Driving apparatus, image forming apparatus, driving method and image forming method

1. A driving apparatus comprising: a plurality of image bearing bodies each of which is rotatable and capable of bearing a latent image and a developer image; a belt provided so as to face the image bearing bodies, the belt being rotatable; a plurality of image-bearing-body-driving units for rotating the image bearing bodies; a belt driving unit for rotating the belt; and a control unit for controlling the image-bearing-body-driving units and the belt driving unit, wherein the control unit causes the image-bearing-body-driving units and the belt driving unit to start rotating the image bearing bodies and the belt so that the image bearing bodies and the belt rotate at a first speed, wherein when the control unit detects that the image bearing bodies and the belt rotate at the first speed, the control unit causes the image-bearing-body-driving units and the belt driving unit to accelerate rotation speeds of the image bearing bodies and the belt to a second speed faster than the first speed; and

wherein the control unit sets an intermediate speed faster than the first speed and slower than the second speed, while the control unit causes the image-bearing-body-driving units and the belt driving unit to accelerate rotation speeds of the image bearing bodies and the belt to the second speed; wherein the intermediate speed includes a first intermediate speed for at least one of the image-bearing-body-driving units and a second intermediate speed for the belt which is different from the first intermediate speed, and wherein the control unit sets the first intermediate speed and the second intermediate speed at different times.

2. The driving apparatus according to claim 1 , wherein the control unit groups the image-bearing-body-driving units and the belt driving unit into a plurality of groups, and causes the respective groups to start at different timings,

wherein when the number of the image bearing bodies of the group to be accelerated to the second speed is less than or equal to a predetermined number, the control unit does not set the intermediate speed.

3. The driving apparatus according to claim 1 , wherein the image-bearing-body driving units and the belt driving units comprise motors;

wherein the driving apparatus further comprises a switching unit that switches current limit values applied to the motors,

wherein the control unit causes the switching unit to switch the current limit values, when the image-bearing-body-driving units and the belt driving unit to accelerate the rotation speeds of the image bearing bodies and the belt to the first speed, the intermediate speed or the second speed.

4. The driving apparatus according to claim 1 , wherein the control unit groups the image-bearing-body-driving units and the belt driving unit into a plurality of groups including a first group and a second group, and

wherein when the control unit detects that the first group reaches the first speed, the control unit causes the first group to start accelerating to a first intermediate speed faster than the first speed, and then when the control unit detects that the second group reaches the first speed, the control unit causes the second group to start accelerating to a second intermediate speed faster than the first intermediate speed.

5. The driving apparatus according to claim 4 , wherein after the control unit causes the second group to start accelerating to the second intermediate speed, the control unit causes the first group to start accelerating to a third intermediate speed faster than the second intermediate speed.

6. The driving apparatus according to claim 4 , wherein the belt carries the developer image transferred from the image bearing bodies, or carries a recording medium to which the developer image is transferred from the image bearing bodies.

7. An image forming apparatus comprising:

the driving apparatus according to claim 2 ;

developing units configured to form developer images on the image bearing bodies;

transfer units configured to transfer the developer images from the image bearing bodies to a recording medium directly or via the belt; and

a fixing unit that fixes the developer image to the recording medium.

8. The driving apparatus according to claim 4 , wherein the control unit groups the image-bearing-body-driving units and the belt driving unit into a plurality of groups, and causes the respective groups to start at different timings.

9. A driving method using a driving apparatus:

the driving apparatus comprising:

a plurality of image bearing bodies each of which is rotatable and capable of bearing a latent image and a developer image;

a belt provided so as to face the image bearing bodies, the belt being rotatable;

a plurality of image-bearing-body-driving units for rotating the image bearing bodies;

a belt driving unit for rotating the belt; and

a control unit for controlling the image-bearing-body-driving units and the belt driving unit,

wherein the image-bearing-body-driving units and the belt driving unit are grouped into a plurality of groups including a first group and a second group,

the driving method comprising:

starting at least one of the image-bearing-body driving units and the belt driving unit so that the image bearing bodies and the belt rotate at a first speed;

detecting that the first group reaches the first speed;

causing the first group to start accelerating to a first intermediate speed faster than the first speed;

detecting that the second group reaches the first speed; and

causing the second group to start accelerating to a second intermediate speed faster than the first intermediate speed.

10. An image forming method using an image forming apparatus:

the image forming apparatus comprising:

a plurality of image bearing bodies each of which is rotatable and capable of bearing a latent image and a developer image;

a belt provided so as to face the image bearing bodies, the belt being rotatable, the belt carrying the developer image transferred from the image bearing bodies, or carrying a recording medium to which the developer image is transferred from the image bearing bodies;

a plurality of image-bearing-body-driving units for rotating the image bearing bodies;

a belt driving unit for rotating the belt;

a control unit for controlling the image-bearing-body-driving units and the belt driving unit;

developing units configured to form developer images on the image bearing bodies;

transfer units configured to transfer the developer images from the image bearing bodies to a recording medium directly or via the belt; and

a fixing unit that fixes the developer image to the recording medium,

wherein the image-bearing-body-driving units and the belt driving unit are grouped into a plurality of groups including a first group and a second group,

the image forming method comprising:

starting at least one of the image-bearing-body driving units and the belt driving unit so that the image bearing bodies and the belt rotate at a first speed;

detecting whether the image bearing bodies and the belt rotate at the first speed;

detecting that the first group reaches the first speed;

causing the first group to start accelerating to a first intermediate speed faster than the first speed;

detecting that the second group reaches the first speed;

causing the second group to start accelerating to a second intermediate speed faster than the first intermediate speed;

forming developer images on the image bearing bodies;

transferring the developer images from the image bearing bodies to the recording medium; and

fixing the developer images to the recording medium.