Setup Guide for Fanuc Pitch Error Compensation Parameters

Introduction

An uncommanded coordinate lurch during a rapid traverse can violently plunge a cutting tool or turret directly into a vise jaw, a secured workpiece clamp, or the chuck, resulting in an immediate hard collision and a scrap part. This severe operational hazard occurs when an operator attempts to configure a pitch error compensation grid using corrupted parameters or fails to cycle the CNC power completely. Because the controller relies on pitch compensation math to dictate its true physical location, any input error or unsynchronized reference return will inject a massive, uncontrolled spatial shift in the background, making the machine blind to its true physical limits.

Technical Summary

Specification Field	Technical Value / Status
Command Code	Parameter-based configuration / N_ P_ ; data tape upload
Modal Group	N/A (Background pitch error compensation)
Applicable Brands	Fanuc
Critical Parameters	Parameter 3620 (Reference position number), Parameter 3624 (Point interval)
Main Constraint	Maximum of 128 compensation points between extremes; full power cycle and reference return (G28) required to initialize grid.

Quick Read

• Verify Spacing Limits: Maintain the number of pitch error compensation points between stroke extremes under the 128-point limit to prevent system alarms.
• Cycle Controller Power: Turn the CNC power completely OFF and ON after modifying any parameters from 3620 through 3627 to apply the new grid math.
• Run Reference Return: Execute a G28 reference position return immediately after startup to synchronize the virtual grid with physical machine home.
• Check Input Format: Upload pitch compensation data incrementally as viewed from the negative direction of the axis when importing offline tapes.
• Audit Magnification Limits: Restrict parameter 3623 magnification values to the 0 to 100 range to avoid injecting dangerous uncommanded coordinate shifts.
• Prevent Spindle Compounding: Define travel distance per revolution in parameter 3625 for rotary axes to wrap compensation and prevent compounding errors.

Basic Concepts

The practical programming effect of Fanuc's pitch error compensation is the ability to create a highly accurate, software-based map of the physical ballscrew to neutralize microscopic mechanical inaccuracies. By establishing a master reference position via parameter 3620 and defining a strict physical interval distance via parameter 3624, the CNC divides the axis stroke into a virtual grid. As the machine travels, the controller automatically injects or removes servo pulses at these grid points to perfectly counteract thread stretching, manufacturing flaws, or thermal growth. Programmers do not need to alter their G-code toolpaths; the CNC handles the spatial shifting entirely in the background.

Fanuc heavily distinguishes its system by offering a dedicated "Bi-directional Pitch Error Compensation" function via parameter 3605#0. Unlike basic systems that rigidly apply the exact same compensation regardless of travel direction, Fanuc allows operators to map completely independent error profiles for both the positive and negative directions. When the axis reverses, the controller automatically references the opposite data registry, perfectly neutralizing asymmetric mechanical twist in a manner similar to advanced backlash compensation. For related backlash setups, refer to the guide on parameter 1851 backlash compensation.

Command Structure

The configuration of Fanuc's pitch error compensation grid operates through the controller's parameter registry rather than inline G-code blocks. Operators establish the physical bounds of the grid using specific start, end, and reference position parameters. Beyond these points, the system requires a defined magnification factor and spacing interval to determine where corrections are applied along each axis stroke.

To populate these values without manual entry, the system accepts bulk data tapes through the reader/puncher interface. This interface uses a specific block format where the block number defines the compensation point number and the address value defines the incremental correction. To manage global write settings before updating these parameters, refer to the guide on Fanuc parameters and PWE. To safeguard against axis overtravel during initial setup, operators should also configure the G22/G23 stored stroke limits.

N_ P_ ;

Parameter	Description	Value Range / Settings
Parameter 3620	Number of the pitch error compensation position for the reference position for each axis.	0 to 1023 (up to 1535 on advanced controllers)
Parameter 3621	Number of the pitch error compensation position at extremely negative position for each axis.	0 to 1023 (up to 1535)
Parameter 3622	Number of the pitch error compensation position at extremely positive position for each axis.	0 to 1023 (up to 1535)
Parameter 3623	Magnification for pitch error compensation for each axis.	0 to 100
Parameter 3624	Interval between pitch error compensation positions for each axis.	8000 to 99999999 (metric), 4000 to 99999999 (inch)
Parameter 3625	Travel distance per revolution for rotary axis pitch error compensation.	0 (defaults to 360 degrees) or non-zero value
Parameter 3605#0	BDPx: Bi-directional pitch error compensation usage.	0: Not used, 1: Used
Parameter 3626	Number of the pitch error compensation point at the negative end for travel in the negative direction.	0 to 1023 (or 1535)
Parameter 3627	Pitch error compensation (absolute value) at reference position when movement is made from opposite direction.	-32768 to 32767
Parameter 1851	Backlash compensating value for each axis (related).	Standard backlash value

Brand Applications

Fanuc

The setup of pitch error compensation on Fanuc systems is governed by a series of parameters that define the physical boundaries of the compensation grid. The reference position for each axis is designated in parameter 3620, while parameter 3624 determines the exact physical interval between compensation points.

To load pitch error compensation values into the controller offline, operators format data block instructions using the syntax N_ P_ ;, where N represents 10000 plus the specific grid point number and P specifies the incremental compensation value.

Configuration Type	Details	Value Range / Description
Parameter 3620	Reference position compensation point number	0 to 1023 (or 1535)
Parameter 3624	Physical spacing between correction points	8000 to 99999999 (metric) / 4000 to 99999999 (inch)
Parameter 3605#0	Bi-directional pitch error compensation (BDPx)	0: Disabled, 1: Enabled
Alarm PW1102 / PW5046	Parameter configuration error alarms	Tripped if compensation point count exceeds 128 or magnitude spacing is invalid
Alarm DS10000	Restart clearing warning alarm	Indicates interpolation pitch error data will be wiped at the next power-on
Version: Legacy Series 0 / 15	Legacy parameter mappings	Uses parameters 1000-6000 (origin), 1001-6128 (comp), and parameters 0011#0/#1 (PML1/PML2 multipliers)
Version: Modern Series 16i / 18i / 21i	Modern parameter block mapping	Uses parameters 3620-3627 with an arbitrary magnification factor (0 to 100) via parameter 3623

Modifying pitch error compensation settings is highly hazardous. Incorrect parameter values can introduce unexpected machine coordinate offsets, causing the turret to crash into fixtures and scrap the workpiece.

Version and Series Comparison

Feature / Capability	Legacy Series 0 / 15	Modern Series 16i / 18i / 21i	Series 0i / 0i-F
Parameter Registry	Origin mapped to parameters 1000–6000; compensation values stored in parameters 1001–6128.	Configuration mapped entirely to parameters 3620–3627.	Configuration mapped entirely to parameters 3620–3627.
Magnification Control	Rigid multipliers of x1, x2, x4, or x8 via parameters 0011#0 and 0011#1 (PML1, PML2).	Flexible magnification from 0 to 100 via parameter 3623.	Flexible magnification from 0 to 100 via parameter 3623.
Bi-directional Compensation	— (no source)	Fully supported via parameter 3605#0 (BDPx) for independent error maps.	Supported via parameter 3605#0 (BDPx) for independent error maps.

Technical Analysis

Analytical examination of Fanuc's pitch error architecture reveals a distinct evolution in how the CNC manages mechanical position correction. In legacy Series 0 and Series 15 controllers, the pitch error compensation system was rigidly integrated into a split parameter range for origin mapping and actual compensation amounts. Legacy systems also relied on hardware-level binary multipliers, restricting resolution adjustments to strict steps of x1, x2, x4, or x8.

Modern Series 16i, 18i, 21i, and Series 0i controllers consolidate the setup parameters into a standardized parameter block. Rather than relying on discrete binary step multipliers, modern systems support a flexible magnification factor set in parameter 3623, allowing operators to fine-tune compensation values with microscopic precision. Integrating bi-directional pitch error compensation via parameter 3605#0 in modern controllers allows for separate calibration profiles based on travel direction, compensating for mechanical hysteresis that older control architectures could not isolate.

Program Examples

The following example illustrates the ISO tape format used to bulk-load pitch error compensation data into the CNC memory, followed by the zero-point return command required to synchronize the grid.

N10000 P1 ;       Incremental compensation +1 at point 10000
N10001 P-3 ;      Incremental compensation -3 at point 10001
N10002 P2 ;       Incremental compensation +2 at point 10002
G28 X0 Y0 Z0 ;    Reference position return to synchronize grid

dry run

During a dry run, the operator executes a reference position return using G28 X0 Y0 Z0 to synchronize the coordinate system and activate the virtual pitch error grid. As the axis moves to the home position, the CNC controller processes the incremental pitch error data points loaded via the N10000 to N10002 blocks. The controller applies a +1 pulse compensation at point 10000, -3 pulses at point 10001, and +2 pulses at point 10002. The operator monitors the servo motor current and coordinates on the diagnostic screen to verify that these corrections are smoothly interpolated and injected as micro-pulses in the background without causing axis hesitation or lurching.

Error Analysis

Alarm Code	Trigger Condition	Operator Symptom	Root Cause & Practical Resolution
Alarm PW1102 ILLEGAL PARAMETER (I-COMP.)	Slope/inclination compensation parameters are incorrect (e.g. number of points exceeds 128 or invalid spacing relationships).	CNC halts operation immediately and blocks axis movement; alarm message displayed.	Verify parameter values, check point spacing, and ensure the compensation point count is below the 128 limit.
Alarm PW5046 ILLEGAL PARAMETER (S-COMP.)	Straightness compensation parameters are incorrect (e.g. non-existent axis, points > 128, invalid magnitude relationship, value too large/small).	CNC enters a hard stop condition; error message is shown on the screen.	Verify parameter values, check number of points, and check min/max limits.
Alarm DS10000 PITCH ERROR DATA CLEAR	Changed a core parameter like 3605#0 (BDPx) that dictates grid structure.	Warning that the interpolation type pitch error compensation data will be wiped at the next power-on.	Warning of data clearing on next startup. Backup all pitch error data via the reader/puncher interface before cycling power, then reload the saved ISO tape.	Backup all pitch error data via the reader/puncher interface before cycling power, then reload the saved ISO tape.

Application Note

Entering incorrect values in parameter 3623 (magnification) or parameter 3624 (interval) immediately corrupts the virtual pitch error grid, causing the CNC to command an unexpected physical axis shift. When the turret rapid traverses, this corrupted grid math forces the slide to lurch past its target limit, sending the tool plunging into a workpiece clamp, vise jaw, or chuck. This catastrophic crash results in severe machine damage, tool breakage, and an immediate scrap part. Operators must verify all parameters before running any automatic cycles.

Related Command Network

• G28 (Reference Position Return): Synchronizes the machine home coordinates to establish the starting alignment of the virtual pitch error compensation grid.
• G30 (Return to 2nd, 3rd, 4th Reference Position): Positions the axis to secondary reference points while maintaining grid synchronization.
• Parameter 1851 (Backlash Compensation): Works in conjunction with the pitch error compensation grid to correct physical play during axis reversals.

Conclusion

A calibrated pitch error compensation grid ensures mechanical precision without modifying G-code toolpaths. Operators must execute a full controller power cycle and a G28 homing sequence whenever grid parameters are modified to prevent coordinate shifts and mechanical damage.

Frequently Asked Questions

How does bi-directional pitch error compensation correct hysteresis?

Bi-directional compensation (activated via parameter 3605#0) allows separate correction values for positive and negative travel. To implement this, map separate positive and negative deviation values using the N_ P_ upload format and verify that the reverse-motion registry is updated to prevent mechanical twist from affecting dimensional accuracy.

Why does changing parameter 3605#0 trigger alarm DS10000?

Alarm DS10000 occurs because changing a core pitch error structure parameter resets the internal interpolation buffer. Before modifying parameter 3605#0, backup all pitch error data via the reader/puncher interface, cycle the power, and then reload the saved .iso tape data to restore the grid values.

What happens if the interval in parameter 3624 is set incorrectly?

An incorrect interval spacing in parameter 3624 distorts the spatial mapping of the ballscrew, causing the controller to inject compensation pulses at the wrong physical locations. Always double-check parameter 3624 against the actual ballscrew pitch specifications and run a G28 homing sequence to verify the grid spacing before initiating any production cuts.