FANUC Pulse Coder Fanuc Encoder A860-0310-T023 A8600310T023 A860-0310-T023

Fanuc A860-0310-T023 | Incremental Pulse Coder — 3000P, CNC Servo Motor Encoder, Replaced by A290-0561-V568

Overview

The Fanuc A860-0310-T023 is a 3000P incremental pulse coder from Fanuc's A860-0310 encoder family — a generation of compact incremental encoders used on Fanuc AC servo motors from the S-series and early alpha motor generations.

At 3,000 pulses per revolution, this encoder provides incremental quadrature feedback to the CNC servo amplifier, which processes the pulse train to calculate motor position, speed, and direction.

Fanuc has officially discontinued the A860-0310-T023 and designated the A290-0561-V568 as its replacement.

This succession is a standard Fanuc practice for encoder obsolescence management: the A290 prefix indicates a different mechanical and electrical form factor that serves the same functional role, packaged for the motor generation it supports.

When sourcing replacement encoders for machines that originally carried the A860-0310-T023, confirming that the A290-0561-V568 mechanically and electrically fits the specific motor in the machine is the critical first step — the Fanuc motor documentation lists the encoder suffix that corresponds to each motor variant, and this should be verified rather than assumed.

The 3000P resolution places this encoder in a specific historical context within the Fanuc encoder lineup.

Early Fanuc AC servo motors used incremental pulse coders ranging from 2000P through 3000P — the higher the pulse count, the finer the speed and position measurement.

The 3000P class was among the more precise options available during the era these motors were produced. 

For machines where these motors remain in service, maintaining a supply of working 3000P encoders is a practical maintenance necessity since the motors themselves are often in otherwise excellent mechanical condition.

Being an incremental type, the A860-0310-T023 does not retain absolute position information between power cycles. Every time the machine powers up, the CNC must perform a reference return cycle — the axis moves to its fixed hardware reference point, the encoder pulse count resets to the reference datum, and from that point, the CNC tracks cumulative position.

This is a fundamental characteristic of all incremental encoders and is expected behaviour on machines equipped with this encoder generation.

Key Specifications

Incremental vs. Absolute — Operational Implications

The distinction between incremental and absolute encoders matters significantly in production settings.

An incremental encoder like the A860-0310-T023 is inherently stateless at power-on: it knows how far the motor has rotated since the last reference pulse, but it has no stored reference for absolute machine position.

The reference return cycle at startup solves this by moving the axis to a known physical reference switch and re-establishing the position datum from that fixed point.

On machines where this encoder generation is still in service, operators and maintenance engineers are familiar with the reference return as a routine startup step.

The limitation becomes significant only in applications where power loss mid-cycle would leave the axis in an unknown position — a consideration more relevant to absolute encoder installations.

For the typical machine tool applications these motors serve, incremental feedback is operationally adequate when the reference return routine is consistently followed.

Sourcing Discontinued Encoders — The A290-0561-V568 Path

Fanuc's official succession from A860-0310-T023 to A290-0561-V568 means that new encoder stock from authorised channels will be in the A290 form.

Confirming compatibility involves checking three things: first, that the A290-0561-V568 physically mounts on the motor in question (the mechanical adapter, shaft coupling, and fastening method must match); second, that the A290-0561-V568's signal interface connects to the machine's existing amplifier and feedback cable without modification; and third, that the CNC's servo parameters are set appropriately for the replacement encoder's pulse count and signal format.

Where the A290-0561-V568 is not a direct physical fit, the alternative is sourcing surplus A860-0310-T023 units from reputable aftermarket channels, understanding that these will be second-hand and should be tested under load before being committed to production duty.

FAQ

Q1: Why was the A860-0310-T023 discontinued, and is the A290-0561-V568 a genuine equivalent?

Fanuc regularly rationalises its encoder product range to reduce the number of distinct part numbers in production. Discontinuation typically means the manufacturing tooling for the specific variant has been retired, not that the technology has failed.

The A290-0561-V568 is Fanuc's published replacement, indicating Fanuc considers it functionally equivalent for the motor applications the T023 served. "Equivalent" in this context means it provides the same 3000P resolution and signal format — the mechanical installation details may differ, which is why confirming the fit on the specific motor remains essential.

Q2: What is the reference return procedure required after power-up on a machine with this incremental encoder?

On a typical Fanuc-controlled machine tool with incremental encoders, the reference return (also called zero-return or machine zero) requires the operator to select Reference mode on the CNC and initiate axis travel in the reference return direction.

The axis moves at a set feed rate until it contacts the reference switch, then creeps slowly until the encoder's Z-pulse (one pulse per revolution index mark) triggers, at which point the CNC latches the axis position reference.

The axis position display then shows the machine's home coordinate, and normal CNC operation can proceed. This procedure must be repeated for every axis with an incremental encoder after each machine power cycle.

Q3: What are the symptoms of a failing A860-0310-T023 encoder in service?

A degrading incremental encoder typically produces intermittent position errors — the CNC may generate servo alarms (SV400-series on Fanuc CNCs), position deviation errors, or erratic axis movement during low-speed operations.

A characteristic symptom is an axis that positions correctly at some speeds but produces alarms at others, which reflects the encoder's signal quality degrading at specific pulse frequencies.

Lost encoder counts produce axis position drift: the machine cuts a slightly wrong dimension without an alarm if the drift is within the following-error tolerance. Bearing wear in the encoder produces noise in the quadrature signals detectable by oscilloscope.

These symptoms should prompt immediate encoder inspection and motor removal for testing.

Q4: Can this 3000P encoder be directly replaced with a higher-resolution incremental encoder from a different part number?

Not without servo parameter adjustment on the CNC. The CNC's axis parameter for encoder resolution (typically expressed as pulses per revolution or the CMR/DMR gear ratio) must be set to match the actual installed encoder's pulse count.

Fitting a 2500P encoder in place of a 3000P changes the servo loop's position calculation — without parameter correction, axis positioning errors and velocity loop instability will result.

If a different resolution encoder is mechanically installed, the corresponding CNC parameters must be updated before the machine is returned to production.

Q5: How should surplus A860-0310-T023 units be evaluated before installation?

At minimum, test the encoder electrically with a dedicated encoder tester or an oscilloscope: confirm clean A, B, and Z-phase pulse trains without noise spikes, verify that all signal levels are within specification, and rotate the encoder through several revolutions to check pulse count accuracy.

Physically inspect the shaft seal and connector for damage or contamination ingress, and check the bearing for roughness or play by rotating the shaft by hand.

An encoder that passes static electrical testing should then be installed and monitored during the first reference return cycle and the first production run — position errors that emerge under thermal or load conditions will show up in this initial validation period.