FANUC G60 single-direction positioning: why a move to X100 may first reach X95
An intermediate stop in 0i-F single-direction positioning explains how G60 preserves the final approach direction. One-axis calculations show additional travel, why an endpoint bounding box misses overrun, and the difference between one-shot and modal configuration.
Contents
Checking only the start and endpoint of a positioning program can miss intermediate motion introduced by G60. Single-direction positioning keeps the final approach direction consistent, so moves to the same endpoint can follow different intermediate motions when starting from opposite sides.
The controlled objective is the final approach direction
The 0i-F machining-center manual B-64604EN-2/01, §3.1, pages 16–18 (public mirror of the original manual) explains that the configuration associated with 5440 determines G60 overrun and positioning direction. A temporary stop occurs before the endpoint even when the initial motion direction matches the specified direction. This article analyzes one linear axis and provides neither a parameter setting nor a sign convention for writing it.
Recalculate travel with a known approach direction
Assume target X=100 mm and a confirmed configuration that makes the final 5 mm approach along +X. The corresponding intermediate position is X=95 mm. This is a path model with the mechanical direction already assumed; it does not mean a positive parameter value produces that direction on every machine.
| Starting position | Position sequence in the model | Total travel |
|---|---|---|
| X=20 | 20→95→100 | 75+5=80 mm |
| X=120 | 120→95→100 | 25+5=30 mm |
A direct move from 120 to 100 needs only 20 mm. The second row adds 10 mm because it first passes the endpoint by 5 mm, then reverses for 5 mm. Passing the endpoint is defined relative to the initial direction from 120 toward 100; the final approach remains +X.
Why checking the endpoint is insufficient
Both programmed endpoints in the second row lie within [100,120], but the modeled path reaches 95. If an obstacle or boundary lies near X=97, endpoints inside the permitted area do not prove the full positioning path is feasible. Multi-axis moves also require identification of the positioning interpolation type. This example does not assume that an intermediate path in two or three dimensions is necessarily straight.
G60 is therefore not a universal remedy for mechanical backlash. It constrains the approach method; actual errors still need to be distinguished by measurement. Validation should record the full position changes and endpoint repeatability when approaching from both sides, not just a single endpoint reading.
Program transfer also requires checking for modal behavior
The same chapter specifies that 5431#0 MDL selects one-shot G60 or its modal form in group 01. Comparing only the line containing G60 can miss whether later blocks remain affected. Single-direction positioning is also not performed on an axis with zero overrun or zero commanded travel. These boundaries must be matched to the current configuration; one move without a detour does not establish function failure.
This article concerns basic positioning behavior and configuration. Inclusion in the OPTION section does not imply that this function must be purchased separately on every model.