Color image forming device which changes developing bias when switching between developer units

An image forming device comprising:

• a plurality of developing devices, each including a developer carrying body driven by a drive means;
• an image carrying body;
• developing device moving means for moving one of said developing devices to a developing position adjacent to the image carrying body which has a latent image thereon;
• a voltage generator for generating a first developing bias having an d.c. component and a d.c component, and for generating a second developing bias;
• and
• developing bias applying means for applying, at different time, the first and second developing biases to the developer carrying body of one of the developing devices at the developing position, the developing bias applying means including a developing bias switching means for switching between the first and second developing biases, the developing bias switching means applying the first developing bias to the developer carrying body when developing the latent image on said image carrying body, and applying the second developing bias when the developer on the developer carrying body comes in contact with the image carrying body and when the developer on the developer carrying body separates from the image carrying body, the second developing bias generating an electric field such that developer on the developer carrying body is more reluctant to move toward the image carrying body as compared with an electric field generated by the first developing bias,
• wherein the voltage generator generates the second developing bias to include only a d.c. component, and
• wherein the voltage generator generates a voltage value of the d.c. component of the second developing bias such that an electric field is generated in which the developer on the developer carrying body is more reluctant to move toward the image carrying body as compared with an electric field generated by a voltage value of the d.c. component of the first developing bias,
• said image forming device further comprising a control means which causes the developing bias applying means, prior to switching from the first developing bias to the second developing bias, to change the voltage value of the d.c. component of the first developing bias to a value which generates an electric field for which the developer on the developer carrying body is more reluctant to move toward the image carrying body as compared with the voltage value of the d.c. component of the first developing bias before the change.

An image forming device comprising:

• a plurality of developing devices, each including a developer carrying body driven by a drive means;
• an image carrying body;
• developing device moving means for moving one of said developing devices to a developing position adjacent to the image carrying body which has a latent image thereon;
• a voltage generator for generating a first developing bias having an a.c. component and a d.c. component, and for generating a second developing bias;
• and
• developing bias applying means for applying, at different time, the first and second developing biases to the developer carrying body of one of the developing devices at the developing position, the developing bias applying means including a developing bias switching means for switching between the first and second developing biases, the developing bias switching means applying the first developing bias to the developer carrying body when developing the latent image on said image carrying body, and applying the second developing bias when the developer on the developer carrying body comes in contact with the image carrying body and when the developer on the developer carrying body separates from the image carrying body, the second developing bias generating an electric field such that developer on the developer carrying body is more reluctant to move toward the image carrying body as compared with an electric field generated by the first developing bias,
• wherein the voltage generator generates a d.c. component of the second developing bias to be different from a d.c. component of the first developing bias such that the developer on the developer carrying body is more reluctant to move toner toward the image carrying body due to the second developing bias as compared with movement caused by the first developing bias.

An image forming device comprising:

• a plurality of developing devices, each including a developer carrying body driven by a drive means;
• an image carrying body;
• developing device moving means for moving one of said developing devices to a developing position adjacent to the image carrying body which has a latent image thereon;
• a voltage generator for generating a first developing bias having an a.c. component and a d.c. component, and for generating a second developing bias;
• and
• developing bias applying means for applying, at different time, the first and second developing biases to the developer carrying body of one of the developing devices at the developing position, the developing bias applying means including a developing bias switching means for switching between the first and second developing biases, the developing bias switching means applying the first developing bias to the developer carrying body when developing the latent image on said image carrying body, and applying the second developing bias when the developer on the developer carrying body comes in contact with the image carrying body and when the developer on the developer carrying body separates from the image carrying body, the second developing bias generating an electric field such that developer on the developer carrying body is more reluctant to move toward the image carrying body as compared with an electric field generated by the first developing bias,
• wherein the voltage generator generates a voltage value of an a.c. component of the second developing bias to be smaller than a voltage value of the a.c. component of the first developing bias.

An image forming device comprising:

• a plurality of developing devices, each including a developer carrying body driven by a drive means;
• an image carrying body;
• developing device moving means for moving one of said developing devices to a developing position adjacent to the image carrying body which has a latent image thereon;
• a voltage generator for generating a first developing bias having an a.c. component and a d.c. component, and for generating a second developing bias;
• and
• developing bias applying means for applying, at different time, the first and second developing biases to the developer carrying body of one of the developing devices at the developing position, the developing bias applying means including a developing bias switching means for switching between the first and second developing biases, the developing bias switching means applying the first developing bias to the developer carrying body when developing the latent image on said image carrying body, and applying the second developing bias when the developer on the developer carrying body comes in contact with the image carrying body and when the developer on the developer carrying body separates from the image carrying body, the second developing bias generating an electric field such that developer on the developer carrying body is more reluctant to move toward the image carrying body as compared with an electric field generated by the first developing bias,
• wherein voltage generator generates the second developing bias to include a d.c. component and an a.c. component, a voltage value of the a.c. component of the second developing bias is set smaller than a voltage value of the a.c. component of the first developing bias.