FANUC flexible synchronization: matching speed and aligning phase are separate conditions
Using 0i-F Plus flexible synchronization and automatic phase synchronization, calculate startup phase difference from the area between velocity curves. Equal speed does not remove a position offset automatically, and the next-block waiting condition has a specific scope.
Contents
A stable speed ratio between two axes does not establish the correct angular-position relationship. At synchronization startup, the slave axis must accelerate. The angle it misses during that interval is not recovered naturally by subsequently maintaining the same speed.
Startup acceleration and phase alignment solve different problems
The FANUC 0i-F Plus descriptions manual B-64692EN/01, §1.55.1–1.55.2, pages 66–67 (public mirror of the original manual) describes flexible synchronization and its automatic phase-synchronization function. The latter applies acceleration/deceleration when starting or cancelling synchronization, allowing switching while the master axis is moving, and can establish the required phase relationship using machine-coordinate zero points. Master axis here means the leading axis in synchronization, not necessarily the cutting spindle.
Availability of automatic phase synchronization cannot be inferred merely from availability of basic flexible synchronization. This edition also states that, in automatic operation, the next block waits for startup or cancellation acceleration/deceleration to finish. This must not be expanded into waiting until every phase error has disappeared.
An original example: equal speeds but a remaining 12° phase difference
Take only an ideal rotary-axis model at a 1∶1 ratio, with both axes at 0° at t=0. The master stays at 60°/s, while the slave accelerates linearly from 0 to 60°/s over 0.4 s and then also maintains 60°/s. This linear ramp is an assumed analysis model, not FANUC's actual acceleration/deceleration profile.
| Time | Master angular position | Slave angular position | Position difference |
|---|---|---|---|
| 0.4 s | 60×0.4=24° | ½×60×0.4=12° | 12° |
| 1.0 s | 60° | 12+60×0.6=48° | Still 12° |
From 0.4 s onward the speeds are identical, but the difference stops changing rather than automatically shrinking. Position difference equals the preceding area between the velocity curves; equal speed only stops that area from growing.
Phase correction requires a change in relative motion
Eliminating the 12° difference in this model requires additional relative displacement during some interval, such as the slave moving an extra 12° relative to the master. How to do this and the permitted speeds and accelerations belong to the actual control strategy. The example specifies no compensation method and does not present manual catch-up as a solution.
Diagnosis must therefore examine separately whether the speed ratio has been established and whether the position relationship meets expectations. Equal speed readings at one instant support only the former. Phase difference alone cannot distinguish startup accumulation, a reference offset or a changing synchronization error.
Retain this edition's compatibility limits
Page 67 of the manufacturer's manual states that this automatic phase-synchronization function is ineffective during AI contour control I and II. This limitation is stated only for the cited edition and must not be generalized to every older and newer system. This is an explanation of mechanisms and ideal timing, with no synchronized-axis machine trial. Further synchronization resources are in the OPTION section.