1. Introduction
The positioning accuracy of CNC machines directly depends on the state of the ball-screw transmission (BSP). A sudden increase in backlash in the system is a critical failure, leading to missing parts and halting the production process. In closed-loop systems using the Heidenhain ROD52910130500 encoder, this condition manifests itself as a constant following error that exceeds the set tolerances. This analysis takes a systematic approach to diagnosing backlash caused by loss of preload, contamination, and lubrication failure.
2. Overview of the component and operating conditions
The ball-screw transmission ensures the transformation of the rotational movement of the engine into linear movement of the working body of the machine. The Heidenhain ROD52910130500 encoder, mounted directly on the motor shaft or through an intermediate coupling, reads the angular position, which the control system interprets as linear position. Operating conditions include high cyclic loads, operating temperatures up to 60°C and exposure to process environments.
3. Evidence of refusal
Technical examination revealed the following symptoms:
- Measured backlash in mechanical transmission: 0.045 mm (manufacturer's tolerance: < 0.005 mm).
- Vibration analysis: an increase in amplitude at frequencies multiples of the ball pass frequency, which indicates wear of the raceways.
- Thermographic study: local heating of the KGP nut is 18°C higher than the temperature of the screw.
- Data from ChPC: systematic excess of tracking error when changing the direction of movement (reverse).
4. Study of root causes
The Ishikawa diagram (fishbone diagram) technique was used for the analysis, focusing on the factors: mechanics, environment, lubrication, operation. According to ISO 230-1, geometric accuracy tests were performed and confirmed that the error is the result of accumulated mechanical wear and not a control loop error.
5. Identified root causes
- Loss of pretension (probability 50%): Natural stress relaxation in the ball mounting system or uneven wear of the tracks, which leads to the appearance of gaps in the contact zone.
- Contamination (probability 30%): Penetration of metal shavings or finely dispersed abrasive through damaged nut seals. This causes abrasive wear of rolling surfaces.
- Lubricant Degradation (20% chance): Oxidation or loss of viscosity of the lubricant, causing extreme friction and increased heating, accelerating wear.
6. Corrective actions
To restore performance, the following steps must be performed:
- In the short term: Flushing the KGP nut with a specialized solvent to remove impurities and replacing the lubricant with the one recommended by the manufacturer (NLGI class 2, compatible with high loads). Nut preload adjustment (requires a precision gauge).
- Long-term: Replace nut seals with new ones to prevent further contamination. Installing an automatic lubrication system or reviewing manual service intervals.
7. Diagnostic checklist for technicians
| № | action | Tool |
|---|---|---|
| 1 | Checking the gap in the nut | Clock type indicator (0.001 mm) |
| 2 | Inspection of nut seals | Visual inspection / endoscope |
| 3 | Analysis of the condition of the lubricant | Visual / microscopic inspection for the presence of chips |
| 4 | Measurement of axial backlash | Dynamometer |
| 5 | Checking the temperature of the nut | Infrared thermometer |
| 6 | Checking the integrity of the engine clutch | feelers |
| 7 | Diagnostics of the ROD 529 encoder | Oscilloscope (A/B signal levels) |
| 8 | Checking the presence of noises during movement | Stethoscope |
8. Prevention strategy
To ensure a long service life of the KGP (MTBF > 20,000 hours), it is necessary to implement:
- Weekly visual inspection of seals.
- Monthly inspection of the condition of the lubricant and the level of contamination.
- Every 500 hours of operation: geometric accuracy control according to ISO 230-1.
- Installation of automated lubrication systems with pressure control.
9. Conclusion
Increasing backlash in a ball-screw transmission is a progressive process that requires timely intervention. Regular diagnostics and compliance with lubrication regulations allow you to avoid emergency failure. For replacement parts, precision lubricants and components for upgrading positioning systems, please refer to the UNITEC-D E-Catalog.
10. Links
- DSTU ISO 230-1:2018 Machine testing. Part 1.
- ISO 3408-1:2006 Ball screw gears.
- Heidenhain ROD 529 operating instructions.
- Handbook of Failure Analysis for Industrial Components.
