Image forming apparatus and method for controlling developing bias voltage

1. An image forming apparatus, comprising:

a charging element to apply a charging voltage to an image-bearing member to charge the image-bearing member;

an optical writing device to form a latent image on a charged surface of the image-bearing member charged by the charging element;

a developer-bearing member to carry toner having a same polarity as that of the charging voltage to the image-bearing member and which applies the toner to the latent image on the image-bearing member to form a toner image when a developing bias voltage is applied thereto; and

a control device to control application of the charging voltage by the charging element and application of the developing bias voltage to the developer-bearing member to increase an absolute value of the charging

voltage to the image-bearing member and an absolute value of the developing bias voltage to the developer-bearing member to a predetermined value in a plurality of steps, respectively;

wherein the control device controls the developing bias voltage applied to the developer-bearing member,

wherein the following relation holds in each of the plurality of steps:

20 V≦(| V D |−|V i |)≦49 V,

wherein V D represents a developing bias voltage applied to the developer-bearing member and V I represents a charged potential of the image-bearing member,

wherein |V D |>750 V and |V I |>650 V.

2. The image forming apparatus of claim 1 , wherein a development line width is greater than or equal to 200 μm.

3. The image forming apparatus of claim 1 , wherein the latent image has an exposure portion and a non-exposure portion.

4. The image forming apparatus of claim 1 , wherein the developer-bearing member rotates at a speed of movement that is higher than or equal to a speed of movement of the image-bearing member.

5. The image forming apparatus of claim 1 , wherein |V D | is greater than 750 V and less than or equal to 1000 V.

6. The image forming apparatus of claim 1 , further comprising a gap situated where the developer-bearing member and the image-bearing member are closest to each other.

7. The image forming apparatus of claim 6 , wherein the gap has length of from about 100 μm to about 500 μm.

8. A method for forming an image, comprising:

rotating a developer-bearing member;

rotating an image-bearing member;

charging a surface of the image-bearing member to a charged potential of the image-bearing member, to form a charged surface of the image-bearing member;

applying a developing bias voltage to the developer-bearing member;

forming a latent image on the charged surface of the image-bearing member;

supplying toner to the latent image on the image-bearing member to form a toner image; and

controlling the application of the developing bias voltage to the developer-bearing member;

setting an absolute value of the charged potential of the image-bearing member and an absolute value of the developing bias voltage to the developer-bearing member to a predetermined value, respectively;

wherein the absolute value of the developing bias voltage applied to the developer-bearing member is greater than the absolute value of the charged potential of the image-bearing member; and

a difference between the absolute value of the developing bias voltage applied to the developer-bearing member and the absolute value of the charged potential of the image-bearing member is between 20 V and 49 V,

wherein the absolute value of the developing bias voltage applied to the developer-bearing member is greater than 750 V and the absolute value of the charged potential of the image-bearing member is greater than 650 V.

9. The method for forming an image according to claim 8 , wherein a development line width is greater than or equal to 200 μm.

10. The method for forming an image according to claim 8 , wherein the latent image has an exposure portion and a non-exposure portion.