roller  16  also increases. 
     As illustrated in  FIG.  5   , in a case where the D-motor  104  is stopped by the number of steps represented by Y, M, C, and K, the D-motor  104  is stopped before the developing rollers ( 16 Y,  16 M,  16 C,  16 K) are brought into contact with the photosensitive members ( 13 Y,  13 M,  13 C,  13 K), respectively. However, the number of steps represented by Y, M, C, and K each overlap the respective indefinite region associated with switching between stopping and driving of the developing rollers ( 16 Y,  16 M,  16 C,  16 K). Accordingly, in the image forming apparatus  100  in which driving of the developing rollers ( 16 Y,  16 M,  16 C,  16 K) is started late, the developing rollers ( 16 Y,  16 M,  16 C,  16 K) are in the stopped state. 
     Similarly, as illustrated in  FIG.  5   , in a case where the D-motor  104  is stopped by the number of steps represented by Y′, M′, C′, and K′, the D-motor  104  is stopped after driving of the developing rollers ( 16 Y,  16 M,  16 C,  16 K) is started. However, the number of steps represented by Y′, M′, C′, and K′ overlap the indefinite region associated with switching between separating and contacting of the developing rollers ( 16 Y,  16 M,  16 C,  16 K). Thus, in the image forming apparatus  100  in which the developing rollers ( 16 Y,  16 M,  16 C,  16 K) are brought into contact early, the developing rollers ( 16 Y,  16 M,  16 C,  16 K) are in contact with photosensitive members ( 13 Y,  13 M,  13 C,  13 K), respectively. 
     As described above, in the method of stopping the D-motor  104  by the predetermined number of steps, it is difficult to reliably achieve the rotation of the developing roller  16  in a state where the developing roller  16  is separate from the photosensitive member  13 . 
     &lt;Detection of Driving of Developing Roller&gt; 
     A method for rotating the developing roller  16  in a state where the developing roller  16  is separate from the photosensitive member  13  will be described with reference to  FIG.  6   . 
     As described above, for the image forming apparatus  100  according to the present exemplary embodiment includes the indefinite region associated with switching between stopping and driving of the developing roller  16  and the indefinite region associated with switching between separating and contacting of the developing roller  16 . If it is detected that the developing roller  16  is actually driven, the D-motor  104  is stoppable before the developing roller  16  is brought into contact with the photosensitive member  13 . 
     In the image forming apparatus  100  according to present exemplary embodiment, the current detection unit detects a change in the current flowing through the A-motor  101 , thus making it possible to detect that driving of the developing roller  16  is actually started. The controller  31  of the image forming apparatus  100  stops the D-motor  104  before the developing roller  16  is brought into contact with the photosensitive member  13  based on the detection of a change in the current flowing through the A-motor  101  performed by the current detection unit. Since the A-motor  101  is in the driven state in this case, the developing roller  16  is rotated in a state where the developing roller  16  is separate from the photosensitive member  13 . 
       FIG.  6    is an explanatory diagram illustrating an operation of driving the developing roller  16 Y and bringing the developing roller  16 Y into contact with the photosensitive member  13 Y. The operation of each of the developing rollers  16 M,  16 C, and  16 K is similar to the operation of the developing roller  16 Y, and thus descriptions thereof are omitted. In  FIG.  6   , the horizontal axis represents time. In  FIG.  6   , the vertical axis represents the drive state of the developing roller  16 Y, the contact or separated state of the developing roller  16 Y, the transition of the number of rotations of the A-motor  101 , torque transition of the A-motor  101 , and current value transition of the A-motor  101 . 
     Initially, the A-motor  101  and the D-motor  104  are activated and the rotation of the respective motors are started. When the number of steps of the D-motor  104  reaches the number of steps corresponding to a timing A in  FIG.  6   , the indefinite region associated with driving of the developing roller  16 Y starts. 
     A timing when the mechanical clutch  105 Y is switched from the non-transmission state to the transmission state is referred to as a timing B. When the mechanical clutch  105  is brought into the transmission state, the torque of the A-motor  101  increases. The speed of the A-motor  101  is controlled by a predetermined number of rotations. Thus, the current value of the A-motor  101  increases as the torque of the A-motor  101  increases. An increase in the current value of the A-motor  101  until the timing A and an increase in the current value at the timing B are detected by the current detection unit. 
     The CPU  32  of the controller  31  causes the current detection unit to detect the magnitude of the current flowing through the A-motor  101 , thus detecting a timing when the driving of the developing roller  16 Y is started. 
     As described above, the developing roller  16 Y is brought into contact with the photosensitive member  13 Y after the developing roller  16 Y is driven. Accordingly, the D-motor  104  is stopped at a timing C before the developing roller  16 Y is brought into contact with the photosensitive member  13 Y after a predetermined period from a timing when driving of the developing roller  16 Y is started. In response to the D-motor  104  being stopped, the developing movement mechanism  106 Y is also stopped and the operation in which the developing roller  16 Y approaches the photosensitive member  13 Y is also stopped. This enables the state where the developing roller  16 Y is driven and is separate from the photosensitive member  13  to be maintained. 
     In other words, in a case where the mechanical clutch  105  transitions from the non-transmission state to the transmission state, and the current detection unit has detected a change in the magnitude of the current flowing through the A-motor  101 , the controller  31  performs an operation to stop the D-motor  104  before the developing roller  16 Y is brought into contact with the photosensitive member  13 Y. At this time, the A-motor  101  is continuously driven and the developing movement mechanism  106  is stopped, while the developing roller  16 Y is continuously rotated. In the present exemplary embodiment, the operation in which the controller  31  stops the D-motor  104  based on the magnitude of the current that flows to the A-motor  101  and is detected by the current detection unit as described above is referred to as a stop operation (stop control, stop sequence). The controller  31  continuously performs the stop operation for a predetermined period, and then drives the D-motor  104  again to drive the developing movement mechanism  106  so that the developing roller  16 Y is brought into contact with the photosensitive member  13 Y. Thus, the developing roller  16 Y is brought into contact with the photosensitive member  13 Y in a state where the developing roller  16 Y is coated with toner. 
     The controller  31  can also execute the stop operation on the developing rollers  16 M,  16 C, and  16 K in a manner similar to the stop operation on the developing roller  16 Y. Thus, the developing rollers  16 M,  16 C, and  16 K can be driven in a state where the developing rollers  16 M,  16 C, and  16 K are separate from the photosensitive members  13 Y,  13 M, and  13 K, respectively. 
     &lt;Seal Removal Sequence&gt; 
     When the cartridge  12  according to the present exemplary embodiment is new, the opening  23   d  is covered with the seal member  24   a  so that toner is prevented from being supplied to the developing roller  16 . When the cartridge  12  is new, the controller  31  performs the seal removal sequence in a state where the stop operation is performed. 
     The seal removal sequence according to the first exemplary embodiment will be described with reference to  FIG.  7   .  FIG.  7    is a flowchart illustrating the seal removal sequence according to the present exemplary embodiment. 
     In response to the seal removal sequence being started, in step S 101 , the CPU  32  sets a counter N=1 as an initial setting and activates the A-motor  101 . In step S 102 , the CPU  32  determines whether the activation of the A-motor  101  is completed. If the activation of the A-motor  101  is completed (YES in step S 102 ), the processing proceeds to step S 103 . 
     Here, the counter N is associated with the respective stations Y, M, C, and K. When the counter N indicates “1”, the seal removal sequence for the cartridge  12 Y is performed. When the counter N indicates “2”, the seal removal sequence for the cartridge  12 M is performed. When the counter N indicates “3”, the seal removal sequence for the cartridge  12 C is performed. When the counter N indicates “4”, the seal removal sequence for the cartridge  12 K is performed. 
     In step S 103 , the CPU  32  starts rotation of the D-motor  104 , sets the number of steps S of the D-motor  104  to “0” (S=0), and then starts counting of the number of steps S. In step S 104 , the current detection unit starts detection of the current flowing through the A-motor  101 . 
     The current value calculated by the current calculation unit  128  is transmitted to the controller  31 . 
     In step S 105 , the CPU  32  determines whether the number of steps S of the D-motor  104  is greater than or equal to the number of steps SNd. The number of steps SNd corresponds to a starting point of the indefinite region associated with driving of the developing roller  16  in the cartridge  12  on which the seal removal sequence is performed (see  FIG.  5   ). 
     In step S 106 , the CPU  32  calculates a current average value Iq_N_REF. The current average value Iq_N_REF is an average of values of current flowing through the A-motor  101  in an interval from S=0 to SNd. 
     In step S 107 , the CPU  32  calculates a moving average Iq_N_AVE of the current values flowing through the A-motor  101  for last 10 microseconds (ms). Further, the CPU  32  determines whether the value obtained by subtracting Iq_N_REF from the moving average Iq_N_AVE is greater than a predetermined value (predetermined current value). When the driving force of the A-motor  101  is transmitted to the developing roller  16 , the current flowing through the A-motor  101  increases. As a result, when the driving force of the A-motor  101  is transmitted to the developing roller  16 , the value obtained by subtracting Iq_N_REF from the moving average Iq_N_AVE is greater than the predetermined value. 
     If the value obtained by subtracting Iq_N_REF from the moving average Iq_N_AVE is greater than the predetermined value (YES in step S 107 ), the processing proceeds to step S 108 . In step S 108 , the CPU  32  determines that the rotation of the developing roller  16  is started. The CPU  32  resets the number of steps S of the D-motor  104  to “0”. 
     Immediately after the value obtained by subtracting Iq_N_REF from the moving average Iq_N_AVE has exceeded the predetermined value, the mechanical clutch  105  may incompletely transition to the transmission state. Thus, the CPU  32  stops the D-motor  104  after a lapse of a predetermined period from a time when the mechanical clutch  105  transitions from the non-transmission state to the transmission state and the magnitude of the current detected by the current detection unit has changed. 
     According to the present exemplary embodiment, in step S 109 , the CPU  32  determines whether the number of steps S of the D-motor  104  is greater than or equal to a predetermined number of steps S_ref. If the number of steps S is greater than or equal to the predetermined number of steps S_ref (YES in step S 109 ), the processing proceeds to step S 110 . 
     In step S 110 , the CPU  32  determines that the developing roller  16  is being rotated and is separate from the photosensitive member  13 , stops the D-motor  104 , and stops the developing movement mechanism  106 . By contrast, the A-motor  101  is continuously driven. Thus, the seal member  24   a  is removed by the unsealing member  24   b . In other words, during the stop operation performed by the CPU  32 , the unsealing member  24   b  moves the seal member  24   a  from the position at which the opening  23   d  is covered to expose the opening  23   d.    
     In step S 111 , the CPU  32  determines whether a predetermined period has elapsed. If the predetermined period has elapsed (YES in step S 111 ), the processing proceeds to step S 112 . In step S 112 , the CPU  32  determines that the seal member  24   a  has been removed. At this time, the CPU  32  may write information indicating that the cartridge  12  is not new (seal member  24   a  has been removed) into the memory  12 MU of the cartridge  12 . 
     In step S 113 , the CPU  32  determines whether the counter N indicates “4”. If the counter N does not indicate “4” (NO in step S 113 ), the processing proceeds to step S 114 . In step S 114 , the CPU  32  adds “1” to the counter N. The processing then returns to step S 103 . In response to the D-motor  104  being driven in step S 103 , the developing movement mechanism  106  is driven. 
     In step S 113 , if the counter N indicates “4” (YES in step S 113 ), the seal removal sequence on all the cartridges ( 12 Y,  12 M,  12 C,  12 K) is complete. After completion of the seal removal sequence, the CPU  32  drives the D-motor  104  to be returned to the home position. 
     The present exemplary embodiment described above illustrates a state where the cartridges ( 12 Y,  12 M,  12 C,  12 K) are new (state where the seal member  24   a  has not been removed from any of the cartridges ( 12 Y,  12 M,  12 C,  12 K)). However, in a state where some of the cartridges ( 12 Y,  12 M,  12 C,  12 K) are new, it is sufficient to execute the seal removal sequence only on the new cartridges. For example, the CPU  32  may start the seal removal sequence in a case where some of the cartridges ( 12 Y,  12 M,  12 C,  12 K) are new, and may determine whether the cartridge  12  corresponding to the counter N is new before the processing returns to step S 103 . In such a case, if the cartridge  12  corresponding to the counter N is not new, the processing proceeds to step S 113 . If the counter N does not indicate “4”, the processing proceeds to step S 114  and the CPU  32  determines again whether the cartridge  12  corresponding to the counter N is new before the processing returns to step S 103 . 
     As described above, the CPU  32  performs the seal removal sequence along with the stop operation to stop the D-motor  104  to allow the developing roller  16  to rotate after the developing roller  16  starts rotation and before the developing roller  16  is brought into contact with the photosensitive member  13 . It is desirable to execute the stop operation and the seal removal sequence when the cartridge  12  is new. By contrast, it is desirable that the CPU  32  does not perform the stop operation or the seal removal sequence when the cartridge  12  is not new, for example, during a normal image forming operation. However, the CPU  32  may perform the stop operation, as needed, when the cartridge  12  is not new. 
     As described above, the magnitude of the current flowing through the A-motor  101  is detected, thus enabling the D-motor  104  to be stopped so that the developing roller  16  is rotated after the developing roller  16  starts rotation and before the developing roller  16  is brought into contact with the photosensitive member  13 . This enables the developing roller  16  to be brought into contact with the photosensitive member  13  in a state where the developing roller  16  is fully coated with toner, while the first printing period is shortened and the wear of the developing roller  16  is prevented. 
     A second exemplary embodiment will now be described. While the first exemplary embodiment described above illustrates a case where the D-motor  104  is a stepping motor, the second exemplary embodiment illustrates a case where the D-motor  104  is a motor other than a stepping motor, that is, the D-motor  104  is a motor for which the number of steps is not manageable. 
     In the second exemplary embodiment, differences from the first exemplary embodiment are mainly described. The components and operations of the second exemplary embodiment that are identical to those of the first exemplary embodiment are denoted by the same reference numerals, and the descriptions thereof are basically omitted. 
     In the second exemplary embodiment, the stop operation for the D-motor  104  is performed using the position sensor of the D-motor  104 . The operation of the developing roller  16 Y will be described below. The operation of each of the developing rollers  16 M,  16 C, and  16 K is also similar to the operation of the developing roller  16 Y, and thus the description thereof is omitted. 
       FIG.  8    is an explanatory diagram illustrating an operation of driving the developing roller  16 Y and bringing the developing roller  16 Y into contact with the photosensitive member  13 Y according to the present exemplary embodiment. In  FIG.  8   , the horizontal axis represents time. In  FIG.  8   , the vertical axis represents the drive state of the developing roller  16 Y, the contact or separated state of the developing roller  16 Y, the transition of the number of rotations of the A-motor  101 , torque transition of the A-motor  101 , current value transition of the A-motor  101 , position sensor output, and the transition of the number of rotations of the D-motor  104 . 
     Initially, the A-motor  101  is activated and the rotation of the D-motor  104  is started. The D-motor  104  is stopped at a position at which the output from the position sensor is at the high level. When the rotation of the D-motor  104  is started, the output from the position sensor is switched to the low level. When it is detected that the output from the position sensor is switched to the low level, the home position is detected. The D-motor  104  is rotated for a predetermined period after the home position is detected, the timing A is reached. The timing A matches the starting point of the indefinite region associated with driving of the developing roller  16 Y. 
     When the mechanical clutch  105 Y transitions from the non-transmission state to the transmission state, the current flowing through the A-motor  101  increases. The CPU  32  issues a stop instruction to the D-motor  104  based on an increase in the current flowing through the A-motor  101 . Thus, the D-motor  104  is stopped at the timing C and the developing roller  16 Y is driven in a state where the developing roller  16 Y is separate from the photosensitive member  13 Y. 
     &lt;Seal Removal Sequence&gt; 
     The seal removal sequence according to the second exemplary embodiment will be described with reference to  FIG.  9   .  FIG.  9    is a flowchart illustrating the seal removal sequence according to the present exemplary embodiment. 
     The seal removal sequence is started and the operations in steps S 101  and S 102  are performed, and then the processing proceeds to step S 201 . In step S 201 , the rotation of the D-motor  104  is started. 
     In step S 202 , the CPU  32  determines whether the low level of the position sensor output is detected. If the low level of the position sensor output is detected (YES in step S 202 ), the processing proceeds to step S 203 . In step S 203 , the CPU  32  resets a timer t of the D-motor  104  and starts counting of the timer t. 
     In step S 104 , the current detection unit starts acquisition of the value of current flowing through the A-motor  101 . In step S 204 , the CPU  32  determines whether the timer t has reached a timing tNd. The timing tNd corresponds to the starting point of the indefinite region associated with driving of the developing roller  16  in the cartridge  12  on which the seal removal sequence is performed (see  FIGS.  5  and  8   ). 
     When the timer t of the D-motor  104  has reached the timing tNd (YES in step S 204 ), the processing proceeds to step S 205 . In step S 205 , the CPU  32  calculates Iq_N_REF. The current average value Iq_N_REF is an average of values of current flowing through the A-motor  101  in an interval from t=0 to tNd. 
     As in the first exemplary embodiment, in step S 107 , the CPU  32  calculates the moving average Iq_N_AVE of the current values flowing through the A-motor  101  for last 10 ms. Further, the CPU  32  determines whether the value obtained by subtracting Iq_N_REF from the moving average Iq_N_AVE is greater than a predetermined value (predetermined current value). 
     If the value obtained by subtracting Iq_N_REF from the moving average Iq_N_AVE is greater than the predetermined value (YES in step S 107 ), the processing proceeds to step S 206 . In step S 206 , the CPU  32  determines that the rotation of the developing roller  16  is started and resets the timer t. 
     Immediately after the value obtained by subtracting Iq_N_REF from the moving average Iq_N_AVE exceeds the predetermined value, the mechanical clutches  105  ( 105 Y,  105 M,  105 C,  105 K) may incompletely transition to the transmission state. Accordingly, the CPU  32  stops the D-motor  104  after a lapse of a predetermined period from a time when the mechanical clutch  105  transitions from the non-transmission state to the transmission state and the magnitude of the current detected by the current detection unit has changed. According to the present exemplary embodiment, in step S 207 , the CPU  32  determines whether the value of the timer t of the D-motor  104  is greater than or equal to a predetermined timing t_ref. If the value of the timer t is greater than or equal to the predetermined timing t_ref (YES in step S 207 ), the processing proceeds to step S 110 . 
     The operations of steps S 111 , S 112 , and S 113  are similar to those in the first exemplary embodiment. In step S 113 , the CPU  32  determines whether the counter N indicates “4”. If the counter N does not indicate “4”, the processing proceeds to step S 208 . In step S 208 , the CPU  32  adds “1” to the counter N and starts rotation of the D-motor  104 . After the timer t is reset, the processing returns to step S 104 . 
     In step S 113 , if the counter N indicates “4” (YES in step S 113 ), the seal removal sequence is complete for all the cartridges ( 12 Y,  12 M,  12 C,  12 K). After completion of the seal removal sequence, the CPU  32  returns the D-motor  104  to the home position. 
     The present exemplary embodiment described above also illustrates a state where the cartridges ( 12 Y,  12 M,  12 C,  12 K) are new (state where the seal member  24   a  has not been removed from each of the cartridges ( 12 Y,  12 M,  12 C,  12 K)). However, in a state where some of the cartridges ( 12 Y,  12 M,  12 C,  12 K) are new, the seal removal sequence may be executed only on the new cartridges. 
     As described above, even in a case where the D-motor  104  is a motor that cannot manage the number of steps, the D-motor  104  can be stopped and the developing roller  16  can be rotated after the rotation of the developing roller  16  is started and before the developing roller  16  is brought into contact with the photosensitive member  13 . This enables the developing roller  16  to be brought into contact with the photosensitive member  13  in a state where the developing roller  16  is fully coated with toner, while the first printing period is shortened and the wear of the developing roller  16  is prevented. 
     (Modified Examples) 
     In the present exemplary embodiment, the A-motor  101  is a brushless motor, but instead may be a brush motor. 
     The present exemplary embodiment described above illustrates an example where the CPU  32  determines whether the rotation of the developing roller  16  is started based on whether the value obtained by subtracting Iq_N_REF from the moving average Iq_N_AVE exceeds the predetermined value. However, the present disclosure is not limited to this example. For example, the CPU  32  may determine whether the rotation of the developing roller  16  is started based on whether the value of current flowing through the A-motor  101  exceeds a predetermined threshold. 
     According to an aspect of the present invention, it is possible to provide an image forming apparatus configured to bring a developing roller into contact with a photosensitive member after the developing roller is fully rotated in a configuration in which the developing roller is movable between a position at which the developing roller is brought into contact with the photosensitive member and a position at which the developing roller is separate from the photosensitive member. 
     Embodiments of the present disclosure can also be realized by a computer of a system or apparatus that reads out and executes computer executable instructions (e.g., one or more programs) recorded on a storage medium (which may also be referred to more fully as a ‘non-transitory computer-readable storage medium’) to perform the functions of one or more of the above-described Embodiments and/or that includes one or more circuits (e.g., application specific integrated circuit (ASIC)) for performing the functions of one or more of the above-described Embodiments, and by a method performed by the computer of the system or apparatus by, for example, reading out and executing the computer executable instructions from the storage medium to perform the functions of one or more of the above-described Embodiments and/or controlling the one or more circuits to perform the functions of one or more of the above-described Embodiments. The computer may include one or more processors (e.g., central processing unit (CPU), micro processing unit (MPU)) and may include a network of separate computers or separate processors to read out and execute the computer executable instructions. The computer executable instructions may be provided to the computer, for example, from a network or the storage medium. The storage medium may include, for example, one or more of a hard disk, a random-access memory (RAM), a read-only memory (ROM), a storage of distributed computing systems, an optical disk (such as a compact disc (CD), digital versatile disc (DVD), or Blu-ray Disc™ (BD)), a flash memory device, a memory card, and the like. 
     While the present disclosure has been described with reference to exemplary embodiments, it is to be understood that the disclosure is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. 
     This application claims the benefit of Japanese Patent Application No. 2021-182334, filed Nov. 9, 2021, which is hereby incorporated by reference herein in its entirety.