Exposure control and other component control for electrostatic copying machine

In an electrostatic copying machine including a photoconductive member, a charging unit for applying a uniform electrostatic charge to the photoconductive member and an exposure means for radiating a light image of an original document onto the photoconductive member to form an electrostatic image thereon through localized photoconduction, the improvement comprising:

• first control means for controlling the exposure unit to radiate a reference light image onto the photoconductive member to form a reference electrostatic image thereon;
• sensor means for sensing an electrostatic potential of the reference electrostatic image;
• and
• second control means for controlling the exposure unit in such a manner as to regulate an intensity of the light image of the original document in accordance with the sensed electro-potential of the reference electrostatic image;
• said exposure means comprising a scan member movable in a scan and a return direction for radiating the light image of the original document onto the photoconductive member, the first control means controlling said exposure means to move the scan member by a predetermined distance in the return direction for radiating the reference light image onto the photoconductive member, the reference light image being constituted by a light image of a portion of the original document corresponding to the predetermined distance the scan member is moved in the return direction.