FANUC 31i-B J831: why G30.1 coordinates are not the final floating reference point
Check J831 authorization, the G30.1 intermediate point and the target stored in 1244; separate PS0010 from an unexpected return position.
Contents
A tool-change location near the workpiece can reduce non-cutting travel, but G30.1 does not simply stop at the coordinates written in its block. It visits a programmed intermediate point and then returns to a separately stored floating reference point. Checking only the block coordinates misses both the stored destination and the second leg.
System, option and activation boundary
This article is limited to FANUC Series 31i-B. Page 190 of the official 2024 function catalogue lists A02B-0327-J831 for Floating Reference Position Return. Motion details come from B-64484EN/03, section 6.2, pages 152–153. “/03” is a manual edition, not a minimum software version. No minimum-version table was verified; FANUC or the original builder must confirm retrofit eligibility. Do not transfer this guidance directly to 0i or B Plus.
Provide the complete CNC model, serial number, software series/version and installed-option list. Have the manufacturer confirm authorization, compatibility and whether the machine supports the intended parking or tool-change arrangement. Any addition belongs in its authorized service process, followed by machine configuration and acceptance. No machine-specific installation procedure was verified, so no option file or unlocking parameters are supplied. J831 cannot turn a fixed-position tool changer into one that can change tools anywhere.
Two moves, not one
The format is G30.1 IP_;. IP specifies the intermediate position for the addressed axes, interpreted according to absolute/incremental programming; it is not the floating reference point. In the manual's G30.1 G90 X50.0 Y40.0; example, X50 and Y40 describe the intermediate point. A further move follows to the stored target. This explains syntax, not a ready-to-run program.
The floating reference point is stored in machine coordinates. The manual describes memorizing the current position with [SETFRP] on the current-position display, in parameter 1244. It survives power-off. Reading 1244 checks destination data, not licensing. Do not overwrite it merely to try the function, or mistake [SETFRP] for an option-activation button.
The specified axes rapid-traverse first to the intermediate point and then to the floating reference point. Before using G30.1, the manual requires cancellation of compensation functions such as cutter-radius and tool-length compensation. Builder-required clearance moves, axis sequencing and tool-change interlocks still apply. A collision-free destination does not establish that both travel legs are clear.
Missing-option alarms and other causes
B-64484EN/03, page 30, states that a G code absent from the applicable table or without its corresponding option can produce PS0010, IMPROPER G-CODE. If a 31i-B rejects G30.1, check J831 availability, but PS0010 is neither unique to J831 nor proof that it is missing. Preserve the complete alarm block and compare the target system's code table, software applicability and licensed functions. Do not copy parameters from another machine.
If G30.1 is accepted but reaches an unexpected location, check absolute/incremental interpretation of the intermediate point, the target in 1244 and compensation state. An unalarmed path error is not evidence of an “incompletely enabled” option. The option record and motion data answer different questions.
Acceptance without trial and error
Suppose a program moves from machine A to machine B. Both have confirmed J831, and the programmed intermediate point is unchanged, but B still stores the previous workpiece's floating reference point. This is an analytical example, not a repair report: an identical G30.1 block does not ensure an identical destination, and switching power off does not clear the old target.
Before motion, record the target, coordinate mode, compensation state and full return block. Have the builder or qualified personnel check both rapid-traverse legs and tool-change permission. Use the builder-approved safe verification procedure after checking fixture, workpiece and tool clearance. Do not assume lowering F slows rapid traverse, or use a production workpiece for trial and error.
Sources
The catalogue establishes the option specification; the operator's manual establishes motion and PS0010 conditions. The manual link is a third-party mirror of manufacturer material. No machine test was performed.