Fanuc Zero Return Procedure – Comprehensive Guide for CNC Operators

Introduction

Precision and repeatability are integral parts of CNC machining for producing top-quality manufacturing. One process which helps achieve these standards is the FANUC Zero Return Procedure; this enlists machine reference positions, aligning their coordinate system for precise motion control.

This guide will cover the importance of Zero Return, how FANUC systems manage reference points, and the impact of absolute vs. incremental encoders on this process.

What is FANUC Zero Return?

FANUC Zero Return (also referred to as machine home positioning) is an essential step in CNC operation, ensuring that a machine aligns its coordinate system correctly upon startup. Without an accurate Zero Return setting, CNC machines may fail to identify their exact axis positions leading to machine errors, misalignment, and possible collisions.

Zero Return establishes the Machine Zero position, providing a central point for tool movement, work offsets, and program execution.

How to Identify Absolute and Incremental Encoders?

Important Note: If the encoder battery voltage is low and not replaced, the machine will lose its reference point, requiring a manual Zero Return to reestablish machine zero.

For a detailed introduction to FANUC encoders, please read this article: [What is FANUC Encoder? – A Comprehensive Guide to FANUC Encoder: 4 Types, Features, and Applications].

Absolute Position Encoders (A-Type)

  • Store position data even when the machine is powered off.
  • Do not require a manual Zero Return at startup.
  • Depend on a backup battery—if the battery is not replaced in time, the machine loses its reference position.
  • All FANUC βi-series motors use absolute encoders by default.
A860-2000-T301
A860-2005-T301 FANUC Encoder

Incremental Position Encoders (I-Type)

  • Do not retain position data when the machine is turned off.
  • Require a manual Zero Return every time the CNC system restarts.
  • Use reference markers to reestablish the zero position.
2 type FANUC encoders
  • Impact on the FANUC Zero Return Procedure
    • If using an absolute encoder, Zero Return is usually unnecessary unless the encoder battery dies or the system undergoes a reset.
    • If using an incremental encoder, a Zero Return must be performed every time the CNC machine is powered on.
    • A dead battery in an absolute encoder can lead to a loss of machine zero, requiring the operator to perform a manual Zero Return.

Fanuc Zero Return Procedure – Step-by-Step Guide

Zero Return in FANUC CNC machines is essential to creating an accurate reference point and must be performed whenever using an absolute position encoder, otherwise home positions must be manually reset manually. Below is a step-by-step guide on how to accurately set the zero return position.

  • Manually move the machine to the home position, set parameter 1815 #4 = 1, shut down the machine and restart with power off, that is to determine the current point as the home position.
  • If 1815 #4 cannot be set to 1
    1. Ensure that the Motor rotates at least one revolution or more
    2. Set parameter 1815#5=0, 1815#4=1, 1815#5=1, power off and restart.
FANUC zero return procedure
  • If 1815#5 APCx = 1, use absolute position encoder
  • If 1815#5 APCx = 0, use relative position encoder
  • If 1815#4 APZx = 1, the absolute encoder zero return is successfully set.
  • If 1815#4 APZx = 0, absolute position encoder home position is not set. (Alarm 300 will be generated)
  • If 1815#1 OPTX = 1, Full closed-loop mode enabled..
  • If 1815#1 OPTX = 0, Semi-closed-loop mode enabled.

For best results when using an absolute position detector, the initial adjustment or when replacing one must be set to 0, with home position later set manually back to reference point or other operations when power returns on after restart. When position correspondence between mechanical position and absolute position detector is achieved, this parameter will automatically set back to 1.

Causes of FANUC Zero Return Procedure Failure and Troubleshooting

If the zero return procedure fails, several factors could be causing the issue. Here are some common reasons and troubleshooting steps:

Insufficient Motor Rotation

  • For an absolute position encoder, the motor must rotate at least one full revolution before setting the zero position.
  • Solution: Manually jog the axis and ensure it completes a full turn before attempting the fanuc zero return procedure again.

Encoder Power Supply Issue or Damaged Wiring

  • The encoder requires a stable 6V power supply. If the encoder cable is damaged, disconnected, or lacks proper voltage, the machine will fail to establish the reference position.
  • Solution:
    • Check the encoder power lines with a multimeter to confirm a stable 6V output.
    • Inspect the wiring for cuts, wear, or loose connections and replace any damaged cables.

Faulty Encoder

  • If the encoder itself is damaged or malfunctioning, it will not correctly store or relay position data, causing zero return failure.
  •  Solution:
    • Try reconnecting the encoder and reattempting the procedure.
    • If the issue persists, replace the encoder with a new or tested functional unit.
Test bench

Conclusion

The FANUC Zero Return Procedure is a fundamental process in CNC machining, ensuring precision, safety, and machine reliability. By understanding the impact of absolute vs. incremental encoders, operators can prevent common issues like position loss, overtravel alarms, and misalignment errors.

Regular maintenance, including checking the encoder battery, will help keep your FANUC CNC machine operating smoothly. Follow the correct FANUC Zero Return procedure to maintain accuracy and efficiency in your machining operations.

Need more FANUC troubleshooting tips? Check out our [Download Center] for FANUC alarm lists and manuals! 

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What is Machine Zero in CNC?

Machine Zero is the fixed reference point set by the manufacturer, defining the absolute origin of the CNC machine’s coordinate system. It is different from Work Zero (G54-G59), which is set by the operator for specific jobs.

Check the encoder model number:
If the encoder has an “I” (Incremental) marking, it is an incremental encoder.
If the encoder has an “A” (Absolute) marking, it is an absolute encoder.
All FANUC βi-series motors use absolute encoders by default.

If the encoder battery is not replaced in time, the machine will lose its reference position. This requires a manual FANUC Zero Return procedure to reset the machine zero.

If using an incremental encoder, Zero Return must be performed after every startup.
If using an absolute encoder, a dead battery may cause the system to lose its position data.

It is recommended to perform Zero Return in the following cases:

  • After each power-up, ensure that the coordinate system is correct
  • After a power failure or emergency stop
  • After the machine has not been used for an extended period of time
  • After a machine collision or abnormal condition
  • Machine Zero: A fixed reference point for a machine tool that is set by the manufacturer and cannot be changed.
  • Work Zero: The origin of the workpiece coordinates set by the operator, usually at a specific location on the workpiece (e.g. corner or centre).
  • Home Position: A safe parking position for the machine tool, usually set at a specific point in the X, Y, or Z axes, to facilitate machining and tool changing.

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