JPS61151565A - Image forming device - Google Patents

Abstract

PURPOSE:To move rotatively a rotating body to a development position accurately in a high speed and stop it quickly in the development position without shock by operating a rotating body holding mechanism to release the rotating body by a holding release means and controlling the rotating body with this release signal as a rotating body driving start signal before the rotating body is driven. CONSTITUTION:In a rotating body holding mechanism 21 engaged with a stopper plate 18, the other end of a pin 20 whose one end is fixed to a device body is inserted to an oblong hole 19a of an L-shaped stopper arm 19. A lock solenoid 25 as the holding release means is stuck axially to one end part of the arm 19 through a connecting member 26 by a pin 27, and a roll 22 is energized by a spring 28 so that it is brought into contact with peripheral parts of stopper plates 18HP, 18Y, 18M, 18C, and 18BK. In case of the start of rotation, the stopper arm 19 is turned around the pin 20 to disengage a groove 18a of the stopper plate 18 and the roll 22 from each other. By this operation, the stopper arm 19 shielding a photointerrupter 29 is removed from the optical path; and when the release signal of the stopper is inputted to a sequence controller 32, the rotation start of a rotating body 4a is instructed to a motor controlling CPU31d from the sequence controller 32.

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 single latent image carrier such as a photosensitive drum is provided with a plurality of developing devices using toners of different colors, one after another on the circumferential surface of the latent image carrier.

In a case where a plurality of developing devices are arranged in a row, the plurality of developing devices are supported by a rotating body, and by rotationally driving this rotating body, only the developing device corresponding to the desired color toner can be used as a latent image carrier. The applicant of the present application has proposed a multi-color developing device in which the two are opposed to each other (Japanese Patent Laid-Open No. 50-93437).

In the latter case, since one developing device always faces the latent image carrier, the circumference of the latent image carrier can be made as small as possible.

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

In this way, the rotating body is rotated at high speed from the - development position to the target position, which is the next development position, and the rotating body, which still has speed at the position where it should be stopped, is moved to that position by W! Although it is desired to stop the motor vehicle quickly and accurately without causing a shock, it has been difficult to achieve this in the past.

〔the purpose〕

This invention was made by focusing on the above-mentioned problems.
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.

:JIj1 is a cross-sectional view showing an example of an electrophotographic copying machine as an image type Jli1i device equipped with a rotationally driven 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. N-destination 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/red color filter and ND filter of the color separation optical system, and the 3 colors of yellow, magenta, and cyan are further added with black.
Development is performed using a color developing device.

For example, when the photosensitive drum 1 is irradiated with blue light (N light), a latent image is formed on the photosensitive drum 1, and the formed latent image is rotated to the developing position in the yellow developing device 4Y. This visible image is transferred onto the transfer paper held by the transfer drum 5b by the transfer charger 5C. This transfer paper is supplied from the cassette 7. After cleaning the photosensitive drum mt, the process from exposure to development described above is performed by the magenta developer 4M for green light and by the cyan developer 4C for red light, and each time the development is completed, Transcription takes place. Furthermore, exposure is performed using the ND filter, and a black developer 48 is used for this exposure.
After development with K, transfer is performed. The transfer material that has completed the transfer process is separated by the separation means 8.

It reaches the tray 10 via the fixing device 9.

In FIG. 2, reference numeral 11 is a rear plate provided at the rear end of the rotating body 4a and having a ring-like shape and having a gear lla on 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 to the gear 14.1.
4.16, and the other end of the motor shaft is provided with, for example, an encoder 17 as means for detecting rotational speed and position. Z is a positioning means for forcibly stopping the rotating body 4a at a predetermined stop position, and the rear plate 11 has a stopper plate 18 having a groove 18a and an edge 18b.
can be installed.

Although FIG. 2 shows two partially broken stopper plates, in this embodiment, five stopper plates 18HP, 18Y, 18M, 18c, and 18BK 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 that 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 pin 20. Stopper arm l9
At the other end, a lock solenoid 25 serving as a holding/releasing means is pivotally attached to a pin 27 via a connecting member 26, and a spring 28 causes the roller 22 to be attached to the stopper plates 18HP, 18Y, 18M, 18c, 188 so as to be brought into contact with the periphery of the holder. A photointerrupter 29 serves as a detection means for detecting the engagement and release of the rotating body 4a and the stopper arm 19, and is arranged so that the light is interrupted in accordance with the movement of the end 24 of the stopper arm 19. has been done.

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 includes 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 is a dryer 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 one rotating body 4a
a vector detection circuit 31a for detecting the rotation direction of the
a position counter 31b that detects the rotational position of the rotating body 4a;
Speed counter 31C1 that detects the rotational speed of the rotating body 4a
A motor control CPU (central process) that controls the motor according to the position and speed of the rotating body 4a.
ing unit) 31d, home position sensor XO, timer 31f and D/A converter 31g
It is composed of

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 input via the vector detection circuit 31a, and the home position (HP) of the rotating body 4a (that is, the yellow developer 4Y is set at 45 degrees from the developing position as shown in FIG. 6). Rotational movement position data based on the lower position) is output to the motor control CPU 31d. The home position sensor xO is disposed at a reference position HP, and inputs a clear signal to the position counter 31b when the rotating body 4a reaches the HP. The speed counter 31c converts the pulses output from the rotary encoder 17 into the timer 31.
The count value, that is, the speed data, is counted for a certain period of time set by
Output to. The timer 31f generates a signal every time a set time elapses, and outputs this signal to an interrupt terminal of the motor control CPU 31d. 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.

The signal from the timer 31f is also applied to the speed counter 31c, clearing the speed counter 31c. Also,
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 1d
) 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.

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 number of rotations, and depending on the combination of developing machines used.

The necessary tables are pulled out from ROM.

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

Table 2 A sequence controller 32 inputs signals to the motor control CPU 31d via the I10 boat 33 and 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 developer @4Y is 45° downstream from the developing position), and 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 three-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.
0” rotation and after cyan development, rotate to HP by 135@Table 1 shows the relationship between one color mode and rotation amount0
As shown in Table 1, the rotation amount between each development is 1,45 as shown in Table 2.
° , 900.135''', 180'', 215@
, 270°, and 315°, and the rotation modes listed in Table 2 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 accelerates toward point D (graph a) or is still in the middle of the deceleration process at the target SD point (graph b). 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 is fixed to the rear plate 11 of the rotating body 4a, and the stopper plate 18 is set at the position where the rotating body 4a is to stop. By engaging 22, the stop position is ensured.

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

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

18 (M) for magenta, 18 (C) for cyan,
There is a black 18 (BK) and 5 types, each of which is screwed in the correct position.

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 18a of the stopper plate 18.

Rotate 45a from the state shown in Figure 8 and develop yellow @4Y.
In order to stop at the developing position, stopper plate 18 (Y
) releases the magnetic force of the solenoid 25 before it reaches the bin 21 position. This timing is calculated from the position counter 31b in FIG. 4, and when the position counter 31b becomes larger than a certain value, the briend signal (PEND
) as the input interface 3 from the CPU (31d).
6 is input.

Stopper arm 1 released from the suction force of the solenoid
9 rotates the roller 22 rotatably supported by the stopper pin by the force of the spring 28. Hit the par board 18.

FIG. 9 shows this state, in which the roller 22 rotates along the arcuate edge of the stopper plate 18 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
An OFF signal is input to the CPU 31d to cut 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 arm 19 moves 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 (
(Fig. 1θ).

When moving to the next rotation, the solenoid 25 is first excited, the 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. Due to this operation, the stopper arm 19 that was shielding the photointerrupter 29 moves out of the optical path of the photointerrupter, and when a stopper release signal is input to the sequence controller 32, the sequence controller 32 sends the motor control CPU 31d to the rotating body. It is sent as a start signal to command the rotation start of 4a.

When this signal is input, the rotating body 4a starts rotating, the solenoid 25 is turned off by the PEND signal, 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 flowchart in FIG.

When the power to the main body of the device is turned on (STEP-1), the device is reset (STEP-2), the amount of input using the keys from the key/display operation section 35 becomes possible (STEP-3), and , When the print key is turned on (STEP-4), pre-copy rotation is performed and the 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, the rotating body 4a is at the HP.
If not, the timer in the sequence controller 32 operates, and the sequence controller 32 sets the rotating body 4a to H.
Input the command signal to move to P to the motor control CPU 31d via the I10 boat 33 and load drive circuit 34 (5TEP-7), press L, and the rotating body 4a is not in HP by the time the timer setting time elapses. At this time, 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-9).

On the other hand, the rotating body 4a reaches the HP before the timer setting time elapses.
or when it is already at HP,
The signals (Mo, Ml, Ml,) shown in Table 2 are transmitted from the sequence controller 32 to the I10 boat 33 and the load drive circuit 34 according to the mode selected by the operator by operating the appropriate keys on the key/display scanning unit 35. The signal is input to the motor control CPU 31d via the motor control CPU 31d. In the motor control CPU 31d, data related to the mode selected by the operator and a table corresponding to the graph shown in FIG. 5 are stored from the ROM 31 dl to the RAM 31 d2.

At the same time, the lock solenoid 25 of the 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 Z is input 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 photo-interrupter 29 has been released, it is determined whether or not there is a start signal from the photointerrupter 29 (STEP-11). If there is no such signal, it is determined.

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, srmp-s is activated. Execute abnormality processing using the same timer determination sequence (5
TEP-14) If there is a start signal, the 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 based on the contents of the set table of the sequence controller 32 and the sensors XY provided corresponding to each developing station.

This is determined based on the correspondence with the inputs to the input interface 36 from XM, XC, and XBK (STEP-113).

If it is not at the target position, set the timer in the sequence controller 32, check the correspondence between the position detection plate Xl and each developing position sensor 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) Outputs the signal ARAM to the motor control CPU 31d and processes the abnormality (STEP-19). On the other hand, if the predetermined developing device is at the target development position, execute the copy mode with that color. 5TEP-20 ), the development position is switched and development is performed by repeating steps 5TEP-10 to 5TEP-21 described above until the copy mode ends, and when the instructed copy mode ends, the after-rotation mode is performed and the rotation is completed once. Move the body 4a to the home position HP (STEP-22), 5TEP-
Return to 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 (JTEP-30), and rotates through the load drive circuit 34. Mode (Mo, Mt,
M2) is output to the motor control CPU 31d (S
TEP-31), when the turn-on signal of the photointerrupter 29 is input via the input interface 36 due to the roller 22 coming off the stopper plate 18 (ST
EP-32), 5TA for motor control CPU31d
The RT signal is output (STEP-33), whereby the motor control CPU 31d controls the movement of the rotating body 1a, and the above-mentioned Briend signal (PEND) is sent from the motor control CPU 31d to the sequence controller via the input interface 36. 32 (ST
EP-34), turns off the solenoid 25 (STE
P-35), and when the off signal of the photointerrupter 29 indicating that the roller 22 of the stopper arm 19 has engaged with the groove of the stopper plate 18 is inputted via the input interface 36 (STEP-38), the I10 port 33. Output the TOFF signal to the motor control CPU 31d via the load drive circuit 34 (STEP-3)
7) As a result, the driving torque of the rotating body is cut off.

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

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 board, etc., and first determines the input of the home position sensor xO of the rotating body 4a. (STEP-40), if it is not at the home position (STEP-41), press D to operate the motor.
Sends predetermined data to the /A converter 31g. 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 (8TEP-43), and if the timer is within one hour, return to (STEP-41) and set the timer value. If it is longer than the time, 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 31 d (STEP-47), then 5T
5TEP-48) to determine whether there is an ART signal.
If there is not, return to (STEP-47), input the mode from the input board, and change the speed table to the ROM 31d inside the motor control CPU 31d according to the input value.
Call out from l.

Stored in RAM31 d2. By interrupting the timer 31f, table values in the RAM 31 d2 are read one after another and used as speed control target values. (STEP-48) 0
Next, load the above target value, operate the motor, and enable the timer 31f to oscillate (5TEP-50).
As a result, a signal is input to the interrupt terminal of the motor control CPU 31d. As a result, a predetermined calculation is performed on the deviation between the previous speed control target value and the actual speed counter 31c with respect to the current speed control target value, and the D/A converter 3
Output to 1g.

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 and 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 0, the motor 12 is set to 0FFL.
Turn off the timer 31f and return to (STEP-47) (
STEP-52), Incidentally, if the TOFF signal is input before the difference between the target position counter value and the actual position counter value becomes 0, the motor control CPU 31d forcibly sets the "difference" to 0. be.

〔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 drawings]

Fig. 1 is a diagram showing the configuration of a color image forming apparatus to which the present invention is applied, Fig. 20 is a perspective view showing the wjA dynamic system and positioning member of the rotary developing device, and Fig. 3 is an enlarged view showing the positioning member of the developing machine. FIG. 4 is a block diagram showing the control unit of the image forming apparatus, FIG. 5 is a graph showing the relationship between rotational movement amount and rotational speed, and FIG. Figure shown. FIG. 7 is an explanatory diagram showing the speed of the rotating body near the target SD to be stopped, and 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.
9 shows a state where the roller 22 is in contact with the arcuate edge of the stopper plate 18, FIG. 10 shows a state where the roller 22 is engaged with the groove 18a of the stopper plate 18, and FIG. The figure shows Δθ after the roller 22 engages with the groove 18a of the stopper plate 18.
FIG. 12 is a control flowchart of the sequence controller, FIG. 13 is a flowchart of a rotating body movement routine, and FIG. 14 is a control flowchart 4a of the motor control CPU 31d.・ Rotating body 4Y... Yellow developer 4M...
・・・・・・Magenta developer 4C・・・・・・・・・
Cyan developer 48K... Black developer 12... Motor (drive means) 22...
・・・・・・・・・・・・・・・・・・・・・ Coro 2
9...Photo interrupter (stop detection means) 30... Driver (driving means) 3
1... Control means X...Development position detection means (reference position detection means) Z...Positioning means

Claims (1)

[Claims] An image forming apparatus that performs multicolor development using a plurality of developing units attached to a rotating body, comprising means for rotationally driving the rotating body, a mechanism for holding the rotating body in a predetermined position, and a means for releasing the holding. , and means for detecting the release of the holding, and prior to driving the rotating body, the holding release means releases the rotating body holding mechanism and controls the release signal to be used as a rotating body drive start signal. An image forming apparatus characterized by: