For laser engravers with dual red-dot focusing, the two red-light spots are normally used as a reference for setting the focus. However, assembly tolerances, transportation vibrations, or galvo displacement may cause the red-light reference point to differ from the laser’s actual optimal focus.

This guide explains how to verify the true focal point through test engraving and gradient testing, and how to calibrate the red-light system when necessary.

1. Preparation

1.1

Power on the machine and make sure that the laser source, galvo scanner, and dual red-light focusing function are working properly.

1.2

Place the workpiece flat and secure it firmly. The material and thickness should be consistent with those used in actual production.

1.3

Prepare a gradient test sample to verify the actual marking performance.

1.4

Confirm that the lens model matches the software settings and that the field lens has no damage, impact marks, or scratches.

2. Focusing

2.1 The Dual Red-Light Spots Overlap at the Correct Focus

2.1.1 Symptoms

●  Basic, Nova, and MOPA:

Adjust the Z-axis height until the two red-light spots on the surface of the workpiece completely converge into a single spot.

Dual and AXI:

Adjust the Z-axis height using the electric lift or manual adjustment knob until the two red-light spots on the surface of the workpiece completely converge into a single spot.

Perform a test marking directly at this Z-axis height. The lines should be sharp, the color should be uniform, and there should be no blurred edges. The marking depth/color should meet the required process standards.

2.1.2 Applicable Conditions

●  The red-light system has already been calibrated.

●  The field lens and galvo scanner have not been removed, reinstalled, or impacted.

● The workpiece is flat and free from warping.

2.1.3 Operating Procedure

●  Adjust the Z-axis until the two red-light spots completely overlap.

●  Perform a test marking on a blank area of the workpiece and confirm that the marking result is sharp and meets the requirements.

●  Lock the Z-axis. This position is the effective focal position and can be used directly for batch processing.

2.1.4 Control Measures

●  When changing the workpiece or field lens, reconfirm the red-light spot overlap and perform a test marking.

●  Perform a first-piece marking quality inspection at the beginning of each shift.

2.2 Condition 2: The Dual Red-Light Spots Overlap, but the Laser Is Not at the Correct Focus

2.2.1 Symptoms

The two red-light spots have completely merged into one spot, but the test marking result is poor:

●  Lines appear blurred.

●  Edges are unclear.

●  The marking color is too light.

●  Marking depth/color is uneven.

●  Deep engraving lacks sufficient strength.

Note: This indicates that there is an offset between the red-light reference position and the actual optimal laser focal point. In this case, the overlapping red-light spots can no longer be used as the final focusing criterion.

2.2.2 Adjustment Procedure

First,keep the current workpiece in place. Secure the workpiece firmly and do not move its XY position.

Second,use the position where the red-light spots overlap as the Z-axis reference zero point. From this position, move the Z-axis slightly upward and downward and perform a series of gradient test markings.

●  Adjust the Z-axis by 1–2 mm each time, and perform multiple tests above and below the reference position.

●  Use the blank area of the workpiece and mark the same test pattern each time, such as lines, squares, and grayscale blocks.

Third,Compare all test samples and select the one with the sharpest lines and the darkest, most uniform marking. This Z-axis position is the actual optimal laser focal point.

Fouth,lock the Z-axis at the optimal height. At this point, the two red-light spots will no longer overlap. Accept the non-overlapping red-light position and use the actual marking result as the final criterion.

Fifth,Record the Z-axis value for subsequent production using the same batch or setup.

Sixth,perform a complete first-piece inspection and confirm that the result meets the requirements before starting batch production.

2.2.3 Important Control Measures

First,at this point, do not use “the red-light spots must overlap” as the evaluation criterion. The actual marking result should be used as the final standard.

Second,when this condition occurs, it indicates that the red-light reference position has shifted. Red-light optical path calibration should be scheduled during equipment maintenance.

Third,after the machine has been impacted, or after the galvo scanner or field lens has been removed/reinstalled, this condition is more likely to occur. A gradient test must be performed instead of relying solely on red-light spot overlap.

Fouth,For curved or warped workpieces, prioritize the actual marking result at the processing area. Do not use the red-light position at the edges as the reference.

Fifth,Do not repeatedly move the workpiece to force the red-light spots to overlap. Once the workpiece is moved, the test reference becomes invalid.

3. Red-Light Calibration (Equipment Maintenance)

If the condition of “the red-light spots overlap but the laser is not at the correct focus” occurs repeatedly, red-light calibration should be performed.

3.1 Basic, MOPA, and Nova

If the red-light spots repeatedly overlap but the marking is not at the optimal focus:

3.1.2 Use the machine's red-light calibration function to adjust the red-light module so that the red-light reference point is aligned as closely as possible with the actual laser focal point.

3.1.3 After calibration, verify the result again: when the red-light spots overlap, the marking result should be optimal.

3.1.4 Even after calibration, the test marking procedure should be retained. Do not rely completely on the red-light reference.

Calibration video:em-smart Basic、MOPA and Nova

3.2 Dual and AXI

3.2.1 Use the machine's red-light calibration function to adjust the red-light module so that the red-light reference point is aligned as closely as possible with the actual laser focal point.

3.2.2 After calibration, verify the result again: when the red-light spots overlap, the marking result should be optimal.

3.2.3 Even after calibration, the test marking procedure should be retained. Do not rely completely on the red-light reference.

3.2.4 As shown in the figure below:

●  Screw 1 controls the horizontal position of the red light.

●  Hole 2 controls the vertical position of the red light.

Calibration video:em-smart Dual and AXI

4. Troubleshooting and Fault Identification

4.1 The red-light spots can never overlap

Possible causes include a loose field lens, galvo scanner displacement, or red-light hardware failure. Stop operation and arrange maintenance. Do not continue production.

4.2 All Z-axis gradient test markings are poor

Check laser power, frequency, field lens selection, and whether the lens is dirty or contaminated. Do not simply continue adjusting the Z-axis.