Introduction and Technical Analysis

Considered the heart of industrial automation, CNC machines play an indispensable role in today’s manufacturing sector, offering precision, speed, and repeatability. However, one of the most critical malfunctions encountered in these complex systems, which disrupts production processes, is the positioning error known as “axis position loss.” Axis position loss occurs when the machine fails to reach its programmed or expected position, deviates from this position, or experiences momentary position loss during machining. This situation leads to deterioration in final product quality, part scrap, tool breakage, machine damage, and consequently, significant cost increases. The problem of axis position loss in a CNC machine can often stem from a combination of many factors—mechanical, electrical, electronic, or software-related—rather than a single cause. This detailed field guide has been prepared for industrial automation specialists and maintenance technicians to understand the origins of axis position loss faults, detect them with a systematic approach, and provide lasting solutions. Our aim is to analyze this complex problem step-by-step, offering practical information to enable quick and accurate intervention on the production line. In precise manufacturing environments where every millimeter, even micron, is critical, correctly diagnosing and resolving axis position loss is vital for production efficiency and operational profitability.

Operating Principle and Technical Data

Field Observations and Checks

• Mechanical Checks: A significant portion of axis position loss problems are mechanical in origin. Carefully inspect all moving parts of the machine. Check for wear or play in ball screws and their nuts. Increased backlash directly affects positioning accuracy. Examine couplings (the connecting element between the motor and the ball screw) for looseness, cracks, or wear. A loose coupling cannot fully transmit motor movement to the ball screw. Observe linear guides and their bearings for wear, contamination, or damage. Proper lubrication of the guides is critically important. Sticking, friction, or abnormal noises in the guides can lead to excessive loading or position loss. It is also important to check the tightness of all mounting bolts for these components.
• Electrical and Electronic Checks: Check the integrity and connections of power cables and signal cables (encoder, limit switch, etc.). Crushed, broken, frayed cables, or loose connectors can lead to signal loss or electrical noise. Fatigue-related breaks in cables within moving cable carriers are common. Ensure that grounding connections are solid and correctly made; poor grounding can cause electrical interference. Measure the winding resistances of servo motors with a multimeter to check for phase imbalance or short circuits. Examine the diagnostic screens and error codes of servo drives and the controller. Warnings such as overcurrent, overvoltage, or encoder error can provide important clues about the source of the problem. Checking encoder signals with an oscilloscope is an advanced method for detecting signal quality and potential interference.
• Drive and Controller Parameters: Axis position loss can result from incorrectly set drive parameters (gain values, filters, PID settings) or controller parameters (electronic gear ratio, backlash compensation, limits). Especially after a new motor or drive replacement, or after mechanical maintenance, ensure these parameters are correctly set. Compare them with the manufacturer’s default or optimum values. Monitor the axis following error (position error) from the controller’s diagnostic screens. A higher-than-normal following error may indicate inadequate drive settings or a mechanical system issue.
• Environmental Factors and Machining Conditions: The temperature and humidity conditions of the environment in which the machine operates can affect the lifespan and performance of electronic components. Excessive temperature can cause drives and motors to overheat and enter protection mode. Voltage fluctuations or noise in the electrical grid can affect sensitive electronic components. Cutting forces applied during machining, tool condition, workpiece clamping method, and cutting parameters (feed rate, RPM, depth of cut) can overload the axes, leading to step loss or position loss. This risk increases particularly when machining hard materials or using dull tools.
• Maintenance Records and Operator Observations: Regular maintenance records show when components were replaced or serviced. These records can help narrow down potential causes of a fault. At the same time, observations from machine operators are very valuable. When did the axis position loss start? Does it occur with a specific tool or workpiece? Are abnormal noises or vibrations present? What exactly was the error message? This information is critical for getting to the root of the problem.

Common Problems and Solutions

Axis position loss problems often arise under specific scenarios. Here are the most common problems and step-by-step solutions:

• Mechanical Backlash and Wear:

  Problem: Backlash felt in the axis, especially when changing direction, staircase effect on machined surfaces, loss of precision. Typically caused by wear in the ball screw nut, bearings, or couplings.

  Detection: Measure axis backlash using a mechanical indicator (dial gauge). Observe the movement of the ball screw by manually rotating the motor coupling. Listen for abnormal noises or vibrations.

  Solution:

  1. Check the backlash in the ball screw nut. Some systems may have adjustable backlash elimination mechanisms. If adjustment is not possible or the nut is worn, replace it.
  2. Check the end bearings of the ball screw and replace them if worn.
  3. Check the coupling between the motor and the ball screw; tighten or replace if loose or damaged.
  4. Check the “Backlash Compensation” setting in the CNC controller and enter the correct value. However, this does not solve the root of the problem, it is only a symptomatic measure. The permanent solution is mechanical repair.
  5. Check the condition of the linear guides and carriage bearings; replace if worn or damaged and ensure regular lubrication.
• Encoder/Resolver Faults:

  Problem: Incorrect reporting of instantaneous axis position to the controller, signal loss, momentary jumps, encoder error message on the controller.

  Detection: Check the encoder cable and connectors. There may be a loose connection, broken cable, or contamination. Observe if the encoder’s optical disk or magnetic strip is contaminated or damaged. Monitor the encoder signal from the controller’s diagnostic screen.

  Solution:

  1. Clean the encoder cable and connectors and connect them securely. Repair or replace broken cables.
  2. Clean the optical disk or magnetic sensor inside the encoder (carefully and according to manufacturer instructions).
  3. Check if the encoder is physically damaged. If damaged, replace the encoder with a new one.
  4. Check for electromagnetic interference (EMI) in the cables. If necessary, use shielded cables or change the cable routing.
• Servo Motor/Drive Problems:

  Problem: Motor overheating, abnormal noises, vibration, overcurrent, overload, or position error messages on the controller.

  Detection: Check the surface temperature of the motor. Measure motor winding resistances and insulation resistance. Read the drive’s error codes. Check servo drive parameters (PID gains, filters). Observe if the motor is struggling under load.

  Solution:

  1. Interpret the error codes on the drive and seek solutions according to the manufacturer’s manual.
  2. Optimize the PID gain values and filter settings of the servo drive. Auto-tuning function can usually be used.
  3. Check and clean the cooling systems (fans, airflow) of the motor and drive.
  4. If there is a short circuit or ground fault in the motor windings, repair or replace the motor.
  5. Ensure the power supply voltage is correct and stable.
  6. Check machining parameters (cutting speed, feed rate); reduce if causing overload.
• Cabling and Connector Issues:

  Problem: Momentary axis position loss, random errors, intermittent operation, communication breakdowns.

  Detection: Visually inspect the physical condition of all power, signal, and encoder cables. Ensure connectors are tightly connected and free of corrosion. Examine cables in moving cable carriers for fatigue and breakage. Perform cable continuity tests with a multimeter.

  Solution:

  1. Tighten loose connectors, clean or replace corroded ones.
  2. Repair or completely replace damaged or broken cables.
  3. Ensure signal cables are routed separately from power cables or with appropriate shielding.
  4. Ensure that the bending radii of cables in cable carriers are correct and that they are not subjected to tension.
• Controller and Software Errors:

  Problem: Systematic or random axis position loss, software error on the controller, parameter corruption, G-code errors.

  Detection: Examine the controller’s error history (alarm history). Compare the machine’s original parameters with current parameters. Check if the G-code used is correct and suitable for the machine’s capacity. Run the controller’s internal diagnostics.

  Solution:

  1. Restart the controller. Some temporary software errors can be resolved this way.
  2. Try loading the saved original machine parameters (if a backup exists).
  3. Check the G-code and CAM software. An incorrect tool path may have been generated.
  4. Check if the controller’s firmware is up to date and update if necessary (be careful, this process can be risky).
  5. If you suspect a hardware fault in the controller, contact authorized service.
• Overload and Tooling Problems:

  Problem: Axis position loss, especially during machining, in demanding cuts. Tool breakage, workpiece displacement.

  Detection: Check cutting parameters (feed rate, RPM, depth of cut). Check the sharpness and correctness of the tool used. Check the workpiece clamping method and stability. Evaluate if machining is being performed beyond the machine’s capacity.

  Solution:

  1. Optimize cutting parameters, especially reduce feed rate and depth of cut.
  2. Use sharp and correct tools. Dull tools cause excessive loading.
  3. Ensure the workpiece is securely clamped to the machine table.
  4. If necessary, use a stronger tool holder or a more rigid machining strategy.

Expert Advice

Axis position loss in CNC machines is one of the most frustrating and costly faults that can be encountered on a production line. As seen in this detailed guide, the root of the problem can range from mechanical wear to electronic failures, software errors, and environmental effects. Therefore, a systematic and holistic approach is essential for successful troubleshooting and resolution. Instead of panicking in the event of a fault, following step-by-step checklists, correctly using diagnostic tools, and reviewing past maintenance records are critically important in narrowing down the source of the problem. Adopting preventive maintenance and predictive maintenance strategies, in particular, can ensure that potential axis position loss issues are detected before they arise. Regular mechanical checks, electrical measurements, and periodic verification of drive and controller parameters are the most effective ways to prevent such faults. Furthermore, continuous training of machine operators and maintenance personnel plays a vital role in enabling them to detect fault symptoms early and convey accurate information. It should not be forgotten that sometimes a seemingly simple loose connection or a contaminated encoder can be the main cause of a complex axis position loss problem. Therefore, proceeding patiently and methodically, without overlooking any detail, is the path to success. If the problem cannot be resolved despite all these steps, or if there is a lack of necessary equipment/expertise for fault detection, the most appropriate approach is to contact the manufacturer’s authorized service or specialized industrial automation companies without hesitation. Remember, production continuity and product quality are directly related to correct and timely intervention.