CNC Machine Parts: X-axis Fault Repair

Repair of Excessive X-Axis Clearance Fault

Symptom: A CNC machine tool using the FANUC OMC model XH754 is experiencing excessive clearance on the X-axis.

Analysis and Resolution: The X-axis clearance can result from several factors, including coupling play, bearing clearance, lead screw backlash, and mechanical elastic deformation. After removing the X-axis guard plate and turning off the power, the operator manually turned the lead screw and felt a noticeable free movement, indicating a significant gap. Adjusting the bearing clearance by tightening the nut showed no improvement, so the issue was suspected to be with the lead screw nut. Further inspection revealed that the inner rings of the two-point contact bearings (back-to-back configuration) were tightly pressed together, which normally should allow for some adjustment. To address this, a small ring washer of 1mm thickness was inserted between the outer diameters of the bearings, creating an 0.8mm clearance in the inner rings. After reassembly and proper tightening of the bearing lock nut, the X-axis clearance was measured at 0.02mm with a dial indicator. By setting parameter 0535 to 15, the clearance was reduced to 0.01mm, effectively eliminating the problem.

Repair of X-Axis Encoder Alarm Fault

Symptoms: During operation, a CNC machine using the FANUC OMC model XH754 triggers an alarm “319” related to the X-axis.

Analysis and Resolution: According to the maintenance manual, the fault is likely due to an abnormal pulse encoder or a communication error. Checking diagnosis number 760, multiple positions were found to be active, suggesting a faulty encoder or feedback cable. Initially, the M185 connector for the X-axis encoder was tested and found normal. Therefore, it was concluded that the X-axis serial encoder was defective. To confirm, the cables M184 and M194, as well as M185 and M195, along with the three-phase drive lines for the motor, were swapped. This resulted in the alarm changing to “339,” indicating a Z-axis issue, confirming the X-axis encoder was faulty. Replacing the encoder resolved the problem.

Repair of Overtravel Alarm Fault

Symptoms: A CNC machine using the FANUC OMC model XH754 generates an “OVER TRAVEL-X” alarm when the X-axis returns to zero.

Analysis and Resolution: Upon checking, the X-axis was not near the physical limit, but the displayed X-coordinate exceeded the axis range, confirming it was a soft limit overtravel alarm. Parameter 0704 was checked and found to be normal. The machine was then powered off, and while holding down the P key, the NC power was turned on, allowing the axis to return to zero without the system checking the soft limit. Alternatively, parameter 0704 could be temporarily set to -99999999, perform the return-to-zero operation, and then reset to the original value. Another method involved pressing the P key and CAN key simultaneously to power on and clear the alarm. These steps successfully resolved the overtravel issue.

Manhole Cover

Manhole Cover,Square Cast Iron Manhole Cover,Ductile Cast Iron Cover,Cast Manhole Cover

Wuan Jianfeng Casting Co., Ltd. , https://www.hbjfcasting.com