Meaning
Frictional heating during rapid linear positioning causes metallic drive components to elongate along their axis of travel. Precision motion systems suffer from positioning drift when ball screw expansion alters the effective lead pitch of the thread during high-speed feed movements. Drive controllers correct for this physical growth using optical linear encoders or software compensation algorithms based on thermal modeling.
The measurement boundary applies to mechanical feed drives in machine tools, terminating where direct linear scale feedback renders mechanical growth irrelevant to axis accuracy.
Displacement Mechanism
Rotary movement creates friction at the contact points between bearing balls and raceway grooves. As feed velocity and duty cycle increase during volume production, ball screw expansion increases axial positioning errors along the full travel length. Uncorrected thermal elongation causes workpiece features to shift relative to origin datum points.
Positioning Verification
Laser interferometer testing according to ISO 230-2 protocols isolates thermal drift from mechanical backlash. Engineers measure ball screw expansion during endurance runs to map linear thermal growth across five hundred millimeter travel intervals. Declaring axis readiness based solely on cold laser calibration leads to out-of-tolerance parts once production machining starts.
Demonstration of thermal stability requires testing drive axes under continuous duty profiles that reflect actual factory cycle times rather than vendor static specifications.
Thermal Compensation
Dual-anchor pretensioning reduces growth by mechanically restraining shaft ends. When ball screw expansion exceeds pre-load limits, software pitch error tables update values in real time. Hollow shaft internal liquid cooling dissipates heat at the generating source during ball screw expansion.
