Fanuc Parameter 1860 Full ((top))

Understanding Fanuc Parameter 1860: Absolute Position Detection

Fanuc Parameter 1860 (often referred to as APZ) is a critical configuration setting in Fanuc CNC systems (such as the Series 0i, 16i, 18i, and 31i) that indicates whether the reference position for an absolute pulse coder has been established for a specific axis.

When a machine is equipped with absolute encoders, it does not require a manual "home" or zero-return operation every time it is powered on, provided the absolute position is correctly saved. Parameter 1860 is the system's "flag" that tells it whether this position is currently valid. 1. The Core Meaning of Parameter 1860

Parameter 1860 is a bit-type parameter where each bit typically corresponds to a different controlled axis (X, Y, Z, etc.).

0: The reference position is not established. The machine does not know its absolute zero, and you will likely see a "Need ZRN" (Zero Return) alarm or a 300-series absolute pulse coder alarm.

1: The reference position is established. The system knows exactly where the axis is located based on the absolute encoder data. 2. When Does Parameter 1860 Revert to 0?

In a perfectly functioning machine, this parameter stays at "1" indefinitely. However, certain events will force it to "0," requiring a re-homing procedure: fanuc parameter 1860 full

Battery Failure: Absolute encoders rely on a backup battery to "remember" their position when the power is off. If the battery dies, the position is lost.

Encoder Disconnection: Unplugging the encoder cable or replacing the motor/encoder resets the stored position.

Mechanical Overhaul: If you disconnect the motor from the ball screw, the physical relationship between the encoder and the machine zero changes.

Manual Reset: A technician may manually change this bit to "0" to force a new home position calibration. 3. How to Set or Reset Parameter 1860

If you encounter an absolute pulse coder alarm (like Alarm 300), you must re-establish the reference position. Simply typing "1" into Parameter 1860 is usually not enough; the CNC must "see" the machine reach its physical home first. Step-by-Step Recovery Procedure: How to Enable Parameter Write Enable (PWE) on a Fanuc CNC

Fanuc Parameter 1860 (Position of the absolute position detector) is a read-only parameter that displays the current position value from the absolute pulse coder. While it is not a setting you typically edit manually, it serves as a critical reference point for the CNC system to maintain axis alignment without needing to re-home after a power cycle. Key Characteristics and Function Data Type: 4-word (integer). Parameter 1860 vs

Function: It tracks the absolute position of each axis. This value is automatically set and updated by the CNC when an axis is zeroed (specifically through Parameter 1815 APZ).

Usage: Maintenance technicians use this parameter to verify that the absolute pulse coder is correctly tracking the machine's physical position.

Modular Arithmetic: The value may "wrap around" based on the encoder's count limits, which is normal behavior for absolute detectors. Related Reference Parameters

When troubleshooting absolute position issues, you will likely need to check these associated parameters:

Parameter 1815: Used to set the absolute position reference (Bit 4: APZ).

Parameter 1850: Sets the grid shift amount to fine-tune the zero position. Parameter 1851: Controls backlash compensation. Safety Note Difference Between 1850, 1851, and 1860 A common

Do not attempt to force a value into Parameter 1860. On most systems, it is read-only. To change the machine's reference position, use the proper zero-point setting procedure involving Parameter 1815.

Are you experiencing a specific alarm code or axis shift that led you to check this parameter? FANUC? M6 toolchange position. | Practical Machinist

Parameter 1860 vs. Other Time Constants (Crucial Distinctions)

Technicians often confuse 1860 with other parameters. Here is a clear comparison:

| Parameter | Function | When Active | Typical Range | | :--- | :--- | :--- | :--- | | 1860 | Cutting feed ACC/DEC time constant | G01, G02, G03 | 20–200 ms | | 1620 | Rapid traverse (G00) ACC/DEC time constant | G00 | 50–500 ms | | 1622 | Rapid traverse DEC time constant (linear) | G00 (end of move) | 0 (off) to 500 ms | | 1825 | Servo loop gain (Position loop gain) | All motions | 30–200 (1/sec) |

Critical Insight: Parameter 1860 and Parameter 1825 (position loop gain) work in tandem. If you increase 1825 for higher stiffness, you may need to decrease 1860 to avoid instability. Conversely, a low 1825 with a very low 1860 will cause overshoot.

Difference Between 1850, 1851, and 1860

A common confusion exists among Fanuc parameters. Here is the breakdown:

On many newer Fanuc controls (0i, 31i, 32i), Parameter 1860 is specifically for the absolute position detector reference position.

Safety Warnings & Best Practices

Never zero out Parameter 1860. A value of 0 implies infinite acceleration, which will cause immediate following error alarms or even servo drive overcurrent trip.
Document original values. Before modifying 1860, take a photo or record the original settings for each axis. Use the CNC's built-in "Input from File/Output to File" function (if available) to back up all parameters.
Test at low feedrate. After changing 1860, run the program at 10% feed override. Gradually increase to 100% while listening for unusual sounds.
Check interaction with dwell (G04). A very low 1860 combined with a short dwell can cause a "jump" on restart. Increase dwell time or raise 1860 slightly.
Use servo analysis software. Fanuc’s Servo Guide or similar software can plot actual acceleration curves. This is essential for machines with critical tolerance requirements (<10 microns).

Step 2: Enter Maintenance Mode

Turn off the CNC.
Turn on the CNC while holding specific keys (often P and CAN or specific diagnostic buttons depending on the model) to bypass parameter write protections, or simply enable Parameter Write Enable (PWE = 1) in the settings screen.