JPS61151566A - Image forming device - Google Patents

Abstract

PURPOSE:To move rotatively a rotating body to a development position accurately in a high speed and stop the rotating body in the development position quickly without shock by making image formation possible when the development position signal of the development position is detected within a preliminarily set prescribed time. CONSTITUTION:A rotating body 1a is controlled and driven by a driver 30, and contents of a table in a sequence controller 32 are compared with inputs to an input interface 36 from sensors XY, XM, XC, and XBK provided in accordance with individual developing stations to discriminate whether a developing device of the moved rotating body 1a is placed correctly in the target development position or not. If it is not placed in the target development position, a timer in the sequence controller 32 is set, and it is confirmed whether a position detecting plate X1 corresponds to development position sensors XY-XBK or not, and the rotating body 4a is moved to the prescribed target position again in a low speed if no plate X1 is placed on any position sensor. Unless this movement is performed within the prescribed time, signal ARAM is outputted to a motor controlling CPU31d, and the abnormality processing is executed. If a prescribed developing device is placed in the target development position, the copy mode of its color is executed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to an image forming apparatus equipped with a multicolor developing device.

[Prior art]

For example, in a configuration in which a plurality of developing devices using toners of different colors are arranged on a single latent image carrier such as a photosensitive drum, a plurality of developing devices are arranged sequentially around the circumference of the latent image carrier. A multicolor developing device in which a plurality of developing devices are supported by a rotating body, and by rotationally driving the rotating body, only the developing devices corresponding to the desired color toner are opposed to the latent image carrier. has been proposed by the applicant (Japanese Unexamined Patent Publication No.
-93437).

In the latter case, since one developing device always faces the latent image carrier, it is possible to - make the circumference of the latent image carrier as small as possible;

However, during actual development, due to encoder accuracy, timer cycle limits, and load fluctuations, the speed of the rotating body may reach 0 before the target position where it should stop, or the speed of the rotating body may reach 0 before the target position where it should stop. It is still in the middle of the deceleration process and often does not reach O.

In this way, it is possible to rotate the rotor at high speed from the negative development position to the target position, which is the next development position, and to quickly and accurately stop the rotating body, which still has speed at the position where it should be stopped, without impacting that position. Although it is desired, it has been difficult to realize it in the past.

〔the purpose〕

This invention was made by focusing on the problems described below.
It is an object of the present invention to provide an image forming apparatus in which a predetermined developing device is accurately rotated at high speed to a predetermined developing position, and is quickly stopped at the developing position without impact.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 to 9.

FIG. 1 is a cross-sectional view showing an example of an electrophotographic copying machine as an image forming apparatus equipped with a single-rotation multicolor developing device.

In the figure, a photosensitive drum l, which is a latent image carrier, rotates in the direction of the arrow. There are two chargers around it. Exposure optical system 3. Developing device 4, transfer system 5. A cleaning device 6 is also provided. The optical system 3 includes a document scanning section 3a and a color separation filter part 3b, and the developing device 4 includes a yellow developer 4Y using yellow toner, a magenta developer 4M using magenta toner, and a cyan developer using cyan toner. 4C and black developer 4B using black toner
Each developing device has a
As disclosed in Japanese Patent No. 5-20579, the toner is prevented from scattering by the action of the magnetic field by the magnet roller R, and as shown in the figure, the toner is detachably held on a rotating body 4a and rotated around a central axis 4b, thereby developing the toner. Replace the developing device depending on the position.

Note that S is a toner stirring screw.

On the other hand, the transfer section 5 includes a drum 5b having a gripper 5a,
It has a transfer discharger 5C inside thereof.

When forming color images, like conventional copying machines,
Color separation is performed by the blue, green, and red color filters and ND filter of the color separation optical system, and the 3 colors of yellow, Q, magenta, cyan, and black are added, and 4
Development is performed using a color developing device.

Now, when the photosensitive drum 1 is irradiated with, for example, blue light (exposure), a latent image is formed on the photosensitive drum l, and the formed latent image is transferred to the yellow developing device 4Y, which is rotated to the developing position at an appropriate timing. This visible image is transferred onto a transfer paper held by a transfer drum 5b by a transfer charger 5C. This transfer paper is supplied from the cassette 7. After cleaning the photosensitive drum 1, the process from exposure to development described above is performed once for green light by the magenta developer 4M and once for red light by the cyan developer 4C. Transcription takes place. Furthermore, exposure is performed using the ND filter, and for this exposure, the black developing unit 4B
After development with K, transfer is performed. The transfer material that has completed the transfer process is separated by the separating means 8 and reaches the tray 10 via the fixing device 9.

In FIG. 2, reference numeral 11 designates a ring-shaped rear plate that is provided at the rear end of the rotating body 4a and has a gear lla around its periphery. 12 is a rotary drive motor, and a gear 13 fixed to one end of the motor shaft is different from the gear lla and gears 14, 14.
．． For example, an encoder 1 is connected to the other end of the motor shaft as means for detecting rotational speed and position.
7 is provided. Z is a positioning means for forcibly stopping the rotating body 4a at a predetermined stop position, and a stopper plate 18 having a groove 18a and an edge tab is attached to the rear plate 11.

Although FIG. 2 shows two partially broken stopper plates, in this embodiment, five stopper plates 18HP, 18Y, 18M, 18c, and 188K are fixed at predetermined positions as described later. .

On the other hand, Zl is a rotation holding mechanism that engages with this stopper plate 18 (see Fig. 3 for details), and 19 is an L-shaped stopper arm, which is inserted into a long hole 19a formed in a part of the elbow.
One end of the pin 20 is fixed to the main body of the device, and the other end is inserted through the pin 20. A roller 22 is rotatably attached to one end of the stopper arm 19 by a stopper pin 21, and a tension coil spring 23 is stretched between the stopper pin 21 and the bottle 20. At the other end of the stopper arm 19, a lock solenoid 25 serving as a holding/releasing means is pivoted by a pin 27 via a connecting member 26, and a spring 28 causes the roller 22 to press against the stopper plate 1.
It is biased to come into contact with the periphery of 8HP, 18Y, 18M, and 18C118BK. 29 is the rotating body 4a
A photointerrupter is used as a detection means for detecting the engagement and release of the stopper arm 19 with the stopper arm 19, and is arranged so that the light is interrupted in accordance with the movement of the end portion 24 of the stopper arm 19.

X is a reference position and development position detection means for the rotating body 4a. A position detection plate XI attached to the terminal of the center shaft 4b, a home position sensor (HP sensor) xO arranged concentrically around the center shaft 4b, a yellow development position sensor XY,
It is equipped with a magenta development position sensor XM, a cyan development position sensor xC, and a black development position sensor XBK. Each sensor outputs a different development position signal when the position detection plate XI is directly above it.

Figure 4 shows the control system. Reference numeral 30 denotes a driver for driving the motor 12, which together with the motor 12 constitutes a driving means for rotationally driving the rotating body 4a. 31
is a control means for controlling the speed of this drive means, and the rotating body 4
Vector detection circuit 31a for detecting the rotation direction of a
A position counter 31b that detects the rotational position of the rotating body 4a
, a speed counter 31C that detects the rotational speed of the rotating body 4a.
A motor control CPU (central processor) that controls the motor according to the position and speed of the rotating body 4a.
sing unit) 31 d, home position, 7
Sensor XO, timer 31f and D/A converter 31
It is composed of g.

The vector detection circuit 31a inputs two-phase pulses from the encoder 17 and outputs data regarding the forward and reverse rotation directions of the rotating body 4a. Direction-related data and pulses output from the encoder 17 are inputted via the vector detection circuit 31a, and the home position (HP) of the rotating body 4a (that is, as shown in FIG. The rotational movement position data with reference to the position below) is output to the motor control CPU 31d. Home position sensor xO is 1. W? It is disposed at HP, which is the 11th position, and inputs a clear signal to the position counter 31b when the rotating body 4a reaches the HP. Speed counter 31c
counts the pulses output from the rotary encoder 17 for a certain period of time set by the timer 31f, and sends this count value, that is, speed data, to the motor control CPU.
Output to 31d. The timer 31f generates a signal every time a set time elapses, and this signal is sent to the motor control CPU 31d.
output to the interrupt terminal. In response to the input of this signal, the motor control CPU 31d executes an interrupt program, takes in the count values of the position counter 31b and speed counter 31c, and controls the motor 12 based on these values. Also, the signal from the timer 31f is sent to the speed counter 3.
1c, and clears the speed counter 31c.

Further, the timer 31f is set and reset by a signal from the motor control CPU 31d.

Table 1 (Y...Yellow, M...Magenta, C...Cyan, BK...Black) Furthermore, CPU3 for motor control
ROM (read only memory) in Ld
) 31dl stores as a table the relationship between the mode and the amount of rotation shown in Table 1 and the relationship between the amount of rotational movement and rotational speed shown in the graph of FIG.

Next, rotation control of the rotating body 4a of the developing device 4 in this embodiment will be explained. As mentioned above, a speed control table corresponding to the target position SD-rotational speed characteristics as shown in FIG. R accessed according to the value of 31b
The speed data in the speed table of the OM 31dl is compared with the speed data detected by the speed counter 31c, and the driving force of the motor 12 is controlled to correct the deviation.

Multiple speed control tables are prepared in the ROM depending on the amount of rotation, and depending on the combination of developing machines used.

The necessary tables are pulled out from the ROM.

Table 2 shows mode settings for setting the rotation mode of a single rotating body.

Table 2 A sequence controller 32 inputs a signal to the motor control CPU 31d via the I10 port 33 and the load drive circuit 34 to control it. 3
Reference numeral 5 represents a key/display operation section provided with keys for operating and displaying the image forming apparatus, and 36 represents an input interface.

In this embodiment, the home position (HP) of the rotary developing device is set when the arrangement is as shown in FIG. 6 (when the yellow developing device 4Y is 45 degrees downstream from the developing position), and after the copy sequence is Return to HP and wait for the next cycle.

As shown in Table 1, 4 types of single color mode, 6 types of 2 color mode, 1 type of 3 color full color mode, and 1 type of 4 color full color mode are prepared. A rotation sequence is selected.

For example, when specifying the 3-color full color mode, first rotate the HP by 45 degrees to develop yellow, then rotate it another 90" to develop magenta, and then rotate the HP by 90" to develop magenta.
@ Rotate and rotate 1351 times to HP after cyan development 0 Table 1
Table 1 shows the relationship between color mode and rotation amount.
As shown in Table 2, the rotation amount between each development is 45@
, 90°, 135°, 180°, 215°, 27
The rotation modes listed in Table 2 corresponding to the seven types of rotation amounts, 0° and 315°, are sent as a 3-bit mode setting signal from the I10 boat 33 to the load drive circuit 34 to the motor control CPO 31d.
, Ml, and M2 are input as 3-bit signals.

By this rotation mode command, a speed data table corresponding to each rotation amount in the CPU 31d is retrieved as a lookup table.

In this way, the speed control table can be selected according to the amount of rotation, and the rotating body can be controlled to be driven to a target position in accordance with the target motion characteristics.

However, as shown in Fig. 5, it is difficult to smoothly decelerate the speed to completely zero when reaching the target position SD, as shown in Fig. 7. As shown in the figure, the speed becomes 0 at a point earlier than the target and destination SD point, and the speed becomes S again.
'In most cases, the rotating body 1a is accelerating toward point D (graph a) or is still in the middle of the deceleration process at the target SD point (graph b).In such cases, the rotating body 1a stops. It has velocity at the desired position.

In this embodiment, in order to absorb the rotational energy of the rotating body at the position where it should be stopped, to stop it at the position where it should stop, and to hold the rotating body at that position, the system shown in Figs. 2 and 3 is used. A positioning member consisting of a stopper arm 19 and a stopper plate 18 is provided.

That is, a stopper plate 18 set at the position where the one-rotator 4a should be stopped is fixed to the rear plate 11 of the one-rotator 4a, and the rollers 22 of the stopper arm 19 engage with the grooves 18a of the stopper plate 18. This ensures the stopping position.

@8 In the illustrated state, the roller 22 is the stopper plate 18 (HP)
, and the rotating body 4a is in the home position S (
(See Figure 6).

The stopper plate 18 is a stopper plate 18 (Y) for holding the yellow developing device 4Y at the developing position.

18 CM) for magenta, 18 (C) for cyan,
There are black 18 (BK) and 5 types, each of which is screwed to the correct position so that it can be adjusted.

The stopper arm 19 is rotatably supported by a pin 19a fixed to the main body, and a force is applied by a spring 28 in the direction in which the roller 22 enters the groove 18a of the stopper plate. When pulled, the arm rotates around the pin 19a, and the roller 22 comes out of the groove lBa of the stopper plate 18.

Rotate the yellow developing machine 4Y by 45 degrees from the state shown in Figure 8.
In order to stop at the developing position, stopper plate 1B (Y
) Release the magnetic force of the solenoid 25 before it reaches the pin 21 position. This timing is calculated from the position counter 31b in FIG. 4. When the position counter 31b becomes greater than a certain value S
) as the input interface 3 from the CPU (31d).
6 is input.

Stopper arm 1 released from the suction force of the solenoid
9 abuts the roller 22 rotatably supported by the stopper pin against the stopper plate 18 by the force of the spring 28.

FIG. 9 shows this state, in which the roller 22 rotates along the arcuate edge of the stopper plate 1B rotating in the N direction and engages with the coming 18a.

The moment the roller 22 enters the engagement groove, the stopper arm 19 blocks the optical path of a photointerrupter 29 attached to the main body, and detects the locked state of the positioning member.

This detection signal is input to the I10 port 23 on the main body side in Fig. 4, and this signal causes the T
OFFM enters the CPU 31d and cuts off the driving torque or braking torque of the rotating body.

FIG. 10 shows the moment when the roller 22 engages with the groove 18a of the stopper plate 18. Note that at this time, although the drive torque of the drive motor 12 is lost, there is full rotation due to inertia. Due to this inertial force, the roller 22 is pulled by the rotating body 4a while being engaged with the groove 18a. The stopper arm 19 moves Δθ along the elongated hole 19a at its center of rotation against the force of the spring 23 connecting the pins 21 and 20, as shown in FIG.

This amount of movement Δθ is determined by the rotational energy of the rotating body
3, the rotating body 4a is returned to its normal position by the restoring force of the spring, and the positioning is completed (
Figure 1O).

When moving to the next rotation, first, the solenoid 25 is energized, the J stopper arm 19 is rotated around the pin 20, and the engagement between the groove 18a of the stopper plate 18 and the roller 22 is released. As a result of this operation, the stopper arm 19 that was shielding the photointerrupter 29 moves out of the optical path of the 7-oto-interrupter, and when a stopper release signal is input to the sequence controller 32, the sequence controller 32 sends the rotating body to the motor control CPU 31d. It is sent as a start signal to command the rotation start of 4a.

When this signal is input, the one-rotating body 4a starts rotating, the PEND signal turns off the renoid 25, and when the photointerrupter 29 detects that the roller 22 has engaged with the groove 18a, the target position counter value is set. The difference between the actual position counter value and the actual position counter value is forced to 0, and the drive motor 1
Turn off the torque of step 2.

The operation will be explained based on the chart 70 in FIG.

When the power to the main body of the device is turned on (STEP-1), the device is reset (STEP-2), and entry reception using keys from the display operation section 35 becomes possible (STEP-3). ), and the print key is O
When it is K (STEP-4), pre-copy rotation is performed and the first rotating body 4a is moved to the HP (STEP-5)
, At the same time, whether or not the rotating body 4a of the multicolor developing device is at the HP is determined based on the presence or absence of a signal from the home position sensor xo (STEP-8). At this time, if the rotating body 4a is not at the HP, the sequence control is The timer in the a-ra 32 is activated, and the sequence controller 32 starts rotating the rotating body 4a.
A command signal for moving the motor to the HP is sent to the motor control CPU 31 via the I10 boat 33 and the load drive circuit 34.
d (5TEP-7), if the rotating body 4a is not at HP by the time the timer setting time elapses, the signal ARAM is output from the CPU 31d (
STEP-8) Based on this signal, the sequence controller 32 regards it as an abnormal state and performs abnormal processing such as stopping the device (STEP-11).

On the other hand, the first rotating body 4a reaches the HP before the timer setting time elapses.
or when it is already at HP,
The signals (Me, Ml, Ml,) shown in Table 1 are transmitted from the sequence controller 32 to the I10 port 33. The signal is input to the motor control CPU 31d via the load drive circuit 34. In the motor control CPU 31d, from the ROM 31dl to the RAM 31
Data regarding the mode selected by the operator and the table corresponding to the graph shown in FIG. 5 is stored in d2.

At the same time, the lock solenoid 25 of 1 positioning means Z is turned ON.
be done. Then, the engagement between the stopper plate 18HP and the roller 22 is disengaged, and at the same time, the end of the stopper arm 19 is removed from the optical path of the photo-interrupter 29, and a release signal for the stopper arm 19 is transmitted from the photo-interrupter 29 to the rotating body 4a.
The above-mentioned positioning means 2 is inputted to the sequence controller 32 as a start signal (STEP-10).
In order to confirm that the holding of the rotating body 4a by the photointerrupter 29 has been released, it is determined whether there is a start signal from the photointerrupter 29 (stgp-t).

Once the lock solenoid ON signal is stopped, it is turned ON again (STEP-12), and at the same time, it is determined whether the timer setting time has elapsed (STEP-13). If there is no lock solenoid ON signal within the time, 5TEP-9 is activated. Execute abnormality processing using the same timer determination sequence (5T
EP-10, if there is a start signal, the single rotating body 4a is controlled and driven by the driver 30 as shown in FIG.

(STEP-15) Whether or not the developing device of the moved rotating body 4a is correctly located at the target developing position is determined by the contents of the table of the sequence controller 32 that has been set and the sensor provided corresponding to each developing stage code. XY, XM, XC,
This is determined based on the correspondence with the input from the XBK to the input interface 36 (STEP-18).

If it is not on any position sensor, set the timer in the sequence controller 32, check the correspondence between the position detection plate x1 and each development position sensor XY-XBK, and if it is not on any position sensor, move it back to the specified target position. Rotating body 4a at low speed
(STEP-17). This is because for some reason, the roller 22 of the stopper arm 19 may disengage after once engaging with the stopper plate 18 at the target development position. In this case, the rotating body 4a is further rotated to reach the target development position.

If this movement is not performed within a predetermined time (STEP-
18) Output the signal ARAM to the motor control CPU 31d and process the abnormality (STEP-1!9)
, On the other hand, if the predetermined developing device is at the target development position, the copy mode with that color is executed (5TEP-20), and the above-mentioned 5TEP-10 to 5TEP-2 are executed until the copy mode ends.
By repeating step 1, the development position is switched and development is performed, and when the instructed copy mode is completed, the after rotation mode is performed, and the rotating body 4a is moved to the home position HP (STEP-22). 5T
Return to EP-4.

FIG. 13 is a flowchart of rotating body drive control.

As described above, if the rotating body 4a is at the home position after the copy key is turned on, the sequence controller 32 executes the rotating body moving routine. First, in order to disengage the roller 22 of the stopper arm 19 from the groove of the stopper plate 18, the solenoid 25 is turned on by outputting a drive signal through the load drive circuit 34 (5TEP-30), and rotates through the load drive circuit 34. Mode (Mo, Ml, M2
) is output to the motor control CPU 31d (STEP-
31) When the turn-on signal of the photointerrupter 29 is inputted via the input interface 36 due to the roller 22 coming off the stopper plate 18 (STEP-3)
2) Outputs the 5TART signal to the motor control CPU 31d (STEP-33), whereby the motor control CPU 31d controls the movement of the rotating body 1a, and the above-mentioned briend signal (PEND) is output from the motor control CPU 31d. When input to the sequence controller 32 via the input interface 36 (STEP-34
), turn off solenoid 25 (STEP-35)
, and a photo interrupter 2 indicating that the roller 22 of the stopper arm 19 has engaged with the groove of the stopper plate 18.
When the off signal of 9 is input through the input interface 36 (STEP-38), the I10 port 33,
A TOFF signal is output to the motor control CPU 31d via the load drive circuit 34 (STEP-37), thereby cutting off the driving torque of the single rotating body.

Next, regarding the control of the motor control CPU 31d, the fourteenth
This will be explained with reference to the figures.

When the power to the device is turned on, the reset signal (RESE) is activated.
T) is supplied to the motor control CPU 31d, initializes the settings of the CPU internal RAM and I10 port, and first determines the input of the home position sensor Xo of the rotating body 4a. (STEP-40), and if it is not at the home position (STEP-41), predetermined data is sent to the D/A converter 31g to operate the motor. Here, data is sent from the motor control CPU 31d via an 8-bit bus, and the motor speed is 0 at OOH and full speed at FFH. Also, set a predetermined timer (STEP-42), determine whether the timer value is reached or not (STEP-43), and if the timer is within one hour, return to (STEP-41) and set the timer to one hour. If the above is the case, the signal ARAM is output to the sequence controller 32 (STEP-■).

When the home position detection signal is input, the motor control CPU 31d resets the position counter 31b to OH (STEP-44).
Since the speed corresponds to the value given in step 3) and the stopping impact is large, the motor 12 is operated again (STE
P-45) At the next home position stop SUB, control the speed using the position counter 31b up to the home position, control the speed so that it becomes sufficiently slow near the stop position, and stop the motor (STEP-4)
8) Next, input and process the signal of the input port of the motor control CPU 31d (STEP-47), then 5TA
5TEP-48) to determine whether there is an RT signal.
If there is not, return to (STEP-47), input the mode from the input port, and change the speed table to the ROM 31dl inside the motor control CPU 31d according to the input value.
and stores it in the RAM 31 d2. By interrupting the timer 31f9, table values in the RAM 31d2 are read one after another and set as speed control target values. (STE
P-49) Next, load the above target value, operate the motor, and enable timer 31f to oscillate (5TE
P-50), thereby the motor control CPU 31 d
A signal is input to the interrupt terminal. As a result, the deviation between the previous speed control target value and the actual speed counter 31c is calculated based on the current speed control target value and D/A is performed.
Output to converter 31g.

The system is controlled to be an acceleration system until the value of the position counter 31b reaches half of the target position, and thereafter is controlled to be a deceleration system, and is controlled so that the control speed reaches the minimum speed when the value of the position counter 31b reaches the target position counter value (STEP-51).

Next, when the TOF, , F signals are input from the sequence controller 32 or the difference between the target position counter value and the actual position counter value becomes O, the motor 12 is set to 0FFL.
, Turn off the timer 31f and return to (STEP-47) (STEP-52). Furthermore, the motor control CPU 31d
The difference between the target position counter value and the actual position counter value is 0.
If the TOFF signal is input before the difference becomes zero, the "difference" is forcibly set to zero.

〔effect〕

As described above, according to the present invention, when rotating a rotating body equipped with a plurality of developing machines, the speed is controlled and the rotating body is positioned at a predetermined stop position, and the positioning state is detected to operate the rotating body. Because of the control, it can be stopped at the developing position quickly, accurately, and without impact.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the configuration of a color image forming apparatus to which the present invention is applied, Fig. 2 is a perspective view showing the drive system and positioning member of the rotary developing device, and Fig. 3 is an enlarged view showing the positioning member of the developing machine. A perspective view, FIG. 4 is a block diagram showing a control unit of the image forming apparatus, FIG. 5 is a graph showing the relationship between rotational movement amount and rotational speed, and FIG. 6 is a diagram showing the rotating body located at the home position. FIG. 7 is an explanatory diagram showing the speed of the rotating body near the target SD to be stopped, FIG. 8 is a diagram showing the state in which the roller 22 is engaged with the groove 18a of the stopper plate 18 at the home position, and FIG. 22 is in contact with the arcuate edge of the stopper plate 18; FIG. 1θ is a diagram showing the roller 22 in engagement with the groove 18a of the stopper plate 18;
FIG. 11 is an explanatory diagram showing that the roller 22 moves by Δθ after engaging with the groove 18a of the stopper plate 18, FIG. 12 is a control flowchart of the sequence controller, and FIG.
The figure is a flowchart of the rotating body movement routine, and FIG. 14 is the control flowchart 4a of the motor control CPU 31d...Rotating body 4Y...Yellow developer 4M...
・・・・・・Magenta developer 4C・・・・・・・・・
Cyan developer 4BK... Black developer 12... Motor (drive means) 29-...
・・・・・・Photo interrupter (stop detection means) 3
0... Driver (driving means) 31.
...... Control means X... Development position detection means (reference position detection means) Z... Positioning means Fig. 5 Fig. 7 θ figure

Claims (1)

[Claims] In an image forming apparatus that performs multicolor development using a plurality of developing devices attached to a rotating body, the developing device includes means for rotationally driving the rotating body, and a developing device that outputs a developing position signal corresponding to a developing position of each developing device. What is claimed is: 1. An image forming apparatus comprising: a position detecting means, and capable of forming an image when a developing position signal at a developing position is detected within a preset predetermined time.