In the electrostatic copying process, many conditions such as changes in temperature, length of time the machine has remained idle, print mode selection (amount of toner on a page), etc., affect image quality, so the machine must frequently sample the machine's development ability (development gamma) at prescribed intervals, and then make adjustments based on these samplings in order to maintain optimum conditions for production of the best possible images.
This sampling of conditions around the drum, and then making adjustments in order to attain and maintain even, consistent image density is called process control. Process control can be divided into two separate phases:
- Potential control. Performs adjustments for development that affect basic image quality such as gradation levels, line width.
- Toner supply control. Standardizes the image density by controlling toner supply.