AiVibeBacklash (Reversal Error)
Backlash is lost motion that occurs when a machine axis reverses direction, caused by clearances and elasticity in the drive train such as the ball screw and nut, bearings, couplings, gears or belts.
When an axis changes direction, any clearance in the mechanical chain between the motor and the slide must be taken up before the slide moves, so the slide lags the command by a small amount. Sources include clearance in the ball screw nut, axial play in support bearings, couplings, gearboxes and belt drives, plus elastic deformation under load. Backlash appears as a reversal value in ISO 230-2 positioning tests and as step-like reversal spikes in ballbar plots.
Backlash affects circular and contour accuracy, especially at quadrant changes where an axis reverses, and can produce visible marks on circular features and steps on surfaces. It also matters for climb milling, where cutting forces can pull the table through the clearance on machines without preloaded drives.
CNC machines use preloaded ball nuts to minimise mechanical backlash, and controls apply backlash compensation by adding a correction when an axis reverses. Linear scales measuring slide position directly reduce the influence of screw errors. Compensation is a correction, not a cure; increasing backlash over time usually indicates wear and is a reason for inspection and repair, which should follow OEM documentation.
Key points
- Lost motion when an axis reverses direction
- Caused by clearance in screws, nuts, bearings, couplings and gears
- Measured as the reversal value or seen as reversal spikes on ballbar plots
- Controls compensate, but growing backlash indicates wear
Where AiVibe comes in
AiVibe designs and manufactures the AiAmbA AI Factory: edge devices plus AI agents that let people talk to CNC, PLC and robot controllers in plain language. Agents only propose changes, and a trained operator confirms each one.