Comprehensive Solution for Double Imaging Problem of Text on Line Number Tubes Marked by Purple Light Laser Marking Machine on Automated Production Lines
#### Abstract
In industrial automated production, the Fly Laser UV laser marking machine is widely used in the marking processing of materials such as wire number tubes, plastic parts, and metals due to its high precision, fast speed, and non-contact advantages. However, when used in conjunction with automated equipment (such as vibrating discs, mechanical arms, conveyor belts, etc.) for dynamic marking, the occasional problem of text ghosting seriously affects the readability and aesthetics of the products, and may even lead to failure in quality traceability. This solution aims to systematically analyze the causes of this problem and provide a complete troubleshooting and resolution process from easy to difficult, and from hardware to software, to ensure the stability of the marking process and the clarity of the markings.
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#### I. In-depth Analysis of Problem Phenomena
The specific manifestation of "double image of characters" is that the outline of characters or patterns appears as double or multiple images, as if they were slightly replicated and shifted. The essence of this phenomenon is that **an unexpected relative displacement occurs between the laser focus and the workpiece (line number tube) at the moment of marking**. This displacement could be due to the movement of the line number tube, the shaking of the laser head, or the asynchrony of the marking control signal timing. Before troubleshooting, it is necessary to first determine whether the double image is **constantly present** or **occasionally and irregularly present**.
**Persistent fixed-direction ghosting**: Usually indicates a systematic deviation in hardware installation or software parameter settings.
Occasional and irregular double images are often related to the interaction with automated systems, mechanical vibrations, signal interference, or material properties. The "occasional appearance" you described falls into this category and is a difficult and key point to investigate.
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#### **II. Systematic Investigation and Resolution Process**
Follow the principle of "external before internal, mechanical before electrical, hardware before software" to gradually isolate the problem.
**Phase One: Basic Environment and Hardware Stability Check**
1. **Mechanical Stability Check of the Automation Platform**
**Firmness Check**: First, turn off the power of all devices. Check whether the connecting bolts between the laser marking machine body and the automated machine are tight. Pay special attention to whether the installation plate, brackets, slides, etc. are loose. Try to shake the laser head by hand to feel if there is any obvious gap or wobbling.
**Vibration Source Analysis**: Common vibration sources on automated production lines include the movement of cylinders, the start and stop of motors, the shaking of conveyor belts, and the operation of vibrating discs. When observing the appearance of ghosting, check if it coincides with the operation of a high-power device (such as a robotic arm or cylinder). The solutions are: install an independent and stable platform for the laser marking machine and physically isolate it from the vibration sources (such as using shock-absorbing pads); optimize the control of cylinders and motors, increase acceleration and deceleration times, and reduce sudden impacts.
2. **Workpiece (Wire Number Tube) Fixation and Positioning Inspection**:
**Jig Design**: Check whether the jig for fixing the wire number tube is reasonably designed. The jig should be able to firmly hold the wire number tube to prevent it from moving or vibrating due to the slight impact force of the laser during the marking process. For circular wire number tubes, it is recommended to use V-blocks or flexible jigs to ensure a tight grip.
**Position Consistency**: Verify that the position of the wire number tube remains consistent each time the automated equipment feeds materials. If the position deviation is significant, although the dynamic focusing system (Galvo) of the marking machine can compensate for the focal length, extensive compensation may introduce errors. Ensure the detection accuracy and consistency of the sensors.
3. **Optical Path and Focusing Check**:
**Laser Fixation**: Check whether the laser itself is firmly fixed and whether the internal optical lenses have become loose due to long-term vibration (this operation should be carried out by professionals).
* **Focal Length of Field Lens**: Confirm whether the focal length of the field lens (F-theta lens) used is appropriate. The longer the focal length, the greater the depth of field, and the lower the requirement for the flatness of the workpiece surface. If the surface of the wire marking tube has a curvature or is not placed flat, a larger depth of field can alleviate the problem of inconsistent clarity caused by height variations, but it will not directly cause double images.
* **Focus Calibration**: Re-calibrate the focus to ensure the laser beam's focal point is accurately positioned on the surface of the tube. An inaccurate focus may cause energy dispersion, but it usually manifests as blurred text rather than double images, and can be checked as an exclusion item.
**Phase Two: Electrical and Signal Synchronization Investigation**
1. **Trigger Signal Synchronization Issues (Extremely Common and Critical)**:
**Problem Description**: Automation equipment (such as PLC) sends a trigger signal (typically a "start marking" signal) to the marking machine through IO ports. If this signal is unstable, has glitches, or is not synchronized with the workpiece in-place signal, it may cause the marking machine to start engraving before the workpiece has completely stopped, resulting in trailing or ghosting.
* **Troubleshooting Method**:
* **Check wiring**: Ensure that the connection of the trigger signal line is firm and the shielding is good. It is recommended to use shielded twisted-pair cables and keep them away from power lines during wiring to prevent electromagnetic interference.
**Signal Timing Analysis**: This is the core troubleshooting point. Use an oscilloscope or advanced PLC programming software to monitor the timing diagram of the "workpiece in place" sensor signal and the "marking start" trigger signal. **Make sure the workpiece is fully in place and stable, and then delay for a short period of time (such as 10-50 ms) before sending the marking trigger signal**. This delay is crucial for eliminating the residual mechanical vibration.
* **Signal Type**: Check whether edge triggering (rising edge/falling edge) is being used instead of level triggering. Edge triggering has higher requirements for signal stability and is more susceptible to interference. You can try changing the triggering mode to level triggering in the PLC program and ensure that the level remains stable during marking.
2. Grounding and Anti-Interference (EMI):
Good grounding is the foundation for the stable operation of equipment. Check whether the grounding wires of the marking machine, automated equipment, and computers are well connected and whether the grounding resistance meets the requirements.
Separate the strong current lines (such as those for motors, cylinders, and solenoid valves) from the weak current lines (such as those for sensors and signal lines) when routing them, and avoid laying them in parallel.
**Phase Three: Software and Control Parameter Optimization**
1. **Marking Parameter Adjustment**:
* **Marking speed**: **Excessively high marking speed is a significant cause of ghosting**. When the speed is too fast, the galvanometer motor requires extremely high acceleration and deceleration, which may result in overshoot and jitter. This is reflected in the marking effect as ghosting. **Significantly reduce the marking speed (for example, from 2000mm/s to 1000mm/s) for testing**. If the ghosting disappears, it indicates that the issue is related to speed. Then gradually increase the speed to find the critical point for stable operation.
* **Jumping Speed**: Appropriately reduce the jumping speed (idle stroke speed) to minimize the sudden stop and start of the galvanometer.
* **Delay Settings**: In the software, there are usually parameters such as "Turn-on Delay", "Turn-off Delay", and "Jump Delay". Appropriately increasing the "Turn-on Delay" ensures that the galvanometer motor has moved to the predetermined starting point and stabilized before the laser is turned on; appropriately increasing the "Turn-off Delay" ensures that the laser is turned off before moving to the next point when a line ends. Fine-tuning these delay parameters is crucial for eliminating ghosting.
* **Acceleration Factor**: Some marking software has an "acceleration factor" parameter. Reducing this value can smooth the galvanometer movement and reduce jitter, but it will slightly decrease the overall speed.
2. **Re-calibrate the galvanometer mirror**
Run the "Galvanometer Calibration" program in the marking software. Long-term vibration may cause deviation of the galvanometer. Re-calibration can correct the mapping relationship of the X and Y-axis galvanometers and solve the systematic deviation caused by inaccurate calibration.
3. Q-switch frequency (applicable only to certain lasers):
If the double image is manifested as dense point superposition, you can try to fine-tune the Q-switch frequency to better match the marking speed.
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#### III. Summary and Suggestions for Operating Procedures
For your situation of "occasional double images", we suggest you follow the priority operations below:
1. **Step 1: Immediately reduce the marking speed**. This is the quickest and most effective initial diagnostic method. If the double imaging disappears after the speed is reduced, the problem is related to speed or vibration.
2. **Step Two: Inspect and Optimize the Timing of the Trigger Signal**. Work with the automation equipment engineer to add a 50-100ms delay to the "workpiece in place" signal in the PLC program before sending out the "marking start" signal.
3. **Step 3: Comprehensive inspection of mechanical fastening**. Tighten all the screws of the laser head, fixtures, and installation platform.
4. **Step 4: Check Signal Lines and Grounding**. Ensure that the trigger signal line is well shielded and kept away from power lines.
5. **Step 5: Fine-tune software delay parameters**. After optimizing speed and timing, further enhance the effect by fine-tuning parameters such as "switching delay".
6. **Step 6: Contact the equipment supplier**. If all the above steps fail to solve the problem, it might be that there is a potential fault in the galvanometer motor, control card or internal components of the laser, which requires professional technicians to conduct inspection and repair.
Through the above systematic investigation, the majority of the text ghosting issues of Unisplendour laser marking machines on the automated production line can be effectively located and resolved, ultimately achieving stable, efficient and high-quality laser marking production. If the problem still cannot be solved, please contact Fly Laser.
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