FANUC SP9036 Alarm 36: Error Counter Overflow and Troubleshooting

FANUC SP9036 means that the spindle amplifier position error counter overflowed. The CNC displays SP9036 / SSPA:36 OVERFLOW ERROR COUNTER, while the spindle amplifier displays alarm 36.

FANUC's detailed spindle-amplifier maintenance procedure identifies two main causes: an excessively large or incorrect spindle-to-motor gear-ratio setting, and an incorrect position-gain setting for the active position-control mode. A sequence problem can also cause the alarm if spindle motor excitation is removed by turning off SFR/SRV while the spindle remains in a position-control mode.

For the surrounding alarm numbers, see the FANUC Spindle Alarm Codes SP9034–SP9092.

What Does FANUC SP9036 Mean?

In a spindle position-control mode, the controller continually compares commanded spindle position with feedback position. The difference is accumulated in a position error counter. SP9036 is generated when that counter exceeds the range that the spindle control can process.

The alarm therefore indicates an excessive internal position error value. It does not, by itself, prove that the spindle amplifier, motor, position coder or feedback cable is defective. FANUC's alarm 36 procedure first directs the technician to the gear-ratio parameters, the applicable position-gain parameters and the control sequence.

The operating condition at the instant of the alarm is essential. The relevant parameter group differs depending on whether SP9036 occurs during:

• Spindle orientation

• Servo mode, including rigid tapping or spindle positioning

• Spindle synchronous control

• Cs contouring control

• A transition into or out of one of these position-control modes

• A change in SFR/SRV, gear selection or clutch selection

Do not begin by changing every parameter from 4056 through 4072. First identify the active mode and selected gear range.

Why Gear Ratio and Position Gain Affect the Error Counter

The spindle control must convert motor motion into spindle motion. If the programmed gear ratio does not match the actual gear, belt, clutch or direct-drive relationship, the calculated spindle position will not agree with the feedback position. The resulting error can accumulate until the counter overflows.

Position gain determines how strongly the position loop commands speed to eliminate position error. FANUC B-65280EN shows, for spindle synchronous control at constant speed, that the expected position error is inversely related to position gain:

Position error pulses = spindle speed / 60 × 4096 / position gain

This relationship explains why a position gain that is too low for the operating condition can produce a large steady position error. However, position gain cannot be increased without limit. An excessive value can cause vibration, overshoot or unstable motion. The correct value depends on the spindle, motor, load inertia, velocity-loop adjustment, gear ratio and control mode.

For that reason, alarm 36 must be handled as a controlled parameter and sequence diagnosis—not as permission to raise or lower gain by trial and error.

Important Note About FANUC's Two Published Gain Instructions

Some FANUC CNC alarm lists summarize SP9036 with the instruction to check whether the position gain is too large and correct it. The detailed αi and αi-D spindle-amplifier maintenance procedures give a more specific sequence: first check whether an excessively large gear ratio has been set; if the gear-ratio data is correct, increase the applicable position gain.

These statements should not be combined into a universal instruction to increase or decrease every gain value. Use the maintenance manual that applies to the exact CNC, spindle amplifier and spindle software. Compare the current setting with the approved machine backup and the applicable B-65280EN parameter table before making a change.

The safest practical rule is:

1. Verify the actual mechanical ratio and selected gear data first.

2. Identify the exact position-control mode and active CTH1/CTH2 range.

3. Compare the active gain with the documented machine value.

4. If the applicable detailed FANUC procedure calls for an increase, raise only that selected gain in controlled steps while observing spindle stability.

5. If the value is already above the documented setting or the spindle vibrates, stop and investigate the configuration and loop adjustment rather than increasing it further.

1. Record When SP9036 Occurs

Before changing any parameter, reproduce the alarm only under a safe, controlled condition and record:

• Complete CNC series and model

• Complete spindle amplifier model and suffix

• Complete spindle motor and spindle sensor models

• Spindle software series and edition, when available

• Whether the alarm occurs during orientation, rigid tapping, spindle positioning, spindle synchronization or Cs contouring

• Commanded spindle speed and actual spindle speed

• Selected physical gear or clutch range

• PMC states of CTH1 and CTH2 at the time of the alarm

• State and transition timing of SFR/SRV

• Whether the alarm began after a parameter reload, amplifier replacement, motor replacement, gearbox work or ladder modification

Back up the current CNC, PMC and spindle parameters before editing anything. Keep the backup from the affected machine separate from files belonging to similar machines.

If SP9036 appears in only one gear or only one position-control mode, that pattern strongly narrows the diagnosis to the ratio, gain or selection data used by that condition.

2. Verify the Actual Spindle-to-Motor Gear Ratio

For the FANUC series covered by B-65285EN/04, parameters 4056–4059 contain the spindle-to-motor gear-ratio data. Series 15i uses the corresponding range 3056–3059.

The four values normally represent high, medium-high, medium-low and low ranges:

Confirm all of the following:

• The actual spindle speed and motor speed produce the expected mechanical ratio.

• The ratio numerator, denominator and setting resolution follow the applicable parameter manual.

• The physical gear or clutch position agrees with the CTH1/CTH2 state.

• The ladder does not select the next range before the mechanical shift is complete.

• A parameter backup from a machine with a different gearbox was not loaded.

• Direct-drive, belt-drive and geared configurations have not been treated as interchangeable.

FANUC specifically instructs technicians to check whether an excessively large gear ratio has been set. Do not simply reduce the value until the alarm disappears; calculate the actual ratio and enter it in the format required by the exact spindle series.

An incorrect gear ratio can also create unexpected spindle behavior during orientation. B-65280EN warns that an improper ratio may prevent the spindle from stopping at orientation. Keep the machine ready for an emergency stop during controlled verification.

3. Confirm the Active Gear-Selection Signals

Correct numbers in 4056–4059 are not sufficient if the control is selecting the wrong member of the group. Monitor the PMC states of CTH1 and CTH2 while the machine changes ranges and while the alarm occurs.

Compare three items at the same moment:

1. The actual mechanical gear or clutch position

2. The spindle and motor speeds

3. The CTH1/CTH2 combination shown by the PMC or spindle monitor

If the machine is mechanically in low gear but the control selects the high-gear ratio and gain, the position calculation can be wrong even though every stored value looks reasonable when viewed separately.

Check the machine builder's gear-change confirmation signals, contactors or hydraulic shift confirmation, and ladder timing. Do not rewrite the ladder merely to force CTH1/CTH2 into the expected state; find why the commanded and confirmed gear states disagree.

4. Check the Position-Gain Group for the Active Mode

After the gear ratio and gear selection are confirmed, inspect only the position-gain group used by the operating mode in which SP9036 occurs.

Within each group, the applicable value is selected according to the gear-range signals. For the cited αi parameter manual, the high, medium-high, medium-low and low entries correspond to the CTH1/CTH2 combinations shown above.

Examples:

• SP9036 during high-range spindle orientation directs attention to the active orientation gain, commonly 4060 on the cited configuration—not to 4065 or 4069.

• SP9036 during low-range rigid tapping directs attention to the applicable servo-mode gain selected from 4065–4068 and the matching gear-ratio entry.

• SP9036 during spindle synchronization requires checking the applicable 4065–4068 values for both participating spindles, the selected ratios and the synchronization sequence.

• SP9036 during Cs contouring requires the applicable 4069–4072 gain, not the ordinary orientation gain.

Parameter numbers and selection rules can differ with CNC generation, spindle series and optional functions. Use the B-65280EN edition and CNC manual that match the installed system.

5. Adjust Position Gain Only After the Ratio Is Confirmed

FANUC B-65285EN/04 and the later αi-D maintenance procedure state that, when the gear-ratio data is correct, the applicable position gain should be increased. Perform this only with the exact machine data and a controlled commissioning procedure.

Before any increase:

• Confirm that the active value was not accidentally restored as 0 or an abnormally low number.

• Compare it with the machine builder's approved backup.

• Confirm that the spindle velocity loop has been adjusted correctly.

• Check for abnormal vibration, mechanical looseness, backlash or excessive inertia.

• Verify that the selected gain corresponds to the actual CTH1/CTH2 state.

• Record the original value and change only one confirmed parameter at a time.

Increase the value in small, documented steps only when the applicable manual calls for it. Test first at low speed and without cutting load. Stop immediately if vibration, hunting, overshoot, abnormal noise or unstable spindle motion appears.

Do not copy FANUC's standard initial values blindly. The standard values in B-65280EN are references for specified configurations; the final machine setting depends on the spindle mechanics and tuning completed by the machine builder.

6. Check SFR/SRV and the Position-Control Sequence

FANUC lists a sequence error as the second main direction for alarm 36. The maintenance manual instructs technicians to check whether the motor is deactivated by turning off SFR/SRV while a position-control mode is active.

This can matter in:

• Rigid tapping

• Spindle positioning or servo mode

• Cs contouring control

• Spindle synchronous control

In these modes, SFR/SRV may serve not only as a rotation-direction command but also as the spindle motor excitation enable, depending on the related parameter setting. If excitation is removed while position commands or synchronization remain active, the motor cannot correct the accumulating position error. Restoring excitation can then cause a large correction demand or alarm.

Review the machine builder's ladder and CNC connection manual to confirm:

• The position-control mode is entered only after the required ready and excitation conditions are established.

• SFR/SRV does not turn off unexpectedly while the position loop remains active.

• Rigid tapping, Cs control or spindle synchronization is cancelled in the documented order before motor excitation is removed.

• Gear or clutch changes do not interrupt excitation at an invalid point in the position-control sequence.

• Emergency-stop and alarm-reset behavior follows the applicable FANUC and machine-builder sequence.

Do not bypass SFR/SRV, ready signals, interlocks or safety circuits to keep the motor excited. Correct the control sequence according to the machine documentation.

7. Perform a Controlled Retest

After correcting the confirmed ratio, gain or sequence problem:

1. Verify that all edited parameters have been recorded and that the intended gear range is selected.

2. Power cycle or reset the system only as required by the applicable manual.

3. Test the spindle at low speed with no cutting load.

4. Repeat the exact mode that previously generated SP9036.

5. Monitor spindle speed, motor speed, CTH1/CTH2, SFR/SRV and available position-error diagnostics.

6. Confirm stable operation in every gear range that uses a separate ratio or gain value.

7. Complete rigid-tapping, synchronization, Cs or orientation accuracy checks required by the machine builder.

If a different alarm appears, diagnose the number actually displayed. Do not continue adjusting SP9036 parameters to clear an unrelated detector, overload, synchronization or excessive-error alarm.

What Not to Do for SP9036

• Do not increase or decrease all position-gain parameters together.

• Do not change gain before verifying the actual mechanical gear ratio.

• Do not assume the physical gear range from commanded speed alone; confirm CTH1/CTH2 and the shift mechanism.

• Do not copy parameters from another machine with a similar spindle motor.

• Do not replace the spindle amplifier as the first response to alarm 36.

• Do not bypass SFR/SRV, ladder interlocks or machine safety functions.

• Do not test a changed gain immediately at maximum speed or under cutting load.

• Do not treat SP9036 as the same alarm as a position-coder disconnect or signal fault.

If the documented parameter and sequence checks are correct but the measured motion or feedback is inconsistent, continue diagnosis using the exact symptoms and any accompanying alarm. A feedback or hardware fault requires separate evidence; it is not the primary repair stated for alarm 36.

Difference Between SP9035, SP9036 and SP9050

SP9035 is a parameter-range alarm. SP9036 can occur even when each parameter is within its permitted numerical range but the value, selected gear or operating sequence is wrong for the machine. SP9050 is specifically an internal spindle-synchronization calculation overflow and has a different troubleshooting procedure.

Difference Between SP9036 and Rigid-Tapping Error-Counter Alarms

FANUC CNC manuals also list rigid-tapping alarms such as SV0413 for tapping-axis LSI overflow and SP0742 for spindle-side LSI overflow on applicable CNC generations. These alarms are not interchangeable with serial spindle-amplifier alarm 36.

Always identify where the alarm originates:

• SP9036 / amplifier 36: spindle amplifier error counter overflow procedure

• SV0413: servo-side tapping-axis error counter overflow

• SP0742: CNC spindle-side rigid-tapping LSI overflow on applicable systems

The operating event may be the same rigid-tapping cycle, but the displayed number determines which manual and parameter set should be used.

FANUC SP9036 Diagnostic Table

Recommended Troubleshooting Order

1. Confirm SP9036 / SSPA:36 on the CNC and alarm 36 on the spindle amplifier.

2. Record the exact CNC, amplifier, motor, sensor, spindle software and machine configuration.

3. Identify whether the alarm occurs during orientation, rigid tapping, spindle positioning, spindle synchronization or Cs contouring.

4. Back up the CNC, PMC and spindle parameters.

5. Measure or calculate the actual spindle-to-motor ratio for the affected gear.

6. Verify parameters 4056–4059 and confirm that CTH1/CTH2 select the physically engaged gear.

7. Check only the gain group used by the active mode: 4060–4063, 4065–4068 or 4069–4072.

8. Compare the active value with the approved machine backup and applicable B-65280EN table.

9. If the detailed manual for the installed system calls for it, increase only the confirmed gain in controlled steps while monitoring stability.

10. Review the ladder to ensure SFR/SRV does not remove excitation while the position-control mode remains active.

11. Retest at low speed and no load, then complete the machine builder's full functional verification.

Technical References

• FANUC AC Servo Motor αis/αi Series, AC Spindle Motor αi Series, Servo Amplifier αi Series Maintenance Manual, B-65285EN/04, Alarm Code 36

• FANUC Spindle Motor αi-D/αi-B/αi Series, AC Spindle Motor βi-B/βi Series, Built-in Spindle Motor Bi-B/Bi Series Maintenance Manual, B-65555EN/02, Alarm Code 36

• FANUC AC Spindle Motor αi/βi Series and Built-in Spindle Motor Bi Series Parameter Manual, B-65280EN, gear-ratio parameters, position-gain parameters and position-control sequences

• Applicable FANUC CNC Maintenance Manual and Connection Manual (Function) for spindle position-control signals and ladder timing

• Machine-builder parameter backup, gearbox documentation and commissioning procedure

• Beijing FANUC SP9036 technical guidance, error counter overflow

Always use the manual edition that applies to the exact CNC, spindle amplifier, spindle software, motor, detector, gearbox, position-control function and machine.

Need Help With FANUC SP9036 Alarm?

REACO CNC provides independent FANUC spindle diagnosis, parameter review, amplifier testing, repair, compatibility checking and replacement support. Send us the CNC alarm screen, spindle amplifier display, complete CNC and amplifier models, spindle motor model, the operating mode and gear in which SP9036 occurs, and a current parameter backup.

Visit the FANUC Technical Support Center for more FANUC alarm guides, browse FANUC servo, spindle and power drives, or contact REACO CNC for assistance.

Reference Source: Beijing FANUC. This article is based on FANUC technical documentation. The correct parameter numbers, adjustment direction, signal sequence and commissioning procedure depend on the exact CNC and spindle configuration.