The registration sensor is one of the most critical components in any Konica Minolta bizhub multifunction printer. It serves as the machine’s “eyes” at the gateway to the imaging section, detecting the precise position of each sheet of paper as it arrives and providing the timing reference that synchronizes paper transport with the image writing process. Without accurate registration sensor operation, every print would suffer from misregistration—images shifted, skewed, or improperly positioned on the page.
This article provides a comprehensive guide to the registration sensor system, covering its physical configuration, operational principles, control logic, timing relationships, and diagnostic procedures.
1. Registration Sensor Overview
1.1 What Is the Registration Sensor?
The registration sensor is an optoelectronic or mechanical actuator-based sensor positioned immediately before the registration roller in the paper path. In most bizhub models, this sensor is designated as PS1 (Primary Registration Sensor). Some models may use different designations—for example, PS38 on certain C-series models, PS44 on others, or PS9 on newer i-series models.
The sensor detects the leading edge of the paper as it approaches the registration roller. This detection event triggers the sequence of operations that correct skew, form the paper loop, and time the arrival of the paper at the transfer section.
1.2 Physical Configuration
The registration sensor typically consists of:
- An actuator (mechanical flag) that is pushed by the leading edge of the advancing paper
- A photo-interrupter (optical sensor) that detects the actuator position
- A mounting bracket that positions the sensor just upstream of the registration roller nip
When paper pushes the actuator, the sensor output changes from “blocked” to “unblocked” (or vice versa, depending on the model’s logic configuration). This state change is read by the MFP board (MFPB) and used for timing control.
2. The Registration Control Sequence
2.1 Paper Arrival and Sensor Activation
The registration control sequence begins when paper is conveyed from any of the available paper sources—trays 1 through 4, the Large Capacity Unit (LU), the bypass tray, or the Automatic Duplex Unit (ADU).
The sequence proceeds as follows:
- Paper reaches the registration sensor actuator — The leading edge of the paper pushes against the actuator.
- Registration sensor output changes — The sensor signal transitions, notifying the MFPB that paper has arrived.
- Registration roller stops — Upon receiving the sensor signal, the MFPB de-energizes the registration clutch (CL1), stopping the registration roller.
- Loop formation begins — With the registration roller stopped while upstream rollers continue to feed paper, a loop forms in the paper.
2.2 Skew Correction Through Loop Formation
The loop formed at the registration roller serves a critical mechanical purpose: skew correction (also known as deskewing).
When paper continues to be fed against the stopped registration roller, the paper bows into a loop. This loop absorbs any angular deviation in the paper’s path, effectively straightening the paper against the nip of the stopped roller. The paper is now aligned square to the paper path, with any skew eliminated before it enters the imaging section.
The roller that creates this loop varies depending on the paper source:
- Trays 1 to 4: Loop roller or vertical transport roller
- LU: Loop roller
- Bypass tray: Feed roller for bypass feed
- ADU: ADU pre-registration roller
2.3 Registration Roller Restart and Image Synchronization
After the loop is formed and skew is corrected, the registration roller must restart at the precise moment that synchronizes paper position with the image write timing.
The control logic works as follows:
- The MFPB calculates the required restart timing based on the sensor detection point and the known distance to the transfer section.
- The registration clutch (CL1) is energized at the calculated moment.
- Driving force from the transport motor (or main motor, depending on the model) is transmitted to the registration roller.
- The paper is conveyed into the transfer section at the exact moment the laser writing unit begins writing the image.
This synchronization is critical: if the paper arrives too early or too late, the image will be misregistered on the page. The registration roller is therefore controlled to synchronize the timing of the image start and paper transport.
3. Timing Relationships and Control Signals
3.1 Print Start Signal and Initial Drive
The registration control sequence is initiated by the print start signal. Upon receiving this signal:
- The feed motor and loop clutch are turned ON
- Driving force is transmitted to the loop roller and upstream conveyance rollers
- Paper begins its journey from the selected paper source toward the registration section
3.2 Leading Edge Detection and Loop Formation Timing
When the registration sensor (PS1) detects the leading edge of the paper and turns ON:
- The loop clutch (CL2) turns OFF a specified period of time after detection
- During this specified period, paper continues to be conveyed against the stopped registration roller
- A loop is formed and skew is corrected
3.3 Registration Clutch Engagement Timing
The print signal (image write start signal) turns ON the registration clutch (CL1) to transmit driving force to the registration roller. At this same time:
- The loop clutch (CL2) also turns ON to drive the loop roller for loop assist
- The loop assist ensures the paper is positively conveyed into the registration nip
3.4 Trailing Edge Detection and Completion
When PS1 detects the trailing edge of the paper and turns OFF:
- CL1 turns OFF a specified period of time after trailing edge detection
- This completes the registration operation for that sheet
- However, CL2 remains ON to begin loop formation for the next sheet
3.5 Sequential Operation for Multiple Sheets
For multiple sheets in a print job, the same sequence repeats:
- CL2 stays ON to form the loop for the next paper
- The same operations are repeated for each subsequent sheet
- When PS1 detects the trailing edge of the last paper and turns OFF
- M9 (feed motor), CL1, and CL2 all turn OFF a specified period of time after that
- This completes the series of registration operations
4. Loop Amount Adjustment
4.1 Why Adjust the Loop Amount?
The amount of loop formed at the registration roller directly affects print quality. Incorrect loop amounts can cause:
- Skewed prints — If the loop is insufficient, skew may not be fully corrected
- Wrinkled paper — If the loop is excessive, paper may buckle or wrinkle
- Paper jams — If the loop is too large or too small, paper may not feed properly into the registration nip
4.2 Service Mode Adjustment
The loop amount can be adjusted in Service Mode. The exact menu path varies by model, but generally follows this pattern:
- bizhub C652 and similar: “Service Mode → Machine Adjustment → Printer Regist Loop Amount”
- bizhub 423 and similar: “Service Mode → Machine → Printer Reg. Loop Adj.”
- bizhub 164 and similar: “SERVICE’S CHOICE → LOOP Ad. (TRAY1) / LOOP Ad. (BYPASS)”
Changing the adjustment value changes the OFF timing of the upstream conveyance motor or clutch. This effectively controls how much paper is fed after the registration roller stops, determining the loop size.
4.3 When to Adjust
Adjustment of the registration loop amount is typically required when:
- The output paper shows skew
- The output paper shows wrinkles
- Paper jams occur in the registration roller section
5. Duplex Registration Control
5.1 Second-Side Registration
In duplex printing, the second side of the paper presents unique registration challenges. The paper must be fed from the ADU and registered with the same precision as the first side.
The registration sequence for the second side follows similar principles, but the paper source is the ADU transport rollers rather than a paper tray.
5.2 Timing Considerations
In duplex mode, special timing considerations apply:
- Loop forming must be completed before the second side of a sheet enters the registration roller
- The rise timing of the load to perform registration must be properly sequenced with the rise timing of the load to form a loop
- If loop formation is not complete before the paper enters the registration roller, jams or misregistration can occur
6. Sensor States and Jam Detection
6.1 Normal Sensor States
The registration sensor (PS1) is unblocked (paper not present) when:
- The main power switch is turned ON
- A door or cover is opened and closed
- A misfeed or malfunction is reset
6.2 Jam Detection Timing
The MFPB continuously monitors the registration sensor to detect paper jams. Common jam conditions include:
| Jam Code | Condition | Description |
|---|---|---|
| 10-01 | PS1 not unblocked | Paper from bypass tray does not reach PS1 within specified time |
| 11-01 | PS1 not unblocked | Paper from tray 1 does not reach PS1 within specified time |
| 20-01 | PS1 not unblocked | Paper from tray 2 does not reach PS1 within specified time |
| 92-01 | PS1 not unblocked | Paper in duplex mode does not reach PS1 within specified time |
6.3 Paper Left Detection
If the registration sensor (PS1) is blocked (paper detected) when:
- The main power switch is turned ON
- A door or cover is opened and closed
- A misfeed or malfunction is reset
The machine regards this as a paper jam in the image transfer section and displays the appropriate error.
7. Troubleshooting Registration Sensor Issues
7.1 Common Symptoms and Causes
| Symptom | Possible Causes | Diagnostic Steps |
|---|---|---|
| Paper jams at registration (jam codes 10-01, 11-01, 20-01, 92-01) | Faulty sensor, blocked actuator, paper path obstruction | Check PS1 operation in Service Mode Sensor Check; verify actuator moves freely; check for foreign objects |
| Misregistered images (image shifted or skewed) | Incorrect loop amount, worn registration roller, clutch slipping | Adjust loop amount in Service Mode; inspect registration roller and clutch |
| Duplex jams at registration | ADU transport issues, timing problems | Check ADU pre-registration roller and sensor; verify loop timing |
| False jam indications | Sensor dirty, actuator sticking, electrical fault | Clean sensor; check actuator spring; verify connector continuity |
7.2 Sensor Check Procedure
To verify registration sensor operation:
- Enter Service Mode
- Navigate to the Sensor Check screen
- Operate the sensor manually using paper or an actuator
- Check the display for correct state changes
7.3 Electrical Testing
The registration sensor connects to the MFP board (MFPB). Electrical checks should include:
- Verify connector seating
- Check for proper voltage supply
- Test sensor output signal with a multimeter
- Inspect wiring for damage or chafing
8. Model-Specific Variations
While the fundamental principles described in this article apply broadly across the bizhub product line, specific component designations and control logic may vary by model:
| Model Series | Sensor Designation | Drive Source | Adjustment Menu |
|---|---|---|---|
| bizhub C652 | PS38 | Registration motor (M2) | Printer Regist Loop Amount |
| bizhub 367/287/227 | PS1 | Transport motor (M1) | — |
| bizhub 500 | PS1 | Feed motor (M9) | — |
| bizhub 423 | PS1 | Transport motor | Printer Reg. Loop Adj. |
| bizhub 164 | PS1 | Main motor | LOOP Ad. (TRAY1) / (BYPASS) |
| bizhub C4000i (i-series) | PS9 | — | — |
| bizhub 751/600 | PS44 | Loop motor (M6) | — |
Always consult the appropriate service manual for model-specific details.
Conclusion
The registration sensor is the cornerstone of accurate paper positioning in Konica Minolta bizhub devices. By detecting the leading edge of each sheet and providing the timing reference for registration roller control, it enables three critical functions:
- Skew correction — Through loop formation against the stopped registration roller
- Image synchronization — By timing the restart of the registration roller to match image write timing
- Jam detection — By monitoring paper arrival and departure times
For service technicians, understanding the registration sensor’s role means recognizing that the sensor is not merely a switch that detects paper—it is the timing reference for the entire imaging process. When troubleshooting registration-related issues, always verify sensor operation first, then consider the mechanical components (registration roller, clutch, loop rollers) and finally the timing parameters (loop amount adjustments) that depend on accurate sensor input.