At the panel, the practical fault is simple: the Excel PMC 10T24 powers up with a Fanuc 21-M, but you do not have a verified operating or recovery sequence for the side-mount toolchanger. Start by identifying the changer’s present mechanical state and every active interlock. Do not test guessed commands, alter parameters, or force outputs; the machine builder’s PMC ladder—not the Fanuc control alone—defines the sequence.
Read the symptoms before commanding motion
Start here. Record what the changer does at power-up and what appears on the control when you request a tool change through a documented machine function.
| Symptom | Likely area to inspect |
|---|---|
| No toolchanger motion and no output indication | Missing operating condition, active interlock, unrecognized command, or PMC sequence not starting |
| An output turns on but the mechanism does not move | Machine-side power, valve, contactor, actuator, pressure source, or mechanical obstruction |
| The changer starts and stops at one step | Expected confirmation input did not change, motion timed out, or the mechanism is between positions |
| Manual functions work but an automatic cycle does not | Sequence prerequisite, tool data, spindle orientation, axis position, or automatic-mode interlock |
| The changer is visibly out of position at power-up | Interrupted cycle requiring controlled recovery, not a normal automatic command |
Check the CNC alarm screen, machine alarm or message screen, PMC diagnostic display, and any toolchanger recovery page supplied by the builder. Photograph the mechanism and record displayed tool numbers before moving anything. If the spindle, arm, magazine, or tool pot is between positions, treat the machine as an interrupted sequence.
Understand what the Fanuc control does
The Fanuc 21-M provides the CNC platform, but the machine builder normally implements the automatic toolchanger in the programmable machine control. The PMC accepts a tool-change request, tests permissives, energizes machine outputs, and waits for position-confirmation inputs before advancing.
A typical side-mount changer may involve spindle stopping and orientation, axis positioning, magazine indexing, pot movement, tool unclamping, arm motion, tool clamping, and return-to-home confirmation. That describes the control architecture, not the confirmed sequence of this machine. Read the ladder and electrical drawings to determine which operations and devices the Excel PMC 10T24 actually uses.
One missing input can hold the sequence even when the mechanism looks correctly positioned. Common prerequisites include referenced axes, an allowed machine mode, spindle-ready status, adequate pneumatic or hydraulic pressure where fitted, closed guards, magazine-home feedback, arm-home feedback, and valid clamp status. The decisive test is whether each required PMC input changes state at the expected mechanical position.
Recover the changer in a controlled sequence
- Secure the work area. Remove loose tools and workpieces from the changer envelope. Keep personnel clear of the arm, spindle, magazine, and tool pots. Stored pneumatic, hydraulic, spring, and gravity energy can move the mechanism unexpectedly.
- Identify the physical state. Note whether a tool is in the spindle, arm, or magazine. Check whether the arm is home, whether a pot is extended, and whether the spindle appears clamped. Do not infer sensor state from appearance alone.
- Capture the control state. Record every alarm and machine message without clearing it first. Inspect the PMC diagnostic display for inputs associated with home, clamp, pot, magazine, pressure, guards, and spindle conditions. Use the electrical documentation to map field devices to PMC signals.
- Verify basic machine prerequisites. Confirm that emergency-stop circuits are reset, required machine power is available, axes are referenced if the builder’s sequence requires it, and the spindle is stopped. Check supply pressure against the machine documentation rather than guessing a setting.
- Use the builder’s recovery functions. Select the documented manual or recovery mode. Move only one recovery step at a time, watching both the mechanism and the corresponding feedback input. Stop if an output operates without the expected input transition.
- Reconcile tool positions. Compare the physical tool in each occupied station with the tool number displayed by the control. Correct the assignment only through the builder’s documented tool-management procedure. Changing a displayed number cannot correct a mechanically misplaced tool.
- Return every mechanism home. Establish the documented home states for the arm, magazine, pot, clamp, and related devices. Confirm the PMC sees those states before requesting an automatic cycle.
- Run the documented command. Use the machine builder’s specified command and prerequisites. The evidence identifies no command code, so obtain it from the operation manual, ladder comments, or official support rather than assuming a generic code.
If no documentation is available, use the PMC ladder as the sequence map. Trace from the tool-change request through the permissive contacts to the first output, then follow each completion input to the next rung. Perform live checks only if you are qualified to work around energized industrial equipment.
Verify the complete automatic cycle
First test with the spindle and magazine clear of avoidable collision risks. Use reduced operating speed or single-step facilities only when the machine provides documented support for them.
- Confirm the requested tool station agrees with the magazine position before motion begins.
- Watch each commanded output and its return input. A position input should change because the mechanism reached its limit, not because the signal was bypassed.
- Confirm the spindle clamp state before allowing the arm to leave the exchange position.
- Verify the arm and pot return home before permitting axis or spindle operation.
- Run several changes involving different magazine positions. A single successful exchange does not prove that indexing, tool records, and every station are correct.
- After testing, inspect tool retention, magazine seating, abnormal noise, air or oil leakage, and any new alarm history.
A valid repair completes the cycle repeatedly without forced signals, altered interlocks, manual assistance, or disagreement between physical and displayed tool locations.
Avoid fixes that create a second fault
Parameter changes are not the first check. They waste time when a home sensor, pressure permissive, guard circuit, or interrupted mechanism is blocking the PMC sequence. They can also remove the machine-specific configuration needed for recovery.
- Do not load parameters from a different machine or toolchanger. Similar model names do not establish compatible axes, magazine counts, ladder logic, options, or data assignments.
- Do not force PMC inputs to imitate home or clamp feedback. The control may advance into a collision because the mechanical device never completed its movement.
- Do not energize solenoids or contactors solely to discover what moves. Use the electrical drawing to identify the load and confirm that the next motion is mechanically safe.
- Do not rotate the magazine until you have recorded its physical and displayed positions. Uncontrolled indexing can corrupt the tool-location relationship.
- Do not repeatedly clear an alarm without recording which sequence step generated it. That removes the most useful clue.
- Do not treat every toolchanger problem as a CNC fault. If the PMC output operates correctly, continue diagnosis through the field wiring, actuator, supply, sensor, and mechanism.
FAQ
How do I start diagnosing an Excel PMC 10T24 toolchanger?
Record the alarms, physical tool locations, arm and pot positions, and PMC input states first. Determine whether the changer is home or stopped partway through a cycle before requesting motion.
How do I find the tool-change sequence on a Fanuc 21-M?
Use the machine builder’s operation manual, electrical drawings, ladder comments, and PMC diagnostic display. The builder’s PMC logic defines the interlocks and outputs; the controller model alone does not define the sequence.
How do I recover a side-mount toolchanger stuck mid-cycle?
Use the documented recovery mode and move one step at a time while verifying each feedback input. Do not run an automatic command until the arm, magazine, pot, clamp, and displayed tool locations agree with their physical states.
How do I know when to stop troubleshooting the toolchanger?
Stop if the mechanism cannot be positively identified, an output produces unexpected motion, the ladder or electrical drawings are unavailable, or recovery would require bypassing an interlock. Preserve the alarms, PMC states, parameter backup, and photographs, then escalate to official machine-builder or Fanuc support with the Excel PMC 10T24 and Fanuc 21-M identification.