Mitsubishi OSE105S2 Rotary Encoder — Original Incremental Feedback Unit for HC / HCR Series Servo Motors

Finding an original, new-in-box replacement for a Mitsubishi servo encoder isn't always straightforward — especially for a legacy unit that's no longer in production. The OSE105S2 is exactly that kind of part: an OEM Mitsubishi incremental rotary encoder, built in Japan, and designed as the factory-fitted feedback device for the HC and HCR series AC servo motors that powered a generation of CNC machinery across global manufacturing floors.

This listing is for a genuine Mitsubishi Electric OSE105S2, new in original packaging — not a rebuild, not a clone.

What This Encoder Does and Why It Matters

Every servo axis on a CNC machine depends on an encoder to close the position loop. The motor turns, the encoder counts, and the servo drive compares the actual position against the commanded position — thousands of times per second. Remove the encoder, damage it, or substitute a lower-quality unit, and the axis either faults out or runs with degraded accuracy.

The OSE105S2 is the factory-matched feedback component for Mitsubishi's HC/HCR motor series. It mounts directly to the rear of the motor shaft and communicates with the servo drive via a structured multi-phase signal — the same signal format the drive was calibrated and tuned to receive. That's the case for using an original OEM part rather than an aftermarket substitute: the system was designed around it.

Technical Specifications

The OSE Series — Built Into Mitsubishi's Servo Architecture

The OSE encoder family occupies a specific role within the Mitsubishi servo ecosystem. Unlike external encoders that mount on machine axes or ballscrews, the OSE105S2 is an internal motor encoder — it lives inside the motor housing, coupled directly to the rotor shaft, and provides primary speed and position feedback to the servo amplifier.

This direct-coupling arrangement matters. There's no flexible coupling between the encoder and the motor shaft, which means zero mechanical compliance and zero backlash in the feedback path. Every rotation the motor makes is counted exactly, without the rounding errors that shaft couplings can introduce on external encoders.

The 8-pin flange connector and the A/B/Z quadrature output format are consistent across the HC/HCR motor range, making the OSE105S2 a common spare for service teams maintaining fleets of older Mitsubishi-driven machines.

A/B/Z Phase Output — What Each Signal Carries

Three channels, three jobs:

A and B phases — the core quadrature pair. These two signals are offset by 90 degrees, which tells the drive both how far the shaft has turned and in which direction. Count the rising and falling edges of both channels and you get four position counts per encoder period — a technique called quadrature decoding.

Z phase — one pulse per complete revolution, used as the reference marker. This is the signal the servo amplifier uses during homing to establish a known angular reference position on the shaft. Without a clean Z pulse, homing cycles become unreliable.

The complementary signals (/A, /B, /Z) are differential pairs — essential for noise immunity over long cable runs, and a standard feature of the line driver output format used in servo applications.

Where You'll Find This Encoder at Work

The HC and HCR motor series were widely deployed across a broad range of Mitsubishi-powered equipment through the 1990s and 2000s. The OSE105S2 still turns up as a needed spare in:

CNC Machining Centers — X, Y, Z and rotary axis servo motors on Mitsubishi MELDAS-controlled mills and machining centers

CNC Lathes — turret positioning and slide axis servo motors on Mitsubishi-driven turning centers

Industrial Robots — joint servo feedback on older Mitsubishi MELFA robot arms using HC-series joint motors

Transfer Lines and FMS — pallet changers, shuttle tables, and transfer systems built around HC series servo drives in the automotive supplier sector

Injection Molding Machines — clamp and injection axis servo feedback on machines using Mitsubishi drives

Condition: New in Original Box

This unit is offered factory-new in original Mitsubishi packaging. For a discontinued component like the OSE105S2, the distinction between new and refurbished matters considerably:

A new encoder has full bearing life remaining, a clean optical disk with no wear or contamination, and factory-calibrated signal alignment. A refurbished unit has an unknown service history — it may have been removed from a motor that faulted for other reasons, or one that ran for years before being decommissioned. For an encoder that lives inside a servo motor and is expected to last the life of the machine, new-in-box is the only condition with a predictable service horizon.

FAQ

Q1: Is the OSE105S2 an incremental or absolute encoder?

It's incremental. It generates A, B, and Z phase quadrature signals as the shaft rotates, but does not retain position data when power is removed. The servo drive establishes an absolute reference at machine startup through a homing cycle using the Z phase pulse.

Q2: Which Mitsubishi servo motors use the OSE105S2?

The OSE105S2 is the factory-fitted encoder for Mitsubishi HC series and HCR series AC servo motors, including models such as the HC-SF, HC-SFS, and associated variants. If your motor part number begins with HC or HCR, the OSE105S2 is very likely the correct encoder — confirm against the label on the existing unit before ordering.

Q3: Can the OSE105S2 be replaced with a newer Mitsubishi encoder?

Not directly. The OSE encoder family uses a specific connector pinout and signal format matched to the servo amplifier it's paired with. Substituting a different encoder type would require amplifier-side parameter changes and potentially hardware modifications. For like-for-like replacement on an existing machine, the OSE105S2 is the correct part.

Q4: Is this encoder still manufactured by Mitsubishi?

No — the OSE105S2 has been discontinued by Mitsubishi Electric. New-in-box stock is available through industrial automation parts suppliers, but it is not being actively produced. If you require a long-term supply, securing multiple units while stock is available is advisable.

Q5: What is the alternative part number for the OSE105S2?

The encoder is also listed as OSE-105S2 (hyphenated format) in Mitsubishi documentation and some supplier catalogs. It is referenced in motor part combinations such as HC-202S-E51+OSE105S2, where "E51" denotes the encoder option. Cross-reference codes include B55028 and E42, depending on the catalog source.