FANUC 0i-F diagnoses 360–363: why subtracting command and feedback totals does not identify a fault
Separate NC commands, compensation, SV reception and feedback. Check the power-on period, axis and detection unit before comparing pulse records, and avoid treating cumulative counts as machine coordinates or machining errors.
Contents
During a maintenance handover, different numbers in two diagnosis screenshots can quickly become a claim that the servo has lost pulses. That conclusion is premature if the records come from different power-on periods, or if an NC movement-command total is compared with an SV received total that includes compensation. Diagnoses 360–363 help organize evidence along the command chain, but do not justify a replacement decision without the acquisition context.
Scope: what each quantity records
This article follows the FANUC Series 0i-MODEL F Maintenance Manual B-64605EN/01, section 1.3.2, printed page 26. It covers matching 0i-F configurations only; identical definitions are not assumed for other series or F Plus. All four entries use detection units, have a two-word data type and a stated valid range of −99999999 to 99999999. This is a data range, not permissible mechanical travel.
| Diagnosis | Recorded quantity | Distinction to preserve |
|---|---|---|
| 360 | Movement commands distributed by the CNC since power-on, accumulated | NC-side movement commands |
| 361 | Compensation pulses distributed by the CNC since power-on, accumulated, including backlash and pitch-error compensation | Compensation is recorded separately |
| 362 | Movement and compensation pulses received by the servo system since power-on, accumulated | SV reception includes compensation |
| 363 | Position-feedback pulses received by the servo system from the pulse coder since power-on, accumulated | A feedback-side record |
First check: do the records share a reference period?
“Since power-on” is central to interpreting these numbers. Our suggested record includes the machine ID, CNC model and software version, path and axis, acquisition time, whether the last power-on time is known, and whether the axis was moving when recorded. If the power-on time cannot be established, mark it unconfirmed rather than infer it from the size of a number.
Yesterday's 360 reading before shutdown and today's 363 reading after power-on are not a suitable pair for calculating a command/feedback difference. Likewise, photographing one screen and another later does not establish simultaneous sampling. Check the sequence using existing records that you are authorized to obtain; do not move a faulty machine simply to complete the record.
Second check: has the comparison omitted compensation?
360 and 362 describe different quantities, so 361 must not silently disappear from the analysis. Consider this hypothetical illustration of accounting scope: on the same axis during one power-on period, 360 reads 100000, 361 reads 20 and 362 reads 100020. Subtracting 360 from 362 gives 20, but calling that difference “20 extra pulses of travel” ignores the recorded compensation.
This is not field data or a manufacturer formula guaranteeing that 360 + 361 strictly equals 362 at every screen refresh. The cited page defines the entries; it does not guarantee synchronized screen sampling or provide a universal difference tolerance. Establish timing and configuration before qualified personnel investigate using the matching servo documentation. Do not turn the example into an automatic rejection rule.
Third check: a feedback count is not a part-accuracy report
If 362 and 363 match, you can record that the observed values match. This does not establish that the ballscrew, coupling, workholding and machined dimensions all pass inspection. Conversely, differing values do not identify a failed encoder or amplifier without acquisition timing, alarms and machine configuration.
Before converting a reading to distance or angle, establish the detection unit and axis type from valid documentation for that machine. Do not assume that one count always means 1 μm. Where the unit is unconfirmed, keep the raw reading and unit field and mark conversion as pending verification rather than present a precise but unsupported millimetre value.
Building a useful maintenance handover
- Retain the four original screens, axis identification and acquisition times, together with the full alarm text present at the time.
- Identify records from the same power-on period, screenshots that were not simultaneous, and configuration details still unchecked.
- Separate observed differences from possible causes. If 361 is missing, write “compensation record missing,” not “compensation is zero.”
- Limit the next task to checking matching servo documentation, existing parameter backups and maintenance-change records. Trial operation, parameter writes and hardware inspections require the machine's separate approval and safety procedures.
This is a read-only interpretation method, not a report of machine testing. It provides no parameter-adjustment values or instructions for bypassing protection, connecting or disconnecting while energized, or forcing outputs. Do not power-cycle, clear alarms or alter compensation to create matching numbers. If danger is present, follow the machine's emergency procedure first.
Source
FANUC Series 0i-MODEL F Maintenance Manual B-64605EN/01, section 1.3.2, printed page 26, diagnoses 360–363. This is a third-party public mirror of a FANUC-authored manual, not an official FANUC download site. The checklist, numerical example and limits on inference are our analysis of the entries, not additional manufacturer acceptance criteria.