Step 1: Safety and Preliminary Inspection Power Off and Isolation: Before conducting any inspection, ensure that the machine is powered off and implement a lockout and tagout (LOTO) procedure to prevent accidental start-up. Cleaning and visual inspection: ruler body and reading head: Use a lint free soft cloth and alcohol to gently clean the glass or metal surface of the grating ruler and the glass window of the reading head. Check for: physical damage: scratches, cracks, debris. Pollution: Accumulation of oil stains, cutting fluid, dust, and metal powder. Installation status: Check if the ruler body is loose and if there are any bumps on the installation surface; Is the gap between the reading head and the ruler body uniform (refer to the instruction manual, usually a few micrometers to a few tenths of a millimeter),

Is the installation screw tightened. Connecting wires and interfaces: Check all cables from the reading head to the amplifier, and then to the CNC system. Check for any damage, bending, or compression, especially on cables in moving parts. Loose or oxidized connectors: Re plug and unplug each connector (in a power-off state) and check if the pins are bent. Step 2: Electrical and signal diagnosis power on self-test: Power on again and observe if there are any alarms related to the ruler when the system starts. In manual mode, try moving the Z-axis slowly and observe whether an alarm is triggered as soon as it moves, or if an alarm is triggered when it moves to a specific position (which may have damage to the ruler surface). Signal measurement (requires oscilloscope and multimeter, performed by professional maintenance personnel): Reference point signal: Dual column ruler usually has one or more distance encoded reference points. Move the Z-axis to find the reference point and observe if the process is smooth and if the signal is stable. Incremental signal: Use an oscilloscope to measure the output signal of the reading head (usually TTL or 1Vpp sine wave). Normal signals should have clear waveforms, regular sine waves, and no distortion or spikes. The amplitude is stable and meets the requirements of the amplifier (such as 1Vpp). The phase difference between the two channels (A/B) is 90 °± a certain angle. The signal quality should remain consistent throughout the entire length of the ruler. If the signal weakens or distorts in a certain area, it indicates that there may be a problem with the ruler surface at that location. System diagnosis page: Enter the servo diagnosis or feedback diagnosis page of the CNC system. Observe whether the Z-axis position feedback value experiences irregular small jumps when the machine tool is stationary. If the number frequently jumps by several micrometers or more when stationary, it is likely that the ruler or reading head is disturbed or damaged. Compare the tracking error between the instruction position and the actual feedback position to determine if it is stable when moving at low speed and constant speed. Step 3: Mechanical and performance testing - Reverse clearance and repeatability accuracy check: Use a micrometer or laser interferometer to perform repeatability accuracy and reverse clearance tests at different heights along the Z-axis. If the error value is unstable (with large differences in measurement results each time), or if there is a sudden change in error at a specific position, it is likely to be a problem with the ruler.

If the error is stable but exceeds the tolerance, it is more likely to be mechanical problems such as screws and bearings. Comparison method (if conditions permit): Main/auxiliary ruler comparison: The dual column ruler system may sometimes be configured with two reading heads for redundancy or averaging. View the feedback values of two reading heads within the system,

Is the difference between stationary and slow-moving stable within a very small range. If the difference is too large or unstable, it indicates that one of them may be faulty. Compared with the spindle encoder (if the spindle has closed-loop control): When the spindle does not rotate and only performs Z-axis motion, some systems can compare the feedback of the spindle encoder (if it also directly measures the position of the spindle head) with the feedback of the Z-axis grating ruler. Swap method (one of the effective judgment methods): If the X/Y axis of the machine tool uses the same model of grating ruler and reading head, under the guidance of the manufacturer, try to swap the Z-axis (double column ruler) reading head or amplifier with the X/Y axis for testing. Important: After swapping, does the fault phenomenon transfer to another axis? If so, it proves that the replaced component is damaged. This operation requires attention to adjusting the installation gap and making proper markings. Step 4: Interference and Environmental Investigation Grounding Check: Ensure that the reading head, amplifier, and machine tool body are well grounded. Poor grounding is a common cause of signal interference. Cable wiring: Check if the feedback cable is routed separately from the power cable (especially servo motor, spindle, and frequency converter cables) to avoid parallel bundling together. Environmental factors: Check if there are high-power equipment (such as welding machines, induction heating furnaces) near the machine tool that frequently start and stop, causing electromagnetic interference. Summary of common fault causes: Damaged reading head: aging and damage of internal photoelectric components. Surface contamination/damage: Oil stains and scratches can cause signal loss or errors. Installation gap variation: Vibration causes the gap between the reading head and the ruler surface to increase or decrease, exceeding the allowable range. Cable/connector issues: Line wear, poor contact, water ingress. Amplifier/interface board malfunction: signal processing unit damaged. System parameter error: Parameters were accidentally modified (such as grid spacing, reference point distance, etc.). Suggest the operation process from soft to hard: record alarm information and refer to the machine tool maintenance manual. After attempting to backup, restore the parameters of the relevant axis or grating ruler. First outside, then inside: Start with simple cleaning, checking joints and cables. Electrical first, mechanical second: perform signal measurement and system diagnosis. Seeking professional support: If the above steps cannot be resolved or involve disassembling core components (such as replacing the ruler body),

It is strongly recommended to contact machine tool manufacturers or professional repair service providers. Grating ruler is a precision component that requires installation and debugging. Improper handling may result in damage. I hope this detailed guide can help you systematically diagnose problems. If you can provide more specific fault symptoms or machine models, the analysis can be more targeted