From Overheated IGBT Modules to Full System Recovery

1. Introduction

In modern screw air compressors, the variable frequency drive (VFD) is the core component responsible for controlling motor speed and optimizing power consumption.
The Chmairss VGS30A compressor, equipped with a 22 kW VEMC inverter, uses variable-speed control to maintain constant discharge pressure while achieving high energy efficiency.

However, after long-term operation, one of the most common issues that field engineers encounter is the “Err14 – Module Overheat” fault on the VEMC inverter.
This error not only causes system shutdown but also indicates potential thermal imbalance or hardware degradation inside the inverter.

This article provides a comprehensive technical explanation and a complete repair workflow — from understanding the root cause of Err14, diagnosing the issue step-by-step, to repairing and preventing future failures. It is based on real-world field data from a VGS30A compressor maintenance case.

2. Fault Symptoms and Display Information

(1) On the Main Control Panel (HMI)

The compressor controller repeatedly shows the following message:

STATE: MOTOR INV FAULT
CODE: 00014

Multiple entries appear in the fault history list (024–028), all labeled “MOTOR INV FAULT.”

(2) On the VEMC Inverter Panel

The inverter LED display reads:

Err14

The red alarm indicator is on, and the motor cannot start.
Once the contactor closes, the inverter trips immediately.

(3) PLC and System Reaction

The PLC detects the inverter fault signal and sends a stop command to the entire compressor.
Frequency display freezes at 0.0 Hz, power output shows 0.0 kW, and total run time stops accumulating.

3. Understanding the “Err14” Code — Module Overheat Fault

According to VEMC documentation:

Err14 = Module Overheat Fault (IGBT Overtemperature)

The inverter continuously monitors the IGBT module temperature via an NTC thermistor attached to the power module.
This analog signal is converted to a voltage and fed to the control CPU through an A/D converter.

• Normal temperature range: 25 °C – 75 °C
• Warning level: ~85 °C
• Trip threshold: ~95 °C

If the module temperature exceeds the limit or the temperature signal becomes abnormal (open circuit, short circuit, or unrealistic value), the inverter will immediately shut down to protect the IGBT module. The control CPU disables PWM output and reports Err14.

4. Common Root Causes of Err14

Based on maintenance experience and field diagnostics, there are five main categories of causes for Err14:

5. Step-by-Step Diagnostic Procedure

Step 1 – Inspect the Cooling Fan and Air Duct

1. Power on the inverter and check whether the internal cooling fan starts automatically.
2. If the fan does not spin, measure the voltage at the fan terminals (usually DC 12 V or DC 24 V).
   • Voltage present but fan not spinning → fan motor failure.
   • No voltage → main control board output failure.
3. Clean the air duct, dust filter, and heat-sink fins thoroughly.

Step 2 – Check Cabinet Temperature

• Use an infrared thermometer to measure temperature inside the control cabinet.
• If it exceeds 45 °C, install additional exhaust fans or ventilation openings.
• Avoid placing the cabinet near heat sources (e.g., compressor discharge pipe).

Step 3 – Test the NTC Thermistor

1. Power off and wait at least 10 minutes for discharge.
2. Remove the drive or power board.
3. Measure resistance between NTC terminals (typically around 10 kΩ at 25 °C).
4. Heat the sensor slightly with a hot-air gun — the resistance should decrease with rising temperature.
5. If resistance is fixed or open circuit → replace the thermistor.

Step 4 – Check the IGBT Power Module

1. Use a multimeter diode-test function to check each phase (U, V, W) to positive/negative bus.
2. Any shorted or low-resistance reading (< 0.3 Ω) indicates IGBT damage.
3. Verify that the power module is tightly clamped to the heat sink.
4. Reapply high-quality thermal grease (e.g., Dow Corning 340) if dried or cracked.

Step 5 – Check the Control Board Temperature Circuit

If all above components are normal but Err14 remains:

• Inspect connector pins (often CN6 or CN8) for oxidation or loose contact.
• Use an oscilloscope to observe temperature signal voltage (should decrease gradually as temperature rises).
• Constant 0 V or 5 V output → indicates A/D converter or amplifier failure.
• Replace the entire driver/control board if signal circuit is defective.

6. Case Study — Actual Field Repair of a VGS30A Compressor

Equipment details:

• Model: Chmairss VGS30A
• Inverter: VEMC 22 kW
• Total runtime: 7 303 hours
• Ambient temperature: ~38 °C
• Fault: Err14 appears within seconds after startup; fan not rotating

Inspection and Findings

After cleaning and replacing the fan, the inverter started normally.
After 30 minutes of continuous operation, module temperature stabilized at 58 °C, confirming successful repair.

7. Electrical and Thermal Theory Behind Err14

(1) Power Loss and Junction Temperature

The IGBT’s heat generation consists of conduction and switching losses:
[
P_{loss} = V_{CE} \times I_C + \tfrac{1}{2}V_{CE} I_C f_{sw} (t_{on}+t_{off})
]
If heat cannot be transferred efficiently to the heat sink, junction temperature (Tj) rises sharply, increasing conduction loss — a positive feedback that can lead to thermal runaway and module destruction.

(2) Importance of Thermal Interface

The thermal resistance (Rθjc) between IGBT and heat sink determines how quickly heat is removed.
Dried or aged thermal compound increases resistance several times, leading to localized hot spots even when load current is normal.

(3) Protection Logic Inside VEMC Drive

The inverter CPU continuously samples the temperature signal:

• Below 0.45 V (≈ 95 °C): trigger Err14 and shut down PWM output.
• Above 0.55 V (≈ 85 °C): allow reset condition.
• Open circuit: immediate fault lockout, manual reset required.

8. Preventive Maintenance Recommendations

Regular maintenance can extend inverter lifetime by 30–50 %, reduce downtime, and prevent expensive module failures.

9. Temporary Reset for Diagnostic Verification

If you suspect a false alarm:

1. Power off and wait at least 10 minutes for cooling.
2. Power on and press STOP/RESET.
3. If Err14 reappears immediately → likely sensor or circuit fault.
4. If it occurs after several minutes of operation → genuine overheating issue.

10. Troubleshooting Flow (Text Version)

Err14 Detected →
   ↓
Check Cooling Fan Running?
   ├─ No → Measure fan supply → replace fan if needed
   └─ Yes →
         ↓
Is Ambient Temperature >45°C?
         ├─ Yes → Improve ventilation
         └─ No →
               ↓
Measure NTC Thermistor Resistance
               ├─ Abnormal → Replace NTC
               └─ Normal →
                     ↓
Inspect IGBT Module & Thermal Grease
                     ├─ Abnormal → Reapply grease / replace module
                     └─ Normal →
                           ↓
Replace Driver Board (temperature circuit failure)

11. Practical Notes and Safety Reminders

• Always discharge DC bus capacitors before touching power terminals (wait >10 minutes).
• When replacing thermal grease, ensure no air gaps between module and heat sink.
• If replacing the IGBT module, apply torque evenly and use original insulation pads.
• Keep cabinet filters clean and avoid placing the compressor near exhaust heat or walls.
• Use infrared thermometer to monitor heat sink temperature during first startup after repair.

12. Lessons Learned

This case of the Chmairss VGS30A compressor with VEMC inverter Err14 demonstrates the critical role of thermal management in power electronics.
Although the message “Module Overheat” seems simple, it reflects a complex interaction between cooling airflow, thermal interface condition, and signal detection circuits.

Field statistics show:

• About 70 % of Err14 faults are resolved by cleaning the cooling path, replacing fans, or re-greasing the module.
• The remaining 30 % involve circuit faults or component failures (NTC or driver board).

Understanding these mechanisms allows engineers to diagnose quickly, repair efficiently, and reduce costly downtime.

13. Conclusion

The Err14 (Module Overheat) fault is not merely an alarm — it is the inverter’s self-protection mechanism preventing irreversible IGBT damage.
Proper analysis requires both electrical and thermal reasoning.
By following the structured diagnostic steps in this guide — inspecting the fan, air duct, thermistor, power module, and control board — maintenance engineers can isolate the root cause systematically.

Regular preventive maintenance, good ventilation, and periodic internal cleaning are the best strategies to ensure long-term reliability of VEMC inverters in air compressor applications.

I. Product Overview

The DOVOL DV950E series permanent magnet synchronous frequency converter is a general-purpose, high-performance current vector frequency converter. It is mainly used to control and adjust the speed and torque of three-phase AC synchronous motors. This guide provides detailed information on the converter’s functional features, operation methods, parameter settings, and troubleshooting, helping users quickly master the skills of using the equipment.

II. Basic Functions and Wiring

Product Main Features

• Control Modes: Supports sensorless vector control (SVC), sensor-based vector control (FVC), and V/F control.
• Frequency Range: 0 – 500Hz.
• Overload Capacity: 150% of the rated current for 60 seconds, 180% of the rated current for 3 seconds.
• Speed Regulation Range: 1:50 in SVC mode, 1:1000 in FVC mode.
• Built-in PID Regulator: Supports process closed-loop control.
• Multiple Communication Protocols Supported: Modbus, ProfiBus-DP, CANlink, CANopen.

Electrical Installation Precautions

• Main Circuit Wiring: Correctly distinguish between input terminals (R, S, T) and output terminals (U, V, W).
• Braking Resistor: Do not connect the braking resistor directly between the DC bus (+) and (-) terminals.
• Motor Cable Length: When the motor cable length exceeds 100m, install an AC output reactor.
• Grounding: Ensure reliable grounding with a grounding wire resistance of less than 10Ω.
• Power Supply Voltage: Before powering on, ensure that the power supply voltage matches the rated voltage of the frequency converter.

III. Operation Panel Usage

Panel Layout and Indicators

• RUN: Running status indicator (lights up when in operation).
• LOCAL/REMOT: Control mode indicator (off – panel control; on – terminal control; flashing – communication control).
• FWD/REV: Forward/reverse rotation indicator (lights up for reverse rotation).
• TUNE/TC: Tuning/torque control/fault indicator.
• Five-digit LED Digital Display Area.
• Function Keys: PRG (programming), ENTER (confirmation), ▲▼ (increase/decrease), ◄ (shift), etc.

Basic Operation Process

1. Enter the parameter setting mode by pressing the PRG key.
2. Select the function group using the ▲▼ keys.
3. Press ENTER to enter the specific parameter setting.
4. After modifying the parameter value, press ENTER to save it.
5. Press the PRG key to return to the previous menu.

IV. Core Function Implementation Methods

Motor Forward/Reverse Rotation Control

Method 1: Panel Control

• Set P0-02 = 0 (panel command channel).
• Set the running direction via P0-09 (0 – same direction; 1 – opposite direction).
• Press the RUN key to start and the STOP key to stop.

Method 2: Terminal Control

• Set P0-02 = 1 (terminal command channel).
• Assign DI terminal functions: P4-00 = 1 (DI1 for forward rotation), P4-01 = 2 (DI2 for reverse rotation).
• Control the on/off state of the DI terminals through external switches to achieve forward/reverse rotation.

Method 3: Communication Control

• Set P0-02 = 2 (communication command channel).
• Send forward/reverse rotation commands through communication (requires a communication card).
• Note: To disable reverse rotation, set P8-13 = 1.

Frequency Regulation Methods

Digital Frequency Setting

• Set P0-03 = 0 or 1 (digital setting).
• Set the preset frequency via P0-08.
• During operation, fine-tune the frequency using the panel ▲▼ keys or UP/DOWN terminals.

Analog Frequency Setting

• Set P0-03 = 2 (AI1)/3 (AI2)/4 (AI3).
• Configure the curve characteristics of the corresponding AI input (P4-13 – P4-27).
• Adjust the frequency using an external potentiometer or PLC analog output.

Multi-speed Control

• Set P0-03 = 6 (multi-speed instruction).
• Assign DI terminals as multi-speed instructions (P4-00 – P4-09 = 12 – 15).
• Set the frequency values for each speed segment in the PC group (PC-00 – PC-15).

PID Frequency Regulation

• Set P0-03 = 8 (PID).
• Configure the PID parameters in the PA group.
• Automatically adjust the frequency based on the feedback signal.

Motor Parameter Tuning

No-load Tuning Steps

1. Ensure that the motor is mechanically decoupled from the load.
2. Correctly input the motor nameplate parameters (P1-01 – P1-05).
3. Set P1-37 = 12 (synchronous motor no-load tuning).
4. Press the RUN key to start tuning (approximately 2 minutes).
5. The parameters are automatically saved after tuning is completed.

Loaded Tuning Steps

1. Set P1-37 = 11 (synchronous motor loaded tuning).
2. Press the RUN key to start tuning.
3. The parameters are automatically saved after tuning is completed.

• Note: Loaded tuning cannot obtain the back electromotive force coefficient, and the control accuracy is slightly lower than that of no-load tuning.

V. Advanced Function Configuration

Frequency Sweeping Function (Textile Applications)

• Set PB-00 = 0 (relative to the center frequency) or 1 (relative to the maximum frequency).
• Set PB-01 (frequency sweeping amplitude), PB-02 (jump amplitude).
• Set PB-03 (frequency sweeping period), PB-04 (triangular wave rise time).
• Control the frequency sweeping pause through the DI terminal (P4-xx = 24).

Fixed-length Control

• Set DI5 function as length counting input (P4-04 = 27).
• Set PB-07 (pulses per meter).
• Set PB-05 (preset length).
• Assign DO terminals as length arrival signals (P5-xx = 10).

Counting Function

• Set DI terminals as counting input (P4-xx = 25) and reset (P4-xx = 26).
• Set PB-08 (preset count value), PB-09 (specified count value).
• Assign DO terminals as counting arrival signals (P5-xx = 8 or 9).

Timing Control

• Set P8-42 = 1 (timing function enabled).
• Set P8-44 (timing operation time) or select AI input via P8-43.
• The equipment automatically stops after reaching the preset time.

VI. Fault Diagnosis and Handling

Common Fault Codes and Handling

Fault Reset Methods

• Panel Reset: Press the STOP/RES key in the fault state.
• Terminal Reset: Set the DI terminal function to 9 (fault reset).
• Communication Reset: Send a reset command through communication.

Fault Record Inquiry

• Recent Fault: Check P9-16 – P9-22.
• Second Fault: Check P9-27 – P9-34.
• First Fault: Check P9-37 – P9-44.

VII. Maintenance and Upkeep

Daily Inspection

• Check if the cooling fan is operating normally.
• Check for loose wiring terminals.
• Check if the enclosure temperature is abnormal.
• Regularly remove dust from the radiator.

Regular Maintenance

• Check the appearance of electrolytic capacitors every six months.
• Check the insulation resistance annually (measure after powering off).
• Replace the cooling fan every 2 years (depending on the operating environment).

Parameter Backup

• Set PP-01 = 4 (backup user parameters).
• To restore, set PP-01 = 501.
• Restore to factory settings: PP-01 = 1.

VIII. Safety Precautions

• Do not open the cover when powered on. After powering off, wait for 10 minutes before performing wiring operations.
• Do not connect the braking resistor directly to the DC bus.
• Perform an insulation check on the motor before the first use (≥5MΩ).
• Derate the equipment when the altitude exceeds 1000m (derate by 1% for every 100m).
• Derate the equipment when the ambient temperature exceeds 40℃ (derate by 1.5% for every 1℃).
• Do not install capacitors or surge suppressors on the output side of the frequency converter.

This guide provides a detailed introduction to the various function implementation methods of the DV950E frequency converter. When using it in practice, please select the appropriate configuration method according to the specific application scenario. For complex application scenarios, it is recommended to contact the manufacturer’s technical support for more professional guidance.

I. Operation Panel Functions and Basic Settings

1.1 Introduction to Operation Panel Functions

The operation panel of the XC-5000 series frequency converters adopts a three-level menu structure, with the main functional components including:

LED Display Area:

• 5-digit LED Digital Tube: Displays set frequency, output frequency, monitoring data, and alarm codes.

Function Indicator Lights:

• RUN: Indicates the running status.
• LOCAL/REMOT: Indicates the control mode (panel/terminal/communication).
• FWD/REV: Indicates forward/reverse rotation.
• TUNE/TC: Indicates tuning/torque control/fault status.

Key Functions:

• Programming Key (PRG): Enters/exits the first-level menu.
• Confirm Key (ENTER): Enters menus/confirms parameters.
• Increment/Decrement Keys (▲/▼): Increases/decreases data.
• Shift Key (◄): Selects display parameters/modification positions.
• Run Key (RUN): Controls keyboard operation.
• Stop/Reset Key (STOP/RES): Stops operation/resets faults.
• Multi-Function Selection Key (MF.K): Defines functions according to F7-01.

1.2 Parameter Initialization Settings

Restore Factory Parameters (excluding motor parameters):

• Set FP-01 = 1 and confirm.

Clear Operation Record Information:

• Set FP-01 = 2 and confirm.

Restore User Backup Parameters:

• Set FP-01 = 501 and confirm.

Notes:

• Initialization operations must be performed in the stop state.
• After initialization, running parameters need to be reset.
• In vector control mode, motor parameter identification needs to be redone.

1.3 Password Setting and Management

Setting a Password:

• Enter the function code FP-00 and set a 4-digit numerical password (1-65535), then confirm.

Password Protection Activation:

• Password protection takes effect after exiting the function code editing state.

Canceling Password Protection:

• Use the password to enter parameter settings and set FP-00 to 0, then confirm.

1.4 Parameter Access Restriction Settings

Function Group Display Control (FP-02):

• Units digit: U group display selection.
• Tens digit: A group display selection.

Personalized Parameter Group Display Control (FP-03):

• Units digit: User-defined parameter group display selection.
• Tens digit: User-modified parameter group display selection.

Function Code Modification Attribute (FP-04):

• Sets whether parameters can be modified (0 for modifiable/1 for non-modifiable).

Manufacturer Parameter Protection:

• Parameters marked with “*” are prohibited from being modified by users.

II. External Terminal Control and Speed Adjustment Settings

2.1 External Terminal Forward/Reverse Rotation Control

Hardware Wiring:

• Control power wiring: +24V-COM provides +24V power.
• Control signal wiring (two-wire control):
  • DI1-COM: Forward rotation signal input.
  • DI2-COM: Reverse rotation signal input.

Parameter Settings:

• Command source selection: F0-02 = 1.
• Terminal function definition: F4-00 = 1 (DI1 for forward rotation), F4-01 = 2 (DI2 for reverse rotation).
• Terminal command mode: F4-11 = 0.
• Reverse rotation control enable: F8-13 = 0.

2.2 External Potentiometer Speed Adjustment Settings

Hardware Wiring:

• Connect the two ends of the potentiometer to +10V and GND, and connect the sliding end to AI1-GND.
• Recommended potentiometer specifications: Resistance 1kΩ-5kΩ, power 0.5W or above.

Parameter Settings:

• Frequency source selection: F0-03 = 2.
• AI curve settings: F4-13 = 0.00V, F4-14 = 0.0%, F4-15 = 10.00V, F4-16 = 100.0%.
• Frequency range limitation: F0-10 = 50.00Hz, F0-12 = 50.00Hz, F0-14 = 0.00Hz.

III. Fault Diagnosis and Handling

3.1 Common Fault Codes and Solutions

3.2 Fault Information Query and Reset

Fault History Query:

• F9-14 to F9-16: Record the types of the last three faults.
• F9-17 to F9-46: Record the operating status parameters at the time of the fault.

Fault Reset Methods:

• Panel reset: Press the STOP/RES key.
• Terminal reset: Set the DI terminal to 9.
• Communication reset: Send a reset command through Modbus communication.

3.3 Fault Protection Action Settings

Fault Action Selection 1 (F9-47):

• Units digit: Motor overload action.
• Tens digit: Input phase loss action.

Fault Action Selection 2 (F9-48):

• Units digit: Encoder fault action.
• Tens digit: Parameter read/write abnormal action.

Fault Action Selection 3 (F9-49):

• Units digit: Custom fault 1 action.
• Tens digit: Custom fault 2 action.

IV. Advanced Functions and Application Examples

4.1 Multi-Motor Control Function

Motor Parameter Group Selection:

• Select the current motor parameter group using F0-24.

Motor Parameter Settings:

• First group: F1 group (motor parameters), F2 group (vector parameters).
• Second group: A2 group (motor parameters), A5 group (vector parameters).

Switching Notes:

• Switching must be performed in the stop state.
• After switching, check the motor rotation direction.

4.2 PID Control Function Application

Basic Parameter Settings:

• FA-00: PID setpoint source selection.
• FA-02: PID feedback source selection.

PID Parameter Settings:

• FA-05: Proportional gain Kp1.
• FA-06: Integral time Ti1.
• FA-07: Differential time Td1.

4.3 Communication Function Configuration

Basic Parameter Settings:

• Fd-00: Baud rate setting.
• Fd-01: Data format.
• Fd-02: Local address.

Communication Control:

• Run command: Communication address 0x1001.
• Frequency setpoint: Communication address 0x1000.

V. Maintenance and Upkeep

5.1 Daily Maintenance Points

Regular Inspection Items:

• Check the operation of the cooling fan.
• Remove dust from the radiator.
• Check the wiring terminals.
• Check the electrolytic capacitors.

Maintenance Cycle Recommendations:

• Daily: Check the operating status.
• Monthly: Clean the radiator.
• Annually: Conduct a comprehensive inspection.

5.2 Long-Term Storage Notes

Storage Environment Requirements:

• Temperature: -20°C to +60°C.
• Humidity: ≤95%RH (no condensation).

Inspection Before Reuse:

• Measure the insulation resistance of the main circuit.
• Check the control board.

5.3 Lifespan Prediction and Replacement

Lifespan Reference for Wear Parts:

• Electrolytic capacitors: Approximately 8-10 years.
• Cooling fans: Approximately 30,000-50,000 hours.

Replacement Notes:

• Cut off the power supply and wait for 10 minutes before operation.
• After replacement, check the parameter settings.

Conclusion

The XC-5000 series frequency converters are powerful and have superior performance. Through this guide, users can comprehensively master core skills such as operation panel usage, parameter settings, external control, and fault diagnosis. Correct installation, parameter settings, and maintenance are key to ensuring the long-term stable operation of the frequency converters. It is recommended that users refer to this guide and make appropriate adjustments according to specific working conditions to fully leverage the performance advantages of the XC-5000 frequency converters.

I. Background and Problem Description

In CNC machining center maintenance and commissioning, the calibration of the Z-axis reference point and tool change point is critical for ensuring the machine’s precision and stability.
This article takes the XD-40A vertical machining center manufactured by Dalian Machine Tool Group as an example. The machine is equipped with a GSK983Ma-H CNC system, DA98D servo drive, and a Sanyo OIH 5000P/R incremental encoder.
The machine adopts an umbrella-type tool magazine, where the Z-axis must accurately position at the second reference point during tool change.

During routine maintenance, the Z-axis servo motor was replaced. After replacement, the machine could start and home normally, but an abnormality appeared during tool change (M06):
The Z-axis stopped about 3 mm higher than before, causing the spindle taper to fail to engage the tool holder. The operator had to manually lower the Z-axis by 3 mm to complete the tool change.

Although this deviation did not trigger any alarms, it seriously affected the reliability of automatic tool change and could lead to tool gripper misalignment, incomplete release, or even tool crashes.

II. System Structure and Signal Relationship Analysis

To solve the issue, it is essential to understand how the GSK983Ma-H system defines the Z-axis “reference point (home position).”
The Z-axis homing position is determined by two signals:

1. Proximity switch signal (HOME/ORG) – used for coarse positioning;
2. Encoder Z-phase signal (Z-phase) – used for fine positioning.

When the machine executes the “Home” (G28 Z0) command after power-up, the sequence is as follows:

• The Z-axis moves in the specified direction until it detects the proximity switch signal.
• The system records the pulse position at this point.
• After the proximity signal is released, the axis continues moving.
• When the next Z-phase pulse is detected, the system defines that position as the machine reference point (zero point).
• Based on parameter 0161, the system then calculates the second reference point (e.g., tool change point).

Thus, the Z-axis zero position is not determined by the limit switch alone, but by the phase relationship between the proximity signal and the encoder Z-phase pulse.

III. Root Cause Analysis After Motor Replacement

In this case, the proximity switch, lead screw, and limit mechanism remained unchanged, yet a 3 mm tool change deviation occurred after replacing the motor.
The underlying causes are as follows:

1. Encoder Z-phase Signal Phase Difference

Even among identical motor models, the internal encoder Z-phase position relative to the rotor magnetic pole can vary slightly due to manufacturing tolerances.
When the system executes “find proximity then find Z-phase,” a phase delay or advance changes the zero-point position.

For a 5000-line encoder:
[
5\text{ mm / rev} \Rightarrow 1 \text{ Z pulse = 5 mm}
]
If the Z-phase triggers 0.6 turns later, the system’s reference point shifts upward by approximately 3 mm.

2. Coupling Installation Angle Deviation

If the motor–lead screw coupling is reassembled with a slight angular misalignment or reversed orientation, the timing between the proximity and Z-phase signals changes, causing a fixed offset.

3. Second Reference Point Parameter Not Recalibrated

Parameter 0161 in the GSK system defines the distance between the first and second reference points.
If the old value is retained after encoder replacement, the stored Z-phase relationship becomes invalid, resulting in a tool change height deviation.

4. Servo Phase Angle or Polarity Mismatch

If the servo drive’s electrical phase offset (in DA98D) is not re-calibrated, it can cause inconsistent homing. However, such errors typically lead to random deviations, not a consistent 3 mm offset.

IV. Parameter Framework and Signal Interaction

The GSK983Ma-H system controls Z-axis referencing using several key parameters:

Thus, the final tool change position can be expressed as:
[
Z_{tool} = Z_{prox} + ΔZ_{Z-phase} + P_{0161}
]
Any change in the above components—especially the Z-phase offset—will cause a physical shift in the tool change height.

V. Comparative Analysis of Available Solutions

When parameter modification (0161) is restricted by password protection, alternative methods must be considered.
Below is a comparison of practical options used in the field.

Conclusion:

• If password access is available, adjusting 0161 is best.
• If not, physically adjusting the proximity switch by 3 mm is the most practical.
• Avoid changing gear ratios unless lead screw or encoder specifications differ.

VI. Practical Solution Without Password Access

When the system password is unknown or locked, the following mechanical method effectively corrects the deviation.

1. Required Tools

Hex wrench, caliper or feeler gauge, insulation gloves, and a tool holder or alignment gauge.

2. Determine Adjustment Direction

• If Z-axis stops too high → move the proximity switch upward.
• If Z-axis stops too low → move the switch downward.

3. Adjustment Procedure

1. Power off the machine.
2. Loosen the Z-axis home switch screws.
3. Move the switch up by approximately 3 mm.
4. Tighten screws and power on.
5. Re-home the Z-axis and test tool change.

4. Verification

Execute:

G28 Z0
M06 T1

Check if the spindle taper aligns with the tool gripper. Fine-tune the switch by ±0.5 mm if needed.

5. Update Work Coordinate

Since the machine reference has shifted, redefine the Z=0 in G54 by touching off the workpiece again.

VII. DA98D Drive Parameter Verification

To ensure that the deviation is not caused by drive scaling, verify the following parameters in the DA98D servo drive:

Any incorrect electronic gear ratio can cause axis scaling errors and must be restored to 1:1.

VIII. Pulse Calculation for 3 mm Offset

Given:

• Lead screw pitch = 5 mm
• Encoder = 5000 PPR
• Pulses per revolution = 5000 × 4 = 20000
• Pulses per mm = 20000 ÷ 5 = 4000

Then:
[
3 \text{ mm} × 4000 = 12000 \text{ pulses}
]
To compensate for a 3 mm height difference, parameter 0161 should change by ±12000 pulses.
For example:

0161: -133500 → -145500

IX. Unlocking System Parameters

If full software correction is preferred, parameter protection can be disabled as follows:

1. Navigate to:
   SYSTEM → PARAM → NC PARAM
2. Press SET;
3. When prompted, enter one of the following passwords:

After successful entry, “Protection Released” appears at the bottom of the screen, allowing parameter editing.

If unavailable, restart and hold DELETE or ALT+M during boot to enter the maintenance menu and disable “Parameter Protection.”

X. Understanding the Z-Axis Homing Logic

The following illustrates the Z-axis homing process:

 ↑ Z+
 │
 │       ┌────────────┐
 │       │ Proximity Switch │
 │       └────────────┘
 │                ↓ (continue)
 │               [Z-phase pulse]
 └──────────────────────────────→ Time

Explanation:

1. Axis moves until proximity signal triggers;
2. After signal release, continues to move;
3. When Z-phase is detected, zero point is set;
4. From that zero, parameter 0161 defines the tool change position.

If the Z-phase occurs later relative to the proximity switch, the zero point shifts upward, making the spindle stop higher during tool change.
By moving the proximity switch 3 mm upward, the zero point effectively moves downward by 3 mm, correcting the deviation.

XI. Key Lessons and Maintenance Practices

1. Always re-calibrate reference points after replacing incremental encoders.
   Even a small Z-phase shift can cause millimeter-level errors.
2. Back up all NC parameters before maintenance.
   Parameter loss or mismatch is a frequent cause of deviation.
3. Prefer software compensation over mechanical adjustments.
   Mechanical adjustments are practical but less precise.
4. Do not change electronic gear ratios arbitrarily.
   They affect all axis scaling, not just tool change height.
5. Umbrella-type tool changers rely heavily on parameter 0161.
   Incorrect values lead to failed or dangerous tool changes.
6. After adjustment, verify through a full test:
   • Home the Z-axis;
   • Execute tool change;
   • Check gripper alignment;
   • Recalibrate work coordinate (G54).

XII. Conclusion

This study analyzed a real case of Z-axis tool change deviation on an XD-40A vertical machining center equipped with GSK983Ma-H control and DA98D servo drives.
Through a detailed investigation of encoder Z-phase behavior, servo drive settings, and CNC reference logic, it was concluded that the 3 mm deviation was caused by a Z-phase timing difference, not mechanical misalignment.

When parameter modification is possible, adjusting parameter 0161 is the optimal solution.
When access is restricted, mechanically adjusting the proximity switch by 3 mm effectively compensates for the offset.
If hardware specifications differ, recalibration of the electronic gear ratio is necessary.

This case highlights that CNC positioning precision depends not only on mechanical accuracy but also on the synchronization between hardware signals and software logic.
A deep understanding of the system’s internal mechanisms allows technicians to restore functionality efficiently, accurately, and safely.