The final stage of the Konica Minolta bizhub electrophotographic printing process is often overlooked, yet it is one of the most important. After the toner image has been transferred to the paper, the OPC (Organic Photoconductor) drum is not immediately ready to create another image.
Even after a successful transfer, a small amount of toner remains on the drum surface, and microscopic electrical charges from the previous image are still present. If these residues are not removed, they will interfere with the next print, causing defects such as ghost images, gray backgrounds, repeating marks, and poor image quality.
To prepare the drum for the next print cycle, the machine performs two essential operations:
- Residual toner removal (Cleaning)
- Surface charge reset (Drum Discharge)
Together, these processes restore the drum to a clean, electrically neutral condition so that a new image can be created.
For field technicians, understanding the cleaning and discharge process is essential because many recurring print defects originate from failures in these final stages of the imaging cycle.
Why Cleaning and Discharging Are Necessary
After the toner image has been transferred:
- Nearly all toner moves to the Intermediate Transfer Belt or directly to the paper.
- A small amount of toner remains on the OPC drum.
- The drum still contains localized electrical charges from the previous image.
If the drum is reused without cleaning and discharging:
- Previous images may reappear.
- Background toner may accumulate.
- Toner may transfer to incorrect areas.
- Print quality gradually deteriorates.
The drum must therefore be restored to its original condition before the next image is created.
Components Involved
The drum cleaning and discharge system typically includes:
- OPC Drum
- Drum Cleaning Blade
- Waste Toner Auger
- Waste Toner Transport System
- Waste Toner Bottle
- Primary Charge Roller (PCR)
- High Voltage Power Supply (HVPS)
- Main Controller Board
Older Konica Minolta models may also include an Erase Lamp, while most modern bizhub machines perform drum discharge electronically through the Primary Charge Roller.
Step 1: Residual Toner Remains on the Drum
After the Primary Transfer stage:
- Most toner has transferred to the Intermediate Transfer Belt.
- A very small percentage of toner remains attached to the drum surface.
This residual toner cannot be reused directly because it may contain contaminants such as:
- Paper dust
- Worn developer particles
- Foreign debris
- Mixed toner particles
The remaining toner must be removed before the next print cycle.
Step 2: The Drum Cleaning Blade Removes Residual Toner
As the OPC drum continues to rotate, it passes beneath the Drum Cleaning Blade.
The cleaning blade is made of a flexible, wear-resistant polyurethane material that maintains constant contact with the drum surface.
Its purpose is to:
- Scrape residual toner from the drum.
- Prevent toner carryover.
- Produce a clean drum surface.
The blade removes nearly all remaining toner without damaging the photoconductive coating.
Step 3: Waste Toner Collection
The removed toner falls into the waste toner chamber.
From there:
- Waste toner augers transport the toner.
- Conveyance screws move it through enclosed channels.
- The toner eventually reaches the waste toner bottle.
This toner is permanently discarded.
It is never returned to the Developing Unit, as its electrical characteristics have changed and contamination would reduce print quality.
Step 4: Drum Surface Inspection
After cleaning:
- The drum surface is physically clean.
- However, invisible electrical charge patterns from the previous image still remain.
These residual charges must be removed before the drum can be uniformly recharged.
Step 5: Surface Charge Reset (Drum Discharge)
Modern Konica Minolta bizhub machines discharge the drum electronically.
The Primary Charge Roller (PCR), working with the High Voltage Power Supply, neutralizes the remaining surface charge.
This process:
- Eliminates residual electrostatic patterns.
- Restores the drum to a neutral electrical state.
- Prepares the drum for the next charging cycle.
Unlike older corona-based systems, this electronic discharge method is more stable, generates less ozone, and requires less maintenance.
Older Models and the Erase Lamp
Some earlier photocopiers used an Erase Lamp positioned near the drum.
The lamp illuminated the drum after cleaning.
Light exposure made the photoconductive coating conductive, allowing the remaining electrical charge to dissipate naturally.
Although effective, the Erase Lamp has largely been replaced in modern bizhub machines by electronic discharge through the Primary Charge Roller.
Step 6: The Drum Is Ready for Charging
After cleaning and discharge:
- No residual toner remains.
- The drum surface is electrically neutral.
- Previous image information has been erased.
The Primary Charge Roller can now apply a new, uniform electrostatic charge.
The next imaging cycle begins immediately.
Why Toner Cannot Be Reused
Residual toner is considered waste because it may contain:
- Paper fibers
- Dust
- Developer particles
- Moisture
- Contaminants from previous prints
Reintroducing this toner into the Developing Unit would:
- Change toner concentration (TCR).
- Affect image density.
- Increase background contamination.
- Accelerate developer wear.
For this reason, Konica Minolta bizhub machines collect waste toner separately.
Automatic Cleaning Control
The cleaning system operates automatically during every print cycle.
The controller synchronizes:
- Drum rotation
- Cleaning blade position
- Waste toner transport
- Drum discharge
- Next charging cycle
No user intervention is required under normal operating conditions.
Relationship to the Electrophotographic Process
Cleaning and discharge complete the electrophotographic printing cycle.
The full sequence is:
- Drum Cleaning
- Drum Discharge (Surface Charge Reset)
- Drum Charging
- Laser Exposure
- Toner Development
- Primary Transfer
- Secondary Transfer
- Fusing
- Residual Toner Removal and Surface Charge Reset for the Next Cycle
Although listed last, this stage prepares the drum for the next image, making the imaging process continuous.
Common Cleaning System Problems
| Symptom | Possible Cause |
|---|---|
| Ghost images | Worn cleaning blade, incomplete drum discharge, or contaminated drum |
| Repeating marks | Damaged cleaning blade or OPC drum surface |
| Gray background | Residual toner left on the drum or incomplete discharge |
| Toner streaks | Cleaning blade damage or toner buildup |
| Waste toner overflow | Full waste toner bottle or blocked waste toner auger |
| Toner contamination inside the machine | Waste toner transport failure or damaged seals |
| Drum scratches | Damaged cleaning blade or foreign object trapped beneath the blade |
| Residual image carryover | Drum not fully discharged before the next cycle |
Diagnostic Tips for Technicians
When investigating cleaning-related image defects:
- Inspect the Drum Cleaning Blade for wear, hardening, or edge damage.
- Examine the OPC drum for scratches, toner buildup, or surface contamination.
- Check the waste toner augers and transport system for blockages.
- Verify that the waste toner bottle is not full.
- Inspect drum electrical contacts and the Primary Charge Roller if ghosting persists.
- Determine whether defects repeat at the drum circumference, indicating drum or cleaning blade issues.
- Run internal test prints to confirm whether the defect originates before or after the transfer stage.
- Replace the Cleaning Blade and OPC drum together when recommended by the service manual to ensure proper sealing and cleaning performance.
Preventive Maintenance
To maintain effective drum cleaning and discharge:
- Replace the Drum Cleaning Blade at the recommended maintenance interval.
- Replace the OPC drum when it reaches its service life.
- Empty or replace the waste toner bottle before it reaches capacity.
- Inspect waste toner augers and transport paths during preventive maintenance.
- Keep drum electrical contacts clean to ensure proper discharge.
- Use only genuine Konica Minolta toner to reduce contamination and extend component life.
- Avoid touching the drum surface with bare hands during servicing.
Why Understanding Drum Cleaning and Discharge Matters
Many recurring image defects are caused not by the developer unit or laser system, but by incomplete cleaning or improper drum discharge. Residual toner and leftover electrostatic charges can create symptoms that closely resemble charging, exposure, or transfer problems. By understanding how the cleaning blade removes waste toner and how the Primary Charge Roller resets the drum’s electrical state, technicians can diagnose ghosting, background contamination, and repeating defects more accurately while avoiding unnecessary replacement of expensive imaging components.
Conclusion
The final stage of the Konica Minolta bizhub imaging process restores the OPC drum to a clean and electrically neutral condition. The Drum Cleaning Blade removes residual toner, the waste toner transport system carries it to the waste toner bottle, and the Primary Charge Roller electronically neutralizes any remaining surface charge before the next print cycle begins. Together, these systems prevent ghost images, background contamination, and image carryover while ensuring that every page starts with a clean, uniformly prepared drum. A thorough understanding of drum cleaning and surface charge reset provides service technicians with the knowledge needed to diagnose recurring image defects, maintain consistent print quality, and maximize the reliability of Konica Minolta bizhub multifunction printers.