Ricoh SP 8400DN Field Service Manual page 880

Process Control
Potential Control
Potential Control adjusts Charge/Development bias and LD power to maintain a constant image output.
Charge roller, development roller, OPC drum and laser unit involve with imaging process.
Charge bias (Vc) is a bias for charge roller. Applying a charge bias to the OPC drum increases the potential of
the OPC drum.
Development bias (Vb) is a bias for development roller. When a development bias is applied to developer
(carrier), the OPC drum which is charged the opposite bias from development part attracts toner.
Development potential (Vd – Vb) is the ability to attract the toner to the OPC drum. A larger development
potential increases the amount of toner adhesion.
In image density adjusting, the potential control process creates an ID pattern patch using the "bias for ID
pattern creation" which has a lower density and lower Charge/Development bias than for printing.
With the results of Vsp (the ID sensor output from ID pattern patch) and Vsg (the ID sensor output from bare
surface of the OPC drum), the potential control process adjusts the development bias so that the amount of toner
adhesion becomes a specified target value.
Charge/Development Bias is done with the following operation. The operation time differs depending on the
line speed.
•
ID sensor Vsg Adjustment
The machine adjusts the LED strength of the ID sensor so that the value of Vsg (the charge which is
detected from the bare surface of the OPC drum) is in the range of 4.0V ±0.5V. When Vsg is detected as
not within the target range three times, SC370 (ID sensor error) appears.
•
Developer Stirring (0 to 5 seconds)
The machine agitates the developer and reads the TD sensor (µ sensor) output.
•
Bias Compensation
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