Fanuc Parameter 1829 Official

Fanuc parameter position error limit when the axis is stopped

This parameter defines the maximum allowable deviation (in detection units) between the commanded position and the actual position while the machine is at a standstill. If the axis drifts or is pushed beyond this limit, the system triggers a Servo Alarm 410 (Excessive Position Error). Key Details & Troubleshooting

It acts as a safety monitor for when the machine is supposed to be stationary. Common Alarm: typically occurs if this limit is exceeded. Potential Causes of Error: Mechanical Load:

Something is physically pushing the axis out of position (e.g., gravity on a vertical axis without a proper brake or counterbalance). Inertia/Braking:

The axis cannot stop fast enough due to a time constant that is too short for the current feedrate. Mechanical Wear:

Issues with lubrication or a faulty ball screw can cause the axis to "jump" or settle poorly, exceeding the limit. Typical Resolution:

While increasing the value in parameter 1829 can stop the alarm, technicians recommend checking for mechanical problems cable issues first to ensure the machine remains accurate. How to Modify To change this value, you must typically: Navigate to the screen and enable PARAMETER WRITE (PWE) Search for

and enter the new value for the specific axis (X, Y, Z, etc.). Disable PWE and reset the CNC to clear the alarm. FANUC 410 Servo Alarm - CNC Machining - Practical Machinist

Fanuc Parameter 1829 (labeled as "Position Error Limit when Stopped") is a critical safety setting that defines the maximum allowable deviation between the commanded position and the actual position while an axis is at a standstill.  Function and Impact 

Purpose: It monitors the "error register" (positional deviation) when the motor is stopped.

Trigger: If the deviation exceeds the value set in 1829, the CNC triggers a 410 Servo Alarm ("Excess Error Stop"). fanuc parameter 1829

Safety Role: It prevents damage if an axis "drifts" or is pushed out of place due to external forces, mechanical failure, or a drop in a vertical axis when the brake is released.  Key Specifications 

Data Type: Typically a 2-word (32-bit) value, set individually for each axis.

Unit: Expressed in detection units (e.g., 0.001 mm or 0.0001 inch depending on your system's resolution).

Common Values: Often set higher than Parameter 1826 (In-Position Width) to allow for minor settle time, but small enough to detect genuine mechanical issues.  Troubleshooting "Excess Error Stop" (Alarm 410) 

If you are receiving an alarm related to this parameter, community and manufacturer guides suggest checking the following: 

Mechanical Bind: Physical obstructions, chip buildup, or poor lubrication on the ballscrew.

Gravity Drop: In vertical or slanted axes, check if the motor brake is failing or if there is insufficient counter-balance.

Parameter Settings: Ensure the value isn't set too low, which can cause "false positive" alarms from minor vibrations.

Diagnostics: Use Fanuc Diagnostic No. 300 to view the live "Error Counter" value to see how much the axis is actually deviating. 

For detailed setting instructions, refer to the Fanuc 0i-MODEL F Plus Parameter Manual or the Series 16i-18i Parameter Manual.  FANUC Series 0i-MODEL F Plus PARAMETER MANUAL Fanuc parameter position error limit when the axis

Fanuc Parameter 1829 defines the Positioning Deviation Limit for each axis in the stopped state. It serves as a safety threshold to ensure that a stationary axis does not drift beyond a specific tolerance due to external forces or mechanical issues. Core Function

When an axis is "stopped" (not currently moving), the CNC monitors the difference between the commanded position and the actual feedback position.

Trigger: If this deviation exceeds the value set in Parameter 1829, the CNC generates a SV0410 EXCESS ERROR (STOP) alarm.

Result: The machine immediately stops all operations to prevent damage or safety hazards. Parameter Specifications Data Type: 2-word axis (Long integer).

Unit: Detection unit (typically microns or pulses, depending on your machine's resolution).

Valid Range: Generally 0 to 99,999,999 (varies by control model, e.g., 0i-F).

Common Setting: Often set to a small value representing a tight tolerance for a stationary axis, whereas Parameter 1828 handles the limit for moving axes. Troubleshooting SV0410 (Excess Error Stop)

If you are seeing an alarm related to this parameter, check the following:

Mechanical Obstructions: Ensure the ball screw, guide rails, and motor are not physically bound or blocked by chips/debris.

Lubrication: Verify the axis is properly lubricated; dry ways can cause enough friction to force an axis out of position. Parameters 1828 and 1829 are often used for

Brake Failure: For vertical axes, a failing motor brake may allow the axis to drop slightly when stopped.

Tuning: Check if the servo gain or position loop parameters have been modified, causing instability at rest. How to Edit Parameter 1829 To change this value, follow the standard Fanuc procedure: MDI Mode: Put the machine in MDI mode or Emergency Stop.

Enable PWE: Press the OFFSET SETTING key, then the SETTING soft key. Set PARAMETER WRITE (PWE) to 1.

Search: Press the SYSTEM function key, then the PARAM soft key. Type 1829 and press NO.SRH.

Input: Enter the new value for the specific axis (X, Y, Z, etc.) and press INPUT.

Reset: Set PWE back to 0 and cycle power if required by the control. PARAMETER MANUAL

5. Relationship with Other Parameters

| Parameter | Function | |-----------|----------| | 1320 | Negative software limit (first stage) | | 1321 | Positive software limit (first stage) | | 1828 | Positive software limit 1 (auxiliary) | | 1829 | Positive software limit 2 (auxiliary) |

• Parameters 1828 and 1829 are often used for dual-limit check in high-speed or heavy-duty axes.
• If 1828 = 0 and 1829 = 0, the CNC may disable the auxiliary check.

A Word of Caution ⚠️

Never treat 1829 as a substitute for proper mechanical maintenance. If an axis is binding due to worn thrust bearings, low lubrication, or way damage, raising 1829 will just mask the problem—until something breaks catastrophically.

Introduction: The Silent Guardian of Your CNC Machine

In the world of FANUC-controlled CNC machining centers and lathes, thousands of parameters dictate everything from axis acceleration to spindle orientation. Most operators are familiar with common settings like parameter 1815 (absolute encoder setup) or parameter 1320 (stroke limits). However, one parameter often remains misunderstood until a machine alarm brings it into the spotlight: FANUC Parameter 1829.

If you have ever encountered a sudden "SV0410 (SERVO ALARM: Excessive Mismatch)" or "SV0401 (SERVO ALARM: Mismatch)" during heavy cutting or a rapid traverse, Parameter 1829 is the critical value controlling that fault detection. This article will dissect what Parameter 1829 is, how it works, how to calculate it, and the step-by-step procedure to modify it safely.

Illegitimate Reasons to INCREASE Parameter 1829 (DANGEROUS):

• "I keep getting alarms and I want them to go away." (You are masking a real problem.)
• After a crash, the axis sounds rough, but you increase 1829 to keep running. (You will crash again, harder.)
• To compensate for low voltage or weak servo drive.

2.2. Units of Measurement

The value entered into Parameter 1829 represents the minimum deviation required to trigger an alarm.

• Unit: Least Input Increment (LI) or Detection Unit.
• Typical Scale: Usually millimeters (mm) or inches, multiplied by the system resolution (e.g., 0.001 mm).

Example: If the machine system resolution is 0.001 mm, and Parameter 1829 is set to 1000:

• Threshold Distance = $1000 \times 0.001 \text mm = 1.0 \text mm$.
• If the axis drifts more than 1.0 mm away from the commanded stop position, the alarm will trigger.

Why does this matter?

• Protection: It prevents mechanical damage (broken tools, bent fixtures, or even structural machine damage) if the axis jams or overloads.
• Performance: Setting it too low causes premature "Excessive Load" alarms (e.g., SV0430, SV0431).
• Safety: Setting it too high can mask a mechanical bind, leading to a burned servo motor or damaged ballscrew.

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